Zeitschriftenartikel: „Chromide“

1

Scheer, M., und P. G. Jones. „Bis(triphenylphosphine-P)iminium Trichloro(η5-cyclopentadienyl)chromide(III)“. Acta Crystallographica Section C Crystal Structure Communications 53, Nr. 8 (15.08.1997): 1038–39. http://dx.doi.org/10.1107/s0108270197005234.

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2

Armstrong, RD, und HW Ferguson. „Systemic viral disease of the chromide cichlid Etroplus maculates“. Diseases of Aquatic Organisms 7 (1989): 155–57. http://dx.doi.org/10.3354/dao007155.

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3

Jithendran, K. P., A. Navaneeth Krishnan, P. T. Aneesh, P. Ezhil Praveena und T. Bhuvaneswari. „Susceptibility of orange chromide, Etroplus maculatus (Bloch, 1795) to experimental infection of Betanodavirus“. Aquaculture International 29, Nr. 2 (22.01.2021): 697–710. http://dx.doi.org/10.1007/s10499-021-00648-y.

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4

Butvina, V. G., S. S. Vorobey, O. G. Safonov, D. A. Varlamov, G. V. Bondarenko und Yu B. Shapovalov. „Experimental study of formation of chromian priderite and yimengite as products of modal mantle metasomatism“. Доклады Академии наук 486, Nr. 6 (28.06.2019): 709–13. http://dx.doi.org/10.31857/s0869-56524866709-713.

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The article presents the data of a series of experiments on the synthesis of exotic titanates (priderite and yimengite) as a result of the reproduction of metasomatic conditions of transformation of mantle minerals (chromite, ilmenite). It was first synthesized chromian priderite not containing Ba. The experiments showed the possibility of crystallization of this mineral as a reaction product of high-chromium spinel and rutile with potassium aqueous carbonate fluid (melt) in the upper mantle. In particular, the obtained experimental data allow us to interpret the relationship between K-Cr-priderite and carbonate-silicate inclusions in chromites of Bohemian garnet peridotites. In the experimental study of the reaction of chromite and ilmenite with aqueous potassium-carbonate fluid (melt) obtained both phases of titanates (priderite and yimengite) - indicator minerals, mantle metasomatