WorldWideScience

Sample records for chromites

  1. Lanthanum chromite colloidal processing

    International Nuclear Information System (INIS)

    Lanthanum chromite (LaCrO3) is currently the most studied material for applications such as solid oxide fuel cell inter connector (HTSOFC). The complexity of microstructures and geometries of HTSOFC devices, require a precise control of processing parameters to get the desired combination of properties and this, the use of techniques involving concentrated ceramic slips conformation are appropriate, therefore, is well controlled, assist in obtaining homogeneous parts, reproductive and complex geometries. Thus, studies involving the surface chemistry, the stability conditions and slips flow behaviour in the forming conditions, provide important elements for processes control in the inter connectors manufacture, where more applied settings have slots and channels for the gases passage. Thus, surface chemistry, stability and rheological behaviour of strontium and cobalt doped LaCrO3 (La)0.80Sr0.20Cr0.92Co0.08O3) slips prepared with ethanol and water, were studied. The doped lanthanum chromite was produced by combustion synthesis in the IPEN/SP labs. The influence of parameters: pH (water), dispersant concentration, homogenization times and conditions, solid concentration, different ratios binder:plasticizer in the stability and the flow behavior of ceramic suspensions prepared were evaluated. The La)0.80Sr0.20Cr0.92Co0.08O3 products obtained by casting aqueous slips in a plaster mould, using alkaline pH and anionic polyelectrolyte and tapes obtained by using ethanol as a dispersant medium, after sintering at 1600 degree C/4 hours presented theoretical density > 94%, suitable for use as HTSOFC inter connector. (author)

  2. THERMODYNAMIC STUDY OF CHROMITE CAUSTICFUSION PROCESS

    Institute of Scientific and Technical Information of China (English)

    S.L. Zheng; Y. Zhang

    2001-01-01

    A new method for chromate cleaning production named chromite caustic fusion pro-cess, is advanced by Institute of Chemical Metallurgy, the Chinese Academy of Sci-ences. With sodium hydroxide as reaction medium, the new process is composed ofthree procedures: liquid phase oxidation of chromite - metastable phase separation -carbonation ammonium transition. Generally illustrating the new process and its fea-tures, this paper mainly studies the thermodynamics of chromite oxidation. The newprocess has much better practical results than the conventional chromate productionprocess in which sodium carbonate is used as reaction medium. The superiority is alsoshown through thermodynamic studies.``

  3. Mechanical properties of lanthanum and yttrium chromites

    Energy Technology Data Exchange (ETDEWEB)

    Paulik, S.W.; Armstrong, T.R. [Pacific Northwest National Lab., Richland, WA (United States)

    1996-12-31

    In an operating high-temperature (1000{degrees}C) solid oxide fuel cell (SOFC), the interconnect separates the fuel (P(O{sub 2}){approx}10{sup -16} atm) and the oxidant (P(O2){approx}10{sup 0.2} atm), while being electrically conductive and connecting the cells in series. Such severe atmospheric and thermal demands greatly reduce the number of viable candidate materials. Only two materials, acceptor substituted lanthanum chromite and yttrium chromite, meet these severe requirements. In acceptor substituted chromites (Sr{sup 2+} or Ca{sup 2+} for La{sup 3+}), charge compensation is primarily electronic in oxidizing conditions (through the formation of Cr{sup 4+}). Under reducing conditions, ionic charge compensation becomes significant as the lattice becomes oxygen deficient. The formation of oxygen vacancies is accompanied by the reduction of Cr{sup 4+} ions to Cr{sup 3+} and a resultant lattice expansion. The lattice expansion observed in large chemical potential gradients is not desirable and has been found to result in greatly reduced mechanical strength.

  4. Reduction Mechanism of Chromite Ore in Blast Furnace

    Institute of Scientific and Technical Information of China (English)

    LI Yi-wei; DING Wei-zhong; LU Xiong-gang; XU Kuang-di

    2004-01-01

    The structural changes and reduction degree of chromite ore in blast furnace were studied by optical micrograph analysis, scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDXA). The smelting reduction mechanism of chromite in blast furnace was primarily discussed.

  5. Occupational health assessment of chromite toxicity among Indian miners

    Directory of Open Access Journals (Sweden)

    Alok Prasad Das

    2011-01-01

    Full Text Available Elevated concentration of hexavalent chromium pollution and contamination has contributed a major health hazard affecting more than 2 lakh mine workers and inhabitants residing in the Sukinda chromite mine of Odisha, India. Despite people suffering from several forms of ill health, physical and mental deformities, constant exposure to toxic wastes and chronic diseases as a result of chromite mining, there is a tragic gap in the availability of ′scientific′ studies and data on the health hazards of mining in India. Occupational Safety and Health Administration, Odisha State Pollution Control Board and the Odisha Voluntary Health Association data were used to compile the possible occupational health hazards, hexavalent chromium exposure and diseases among Sukinda chromite mines workers. Studies were reviewed to determine the routes of exposure and possible mechanism of chromium induced carcinogenicity among the workers. Our studies suggest all forms of hexavalent chromium are regarded as carcinogenic to workers however the most important routes of occupational exposure to Cr (VI are inhalation and dermal contact. This review article outlines the physical, chemical, biological and psychosocial occupational health hazards of chromite mining and associated metallurgical processes to monitor the mining environment as well as the miners exposed to these toxicants to foster a safe work environment. The authors anticipate that the outcome of this manuscript will have an impact on Indian chromite mining industry that will subsequently bring about improvements in work conditions, develop intervention experiments in occupational health and safety programs.

  6. Sulfuric acid leaching kinetics of South African chromite

    Institute of Scientific and Technical Information of China (English)

    Qing Zhao; Cheng-jun Liu; Pei-yang Shi; Bo Zhang; Mao-fa Jiang; Qing-song Zhang; Ron Zevenhoven; Henrik Saxn

    2015-01-01

    The sulfuric acid leaching kinetics of South African chromite was investigated. The negative influence of a solid product layer constituted of a silicon-rich phase and chromium-rich sulfate was eliminated by crushing the chromite and by selecting proper leaching con-ditions. The dimensionless change in specific surface area and the conversion rate of the chromite were observed to exhibit a proportional re-lationship. A modified shrinking particle model was developed to account for the change in reactive surface area, and the model was fitted to experimental data. The resulting model was observed to describe experimental findings very well. Kinetics analysis revealed that the leach-ing process is controlled by a chemical reaction under the employed experimental conditions and the activation energy of the reaction is 48 kJ·mol–1.

  7. Stratiform chromite deposit model: Chapter E in Mineral deposit models for resource assessment

    Science.gov (United States)

    Schulte, Ruth F.; Taylor, Ryan D.; Piatak, Nadine M.; Seal, Robert R., II

    2012-01-01

    A new descriptive stratiform chromite deposit model was prepared which will provide a framework for understanding the characteristics of stratiform chromite deposits worldwide. Previous stratiform chromite deposit models developed by the U.S. Geological Survey (USGS) have been referred to as Bushveld chromium, because the Bushveld Complex in South Africa is the only stratified, mafic-ultramafic intrusion presently mined for chromite and is the most intensely researched. As part of the on-going effort by the USGS Mineral Resources Program to update existing deposit models for the upcoming national mineral resource assessment, this revised stratiform chromite deposit model includes new data on the geological, mineralogical, geophysical, and geochemical attributes of stratiform chromite deposits worldwide. This model will be a valuable tool in future chromite resource and environmental assessments and supplement previously published models used for mineral resource evaluation.

  8. SEM, optical, and Moessbauer studies of submicrometer chromite in Allende

    Science.gov (United States)

    Housley, R. M.

    1982-01-01

    New scanning electron and optical microscope results are presented showing that sub-micrometer chromite is abundant along healed cracks and grain boundaries in Allende chondrule olivine. Some wider healed cracks also contain pentlandite and euhedral Ni3Fe grains. Also reported are Moessbauer measurements on Allende HF-HCl residues confirming a high Fe(+++)/Fe(++) ratio.

  9. Advances towards a Clean Hydrometallurgical Process for Chromite

    Directory of Open Access Journals (Sweden)

    Bo Zhang

    2016-01-01

    Full Text Available Because of the acute toxicity of Cr(VI-bearing substances, the pollution problem caused by chromite process residue has become a worldwide concern. In the view of relevant studies, the technologies based on the alkali treatment cannot fundamentally resolve the pollution problem, because the oxidation of Cr(III to Cr(VI is unavoidable during chromite decomposition. In contrast, the oxidation of Cr(III to Cr(VI can be controlled by the sulfuric acid treatment of chromite, and the Cr(VI pollution can be eliminated from the original source of production. Many research studies focusing on the resolutions of the key obstacles hindering the development of the sulfuric acid treatment process have been carried out, and significant progress has been achieved. In this study, a clean hydrometallurgical process without the generation of hexavalent chromium is demonstrated. First, the chromite was decomposed and leached by sulfuric acid solution in the presence of an oxidant. Then, iron was hydrothermally removed from the acid solution as the precipitate of jarosite. Finally, chromium salts were obtained by adjusting the basicity of the solution, separation and drying. With the aim of realizing industrialization, future research emphasis on the development of the sulfuric acid treatment process is proposed in this study.

  10. THERMODYNAMICS STUDY ON THE DECOMPOSITION OF CHROMITE WITH KOH

    Institute of Scientific and Technical Information of China (English)

    Z. Sun; S.L. Zheng; Y. Zhang

    2007-01-01

    Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature,which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.

  11. Applications and Preparation Methods of Copper Chromite Catalysts: A Review

    Directory of Open Access Journals (Sweden)

    Ram Prasad

    2011-11-01

    Full Text Available In this review article various applications and preparation methods of copper chromite catalysts have been discussed. While discussing it is concluded that copper chromite is a versatile catalyst which not only catalyses numerous processes of commercial importance and national program related to defence and space research but also finds applications in the most concerned problem worldwide i.e. environmental pollution control. Several other very useful applications of copper chromite catalysts are in production of clean energy, drugs and agro chemicals, etc. Various preparation methods about 15 have been discussed which depicts clear idea about the dependence of catalytic activity and selectivity on way of preparation of catalyst. In view of the globally increasing interest towards copper chromite catalysis, reexamination on the important applications of such catalysts and their useful preparation methods is thus the need of the time. This review paper encloses 369 references including a well-conceivable tabulation of the newer state of the art. Copyright © 2011 by BCREC UNDIP. All rights reserved.(Received: 19th March 2011, Revised: 03rd May 2011, Accepted: 23rd May 2011[How to Cite: R. Prasad, and P. Singh. (2011. Applications and Preparation Methods of Copper Chromite Catalysts: A Review. Bulletin of Chemical Reaction Engineering & Catalysis, 6 (2: 63-113. doi:10.9767/bcrec.6.2.829.63-113][How to Link / DOI: http://dx.doi.org/10.9767/bcrec.6.2.829.63-113 || or local:  http://ejournal.undip.ac.id/index.php/bcrec/article/view/829 ] | View in 

  12. Geological and Mineralogical-technological features chromite ore from nickel-weathering crusts Average Bug

    Directory of Open Access Journals (Sweden)

    Perkov E.S.

    2013-09-01

    Full Text Available Conditions of occurrence and distribution features of chromites ore bodies in the ultra-basic nickel bearing weathering crusts of Middle Bug Area are considered. Main types of exogenous chromites ores in weathering crusts and beyond of them are identified as well as mineralogical, chemical and grain features of mineralization are given. Obtained data are substantiated in order to apply them while developing the efficient schemes of mining and processing of exogenous chromites ores.

  13. Effects of mechanical activation on the carbothermal reduction of chromite with metallurgical coke

    Directory of Open Access Journals (Sweden)

    Kenan Yıldız

    2010-06-01

    Full Text Available The carbothermal reduction of mechanically activated chromite with metallurgical coke under an argon atmosphere was investigated at temperatures between 1100 and 1400°C and the effects of the mechanical activation on chromite structure were analyzed by x-ray diffraction (XRD and scanning electron microscopy (SEM. An increase in specific surface area resulted in more contact points. The activation procedure led to amorphization and structural disordering in chromite and accelerated the degree of reduction and metalization in the mixture of chromite and metallurgical coke. Carbothermal reduction products were analzed by using scanning electron microscopy (SEM/EDS.

  14. Studies on genesis of chromite and PGE in Naein ophiolite melange

    Directory of Open Access Journals (Sweden)

    Reza Shamsipour Dehkordi

    2011-10-01

    Full Text Available Nain ophiolite melange is located 140 Km east of Isfahan. Based on the geological studies, this area belongs to Mesozoic ophiolite of Urumieh – Dokhtar zone, west of central Iran. Country rocks are pridotite and serpentinized pridotite. The pridotite rocks are composed of Harzburgite, Lherzolite and replacement Dunite which is belong to spinel pridotite facies. Paragenesis of ore minerals are Chromite, Irarsite, Magnetite, Hematite, Pentlandite, Millerite, Chalcopyrite, Pyrite, and Covelline. Geochemical surveys of host rock and chromite show tholeiite series of magma and alpine type chromite. PGE (Ir, Pt, Pd, and Os are enriched in chromite. REE spider diagram pattern show the processes of boninitic magma and partial melting.

  15. Chromite deposits of the north-central Zambales Range, Luzon, Philippines

    Science.gov (United States)

    Rossman, D.L.

    1970-01-01

    Peridotite and gabbro form an intrusive complex which is exposed over an area about 35 km wide and 150 km long in the center of the Zambales Range of western Luzon. The Zambales Complex is remarkable for its total known resources, mined and still remaining, of about 15 million metric tons of chromite ore. Twenty percent of Free World production was obtained from this area between 1950 and the end of 1964; in 1960 production reached a high of 606,103 metric tons of refractory-grade ore, mostly from the Coto mine near Masinloc, and 128,426 metric tons of metallurgical ore from the Acoje mine. The United States imports 80 to 90 percent of its refractory-grade chromite from the Philippines, and its basic refractory technology has been designed upon the chemical and physical characteristics of Coto high-alumina chromite ore. Continuation of this pattern will depend upon discovery of additional ore reserves to replace those depleted by mining. The Zambales Ultramafic Complex is of the alpine type in which lenticular or podiform deposits of chromite lie in peridotite or dunite, mostly near Contacts with gabbroic rocks. Layered structures, foliation, and lineation commonly are well developed and transect boundaries between major rock units, including chromite deposits, at any angle. Accordingly, these structures cannot be used as guides in exploration and mining as they are used in stratiform complexes such as the Bushveld, where chromite layers extend for many miles. Probably 90 percent of the known deposits in the Zambales Complex are located in two belts in its northern part. One zone containing high-aluminua refractory-grade deposits extends northeast from the Coto mine and Chromite Reservation No. I along a peridotite contact with olivine gabbro, and another of high-chromium metallurgical grade chromite extends south through the Zambales and Acoje properties, and swings westward around the south side of Mount Lanai along a peridotite contact with norite. The textures

  16. Optics of Chromites and Charge-Transfer Transitions

    Directory of Open Access Journals (Sweden)

    Andrei V. Zenkov

    2008-01-01

    Full Text Available Specific features of the charge-transfer (CT states and O2p→Cr3d transitions in the octahedral (CrO69− complex are considered in the cluster approach. The reduced matrix elements of the electric-dipole transition operator are calculated on many-electron wave functions of the complex corresponding to the initial and final states of a CT transition. Modeling the optic spectrum of chromites has yielded a complicated CT band. The model spectrum is in satisfactory agreement with experimental data which demonstrates the limited validity of the generally accepted concept of a simple structure of CT spectra.

  17. Brief report on thermodynamics of chromium slags and kinetic modelling of chromite reduction (1995-96)

    Energy Technology Data Exchange (ETDEWEB)

    Xiao Yamping; Holappa, L. [Helsinki Univ. of Technology, Otaniemi (Finland). Lab. of Metallurgy

    1996-12-31

    This article summaries the research work on thermodynamics of chromium slags and kinetic modelling of chromite reduction. The thermodynamic properties of FeCr slag systems were calculated with the regular solution model. The effects of CaO/MgO ratio, Al{sub 2}0{sub 3} amount as well as the slag basicity on the activities of chromium oxides and the oxidation state of chromium were examined. The calculated results were compared to the experimental data in the literature. In the kinetic modelling of the chromite reduction, the reduction possibilities and tendencies of the chromite constitutes with CO were analysed based on the thermodynamic calculation. Two reaction models, a structural grain model and a multi-layers reaction model, were constructed and applied to simulate the chromite pellet reduction and chromite lumpy ore reduction, respectively. The calculated reduction rates were compared with the experimental measurements and the reaction mechanisms were discussed. (orig.) SULA 2 Research Programme; 4 refs.

  18. GEOLOGICAL AND GEOCHEMICAL FEATURES OF THE KIZILDAĞ (AKSEKİ- ANTALYA CHROMITE OCCURRENCES

    Directory of Open Access Journals (Sweden)

    Adnan DÖYEN

    2002-01-01

    Full Text Available The study area is located at 20 km southwest of Seydişehir (Konya and the chromites are cropped out in the dunitic rocks of the Kızıldağ ultramafics. The chromites are found as banded, schliren and massive occurrences and their chemical composition have a features of Alpine type chromites. These chromites can be classified as Al- rich and ferric chromites and their Cr/Fet is between 2.77 and 3.28 (mean 2.99. In the Cr/Cr+AlMg/Mg+Fe +2 binary diagram, r/Cr+Al values covers a festricted area while Mg/Mg + Fe+2 ratios distrubuted in a wider range. There is a strong negative correlation between Cr and Mg and negative (not too strong correlation between Cr and Al.

  19. PROMOTED ZINC CHROMITE CATALYSTS FOR HIGHER ALCOHOL SYNTHESIS

    Energy Technology Data Exchange (ETDEWEB)

    Ms. Xiaolei Sun; Professor George W. Roberts

    2000-06-21

    Work during the report period was concentrated on developing analytical techniques. Thin-layer chromatography (TLC) was used in an attempt to define the best mobile phase to separate the components of ''spent'' tetrahydroquinoline by liquid chromatography in a silica gel column. Conditions have been defined for separating the light gases produced by the reaction of carbon monoxide (CO) and hydrogen (H{sub 2}) over promoted ''zinc chromite'' catalysts. This will be done with a temperature-programmed Carboxen-1000 column, using a thermal conductivity detector for analysis. A Petrocol DM 150 capillary column will be purchased to separate the heavier products, which will be analyzed using a flame ionization detector.

  20. Lanthanum chromite colloidal processing; Processamento coloidal de cromito de lantanio

    Energy Technology Data Exchange (ETDEWEB)

    Setz, Luiz Fernando Grespan

    2009-07-01

    Lanthanum chromite (LaCrO{sub 3}) is currently the most studied material for applications such as solid oxide fuel cell inter connector (HTSOFC). The complexity of microstructures and geometries of HTSOFC devices, require a precise control of processing parameters to get the desired combination of properties and this, the use of techniques involving concentrated ceramic slips conformation are appropriate, therefore, is well controlled, assist in obtaining homogeneous parts, reproductive and complex geometries. Thus, studies involving the surface chemistry, the stability conditions and slips flow behaviour in the forming conditions, provide important elements for processes control in the inter connectors manufacture, where more applied settings have slots and channels for the gases passage. Thus, surface chemistry, stability and rheological behaviour of strontium and cobalt doped LaCrO{sub 3} (La{sub 0.80}Sr{sub 0.20}Cr{sub 0.92}Co{sub 0.08}O{sub 3}) slips prepared with ethanol and water, were studied. The doped lanthanum chromite was produced by combustion synthesis in the IPEN/SP labs. The influence of parameters: p H (water), dispersant concentration, homogenization times and conditions, solid concentration, different ratios binder:plasticizer in the stability and the flow behavior of ceramic suspensions prepared were evaluated. The La{sub 0.80}Sr{sub 0.20}Cr{sub 0.92}Co{sub 0.08}O{sub 3} products obtained by casting aqueous slips in a plaster mould, using alkaline p H and anionic polyelectrolyte and tapes obtained by using ethanol as a dispersant medium, after sintering at 1600 deg C/4h presented theoretical density > 94%, suitable for use as HTSOFC inter connector. (author)

  1. Lanthanum chromite colloidal processing; Processamento coloidal de cromito de lantanio

    Energy Technology Data Exchange (ETDEWEB)

    Setz, Luiz Fernando Grespan

    2009-07-01

    Lanthanum chromite (LaCrO{sub 3}) is currently the most studied material for applications such as solid oxide fuel cell inter connector (HTSOFC). The complexity of microstructures and geometries of HTSOFC devices, require a precise control of processing parameters to get the desired combination of properties and this, the use of techniques involving concentrated ceramic slips conformation are appropriate, therefore, is well controlled, assist in obtaining homogeneous parts, reproductive and complex geometries. Thus, studies involving the surface chemistry, the stability conditions and slips flow behaviour in the forming conditions, provide important elements for processes control in the inter connectors manufacture, where more applied settings have slots and channels for the gases passage. Thus, surface chemistry, stability and rheological behaviour of strontium and cobalt doped LaCrO{sub 3} (La){sub 0.80}Sr{sub 0.}2{sub 0}Cr{sub 0.92}Co{sub 0.08}O{sub 3}) slips prepared with ethanol and water, were studied. The doped lanthanum chromite was produced by combustion synthesis in the IPEN/SP labs. The influence of parameters: pH (water), dispersant concentration, homogenization times and conditions, solid concentration, different ratios binder:plasticizer in the stability and the flow behavior of ceramic suspensions prepared were evaluated. The La){sub 0.80}Sr{sub 0.}2{sub 0}Cr{sub 0.92}Co{sub 0.08}O{sub 3} products obtained by casting aqueous slips in a plaster mould, using alkaline pH and anionic polyelectrolyte and tapes obtained by using ethanol as a dispersant medium, after sintering at 1600 degree C/4 hours presented theoretical density > 94%, suitable for use as HTSOFC inter connector. (author)

  2. Borohydride electro-oxidation by Ag-doped lanthanum chromites

    Indian Academy of Sciences (India)

    S Suresh Balaji; A Usha; V V Giridhar

    2014-05-01

    The electrocatalytic activity of Ag-doped lanthanum chromites electrode materials viz., LaCr0.4Ag0.6O3 and LaCr0.7Ag0.3O3 prepared by decomposing the precursor complex is studied. Pure LaCrO3 is synthesized by combustion route using oxalic acid as a fuel. The decomposition behaviour of the assynthesized powder obtained in the latter method is characterized by TGA-DTA and XRD. Both the precursor complex and the as-synthesized powder are calcined at 900°C for 7 and 10 h, respectively. XRD of the final product after calcinations indicated the formation of perovskite phase with minor amounts of impurity phases of component oxides in the Ag-doped lanthanum chromites and pure perovskite phase in the undoped one. The surface morphology of the perovskites is studied by SEM. The electrocatalytic activity of the perovskite powders for borohydride oxidation is studied by using cyclic voltammetry (CV) at a catalyst loading of 0.7 mgcm−2 for both Ag-doped and undoped LaCrO3 coated on glassy carbon substrate. Calibration plots are obtained by plotting the anodic peak current versus concentration of borohydride in the range of 20-100 mM. The sensitivities of the three perovskites towards borohydride oxidation indicated that LaCr0.4Ag0.6O3 is the best among all the perovskites studied giving a value of 1.395 A/mM.

  3. Occurrence and emplacement of chromite ores in Sindhudurg district, Maharashtra, India

    Digital Repository Service at National Institute of Oceanography (India)

    Iyer, S.D.; Babu, E.V.S.S.K.; Mislankar, P.G.; Gujar, A.R.; Ambre, N.V.; Loveson, V.J.

    In the present study, the occurrence and emplacement of chromite ore deposits from two abandoned mines (Kankavali (Janoli) and Wagda) in the Sindhudurg district of Maharashtra, India are presented. These ores, that occurred as lenses...

  4. Compositional variations in the Mesoarchean chromites of the Nuggihalli schist belt, Western Dharwar Craton (India)

    DEFF Research Database (Denmark)

    Mukherjee, Ria; Mondal, Sisir Kanti; Rosing, Minik Thorleif;

    2010-01-01

    bell: that are surrounded by the tonalite-trondhjemite-granodiorite (TTG) suite of rocks. The entire succession is exposed in the Tagdur mining district. The succession has been divided into the lower and the upper ultramafic units, separated by a middle gabbro unit. The ultramafic units comprise......-98)) and pyroxene grains (Mg-numbers = 97-99). Compositional variability on the scale of a single chromite grain occurs in the form of zoning, and it is common in the accessory chromite grains in serpentinite and in the altered grains in chromitite. In the zoned grains, the composition of the core is modified....... In some occurrences, the ferritchromit rim is very well developed, and only a small relict core appears to remain in the chromite grain. However, complete alteration of the chromite grains to ferritchromit without any remnant core is also present. The regular, well-developed and continuous occurrence...

  5. Thermal metamorphism of mantle chromites and the stability of noble-metal nanoparticles

    Science.gov (United States)

    González-Jiménez, José M.; Reich, Martin; Camprubí, Antoni; Gervilla, Fernando; Griffin, William L.; Colás, Vanessa; O'Reilly, Suzanne Y.; Proenza, Joaquín A.; Pearson, Norman J.; Centeno-García, Elena

    2015-08-01

    The Loma Baya complex in south-western Mexico is a volume of chromitite-bearing oceanic mantle that records a complex metamorphic history, defined by a first stage of hydrous metamorphism overprinted by a short-lived thermal event associated with an Eocene granite intrusion. During the hydrous metamorphism, the primary magmatic chromite-olivine assemblage was replaced by a secondary, porous intergrowth of Fe2+-rich chromite and chlorite. The heat supplied by an Eocene-age granite intrusion reversed the hydration reaction, producing chromite rims with perfectly developed crystal faces. This third-generation chromite is in equilibrium with highly magnesian (neoformed) olivine and defines a chemical trend analogous to the original magmatic one. The preservation of both reactions in the Loma Baya chromitite provides compelling evidence that the hydration of chromite can be reversed by either prograde metamorphism or any heating event, confirming previous thermodynamic predictions. Understanding these complex features is of particular interest due to the fact that changes in temperature and variable degrees of fluid/rock interaction during metamorphism and intrusion have also significantly affected the chromite-hosted IPGE carrier phases. Here, we propose that the metamorphic fluids involved in the hydrous metamorphism have caused the desulphurization of laurite RuS2, releasing minute particles of Ru-Os-Ir alloys phenomena in natural systems, shedding new light on the kinetic controls of nano- to micron-scale IPGE particle distributions during metamorphism.

  6. Palladium, platinum, rhodium, iridium and ruthenium in chromite- rich rocks from the Samail ophiolite, Oman.

    Science.gov (United States)

    Page, N.J.; Pallister, J.S.; Brown, M.A.; Smewing, J.D.; Haffty, J.

    1982-01-01

    30 samples of chromitite and chromite-rich rocks from two stratigraphic sections, 250 km apart, through the basal ultramafic member of the Samail ophiolite were spectrographically analysed for platinum-group elements (PGE) and for Co, Cu, Ni and V. These data are reported as are Cr/(Cr + Al), Mg/(Mg + Fe) and wt.% TiO2 for most samples. The chromitite occurs as pods or lenses in rocks of mantle origin or as discontinuous layers at the base of the overlying cumulus sequence. PGE abundances in both sections are similar, with average contents in chromite-rich rocks: Pd 8 ppb, Pt 14 ppb, Rh 6 ppb, Ir 48 ppb and Ru 135 ppb. The PGE data, combined with major-element and petrographic data on the chromitite, suggest: 1) relatively larger Ir and Ru contents and highest total PGE in the middle part of each section; 2) PGE concentrations and ratios do not correlate with coexisting silicate and chromite abundances or chromite compositions; 3) Pd/PGE, on average, increases upward in each section; 4) Samail PGE concentrations, particularly Rh, Pt and Pd, are lower than the average values for chromite-rich rocks in stratiform intrusions. 2) suggests that PGEs occur in discrete alloy or sulphide phases rather than in the major oxides or silicates, and 4) suggests that chromite-rich rocks from the oceanic upper mantle are depleted in PGE with respect to chondrites. L.C.C.

  7. Cation distribution and magnetic properties of natural chromites

    Energy Technology Data Exchange (ETDEWEB)

    Rais, A.; Yousif, A.A.; Al-shihi, M.H.; Al-rawas, A.D.; Gismelseed, A.M.; El-zain, M.E. [Department of Physics, College of Science, Sultan Qaboos University (Oman)

    2003-10-01

    Ten specimens of chromites from Oman ophiolites have been studied using magnetic susceptibility {chi} measurements, Moessbauer spectroscopy (MS), Scanning electron microscopy (SEM), and X-ray diffraction (XRD). XRD shows that all samples have a face-centered cubic spinel structure. MS analysis and SEM data at room temperature enabled to derive the chemical formula and the cations distribution among tetrahedral (A1 and A2) and octahedral (B) sites. For all specimens, paramagnetic variations of 1/{chi} with the temperature T show a systematic curve bending at a critical temperature T{sub 0}, which indicates a change of the effective paramagnetic moment {mu}{sub eff}. This deviation from Curie-Weiss law is interpreted as due to spin inversion of a fraction {delta} of Cr{sup 3+} cations located in the octahedral sites of the spinel structure. This interpretation is supported by a decrease in the Moessbauer peak areas of Fe{sup 2+} located in A1 sites from 300 to 80 K at the expense of Fe{sup 2+} located in A2 sites. The values of {delta} and {mu}{sub eff} for each specimen are calculated by fitting this model separately to the experimental 1/{chi} versus T above and below T{sub 0}. (Abstract Copyright [2003], Wiley Periodicals, Inc.)

  8. Osmium, ruthenium, iridium and uranium in silicates and chromite from the eastern Bushveld Complex, South Africa

    Science.gov (United States)

    Gijbels, R.h.; Millard, H.T., Jr.; Desborough, G.A.; Bartel, A.J.

    1974-01-01

    Osmium, ruthenium, iridium and uranium contents were determined in eight ortho pyroxene, seven plagioclase, and three chromite mineral separates from the eastern Bushveld Complex. Neutron activation analysis was used to measure the platinum metals, and uranium was determined by a fission track technique. The platinum metals were found to be present within each mine??ral in the proportions Os:Ru:Ir = 1:7:1, while the concentrations of these metals in the minerals are in the ratios orthopyroxene:plagioclase:chromite = 1:16:700. The concentration of uranium was found to range from 11 to 66 ppb (parts per billion) and not to vary significantly from mineral to mineral. The data for the platinum metals are consistent with a model in which the eastern Bushveld Complex was formed by the fractional crystallization of two separately injected magmas. A computer fit of this model to these data indicates that the initial concentrations of Os, Ru and Ir in the first magma were 0.24, 2.0 and 0.21 ppb and in the second magma were 0.16, 1.1 and 0.18 ppb, respectively. The fit also yields the distribution coefficients for the partitioning between the liquid and cumulus orthopyroxene, cumulus plagioclase and cumulus chromite. These coefficients (mineral/liquid) for osmium are 4.5, 66 and 2700; for ruthenium, they are 5, 65 and 2700; and for iridium, they are 4, 60 and 1600. To make this fit, it was necessary to hypothesize the existence of two types of chromite: one type with a large distribution coefficient, presumably formed as a cumulus phase at high temperature, and another, more prevalent type with a smaller distribution coefficient, which may have been formed by postcumulus growth at a lower temperature. This hypothesis is supported by data for coexisting chromite-silicate pairs, which indicate that the chromite grains expelled these platinum metals as they cooled. ?? 1974.

  9. Compositional variations in the Mesoarchean chromites of the Nuggihalli schist belt, Western Dharwar Craton (India): potential parental melts and implications for tectonic setting

    DEFF Research Database (Denmark)

    Mukherjee, R.; Mondal, S.K.; Rosing, M.T.;

    2010-01-01

    -98)) and pyroxene grains (Mg-numbers = 97-99). Compositional variability on the scale of a single chromite grain occurs in the form of zoning, and it is common in the accessory chromite grains in serpentinite and in the altered grains in chromitite. In the zoned grains, the composition of the core is modified....... In some occurrences, the ferritchromit rim is very well developed, and only a small relict core appears to remain in the chromite grain. However, complete alteration of the chromite grains to ferritchromit without any remnant core is also present. The regular, well-developed and continuous occurrence...... of ferritchromit rims around the chromite grain boundaries, the complete alteration of the chromite grains and the modification of the core composition indicate the alteration in the Nuggihalli schist belt to be intense, pervasive and affected by later low-grade metamorphism. The primary composition of chromite...

  10. An Exercise in X-Ray Diffraction Using the Polymorphic Transition of Nickel Chromite.

    Science.gov (United States)

    Chipman, David W.

    1980-01-01

    Describes a laboratory experiment appropriate for a course in either x-ray crystallography or mineralogy. The experiment permits the direct observation of a polymorphic transition in nickel chromite without the use of a special heating stage or heating camera. (Author/GS)

  11. A MIXED CHEMICAL REDUCTANT FOR TREATING HEXAVALENT CHROMIUM IN A CHROMITE ORE PROCESSING SOLID WASTE

    Science.gov (United States)

    We evaluated a method for delivering ferrous iron into the subsurface to enhance chemical reduction of Cr(VI) in a chromite ore processing solid waste (COPSW). The COPSW is characterized by high pH (8.5 -11.5), high Cr(VI) concentrations in the solid phase (up to 550 mg kg-1) and...

  12. Performance evaluation of commercial copper chromites as burning rate catalyst for solid propellants

    Directory of Open Access Journals (Sweden)

    Milton Faria Diniz

    2010-09-01

    Full Text Available Copper chromites are well known as burning rate catalysts for the combustion of composite solid propellants, used as a source of energy for rocket propulsion. The propellant burning rate depends upon the catalyst characteristics such as chemical composition and specific surface area. In this work, copper chromite samples from different suppliers were characterized by chemical analysis, FT-IR spectroscopy and by surface area measurement (BET. The samples were then evaluated as burning rate catalyst in a typical composite propellant formulation based on HTPB binder, ammonium perchlorate and aluminum. The obtained surface area values are very close to those informed by the catalyst suppliers. The propellant processing as well as its mechanical properties were not substantially affected by the type of catalyst. Some copper chromite catalysts caused an increase in the propellant burning rate in comparison to the iron oxide catalyst. The results show that in addition to the surface area, other parameters like chemical composition, crystalline structure and the presence of impurities might be affecting the catalyst performance. All evaluated copper chromite samples may be used as burning rate catalyst in composite solid propellant formulations, with slight advantages for the SX14, Cu-0202P and Cu-1800P samples, which led to the highest burning rate propellants.

  13. The 3.1 Ga Nuggihalli chromite deposits, Western Dhawar craton (India)

    DEFF Research Database (Denmark)

    Mukherjee, Ria; Mondal, Sisir K.; Frei, Robert;

    2012-01-01

    likely related to a supercontinent cycle. High-Mg magmas such as komatiites host important metal deposits like chromite, Ni-sulfide and associated PGE mineralization. The uneven distribution of metal deposits over time can be explained by plate tectonic cycles that included repeated periods...

  14. Beneficiation of Konya-Beyşehir Chromite for Producing Concentrates Suitable for Industry

    Science.gov (United States)

    Öztürk, Fatma Deniz; Abakay Temel, Halime

    2016-09-01

    Turkey has a 6% share of world chromite mining and possesses 25 million tons of reserves. Despite their economic importance, the most important Turkish chromite reserves have not been extensively studied with respect to their composition. In this study, the possibility of upgrading Konya-Beyşehir (Turkey) chromite to produce chromite concentrates suitable for industry is investigated. Two groups of enrichment experiments were made. The effects of some parameters that markedly influence the separation of a shaking table, such as the amplitude and slope of the shaking table and the frequency of strokes were investigated in the first group of experiments, The shaking table experiments were planned and carried out using the statistical methods of Design of Experiments (Yate's and ANOVA) in the second group of experiments. As a result, it was found that a concentrate containing 46.89% Cr2O3 content with a yield of 85.18% was obtained from a feed containing 3.98% Cr2O3 content in 0.2 + 0.1 mm size fraction.

  15. Magnetic separation studies on ferruginous chromite fine to enhance Cr:Fe ratio

    Institute of Scientific and Technical Information of China (English)

    Sunil Kumar Tripathy; PK Banerjee; Nikkam Suresh

    2015-01-01

    The Cr:Fe ratio (chromium-to-iron mass ratio) of chromite affects the production of chrome-based ferroalloys. Although the lit-erature contains numerous reports related to the magnetic separation of different minerals, limited work concerning the application of mag-netic separation to fine chromite from the Sukinda region of India to enhance its Cr:Fe ratio has been reported. In the present investigation, magnetic separation and mineralogical characterization studies of chromite fines were conducted to enhance the Cr:Fe ratio. Characterization studies included particle size and chemical analyses, X-ray diffraction analysis, automated mineral analysis, sink-and-float studies, and mag-netic susceptibility measurements, whereas magnetic separation was investigated using a rare earth drum magnetic separator, a rare earth roll magnetic separator, an induced roll magnetic separator, and a wet high-intensity magnetic separator. The fine chromite was observed to be upgraded to a Cr:Fe ratio of 2.2 with a yield of 55.7%through the use of an induced roll magnetic separator and a feed material with a Cr:Fe ratio of 1.6.

  16. High temperature oxidation resistance of rare earth chromite coated Fe-20Cr and Fe-20Cr-4Al alloys

    Directory of Open Access Journals (Sweden)

    Marina Fuser Pillis

    2007-09-01

    Full Text Available Doped lanthanum chromite has been used in solid oxide fuel cell (SOFC interconnects. The high costs involved in obtaining dense lanthanum chromite have increased efforts to find suitable metallic materials for interconnects. In this context, the oxidation behavior of lanthanum chromite coated Fe-20Cr and Fe-20Cr-4Al alloys at SOFC operation temperature was studied. Isothermal oxidation tests were carried out at 1000 °C for 20, 50 and 200 hours. Cyclic oxidation tests were also carried out and each oxidation cycle consisted of 7 hours at 1000/°C followed by cooling to room temperature. The oxidation measurements and the results of SEM/EDS as well as XRD analyses indicated that lanthanum chromite coated Fe-20Cr and Fe-20Cr-4Al alloys were significantly more resistant to oxidation compared with the uncoated alloys.

  17. Investigation of nanocrystalline zinc chromite obtained by two soft chemical routes

    Energy Technology Data Exchange (ETDEWEB)

    Gingasu, Dana [Ilie Murgulescu Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, Bucharest 060021 (Romania); Mindru, Ioana, E-mail: imandru@yahoo.com [Ilie Murgulescu Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, Bucharest 060021 (Romania); Culita, Daniela C.; Patron, Luminita; Calderon-Moreno, Jose Maria; Preda, Silviu [Ilie Murgulescu Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, Bucharest 060021 (Romania); Oprea, Ovidiu [“Politehnica” University of Bucharest, Faculty of Chemistry, Polizu Street 1-7, Bucharest (Romania); Osiceanu, Petre [Ilie Murgulescu Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, Bucharest 060021 (Romania); Morena Pineda, Eufemio [School of Chemistry, University of Manchester, Oxford Road, M 13 9PL Manchester (United Kingdom)

    2014-01-01

    Graphical abstract: - Highlights: • Two soft chemical routes to synthesize zinc chromites are described. • Glycine is used as chelating agent (precursor method) and fuel (solution combustion method). • The synthesized chromites have crystallite size in the range of 18–27 nm. • An antiferromagnetic (AFM) transition is observed at about T{sub N} ∼ 18 K. - Abstract: Zinc chromite (ZnCr{sub 2}O{sub 4}) nanocrystalline powders were obtained by two different chemical routes: the precursor method and the solution combustion method involving glycine-nitrates. The complex compound precursors, [ZnCr{sub 2}(NH{sub 2}CH{sub 2}COO){sub 8}]·9H{sub 2}O and [ZnCr{sub 2}(NH{sub 2}CH{sub 2}COOH){sub 4.5}]·(NO{sub 3}){sub 8}·6H{sub 2}O, were characterized by chemical analysis, infrared spectroscopy (IR), ultraviolet–visible spectroscopy (UV–vis) and thermal analysis. The structure, morphology, surface chemistry and magnetic properties of ZnCr{sub 2}O{sub 4} powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), infrared and Raman spectroscopy (RS), ultraviolet–visible spectroscopy (UV–vis) and magnetic measurements. X-ray diffraction patterns indicated the chromite spinel phase with good crystallinity and an average crystallite size of approximately 18–27 nm. The band gap values ranged between 3.31 and 3.33 eV. The magnetic measurements indicated an antiferromagnetic transition at T{sub N} ∼ 17.5/18 K.

  18. Flocculation of chromite ore fines suspension using polysaccharide based graft copolymers

    Indian Academy of Sciences (India)

    N C Karmakar; B S Sastry; R P Singh

    2002-11-01

    Graft copolymers are being experimented at the laboratory scale as flocculants. All the four graft copolymers, viz. starch--polyacrylamide, amylopectin--polyacrylamide, sodium alginate--polyacylamide and carboxymethyl cellulose--polyacrylamide performed well as flocculants on chromite ore fines suspension. Amylopectin--polyacrylamide, in particular, performed superior to the rest of the series from the point of view of settling velocity of flocs which is the most important aspect in solid–liquid separation.

  19. Reduction of Hexavalent Chromium by Viable Cells of Chromium Resistant Bacteria Isolated from Chromite Mining Environment

    OpenAIRE

    Satarupa Dey; Baishali Pandit; A. K. Paul

    2014-01-01

    Environmental contamination of hexavalent chromium [Cr(VI)] is of serious concern for its toxicity as well as mutagenic and carcinogenic effects. Bacterial chromate reduction is a cost-effective technology for detoxification as well as removal of Cr(VI) from polluted environment. Chromium resistant and reducing bacteria, belonging to Arthrobacter, Pseudomonas, and Corynebacterium isolated from chromite mine overburden and seepage samples of Orissa, India, were found to tolerate 12–18 mM Cr(VI...

  20. Hexavalent chromium reduction by aerobic heterotrophic bacteria indigenous to chromite mine overburden

    OpenAIRE

    Dey Satarupa; A. K. Paul

    2013-01-01

    Microbiological analysis of overburden samples collected from chromite mining areas of Orissa, India revealed that they are rich in microbial density as well as diversity and dominated by Gram-negative (58%) bacteria. The phenotypically distinguishable bacterial isolates (130) showed wide degree of tolerance to chromium (2–8 mM) when tested in peptone yeast extract glucose agar medium. Isolates (92) tolerating 2 mM chromium exhibited different degrees of Cr+6 reducing activity in chemically d...

  1. Optical constants of various chromites as determined by Kramers-Kronig analysis.

    Science.gov (United States)

    Anki, M M; Lefez, B

    1996-03-20

    The infrared optical constants of a few different powders of chromites, XCr(2)O(4) (where X is Fe, Ni, Mg, Zn, or Cu), have been determined by Kramers-Kronig analysis of their infrared transmission and reflection spectra. The knowledge of these constants allows one to predict the different thin-layer infrared reflection spectra and to compare them, when it is possible, with the reflection spectra calculated with n and k obtained by the use of the classical oscillator method.

  2. Deactivation mechanistic studies of copper chromite catalyst for selective hydrogenation of 2-furfuraldehyde

    OpenAIRE

    Liu, Dongxia; Zemlyanov, Dmitry; Win, Tianpin; Lobo-Lapidus, Rodrigo J.; Dumesic, James A.; Miller, Jeffrey T.; Marshall, Christopher L.

    2013-01-01

    Deactivation mechanisms of copper chromite (CuCr2O4 center dot CuO) catalyst for vapor-phase selective hydrogenation for furfuryl alcohol have been investigated using ex situ and in situ X-ray absorption fine structure (XAFS), X-ray photon spectroscopy (XPS), and Auger Electron Spectroscopy (AES). At 200 degrees C, the catalyst steadily deactivated. One of the dominant origins of catalyst deactivation is poisoning due to strong adsorption of polymeric species formed from the reactant and/or p...

  3. Preparation of Ca Doped Lanthanum Chromite by Sol-Gel Process

    Institute of Scientific and Technical Information of China (English)

    Zang Bangqiang; Ao Qing; Li Dehui; Sun Liangcheng; Liu Ruwei

    2004-01-01

    Super fine particles of calcium-doped lanthanum chromites were prepared by the sol-gel process in which the chelating agent was citric acid and the dispersant agent was ethylene glycol. The phase of fine particles was analyzed by XRD and the size and shape of the particles were investigated by TEM. The result shows that the nano-particles of La1-xCaxCrO3 can be obtained by the way of Ca2+ complex singly with citric acid and being calcined at 700 ℃.

  4. On preparation of nanocrystalline chromites by co-precipitation and autocombustion methods

    Energy Technology Data Exchange (ETDEWEB)

    Matulkova, Irena [Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 8, 128 43 Prague 2 (Czech Republic); Department of Radiation and Chemical Physics, Institute of Physics of the ASCR, v.v.i., Na Slovance 2, 182 21 Prague 8 (Czech Republic); Holec, Petr [Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 8, 128 43 Prague 2 (Czech Republic); Department of Materials Chemistry, Institute of Inorganic Chemistry of the ASCR, v.v i., Husinec-Rez 1001, 250 68 Rez (Czech Republic); Pacakova, Barbara; Kubickova, Simona; Mantlikova, Alice [Department of Magnetic Nanosystems, Institute of Physics of the ASCR, v.v.i., Na Slovance 2, 182 21 Prague 8 (Czech Republic); Plocek, Jiri [Department of Materials Chemistry, Institute of Inorganic Chemistry of the ASCR, v.v i., Husinec-Rez 1001, 250 68 Rez (Czech Republic); Nemec, Ivan; Niznansky, Daniel [Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 8, 128 43 Prague 2 (Czech Republic); Vejpravova, Jana, E-mail: vejpravo@fzu.cz [Department of Magnetic Nanosystems, Institute of Physics of the ASCR, v.v.i., Na Slovance 2, 182 21 Prague 8 (Czech Republic)

    2015-05-15

    Highlights: • ACr{sub 2}O{sub 4} nanopowders, A = Cu, Fe, Ni, Mn and Mg were obtained in high yield. • Co-precipitation and autocombustion routes were optimized for single-phase product. • The nanopowders were examined by X-ray diffraction and vibrational spectroscopy. • Formation of cubic or tetragonal phase in Jahn–Teller NiCr{sub 2}O{sub 4} can be controlled. - Abstract: We present a comprehensive study on optimization of wet preparation routes yielding well-crystalline spinel chromite, ACr{sub 2}O{sub 4} nanoparticles (A = Cu, Fe, Ni, Mn and Mg). The auto-combustion and co-precipitation methods in the presence of nitrate or chloride ions and under different atmospheres, followed by annealing of final products at different temperatures were tested. All samples were characterized by powder X-ray diffraction (PXRD) and vibrational spectroscopy in order to evaluate their phase composition, particle size and micro-strain. Selected samples were subjected to investigation by transmission electron microscopy (TEM). The degree of the particle crystallinity was estimated by relating the apparent crystallite size obtained from the PXRD analysis to the physical grain size observed by the TEM. Optimal conditions leading to single-phase and highly-crystalline chromite nanoparticles are proposed.

  5. Magnetic properties of rare earth HoCrO3 chromites

    Institute of Scientific and Technical Information of China (English)

    SU Yuling; ZHANG Jincang; FENG Zhenjie; LI Zijiong; SHEN Yan; CAO Shixun

    2011-01-01

    The temperature dependence of the magnetic properties was systemically studied by dc/ac magnetization and specific heat measurement for heavy rare earth HoCrO3 chromites.The results revealed the existence of complex phase coexistence and competitive magnetic behavior in HoCrO3 chromites.It was found that,in the region of higher temperature above 141.0 K,HoCrO3 behaved as a typical Cufie-Weiss paramagnetic (PM).And in the region of low temperature,a novel magnetization behavior was observed with negative magnetization (diamagnetism-like) characteristics under an external field of 100 Oe and M-Tcurves exhibited two symmetrical branches for field cooling (FC) and zero field cooling (ZFC) modes.This behavior indicated the coexistence of canted antiferromagnetic (CAFM) and weak ferromagnetic (FM) phase.These also exhibited the existence of competition mechanism below characteristic temperature TN1=141.0 K and the magnetic order of Ho ion below 7.5 K.The current complex magnetization might be attributed to the interaction between paramagnetic Ho3+moments and canted Cr3+ moments.

  6. On preparation of nanocrystalline chromites by co-precipitation and autocombustion methods

    International Nuclear Information System (INIS)

    Highlights: • ACr2O4 nanopowders, A = Cu, Fe, Ni, Mn and Mg were obtained in high yield. • Co-precipitation and autocombustion routes were optimized for single-phase product. • The nanopowders were examined by X-ray diffraction and vibrational spectroscopy. • Formation of cubic or tetragonal phase in Jahn–Teller NiCr2O4 can be controlled. - Abstract: We present a comprehensive study on optimization of wet preparation routes yielding well-crystalline spinel chromite, ACr2O4 nanoparticles (A = Cu, Fe, Ni, Mn and Mg). The auto-combustion and co-precipitation methods in the presence of nitrate or chloride ions and under different atmospheres, followed by annealing of final products at different temperatures were tested. All samples were characterized by powder X-ray diffraction (PXRD) and vibrational spectroscopy in order to evaluate their phase composition, particle size and micro-strain. Selected samples were subjected to investigation by transmission electron microscopy (TEM). The degree of the particle crystallinity was estimated by relating the apparent crystallite size obtained from the PXRD analysis to the physical grain size observed by the TEM. Optimal conditions leading to single-phase and highly-crystalline chromite nanoparticles are proposed

  7. Microbial leaching of chromite overburden from Sukinda mines, Orissa, India using Aspergillus niger

    Science.gov (United States)

    Biswas, Supratim; Samanta, Saikat; Dey, Rajib; Mukherjee, Siddhartha; Banerjee, Pataki C.

    2013-08-01

    Leaching of nickel and cobalt from two physical grades (S1, 125-190 μm, coarser and S3, 53-75 μm, finer) of chromite overburden was achieved by treating the overburden (2% pulp density) with 21-d culture filtrate of an Aspergillus niger strain grown in sucrose medium. Metal dissolution increases with ore roasting at 600°C and decreasing particle size due to the alteration of microstructural properties involving the conversion of goethite to hematite and the increase in surface area and porosity as evident from X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (DT-TGA), and field emission scanning electron microscopy (FESEM). About 65% Ni and 59% Co were recovered from the roasted S3 ore employing bioleaching against 26.87% Ni and 31.3% Co using an equivalent amount of synthetic oxalic acid under identical conditions. The results suggest that other fungal metabolites in the culture filtrate played a positive role in the bioleaching process, making it an efficient green approach in Ni and Co recovery from lateritic chromite overburden.

  8. Preparation and Charge Density in (Co, Fe)-Doped La-Ca-Based Chromite

    Science.gov (United States)

    Saravanan, R.; Thenmozhi, N.; Fu, Yen-Pei

    2016-08-01

    Transition metal-doped lanthanum chromites (La0.8Ca0.2)(Cr0.9- x Co0.1Fe x )O3 ( x = 0.03, 0.06, 0.09, 0.12) have been synthesized by solid state reaction method. The synthesized samples were characterized for their structural properties using powder x-ray diffraction analysis, which shows that the grown samples are orthorhombic in structure with single phase. The nature of bonding and the charge distribution of the grown samples have been analyzed by maximum entropy method. Further, the samples were characterized for their optical and magnetic properties using ultraviolet-visible spectra and vibrating sample magnetometry. The microstructural studies were carried by scanning electron microscopy/electron dispersive x-ray spectroscopy techniques. From the optical absorption spectra, it was found that the energy band gap of the samples ranges from 2.135 eV to 2.405 eV. From vibrating sample magnetometer measurements, ferromagnetic like behaviour with large coercive field was observed for Fe doping concentration of x = 0.12. Since the doped lanthanum chromites have good mechanical properties and electrical conductivity at high temperature, these materials are used in solid oxide fuel cells.

  9. High performance ceramic interconnect material for solid oxide fuel cells (SOFCs): Ca- and transition metal-doped yttrium chromite

    Science.gov (United States)

    Yoon, Kyung Joong; Stevenson, Jeffrey W.; Marina, Olga A.

    2011-10-01

    The effect of transition metal substitution on thermal and electrical properties of Ca-doped yttrium chromite was investigated in relation to use as a ceramic interconnect in high temperature solid oxide fuel cells (SOFCs). 10 at.% Co, 4 at.% Ni, and 1 at.% Cu substitution on B-site of 20 at.% Ca-doped yttrium chromite led to a close match of thermal expansion coefficient (TEC) with that of 8 mol% yttria-stabilized zirconia (YSZ), and a single phase Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 remained stable between 25 and 1100 °C over a wide oxygen partial pressure range. Doping with Cu significantly facilitated densification of yttrium chromite. Ni dopant improved both electrical conductivity and dimensional stability in reducing environments, likely through diminishing the oxygen vacancy formation. Substitution with Co substantially enhanced electrical conductivity in oxidizing atmosphere, which was attributed to an increase in charge carrier density and hopping mobility. Electrical conductivity of Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 at 900 °C is 57 S cm-1 in air and 11 S cm-1 in fuel (pO2 = 5 × 10-17 atm) environments. Chemical compatibility of doped yttrium chromite with other cell components was verified at the processing temperatures. Based on the chemical and dimensional stability, sinterability, and thermal and electrical properties, Y0.8Ca0.2Cr0.85Co0.1Ni0.04Cu0.01O3 is suggested as a promising SOFC ceramic interconnect to potentially overcome technical limitations of conventional acceptor-doped lanthanum chromites.

  10. A crystal-chemical investigation of phases of relevance to lime-chromite roast reactions

    International Nuclear Information System (INIS)

    The aim of this investigation was to elucidate the crystal chemistry of phases in the CaO-chromium oxide-Si-O2 system, by single crystal x-ray diffractometry. The crystal chemistry of calcium and chromium-containing phases, with chromium valencies higher than trivalent, which occur in the chromite-lime roast process has been investigated. The phases include the monocalcium, tricalcium and pentacalcium ortho-chromates and the fluor and oxy-chromium apatites. The crystal structures of Ca5Cr3O12 and Ca5Cr1.8Si1.2O12, the chromium analogues of silico-carnotite, Ca5P2SiO12, have been determined. An alternative model for the structure of Ca3(CrO4)2 has been investigated in which some of the (CrO4) tetrahedra are positionally disordered. It is proposed that the structure determined may represent an average of two different structure types and the transformation from the one polymorph to the other involves the alternate flipping of the disordered tetrahedra. The disordered model implies an alternative stoichiometry Ca10(CrO4)7 in which 6/7 of the chromium is pentavalent and 1/7 is hexavalent. The phase chemistry of mixtures of lime and chromite has been examined at temperatures above 850 0C in air. Ca5Cr3O12' Ca5(CrO4)F and Ca3(CrO4)2 are produced as relatively pure phases. Optimum chromite: lime addition is in the order 1:1, such that the product phases include Ca5Cr3O12, Ca4Fe+32Al2O10 and MgO. Reaction kinetics are however unfavourable. By replacing 7% CaO with CaF2, the kinetics are improved. The product phases are fluor-chromium apatite Ca5Cr3O10F, Ca4Fe+32Al2O12 and MgO. The apatite, like Ca5Cr3O12, may be preferentially leached with dilute acid

  11. High temperature dissolution of ferrites, chromites and bonaccordite in chelating media

    International Nuclear Information System (INIS)

    Different methods have been employed world wide for the decontamination of reactor coolant system surfaces. The success of a decontamination process mainly depends on the oxide dissolution efficiency of the decontamination formulation. Among the oxides, Fe3O4 undergoes easy dissolution in organic acid media at normal temperatures. However, dissolution of chromites and mixed ferrites is not that easy in organic chelant media at normal temperatures even in the presence of redox reagents. Hence, a high temperature process was attempted for the dissolution of ferrites and chromites. A re-circulation system consisting of an autoclave, pump, heat exchanger etc. all lined with teflon was used for carrying out high temperature dissolution experiments. This study describes the high temperature dissolution kinetics of Fe3O4, NiFe2O4, and Cr2O3. Nitrilotriacetic acid (NTA), a well known solvent for metal oxides, was applied at temperatures ranging from 80 to 180oC. About six fold increase in dissolution rate was observed for Fe3O4 in this temperature range. Effect of N2H4 on oxide dissolution was studied. Lower dissolution rates were observed for Fe3O4 and NiFe2O4 in the presence of hydrazine. Oxide dissolution efficiency of other chelating agents like EDTA, PDCA etc. and the effect of reducing agents like oxalic acid and ascorbic acid on high temperature dissolution also has been studied. The effect of incorporation of boron and zinc in the iron and chromium oxides has also been studied. Bonaccordite (Ni2FeBO5) has been observed in the fuel deposits of pressurized Water Reactors especially in the AOA affected plants. Zinc ferrite/chromite are formed in reactors adopting zinc injection passivation technique to control radiation field. Bonaccordite and zinc ferrite/chromite formed over the reactor coolant system structural materials are also difficult to dissolve by the reagents used in chemical decontamination processes. Sample of bonaccordite was prepared by solid state

  12. Hydrothermal synthesis of perovskite strontium doped lanthanum chromite fine powders and its sintering

    Energy Technology Data Exchange (ETDEWEB)

    Rendon-Angeles, J.C., E-mail: jcarlos.rendon@cinvestav.edu.m [Research Institute for Advanced Studies of the NPI, Campus-Saltillo, Ramos Arizpe 25900, Coah. (Mexico); Research Laboratory of Hydrothermal Chemistry, Kochi University, Kochi 780-8520 (Japan); Yanagisawa, K. [Research Laboratory of Hydrothermal Chemistry, Kochi University, Kochi 780-8520 (Japan); Matamoros-Veloza, Z. [Saltillo Institute of Technology, Dep. Metal-Mecanica, Saltillo 25820, Coah. (Mexico); Pech-Canul, M.I.; Mendez-Nonell, J. [Research Institute for Advanced Studies of the NPI, Campus-Saltillo, Ramos Arizpe 25900, Coah. (Mexico); Torre, S. Diaz-de la [Research Institute for Technology Innovation, CIITEC-IPN, Azcapotzalco 02250 (Mexico)

    2010-08-13

    Sr doped lanthanum chromite powders with two different compositions, La{sub 0.9}Sr{sub 0.1}CrO{sub 3} and La{sub 0.8}Sr{sub 0.2}CrO{sub 3}, were prepared from precursor lanthanum chromite gels obtained by the coprecipitation method, followed by hydrothermal treatments at temperatures from 400 to 450 {sup o}C, for various reaction times varying from 0.5 to 2 h. The reaction products were characterized by XRD, SEM and TEM techniques. The powder was cold isostatically pressed at 200 MPa, and then sintered in air at 1500 {sup o}C for several intervals (1-20 h). Relative density measurements were conducted by helium pycnometry and the microstructure was revealed by SEM after thermal etching. The X-ray diffraction patterns of the powders corresponding to La{sub 0.9}Sr{sub 0.1}CrO{sub 3} and La{sub 0.8}Sr{sub 0.2}CrO{sub 3} nominal compositions obtained at 400 and 425 {sup o}C for 1 h, respectively, were indexed with that of the orthorhombic single LaCrO{sub 3} phase. SEM and TEM micrographs showed that the particles had irregular peanut-like morphology, and the average particle size was 300 nm. Furthermore, the maximum relative density of the La{sub 0.8}Sr{sub 0.2}CrO{sub 3} sample obtained by the heat treatment in air at 1500 {sup o}C for 20 h was 97% of the theoretical density and the average grain size of the sintered pellet was of 5 {mu}m. The electric conductivity and activation energy determined for this pellet were 14477.3 S m{sup -1} and 0.13 eV, respectively.

  13. Fabrication of Sr- and Co-doped lanthanum chromite interconnectors for SOFC

    Energy Technology Data Exchange (ETDEWEB)

    Setz, L.F.G. [Departamento de Engenharia de Materiais, Universidade Federal de Sao Carlos - DEMa/UFSCar (Brazil); Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN (Brazil); Santacruz, I. [Departamento de Quimica Inorganica, Cristalografia y Mineralogia, Universidad de Malaga, 29071 Malaga (Spain); Colomer, M.T., E-mail: tcolomer@icv.csic.es [Instituto de Ceramica y Vidrio, ICV (CSIC), 28049 Madrid (Spain); Mello-Castanho, S.R.H. [Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN (Brazil); Moreno, R. [Instituto de Ceramica y Vidrio, ICV (CSIC), 28049 Madrid (Spain)

    2011-07-15

    Graphical abstract: FESEM micrographs of the fresh fracture surfaces for the La{sub 0.80}Sr{sub 0.20}Cr{sub 0.92}Co{sub 0.08}O{sub 3} sintered specimens cast from optimised suspensions with 13.5, 15 and 17.5 vol.% solids loading. Aqueous suspensions were prepared using ammonium polyacrylate (PAA) as dispersant and tetramethylammonium hydroxide (TMAH) to assure a basic pH and providing stabilization. Sintering of the green discs was performed in air at 1600 {sup o}C for 4 h. Highlights: {yields} Optimum casting slips were achieved with 3 wt.% of ammonium polyacrylate and 1 wt.% of tetramethylammonium hydroxide. -- Abstract: Many studies have been performed dealing with the processing conditions of electrodes and electrolytes in solid oxide fuel cells (SOFCs). However, the processing of the interconnector material has received less attention. Lanthanum chromite (LaCrO{sub 3}) is probably the most studied material as SOFCs interconnector. This paper deals with the rheology and casting behaviour of lanthanum chromite based materials to produce interconnectors for SOFCs. A powder with the composition La{sub 0.80}Sr{sub 0.20}Cr{sub 0.92}Co{sub 0.08}O{sub 3} was obtained by combustion synthesis. Aqueous suspensions were prepared to solids loading ranging from 8 to 17.5 vol.%, using ammonium polyacrylate (PAA) as dispersant and tetramethylammonium hydroxide (TMAH) to assure a basic pH and providing stabilization. The influence of the additives concentrations and suspension ball milling time were studied. Suspensions prepared with 24 h ball milling, with 3 wt.% and 1 wt.% of PAA and TMAH, respectively, yielded the best conditions for successful slip casting. Sintering of the green discs was performed in air at 1600 {sup o}C for 4 h leading to relatively dense materials.

  14. Experimental study on solid state reduction of chromite with rising temperature

    Energy Technology Data Exchange (ETDEWEB)

    Kekkonen, M.; Syynimaa, A.; Holappa, L.

    1998-07-01

    The solid state reduction of preoxidized sintered chromite pellets, raw pellets, process pellets and lumpy ores have been studied with rising temperature 700-1520 deg C under CO-atmosphere in order to better simulate the conditions in the upper part of a real submerged arc furnace. According to the reduction degree curves the reduction behaviour of chromite pellets seems to be similar. The reduction rate was slow at the beginning but increased rapidly when the temperature reached about 1000 deg C. The final reduction degree was highest in the case of process pellets and lowest in the case of raw pellet. In the case of preoxidized pellets there was not much difference of the reduction rate and final reduction degree between different oxidation states. In the case of lumpy ores the reduction rate and the final reduction degree was much lower compared to the pellets. Optical photographs, phase and microanalysis show that the reduction has proceeded further in the surface of the samples and confirmed also that the reduction degree remained lower in the case of raw pellet and lumpy ores which was also seen from the reduction degree curves. According to the experiments in the case of preoxidized pellets the effect of oxidation state on the reduction rate was not observed due to small difference in the oxidation state of the samples. But when comparing the reduction of preoxidized pellets and unoxidised raw pellet we can say that preoxidation promotes the reduction. The final reduction degree of the raw pellet remained lower than in the case of preoxidized pellets. (orig.)

  15. The chromite deposits associated with ophiolite complexes, Southeastern Desert, Egypt: Petrological and geochemical characteristics and mineralization

    Institute of Scientific and Technical Information of China (English)

    Gehad M.Saleh

    2006-01-01

    The podiform chromitites occur in a well-preserved mantle sequence consisting of lherzolite-harzburgite with abundant lenses of olivine dunite. The podiform chromitite deposits are common as small and irregularly shaped masses in the Southeastern Desert (SED) of Egypt. The podiform chromitites exhibit a wide range of compositions from high Cr to high Al varieties. The Cr of chrome spinel ranges from 0.67 to 0.88 in olivine-dunite, quite similar to that of the high-Cr chromitite, whereas it is around 0.62 in lherzolite-harzburgite. Primary hydrous mineral inclusions, amphibole and phlogopite, in chrome spinel have been reported for the first time from the Pan-African Proterozoic podiform chromitites. On the other hand, petrographic and geochemical evidence suggests that podiform chromitites in the SED of Egypt were formed as a result of crystallization of mafic melts, probably of boninitic composition, the boninitic parental magmas were probably produced by a second stage of melting above a subduction zone. Three types of chromite ores can be distinguished within the SED of Egypt: (a) sulphide-poor podiform ores; (b) brecciated ores; and (c) sulphide-rich ores. Two textural types of inclusions in chromite are distinguished: (1) primary silicate inclusions generally have high Mg-number (>96), Cr and Ni, and are dominated by pargasitic amphibole, forsterite, diopside, enstatite and Na-phlogopite. A diversity of primary and secondary platinum group minerals (PGM) is described from the chromitites, including alloys, sulphides, sulpharsenides and arsenides of Ru, Os, Ir, Rh, Ni, Cu, Fe and Co; (2) in addition to primary PGM and hydrous silicates, the fluids are of low to moderate salinity, sodium-dominated aqueous solutions with complex gas contents. Variable amounts of water, hydrogen, hydrocarbons, carbon dioxides and nitrogen have been determined in inclusion-rich samples. The chondrite-normalized PGE patterns of lherzolite-harzburgite and olivine-dunite have

  16. A comparison of selected Precambrian Brazilian chromitites: Chromite, PGE-PGM, and Re/Os as parental source indicators

    Science.gov (United States)

    Girardi, V. A. V.; Ferrario, A.; Correia, C. T.; Diella, V.

    2006-03-01

    Mineralogical and geochemical studies were carried out in chromitites belonging to the mafic-ultramafic bodies of Niquelândia, Luanga, and Campo Formoso, which are, respectively, included in the Goiás Massif and the Amazon and São Francisco cratons. The main platinum-group minerals (PGM) included or associated with chromite grains are laurite in Niquelândia and Campo Formoso and sperrylite and braggite in Luanga. The most common primary base metal sulfides (BMS) are pentlandite, chalcopyrite, and minor pyrrhotite. Also present are base metal alloys (BMA), such as awaruite, and the BMS millerite, pyrite, and copper as secondary mineral phases linked to later alteration process. The Luanga chromites display the lowest Cr 2O 3/Al 2O 3 and Cr 2O 3/FeO t ratios. The chondrite-normalized profiles are strongly enriched in the platinum PGE subgroup (PPGE, Pt, Pd, Rh). The average Pd/Ir ratio (24.2) and 187Os/ 188Os values (0.17869-0.18584) are very high. Niquelândia chromites have higher Cr 2O 3/Al 2O 3 and Cr 2O 3/FeO t ratios than Luanga. Its PGE contents are low and chondrite-normalized profiles depleted, mainly in the PPGE subgroup. The average Pd/Ir ratio (0.45) and 187Os/ 188Os values (0.12598-0.12777) are low. Campo Formoso chromites have the highest Cr 2O 3/Al 2O 3 and Cr 2O 3/FeO t ratios; its average Pd/Ir ratio (0.72) and chondrite-normalized profiles (except the pronounced Ru spike) are closer to those of Niquelândia. The remarkable differences in terms of chromite bulk-composition, PGE contents and patterns, Pd/Ir ratios, and 187Os/ 188Os values associated with probable distinctions in the inferred geochemical compositions of the respective parental magmas indicate that the Luanga and Niquelândia complexes originated from distinct parental sources. Geochemical and isotopic features indicate that Luanga chromitites and associated rocks are consistent with a parental magma, either originated from an enriched mantle reservoir or strongly contaminated

  17. Application of the Rietveld method to assess chromium(VI) speciation in chromite ore processing residue.

    Science.gov (United States)

    Chrysochoou, Maria; Dermatas, Dimitris

    2007-03-15

    The Rietveld method allows the quantification of crystalline phases and amorphous material identified by X-ray powder diffraction (XRPD) and other diffraction methods. The method assists in determining the speciation of contaminants in solid matrices both qualitatively and quantitatively in a statistically defensible approach, as it does not focus on a microscale. Rietveld was applied to chromite ore processing residue (COPR), a cementitious waste containing hexavalent chromium. Calcium aluminum chromium oxide hydrates (CACs) were the crystalline phases identified by XRPD that bind Cr(6+) in COPR according to their chemical formula. Rietveld quantification, combined with mass balances on Cr(6+), showed that CACs may bind Cr(6+) in variable percentages, ranging from 25% to 85%. Analysis of duplicate samples showed that material variability is the predominant factor of uncertainty in evaluating the role of CACs in Cr(6+) speciation, provided that a consistent quantification strategy is pursued. The choice of strategy was performed on the basis of the pertinent literature, preliminary analyses of the equipment and the software settings, and mass balances. The correlation between the average CAC-bound Cr(6+) concentration and the total Cr(6+) for five samples (R(2)=0.94), extracted from different zones and soil borings, suggests that CACs are a primary sink for Cr(6+) in COPR. PMID:16842911

  18. Hexavalent chromium reduction by aerobic heterotrophic bacteria indigenous to chromite mine overburden

    Directory of Open Access Journals (Sweden)

    Dey Satarupa

    2013-01-01

    Full Text Available Microbiological analysis of overburden samples collected from chromite mining areas of Orissa, India revealed that they are rich in microbial density as well as diversity and dominated by Gramnegative (58% bacteria. The phenotypically distinguishable bacterial isolates (130 showed wide degree of tolerance to chromium (2-8 mM when tested in peptone yeast extract glucose agar medium. Isolates (92 tolerating 2 mM chromium exhibited different degrees of Cr+6 reducing activity in chemically defined Vogel Bonner (VB broth and complex KSC medium. Three potent isolates, two belonging to Arthrobacter spp. and one to Pseudomonas sp. were able to reduce more than 50 and 80% of 2 mM chromium in defined and complex media respectively. Along with Cr+6 (MIC 8.6-17.8 mM, the isolates showed tolerance to Ni+2, Fe+3, Cu+2 and Co+2 but were extremely sensitive to Hg+2 followed by Cd+2, Mn+2 and Zn+2. In addition, they were resistant to antibiotics like penicillin, methicillin, ampicillin, neomycin and polymyxin B. During growth under shake-flask conditions, Arthrobacter SUK 1201 and SUK 1205 showed 100% reduction of 2 mM Cr+6 in KSC medium with simultaneous formation of insoluble precipitates of chromium salts. Both the isolates were also equally capable of completely reducing the Cr+6 present in mine seepage when grown in mine seepage supplemented with VB concentrate.

  19. Microstructural analyses of Cr(VI) speciation in chromite ore processing Residue (COPR)

    Energy Technology Data Exchange (ETDEWEB)

    CHRYSOCHOOU, MARIA; FAKRA, SIRINE C .; Marcus, Matthew A.; Moon, Deok Hyun; Dermatas, Dimitris

    2010-03-01

    The speciation and distribution of Cr(VI) in the solid phase was investigated for two types of chromite ore processing residue (COPR) found at two deposition sites in the United States: gray-black (GB) granular and hard brown (HB) cemented COPR. COPR chemistry and mineralogy were investigated using micro-X-ray absorption spectroscopy and micro-X-ray diffraction, complemented by laboratory analyses. GB COPR contained 30percent of its total Cr(VI) (6000 mg/kg) as large crystals(>20 ?m diameter) of a previously unreported Na-rich analog of calcium aluminum chromate hydrates. These Cr(VI)-rich phases are thought to be vulnerable to reductive and pH treatments. More than 50percent of the Cr(VI) was located within nodules, not easily accessible to dissolved reductants, and bound to Fe-rich hydrogarnet, hydrotalcite, and possibly brucite. These phases are stable over a large pH range, thus harder to dissolve. Brownmilleritewasalso likely associated with physical entrapment of Cr(VI) in the interior of nodules. HB COPR contained no Cr(VI)-rich phases; all Cr(VI) was diffuse within the nodules and absent from the cementing matrix, with hydrogarnet and hydrotalcite being the main Cr(VI) binding phases. Treatment ofHBCOPRis challenging in terms of dissolving the acidity-resistant, inaccessible Cr(VI) compounds; the same applies to ~;;50percent of Cr(VI) in GB COPR.

  20. Infiltrated lanthanum strontium chromite anodes for solid oxide fuel cells: Structural and catalytic aspects

    Science.gov (United States)

    Oh, Tae-Sik; Yu, Anthony S.; Adijanto, Lawrence; Gorte, Raymond J.; Vohs, John M.

    2014-09-01

    Infiltration is a widely used fabrication method for solid oxide fuel cell (SOFC) composite electrodes. Here we report a study of the structure and electrocatalytic properties of SOFC anodes composed of a layer of lanthanum, strontium chromite (La0.8Sr0.2CrO3, LSCr), both with and without added transition metal dopants, infiltrated into a porous yttria-stabilized zirconia (YSZ) matrix. The structural evolution of the electrode upon reduction and under typical SOFC operating conditions is compared to that reported previously for La0.8Sr0.2Cr0.5Mn0.5O3-YSZ composite anodes. For the transition metal doped materials, a portion of the metal dopants were found to be exsolved from the LSCr lattice upon reduction and to be effective in promoting electro-oxidation of hydrogen. Exsolved cobalt particles were also found to be relatively stable when exposed to hydrocarbon fuels with low activity for the formation of carbon deposits.

  1. Structural, Optical, and Magnetic Characterization of Spinel Zinc Chromite Nanocrystallines Synthesised by Thermal Treatment Method

    Directory of Open Access Journals (Sweden)

    Salahudeen A. Gene

    2014-01-01

    Full Text Available The present study reports the structural and magnetic characterization of spinel zinc chromite (ZnCr2O4 nanocrystallines synthesized by thermal treatment method. The samples were calcined at different temperatures in the range of 773 to 973 K. Polyvinylpyrrolidone was used to control the agglomeration of the nanoparticles. The average particle size of the synthesized nanocrystals was determined by powder X-ray diffraction which shows that the crystallite size increases from 19 nm at 773 K to 24 nm at 973 K and the result was in good agreement with the transmission electron microscopy images. The elemental composition of the samples was determined by energy dispersed X-ray spectroscopy which confirmed the presence of Zn, Cr, and O in the final products. Fourier transform infrared spectroscopy also confirmed the presence of metal oxide bands for all the samples calcined at different temperature. The band gap energy was calculated from UV-vis reflectance spectra using the Kubelka-Munk function and the band gap energy of the samples was found to decrease from 4.03 eV at 773 K to 3.89 eV at 973 K. The magnetic properties were also demonstrated by electron spin resonance spectroscopy, the presence of unpaired electrons was confirmed, and the resonant magnetic field and the g-factor of the calcined samples were also studied.

  2. Comparison of the Oxidation Behaviors of High FeO Chromite and Magnetite Concentrates Relevant to the Induration of Ferrous Pellets

    Science.gov (United States)

    Zhu, Deqing; Yang, Congcong; Pan, Jian; Li, Xiaobo

    2016-10-01

    Oxidation process plays an important role in producing sufficiently strong ferrous pellets for blast furnace, and the oxidation behavior of pellet feed greatly affects the quality of pellets. As a supplementary research to earlier published work, the present study fixes its particular attention on the fundamental oxidation behavior of a high FeO South African chromite concentrate in comparison to that of typical magnetite concentrate using differential scanning calorimetry, X-ray diffraction analysis, and thermogravimetry at various temperatures ranging from 473 K to 1273 K (200 °C to 1000 °C). The reaction mechanism and phase transformation during the oxidation process of chromite spinel is further explained by thermodynamics calculation performed by FactSage software. Besides, routine laboratory preheating-roasting test of single ore pellets is also conducted to reveal the relevance of oxidizability to the consolidation of pellets. The results show that the chromite spinel possesses much poorer oxidizability than magnetite, usually accompanying complex phase transformations via a preferential nucleation of Fe-rich sesquioxide from the chromite spinel matrix at low temperatures and thereafter the formation of Cr-rich sesquioxide on the substrate of Fe-rich phase at high temperatures. The oxidation of chromite spinel is inferior to that of magnetite from the viewpoint of thermodynamics and dynamic kinetics. Good inherent oxidizability of raw materials is found to have a positive effect on the induration process of pellet.

  3. Comparison of the Oxidation Behaviors of High FeO Chromite and Magnetite Concentrates Relevant to the Induration of Ferrous Pellets

    Science.gov (United States)

    Zhu, Deqing; Yang, Congcong; Pan, Jian; Li, Xiaobo

    2016-08-01

    Oxidation process plays an important role in producing sufficiently strong ferrous pellets for blast furnace, and the oxidation behavior of pellet feed greatly affects the quality of pellets. As a supplementary research to earlier published work, the present study fixes its particular attention on the fundamental oxidation behavior of a high FeO South African chromite concentrate in comparison to that of typical magnetite concentrate using differential scanning calorimetry, X-ray diffraction analysis, and thermogravimetry at various temperatures ranging from 473 K to 1273 K (200 °C to 1000 °C). The reaction mechanism and phase transformation during the oxidation process of chromite spinel is further explained by thermodynamics calculation performed by FactSage software. Besides, routine laboratory preheating-roasting test of single ore pellets is also conducted to reveal the relevance of oxidizability to the consolidation of pellets. The results show that the chromite spinel possesses much poorer oxidizability than magnetite, usually accompanying complex phase transformations via a preferential nucleation of Fe-rich sesquioxide from the chromite spinel matrix at low temperatures and thereafter the formation of Cr-rich sesquioxide on the substrate of Fe-rich phase at high temperatures. The oxidation of chromite spinel is inferior to that of magnetite from the viewpoint of thermodynamics and dynamic kinetics. Good inherent oxidizability of raw materials is found to have a positive effect on the induration process of pellet.

  4. Rapid synthesis of nanocrystalline magnesium chromite and ferrite ceramics with concentrated sunlight

    Energy Technology Data Exchange (ETDEWEB)

    Michalsky, Ronald, E-mail: michalskyr@ethz.ch; Peterson, Brian A.; Pfromm, Peter H.

    2014-04-01

    Highlights: • Refractory ceramics are produced via rapid solar-thermal processing. • The formed chromite and ferrite spinels have a high specific surface area. • The presence of transition metal oxides enables reduction of Mg cations. • Dinitrogen is reduced only by chromium. • The spinels are stable in reducing environments and in the presence of solar radiation. - Abstract: High-temperature refractory ceramics and catalysts such as MgM{sub 2}O{sub 4} (M = Cr, Fe) are produced conventionally via energy-intensive solid-state syntheses (using 0.44–10 GJ electricity for sintering per ton oxide, equivalent to combustion of 48–1088 kg coal per ton oxide). This article reports rapid production of 17 ± 2 mol% MgFe{sub 2}O{sub 4} and 8.6 ± 0.9 mol% MgCr{sub 2}O{sub 4} after 30 min at 1200 °C employing 0.82 kW m{sup −2} sunlight concentrated at a geometric ratio of about 900 m{sup 2} m{sup −2} using a Fresnel lens. Solar radiation promotes the diffusion-limited ferrite formation (42 ± 5 μmol MgFe{sub 2}O{sub 4} per mol Fe{sub 2}O{sub 3} s{sup −1} vs. 26 ± 3 μmol mol{sup −1} s{sup −1} in absence of sunlight) while the transition metals promote the reduction of Mg{sup 2+}. The nanocrystalline and macroporous spinel has a specific surface area of 9.7–11.9 m{sup 2} g{sup −1} (in the order of sol–gel synthesis methods) and is stable under extreme conditions, i.e., high temperature, solar radiation, and reducing agents.

  5. Heavy metal and nutrient concentration in soil and plants growing on a metalliferous chromite minespoil.

    Science.gov (United States)

    Samantaray, S; Rout, G R; Das, P

    2001-10-01

    Metal contamination in soil and plant samples from a chromite mine and its adjoining regions was determined. The metal concentration varied in stem, leaf and root of different tree species. In the case of shrubs, the highest concentration of iron (18.5 mg kg(-1) was detected in the stem of Combretum roxburghii. The concentration of aluminium varied from 1.8 - 5.3 mg kg(-1) dry weight, whereas the nickel content was found to be the highest in the stem of Calotropis gigantea. In the case of herbs, chromium concentration was highest (60.9 mg kg(-1) dry weight) in Evovulus alsenoides and the lowest (18.8 mg kg(-1) dry weight) in Andrographis paniculata. There was a significant correlation observed between chromium in soil with the root of tree species like Lagerstroemia parviflora, Madhuca longifolia, Anogeissus latifolia and Haldina cordyfolia. Nickel in soil was significantly correlated with the stem and leaf of all the tree species except Chlroxylon sweitenta. Iron in soil showed correlation with the stem and leaf of Chloroxylon sweitenia. Among the shrubs (Calotropis gigantea, Combretum roxburghii and Smilax zeylancia), chromium in soil showed a correlation with the root. Nickel in soil was positively correlated with the stem and leaf of Calotropis gigantea and Combretum roxburghii. Among the herbs, chromium in the whole plant of Evolvulus alsenoids, Solanum surattense and Phyllanthus fraternus showed significant positive correlation with soil; nickel in Solanum surattense showed significant positive correlation with soil. The positive correlation coefficient was observed between iron in the whole plant and soil on Phyllanthus virgatus, Phyllanthus fraternus and Andrographis paniculata. The above information would be useful for the establishment of a vegetation cover on the minewaste heaps. PMID:11766037

  6. Heavy metal and nutrient concentration in soil and plants growing on a metalliferous chromite minespoil.

    Science.gov (United States)

    Samantaray, S; Rout, G R; Das, P

    2001-10-01

    Metal contamination in soil and plant samples from a chromite mine and its adjoining regions was determined. The metal concentration varied in stem, leaf and root of different tree species. In the case of shrubs, the highest concentration of iron (18.5 mg kg(-1) was detected in the stem of Combretum roxburghii. The concentration of aluminium varied from 1.8 - 5.3 mg kg(-1) dry weight, whereas the nickel content was found to be the highest in the stem of Calotropis gigantea. In the case of herbs, chromium concentration was highest (60.9 mg kg(-1) dry weight) in Evovulus alsenoides and the lowest (18.8 mg kg(-1) dry weight) in Andrographis paniculata. There was a significant correlation observed between chromium in soil with the root of tree species like Lagerstroemia parviflora, Madhuca longifolia, Anogeissus latifolia and Haldina cordyfolia. Nickel in soil was significantly correlated with the stem and leaf of all the tree species except Chlroxylon sweitenta. Iron in soil showed correlation with the stem and leaf of Chloroxylon sweitenia. Among the shrubs (Calotropis gigantea, Combretum roxburghii and Smilax zeylancia), chromium in soil showed a correlation with the root. Nickel in soil was positively correlated with the stem and leaf of Calotropis gigantea and Combretum roxburghii. Among the herbs, chromium in the whole plant of Evolvulus alsenoids, Solanum surattense and Phyllanthus fraternus showed significant positive correlation with soil; nickel in Solanum surattense showed significant positive correlation with soil. The positive correlation coefficient was observed between iron in the whole plant and soil on Phyllanthus virgatus, Phyllanthus fraternus and Andrographis paniculata. The above information would be useful for the establishment of a vegetation cover on the minewaste heaps.

  7. Health risk assessment from contaminated foodstuffs: a field study in chromite mining-affected areas northern Pakistan.

    Science.gov (United States)

    Nawab, Javed; Li, Gang; Khan, Sardar; Sher, Hassan; Aamir, Muhammad; Shamshad, Isha; Khan, Anwarzeb; Khan, Muhammad Amjad

    2016-06-01

    This study aimed to investigate the potential health risk associated with toxic metals in contaminated foodstuffs (fruits, vegetables, and cereals) collected from various agriculture fields present in chromite mining-affected areas of mafic and ultramafic terrains (northern Pakistan). The concentrations of Cr, Ni, Zn, Cd, and Pb were quantified in both soil and food samples. The soil samples were highly contaminated with Cr (320 mg/kg), Ni (108 mg/kg), and Cd (2.55 mg/kg), which exceeded their respective safe limits set by FAO/WHO. Heavy metal concentrations in soil were found in the order of Cr>Ni>Pb>Zn>Cd and showed significantly (p risk assessment revealed no potential risk for both adults and children for the majority of heavy metals, except Cd, which showed health risk index (HRI) >1 for children and can pose potential health threats for local inhabitants. Graphical Abstract Heavy metals released from chromite mining lead to soil and foodstuff contamination and human health risk.

  8. Garnet and chromite- bearing mantle peridotite xenoliths from Komsomolskaya pipe, Alakit field, Yakutia

    Science.gov (United States)

    Ashchepkov, Igor; Logvinova, Alla; Valdykin, Nikolai; Makovchuk, Igor; Karpenko, Mikhail; Spetsius, Zdislav; Khmelnikova, Olga; Palessky, Stanislav

    2014-05-01

    Fresh xenoliths in Alakit field in Siberian platform are rare. In the xenoliths from Komsomolskaya pipe there were found 30 xenoliths with fresh Cpx, Gar as well as chromites, phlogopites and ilmenites which allows to construct the Cpx - based geotherm which was before constructed for the Yubileynaya pipe (Ashchepkov et al., 2004). The comparison of the garnets from the breccias and porphyric kimberlites show more depleted and Cr- rich varieties of garnets as it is common for the other pipes. Only relatively fresh material from the dark - grey breccia good relatively fresh xenoliths could be used for the mineral thermobarometry. Large xenolths from the Komsomolskaya pipe belong mainly to the Gar harzburgite or refertilized lherzolite types as also detected on the Cr2O3 - CaO diagram where they belong mainly to the 5-11% Cr2O3 interval. The low Cr varieties are mainly referring to the Fe- enriched pyroxenites or to Phl metasomatites. In SCLM beneath Komsomolskaya pipe is essentially more heated then those beneath Yubileynaya and Sytykanskaya pipes and in lower part they are close to the PTXFO2 are closer in conditrions to the ilmenites which determined the . Peridotites from the lithosphere base (7-6GPa) are enriched in Fe and belong to the porphyroclustic or deformed type by chemistry Fe# =0.14-0.15. the relatively HT conditions were determined also for the peridotites from the 5.0-4. GPa. The most of the Cpx- refertilized varieties give the conditions of the middle part of the mantle section. Their garnest are enriched in CaO probably reflection reactions with the Ca- rich protokimberlites. The Na- richterite bearin xenoliths are from the same PT interval The cold clot in the 60-5.5 GPa (34 mwm-2) are represented by the peridotites of low Fe# 7-9 Fe- low peridotites with the garnets of sub-Ca types. But there are also varieties of reduced Cr and the Fe-enriched which are closer to the pyroxenites or Phl metasomatites which in Pt are from the upper part of mantle

  9. Present situation and advances in the study of podiform chromite deposits%豆荚状铬铁矿床的研究现状及进展

    Institute of Scientific and Technical Information of China (English)

    周二斌

    2011-01-01

    The podiform chromite deposit constitutes the main source of metallurgical-grade chromite in industry, but its genesis remains one of the problems for which geologists all over the world show great concern.This paper outlined the status and latest progress in the study of podiform chromite deposits.The latest studies show that podiform deposits mainly occur in a certain layer of the mantle peridotite, which has been the lowest part of ophiolite (CMB, crust-mantle boundary) since Phanerozoic.The podiform chromite deposit-bearing mantle peridotites in the world usually exhibit vertical zoning of melting, with more basic material in the upper part and more acid material in the lower part.With the increasing of partial melting from the bottom upward, there appears lherzolite, harzburgite and dunite in turn.Alpine-type podiform chromite deposits generally have a fairly thick dunitic "envelop".After the mineralization of the podiform chromite deposit, the gravity of itself caused the sinking and dragging of some of the dunite around the ore body downward into the harzburegite fades side under the contact interface with the upside dunite facies, thus forming the typical dunitic "envelop" of the Alpine-type chromite deposit.The authors have thus reached the conclusion that the harzburgite facies under the contact interface is the best target area in search for large chromite deposits.Podiform deposits have a very close genetic relationship with harzburgite and dunite; however, it is really rare to find chromite deposits in lherzolite.The abundance of chromium in primitive mantle is much higher than that in the crust, the chromium element of chromitite was derived from primitive mantle itself, mainly coming from the alteration of associated spinel and the incongruent melting of the two pyroxene (chromium diopside and enstatite).With the increase of partial melting, the mantle peridotite gradually evolved in the magnesium-rich direction, and the mineralization of spinel

  10. Biogenic nano-magnetite and nano-zero valent iron treatment of alkaline Cr(VI) leachate and chromite ore processing residue

    OpenAIRE

    Watts, Mathew P.; Coker, Victoria S.; Parry, Stephen A.; Pattrick, Richard A.D.; Thomas, Russell A.P.; Kalin, Robert; Lloyd, Jonathan R.

    2015-01-01

    Highly reactive nano-scale biogenic magnetite (BnM), synthesized by the Fe(III)-reducing bacterium Geobacter sulfurreducens, was tested for the potential to remediate alkaline Cr(VI) contaminated waters associated with chromite ore processing residue (COPR). The performance of this biomaterial, targeting aqueous Cr(VI) removal, was compared to a synthetic alternative, nano-scale zero valent iron (nZVI). Samples of highly contaminated alkaline groundwater and COPR solid waste were obtained fro...

  11. Sorption of noble gases by solids, with reference to meteorites. II - Chromite and carbon. III - Sulfides, spinels, and other substances; on the origin of planetary gases

    Science.gov (United States)

    Yang, J.; Anders, E.

    1982-01-01

    The trapping of noble gases by chromite and carbon, two putative carriers of primordial noble gases in meteorites, was studied by synthesizing 19 samples in a Ne-Ar-Kr-Xe atmosphere at 440-720 K. Noble gas contents are found to approximately obey Henry's Law, but only slight correlations are found with composition, surface area, or adsorption temperature. Geometric mean distribution coefficients for bulk samples and HCl residues in 10 cu cm STP/g atm are: Xe 100, Kr 15, Ar 3.5, and Ne 0.62. Elemental fractionation data support the suggestion of Lewis et al. (1977) that chromite and carbon in C2 and C3 chondrites were formed by the reaction: Fe, Cr + 4CO yields (Fe, Cr)3O4 + 4C + carbides. In contrast to meteoritic minerals, the synthetic specimens show no isotopic fractionation of noble gases. In a subsequent study, attention is given to the cases of sulfides and spinels, on the way to consideration of the origin of planetary gases. Sulfides showed three distinctive trends relative to chromite or magnetite. The elemental fractionation pattern of Ar, Kr and Xe in meteorites, terrestrial rocks and planets resembles the adsorption patterns on the carbons, spinels, sulfides, and other solids studied. The high release temperature of meteoritic noble gases may be explained by transformation of the physisorbed or chemisorbed gas. The ready loss of meteoritic heavy gases on surficial oxidation is consistent with adsorption, as is the high abundance.

  12. Sorption of noble gases by solids, with reference to meteorites. II - Chromite and carbon. III - Sulfides, spinels, and other substances; on the origin of planetary gases

    Science.gov (United States)

    Yang, J.; Anders, E.

    1982-06-01

    The trapping of noble gases by chromite and carbon, two putative carriers of primordial noble gases in meteorites, was studied by synthesizing 19 samples in a Ne-Ar-Kr-Xe atmosphere at 440-720 K. Noble gas contents are found to approximately obey Henry's Law, but only slight correlations are found with composition, surface area, or adsorption temperature. Geometric mean distribution coefficients for bulk samples and HCl residues in 10 cu cm STP/g atm are: Xe 100, Kr 15, Ar 3.5, and Ne 0.62. Elemental fractionation data support the suggestion of Lewis et al. (1977) that chromite and carbon in C2 and C3 chondrites were formed by the reaction: Fe, Cr + 4CO yields (Fe, Cr)3O4 + 4C + carbides. In contrast to meteoritic minerals, the synthetic specimens show no isotopic fractionation of noble gases. In a subsequent study, attention is given to the cases of sulfides and spinels, on the way to consideration of the origin of planetary gases. Sulfides showed three distinctive trends relative to chromite or magnetite. The elemental fractionation pattern of Ar, Kr and Xe in meteorites, terrestrial rocks and planets resembles the adsorption patterns on the carbons, spinels, sulfides, and other solids studied. The high release temperature of meteoritic noble gases may be explained by transformation of the physisorbed or chemisorbed gas. The ready loss of meteoritic heavy gases on surficial oxidation is consistent with adsorption, as is the high abundance.

  13. Assessment of heavy metal tolerance and hexavalent chromium reducing potential of Corynebacterium paurometabolum SKPD 1204 isolated from chromite mine seepage

    Directory of Open Access Journals (Sweden)

    Satarupa Dey

    2016-07-01

    Full Text Available Corynebacterium paurometabolum SKPD 1204 (MTCC 8730, a heavy metal tolerant and chromate reducing bacterium isolated from chromite mine seepage of Odisha, India has been evaluated for chromate reduction under batch culture. The isolate was found to tolerate metals like Co(II, Cu(II, Ni(II, Mn(II, Zn(II, Fe(III and Hg(II along with Cr(VI and was resistant to different antibiotics as evaluated by disc-diffusion method. The isolate, SKPD 1204 was found to reduce 62.5% of 2 mM Cr(VI in Vogel Bonner broth within 8 days of incubation. Chromate reduction capability of SKPD 1204 decreased with increase in Cr(VI concentration, but increased with increase in cell density and attained its maximum at 1010 cells/mL. Chromate reducing efficiency of SKPD 1204 was promoted in the presence of glycerol and glucose, while the highest reduction was recorded at pH 7.0 and 35 °C. The reduction process was inhibited by divalent cations Zn(II, Cd(II, Cu(II, and Ni(II, but not by Mn(II. Anions like nitrate, phosphate, sulphate and sulphite was found to be inhibitory to the process of Cr(VI reduction. Similarly, sodium fluoride, carbonyl cyanide m-chlorophenylhydrazone, sodium azide and N, N,-Di cyclohexyl carboiimide were inhibitory to chromate reduction, while 2,4-dinitrophenol appeared to be neither promotive nor inhibitory to the process.

  14. Effect of Organic Manures on the Growth of Cymbopogon citratus and Chrysopogon zizanioides for the Phytoremediation of Chromite-Asbestos Mine Waste: A Pot Scale Experiment.

    Science.gov (United States)

    Kumar, Adarsh; Maiti, Subodh Kumar

    2015-01-01

    The abandoned chromite-asbestos mines are located in the Roro hills, West Singhbhum, Jharkhand, India, where mining operation ceased in 1983, and since then these mines are causing environmental pollution. The present study was planned to phytoremediate these metalloid and metal contaminated mine waste by using two aromatic grasses, Cymbopogon citratus and Chrysopogon zizanioides by applying different proportions of amendments (chicken manure, farmyard manure and garden soil). Mine waste has neutral pH, low electrical conductivity and organic carbon with higher concentration of total metals (Cr and Ni) as compared to soil. Application of manures resulted significant improvements of mine waste characteristics and plant growth, reduction in the availability of total extractable toxic metals (Cr, Ni) and increase in Mn, Zn and Cu concentration in the substrate. The maximum growth and biomass production for C. citratus and C. zizanioides were found in T-IV combination comprising of mine waste (90%), chicken manure (2.5%), farmyard manure (2.5%) and garden soil (5%). Addition of T-IV combination also resulted in low Cr and Ni accumulation in roots and reduction in translocation to shoots. Study indicates that C. citratus and C. zizanioides can be used for phytostabilization of abandoned chromite-asbestos mine waste with amendments. PMID:25495934

  15. Evaluation of chromate reductase activity in the cell-free culture filtrate of Arthrobacter sp. SUK 1201 isolated from chromite mine overburden.

    Science.gov (United States)

    Dey, Satarupa; Paul, A K

    2016-08-01

    Arthrobacter sp. SUK 1201, a chromate resistant and reducing bacterium isolated from chromite mine overburden of Sukinda valley, Odisha, India has been evaluated for its hexavalent chromium [Cr(VI)] reduction potential using cell-free culture filtrate as extracellular chromate reductase enzyme. Production of the enzyme was enhanced in presence of Cr(VI) and its reducing efficiency was increased with increasing concentration of Cr(VI). The Michaelis-Menten constant (Km) and the maximum specific velocity (Vmax) of the extracellular Cr(VI) reductase were calculated to be 54.03 μM Cr(VI) and 5.803 U mg(-1) of protein respectively showing high affinity towards Cr(VI). The reducing activity of the enzyme was maximum at pH 6.5-7.5 and at a temperature of 35 °C and was dependent on NADH. The enzyme was tolerant to different metals such as Mn(II), Mg(II) and Fe(III) and was able to reduce Cr(VI) present in chromite mine seepage. These findings suggest that the extracellular chromate reductase of Arthrobacter sp. SUK 1201 has a great promise for use in Cr(VI) detoxification under different environmental conditions, particularly in the mining waste water treatment systems. PMID:27176938

  16. Enhancing the stability of copper chromite catalysts for the selective hydrogenation of furfural with ALD overcoating (II) – Comparison between TiO2 and Al2O3 overcoatings

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hongbo; Canlas, Christian; Kropf, A. Jeremy; Elam, Jeffrey W.; Dumesic, James A; Marshall, Christopher L.

    2015-01-01

    TiO2 atomic layer deposition (ALD) overcoatings were applied to copper chromite catalysts to increase the stability for 2-furfuraldehyde (“furfural”) hydrogenation. After overcoating, about 75% activity was preserved compared to neat copper chromite: much higher activity than an alumina ALD overcoated catalyst with a similar number of ALD cycles. The effects of ALD TiO2 on the active Cu nanoparticles were studied extensively using both in-situ TPR/isothermal-oxidation and in-situ furfural hydrogenation via Cu XAFS. The redox properties of Cu were modified only slightly by the TiO2 ALD overcoat. However, a subtle electronic interaction was observed between the TiO2 ALD layers and the Cu nanoparticles. With calcination at 500 °C the interaction between the TiO2 overcoat and the underlying catalyst is strong enough to inhibit migration and site blocking by chromite, but is sufficiently weaker than the interaction between the Al2O3 overcoat and copper chromite that it does not strongly inhibit the catalytic activity of the copper nanoparticles.

  17. Podiform chromite deposits

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Location and characteristics of 1,124 individual mineral deposits of this type, with grade and tonnage models for chromium as well as several related elements.

  18. LEACHABILITY OF CHROME FROM MAGNESIA-CHROMITE REFRACTORY BRICKS CORRODED BY Cu/CuO- Na2O.2SiO2 SLAGS

    Directory of Open Access Journals (Sweden)

    David Medved

    2015-06-01

    Full Text Available The interactions of magnesia-chromite refractory brick with Cu-Na2O.2SiO2 and CuO-Na2O.2SiO2 melts are studied and the chemical durability of corrosion products in water is evaluated. The corrosion tests confirm intensive infiltration of the slag melts into the tested refractory bricks and formation of Cr(6+ compounds. The molten copper partially oxidizes during corrosion test by air and penetrates into bricks. Interactions among periclase (MgO and chromite (FeCr2O4 grains with the melt Na2O.2SiO2 and copper oxides makes possible to form several compounds (e.g. Cu2MgO3, CuCrO4, CaCrO4, Na2CrO4, MgCrO4. Just the marked yellow spots, which were observed on the corroded brick surface after 30 days of free storage, suggest hydration of the high-temperature corrosion products. The yellow color of spots points out to chromates as Na2CrO4 and MgCrO4, which are well soluble in water. The leaching of corroded bricks in water (batch leaching test of a ratio of S (solid : W (water = 0.1 taking up to 28 days confirmed the Cr, Na, Mg and Ca ions leach-out. The pH value of solution increased up to 9 during leaching mainly as a consequence of elevated Na+ ion concentration. The Cr ion concentration rises in the solution up to 1 mmol.l-1. The observed moderate decrease of Cr ion concentration in the solution with the length of leaching indicates super-saturation of the solution and precipitation of the products.

  19. DETERMINATION OF POTASSIUM FERRATE(VI) BY REDOX TITRATION BASED ON THE OXIDATION OF CHROMITE%亚铬酸盐滴定法测定高铁酸钾

    Institute of Scientific and Technical Information of China (English)

    姜洪泉; 刘红

    2001-01-01

    以亚铬酸盐氧化还原反应为基础建立了高铁酸钾的滴定分析方法.对滴定分析条件进行了优化研究,结果表明,用碱度为11~12M的亚铬酸盐溶液测定高铁时,测定结果稳定,与用亚砷酸盐法测的结果一致.方法简便、快速、准确.与亚砷酸盐法相比,该法特别适合于低浓度的高铁酸钾溶液的定量分析.%A method for the determination of potassium ferrate(VI) based on the oxidation of chromite was introduced in this paper. Investigation to determine the optimum alkalinity of the chromite solution used in the determination of potassium ferrate(VI) showed that consistent results were obtained by using chromite solutions with hydroxyl ion of 11 to 12 mol/L. The method is rapid, simple and accurate. This method, compared with the previously reported arsenite method, is particularly suitable for the analysis of dilute solutions of ferrate(VI) ion.

  20. The enhancement effect of pre-reduction using zero-valent iron on the solidification of chromite ore processing residue by blast furnace slag and calcium hydroxide.

    Science.gov (United States)

    Li, Jinchunzi; Chen, Zhonglin; Shen, Jimin; Wang, Binyuan; Fan, Leitao

    2015-09-01

    A bench scale study was performed to assess the effectiveness of the solidification of chromite ore processing residue (COPR) by blast furnace slag and calcium hydroxide, and investigate the enhancement effect of pre-reduction using zero-valent iron (ZVI) on the solidification treatment. The degree of Cr immobilization was evaluated using the Toxicity Characteristic Leaching Procedure (TCLP) as well as the solid waste-extraction procedure for leaching toxicity-sulfuric acid & nitric acid method (Chinese standard HJ/T299-2007). Strength tests and semi-dynamic leaching tests were implemented to investigate the potential for reusing the final treatment product as a readily available construction material. The experimental results showed that the performance of pre-reduction/solidification (S/S) was superior to that of solidification alone. After pre-reduction, all of the S/S treated COPR samples met the TCLP limit for total Cr (5 mg L(-1)), whereas the samples with a COPR content below 40% met the pollution control limit of bricks and building block products (Chinese standard HJ/T 301-2007) produced with COPR for total Cr (0.3 mg L(-1)). At the same time, all of the S/S treated specimens tested were suitable for utilization at certain levels. PMID:25929874

  1. Comportamento reológico de suspensões aquosas de cromito de lantânio Rheological behaviour of lanthanum chromite aqueous suspension

    Directory of Open Access Journals (Sweden)

    L. F. G. Setz

    2011-06-01

    Full Text Available O cromito de lantânio (LaCrO3 é o material mais estudado para a produção de interconectores para células a combustível de ��xido sólido (SOFC. Devido a complexidade das microestruturas e geometrias das SOFCs, freqüentemente são necessárias, técnicas de processamento coloidal, os quais têm recebido maior atenção nos últimos anos por permitirem a obtenção de partes complexas com microestrutura controlada e reprodutíveis. Nos últimos anos, muito esforço tem sido direcionado ao processamento dos eletrólitos e eletrodos, mas aos componentes como o interconector, pouca atenção tem sido dada. Este artigo apresenta o estudo reológico e de conformação em moldes de gesso do cromito de lantânio para a produção de interconectores para SOFCs. A composição La0,80Sr0,20Cr0,92Co0,08O3, obtida por reação de combustão, foi utilizada. As suspensões aquosas foram preparadas com conteúdo de sólidos variando de 8 a 17,5% vol. utilizando-se, poliacrilato de amônia (PAA como polieletrólito/dispersante e hidróxido de tetrametilamônio (HTMA como provedor de alcalinidade. A influência da concentração dos aditivos e o tempo em moinho de bolas foram estudados. Os resultados indicam que o tempo 24 h de homogeneização em moinho de bolas, com 3% e 1%, em massa, de PAA e HTMA respectivamente, proporcionam as melhores condições para colagem em moldes de gesso, sendo possível obter peças após sinterização com densidades relativas elevadas.Lanthanum chromite (LaCrO3 is the most studied material for SOFC's interconnectors' production. The complexity of microstructures and geometries of SOFC devices often requires the use of colloidal processing techniques, which have received increased attention in the last years for obtaining complex parts with controlled microstructure and high reliability. Much effort has been devoted to the processing of electrodes and electrolytes but the other layers, such as that of interconnecting

  2. Meteorology drives ambient air quality in a valley: a case of Sukinda chromite mine, one among the ten most polluted areas in the world.

    Science.gov (United States)

    Mishra, Soumya Ranjan; Pradhan, Rudra Pratap; Prusty, B Anjan Kumar; Sahu, Sanjat Kumar

    2016-07-01

    The ambient air quality (AAQ) assessment was undertaken in Sukinda Valley, the chromite hub of India. The possible correlations of meteorological variables with different air quality parameters (PM10, PM2.5, SO2, NO2 and CO) were examined. Being the fourth most polluted area in the globe, Sukinda Valley has always been under attention of researchers, for hexavalent chromium contamination of water. The monitoring was carried out from December 2013 through May 2014 at six strategic locations in the residential and commercial areas around the mining cluster of Sukinda Valley considering the guidelines of Central Pollution Control Board (CPCB). In addition, meteorological parameters viz., temperature, relative humidity, wind speed, wind direction and rainfall, were also monitored. The air quality data were subjected to a general linear model (GLM) coupled with one-way analysis of variance (ANOVA) test for testing the significant difference in the concentration of various parameters among seasons and stations. Further, a two-tailed Pearson's correlation test helped in understanding the influence of meteorological parameters on dispersion of pollutants in the area. All the monitored air quality parameters varied significantly among the monitoring stations suggesting (i) the distance of sampling location to the mine site and other allied activities, (ii) landscape features and topography and (iii) meteorological parameters to be the forcing functions. The area was highly polluted with particulate matters, and in most of the cases, the PM level exceeded the National Ambient Air Quality Standards (NAAQS). The meteorological parameters seemed to play a major role in the dispersion of pollutants around the mine clusters. The role of wind direction, wind speed and temperature was apparent in dispersion of the particulate matters from their source of generation to the surrounding residential and commercial areas of the mine. PMID:27289470

  3. Detrital magnetite and chromite in Jack Hills quartzite cobbles: Further evidence for the preservation of primary magnetizations and new insights into sediment provenance

    Science.gov (United States)

    Dare, Matthew S.; Tarduno, John A.; Bono, Richard K.; Cottrell, Rory D.; Beard, James S.; Kodama, Kenneth P.

    2016-10-01

    The magnetization of zircons from sedimentary rocks of the Jack Hills (Yilgarn Craton, Western Australia) provide evidence for a Hadean to Paleoarchean geodynamo, 4.0 to 4.2 billion years old. These magnetizations pass a microconglomerate test, attesting to the fidelity of Jack Hills zircons as recorders of these most ancient magnetic signals. The lack of pervasive remagnetization of the Jack Hills is also documented through a positive conglomerate test conducted on cobble-sized clasts. A key element of the latter test is the preservation of a high unblocking temperature magnetization that can survive peak metamorphic temperatures. Rock magnetic studies suggest the mineral carrier is magnetite. Herein, we investigate the magnetic mineral carriers in cobble samples through scanning electron microscope and microprobe analyses, conduct an inter-laboratory paleomagnetic study to evaluate sensitivities required to evaluate the weak magnetizations carried by the Jack Hills sediments, and assess provenance information constrained by the opaque minerals. These data confirm magnetite as a detrital phase and the presence of high unblocking temperature magnetizations, further supporting the posit that the Jack Hills sediments can preserve primary magnetic signatures. We note that some of these magnetizations are near the measurement resolution of standard cryogenic magnetometers and thus exacting laboratory procedures are required to uncover these signals. In addition to magnetite, the cobbles contain an assemblage of Mg poor Cr-Fe chromites, Ni-sulfides and pyrrhotite that suggest a source in a layered intrusion different from the granitoid source of the zircons. Any Hadean rock fragment in these sediments, if present, remains elusive.

  4. Meteorology drives ambient air quality in a valley: a case of Sukinda chromite mine, one among the ten most polluted areas in the world.

    Science.gov (United States)

    Mishra, Soumya Ranjan; Pradhan, Rudra Pratap; Prusty, B Anjan Kumar; Sahu, Sanjat Kumar

    2016-07-01

    The ambient air quality (AAQ) assessment was undertaken in Sukinda Valley, the chromite hub of India. The possible correlations of meteorological variables with different air quality parameters (PM10, PM2.5, SO2, NO2 and CO) were examined. Being the fourth most polluted area in the globe, Sukinda Valley has always been under attention of researchers, for hexavalent chromium contamination of water. The monitoring was carried out from December 2013 through May 2014 at six strategic locations in the residential and commercial areas around the mining cluster of Sukinda Valley considering the guidelines of Central Pollution Control Board (CPCB). In addition, meteorological parameters viz., temperature, relative humidity, wind speed, wind direction and rainfall, were also monitored. The air quality data were subjected to a general linear model (GLM) coupled with one-way analysis of variance (ANOVA) test for testing the significant difference in the concentration of various parameters among seasons and stations. Further, a two-tailed Pearson's correlation test helped in understanding the influence of meteorological parameters on dispersion of pollutants in the area. All the monitored air quality parameters varied significantly among the monitoring stations suggesting (i) the distance of sampling location to the mine site and other allied activities, (ii) landscape features and topography and (iii) meteorological parameters to be the forcing functions. The area was highly polluted with particulate matters, and in most of the cases, the PM level exceeded the National Ambient Air Quality Standards (NAAQS). The meteorological parameters seemed to play a major role in the dispersion of pollutants around the mine clusters. The role of wind direction, wind speed and temperature was apparent in dispersion of the particulate matters from their source of generation to the surrounding residential and commercial areas of the mine.

  5. Biogenic nano-magnetite and nano-zero valent iron treatment of alkaline Cr(VI) leachate and chromite ore processing residue

    International Nuclear Information System (INIS)

    Highlights: • Remediation of high pH Cr(VI) contamination related to COPR and its groundwater. • Extensive characterization of COPR and its related groundwater. • Cr(VI) reduction to Cr(III) by biogenic nano-magnetite and nano-zero valent iron. • Critical assessment of reactivity and passivation using spectroscopy and imaging. • Stabilization of the COPR Cr(VI) source by addition of nanoparticles. - Abstract: Highly reactive nano-scale biogenic magnetite (BnM), synthesized by the Fe(III)-reducing bacterium Geobacter sulfurreducens, was tested for the potential to remediate alkaline Cr(VI) contaminated waters associated with chromite ore processing residue (COPR). The performance of this biomaterial, targeting aqueous Cr(VI) removal, was compared to a synthetic alternative, nano-scale zero valent iron (nZVI). Samples of highly contaminated alkaline groundwater and COPR solid waste were obtained from a contaminated site in Glasgow, UK. During batch reactivity tests, Cr(VI) removal from groundwater was inhibited by ∼25% (BnM) and ∼50% (nZVI) when compared to the treatment of less chemically complex model pH 12 Cr(VI) solutions. In both the model Cr(VI) solutions and contaminated groundwater experiments the surface of the nanoparticles became passivated, preventing complete coupling of their available electrons to Cr(VI) reduction. To investigate this process, the surfaces of the reacted samples were analyzed by TEM-EDX, XAS and XPS, confirming Cr(VI) reduction to the less soluble Cr(III) on the nanoparticle surface. In groundwater reacted samples the presence of Ca, Si and S was also noted on the surface of the nanoparticles, and is likely responsible for earlier onset of passivation. Treatment of the solid COPR material in contact with water, by addition of increasing weight % of the nanoparticles, resulted in a decrease in aqueous Cr(VI) concentrations to below detection limits, via the addition of ⩾5% w/w BnM or ⩾1% w/w nZVI. XANES analysis of the

  6. Magnetic Properties and Specific Heat on Multiferroics YCrO3 Chromites%多铁性铬氧化物YCrO3体系的磁特性及比热研究

    Institute of Scientific and Technical Information of China (English)

    苏玉玲; 沈岩; 李子炯; 刘德伟; 曹世勋; 张金仓

    2011-01-01

    系统研究了低温条件下铬氧化物YCrO3体系的磁特性及比热特点.实验结果表明,在高温区(T>140 K)直流磁化率随温度的变化遵从居里-外斯定律,YCrO3体系处于顺磁状态,样品的有效平均磁矩μefr=3.99μB、顺磁居里-外斯温度TCw =-340 K,即体系具有反铁磁性.在TN =140 K附近,YCrO3体系经历了由顺磁态向倾角反铁磁态的相转变,其自旋磁结构一直保持为Г4(Gx,Ay,Fz;FRz);低温条件下(T<140 K),体系具有完整闭合的磁滞回线,表明YCrO3样品具有反铁磁性的同时,具有明显的弱铁磁性,且随温度的降低铁磁性逐渐增强.对应于磁相变温度TN,比热曲线在140 K附近出现尖锐的λ形反常突起,由于Y离子没有磁性,显示了Cr3+磁矩亚晶格的顺磁-反铁磁相变对比热的贡献.%The magnetic and specific-heat properties were systemically investigated for multiferroic YCrO3 chromites with a temperature range of 2. 0 ~ 300 K. The results showed that the susceptibility followed the Curie-Weiss law at elevated temperature. The corresponding effective magnetic moment μeff = 3. 99 μB and asymptotic paramagnetic Curie temperature Tcw= - 340 K, suggested the predominance of antiferromag-netic interactions in YCrO3 chromites. At TN = 140 K, YCrO3 possessed a significant transition of the Cr sub-lattice from a paramagnetic to a canted antiferromag-netic (CAFM) order. The allowed spin configurationswere denoted as F4 (GxArFz; Fz). Simultaneously, the hysteretic loops confirmed the canted antiferromag-netic behaviors, where the ferromagnetic contribution increased with lowering the temperature. Furthermore, the specific heat data showed the typical second order phase transition from paramagnetic to CAFM ordering at TH = 140 K. Owing to the nonmagnetic property of Y3+ , the present results exhibited the interaction of the canted Cr3+ moments, and it would be helpful to understanding the physical mechanism and have possible application for

  7. COMPOSITION AND IMPLICATION OF THE CHROMITE IN KIMBERLITE FROM WAFANGDIAN, LIAONING AND MENGYIN, SHANDONG%辽宁瓦房店和山东蒙阴金伯利岩中铬铁矿成分特征及指示意义

    Institute of Scientific and Technical Information of China (English)

    迟广成; 李国武; 肖刚; 伍月; 岳明新; 郝原芳

    2013-01-01

    In order to research the relation between composition of chromite and ore content of kimberlite, samples were obtained from Wafangdian orefield in Liaoning and Mengyin orefield in Shandong for micro-area chemical composition analysis of chromite in kimberlite pipe by electronic probe spectrum. The result indicates that the chemical compositions of the chromite vary in different generations, particularly for chrome and aluminum. The value of Cr' = Cr/(Cr+Al) is used to represent the relation between chromite and the ore-bearing potentiality of kimberlite. The Cr' values of chromite decrease with the increasing diamond contents in kimberlite, which is a significant guide for prospecting mineralogy.%为了研究瓦房店和蒙阴矿区铬铁矿成分与金伯利岩含矿性关系,对2个矿区的铬铁矿进行了系统的采样,利用电子探针波谱技术测定了不同品位含矿岩管金伯利岩中的100个铬铁矿微区化学成分.分析结果表明:不同世代的铬铁矿的化学成分不同,主要差别在铬和铝2个元素上.如果用Cr/(Cr+Al)=Cr'来表示铬铁矿与金伯利岩含矿性的关系,那么金刚石包裹体中铬铁矿的Cr'值为89.75%;富矿岩体中的第一世代铬铁矿Cr'值为89.47%;中等含矿岩体中第一世代铬铁矿Cr'值为86.83%,第二世代铬铁矿Cr'值为82.74%;贫矿的岩体中第三世代铬铁矿Cr'值为68.98%.金伯利岩岩体中含金刚石由富到贫,对应岩石中铬铁矿Cr'值依次变低,具有明显的找矿矿物学特征.

  8. Studies on Effect of Impregnation with Sols on Pore Characteristic of Magnesia Chromite Brick Used in RH%浸溶胶对RH炉用镁铬砖气孔特性的影响研究

    Institute of Scientific and Technical Information of China (English)

    陈希来; 邹龙; 曹锟; 宋仪杰; 李亚伟; 徐国涛

    2012-01-01

    研究了浸铝溶胶、锆溶胶镁铬砖的气孔特性变化及对抗渣性能的影响.结果表明:浸溶胶后镁铬砖的气孔率减小、气孔孔径分布变好,确定合适的溶胶浸渍次数为3~4次;浸溶胶会提高镁铬砖的抗渣性能,铝溶胶更能提高材料的抗渣渗透性而锆溶胶则更能改善材料的抗渣侵蚀性.%Pore characteristic evolution and slag resistance of magnesia chromite brick impregnated with amumi-na sol and zirconia sol were studied. The results indicate that the porosity decreases and pore size distribution becomes better after the specimens impregnated with sols. The appropriate impregnation times is 3 or 4. The slag resistance characteristic is improved after the specimens impregnated with sols. Alumina sol can be beneficial to enhance the slag anti-penetration and zirconia sol is better to improve the slag anti-corrosion.

  9. 藏南罗布莎铬铁矿床铬尖晶石矿物学与矿床成因研究%Study on mineralogy of Cr-spinel and genesis of Luobusha chromite deposit in South Tibet

    Institute of Scientific and Technical Information of China (English)

    周二斌; 杨竹森; 江万; 侯增谦; 郭福生; 洪俊

    2011-01-01

    俯冲环境的转变过程,洋内俯冲带之上(SSZ)的弧间盆地环境是形成冶金级豆荚状铬铁矿的最为有利构造环境.研究提出了罗布莎铬铁矿的“三阶段”成矿模式,即,经历了大洋中眷预富集阶段,俯冲带之上主成矿阶段及之后的构造抬升改造阶段.纯橄岩与方辉橄榄岩接触带之下的方辉橄榄岩相带是寻找较大规模铬铁矿床的有利地带.%The Luobusha chromite deposit, which is the largest podiform deposit with maximum study in China, occurred in a fresh mantle peridotite in the east part of Yarlung Zangbo ophiolite belt in South Tibet The economic ore bodies of Luobusha chromite deposits are mainly hosted in a specific lithological horizon of harzburgite facies beneath the boundary of ophiolitic crust and mantle (beneath the Moho boundary) , and the ore type mainly includes massive, disseminated and nodular chromitite ores. Luobusha Cr-spinel have a large variety in composition, based on the chemical composition and the detailed mineralogical study of Cr-spinel, at least three crystalline epochs of the Cr-spinel in the Luobusha podiform chromite deposit can be recognized. (1) Pre-mineralization Cr-spinel : This kind of Cr-spinel is mainly as accessory mineral in the harzburgite, and occurred in the form of residual phenocryst, exsolution crystal and euhedral crystal with high A12O3 content, most of the Cr value of the Cr-spinel is less than 60, and has a negative correlation ship with Mg#. The overall evolution of this kind of Cr-spinel from exsolution crystal, residual phenocryst to euhedral crystal of Cr-spinel tends to be riched in Cr and Fe; (2) Main mineralization Cr-spinel can also be divided into two stages. The early stage of Cr-spinel, has a typical characteristic of Cr-riched, is a major mineral with anhedral crystal in a variety type of chromitite ores, and a minor mineral with euhedral crystal in dunite ' envelop' crust outside of the orebodies. Most of the Cr value of

  10. Ecosystem Health in Mineralized Terrane-Data from Podiform Chromite (Chinese Camp Mining District, California), Quartz Alunite (Castle Peak and Masonic Mining Districts, Nevada/California), and Mo/Cu Porphyry (Battle Mountain Mining District, Nevada) Deposits

    Science.gov (United States)

    Blecker, Steve W.; Stillings, Lisa L.; Amacher, Michael C.; Ippolito, James A.; DeCrappeo, Nicole M.

    2010-01-01

    various mineralized terranes. We were also interested in examining these relations in the context of determining appropriate reference conditions with which to compare reclamation efforts. The purpose of this report is to present the data used to develop indices of soil and ecosystem quality associated with mineralized terranes (areas enriched in metal-bearing minerals), specifically podiform chromite, quartz alunite, and Mo/Cu porphyry systems. Within each of these mineralized terranes, a nearby unmineralized counterpart was chosen for comparison. The data consist of soil biological, chemical, and physical parameters, along with vegetation measurements for each of the sites described below. Synthesis of these data and index development will be the subject of future publications.

  11. Mineralogy of chromites in Mandaleke ophiolite of South Tianshan Mountains and its geological implications%南天山满大勒克蛇绿岩铬铁矿矿物学特征及其意义

    Institute of Scientific and Technical Information of China (English)

    张炜斌; 张东阳; 张招崇; 黄河; 赵莉

    2011-01-01

    满大勒克蛇绿岩属于南天山晚古生代蛇绿岩带,主要由蛇纹石化橄榄岩、玄武岩和含放射虫硅质岩组成.其中蛇纹岩富含铬铁矿,并具有豆英状特征.显微镜观察和电子探针分析表明,铬铁矿具有明显的环带结构,从核部到边部呈现出由铬尖晶石到铬铁矿到磁铁矿的变化特征,元素组成上具有由富Al和Cr、贫Fe到贫Al和Cr、富Fe的变化趋势.利用铬铁矿(铬尖晶石)核部矿物的化学成分,得出铬尖晶石的结晶温度为1359~1394℃,平均1379℃;压力为2.76~3.00 GPa,平均2.87 GPa;相对于FMQ缓冲剂的地幔氧逸度为FMQ-1.50~FMQ-2.92log单位,平均值为FMQ-2.14 log单位;地幔熔融程度F为16.7%~18.0%.结合已有研究成果,推测满大勒克蛇绿岩的基底橄榄岩单元源区为石榴石二辉橄榄岩,形成于亏损的软流圈地慢,对应的大地构造位置为弧前盆地.研究区铬尖晶石的环带特征显示其经历了温度由高到低、氧逸度由低到高的演变,反映了满大勒克蛇绿岩套的橄榄岩单元经历了高温高压的地幔环境(低氧逸度),之后随构造变动被推覆到地壳,定位之后又经历了区域变质作用的演化过程(高氧逸度).%The Mandaleke ophiolite belongs to the late Paleozoic ophiolite belt in South Tianshan Mountains and is composed of serpentinized peridotites, basalts and radiolarian cherts.The chromite or Cr-spinel occurs in the serpentinized peridotites as a ubiquitous accessory mineral, some of which has the podiform texture.Petrographic observation and electron microprobe analysis indicate that the Cr-spinel grains display obvious composition zoning, suggesting the path of such thermal events as crystallization, upwelling and alteration.The core of the Crspinel crystal represents the provenance where the mineral crystallized.The authors thus chose cores of the Crspinel to trace the nature of the mantle and the whole crystals to deduce the thermal events that the

  12. Placer chromite along south Maharashtra, central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Gujar, A.R.; Ambre, N.V.; Iyer, S.D.; Mislankar, P.G.; Loveson, V.J.

    Janoli river, the main tribu- tary joining the Gad river at Varvada (Figure 1), and the entrenched drainage pattern imply the vital role of tectonic lineaments (S. N. Karlekar, unpublished). Com- pared to Achara, the Gad river has a steeper graded pro... mineral fractions from the bed load of the rivers were analysed by X-ray RESEARCH ARTICLES CURRENT SCIENCE, VOL. 99, NO. 4, 25 AUGUST 2010 493 Figure 1. Location of study area, general geology and drainage patterns. R11 to R17 are sediment samples...

  13. Observation of bimodality in nanocrystalline cobalt - ferri - chromites

    Science.gov (United States)

    Modi, K. B.; Saija, K. G.; Zankat, K. B.; Kathad, C. R.; Shah, S. J.; Lakhani, V. K.; Vasoya, N. H.; Pathak, T. K.

    2015-06-01

    In this communication we present detail analysis of particle size distribution curves, differential size distribution and cumulative undersize distribution, recorded for nano particles of spinel ferrite system, CoCrxFe2-xO4 (x = 0.0, 1.1 and 2.0), synthesized by chemical co-precipitation technique. It is found that the distribution is bimodal as well as not mono disperse. Observed bimodality has been explained in the light of Ostwald ripening. Various parameters have been determined and the role of Cr3+ - substitution in governing signature of distribution patterns has been discussed.

  14. Enhancement in magnetocaloric properties of holmium chromite by gadolinium substitution

    Science.gov (United States)

    Yin, S.; Jain, M.

    2016-07-01

    HoCrO3, Ho0.67Gd0.33CrO3, and GdCrO3 bulk powder samples were prepared by citrate route. The phase purity and the structural properties of the samples were examined by x-ray diffraction and Raman spectroscopic measurements. The dc magnetization data revealed that the Cr3+ ordering temperatures (Néel temperature) for the HoCrO3, Ho0.67Gd0.33CrO3, and GdCrO3 samples are 140 K, 148 K, and 167 K, respectively, while the ac magnetization data revealed that the rare-earth (Ho) ordering occurs at ˜8 K for HoCrO3 and Ho0.67Gd0.33CrO3 samples. Temperature-induced magnetization reversal and spin reorientation were observed in GdCrO3 bulk sample, which depends on applied magnetic field and disappears at ˜1500 Oe and 500 Oe, respectively. By fitting the dc magnetic data with Curie-Weiss law, the effective magnetic moments were calculated to be 11.66 μB, 10.23 μB, and 9.90 μB for the HoCrO3, Ho0.67Gd0.33CrO3, and GdCrO3 samples, respectively. The isothermal magnetization data showed that the magnetic behavior changed from canted antiferromagnetic in low temperature region (below Néel temperature) to paramagnetic at high temperature. It was found that Gd substitution considerably improves the magnetocaloric effect of HoCrO3. Pure GdCrO3 bulk sample showed giant magnetocaloric entropy change (31.6 J/kg K at temperature ˜5 K and at ˜70 kOe), which is higher than that for polycrystalline RMnO3, RCrO3, and RFeO3 bulk powder samples. This renders GdCrO3 useful for potential applications in low-temperature magnetic refrigeration.

  15. Low Temperature Phase Transition Behavior of Ca-Doped Lanthanum Chromites

    Institute of Scientific and Technical Information of China (English)

    Li Shengli; Fu Guifu; Liu Weiming; Ao Qing; Sun Liangcheng; Zhu Xinde

    2005-01-01

    Phase transition of LaCrO3 and doped-LaCrO3 was studied by DSC, TG and XRD, and thermal expansion during the transition was analyzed. It is found that phase transition of LaCrO3 begins at about 240 ℃ and ends at about 265 ℃. Temperatures of phase transition rise obviously with increasing Ca2+ content. The transition of LaCrO3 and Ca-doped LaCrO3 from orthorhombic to rhombohedral is accompanied with endothermic reaction. No obvious change occurs in mass, but remarkable shrinkage occurs during phase transition.

  16. Ilmenite, magnetite and chromite beach placers from south Maharashtra, central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Gujar, A.R.; Ambre, N.V.; Mislankar, P.G.; Iyer, S.D.

    . Geo-Resour. Geotech., 23, 137-174. Blott, S. (2000) Grain size distribution and statistics package for the analysis of unconsolidated sediments by sieving or by laser granulometer. Grandistat Version 4.0, 1-6. Chari, G.N., Marwar, S.A., Bobade, G...

  17. Experimental Research on a Chromite in India%印度某铬铁矿选矿试验研究

    Institute of Scientific and Technical Information of China (English)

    刘水红

    2016-01-01

    针对印度某地Cr2 03品位25.67%、铁含量为27.60%的铬铁矿,分别进行了原矿摇床选别、原矿螺旋溜槽选别、原矿螺旋溜槽与摇床联合选别三种工艺流程的选矿试验研究.研究结果表明,原矿螺旋溜槽抛尾—螺旋溜槽精选—中矿再磨分级摇床选别流程较为合理,可以获得产率43.17%、Cr2 03品位45.97%、回收率81.83%的铬精矿,为充分开发利用该地的铬铁矿资源提供了合理依据.

  18. Bio-reduction of Cr(VI) by exopolysaccharides (EPS) from indigenous bacterial species of Sukinda chromite mine, India.

    Science.gov (United States)

    Harish, R; Samuel, Jastin; Mishra, R; Chandrasekaran, N; Mukherjee, A

    2012-07-01

    Chrome mining activity has contributed intensively towards pollution of hexavalent chromium around Sukinda Valley, Orissa, India. In an attempt to study the specific contribution of exopolysaccharides (EPS) extracted from indigenous isolates towards Cr(VI) reduction, three chromium (VI) tolerant strains were isolated from the effluent mining sludge. Based on the tolerance towards Cr(VI) and EPS production capacity, one of them was selected for further work. The taxonomic identity of the selected strain was confirmed to be Enterobacter cloacae (showing 98% similarity in BLAST search to E. cloacae) through 16S rRNA analysis. The EPS production was observed to increase with increasing Cr(VI) concentration in the growth medium, highest being 0.078 at 100 mg/l Cr(VI). The extracted EPS from Enterobacter cloacae SUKCr1D was able to reduce 31.7% of Cr(VI) at 10 mg/l concentration, which was relevant to the prevailing natural concentrations at Sukinda mine effluent sludge. The FT-IR spectral studies confirmed the surface chemical interactions of hexavalent chromium with EPS.

  19. An X-Ray Diffraction Study of an Inclusion in Diamond from the Luobusha Chromite Deposit in Tibet,China

    Institute of Scientific and Technical Information of China (English)

    SHI Nicheng; BAI Wenji; MA Zhesheng; FANG Qingsong; XIONG Ming; YAN Binggang; DAI Mingquan; YANG Jingsui

    2003-01-01

    Diamond was found in podiform chromitites of ophiolite and harzburgite from Luobusha, Tibet. There are silicate inclusions in some diamond grains from this area. In the present work, the CCD (charge coupled detector) technology of X-ray powder diffraction was applied to the study of the inclusion in diamond from the ophiolite of Tibet. Diffraction patterns are obtained even though the inclusion is only 20 μm in crystal size. The results show that the inclusion in diamond consists of talc and clinochrysotile. Therefore, it is clear that the diamond from the ophiolite of Luobusha, Tibet, is natural diamond rather than a synthetic one.

  20. Magnetization reversal in mixed ferrite-chromite perovskites with non magnetic cation on the A-site

    Science.gov (United States)

    Billoni, Orlando V.; Pomiro, Fernando; Cannas, Sergio A.; Martin, Christine; Maignan, Antoine; Carbonio, Raul E.

    2016-11-01

    In this work, we have performed Monte Carlo simulations in a classical model for RFe1-x Cr x O3 with R  =  Y and Lu, comparing the numerical simulations with experiments and mean field calculations. In the analyzed compounds, the antisymmetric exchange or Dzyaloshinskii-Moriya (DM) interaction induced a weak ferromagnetism due to a canting of the antiferromagnetically ordered spins. This model is able to reproduce the magnetization reversal (MR) observed experimentally in a field cooling process for intermediate x values and the dependence with x of the critical temperatures. We also analyzed the conditions for the existence of MR in terms of the strength of DM interactions between Fe3+ and Cr3+ ions with the x values variations.

  1. Study of chromites YbMIICr2O5,5 (MII - Mg, Ca, Sr, Ba by X-ray diffraction

    Directory of Open Access Journals (Sweden)

    B. Kasenov

    2012-03-01

    Full Text Available Compounds of composition YbMeMnFeO5,5 (Me – Mg, Ca, Sr, Ba are synthesized from Yb2O3, , Cr2O3 and MgCO3, CaCO3, SrCO3, BaCO3 by solid phase method. X-ray powder diffraction showed that the compound YbMgCr2O5,5, YbCaCr2O5,5, YbSrCr2O5,5, YbBaCr2O5,5 crystallizes in the tetragonal crystal system.

  2. Metallographic study of heat-treated chrome ore briquettes

    Energy Technology Data Exchange (ETDEWEB)

    Patnaik, S.K.; Mohanty, J.N.; Satapathy, B.K.; Nayak, B.; Tripathy, A.K.; Dey, D.N.

    1987-07-01

    The paper deals with the metallographic study of heat treated chromite and chromite-coke composite briquettes. The briquettes, prepared from chromite concentrate of Orissa Mines using molasses-lime, dextrinelime and tamarind seed as binders, were subjected to different temperatures and examined metallographically. The change of phase with temperature was analysed by X-ray diffraction.

  3. 混合岩化作用改造的铬铁矿床

    Institute of Scientific and Technical Information of China (English)

    张宝贵

    1977-01-01

    Discussion has been given to the geology and origin of a certain chromite deposit from a viewpoint of migmatization. 47 chromite orebodies have been discovered in this area. All of them, variously shaped as irregular lens, chambers, kidneys,etc., occur in migmatite, showing dear-cut contacts with the latter. Mineralogical composition of these deposits are exceedingly simple, composing mainly of chromium phlogopitc and chromite and, to the less extent, of pyrite, chalcopyrite, galena,rosite aaad etc. The pre-existing chromite deposit, which is magmatic in origin, is decply altered by migmatization, eventually giving rise to metamorphosed chromite deposits as are seen at present day.

  4. Experimental petrology of ancient lunar mare basalt Asuka-881757: Spinel crystallization as a petrologic indicator

    OpenAIRE

    Arai,Tomoko/Takeda,Hiroshi /Miyamoto,Masamichi

    2006-01-01

    The paucity of titanian chromites in lunar-meteorite basalt Asuka (A)-881757 is unusual compared to the general occurrence of co-existing chromites and ulvospinels in the Apollo and Luna mare basalts. The unique spinel crystallization of A-881757 is expected to hold a key to elucidate the crystallization and cooling episodes of the basalt. In this study, we investigated the possible reason for the missing chromite by conducting isothermal and cooling experiments on the bulk-rock composition o...

  5. 超基性岩矿物化学特征与成矿关系讨论

    Institute of Scientific and Technical Information of China (English)

    顾鹏

    1983-01-01

    The most productive chromite ore deposits are formed by crystallizing from chromite-ore magmas under definite physico-chemical conditions. The formation of chromite ore is controlled mainly by the degree of differentiation of ultrabasic magma. How to diagnose uitrabasic magmatie differentiation is key to the understanding of the mechanism of formation of chromite ore. It is considered that chromite ore is derived from ulttabasic rocks. The rock-forming minerals include olivine, pyroxene and spinel. The minerals are well homomorphous minerals. The contents of major chemical elements in these minerals show little variation. On the contrary in those ultrubasie rocks which show no association with chromite ore deposits the contents of the elements vary over a wide range. Abundant data available.indicate that chromite ore deposits arc derived from chrore.ire-ore magmas resulting from the transport and accumulation of chromic elements. Since the transport and accumulation of chromic elements follows the statistical law,we must study the mechanism of formation of ehromite ore from the statistical point of view. If chromite ore is formed from spinel under the action of gravitation o.r other dynamic actions, we must elucidate the mechanism of formation of chromite ore from the dynamic viewpoint.

  6. The I-Xe System in the IVA Iron Meteorite Steinbach

    Science.gov (United States)

    Pravdivtseva, O.; Meshik, A.; Hohenberg, C. M.

    2013-09-01

    Non-metallic phases from IVA Steinbach were separated and identified to be troilite, chromite, tridymite, and clino- and orthopyroxene. Xenon isotopic compositions are measured to identify possible iodine carrier phases suitable for the I-Xe dating.

  7. A Stranger in the Midst: Searching for Relict Grains from Rare Meteorite Types in Mid-Ordovician Limestone Strata

    Science.gov (United States)

    Martin, E.; Schmitz, B.

    2016-08-01

    A layer of Mid-Ordovician limestone harbors exceptional amounts of L-chondritic chromite grains. The layer also contains grains from potentially rarer types of meteorites, following the discovery of the fossil meteorite Österplana 065.

  8. Spinel-silicate co-crystallization relations in sample 15555. [lunar rocks

    Science.gov (United States)

    Dalton, J.; Hollister, L. S.

    1974-01-01

    The results on the crystallization history of medium-grained mare basalt sample 15555,171, based on microprobe analyses (Dalton, 1973) of host and inclusion mineral pairs are summarized with emphasis placed on that part of the crystallization history during which chromite and ulvospinel were crystallizing. Compositional data on pyroxene olivine, chromite and ulvospinel in 15555,171 were collected using microprobe; data are based on corrected counts ratios for nine elements. It is concluded that systematic chemical relations between host and inclusion minerals suggest continuous in situ nucleation and growth of these minerals; that the data allow the possibility of some minerals, especially chromite, settling out of the melt during crystallization; and that the chromite to ulvospinel transition is correlated with a compositional change of the melt resulting from nucleation and growth of plagioclase.

  9. Petrology and mineralogy of the Y-793605 martian meteorite

    OpenAIRE

    Yukio, Ikeda

    1997-01-01

    Yamato-793605 is a lherzolitic shergottite and very similar in texture and mineralogy to other two lherzolitic shergottites, ALHA77005 and LEW88516,but is not a pair with the latter two. It consists mainly of olivine, pyroxene, maskelynite, chromite, ilmenite, and pyrrhotite. Small silicate inclusions occur in olivine and pyroxene. Olivine has a wide compositional range from Fo_ to Fo_, that included in pyroxene is more magnesian, and that in contact with maskelynite is more ferroan. Chromite...

  10. Quantitative mineralogical characterization of chrome ore beneficiation plant tailing and its beneficiated products

    Science.gov (United States)

    Das, S. K.

    2015-04-01

    Mineralogical characterization and liberation of valuable minerals are primary concerns in mineral processing industries. The present investigation focuses on quantitative mineralogy, elemental deportment, and locking-liberation characteristics of the beneficiation of tailings from a chrome ore beneficiation plant in the Sukinda region, Odisha; methods used for the study of the beneficiated tailings are QEMSCAN®, X-ray diffraction (XRD), and mineral chemistry by a scanning electron microscope equipped with an energy-dispersive spectrometer (SEM-EDS). The tailing sample was fine grained (69.48wt% below 45 μm size), containing 20.25wt% Cr2O3 and 39.19wt% Fe2O3, with a Cr:Fe mass ratio of 0.51. Mineralogical investigations using QEMSCAN studies revealed that chromite, goethite, and gibbsite are the dominant mineral phases with minor amounts of hematite, kaolinite, and quartz. The sample contained 34.22wt% chromite, and chromite liberation is more than 80% for grains smaller than 250 μm in size. Based on these results, it was predicted that liberated chromite and high-grade middling chromite particles could be separated from the gangue by various concentration techniques. The tailing sample was beneficiated by hydrocyclone, tabling, wet high-intensity magnetic separation (WHIMS), and flotation in order to recover the chromite. A chromite concentrate with 45.29wt% Cr2O3 and a Cr:Fe mass ratio of 1.85 can be produced from these low-grade chromite ore beneficiation plant rejects.

  11. Understanding Re-Os systematics and model ages in metamorphosed Archean ultramafic rocks: A single mineral to whole-rock investigation

    Science.gov (United States)

    Coggon, Judith A.; Luguet, Ambre; Fonseca, Raúl O. C.; Lorand, Jean-Pierre; Heuser, Alexander; Appel, Peter W. U.

    2015-10-01

    187Rhenium-187Os model ages are used to infer the timing of crust-mantle differentiation events and evolution of lithospheric mantle. However, ancient samples often have long and complex histories of metamorphism, metasomatism and deformation that may be problematic if these processes caused disturbance the Re-Os system. Such processes have been shown to disturb the Re-Os systematics of ophiolitic chromitites, but the effect on stratiform chromitites has not previously been investigated. Here we present a detailed petrographic and Re-Os isotopic study of chromitites, chromite-bearing meta-peridotites and single chromite grains from the Ujaragssuit nunât layered ultramafic intrusion, southwest Greenland, which has experienced intense deformation and at least two episodes of metamorphism up to amphibolite facies. We report the first ever Re-Os isotope and platinum-group element concentration data for single chromite grains achieved by single grain dissolution and isotope dilution. Micrometric Os-, Ir-, Ru - sulphide and sulpharsenide inclusions in chromite occur in the massive chromitites; these accessory phases host a significant portion of the Os, Ir and Ru in these samples. The remaining Os-Ir-Ru budget, along with Pt and Pd, appears to be homogeneously distributed within the chromite, occurring either in the lattice itself, as evenly distributed sub-micrometric alloy inclusions in chromite (unresolvable using the techniques applied in this study) or a combination of both. Rhenium is hosted in silicates, as predicted by previous studies. Both single-grain and whole-rock Re-Os isotope systematics yield unfeasibly young Re-Os model ages due to their radiogenic 187Os/188Os compositions. This could result from country rock contamination of the original melt from which the Ujaragssuit nunât intrusion crystallised, and/or from disturbance of the Re-Os isotope systematics of these rocks during regional metamorphic events at ∼2.8 and/or ∼3.75 Ga. We conclude that it

  12. Iron and magnesium isotopic constraints on the origin of chemical heterogeneity in podiform chromitite from the Luobusa ophiolite, Tibet

    Science.gov (United States)

    Xiao, Yan; Teng, Fang-Zhen; Su, Ben-Xun; Hu, Yan; Zhou, Mei-Fu; Zhu, Bin; Shi, Ren-Deng; Huang, Qi-Shuai; Gong, Xiao-Han; He, Yong-Sheng

    2016-03-01

    We present high-precision measurements of iron (Fe) and magnesium (Mg) isotopic compositions of olivine, orthopyroxene, and chromite separates from harzburgites, dunites, and chromitites in the mantle section of the Luobusa ophiolite, southern Tibet, to investigate the origins of podiform chromitite. Two harzburgites in the Zedong ophiolite, southern Tibet, are also reported for comparison. The olivine and orthopyroxene in the Luobusa and Zedong harzburgites have similar Fe and Mg isotopic compositions, with δ56Fe values ranging from 0‰ to +0.083‰ in olivine, from -0.034‰ to +0.081‰ in orthopyroxene and δ26Mg values ranging from -0.25‰ to -0.20‰ in olivine, from -0.29‰ to -0.26‰ in orthopyroxene, respectively. The olivines of two dunites from the Luobusa display small Fe and Mg isotopic variations, with δ56Fe values of +0.014‰ and +0.116‰ and δ26Mg values of -0.21‰ and -0.29‰. All chromites in the Luobusa chromitites have lighter Fe isotopic compositions than the coexisting olivines, with δ56Fe values ranging from -0.247‰ to +0.043‰ in chromite and from -0.146‰ to +0.215‰ in olivine (Δ56FeChr-Ol = -0.294 to -0.101‰). The chromite δ26Mg values span a significant range from -0.41‰ to +0.14‰. Large disequilibrium Fe and Mg isotope fractionation between chromite and olivine, as well as positive correlation of chromite δ56Fe values with their MgO contents, could be attributed to Fe-Mg exchange between chromite and olivine. In the disseminated chromitites, the higher modal abundances of olivine than chromite would result in a more extensive Fe-Mg exchange, whereas chromite in the massive chromitite where olivine is rare could not be affected by this process.

  13. 河南某铬铁矿床中铬尖晶石蚀变的地球化学研究

    Institute of Scientific and Technical Information of China (English)

    万欣

    1977-01-01

    In the light of mineral assemblages, mineralogical generation and genesis of chromite ores, some geochemical aspects are investigated with respect to . relative abundance, the transportion and association mechanisms of Cr and related elements in the process of metasomatie alteration of primary chromian spinel during migmatization. The formation of Fe-chromite is a result of metasomatism from primary magnesian Al-chromite through ultrametamorphism. A knowledge of its chemical characteristics will not only be desirable to understanding the chemistry of the oreforming fluid during later metasomatism, but also provide valuable informatinns as to the transport of Cr and some other points concerning geochemical evolution. Critical influence of SiO2 and Al2O3 concentrations has been recognized upon the enrichment and dispersion of Cr in the course of ultrametamorphism.

  14. Synthesis of chromium and ferrochromium alloy in molten salts by the electro-reduction method

    Directory of Open Access Journals (Sweden)

    Ge X.

    2015-01-01

    Full Text Available In this work, we successfully applied the Fray-Farthing-Chen Cambridge electro-reduction process on the preparation of chromium from chromium oxide, and for the first time, the synthesis of ferrochromium alloy from chromium oxide and iron oxide mixture and the chromite ore in molten calcium chloride. The present work systematically investigated the influences of sintered temperature of the solid precursor, electrochemical potential, electrolysis temperature and time on the products by using a set of advanced characterization techniques, including XRD and SEM/EDS analyses. In particular, our results show that this process is energy-friendly and technically-feasible for the direct extraction of ferrochromium alloy from chromite ore. Our findings thus provide useful insights for designing a novel green process to produce ferrochromium alloy from low-grade chromite ore or stainless steel slag.

  15. Stability of solid oxide fuel cell materials

    Energy Technology Data Exchange (ETDEWEB)

    Armstrong, T.R.; Bates, J.L.; Coffey, G.W.; Pederson, L.R. [Pacific Northwest National Lab., Richland, WA (United States)] [and others

    1996-08-01

    Chromite interconnection materials in an SOFC are exposed to both highly oxidizing conditions at the cathode and to highly reducing conditions at the anode. Because such conditions could lead to component failure, the authors have evaluated thermal, electrical, chemical, and structural stabilities of these materials as a function of temperature and oxygen partial pressure. The crystal lattice of the chromites was shown to expand for oxygen partial pressures smaller than 10{sup {minus}10} atm, which could lead to cracking and debonding in an SOFC. Highly substituted lanthanum chromite compositions were the most susceptible to lattice expansion; yttrium chromites showed better dimensional stability by more than a factor of two. New chromite compositions were developed that showed little tendency for lattice expansion under strongly reducing conditions, yet provided a good thermal expansion match to other fuel cell components. Use of these new chromite interconnect compositions should improve long-term SOFC performance, particularly for planar cell configurations. Thermodynamic properties of substituted lanthanum manganite cathode compositions have been determined through measurement of electromotive force as a function of temperature. Critical oxygen decomposition pressures for Sr and Ca-substituted lanthanum manganites were established using cells based on a zirconia electrolyte. Strontium oxide and calcium oxide activities in a lanthanum manganite matrix were determined using cells based on strontium fluoride and calcium fluoride electrolytes, respectively. The compositional range of single-phase behavior of these ABO{sub 3}-type perovskites was established as a function of A/B cation ratios and the extent of acceptor doping. Before this work, very little thermodynamic information was in existence for substituted manganite compositions. Such information is needed to predict the long-term stability of solid oxide fuel cell assemblies.

  16. H2O-driven generation of picritic melts in the Middle to Late Triassic Stuhini arc of the Stikine terrane, British Columbia, Canada

    Science.gov (United States)

    Milidragovic, Dejan; Chapman, John B.; Bichlmaier, Sebastian; Canil, Dante; Zagorevski, Alex

    2016-11-01

    Basaltic to andesitic compositions predominate island arc magmatism; ultramafic magmas are rare. Ultramafic (MgO = 21-33 wt.%) tuff breccia, lapilli tuff, and ash tuff of the Middle to Upper Triassic Stuhini Group were erupted in the Stikine arc of the North American Cordillera shortly preceding an episode of prolific porphyry Cu-Mo(-Au) mineralization. The ultramafic tuff shows accumulation (20-65%) of olivine (Fo91) and minor chromite into a subalkaline picritic parental magma with MgO ∼16 wt.%. Despite the inferred high MgO content of the parental liquid, chromite phenocrysts record relatively low liquidus temperatures (mineralization.

  17. Exsolutions of Diopside and Magnetite in Olivine from Mantle Dunite, Luobusa Ophiolite, Tibet, China

    Institute of Scientific and Technical Information of China (English)

    REN Yufeng; CHEN Fangyuan; YANG Jingsui; GAO Yuanhong

    2008-01-01

    The exsolutions of diopside and magnetite occur as intergrowth and orient within olivine from the mantle dunite, Luobusa ophiolite, Tibet. The dunite is very fresh with a mineral assemblage of olivine (>95%) + chromite (1%-4%) + diopside (<1%). Two types of olivine are found in thin sections: one (Fo = 94) is coarse-grained, elongated with development of kink bands, wavy extinction and irregular margins; and the other (Fo = 96) is fine-grained and poly-angled. Some of the olivine grains contain minor Ca, Cr and Ni. Besides the exsolutions in olivine, three micron-size inclusions are also discovered. Analyzed through energy dispersive system (EDS) with unitary analytical method, the average compositions of the inclusions are: Na20, 3.12%-3.84%; MgO, 19.51%-23.79%; Al2O3,9.33%-11.31%; SiO2, 44.89%-46.29%; CaO, 11.46%-12.90%; Cr2O3, 0.74%-2.29%; FeO, 4.26%-5.27%, which is quite similar to those of amphibole. Diopside is anhedral filling between olivines, or as micro-inclusions oriented in olivines. Chromite appears euhedral distributed between olivines,sometimes with apparent compositional zone. From core to rim of the chromite, Fe content increases and Cr decreases; and Al and Mg drop greatly on the rim. There is always incomplete magnetite zone around the chromite. Compared with the nodular chromite in the same section, the euhedral chromite has higher Fe3O4 and lower MgCr2O4 and MgAl2O4 end member contents, which means it formed under higher oxygen fugacity environment. With a geothermometer estimation, the equilibrium crystalline temperature is 820℃-960℃ for olivine and nodular chromite, 630℃-770℃ for olivine and euhedral chromite, and 350℃-550℃ for olivine and exsoluted magnetite, showing that the exsolutions occurred late at low temperature. Thus we propose that previously depleted mantle harzburgite reacted with the melt containing Na, Al and Ca, and produced an olivine solid solution added with Na+,Al3+, Ca2+, Fe3+, Cr3+. With temperature

  18. Controlled reactions between chromia and coating on alloy surface

    DEFF Research Database (Denmark)

    Linderoth, Søren

    1996-01-01

    An electrically conducting Sr-doped lanthanum chromite (LSC) coating has been produced by reacting a coating of fine particles of La oxide and Sr oxide with chromia formed as an external scale on a metallic alloy. In addition to the formation of LSC the coating also resulted in much reduced...

  19. METALS DEPOSITS

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    <正>20102341 Bao Peisheng(Institute of Geology,Chinese Academy of Geological Science,Beijing 100037,China)Further Discussion on the Genesis of the Podiform Chromite Deposits in the Ophiolites-Questioning about the Rock:Melt Interaction Metallogeny(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,28(12),2009,p.1741-1761

  20. Chromium valences in ureilite olivine and implications for ureilite petrogenesis

    Science.gov (United States)

    Goodrich, C. A.; Sutton, S. R.; Wirick, S.; Jercinovic, M. J.

    2013-12-01

    Ureilites are a group of ultramafic achondrites commonly thought to be residues of partial melting on a carbon-rich asteroid. They show a large variation in FeO content (olivine Fo values ranging from ∼74 to 95) that cannot be due to igneous fractionation and suggests instead variation in oxidation state. The presence of chromite in only a few of the most ferroan (Fo 75-76) samples appears to support such a model. MicroXANES analyses were used in this study to determine the valence states of Cr (previously unknown) in olivine cores of 11 main group ureilites. The goal of this work was to use a method that is independent of Fo to determine the oxidation conditions under which ureilites formed, in order to evaluate whether the ureilite FeO-variation is correlated with oxidation state, and whether it is nebular or planetary in origin. Two of the analyzed samples, LEW 88774 (Fo 74.2) and NWA 766 (Fo 76.7) contain primary chromite; two others, LAP 03587 (Fo 74.4) and CMS 04048 (Fo 76.2) contain sub-micrometer-sized exsolutions of chromite + Ca-rich pyroxene in olivine; and one, EET 96328 (Fo 85.2) contains an unusual chromite grain of uncertain origin. No chromite has been observed in the remaining six samples (Fo 77.4-92.3). Chromium in olivine in all eleven samples was found to be dominated by the divalent species, with valences ranging from 2.10 ± 0.02 (1σ) to 2.46 ± 0.04. The non-chromite-bearing ureilites have the most reduced Cr, with a weighted mean valence of 2.12 ± 0.01, i.e., Cr2+/Cr3+ = 7.33. All low-Fo chromite-bearing ureilites have more oxidized Cr, with valences ranging from 2.22 ± 0.03 to 2.46 ± 0.04. EET 96328, whose chromite grain we interpret as a late-crystallizing phase, yielded a reduced Cr valence of 2.15 ± 0.07, similar to the non-chromite-bearing samples. Based on the measured Cr valences, magmatic (1200-1300 °C) oxygen fugacities (fO2) of the non-chromite-bearing samples were estimated to be in the range IW-1.9 to IW-2.8 (assuming

  1. Cr-Bearing Inclusions in IVA Irons: Implication for Cr and Volatile Behaviors in the Metallic Cores

    Science.gov (United States)

    Isa, J.; McKeegan, K. D.; Wasson, J. T.

    2015-07-01

    We found inclusions that contribute to bulk Cr concentrations and found fO2 or fS2 changes during crystallization. O-isotope compositions of chromite are mass-dependently lighter than other IVA oxides. Also, we discovered a new mineral MnCr2S4.

  2. Five Major State-Level Copper,Lead, Zinc Resource Succession Bases in Tibet Have Initially Taken Shape

    Institute of Scientific and Technical Information of China (English)

    2015-01-01

    According to the Chengdu Center of China Geological Survey,five major state-level copper-lead-zinc resource succession bases in Tibet have initially taken shape,featuring tremendous resource potentials.It has been learned that these five major resource succession bases are respectively copper-lead-zinc molybdenum iron prospecting development base in Central Tibet,chromite

  3. Catalysis by Oxidic Spinel Ferrites

    OpenAIRE

    Darshane, V.; Lokegaonkar, S.; Oak, S.

    1997-01-01

    Mixed metal oxides viz. ferrites, ferrochromites and chromites have been studied with a view to investigating a correlation between bulk physical properties and catalytic performance over decomposition of alcohols. We could observe a satisfactory relationship between lattice parameter, electronic activation energy, nature and mobility of charge carriers and Curie temperature with reference to catalytic activity of various spinel ferrites.

  4. Platinum-Group Minerals in Chromitites of the Niquelândia Layered Intrusion (Central Goias, Brazil: Their Magmatic Origin and Low-Temperature Reworking during Serpentinization and Lateritic Weathering

    Directory of Open Access Journals (Sweden)

    Nelson Angeli

    2012-10-01

    Full Text Available A variety of platinum-group-minerals (PGM have been found to occur associated with the chromitite and dunite layers in the Niquelândia igneous complex. Two genetically distinct populations of PGM have been identified corresponding to phases crystallized at high temperatures (primary, and others formed or modified during post-magmatic serpentinization and lateritic weathering (secondary. Primary PGM have been found in moderately serpentinized chromitite and dunite, usually included in fresh chromite grains or partially oxidized interstitial sulfides. Due to topographically controlled lateritic weathering, the silicate rocks are totally transformed to a smectite-kaolinite-garnierite-amorphous silica assemblage, while the chromite is changed into a massive aggregate of a spinel phase having low-Mg and a low Fe3+/Fe2+ ratio, intimately associated with Ti-minerals, amorphous Fe-hydroxides, goethite, hematite and magnetite. The PGM in part survive alteration, and in part are corroded as a result of deep chemical weathering. Laurite is altered to Ru-oxides or re-crystallizes together with secondary Mg-ilmenite. Other PGM, especially the Pt-Fe alloys, re-precipitate within the altered chromite together with kaolinite and Fe-hydroxides. Textural evidence suggests that re-deposition of secondary PGM took place during chromite alteration, controlled by variation of the redox conditions on a microscopic scale.

  5. Biodegradation of the metallic carcinogen hexavalent chromium Cr(VI by an indigenously isolated bacterial strain

    Directory of Open Access Journals (Sweden)

    Das Alok

    2010-01-01

    Full Text Available Background : Hexavalent chromium [Cr(VI], a potential mutagen and carcinogen, is regularly introduced into the environment through diverse anthropogenic activities, including electroplating, leather tanning, and pigment manufacturing. Human exposure to this toxic metal ion not only causes potential human health hazards but also affects other life forms. The World Health Organization, the International Agency for Research on Cancer, and the Environmental Protection Agency have determined that Cr(VI compounds are known human carcinogens. The Sukinda valley in Jajpur District, Orissa, is known for its deposit of chromite ore, producing nearly 98% of the chromite ore in India and one of the prime open cast chromite ore mines in the world (CES, Orissa Newsletter. Materials and Methods: Our investigation involved microbial remediation of Cr(VI without producing any byproduct. Bacterial cultures tolerating high concentrations of Cr were isolated from the soil sample collected from the chromite-contaminated sites of Sukinda, and their bioaccumulation properties were investigated. Strains capable of growing at 250 mg/L Cr(VI were considered as Cr resistant. Results: The experimental investigation showed the maximum specific Cr uptake at pH 7 and temperature 30oC. At about 50 mg/L initial Cr(VI concentrations, uptake of the selected potential strain exceeded 98% within 12 h of incubation. The bacterial isolate was identified by 16S rRNA sequencing as Brevebacterium casei. Conclusion: Results indicated promising approach for microbial remediation of effluents containing elevated levels of Cr(VI.

  6. Origin of Archean Chromitites in the Nuggihalli Schist Belt, Dharwar Craton (India)

    Science.gov (United States)

    Mukherjee, R.; Mondal, S. K.; Rosing, M. T.; Frei, R.

    2009-12-01

    Layered ultramafic-mafic rocks with chromitite bodies occur as sill-like intrusions within the Archean greenstone sequences of the Nuggihalli belt, Western Dharwar Craton. The 3.1Ga chromitite-bearing ultramafic-mafic rocks occur as dismembered en echelon, lenticular units that are conformable within the metasedimentary rocks, and surrounded by the tonalite-trondhjemite-granodiorite suite. The chromitite bodies are hosted within intensely deformed serpentinite, and associated with gabbro. The chromitite bodies have high length/width ratio (60-500 m/15 m) and occur in the form of pods and elongated lenses. Detailed electron microprobe study reveals high Cr/(Cr+Al)=0.85-0.86 and moderate Mg/(Mg+Fe2+)=0.38-0.58 of the primary chromite from the massive chromitite. Interstitial and included olivine and pyroxene grains within massive chromitite, exhibit very high Fo content (Fo96-98) and Mg-numbers (94-99) respectively. Chromite grains exhibit intense compositional variability due to subsolidus re-equilibration and low temperature hydrothermal alteration processes such as in the altered massive chromitite (70% chromite), serpentinite (2% chromite) and silicate-rich chromitite (45% chromite). In these associations, chromite grains are compositionally zoned and commonly altered to ferritchromit (rarely magnetite) along the rim and fractures. The primary chromite compositions are used to compute the parent melt that is characterised by low Al2O3 (8.38-10.63 wt%), moderate to high TiO2 (0.94-1.58 wt%) and FeO/MgO ratios of 0.46-0.92 wt%. The parent melt calculations indicate derivation from a high-Mg komatiitic basalt, and matches with the compositions of komatiitic rocks reported from the greenstone terrain. Parent melts are produced by high degrees of partial melting of a depleted source mantle evident from the refractory compositions of chromite, olivine and pyroxene. Tectonic discrimination diagrams indicate a supra-subduction zone setting (SSZ) for the Archean

  7. The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle

    Directory of Open Access Journals (Sweden)

    Yuri de Melo Portella

    2016-09-01

    Full Text Available The Cedrolina chromitite body (Goiás-Brazil is concordantly emplaced within talc-chlorite schists that correspond to the poly-metamorphic product of ultramafic rocks inserted in the Pilar de Goiás Greenstone Belt (Central Brazil. The chromite ore displays a nodular structure consisting of rounded and ellipsoidal orbs (up to 1.5 cm in size, often strongly deformed and fractured, immersed in a matrix of silicates (mainly chlorite and talc. Chromite is characterized by high Cr# (0.80–0.86, high Fe2+# (0.70–0.94, and low TiO2 (av. = 0.18 wt % consistent with variation trends of spinels from metamorphic rocks. The chromitite contains a large suite of accessory phases, but only irarsite and laurite are believed to be relicts of the original igneous assemblage, whereas most accessory minerals are thought to be related to hydrothermal fluids that emanated from a nearby felsic intrusion, metamorphism and weathering. Rutile is one of the most abundant accessory minerals described, showing an unusually high Cr2O3 content (up to 39,200 ppm of Cr and commonly forming large anhedral grains (>100 µm that fill fractures (within chromite nodules and in the matrix or contain micro-inclusions of chromite. Using a trace element geothermometer, the rutile crystallization temperature is estimated at 550–600 °C (at 0.4–0.6 GPa, which is in agreement with P and T conditions proposed for the regional greenschist to low amphibolite facies metamorphic peak of the area. Textural, morphological, and compositional evidence confirm that rutile did not crystallize at high temperatures simultaneously with the host chromitite, but as a secondary metamorphic mineral. Rutile may have been formed as a metamorphic overgrowth product following deformation and regional metamorphic events, filling fractures and incorporating chromite fragments. High Cr contents in rutile very likely are due to Cr remobilization from Cr-spinel during metamorphism and suggest that Ti was

  8. Contingency plans for chromium utilization. Publication NMAB-335

    International Nuclear Information System (INIS)

    The United States depends entirely on foreign sources for the critical material, chromium, making it very vulnerable to supply disruptions. This vulnerability results because chromium is essential for the fabrication of corrosion-resisting steels and high-temperature, oxidation-resisting alloys in applications that are vital to the nation's technological well-being; because no substitutes are known for these materials in those applications; and because the known, substantial deposits of chromite ore are only in a few geographical locations that could become inaccessible to the United States as a result of political actions. The effectiveness of programs such as stockpiling, conservation, and research and development for substitutes to reduce the impact of disruption of imports of chromite and ferrochromium are discussed. Alternatives for decreasing chromium consumption also are identified for chromium-containing materials in the areas of design, processing, and substitution

  9. Mid amphibolite facies metamorphism of harzburgites in the Neoproterozoic Cerro Mantiqueiras Ophiolite, southernmost Brazil

    Directory of Open Access Journals (Sweden)

    HARTMANN LÉO A.

    2003-01-01

    Full Text Available Valuable information is retrieved from the integrated investigation of the field relationships, microstructure and mineral compositions of harzburgites from the Neoproterozoic Cerro Mantiqueiras Ophiolite. This important tectonic marker of the geological evolution of southernmost Brazilian Shield was thoroughly serpentinized during progressive metamorphism, because the oldest mineral assemblage is: olivine + orthopyroxene + tremolite + chlorite + chromite. This M1 was stabilized in mid amphibolite facies - 550-600ºC as calculated from mineral equilibria. No microstructural (e.g. ductile deformation of olivine or chromite or compositional (e.g. mantle spinel remnant of mantle history was identified. A metamorphic event M2 occurred in the low amphibolite facies along 100 m-wide shear zones, followed by intense serpentinization (M3 and narrow 1-3 m-wide shear zones (M4 containing asbestos.

  10. Possible spinel absorption bands in S-asteroid visible reflectance spectra

    Science.gov (United States)

    Hiroi, T.; Vilas, F.; Sunshine, J. M.

    1994-01-01

    Minor absorption bands in the 0.55 to 0.7 micron wavelength range of reflectance spectra of 10 S asteroids have been found and compared with those of spinel-group minerals using the modified Gaussian model. Most of these S asteroids are consistently shown to have two absorption bands around 0.6 and 0.67 micron. Of the spinel-group minerals examined in this study, the 0.6 and 0.67 micron bands are most consistent with those seen in chromite. Recently, the existence of spinels has also been detected from the absorption-band features around 1 and 2 micron of two S-asteroid reflectance spectra, and chromite has been found in a primitive achondrite as its major phase. These new findings suggest a possible common existence of spinel-group minerals in the solar system.

  11. Luna 24 - Systematics in spinel mineral chemistry in the context of an intrusive petrogenetic grid

    Science.gov (United States)

    Haggerty, S. E.

    1978-01-01

    Spinels in the Luna 24 gabbroic fragments have a restricted bimodal distribution of aluminum chromite and ulvospinel, whereas those in the Luna 24 basalts form a continuous sequence which defines a compositional variation from Al-Mg-chromites to ulvospinels containing 1 wt% Al2O3. A comparison of these spinel mineral chemistries with basaltic spinels from other mare regions and with spinels from other lunar intrusive rocks suggest that the Luna 24 gabbroic spinels lie at the low pressure end of a P-T spinel grid, and that titanium enrichment trends on Mg-Al-Cr rich spinel cores are related to extrusion and formed at the terminal stages of magmatic crystallization.

  12. Origin of unusual impact melt rocks, Yamato-790964 and 790143 (LL-chondrites)

    OpenAIRE

    Yamaguchi,Akira/Scott,Edward R.D./Keil,Klaus

    1998-01-01

    We have studied Yamato (Y)-790964 and-790143,which are unusual paired impact-melted LL chondrites. Some petrologic aspects of these impact melt rocks are similar to those of the impact melted L-chondrite, Ramsdorf; these meteorites experienced nearly total melting, yet partly preserve chondritic textures. Olivine and chromite grains in Y-790964 and olivine in Y-790143 are the only relicts of the precursor materials; they were solid clasts during impact melting. All other portions (i.e., chond...

  13. Physical and chemical characteristics of co-precipitated Magnesium, Ferum, Chromium hydroxide and products of their thermal decomposition

    OpenAIRE

    Луцась, Анна Віталіївна; Яремій, Іван Петрович; Матківський, Микола Петрович; Яремій, Софія Іванівна

    2016-01-01

    Magnesium ferrite-chromites of the system Mg(FeᵪCr₂₋ᵪ)O₄ were synthesized from aqueous solutions of the corresponding chlorides using the coprecipitation method. It was obtained homogeneous reactive active hydroxides with a high specific surface area, the value of which increases with the chromium content in the system. The conditions of magnesium, iron and chromium hydroxides coprecipitation are defined. The presence of chemical hydroxide interactions in co-precipitation and formation of pol...

  14. Stability of solid oxide fuel cell materials

    Energy Technology Data Exchange (ETDEWEB)

    Armstrong, T.R.; Bates, J.L.; Chick, L.A. [Pacific Northwest Lab., Richland, WA (United States)

    1996-04-01

    Interconnection materials in a solid oxide fuel cell are exposed to both highly oxidizing conditions at the cathode and to highly reducing conditions at the anode. The thermal expansion characteristics of substituted lanthanum and yttrium chromite interconnect materials were evaluated by dilatometry as a function of oxygen partial pressures from 1 atm to 10{sup -18} atm, controlled using a carbon dioxide/hydrogen buffer.

  15. Nationalised large-scale mining, trade unions and community representation: perspectives from Northern Madagascar

    OpenAIRE

    Smith, Shirley; Dorward, Peter

    2014-01-01

    This article critically explores the nature and purpose of relationships and inter-dependencies between stakeholders in the context of a parastatal chromite mining company in the Betsiboka Region of Northern Madagascar. An examination of the institutional arrangements at the interface between the mining company and local communities identified power hierarchies and dependencies in the context of a dominant paternalistic environment. The interactions, inter alia, limited social cohesion and ...

  16. Sulfide mineralization in ultramafic rocks of the Faryab ophiolite complex, southern Kerman

    OpenAIRE

    Mohammad Ali Rajabzadeh; Fatemeh Al Sadi

    2015-01-01

    Introduction Worldwide, Ni-Cu and PGE magmatic sulfide deposits are confined to the lower parts of stratiform mafic and ultramafic complexes. However, ophiolite mafic and ultramafic complexes have been rarely explored for sulfide deposits despite the fact that they have been extensively explored and exploited for chromite. Sulfide saturation during magmatic evolution is necessary for sulfide mineralization, in which sulfide melts scavenge chalcophile metals from the parent magma and conc...

  17. Magnetic Behavior of Some Rare-Earth Transition-Metal Perovskite Oxide Systems

    Institute of Scientific and Technical Information of China (English)

    Kenji Yoshii; Akio Nakamura; Masaichiro Mizumaki; Naoshi Ikeda; Jun'ichiro Mizuki

    2004-01-01

    Magnetic properties were investigated for the rare-earth 3d-transition metal oxides with the perovskite structure. Intriguing magnetic phenomena were reviewed for a few systems:magnetization peak effect in the titanates, magnetization reversal in the chromites and metallic ferromagnetism in the cobaltites. The results suggest an important role of the rare-earth ions for the magnetic properties of such complex oxides.

  18. 菲律宾采矿业期待腾飞%Philippines's Mining Industry Awaiting Prosperity

    Institute of Scientific and Technical Information of China (English)

    刘静

    2005-01-01

    Because of its favorable location, the Philippines possess sufficient natural mineral materials according to its relatively small territory. The Philippines used to be one of the top 10 world producers of copper, gold, nickel and chromites in the 1980s. Since then, however, its mining industry has steadily deteriorated owing to some reasons. This essay probes into the process of its development, its drawbacks and its prospect.

  19. Reduced creep strength and ductility of Type 304 steel in sodium

    International Nuclear Information System (INIS)

    Reductions in creep strength and ductility have been observed in Type 304 steel tested in flowing sodium. This effect is associated with a reduction in the extent of tertiary creep arising from more extensive surface grain boundary cracking in sodium. A mechanism involving the dissolution of chromium rich grain boundary carbides to allow the formation of a relatively brittle sodium chromite phase has been used to explain these results. (author)

  20. Solid phase distribution of chromium in industrially contaminated urban soil, Glasgow

    OpenAIRE

    Broadway, A.; Farmer, J G; Ngwenya, B. T.; Cave, M.R.; Fordyce, F.M.; Bewley, R.J.F.

    2007-01-01

    Like many cities throughout the UK, Glasgow has a long history of both urbanisation and industrialisation, resulting in elevated concentrations of potentially harmful elements. Between 1830 and 1968 Glasgow was home to one of the world’s largest producers of chromium-based chemicals. Chromite ore processing residue (COPR) arising from the factory was used as infill material across large areas of SE Glasgow, resulting in widespread land contamination with Cr(VI), a known carcino...

  1. Assessing the human health risks posed by chromium-contaminated land in Glasgow and its environs

    OpenAIRE

    Broadway, A.; Farmer, J G; Ngwenya, B. T.; Fordyce, F.M.; Cave, M.R.

    2007-01-01

    Like many cities throughout the UK, Glasgow has a long history of both urbanisation and industrialisation, resulting in elevated concentrations of potentially harmful elements (PHEs). Between 1830 and 1968 Glasgow was home to one of the world’s largest producers of Cr-based chemicals. Chromite ore processing residue (COPR) arising from the factory was used as infill material across large areas of SE Glasgow, resulting in widespread land contamination with Cr(VI), a known human ...

  2. Effect of Burning Rate Modifiers on Subatmospheric Flame Temperatures of AP/HTPB Composite Solid Propellants

    OpenAIRE

    Krishnan, S; R. D. Swami

    1998-01-01

    Using 30 um. pt and Pt 13 percent Rh thermocouples, flame temperatures of uncatalysed andcatalysed ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/lffPB) composite solidpropellants were measured under subatmospheric conditions. Ferric oxide F e 2 and copper chromite(CC) were the catalysts used. The study demonstrates that Fe2O3 catalysed propellant, notwithstandingits least combustion efficiency undt;r subatmospheric conditions and weak gas-phase flame, has themaximum burning rate ...

  3. Diamond exploration and mantle structure imaging using PIXE microanalysis

    Energy Technology Data Exchange (ETDEWEB)

    Ryan, C.G.; Griffin, W.L.; Win, T.T. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), North Ryde, NSW (Australia). Div. of Exploration Geoscience

    1996-12-31

    Geochemical methods of diamond exploration rely on recognizing indicator minerals that formed in the earth`s upper mantle, within the diamond stability field, and were entrained in rapidly rising volatile-rich magmas and emplaced in or on the crust. Diamond is only stable at high pressure. Therefore, diamond exploration commonly targets prospects containing high pressure minerals, such as low-Ca, high-Cr (`G10`) garnets and high-Cr chromites, similar to inclusions in diamonds. However, this procedure can be ambiguous; some barren pipes contain abundant `G10` garnets. while such garnets are extremely rare in the Argyle pipe, the world`s largest diamond producer. Similarly, high-Cr chromites are shed by a wide variety of barren rock types. PIXE microanalysis of trace elements in concentrate garnets and chromites from kimberlites and other volcanic rocks helps to remove the ambiguities by pinning down the source temperature (T), pressure (P) and local (paleo)geotherm (P-T relation), which permits the rich store of trace element information in these minerals, reflecting rock chemistry and metasomatic processes, to be placed in a stratigraphic context. 11 refs., 4 figs.

  4. Formation and modification of chromitites in the mantle

    Science.gov (United States)

    Arai, Shoji; Miura, Makoto

    2016-11-01

    Podiform chromitites have long supplied us with unrivaled information on various mantle processes, including the peridotite-magma reaction, deep-seated magmatic evolution, and mantle dynamics. The recent discovery of ultrahigh-pressure (UHP) chromitites not only sheds light on a different aspect of podiform chromitites, but also changes our understanding of the whole picture of podiform chromitite genesis. In addition, new evidence was recently presented for hydrothermal modification/formation chromite/chromitite in the mantle, which is a classical but innovative issue. In this context, we present here an urgently needed comprehensive review of podiform chromitites in the upper mantle. Wall-rock control on podiform chromitite genesis demonstrates that the peridotite-magma reaction at the upper mantle condition is an indispensable process. We may need a large system in the mantle, far larger than the size of outcrops or mining areas, to fulfill the Cr budget requirement for podiform chromitite genesis. The peridotite-magma reaction over a large area may form a melt enriched with Na and other incompatible elements, which mixes with a less evolved magma supplied from the depth to create chromite-oversaturated magma. The incompatible-element-rich magma trapped by the chromite mainly precipitates pargasite and aspidolite (Na analogue of phlogopite), which are stable under upper mantle conditions. Moderately depleted harzburgites, which contain chromite with a moderate Cr# (0.4-0.6) and a small amount of clinopyroxene, are the best reactants for the chromitite-forming reaction, and are the best hosts for podiform chromitites. Arc-type chromitites are dominant in ophiolites, but some are of the mid-ocean ridge type; chromitites may be common beneath the ocean floor, although it has not yet been explored for chromitite. The low-pressure (upper mantle) igneous chromitites were conveyed through mantle convection or subduction down to the mantle transition zone to form

  5. Spade: An H Chondrite Impact-melt Breccia that Experienced Post-shock Annealing

    Science.gov (United States)

    Rubin, Alan E.; Jones, Rhian H.

    2006-01-01

    The low modal abundances of relict chondrules (1.8 Vol%) and of coarse (i.e. >= 2200 micron-size) isolated mafic silicate grains (1.8 Vol%) in Spade relative to mean H6 chondrites (11.4 and 9.8 vol%, respectively) show Spade to be a rock that has experienced a significant degree of melting. Various petrographic features (e.g., chromite-plagioclase assemblages, chromite veinlets, silicate darkening) indicate that melting was caused by shock. Plagioclase was melted during the shock event and flowed so that it partially to completely surrounded nearby mafic silicate grains. During crystallization, plagioclase developed igneous zoning. Low-Ca pyroxene that crystallized from the melt (or equilibrated with the melt at high temperatures) acquired relatively high amounts of CaO. Metallic Fe-Ni cooled rapidly below the Fe-Ni solws and transformed into martensite. Subsequent reheating of the rock caused transformation of martensite into abundant duplex plessite. Ambiguities exist in the shock stage assignment of Spade. The extensive silicate darkening, the occurrence of chromite-plagioclase assemblages, and the impact-melted characteristics of Spade are consistent with shock stage S6. Low shock (stage S2) is indicated by the undulose extinction and lack of planar fractures in olivine. This suggests that Spade reached a maximum prior shock level equivalent to stage S6 and then experienced post-shock annealing (probably to stage Sl). These events were followed by a less intense impact that produced the undulose extinction in the olivine, characteristic of shock stage S2. Annealing could have occurred if Spade were emplaced near impact melts beneath the crater floor or deposited in close proximity to hot debris within an ejecta blanket. Spade firmly establishes the case for post-shock annealing. This may have been a common process on ordinary chondrites (OC) asteroids.

  6. Mass transfer of stainless steel in pumped sodium loops and its effect on microstructure

    International Nuclear Information System (INIS)

    Metallography and supporting analytical techniques have been used to study the corrosion and deposition behaviour of steel material in two pumped figure-of-eight loops operating at oxygen levels of 10 and 25 ppm. Corrosion has been identified in the high temperature parts of the system and ferrite layer formation and the undercutting of steel surfaces through the formation of sodium chromite have been established in the maximum temperature and downstream positions respectively. The damaged surface layer consists of Fe-Ni particles which after removal by the flowing sodium deposit in the low temperature part of the loop. (orig.)

  7. Elaboration et réactivité interfaciale d'oxydes pérovskites à base de Lanthane Strontium Chrome Ruthénium (LSCrRu) comme composés d'anode de piles à combustible à température intermédiaire (ITSOFC).

    OpenAIRE

    Combemale, L.

    2005-01-01

    New data on the interest of ruthenium doped lanthanum strontium chromite La1-xSrxCr1-yRuyO3δ (LSCrRu) as anode in ITSOFC are presented. Microwave synthesis of mixed oxides allowed shaping of half-cells and complete cells using sputtering and screen printing methods. LSCrRu methane reforming property had been studied in a mono-chamber system coupled with a mass spectrometer in collaboration with Institut de REcherche Hydro-Québec. Anode/electrolyte interfacial reactivity had been analysed usi...

  8. A literature survey of the matallurgical aspects of minerals in Witwatersrand gold ores

    International Nuclear Information System (INIS)

    This survey reviews the information in the literature on the auriferous rock formations in the Witwatersrand-Orange Free State gold-mining area, the gold-bearing horizons, and the mineralogy and petrography of the different ore types. The metallurgical aspects of the gold, silver, uranium, platinum-group elements, cobalt, nickel, copper, and chromite in these ores are examined and, on the strength of this information, a list is given of those problems in metallurgical extraction that are of a mineralogical nature. Finally, a number of research projects, aimed to support current research at the Council for Mineral Technology, are suggested

  9. BALD ROCK AND MIDDLE FORK FEATHER RIVER ROADLESS AREAS, CALIFORNIA.

    Science.gov (United States)

    Sorensen, Martin L.; Buehler, Alan R.

    1984-01-01

    The results of a mineral-resource assessment of the Bald Rock and Middle Fork Feather River Roadless Areas in California indicate several areas within the Middle Fork Feather River Roadless Area that have probable mineral-resource potential. A probable potential for placer gold exists at various localities, both in areas covered by Tertiary volcanic rocks and in small streams that drain into the Middle Fork of the Feather River. A probable potential for small deposits of chromite exists in tracts underlain by ultramafic rocks in the Melones fault zone. A probable potential for lead-silver deposits is recognized at the east end of the Middle Fork Feather River Roadless Area.

  10. INSOLUBILIZATION METHOD OF THE FLUORINE IN WASTE FOUNDRY SAND AND THE PRODUCTION METHOD OF THE ROADBED MATERIAL

    Science.gov (United States)

    Fukayama, Masamitu; Terazono, Katsuhiro; Koga, Yasuyuki

    We have studied how the fluorine-insoluble in the waste foundry sand (chromite sand) and production method of the roadbed material with insolubilized waste foundry sand. And we got following knowledges. (1) We found a minimum mixing rate to insolubilize of fluorine in the waste foundry sand by the ingenuity of mixing procedure. (2) Now we can insolubilize the waste foundry sand including comparatively high concentration fluorine (elution concentration: 20-70mg/l) by the mixing time difference of MgO and blast furnace cement. (3) In the verification test the roadbed material made from the insolubilized waste foundry sand satisfied reference value of environment safety.

  11. Magnetocaloric properties of rare-earth substituted DyCrO3

    Science.gov (United States)

    McDannald, A.; Jain, M.

    2015-07-01

    Recently, there has been a focus on the need for efficient refrigeration technology without the use of expensive or harmful working fluids, especially at temperatures below 30 K. Solid state refrigeration, based on the magnetocaloric effect, provides a possible solution to this problem. The rare-earth chromites (RCrO3), especially DyCrO3, with its large magnetic moment dysprosium ion, are potential candidates for such an application. The Dy3+ ordering transition at low temperatures (cooling power of 237 J/kg at 40 kOe and 5 K) indicates that this material system is well suited for low temperature (<30 K) solid state refrigeration applications.

  12. Studies on Environmentally Friendly Leaching Processes in China

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The newly developed green leaching processes for chromium, lead and gold extraction from ores or concentrates are described. The chromium is extracted from the iron chromite ore with fused sodium hydroxide at 500-550°C as sodium chromate. The galena in lead sulfide concentrate is converted into lead carbonate in ammonium or sodium carbonate solution at 50-80°C followed by the separation of lead carbonate formed from the unconverted sulfide ores by flotation. Gold associated with sulfide ore (such as pyrite and chalcopyrite) can be extracted into sodium thiosulfate solution without any pretreatment such as roasting, high pressure aqueous oxidation or bacteria pre-leaching.

  13. Petrologic and Oxygen-Isotopic Investigations of Eucritic and Anomalous Mafic Achondrites

    Science.gov (United States)

    Mittlefehldt, D. W.; Greenwood, R. C.; Peng, Z. X.; Ross, D. K.; Berger, E. L.; Barrett, T. J.

    2016-01-01

    The most common asteroidal igneous meteorites are eucrite-type basalts and gabbros rocks composed of ferroan pigeonite and augite, calcic plagioclase, silica, ilmenite, troilite, Ca-phosphate, chromite and Fe-metal. These rocks are thought to have formed on a single asteroid along with howardites and diogenites (HEDs). However, Northwest Africa (NWA) 011 is mineralogically identical to eucrites, but has an O-isotopic composition distinct from them and was derived from a different asteroid. Modern analyses with higher precision have shown that some eucrites have smaller O-isotopic differences that are nevertheless well-resolved from the group mean.

  14. Effects of different casting mould cooling rates on microstructure and properties of sand-cast Al-7.5Si-4Cu alloy

    OpenAIRE

    Liu Guanglei; Si Naichao; Sun Shaochun

    2013-01-01

    In this work, Al-7.5Si-4Cu alloy melt modified by Al-10Sr, RE and Al-5Ti-B master alloys was poured into multi-step moulds made from three moulding sands, including quartz, alumina and chromite, to investigate comparatively the effects of different cooling rates of the casting mould on the alloy's microstructures and mechanical properties. The results show that with an increase in wall thickness, the cooling rate decreases, the dendrite arm spacing (DAS) increases significantly and the mecha...

  15. Stability of solid oxide fuel cell materials

    Energy Technology Data Exchange (ETDEWEB)

    Armstrong, T.R.; Pederson, L.R.; Stevenson, J.W.; Raney, P.E. [Pacific Northwest Lab., Richland, WA (United States)

    1995-08-01

    The phase stability and sintering behavior of materials used in SOFCs has been evaluated. The sintering behavior of Ca and Sr doped lanthanum. manganite (the preferred SOFC cathode material) is highly dependent on the relative proportion of A and B site cations in the material. Ca and Sr doped lanthanum chromite (the preferred interconnect material) have been shown to rapidly expand in reducing atmospheres at temperatures as low as 700{degrees}C. This expansion is due to the reduction of Cr{sup 4+} to Cr{sup 3+} in reducing environments.

  16. Aqueous solubility speciation of Cr(VI) in ferrochrome bag filter dust / Willem Petrus Johannes van Dalen

    OpenAIRE

    Van Dalen, Willem Petrus Johannes

    2015-01-01

    The production of ferrochrome (FeCr) from chromite ore is a reducing process, whereby the Cr(III) and Fe(II) in the ore are reduced to metallic chromium (Cr) and iron (Fe) in the final product. FeCr is mostly used for the production of stainless steel, which is a vital alloy in modern society. It is, however, impossible to exclude oxygen completely from all the high temperature steps during the production process and very small amounts of Cr(VI) are therefore formed, although not intended. Th...

  17. 大型不锈钢铸件粘砂及表面烧结机理研究与改进%Mechanisum and Prevention of Surface Burnning-on of Large Sized Stainness Steel Casting

    Institute of Scientific and Technical Information of China (English)

    扈广麒; 王培; 彭凡; 肖纳敏

    2011-01-01

    对采用呋喃树脂自硬铬矿砂生产高铬不锈钢水轮机叶片铸件表面易出现"釉化"涂料层、界面型砂"釉化"烧结和粘砂缺陷进行了研究,并提出了解决措施.铸件粘砂的主要原因为钢液透过涂料层渗入铬矿砂,在界面发生氧化还原反应,将铬铁矿砂的铁还原出来,还原出的铁和砂粒形成致密混合物,并附着在铸件表面形成"釉化"烧结层.还原出的铁和铬渣以及砂粒中的未反应物,形成了致密的机械混合物,和铸件金属直接相连,附着在铸件的表面,形成粘砂.锆英粉涂料本身也和高铬钢发生微弱的化学反应.用新型添加剂及复合涂料改进型砂和替代锆英粉涂料,提高了钢液和铬矿砂界面涂料层的致密度、化学稳定性和耐火性,可以有效地解决这类问题.%Some defects such as coating glazing, interface sand glazing and sintering and sand fusion always appear on surface of cast high-chromium stainless steel hydraulic turbine blade castings when using furan resin chromite sand. The main reason for these defects is the infiltration of liquid steel through the coating to chromite and the redox reaction took place which reduces iron out of chromite sand. First, the iron and sand are mixed together and become dense mixture, and then iron, sand and the un-reacted material in sand are mixed together to form dense mechanical mixtures attached to the surface of casting causing the sand burning. Second, a weak chemical reaction occurs between zircon powder coating and the high-chromium steel. According to the analyses, the powder coating with higher chemical stability and fire resistance was chosen instead of zircon powder coating. Additionally, the corundum powder coating can improve the coasting density at the interface of the molten steel and chromite sand. And this method is useful for solving such kind of problems.

  18. Development of transition metal oxide catalysts for treatment of off-gases released during pyrolysis of organic ion exchange resins

    International Nuclear Information System (INIS)

    The spent IX resin wastes arising from nuclear power plants have high radiation level due to fission product 137Cesium and activation product 60Cobalt. The pyrolysis and oxidative pyrolysis processes have potential to minimize final waste form volumes of these wastes. The major difficulty in deploying these processes for treatment of spent IX resins is release of off-gases containing large quantities of aromatic hydrocarbons, amines, sulphur dioxide, hydrogen sulphide, carbonyl sulphide etc. As an alternative to high temperature incineration of the pyrolysis off gases, feasibility of using catalytic combustion at moderate temperatures was investigated in the laboratory. Copper chromite, copper oxide-ceric oxide and vanadium pentaoxide catalysts supported on alumina were prepared and tested for oxidation of styrene monomer, toluene, ethyl benzene and trimethyl amine at 22500 hr-1 space velocity and temperature range of 300 to 500 degC. At temperatures over 475 degC, all three catatyst gave oxidation efficiency of over 97% for these compounds over concentration range of few tens of ppm to few thousands ppm. A composite catalyst bed of three catalysts comprising principally of copper chromite is proposed for treatment of IX resin pyrolysis off-gases. (author)

  19. Characterization of corrosion scale formed on stainless steel delivery pipe for reclaimed water treatment.

    Science.gov (United States)

    Cui, Yong; Liu, Shuming; Smith, Kate; Yu, Kanghua; Hu, Hongying; Jiang, Wei; Li, Yuhong

    2016-01-01

    To reveal corrosion behavior of stainless steel delivery pipe used in reclaimed water treatment, this research focused on the morphological, mineralogical and chemical characteristics of stainless steel corrosion scale and corroded passive film. Corrosion scale and coupon samples were taken from a type 304 pipe delivering reclaimed water to a clear well in service for more than 12 years. Stainless steel corrosion scales and four representative pipe coupons were investigated using mineralogy and material science research methods. The results showed corrosion scale was predominantly composed of goethite, lepidocrocite, hematite, magnetite, ferrous oxide, siderite, chrome green and chromite, the same as that of corroded pipe coupons. Hence, corrosion scale can be identified as podiform chromite deposit. The loss of chromium in passive film is a critical phenomenon when stainless steel passive film is damaged by localized corrosion. This may provide key insights toward improving a better comprehension of the formation of stainless steel corrosion scale and the process of localized corrosion. The localized corrosion behavior of stainless steel is directly connected with reclaimed water quality parameters such as residual chlorine, DO, Cl(-) and SO4(2-). In particular, when a certain amount of residual chlorine in reclaimed water is present as an oxidant, ferric iron is the main chemical state of iron minerals.

  20. Structural characterization and electron density distribution studies of (La0.8Ca0.2)(Cr0.9-xCo0.1Mnx)O3

    Science.gov (United States)

    Saravanan, R.; Thenmozhi, N.; Fu, Yen-Pei

    2016-07-01

    The doped lanthanum chromite (La0.8Ca0.2)(Cr0.9-xCo0.1Mnx)O3 (x=0.03, 0.06, 0.09 and 0.12) were synthesized by solid state reaction technique. The samples have been characterized by X-ray diffraction for structural and charge density analysis. XRD data show that the grown samples are orthorhombic in structure with single phase. The spatial charge density distribution in the unit cell for the synthesized samples has been studied using maximum entropy method. Further, the samples were analyzed by UV-visible spectrometry for optical properties and scanning electron microscopy for surface morphology. From the optical data, it was found that the direct band gap of the samples range from 2.27 to 2.46 eV. The samples were also investigated by vibrating sample magnetometry for magnetic properties. From VSM data, it is inferred that all the samples in this series are found to be predominantly antiferromagnetic in nature. Since the doped lanthanum chromites have good mechanical properties and electrical conductivity at high temperature, these materials are used in solid oxide fuel cells (SOFC).

  1. Novel Approaches to the Production of Higher Alcohols From Synthesis Gas. Quarterly report, January 1 - March 31, 1996

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, George W

    1997-02-13

    Effort during this quarter was devoted to three areas: 1) analyzing the data from earlier runs with "zinc chromite"catalyst and three different slurry liquids: decahydronaphthalene (Decalin®, DHN), tetrahydronaphthalene (tetralin, THN) and tetrahydroquinoline (THQ); 2) analyzing newly-obtained data from earlier thermal stability tests on DHN and THN, and 3) carrying out a thermal stability test on THQ. Both the activity and selectivity of "zinc chromite" catalyst depended on the slurry liquid that was used. The catalyst activity for methanol synthesis was in the order: THQ > DHN > THN. Despite the basic nature of THQ, it exhibited the highest dimethyl ether (DME) production rates of the three liquids. Gas chromatography/mass spectroscopy (GC/MS) analyses of samples of THN and DHN were taken at the end of standard thermal stability tests at 375°C. With both liquids, the only measurable compositional change was a minor amount of isomerization. Analysis of a sample of THN after a thermal stability test at 425°C showed a small reduction in molecular weight, and a significant amount of opening of the naphthenic ring. Preliminary data from the tehrmal stability test of THQ showed that this molecule is more stable than DHN, but less stable than THN.

  2. Effects of different casting mould cooling rates on microstructure and properties of sand-cast Al-7.5Si-4Cu alloy

    Directory of Open Access Journals (Sweden)

    Liu Guanglei

    2013-11-01

    Full Text Available In this work, Al-7.5Si-4Cu alloy melt modified by Al-10Sr, RE and Al-5Ti-B master alloys was poured into multi-step moulds made from three moulding sands, including quartz, alumina and chromite, to investigate comparatively the effects of different cooling rates of the casting mould on the alloy's microstructures and mechanical properties. The results show that with an increase in wall thickness, the cooling rate decreases, the dendrite arm spacing (DAS increases significantly and the mechanical properties decrease steadily. The elongation is more sensitive to the cooling rate than the tensile strength. No obvious trend of the effect of wall thickness on hardness of the alloy was found. When the cooling rate is at its greatest, the microstructures and mechanical properties are the best when using chromite sand. The improvement of the properties is mainly attributed to the decrease of the DAS, the grain refinement and the metamorphic effect. Each of the three has a strong impact on the microstructures. Furthermore, a series of fitting models was established based on the data of the DAS to predict the mechanical properties of the multivariate sand-cast Al-7.5Si-4Cu alloy.

  3. Deep PIXE: finding diamonds with the proton microprobe

    International Nuclear Information System (INIS)

    Since 1987 the CSIRO Div. of Exploration Geoscience has carried out a program of proton-microprobe (PIXE) analysis aimed at using trace-element data on indicator minerals to discriminate between those from diamondiferous and barren source rocks. The results have provided both important new tools for the exploration industry, and significant new information on the conditions and processes of diamond growth. Cr-pyrope garnet has been used as Ni thermometer while chromites, in partcular their Zn content, has allowed correlation of chromite composition with temperature. The two techniques described provide a significant increase in exploration efficiency, through early recognition and rejection of barren targets and concentration of resources on more promising targets. They also provide direct cost savings in evaluation of ore bodies once they are found. It is estimated that evaluation of a prospect by conventional bulk testing is expensive ($100-500K) and time-consuming; an evaluation by PIXE methods is done quickly for a tiny fraction of that cost. 1 refs., 4 figs

  4. Cosmic-ray exposure ages of fossil micrometeorites from mid-Ordovician sediments at Lynna River, Russia

    CERN Document Server

    Meier, Matthias M M; Lindskog, Anders; Maden, Colin; Wieler, Rainer

    2014-01-01

    We measured the He and Ne concentrations of 50 individual extraterrestrial chromite grains recovered from mid-Ordovician (lower Darriwilian) sediments from the Lynna River section near St. Petersburg, Russia. High concentrations of solar wind-like He and Ne found in most grains indicate that they were delivered to Earth as micrometeoritic dust, while their abundance, stratigraphic position and major element composition indicate an origin related to the L chondrite parent body (LCPB) break-up event, 470 Ma ago. Compared to sediment-dispersed extraterrestrial chromite (SEC) grains extracted from coeval sediments at other localities, the grains from Lynna River are both highly concentrated and well preserved. As in previous work, in most grains from Lynna River, high concentrations of solar wind-derived He and Ne impede a clear quantification of cosmic-ray produced He and Ne. However, we have found several SEC grains poor in solar wind Ne, showing a resolvable contribution of cosmogenic 21Ne. This makes it possi...

  5. Effects of CaO, MgO, Al2O3 and SiO2 on the carbothermic reduction of synthetic FeCr2O4

    Directory of Open Access Journals (Sweden)

    Wang Y.

    2015-01-01

    Full Text Available In order to optimize the current reduction process of chromite, a good knowledge of reduction mechanism involved is required. The basic component in chromite ore is FeCr2O4 with gangue component like MgO and Al2O3. In lack of clear and consistent explanation about the effect of addition on the reduction of FeCr2O4, investigation of synthetic FeCr2O4 with different kind and amount of additions was carried out at 1673K under isothermal mode. Kinetic mechanism was also studied by linear fitting of different kinetic equations. Combined with rate-controlling step, it could be concluded as follows. CaO could enhance the reduction because Ca2+ would replace Fe2+, thus facilitated the ion diffusion in solid phase. Al2O3 had a positive influence as well, since Al3+ could form a solid solution phase with Cr3+ and made Cr3+ reduced more easily. MgO would hinder the reduction due to formation of a more stable phase MgCr2O4. SiO2 would also hamper the Cr metallization because there was a liquid phase formed when Cr3+ was reduced to divalent, which would impede the nucleation of reduction product.

  6. Elemental analysis by nuclear reactions in selected mineral assemblages

    International Nuclear Information System (INIS)

    The sensitivity of proton induced X-ray emission (PIXE) as a multi-elemental analytical technique for application in geochemical studies has been investigated. The contribution and unique features of PIXE as compared with other well-established analytical techniques is discussed. One such contribution is the analysis of minute (few microgram) grains of separated mineral phases, where these have a low frequency of occurence on the one hand, and / or require meticulous separation or collection on the other hand, or if variations in composition from grain to grain are meaningful. Mineral separates used in the investigation were selected specifically for their significance in geochemical studies related to the mineralisation of the Witwatersrand goldbearing system. These include gold, zircon and chromite. The success of PIXE in the analysis of gold, zircon, chromite and diamond samples is discussed. Comparisons are made of single grain and bulk (many grain) sample analyses and of PIXE measurements on such samples with instrumental activation analysis (INAA). The contribution of such analysis to the study of the evolution of the Witwatersrand system is discussed. The specific features of PIXE were exploited in a search for superheavy elements. A monazite sample from Malaysia was investigated for the occurrence of the element Z = 126. An upper limit of 110 plus minus 33 ppm for the possible concentration of this superheavy element in monazite is deduced

  7. Ophiolitic Chromitites from the Andriamena Greenstone Belt, Madagascar: Possible Evidence for mid-Archean Plate Tectonics

    Science.gov (United States)

    Reisberg, L. C.; Ohnenstetter, M.; Zimmermann, C.; Ratefiarimino, A.; Levy, D.

    2015-12-01

    Determining the time of the onset of plate tectonics is critical to understanding the geodynamic processes that controlled the evolution of the early Earth. The near absence of Archean ophiolites, as defined by the presence of a residual ultramafic section, has been considered to be one of the primary arguments against Archean plate tectonics. The Andriamena greenstone belt of Madagascar contains massive chromitite bodies consisting of about 90% chromite and about 10% gangue minerals, mostly secondary (talc, green amphibole, orthopyroxene, Ca and Mg carbonate). Numerous observations argue in favor of an ophiolitic origin for these chromitites, including the high Cr# (0.67-0.74), coupled with relatively high Mg# (0.6-0.78) of the constituent chromite. In addition, these phases display extremely low TiO2 contents (clustered, with 187Os/188Os ranging from 0.1057 to 0.1059, corresponding to TRD model ages of ~ 3.2 Ga, assuming primitive upper mantle parameters. 186Os/188Os measurements are in progress. If the ophiolitic nature of the chromitites is confirmed, our results might imply that geodynamic mechanisms similar to present-day plate tectonic processes may already have been active in the mid-Archean Earth.

  8. Experimental constraints on the formation of the Tibetan podiform chromitites

    Science.gov (United States)

    Wu, Yao; Xu, Mengjing; Jin, Zhenmin; Fei, Yingwei; Robinson, Paul T.

    2016-02-01

    The discovery of diamonds and highly reduced minerals in podiform chromitites, which have generally been interpreted as magmatic rocks formed from partial melts of upper mantle peridotites under low-pressure conditions, has raised many questions about the origin of these enigmatic bodies. In order to provide experimental constraints on the formation and emplacement of podiform chromititesin ophiolites, we carried out a number of multi-anvil experiments in the magnesiochromite + SiO2 system at temperatures of 1000-1600 °C and pressures of 5-15 GPa. The experimental results demonstrate that magnesiochromite is stable up to 14 GPa and decomposed into eskolaite (Cr2O3) together with a quenchable modified ludwigite-structured phase [(Fe, Mg)2(Al, Cr)2O5] at higher pressures, thus placing an approximate maximum depth for chromite crystallization and/or metamorphism. This depth corresponds to the top of the mantle transition zone (MTZ) at 410 km. The ludwigite-structured post-chromite phase has significant implications for understanding phase transformations and Cr incorporation/partitioning of minerals in the MTZ. On the basis of our results, we propose a multi-stage model for the formation of podiform chromitites that incorporates the geochemical, textural and mineralogical features of these bodies.

  9. Fabrication of nanospinel ZnCr2O4 using sol-gel method and its application on removal of azo dye from aqueous solution

    International Nuclear Information System (INIS)

    For the first time, nanoparticles of zinc chromite, spinel ZnCr2O4 have been fabricated by the thermal decomposition of Zn-Cr gel prepared by sol-gel method in the presence of oxalic acid as a chelating agent. It was shown that the well-crystallized spinel structure is formed after calcination at 450 deg. C. The nanospinel has been characterized by differential thermal analysis (DTA), X-ray powder diffraction (XRD), infrared spectroscopy (IR), and transmission electron microscope (TEM). The average particle size is approximately 13 nm according to the TEM image. The nanoparticles of zinc chromites showed excellent adsorption properties towards reactive dye, reactive blue 5 (RB5). The adsorption studies have been carried out for contact time, different pH values, different temperatures, and adsorbent doses. The investigation of removal kinetics of RB5 indicates that the removal process obeys the rate of second-order kinetic equation. The results indicate that the Langmuir adsorption isotherm fitted the data better than the Freundlich. Also, the photocatalytic degradation of RB5 using spinel ZnCr2O4 under UV irradiation at pH = 1 has been also examined. The results showed that the degradation of RB5 dye follows merely an adsorption process.

  10. Feature level fusion for enhanced geological mapping of ophiolile complex using ASTER and Landsat TM data

    International Nuclear Information System (INIS)

    Chromite ore deposit occurrence is related to ophiolite complexes as a part of the oceanic crust and provides a good opportunity for lithological mapping using remote sensing data. The main contribution of this paper is a novel approaches to discriminate different rock units associated with ophiolite complex using the Feature Level Fusion technique on ASTER and Landsat TM satellite data at regional scale. In addition this study has applied spectral transform approaches, consisting of Spectral Angle Mapper (SAM) to distinguish the concentration of high-potential areas of chromite and also for determining the boundary between different rock units. Results indicated both approaches show superior outputs compared to other methods and can produce a geological map for ophiolite complex rock units in the arid and the semi-arid region. The novel technique including feature level fusion and Spectral Angle Mapper (SAM) discriminated ophiolitic rock units and produced detailed geological maps of the study area. As a case study, Sikhoran ophiolite complex located in SE, Iran has been selected for image processing techniques. In conclusion, a suitable approach for lithological mapping of ophiolite complexes is demonstrated, this technique contributes meaningfully towards economic geology in terms of identifying new prospects

  11. Using Vanadium in Spinel as a Sensor of Oxygen Fugacity in Meteorites: Applications to Mars, Vesta, and Other Asteroids

    Science.gov (United States)

    Righter, K.; Sutton, S.; Danielson, L.; Le, L.; Newville, M.; Pando, K.

    2009-01-01

    Igneous and metamorphic rocks commonly contain a mineral assemblage that allows oxygen fugacity to be calculated or constrained such as FeTi oxides, olivine-opx-spinel, or some other oxybarometer [1]. Some rocks, however, contain a limited mineral assemblage and do not provide constraints on fO2 using mineral equilibria. Good examples of the latter are orthopyroxenites or dunites, such as diogenites, ALH 84001, chassignites, or brachinites. In fact it is no surprise that the fO2 of many of these samples is not well known, other than being "reduced" and below the metal saturation value. In order to bridge this gap in our understanding, we have initiated a study of V in chromites in natural meteorite samples. Because the V pre-edge peak intensity and energy in chromites varies with fO2 (Fig. 1) [2], and this has been calibrated over a large fO 2 range, we can apply this relation to rocks for which we otherwise have no fO2 constraints.

  12. Spinel-bearing, Al-rich chondrules in two chondrite finds from Roosevelt County, New Mexico - Indicators of nebular and parent body processes

    Science.gov (United States)

    Mccoy, Timothy J.; Pun, Aurora; Keil, Klaus

    1991-01-01

    Two rare spinel-bearing Al-rich chondrules are identified in chondrite finds from Roosevelt County, New Mexico-RC 071 (L4) and RC 072 (L5). These chondrules have unusual mineralogies dominated by highly and asymmetrically zoned Al-Cr-rich spinels. Two alternatives exist to explain the origin of this zoning-fractional crystallization or metamorphism. Fractional crystallization formed the zoning of the trivalent cations and caused a localized depletion in chromites around the large Al-Cr-rich spinels. Diffusive exchange and partitioning of Fe and Mg between olivine and spinel during parent-body metamorphism can explain the asymmetric zoning of these elements. The bulk compositions of the chondrules suggest affinities with the Na-Al-Cr-rich chondrules, as would be expected from the abundance of Al-Cr-rich spinels. The most important factors are the temperature to which the molten chondrule was heated and the cooling rate during crystallization. These two chondrules cooled rapidly from near the liquidus, as indicated by the zoning, occurrence and sizes of spinels, radiating chondrule textures and localized chromite depletions.

  13. Thermodynamic Modelling of Fe-Cr-Ni-Spinel Formation at the Light-Water Reactor Conditions

    Energy Technology Data Exchange (ETDEWEB)

    Kurepin, V.A.; Kulik, D.A.; Hitpold, A.; Nicolet, M

    2002-03-01

    In the light water reactors (LWR), the neutron activation and transport of corrosion products is of concern in the context of minimizing the radiation doses received by the personnel during maintenance works. A practically useful model for transport and deposition of the stainless steel corrosion products in LWR can only be based on an improved understanding of chemical processes, in particular, on the attainment of equilibrium in this hydrothermal system, which can be described by means of a thermodynamic solid-solution -aqueous-solution (SSAS) model. In this contribution, a new thermodynamic model for a Fe-Cr-Ni multi-component spinel solid solutions was developed that considers thermodynamic consequences of cation interactions in both spinel sub-Iattices. The obtained standard thermodynamic properties of two ferrite and two chromite end-members and their mixing parameters at 90 bar pressure and 290 *c temperature predict a large miscibility gap between (Fe,Ni) chromite and (Fe,Ni) ferrite phases. Together with the SUPCRT92-98 thermo- dynamic database for aqueous species, the 'spinel' thermodynamic dataset was applied to modeling oxidation of austenitic stainless steel in hydrothermal water at 290*C and 90 bar using the Gibbs energy minimization (GEM) algorithm, implemented in the GEMS-PSI code. Firstly, the equilibrium compositions of steel oxidation products were modelIed as function of oxygen fugacity .fO{sub 2} by incremental additions of O{sub 2} in H{sub 2}O-free system Cr-Fe- Ni-O. Secondly, oxidation of corrosion products in the Fe-Cr-Ni-O-H aquatic system was modelIed at different initial solid/water ratios. It is demonstrated that in the transition region from hydrogen regime to oxygen regime, the most significant changes in composition of two spinel-oxide phases (chromite and ferrite) and hematite must take place. Under more reduced conditions, the Fe-rich ferrite (magnetite) and Ni-poor chromite phases co-exist at equilibrium with a metal Ni

  14. Generalized corrosion of nickel base alloys in high temperature aqueous media: a contribution to the comprehension of the mechanisms; Corrosion generalisee des alliages a base nickel en milieu aqueux a haute temperature: apport a la comprehension des mecanismes

    Energy Technology Data Exchange (ETDEWEB)

    Marchetti-Sillans, L

    2007-11-15

    In France, nickel base alloys, such as alloy 600 and alloy 690, are the materials constituting steam generators (SG) tubes of pressurized water reactors (PWR). The generalized corrosion resulting from the interaction between these alloys and the PWR primary media leads, on the one hand, to the formation of a thin protective oxide scale ({approx} 10 nm), and on the other hand, to the release of cations in the primary circuit, which entails an increase of the global radioactivity of this circuit. The goal of this work is to supply some new comprehension elements about nickel base alloys corrosion phenomena in PWR primary media, taking up with underlining the effects of metallurgical and physico-chemical parameters on the nature and the growth mechanisms of the protective oxide scale. In this context, the passive film formed during the exposition of alloys 600, 690 and Ni-30Cr, in conditions simulating the PWR primary media, has been analyzed by a set of characterization techniques (SEM, TEM, PEC and MPEC, XPS). The coupling of these methods leads to a fine description, in terms of nature and structure, of the multilayered oxide forming during the exposition of nickel base alloys in primary media. Thus, the protective part of the oxide scale is composed of a continuous layer of iron and nickel mixed chromite, and Cr{sub 2}O{sub 3} nodules dispersed at the alloy / mixed chromite interface. The study of protective scale growth mechanisms by tracers and markers experiments reveals that the formation of the mixed chromite is the consequence of an anionic mechanism, resulting from short circuits like grain boundaries diffusion. Besides, the impact of alloy surface defects has also been studied, underlining a double effect of this parameter, which influences the short circuits diffusion density in oxide and the formation rate of Cr{sub 2}O{sub 3} nodules. The sum of these results leads to suggest a description of the nickel base alloys corrosion mechanisms in PWR primary

  15. Provenance of the Lower Paleozoic Balcarce Formation (Tandilia System, Buenos Aires Province, Argentina): Implications for paleogeographic reconstructions of SW Gondwana

    Science.gov (United States)

    Zimmermann, Udo; Spalletti, Luis A.

    2009-07-01

    Lower Paleozoic moderately sorted quartz-arenites from the Balcarce Formation deposited in eastern Argentina (Tandilia System) comprise mainly detrital material derived from old upper crustal material. The sources were magmatic, sedimentary, and subordinated felsic metamorphic terranes. High concentrations of tourmaline and Ti-rich heavy minerals, including zircon and nearly euhedral chromite, are common. Trace element concentrations (Nb, Cr) on rutile indicate pelitic and metabasaltic sources, respectively. Major element analyses on chromites indicate a basic volcanic protolith of mid-oceanic ridge origin, which was exposed close to the depositional basin. The delivery of chromite may be associated with convergent tectonics causing the consumption and obduction of oceanic crust during pre-Upper Ordovician times. The oblique/orthogonal collision of the Precordillera Terrane with the western border of the Rio de la Plata Craton, west of the Balcarce Basin or source further to the east from a Lower Palaeozoic extensional basin are possibilities. Geochemical and petrographic data exclude the underlying Precambrian and Cambrian sedimentary rocks as dominant sources, and favour the basement of the Río de La Plata Craton, including Cambrian rift-related granites of South Africa and the Sierras Australes (eastern Argentina), as main suppliers of detritus. Trace element geochemistry of recycled pyroclastic material, associated with the quartz-arenites, also suggests volcanic arc sources. The provenance of the pyroclastic material may either be the Puna-Famatina arc, located in north and central Argentina, or a hypothetical active margin further to the south. These ash layers are equivalent in age to volcanic zircons found in the Devonian Bokkeveld Group in western South Africa. The deposition of a glacial diamictite of Hirnantian age (Sierra del Volcán Diamictite) is interpreted as a member of the Balcarce Formation. Based on the stratigraphic re-location of the glacial

  16. Zinc Treatment Effects on Corrosion Behavior of Alloy 600 in High Temperature, Hydrogenated Water

    International Nuclear Information System (INIS)

    Trace levels of soluble zinc(II) ions (30 ppb) maintained in mildly alkaline, hydrogenated water at 260 C were found to reduce the corrosion rate of Alloy 600 (UNS N06600) by about 40% relative to a non-zinc baseline test [2]. Characterizations of the corrosion oxide layer via SEM/TEM and grazing incidence X-ray diffraction confirmed the presence of a chromite-rich oxide phase and recrystallized nickel. The oxide crystals had an approximate surface density of 3500 (micro)m-2 and an average size of 11 ± 5 nm. Application of X-ray photoelectron spectroscopy with argon ion milling, followed by target factor analyses, permitted speciated composition vs. depth profiles to be obtained. Numerical integration of the profiles revealed that: (1) alloy oxidation occurred non-selectively and (2) zinc(II) ions were incorporated into the chromite-rich spinel: (Zn0.55Ni0.3Fe0.15)(Fe0.25Cr0.75)2O4. Spinel stoichiometry places the trivalent ion composition in the single phase oxide region, consistent with the absence of the usual outer, ferrite-rich solvus layer. By comparison with compositions of the chromite-rich spinel obtained in the non-zinc baseline test, it is hypothesized that zinc(II) ion incorporation was controlled by the equilibrium for 0.55 Zn2+(aq) + (Ni0.7Fe0.3)(Fe0.3Cr0.7)2O4(s) (requilibrium) 0.40 Ni2+(aq) + 0.15 Fe2+(aq) + (Zn0.55Ni0.3Fe0.15)(Fe0.3Cr0.7)2O4(s). It is estimated that only 8% of the Ni(II) ions generated during non-selective oxidation of the alloy were retained as Ni(II) in the corrosion layer; the remainder either recrystallized to Ni(0) (38%) or were released to the aqueous phase (54%)

  17. Generalized corrosion of nickel base alloys in high temperature aqueous media: a contribution to the comprehension of the mechanisms

    International Nuclear Information System (INIS)

    In France, nickel base alloys, such as alloy 600 and alloy 690, are the materials constituting steam generators (SG) tubes of pressurized water reactors (PWR). The generalized corrosion resulting from the interaction between these alloys and the PWR primary media leads, on the one hand, to the formation of a thin protective oxide scale (∼ 10 nm), and on the other hand, to the release of cations in the primary circuit, which entails an increase of the global radioactivity of this circuit. The goal of this work is to supply some new comprehension elements about nickel base alloys corrosion phenomena in PWR primary media, taking up with underlining the effects of metallurgical and physico-chemical parameters on the nature and the growth mechanisms of the protective oxide scale. In this context, the passive film formed during the exposition of alloys 600, 690 and Ni-30Cr, in conditions simulating the PWR primary media, has been analyzed by a set of characterization techniques (SEM, TEM, PEC and MPEC, XPS). The coupling of these methods leads to a fine description, in terms of nature and structure, of the multilayered oxide forming during the exposition of nickel base alloys in primary media. Thus, the protective part of the oxide scale is composed of a continuous layer of iron and nickel mixed chromite, and Cr2O3 nodules dispersed at the alloy / mixed chromite interface. The study of protective scale growth mechanisms by tracers and markers experiments reveals that the formation of the mixed chromite is the consequence of an anionic mechanism, resulting from short circuits like grain boundaries diffusion. Besides, the impact of alloy surface defects has also been studied, underlining a double effect of this parameter, which influences the short circuits diffusion density in oxide and the formation rate of Cr2O3 nodules. The sum of these results leads to suggest a description of the nickel base alloys corrosion mechanisms in PWR primary media and to tackle some

  18. Formational history of lunar rocks - Applications of experimental geochemistry of the opaque minerals

    Science.gov (United States)

    Taylor, L. A.; Williams, K. L.

    1974-01-01

    Experimental data on the cooling histories of lunar rocks are presented along with a descriptive mineralogy of certain opaque minerals in Apollo 17 samples. Lunar rocks having Zr partitionings of coexisting ilmenite and ulvospinel indicative of high-temperature equilibrium (above 1000 C) appear to have cooled rapidly to temperatures below 800-900 C. The Ti content of troilite coexisting with ilmenite can be used to differentiate rock fragments which are mineralogically and texturally similar. It is found that Cr and Mg partitionings between coexisting armalcolite and ilmenite vary notably between rocks so that they can be used to distinguish otherwise similar samples. The spinels are analyzed as varieties of chromian ulvospinel and titanian chromite.

  19. The Porgera gold deposit, Papua, New Guinea, 1: association with alkalic magmatism in a continent-island-arc collision zone

    International Nuclear Information System (INIS)

    The meso thermal to epithermal Porgera gold deposit is spatially and temporally associated with shallow level (≤ 2 km emplacement depth) stocks and dykes of the Porgera Intrusive Complex (PIC). Gold mineralization immediately followed emplacement of the PIC, and is dated between 5 and 6 Ma ago. The Porgera intrusive suite is comprised of fine- to medium-grained, porphyritic to euhedral granular, volatile-rich, sodic alkali basalts/gabbros, hawaiites, and mugearites (TAS chemical classification scheme). The rocks display chemical and isotopic characteristics similar to those of intra plate alkalic basalts, but their unusually high volatile contents result in stabilization of hornblende as a phenocryst and intergranular phase in more evolved rock types. The observed order of cotectic crystallization is olivine - clinopyroxene - hornblende -plagioclase, with ubiquitous spinel (chromite/magnetite) and fluor-apatite. (author)

  20. ACr{sub 2}O{sub 4} /SiO{sub 2} (A = Zn, Cu, Cd) nanocomposites, their preparation and physical properties

    Energy Technology Data Exchange (ETDEWEB)

    Holec, Petr; Plocek, Jiri; Nemec, Ivan [Institute of Inorganic Chemistry, Academy of Sciences of the CR, 250 68 - Rez (Czech Republic); Vejpravova, Jana Poltierova [Charles University Prague, Faculty of Mathematics and Physics, Department of Condensed Matter Physics, Ke Karlovu 5, 121 16 - Prague 2 (Czech Republic); Kitazawa, Hideaki [National Institute for Material, Quantum Beam Center, Neutron Scattering Group, 1-2-2 Sengen, Tsukuba-shi, Ibaraki 305-0047 (Japan); Niznansky, Daniel, E-mail: holec@iic.cas.cz [Charles University Prague, Faculty of Sciences, Department of Inorganic Chemistry, Hlavova 2, 121 16 - Prague 2 (Czech Republic)

    2011-10-29

    This article presents preparation and characterization of zinc, copper and cadmium chromites nanocrystals embedded in a silica matrix. The ZnCr{sub 2}O{sub 4}/SiO{sub 2}, CuCr{sub 2}O{sub 4}/SiO{sub 2} and CdCr{sub 2}O{sub 4}/SiO{sub 2} samples were prepared by a conventional sol-gel method using HNO{sub 3} as an acid catalyst, formamide as a modifier, methanol as a solvent and TEOS. Final heat treatment of the nanocomposites was carried out at temperatures in the range of 900 - 1100 deg. C. The resulting samples were characterized by X-ray diffraction, High Resolution Transmission Electron Microscopy, and magnetic measurements.

  1. Constitutional diagram of Fe-Cr-O system at temperatures of 900-1300 deg C

    International Nuclear Information System (INIS)

    Based on available data about thermodynamic properties of Fe-Cr-O system components isothermal state diagrams are built for the system at 1000, 1100, 1200 and 1300 deg C. The calculated conditions of monovariant equilibria in the Fe-Cr-O system, the conditions of equilibrium of chromium-substituted wustite with iron chromite and magnetite solid solution as well as equilibrium conditions for the varying composition spinel with the Fe3O3-Cr2O3 solution are taken into consideration when plotting the diagrams. It is noted that at any temperature within the range of 900-1300 deg C the form of the isothermal section of the Fe-Cr-O system state diagram is similar to that for 1300 deg C

  2. New possibilities of chemical concentration in activation analysis of some noble and rare metals

    International Nuclear Information System (INIS)

    The possibility of concentrating Pt, Ir, Au, Ag, Re and some other elements from samples of chromites, sulfide ores, laterites, shales, titanium magnetites, and ultrabasic rocks was studied. A new simple procedure is based on sublimation of elements to be determined in air stream at 1200 deg C in the presence of some powdered reagents (e.g., TiO2, Nb2O5, Nb) to enhance the yield, and on the use of chemical filters (CaO, MgO, TiO2, Al2O3, Nb2O5) absorbing the interfering volatile elements from the gas phase. Methods of neutron activation and X-ray fluorescence isotopic excitation were used to analyze the obtained concentrates

  3. Influence of the sintering temperature on the structural and electronic properties of LaCrO{sub 3} doped with barium; Influencia da temperatura de sinterizacao nas propriedades estruturais e eletronicas de LaCrO{sub 3} dopadas com bario

    Energy Technology Data Exchange (ETDEWEB)

    Silva, A.L.A. da; Souza, M.V.M.M., E-mail: adneybr@yahoo.com.b [Universidade Federal do Rio de Janeiro (LabTecH/EQ/UFRJ), RJ (Brazil). Escola de Quimica. Lab. de Tecnologias do Hidrogenio; Rocco, A.M. [Universidade Federal do Rio de Janeiro (GMCE/EQ/UFRJ), RJ (Brazil). Escola de Quimica. Grupo de Materiais Condutores e Energia

    2010-07-01

    Ba-doped lanthanum chromites were synthesized by combustion method, utilizing urea and glycine as fuel agents. The powders were calcined (800 deg C/6 h), pelletized, sintered in various temperatures and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), density/porosity and electrical conductivity. The diffractograms of the sintered samples presented a well-defined structure, with presence of secondary phases which increase with the sintering temperature. The samples presented low densities and a high porosities (40 - 50%), which was also observed in SEM analysis. The urea-synthesized sample presented a higher conductivity (10.4 S/cm at 1000 deg C), which is related to the influence of the fuel agent in the material properties. (author)

  4. Evaluation of electromagnetic absorbing capacity of materials in foundry industry

    Directory of Open Access Journals (Sweden)

    D. Nowak

    2010-01-01

    Full Text Available In the paper, a research on determining the standing wave ratio as a measure of electromagnetic absorbing capacity of moulding materials is presented. Preliminary tests performed using a microwave strip line showed that high-silica, chromite and magnesite moulding sands are characterised by low absorbing capacity of microwaves. It was demonstrated that microwave absorbing capacity is significantly affected by chemical compounds included in the examined substrates. It was found that use of a microwave strip line permits precise determining characteristic microwave absorbing capacities of various moulding materials and thus their suitability for microwave drying/hardening of moulds and cores or for other foundry processes. Such a microwave drier can be applied for identifying mass components and for determining e.g. base granularity by means of precisely determined reflection ratios |Γ| and positions of minimum signal values.

  5. Catalytic surface promotion of highly active La0.85Sr0.15Cr0.8Ni0.2O3-δ anodes for La5.6WO11.4-δ based proton conducting fuel cells

    DEFF Research Database (Denmark)

    Solis, C.; Balaguer, M.; Bozza, Francesco;

    2014-01-01

    La0.85Sr0.15CrO3-delta (LSC), La0.85Sr0.15Cr0.8Ni0.2O3-delta (LSCN) and LSCN infiltrated with Ni nanoparticles were tested as anodes for symmetrical cells based on La5.6WO11.4-delta (LWO) protonic electrolyte. These chromite-based electrode materials are compatible with LWO material, in contrast...... in proton conducing anodes and the electrode performance is substantially improved regarding to pure LSC. Ni nanoparticle infiltration further improves the catalytic promotion of the anode, reducing the polarization resistance (R-p) previously limited by low frequency surface related processes. Indeed...

  6. The present status of mining and metallurgy in Iran

    Energy Technology Data Exchange (ETDEWEB)

    Najin, K.

    1988-09-01

    This article gives an overview of the mining and metallurgy industries in Iran. Iran's mineral products include petroleum, coal, iron ore, copper, lead and zinc, chromite, antimony, uranium, borax, barytes, kaoline and building stones. In 1986, Iran's coal production was about 1.3 Mt, virtually all mined by the National Iranian Steel Co. (NISC), the operator of the sole steel plant at Esfahan. Coal is made into metallurgical coke for two blast furnaces. To improve the quality of local coal some 200,000 t of higher quality coal was imported from the FRG and Australia. About 60% of local coal comes from the Kerman basin and 40% from mines in the Alborz range.

  7. Novel Approaches to the Production of Higher Alcohols From Synthesis Gas. Quarterly report, January 1 - March 31, 1997

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, George W

    1998-12-11

    A modified analytical system was assembled and calibrated, in preparation for a second run with cesium (Cs)-promoted "zinc chromite" catalyst. A new column for the on-line gas chromatography (GC) was purchased for the analysis of various light olefin and paraffin isomers. A run was carried out in the continuous stirred autoclave using the Cs-promoted catalyst. Decahydronaphfialene was used as the slurry liquid. Reaction conditions were 375°C, 2000 psig total pressure, 0.5 H₂/CO ratio, and 5000 sL/Kg (cat.)-hr. Analysis of the data from this run is in progress. A manuscript on the thermal stability of potential slurry liquids was submitted to 'Industrial and Engineering Chemistry Research,' and a paper was presented at the 1997 Spring National Meeting of the American Institute of Chemical Engineers, Houston, Texas.

  8. LaCrO3 composite coatings for AISI 444 stainless steel solid oxide fuel cell interconnects

    Directory of Open Access Journals (Sweden)

    Wilson Acchar

    2012-12-01

    Full Text Available Doped lanthanum chromite-based ceramics are the most widely used interconnector material in solid fuel cells (SOFC since they exhibit significant electrical and thermal conductivity, substantial corrosion resistance and adequate mechanical strength at ambient and high temperatures. The disadvantage of this material is its high cost and poor ductility. The aim of this study is to determine the mechanical and oxidation behavior of a stainless steel (AISI 444 with a LaCrO3 deposition on its surface obtained through spray pyrolisis. Coated and pure AISI 444 materials were characterized by mechanical properties, oxidation behavior, X-ray diffraction and scanning electronic microscopy. Results indicated that the coated material displays better oxidation behavior in comparison to pure stainless steel, but no improvement in mechanical strength. Both materials indicate that deformation behavior depends on testing temperatures.

  9. Characterization of Maghsail meteorite from Oman by Moessbauer spectroscopy, X-ray diffraction and petrographic microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Al-Rawas, A. D., E-mail: arawas@squ.edu.om; Gismelseed, A. M. [College of Science, SQU, Department of Physics (Oman); Al-Kathiri, A. F. [Ministry of Commerce and Industry (Oman); Elzain, M. E.; Yousif, A. A. [College of Science, SQU, Department of Physics (Oman); Al-Kathiri, S. B. [Ministry of Commerce and Industry (Oman); Widatallah, H. M. [College of Science, SQU, Department of Physics (Oman); Abdalla, S. B. [College of Science, SQU, Department of Earth Sciences (Oman)

    2008-09-15

    The meteorite found at Maghsail (16 55 70 N-53 46 69 E) west of Salalah Oman, has been studied by {sup 57}Fe Moessbauer spectroscopy, X-diffractometry and petrographic microscopy. In the polished section the meteorite exhibits a porphyritic texture consisting of pyroxene and olivine phenocrysts in a fine to medium grained ground mass in addition to minor phases possibly skeletal chromite, troilite and minute amount of iron oxides. X-ray diffraction supports the existence of these compounds. The Moessbauer spectra of powdered material from the core of the rock at 298 K and 78 K exhibit a mixture of magnetic and paramagnetic components. The paramagnetic components are assigned to the silicate minerals olivine and pyroxene. On the other hand, the magnetic spectra reveal the presence of troilite and iron oxides. The petrographic analyses indicate that the iron oxides are terrestrial alteration products.

  10. Geochemical prospecting for copper and nickel in the Wulgai and Tor Tangi areas southeast of Hindubagh, Quetta Division, Pakistan

    Science.gov (United States)

    Stanin, S. Anthony; Wahid, M.A.; Khan, Shamsher

    1975-01-01

    Showings of magnetite, copper, and possible nickel mineralization in the Hindubagh chromite mining district are near Wulgai and Tor Tangi. Several hundred samples of clastic material from dry streambeds in these areas were sieved for the minus-80-mesh fraction and analyzed for copper using 2, 2'-biquinoline and for nickel using alpha-furildioxime. The copper threshold is 75 ppm, and the nickel threshold is 400 ppm. A geochemical map has been prepared that shows nine areas of anomalously high copper and six areas of high nickel. The nickel anomalies may represent secondary dispersion patterns derived from the erosion of nickeliferous ultramafic rocks of the Hindubagh intrusive complex. Copper showings in and near four of the anomalous copper areas indicate that detailed geological investigation and detailed geochemical sampling of rocks, soil, and unconsolidated clastic material are required to determine the source of the anomalies.

  11. Effect of Bi2O3 Additives on Properties of La0.7Ca0.3CrO3

    Institute of Scientific and Technical Information of China (English)

    Zhong Honghai; Zhou Xiaoliang; Liu Xingqin; Meng Guangyao

    2005-01-01

    Sintering characteristics of Ca-doped lanthanum chromite [La(Ca)CrO3] powder, prepared by gel-casting process were studied by measuring density and the evaluation of micro structural information. Bi2O3 is found to be an effective sintering additive for this material. The amount of Bi2O3 is altered to investigate Bi2O3 effect on the properties of La0.7Ca0.3CrO3. The amount of 10% (mass fraction) Bi2O3 is suitable to increase sinter-ability of La0.7Ca0.3CrO3. Increased concentration of point defects arising form substitution of Bi in La site is the plausible cause of enhanced sintering. Measurement of electrical conductivity and thermal expansion coefficient indicate that the doping of Bi2O3 does not have any significant effect on these properties.

  12. Conditions of diamond formation beneath the Sino-Korean craton: paragenesis, temperatures and the isotopic composition of carbon

    International Nuclear Information System (INIS)

    Mineral inclusions (23 pyrope garnets, 30 chromites) have been extracted from 28 diamonds selected from the Pipe 50 kimberlite in Liaoning Province, and the pipes of the Shengli 1 and Hongqi 6 kimberlites in Shandong province. These inclusions, and several from the collection of Meyer et al., (1994), have been analysed for major elements using EMP and for trace elements using the proton microprobe. Carbon-isotope compositions have been measured on 44 diamonds (23 from Liaoning, 21 from Shandong), of which 32 contained identified inclusions. The δ13C values range from +0.9 to -6.0 per mill; the heaviest carbon is found in stones with very low-Ca garnets. This implies that the isotopic composition of carbon in harzburgitic rocks is related to the primary depletion process, which suggests ancient formation of the diamonds

  13. Oxidative release of chromium from Archean ultramafic rocks, its transport and environmental impact – A Cr isotope perspective on the Sukinda valley ore district (Orissa, India)

    DEFF Research Database (Denmark)

    Paulukat, Cora Stefanie; Døssing, Lasse Nørbye; Mondal, Sisir K.;

    2015-01-01

    This study investigates Cr isotope fractionation during soil formation from Archean (3.1–3.3 Ga) ultramafic rocks in a chromite mining area in the southern Singhbhum Craton (Orissa, India). The Cr-isotope signatures of two studied weathering profiles, range from non-fractionated mantle values...... in controlling the hazardous impact of Cr(VI) on health and environment. The positive Cr isotope signatures of the Brahmani estuary and coastal seawater collected from the Bay of Bengal further indicate that the positively fractionated Cr isotope signal from the catchment area is preserved during its transport...... to the sea. Isotopically lighter Cr(VI) downstream from the mine is probably back-reduced to Cr(III) during riverine transport leading to similar Cr-isotope values in the estuary as observed upstream from the mine....

  14. Enhancing the hexavalent chromium bioremediation potential of Acinetobacter junii VITSUKMW2 using statistical design experiments.

    Science.gov (United States)

    Pulimi, Mrudula; Jamwal, Subika; Samuel, Jastin; Chandrasekaran, Natarajan; Mukherjee, Amitava

    2012-12-01

    The Cr(VI) removal capability of Acinetobacter junii VITSUKMW2 isolated from the Sukinda chromite mine site was evaluated and enhanced using statistical design techniques. The removal capacity was evaluated at different pH values (5-11) and temperatures (30-40 degrees C) and with various carbon and nitrogen sources. Plackett- Burman design was used to select the operational parameters for bioremediation of Cr(VI). Three parameters (molasses, yeast extract, and Cr(VI) concentration) were chosen for further optimization using central composite design. The optimal combination of parameters was found to be 14.85 g/l molasses, 4.72 g/l yeast extract, and 54 mg/l initial Cr(VI), with 99.95% removal of Cr(VI) in 12 h. A. junii VITSUKMW2 was shown to have significant potential for removal of Cr(VI).

  15. Characterization of Maghsail meteorite from Oman by Moessbauer spectroscopy, X-ray diffraction and petrographic microscopy

    International Nuclear Information System (INIS)

    The meteorite found at Maghsail (16 55 70 N-53 46 69 E) west of Salalah Oman, has been studied by 57Fe Moessbauer spectroscopy, X-diffractometry and petrographic microscopy. In the polished section the meteorite exhibits a porphyritic texture consisting of pyroxene and olivine phenocrysts in a fine to medium grained ground mass in addition to minor phases possibly skeletal chromite, troilite and minute amount of iron oxides. X-ray diffraction supports the existence of these compounds. The Moessbauer spectra of powdered material from the core of the rock at 298 K and 78 K exhibit a mixture of magnetic and paramagnetic components. The paramagnetic components are assigned to the silicate minerals olivine and pyroxene. On the other hand, the magnetic spectra reveal the presence of troilite and iron oxides. The petrographic analyses indicate that the iron oxides are terrestrial alteration products.

  16. Magnetic properties of sonochemically synthesized CoCr2O4 nanoparticles

    Science.gov (United States)

    Dutta, Dimple P.; Manjanna, J.; Tyagi, A. K.

    2009-08-01

    Cobalt chromite (CoCr2O4) is a potential multiferroic material. In order to understand the temperature dependent magnetic transitions on particle morphology, here we prepared CoCr2O4 nanoparticles by sonochemical technique. We used powder x-ray diffraction, transmission electron microscopy, selected area electron diffraction, superconducting quantum interference device magnetometer, and ac susceptibility measurement techniques for characterization. The low-temperature magnetic behavior of CoCr2O4 nanoparticles have been investigated in more detail. While the bulk CoCr2O4 exhibits two magnetic transitions viz., Tc≈98 K and Ts≈26 K, the nanoparticles here showed a Tc≈84 K and Ts≈25 K. We tentatively attribute this shift in Tc to finite size effects.

  17. Petrography and Metamorphism of the Metasedimentary Country-Rocks of the Jacurici Valley Chromitite-Hosting Mafic-Ultramafic Complexes, Bahia, Northeastern Brazil

    Directory of Open Access Journals (Sweden)

    Eliane A. Del Lama

    2001-11-01

    Full Text Available This paper deal with on the metasedimentary country-rocks of the chromite-bearing ultramafic rocks that occur in the “Jacurici River Valley Chromium District” northeastern Bahia, Brazil. This region presents a complex geologic-petrologic framework of rocks that were intensely deformed, metamorphosed and transformed by metasomatic processes, making it difficult to interpret their volutionary/metamorphic record. Although the metasedimentary country rocks have also been affected by such processes, it is possible to distinguish evidence of a previous high-grade metamorphism that affected them. Thermobarometric data for the observed mineralogical associations indicate P-T conditions around 750-800ºC and 7-8 kb for the metamorphic peak, based mainly on the presence of olivine in marbles and the cordierite-garnet-sillimanitespinel association in aluminous gneisses.

  18. Temperature-Induced Magnetization Reversal in the Mn^{3+}-Doped SmCrO3

    Science.gov (United States)

    Wu, Yuying; Xu, Jian; Xia, Zhengcai

    2016-04-01

    The temperature dependence of dc magnetization is investigated for the rare earth chromites SmCrO3 and the doped compound SmCr_{0.9}Mn_{0.1}O3. Different from the magnetization behavior of SmCrO3, temperature-induced magnetization reversals are observed in the Mn^{3+}-doped compound. Moreover, low-temperature isothermal magnetization measurement indicates the magnetic ground state of SmCr_{0.9}Mn_{0.1}O3 to be antiferromagnetic with a spin canting. The field-cooling magnetic hysteresis loop reveals that an exchange bias (EB) phenomenon is present in the sample. The reversal of magnetization and the corresponding EB field is discussed on the basis of the competitive interaction between the antiferromagnetically coupled Cr-rich clusters and Cr-Mn ordered clusters.

  19. Platinum mineralization in the Kapalagulu Intrusion, western Tanzania

    Science.gov (United States)

    Wilhelmij, Harry R.; Cabri, Louis J.

    2016-03-01

    Low-grade copper and nickel mineralization was found near the eastern shore of Lake Tanganyika at Kungwe Bay in the early part of the twentieth century. The mineralization occurs in harzburgite at the base of a layered gabbro complex known as the Kapalagulu Intrusion, emplaced between the Paleoproterozoic Ubendian basement and overlying Neoproterozoic Itiaso Group metasediments. Several mining and exploration companies continued the geophysical and drilling exploration for base metals throughout the last century culminating in the discovery of high-grade platinum-group element (PGE) mineralization associated with chromitite and sulfide-bearing harzburgite within the southeastern extension of the Kapalagulu Intrusion (known as the Lubalisi Zone) that is covered by a layer of nickel-rich laterite regolith. The poorly layered southeastern harzburgite forms part of the >1500 m-thick Lower Ultramafic Sequence and resembles a dike-like body that flares upwards into a succession of well-layered gabbroic rocks of the Upper Mafic Sequence. No PGE mineralization has been found in the layered gabbro; all the mineralization is associated with the chromite- and sulfide-rich harzburgite of the Lower Ultramafic Sequence and the laterite regolith overlying the mineralized harzburgite. The Lubalisi Zone harzburgite is underlain by basal dunite and overlain by an interval of layered harzburgite and troctolite and this ultramafic sequence is folded into a syncline that plunges towards the northwest that has been modified by major dolerite-filled faults orientated subparallel to the fold axial surface. Extensive deep drilling in the Lubalisi Zone of the Kapalagulu Intrusion shows that the folded harzburgite can be subdivided into a lower feldspathic harzburgite, a harzburgite containing chromitite seams and intervals of sulfide and chromite mineralization known as the Main Chromite Sulfide Succession (MCSS), an overlying sulfide-rich harzburgite, and an upper feldspathic harzburgite

  20. Advanced Sensor Arrays and Packaging

    Energy Technology Data Exchange (ETDEWEB)

    Ryter, John Wesley [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Romero, Christopher J. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Ramaiyan, Kannan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Brosha, Eric L. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-08-11

    Novel sensor packaging elements were designed, fabricated, and tested in order to facilitate the transition of electrochemical mixed-potential sensors toward commercialization. Of the two designs completed, the first is currently undergoing field trials, taking direct measurements within vehicle exhaust streams, while the second is undergoing preliminary laboratory testing. The sensors’ optimal operating conditions, sensitivity to hydrogen, and long-­term baseline stability were also investigated. The sensing capabilities of lanthanum chromite (La0.8Sr0.2CrO3) and indium-­doped tin oxide (ITO) working electrodes were compared, and the ITO devices were selected for pre-­commercial field trials testing at a hydrogen fuel cell vehicle fueling station in California. Previous data from that fueling station were also analyzed, and the causes of anomalous baseline drift were identified.

  1. A new method for the preparation of strontium titanate and strontium hypovanadate

    International Nuclear Information System (INIS)

    Strontium titanate has been a prized chemical by virtue of its dielectric, photoelectric and surface properties. The compound crystallises with the cubic perovskite structure. Till now only two techniques (and a few variants therein) have been employed for its synthesis, one of them is a solid state reaction between SrCO3 and TiO2 at 1100deg, and the other is a coprecipitation of strontium titanyl oxalate followed by calcination at 850deg. As ternary oxides, such as copper chromite, have been prepared by complex formation, the author found it interesting to apply this method to the preparation of strontium titanate. The most easily accessible and versatile complexing agent, EDTA, was used. (author)

  2. Effect of Burning Rate Modifiers on Subatmospheric Flame Temperatures of AP/HTPB Composite Solid Propellants

    Directory of Open Access Journals (Sweden)

    S. Krishnan

    1998-04-01

    Full Text Available Using 30 um. pt and Pt 13 percent Rh thermocouples, flame temperatures of uncatalysed andcatalysed ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/lffPB composite solidpropellants were measured under subatmospheric conditions. Ferric oxide F e 2 and copper chromite(CC were the catalysts used. The study demonstrates that Fe2O3 catalysed propellant, notwithstandingits least combustion efficiency undt;r subatmospheric conditions and weak gas-phase flame, has themaximum burning rate enhancement. This is argued to be due to the increased surface and subsurfacereactions caused by Fe2O3. CC-catalysed propellant burns to the least subatmospheric pressure withminimum loss in combustion efficiency indicating that this class of propellant may be more suitablefor base-bleed applications.

  3. 铬酸盐化

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    [ 篇名] Chromate-free conversion coatings for aluminum, [篇名 ] Chrome-Free Conversion Coating for in Service Repair of Aircraft Components, [ 篇名 ] Chromium remediation or release: effect of iron (Ⅱ)sulfate addition on chromium (Ⅵ) leaching from columns of chromite ore processing residue, [篇名] Coating steel wires by polymers in hydrodynamic drawing, [篇名 ] Composition of chromate conversion coatings formed on multi-layered thin films of AA2024-T3 matrix and Al{sub}2Cu, Al{sub}CuMg and Al{sub}20Cu {sub }2(MnFe){ sub } 3, [篇名] Conversion coating science and technology: is it evolving or is it stuck? [篇名] Corrosion and biofouling control in refinery cooling water system using sewage water as a makeup.

  4. Platinum-group minerals in the LG and MG chromitites of the eastern Bushveld Complex, South Africa

    Science.gov (United States)

    Oberthür, Thomas; Junge, Malte; Rudashevsky, Nikolay; de Meyer, Eveline; Gutter, Paul

    2016-01-01

    The chromitites of the Bushveld Complex in South Africa contain vast resources of platinum-group elements (PGE); however, except for the economic upper group (UG)-2 chromitite seam, information on the distribution of the PGE in the ores and on the mineralogical nature, assemblages, and proportions of platinum-group minerals (PGM) is essentially missing. In the present geochemical and mineralogical study, PGE concentrates originating from the lower group (LG)-6 and middle group (MG)-1/2 chromitites were investigated with the intention to fill this gap of knowledge. Chondrite-normalized PGE patterns of bulk rock and concentrates are characterized by a positive slope from Os to Rh, a slight drop to Pt, and an increase to Pd again. The pronounced similarities of the PGE patterns indicate similar primary processes of PGE concentration in the chromitites, namely "sulfide control" of the PGE mineralization, i.e., co-precipitation of chromite and sulfide. Further, the primary control of PGE concentration in chromitites appears to be dual in character: (i) base-level concentrations of IPGE (up to ˜500 ppb) hosted within chromite and (ii) co-precipitation of chromite and sulfide, the latter containing virtually the entire remaining PGE budget. Sulfides (chalcopyrite, pentlandite, and pyrite; pyrrhotite is largely missing) are scarce within the chromitites and occur mainly interstitial to chromite grains. Pd and Rh contents in pentlandite are low and erratic. Essentially, the whole PGE inventory of the ores occurs in the form of discrete PGM. The PGM are almost always associated with sulfides. The dominant PGM are various Pt-Pd-Rh sulfides (cooperite/braggite [(Pt,Pd)S] and malanite/cuprorhodsite [CuPt2S4]/[CuRh2S4]), laurite [RuS2], the main carrier of the IPGE (Os, Ir, Ru), sulfarsenides [(Rh,Pt,Ir)AsS], sperrylite [PtAs2], Pt-Fe alloys, and a large variety of mainly Pd-rich PGM. The LG and MG chromitites have many characteristics in common and define a general, "typical

  5. Westward prograding metamorphism in mantle peridotites from the Eastern Desert of Egypt: clues to the subduction polarity of the Arabian Nubian Shield intra-oceanic arc ophiolite

    Science.gov (United States)

    Salam Abu El-Ela, Abdel; Hamdy, Mohamed; Abu-Alam, Tamer; Hassan, Adel; Gamal El Dien, Hamed

    2013-04-01

    hourglass texture and the penetrative fabric of the serrate veins in all serpentinized peridotites indicate that fracturing of these rocks was developed in a dynamic regime. The late emplacement of veins of brucite, carbonates and oxides were most probably formed during the final stage of exhumation and under a stress regime in the brittle-ductile transition. As the grade of metamorphism increases Fe released from olivine and orthopyroxene and Cr released from chromite are accommodating in antigorite-rich serpentinites. Serpentine in veins also tends to have less substitutions, which is consistent with the fact that Al, Cr and Ni are relatively immobile during alteration and therefore remain in their original microstructural site. Compositional zoning in spinel grains in all serpentinites reflect variation in the degree of alteration. The biggest variation of spinel compositions are among serpentinites from Um El-Saneyat and W. Atalla. With increasing the degree of alteration, size of the aluminian chromite core decreases while width of the intermediate Fe3+-rich aluminian chromite to ferrian-chromite zone and the outer Cr-magnetite to magnetite zones increase. The alteration zones were formed in a temperature < 400 ° C to 550 ° C corresponding to the low green-schist to the lower amphibolite facies. We propose that this is concordant with a westward polarity of the subducting oceanic lithosphere, associating the intra-oceanic arc ophiolite during the closure of the Mozambique ocean.

  6. Influence of the sintering temperature on the structural and electronic properties of LaCrO3 doped with barium

    International Nuclear Information System (INIS)

    Ba-doped lanthanum chromites were synthesized by combustion method, utilizing urea and glycine as fuel agents. The powders were calcined (800 deg C/6 h), pelletized, sintered in various temperatures and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), density/porosity and electrical conductivity. The diffractograms of the sintered samples presented a well-defined structure, with presence of secondary phases which increase with the sintering temperature. The samples presented low densities and a high porosities (40 - 50%), which was also observed in SEM analysis. The urea-synthesized sample presented a higher conductivity (10.4 S/cm at 1000 deg C), which is related to the influence of the fuel agent in the material properties. (author)

  7. Delineation of geochemical anomalies based on stream sediment data utilizing fractal modeling and staged factor analysis

    Science.gov (United States)

    Afzal, Peyman; Mirzaei, Misagh; Yousefi, Mahyar; Adib, Ahmad; Khalajmasoumi, Masoumeh; Zarifi, Afshar Zia; Foster, Patrick; Yasrebi, Amir Bijan

    2016-07-01

    Recognition of significant geochemical signatures and separation of geochemical anomalies from background are critical issues in interpretation of stream sediment data to define exploration targets. In this paper, we used staged factor analysis in conjunction with the concentration-number (C-N) fractal model to generate exploration targets for prospecting Cr and Fe mineralization in Balvard area, SE Iran. The results show coexistence of derived multi-element geochemical signatures of the deposit-type sought and ultramafic-mafic rocks in the NE and northern parts of the study area indicating significant chromite and iron ore prospects. In this regard, application of staged factor analysis and fractal modeling resulted in recognition of significant multi-element signatures that have a high spatial association with host lithological units of the deposit-type sought, and therefore, the generated targets are reliable for further prospecting of the deposit in the study area.

  8. Experimental Determination of Spinel/Melt, Olivine/Melt, and Pyroxene/Melt Partition Coefficients for Re, Ru, Pd, Au, and Pt

    Science.gov (United States)

    Righter, K.; Campbell, A. J.; Humayun, M.

    2003-01-01

    Experimental studies have identified spinels as important hosts phases for many of the highly siderophile elements (HSE). Yet experimental studies involving chromite or Cr-rich spinel have been lacking. Experimental studies of partitioning of HSEs between silicate, oxides and silicate melt are plagued by low solubilities and the presence of small metallic nuggets at oxygen fugacities relevant to magmas, which interfere with analysis of the phases of interest. We have circumvented these problems in two ways: 1) performing experiments at oxidized conditions, which are still relevant to natural systems but in which nuggets are not observed, and 2) analysis of run products with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), allowing a combination of high sensitivity and good spatial resolution.

  9. Petrology and shock metamorphism of the olivine-phyric shergottite Yamato 980459 - Evidence for a two-stage cooling and a single-stage ejection history

    Science.gov (United States)

    Greshake, Ansgar; Fritz, Jörg; Stöffler, Dieter

    2004-05-01

    The basaltic Martian meteorite Yamato 980459 consists of large olivine phenocrysts and often prismatic pyroxenes set into a fine-grained groundmass of smaller more Fe-rich olivine, chromite, and an interstitial residual material displaying quenching textures of dendritic olivine, chain-like augite and sulfide droplets in a glassy matrix. Yamato 980459 is, thus, the only Martian meteorite without plagioclase/maskelynite. Olivine is compositionally zoned from a Mg-rich core to a Fe-rich rim with the outer few micrometers being especially rich in iron. With Fo 84 the cores are the most magnesian olivines found in Martian meteorites so far. Pyroxenes are also mostly composite crystals of large orthopyroxene cores and thin Ca-rich overgrowths. Separate pigeonite and augites are rare. On basis of the mineral compositions, the cooling rates determined from crystal morphologies, and crystal grain size distributions it is deduced that the parent magma of Yamato 980459 initially cooled under near equilibrium conditions e.g., in a magma chamber allowing chromite and the Mg-rich silicates to form as cumulus phases. Fractional crystallization at higher cooling rates and a low degree of undercooling let to the formation of the Ca-, Al-, and Fe-rich overgrowths on olivine and orthopyroxene while the magma was ascending towards the Martian surface. Finally and before plagioclase and also phosphates could precipitate, the magma was very quickly erupted quenching the remaining melt to glass, dendritic silicates and sulfide droplets. The shape preferred orientation of olivine and pyroxene suggests a quick, thin outflow of lava. According to the shock effects found in the minerals of Yamato 980459, the meteorite experienced an equilibration shock pressure of about 20-25 GPa. Its near surface position allowed the ejection from the planet's surface already by a single impact event and at relatively low shock pressures.

  10. Catalyst in Basic Oleochemicals

    Directory of Open Access Journals (Sweden)

    Eva Suyenty

    2007-10-01

    Full Text Available Currently Indonesia is the world largest palm oil producer with production volume reaching 16 million tones per annum. The high crude oil and ethylene prices in the last 3 – 4 years contribute to the healthy demand growth for basic oleochemicals: fatty acids and fatty alcohols. Oleochemicals are starting to replace crude oil derived products in various applications. As widely practiced in petrochemical industry, catalyst plays a very important role in the production of basic oleochemicals. Catalytic reactions are abound in the production of oleochemicals: Nickel based catalysts are used in the hydrogenation of unsaturated fatty acids; sodium methylate catalyst in the transesterification of triglycerides; sulfonic based polystyrene resin catalyst in esterification of fatty acids; and copper chromite/copper zinc catalyst in the high pressure hydrogenation of methyl esters or fatty acids to produce fatty alcohols. To maintain long catalyst life, it is crucial to ensure the absence of catalyst poisons and inhibitors in the feed. The preparation methods of nickel and copper chromite catalysts are as follows: precipitation, filtration, drying, and calcinations. Sodium methylate is derived from direct reaction of sodium metal and methanol under inert gas. The sulfonic based polystyrene resin is derived from sulfonation of polystyrene crosslinked with di-vinyl-benzene. © 2007 BCREC UNDIP. All rights reserved.[Presented at Symposium and Congress of MKICS 2007, 18-19 April 2007, Semarang, Indonesia][How to Cite: E. Suyenty, H. Sentosa, M. Agustine, S. Anwar, A. Lie, E. Sutanto. (2007. Catalyst in Basic Oleochemicals. Bulletin of Chemical Reaction Engineering and Catalysis, 2 (2-3: 22-31.  doi:10.9767/bcrec.2.2-3.6.22-31][How to Link/DOI: http://dx.doi.org/10.9767/bcrec.2.2-3.6.22-31 || or local: http://ejournal.undip.ac.id/index.php/bcrec/article/view/6

  11. Origin and significance of high nickel and chromium concentrations in Pliocene lignite of the Kosovo Basin, Serbia

    Energy Technology Data Exchange (ETDEWEB)

    Ruppert, L.; Finkelman, R.; Boti, E.; Milosavljevic, M.; Tewalt, S.; Simon, M.; Dulong, F. [US Geological Survey, Reston, VA (United States)

    1996-03-01

    Trace element data from 59 Pliocene lignite cores from the lignite field in the Kosovo Basin, southern Serbia, show localized enrichment of Ni and Cr (33-304 ppm and 8-176 ppm, respectively, whole-coal basis). Concentrations of both elements decrease from the western and southern boundaries of the lignite field. Low-temperature ash and polished coal pellets of selected bench and whole-coal samples were analyzed by X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray analyses. These analyses show that most of the Ni and Cr are incorporated in detrital and, to a lesser degree, in authigenic minerals. The Ni- and Cr-bearing detrital minerals include oxides, chromites, serpentine-group minerals and rare mixed-layer clays. Possible authigenic minerals include Ni-Fe sulfates and sulfides. Analyses of three lignite samples by a supercritical fluid extraction technique indicate that some (1-11%) of the Ni is organically bound, Ni- and Cr-bearing oxides, mixed-layer clays, chromites and serpentine-group minerals were also identified in weathered and fresh samples of laterite developed on serpentinized Palaeozoic peridotite at the nearby Glavica and Cikatovo Ni mines. The detrital Ni- and Cr-bearing minerals identified in lignite samples from the western part of the Kosovo Basin may have been transported into the paleoswamp by rivers that drained the two Palaeocene laterites. Some Ni may have been transported directly into the paleoswamp in solution or, alternatively, Ni may have been leached from detrital minerals by acidic peat water and adsorbed onto organic matter and included into authigenic mineral phases. No minable source of Ni and Cr is known in the southern part of the lignite field; however, the mineral and chemical data from the lignite and associated rocks suggest that such a source area may exist. 15 refs., 10 figs., 6 tabs.

  12. Luminescence and micro-Raman investigations on inclusions of unusual habit in chrysoprase from Turkey

    Energy Technology Data Exchange (ETDEWEB)

    Ayvac Latin-Small-Letter-Dotless-I kl Latin-Small-Letter-Dotless-I , M., E-mail: mayvacikli@yahoo.com [Celal Bayar University, Faculty of Arts and Sciences, Department of Physics, 45010 Muradiye-Manisa (Turkey); Garcia-Guinea, J.; Jorge, A. [Museo Nacional Ciencias Naturales, Jose Gutierrez Abascal 2, Madrid 28006 (Spain); Akal Latin-Small-Letter-Dotless-I n, I.; Kotan, Z. [Celal Bayar University, Faculty of Arts and Sciences, Department of Physics, 45010 Muradiye-Manisa (Turkey); Can, N., E-mail: cannurdogan@yahoo.com [Celal Bayar University, Faculty of Arts and Sciences, Department of Physics, 45010 Muradiye-Manisa (Turkey)

    2012-07-15

    Chemical analyses performed on chrysoprase from Turkey have shown many trace elements as well as rare earth impurities. Quantitative chemical analyses of inclusions in minerals can improve our understanding of the chemistry of surface. The environmental scanning electron microscope (ESEM) with an attached X-ray energy dispersive system (EDS) is capable of producing rapid and accurate major element chemical analyses of individual inclusions in crystals larger than about 30 {mu}m in diameter. The samples were examined with lifetime-resolved and spatially-resolved cathodoluminescence (CL), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Spatially resolved CL results at room temperature were recorded for two different areas. Bulk area displays with low CL emission and pores contain iron phases such as chromite, hematite and anatase which cause the green color. For the raw data in the lifetime resolved CL spectrum, at least three broad emission bands were detected in a yellow band of the highest intensity at about 550 nm, a weaker orange band at about 650 nm, and a red band at 720 nm. It is assumed that there are links between the CL emissions and the presence of some transition metal and REE elements, but it is obvious that all trace elements do not play a direct role. Micro-Raman measurements were performed on chrysoprase and these showed a characteristic intensive Raman band peaked at 464 cm{sup -1} which can be inferred to {nu}{sub 2} doubly symmetric bending mode of [SiO{sub 4}/M] centers. Raman spectrum of all inclusions found in the material are also given and discussed in detail. - Highlights: Black-Right-Pointing-Pointer Luminescence and Raman investigations of Chrysoprase. Black-Right-Pointing-Pointer Characteristic intensive Raman band peaked at 464 cm{sup -1}. Black-Right-Pointing-Pointer Ironed phases such as chromite, hematite and anatase.

  13. Platinum group elements geochemistry of ultramafic and associated rocks from Pindar in Madawara Igneous Complex, Bundelkhand massif, central India

    Indian Academy of Sciences (India)

    V Balaram; S P Singh; M Satyanarayanan; K V Anjaiah

    2013-02-01

    Ultramafic rocks comprising dunite, harburgite, lehzolite, olivine webserite and websterite occur as intrusives in the form of small hillocks at around Pindar into the granite–gneisses of Bundelkhand Gneissic Complex (BnGC). The peridotites are dominated by olivine cumulates where chromite and precious metal-bearing sulphides crystallized along with pyroxenes, subsequent to crystallization of olivine into the interstitial spaces of cumulates during cooling. Ultramafic rocks of Pindar are characterized by high MgO (up to 46.0 wt%) and FeO (up to 5.8 wt%); low SiO2 (40.8 to 48.0 wt%), TiO2 (0.2 to 0.5 wt%), Al2O3 (∼3.2 wt% av.), CaO(∼ 2.7 wt% av.) and Cu (11 to 73 g/g). Cr and Ni values range from 2297 to 3150 g/g and 2434 to 2767 g/g, respectively. Distribution of Ir (up to 20 ng/g), Ru (27 to 90 ng/g), Rh (3 to 14 ng/g), Pt (18 to 72 ng/g), Pd (10 to 27 ng/g) and Au (22 to 57 ng/g) indicate platinum group element (PGE) and associated gold mineralization in these ultramafic rocks. A mineral phase representing sperrylite (PtAs2) was also identified within the sulphides in Scanning electron microscopy with energy dispersive spectrometer (SEM–EDS) studies. The primitive mantle-normalized siderophile elements pattern shows platinum group element PGE (PPGE) enrichment (Rh, Pt, Pd). Discrimination diagrams of Pd/Ir vs. Ni/Cu, Pd/Pt vs. Ni/Cu, Cu/Pd vs. Pd, and Cu vs. Pd for the peridotites of Pindar attribute to affinity towards komatiite magma, derived from high degree of partial melting of prolonged depleted mantle, and the sulphur saturation condition incurred during the crystallization of chromite which was favourable for PGE mineralization.

  14. CHROMITITE PROSPECTING USING LANDSAT TM AND ASTER REMOTE SENSING DATA

    Directory of Open Access Journals (Sweden)

    A. Beiranvand Pour

    2015-10-01

    Full Text Available Studying the ophiolite complexes using multispectral remote sensing satellite data are interesting because of high diversity of minerals and the source of podiform chromitites. This research developed an approach to discriminate lithological units and detecting host rock of chromitite bodies within ophiolitic complexes using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER and Landsat Thematic Mapper (TM satellite data. Three main ophiolite complexes located in south of Iran have been selected for the study. Spectral transform techniques, including minimum noise fraction (MNF and specialized band ratio were employed to detect different rock units and the identification of high-potential areas of chromite ore deposits within ophiolitic complexes. A specialized band ratio (4/1, 4/5, 4/7 of ASTER, MNF components and Spectral Angle Mapper (SAM on ASTER and Landsat TM data were used to distinguish ophiolitic rock units. Results show that the specialized band ratio was able to identify different rock units and serpentinized dunite as host rock of chromitites within ophiolitic complexes, appropriately. MNF components of ASTER and Landsat TM data were suitable to distinguish ophiolitic rock complexes at a regional scale. The integration of SAM and Feature Level Fusion (FLF used in this investigation discriminated the ophiolitic rock units and prepared detailed geological map for the study area. Accordingly, high potential areas (serpentinite dunite were identified in the study area for chromite exploration targets.The approach used in this research offers the image processing techniques as a robust, reliable, fast and cost-effective method for detecting serpentinized dunite as host rock of chromitite bodies within vast ophiolite complexes using ASTER and Landsat TM satellite data.

  15. Formation of H2 and CH4 by weathering of olivine at temperatures between 30 and 70°C

    Directory of Open Access Journals (Sweden)

    Crill Patrick

    2011-06-01

    Full Text Available Abstract Hydrocarbons such as CH4 are known to be formed through the Fischer-Tropsch or Sabatier type reactions in hydrothermal systems usually at temperatures above 100°C. Weathering of olivine is sometimes suggested to account for abiotic formation of CH4 through its redox lowering and water splitting properties. Knowledge about the CH4 and H2 formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian CH4 and for CO2 sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the CH4 and H2 formation potential of forsteritic olivine. The results show low temperature CH4 production that is probably influenced by chromite and magnetite as catalysts. Extensive analyses of a potential CH4 source trapped in the crystal structure of the olivine showed no signs of incorporated CH4. Also, the available sources of organic carbon were not enough to support the total amount of CH4 detected in our experiments. There was also a linear relationship between silica release into solution and the net CH4 accumulation into the incubation bottle headspaces suggesting that CH4 formation under these conditions could be a qualitative indicator of olivine dissolution. It is likely that minerals such as magnetite, chromite and other metal-rich minerals found on the olivine surface catalyze the formation of CH4, because of the low temperature of the system. This may expand the range of environments plausible for abiotic CH4 formation both on Earth and on other terrestrial bodies.

  16. Solid speciation and availability of nickel and chromium in Ni mining spoils

    Science.gov (United States)

    Raous, Sophie; Garnier, Jérémie; Sterckeman, Thibaul; Echevarria, Guillaume; Becquer, Thierry; Thomas, Fabien

    2010-05-01

    Nickel mining of ultramafic laterites generates different types of wastes, topsoils and ores that are too poor in Ni to be currently processed. These are mixed and stored on heaps which could be a potential source of Ni and Cr pollution. Chemical reactivity of the main metal bearing phases present in the mining spoils of Goiás (Brasil) was investigated. Principally a silicated 'saprolite' material and a Fe-oxide rich limonitic material were isolated from the wastes. Their total Ni and Cr content are high, respectively for Ni and Cr : 7,170 and 54,970 mg kg-1 in limonite and 12,200 and 12,650 mg kg-1 in saprolite. The main metal-bearing minerals, identified and localized using XRD, TEM-EDX, Raman spectroscopy and Mossbaüer spectrometry are well-crystallized minerals: goethite (75%), hematite (13%) and chromite in limonite and ferruginous smectite, talc and chromite in saprolite. Single and sequential extractions showed that the amounts of 1M KCl exchangeable Ni and Cr reached respectively 7.1% and 0.03% of total contents in saprolite. Moreover, Cr(VI) extraction by KH2PO4 showed that more than 2% (980 mg kg-1) of total Cr was under this labile toxic form in limonite. This study allowed us to determine the main reactions controlling the Ni and Cr mobility in the spoils i.e. Ni2+ cationic exchange in saprolitic spoil and CrO32- surface complexation in limonitic spoil. This study allowed us to demonstrate the need of chemical rehabilitation of mining wastes in order to avoid the dispersion of the high contents of Ni and Cr available. It constitutes the system definition needed to predict the Cr and Ni mobility in ultramafic mining spoils.

  17. Analysis of Cr with various valence states in industrial EAF slag for making stainless steel

    International Nuclear Information System (INIS)

    Slags of stainless steel making by EAF process in one plant from south and the other from north China were selected. The qualitative and quantitative analysis of all elements in samples were investigated first, the possible phases were identified by diffraction. Micro-morphology and composition analysis showed that Cr exist in iron-based alloy, chromite phase and Cr-containing silicate phase. It inferred that Cr (0) would be in iron-based alloy drops, Cr (III) would be in chromite phase. The Cr valence states in slag were assumed as 0, +2, +3 and +6. The caustic plus carbonate sodium solution was adopted to leach Cr (VI) as CrO42-; oxalic acid was applied to leach the Cr (0) in alloy drops; FeCl3-HCl-NH4Cl combined with V2+-HCl leaching process, the Cr (II) in slag would change to Cr2+ in solution; the resident containing Cr (III) was smelting by Na2O2. Cr in different valence states were separated and detected. The optimized leaching processes of Cr (VI) and Cr (0) were investigated. The influence of the leaching process on existence of other phase was checked also. The analysis results showed the route of separation and analysis is suitable for the slag samples. Both slag samples were with the same trend of contents in various Cr states. Among the states, Cr (0) content is highest, about 2.0-4.5 mass%; the second highest content is Cr (III), about 1.4-2.7 mass%; the content of toxic Cr (VI) is about 80-310 ppm, the lest one is Cr (II), about 1.0-2.1 ppm. This study would provide an experimental method and basis for the utilization and environmental impact of stainless steel smelting slag. (author)

  18. High-temperature hydrothermal activities around suboceanic Moho: An example from diopsidite and anorthosite in Wadi Fizh, Oman ophiolite

    Science.gov (United States)

    Akizawa, Norikatsu; Tamura, Akihiro; Fukushi, Keisuke; Yamamoto, Junji; Mizukami, Tomoyuki; Python, Marie; Arai, Shoji

    2016-10-01

    Reaction products between hydrothermal fluids and uppermost mantle harzburgite-lowermost crustal gabbro have been reported along Wadi Fizh, northern Oman ophiolite. They are named mantle diopsidite (MD) or crustal diopsidite (CD) depending on the stratigraphic level. They construct network-like dikes crosscutting structures of the surrounding harzburgite or gabbro. The MD is mainly composed of diopsidic clinopyroxene, whereas the CD is of diopsidic clinopyroxene and anorthitic plagioclase. Here, we report a new reaction product, crustal anorthosite (CA), from the lowermost crustal section. The CA is always placed in the center of the CD network, and mainly consists of anorthitic plagioclase with minor titanite and chromian minerals such as chromite and uvarovite. Aqueous fluid inclusions forming negative crystals are evenly distributed in minerals of the CA. The fluid inclusions contain angular-shaped or rounded daughter minerals as calcite or calcite-anhydrite composite, which were identified by Raman spectroscopic analysis. We estimated their captured temperature at 530 °C at least by conducting microthermometric analysis of the fluid inclusions. Furthermore, we examined their chemical characteristics by direct laser-shot sampling conducted by laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS). The results indicate that the trapped aqueous fluids contain an appreciable amount of Na, but no K and Cr. Hydrothermal fluids involved in the CA formation transported Cr, which was probably taken up from chromite seams in the uppermost mantle section. Cr got soluble by forming complexes with anions as SO42-, CO32- and Cl-. In addition, these hydrothermal fluids transported Fe, Mg and trace elements (Ti, Sr, Y, Zr and rare-earth elements) governing whole-rock chemical compositions of the MDs, CDs and CAs. Our estimation for the condition of CA formation yielded rather low temperatures (530-600 °C), which indicates a later stage production of the CA

  19. Martian Dunite NWA 2737: Petrographic constraints on geological history, shock events, and olivine color

    Science.gov (United States)

    Treiman, Allan H.; Dyar, M. Darby; McCanta, Molly; Noble, Sarah K.; Pieters, Carle M.

    2007-04-01

    Meteorite Northwest Africa (NWA) 2737 is the second known chassignite, an olivine-rich igneous rock with mineral compositions and isotopic ratios that suggest it formed on Mars. NWA 2737 consists of ~85% vol. olivine (Mg#, molar Mg/(Mg + Fe), of 78.3 +/- 0.4%), which is notable because it is black in hand sample and brown in thin section. Other minerals include chromite, pyroxenes (augite, pigeonite, orthopyroxene), and diaplectic glass of alkali-feldspar composition. Aqueous alteration is minimal and appears only as slight dissolution of glass. NWA 2737 formed by accumulation of olivine and chromite from a basaltic magma; the other minerals represent magma trapped among the cumulus grains. Minerals are compositionally homogeneous, consistent with chemical equilibration in late and postigneous cooling. Two-pyroxene thermometry gives equilibration temperatures ~1150°C, implying a significant time spent at the basalt solidus. Olivine-spinel-pyroxene equilibria give ~825°C (possibly the T of mesostasis crystallization) at an oxidation state of ~QMF-1. This oxidation state is consistent with low Fe3+ in olivine (determined by EMP, Mössbauer spectra, and synchrotron micro-XANES spectroscopy) and with ~10% of the iron in pyroxene being Fe3+. NWA 2737 experienced two shock events. The first shock, to stage S5-S6, affected the olivine by producing in it planar deformation features, intense mosaicism and lattice strain, and abundant droplets of iron-nickel metal, 5-15 nm in diameter. At this stage the olivine became deeply colored, i.e., strongly absorbing at visible and near-infrared (NIR) wavelengths. This shock event and its thermal pulse probably occurred at ~170 Ma, the Ar-Ar age of NWA 2737. The colored olivine is cut by ribbons of coarser, uncolored olivine with long axes along [100] and shorter axes on {021} planes: These are consistent with the easy slip law for olivine [100]{021}, which is activated at moderate strain rate at high temperature. Within these

  20. Martian Dunite NWA 2737: Petrographic Constraints on Geological History, Shock Events, and Olivine Color

    International Nuclear Information System (INIS)

    Meteorite Northwest Africa (NWA) 2737 is the second known chassignite, an olivine-rich igneous rock with mineral compositions and isotopic ratios that suggest it formed on Mars. NWA 2737 consists of ?85% vol. olivine (Mg, molar Mg/(Mg + Fe), of 78.3 ± 0.4%), which is notable because it is black in hand sample and brown in thin section. Other minerals include chromite, pyroxenes (augite, pigeonite, orthopyroxene), and diaplectic glass of alkali-feldspar composition. Aqueous alteration is minimal and appears only as slight dissolution of glass. NWA 2737 formed by accumulation of olivine and chromite from a basaltic magma; the other minerals represent magma trapped among the cumulus grains. Minerals are compositionally homogeneous, consistent with chemical equilibration in late and postigneous cooling. Two-pyroxene thermometry gives equilibration temperatures 1150 C, implying a significant time spent at the basalt solidus. Olivine-spinel-pyroxene equilibria give ?825 C (possibly the T of mesostasis crystallization) at an oxidation state of QMF-1. This oxidation state is consistent with low Fe3+ in olivine (determined by EMP, Moessbauer spectra, and synchrotron micro-XANES spectroscopy) and with ∼10% of the iron in pyroxene being Fe3+. NWA 2737 experienced two shock events. The first shock, to stage S5-S6, affected the olivine by producing in it planar deformation features, intense mosaicism and lattice strain, and abundant droplets of iron-nickel metal, 5-15 nm in diameter. At this stage the olivine became deeply colored, i.e., strongly absorbing at visible and near-infrared (NIR) wavelengths. This shock event and its thermal pulse probably occurred at ∼170 Ma, the Ar-Ar age of NWA 2737. The colored olivine is cut by ribbons of coarser, uncolored olivine with long axes along [100] and shorter axes on {021} planes: These are consistent with the easy slip law for olivine [100]{021}, which is activated at moderate strain rate at high temperature. Within these

  1. Martian Dunite NWA 2737: Petrographic Constraints on Geological History, Shock Events, and Olivine Color

    Energy Technology Data Exchange (ETDEWEB)

    Treiman,A.; Dyar, M.; McCanta, M.; Noble, S.; Pieters, C.

    2007-01-01

    Meteorite Northwest Africa (NWA) 2737 is the second known chassignite, an olivine-rich igneous rock with mineral compositions and isotopic ratios that suggest it formed on Mars. NWA 2737 consists of ?85% vol. olivine (Mg, molar Mg/(Mg + Fe), of 78.3 {+-} 0.4%), which is notable because it is black in hand sample and brown in thin section. Other minerals include chromite, pyroxenes (augite, pigeonite, orthopyroxene), and diaplectic glass of alkali-feldspar composition. Aqueous alteration is minimal and appears only as slight dissolution of glass. NWA 2737 formed by accumulation of olivine and chromite from a basaltic magma; the other minerals represent magma trapped among the cumulus grains. Minerals are compositionally homogeneous, consistent with chemical equilibration in late and postigneous cooling. Two-pyroxene thermometry gives equilibration temperatures 1150 C, implying a significant time spent at the basalt solidus. Olivine-spinel-pyroxene equilibria give ?825 C (possibly the T of mesostasis crystallization) at an oxidation state of QMF-1. This oxidation state is consistent with low Fe3+ in olivine (determined by EMP, Moessbauer spectra, and synchrotron micro-XANES spectroscopy) and with {approx}10% of the iron in pyroxene being Fe3+. NWA 2737 experienced two shock events. The first shock, to stage S5-S6, affected the olivine by producing in it planar deformation features, intense mosaicism and lattice strain, and abundant droplets of iron-nickel metal, 5-15 nm in diameter. At this stage the olivine became deeply colored, i.e., strongly absorbing at visible and near-infrared (NIR) wavelengths. This shock event and its thermal pulse probably occurred at {approx}170 Ma, the Ar-Ar age of NWA 2737. The colored olivine is cut by ribbons of coarser, uncolored olivine with long axes along [100] and shorter axes on {l_brace}021{r_brace} planes: These are consistent with the easy slip law for olivine [100]{l_brace}021{r_brace}, which is activated at moderate strain

  2. Grain-scale alignment of melt in sheared partially molten rocks: implications for viscous anisotropy

    Science.gov (United States)

    Pec, Matej; Quintanilla-Terminel, Alejandra; Holtzman, Benjamin; Zimmerman, Mark; Kohlstedt, David

    2016-04-01

    Presence of melt significantly influences rheological properties of partially molten rocks by providing fast diffusional pathways. Under stress, melt aligns at the grain scale and this alignment induces viscous anisotropy in the deforming aggregate. One of the consequences of viscous anisotropy is melt segregation into melt-rich sheets oriented at low angle to the shear plane on much larger scales than the grain scale. The magnitude and orientation of viscous anisotropy with respect to the applied stress are important parameters for constitutive models (Takei and Holtzman 2009) that must be constrained by experimental studies. In this contribution, we analyze the shape preferred orientation (SPO) of individual grain-scale melt pockets in deformed partially molten mantle rocks. The starting materials were obtained by isostatically hot-pressing olivine + basalt and olivine + chromite + basalt powders. These partially molten rocks were deformed in general shear or torsion at a confining pressure, Pc = 300 MPa, temperature, T = 1200° - 1250° C, and strain rates of 10-3 - 10-5 s-1to finite shear strains, γ, of 0.5 - 5. After the experiment, high resolution backscattered electron images were obtained using a SEM equipped with a field emission gun. Individual melt pockets were segmented and their SPO analyzed using the paror and surfor methods and Fourier transforms (Heilbronner and Barret 2014). Melt segregation into melt-rich sheets inclined at 15° -20° antithetic with respect to the shear plane occurs in three-phase system (olivine + chromite + basalt) and in two-phase systems (olivine + basalt) twisted to high strain. The SPO of individual melt pockets within the melt-rich bands is moderately strong (b/a ≈ 0.8) and is always steeper (20° -40°) than the average melt-rich band orientation. In the two-phase system (olivine + basalt) sheared to lower strains, no distinct melt-rich sheets are observed. Individual grain-scale melt pockets are oriented at 45° -55

  3. Ultra-reducing conditions in average mantle peridotites and in podiform chromitites: a thermodynamic model for moissanite (SiC) formation

    Science.gov (United States)

    Golubkova, Anastasia; Schmidt, Max W.; Connolly, James A. D.

    2016-05-01

    Natural moissanite (SiC) is reported from mantle-derived samples ranging from lithospheric mantle keel diamonds to serpentinites to podiform chromitites in ophiolites related to suprasubduction zone settings (Luobusa, Dongqiao, Semail, and Ray-Iz). To simulate ultra-reducing conditions and the formation of moissanite, we compiled thermodynamic data for alloys (Fe-Si-C and Fe-Cr), carbides (Fe3C, Fe7C3, SiC), and Fe-silicides; these data were augmented by commonly used thermodynamic data for silicates and oxides. Computed phase diagram sections then constrain the P- T- fO2 conditions of SiC stability in the upper mantle. Our results demonstrate that: Moissanite only occurs at oxygen fugacities 6.5-7.5 log units below the iron-wustite buffer; moissanite and chromite cannot stably coexist; increasing pressure does not lead to the stability of this mineral pair; and silicates that coexist with moissanite have X Mg > 0.99. At upper mantle conditions, chromite reduces to Fe-Cr alloy at fO2 values 3.7-5.3 log units above the moissanite-olivine-(ortho)pyroxene-carbon (graphite or diamond) buffer (MOOC). The occurrence of SiC in chromitites and the absence of domains with almost Fe-free silicates suggest that ultra-reducing conditions allowing for SiC are confined to grain scale microenvironments. In contrast to previous ultra-high-pressure and/or temperature hypotheses for SiC origin, we postulate a low to moderate temperature mechanism, which operates via ultra-reducing fluids. In this model, graphite-/diamond-saturated moderately reducing fluids evolve in chemical isolation from the bulk rock to ultra-reducing methane-dominated fluids by sequestering H2O into hydrous phases (serpentine, brucite, phase A). Carbon isotope compositions of moissanite are consistent with an origin of such fluids from sediments originally rich in organic compounds. Findings of SiC within rocks mostly comprised by hydrous phases (serpentine + brucite) support this model. Both the hydrous phases

  4. Density functional theory based comparative study of electronic structures and magnetic properties of spinel ACr2O4 (A  =  Mn, Fe, Co, Ni) compounds

    Science.gov (United States)

    Das, Debashish; Ghosh, Subhradip

    2015-10-01

    Using the DFT+U method and generalized gradient approximation (GGA) we perform the first systematic study of the chromite series ACr2O4 (A  =  Mn, Fe, Co, Ni) by computing their structural and magnetic properties. The results are analyzed by their electronic structures. We find that in spite of varying structural distortions, the electronic structures are very similar across the series. Such similarities are responsible for qualitative uniformities in their magnetic phases at low temperatures, as observed in the experiments. We find that the strong electron-electron correlation, along with competing magnetic exchange splitting and the crystal field splitting, are responsible for their electronic properties such as the electronic band gaps. Our results regarding the magnetic exchange parameters are in good agreement with the available results and show the relative importance of the pairwise exchange interactions in each of the compounds. The ground state magnetic spin structures and the ferrimagnetic transition temperatures obtained from these exchange parameters, in combination with a phenomenological theory, qualitatively agree with the experiments and other theoretical results.

  5. ZnCr2O4 Nanoparticles: Facile Synthesis, Characterization, and Photocatalytic Properties

    Science.gov (United States)

    Mousavi, Zahra; Soofivand, Faezeh; Esmaeili-Zare, Mahdiyeh; Salavati-Niasari, Masoud; Bagheri, Samira

    2016-02-01

    In this work, zinc chromite (ZnCr2O4) nanostructures have been synthesized through co-precipitation method. The effect of various parameters such as alkaline agent, pH value, and capping agent type was investigated on purity, particle size and morphology of samples. It was found that particle size and morphology of the products could be greatly influenced via these parameters. The synthesized products were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), fourier transform infrared (FT-IR) spectra, X-ray energy dispersive spectroscopy (EDS), photoluminescence (PL) spectroscopy, diffuse reflectance spectroscopy (DRS) and vibrating sample magnetometry (VSM). The superhydrophilicity of the calcined oxides was investigated by wetting experiments and a sessile drop technique which carried out at room temperature in air to determine the surface and interfacial interactions. Furthermore, the photocatalytic activity of ZnCr2O4 nanoparticles was confirmed by degradation of anionic dyes such as Eosin-Y and phenol red under UV light irradiation. The obtained ZnCr2O4 nanoparticles exhibit a paramagnetic behavior although bulk ZnCr2O4 is antiferromagnetic, this change in magnetic property can be ascribed to finite size effects.

  6. Rapid high-performance sample digestion of base metal ores using high-intensity infrared radiation with determination by nitrogen-based microwave plasma optical spectrometry

    Directory of Open Access Journals (Sweden)

    Yong Wang

    2016-03-01

    Full Text Available Infrared sample digestion technology has been rapidly developed in recent years and its application and digestion performance on a variety of ores of base metals was assessed in this study, using a 6-channel infrared digester. Digestion times of 10 min or less were achieved for all base metal ores investigated, including oxides, sulfides, and silicates of Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Ti, W, and Zn. Performance criteria for all samples were excellent, reflected in z values of less than 2 in all cases. Various acid digestion methods were developed for the selected ore samples under high intensity infrared radiation and delivered virtually complete recoveries of all of the elements of interest. Chromite, the notoriously refractory chromium ore was digested within 10 min and gave 100% recovery of chromium. These digestions were accomplished without resorting to perchloric acid and, for most sample types, without hydrofluoric acid, significantly improving the workplace safety for analysts. Between-channel variation of the analyte recoveries from the 6-channel unit were generally below 2%, suggesting that the digestion methods developed with this platform provide reproducible results to meet various sample preparation demands. The high speed and analyte recovery of these digestions makes this methodology especially attractive for prospectors and developers who demand rapid and reliable results from exploration samples.

  7. Magnetism at spinel thin film interfaces probed through soft x-ray spectroscopy techniques

    Energy Technology Data Exchange (ETDEWEB)

    Chopdekar, R.V.; Liberati, M.; Takamura, Y.; Kourkoutis, L. Fitting; Bettinger, J. S.; Nelson-Cheeseman, B. B.; Arenholz, E.; Doran, A.; Scholl, A.; Muller, D. A.; Suzuki, Y.

    2009-12-16

    Magnetic order and coupling at the interfaces of highly spin polarized Fe{sub 3}O{sub 4} heterostructures have been determined by surface sensitive and element specific soft x-ray spectroscopy and spectromicroscopy techniques. At ambient temperature, the interface between paramagnetic CoCr{sub 2}O{sub 4} or MnCr{sub 2}O{sub 4} and ferrimagnetic Fe{sub 3}O{sub 4} isostructural bilayers exhibits long range magnetic order of Co, Mn and Cr cations which cannot be explained in terms of the formation of interfacial MnFe{sub 2}O{sub 4} or CoFe{sub 2}O{sub 4}. Instead, the ferrimagnetism is induced by the adjacent Fe{sub 3}O{sub 4} layer and is the result of the stabilization of a spinel phase not achievable in bulk form. Magnetism at the interface region is observable up to 500 K, far beyond the chromite bulk Curie temperature of 50-95 K.

  8. The crystal structure of (Fe4Cr4Ni)9C4

    Institute of Scientific and Technical Information of China (English)

    SHI; Nicheng; MA; Zhesheng; XIONG; Ming; DAI; Mingquan; BA

    2005-01-01

    (Fe4Cr4Ni)9C4 is a metal carbide mineral formed by combination of Fe, Cr and Ni with C. It occurs in a chromite deposit in the Luobusha ophiolite, Tibet. Based on the determination of its crystal structure, the empirical formula is (Fe4.12Cr3.84Ni0.96)8.92C3.70 and the simplified formula is (Fe4Cr4Ni)4C9. The mineral is hexagonal with a = 1.38392(2) nm, c = 0.44690(9) nm,space group P63 m c, Z=6 and the calculated specific gravity Dx = 7.089 g/cm3. Fe, Cr and Ni occupy different crystallographic sites and their coordination numbers are approximately 12,forming an alternate stacking sequence of flat and puckered layers along the c axis. Some metallic atoms have a defect structure. The interatomic distances of Fe, Cr and Ni are 0.2525-0.2666 nm, and the distances between Fe, Cr, Ni and C are 0.1893-0.2169 nm. The coordination number of carbon is 6. It occurs in interstices of the metallic atoms Fe, Cr and Ni to form trigonal-prismatically coordinated polyhedra. These coordination polyhedra are linked with each other via shared corners or shared edges into a new type of metal carbide structure.

  9. Effects of thermal metamorphism on compositions of lunar spinels

    Science.gov (United States)

    Misra, K. C.; Taylor, L. A.

    1977-01-01

    The reported study represents an attempt to evaluate experimentally the compositional and textural changes that are likely to be observed in the Fe-Ti-Cr spinels of lunar igneous rocks by subsequent thermal metamorphism. The Apollo 12 igneous rock, 12018,43, was chosen for this investigation because an earlier study of another fraction of this rock by El Goresy et al. (1971) has reported an almost continuous trend of spinel compositions between Cr-Ulvoespinel and Ti-chromite. The nature of the compositional changes in the heated spinels (and ilmenites) is found to be such that the changes cannot be explained by intragranular adjustments alone. In the heated sample, pyroxene grains adjacent to the high-Ti spinels show a decrease in FeO, and an increase in MgO and Al2O3 at the interface. This may account for the MgO depletion and a part of the FeO enrichment in the high-Ti spinels. It is believed that the heating experiment demonstrates that thermal metamorphism of lunar basalts is likely to modify the compositions of their preexisting spinels (and ilmenites).

  10. Laboratory photometry of regolith analogues: Effect of porosity

    Science.gov (United States)

    Kar, A.; Sen, A. K.; Gupta, R.

    2016-10-01

    New Laboratory phase curves are presented, to examine the effect of porosity on reflectance as a function of phase angle for grain size having dimension about half, twice and those larger than the illuminating wavelength. The experimental setup used for generating reflectance data is a goniometric device developed at the Department of Physics, Assam University, Silchar, India. Some of the well-documented samples having different sizes were chosen; alumina, olivine, basalt, rutile, chromite and iron. The sample surfaces were prepared with different porosities, in order to simulate natural regolith surface as much as possible. The wavelength of observation is 632.8 nm. A model based on the Radiative Transfer Equation is presented here to analyze and model the laboratory data. In the present modelling work, the empirical relation of Hapke, Mie theory and Henyey-Greenstein phase function are used. For particles having dimension about half, twice to the wavelength, Mie theory is used to calculate single scattering albedo. Although the Mie theory is insufficient for describing the scattering properties of particles larger than the wavelength, for such large particle single scattering albedo (SSA) is estimated through method of best fit. It has been found that, the porosity has a distinguishable effect on reflectance. Also the contribution of multiple scattering function for different porosity is examined. Further the results presented in the current work, demonstrates the light scattering properties of a diverse collections of regolith like samples.

  11. Yarlongite:A New Metallic Carbide Mineral

    Institute of Scientific and Technical Information of China (English)

    SHI Nicheng; BAI Wenji; LI Guowu; XIONG Ming; FANG Qingsong; YANG Jingsui; MA Zhesheng; RONG He

    2009-01-01

    Yarlongite occurs in ophiolitic chromitite at the Luobusha mine(29°5'N 92°,5'E,about 200 km ESE of Lhasa),Qusum County,Shannan Prefecture,Tibet Autonomous Region,People'S Republic of China.Associated minerals are:diamond,moissanite,wiistite,iridium("osmiridium"), osmium("iridosmine"),periclase,chromite,native irun,native nickel,native chromium,forsterite. Cr-rich diopside,intermetallic compounds Ni-Fe-Cr,Ni-Cr,Cr-C,etc.Yariongite and its associated minerals were handpicked from a large heavy mineral sample of chromitite.The metallic carbides associated with yarlongite are cohenite,tongbaite,khamrabaevite and qusongite(IMA2007.034). Yarlongite occurs as irregular grains,with a size between 0.02 and 0.06 mm,steel-grey colour,H Mohs:5 1/2-6.Tenacity:brittle.Cleavage:{0 0 1}perfect.Fracture:conchoidal.Chemical formula: (Cr4Fe4Ni)∑9C4,or(Cr,Fe,Ni)∑9C4,Crystal system:Hexagonal,Space Group:P63/mc,a=18.839(2)A,C =4.4960(9)A,V=745.7(2)A3,Z=6,Density(calc.)=7.19 g/cm3(with simplified formula).Yarlongite has been approved as a new mineral by the CNMNC(IMA2007-035).Holotype material is deposited at the Geological Museum of China(No.M11650).

  12. Investigations of Protective Coatings for Castings of High-manganese Cast Steels

    Directory of Open Access Journals (Sweden)

    M. Holtzer

    2013-01-01

    Full Text Available When cast steel castings are made in moulding sands on matrices of high-silica sand, which has a low fire resistance the problem of theso-called chemical penetration is distinctly visible. Whereas this effect appears to a small degree only when moulding sand matrices are of chromite, zircon or olivine sands. Therefore in case of making castings of high-manganese cast steel (e.g. Hadfield steel sands not containing free silica should be applied (e.g. olivine sand or in case of a high-silica matrix protective coatings for moulds and cores should be used. Two protective coatings, magnesite alcoholic (marked as coating 1 and coating 2 originated from different producers and intended for moulds for castings of the Hadfield steel, were selected for investigations. Examinations of the basic properties were performed for these coatings: viscosity, thermal analysis, sedimentation properties, wear resistance. In order to estimate the effectiveness of protective coatings the experimental castings were prepared. When applying coating 1, the surface quality of the casting was worse and traces of interaction between the casting material (cast steel and the coating were seen. When protective coating 2 was used none interactions were seen and the surface quality was better.

  13. High-pressure highly reduced nitrides and oxides from chromitite of a Tibetan ophiolite

    Science.gov (United States)

    Dobrzhinetskaya, Larissa F.; Wirth, Richard; Yang, Jingsui; Hutcheon, Ian D.; Weber, Peter K.; Green, Harry W.

    2009-01-01

    The deepest rocks known from within Earth are fragments of normal mantle (≈400 km) and metamorphosed sediments (≈350 km), both found exhumed in continental collision terranes. Here, we report fragments of a highly reduced deep mantle environment from at least 300 km, perhaps very much more, extracted from chromite of a Tibetan ophiolite. The sample consists, in part, of diamond, coesite-after-stishovite, the high-pressure form of TiO2, native iron, high-pressure nitrides with a deep mantle isotopic signature, and associated SiC. This appears to be a natural example of the recently discovered disproportionation of Fe2+ at very high pressure and consequent low oxygen fugacity (fO2) in deep Earth. Encapsulation within chromitite enclosed within upwelling solid mantle rock appears to be the only vehicle capable of transporting these phases and preserving their low-fO2 environment at the very high temperatures of oceanic spreading centers. PMID:19880742

  14. Geochemical, petrological and structural diversities of Albanides ophiolites; Diversites geochimiques, petrologiques et structurales des ophiolites des Albanides

    Energy Technology Data Exchange (ETDEWEB)

    Tashko, A.

    1996-12-31

    Two types of ophiolites have been distinguished in the Albanides, the E (eastern) and the W (western) types (belts). The tectonites of the W ophiolite type are mainly lherzolites and clinopyroxene - bearing harzburgites whereas those of the E type are essentially harzburgites. The later are very rich in chromite ore deposits. The thickness of the ophiolites is more important in the E type than in the W one, and the fraction of melt is higher in the E type tectonites. In the north (N group) some particular features distinguish them from the ophiolites of the eastern belt. The magmatic rocks are more developed in the N group and the thickness reaching 10-14 km is a unique case in the Dinaride-Albanide-Hellenide sector of the Alpine chain. The expansion zone is oriented here SSW-NNE, instead of SSE-NNW in the E and W groups. The N ophiolite group is located in he northern termination of the Korabi micro-continent while the ophiolites of the two other groups are at the western margin of this consolidated zone. The absolute age of the N group tectonites is 188 Ma (phlogopite) or 28 Ma older than the others. The existence of a unique type ophiolite (N group) accompanied by two different ophiolite types, located at the western margin of Korabi (Pelagonian) zone, distinguish the ophiolites of the Albanides from those of the Dinarides and Hellenides. (author). 46 refs., 12 figs., 5 tabs.

  15. Hibonite, Ca2/Al, Ti/24O38, from the Leoville and Allende chondritic meteorites.

    Science.gov (United States)

    Keil, K.; Fuchs, L. H.

    1971-01-01

    Hibonite was discovered in light-colored, Ca-Al-Ti-rich and Si-Fe-poor, achondritic inclusions of the Leoville and Allende HL-group chondrites. Two varieties of hibonite occur: one emits a bright red-orange luminescence under electron bombardment and has high amounts of Al2O3 (87.7; 87.9) and low amounts of MgO (0.65; 0.8) and TiO2 (0.68; 0.8). The other emits a bright blue luminescence and is low in Al2O3 (78.7; 79.2) and high in MgO (3.3; 3.7) and TiO2 (6.5; 7.9) (in wt. %). The oxide CaO is about the same in both varieties. It is suggested that the change in the color of the visible luminescence results from changes in composition. The origin of hibonite which occurs in complex mineral assemblages together with anorthite, gelhenite, wollastonite, aluminous diopside, andradite, Ca-pyroxene, perovskite, spinel, taenite, chromite, and pentlandite, and in close proximity to nodules containing calcite, whewellite, forsterite and many of the aforementioned phases, is discussed. The proposition that hibonite and associated phases originated by contact metamorphism and metasomatism of calcite-dolomite bearing assemblages cannot, at this time, be completely ruled out.

  16. Chemical Composition of Magnetic Minerals in the Sedimentary Interval Containing the Mono Lake Excursion from Summer Lake, Oregon, U.S.A

    Science.gov (United States)

    Horton, R. A.; Lopez, J.; Thompson, G. R.; Soto, C.; Herrera, I. S.; Sevier, K. L.; Negrini, R. M.

    2011-12-01

    Oriented piston cores were taken from Summer Lake for the purpose of obtaining a high-resolution paleomagnetic record of the Mono Lake Excursion. McCuan (2011) reported that the main magnetic carrier mineral is consistent throughout the cores and is composed principally of pseudo-single domain titanomagnetite. This result is based on XRD scans of magnetic mineral separates and modified Day plots of bulk sediment hysteresis parameters. In addition, small amounts of maghemite, hematite, and ilmenite were identified using reflected light microscopy though these did not show up in the XRD patterns or bulk hysteresis analyses. In contrast to the above results, preliminary SIRM unmixing results suggest the presence of at least three different significant magnetic carriers with moderately low coercivities. To test the unmixing results, magnetic separates were obtained from core samples and prepared into polished sections for analysis using the SEM-EDS at CSUB. Grains in excess of 10 um were randomly analyzed (N = 646). The vast majority of grains were titanomagnetites with atomic Fe:Ti ranging from 7.5:2.5 to 8.5:1.5, but there are also small amounts of ulvospinel, magnetite, and occasionally Fe-rich chromite, and most grains contain small amounts of Mg, Al, and Cr. Ternary plots of Fe-Ti-Cr show multiple wide but similar compositional ranges at all depths. These compositional data generally support the SIRM unmixing results suggesting three or so families of magnetic minerals.

  17. Heavy mineral distribution in stream sediment of Tapah area, Perak, Malaysia

    Science.gov (United States)

    Sibon, Mahat Hj; Jamil, Habibah; Umor, Mohd Rozi; Hassan, Wan Fuad Wan

    2013-11-01

    This paper aims to provide the overview of occurrence, distribution and origin of the heavy minerals in the study area. A total of 45 selected stream sediment heavy mineral concentrate samples were panned using standard dulangs, dried and separated from other light minerals using bromoform. The heavy minerals were separated into different fractions at different amperes using Frantz Isodynamic magnetic separator. Mineral identification was done using binocular microscope augmented by X-ray diffraction analyses. Mineral abundance data were analysed graphically using triangular diagrams to show their origin. Dominant minerals present in the heavy mineral samples collected are ilmenite, cassiterite, tourmaline, zircon, topaz, and magnetite. The less common minerals, present in trace amounts are hematite, xenotime, allanite, monazite, rutile, anatase, leucoxene, chromite, garnet and olivine. Examination of the heavy mineral assemblage shows that they originated from granite batholiths of the Main Range, Changkat Rembian as well as from the metasedimentary rock in the area. The gold flakes present are found together with cassiterite and topaz indicating that gold originates from the mineralized veins contact-metamorphosed metasedimentary rocks. Almost all samples collected contain cassiterite grains in various amounts. From the mineral assemblage, the source of cassiterite originates from the mineralized quartz veins that cut granitic rocks of Main Range, Changkat Rembian as well as the metasedimentary rock in the area. Greisenized veins containing quartz, mica and tourmaline with the presence of wolframite and arsenopyrite also contribute to the presence of cassiterite in this study area.

  18. The Junggar Immature Continental Crust Province and Its Mineralization

    Institute of Scientific and Technical Information of China (English)

    WANG Jingbin; WANG Yuwang; WANG Lijuan

    2004-01-01

    According to the study on the peripheral orogenic belts of the Junggar basin and combined with the interpretation of geophysical data, this paper points out that there is an Early Paleozoic basement of immature continental crust in the Junggar area, which is mainly composed of Neoproterozoic-Ordovician oceanic crust and weakly metamorphosed covering sedimentary rocks. The Late Paleozoic tectonism and mineralization were developed on the basement of the Early Paleozoic immature continental crust. The Junggar metallogenic province is dominated by Cr, Cu,Ni and Au mineralization. Those large and medium-scale deposits are mainly distributed along the deep faults and particularly near the ophiolitic me1ange zones, and formed in the Late Paleozoic with the peak of mineralization occurring in the Carboniferous-Permian post-collisional stage. The intrusions related to Cu, Ni and Au mineralization generally have low Isr and positive εNd(t) values. The δ34S values of the ore deposits are mostly near zero, and the lead isotopes are mostly of normal lead. All these indicate that the ore-forming material comes either directly from the mantle-derived magma (for chromite and Cu-Ni deposits) or from recirculation of the basement material of the Early Paleozoic immature crust (for most Cu and Au deposits).

  19. Attenuation of Chromium toxicity in mine waste water using water hyacinth

    Directory of Open Access Journals (Sweden)

    Mohanty M.

    2011-12-01

    Full Text Available The mine waste water at South Kaliapani chromite mining area of Orissa (India showed high levels of toxic hexavalent chromium (Cr+6. Cr+6 contaminated mine waste water poses potential threats for biotic community in the vicinity. The current field based phytoremediation study is an in situ approach for attenuation of Cr+6 from mine waste water using water hyacinth (Eichhornia crassipes weeds by rhizofiltration method. The weeds significantly reduced (up to 54% toxic concentrations of Cr+6 from contaminated mine waste water when passed through succeeding water hyacinth ponds. The reduction of toxic chromium level varied with the plant age and passage distance of waste water. Chromium phytoaccumulation and Bio-Concentration Factor (BCF was maximum at growing stage of plant i.e. 75 days old plant. High BCF (10,924 and Transportation Index (32.09 for water hyacinth indicated that the weeds can be used as a tool of phytoremediation to combat the problem of in situ Cr contamination in mining areas.

  20. Thermodynamic properties of chromium bearing slags and minerals. A review

    Energy Technology Data Exchange (ETDEWEB)

    Xiao Yanping; Holappa, L.

    1996-12-31

    In this report, the thermodynamic properties of chromium bearing slags and minerals were reviewed based on the available information in the literature. It includes the analysing methods for oxidation state of chromium in slags, oxidation state of chromium and activities of chromium oxides in slags and minerals. The phase diagrams of chromium oxide systems and chromium distributions between slag and metal phases are also covered ill this review. Concerning the analysing methods, it was found that most of the available approaches are limited to iron free slag systems and the sample preparation is very sensitive to the analysing results. In silicate slags under reducing atmosphere, divalent and trivalent chromium co-exist in the slags. It is agreed that the fraction of divalent chromium to total chromium increases with higher temperature, lower slag basicity and oxygen potential. For the slags under oxidising atmosphere, trivalent, pentavalent and hexavalent states were reported to be stable. The activities of CrO and CrO{sub 1.5} were concluded to have positive deviation from ideal solution. Slag basicity has a positive effect and temperature has a negative effect on the activities of chromium oxides. The phase diagrams of the Cr-O, binary, and ternary chromium containing oxide systems have been examined systematically. The analysis shows that the data on the quaternary and quinary systems are insufficient, and require further investigation. The most important features of the chromium containing silicate slags are the large miscibility gaps and the stability of the chromite spinel. (orig.) (76 refs.)

  1. Mineralogical and geochemical characterization of a rare ultramafic lamprophyre in the Tandilia belt basement, Río de la Plata Craton, Argentina

    Science.gov (United States)

    Dristas, Jorge A.; Martínez, Juan Cruz; Massonne, Hans-Joachim; Pimentel, Marcio M.

    2013-04-01

    A metre-thick ultramafic lamprophyre dyke intrudes the basement of the Tandilia belt at the Sierra Alta de Vela, Argentina. A petrological and geochemical study of this rock and associated small dykes indicates a predominantly calc-alkaline trend. Phlogopite K-Ar dating of the ultramafic lamprophyre gave a minimum age of 1928 ± 54 Ma as a late event of the Transamazonian Orogeny, which is well represented in the basement of the Tandilia belt. An electron microprobe study indicates the presence of phlogopite, albite, chromite and Cr-rich phenocrysts and Cr-free microphenocrysts of diopside as primary minerals. Subsequent to deformation at the contacts with the wall rock, metasomatism generated strongly zoned amphibole (edenite, pargasite, Mg-hastingite and tremolite compositions) and andradite as well as chlorite, sericite, albite, apatite and calcite. The central zone of the lamprophyre is almost undeformed and exhibits some ocellar texture. Geochemical and isotopic signatures of the lamprophyre suggest that its magma source may have previously undergone incompatible element enrichment of the mantle source, representing the original precursor magma for the calc-alkaline dyke series of the Sierra Alta de Vela.

  2. Electrochemical Reduction of Oxygen and Nitric oxide at low Temperature on La1-xSrxCr0.97V0.03O3-δ Cathodes

    DEFF Research Database (Denmark)

    Kammer Hansen, Kent

    2013-01-01

    Five La1-xSrxCr0.97V0.03O3-δ (x = 0, 0.05, 0.15, 0.25, 0.35) perovskites were synthesized and characterized by powder XRD and cyclic voltammetry on cone-shaped electrodes in 10% oxygen in argon or 1% nitric oxide in argon at 200, 300 and 400°C. It was shown that the activation energy...... for the reduction of oxygen is higher than the activation energy for the reduction nitric oxide. The activity for the reduction of both oxygen and nitric oxide was shown to be highest for the end member La0.65Sr0.35Cr0.97V0.03O3-δ. The highest ratio between the current densities in the nitric oxide and oxygen...... containing atmospheres was found for the end member LaCr0.97V0.03O3-δ. The chromites also showed activity as anodes for either oxygen evolution or oxidation of nitric oxide to nitrogen dioxide....

  3. TECTONIC SETTING AND METALLOGENESIS OF THE PRINCIPAL SECTORS OF THE TETHYAN EURASIAN METALLOGENIC BELT

    Institute of Scientific and Technical Information of China (English)

    Slobodan; Jankovic

    2001-01-01

    Three global metallogenic belts were formed in the world during Mesozoic and post-Mesozoic times. Two of them are situated along the western and eastern Pacific margins, and the third one - the Tethyan Eurasian metallogenic belt (TEMB) is related to the domain of Eurasian plate and flanked on the south by the Afro-Arabian and Indian plates. The general tectonic evolution of the realm where the TEMB was formed is closely connected with the history of Tethys. The emplacement of ore deposits and the development of regional metallogenic units are related to a definitive time interval and to specific tectonic settings such as: (1) Intracontinental rifting along the northern margin of Gondwana and/or fragments already separated; (2) Oceanic environments (i.e. ophiolite complexes and ocean floor sediments) host podiform chromite deposits, volcano-sedimentary cupriferous pyrite deposits (Cyprus type), stratiform manganese deposits, and sporadically PGE deposits; (3) Subduction related settings involve mainly porphyry copper deposits, hydrothermal massive sulphide polymetallic deposits, and epithermal deposits. So far identified mineralization of porphyry copper exceeds in the TEMB over 100 million tons of copper metal; and(4) Collision and post-collision continent-continent setting includes deposits of lead-zinc, antimony, gold, in some sectors tin deposits, as well. The giant deposits of Li-pegmatite occur sporadically.The TEMB is almost a continuously mineralized belt, but within it, some sectors display specific features of tectonic settings, association of elements, minerals and morphogenetic types of mineralization.

  4. Low temperature hydrothermal synthesis, structure and magnetic properties of RECrO3 (RE = La, Pr, Nd, Sm).

    Science.gov (United States)

    Wang, Shan; Huang, Keke; Hou, Changmin; Yuan, Long; Wu, Xiaofeng; Lu, Dayong

    2015-10-21

    Perovskite structured rare-earth chromites (RECrO3) are an interesting family of functional materials due to their wide application in numerous areas. Various methods have been used to synthesize this family of materials; however, such methods usually need a high temperature crystallization process above 800 °C, and only produce polycrystalline ceramics. Herein, a series of RECrO3 single crystal samples with uniform particle sizes were prepared via a mild hydrothermal method with temperatures as low as 240-260 °C, and the synthesis conditions were studied in detail. Samples of LaCrO3, PrCrO3, and NdCrO3 were indexed to the Pnma space group, whereas SmCrO3 was indexed to Pbnm. The shapes of the crystals changed from cubic to plate as a result of the crystal lattice distortions induced by the reduction in the size of the A-site rare-earth cation. Raman spectra of the samples showed characteristic vibration modes of CrO6 clusters. Temperature dependent magnetization studies showed a transition from antiferromagnetism to paramagnetism in all the samples. Higher maximum and residual magnetization was achieved in all the hydrothermally prepared samples compared with those prepared by other methods. PMID:26374249

  5. Comparison of Different Machine Learning Algorithms for Lithological Mapping Using Remote Sensing Data and Morphological Features: A Case Study in Kurdistan Region, NE Iraq

    Science.gov (United States)

    Othman, Arsalan; Gloaguen, Richard

    2015-04-01

    Topographic effects and complex vegetation cover hinder lithology classification in mountain regions based not only in field, but also in reflectance remote sensing data. The area of interest "Bardi-Zard" is located in the NE of Iraq. It is part of the Zagros orogenic belt, where seven lithological units outcrop and is known for its chromite deposit. The aim of this study is to compare three machine learning algorithms (MLAs): Maximum Likelihood (ML), Support Vector Machines (SVM), and Random Forest (RF) in the context of a supervised lithology classification task using Advanced Space-borne Thermal Emission and Reflection radiometer (ASTER) satellite, its derived, spatial information (spatial coordinates) and geomorphic data. We emphasize the enhancement in remote sensing lithological mapping accuracy that arises from the integration of geomorphic features and spatial information (spatial coordinates) in classifications. This study identifies that RF is better than ML and SVM algorithms in almost the sixteen combination datasets, which were tested. The overall accuracy of the best dataset combination with the RF map for the all seven classes reach ~80% and the producer and user's accuracies are ~73.91% and 76.09% respectively while the kappa coefficient is ~0.76. TPI is more effective with SVM algorithm than an RF algorithm. This paper demonstrates that adding geomorphic indices such as TPI and spatial information in the dataset increases the lithological classification accuracy.

  6. High-pressure X-ray diffraction and Raman spectroscopy of CaFe2O4-type β-CaCr2O4

    Science.gov (United States)

    Zhai, Shuangmeng; Yin, Yuan; Shieh, Sean R.; Shan, Shuangming; Xue, Weihong; Wang, Ching-Pao; Yang, Ke; Higo, Yuji

    2016-04-01

    In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic studies of orthorhombic CaFe2O4-type β-CaCr2O4 chromite were carried out up to 16.2 and 32.0 GPa at room temperature using multi-anvil apparatus and diamond anvil cell, respectively. No phase transition was observed in this study. Fitting a third-order Birch-Murnaghan equation of state to the P-V data yields a zero-pressure volume of V 0 = 286.8(1) Å3, an isothermal bulk modulus of K 0 = 183(5) GPa and the first pressure derivative of isothermal bulk modulus K 0' = 4.1(8). Analyses of axial compressibilities show anisotropic elasticity for β-CaCr2O4 since the a-axis is more compressible than the b- and c-axis. Based on the obtained and previous results, the compressibility of several CaFe2O4-type phases was compared. The high-pressure Raman spectra of β-CaCr2O4 were analyzed to determine the pressure dependences and mode Grüneisen parameters of Raman-active bands. The thermal Grüneisen parameter of β-CaCr2O4 is determined to be 0.93(2), which is smaller than those of CaFe2O4-type CaAl2O4 and MgAl2O4.

  7. Electron Energy-Loss Spectroscopy: Fundamentals and applications in the characterization of minerals

    International Nuclear Information System (INIS)

    The combined use of an energy-loss spectrometer and an analytical electron microscope with fine probe forming capabilities provides a wealth of information about the sample at high spatial resolution. Fundamental principles governing the physics of the interaction between the fast electron and a thin foil sample, to account for the fine structure in the inelastically scattered fast electron distribution (Electron-Energy Loss Spectroscopy, EELS), will be reviewed. General application of EELS is in the area of low atomic number elements (Z < 11) microanalysis, where it significantly complements the more widely used Energy Dispersive X-ray Spectroscopy (EDXS). However, a careful analysis of the low loss plasmon oscillations and the fine structure in the core-loss edges, can provide additional information related to the bonding and electronic structure of the sample. An illustration of this is presented from our study of Cδ diamond residue from the Allende carbonaceous chondrite. Combination of EELS with channeling effects can provide specific site occupation/valence information in crystalline materials. Details of this novel crystallographic method will be outlined and illustrated with an example of the study of chromite spinels. Finally, some pertinent experimental details will be discussed. 7 figs

  8. Development of novel copper-based sorbents for hot-gas cleanup. Technical report, March 1, 1992--May 31, 1992

    Energy Technology Data Exchange (ETDEWEB)

    Abbasian, J.; Hill, A.H.; Wangerow, J.R. [Institute of Gas Technology, Chicago, IL (United States); Flytzani-Stephanopoulos, M.; Bo, L.; Patel, C. [Massachusetts Inst. of Tech., Cambridge, MA (United States)

    1992-10-01

    The objective of this investigation is to evaluate several novel copper-based binary oxides for their suitability as regenerable sorbents for hot gas cleanup application in the temperature range of 650{degrees} to 850{degrees}C. During this quarter cyclic sulfidation/regeneration tests of the sorbents Cu{sub 2}Cr-O and Cu-Ce-0 were conducted using different compositions of the feed gases to investigate the effects of H{sub 2}0, H{sub 2} and CO. These tests were conducted in a packed-bed microreactor at 850{degrees}C. The results of these tests showed that H{sub 2} and CO (along with C02) had a significant effect on the H{sub 2}S pre-breakthrough levels, whereas H{sub 2}0 did not have an effect. The physical properties of the fresh and reacted samples of the Cu-2Cr-O and Cu-Ce-0 sorbents prepared in this program and used in the cyclic sulfidation/regeneration tests were also measured. In addition, sulfidation/regeneration tests were conducted using two commercial copper chromite sorbents (G-13 and G-89, United Catalyst, Inc.) and a zinc titanate sorbent (L-3014) in a one-inch fluidized-bed reactor at 650{degrees}C. The G-13 sorbent appears to have a much higher sulfur capacity than the G-89 sorbent.

  9. Empleo de cromitas refractarias para la obtención de fundentes aglomerados utilizados en la soldadura automática por arco sumergido (SAW

    Directory of Open Access Journals (Sweden)

    Perdomo-González, L.

    2003-08-01

    Full Text Available In the present work high carbon ferrochrome (load ferrochrome and slags are obtained, starting frora the métallurgie reductive processing of refractory chromites. The obtaining of alloys and slags is studied using an experiment design based in the relationships among components. The chemical compositions of alloys and slags guarantee their application for the conformation of alloys loads and matrix fluxes amassed for the superficial filling by means of submerged arc welding (SAW. The melting-reduction process is carried out in an electric arc furnace.

    En el presente trabajo se obtienen ferrocromo de alto carbono (ferrocromo de carga y escorias a partir del proceso de reducción de cromitas refractarias. Mediante la utilización de un diseño de experimento de relaciones entre componentes, se estudia la obtención de aleaciones y escorias. La composición química de ambas garantiza su aplicación para la conformación de cargas aleantes y matrices de fundentes aglomerados, para el relleno superficial mediante soldadura automática por arco sumergido (SAW. El proceso de fusión-reducción se realiza en un horno eléctrico de arco.

  10. Reactions of metal ions at surfaces of hydrous iron oxide

    Science.gov (United States)

    Hem, J.D.

    1977-01-01

    Cu, Ag and Cr concentrations in natural water may be lowered by mild chemical reduction involving ferric hydroxide-ferrous ion redox processes. V and Mo solubilities may be controlled by precipitation of ferrous vanadate or molybdate. Concentrations as low as 10-8.00 or 10-9.00 M are readily attainable for all these metals in oxygen-depleted systems that are relatively rich in Fe. Deposition of manganese oxides such as Mn3O4 can be catalyzed in oxygenated water by coupling to ferrous-ferric redox reactions. Once formed, these oxides may disproportionate, giving Mn4+ oxides. This reaction produces strongly oxidizing conditions at manganese oxide surfaces. The solubility of As is significantly influenced by ferric iron only at low pH. Spinel structures such as chromite or ferrites of Cu, Ni, and Zn, are very stable and if locally developed on ferric hydroxide surfaces could bring about solubilities much below 10-9.00 M for divalent metals near neutral pH. Solubilities calculated from thermodynamic data are shown graphically and compared with observed concentrations in some natural systems. ?? 1977.

  11. Magnetocaloric properties of rare-earth substituted DyCrO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    McDannald, A. [Material Science and Engineering Department, University of Connecticut, Storrs, Connecticut 06269 (United States); Jain, M., E-mail: menka.jain@uconn.edu [Institute of Material Science, University of Connecticut, Storrs, Connecticut 06269 (United States); Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States)

    2015-07-28

    Recently, there has been a focus on the need for efficient refrigeration technology without the use of expensive or harmful working fluids, especially at temperatures below 30 K. Solid state refrigeration, based on the magnetocaloric effect, provides a possible solution to this problem. The rare-earth chromites (RCrO{sub 3}), especially DyCrO{sub 3}, with its large magnetic moment dysprosium ion, are potential candidates for such an application. The Dy{sup 3+} ordering transition at low temperatures (<10 K) likely causes a large magnetocaloric response in this material. This study investigates the possibility of tuning the magnetocaloric properties through the use of rare-earth substitution. Both Y{sup 3+} and Ho{sup 3+} substitutions were found to decrease the magnetocaloric response by disrupting the R{sup 3+} ordering. Whereas Er{sup 3+} substitution was found to increase the magnetocaloric response, likely due to an increase in the R{sup 3+} ordering temperature. The large magnetocaloric entropy change of Er{sup 3+} substituted DyCrO{sub 3} (10.92 J/kg K with a relative cooling power of 237 J/kg at 40 kOe and 5 K) indicates that this material system is well suited for low temperature (<30 K) solid state refrigeration applications.

  12. Size dependence of structure and magnetic properties of CoCr2O4 nanoparticles synthesized by hydrothermal technique

    Science.gov (United States)

    Tian, Zhaoming; Zhu, Changming; Wang, Junfeng; Xia, Zhengcai; Liu, Yong; Yuan, Songliu

    2015-03-01

    The size dependence of structure and magnetic behavior has been investigated on spinel chromite CoCr2O4 nanoparticles (NPs) with different particles from ~2.8 to ~19.7 nm, synthesized by a hydrothermal technique. The microstructure analysis shows that the lattice parameter increases monotonically with reduced particle sizes. Compared with the bulk sample, all synthesized NPs exhibit lower Curie temperature (TC~87 K) from paramagnetic (PM) to collinear short-range ferrimagnetic (FiM) state, and this PM-FiM transition is gradually degraded with decreased particle sizes and nearly vanishes for ~2.8 nm NPs. No magnetic transition from short-range FiM order to long-range spiral spin structure is found at low temperatures contrast to the bulk ones. Instead, a cluster spin-glass (SG) transition appears for NPs with D≤5.4 nm. The dynamic behavior of the cluster SG can be described by a power law with the spin relaxation time in the range of 10-10-10-8 s and critical exponent zv‧=9.9±0.6, in accordance with a three-dimensional Ising SG behavior. The glass transition temperature (Tg) decreases from 16.3 K for ~5.4 nm to 12.8 K for ~2.8 nm NPs.

  13. Review: Perspectives on the metallic interconnects for solid oxide fuel cells

    Institute of Scientific and Technical Information of China (English)

    ZHUWei-zhong; YANMi

    2004-01-01

    The various stages and progress in the development of interconnect materials for solid oxide fuel cells (SOFCs )over the last two decades are reviewed. The criteria for the application of materials as interconnects are highlighted. Interconnects based on lanthanum chromite ceramics demonstrate many inherent drawbacks and therefore are only useful for SOFCs operating around 1000℃. The advance in the research of anode-supported flat SOFCs facilitates the replacement of ceramic interconnects with metallic ones due to their significantly lowered working temperature. Besides, interconnects made of metals or alloys offer many advantages as compared to their ceramic counterpart. The oxidation response and thermal expansion behaviors of various prospective metallic interconnects are examined and evaluated. The minimization of contact resistance to achieve desired and reliable stack performance during their projected lifetime still remains a highly challenging issue with metallic interconnects. Inexpensive coating materials and techniques may play a key role in promoting the commercialization of SOFC stack whose interconnects are constructed of some current commercially available alloys. Alternatively, development of new metallic materials that are capable of forming stable oxide scales with sluggish growth rate and sufficient electrical conductivity is called for.

  14. Perspectives on the metallic interconnects for solid oxide fuel cells

    Institute of Scientific and Technical Information of China (English)

    ZHU Wei-zhong; YAN Mi

    2004-01-01

    The various stages and progress in the development of interconnect materials for solid oxide fuel cells (SOFCs) over the last two decades are reviewed. The criteria for the application of materials as interconnects are highlighted. Interconnects based on lanthanum chromite ceramics demonstrate many inherent drawbacks and therefore are only useful for SOFCs operating around 1000 ℃. The advance in the research of anode-supported flat SOFCs facilitates the replacement of ceramic interconnects with metallic ones due to their significantly lowered working temperature. Besides, interconnects made of metals or alloys offer many advantages as compared to their ceramic counterpart. The oxidation response and thermal expansion behaviors of various prospective metallic interconnects are examined and evaluated. The minimization of contact resistance to achieve desired and reliable stack performance during their projected lifetime still remains a highly challenging issue with metallic interconnects. Inexpensive coating materials and techniques may play a key role in pro moting the commercialization of SOFC stack whose interconnects are constructed of some current commercially available alloys. Alternatively, development of new metallic materials that are capable of forming stable oxide scales with sluggish growth rate and sufficient electrical conductivity is called for.

  15. Cr-isotope fractionation during oxidative weathering of ultramafic rocks and its impact on river waters

    DEFF Research Database (Denmark)

    Paulukat, Cora Stefanie; Døssing, Lasse Nørbye; Mondal, Sisir K.;

    We investigated Cr isotope fractionation during soil formation from Precambrian ultramafic rocks. A soil profile was logged in an active open-cast chromite mine (Sukinda Valley, India). In addition, mine and river waters, as well as seawater were collected to trace the Cr-isotope signal...... into the sea. The aim of the study is to recognize Cr isotope fractionation processes within the mining-area and the impact of the mine runoff on the δ53Cr of the nearby river. The weathering profile shows a distinct upward trend to more negative δ53Cr values. While the well preserved rocks at the base closely...... reflect mantle inventory (-0.124±0.101‰ 1), the δ53Cr from the more weathered upper part of the profile is as low as -1.28±0.022‰. These data are consistent with the findings of Crowe et al. (in press). They demonstrated that Cr(III) becomes oxidised during rock weathering, which leads to an isotopic...

  16. The Behaviour of Chromium Isotopes during the Oxidative Weathering of Ultramafic Rocks

    DEFF Research Database (Denmark)

    Paulukat, Cora Stefanie; Døssing, Lasse Nørbye; Mondal, Sisir K.;

    The chromium isotope system has been proven to be a redox-sensitve proxy in ancient and modern environmental studies (e.g. [1], [2]). In this study we investigated Cr isotope fractionation during soil formation from Archean (3.1-3.3 Ga) ultramafic rocks, intruded into metamorphic rocks of the Iron...... Ore Group in the southern Singhbhum Craton (Orissa, India)[3]. A modern weathering profile was logged in an active open cast chromite mine (Sukinda valley). The Cr isotope data of samples from the weathering profile are fractionaed. While the least weathered horizons at the base of the profile reflect...... mantle inventory values (-0.124±0.101‰ [4]), the δ53Cr values from the more weathered upper part of the profile are as low as -1.28±0.08‰, indicative of the loss of an isotopically heavy (53Cr enriched) fraction to the runoff. Mass-balance calculations show that the highly weathered horizons...

  17. Contamination of soil, medicinal, and fodder plants with lead and cadmium present in mine-affected areas, Northern Pakistan.

    Science.gov (United States)

    Nawab, Javed; Khan, Sardar; Shah, Mohammad Tahir; Qamar, Zahir; Din, Islamud; Mahmood, Qaisar; Gul, Nayab; Huang, Qing

    2015-09-01

    This study aimed to investigate the lead (Pb) and cadmium (Cd) concentrations in the soil and plants (medicinal and fodder) grown in chromite mining-affected areas, Northern Pakistan. Soil and plant samples were collected and analyzed for Pb and Cd concentrations using atomic absorption spectrometer. Soil pollution load indices (PLIs) were greater than 2 for both Cd and Pb, indicating high level of contamination in the study area. Furthermore, Cd concentrations in the soil surrounding the mining sites exceeded the maximum allowable limit (MAL) (0.6 mg kg(-1)), while the concentrations of Pb were lower than the MAL (350 mg kg(-1)) set by State Environmental Protection Administration (SEPA) for agriculture soil. The concentrations of Cd and Pb were significantly higher (P soil of the mining-contaminated sites as compared to the reference site, which can be attributed to the dispersion of toxic heavy metals, present in the bed rocks and waste of the mines. The concentrations of Pb and Cd in majority of medicinal and fodder plant species grown in surrounding areas of mines were higher than their MALs set by World Health Organization/Food Agriculture Organization (WHO/FAO) for herbal (10 and 0.3 mg kg(-1), respectively) and edible (0.3 and 0.2 mg kg(-1), respectively) plants. The high concentrations of Cd and Pb may cause contamination of the food chain and health risk.

  18. A Petrographic and Mineralogical Study of Volcanic Rocks from the Mayaxueshan Area, North Qilian Fold Belt, NW China

    Institute of Scientific and Technical Information of China (English)

    徐达伟; 萧炎宏

    2002-01-01

    The Ordovician volcanic rocks in the Mayaxueshan area have been pervasively altered or metamorphosedand contain abundant secondary minerals such as albite, chlorite, epidote, prehnite, pumpellyite, actinolite, titanite, quartz,and/or calcite. They were denoted as spilites or spilitic rocks in terms of their petrographic features and mineral assem-blages. The metamorphic grades of the volcanic rocks are equivalent to that of the intercalated metaclastic rocks. Thisindicates that both the spilitic volcanic rocks and metaclastic rocks in the Mayaxueshan area have formed as a result ofCaledonian regional metamorphism. We suggest that the previously denoted spilitic rocks or altered volcanic rocks shouldbe re-denoted as metabasalts or metabasaltic rocks. The metamorphic grade of the volcanic rocks increases with their age:prehnite-pumpellyite facies for the upper part of the Middle Ordovician volcanic rocks, prehnite-pumpellyite to lowergreenschist facies for the lower part of the Middle Ordovician volcanic rocks, and lower greenschist facies for the LowerOrdovician volcanic rocks. The P-T conditions are estimated as T = 240 - 290C and P = 1.5 - 4.5 kbar for the lower partof the Middle Ordovician rocks, and T = ~ 300~C for the Lower Ordovician rocks. The variations of mineral assemblagesoccurring at different domains of the volcanic rocks were controlled by the variations of the effective bulk composition inthose domains during metamorphism. The geochemical characteristics of Mg-Al chromite in the Mayaxueshan volcanicrocks are consistent with an origin of island arc environment.

  19. Potentiostatic Oxide Growth Kinetics on Ni-Cr and Co-Cr Alloys: Potential and pH Dependences

    International Nuclear Information System (INIS)

    Oxide growth kinetics on the Ni-Cr-Fe alloy Inconel 600 and the Co-Cr alloy Stellite 6 under potentiostatic polarization have been investigated by current measurements augmented by ex-situ surface analyses. The results reveal a mechanism for metal oxidation and oxide formation that is common to both alloys. The reaction thermodynamics for the oxidation of a metal determine whether a certain metal oxidation can or cannot occur. However, the metal oxidation proceeds via two competing pathways, oxide formation and metal ion dissolution. At pH 10.6 where the solubilities of FeII, NiII or CoII species are near their minima, oxide formation is favoured over metal ion dissolution. As the oxide grows, the rate of metal oxidation decreases with time due to an increase in the electrochemical potential barrier. The oxide formation occurs sequentially; the conversion of the preformed Cr2O3 film to chromite (FeCr2O4 or CoCr2O4) proceeds before the next layers of Fe3O4/NiFe2O4 and NiO/Ni(OH)2 grow on Inconel 600, or CoO/Co(OH)2 grows on Stellite 6. The effect of a different EAPP is to limit the oxidation sequence. The pH does not directly affect the driving force for metal oxidation but it strongly influences the relative rates of oxide formation and metal dissolution, thereby affecting metal oxidation kinetics

  20. Estimation of individual dust exposure by magnetopneumography in stainless steel production.

    Science.gov (United States)

    Huvinen, M; Oksanen, L; Kalliomäki, K; Kalliomäki, P L; Moilanen, M

    1997-06-20

    The objectives of the study were to measure the magnetic dust lung burden of workers in stainless steel production by magnetopneumography (MPG) and to investigate the relationship of the results with air-borne concentrations of dust, total and hexavalent chromium as well as urinary excretion of chromium. There were 128 workers from the chromite mine, sintering plant, ferrochrome smelter, stainless steel smelting shop, cold rolling mill and welding shop in the exposed groups and five persons from the office staff in the control group. The remanent magnetic field (RMF) in the lungs was slightly elevated among workers in the ferrochromium and steel smelting shops; the levels were, however, lower than those reported for welders earlier and those observed in the welding/repair shop. Workers in the mine, concentrator and sintering plants and in the cold rolling mill exhibited remanent magnetic fields comparable to the referents. There was a relationship between the RMF and the actual urinary chromium concentration. Miners and concentrator and sintering plant workers showed retarded relaxation rate (ReR) of the remanent magnetic field. However, the RMF of the first two of these groups were low (< 0.1 nT) and this made it difficult to measure the ReR accurately. The duration of exposure correlated weakly but significantly with the relaxation rate, while smoking was not related to it.

  1. Elemental and mineralogical characteristic and speciation of some elements in Canadian coals

    Energy Technology Data Exchange (ETDEWEB)

    Goodarzi, F.; Labonte, M. [Natural Resources Canada, Calgary, AB (Canada). Geological Survey of Canada

    2005-07-01

    This study examined Canadian feed coals that are subbituminous to bituminous in rank with a sulphur content of 0.32-3.55 per cent. The main minerals within these coals are quartz and aluminosilicates. The accessory minerals include pyrite, sphalerite, barite, calcite, anhydrite, chromite, zircon, biotite, and monazite. Gorceixite, which is typically associated with degraded volcanic ash, is found in one of the subbituminous feed coals. The sulphur content of the feed coals suggests that the feed coal formed in a fresh water setting containing the least amount of sulphur. Those associated with evaporites have the highest S content. The concentrations of cadmium, chromium, copper, mercury, nickel, selenium, vanadium and zinc in these feed coals are low compared to world coals. Mercury content of these feed coals ranges from 0.04 ppm to 0.16 ppm, also a low value compared to world coals. Mercury is generally associated with the pyritic portion of coal and has direct correlation to arsenic and sulphur content in these coals. Arsenic in low sulphur coals is generally associated with coal macerals and in higher sulphur coals with pyrite. The speciation of arsenic, chromium and nickel indicates that arsenic is present in the less-toxic form As{sup +5} and Cr is present as Cr{sup 3+}, an essential human trace nutrient, found in subbituminous and bituminous ranked coals and nickel is present mostly as non-toxic Ni{sup 2+}.

  2. Gibbs energy of formation of cobalt divanadium tetroxide

    Science.gov (United States)

    Jacob, K. T.; Pandit, S. Shashidhara

    1985-11-01

    The Gibbs energy of formation of V 2O 3-saturated spinel CoV 2O 4 has been measured in the temperature range 900-1700 K using a solid state galvanic cell, which can be represented as Pt, Co + CoV 2O 4 + {V2O3}/{(CaO)}{ZrO2}/{Co} + CoO, Pt. The standard free energy of formation of cobalt vanadite from component oxides can be represented as CoO (rs) + V 2O 3 (cor) → CoV 2O 4 (sp), ΔG° = -30,125 - 5.06 T (± 150) J mole -1. Cation mixing on crystallographically nonequivalent sites of the spinel is responsible for the decrease in free energy with increasing temperature. A correlation between "second law" entropies of formation of cubic 2-3 spinels from component oxides with rock salt and corundum structures and cation distribution is presented. Based on the information obtained in this study and trends in the stability of aluminate and chromite spinels, it can be deduced that copper vanadite is unstable.

  3. Distribution and characteristics of diamonds from Myanmar

    Science.gov (United States)

    Win, T. T.; Davies, R. M.; Griffin, W. L.; Wathanakul, P.; French, D. H.

    2001-08-01

    Diamonds occur in headless placers at several locations within Myanmar. Twenty-six stones from the Momeik area of northern Myanmar and 111 stones from the Theindaw area of southern Myanmar have been studied to characterise their morphology, crystal forms, colour, degree of resorption, surface features, internal structures, mineral inclusions, and nitrogen content and aggregation state. Most stones grew originally as octahedra, but now show very high degrees of resorption, and highly polished surfaces, reflecting transport in a magma. Etch features are abundant, and breakage and abrasion are common, due to alluvial transport. Brown radiation spots are common, suggesting that these diamonds have a long history in surface environments. Cathodoluminescence (CL) images of plates and whole stones commonly display marked oscillatory zoning of yellow and blue bands, outlining octahedral growth zones. Many other stones show uniform yellow CL. Syngenetic mineral inclusions identified thus far are mainly of peridotitic paragenesis and include olivine, chromite and native iron. Infrared spectroscopy studies show that ˜10% of the diamonds have very low-N contents (Type II diamonds). More N-rich diamonds show high degrees of aggregation (Type IaAB). Both types are consistent with derivation from the upper mantle, rather than from crustal metamorphic sources. The primary source of these diamonds is believed to be an alkaline igneous rock (lamproitic rather than kimberlitic) but they may have reached their present locations via a secondary collector such as a sedimentary rock.

  4. [Multi-spectroscopy applied to study on a late neolithic colored stone from Yuhui Site in Huaihe Basin].

    Science.gov (United States)

    Wang, Hai-gang; Jin, Zheng-yao; Xie, Zhi; Fan, An-chuan; Yan, Li-feng; Zhu, Bing-quan; Wang, Ji-huai

    2013-09-01

    The unearthing of a large number of red-yellow colored stones in Yuhui Site, Bengbu city, Anhui province of China, which was the only site of Longshan culture appointed by "Origin of the Chinese Civilization Project" in the Huaihe River basin, has drawn a widespread attention in archaeology. The present research was undertaken to examine elements, mineral composition and thermal history of one red-yellow color stone in different positions, classified according to specialized colors, by means of synchrotron radiation X-ray fluorescence (SR-XRF), X-ray diffraction (XRD), laser Raman spectroscopy (LRS), electron probe micro-analysis (EPMA) and thermoluminescence (TL). The results show that the main body of the color stone is limonite with a large amount of quartz inclusion. The yellow substances on the surface layer of the color stone were identified as goethite (alpha-FeOOH), and the red ones as red ochre (alpha-Fe2O3+clay+silica). The internal yellow brown substances inside the stone are mainly aphanitic goethite with a number of chromites and manganese dioxide, and also with small quantity of barite and bismuth. And the color stones are without historical firing treatment. These kinds of special polymetallic ores with unique nature and complex geologic history, which were unearthed in the late neolithic site with large numbers, may be closely related to some kind of primitive religious beliefs and special sacrificial practices. PMID:24369621

  5. Preparation of sodium bichromate dihydrate by hydrothermal oxidizing reaction%碳素铬铁水热法制红矾钠

    Institute of Scientific and Technical Information of China (English)

    纪柱

    2012-01-01

    在碳素铬铁水热法制铬酸钠的基础上,充分利用二氧化碳的酸化、催化作用,可在不增添设备和原料的情况下,使反应产物由含少量游离碱的铬酸钠碱性液,转变为含少量铬酸钠的重铬酸钠溶液,同时碱耗下降1/3.该反应可用纯碱代替烧碱.结果表明,采用炉料铬粉水热反应制得的红矾钠成本可望低于铬铁矿焙烧法的成本.%Based on hydrothermal oxidizing reaction of high content carbon ferrochrome for manufacturing sodium chromate, the reaction product sodium chromate alkaline solution containing a small amount of free alkali was converted into sodium bichromate solution containing a small amount of sodium chromate,and meanwhile alkali consumption declined by 1/3,by taking full advantage of acidification and catalytic effect of carbon dioxide, and without adding equipment and raw material. Soda can be used to replace caustic soda in the reaction.Experiment results showed that sodium bichromate cost of applying high content carbon ferrochrome powder hydrothermal oxidizing reaction promises to be less than that of high-temperature chromite roasting.

  6. Ultrasound Velocity Measurements in the Geometrically Frustrated Spinel MgCr2O4

    Science.gov (United States)

    Watanabe, Tadataka; Kousaka, Yusuke; Tomiyasu, Keisuke

    2012-02-01

    Magnesium chromite spinel MgCr2O4 is a geometrically frustrated magnet with the Néel temperature TN˜13 K, and the Weiss temperature θW= -390 K. Recent inelastic neutron scattering experiments provided a compelling evidence for the spin molecular ground states in not only the paramagnetic phase but also the antiferromagnetic phase. We performed ultrasound velocity measurements of MgCr2O4 in all the symmetrically independent elastic moduli of C11, (C11-C12)/2, and C44. Temperature dependence of all of these elastic moduli exhibits a remarkable softening in the paramagnetic phase. Taking into account the absence of orbital degrees of freedom in Cr^3+ (3d^3) in MgCr2O4, the spin degrees of freedom should play a significant role for the elastic softening. The most probable origin for the elastic softening in the paramagnetic phase is the strong coupling of the acoustic phonons to the molecular spin fluctuations.

  7. Sulfide mineralization in ultramafic rocks of the Faryab ophiolite complex, southern Kerman

    Directory of Open Access Journals (Sweden)

    Mohammad Ali Rajabzadeh

    2015-10-01

    Full Text Available Introduction Worldwide, Ni-Cu and PGE magmatic sulfide deposits are confined to the lower parts of stratiform mafic and ultramafic complexes. However, ophiolite mafic and ultramafic complexes have been rarely explored for sulfide deposits despite the fact that they have been extensively explored and exploited for chromite. Sulfide saturation during magmatic evolution is necessary for sulfide mineralization, in which sulfide melts scavenge chalcophile metals from the parent magma and concentrate them in specific lithological zones. The lack of exploration for sulfides in this environment suggests that sulfide saturation is rarely attained in ophiolite-related magmas. Some ophiolites, however, contain sulfide deposits, such as at Acoje in Philippines, and Cliffs in Shetland, U.K. (Evans, 2000; Naldrett, 2004. The Faryab ophiolite complex in southern Kerman Province, the most important mining area for chromite deposits in Iran, is located in the southwest part of the Makran Zone. Evidence of sulfide mineralization has been reported there by some authors (e.g. Rajabzadeh and Moosavinasab, 2013. This paper discusses the genesis of sulfides in the Faryab ophiolite using mineral chemistry of the major mineral phases in different rocks of the ophiolite column in order to determine the possible lithological location of sulfide deposits. Materials and methods Seventy three rock samples from cumulate units were collected from surficial occurrences and drill core. The samples were studied using conventional microscopic methods and the mineralogy confirmed by x-ray diffraction. Electron microprobe analysis was carried out on different mineral phases in order to determine the chemistry of the minerals used in the interpretation of magma evolution in the Faryab ophiolite. Lithologically, the Faryab ophiolite complex is divided into two major parts: the northern part includes magmatic rocks and the southern part is comprised of rocks residual after partial

  8. Hf, Zr, and REE partition coefficients between ilmenite and liquid - Implications for lunar petrogenesis

    Science.gov (United States)

    Nakamura, Y.; Fujimaki, H.; Nakamura, N.; Tatsumoto, M.; Mckay, G. A.

    1986-01-01

    Partition coefficients (D) between ilmenite and coexisting liquid were determined under near-lunar conditions for Hf, Zr, and REE. Through isotope dilution analysis, ilmenite D values of 0.41 and 0.33 were obtained for Hf and Zr respectively, values significantly lower than those of ilmenite from a kimberlite megacryst. Partition coefficients of REE for the synthesized ilmenite are slightly smaller than those of ilmenite from the kimberlite megacryst, and the lunar (Lu) partition coefficient is 0.056. These results suggest that ilmenite was significant in the lunar-Hf evolution of lunar mare basalts. Using lunar and Hf D values for ilmenite, the Lu-Hf evolution of lunar cumulates and the coexisting magma was examined for various crystallization sequences. The Lu-Hf variation trend of most high-Ti mare basalts is explained by a small degree of partial cumulate melting, though a higher degree is required to explain the variation of very low-Ti basalts, green glass, and Apollo 12 low-Ti basalts. Apollo 15 low-Ti basalts may require chromite crystallization as well.

  9. DFT+U calculation of the Cr K pre-edge structures in ZnCr2O4

    Science.gov (United States)

    Rozsályi, E.; Verger, L.; Cabaret, D.; Juhin, A.

    2016-05-01

    Zinc chromite ZnCr2O4 has been investigated by X-ray absorption near edge structure (XANES) spectroscopy at the Cr K-edge, with the objective of better understanding the origin of the electronic excitations giving rise to the pre-edge features. In particular, the origin of a third feature visible only in Cr-rich compounds of the ZnAl2O4-ZnCr2O4 solid solution is studied. Standard density functional theory (DFT) XANES calculations were first performed, then a Hubbard U parameter was included in an attempt to improve the relative peak positions by increasing the localization of the Cr 3d states. The origin of the pre-edge features in ZnCr2O4 has been analyzed using DFT+U calculations, local projected densities of states and the assignment of the spectral features for the dilute ZnAl2O4:Cr3+ compound. We show that DFT+U does not overcome the limitations of standard DFT in modeling the relative peak positions, and that approaches including advanced description of the electron-hole interaction are needed.

  10. Isotopic anomalies of noble gases in meteorites and their origins. III - LL-chondrites

    Science.gov (United States)

    Alaerts, L.; Lewis, R. S.; Anders, E.

    1979-01-01

    Nine LL-chondrites were studied by selective etching to characterize the noble gas components in three mineral fractions: HF-HCl-solubles, chromite and carbon. The Ne-20/Ar-36 ratio is considered, noting that chondrites of different petrologic types cannot all be derived from the same volatile rich ancestor, but must have formed over a range of temperatures, with correspondingly different volatile contents. Variations in the carbonaceous chondrite fission (CCFXe) component in LL3, LL5, and LL6 chondrites are discussed, noting that if CCFXe comes from a supernova, then its distribution in LL-chondrites requires three presolar carrier minerals of the right solubility properties, containing three different xenon components. However, if CCFXe comes from fission of a volatile superheavy element, then its decrease from LL3 to LL6 can be attributed to less complete condensation from the solar nebula. Finally, the three types of primordial xenon components which occur in different minerals of the same meteorite are described.

  11. Asteroid breakup linked to the Great Ordovician Biodiversification Event

    Science.gov (United States)

    Schmitz, Birger; Harper, David A. T.; Peucker-Ehrenbrink, Bernhard; Stouge, Svend; Alwmark, Carl; Cronholm, Anders; Bergström, Stig M.; Tassinari, Mario; Xiaofeng, Wang

    2008-01-01

    The rise and diversification of shelled invertebrate life in the early Phanerozoic eon occurred in two major stages. During the first stage (termed as the Cambrian explosion), a large number of new phyla appeared over a short time interval ~540Myrago. Biodiversity at the family, genus and species level, however, remained low until the second stage marked by the Great Ordovician Biodiversification Event in the Middle Ordovician period. Although this event represents the most intense phase of species radiation during the Palaeozoic era and led to irreversible changes in the biological make-up of Earth's seafloors, the causes of this event remain elusive. Here, we show that the onset of the major phase of biodiversification ~470Myrago coincides with the disruption in the asteroid belt of the L-chondrite parent body-the largest documented asteroid breakup event during the past few billion years. The precise coincidence between these two events is established by bed-by-bed records of extraterrestrial chromite, osmium isotopes and invertebrate fossils in Middle Ordovician strata in Baltoscandia and China. We argue that frequent impacts on Earth of kilometre-sized asteroids-supported by abundant Middle Ordovician fossil meteorites and impact craters-accelerated the biodiversification process.

  12. Development of a standard reference material for Cr(vi) in contaminated soil

    Science.gov (United States)

    Nagourney, S.J.; Wilson, S.A.; Buckley, B.; Kingston, H.M.S.; Yang, S.-Y.; Long, S.E.

    2008-01-01

    Over the last several decades, considerable contamination by hexavalent chromium has resulted from the land disposal of Chromite Ore Processing Residue (COPR). COPR contains a number of hexavalent chromium-bearing compounds that were produced in high temperature industrial processes. Concern over the carcinogenic potential of this chromium species, and its environmental mobility, has resulted in efforts to remediate these waste sites. To provide support to analytical measurements of hexavalent chromium, a candidate National Institute of Standards and Technology (NIST) Standard Reference Material?? (SRM 2701), having a hexavalent chromium content of approximately 500 mg kg -1, has been developed using material collected from a waste site in Hudson County, New Jersey, USA. The collection, processing, preparation and preliminary physico-chemical characterization of the material are discussed. A two-phase multi-laboratory testing study was carried out to provide data on material homogeneity and to assess the stability of the material over the duration of the study. The study was designed to incorporate several United States Environmental Protection Agency (USEPA) determinative methods for hexavalent chromium, including Method 6800 which is based on speciated isotope dilution mass spectrometry (SIDMS), an approach which can account for chromium species inter-conversion during the extraction and measurement sequence. This journal is ?? The Royal Society of Chemistry 2008.

  13. Re-Os Abundance and Isotope Systematics of Al-undepleted Komatiites in the Kidd-Munro Assemblage: Results From Dundonald Beach, Abitibi Greenstone Belt, Canada

    Science.gov (United States)

    Gangopadhyay, A.; Sproule, R. A.; Walker, R. J.; Lesher, C. M.

    2004-05-01

    Petrographic and geochemical studies suggest that all Precambrian komatiites have undergone variable degrees of weathering, hydrothermal alteration and metamorphism. The effects of these secondary processes in some suites have manifested into large-scale open-system behavior of Re-Os elemental and isotope systematics of whole rocks, which, in some cases, yield inaccurate age and large uncertainties in calculated initial Os isotopic compositions of the emplaced lavas. Thus, some of the previous Os isotopic studies of Precambrian komatiites for which the crystallization ages were known from other radiogenic isotope systematics (e.g., Sm-Nd, Pb-Pb) have relied on Os-rich, relatively well-preserved primary igneous minerals (e.g., olivine and chromite) in order to calculate the initial Os isotopic compositions of the host lavas. Consequently, the whole-rock concentrations of Re and Os in these altered komatiites can neither be used to infer their concentrations in the parental liquids nor their partitioning behaviors during generation and subsequent differentiation of komatiitic magmas. Here we report the Re-Os concentrations of whole rocks from a suite of ca. 2.7-Ga komatiitic rocks from the Dundonald Beach area, part of the Kidd-Munro volcanic assemblage in the Abitibi greenstone belt, Canada. We show that it is possible to calculate the original Re concentrations in the emplaced lavas, and to estimate the gain or loss of Re through comparison of their measured concentrations and those recalculated from their correlations with other incompatible, yet relatively immobile major oxide and trace elements (e.g., Al2O3, Zr, Hf, Yb). We also demonstrate the statistical significance of this scheme of correction with the reduced values of MSWD (by an order of magnitude) and respective uncertainties in slope (by 2-3 orders of magnitude) of regressions involving Re and the immobile elements. Based on the absence of a correlation between loss of Re and the Os isotopic

  14. Interesting Inclusions From Podiform Chromitites in Luobusa Ophiolite, Tibet

    Science.gov (United States)

    Yamamoto, S.; Komiya, T.; Hirose, K.; Maruyama, S.

    2003-12-01

    For the past decade, diamonds and unusual mineral asemblages were reported in podiform chromitites of the Luobusa ophiolite, southern Tibet, China (Bai 1993, Bai 2000, Yan 2001). These minerals were found from heavy mineral separation of chromitites. These minerals include (1) native elements, (2) alloys, (3) carbide (SiC, CrC), (4) platinium group elements (PGE) and arsenides, (5) silicates (Ol, Opx, Cpx, Amp, Srp, Chl, Uv, Prp, Alm, Wo, Zrn, Ap, Bt, Spn, Rt, Pl, Kfs, Phl, Sil, Qz and octahedral serpentine (possible pseduomorph after ringwoodite?), (5) oxide (corundum and chromite), (6) carbonates. Despite many questions as to these minerals above still remain open, these mineral inclusions would provide us the important infomation on the formation of the podiform chromitites. In this study, octahedral serpentine was discovered both on a thin section and from the heavy mineral separation. These octahedral inclusions exist within chromites, forming a line. These minerals are approximately 5-15μ m in diameter and have well octahedral morphology. EPMA, laser raman spectrometer and transmission electron microscopy (TEM) were used to determine the structure and chemical composition of this crystal. For the present, there are several interpretations of this octahedral silicate. One possibility is that if the octahedral structuer is euhedral so this octahedral serpentine may be pseudomorph after ringwoodite because of its chemical composition and octahedral crystal shape. Another is that ocahedral minerals are melt inclusions. Linear occurrence of octahedral minerals is similar to that of fuluid inclusions. If the octahedral structuer is negative crystal shape reflecting octahedral crystal of cromian spinel, then octahedral inclusions may be melt inclusions judging from linear occurrence. At the same time, zircons were obtained from the mineral separation from chromitites. U-Pb dating of these zircons by LA-ICP-MS yielded two different ages. One group has relatively

  15. Xenoliths in the EETA 79001 Shergottite: Geological and Astronomical Implications of Similarities to the ALHA 77005 and LEW 88516 Shergottites

    Science.gov (United States)

    Treiman, A. H.

    1993-07-01

    The EETA79001 shergottite basalt contains xenoliths (to 1 cm diameter) that are comparable to the nonpoikilitic lithologies in the ALHA77005 and LEW88516 shergottites. The xenoliths are fragments of an olivine-low-Ca-pyroxene rock, with lesser augite, chromite, and maskelynite; their textural patterns suggest an original heteradcumulate igneous rock [1,2] similar to ALHA77005 and LEW88516 [3,4]. Mineral phases in the xenoliths have experienced some chemical exchange with the host basalt [5]; however, their core compositions, especially pyroxenes, are nearly identical to those in LEW88516, and somewhat less restricted than those in ALHA77005 (new data; [1]; [2]; G. McKay, personal communication). Olivines in the xenoliths contain multiphase inclusions, ellipsoidal aggregates (to 200 micrometers diameter) of augite, alkali-rich, and Si-rich glasses, chromite, and a phosphate, in radiating or variolitic textures. These are interpreted as magmatic inclusions, remnants of original magma trapped in the olivines, and are petrographically identical to magmatic inclusions in the olivines of ALHA77005 and LEW88516 [4,6,7]. Shock effects in the xenoliths include zones of brown pleochroism in olivine, mosaickism of both olivine and pyroxene, formation of maskelynite from original plagioclase, recrystallization, and melting; these same effects are present but more severe in ALHA77005 and LEW88516 [8,9]. These many similarities among ALHA77005, LEW88516, and the EETA79001 xenoliths suggest that all were derived from similar, closely related igneous rocks (radioisotope ratios apparently preclude a comagmatic origin for ALHA77005 and the EETA79001 xenoliths [7,10,11]). If these three lithologies are closely related, they may be contemporaneous, and thus older than the EETA79001 basalt (host to the xenoliths). This inference may be consistent with radiometric crystallization ages: for ALHA77005 the age is 187 +- 12 (2 sigma) m.y. [11,5] or 154 +- 6 (2 sigma) m.y. [7]; for the EETA

  16. New model of the mantle lithosphere beneath Kuoyka kimberlite field Yakutia.

    Science.gov (United States)

    Ashchepkov, Igor; Kostrovitsky, Sergey; Ovchinnikov, Yury; Tychkov, Nikolai; Khmelnikova, Olga; Palessky, Stanislav

    2013-04-01

    New data for the 11 pipes from Kuoyka field show that high Cr2O3 garnets to 10- 12% as well as high Cr chromites (to 64%Cr2O3) are found in several more pipes Zaozernaya, Seraya, Slyudyanka, Vodorasdelnaya, Titan, Lusya in addition to Djanga pipe. All garnets belong o lherzolite field and not less than 1/3 are TiO rich. The TiO2 rich chromites are dominating in the Cr- rich population. Metasomatic Cr2O3- rich (to 6%) ilmenites pre in the MgO and TiO2- part of the variation diagrams. The Cr- diopside variations show high variations of Fe and Na content to 4 % suggesting the hybridic origin similar to the Cr- pyroxeneis from Obnazhennaya pyroxenites (Taylor et al ., 2003). Omphicites (to 7 % Na2O) are rare. Cr-amphiboles (pargasites and hornblendes) are common in the upper part of the SCLM as well as in the Anabar and Kharamai region. Reconstructions of the mantle sections show the deep lithospheric roots beneath the Zosernaya pipe (7.5 GPa) traced by the PT conditions for Opx, Cpx, Gar, Cr and Ilm. SCLM is divided in to 4 sections and Ilm trace tow intervals in lower and upper part form 4 GPa. Th HT branch is sporadically found from 7 GPa to the Moho. In other pipes ilmenite and garnet PT estimates are more common in the lower part o mantle section while the Cpx trace mainly middle part of SCLM similar to the Obnazhennaya pip. It seems that kimberlites captured mainly the walls of feeders traced by Cr- low garnets and ilmenites in the lower part of SCLM while peridotitic mantle column was captured starting from the middle part of SCLM. The NS transsect of the Kuoyka field show more fertile mantle sections in the NNW part of the field. The TRE determined for the minerals from Kuoyka field show rather rounded patterns for REE of garnets with high variations in HREE part and small elevation in LREE . The depleted compositions reval the inflection in Eu TRE spidergrams well as relatively small Sr minima. Many of them show Ta peak, relatively small Pb elevation and Th

  17. The Chelyabinsk meteorite fall: Geochemistry and Mineralogy

    Science.gov (United States)

    Galimov, Eric

    Just after the Chelyabinsk meteorite fall, the Vernadsky Institute and the Committee on Meteorites of the Russian Academy of Sciences have organized an expedition to collect fragments of the meteorite shower. The collected material has been comprehensively studied for textural characteristics, mineral chemistry, major and trace elements, nuclear tracks, and isotopic composition. The texture, mineral chemistry, and major element contents indicate that the Chelyabinsk meteorite belongs to the LL5group of ordinary chondrites and was affected by a moderate degree of shock metamorphism (stage S4). The majority (2/3) of the collected stones is composed from a light lithology with a typical chondritic texture. Chondrules ( 63%) are readily delineated and set within a fragmental matrix. The chondrule glass is devitrified. The main phases are olivine and orthopyroxene. Olivine has mosaicism and planar fractures. Rare grains of augite and clinobronzite are present. Small and rare feldspar grains show undulutory extinction, planar deformation features, and are partly isotropic. Troilite (4 vol.%) and FeNi metal (1.3 vol.%) occur as irregularly shaped grains. Accessories are chromite, ilmenite, Cl-apatite, and native Cu. A significant portion (1/3) of the stones consists of a dark impact melt breccia containing mineral and chondrule fragments. Feldspar of the lithology is well developed and practically isotropic. No high-pressure phases were found in the impact melt. There are black colored thin shock veins in both light and dark lithologies. Olivine Fa 27.9±0.35, N=22; ortopyroxene Fs 22.8±0.79, Wo 1.30±0.26, N=17; feldspar Ab 86; chromite Fe/Fe+Mg=0.90, Cr/Cr+Al=0.85 (at.). Major element composition of the light lithology (wt%): Si=18.3, Ti=0.053, Al=1.12, Cr=0.40, Fe=19.8, Mn=0.26, Ca=1.43, Na=0.74, K=0.11, P=0.10, Ni=1.06, Co=0.046, S=1.7. The dark lithology has almost the same composition but it is distinctly higher in Ag, Pb, Bi. Sm-Nd isotopic characteristics

  18. Iron Mineralogy and Aqueous Alteration on Mars from the MER Moessbauer Spectrometers. Chapter 15

    Science.gov (United States)

    Morris, Richard V.; Klingelhoefer, Goestar

    2007-01-01

    The twin Mars Exploration Rovers Spirit (Gusev crater) and Opportunity (Meridiani Planum) used MIMOS II Moessbauer spectrometers to analyze martian surface materials in the first application of extraterrestrial Moessbauer spectroscopy. The instruments acquired spectra that identified the speciation of Fe according to oxidation state, coordination state, and mineralogical composition and provided quantitative information about the distribution of Fe among oxidation states, coordination states, and Fe-bearing phases. A total of 12 unique Fe-bearing phases were identified: Fe(2+) in olivine, pyroxene, and ilmenite; Fe(2+) and Fe(3+) in magnetite and chromite; Fe(3+) in nanophase ferric oxide (npOx), hematite, goethite, jarosite, an unassigned Fe3+ sulfate, and an unassigned Fe(3+) phase associated with jarosite; and Fe(0) in kamacite. Weakly altered basalts at Gusev crater (SO3 = 2.5 +/- 1.4 wt.% and Fe(3+)/Fe(sub T) = 0.24 +/- 0.11) are widespread on the Gusev plains and occur in less abundance on West Spur and Husband Hill in the Columbia Hills. Altered low-S rocks (SO3 = 5.2 +/- 2.0 wt.% and Fe(3+)/Fe(sub T) = 0.63 +/- 0.18) are the most common type of rock in the Columbia Hills. Ilm-bearing, weakly altered basalts were detected only in the Columbia Hills, as was the only occurrence of chromite in an altered low-S rock named Assemblee. Altered high-S rocks (SO3 > 14.2 wt.% and Fe(3+)/Fe(sub T) = 0.83 +/- 0.05) are the outcrop rocks of the ubiquitous Burns formation at Meridiani Planum. Two Fe(0)-bearing rocks at Meridiani Planum (Barberton and Heat Shield Rock) are meteorites. Laguna Class soil is weakly altered (SO3 = 6 +/- 2 wt.% and Fe(3+)/Fe(sub T) = 0.29 +/- 0.08) and widely distributed at both Gusev crater and Meridiani Planum, implying efficient global mixing processes or a global distribution of precursor rocks with comparable Fe mineralogical compositions. Paso Robles Class soil is heavily altered (SO3 approx. 31 wt.% and Fe(3+)/Fe(sub T) = 0.83 +/- 0

  19. Alpe Arami garnet peridotite from depth >300 km: revisited in 15 years (Invited)

    Science.gov (United States)

    Dobrzhinetskaya, L.; Lesher, C. E.; Bozhilov, K. N.; Green, H. W.

    2009-12-01

    In the mid-1990s we recognized that collisional orogenic belts with UHP metamorphic rocks of crustal affinities, might contain mantle peridotites uplifted from depths of >300km (Dobrzhinetsklaya et al., 1996). We proposed that ilmenite rods + chromite flakes in olivine are the result of exsolution, and that they imply high solubility of TiO2 in Ol at high P-T. The conclusion that the Alpe Arami peridotite massif originates from great depth remains controversial despite the subsequent discovery of Cpx inclusions in Grt containing exsolution lamellae of clinoenstatite displaying antiphase domains. The latter observation requires that the originally precipitated pyroxene had a high-pressure C2/c space group structure consistent with an origin from >8 GPa (~250 km) (Bozhilov et al., 1999). We used confocal laser scanning microscopy to obtain quantitative 3D measurements of Ilm abundance in Ol. We find that Ilm rods can reach >1 vol. % in Ol supporting our contention that Ilm rods exsolved from olivine at 9-12 GPa, e.g. >300 km (Bozhilov et al., 2003). Arguments that Ilm rods hosted by Ol are reaction products from the breakdown of Ti-clinohumite (Risold et al., 2003) are unconvincing given that Ti-clinohumite breakdown does not produce Ilm + chromite that are characteristic of Alpe Arami olivine. Likewise, we have confirmed the high solubility of Ti in olivine at high P-T conditions in multianvil experiments (Dobrzhinetskaya et al., 2000) - findings that are strengthened by the experiments of Tinker & Lesher (2001). Using Focused Ion Beam we prepared TEM foils of the later experiments and confirm that the concentration of TiO2 in Ol increases with pressure under nearly isothermal conditions. Two reactions are proposed to account for these observations. If Ti enters the octahedral site of olivine, either an oxide phase must be formed or a phase richer in SiO2 than olivine must be consumed, leading to reaction 1: 6MgSiO3 + 2FeTiO3 = 2Ti△SiO4 + 3Mg2SiO4 + Fe2SiO4 [1

  20. Coexistence of compositionally heterogeneous podiform chromitites in the Antalya-Isparta ophiolitic suite, SW Turkey: a record of sequential magmatic processes in the sub-arc lithospheric mantle

    Science.gov (United States)

    Uysal, Ibrahim; Kapsiotis, Argyrios; Melih Akmaz, Recep; Saka, Samet; Avci, Erdi; Müller, Dirk

    2015-04-01

    The Antalya-Isparta region in southwestern Turkey is well known for large, ophiolitic in origin, peridotite exposures hosting various chromite orebodies. These are small-sized, massive to disseminated in texture chromitites that occur in the form of lenses or veinlets and are commonly surrounded by dunite envelopes of variable thickness. Chromitite seams from the Antalya mantle suite belong to both high-Cr and high-Al varieties (Cr#: 0.56-0.83), whereas chromitites in the Isparta mantle sequence are merely Cr-rich (Cr#: 0.75-0.85). In situ minor and trace element abundances obtained by LA-ICP-MS analyses of unaltered Cr-spinel from the Cr-rich chromitites are comparable to those reported in Cr-spinel of chromitites from typical fore-arc peridotite complexes. Nevertheless, minor and trace element concentrations in Cr-spinel from the Al-rich chromitites do not bear resemblance with those acquired from Cr-spinels of chromitites from well-known back-arc basin-derived ultramafic massifs. Calculation of parental magma compositions indicates that both types of chromitites share a common parentage with progressively fractionating arc-related melts. A quite interesting dissimilarity between the unaltered Cr-spinel compositions from both Cr-rich and Al-rich chromitites is that the former display a perceptible positive Ti anomaly in ChromiteMORB-normalized profiles, which signifies the hidden impact of post-magmatic processes in the composition of the high-Cr chromitite bodies that otherwise seem to be unaffected by metamorphism. The studied chromitites are characterized by a systematic enrichment in IPGE [Os, Ir and Ru (41-317 ppb)] with respect to PPGE [Rh, Pt and Pd (3-49 ppb)], resulting to negatively sloping chondrite-normalized PGE patterns that are less fractionated in case of high-Al chromitites. Their noble mineral assemblage is vastly dominated by tiny (up to 10 μm), euhedral laurite crystals followed by subsidiary irarsite and trivial Os-Ir alloy grains. PGM

  1. Materials for Advanced Ultrasupercritical Steam Turbines Task 4: Cast Superalloy Development

    Energy Technology Data Exchange (ETDEWEB)

    Thangirala, Mani

    2015-09-30

    demonstrated the importance of proper heat treat cycles for Homogenization, and Solutionizing parameters selection and implementation. 3) Step blocks casting of Nimonic 263: Carried out casting solidification simulation analysis, NDT inspection methods evaluation, detailed test matrix for Chemical, Tensile, LCF, stress rupture, CVN impact, hardness and J1C Fracture toughness section sensitivity data and were reported. 4) Centrifugal Casting of Haynes 282, weighing 1400 lbs. with hybrid mold (half Graphite and half Chromite sand) mold assembly was cast using compressor casing production tooling. This test provided Mold cooling rates influence on centrifugally cast microstructure and mechanical properties. Graphite mold section out performs sand mold across all temperatures for 0.2% YS; %Elongation, %RA, UTS at 1400°F. Both Stress-LMP and conditional Fracture toughness plots data were in the scatter band of the wrought alloy. 5) Fundamental Studies on Cooling rates and SDAS test program. Evaluated the influence of 6 mold materials Silica, Chromite, Alumina, Silica with Indirect Chills, Zircon and Graphite on casting solidification cooling rates. Actual Casting cooling rates through Liquidus to Solidus phase transition were measured with 3 different locations based thermocouples placed in each mold. Compared with solidification simulation cooling rates and measurement of SDAS, microstructure features were reported. The test results provided engineered casting potential methods, applicable for heavy section Haynes 282 castings for optimal properties, with foundry process methods and tools. 6) Large casting of Haynes 282 Drawings and Engineering FEM models and supplemental requirements with applicable specifications were provided to suppliers for the steam turbine proto type feature valve casing casting. Molding, melting and casting pouring completed per approved Manufacturing Process Plan during 2014 Q4. The partial valve casing was successfully cast after casting methods were

  2. Fractionation of the platinum-group elments and Re during crystallization of basalt in Kilauea Iki Lava Lake, Hawaii

    Science.gov (United States)

    Pitcher, L.; Helz, R.T.; Walker, R.J.; Piccoli, P.

    2009-01-01

    Kilauea Iki lava lake formed during the 1959 summit eruption of Kilauea Volcano, then crystallized and differentiated over a period of 35??years. It offers an opportunity to evaluate the fractionation behavior of trace elements in a uniquely well-documented basaltic system. A suite of 14 core samples recovered from 1967 to 1981 has been analyzed for 5 platinum-group elements (PGE: Ir, Os, Ru, Pt, Pd), plus Re. These samples have MgO ranging from 2.4 to 26.9??wt.%, with temperatures prior to quench ranging from 1140????C to ambient (110????C). Five eruption samples were also analyzed. Osmium and Ru concentrations vary by nearly four orders of magnitude (0.0006-1.40??ppb for Os and 0.0006-2.01??ppb for Ru) and are positively correlated with MgO content. These elements behaved compatibly during crystallization, mostly likely being concentrated in trace phases (alloy or sulfide) present in olivine phenocrysts or included chromite. Iridium also correlates positively with MgO, although less strongly than Os and Ru. The somewhat poorer correlation for Ir, compared with Os and Ru, may reflect variable loss of Ir as volatile IrF6 in some of the most magnesian samples. Rhenium is negatively correlated with MgO, behaving as an incompatible trace element. Its behavior in the lava lake is complicated by apparent volatile loss of Re, as suggested by a decrease in Re concentration with time of quenching for lake samples vs. eruption samples. Platinum and Pd concentrations are negatively, albeit weakly, correlated with MgO, so these elements were modestly incompatible during crystallization of the major silicate phases. Palladium contents peaked before precipitation of immiscible sulfide liquid, however, and decline sharply in the most differentiated samples. In contrast, Pt appears to have been unaffected by sulfide precipitation. Microprobe data confirm that Pd entered the sulfide liquid before Re, and that Pt is not strongly chalcophile in this system. Occasional high Pt values

  3. Exploration of gold occurrences in alteration zones at Dungash district, Southeastern Desert of Egypt using ASTER data and geochemical analyses

    Science.gov (United States)

    Salem, S. M.; El Sharkawi, M.; El-Alfy, Z.; Soliman, N. M.; Ahmed, S. E.

    2016-05-01

    The present study aims at exploration of new gold occurrences in the alteration zones at Dungash district. Processed ASTER images band ratios 7/6 × 4/6 and (7 + 9/8), field geology and mineralogical and geochemical data help characterize three types of alterations in three areas 1 to 3 that may be targeted for Au exploration. Area1 confined to the metavolcanics located in the SE of Dungash gold mine and revealed silicified and sericitized type alterations, composed of quartz, epidote, chlorite, biotite and opaque minerals mainly pyrite and chalcopyrite. Area2 occurs in the gabbro-diorite rocks at Abu Meraiwa area NE of Dungash gold mine, which are rich in kaolinite, illite, sericite, pyrite, arsenopyrite and chalcopyrite that record kaolinitized alteration. Area3 is hosted in carbonaceous listwaenized serpentinite thus indicating the role of listwaenitization type alteration in ore genesis. It is composed of calcite, chromite, pyrite, arsenopyrite, chalcopyrite and Ni-bearing sulphides. Au contents in area 1 range between 0.12 and 14.91 ppm, and between 6.1 and 16.3 ppm in area 2, while gold values in area 3 vary from <0.01 to 0.03 ppm. Dungash district is comprised of Pan-African assemblages of ophiolitic ultramafics thrusted over the island arc metavolcanics of dacitic- andesite composition. Gabbro-diorite rocks are intruded in the ultramafics and the acidic metavolcanics as well as diorite-quartz diorite suite intruded in the intermediate metavolcanics. Several acidic dykes, granitic dykes and quartz veins cut through the different rocks types.

  4. Comparative Planetary Mineralogy: Valence State Partitioning of Cr, Fe, Ti, and V Among Crystallographic Sites in Olivine, Pyroxene, and Spinel from Planetary Basalts

    Science.gov (United States)

    Papike, J. J.; Karner, J. M.; Shearer, C. K.

    2005-01-01

    We have considered the valence-state partitioning of Cr, Fe, Ti, and V over crystallographic sites in olivine, pyroxene, and spinel from planetary basalts. The sites that accommodate these cations are the M2 site (6-8 coordinated) and M1 site (6 coordinated) in pyroxene, the M2 site (6-8 coordinated) and M1 site (6 coordinated) in olivine, and the tetrahedral and octahedral sites in spinel. The samples we studied are basalts from Earth, Moon, and Mars, which have fO2 conditions that range from IW-2 (Moon) to IW+6 (Earth) with Mars somewhere between at IW to IW+2. In this range of fO2 the significant elemental valences are (from low to high fO2) Ti4+, V3+, Fe2+, Cr2+, Cr3+, V3+, V4+, and Fe3+. V2+ and Ti3+ play a minor role in the phases considered for the Moon, and are probably in very low concentrations. V5+ plays a minor role in these phases in terrestrial basalts because it is probably in lower abundance than V4+ and it has an ionic radii that is so small (0.054 nm, 6- coordinated,[1]) that it is almost at the lower limit for octahedral coordination. The role of Cr2+ in the Moon is significant, as Sutton et al. [2] found that lunar olivine contains mostly Cr2+ while coexisting pyroxene contains mostly Cr3+. Hanson one vacancy only accommodates one V4+. Thus more vacancies are required in V4+ substitutions into olivine. In the Moon V3+ is much more abundant than V4+ [7, 8]. Thus in lunar chromite V3+ follows Cr3+, whereas in Earth V4+ (which is much greater in abundance than V3+) follows Ti4+ (eg in ulv spinel). We could go on in this vein for some time but space limitations do not permit us to do so.

  5. CO2 Energy Reactor - Integrated Mineral Carbonation: Perspectives on Lab-Scale Investigation and Products Valorization

    Directory of Open Access Journals (Sweden)

    Rafael M Santos

    2016-02-01

    Full Text Available To overcome the challenges of mineral CO2 sequestration, Innovation Concepts B.V. is developing a unique proprietary Gravity Pressure Vessel (GPV reactor technology, and has focussed on generating reaction products of high economic value. The GPV provides intense process conditions through hydrostatic pressurization and heat exchange integration that harvests exothermic reaction energy, thereby reducing energy demand of conventional reactor designs, in addition to offering other benefits. In this paper, a perspective on the status of this technology and outlook for the future is provided. To date, laboratory-scale tests of the envisioned process have been performed in a tubular rocking autoclave reactor. The mineral of choice has been olivine (~Mg1.6Fe2+0.4(SiO4 + ppm Ni/Cr, although asbestos, steel slags and oil shale residues are also under investigation. The effect of several process parameters on reaction extent and product properties have been tested: CO2 pressure, temperature, residence time, additives (buffers, lixiviants, chelators, oxidizers, solids loading, and mixing rate. The products (carbonates, amorphous silica and chromite have been physically separated (based on size, density and magnetic properties, characterized (for chemistry, mineralogy and morphology and tested in intended applications (as pozzolanic carbon-negative building material. Economically, it is found that product value is the main driver for mineral carbonation, rather than, or in addition to, the sequestered CO2. The approach of using a GPV and focusing on valuable reaction products could thus make CO2 mineralization a feasible and sustainable industrial process.

  6. The crystallization of shoshonitic to peralkaline trachyphonolitic magmas in a H2O-Cl-F-rich environment at Ischia (Italy), with implications for the feeder system of the Campania Plain volcanoes

    Science.gov (United States)

    Melluso, L.; Morra, V.; Guarino, V.; de'Gennaro, R.; Franciosi, L.; Grifa, C.

    2014-12-01

    Bulk-rock and mineralogical characterization of massive samples (lava flows, lava domes, scoria, spatter), chosen to be representative of different activity periods and of the whole known compositional range of Ischia island (Roman Magmatic Province, Campanian district) is reported in this paper. The rocks vary in composition from shoshonites to peralkaline trachyphonolites. Crystallization started with Al-rich chromite inclusions and their host magnesian olivine in shoshonites and latites, and ended with låvenite, rinkite, kochite, hiortdahlite, hainite, Mn-aenigmatite, britholite and Ti-Zr-rich aegirine in the groundmass of the peralkaline trachyphonolites. Removal of feldspar-bearing assemblages (with calcic-to-sodic plagioclase in shoshonites and latites, sodic sanidine and anorthoclase in trachytes and trachyphonolites) is established throughout the compositional range, and is accompanied by interaction between variably evolved magmas (with their differing phenocryst assemblage), mostly in mafic and intermediate compositions. This led to enrichment in Mn, alkalis, Zr, Nb, REE, Rb, Th, U, Cl and F, and depletion in Mg, Fe, V, Ca, Ba, Sr and Eu in the most evolved magmas. The Ischian rocks have a tendency to sodic affinity and by peculiar mineral compositions and compositional trends, which do not indicate extremely oxidizing conditions. The Ischian rocks thus differ from the Phlegrean Fields analogues and the ultrapotassic, more silica undersaturated rocks of Somma-Vesuvius. Overall, variations in the chemical compositions of the rocks and their trends imply unrelated feeding systems and thus are inconsistent with the hypothesis of a common magma reservoir beneath the main volcanic areas of the Campanian Plain.

  7. Identification and significance of accessory minerals from a bituminous coal

    Science.gov (United States)

    Finkelman, R.B.; Stanton, R.W.

    1978-01-01

    A scanning electron microscope (SEM) has been used to study the in situ accessory minerals in polished blocks and pellets of petrographically analysed samples of the Waynesburg coal (hvb). Individual grains from the low-temperature ash (LTA) of the same coal were also studied. The visual resolution of the SEM permitted the detection of submicron mineral grains, which could then be analysed by the attached energy-dispersive system. Emphasis was placed on the highly reflective grains in the carbominerite bands. Among the most abundant accessory minerals observed were rutile, zircon, and rare-earth-bearing minerals. Small (1-5 ??m) particles of what may be authigenic iron-rich chromite and a nickel silicate form rims on quartz grains. The SEM also permits the observation of grain morphology and mineral intergrowths. These data are useful in determining authigenicity and diagenic alteration. Substances in density splits of LTA include authigenic, detrital, extraterrestrial magnetite, tourmaline, and evaporite (?) minerals, and a fluorine-bearing amphibole. This analytical approach allows the determination of specific sites for many of the trace elements in coals. In the Waynesburg coal, most of the chromium is in the iron-chromium rims, the fluorine is in the amphibole, and the rare-earth elements are in rare-earth-bearing minerals. The ability to relate trace-element data to specific minerals will aid in predicting the behaviour of elements in coal during combustion, liquefaction, gasification, weathering, and leaching processes. This ability also permits insight into the degree of mobility of these elements in coal and provides clues to sedimentological and diagenetic conditions. ?? 1978.

  8. Zirconium - an imported mineral commodity

    International Nuclear Information System (INIS)

    This report examines Canada's position in regard to the principal zirconium materials: zircon; fusion-cast zirconium-bearing refractory products; zirconium-bearing chemicals; and zirconium metal, master alloys, and alloys. None of these is produced in Canada except fused alumina-zirconia and certain magnesium-zirconium alloys and zirconium-bearing steels. Most of the 3 000-4 000 tonnes of the various forms of zircon believed to be consumed in Canada each year is for foundry applications. Other minerals, notably chromite, olivine and silica sand are also used for these purposes and, if necessary, could be substituted for zircon. Zirconium's key role in Canada is in CANDU nuclear power reactors, where zirconium alloys are essential in the cladding for fuel bundles and in capital equipment such as pressure tubes, calandria tubes and reactivity control mechanisms. If zirconium alloys were to become unavailable, the Canadian nuclear power industry would collapse. As a contingency measure, Ontario Hydro maintains at least nine months' stocks of nuclear fuel bundles. Canada's vulnerability to short-term disruptions to supplies of nuclear fuel is diminished further by the availability of more expensive electricity from non-nuclear sources and, given time, from mothballed thermal plants. Zirconium minerals are present in many countries, notably Australia, the Republic of South Africa and the United States. Australia is Canada's principal source of zircon imports; South Africa is its sole source of baddeleyite. At this time, there are no shortages of either material. Canada has untapped zirconium resources in the Athabasca Oil Sands (zircon) and at Strange Lake along the ill-defined border between Quebec and Newfoundland (gittinsite). Adequate metal and alloy production facilities exist in France, Japan and the United States. No action by the federal government in regard to zirconium supplies is called for at this time

  9. Chromium Release from a COPR-Contaminated Soil at Varying Water Content and Redox Conditions.

    Science.gov (United States)

    Matern, Katrin; Mansfeldt, Tim

    2016-07-01

    Many soils in the region of Kanpur, North India, are heavily affected by the leather industry and its upstream supplier sector, as indicated by elevated chromium (Cr) contents. Under reducing conditions-for instance, at water saturation after monsoon rain or flood irrigation-the dynamic and species distribution of Cr may be affected due to changes in redox potential (E). In this study, the influence of E on the speciation and release of Cr from a contaminated agricultural soil was investigated. A soil sample that was affected by hyperalkaline leachate from chromite ore processing residue, was taken and packed in soil columns, and subjected to a saturation-drainage-saturation cycle. After initial water saturation, the E dropped slowly to minimum values of around ‒100 mV (calculated to pH 7), while E was controlled by CrO/CrO(s), or CrO/(Fe,Cr)OOH redox couples. Soil drainage resulted in a quick return to oxidizing conditions; i.e., E > 300 mV. The Cr species distribution and release showed a clear trend with E. At the beginning of the experiment, under oxidizing and weakly reducing conditions (E range from >100 to 300 mV), Cr(VI) was released in particular. However, under moderately reducing conditions (E range from 100 to -100 mV), Cr was gradually immobilized and irreversible sequestered via reductive precipitation. The results presented in this study provide an improved understanding of the mobility of Cr(VI) in contaminated soils at varying water contents, which is essential for the evaluation of environmental risks in this region. PMID:27380074

  10. A detailed TEM and SEM study of Ni-base alloys oxide scales formed in primary conditions of pressurized water reactor

    Energy Technology Data Exchange (ETDEWEB)

    Sennour, Mohamed, E-mail: mohamed.sennour@ensmp.f [MINES, ParisTech, Centre des Materiaux, UMR CNRS 7633, B.P. 87, 91003 Evry Cedex (France); Marchetti, Loic; Martin, Frantz; Perrin, Stephane [CEA, DEN, DPC, SCCME, Laboratoire d' Etude de la Corrosion Aqueuse, F-91191 Gif-sur-Yvette (France); Molins, Regine [MINES, ParisTech, Centre des Materiaux, UMR CNRS 7633, B.P. 87, 91003 Evry Cedex (France); Pijolat, Michele [LPMG-UMR CNRS 5148 , Centre SPIN, Ecole Nationale Superieure des Mines, 158 Cours Fauriel, F-42023 Saint-Etienne (France)

    2010-07-31

    The oxide film formed on nickel-based alloys in pressurized water reactors (PWR) primary coolant conditions (325 {sup o}C, aqueous media) is very thin, in the range of 1-100 nm thick, depending on the surface state and on the corrosion test duration. The nature and the structure of this scale have been investigated by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). TEM observations revealed an oxide layer divided in two parts. The internal layer was mainly composed of a continuous spinel layer, identified as a mixed iron and nickel chromite (Ni{sub (1-x)}Fe{sub x}Cr{sub 2}O{sub 4}). Moreover, nodules of Cr{sub 2}O{sub 3}, with a size about 5 nm, were present at the interface between this spinel and the alloy. No chromium depletion was observed in the alloy, at the alloy/oxide interface. The external layer is composed of large crystallites corresponding to a spinel structure rich in iron (Ni{sub (1-z)}Fe{sub (2+z)}O{sub 4}) resulting from precipitation phenomena. SEM and TEM observations showed a link between the nucleation and/or the growth of crystallites of nickel ferrite and the crystallographic orientation of the substrate. A link between the presence of surface defects and the nucleation of the crystallites was also underlined by SEM observations. Partially hydrated nickel hydroxide, was also observed by TEM in the external scale. Based on these results, some considerations about the mechanism of formation of this oxide layer are discussed.

  11. Kinetics and Mechanisms of Cr(VI) Formation via the Oxidation of Cr(III) Solid Phases by Chlorine in Drinking Water.

    Science.gov (United States)

    Chebeir, Michelle; Liu, Haizhou

    2016-01-19

    Hexavalent chromium Cr(VI), typically existing as the oxyanion form of CrO4(2-), is being considered for more stringent drinking water standards by regulatory agencies. Cr(VI) can be inadvertently produced via the oxidation of trivalent chromium Cr(III) solids. This study investigated the kinetics and mechanisms of Cr(III) solids oxidation by chlorine in drinking water and associated Cr(VI) formation. Batch experiments were carried out with three Cr(III) solids of environmental relevance, i.e., chromium hydroxide Cr(OH)3(s), chromium oxide Cr2O3(s), and copper chromite Cu2Cr2O5(s). Impacts of water chemical parameters including pH (6.0-8.5) and bromide concentration (0-5 mg/L) were examined. Results showed that the rapid oxidation of Cr(III) solid phases by chlorine was accompanied by Cr(VI) formation and an unexpected production of dissolved oxygen. Analysis of reaction stoichiometry indicated the existence of Cr intermediate species that promoted the autocatalytic decay of chlorine. An increase in pH modestly enhanced Cr(VI) formation due to changes of reactive Cr(III) surface hydroxo species. Bromide, a trace chemical constituent in source waters, exhibited a catalytic effect on Cr(VI) formation due to an electron shuttle mechanism between Cr(III) and chlorine and the bypass of Cr intermediate formation. The kinetics data obtained from this study suggest that the oxidation of Cr(III) solids by chlorine in water distribution systems can contribute to Cr(VI) occurrence in tap water, especially in the presence of a trace level of bromide.

  12. Phase separation and exchange bias effect in Ca doped EuCrO3

    International Nuclear Information System (INIS)

    The rare-earth chromites have attracted increasing interests in recent years, as a member of a few single-phase multiferroic materials. We studied the structure and magnetic property of a series of Ca-doped EuCrO3 samples by using X-ray powder diffraction and Physical Property Measurement System. Phase separation, rotation of magnetization in M(T) curve and exchange bias effect have been identified. The Eu0.7Ca0.3CrO3 polycrystalline sample may be intrinsically phase-separated, with Cr3+-rich, Cr4+-rich canted antiferromagnetic regions surrounded by spin glass-like frustrated phase, resulting in several magnetic features including: (1) a broad and slow increase of M(T) curve with the decrease of temperature; (2) rotation of magnetization with increasing cooling field; (3) exchange bias and glassy magnetism. The rotation of magnetization is ascribed to the rotation of the moment of Cr4+-rich regions, arising from the competition between exchange coupling energy and magnetostatic energy. The exchange bias effect suggests the formation of weak ferromagnetic unidirectional anisotropy during field cooling, due to the exchange coupling among weak ferromagnetic domains and surrounding spin glass-like regions. This result helps understanding the interaction among different magnetic domains and phases in a complex system. - Highlights: • Exchange bias effect and glassy magnetism were observed in Eu0.7Ca0.3CrO3. • Rotation of the moments of Cr4+-rich regions result in the rotation of magnetization in M(T) curve. • Spin glass-like regions contribute to the observed exchange bias effect

  13. Platinum-group elements and minerals in the lower and middle group chromitites of the western Bushveld Complex, South Africa

    Science.gov (United States)

    Junge, Malte; Oberthür, Thomas; Osbahr, Inga; Gutter, Paul

    2016-10-01

    The chromitites of the Bushveld Complex in South Africa contain vast resources of platinum-group elements (PGE). However, knowledge of the distribution and the mineralogical siting of the PGE in the lower group (LG) and middle group (MG) chromitite seams of the Bushveld Complex is limited. We studied concentrates from the LG-6 and MG-2 chromitites of the western Bushveld Complex by a variety of microanalytical techniques. The dominant PGM are sulfides, namely laurite, cooperite-braggite, and malanite-cuprorhodsite, followed by PGE-sulfarsenides, sperrylite, and Pt-Fe alloys. Laurite is the most abundant PGM (vol%). The matching sets of PGM present in the LG and MG chromitites of both the western and the eastern Bushveld Complex, and in the UG-2 chromitite, show strong similarities which support the assumption of a characteristic and general chromitite-related PGM assemblage. Palladium and Rh contents in pentlandite are low and erratic although maximum contents of 7730 ppm Pd and 6020 ppm Rh were detected. Rare thiospinels of the polydymite-linnaeite-greigite series have PGE contents of 1430 ppm Pt, 5370 ppm Rh, and 1460 ppm Pd. The various PGE occur in different deportment: Platinum is generally present in the form of discrete PGM (sulfides, arsenides, alloys). Palladium is present as a large variety of discrete PGM and also incorporated in pentlandite. Rhodium forms discrete PGM and is occasionally present in pentlandite. The IPGE (Os, Ir, and Ru) are dominantly incorporated in laurite (often as inclusions in chromite) and also occur as sulfarsenides.

  14. A chilled margin of komatiite and Mg-rich basaltic andesite in the western Bushveld Complex, South Africa

    Science.gov (United States)

    Maier, W. D.; Barnes, S.-J.; Karykowski, B. T.

    2016-06-01

    A chill sequence at the base of the Lower Zone of the western Bushveld Complex at Union Section, South Africa, contains aphanitic Mg-rich basaltic andesite and spinifex-textured komatiite. The basaltic andesite has an average composition of 15.2 % MgO, 52.8 % SiO2, 1205 ppm Cr, and 361 ppm Ni, whereas the komatiite has 18.7 % MgO, 1515 ppm Cr, and 410 ppm Ni. Both rock types have very low concentrations of immobile incompatible elements (0.14-0.72 ppm Nb, 7-31 ppm Zr, 0.34-0.69 ppm Th, 0.23-0.27 wt% TiO2), but high PGE contents (19-23 ppb Pt, 15-16 ppb Pd) and Pt/Pd ratios (Pt/Pd 1.4). Strontium and S isotopes show enriched signatures relative to most other Lower Zone rocks. The rocks could represent a ~20 % partial melt of subcontinental lithospheric mantle. This would match the PGE content of the rocks. However, this model is inconsistent with the high SiO2, Fe, and Na2O contents and, in particular, the low K2O, Zr, Hf, Nb, Ta, Th, LREE, Rb, and Ba contents of the rocks. Alternatively, the chills could represent a komatiitic magma derived from the asthenosphere that underwent assimilation of the quartzitic floor accompanied by crystallization of olivine and chromite. This model is consistent with the lithophile elements and the elevated Sr and S isotopic signatures of the rocks. However, in order to account for the high Pt and Pd contents of the magma, the mantle must have been twice as rich in PGE as the current estimate for PUM, possibly due to a component of incompletely equilibrated late veneer.

  15. Olivine in Martian Meteorite Allan Hills 84001: Evidence for a High-Temperature Origin and Implications for Signs of Life

    Science.gov (United States)

    Shearer, C. K.; Leshin, L. A.; Adcock, C. T.

    1999-01-01

    Olivine from Martian meteorite Allan Hills (ALH) 84001 occurs as clusters within orthopyroxene adjacent to fractures containing disrupted carbonate globules and feldspathic shock glass. The inclusions are irregular in shape and range in size from approx. 40 microns to submicrometer. Some of the inclusions are elongate and boudinage-like. The olivine grains are in sharp contact with the enclosing orthopyroxene and often contain small inclusions of chromite The olivine exhibits a very limited range of composition from Fo(sub 65) to Fo(sub 66) (n = 25). The delta(sup 18)O values of the olivine and orthopyroxene analyzed by ion microprobe range from +4.3 to +5.3% and are indistinguishable from each other within analytical uncertainty. The mineral chemistries, O-isotopic data, and textural relationships indicate that the olivine inclusions were produced at a temperature greater than 800 C. It is unlikely that the olivines formed during the same event that gave rise to the carbonates in ALH 84001, which have more elevated and variable delta(sup 18)O values, and were probably formed from fluids that were not in isotopic equilibrium with the orthopyroxene or olivine The reactions most likely instrumental in the formation of olivine could be either the dehydration of hydrous silicates that formed during carbonate precipitation or the reduction of orthopyroxene and spinel If the olivine was formed by either reaction during a postcarbonate beating event, the implications are profound with regards to the interpretations of McKay et al. Due to the low diffusion rates in carbonates, this rapid, high-temperature event would have resulted in the preservation of the fine-scale carbonate zoning' while partially devolatilizing select carbonate compositions on a submicrometer scale. This may have resulted in the formation of the minute magnetite grains that McKay et al attributed to biogenic activity.

  16. Method and device for electroextraction of heavy metals from technological solutions and wastewater

    Science.gov (United States)

    Khalemsky, Aron Mikhailov; Payusov, Sergei Abramovic; Kelner, Leonid; Jo, Jae

    2005-05-03

    The basic principles of the method for heavy metals electroextraction from technological solutions and wastewater includes pretreating to remove Chromium-6 and high concentrations of heavy metals and periodically treating in a six-electrode bipolar cylindrical electroreactor made of non-conducting material to achieve lower accepted levels of impurities. Six cylindrical steel electrodes form two triode stacks and are fed with three-phase alternating current of commercial frequency (50-60 Hz), which can be pulsed. Each phase of the three-phase current is connected to three electrodes of one triode stack or in parallel to two triode stacks. The parallel connection of three-phase current to two triode stacks is performed so that the same phase of the three phase current is connected in parallel with each two opposite electrodes of six electrodes located along the periphery, or with two adjacent electrodes. A bipolar stationary aluminum electrode is situated in the inter-electrode space. In one of the embodiments, the bipolar electrode is made of a perforated heat-resistant plastic container filled with secondary aluminum and duralumin scrap. In another embodiment, the bipolar electrode of aluminum or duralumin scrap may be made without a perforated container and is placed in the inter-electrode space as a bulk scrap. In this case, to prevent shorts, each of six steel electrodes is placed in isolated perforated plastic shell with holes of 5 mm in diameter. Non-ferrous metals are extracted in a form of ferrite-chromites, and aluminates as well as hydroxyl salts deposited in the inter-electrode space without electrolysis deposits on electrodes. Deposits are separated from solution by known methods of filtration.

  17. Alternative granular media for the metal casting industry. Final report, September 30, 1994

    Energy Technology Data Exchange (ETDEWEB)

    Guichelaar, P.J.; Ramrattan, S.N.; Tieder, R.E. [Michigan Technological Univ., Houghton, MI (United States)

    1995-09-01

    Silica sand for foundry use is inexpensive to purchase, readily transported and widely available. As a result, it is universally used. However, three factors are becoming increasingly significant as more environmental regulations are promulgated. First, the disposal of waste foundry sand has become an excessively burdensome cost. Second, the phase changes which occur in the silica structure on heating and cooling cause thermal breakdown of the sand into smaller unusable fractions. Third, silica is a relatively weak mineral. Alternatives to silica sand which can withstand the rigors of repetitive reuse must be seriously evaluated as a way to control production costs of the domestic metal casting industry. Chromite sands, olivine sands and carbon sands have each been successfully used to solve operating problems and thus have developed their specific niches in the foundry materials inventory. However, there are several other materials that are candidates for replacing silica sand, such as fused alumina, sintered bauxite and sintered oil well proppants. These media, and others that are generically similar, are manufactured for specific purposes. Compositions and shapes could be readily tailored for used in a metal casting environment of total recycling and materials conservation. This study examines materials that are readily available as alternatives to silica sand from a functionality perspective and a cost perspective. Some of the alternative materials are natural and others are synthetic and thus referring to them as ``sands`` has the potential to cause confusion; the generic term ``granular medium`` is used in this study to mean any material that could functionally substitute for silica sand in the foundry process.

  18. Watson: A new link in the IIE iron chain

    Science.gov (United States)

    Olsen, Edward; Davis, Andrew; Clarke, Roy S., Jr.; Schultz, Ludolf; Weber, Hartwig W.; Clayton, Robert; Mayeda, Toshiko; Jarosewich, Eugene; Sylvester, Paul; Grossman, Lawrence

    1994-01-01

    Watson, which was found in 1972 in South Australia, contains the largest single silicate rock mass seen in any known iron meteorite. A comprehensive study has been completed on this unusual meteorite: petrography, metallography, analyses of the silicate inclusion (whole rock chemical analysis, INAA, RNAA, noble gases, and oxygen isotope analysis) and mineral compositions (by electron microprobe and ion microprobe). The whole rock has a composition of an H-chondrite minus the normal H-group metal and troilite content. The oxygen isotope composition is that of the silicates in the IIE iron meteorites and lies along an oxygen isotope fractionation line with the H-group chondrites. Trace elements in the metal confirm Watson is a new IIE iron. Whole rock Watson silicate shows an enrichment in K and P (each approximately 2X H-chondrites). The silicate inclusion has a highly equilibrated igneous (peridotite-like) texture with olivine largely poikilitic within low-Ca pyroxene: olivine (Fa20), opx (Fs17Wo3), capx (Fs9Wo14)(with very fine exsolution lamellae), antiperthite feldspar (An1-3Or5) with less than 1 micron exsolution lamellae (An1-3Or greater than 40), shocked feldspar with altered stoichiometry, minor whitlockite (also a poorly characterized interstitial phosphate-rich phase) and chromite, and only traces of metal and troilite. The individual silicate minerals have normal chondritic REE patterns, but whitlockite has a remarkable REE pattern. It is very enriched in light REE (La is 720X C1, and Lu is 90X C1, as opposed to usual chonditic values of approximately 300X and 100-150X, respectively) with a negative Eu anomaly. The enrichment of whole rock K is expressed both in an unusually high mean modal Or content of the feldspar, Or13, and in the presence of antiperthite.

  19. Elucidating the mechanism of Cr(VI) formation upon the interaction with metal oxides during coal oxy-fuel combustion.

    Science.gov (United States)

    Chen, Juan; Jiao, Facun; Zhang, Lian; Yao, Hong; Ninomiya, Yoshihiko

    2013-10-15

    The thermodynamics underpinning the interaction of Cr-bearing species with basic metal oxides, i.e. K2O, Fe2O3, MgO and CaO, during the air and oxy-fuel combustion of coal have been examined. The synchrotron-based X-ray adsorption near-edge spectroscopy (XANES) was used for Cr speciation. For the oxides tested, Cr(VI) formation is dominated by the reduction potential of the metals. The oxides of Ca(2+) with high reduction potential favored the oxidation of Cr(III), same for K(+). The other two basic metals, Fe2O3 and MgO with lower reduction potentials reacted with Cr(III) to form the corresponding chromites at the temperatures above 600°C. Coal combustion experiments in drop-tube furnace have confirmed the rapid capture of Cr vapors, either trivalent or hexavalent, by CaO into solid ash. The existence of HCl in flue gas favored the vaporization of Cr as CrO2Cl2, which was in turn captured by CaO into chromate. Both Fe2O3 and MgO exhibited less capability on scavenging the Cr(VI) vapor. Particularly, MgO alone exhibited a low capability for capturing the vaporized Cr(III) vapors. However, its co-existence with CaO in the furnace inhibited the Cr(VI) formation. This is beneficial for minimizing the toxicity of Cr in the coal combustion-derived fly ash. PMID:23969010

  20. Study on application of biological iron sulfide composites in treating vanadium-extraction wastewater containing chromium (VI) and chromium reclamation.

    Science.gov (United States)

    Xie, Yi-Fei; Li, Xu-Dong; Li, Fu-De

    2013-04-01

    In this study, the Cr(VI)-resistant properties and regeneration characteristics of biological iron sulfide composites were investigated, which consist of sulfate reducing bacteria (SRB) and its in situ synthesized nanosized iron sulfides. Then the application of the composites in treating vanadium-extraction wastewater containing high concentration Cr(VI) and reclaiming Cr were performed. It was found that SRB in composites still survived after being used to treat vanadium-extraction wastewater, which could reduce reaction products Fe3+ and sulphur into Fe2+ and S2 by using them as the electron accepters and thus regenerating biological iron sulfide composites. The SRB also could be resistant to 600 mgl(-1) Cr(VI) and reduce it gradually. Based on the Cr(VI)-resistant properties and regeneration characteristics of the composites, a reduction-regeneration recirculation process for treating vanadium-extraction wastewater and reclamation of Cr was developed. The results indicated that the contaminants in effluent reached the Chinese discharge standard of pollutants for vanadium industry (GB 26452-2011), i.e. the concentration of total Cr(TCr) was less than 0.912 mgl(-1), Cr(VI) was less than 0.017 mgl(-1) and V was less than 0.260 mgl(-1). After 10 cycles of treatment, the Cr2O3 content in sludge reached 41.03%, and the ratio of Cr2O3/FeO was 7.35. The sludge reached the chemical and metallurgical (hydrometallurgy) grade of chromite ore and could be reclaimed. PMID:24620597

  1. Supra-subduction zone tectonic setting of the Muslim Bagh Ophiolite, northwestern Pakistan: Insights from geochemistry and petrology

    Science.gov (United States)

    Kakar, Mohammad Ishaq; Kerr, Andrew C.; Mahmood, Khalid; Collins, Alan S.; Khan, Mehrab; McDonald, Iain

    2014-08-01

    The geology of the Muslim Bagh area comprises the Indian passive continental margin and suture zone, which is overlain by the Muslim Bagh Ophiolite, Bagh Complex and a Flysch Zone of marine-fluvial successions. The Muslim Bagh Ophiolite has a nearly-complete ophiolite stratigraphy. The mantle sequence of foliated peridotite is mainly harzburgite with minor dunite and contains podiform chromite deposits that grade upwards into transition zone dunite. The mantle rocks (harzburgite/dunite) resulted from large degrees of partial melting of lherzolite and have also been affected by melt-peridotite reaction. The Muslim Bagh crustal section has a cyclic succession of ultramafic-mafic cumulate with dunite at the base, that grades into wehrlite/pyroxenite with gabbros (olivine gabbro, norite and hornblende gabbro) at the top. The sheeted dykes are immature in nature and are rooted in crustal gabbros. The dykes are mainly metamorphosed dolerites, with minor intrusions of plagiogranites. The configuration of the crustal section indicates that the crustal rocks were formed over variable time periods, in pulses, by a low magma supply rate. The whole rock geochemistry of the gabbros, sheeted dykes and the mafic dyke swarm suggests that they formed in a supra-subduction zone tectonic setting in Neo-Tethys during the Late Cretaceous. The dykes of the mafic swarm crosscut both the ophiolite and the metamorphic sole rocks and have a less-marked subduction signature than the other mafic rocks. These dykes were possibly emplaced off-axis and can be interpreted to have been generated in the spinel peridotite stability zone i.e., Muslim Bagh Ophiolite in the final stage of tectonic emplacement.

  2. Production of pure hydrogen by ethanol dehydrogenation

    Energy Technology Data Exchange (ETDEWEB)

    Santacesaria, Elio; Carotenuto, Giuseppina; Tesser, Riccardo; Di Serio, Martino [Naples Univ. (Italy). Dipt. di Chimica

    2011-06-15

    Hydrogen production from bio-ethanol is one of the most promising renewable processes to generate electricity using fuel cells. In this work, we have studied the production of pure hydrogen as a by-product of the ethanol dehydrogenation reaction. This reaction is promoted by copper based catalysts and according to the catalyst used and the operating conditions gives place to acetaldehyde or ethyl acetate as main products. We studied in particular the performance of a commercial copper/copper chromite catalyst, supported on alumina and containing barium chromate as a promoter, which gave the best results. By operating at low pressure and temperature with short residence times, acetaldehyde is more selectively produced, while, by increasing the pressure (10-30 bars), the temperature (200-260 C) and the residence time (about 100 grams hour/mol of ethanol contact time) the selectivity is shifted to the production of ethyl acetate. However, in both cases pure hydrogen is obtained, as a by-product, which can easily be separated. Hydrogen obtained in this way is free of CO and can be directly fed to fuel cells without any inconvenience. In this work, runs performed under different operating conditions have been reported with the scope to select the best conditions. A carrier of H2 6% in N{sub 2} has been used. The studied catalyst has also shown a good thermal stability with respect to sintering phenomena, which generally occur during the dehydrogenation over other copper catalysts. Hydrogen productivities of 8-39 g{sub H2} (Kgcat){sup -1} (h){sup -1} were obtained for the explored temperature range of 200-260 C. Finally the most accredited reaction mechanism is reported and discussed on the basis of the obtained results. (orig.)

  3. Soil-plant relationship of Pteropyrum olivieri, a serpentine flora of Wadh, Balochistan, Pakistan and its use in mineral prospecting

    Directory of Open Access Journals (Sweden)

    Shahid Naseem

    2009-09-01

    Full Text Available Biogeochemical investigation of Pteropyrum olivieri, a flora of Wadh area in perspective of plant-soil-rock relationship has been made. It is a native of Irano-Turanian region which extended into Saharo-Sindian region of Pakistan. The distribution of P. olivieri and some other co-ecological flora in relation to lithology was also discussed. Field observations showed its controlled population on the serpentine soil. The average abundance of Mg and Ca in soil was estimated as 2.43% and 5.46 respectively. The Mg/Ca ratio of the soils of the study area was below unity (0.445, indicating pedogenesis from serpentinite. Quantitative estimation of Cr, Ni, Co and Cu in soils and plant ash was made. Distribution of these elements has been discussed in context with soil chemistry, average abundance in plant ash and the exclusion mechanism of the flora. The concentration of Cr, Ni and Co in the twigs of P. olivieri is more than the average abundance in the plant ash, while Cu concentration was less. Relationship among Cr, Ni, Co and Cu has been established using scatter-grams to evaluate biogeochemistry of the P. olivieri. Bio-concentration factor (BCF of the specie attributed Co>Cu>Ni>Cr trend. Present study signifies a number of anomalous zones which can be utilized for the exploration of new hidden mineral deposits in and around Wadh area. The rocks in the anomalous zone served as good host for podiform chromite and associated mineralization.

  4. A Geochemical Investigation of the Early Cretaceous Ultrapotassic Dykes in the Raniganj Coalfields in Damodar Valley, India

    Science.gov (United States)

    Jude, T. A.

    2015-12-01

    The early Cretaceous ultrapotassic dyke rocks intruding the Permocarboniferous coal bearing Gondwana sediments of the Eastern Damodar Valley, Singhbum craton, are known for their petrographic and geochemical diversity. They remain a 'Pandora's box of petrological confusion' with a variety of exotic, and potentially diamondiferous, rocks such as lamprophyre, lamproite, orangeite and kimberlite being continuously reported from them for over one century or more. Intra-plate volcanism of this type discloses hidden information about the interior of the Earth. Samples from two dykes intruding Raniganj coalfield is studied here. The samples from Dyke1 are characterized by fine grained texture and phlogopite+apatite+K-feldspar+rutile+ankerite+dolomite+ chromite+chlorite+quartz assemblage while the samples from Dyke2 are characterized by coarse grained texture and phlogopite+ pseudomorphosed-olivine+apatite+ clinopyroxene +dolomite+ankerite+calcite+norsethite+talc+rutile+quartz+Ca-Mg-Fe-Zr silicate+K-feldspar+monazite+ perovskite assemblage. Based on the TiO2-Al2O3-FeO trends observed in phlogopites, the dykes seem to be a lamproite-orangeite transitional variety. The phlogopites observed in Dyke2 show two stages of crystallization defined by Ti-poor overgrowths on Ti-rich cores indicating that Dyke2 consolidated from a melt that fractionated from a magma which was initially emplaced at a different depth while the Dyke 1 phlogopites do not show any such sudden drop in Ti concentration in their rims indicating single stage crystallization. Ti-in-Quartz Thermometry yields temperatures between 769°C to 1115°C for Dyke1 and 779°C to 1019°C for Dyke2 which must corresponds to the emplacement and crystallization of these dykes. Trace element and isotopic ratios can be used to constrain particular mantle source characteristics of the dykes. Rb-Sr method can be used to determine the emplacement ages of these dykes.

  5. 常德陨石雨物质成分和球粒结构的初步研究

    Institute of Scientific and Technical Information of China (English)

    王道德

    1977-01-01

    On Mareh 11,1977,the Changde stone meteorite shower fell near the town of Changde,Hunan Province(29°05'N,111°45'E).The total recovered mass vas 1.81kg in weight(900g,254g,220g,184g,50g,20g,11.8g,20g,20g,18.3g,and 113g)X-ray diffraction analyses and microseopic identification have indicated the presence of the following minerals:olivine(175,Fa),orthopyroxene(18% Fs),elinopyroxene,plagioclase,orthoclase,whitlockite,kamocite,taenite,troilite and chromite,Turbid glass has been found in chondrules.Shock effect has bee also observed in olivinc and pyroxene.Chemical analyses have given;SiO2 37.61,TiO2 0.086,Al2O3 2.18,Cr2O3 0.52,FeO 8.00,MnO 0.18,MgO22.87,CaO 1.92,Na2O 0.87,K2O 0.11,H2O- 0.06,H2O+0.06,P2O5 0.21,Fe°18.44,Ni 1.80,Co0.091,Cu0.014,Zn0.006,FeS5.59,C 0.16,total 100.78 Model analysis gives;olivine 26.86%,pyroxene 36.62%,plagioclase 9.06%,orthoclase 0.65%,whitlockite 0.46%,titanite 0.17%,kamocite and taenite 20.24%,troilite 5.59%,Chemieo-petrological stndies have shown that the meteorite bclongs to H-group chondrites,and petrologically to Type 5.Based upon the textures of the chondrules,a model of the evolution for the Changde chondrite is presented.

  6. Mineralogy and Geochemistry of the Pliocene Iron-Rich Laterite in the Vatera Area, Lesvos Island, Greece and Its Genesis

    Institute of Scientific and Technical Information of China (English)

    A.E. KELEPERTSIS

    2002-01-01

    A nickel laterite deposit occurs in the Vatera area of Lesvos Island, Greece, and is transgressively developed on serpentinized basic rock (norite). The overlying sedimentary rocks include marls and marly limestones with sandstone intercalations and belong to the Pliocene sediments. The following lateritic zones are defined from the bottom to top layers: a) bedrock (norite); b) serpentinized zone; c) goethitic zone. The bedrock consists of the following primary minerals: basic plagioclase, orthopyroxenes and clinopyroxenes. The serpentinized zone includes clinochrysotile, lizardite, antigorite clinoenstatite, calcite and dolomite while in the goethic zone there are goethite, quartz, pyrite, chromite, dolomite. Al2O3, Fe2O3, CaO,Na2O, K2O, Ba, Sr, Ni, C and S are enriched in the goethitic zone. Nickel enrichment is related to the formation of nickeliferons minerals substituting for Mg or/and Fe in the goethite and pyrite. Enrichment of Ni in the matrix may be due to the presence of amorphous Ni-silicates (pimelite). There is a significant change (decrease) in the concentration of Ni from the top to bottom parts of the laterite formation, indicating that there was no tendency to migrate downwards (immature laterite). A second support of the immaturity of the Vatera laterite is the incomplete oxidation of ferrous iron to form ferric iron hydroxides. Under tropical/subtropical conditions, which dominated from the end of Miocene to the Pliocene the norite rocks of the Vatera area altered in response to reaction with acid solutions enriched in CO2. Due to hydrolysis and oxidation of pyroxenes, Mg2 +, H4 SiO4 and Ni2 + were removed in the continental acid solutions.

  7. The crater-facies kimberlite system of Tokapal, Bastar District, Chhattisgarh, India

    Science.gov (United States)

    Mainkar, Datta; Lehmann, Bernd; Haggerty, Stephen E.

    2004-09-01

    observed, and phlogopite is very rare. Very limited microdiamond testing (two 18-kg samples) proved negative; however, the composition of chromite grains indicate crystallization in the diamond stability field.

  8. LaCrO{sub 3}-dispersed Cr for metallic interconnect of planar SOFC

    Energy Technology Data Exchange (ETDEWEB)

    Song, Rak-Hyun; Shin, Dong Ryul [Korea Institute of Energy Research, Taejon (Korea, Republic of); Dokiya, Masayuki [National Institute of Materials and Chemical Research, Ibaraki (Japan)

    1996-12-31

    In the planar SOFC, the interconnect materials plays two roles as an electrical connection and as a gas separation plate in a cell stack. The interconnect materials must be chemically stable in reducing and oxidizing environments, and have high electronic conductivity, high thermal conductivity, matching thermal expansion with an electrolyte, high mechanical strength, good fabricability, and gas tightness. Lanthanum chromite so far has been mainly used as interconnect materials in planar SOFC. However, the ceramic materials are very weak in mechanical strength and have poor machining property as compared with metal. Also the metallic materials have high electronic conductivity and high thermal conductivity. Recently some researchers have studied metallic interconnects such as Al{sub 2}O{sub 3}/Inconel 600 cermet, Ni-20Cr coated with (LaSr)CoO{sub 3}, and Y{sub 2}O{sub 3-} or La{sub 2}O{sub 3}-dispersed Cr alloy. These alloys have still some problems because Ni-based alloys have high thermal expansion, the added Al{sub 2}O{sub 3}, Y{sub 2}O{sub 3} and La{sub 2}O{sub 3} to metals have no electronic conductivity, and the oxide formed on the surface of Cr alloy has high volatility. To solve these problems, in this study, LaCrO{sub 3}-dispersed Cr for metallic interconnect of planar SOFC was investigated. The LaCrO{sub 3}-dispersed Cr can be one candidate of metallic interconnect because LaCrO{sub 3} possesses electronic conductivity and Cr metal has relatively low thermal expansion. The content of 25 vol.% LaCrO{sub 3} Was selected on the basis of a theoretically calculated thermal expansion. The thermal expansion, electrical and oxidation properties were examined and the results were discussed as related to SOFC requirements.

  9. Treatment of Alkaline Cr(VI)-Contaminated Leachate with an Alkaliphilic Metal-Reducing Bacterium.

    Science.gov (United States)

    Watts, Mathew P; Khijniak, Tatiana V; Boothman, Christopher; Lloyd, Jonathan R

    2015-08-15

    Chromium in its toxic Cr(VI) valence state is a common contaminant particularly associated with alkaline environments. A well-publicized case of this occurred in Glasgow, United Kingdom, where poorly controlled disposal of a cementitious industrial by-product, chromite ore processing residue (COPR), has resulted in extensive contamination by Cr(VI)-contaminated alkaline leachates. In the search for viable bioremediation treatments for Cr(VI), a variety of bacteria that are capable of reduction of the toxic and highly soluble Cr(VI) to the relatively nontoxic and less mobile Cr(III) oxidation state, predominantly under circumneutral pH conditions, have been isolated. Recently, however, alkaliphilic bacteria that have the potential to reduce Cr(VI) under alkaline conditions have been identified. This study focuses on the application of a metal-reducing bacterium to the remediation of alkaline Cr(VI)-contaminated leachates from COPR. This bacterium, belonging to the Halomonas genus, was found to exhibit growth concomitant to Cr(VI) reduction under alkaline conditions (pH 10). Bacterial cells were able to rapidly remove high concentrations of aqueous Cr(VI) (2.5 mM) under anaerobic conditions, up to a starting pH of 11. Cr(VI) reduction rates were controlled by pH, with slower removal observed at pH 11, compared to pH 10, while no removal was observed at pH 12. The reduction of aqueous Cr(VI) resulted in the precipitation of Cr(III) biominerals, which were characterized using transmission electron microscopy and energy-dispersive X-ray analysis (TEM-EDX) and X-ray photoelectron spectroscopy (XPS). The effectiveness of this haloalkaliphilic bacterium for Cr(VI) reduction at high pH suggests potential for its use as an in situ treatment of COPR and other alkaline Cr(VI)-contaminated environments. PMID:26048926

  10. Eucrite Impact Melt NWA 5218 - Evidence for a Large Crater on Vesta

    Science.gov (United States)

    Wittmann, Axel; Hiroi, Takahiro; Ross, Daniel K.; Herrin, Jason S.; Rumble, Douglas, III; Kring, David A.

    2011-01-01

    Northwest Africa (NWA) 5218 is a 76 g achondrite that is classified as a eucrite [1]. However, an initial classification [2] describes it as a "eucrite shock-melt breccia...(in which) large, partially melted cumulate basalt clasts are set in a shock melt flow...". We explore the petrology of this clast-bearing impact melt rock (Fig. 1), which could be a characteristic lithology at large impact craters on asteroid Vesta [3]. Methods: Optical microscopy, scanning electronmicroscopy, and Raman spectroscopy were used on a thin section (Fig. 1) for petrographic characterization. The impact melt composition was determined by 20 m diameter defocused-beam analyses with a Cameca SX-100 electron microprobe. The data from 97 spots were corrected for mineral density effects [4]. Constituent mineral phases were analyzed with a focusedbeam. Bidirectonal visible and near-infrared (VNIR) and biconical FT-IR reflectance spectra were measured on the surface of a sample slab on its central melt area and on an eucrite clast, and from 125-500 m and rock. The thin section captures a central, subophitic-textured melt that contains 1 cm to tens of m-size subangular to rounded, variably-shocked eucrite clasts. Clasts >100 m are coarse-grained with equigranular 1 mm size plagioclase, quartz, and clinopyroxene (Fig. 1). Single crystals of chromite, ilmenite, zircon, Ca-Mg phosphate, Fe-metal, and troilite are embedded in the melt. Polymineralic clasts are mostly compositionally similar to the above mentioned larger clasts but scarce granulitic fragments are observed as well.

  11. Rapid planetesimal cooling after core formation: Pallasite meteorites

    Science.gov (United States)

    McKibbin, Seann; Ireland, Trevor; O'Neill, Hugh; Holden, Peter; Mallmann, Guilherme; Claeys, Philippe

    2016-04-01

    Pallasite meteorites consist of olivine-metal mixtures and accessory minerals (chromite, sulfide, phosphide, phosphate, phosphoran olivine) and represent core-mantle interaction zones in early differentiated planetesimals. They can be linked to five distinct planetesimals, indicating that they are default differentiation products, but their formation modes (deep, shallow, and impact environments) and age are elusive. Using new trace element, Cr isotope, and previously published datasets, we re-interpret some Main-group pallasites (low-MnO and high-FeO subgroups, e.g. Brenham and Springwater types respectively) as samples of core-mantle reaction zones. These meteorites host rounded olivine and near-solidus phosphate minerals, which record back-reaction of metal and silicate reservoirs during decreasing temperature after core formation and removal of primitive silicate melts. These phosphates form via late oxidation of phosphorus, which is siderophile at high temperature but lithophile at low temperature. Mn-Cr dates this event to before ~2.5 to 4 Myr after Solar System formation (range is model-dependent). Importantly, this is in agreement with Hf-W ages for very early metal-silicate (i.e. core-mantle) separation, but also indicates rapid planetesimal cooling within a few million years. Near-solidus silico-phosphate melts probably formed before most known planetesimal crusts (eucrite and angrite meteorites) and are among the earliest evolved planetary silicates. Similar phosphates in non-Main-Group pallasites from other parent bodies also suggest that core-mantle reaction zones are generic, datable features of differentiation. The absence of near-solidus phosphates in common cluster pallasites suggests that these were quenched from high temperature and are mechanical mixtures, rather than samples of genuine core-mantle boundaries.

  12. Spatial Evolution of the Chromium Contamination in Soils from the Assopos to Thiva Basin and C. Evia (Greece and Potential Source(s: Anthropogenic versus Natural Processes

    Directory of Open Access Journals (Sweden)

    Charalambos Vasilatos

    2013-04-01

    Full Text Available The investigation of the contamination in soil, plants and groundwater revealed a spatial evolution, with an increasing trend in the Cr, Fe, Ni, Mn and Co contents in soils from the Assopos to Thiva basin, followed by C. Evia and Ni-laterite deposits, suggesting that the latter and their parent ophiolites are a potential source for these metals. In contrast, the contamination in groundwater by Cr(VI, ranging from 2 to 360 μg/L Cr, and a varying degree of salinization is probably due to both human activities and natural processes. A diverse source for the contamination of soil and groundwater in the Assopos-Thiva basins is consistent with the increasing trend of the Mg/Si ratio and Cr(VI concentration in water. The use of deep karst-type aquifer instead of the shallow-Neogene one may provide a solution to the crucial environmental problem. The selective extraction by EDTA and alkaline solution showed that Cr and Fe are less available than Mn. The Cr contents in plants range from <1 to tens of mg/kg, due probably to the high resistance of chromite. However, the average Crtotal contents in plants/crops are higher than normal or sufficient values, whilst Crtotal accumulation [(% metals in plants × 100/metal in soil] and Cr(VI accumulation are relatively low. There is a very good positive correlation between accumulation factors for Cr and Fe (R2 = 0.92, suggesting a similarity concerning their uptake.

  13. Design of a Compact and Versatile Bench Scale Tubular Reactor

    Directory of Open Access Journals (Sweden)

    R. Prasad

    2009-06-01

    Full Text Available A compact and versatile laboratory tubular reactor has been designed and fabricated keeping in view of reducing capital cost and minimising energy consumption for gas/vapor-phase heterogeneous catalytic reactions. The reactor is consisted of two coaxial corning glass tubes with a helical coil of glass tube in between the coaxial tubes serving as vaporiser and pre-heater, the catalyst bed is in the inner tube. A schematic diagram of the reactor with detailed dimensions and working principles are described. The attractive feature of the reactor is that the vaporiser, pre-heater and fixed bed reactor are merged in a single compact unit. Thus, the unit minimises separate vaporiser and pre-heater, also avoids separate furnaces used for them and eliminate auxiliary instrumentation such as temperature controller etc. To demonstrate the system operation and illustrate the key features, catalyst screening data and the efficient collection of complete, and accurate intrinsic kinetic data are provided for oxidation of CO over copper chromite catalyst. CO oxidation is an important reaction for auto-exhaust pollution control. The suitability of the versatile nature of the reactor has been ascertained for catalytic reactions where either volatile or vaporizable feeds can be introduced to the reaction zone, e.g. oxidation of iso-octane, reduction of nitric oxide, dehydrogenation of methanol, ethanol and iso-propanol, hydrogenation of nitrobenzene to aniline, etc. Copyright (c 2009 by BCREC. All Rights reserved.[Received: 10 February 2009, Accepted: 9 May 2009][How to Cite: R. Prasad, G. Rattan. (2009. Design of a Compact and Versatile Bench Scale Tubular Reactor. Bulletin of Chemical Reaction Engineering and Catalysis, 4(1: 5-9.  doi:10.9767/bcrec.4.1.1250.5-9][How to Link/ DOI: http://dx.doi.org/10.9767/bcrec.4.1.1250.5-9

  14. Facile synthesis of spinel CuCr{sub 2}O{sub 4} nanoparticles and studies of their photocatalytic activity in degradation of some selected organic dyes

    Energy Technology Data Exchange (ETDEWEB)

    Paul, Bappi; Bhuyan, Bishal [Department of Chemistry, National Institute of Technology Silchar, Silchar, 788010, Assam (India); Purkayastha, Debraj Dhar, E-mail: debrajdp@yahoo.com [Department of Chemistry, National Institute of Technology Silchar, Silchar, 788010, Assam (India); Dhar, Siddhartha Sankar, E-mail: ssd_iitg@hotmail.com [Department of Chemistry, National Institute of Technology Silchar, Silchar, 788010, Assam (India); Behera, Satyananda [Department of Ceramic Engineering, National Institute of Technology Rourkela, Rourkela, 769008, Odisha (India)

    2015-11-05

    Copper chromite (CuCr{sub 2}O{sub 4}) spinel nanoparticle catalysts have been successfully synthesized employing urea assisted co-precipitation followed by calcination. The synthesized nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and N{sub 2} adsorption-desorption isotherm (BET). The XRD pattern revealed formation of tetragonal body-centered CuCr{sub 2}O{sub 4} and TEM image showed quasi-spherical particles of size 5–35 nm. The photocatalytic activity of CuCr{sub 2}O{sub 4} was evaluated in degradation of some organic dyes such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB), without and with the assistance of H{sub 2}O{sub 2} under solar irradiation. The CuCr{sub 2}O{sub 4} photocatalysts showed high activity in degradation of RhB (93.6%) and MO (92.3%), but low activity in degradation of MB (80.6%). The catalyst reusability was tested by conducting the degradation of RhB dye with the spent catalyst and it was observed that the catalyst did not show any significant loss in its activity even after five cycles. - Highlights: • CuCr{sub 2}O{sub 4} nanoparticles were synthesized by urea assisted co-precipitation followed by calcination. • The XRD pattern revealed formation of tetragonal body-centered CuCr{sub 2}O{sub 4}. • The TEM images showed the material to be quasi-spherical in shape with sizes 5–35 nm. • CuCr{sub 2}O{sub 4} nanoparticles exhibited pronounced photocatalytic activity.

  15. Platinum-group elements and minerals in the lower and middle group chromitites of the western Bushveld Complex, South Africa

    Science.gov (United States)

    Junge, Malte; Oberthür, Thomas; Osbahr, Inga; Gutter, Paul

    2016-08-01

    The chromitites of the Bushveld Complex in South Africa contain vast resources of platinum-group elements (PGE). However, knowledge of the distribution and the mineralogical siting of the PGE in the lower group (LG) and middle group (MG) chromitite seams of the Bushveld Complex is limited. We studied concentrates from the LG-6 and MG-2 chromitites of the western Bushveld Complex by a variety of microanalytical techniques. The dominant PGM are sulfides, namely laurite, cooperite-braggite, and malanite-cuprorhodsite, followed by PGE-sulfarsenides, sperrylite, and Pt-Fe alloys. Laurite is the most abundant PGM (vol%). The matching sets of PGM present in the LG and MG chromitites of both the western and the eastern Bushveld Complex, and in the UG-2 chromitite, show strong similarities which support the assumption of a characteristic and general chromitite-related PGM assemblage. Palladium and Rh contents in pentlandite are low and erratic although maximum contents of 7730 ppm Pd and 6020 ppm Rh were detected. Rare thiospinels of the polydymite-linnaeite-greigite series have PGE contents of 1430 ppm Pt, 5370 ppm Rh, and 1460 ppm Pd. The various PGE occur in different deportment: Platinum is generally present in the form of discrete PGM (sulfides, arsenides, alloys). Palladium is present as a large variety of discrete PGM and also incorporated in pentlandite. Rhodium forms discrete PGM and is occasionally present in pentlandite. The IPGE (Os, Ir, and Ru) are dominantly incorporated in laurite (often as inclusions in chromite) and also occur as sulfarsenides.

  16. Oxidation behavior of steels and Alloy 800 in supercritical water

    International Nuclear Information System (INIS)

    The oxidation behavior of a ferritic-martensitic steel T91 and a martensitic steel AISI 403 up to 750 h, and of AISI 316L and Alloy 800 up to 336 h in deaerated supercritical water, 450ºC-25 MPa, was investigated in this paper. After exposure up to 750 h, the weight gain data, for steels T91 and AISI 403, was fitted by ∆W=k tn, were n are similar for both steels and k is a little higher for T91. The oxide films grown in the steels were characterized using gravimetry, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction. The films were adherent and exhibited a low porosity. For this low oxygen content supercritical water exposure, the oxide scale exhibited a typical duplex structure, in which the scale is composed of an outer iron oxide layer of magnetite (Fe3O4) and an inner iron/chromium oxide layer of a non-stoichiometric iron chromite (Fe,Cr)3O4. Preliminary results, with AISI 316L and Alloy 800, for two exposure periods (168 and 336 h), are also reported. The morphology shown for the oxide films grown on both materials up to 336 h of oxidation in supercritical water, resembles that of a duplex layer film like that shown by stainless steels and Alloy 800 oxide films grown in a in a high temperature and pressure (220-350ºC) of a primary or secondary coolant of a plant. (author)

  17. Production of a microcapsule agent of chromate-reducing Lysinibacillus fusiformis ZC1 and its application in remediation of chromate-spiked soil.

    Science.gov (United States)

    Huang, Jun; Li, Jingxin; Wang, Gejiao

    2016-01-01

    Lysinibacillus fusiformis ZC1 is an efficient Cr(VI)-reducing bacterium that can transform the toxic and soluble chromate [Cr(VI)] form to the less toxic and precipitated chromite form [Cr(III)]. As such, this strain might be applicable for bioremediation of Cr(VI) in soil by reducing its bioavailability. The study objective was to prepare a microcapsule agent of strain ZC1 for bioremediation of Cr(VI)-contaminated soil. Using a single-factor orthogonal array design, the optimal fermentation medium was obtained and consisted of 6 g/L corn flour, 12 g/L soybean flour, 8 g/L NH4Cl and 6 g/L CaCl2. After enlarged fermentation, the cell and spore densities were 5.9 × 10(9) and 1.7 × 10(8) cfu/mL, respectively. The fermentation products were collected and embedded with 1 % gum arabic and 1 % sorbitol as the microcapsule carriers and were subsequently spray-dried. Strain ZC1 exhibited viable cell counts of (3.6 ± 0.44) × 10(10) cfu/g dw after 50-day storage at room temperature. In simulated soil bioremediation experiments, 67 % of Cr(VI) was reduced in 5 days with the inoculation of this microcapsule agent, and the Cr(VI) concentration was below the soil Cr(VI) standard level. The results demonstrated that the microcapsule agent of strain ZC1 is efficient for bioremediation of Cr(VI)-contaminated soil.

  18. Alcohol synthesis in a high-temperature slurry reactor

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, G.W.; Marquez, M.A.; McCutchen, M.S. [North Carolina State Univ., Raleigh, NC (United States)

    1995-12-31

    The overall objective of this contract is to develop improved process and catalyst technology for producing higher alcohols from synthesis gas or its derivatives. Recent research has been focused on developing a slurry reactor that can operate at temperatures up to about 400{degrees}C and on evaluating the so-called {open_quotes}high pressure{close_quotes} methanol synthesis catalyst using this reactor. A laboratory stirred autoclave reactor has been developed that is capable of operating at temperatures up to 400{degrees}C and pressures of at least 170 atm. The overhead system on the reactor is designed so that the temperature of the gas leaving the system can be closely controlled. An external liquid-level detector is installed on the gas/liquid separator and a pump is used to return condensed slurry liquid from the separator to the reactor. In order to ensure that gas/liquid mass transfer does not influence the observed reaction rate, it was necessary to feed the synthesis gas below the level of the agitator. The performance of a commercial {open_quotes}high pressure {close_quotes} methanol synthesis catalyst, the so-called {open_quotes}zinc chromite{close_quotes} catalyst, has been characterized over a range of temperature from 275 to 400{degrees}C, a range of pressure from 70 to 170 atm., a range of H{sub 2}/CO ratios from 0.5 to 2.0 and a range of space velocities from 2500 to 10,000 sL/kg.(catalyst),hr. Towards the lower end of the temperature range, methanol was the only significant product.

  19. Nature and evolution of Neoproterozoic ocean-continent transition: Evidence from the passive margin of the West African craton in NE Mali

    Science.gov (United States)

    Renaud, Caby

    2014-03-01

    The Timétrine massif exposed west of the Pan-African suture zone in northeastern Mali belongs to the passive margin of the West African craton facing to the east intra-oceanic arc assemblages and 730 Ma old pre-collisional calc-alkaline plutons. The Timétrine lithologic succession includes from the base to the top Mesoproterozoic cratonic to passive margin formations overlain by deep-sea Fe-Mg schists. Submarine metabasalts and two ultramafic massifs of serpentinized mantle peridotites are inserted as olistoliths towards the top whereas turbidites of continental origin represent the younger unit. Field and petrological data have revealed a distinct metasedimentary sequence attached to the serpentinized peridotites. It essentially consists of impure carbonates, Fe jaspers and polymictic breccias containing altered blocks of mantle peridotites, most rocks being enriched in detrital chromite. This association is interpreted as reworked chemical and detrital sediments derived from the alteration of mafic-ultramafic rocks. It is argued that mantle exhumation above sea floor took place during the Neoproterozoic rifting and crustal thinning period under possible tropical conditions, as suggested by the large volume of silicified serpentinites. In spite of greenschist facies metamorphic overprint characterized by widespread Fe-rich blue amphiboles that are not diagnostic of high-pressure conditions, it is possible to reconstruct a former ocean-continent transition similar to that evidenced for the Mesozoic period, followed by the deposition of syn-to post rift terrigeneous turbidites roughly coeval with ocean spreading some time before 800 Ma. It is concluded that the serpentinite massifs were tectonically emplaced first in an extensional setting, then incorporated within deep-sea sediments as olistoliths and finally transported westward during late Neoproterozoic collisional tectonics onto the West African craton.

  20. Phase separation and exchange bias effect in Ca doped EuCrO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Dongmei, E-mail: dmdeng@shu.edu.cn [Department of Physics and Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Wang, Xingyu; Zheng, Jiashun; Qian, Xiaolong [Department of Physics and Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Yu, Dehong; Sun, Dehui [Bragg Institute, Australian Nuclear Science and Technology Organization, Kirrawee DC, NSW 2232 (Australia); Jing, Chao [Department of Physics and Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Lu, Bo [Analysis and Measurement Center and Laboratory for Microstructures of Shanghai University, Shanghai 200444 (China); Kang, Baojuan; Cao, Shixun; Zhang, Jincang [Department of Physics and Materials Genome Institute, Shanghai University, Shanghai 200444 (China)

    2015-12-01

    The rare-earth chromites have attracted increasing interests in recent years, as a member of a few single-phase multiferroic materials. We studied the structure and magnetic property of a series of Ca-doped EuCrO{sub 3} samples by using X-ray powder diffraction and Physical Property Measurement System. Phase separation, rotation of magnetization in M(T) curve and exchange bias effect have been identified. The Eu{sub 0.7}Ca{sub 0.3}CrO{sub 3} polycrystalline sample may be intrinsically phase-separated, with Cr{sup 3+}-rich, Cr{sup 4+}-rich canted antiferromagnetic regions surrounded by spin glass-like frustrated phase, resulting in several magnetic features including: (1) a broad and slow increase of M(T) curve with the decrease of temperature; (2) rotation of magnetization with increasing cooling field; (3) exchange bias and glassy magnetism. The rotation of magnetization is ascribed to the rotation of the moment of Cr{sup 4+}-rich regions, arising from the competition between exchange coupling energy and magnetostatic energy. The exchange bias effect suggests the formation of weak ferromagnetic unidirectional anisotropy during field cooling, due to the exchange coupling among weak ferromagnetic domains and surrounding spin glass-like regions. This result helps understanding the interaction among different magnetic domains and phases in a complex system. - Highlights: • Exchange bias effect and glassy magnetism were observed in Eu{sub 0.7}Ca{sub 0.3}CrO{sub 3}. • Rotation of the moments of Cr{sup 4+}-rich regions result in the rotation of magnetization in M(T) curve. • Spin glass-like regions contribute to the observed exchange bias effect.

  1. Detecting of the processes of the diamond formation using the monomineral thermobarometry .

    Science.gov (United States)

    Ashchepkov, Igor; Afanasiev, Valentin; Pokhilenko, Lyudmila; Logvinova, Alla; Vladykin, Nikolai

    2010-05-01

    The methods of the monomineral thermobarometry used for the reconstruction of the mantle sections beneath the kimberlite pipes (Ashchepkov et al., 2009) allow to determined PT range for the diamond inclusions (DI) and diamond bearing associations. They show various conditions for the crystallization of diamond for in mantle lithosphere beneath the Yakutia, Africa, and North America. In Yakutia most DI (Sobolev ea 1997, 2004; Logvinova ea., 2005 and ref their in) (Cr-pyropes, Mg -opx) form Mir and Udachnaya pipes are referred to the cold geotherms 35 (partly 33 mvm-2) at the pressure range from 35 to 80 kbar. Cr- pyropes (Ti-bearing) partly drops the on the heated area near convective branches 40-45 mvm-2 convective geotherms. Most Cr- rich pyroxenes refer to the coldest or heated (metasomatic type) at the deeper parts of the mantle columns while mildly Cr-rich varieties refer to the conditions of the crystallization from the melts related to the protokimberlites and associated carbonatites near the Graphite-Diamond boundary (G-D). They are more widely distributed in mantle beneath the Mir pipe where the essential part of mantle column from 50 to 35kbar was subjected to the refertilization. But chromite PT estimates mostly refer the heated conditions of the convective branch at the lithosphere base (~70-60kbar). They are most typical for the Alakite pipes. Diamond bearing eclogites show the some separate levels of crystallization with the high T-range reflecting conditions 35 to 45 mvm-2 mostly in the 60-50 kbar interval. They coincide with the levels of the intensive heating in the mantle columns. For the South Africa in the Mesozoic pipes beneath Lesotho - Jagersfontein (Viljoen ea. 2005), Finsch (Appleyard ea., 2004; Gurney, Switzer, 1973; She ea., 1983), Koffiefontein (Rickard ea., 1986), diamond bearing associations refer to three geotherm branches. The coldest (Cr-pyropes and Mg-Opx) is related to ancient subduction with the heating at 60 and 75 kbars. The 40

  2. The Acapulco Parent Planetesimal: An Early Collisional History in the Solar System

    Science.gov (United States)

    Marti, K.; Kim, Y.

    2007-05-01

    The Acapulco, Mexico, meteorite was recovered in 1976 from a crater of approx. 30 cm diameter. An old crystallization age of 4.60 (error 0.03) Ga (Prinzhofer et al., 1992) establishes that its parent object is one of the oldest known planetesimals in the solar system, although not in a pristine form. Other dating systems indicated somewhat younger ages and isotopic variabilities in several elements documented a complex early history. The younger ages date the closure times in secondary minerals. The initial parent object was in a partially molten state when isotopically distinct foreign matter invaded the chondritic parent and some of the isotopic signatures survived. Nitrogen in the primitive achondrite Acapulco was found to have distinct isotopic signatures for the metal and silicate phases and also in different morphologies of graphites (El Goresy, 1995, 2005). The delayed collisional event probably disrupted the parent object, as Acapulco cooled very rapidly. Nitrogen in the injected metal and graphite did not isotopically exchange with the host silicates. We observed nitrogen isotopic signatures of several separated mineral phases which cover a range of delta 15N values from -150 permil to +13 permil. The lightest nitrogen signatures observed in metal separates are comparable to those in some morphologies of Acapulco graphites. The heavy N signatures observed in several silicate minerals are consistent with each other, while nitrogen in chromite is distinctly light (delta 15N of -80 permil), intermediate between those of metal and silicates. The incipient rapid cooling history is well documented down to approx. 120° C, as recorded by U/Th-4He ages in phosphates (Min et al., 2003). The history of the Acapulco parent object was uneventful after its early evolution in an environment where no perturbation by collisions occurred, until the meteorite's recent (6.0 Ma ago) injection into an earth-crossing orbit. References: El Goresy, A., Zinner, E., and Marti, K

  3. Studies on the growth of oxide films on alloy 800 and alloy 600 in lithiated water at high temperature

    International Nuclear Information System (INIS)

    In this work, the oxide films grown on Alloy 800 and Alloy 600 in lithiated (pH25Cdegrees = 10.2-10.4) water at high temperature, with and without hydrogen overpressure (HO) and an initial oxygen dissolved in the water have been studied. The oxide films were grown at different temperatures (220-350 C degrees) and exposure times with HO, and at 315 C degrees without HO in static autoclaves. Some results are also reported for oxide layers grown on Alloy 800 coupons exposed in a high temperature loop during extended exposure times. The average oxide thickness was determined using descaling procedures. The morphology and composition of the oxide films were analyzed with scanning electron microscopy (SEM), EDS and X-ray diffraction (XRD). For both Alloys, at 350 C degrees with HO, the oxide layers were clearly composed of a double layer: an inner one of very small crystallites and an outer layer formed by bigger crystals scattered over the inner one. The analysis by X-ray diffraction indicated the presence of spinel structures like magnetite (Fe3O4) and ferrites and/or nickel chromites. In this case the average oxide thickness was around 0.12 to 0.15 μm for both Alloys. Similar values were found at lower temperatures. The morphology of the oxide layer was similar at lower temperatures for Alloy 800, but a different morphology consisting of platelets or needles was found for Alloy 600. The oxide morphology found at 315 C degrees, without HO and with initial dissolved oxygen in the water, was also very different between both Alloys. The oxide film grown on Alloy 600 with an initial dissolved oxygen in the water, showed clusters of platelets forming structures like flowers that were dispersed on an rather homogeneous layer consisting of smaller platelets or needles. The average oxide film grown in this case was around 0.25 μm for Alloy 600 and 0.18 μm for Alloy 800. (author)

  4. Tracing ancient events in the lithospheric mantle: A case study from ophiolitic chromitites of SW Turkey

    Science.gov (United States)

    Akbulut, Mehmet; González-Jiménez, José María; Griffin, William L.; Belousova, Elena; O'Reilly, Suzanne Y.; McGowan, Nicole; Pearson, Norman J.

    2016-04-01

    New major-, minor- and trace-element data on high-Cr chromites from several ophiolitic podiform chromitites from Lycian and Antalya peridotites in southwestern Turkey reveal a polygenetic origin from a range of arc-type melts within forearc and back-arc settings. These forearc and the back-arc related high-Cr chromitites are interpreted to reflect the tectonic juxtaposition of different lithospheric mantle segments during the obduction. The diversity of the γOs(t=0) values (-8.28 to +13.92) in the Antalya and Lycian chromitite PGMs and their good correlations with the sub- to supra-chondritic 187Os/188Os ratios (0.1175-0.1459) suggests a heterogeneous mantle source that incorporated up to 40% recycled crust, probably due to subduction processes of the orogenic events. The few model ages calculated define two significant peaks in TRD model ages at 1.5 and 0.25 Ga, suggesting that the chromitites are younger than 0.25 Ga and include relics of an at least Mesoproterozoic or older (>1.0 Ga) mantle protolith. Eight of the nine zircon grains separated from the chromitites, are interpreted as detrital and/or resorbed xenocrystic relics, whilst a significantly less reworked/resorbed one is considered to be of metasomatic origin. In-situ U-Pb dating of the xenocrystic zircon grains yielded a spread of ages within ca 0.6-2.1 Ga, suggesting recycling of crustal rocks younger than 0.6 Ga (Late Neoproterozoic). The notable coincidence between the lower age limit of the older zircons (ca 1.6 Ga) and the oldest Os model age peak (ca 1.5 Ga) from the PGM may suggest a Mesoproterozoic rifting stage. These findings imply a Paleoproterozoic sub-continental lithospheric mantle (SCLM) protolith for the SW Anatolian mantle which was later converted into an oceanic lithospheric mantle domain possibly following a rifting and continental break-up initiated during Mesoproterozoic (ca 1.5-1.0 Ga). The single metasomatic zircon of ca 0.09 Ga age coinciding with the initiation of the

  5. FE-SEM/EDS and μ-IR combined analysis of HED meteorites in relation to infrared spectra of Vesta-like asteroids

    Science.gov (United States)

    Ferrari, Marco; Dirri, Fabrizio; Palomba, Ernesto; Longobardo, Andrea; Rotundi, Alessandra

    2016-10-01

    Knowing the chemico-mineralogical composition of an extraterrestrial body is key to understanding its geological evolution. For this reason, remote-sensing instruments that can gather compositional data by using infrared spectroscopy are often part of the spacecraft missions. In order to acquire a fuller grasp of these data it is fundamental to compare them to analogue samples analysed by means of spectroscopy techniques.This study is focused on the Howardite-Eucrite-Diogenite meteorites (HEDs) [1] originated from the differentiated asteroid 4 Vesta [2]; this hypothesis was lately reinforced by the data provided by the Dawn mission [3].These meteorites consist of pyroxene basalts either brecciated or not (eucrites), brecciated orthopyroxenites (diogenites) and polymictic breccias of diogenites and eucrites originated by impacts on their parent body's surface (howardites).Here we report a FE-SEM/EDS and μ-IR spectroscopy combined study of three HED meteorite samples: 1) NWA 7159, a monomictic brecciated eucrite consisting of exolved orthopyroxene (Fs56.6-57.1 Wo2.0-1.9) and anorthite with accessory silica polymorph and ilmenite; 2) NWA 7490 a diogenite with a cumulate texture dominated by orthopyroxene (Fs24.1-26 Wo3.4-4.6), with Ca-plagioclase, minor olivine and chromite and troilite as accessory minerals; 3) NWA 2698, an howardite with eucritic pyroxene (Fs45-40 Wo7-20).The FE-SEM backscattered images coupled with the EDS maps gives information on the morphology (e.g. grain size and texture) and chemistry of the three samples. The μ-IR spectrometer provides reflectance spectra of the selected features of interest and spectral maps of larger areas. With the combined analyses we obtained a comprehensive mineralogical framework for the three HED samples. It was proven that the mineralogical heterogeneity of the HED meteorites is consistent with the spectroscopic diversity seen on Vesta [4], thus this study helps in better constraining and characterising the

  6. Bald Friar Metabasalt and Kennett Square Amphibolite: Two Iapetan Ocean Floor Basalts

    Science.gov (United States)

    Smith, R.C., II

    2006-01-01

    The Bald Friar Metabasalt (BFM) and Kennett Square Amphibolite (KSA) are basaltic units found in the Piedmont of southeastern Pennsylvania. The BFM is also recognized in northern Maryland. Both are believed to represent fragments of the floor of the Iapetus Ocean, but are not known occur in direct association with one another. The BFM typically occurs as small fragments having typical stratigraphic thicknesses of 2.5 m, and composed of greenish, fine-grained chlorite-epidote-actinolite-albite metabasalt in ophiolite me??lange. One bed of pillow basalt has been found at the type locality, Bald Friar, Cecil County, Maryland. Even though outcrops of BFM are highly discontinuous, they have a remarkable chemical uniformity over a strike length of 143 km and appear to be equivalent to the Caldwell Group 1b metabasalt of the Thetford, Quebec, area. The BFM is typically associated with ultramafic fragments and may be affiliated with the Baltimore Mafic Complex (BMC), from which a baddeleyite date of 442 +/- 7 Ma (Silurian) has been obtained. The BFM is probably a back arc basin basalt (BABB). Pod and schlieren chromite compositions suggest an island arc environment for the BMC itself. The poorly defined, informal "Conowingo Creek metabasalt" of Lancaster County, Pennsylvania, occurs on the north margin of the BMC and appears to be a fore arc boninite. The BFM and associated ultramafic fragments serve as a field-mappable marker for the structural equivalent of the Baie Verte-Brompton line in southeastern Pennsylvania and northern Maryland. Steatization of the associated ultramafic fragments has produced zones of extremely low competence that facilitated and localized thrusts of presumed Silurian age and later Alleghanian folding. The KSA typically occurs as much larger bodies having lengths of 3 km and composed of dark, medium-grained hornblende-plagioclase-clinopyroxene gneiss. No ultramafic rocks or me??lange have been recognized with the KSA. In Pennsylvania, the KSA

  7. An integrated geochemical, geophysical and mineralogical study of river sediments in alpine area and soil samples near steel plant, in Austria

    Science.gov (United States)

    Irfan, M. I.; Meisel, T.

    2012-04-01

    Concentration of nickel and chromium in any part of the ecosystem is important for environmental concerns in particular human health due to the reason that some species of them can cause health problem e.g. dermatitis and cancer. Sediment samples collected form a river Vordernberger Bach (Leoben, Austria) in an alpine region and soil samples collected in an area adjacent to steel production unit in same narrow valley were investigated. In previous studies a correlation between magnetic susceptibility values and concentration of nickel and chromium showed that a magnetic susceptibility meter can be used to point out the contaminated areas as in-situ device. The purpose of the whole study is to understand the real (point or diffuse, anthropogenic or geogenic) sources of contamination of soils, water and river sediments through heavy metal deposition. Unseparated, magnetic and non-magnetic fractions of soil samples were investigated for geochemical and mineralogical aspects with XRF, ICP-MS, EMPA, Multi-Functional Kappabridge (MFK1) and laser ablation coupled with ICP-MS. Mineralogical study of sediment samples for several sampling points with higher Ni and Cr content was performed. Sediment samples were sieved below 1.4 mm and then a concentrate of heavy minerals was prepared in the field through panning. Concentrated heavy minerals were then subjected for heavy liquid separation in the laboratory. Separated magnetic and non-magnetic fractions below 0.71/0.1 mm and density greater than 2.9 g/cm3 were selected for mineralogical investigation. The abundance of typical anthropogenic particles, e.g., spherical, tinder, roasted ores, iron and steel mill slag was observed under the microscope. Magnetite (mostly anthropogenic), maghemite, chromspinel, chromite (type I & II), (Ca,Al)-ferrite, wustite, apatite (anthropogenic), olivine mixed crystals, calcium silicate and spinel (anthropogenic) are found in magnetic fraction. Non-magnetic fractions contain hematite, siderite

  8. Using chalcophile elements to constrain crustal contamination and xenolith-magma interaction in Cenozoic basalts of eastern China

    Science.gov (United States)

    Zeng, Gang; Huang, Xiao-Wen; Zhou, Mei-Fu; Chen, Li-Hui; Xu, Xi-Sheng

    2016-08-01

    Continental basalts have complicated petrogenetic processes, and their chemical compositions can be affected by multi-staged geological evolution. Compared to lithophile elements, chalcophile elements including Ni, platinum-group elements (PGEs) and Cu are sensitive to sulfide segregation and fractional crystallization during the evolution of mantle-derived magmas and can provide constraints on the genesis of continental basalts. Cenozoic intra-continental alkaline basalts in the Nanjing basaltic field, eastern China, include high-Ca and low-Ca varieties. All these basalts have poor PGE contents with Ir ranging from 0.016 ppb to 0.288 ppb and high Cu/Pd ratios from 0.7 × 105 to 4.7 × 105 (5.7 × 103 for DMM), indicating that they were derived from sulfide-saturated mantle sources with variable amounts of residual sulfide during melting or might undergo an early-sulfide segregation in the mantle. Relatively high Cu/Pd ratios along with high Pd concentrations for the high-Ca alkaline basalts indicate an additional removal of sulfide during magma ascent. Because these basalts have high, variable Pd/Ir ratios (2.8-16.8) with low Ce/Pb (9.9-19.7) ratios and εNd values (+ 3.6-+6.4), crustal contamination is proposed to be a potential process to induce the sulfide saturation and removal. Significantly increased Pd/Ir ratios for few high-Ca basalts can be explained by the fractionation of laurite or Ru-Os-Ir alloys with olivine or chromite. For low-Ca alkaline basalts, their PGE contents are well correlated with the MgO, Sc contents, incompatible element ratios (Lu/Hf, Na/Ti and Ca/Al) and Hf isotopes. Good correlations are also observed between Pd/Ir (or Rh/Ir) and Na/Ti (or Ca/Al) ratios. Variations of these elemental ratios and Hf isotopes is previously documented to be induced by the mixing of peridotite xenolith-released melts during ascent. Therefore, we suggest that such xenolith-magma interaction are also responsible for the variable PGE compositions of low

  9. Thorium partitioning in Greek industrial bauxite investigated by synchrotron radiation and laser-ablation techniques

    Energy Technology Data Exchange (ETDEWEB)

    Gamaletsos, P. [Faculty of Geology and Geoenvironment, University of Athens, Panepistimioupolis, 15784 Zographou (Greece); Godelitsas, A., E-mail: agodel@geol.uoa.gr [Faculty of Geology and Geoenvironment, University of Athens, Panepistimioupolis, 15784 Zographou (Greece); Mertzimekis, T.J. [Department of Physics, University of Athens, Panepistimioupolis, 15771 Zographou (Greece); Goettlicher, J.; Steininger, R. [Karlsruhe Institute of Technology, Institute for Synchrotron Radiation, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Xanthos, S. [Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, GR-54124 Thessaloniki (Greece); Berndt, J.; Klemme, S. [Institut fuer Mineralogie, Corrensstrasse 24, Universitaet Muenster, 48149 Muenster (Germany); Kuzmin, A. [Institute of Solid State Physics, University of Latvia, Kengaraga st. 8, 1063 Riga (Latvia); Bardossy, G. [Hungarian Academy of Sciences, H-1051 Budapest (Hungary)

    2011-12-15

    Typical red-brown (Fe-rich) and high-quality white-grey (Fe-depleted) bauxite samples from active mines of the Parnassos-Ghiona area, central Greece, were investigated. According to XRF and ICP-MS analyses their actinide content, and particularly of Th, is relatively increased. Fe-depleted samples contain up to 62.75 ppm Th corresponding to 220 Bq/kg due to {sup 228}Ac ({sup 232}Th-series), whereas Fe-rich samples are less Th-radioactive (up to 58.25 ppm Th, 180 Bq/kg due to {sup 228}Ac). Powder-XRD patterns showed that Th-enriched (Fe-depleted) bauxite consists mostly of diaspore (AlOOH polymorph), anatase and rutile (TiO{sub 2} polymorphs). SEM-EDS indicated the presence of Ti-Fe-containing phases (e.g. ilmenite, FeTiO{sub 3}), chromite (Cr-spinel) and besides LREE-minerals (mostly bastnaesite/parisite-group) and zircon (ZrSiO{sub 4}) hosting a part of the bulk Th. The presence of Th in diaspore and in Ti-containing phases (not detected by SEM-EDS as in the case of REE-minerals and zircon) was investigated, into distinct pisoliths of Fe-depleted bauxite, using {mu}-XRF and {mu}-XAFS in the SUL-X beamline of the ANKA Synchrotron facility (KIT, Germany). XAFS spectra of Th salts and Th-containing reference materials were obtained as well. Accordingly it was revealed, for the first time in the literature, that Ti-phases, and particularly anatase, host significant amounts of Th. This novel conclusion was complementary supported by LA-ICP-MS analyses indicated an average of 73 ppm Th in anatase grains together with abundant Nb (3356 ppm), Ta (247 ppm) and U (33 ppm). The Th L{sub III}-edge XAFS spectra as compared to reference materials, give also evidence that Th{sup 4+} may not replace Ti{sup 4+} in distorted [TiO{sub 6}] fundamental octahedral units of anatase and ilmenite lattice (CN = 6). The occupation of either extraframework sites of higher coordination (CN = 6.9 or even CN = 7.4), according to EXAFS signals evaluation, or of defected/vacant (**) sites is more

  10. Re-Os systematics of komatiites and komatiitic basalts at Dundonald Beach, Ontario, Canada: Evidence for a complex alteration history and implications of a late-Archean chondritic mantle source

    Science.gov (United States)

    Gangopadhyay, Amitava; Sproule, Rebecca A.; Walker, Richard J.; Lesher, C. Michael

    2005-11-01

    Osmium isotopic compositions, and Re and Os concentrations have been examined in one komatiite unit and two komatiitic basalt units at Dundonald Beach, part of the 2.7 Ga Kidd-Munro volcanic assemblage in the Abitibi greenstone belt, Ontario, Canada. The komatiitic rocks in this locality record at least three episodes of alteration of Re-Os elemental and isotope systematics. First, an average of 40% and as much as 75% Re may have been lost due to shallow degassing during eruption and/or hydrothermal leaching during or immediately after emplacement. Second, the Re-Os isotope systematics of whole rock samples with 187Re/ 188Os ratios >1 were reset at ˜2.5 Ga, possibly due to a regional metamorphic event. Third, there is evidence for relatively recent gain and loss of Re in some rocks. Despite the open-system behavior, some aspects of the Re-Os systematics of these rocks can be deciphered. The bulk distribution coefficient for Os (D Ossolid/liquid) for the Dundonald rocks is ˜3 ± 1 and is well within the estimated D values obtained for komatiites from the nearby Alexo area and stratigraphically-equivalent komatiites from Munro Township. This suggests that Os was moderately compatible during crystal-liquid fractionation of the magmas parental to the Kidd-Munro komatiitic rocks. Whole-rock samples and chromite separates with low 187Re/ 188Os ratios (Kidd-Munro volcanic assemblage had evolved with a long-term chondritic Re/Os before eruption. The chondritic initial Os isotopic composition of the Kidd-Munro komatiites is indistinguishable from that of the projected contemporaneous convective upper mantle. The uniform chondritic Os isotopic composition of the Kidd-Munro komatiites contrasts with the typical large-scale Os isotopic heterogeneity in the mantle sources for ca. 89 Ma komatiites from the Gorgona Island, arc-related rocks and present-day ocean island basalts. This suggests that the Kidd-Munro komatiites sampled a late-Archean mantle source region that was

  11. Diamonds in ophiolites: Contamination or a new diamond growth environment?

    Science.gov (United States)

    Howell, D.; Griffin, W. L.; Yang, J.; Gain, S.; Stern, R. A.; Huang, J.-X.; Jacob, D. E.; Xu, X.; Stokes, A. J.; O'Reilly, S. Y.; Pearson, N. J.

    2015-11-01

    For more than 20 years, the reported occurrence of diamonds in the chromites and peridotites of the Luobusa massif in Tibet (a complex described as an ophiolite) has been widely ignored by the diamond research community. This skepticism has persisted because the diamonds are similar in many respects to high-pressure high-temperature (HPHT) synthetic/industrial diamonds (grown from metal solvents), and the finding previously has not been independently replicated. We present a detailed examination of the Luobusa diamonds (recovered from both peridotites and chromitites), including morphology, size, color, impurity characteristics (by infrared spectroscopy), internal growth structures, trace-element patterns, and C and N isotopes. A detailed comparison with synthetic industrial diamonds shows many similarities. Cubo-octahedral morphology, yellow color due to unaggregated nitrogen (C centres only, Type Ib), metal-alloy inclusions and highly negative δ13C values are present in both sets of diamonds. The Tibetan diamonds (n = 3) show an exceptionally large range in δ15N (-5.6 to + 28.7 ‰) within individual crystals, and inconsistent fractionation between {111} and {100} growth sectors. This in contrast to large synthetic HPHT diamonds grown by the temperature gradient method, which have with δ15N = 0 ‰ in {111} sectors and + 30 ‰ in {100} sectors, as reported in the literature. This comparison is limited by the small sample set combined with the fact the diamonds probably grew by different processes. However, the Tibetan diamonds do have generally higher concentrations and different ratios of trace elements; most inclusions are a NiMnCo alloy, but there are also some small REE-rich phases never seen in HPHT synthetics. These characteristics indicate that the Tibetan diamonds grew in contact with a C-saturated Ni-Mn-Co-rich melt in a highly reduced environment. The stable isotopes indicate a major subduction-related contribution to the chemical environment. The

  12. Thermobarometry of mantle-derived garnets and pyroxenes of Kola region (NW Russia: lithosphere composition, thermal regime and diamond prospectivity

    Directory of Open Access Journals (Sweden)

    Dmitry R. Zozulya

    2009-12-01

    Full Text Available More than 700 pyrope, chrome diopside and chromite grains recovered from Quaternary sediments of the Kola craton, and from the Ermakovsky kimberlite in the Terskii Coast field were analyzed in order to determine their P-T parameters. Ni-thermometry on pyropes from SE Kola gives a range of temperatures between 650–1250 °C, corresponding to a sampling interval of c. 75–190 km. Pyrope compositions imply a stratified structure to the SE Kola lithospheric mantle, with G10-pyropes absent in the shallow mantle (75–110 km where the bulk of the G9-pyropes are sourced, while a deeper mantle horizon, between110 and 190 km, has contributed abundant G10-pyropes. Approximately 16 % of all these pyropes are derived from the diamond stability field. The Ni-temperatures of garnets from the Ermakovsky kimberlite reveal a relatively shallow sampling interval of the mantle (c.75–140 km, dominantly within the graphite-stability field. P-T values for peridotitic chrome diopsides imply that most grains from SE Kola were derived from the graphite stability field, apparently originating from non-diamondiferous alkaline-ultramafic dykes. Nevertheless, c. 15 % of SE Kola diopsides have been derived from the stability field of diamond. Diopsides from SW Kola mostly plot in the diamond stability field. 20 % of diopsides from central Kolaare derived from the diamond stability field, whereas diopsides from northern Kola region all fall within the stability field of graphite. The maximum depth of diopside xenocryst sampling varies from up to 200 km in SE and SW Kola, to 170 km in central Kola, and only to 140 km in the northern Kola region. The P-T values for chrome diopsides imply significant regional differences in heat flow: 38–44 mW/m^2 within the southern part of Kola adjacent to the Kandalaksha graben; 35–38 mW/m^2 towards the SE and SW away from the graben; 38–44 mW/m^2 in central Kola; and up to 50 mW/m^2 in northernmost Kola. These data indicate that

  13. Cooling History and Redox State of NWA 8694 Chassignite: Comparison with Chassigny and NWA 2737

    Science.gov (United States)

    Mikouchi, T.; Takenouchi, A.; Zolensky, M. E.

    2016-01-01

    NWA 8694 is a new chassignite whose constituent minerals are more Fe-rich than those in the other known chassignites (Chassigny and NWA 2737), and may suggest a petrogenetic relationship to nakhlites. In this abstract we report mineralogy of NWA 8694 to infer its cooling rate and redox state, and discuss its thermal and shock history in comparison with other chassignites. NWA 8694 is a cumulate dunite of approximately 2 mm olivine with interstitial pyroxene and feldspar. Olivine is homogeneous (Fo(sub 55-56)), but Ca decreases at the approximately 50-100 micrometer rim (0.25-0.1 wt% CaO). Because the Ca-depleted rim is narrower than those in other chassignites (approximately 50 ?micrometer), NWA 8694 may have cooled slightly faster than the others (approximately 30 C/yr), but would be in the same order. Pyroxenes are low- and high-Ca pyroxenes, both exhibiting sub-micron exsolution textures (0.2-0.3 micrometer wide lamellae with the spacing of 0.8-1.8 micrometers). Although the low-Ca pyroxene host has an orthopyroxene composition (Wo approximately 2), the EBSD analysis suggests a pigeonite structure (P2(sub 1)/c), which is also reported from the Chassigny pyroxene. The size of exsolution texture is a bit smaller, but broadly similar to those in other chassignites, implying a similar fast cooling rate (35-43 C/yr). Feldspars are isotropic (plagioclase: clustered around An25Or10, K-feldspar: approximately An19Or78), suggestive of extensive shock metamorphism, consistent with undulatory extinction of olivine. Feldspar compositions are around the equilibrium isotherm of approximately 800 C. The olivine and chromite compositions give an equilibration temperature of 760-810 C and logfO2 of QFM+/-0.3. The inferred fast cooling rate and high fO2 of NWA 8694 are both similar to those of Chassigny and NWA 2737, and suggest a common formation condition (e.g., thick lava flow or shallow intrusion) under oxidizing condition. The Fe-rich mineral compositions of NWA 8694 may be

  14. Ophiolitic detritus in Kimmeridgian resedimented limestones and its provenance from an eroded obducted ophiolitic nappe stack south of the Northern Calcareous Alps (Austria

    Directory of Open Access Journals (Sweden)

    Gawlick Hans-Jürgen

    2015-12-01

    Full Text Available The causes for the Middle to Late Jurassic tectonic processes in the Northern Calcareous Alps are still controversially discussed. There are several contrasting models for these processes, formerly designated “Jurassic gravitational tectonics”. Whereas in the Dinarides or the Western Carpathians Jurassic ophiolite obduction and a Jurassic mountain building process with nappe thrusting is widely accepted, equivalent processes are still questioned for the Eastern Alps. For the Northern Calcareous Alps, an Early Cretaceous nappe thrusting process is widely favoured instead of a Jurassic one, obviously all other Jurassic features are nearly identical in the Northern Calcareous Alps, the Western Carpathians and the Dinarides. In contrast, the Jurassic basin evolutionary processes, as best documented in the Northern Calcareous Alps, were in recent times adopted to explain the Jurassic tectonic processes in the Carpathians and Dinarides. Whereas in the Western Carpathians Neotethys oceanic material is incorporated in the mélanges and in the Dinarides huge ophiolite nappes are preserved above the Jurassic basin fills and mélanges, Jurassic ophiolites or ophiolitic remains are not clearly documented in the Northern Calcareous Alps. Here we present chrome spinel analyses of ophiolitic detritic material from Kimmeridgian allodapic limestones in the central Northern Calcareous Alps. The Kimmeridgian age is proven by the occurrence of the benthic foraminifera Protopeneroplis striata and Labyrinthina mirabilis, the dasycladalean algae Salpingoporella pygmea, and the alga incertae sedis Pseudolithocodium carpathicum. From the geochemical composition the analysed spinels are pleonastes and show a dominance of Al-chromites (Fe3+–Cr3+–Al3+ diagram. In the Mg/(Mg+ Fe2+ vs. Cr/(Cr+ Al diagram they can be classified as type II ophiolites and in the TiO2 vs. Al2O3 diagram they plot into the SSZ peridotite field. All together this points to a harzburgite

  15. Thorium partitioning in Greek industrial bauxite investigated by synchrotron radiation and laser-ablation techniques

    Science.gov (United States)

    Gamaletsos, P.; Godelitsas, A.; Mertzimekis, T. J.; Göttlicher, J.; Steininger, R.; Xanthos, S.; Berndt, J.; Klemme, S.; Kuzmin, A.; Bárdossy, G.

    2011-12-01

    Typical red-brown (Fe-rich) and high-quality white-grey (Fe-depleted) bauxite samples from active mines of the Parnassos-Ghiona area, central Greece, were investigated. According to XRF and ICP-MS analyses their actinide content, and particularly of Th, is relatively increased. Fe-depleted samples contain up to 62.75 ppm Th corresponding to 220 Bq/kg due to 228Ac ( 232Th-series), whereas Fe-rich samples are less Th-radioactive (up to 58.25 ppm Th, 180 Bq/kg due to 228Ac). Powder-XRD patterns showed that Th-enriched (Fe-depleted) bauxite consists mostly of diaspore (AlOOH polymorph), anatase and rutile (TiO 2 polymorphs). SEM-EDS indicated the presence of Ti-Fe-containing phases (e.g. ilmenite, FeTiO 3), chromite (Cr-spinel) and besides LREE-minerals (mostly bastnäsite/parisite-group) and zircon (ZrSiO 4) hosting a part of the bulk Th. The presence of Th in diaspore and in Ti-containing phases (not detected by SEM-EDS as in the case of REE-minerals and zircon) was investigated, into distinct pisoliths of Fe-depleted bauxite, using μ-XRF and μ-XAFS in the SUL-X beamline of the ANKA Synchrotron facility (KIT, Germany). XAFS spectra of Th salts and Th-containing reference materials were obtained as well. Accordingly it was revealed, for the first time in the literature, that Ti-phases, and particularly anatase, host significant amounts of Th. This novel conclusion was complementary supported by LA-ICP-MS analyses indicated an average of 73 ppm Th in anatase grains together with abundant Nb (3356 ppm), Ta (247 ppm) and U (33 ppm). The Th LIII-edge XAFS spectra as compared to reference materials, give also evidence that Th 4+ may not replace Ti 4+ in distorted [TiO 6] fundamental octahedral units of anatase and ilmenite lattice (CN = 6). The occupation of either extraframework sites of higher coordination (CN = 6.9 or even CN = 7.4), according to EXAFS signals evaluation, or of defected/vacant (**) sites is more probable. This is likely explained by the difficulty of

  16. International Field School on Permafrost, Polar Urals, 2012

    Science.gov (United States)

    Streletskiy, D. A.; Grebenets, V.; Ivanov, M.; Sheinkman, V.; Shiklomanov, N. I.; Shmelev, D.

    2012-12-01

    The international field school on permafrost was held in the Polar Urals region from June, 30 to July 9, 2012 right after the Tenth International Conference on Permafrost which was held in Salekhard, Russia. The travel and accommodation support generously provided by government of Yamal-Nenets Autonomous Region allowed participation of 150 permafrost young research scientists, out of which 35 students from seven countries participated in the field school. The field school was organized under umbrella of International Permafrost Association and Permafrost Young Research Network. The students represented diverse educational backgrounds including hydrologists, engineers, geologists, soil scientists, geocryologists, glaciologists and geomorphologists. The base school camp was located near the Harp settlement in the vicinity of Polar Urals foothills. This unique location presented an opportunity to study a diversity of cryogenic processes and permafrost conditions characteristic for mountain and plain regions as well as transition between glacial and periglacial environments. A series of excursions was organized according to the following topics: structural geology of the Polar Urals and West Siberian Plain (Chromite mine "Centralnaya" and Core Storage in Labitnangy city); quaternary geomorphology (investigation of moraine complexes and glacial conditions of Ronamantikov and Topographov glaciers); principles of construction and maintains of structures built on permafrost (Labitnangy city and Obskaya-Bovanenkovo Railroad); methods of temperature and active-layer monitoring in tundra and forest-tundra; cryosols and soil formation in diverse landscape condition; periglacial geomorphology; types of ground ice, etc. Every evening students and professors gave a series of presentations on climate, vegetation, hydrology, soil conditions, permafrost and cryogenic processes of the region as well as on history, economic development, endogenous population of the Siberia and the

  17. Comparative petrology of silicates in the Udei Station (IAB) and Miles (IIE) iron meteorites: Implications for the origin of silicate-bearing irons

    Science.gov (United States)

    Ruzicka, Alex; Hutson, Melinda

    2010-01-01

    The textures and mineral chemistries of silicate inclusions in the Udei Station (IAB) and Miles (fractionated IIE) iron meteorites were studied using optical and electron microscopy, SEM, EMPA, and LA-ICP-MS techniques to better understand the origin of silicate-bearing irons. Inclusions in Udei Station include near-chondritic, basaltic/gabbroic, feldspathic orthopyroxenitic, and harzburgitic lithologies. In Miles, most inclusions can be described as feldspathic pyroxenite or pyroxene-enriched basalt/gabbro. The trace-element compositions of both orthopyroxene and plagioclase grains are similar in different lithologies from Udei Station; whereas in different inclusions from Miles, the compositions of orthopyroxene grains are similar, while those of clinopyroxene, plagioclase, and especially Cl-apatite are variable. Orthopyroxene in Miles tends to be enriched in REE compared to that in Udei Station, but the reverse is true for plagioclase and clinopyroxene. The data can be explained by models involving partial melting of chondritic protoliths, silicate melt migration, and redox reactions between silicate and metal components to form phosphate. The extent of heating, melt migration, and phosphate formation were all greater in Miles. Silicates in Miles were formed from liquids produced by ˜30% partial melting of a chondritic precursor brought to a peak temperature of ˜1250 °C. This silicate melt crystallized in two stages. During Stage 1, crystallizing minerals (orthopyroxene, clinopyroxene, chromite, and olivine) were largely in equilibrium with an intercumulus melt that was evolving by igneous fractionation during slow cooling, with a residence time of ˜20 ka at ˜1150 °C. During Stage 2, following probable re-melting of feldspathic materials, and after the silicate "mush" was mixed with molten metal, plagioclase and phosphate fractionally crystallized together during more rapid cooling down to the solidus. In Udei Station, despite a lower peak temperature (IIE

  18. Petrology of silicate inclusions in the Sombrerete ungrouped iron meteorite: Implications for the origins of IIE-type silicate-bearing irons

    Science.gov (United States)

    Ruzicka, Alex; Hutson, Melinda; Floss, Christine

    2006-11-01

    The petrography and mineral and bulk chemistries of silicate inclusions in Sombrerete, an ungrouped iron that is one of the most phosphate-rich meteorites known, was studied using optical, scanning electron microscopy (SEM), electron microprobe analysis (EMPA), and secondary ion mass spectrometry (SIMS) techniques. Inclusions contain variable proportions of alkalic siliceous glass (˜69 vol% of inclusions on average), aluminous orthopyroxene (˜9%, Wo1-4Fs25-35, up to ˜3 wt% Al), plagioclase (˜8%, mainly An70-92), Cl-apatite (˜7%), chromite (˜4%), yagiite (˜1%), phosphate-rich segregations (˜1%), ilmenite, and merrillite. Ytterbium and Sm anomalies are sometimes present in various phases (positive anomalies for phosphates, negative for glass and orthopyroxene), which possibly reflect phosphate-melt-gas partitioning under transient, reducing conditions at high temperatures. Phosphate-rich segregations and different alkalic glasses (K-rich and Na-rich) formed by two types of liquid immiscibility. Yagiite, a K-Mg silicate previously found in the Colomera (IIE) iron, appears to have formed as a late-stage crystallization product, possibly aided by Na-K liquid unmixing. Trace-element phase compositions reflect fractional crystallization of a single liquid composition that originated by low-degree (˜4-8%) equilibrium partial melting of a chondritic precursor. Compositional differences between inclusions appear to have originated as a result of a "filter-press differentiation" process, in which liquidus crystals of Cl-apatite and orthopyroxene were less able than silicate melt to flow through the metallic host between inclusions. This process enabled a phosphoran basaltic andesite precursor liquid to differentiate within the metallic host, yielding a dacite composition for some inclusions. Solidification was relatively rapid, but not so fast as to prevent flow and immiscibility phenomena. Sombrerete originated near a cooling surface in the parent body during rapid

  19. Comparison of the mantle modification of the mantle column between two phases of kimberlite intrusion in Dalnyaya pipe, Yakutia

    Science.gov (United States)

    Ashchepkov, Igor; Spetsius, Zdislav; Salikhov, Ravil; Khmelnikova, Olga

    2013-04-01

    Dalnaya pipe is one of the largest in Daldyn field, Yakutia is composed of autolite breccia (AKB) and porphyric kimberlite (PK). Minerals from concentrates of both phases were compared and with the peridotite xenoliths minerals. Cpx from Dalnyaya are showing common tendencies Fe--Ti rise and Cr, Al, Na decrease. Garnets belong to lherzolite field with more deviation to harzbuirgitic one for (PK) . The chromites show two subtrends for Cr Fe, Ni vs TiO2. In general the variations of the AKB minerals and dispersion are higher but amount of depleted varieties is higher in PK. We used >50 xenoliths and ~1200 concentrate minerals for PT reconstructions. Combine PTX diagram show deep SCLM root beneath Dalnyaya with the main heating ~7 GPa. The HT 45mwm-2 branch is traced by some xenoliths from base to 2GPa. Essential inflection and heating detected by PT for OPx ~3GPa referring to Ca- enriched pyroxenitic garnets . Small Fe enrichment for Cpx and Gar found near 6 GPa referring to heated porhyroclastic varieties. Continuous and irregular growth of Fe# for Gar and low Fe Cpx Fe# 6 to 12# suggest that primary mantle layering beneath this pipe was smoothed by the high scale interaction with melts. The refertilization trend with Fe#9-15% rising upward in two branches refer to the Ilm and Cpx parental melt evolutions produced the intergrowth sometimes with garnets. In the PFO2 diagrams garnets and Cpx show continuous reduction to the lithosphere base to 4QMF higher for Cpx. Ilm - garnet trend is rising upward between -2 -0 QMF. The PT diagram for the AKB minerals from Dalnyaya pipe is nearly the same with the high dispersion to Fe rich varieties and smaller amount o f Mg rich minerals. Since the diamond grade is often determined by the amount of depleted varieties it is higher for the PK. Trace elements determined for Gar and Cpx from 13 xenoliths from the middle part of mantle section reveal very similar patterns in general. Supported by RBRF grant 11-05-00060.

  20. Mapping of groundwater potential zones in Salem Chalk Hills, Tamil Nadu, India, using remote sensing and GIS techniques.

    Science.gov (United States)

    Thilagavathi, N; Subramani, T; Suresh, M; Karunanidhi, D

    2015-04-01

    This study proposes to introduce the remote sensing and geographic information system (GIS) techniques in mapping the groundwater potential zones. Remote sensing and GIS techniques have been used to map the groundwater potential zones in Salem Chalk Hills, Tamil Nadu, India. Charnockites and fissile hornblende biotite gneiss are the major rock types in this region. Dunites and peridodites are the ultramafic rocks which cut across the foliation planes of the gneisses and are highly weathered. It comprises magnesite and chromite deposits which are excavated by five mining companies by adopting bench mining. The thickness of weathered and fracture zone varies from 2.2 to 50 m in gneissic formation and 5.8 to 55 m in charnockite. At the contacts of gneiss and charnockite, the thickness ranges from 9.0 to 90.8 m favoring good groundwater potential. The mine lease area is underlined by fractured and sheared hornblende biotite gneiss where groundwater potential is good. Water catchment tanks in this area of 5 km radius are small to moderate in size and are only seasonal. They remain dry during summer seasons. As perennial water resources are remote, the domestic and agricultural activities in this region depend mainly upon the groundwater resources. The mines are located in gently slope area, and accumulation of water is not observed except in mine pits even during the monsoon period. Therefore, it is essential to map the groundwater potential zones for proper management of the aquifer system. Satellite imageries were also used to extract lineaments, hydrogeomorphic landforms, drainage patterns, and land use, which are the major controlling factors for the occurrence of groundwater. Various thematic layers pertaining to groundwater existence such as geology, geomorphology, land use/land cover, lineament, lineament density, drainage, drainage density, slope, and soil were generated using GIS tools. By integrating all the above thematic layers based on the ranks and

  1. Pd-Ag chronology of volatile depletion, crystallization and shock in the Muonionalusta IVA iron meteorite and implications for its parent body

    Science.gov (United States)

    Horan, M. F.; Carlson, R. W.; Blichert-Toft, J.

    2012-10-01

    Muonionalusta, a Group IVA iron meteorite, was analyzed for its 107Pd-107Ag isotope systematics by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in order to better constrain the initial Solar System abundance of 107Pd and to provide high resolution chronology of the evolution of its parent body. Six metal samples from Muonionalusta yield Ag abundances between 0.1012 and 1.461 ng/g, 107Ag/109Ag between 1.131 and 1.805, with 108Pd/109Ag ratios of 2201 to 52,300. The metal Pd/Ag and Ag isotopic data are correlated with a slope corresponding to a 107Pd/108Pd of (2.15±0.30)×10-5. If the Pd-Ag and Pb-Pb isotope systems closed at the same time in Muonionalusta, i.e., 2-3 Ma after CAI formation, then an initial Solar System ratio of 107Pd/108Pd=(2.8±0.5)×10-5 can be inferred. One troilite sample contains 8.478 ng/g Ag and has a 107Ag/109Ag ratio of 1.0833; its Pd concentration is 205.2 ng/g corresponding to a low 108Pd/109Ag of 13.56. The Pd-Ag results for this troilite plot near the extrapolation of the line passing through the metal points and define an initial 107Ag/109Ag that is substantially higher than chondritic, indicating that Muonionalusta formed from a precursor with high Pd/Ag. Pd and Ag concentrations in Muonionalusta metal suggest fractional crystallization from a source having Pd/Ag>4500, but the initial Ag isotopic composition for Muonionalusta troilite limits the duration of the high Pd/Ag to an interval of ≤0.6 Ma before cooling to closure of the Pd-Ag system. This result suggests that depletion of Ag and other volatile elements occurred shortly before accretion and cooling of the IVA parent body, and may have been associated with violent disruption of a progenitor to the IVA parent. Another troilite sample, its chromite inclusions and adjacent metal were isotopically homogenized locally after 107Pd had decayed, possibly by a later episode of shock >50 Ma after Solar System formation.

  2. Quantifying Density, Water Adsorption and Equilibration Properties of Wind Tunnel Materials

    Science.gov (United States)

    Yu, Xinting; Horst, Sarah; He, Chao; Bridges, Nathan; Burr, Devon M.; Sebree, Joshua

    2016-10-01

    Aeolian processes are found on various planetary bodies including Earth, Venus, Mars, Titan, Triton, Pluto, and Comet 67P. Wind tunnels can simulate aeolian processes under different planetary parameters, with the robustness of results relying on experimental conditions and understanding of experimental materials. Threshold wind speed, the minimum wind speed to initiate saltation, is one parameter that can be investigated in wind tunnels. Liquid water adsorbed on wind tunnel materials could greatly enhance the threshold wind speed by increasing the interparticle force, density, and effective size of particles. Previous studies have shown that this effect could increase the threshold by 100% by putting 0.3-0.6% of water into typical dry quartz sand (Fecan et al. 1998). In order to simulate the weight of particles on other planetary bodies where gravity is significantly lower than on Earth, low-density materials are used in planetary wind tunnels, including walnut shells, activated charcoal, iced tea, and instant coffee.We first quantified the densities for all wind tunnel materials using a pycnometer and updated the density for low-density materials (e.g., walnut shells have density of 1.4 g/cm3 instead of 1.1 g/cm3 in the literature (Greeley et al. 1980)). Then we present a set of measurements that quantify water adsorption for both low and high-density materials (sand, basalt, and chromite). We first measured the water content and equilibration timescales for the materials through gravimetric measurements. We found low-density materials tend to have much more water (>5%) compared to high-density materials ( 6 hrs) compared to high-density materials (10–50 minutes). Since only water adsorbed on the particle surface would change the interparticle force, we then separate the surface and internal water using thermo-gravimetric analysis, and found that >80% of the water is still on the surface. Thus we assume water adsorption for low-density materials could greatly

  3. Kimberlite Ascent: Insights from Olivine

    Science.gov (United States)

    Brett, C.; Russell, K.

    2009-05-01

    Olivine is ubiquitous in both extrusive and intrusive kimberlite deposits worldwide. Within kimberlite, it is mainly present as xenocrysts derived from the disaggregation of mantle-derived peridotitic xenoliths. Many textural and chemical features within the mantle-derived olivine xenocrysts result from post entrainment processes. On that basis, these features record physical and chemical changes attending kimberlite ascent and can be used to elucidate the transport and eruption of kimberlite magma. Our textural study of kimberlitic olivine is based on intrusive and pyroclastic kimberlite from the Diavik kimberlite cluster and from the Igwisi Hills kimberlitic lava flows. Based on these observations and the physical and chemical properties of olivine we derive a relative sequence of textural events. Textural features include: sealed cracks, healed cracks, phases trapping in cracks, rounded grains, overgrowths and phase trapping in overgrowths. These features record processes that operate in kimberlite during ascent, and from these features we create a summary model for kimberlite ascent: -- Olivine is incorporated into kimberlitic melts in peridotitic mantle xenoliths continuously during ascent. Xenolith incorporation is focused at the crack tip where the stress regime is highest. -- Shortly after the incorporation of these xenocrysts the tensile strength of the xenoliths is reached at a maximum of 2 km from its source. Disaggregation of mantle xenoliths (producing xenocrysts) is facilitated by expansion of the minerals within the xenoliths causing intra-crystal slip (i.e. along grain boundaries). -- Continued decompression causes olivine to also break in tension approximately 20 km from source. The void space produced by the failure of the crystals (inter-crystal cracks) is filled with melt and crystals consisting of primary carbonate (high-Sr), chromite and spinel crystals. The carbonate later crystallizes to produce sealed fractures. -- Mechanical rounding of

  4. Geological setting, emplacement mechanism and igneous evolution of the Atchiza mafic-ultramafic layered suite in north-west Mozambique

    Science.gov (United States)

    Ibraimo, Daniel Luis; Larsen, Rune B.

    2015-11-01

    The Atchiza mafic and ultramafic-layered suite (hereafter, "Atchiza Suite) crops out in an area 330 km2 west of the Mozambican Tete province. In an early account of the geology of this intrusion, it was considered the continuation of the Great Dyke of Zimbabwe, an idea that was aborted after detailed studies. Nevertheless, the Ni concentrations in the Atchiza outcrop rocks are considerable. Our investigation used field evidence, hand specimens and petrography descriptions, mineral chemistry studies using electron microprobe analysis and tectonic analysis to arrive at a plausible mineralogical composition and understanding of the tectonic setting for the igneous evolution. The mineral composition from the Atchiza Suite indicates that these are cumulates. The magmatic segregation from the petrographic and mineral composition reasoning indicates that dunite-lherzolitic peridotite-olivine gabbro-gabbronorite-gabbro-pegmatitic gabbro is the rock formation sequence. Olivine and chromite were the first phases formed, followed by pyroxene and plagioclase. In addition, it is shown that these minerals are near-liquidus crystallization products of basaltic magma with olivine Fo: 87.06 in dunite, mean values of clinopyroxene are (Wo: 36.4, En: 48.0, Fs: 15.2), orthopyroxene (Wo: 2.95, En: 73.0, Fs: 24.2) and plagioclase An: 71.3, respectively. Opaque minerals comprise Fe-Ti oxides and (Fe, Cr) spinel up to 4.8 vol.%, but chromitite layers are not present. Most of the opaque minerals are interstitial to pyroxene. Sulphides are common in gabbros, with pyrrhotite, pentlandite, chalcopyrite, pyrite and covellite together comprising 0.4-2.0 vol.%. The whole rock Rare Earth Element (REE) concentrations are mainly a result of differentiation, but slight crustal contamination/assimilation contributed to the REE contents. In addition, they also show Eu enrichment, suggesting that plagioclase fractionation was important in the rock. The Atchiza Suite preserves a deep-seated plumbing

  5. The effects of water rock interaction and the human activities on the occurrence of hexavalent chromium in waters. The case study of the Psachna basin, Central Euboea, Greece.

    Science.gov (United States)

    Vasileiou, Eleni; Perraki, Maria; Stamatis, George; Gartzos, Efthimios

    2014-05-01

    High concentrations of heavy metals, particularly of the toxic hexavalent chromium, are recorded in surface and ground waters in many areas, and constitute one of the most severe environmental problems nowadays. The natural genesis of chromium is associated with the geological environment (peridotites and serpentintites). Chromium is structured in many minerals, mainly in spinel (e.g. chromite), in silicate minerals such as phyllosilicate serpentine minerals, chlorite, talc and chain-silicate minerals of pyroxene and amphibole group. Chromium is found in two forms in soils, waters and rocks, the hexavalent and the trivalent one. The relation between Cr(III) and Cr(VI) strongly depends on pH and oxidative properties of the area; however, in most cases, Cr(III) is the dominating variant. The natural oxidation of trivalent to hexavalent chromium can be achieved by manganese oxides, H2O2, O2 gas and oxy-hydroxides of trivalent iron. Anthropogenic factors may also cause the process of chromium's oxidation. In the Psachna basin, Central Euboea, Greece, high concentrations of hexavalent chromium were recently measured in spring- and drill- waters. In this work, we study the effect of the geological environment and of the anthropogenic activities on the water quality with emphasis on chromium. A detailed geochemical, petrological and mineralogical study of rocks and soils was carried out by means of optical microscopy, XRF, XRD and SEM/EDS. Ground and surface water samples were physically characterized and hydrochemically studied by means of ICP and AAF. Combined result evaluation indicates a natural source for the trivalent chromium in waters, attributed to the alteration of Cr-bearing minerals of the ultramafic rocks. However the oxidation of trivalent to hexavalent chromium results from anthropogenic activities, mainly from intensive agricultural activities and the extensive use of fertilizers and pesticides causing nitrate pollution in groundwater. It has been shown

  6. Combined Whole-Rock to Nano-Scale Investigations Reveal Contrasting Response of Pt-Os and Re-Os Isotope Systematics During Magmatic and Post-Magmatic Processes

    Science.gov (United States)

    Coggon, J. A.; Luguet, A.; Lorand, J. P.; Fonseca, R.; Wainwright, A.; Appel, P.; Hoffmann, J. E.; Nowell, G. M.

    2015-12-01

    Advances in single-grain and micro- and nano-analytical techniques in recent years have been particularly important to the study of highly siderophile elements (HSE) and have contributed significantly to our knowledge and understanding of their host phases and behaviour. Furthermore, whole-rock- to nano-scale studies provide new perspectives for investigation of HSE isotope systematics. Recent multi-scale 187Re-187Os and 190Pt-186Os studies facilitate comparison, to a previously unattainable degree, of the differing responses of these two decay systems to magmatic and post-magmatic processes. It is well established that mafic-ultramafic melts are sensitive to disturbance of their Re-Os isotope systematics by crustal assimilation, due to the incompatibility and resulting enrichment of Re in crustal lithologies. In contrast the very long half-life and extremely low atomic abundance of 190Pt, combined with relatively low Pt concentrations in crustal rocks, generally render the Pt-Os isotope system insensitive to modification during assimilation. However, using new single chromite grain data (Coggon et al., 2015) from the >3.811 Ga Ujaragssuit nunât layered ultramafic body, Greenland, we show that it is possible to distinguish two distinct episodes of 187Os/188Os modification; Country rock contamination of the parent melt was followed by later metamorphic disturbance of the isotope system. The Pt-Os data (Coggon et al., 2013) from the same samples show no evidence of crustal assimilation, but preserve signatures of mantle melting at ~4.1 Ga as well as disturbance during metamorphism. Macro- to micro-petrographic study clearly demonstrates that Pt, Re and Os are hosted by different mineral phases, of different origins, in these samples. This, together with the physical parameters of the decay systems reported above, leads to the dissimilar behaviour and response of the 187Re-187Os and 190Pt-186Os isotope systems during both magmatic and post-magmatic processes and

  7. Model parameter estimations from residual gravity anomalies due to simple-shaped sources using Differential Evolution Algorithm

    Science.gov (United States)

    Ekinci, Yunus Levent; Balkaya, Çağlayan; Göktürkler, Gökhan; Turan, Seçil

    2016-06-01

    An efficient approach to estimate model parameters from residual gravity data based on differential evolution (DE), a stochastic vector-based metaheuristic algorithm, has been presented. We have showed the applicability and effectiveness of this algorithm on both synthetic and field anomalies. According to our knowledge, this is a first attempt of applying DE for the parameter estimations of residual gravity anomalies due to isolated causative sources embedded in the subsurface. The model parameters dealt with here are the amplitude coefficient (A), the depth and exact origin of causative source (zo and xo, respectively) and the shape factors (q and ƞ). The error energy maps generated for some parameter pairs have successfully revealed the nature of the parameter estimation problem under consideration. Noise-free and noisy synthetic single gravity anomalies have been evaluated with success via DE/best/1/bin, which is a widely used strategy in DE. Additionally some complicated gravity anomalies caused by multiple source bodies have been considered, and the results obtained have showed the efficiency of the algorithm. Then using the strategy applied in synthetic examples some field anomalies observed for various mineral explorations such as a chromite deposit (Camaguey district, Cuba), a manganese deposit (Nagpur, India) and a base metal sulphide deposit (Quebec, Canada) have been considered to estimate the model parameters of the ore bodies. Applications have exhibited that the obtained results such as the depths and shapes of the ore bodies are quite consistent with those published in the literature. Uncertainty in the solutions obtained from DE algorithm has been also investigated by Metropolis-Hastings (M-H) sampling algorithm based on simulated annealing without cooling schedule. Based on the resulting histogram reconstructions of both synthetic and field data examples the algorithm has provided reliable parameter estimations being within the sampling limits of

  8. Reconnaissance geologic map of the Dubakella Mountain 15 quadrangle, Trinity, Shasta, and Tehama Counties, California

    Science.gov (United States)

    Irwin, William P.; Yule, J. Douglas; Court, Bradford L.; Snoke, Arthur W.; Stern, Laura A.; Copeland, William B.

    2011-01-01

    Cretaceous (about 120 Ma) metamorphic age. Remnants of the Great Valley sequence of dominantly Cretaceous marine sedimentary strata, which once covered much of the southern fringe of the Klamath Mountains, are present at three places in the Dubakella Mountain quadrangle. Mineral production in the quadrangle has included small amounts of gold, chromite, and manganese. This map of the Dubakella Mountain 15' quadrangle is a digital rendition of U.S. Geological Survey Miscellaneous Field Studies Map MF-1808, with various improvements and additions.

  9. Regional tectonics, geology, magma chamber processes and mineralisation of the Jinchuan nickel-copper-PGE deposit, Gansu Province, China:A review

    Institute of Scientific and Technical Information of China (English)

    T.M. Mike Porter

    2016-01-01

    The Jinchuan Ni-Cu-PGE deposit (>500 Mt@1.2%Ni, 0.7%Cu, w0.4 g/t PGE), one of the largest magmatic sulphide deposits in the world, is located within the westernmost terrane of the North China Craton. It is hosted within the 6.5 km long, Neoproterozoic (w0.83 Ga) Jinchuan ultramafic intrusion, emplaced as a sill-like body into a Palaeoproterozoic suite of gneisses, migmatites, marbles and amphibolites, below an active intracratonic rift. The parental magma was high-Mg basalt, generated through melting of sub-crustal lithospheric mantle by a mantle plume during the initiation of Rodinia supercontinent breakup. The lower Palaeozoic collision of the exotic Qilian Block with the breakup-related southern margin of the craton accreted a subduction complex, and emplaced voluminous granitic intrusions and foreland basin sequences within the craton, to as far north as Jinchuan. During the Cainozoic, allochthonous lower Palaeozoic rocks were thrust up to 300 km to the northeast over cratonic basement, to within 25 km of the Jinchuan deposit. The Jinchuan ultramafic intrusion was injected into three interconnected sub-chambers, each containing a separate orebody. It essentially comprises an olivine-orthopyroxene-chromite cumulate, with interstitial orthopyroxene, clinopyroxene, plagioclase and phlogopite, and is predominantly composed of lherzolite (w80%), with an outer rim of olivine pyroxenite and cores of mineralised dunite. Mineralisation occurs as disseminated and net-textured sulphides, predominantly within the dunite, with lesser, PGE rich lenses, late massive sulphide accumulations, small copper rich pods and limited mineralised diopside skarn in wall rock marbles. The principal ore minerals are pyrrhotite (the dominant sulphide), pentlandite, chalcopyrite, cubanite, mackinawite and pyrite, with a variety of platinum group minerals and minor gold. The deposit underwent significant post-magmatic tremolite-actinolite, chlorite, serpentine and magnetite alteration. The

  10. Coexistence of compositionally heterogeneous chromitites in the Antalya-Isparta ophiolitic suite, SW Turkey: A record of sequential magmatic processes in the sub-arc lithospheric mantle

    Science.gov (United States)

    Uysal, Ibrahim; Akmaz, Recep Melih; Saka, Samet; Kapsiotis, Argyrios

    2016-04-01

    The Antalya-Isparta region in southwestern Turkey is well known for its large ophiolitic peridotite exposures, which host various chromite orebodies. These are small-sized, massive to disseminated in texture chromitites occurring in the form of lenses or veinlets, and commonly surrounded by dunite envelopes of variable thickness. Chromitite seams from the Antalya mantle suite are both high- and intermediate-Cr varieties (Cr# = 0.56-0.83), whereas chromitites in the Isparta mantle sequence are exclusively Cr-rich (Cr# = 0.75-0.85). In situ minor and trace element abundances obtained by LA-ICP-MS analyses of unaltered Cr-spinel from the Cr-rich chromitites are comparable to those reported in Cr-spinel of chromitites from typical fore-arc peridotite complexes. However, minor and trace element concentrations in Cr-spinel from intermediate chromitites are dissimilar to those acquired from Cr-spinels of chromitites from well-known back-arc basin-derived ultramafic massifs. Calculation of parental magma compositions indicates that both types of chromitites share a common parentage with progressively fractionating arc-related melts. The studied chromitites are characterized by a systematic enrichment in IPGE [Os, Ir, and Ru (41-317 ppb)] with respect to PPGE [Rh, Pt, and Pd (3-49 ppb)], resulting in negatively-sloping chondrite-normalized PGE patterns that are less fractionated in intermediate chromitites. Their noble mineral assemblage is vastly dominated by tiny (≥ 10 μm) euhedral laurite crystals, followed by subsidiary irarsite and trivial amounts of Os-Ir alloy grains. PGM grains are not encountered in the intermediate chromitites, potentially due to crystallization resulting from PGE-poor melt. Laurite is Os-poor and exhibits a narrow range of Os-for-Ru substitution [Ru/(Ru + Os) = 0.75-0.99]. However, the concomitance of laurite and millerite in the Cr-rich chromitites of the mutual Antalya-Isparta mantle suite is in favour of their precipitation from an Os

  11. Controls on Highly Siderophile Element Concentrations in Martian Basalt: Sulfide Saturation and Under-Saturation

    Science.gov (United States)

    Righter, Kevin

    2009-01-01

    Highly siderophile elements (HSE; Re, Au and the platinum group elements) in shergottites exhibit a wide range from very high, similar to the terrestrial mantle, to very low, similar to sulfide saturated mid ocean ridge basalt (e.g., [1]). This large range has been difficult to explain without good constraints on sulfide saturation or under-saturation [2]. A new model for prediction of sulfide saturation places new constraints on this problem [3]. Shergottite data: For primitive shergottites, pressure and temperature estimates are between 1.2-1.5 GPa, and 1350-1470 C [4]. The range of oxygen fugacities is from FMQ-2 to IW, where the amount of Fe2O3 is low and thus does not have a significant effect on the S saturation values. Finally, the bulk compositions of shergottites have been reported in many recent studies (e.g., [5]). All of this information will be used to test whether shergottites are sulfide saturated [3]. Modeling values and results: The database for HSE partition coefficients has been growing with many new data for silicates and oxides [6-8] to complement a large sulfide database [9- 11]. Combining these data with simple batch melting models allows HSE contents of mantle melts to be estimated for sulfide-bearing vs. sulfide-free mantle. Combining such models with fractional crystallization modeling (e.g., [12]) allows HSE contents of more evolved liquids to be modeled. Most primitive shergottites have high HSE contents (and low S contents) that can be explained by sulfide under-saturated melting of the mantle. An exception is Dhofar 019 which has high S contents and very low HSE contents suggesting sulfide saturation. Most evolved basaltic shergottites have lower S contents than saturation, and intermediate HSE contents that can be explained by olivine, pyroxene, and chromite fractionation. An exception is EET A79001 lithology B, which has very low HSE contents and S contents higher than sulfide saturation values . evidence for sulfide saturation

  12. Simultaneous determination of 5 elements in chrome iron ore samples by inductively coupled plasma-opti-cal emission spectrometry%电感耦合等离子体发射光谱法测定铬铁矿中5种主量元素

    Institute of Scientific and Technical Information of China (English)

    龚迎莉; 王宇; 张宁; 谢莲英

    2014-01-01

    A method for the determination of 5 elements ,including Cr ,Si ,Fe ,Mg ,Al in chrome iron ore by inductively coupled plasma-optical emission spectrometry (ICP-OES) was applied.Samples were decom-posed with lithium metaborate under 1000℃ and dissolved with ultrasonic extraction. The detection limits of the five elements were 0.003 -0.020 μg/mL. Matrix matching was used to reduce matrix effect. Na-tional standard reference materials including GBW07820 ,GBW 07202 ,Si ,Fe ,Mg ,Al were in agreement with the slandard values with recovery of 101.6% -105.3% . The method is suitable for the chromite SiO2 ,T Fe ,M gO ,Al2 O3 4constant componeng in quantitative analysis.%借助偏硼酸锂于1000℃熔融消解铬铁矿,超声波振荡提取,电感耦合等离子体发射光谱法测定铬铁矿中主量组分铬、硅、铁、镁、铝。5个元素的检出限为0.003~0.020μg/m L。采用基体匹配减少基体效应干扰,通过对国家一级铬铁矿标准物质GBW07820、GBW07202等测定验证,硅、铁、镁、铝测定值和标准值吻合,方法精密度(RSD ,n=10)为:0.78~1.67%,加标回收率为101.6~105.3%。适于铬铁矿中SiO2、TFe、MgO、Al2 O3等4种常量组分的定量分析。过氧化钠熔融消解样品,电感耦合等离子体发射光谱法能够对铬进行定量分析。

  13. Cooperative Jahn–Teller effect and the role of strain in the tetragonal-to-cubic phase transition in MgxCu1 − xCr2O4

    Directory of Open Access Journals (Sweden)

    Serena C. Tarantino

    2016-09-01

    Full Text Available Temperature and composition dependences of the I41/amd → Fd\\bar 3m phase transition in the MgxCu1 − xCr2O4 spinel solid solution, due to the melting of the cooperative Jahn–Teller distortion, have been studied by means of single-crystal X-ray diffraction. Crystals with x = 0, 0.10, 0.18, 0.43, 0.46, 0.53, 1 were grown by flux decomposition methods. All crystals have been refined in the tetragonal I41/amd space group except for the Mg end-member, which has cubic symmetry. In MgxCu1 − xCr2O4 the progressive substitution of the Jahn–Teller, d9 Cu2+ cation with spherical and closed-shell Mg2+ has a substantial effect on the crystal structure, such that there is a gradual reduction of the splitting of a and c unit-cell parameters and flattening of the tetrahedra. Single-crystal diffraction data collected in situ up to T = 1173 K show that the tetragonal-to-cubic transition temperature decreases with increasing Mg content. The strength of the Cu—Cu interaction is, in effect, modulated by varying the Cu/Mg ratio. Structure refinements of diffraction data collected at different temperatures reveal that heating results in a gradual reduction in the tetrahedron compression, which remains significant until near the transition temperature, however, at which point the distortion of the tetrahedra rapidly vanishes. The spontaneous strain arising in the tetragonal phase is large, amounting to 10% shear strain, et, and ∼ 1% volume strain, Vs, in the copper chromite end-member at room temperature. Observed strain relationships are consistent with pseudoproper ferroelastic behaviour (e_{\\rm t}^2 ∝ Vs ∝ q_{\\rm JT}^2, where qJT is the order parameter. The I41/amd → Fd\\bar 3m phase transition is first order in character for Cu-rich samples and then evolves towards second-order character. Although a third order term is permitted by symmetry in the Landau expansion, this behaviour appears to be more accurately represented by a 246

  14. Implications of spinel compositions for the petrotectonic history of abyssal peridotite from Southwest Indian Ridge (SWIR)

    Science.gov (United States)

    Chen, T.; Jin, Z.; Wang, Y.; Tao, C.

    2012-12-01

    Abyssal peridotites generate at mid-ocean ridges. Lherzolite and harzburgite are the main rock types of peridotites in the uppermost mantle. The lherzolite subtype, less depleted and less common in ophiolites, characterizes mantle diapirs and slow-spreading ridges. Along the Earth's mid-ocean ridges, abyssal peridotites undergo hydration reactions to become serpentinite minerals, especially in slow to ultraslow spreading mid-ocean ridges. Spinel is common in small quantities in peridotites, and its compositions have often been used as petrogenetic indicators [1]. The Southwest Indian Ridge (SWIR) is one of the two ultraslow spreading ridges in the world. The studied serpentinized peridotite sample was collected by the 21st Voyage of the Chinese oceanic research ship Dayang Yihao (aka Ocean No. 1) from a hydrothermal field (63.5°E, 28.0°S, and 3660 m deep) in SWIR. The studied spinels in serpentinized lherzolite have four zones with different compositions: relic, unaltered core is magmatic Al-spinels; micro- to nano- sized ferrichromite zoned particles; narrow and discontinuous magnetite rim; and chlorite aureoles. The values Cr# of the primary Al-spinels indicate the range of melting for abyssal peridotites from SWIR extends from ~4% to ~7% [2]. The alteration rims of ferrichromite have a chemical composition characterized by Fe enrichment and Cr# increase indicating chromite altered under greenschist-amphibolite facies. Magnetites formed in syn- and post- serpentinization. Chlorite (clinochlore) formed at the boundary and crack of spinel indicating it had undergone with low-temperature MgO- and SiO2-rich hydrothermal fluids [3]. It suggests that serpentinized lherzolite from SWIR had undergone poly-stage hydration reactions with a wide range of temperature. Acknowledgments: EMPA experiment was carried out by Xihao Zhu and Shu Zheng in The Second Institute of Oceanography and China University of Geosciences, respectively. The work was supported by NSFC

  15. Optimizing the application of magnetic nanoparticles in Cr(VI) removal

    Science.gov (United States)

    Simeonidis, Konstantinos; Kaprara, Efthymia; Mitrakas, Manassis; Tziomaki, Magdalini; Angelakeris, Mavroidis; Vourlias, Georgios; Andritsos, Nikolaos

    2013-04-01

    The presence of heavy metals in aqueous systems is an intense health and environmental problem as implied by their harmful effects on human and other life forms. Among them, chromium is considered as an acutely hazardous compound contaminating the surface water from industrial wastes or entering the groundwater, the major source of drinking water, by leaching of chromite rocks. Chromium occurs in two stable oxidation states, Cr(III) and Cr(VI), with the hexavalent form being much more soluble and mobile in water having the ability to enter easily into living tissues or cells and thus become more toxic. Despite the established risks from Cr(VI)-containing water consumption and the increasing number of incidents, the E.U. tolerance limit for total chromium in potable water still stands at 50 μg/L. However, in the last years a worldwide debate concerning the establishment of a separate and very strict limit for the hexavalent form takes place. In practice, Cr(VI) is usually removed from water by various methods such as chemical coagulation/filtration, ion exchange, reverse osmosis and adsorption. Adsorption is considered as the simplest method which may become very effective if the process is facilitated by the incorporation of a Cr(VI) to Cr(III) reduction stage. This work studies the potential of using magnetic nanoparticles as adsorbing agents for Cr(VI) removal at the concentration levels met in contaminated drinking water. A variety of nanoparticles consisting of ferrites MFe2O4 (M=Fe, Co, Ni, Cu, Mn, Mg, Zn) were prepared by precipitating the corresponding bivalent or trivalent sulfate salts under controlled acidity and temperature. Electron microscopy and X-ray diffraction techniques were used to verify their crystal structure and determine the morphological characteristics. The mean particle size of the samples was found in the range 10-50 nm. Batch Cr(VI) removal tests were performed in aqueous nanoparticles dispersions showing the efficiency of ferrite

  16. Materials for Advanced Ultrasupercritical Steam Turbines Task 4: Cast Superalloy Development

    Energy Technology Data Exchange (ETDEWEB)

    Thangirala, Mani

    2015-09-30

    demonstrated the importance of proper heat treat cycles for Homogenization, and Solutionizing parameters selection and implementation. 3) Step blocks casting of Nimonic 263: Carried out casting solidification simulation analysis, NDT inspection methods evaluation, detailed test matrix for Chemical, Tensile, LCF, stress rupture, CVN impact, hardness and J1C Fracture toughness section sensitivity data and were reported. 4) Centrifugal Casting of Haynes 282, weighing 1400 lbs. with hybrid mold (half Graphite and half Chromite sand) mold assembly was cast using compressor casing production tooling. This test provided Mold cooling rates influence on centrifugally cast microstructure and mechanical properties. Graphite mold section out performs sand mold across all temperatures for 0.2% YS; %Elongation, %RA, UTS at 1400°F. Both Stress-LMP and conditional Fracture toughness plots data were in the scatter band of the wrought alloy. 5) Fundamental Studies on Cooling rates and SDAS test program. Evaluated the influence of 6 mold materials Silica, Chromite, Alumina, Silica with Indirect Chills, Zircon and Graphite on casting solidification cooling rates. Actual Casting cooling rates through Liquidus to Solidus phase transition were measured with 3 different locations based thermocouples placed in each mold. Compared with solidification simulation cooling rates and measurement of SDAS, microstructure features were reported. The test results provided engineered casting potential methods, applicable for heavy section Haynes 282 castings for optimal properties, with foundry process methods and tools. 6) Large casting of Haynes 282 Drawings and Engineering FEM models and supplemental requirements with applicable specifications were provided to suppliers for the steam turbine proto type feature valve casing casting. Molding, melting and casting pouring completed per approved Manufacturing Process Plan during 2014 Q4. The partial valve casing was successfully cast after casting methods were

  17. Marché des catalyseurs d'hydrogénation des corps gras Market of Hydrogenation Catalysts for Fats and Derivatives

    Directory of Open Access Journals (Sweden)

    Barraque M.

    2006-11-01

    Full Text Available L'institut Français du Pétrole (IFP ayant acquis une grande expérience dans le domaine des catalyseurs, notamment d'hydrogénation, le Département Evaluation a effectué à diverses reprises des études qui en évaluent les marchés potentiels. L'analyse qui suit a été réalisée en vue de déterminer les débouchés possibles des catalyseurs utilisés dans l'hydrogénation des corps gras; elle couvre l'industrie alimentaire, l'hydrogénation des acides gras d'origine animale ou végétale, la production d'alcools gras et d'amines grasses. Ce marché dépasse 60 millions de dollars/an et correspond à près de 11 000 t/an de catalyseurs utilisés. Ces valeurs tiennent compte des consommations captives de catalyseurs produits par les compagnies utilisatrices. Ce chiffre d'affaires est du même ordre que celui des catalyseurs d'hydrogénation utilisés dans la synthèse des grands intermédiaires pétrochimiques. Plus de 64 % des applications concernent l'industrie alimentaire : production de margarine et shortening, hydrogénation d'huiles de salade et de friture aux États-Unis. Alors que la consommation de catalyseurs utilisés en lipochimie est très fortement concentrée dans les principales régions industrialisées : États-Unis, Europe occidentale et Japon, celle de I'lindustrie alimentaire est beaucoup plus dispersée : les 3 régions précitées représentent moins de 64 % de la consommation mondiale. Les débouchés estimés représentent des chiffres d'affaires annuels de 41×10·6 dollars pour l'industrie alimentaire, 8,3×10·6 dollars pour la production d'acide gras, 11×10·6 dollars pour la production d'alcools gras et 1,3×10·6 dollars pour la production d'amines grasses. Ces hydrogénations sont effectuées en présence de nickel sur support (industrie alimentaire, production d'acides gras et d'amines secondaires et tertiaires, en présence de nickel de Raney (production d'amines primaires ou de chromite de cuivre

  18. Relaciones entre la zonalidad petrológica y metalogénica de los macizos lerzolíticos de las cadenas alpinas del Mediterráneo Occidental (Cordillera Bético-Rifeña y Kabylias

    Directory of Open Access Journals (Sweden)

    Torres-Ruiz, J.

    1988-12-01

    Full Text Available Gamet-lherzolite facies, Ariegite and Seiland subfacies of the spinel-lherzolite facies and plagioclase-lherzolite facies have been identified in the Serranía de Ronda, Beni Bousera and Collo lherzolitic massifs. These petrological facies occur in a zonal arrangement: gamet lherzolite are in contact with the overlaying metapelitic sequence and spinel then plagioclase lherzolite occur inwards, representing the innermost zones in the former mantle body. The various occurrences of mineralizations can be classified in two main groups: one of them is essentialIy made up of chromite and Ni arsenides with pyroxene and/or cordierite as gangue minerals; the other consists Qf Fe-Ni-Cu sulfides and graphite, with pyroxene, plagioclase and phlogopite as gangue minerals. In both groups, the ores with the more refractory composition were the first to crystallize in the hotter core of the diapir while those other with a more differentiated composition were formed later within the external zones. The close correlation between petrological and metallogenical roning supports a magmatic origin of the mineralizations related to the petrologic evolution of the mantle bodies. The mineralizing liquids• originated from magmas generated by partial melting of the peridotites. The former migrated outwards, from the internal part of the bodies, during which marked interaction with the enclosing rocks and complex fractionation processes took place under moderate to low pressure conditions.En los macizos lerzolíticos de la Serranía de Ronda, de Beni Bousera y de Collo se han identificado facies de lerzolitas con granate, facies de lerzolitas con espinela (subfacies Ariegita y Seiland y facies de lerzolitas con plagioclasa. Estas facies petrológicas se distribuyen de forma que las lerzolitas con granate se sitúan en contacto con la unidad metapelítica suprayacente, mientras que las lerzolitas con espinela y con plagioclasa lo hacen en posiciones progresivamente m

  19. Mineral replacements during carbonation of peridotite: implications for carbon dioxide sequestration in ultramafic rocks

    Science.gov (United States)

    Beinlich, Andreas; Hövelmann, Jörn; Plümper, Oliver; Austrheim, Hâkon

    2010-05-01

    In contact with CO2, ultramafic rocks are known to be reactive and eventually form ophicarbonates and listwaenites. Here we present observations from serpentinized peridotite clasts from the Solund Devonian Basin, SW Norway. These clasts show evidence for a stepwise reaction history starting with initial serpentinization and resulting in the formation of carbonates (mainly calcite and dolomite) and quartz. Thus, they represent a natural analogue for CO2 sequestration in ultramafic rocks, which was proposed by the Inter Governmental Panel on Climate Change (IPCC 2005) as one possibility for long-term CO2 storage. In several layers of the basin, the carbonatized ultramafic clasts are important constituents and account for up to 20 vol. % of the basin infill. The investigated clasts show a concentric build-up with green to grey colored cores surrounded by mm to 10 cm thick zones of red to black shades. Textural evidence indicates the following alteration sequence: An early stage is represented by serpentinization of peridotite resulting in a typical mesh texture, with veins of serpentine and Ni-rich hematite surrounding compartments of relict olivine (Fo90). Subsequently, relict olivine breaks down to form an alteration product which is significantly depleted in Mg relative to the precursor olivine. In the more advanced ophicarbonate stage, compartments are filled with calcite, quartz, and talc. In the most advanced stage, quartz, calcite, and hematite dominate and occur together with minor amounts of chromite, talc, and chlorite. The textural evolution is accompanied by a decrease in whole-rock MgO from 40 to 2 wt. % and a CaO increase from 1 to 35 wt. %. All clasts are characterized by high Cr and Ni (1000-4000 and 500-3000 ppm, respectively) revealing their ultramafic origin. Transmission electron microscopy (TEM) observations indicate that the alteration product after olivine is composed of an amorphous material, which is compositionally close to serpentine

  20. Geology of the Plumtree area, Spruce Pine district, North Carolina

    Science.gov (United States)

    Brobst, Donald Albert

    1953-01-01

    dikes of post-pegmatite age (Triassic?). The alaskite and pegmatite have similar bulk compositions, notably low in iron (0.3 percent). The major constituents in order of decreasing abundance are plagioclase, perthitic microcline, quartz, and muncovite. All of these minerals, as well as clay deposits derived from the weathering of alaskite under old terraces, have economic value. The zoned pegmatites contain fewer zones which are less complex mineralogically than those in the pegmatites of many other areas. These essentially unmetamorphosed bodies were intruded approximately at the peak of the regional metamorphism. Their emplacement was controlled by local structure and rock type. The source of this igneous material may have been the mobilized portions of the Cranberry gneiss which underlies the area. The dunite bodies were intruded early in the metamorphic cycle. The bodies are commonly zoned: from the wall rock inwards (1) talc-antrophyllite-serpentine fringe, (3) serpentinized dunite, (3) granular olivine core. Dunite, chromite, vermiculite, and anthophyllite are the major economic commodities. Extensive hydrothermal alteration of dunite bodies produced soapstone. The area is the northeast end of a southwest plunging synclinorium about 20 miles wide with the steeper limb on the northwest side. There are three structural zones: zone I on the northwest is characterized by the northeast-trending isoclinal folds with steep southeast dips; zone II on the southwest includes an area of rocks with low and variable dip; zone III is the complex central core. In the extreme northeast zones I and II have an indistinct boundary where they coalesce along the rim of the synclinorium. Six stratigraphic units are exposed totaling approximately 10,500 feet of metamorphic rocks. Small scale structural features include a foliation, and a lineation in the planes of the foliation. Minor folding reflects the trends of the major structures. There are randomly orient

  1. Electrical characteristics of the hydroxyapatite for biomedical applications; Caracteristicas electricas de la hidroxiapatita para aplicaciones biomedicas

    Energy Technology Data Exchange (ETDEWEB)

    Lopez Buisan N, M.G.; Mendez G, M.M. [Laboratorio de Corrosion, ESFM-IPN, 07738 Mexico D.F. (Mexico)

    2006-07-01

    The electric characteristics of hydroxyapatite films were studied (HAP) deposited on metallic substrates oxidized naturally. The substrates was made of steel 316L and of titanium. These materials are used in reconstructive surgery for prosthesis and osseous implants. The studies were carried out with the techniques of potentiostatic polarization and faraday impedance. The potentiostatic polarization reveals that the very well-known piezoelectricity of the HAp subsists after the coating processes (it captures thermal and spray-pyrolysis). Its also revealed a semiconductor behavior of the HAp that until now had not been reported. This characteristic is important, by its relationship with the stability of the HAp coating in front of corrosion processes in the alive tissues. The results of the impedance tests were mathematically analyzed starting from the Nyquist diagrams, of Bode and of power. The physical interpretation is presented under the form of equivalent circuits (CE). In the case of the HAp on a steel 316L substrate, the CE is a Rancles-Voigt module that corresponds to the behavior of a dielectric with flights. In the case of the titanium substrate an element of constant phase appears to high frequencies (CPE), in series with the Rancles-Voigt module. The CPE reveals the presence of a rectifier of the metal/SC-n type that only it could be located in the interface among the titanium and its natural oxide (TiO{sub 2}). The absence of the CPE in the case of the steel 316L substrate indicates that the natural oxide (Cr{sub 2}O{sub 3}) it doesn't form with the steel a Schottky diode, possibly because the chromite is as a SC-n degenerate. On the interface Ti/TiO{sub 2} exists results qualitatively identical by other researchers that have worked with the same impedance technique, but applied by humid via (EIS). The CE that have proposed are based on the anodic processes of accretion/dissolution of the film at low pH. This proposal is questioned by our results

  2. Late Neoarchean arc magmatism and crustal growth associated with microblock amalgamation in the North China Craton: Evidence from the Fuping Complex

    Science.gov (United States)

    Tang, Li; Santosh, M.; Tsunogae, Toshiaki; Teng, Xue-Ming

    2016-04-01

    The Fuping, Wutai, and Hengshan Complexes in the North China Craton preserve imprints of widespread late Neoarchean magmatism. Here, we report results from systematic petrology, mineral chemistry, whole-rock major, trace and platinum-group element geochemistry, zircon U-Pb geochronology and Hf-O isotopes from the Yangmuqiao mafic-ultramafic intrusion and coeval tonalite-trondhjemite-granodiorite (TTG) gneiss from the Fuping Complex. The mafic-ultramafic intrusion is composed of pyroxene hornblendites, hornblendites, and minor harzburgites. The salient geochemical features of the mafic-ultramafic intrusion and the Fuping TTG gneiss display subduction-related island arc signature, such as fractionated REE patterns with elevated LREE, enrichment of LILE (K, Rb, and Ba) and LREE (La and Ce), and depletion of HFSE (Nb, Ta, Zr, and Hf) and HREE. The chemistry of the clinopyroxene and chromite in the pyroxene hornblendites shows affinity with Alaskan-type mafic-ultramafic intrusions. Zircons from the pyroxene hornblendite yield weighted mean 207Pb/206Pb age of 2514 ± 15 Ma, and those in the Fuping TTG gneiss show mean age of 2513 ± 13 Ma. Zircon Hf and O isotopic compositions are used as magma source and crustal evolution indicators. Zircon grains in the pyroxene hornblendite display positive εHf(t) values (2.6-6.7), Neoarchean TDM (2570-2723 Ma), and their δ18O values vary from 3.8‰ to 7.0‰ (average 6.2‰). Zircons in the TTG gneiss show εHf(t) values in the range of - 1.8 to 4.9, TDM of 2637-2888 Ma, and δ18O values of 4.1‰-6.7‰ (average of 6.1‰). These results suggest that the parental magma of the late Neoarchean magmatism in the Fuping area was dominantly extracted from the depleted mantle and contaminated to different degrees by crustal components. The pyroxene hornblendites have obviously higher IPGE contents (ΣIPGE = 1.69-2.39 ppb) and lower Pd/Ir ratios (5.97-6.28) than those in the hornblendites (ΣIPGE = 0.56-0.72 ppb, Pd/Ir = 6

  3. Regularities of spatial association of major endogenous uranium deposits and kimberlitic dykes in the uranium ore regions of the Ukrainian Shield

    Science.gov (United States)

    Kalashnyk, Anna

    2015-04-01

    During exploration works we discovered the spatial association and proximity time formation of kimberlite dykes (ages are 1,815 and 1,900 Ga for phlogopite) and major industrial uranium deposits in carbonate-sodium metasomatites (age of the main uranium ore of an albititic formation is 1,85-1,70 Ga according to U-Pb method) in Kirovogradsky, Krivorozhsky and Alekseevsko-Lysogorskiy uranium ore regions of the Ukrainian Shield (UkrSh) [1]. In kimberlites of Kirovogradsky ore region uranium content reaches 18-20 g/t. Carbon dioxide is a major component in the formation of hydrothermal uranium deposits and the formation of the sodium in the process of generating the spectrum of alkaline ultrabasic magmas in the range from picritic to kimberlite and this is the connection between these disparate geochemical processes. For industrial uranium deposits in carbonate-sodium metasomatitics of the Kirovogradsky and Krivorozhsky uranium ore regions are characteristic of uranyl carbonate introduction of uranium, which causes correlation between CO2 content and U in range of "poor - ordinary - rich" uranium ore. In productive areas of uranium-ore fields of the Kirovogradsky ore region for phlogopite-carbonate veinlets of uranium ore albitites deep δ13C values (from -7.9 to -6.9o/oo) are characteristic. Isotope-geochemical investigation of albitites from Novokonstantynovskoe, Dokuchaevskoe, Partyzanskoe uranium deposits allowed obtaining direct evidence of the involvement of mantle material during formation of uranium albitites in Kirovogradsky ore region [2]. Petrological characteristics of kimberlites from uranium ore regions of the UkrSh (presence of nodules of dunite and harzburgite garnet in kimberlites, diamonds of peridotite paragenesis, chemical composition of indicator minerals of kimberlite, in particular Gruzskoy areas pyropes (Cr2O3 = 6,1-7,1%, MgO = 19,33-20,01%, CaO = 4,14-4,38 %, the content of knorringite component of most grains > 50mol%), chromites (Cr2O3 = 45

  4. [The preparation and characterization of fine dusts carried out in the Clinica del Lavoro di Milano in support of experimental studies].

    Science.gov (United States)

    Occella, E; Maddalon, G; Peruzzo, G F; Foà, V

    1999-01-01

    This paper aims to illustrate the conditions selected at the Clinica del Lavoro of the University of Milan to prepare and analyze a large number of fine dust samples produced over a period of about 50 years, that were initially used for studies within the Clinic performed in its own facilities, and since 1956 were sent to other Italian and overseas laboratories (Luxembourg, UK, Germany, Norway, Sweden, South Korea, USA). The total quantity of material distributed (with maximum size 7-10 microns) was about 2 kg and consisted of the following mineral and artificial compounds: quartz, HF-treated quartz, tridymite, HF-treated tridymite, cristobalite, chromite, anthracite, quartz sand for foundry moulds, sand from the Lybian desert, vitreous silica, pumice, cement, as well small quantities of metallic oxides, organic resins, chrysotile, crocidolite, fibres (vitreous, cotton and polyamidic). About half of the entire quantity of dusts produced consisted of partially HF-treated tridymite. Initially, research on the etiology of silicosis used quartz dust samples, simply sieved or ventilated (consisting of classes finer than 0.04 mm, containing a 15-20% respirable fraction). From 1956 to 1960 the dusts were produced by manual grinding in an agate mortar, below about 10 microns, starting from quartz from Quincinetto (near Ivrea, Province of Turin), containing about 99.5% quartz: particle size and composition were checked using an optical-petrographic technique, with identification of the free and total silica content. Subsequently, the dusts used for biological research were obtained by grinding coarse material with a cast iron pestle and planetary mills, agate and corundum jars. The grinding products were sized by means of centrifugal classification, using the selector developed by N. Zurlo, ensuring control of dust size both optically and by means of wet levigators and hydraulic classifiers (in cooperation with the Institute of Mines of Turin Polytechnic School). After 1990

  5. Origin of the Luobusa diamond-bearing peridotites from the sub-arc mantle

    Science.gov (United States)

    Liu, Chuanzhou; Zhang, Chang; Wu, Fuyuang; Chung, Sunlin

    2016-04-01

    . T. et al. The origin and significance of crustal minerals in ophiolitic chromitites and peridotites. Gond. Res., 486-506 (2015). Yang, J. S. et al. Diamond- and coesite-bearing chromitites from the Luobusa ophiolite, Tibet. Geology 35, 875-878 (2007). Yang, J. S., Robinson, P. T. & Dilek, Y. Diamonds in ophiolites. Elements 10, 127-130 (2014). Zhang, C., Liu, C. Z., Wu, F. Y., Zhang, L. L. & Ji, W. Q. Geochemistry and geochronology of maifc rocks from the Luobusa ophiolite, South Tibet. Lithos, 10.1016/j.lithos.2015.1006.1031 (2015). Zhou, M. F., Robinson, P. T., Malpas, J. & Li, Z. J. Podiform chromitites in the Luobusa Ophiolite (Southern Tibet): Implications for melt-rock interaction and chromite segregation in the upper mantle. J. Petrol. 37, 3-21 (1996).

  6. Characterisation of chrome-spinel grains in ilmenite concentrates using combined EPMA imaging and analysis methods

    International Nuclear Information System (INIS)

    Full text: The production of clean ilmenite concentrates from some mineral sands deposits is hampered by the presence of chromium-containing minerals. The majority of the chromium occurs in separate chrome-spinel grains, so in principal they can be separated from ilmenite grains by physical concentration procedures. However, in practice, the separation is difficult because the physical properties of the chrome-spinel grains, such as specific gravity, conductivity and magnetic susceptibility, are similar to those of ilmenite grains. The situation is further complicated by a) the chrome-spinels have a relatively wide range of compositions due to varying amounts of Mg, Al, Fe and Cr in solid solution, and, b) chemical weathering of both the ilmenite and chrome spinels in the deposits, which involves oxidation and leaching of iron. Both these factors modify the composition ranges of the minerals and influence their subsequent separation characteristics. In mineral sands deposits in which the chrome-spinel population falls into chemically and magnetically 'tight' populations, effective separation treatments have been developed. These usually involve roasting under various conditions to increase the magnetic susceptibility of Fe2O3-FeTiO3 solid solutions, enabling the removal of chromium-bearing spinel from ilmenite concentrates through magnetic separation. In areas such as the Murray Basin region of Eastern Australia however, previous characterisation testwork by CSIRO Minerals have demonstrated that the chrome-spinel populations are highly variable often exhibiting a broad range of composition. Individual chrome-spinel grain types can span the entire compositional spectrum from close to ideal chromite (FeCr2O4) to almost pure MgAl2O4. The effect of various roasting regimes on the magnetic separation characteristics of these complex spinels is largely unknown. In this paper we describe the application of EPMA imaging techniques developed at CSIRO Minerals to quantify

  7. Heavy mineral concentrations in the sandstones of Amij Formation with particular emphasis on the mineral chemistry and petrographic characteristics of monazite, western desert of Iraq

    Science.gov (United States)

    Kettanah, Yawooz A.; Ismail, Sabah A.

    2016-11-01

    The heavy minerals in the clastic unit of the Lower Jurassic Amij Formation exposed in the western desert of Iraq were studied. The uppermost part of the clastic unit contains thin, placer-like black sandstone horizons that are radioactive and abnormally rich in heavy minerals (0.6-56%), dominated by opaque (65%) and transparent (35%) heavy minerals. The minerals, in the order of decreasing abundance are pseudorutile, goethite, zircon, hematite, magnetite, monazite, rutile, leucoxene, tourmaline, ilmenite, chromite, and few others. Electron probe microanalysis (EPMA), microscopic and autoradiographic observations and analysis showed that the monazite is monazite-(Ce) type with an average composition of (Ce0.39Nd0.16La0.19Pr0.04Sm0.02Gd0.02Eu0.01Y0·04Th0·06U0·01Ca0·05Fe0.01)(P0·98Si0.03)O4. Monazite consists predominantly of REE-oxides (57.93%) and P2O5 (29.31%), with minor amounts of ThO2 (6.60%), Y2O3 (1.92%), UO2 (0.76%), CaO (1.14%), SiO2 (0.69%), and FeOt (0.17%). The dominant compositional substitution operating between REE and P were a mixture of the complex cheralite type substitution ([REE]-2 [Th][Ca]) and the coupled huttonite type substitution ([REE]-1 [P]-1 [Th][Si]). The chondrite-normalized REE distribution patterns of monazite show enrichment in LREE with positive Eu- and Pr-anomalies of 1.46 and 9.13, respectively. The median values of (La/Sm)CN and (La/Nd)CN ratios are 4.35 and 1.97, respectively. Zircon which is the dominant transparent mineral is Hf-rich that is composed of 30.61% SiO2, 57.58% ZrO2, 7.03% HfO2, 2.04% Y2O3, 0.56% ThO2, 0.19% UO2, and 0.19% Al2O3 corresponding to a formula (Zr0.909Hf0.065Th0·004U0·001Y0.031)Σ1.011(Si3·966Al0.028)Σ0.999O4. Rutile and tourmaline form 7% and 4% of the heavy minerals. Ilmenite which is one of the predominant heavy minerals forms 2.5% of the opaques because it is pervasively altered to Ti-Fe oxides. In addition of zircon and monazite, the chemical compositions of most of the other heavy

  8. Multi-Spectroscopy Applied to Study on a Late Neolithic Colored Stone from Yuhui Site in Huaihe Basin%新石器晚期祭祀彩石的多种谱学方法研究

    Institute of Scientific and Technical Information of China (English)

    汪海港; 金正耀; 谢治; 范安川; 闫立峰; 朱炳泉; 王吉怀

    2013-01-01

    The unearthing of a large number of red-yellow colored stones in Yuhui Site,Pengbu city,Anhui province of China,which was the only site of Longshan culture appointed by "Origin of the Chinese Civilization Projeet" in the Huaihe River basin,has drawn a widespread attention in archaeology.The present research was undertaken to examine elements,mineral composition and thermal history of one red-yellow color stone in different positions,classified according to specialized colors,by means of synchrotron radiation X-ray fluorescence (SR-XRF),X-ray diffraction (XRD),laser Raman spectroscopy (LRS),electron probe micro-analysis (EPMA) and thermolurninescence (TL).The results show that the main body of the color stone is limonite with a large amount of quartz inclusion.The yellow substances on the surface layer of the color stone were identified as goethite (α-FeOOH),and the red ones as red ochre (α-Fe2O3 +clay+silica).The internal yellow brown substances inside the stone are mainly aphanitic goethite with a number of chromites and manganese dioxide,and also with small quantity of barite and bismuth.And the color stones are without historical firing treatment.These kinds of special polymetallic ores with unique nature and complex geologic history,which were unearthed in the late neolithic site with large numbers,may be closely related to some kind of primitive religious beliefs and special sacrificial practices.%作为“中国古代文明探源工程”在淮河流域确定的唯一一处重要的龙山文化时期遗址,安徽省蚌埠市禹会遗址出土了大量彩石,引起考古学界广泛关注.本文利用同步辐射X射线荧光(SR-XRF)、X射线衍射(XRD)、激光拉曼光谱(LRS)、热释光光谱(TL)等多种光谱分析手段,并结合电子探针(EPMA)分析结果,对禹会遗址出土“红-黄”彩石不同颜色区域的元素、物相组成及经热历史进行了测定.结果表明,该矿石主体为褐铁矿,有大量石英夹杂,表层黄色物

  9. Some kinetics aspects of chlorine-solids reactions

    Directory of Open Access Journals (Sweden)

    Kanari, N.

    2010-02-01

    Full Text Available The present paper describes detailed kinetics investigations on some selected chlorine-solid reactions through thermogravimetric measurements. The solids studied in this article include chemical pure oxides and sulfides as well as their natural bearing materials. The chlorinating agents employed are gaseous mixtures of Cl2+N2 (chlorination, Cl2+O2 (oxychlorination, and Cl2+CO (carbochlorination. Results are presented as effects of various parameters on the reaction rate of these solids with these chlorinating agents. It was observed that the reactivity of these solids towards different chlorinating agents varied widely. Sulfides could be chlorinated at room temperature, while carbochlorination of chromium (III oxide was possible only above 500 °C. The variation of the chlorination rate of these complex materials with respect to gas velocity, composition and temperature enabled us to focus some light on the plausible reaction mechanisms and stoichiometries. The obtained results were used for selective removal of iron from chromite concentrates, extraction of valuable metals from sulfide materials, purification of MgO samples, etc.

    Este trabajo describe detalladas investigaciones cinéticas en algunas reacciones seleccionadas de cloro-sólido a través de medidas termogravimétricas. Los sólidos estudiados en este artículo incluyen óxidos químicos puros y sulfuros, así como sus materiales naturales de soporte. Los agentes de cloración empleados son mezclas de gases de Cl2+N2 (cloración, Cl2+O2 (oxicloración y Cl2+O2 (carbocloración. Los resultados se presentan como efecto de varios parámetros en el porcentaje de reacción de estos sólidos con los agentes de cloración. Se ha observado que la reactividad de estos sólidos a través de diferentes agentes de cloración varía ampliamente. Los sulfuros se pudieron

  10. Petrology, geochemistry, and age of low-Ti mare-basalt meteorite Northeast Africa 003-A: A possible member of the Apollo 15 mare basaltic suite

    Science.gov (United States)

    Haloda, Jakub; Týcová, Patricie; Korotev, Randy L.; Fernandes, Vera A.; Burgess, Ray; Thöni, Martin; Jelenc, Monika; Jakeš, Petr; Gabzdyl, Pavel; Košler, Jan

    2009-06-01

    Northeast Africa 003 (NEA 003) is a lunar meteorite found as a two paired stones (6 and 118 g) in Libya, 2000 and 2001. The main portion (˜75 vol%) of the 118 g meteorite, used for this study, (NEA 003-A) consists of mare-basalt and a smaller adjacent portion (˜25 vol%) is a basaltic breccia (NEA 003-B). NEA 003-A has a coarse-grained magmatic texture consisting mainly of olivine, pyroxene and plagioclase. The late-stage mineral association is composed mainly of elongated plagioclase, ilmenite, troilite, fayalite, Si-K-rich glass, apatite, and a rare SiO 2 phase. Other accessory minerals include ulvöspinel, chromite, and trace Fe-Ni metal. Olivine and pyroxene contain shock-induced fractures, and plagioclase is completely converted into maskelynite. The Fe/Mn values of the whole rock, olivines and pyroxenes, and the bulk-rock oxygen isotopic composition provide evidence for the lunar origin of NEA 003-A meteorite. This is further supported by the presence of Fe-Ni metal and the anhydrous mineral association. NEA 003-A is geochemically and petrographically distinct from previously described mare-basalt meteorites and is not paired with any of them. The petrography and major element composition of NEA 003-A is similar to the composition of low-Ti olivine mare basalts from Apollo 12 and olivine-normative basalts from Apollo 15. The NEA 003-A meteorite shows obvious geochemical similarities in trace elements contents with Apollo 15 olivine-normative basalts and could represent a yet unknown geochemically primitive member of the olivine-normative basalt series. The meteorite is depleted in rare earth elements (REE) and incompatible trace elements indicating a primitive character of the parental magma. The bulk-rock chemical composition demonstrates that the parent melt of NEA 003-A was not contaminated with KREEP components as a result of magma mixing or assimilation processes. Results of crystallization modelling and low minimum cooling rate estimates (˜0.07

  11. In Situ Trace Element Measurements on Roda and the Origin of Diogenites

    Science.gov (United States)

    Mittlefehldt, David W.; Herrin, J. S.

    2011-01-01

    The origin of diogenites remains poorly understood. A recent model interprets many diogenites to have been formed from melts that were derived by remelting initial magma ocean cumulates, and these penultimate parent melts were then contaminated by melts derived from remelting of the basaltic (eucritic) crust to form the ultimate diogenite parent melts [1] (hereafter the remelting model). This is a very complicated petrogenesis that has profound implications for the geological evolution of 4 Vesta if correct. This model was developed based on trace element analyses of bulk rock samples that had been leached in acids to remove phosphates; the compositions of the residues were interpreted to be close to those of cumulus orthopyroxenes plagioclase, chromite and olivine [1]. In situ measurements of phases in diogenites can be used to test this model. We have begun a campaign of laser ablation ICP-MS of orthopyroxene grains in diogenites for this purpose. Here we report our first results on one diogenite, Roda. We have determined a suite of trace lithophile elements on nine, mm-sized pyroxene grains separated from Roda that have previously been studied [2, 3]. A key observation supporting the remelting model is the very low Eu/Eu* of leached residues; values too low to represent orthopyroxene that crystallized from melts with chondritic Sm/Eu and Gd/Eu [1]. (Eu* = Eu interpolated from REE diagrams.) Crustal remelts have low Sm/Eu and Gd/Eu, and orthopyroxenes that crystallized from parent melts contaminated by them would have very low Eu/Eu* [1]. Roda grains have Eu/Eu* of 0.243 to 0.026; the latter a value lower than any measured on bulk diogenite leached residues (0.041) [1]. There is a general negative correlation between Eu/Eu* and some incompatible elements (Zr, Nb, Hf), but not others (LREE). This appears inconsistent with the remelting model as it would suggest an evolving parent melt with La de-creasing as Zr increased and Eu/Eu* decreased. Grain R-15 includes

  12. 大兴安岭诺敏河石榴石橄榄岩捕虏体的发现及其地质意义%Discovery of peridotite xenoliths from the Nuomin river Quaternary volcanic field, the Great Xing'an Range, and its geological significance

    Institute of Scientific and Technical Information of China (English)

    隋建立; 樊祺诚; 徐义刚

    2012-01-01

    在重力梯度带北端的大兴安岭诺敏河第四纪火山岩中发现石榴石相和尖晶石相地幔橄榄岩捕虏体,其矿物组成分别为Ol40~55Opx20~35Cpx0~10Grt5~25和Ol45~65Opx30~40Cpx0~15Sp0~10.两种地幔相橄榄岩均以方辉橄榄岩为主,说明研究区上地幔具有难熔的特点.其高Mg*橄榄石Fo91-92和高Cr*31~47尖晶石特征与南区哈河的地幔橄榄岩特征一致.在橄榄石含量与Fo图解上,敏河橄榄岩包体落在太古代和元古代地幔区域,揭示大兴安岭地区岩石圈地幔可能保留了较多古老的残余地幔.根据石榴石橄榄岩的平衡温压条件(1114~1168℃和2.14 ~2.33GPa),推测来源深度为70 ~ 75km.这些数据暗示研究区具有较高的地温梯度,与中国东部新生代火山岩区的地温梯度相似.%The Nuomin river Quartemary volcanos are located in northern Great Xing' an Range, at the northern part of the North-South Gravity lineament. Mantle xenoliths from these volcanos include abundant Sp-peridotite (Ol40-55Opx20-35Cpx0-10Grt5-25) and subordinate Gt-peridotite (Ol,45-65Opx30-40Cpx0-15Sp0-10). ThelowCpx mode (usually less rhan3% ) in these peridotites reveals that the mantle rocks are mainly harzhurgites. Similar to mantle xenoliths recovered in Hahe area, most of the Nuomin river Sp-harzburgites have high-Mg# olivine (Fo91-92) and high Cr#(31 -47) chromite, indicating a refractory nature of the lithospheric mantle beneath the Great Xing' an Range. The plot of olivine mode again Fo contents in olivine further indicates the preservation of Proterozoic-Late Archeacn mantle in this area. Application of geothermobarometers to the mantle xenoliths suggests that the Gt-peridotites are equilibrated at a pressure of 2. 14 -2. 33GPa (corresponding to 70 ~75km) and a temperature of 1114 ~ l68℃. These data define a relatively high thermal gradient for the upper mantle beneath the Great Xing' an Range, similar to those for many Cenozoic volcanic

  13. Structure and evolution of the mantle column beneath the Nakyn kimberlite field.

    Science.gov (United States)

    Ashchepkov, I.; Stegnitsky, Yu; Minin, V.; Tolstov, A.; Vladykin, N.; Rotman, A.; Palessky, S.; Agashev, A.; Khmelnikova, O.; Skvortsova, M.,

    2012-04-01

    Nakyn kimberlites refer to the main stage of kimberlite magmatism in Yakutia (Agashgev et al., 2004) Upper Devonian (UD) kimberlites. Minerals from the concentrates analyzed by EPMA and LAM ICP from Nyurbinskaya, Botuobinskaya pipes and Maiskaya body and placer were compared to determine mantle structure and compositions. Peridotite garnet population of all pies corresponds the lherzolite field to pyroxenitic 15% Cr2O3 (Pokhilenko, Sobolev, 2004), the subcalsic garnets prevail in (8-11; Cr2O3). Peaks of the TiO2 and Na2O correspond to the same Cr2O3 intervals. (Zinchuk et al, 2003). In chromite trend Cr2O3 ( 65-20% ) lognormal decrease with TiO2 enrichment 3.5% in the beginning. In tuffs containing clinopyroxenes from Nyurbinskaya, Botuobinskaya pipes show decrease of Na, Al Ti and Cr rise with Fe as for Mir pie. The Cp in Nurbinskaya tuffs with Ilm are higher in TiO2 Restricted in TiO2 ilmenite trend show rapid decrease of Na2O, MgO content and V2O5 -FeO rise (Fig. 4). The PTFO2 diagrams determined with new variant of the monomineral thermobarometry (Ashchepkov et al., 2010; 2012) reveal a bit different geotherms for Nyurbinskaya pipe 38 to 43 mv/m2 for garnets and Sp estimates and colder for CPx. The refertillization interval markedby Fe rich Cpx and Ilm is 65-30 kbar. For the Botuobinskaya pipe there are 2 branches 40 and 35 mv/m2 and the heating branch at 65 kbars. Mayskaya is showing the colder geotherm but deviations to the hotter part correspondent to the pyroxenites. The Placer in this area show the wider variations of PT conditions and refertillization interval possibly showing possibility of another source of the disintegration which is much rich in the pyroxenites which amount is highly increase with the depth. The comparisons of the PT conditions show that possibly the Mayskaya and Botuobinskaya pipes represent the earlier stages of the developing of mantle columns while Nyurbinskaya the later one but amount of pyroxenites in Nyurbinskaya is less then

  14. Comportamento de sinterização do LaCrO3 dopado com Sr e Co Sintering behavior of Sr and Co doped LaCrO3

    Directory of Open Access Journals (Sweden)

    L. F. G. Setz

    2011-09-01

    Full Text Available O cromito de lantânio (LaCrO3, para ser utilizado como interconector, é fundamental que além da condutividade elétrica adequada, apresente alta densidade, contribuindo deste modo para estanqueidade tanto do hidrogênio presente no ânodo como do oxigênio presente no cátodo das células a combustível de óxido sólido. Utilizando-se LaCrO3 dopado com Sr e Co sintetizado pela rota de síntese por combustão, estudou-se o comportamento de densificação em função do tempo, da temperatura e da concentração dos aditivos. Os pós de cromito de lantânio obtidos foram caracterizados por meio de difração de raios X e método de Rietveld na determinação de parâmetros estruturais e quantificação de fases presentes, microscopia eletrônica de varredura, determinação de área de superfície específica e distribuição de tamanhos de partículas. As peças sinterizadas tiveram suas densidades determinadas pelo método de Arquimedes, análise por microscopia eletrônica de varredura para verificação das microestruturas formadas e de dilatometria na avaliação do coeficiente de expansão térmica. Os resultados mostram que o aumento da temperatura de sinterização tem maior influência no comportamento de densificação do LaCrO3 do que o tempo de tratamento, e o aumento na concentração de dopantes contribui acentuadamente nos processos de sinterização e densificação do material.Lanthanum chromite (LaCrO3 is one of the most adequate materials for use as interconnector in solid oxide fuel cell applications, due to its intrinsic properties, namely its good electrical conductivity and resistance to environment conditions in fuel cell operations. Due to difficulties in sintering, additives are usually added to help in the densification process. In this work, the influence of added cobalt and strontium, time and temperature in the sintering of LaCrO3 obtained by combustion synthesis, was studied. The LaCrO3 powders were characterized

  15. Minerals and melt inclusions as keys to understanding magma reservoir processes during formation of volcanic and plutonic mafic-ultramafic complexes in the Maimecha Kotui Province (Polar Siberia)

    Science.gov (United States)

    Simonov, Vladimir; Vasiliev, Yurii; Kotlyarov, Alexey; Stupakov, Sergey

    2016-04-01

    Magmatic complexes in the Maimecha Kotui Province (Polar Siberia) attract attention of researchers because they contain ultramafic volcanic rocks - meimechites, being products of crystallization of the ultrabasic deep mantle melts (Sobolev et al., 1991, 2009, 2011; Ryabchikov et al., 2002; Vasiliev, Gora, 2014). Effusive meimechites together with intrusive dunites of the Guli massif form ancient (253-246 Ma) volcanic and plutonic association, in which also pyroxenites and alkaline rocks are situated. Conditions of formation of this association were established with the help of minerals and melt inclusions study. The cumulative structure of the Guli massif dunites consists of rather large (2-4 mm) olivine crystals and dividing them zones (0.5-0.7 mm), filled with fine grains of clinopyroxenes and ore minerals (magnetite, ilmenite and chromite). The extended forms of well faceted pyroxene crystals testify to their fast growth from melt between cumulative olivines. Thus, crystallization of clinopyroxenes and ore minerals leads to formation between olivines ore pyroxenites, which are presented in the Guli massif by independent bodies. Analysis of olivine, Cr-spinel and clinopyroxene compositions testify to similarity of conditions of the Guli massif dunites crystallization on the one hand with formation of platinum-bearing Uralian-Alaskan-type mafic-ultramafic complexes and with another - show participation of meimechite magma. Major element composition of melt inclusions in Cr-spinel has shown that dunites of the Guli massif were crystallized with participation of subalkaline picrite magmatic systems, that are relative to melts, responsible of formation of platinum-bearing mafic-ultramafic complexes and meimechites. Peculiarities of trace and rare-earth elements distribution in melt inclusions in Cr-spinel of dunites are actually similar to inclusions in olivine of meimechites. Overall, data on composition of inclusions directly testify to formation of considered

  16. Chromium-rich lawsonite in high-Cr eclogites from the Făgăras Massif (South Carpathians)

    Science.gov (United States)

    Negulescu, E.; Săbău, G.

    2012-12-01

    Lawsonite is a relatively rare phase in natural rocks, because of its thermal decomposition during exhumation, and Cr-bearing lawsonite being restricted to only a few occurrences worldwide. Here we report Cr-lawsonite in eclogites hosted in a medium-grade metamorphic complex. Several high-Cr eclogite lenses occur in the Topolog Complex (Făgăras Massif) of dominantly gneissic-amphibolitic composition. High Cr contents are the result of emerald-green mm-sized nodules containing Cr-rich minerals, embedded in a gray-green matrix of kyanite, clinopyroxene, garnet, amphibole, zoisite, and rutile. Garnets occur as porphyroblasts or in coronas around clinopyroxene aggregates probably replacing former magmatic pyroxene. Relict gabbroic textures (sometimes pegmatoid) and whole rock geochemistry indicate a gabbroic cumulate origin. The REE pattern, displaying a slight positive Eu anomaly and a tea spoon-shaped LREE depletion is also indicative of a cumulate origin, as also noted by Pe Piper & Piper (2002) for the Othrys gabbro (as well as others in the Vourinos and Pindos ophiolitic suites) with the same unusual REE-pattern. The emerald-green Cr-rich nodules are unevenly distributed in the rock, and always enclosed in Cr-rich clinopyroxenes (up to 5.46% Cr2O3) which may exhibit Cr-diffusion haloes towards normal Cr-free matrix pyroxene. The nodules consist of diablastic chromite, rutile and Cr-rich kyanite of up to 15.67 wt% Cr2O3, Cr-bearing epidote, to which Cr-rich staurolite (up to 10.45% Cr2O3; XMg up to 0.68) and Cr-rich lawsonite (up to 9.17% Cr2O3) may exceptionally associate. Cr concentrations in kyanite and lawsonite are, to our knowledge, the highest reported so far. Cr-lawsonite was identified in a single sample, as small single phase inclusions armoured in Cr-kyanite. Equilibrium PT-conditions of 2.6 GPa and 610o C were derived from the garnet-mantled clinopyroxene aggregates using multi-equilibria calculation with the PTGIBBS routine of Brandelik & Massonne

  17. Mineralogy and crystal chemistry of a low grade nickel laterite ore%某印尼低品位红土镍矿的微观结构及晶体化学

    Institute of Scientific and Technical Information of China (English)

    朱德庆; 崔瑜; Sarath HAPUGODA; Keith VINING; 潘建

    2012-01-01

    To acquire understanding of Ni enrichment from laterite ore,the mineralogy and crystal chemistry of a low grade limonite type nickel laterite ore sample assaying 0.97% Ni from Indonesia were studied using optical microscopy,X-ray diffraction (XRD),scanning electron microscopy (SEM) and electron probe microanalysis (EPMA).According to EPMA results,the mineral includes 80% goethite ((Fe,Ni,Al)O(OH)) with 0.87% Ni,15% silicate minerals with lizardite ((Mg,Fe,Ni)3Si2O5(OH)) and olivine ((Mg,Fe,Ni)2SiO4),and 1.19% Ni,and other minor phases,such as hematite,maghemitc,chromite and quartz,and no Ni was detected.The mineralogy of the laterite ore indicates that due to the complicated association of the various phases and the variable distribution of Ni,this refractory laterite ore can not be upgraded by traditional physical beneficiation processes.%为深入研究红土镍矿的镍富集原理,利用电子显微镜、扫描电镜、X射线衍射分析以及电子探针微区分析对含镍0.97%的某印尼低品位红土镍矿的工艺矿物学进行研究,以了解镍钴有价金属的分布及赋存状态.实验表明:该矿样主要矿物为针铁矿(含量约为80%),镍含量约为0.87%;含镍、铁、镁的结晶水硅酸盐矿物((Mg,Fe,Ni)2SiO4)的含量约为15%,如利蛇纹石((Fe,Ni,ADO(OH))和橄榄石((Mg,Fe,Ni)3Si2O5(OH))等,镍含量约在1.19%左右;其它含量较低的物相为赤铁矿、磁赤铁矿、铬铁矿和石英等,这些矿物的镍含量极低.钴土矿是含钴矿物,分析发现该矿物往往有较高的镍和钴含量.微观检测发现:红土镍矿微观结构复杂,不同矿物之间共生普遍,主要矿物的微观结构松散,因而传统选矿方式很难实现镍的富集.

  18. The post-spinel transition in Fe3O4-Fe2SiO4 and Fe3O4- FeCr2O4 solid solutions

    Science.gov (United States)

    Woodland, Alan; Schollenbruch, Klaus; Frost, Daniel; Langenhorst, Falko

    2010-05-01

    Minerals with spinel structure are important phases in the Earth's mantle. Both magnetite (mt, Fe3O4) and chromite (chr, FeCr2O4) are known to transform to denser orthorhombic post-spinel phases at pressures≥10 GPa and ≥12.5 GPa, respectively (Schollenbruch et al. 2009a; Chen et al. 2003). On the other hand, Fe2SiO4 decomposes to its constituent oxides, FeO and SiO2 at high P and no post-spinel polymorph appears to be stable (e.g. Ito & Takahashi 1989). An important question is how spinel solid solutions behave at high pressures and temperatures since such compositions are arguably more petrologically relevant. In addition, since h-Fe3O4 is apparently not quenchable, it is difficult to investigate its structure. In contrast, two high-P polymorphs of FeCr2O4-rich compositions have been found in a meteorite (Chen et al. 2003), suggesting that the addition of Cr might allow us to recover the post-spinel phase of Fe3O4-bearing compositions from experiments. Building on recent results for the Fe3O4 end member (Schollenbruch et al. 2009a, 2009b), we have begun a study of the high-pressure behaviour of solid solutions along the Fe3O4 -Fe2SiO4 and Fe3O4- FeCr2O4 joins. Multianvil experiments were performed at 10 and 13 GPa and 1200-1300°C on pre-synthesised spinels with compositions 85mt-15 Fe2SiO4, 50mt-50chr and 80mt-20chr. For the Si-bearing experiments, stishovite was present in the run products. This occurrence, along with observed twinning in the Fe-oxide phase (Schollenbruch et al. 2009a) allows us to conclude that the original spinel had transformed to a high-P polymorph at a pressure and that Si is essentially excluded from this new structure. However, the powder XRD data from the run products could not be indexed either to magnetite (spinel structure) or to any other expected phase, including the known post-spinel structures. Interestingly, these are the same reflections reported by Koch et al. (2004) for an unidentified phase in their high-P (> 9 GPa

  19. Remote Compositional Analyses of Lunar Olivine-Bearing Lithologies

    Science.gov (United States)

    Isaacson, P.; Clark, R. N.; Head, J. W.; Klima, R.; Petro, N. E.; Pieters, C. M.; Staid, M.; Sunshine, J. M.; Taylor, L. A.; Thaisen, K. G.; Tompkins, S.

    2009-12-01

    The Moon Mineralogy Mapper (M3) is a guest instrument on Chandrayaan-1, India’s first mission to the Moon. M3 is an imaging spectrometer covering the wavelength range of 430 nm - 3000 nm, and was designed to map the mineralogy of the lunar surface. The high spectral resolution of M3 enables the diagnostic absorption features of lunar minerals to be identified clearly, while the high spatial resolution of M3 allows the identification and mapping of distinct lithologic units. Olivine is an important mineral with which to interpret the petrologic evolution of igneous rocks. The composition of olivine (Mg#) is used to indicate the degree of evolution of the source magma from which a sample crystallized. Visible to near-infrared reflectance spectroscopy is sensitive to the Mg# of olivine, as the diagnostic olivine absorption features shift in response to changing major element abundances (Mg and Fe) content. These changes in diagnostic absorption features can be detected by modeling the individual absorption bands with the Modified Gaussian Model (MGM). Spectra of lunar olivines differ from spectra of their terrestrial and synthetic counterparts due to the inclusions of Cr-spinel common to lunar olivines; however, analysis of lunar olivine mineral separates in terrestrial laboratories and modeling of the resulting reflectance spectra have been able to unravel the chromite effects on the olivine spectrum. Previous efforts at remote compositional analysis of lunar olivine have been limited by spectral resolution and coverage or by spatial resolution. However, the spatial and spectral resolution provided by M3 enable olivine composition to be determined remotely in a spatial context. We are in the process of identifying olivine-bearing lithologies on the lunar farside and analyzing the olivine composition with the modified MGM approach. Initial compositional analyses have been completed for a crater on the rim of the Moscoviense basin that appears to be largely dominated

  20. Behavior of major and trace elements upon weathering of peridotites in New Caledonia : A possible site on ultramafic rocks for the Critical Zone Exploration Network (CZEN) ?

    Science.gov (United States)

    Juillot, Farid; Fandeur, D.; Fritsch, E.; Morin, G.; Ambrosi, J. P.; Olivi, L.; Cognigni, A.; Hazemann, J. L.; Proux, O.; Webb, S.; Brown, G. E., Jr.

    2010-05-01

    Ultramafic rocks cover about 1% of the continental surfaces and are related to ophiolitic bodies formed near convergent plate boundaries (Coleman, 1977). The most typical ultramafic rocks are dunite and harzburgite, which are composed of easily weatherable ferromagnesian mineral species (olivines and pyroxenes), but also of more resistant spinels (chromite and magnetite). Oceanic serpentinization of these ultramafic rocks usually lead to partial transformation of these initial mineral assemblages by forming hydrous layer silicates such as serpentine (lizardite, chrysotile and antigorite) talc, chlorite and actinolite (Malpas, 1992). It also lead to the formation of highly sheared textures, which favor meteoric weathering through preferential water flows. Compared to their crystalline rock counterpart that covers most of the continental surfaces, these ultramafic rocks mainly differ by their lower SiO2, Al2O3 and K2O contents (less than 50%, 10% and 1%, respectively) and, on the opposite, much higher MgO content (more than 18%). Moreover, they commonly have higher concentrations in FeO and other trace elements, such as Ni, Cr, Mn and Co. Weathering of these rocks is then at the origin of major geochemical anomalies on continental surfaces, especially when they occur in tropical and subtropical regions. Such conditions are encountered in New Caledonia where one third of the surface is covered with peridotites (mainly harzburgite with small amounts of dunite) obducted about 35 millions years ago during large tectonic events in the Southwest Pacific at the Late Eocene (Cluzel et al., 2001). Tropical weathering of these ultramafic rocks lead to the development of thick lateritic regoliths where almost all Mg and Si have been leached out and Fe, Mn, Ni, Cr and Co have been relatively concentrated. In these oxisols, Ni, Cr and Co can exhibit concentration up to several wt%, which make them good candidates for ore mining (New Caledonia is the third Ni producer in the world

  1. Chromium(VI) generation in vadose zone soils and alluvial sediments of the southwestern Sacramento Valley, California: a potential source of geogenic Cr(VI) to groundwater

    Science.gov (United States)

    Mills, Christopher T.; Morrison, Jean M.; Goldhaber, Martin B.; Ellefsen, Karl J.

    2011-01-01

    Concentrations of geogenic Cr(VI) in groundwater that exceed the World Health Organization’s maximum contaminant level for drinking water (50 μg L−1) occur in several locations globally. The major mechanism for mobilization of this Cr(VI) at these sites is the weathering of Cr(III) from ultramafic rocks and its subsequent oxidation on Mn oxides. This process may be occurring in the southern Sacramento Valley of California where Cr(VI) concentrations in groundwater can approach or exceed 50 μg L−1. To characterize Cr geochemistry in the area, samples from several soil auger cores (approximately 4 m deep) and drill cores (approximately 25 m deep) were analyzed for total concentrations of 44 major, minor and trace elements, Cr associated with labile Mn and Fe oxides, and Cr(VI). Total concentrations of Cr in these samples ranged from 140 to 2220 mg per kg soil. Between 9 and 70 mg per kg soil was released by selective extractions that target Fe oxides, but essentially no Cr was associated with the abundant reactive Mn oxides (up to ~1000 mg hydroxylamine-reducible Mn per kg soil was present). Both borehole magnetic susceptibility surveys performed at some of the drill core sites and relative differences between Cr released in a 4-acid digestion versus total Cr (lithium metaborate fusion digestion) suggest that the majority of total Cr in the samples is present in refractory chromite minerals transported from ultramafic exposures in the Coast Range Mountains. Chromium(VI) in the samples studied ranged from 0 to 42 μg kg−1, representing a minute fraction of total Cr. Chromium(VI) content was typically below detection in surface soils (top 10 cm) where soil organic matter was high, and increased with increasing depth in the soil auger cores as organic matter decreased. Maximum concentrations of Cr(VI) were up to 3 times greater in the deeper drill core samples than the shallow auger cores. Although Cr(VI) in these vadose zone soils and sediments was only a

  2. Lithophile and siderophile element systematics of Earth's mantle at the Archean-Proterozoic boundary: Evidence from 2.4 Ga komatiites

    Science.gov (United States)

    Puchtel, I. S.; Touboul, M.; Blichert-Toft, J.; Walker, R. J.; Brandon, A. D.; Nicklas, R. W.; Kulikov, V. S.; Samsonov, A. V.

    2016-05-01

    New Os isotope and highly siderophile element (HSE) abundance data, in combination with lithophile trace element and Sm-Nd, Lu-Hf, and Hf-W isotope data, are reported for komatiitic basalts from the Vetreny Belt and tonalites from the adjacent Vodla Block in the Fennoscandian Shield. Komatiitic basalts define a Re-Os isochron with an age of 2407 ± 6 Ma and an initial γ187Os = +1.7 ± 0.2 (2 SE). The Pt-Os data for chromite separates yield an average initial ε186Os = +0.03 ± 0.02 (2 SE). The 147Sm-143Nd and 176Lu-176Hf data for the komatiitic basalts give isochron ages and initial ratios of, respectively, 2403 ± 32 Ma and ε143Nd = -0.90 ± 0.09, and 2451 ± 79 Ma and ε176Hf = +0.4 ± 0.2 (2 SE). Bulk tonalites are characterized by average initial γ187Os, ε143Nd, and ε176Hf values of +304 ± 64, +1.8 ± 0.6, and +2.5 ± 1.6 (2 SE), respectively, when calculated for the ∼3.21 Ga age of the rocks. The komatiitic basalts and tonalites have μ142Nd values of, respectively, +0.5 ± 2.8 and -0.4 ± 5.2 (2 SD). By contrast, both the komatiitic basalts and tonalites exhibit positive 182W anomalies of +7.1 ± 4.5 and +12.6 ± 4.5 ppm (2 SD), respectively. The komatiitic basalts were derived from a komatiitic parental magma with ∼27 wt.% MgO; it was modified by both assimilation of the tonalites and fractional crystallization en route to the surface. Lithophile trace element data constrain the degree of crustal contamination to be 4.0 ± 0.4%. Highly siderophile element abundance data indicate that crustal contamination must have had a negligible effect on the Os isotopic composition of the komatiitic parental magma. By contrast, the Nd, Hf, and W isotope systematics of the komatiitic parental magma were strongly modified as a result of assimilation of the tonalites. The positive initial ε143Nd and ε176Hf values of the tonalites indicate that they formed via melting of a precursor with time-integrated suprachondritic Sm/Nd and Lu/Hf. This precursor was most

  3. Electrical characteristics of the hydroxyapatite for biomedical applications

    International Nuclear Information System (INIS)

    The electric characteristics of hydroxyapatite films were studied (HAP) deposited on metallic substrates oxidized naturally. The substrates was made of steel 316L and of titanium. These materials are used in reconstructive surgery for prosthesis and osseous implants. The studies were carried out with the techniques of potentiostatic polarization and faraday impedance. The potentiostatic polarization reveals that the very well-known piezoelectricity of the HAp subsists after the coating processes (it captures thermal and spray-pyrolysis). Its also revealed a semiconductor behavior of the HAp that until now had not been reported. This characteristic is important, by its relationship with the stability of the HAp coating in front of corrosion processes in the alive tissues. The results of the impedance tests were mathematically analyzed starting from the Nyquist diagrams, of Bode and of power. The physical interpretation is presented under the form of equivalent circuits (CE). In the case of the HAp on a steel 316L substrate, the CE is a Rancles-Voigt module that corresponds to the behavior of a dielectric with flights. In the case of the titanium substrate an element of constant phase appears to high frequencies (CPE), in series with the Rancles-Voigt module. The CPE reveals the presence of a rectifier of the metal/SC-n type that only it could be located in the interface among the titanium and its natural oxide (TiO2). The absence of the CPE in the case of the steel 316L substrate indicates that the natural oxide (Cr2O3) it doesn't form with the steel a Schottky diode, possibly because the chromite is as a SC-n degenerate. On the interface Ti/TiO2 exists results qualitatively identical by other researchers that have worked with the same impedance technique, but applied by humid via (EIS). The CE that have proposed are based on the anodic processes of accretion/dissolution of the film at low pH. This proposal is questioned by our results, obtained under non

  4. The Siuna Serpentinite Melange: An Early Cretaceous Subduction/Accretion of a Jurassic Arc

    Science.gov (United States)

    Flores, K.; Baumgartner, P. O.; Skora, S.; Baumgartner, L.; Muntener, O.; Cosca, M.; Cruz, D.

    2007-12-01

    The Siuna Serpentinite Mélange (SSM), located in northeastern Nicaragua, is a small tectonic window of a large assemblage, the Mesquito Oceanic Terranes (MOT). The SSM was subducted during the Early Cretaceous at the border of continental Chortis Block (sensu stricto). The occurrence of the SSM is in conflict with the current plate tectonic schemes. The pre-Albian, N-S striking subduction-related mélange of SSM zone is exposed SW of the town of Siuna. It consists of metamorphosed, Ca-depleted ultramafic rocks. Relict Cr-rich spinel (Cr # 0.57-0.79) in serpentinites and chromite pods indicates a high degree of melting. The serpentinite matrix contains blocks of sedimentary and igneous origin. Late Bajocian-early Bathonian (169-167 Ma) red- ribbon-bedded radiolarites are in sedimentary contact with greenstones (calc-alkaline metandesites) and volcanic arenites. Middle Oxfordian to late Kimmeridgian/early Tithonian (159-151/148 Ma) black radiolarian-rich cherts, minor shales and siliceous mudstones blocks were found, as well as quartzites, metasandstones and riebeckite-rich metaturbidites. Furthermore, various metamafic rocks including gabbros can be found. This indicates an oceanic setting for the mélange blocks. The metamafic rocks of the mélange exhibit assemblages corresponding to different metamorphic conditions. They range from typical greenschist and amphibolite facies assemblages to high pressure barroisite bearing greenschists. Possible blueschist to eclogite facies conditions are indicated by mica schist with silica rich phengites yielding 139.2 ± 0.4 Ma 40 Ar/39Ar geochronology and blocks containing garnet with inclusions of aegirine/omphacite. Hence, the SSM resembles typical subduction zone mélanges (e.g. Franciscan, Motagua). It exposes parts of a major zone of oceanic terranes of pacific origin, the MOT, that are placed between the Chortis Block and the Caribbean Large Igneous Province (CLIP). The overlap sequence documents Aptian/Albian deep

  5. Workshop on Oxygen in the Terrestrial Planets

    Science.gov (United States)

    2004-01-01

    Lunar Metal Grains: Solar, Lunar or Terrestrial Origin? 22) Isotopic Zoning in the Inner Solar System; 23) Redox Conditions on Small Bodies; 24) Determining the Oxygen Fugacity of Lunar Pyroclastic Glasses Using Vanadium Valence - An Update; 25) Mantle Redox Evolution and the Rise of Atmospheric O2; 26) Variation of Kd for Fe-Mg Exchange Between Olivine and Melt for Compositions Ranging from Alkaline Basalt to Rhyolite; 27) Determining the Partial Pressure of Oxygen (PO,) in Solutions on Mars; 28) The Influence of Oxygen Environment on Kinetic Properties of Silicate Rocks and Minerals; 29) Redox Evolution of Magmatic Systems; 30) The Constancy of Upper Mantlefo, Through Time Inferred from V/Sc Ratios in Basalts: Implications for the Rise in Atmospheric 0 2; 31) Nitrogen Solubility in Basaltic Melt. Effects of Oxygen Fugacity, Melt Composition and Gas Speciation; 32) Oxygen Isotope Anomalies in the Atmospheres of Earth and Mars; 33) The Effect of Oxygen Fugacity on Interdiffusion of Iron and Magnesium in Magnesiowiistite 34) The Calibration of the Pyroxene Eu-Oxybarometer for the Martian Meteorites; 35) The Europium Oxybarometer: Power and Pitfalls; 36) Oxygen Fugacity of the Martian Mantle from PigeoniteMelt Partitioning of Samarium, Europium and Gadolinium; 37) Oxidation-Reduction Processes on the Moon: Experimental Verification of Graphite Oxidation in the Apollo 17 Orange Glasses; 38) Oxygen and Core Formation in the Earth; 39) Geologic Record of the Atmospheric Sulfur Chemistry Before the Oxygenation of the Early Earth s Atmosphere; 40) Comparative Planetary Mineralogy: V/(CrCAl) Systematics in Chromite as an Indicator of Relative Oxygen Fugacity; 41) How Well do Sulfur Isotopes Constrain Oxygen Abundance in the Ancient Atmospheres? 42) Experimental Constraints on the Oxygen Isotope (O-18/ O-16) Fractionation in the Ice vapor and Adsorbant vapor Systems of CO2 at Conditions Relevant to the Surface of Mars; 43) Micro-XANES Measurements on Experimental Spinels andhe

  6. Estudo petrográfico e metalográfico dos meteoritos Bocaiúva e João Pinheiro aliado à técnica de MEV/EDS Metallographic and petrographic study of meteorites Bocaiúva and João Pinheiro combined with SEM/EDS microscopy

    Directory of Open Access Journals (Sweden)

    Flavia Noelia Pucheta

    2011-06-01

    , another fragment cataloged as "Bocaiúva meteorite", which is actually a fragment from a different meteoritic body, called João Pinheiro, yet to be cataloged. The mineralogical differences, especially regarding the silicate portions of the Bocaiúva, as well as fluid and melted inclusions, leave no doubt that they belong to different meteorites. Minerals such as kamacite, taenita, troilite, schreibersita and graphite are found in the João Pinheiro meteorite, while in Bocaiúva are present forsterite, kamacite, taenita, troilite, schreibersite, pentlandita, magnetite, chromite, pigeonite, diopside, enstatite, plagioclase, apatite, calcite and goethite.

  7. Nickeltalmessite, Ca2Ni(AsO4)2 · 2H2O, a new mineral species of the fairfieldite group, Bou Azzer, Morocco

    Science.gov (United States)

    Chukanov, N. V.; Mukhanova, A. A.; Möckel, S.; Belakovsky, D. I.; Levitskaya, L. A.

    2010-12-01

    Nickeltalmessite, Ca2Ni(AsO4)2 · 2H2O, a new mineral species of the fairfieldite group, has been found in association with annabergite, nickelaustinite, pecoraite, calcite, and a mineral of the chromite-manganochromite series from the dump of the Aït Ahmane Mine, Bou Azzer ore district, Morocco. The new mineral occurs as spheroidal aggregates consisting of split crystals up to 10 × 10 × 20 μm in size. Nickeltalmessite is apple green, with white streak and vitreous luster. The density measured by the volumetric method is 3.72(3) g/cm3; calculated density is 3.74 g/cm3. The new mineral is colorless under a microscope, biaxial, positive: α = 1.715(3), β = 1.720(5), γ = 1.753(3), 2 V meas = 80(10)°, 2 V calc = 60.4. Dispersion is not observed. The infrared spectrum is given. As a result of heating of the mineral in vacuum from 24° up to 500°C, weight loss was 8.03 wt %. The chemical composition (electron microprobe, wt %) is as follows: 25.92 CaO, 1.23 MgO, 1.08 CoO, 13.01 NiO, 52.09 As2O5; 7.8 H2O (determined by the Penfield method); the total is 101.13. The empirical formula calculated on the basis of two AsO4 groups is Ca2.04(Ni0.77Mg0.13Co0.06)Σ0.96 (AsO4)2.00 · 1.91H2O. The strongest reflections in the X-ray powder diffraction pattern [ d, Å ( I, %) ( hkl)] are: 5.05 (27) (001) (100), 3.57 (43) (011), 3.358 (58) (110), 3.202 (100) (020), 3.099 (64) (0 bar 2 1), 2.813 (60), ( bar 1 21), 2.772 (68) (2 bar 1 0), 1.714 (39) ( bar 3 31). The unit-cell dimensions of the triclinic lattice (space group P1 or P) determined from the X-ray powder data are: a = 5.858(7), b = 7.082(12), c = 5.567(6) Å, α = 97.20(4), β = 109.11(5), γ = 109.78(5)°, V = 198.04 Å3, Z = 1. The mineral name emphasizes its chemical composition as a Ni-dominant analogue of talmessite. The type material of nickeltalmessite is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, registration number 3750/1.

  8. Mechanism for the effect of sulphate on SCC in BWRs. Part 1: Hypothesis; Part 2: Microstructural examination of an oxide layer on steel

    International Nuclear Information System (INIS)

    Part 1: Stress corrosion cracking is one of the most serious materials related problems encountered in BWRs. The crack propagation rate has been shown to be strongly affected by sulphates in the coolant. Typical concentrations of sulphates and other anions in the primary water is 1 ppb. The values can increase temporarily to much higher values during transients. Shorter periods of such extra exposure give no effect, but there seems to be an integrated threshold value ('Memory effect') beyond which the propagation rate increases rapidly. The primary system surfaces communicating with the bulk water are normally protected by a very thin, passivating oxide film. This is composed of spinel phases like chromite, situated closest to the metal upon which there could be a layer of nickel ferrite. On top of the spinels there is also normally a cover of deposits. This composite film is going to act as a surface for adsorption, transportation and storage of sulphates from the primary bulk water. Starting from a comparison of the surface conditions around a corrosion pit it was proposed that in the close vicinity of an active crack, the surface oxide is going to function as a cathode on which pH and also the potential are high compared to the surrounding surfaces. The permeability of the oxide is essential for the cathodic function as chemical species and charge have to be transported through it. This has led to the hypothesis that the rate determining step of the crack propagation should be found in the set of processes on the cathode like adsorption, transportation, chemical transformation and precipitation in which hydrogen sulphate and sulphate participate while migrating through the cathodic area towards the crack. It is also postulated that the permeability and geometry of the cathodic surface oxide will be influenced by sulphate and other sulphur containing species breaking down the passive film. Sulphate entering the crack environment can be reduced down to sulphide

  9. An experimental and petrologic investigation of the source regions of lunar magmatism in the context of the primordial differentiation of the moon

    Science.gov (United States)

    Elardo, Stephen M.

    The primordial differentiation of the Moon via a global magma ocean has become the paradigm under which all lunar data are interpreted. The success of this model in explaining multiple geochemical, petrologic, and isotopic characteristics lunar geology has led to magma oceans becoming the preferred model for the differentiation of Earth, Mars, Mercury, Vesta, and other large terrestrial bodies. The goal of this work is to combine petrologic analyses of lunar samples with high pressure, high temperature petrologic experiments to place new and detailed constraints the petrogenetic processes that operated during different stages of lunar magmatism, the processes that have acted upon these magmas to obscure their relationship to their mantle source regions, and how those source regions fit into the context of the lunar magma ocean model. This work focuses on two important phases of lunar magmatism: the ancient crust-building plutonic lithologies of the Mg-suite dating to ~4.3 Ga, and the most recent known mare basaltic magmas dating to ~3 Ga. These samples provide insight into the petrogenesis of magmas and interior thermal state when the Moon was a hot, juvenile planet, and also during the last gasps of magmatism from a cooling planet. Chapter 1, focusing on Mg-suite troctolite 76535, presents data on chromite symplectites, olivine-hosted melt inclusions, intercumulus mineral assemblages, and cumulus mineral chemistry to argue that the 76535 was altered by metasomatism by a migrating basaltic melt. This process could effectively raise radioisotope systems above their mineral-specific blocking temperatures and help explain some of the Mg-suite-FAN age overlap. Chapter 2 focuses on lunar meteorites NWA 4734, 032, and LAP 02205, which are 3 of the 5 youngest igneous samples from the Moon. Using geochemical and isotopic data combined with partial melting models, it is shown that these basalts do not have a link to the KREEP reservoir, and a model is presented for low

  10. Disscussion on the metallogenesis of Bushveld magmatic Cu-Ni-PGE sulphide deposit in South Africa%南非布什维尔德岩浆型Cu-Ni-PGE硫化物矿床成因探讨

    Institute of Scientific and Technical Information of China (English)

    吕林素; 汪云峰; 李宏博; 周振华; 张作衡; 谢桂青

    2011-01-01

    450 km and NS width being 250 km. It is also the most important single-reposi-tory platinum group elements (PGE), chromite and vanadiferous magnetite deposit. The Bushveld Deposit (BD) is the largest PGE deposit in the world, with reserves of PGE 65 473 tons, occupying 75% of this kind of resource in the world. It includes more than 30 PGE deposits along the Rustenburg Layered Suite (RLS, 7~9 km in thickness), in which three ore bodies within the BIC, I. E. The Upper Group 2 chromitite (UG2, accounting for 58%), the Merensky Reef (MR, accounting for 32%) and the Platreef (PR, accounting for 9%) are especially remarkable. RLS has been divided into five major zones from bottom to top: marginal zone (mgZ), lower zone (LZ), critical zone (CZ), main zone (MZ) and upper zone (UZ), in which CZ is the major ore-bearing zone. RLS has two major ore-forming features: one is that enormous amounts of PGE mineralization are always associated with beds of base metal sulfides (BMS) characterized by low-grade (Ni 0.15% ~0.36%, Cu 0.03% ~0.18% ) and low-density, and the other is that there exist integral sequence and mineralizing position, forming multilayered chromites in LZ and CZ, and the major platinum-bearing layers are UG2 and MR at the top of CZ. Multilayered platinum mineralization is in MZ and only magnetite occurs in UZ. The rock-forming and ore-forming ages of BD range from 2 050 Ma to 2 060 Ma, suggesting products of Paleoproterozoic. The metallogenic setting of the Bushveld deposit was epicontinental rift. The metallogenic mechanism of the deposit is that the assimilation and contamination of hydrosillicate components in the crust caused the differentiation of sulfides to form base metal sulfides (BMS), and the enrichment of PGE resulted from sulfide differentiation and adsorption. The parent magma of RLS was derived from the deep magma chamber and then the parent magma of CZ entered the major magma chamber of Bushveld deposit to generate sulfide facies or enriched PGE

  11. Metasomatismo en ortoanfibolitas de la Faja máfica-ultramáfica del río de las tunas, Mendoza Metasomatism in orthoamphibolites from the Río de Las Tunas mafic-ultramafic belt, Mendoza

    Directory of Open Access Journals (Sweden)

    M. Florencia Gargiulo

    2012-06-01

    áticos y la secuencia de reemplazo observada en ellos, sugieren que tales asociaciones se generaron a causa de un proceso metasomático, acontecido en condiciones de bajo grado a una presión menor a 4 kbar, durante los estadios finales del ciclo de metamorfismo regional evidenciado en el área.In this contribution, petro-mineralogical and chemical evidences of metasomatism in orthoamphibolites from the Río de Las Tunas mafic-ultramafic belt in Frontal Cordillera of Mendoza province are provided. These orthoamphibolites integrate the metamorphic basement of the Frontal Cordillera and they belong to the Guarguaráz Metamorphic Complex. These rocks show mineral associations and textural relationships indicating disequilibrium conditions between some of the mineral phases. Hornblendic amphibole crystals show a reaction border with development of clinopyroxene (ferroan dioside; meanwhile the calcicplagioclase is mostly replaced by a fine-grained matrix integrated by the mineral association of garnet-epidotes.l -prehnite-pumpellyite- albite. The amphibole and clinopyroxene crystals are also partially replaced by pumpellyite and/or chlorite, meanwhile the matrix is slightly replaced by muscovite and calcite. Garnet compositions belong to the grossular-andradite series and their average composition is: Alm05Adr53Prp01Sps04Grs36Uv01. Some crystals with Cr2O3 content between 11.69-13.17 wt.% and with a subtle chemical zonation (uvarovitic core: Alm03Adr13Prp00Sps02Grs35Uv47 with more grossularic border: Alm03Adr12 Prp00Sps01Grs44Uv40 occur in relationship with magnetite crystals with up to 20% of the chromite component. Pressure estimations based on the compositional zoning of amphibole crystals gave values between 2.5-4.5 kbar. The observed mineral associations together with the textural and chemical characteristics of these rocks show that this kind of orthoamphibolites is completely different from the classical amphibolites of igneous protoliths outcropping in the study area

  12. PGE geochemistry of Jiding ophiolite in Tibet and its constraint on mantle processes

    Institute of Scientific and Technical Information of China (English)

    XIA; Bin

    2001-01-01

    ., Gorton, M. P., The origin of the fractionation of platinum-group elements in terrestrial magmas. Chem. Geol.. 1985,53: 303-323.[23]Mecher, F G., Thalhammer, T. V., The giant chromite deposits at Kempirsal. Ural: Constraints from trace element (PGE,REE) and isotope data, Mineralium Deposta, 1999, 34: 250-272.[24]Amosse. J., Analytical determination of PGE in geological samples by EAA and ICP-MS, in On Mineralisation Related to Mafic and Ultramafic Magmatism, Orleans, 1993.[25]Gueddari, K., Pioule, M., Amosse, J., Differentiation of platinum-group elements (PGE) and of gold during parting of peridotites in the lherzolitic massif of the Berico-Rifean rifean range (Ronda and Beni Bousera), Chem. Geol., 1996. 134:181-197.[26]Capobianco, C. J., Drake. M. J., Partioning of ruthenium, rhodium, palladium beteewn spinel and silicate melt and implications for platinum group element fractionation trends, Geochim. Cosmochim. Acta. 1990, 54: 869-874.[27]Mairer. W. D., Barnes, S. J., Platinum-group elements in silicate rocks of the lower, critical and main zonest at union section. western Bushveld complex, J. Petrol., 1999.40: 1647-1671.

  13. Determination of Major and Minor Components in High-Cr Red Mud by X-ray Fluorescence Spectrometry with Fusion Sample Preparation%熔融制样X射线荧光光谱法测定高铬赤泥中主次量组分

    Institute of Scientific and Technical Information of China (English)

    朱忠平; 曾精华; 王长根; 吕立超

    2014-01-01

    be analyzed by X-ray Fluorescence Spectrometry (XRF).However,a use of sodium flux and a high dilution ratio are not conducive to sodium and low content elements.In this paper,a method of XRF analysis is developed for the determination of the major and minor components (Cr,Si,Al,Fe,Mg,Ca,Na,K,S,P,Ti,Mn and V)in high-Cr red mud by fused bead preparation with Li2B4O7-LiBO2(67∶33)flux,NH4NO3 oxidizer and saturated LiBr solution parting medium.When the dilution ratio of the melting sample is lower than 24∶1 ,the lower dilution ratio,the more serious is the corrosion on the Pt-Au crucible;the RSD (n=1 0)of the sample preparation method is at a minimum when the dilution ratio is 24∶1;the longer the melting time and the higher the melting temperature,the RSD becomes lower.The optimization conditions of fused bead are obtained when the dilution ratio is 24∶1 ,the melting temperature is 1 1 00℃ and the melting time is 1 5 min.The working curve was established by chromite,bauxite,clay,iron ore standards and manual preparation standard materials.The matrix effect and spectrum line overlap interference were corrected by a fundamental parameter method and standard regression.The results are consistent with certified values and the RSD (n=10)is from 0.3% to 3.9%.Compared with domestic and foreign XRF methods for chromium-containing minerals,this method uses no sodium salt,a fuse piece,conventional sample melting temperature (1 1 00℃),low dilution ratio (24 ∶1 )for sample preparation,and the sampling precision and analysis precision are low.The problem with XRF analysis of high-Cr red mud has been solved by this method,which can be used to analyze Cr,Al, Si and Fe in roasting,concentrates and tailings and other ores processed by sodium.

  14. Oxygenates vs. synthesis gas

    Energy Technology Data Exchange (ETDEWEB)

    Kamil Klier; Richard G. Herman; Alessandra Beretta; Maria A. Burcham; Qun Sun; Yeping Cai; Biswanath Roy

    1999-04-01

    Methanol synthesis from H{sub 2}/CO has been carried out at 7.6 MPa over zirconia-supported copper catalysts. Catalysts with nominal compositions of 10/90 mol% and 30/70 mol% Cu/ZrO{sub 2} were used in this study. Additionally, a 3 mol% cesium-doped 10/90 catalyst was prepared to study the effect of doping with heavy alkali, and this promoter greatly increased the methanol productivity. The effects of CO{sub 2} addition, water injection, reaction temperature, and H{sub 2}/C0 ratio have been investigated. Both CO{sub 2} addition to the synthesis gas and cesium doping of the catalyst promoted methanol synthesis, while inhibiting the synthesis of dimethyl ether. Injection of water, however, was found to slightly suppress methanol and dimethyl ether formation while being converted to CO{sub 2} via the water gas shift reaction over these catalysts. There was no clear correlation between copper surface area and catalyst activity. Surface analysis of the tested samples revealed that copper tended to migrate and enrich the catalyst surface. The concept of employing a double-bed reactor with a pronounced temperature gradient to enhance higher alcohol synthesis was explored, and it was found that utilization of a Cs-promoted Cu/ZnO/Cr{sub 2}O{sub 3} catalyst as a first lower temperature bed and a Cs-promoted ZnO/Cr{sub 2}O{sub 3} catalyst as a second high-temperature bed significantly promoted the productivity of 2-methyl-1-propanol (isobutanol) from H{sub 2}/CO synthesis gas mixtures. While the conversion of CO to C{sub 2+} oxygenates over the double-bed configuration was comparable to that observed over the single Cu-based catalyst, major changes in the product distribution occurred by the coupling to the zinc chromite catalyst; that is, the productivity of the C{sub 1}-C{sub 3} alcohols decreased dramatically, and 2-methyl branched alcohols were selectively formed. The desirable methanol/2-methyl oxygenate molar ratios close to 1 were obtained in the present double

  15. Natural geochemical risk in the Pollino Massif: a case-study of chromium

    Directory of Open Access Journals (Sweden)

    Priscilla Boccia

    2015-06-01

    Full Text Available The geochemical risk linked to heavy metal contamination of soils and waters, commonly associated with anthropogenic causes, may, however, be linked to the presence of rocks and soils that naturally contain these metals. Chromium and nickel are particularly abundant in the ultramafic rocks and ophiolitic and in some crystalline rocks, as well as in soils resulting from these pedogenetic processes (Kierczak et al., 2007. The phenomenon of alteration in charge of such rocks can also determine the release in ionic form, in the circulating waters, of high amounts of such metals. In this regard, the north-central sector of the Pollino massif is an important pilot case, characterized by the presence of ophiolite and crystalline rocks of continental origin which are natural reservoirs of chromium and nickel. In the Pollino Massif outcrop ultramafic rocks, such as serpentinites and metabasites, and lower-crustal continental rocks, such as garnet-rich gneiss exhibit high concentrations of Mg, V, Cr, Co, and Ni, more than one or two orders of magnitude higher than the average composition of the upper continental crust. In general, the weathering of these rocks may cause groundwater pollution (Kierczak et al., 2007 that, in the case of the Pollino Massif, is mostly related to the release of Cr and Ni in solution and, to a lesser extent, also to the release of Mg and Pb (Margiotta et al., 2012. The principal geochemical process able to release Cr (VI starting from the rock is the dissolution of chromite and, to a lesser extent, magnetite and diopside, all phases containing Cr (III. Very high concentrations of Cr (VI were also detected in water circulating in Pleistocene conglomerates, due to the presence of a significant serpentine component. Within the project " Geochemical vulnerability monitoring aimed at a correct management of the soil use in some risk areas of the Pollino National Park (Basilicata" (MoGeSPol, funded by the Region of Basilicata in

  16. THE CHARACTERISTICS OF THE SEDIMENT IN NORTHERN SOUTH CHINA SEA AND ITS RESPONSE TO THE EVOLUTION OF THE PEARL RIVER%南海北部沉积物特征及其对珠江演变的响应

    Institute of Scientific and Technical Information of China (English)

    邵磊; 赵梦; 乔培军; 庞雄; 吴梦霜

    2013-01-01

    The geochemical data of sediments from the South China Sea(SCS) provide constraints on both the composition of potential source rocks and the effects of sedimentary environments.In combination with knowledge of the regional geology,this data set allows us to decipher the tectonic implications since 32Ma on the basis of trends and major discontinuities observed in the stratigraphic succession of geochemical sediments compositions.This abrupt change coincided with a series of events including a seafloor spreading axis jump in the South China Sea and uplift of the western Yunnan Plateau and eastern Tibet Plateau,leading to obvious changes in sediment geochemical composition such as clay mineral,sand-mud ratio,major elements and sedimentary environments,suggesting great changes in the drainage areas of the paleo-Pearl River.Through this tectonic event,the sedimentary environment in the Baiyun Sag area transformed from continental shelf in the Late Oligocene to continental slope since the Early Miocene,and the sea level rose since the Early Miocene in the area.Heavy minerals in Pearl River sediments show excellent correlation with their source rocks,and obvious differences exist between heavy minerals assemblages and their representative minerals from different branches of the River.The source region of heavy minerals can be divided into three parts from west to east on the basis of assemblage types,index mineral (Ati,ZTi,and ZTR)values and their correlation.The western part includes the source region of the upper reaches with a zircon-leucoxene-apitite assemblage characterized by apitite and chromite,in an area largely covered by carbonate,partly by metamorphite and basic rocks.The middle part features a zircontourmaline-leucoxene-epidote assemblage,in which pyroxene,leucoxene,zircon and epidote are characteristic from a region predominated by clastic rocks and other sedimentary rocks,as a result of mixing between heavy minerals from local source rocks and alteration

  17. 珠江流域沉积物重矿物特征及其示踪意义%CHARACTERISTICS OF HEAVY MINERALS IN PEARL RIVER SEDIMENTS AND THEIR IMPLICATIONS FOR PROVENANCE

    Institute of Scientific and Technical Information of China (English)

    向绪洪; 邵磊; 乔培军; 赵梦

    2011-01-01

    Heavy minerals in the Pearl River sediments have excellent correlation with their source rocks. Obvious differences in heavy minerals assemblages and their diagnostic minerals have been studied in dif-ferent branches of the River. The source of the river deposits can be divided into three provinces from west to east on the basis of heavy minerals assemblage types, mineral index(ATi,ZTi,ZTR) values and their correlation. The western province includes the upper reaches of the Xijiang River, where occurs a magne-tite-ilmenite-zircon-leucoxene-apatite assemblage characterized by magnetite, ilmenite, apatite and chro-mite, indicating a provenance dominated by carbonate, with some metamorphic and basic rocks, and scarce ultrabasic and acid rocks. The middle province is located in the lower reaches of the Xijiang River, which is featured by a zircon-ilmenite-magnetite-tourmaline-leucoxene-epidote assemblage, characterized by pyrox-ene, leucoxene, zircon and epidote, indicating a provenance of clastic rocks and other sedimentary rocks with some metamorphic, basic and acid igneous rocks, as a mixture of local sources and the heavy minerals from upper reaches. The eastern province is the source area of the Dongjiang and Beijiang Rivers dominated by the assemblage of hornblende-tourmaline-magnetite-ilmenite-epidote-garnet characterized by horn-blende, tourmaline, garnet, titanite and sillimanite, indicating a provenance of acid rocks with some meta-morphic and small amount of sedimentary rocks. The results demonstrate that the characteristics of heavy minerals assemblages are useful tools to trace the provenance evolution of the Pearl River, and of signifi-cance in revealing the erosion-transportation-sedimentation pattern in the Pearl River region for source-sink comparison and analysis.%珠江流域沉积物重矿物组合与源区岩石特征具有极好的相关性,不同支流的重矿物组合及其代表性特征矿物差别明显.根据重矿物组合类型、重矿

  18. Speciation of Zinc in ash investigated by X-ray absorption spectroscopy; Zinks foerekomstformer i aska studerade med en roentgenabsorptionsspektrometrisk metod

    Energy Technology Data Exchange (ETDEWEB)

    Steenari, Britt-Marie; Noren, Katarina

    2008-06-15

    Direct identification of trace metal compounds in solid materials is difficult to achieve due to the detection limits of available analytical methods. Although zinc is the most abundant trace metal in combustion residues, the number of publications dealing with its direct speciation is small. Struis and co-workers have published an investigation where they used Extended X-ray Absorption Fine Structure spectroscopy (EXAFS) measurements to identify zinc compounds in municipal solid waste incineration fly ash. The EXAFS technique has been used more often for speciation of Zn in contaminated soil. EXAFS data for farm soil samples showed that zinc was most commonly sequestered in layer silicates, but soil particles containing zinc sulphide, zinc chromite and zinc phosphate were also found. Generally, published results show that zinc after being mobilised in a soil, has a clear tendency to be sequestered in silicates, as sulphides or, if there is phosphate available, as phosphate. The aim of the work presented in this work was to use the EXAFS method to show how zinc in chemically bound in ash from woody fuels and from municipal solid waste (MSW). The results can be used for evaluations of the possible toxicity of ash and in predictions of the leaching of zinc from ash. The investigation comprised dry ashes from two fluidised bed combustors fired with forestry litter, bark and other wood fuels, moistened and aged wood ashes and dry ashes from three MSW incinerators: one fluidised bed combustor and two stoker fired combustors. The spectroscopic measurements were carried out at the beam line I811 in the Swedish national synchrotron facility Maxlab at Lund University. The results showed that the lowest concentration of Zn in ash for which it is possible to get any information about the nearest neighbour atoms around zinc is about 500 mg Zn per kg dry ash. If the concentration is higher than 1000 mg/ kg it is possible to obtain information, not only about the nearest

  19. Synthesis, Characterization, and Optimization of Novel Solid Oxide Fuel Cell Anodes

    Science.gov (United States)

    Miller, Elizabeth C.

    presents opportunities for the new kinds of ex situ and in situ experiments performed in this thesis. Ex situ experiments involved reducing powder samples at SOFC operating temperatures under hydrogen gas and characterizing them via electron microscopy and X-ray diffraction (XRD). For the in situ experiments, powders were heated, then reduced at temperature, and catalyst exsolution was observed in real-time. Pechini-synthesized cerium oxide substituted with 2-5 mol% Pd was studied using in situ X-ray heating experiments at Argonne National Laboratory's Advanced Photon Source. In these experiments, the powder was subjected to several cycles of reduction and oxidation at 800°C, and Pd metal formation was confirmed through the appearance of Pd peaks in the X-ray spectra. Next, Fe- and Ru-substituted lanthanum strontium chromite (LSCrFeRu14) synthesized by solid state reaction was characterized with ex situ and in situ microscopy. Transmission electron microscopy (TEM) in situ heating experiments were conducted to observe Ru nanoparticle evolution under the reducing conditions of the TEM vacuum chamber. LSCrFeRu14 was heated to 750°C and observed over ˜ 90 min at temperature during which time nanoparticle formation, coarsening, and di?usion were observed. Experiments on both materials sought to understand the conditions and timing of nanoparticle formation in the anode, which is not necessarily apparent from electrochemical data. Reducing the operating temperature of SOFCs from the current state-of-the-art range of 700-800°C to ≤ 650°C has many advantages, among them increased long-term stability, reduced balance of plant costs, fewer interconnect/seal material issues, and decreased start-up times. In order to maintain good performance at reduced temperature, these intermediate temperature SOFCs require new materials including highly active alternatives to micron-scale Ni-YSZ composite anodes. The present work focuses on the development of IT-SOFCs with Sr0.8La 0.2TiO3

  20. Geology, petrology and geochronology of the Lago Grande layered complex: Evidence for a PGE-mineralized magmatic suite in the Carajás Mineral Province, Brazil

    Science.gov (United States)

    Teixeira, Antonio Sales; Ferreira Filho, Cesar Fonseca; Giustina, Maria Emilia Schutesky Della; Araújo, Sylvia Maria; da Silva, Heloisa Helena Azevedo Barbosa

    2015-12-01

    ultramafic lithotypes render Nd model ages between 2.94 and 3.56 Ga, with variably negative ɛNd (T = 2.72 Ga) values (-0.32 to -4.25). The crystallization sequence of the intrusion and the composition of cumulus minerals, together with lithogeochemical and Nd isotopic results, are consistent with an original mantle melt contaminated with older continental crust. The contamination of mafic magma with sialic crust is also consistent with intra-plate rifting models proposed in several studies of the CMP. Lithogeochemical and isotopic data from the Lago Grande Complex may also be interpreted as the result of melting an old lithospheric mantle, and alternative models should not be disregarded. PGE mineralizations occur in chromitites and associated with base metal sulfides in the Lago Grande Complex. Chromitite has the highest PGE content (up to 10 ppm) and is characterized by high Pt/Pd ratio (4.3). Mantle-normalized profile of chromitite is highly enriched in PPGE and similar to those from Middle Group (MG) and Upper Group (UG) chromitites from the Bushveld Complex. Platinum group minerals (PGM) occur mainly at the edge of chromite crystals in the Lago Grande chromitite, consisting of arsenides and sulfo-arsenides. Sulfide-bearing harzburgite samples of the Lago Grande complex have PGE content of up to 1 ppm and low Pt/Pd (0.2-0.3) ratios. The 2722 ± 53 Ma U-Pb zircon age determined in this study for the Lago Grande Complex overlaps with the crystallization age of the Luanga Complex. Previous interpretation that the Lago Grande and Luanga layered intrusions are part of a magmatic suite (i.e., Serra Leste Magmatic Suite) is now reinforced by similar fractionation sequences, comparable petrological evolution and overlapped U-Pb zircon ages. The occurrence of the same styles of PGE mineralization in the Lago Grande and Luanga complexes, together with remarkably similar chondrite-normalized PGE profiles and PGE minerals for chromitites of both complexes, support the concept that

  1. 辽宁瓦房店金伯利岩中尖晶石族矿物种类划分及指示意义%The Characteristics and Classification of Spinel Group Minerals in Kimberlite in Wafangdian,Liaoning Province

    Institute of Scientific and Technical Information of China (English)

    迟广成; 伍月

    2014-01-01

    minerals in kimberlite will be obviously different. Through the determination of the lattice parameters and chemical compositions of spinel group minerals from non-lean ore mines and Bonanza kimberlite pipe, the study of internal relations of chemical composition and lattice parameter changes in spinel group minerals among no ore,lean ore and bonanza kimberlite plays an important role for kimberlite diamond deposits prospecting. In order to determine the species of spinel group minerals,MgO,FeO,TiO2 ,Al2 O3 ,MnO and Cr2 O3 of 50 spinel group minerals were analyzed by using micro area chemical analysis with Electron Microprobe. The lattice parameters of 136 spinel group minerals were determined by single-crystal X-ray Diffraction. The results show that spinel group minerals in kimberlite Wafangdian of Liaoning province are magnesium-rich chromite. Based on the main cations occupying chemical formulae groups A and B,the spinel group minerals in mining can be divided into 10 subspecies. If the ratio of Cr2 O3/( Cr2 O3 +Al2 O3 )content( Cr′ values)in spinel group minerals represent the degree of mineralization of kimberlite ore-bearing deposit,the Cr′values in high-grade ore,medium-grade ore and lean ore of kimberlite rock in Wafangdian Liaoning are 89. 5%,83. 4% -87. 1% and 70. 2%,respectively. Lattice parameters of the spinel group minerals were 0. 831 -0. 832 nm,0. 834 -0. 836 nm and larger than 0. 837 nm from non-rock,lean ore rock,medium-grade ore and high-grade ore. A case that the spinel mineral lattice parameter of the first generation and Cr′value are the indicators of the ore bearing in Wafangdian kimberlite,Liaoning province is described.

  2. Evolución metalogenética de las Sierras Pampeanas de Córdoba y sur de Santiago del Estero: Ciclos prepampeano y pampeano Metallogenic evolution of the Sierras Pampeanas of Córdoba and south of Santiago del Estero: Prepampean and Pampean cycles

    Directory of Open Access Journals (Sweden)

    D. Mutti

    2005-03-01

    éticas más significativas.This hypothesis of metallogenic evolution of the Sierras Pampeaneas of Córdoba and south of Santiago del Estero proposes the existence of five metallogenic stages, two of wich are treated in this paper: stage 1 belongs to the prepampean extensional cycle and is connected with the Neoproterozoic opening and expansion of the proto-Atlantic ocean. During this stage submarine volcanogenic deposits were developed such as Cu-Fe (Zn-Au-Ag-Co in basalts, W (B-F-Zn in impure limestones and dolomites, and Fe in silicoclastic sediments, as well as transition occurrences from them to MVT deposits of Cu (Au-Ag and Pb- Zn (Ag-Cu-Au in impure limestones and dolomites. Chromite magmatic deposits in mantle tectonites and of Fe-Ti in ultramaficmafic rocks in the transition crust-mantle zone are also related to stage 1. Distribution of the Prepampean deposits and their space relationship with the main submarine volcanogenic, SEDEX and MVT áreas in the proto-atlantic ocean are placed on a global reconstruction for Neoproterozoic age. The compressive Pampean - Famatinian cycle comprises two stages. Metallogenic stage 2 (Neoproterozoic - early Cambrian corresponds to the pampean orogenic cycle, during which numerous deformation structures and magmatism were developed. During this stage magmatic-metamorphic occurrences of Fe-Ti in ultramafic and mafic dikes in mantle tectonites, metasomatic occurrences of Fe-Ti in rodingites and Be-Li-U-ETR rich pegmatites were generated, besides transformation events comprising metamorphism, deformation, remobilization and recrystallization occurred in deposits of Cr, Cu-Fe (Zn-Au-Ag- Co, W (B-F-Zn, Cu (Au-Ag, Pb-Zn (Ag-Cu-Au and Fe, which affected their magnetic response.Ore deposits and occurrences included in the above metallogenic stages are distributed in this study in belts related to megastructures activated during the Prepampean and Pampean cycles and the most significant petrogenétic associations are indicated.

  3. METASOMATIC AND MAGMATIC PROCESSES IN THE MANTLE LITHOSPHERE OF THE BIREKTE TERRAIN OF THE SIBERIAN CRATON AND THEIR EFFECT ON THE LITHOSPHERE EVOLUTION

    Directory of Open Access Journals (Sweden)

    Lidia V. Solov’eva

    2015-10-01

    metasomatic phlogopite-amphibole aggregate mainly replace laminar intergrowths of one of pyroxenes and garnet and also develops in the re-crystallized fine-grained rock matrix. This suggests a considerable period of time between the crystallization of rocks of the pyroxenite-peridotite series and the development of phlogopite-amphibole metasomatism.The Phl-Ilm hyperbasites comprise a complex association of parageneses represented by garnet- and garnetless pyroxenites, websterites, olivine websterites, orthopyroxenites, lherzolites and olivinites. A specific feature of this series is high contents of K, Ti and Fe in the rocks and minerals. The content of phlogopite is widely variable, from a few percent to 40–80 %. The content of ilmenite ranges from a few percent to 15 %, rarely to 30–40 %. Mica and ilmenite contents sharply decrease in garnetized xenolithes, where these two minerals, as soon as olivine and pyroxenes are replaced by garnet.Euhedral, subhedral, sideronitic and porphyraceous structures in garnetless xenoliths suggest the primary magmatic genesis of the rocks. In the series of Phl-Ilm hyperbasites, a special type of parageneses is represented by strongly deformed phlogopite-amphibole rocks with newly-formed chromite and relict resorbed ilmenite and clinopyroxene. Phl-Ilm rock series is also characterized by a variety of autometasomatic and metasomatic reaction structures. Garnet and phlogopite develop nearly simultaneously at the sub-solidus stage: garnet develops due to cooling of the primary magmatic rocks, and phlogopite develops under the influence of residual rich in potassium and volatiles fluids – melts. Phlogopite in the rocks of the Phl-Ilm series form porphyraceous plates, late intergranular xenomorphic grains, porphyroblasts of the solidus stage and strongly deformed irregular plates in the phlogopite-amphibole rocks. Amphibole occurs in garnetless parageneses and deformed phlogopite-amphibole rocks in amounts of a few percent and up to 40–50

  4. About some processes of replacement of PGM from the placers of Southern Siberia

    Science.gov (United States)

    Shvedov, G. I.; Knyazev, V. N.; Nekos, V. V.

    2003-04-01

    placer of Sysim river (Eastern Sayan). The similar composition of phase was described by S.A.Toma and S.Murphy /6/. In placer of Talanovaya river (Kuznetsky Alatau) the edging of idealized composition Os_2S (tab., No. 4-1) are develops on the grain of Os-Ir-ruthenium (tab., No.4). It indicates deficit of sulfur in a solution. In case of increased concentration of arsenic the minerals of Os-Ir-Ru system (tab., No. 5) are replaced by diarsenides (anduoite - omeiite series) (tab., No. 5-1) or sulfoarsenides of these elements as it was observed in PGM from placer of Rudnaya river (Western Sayan). In the extremely rare cases at superposition of sulfurless and arsenicless solutions the replacement of alloys Os-Ir-Ru by exotic phases can happen. For example, authors find the grain of native iridium, which was heavily deformed and impregnated on microgaps by phases of generalized composition from Pt(Ni,Cu,Fe)_2 to Ir(Ni,Fe,Cu)_3 in placer of Bolshoy Khaylik river /7/. The forming of similar phases can be initiated by very specific conditions: the extremely reducing conditions, very low fugitivity of sulfur and oxygen, absence of other anion-forming elements, high activity of a nickel, iron and cooper. The similar phases were found in streak-schlieren chromitic ores in one massif of alpine-type ultramafic rocks of Koryak Highland /3/. Also rather rare replacement of platinum with the high contents of ruthenium and iridium (platruthenosmiridium by old nomenclature) (tab., No.6) by Pt-Fe alloys (tab., No.6-1). It was observed by authors in PGM from placer of Talanovaya river (Kuznetsky Alatau). In the system Pt-Fe most widespread placer-forming minerals are ferriferous platinum, tetraferroplatinum and isoferroplatinum. In placers that were investigated by the authors the Pt-Fe alloys most frequently is replaced by cuperite, which forms the various thickness edgings. It usual phenomenon in some cases becomes complicated by forming of narrow (first microns) intermittent band of high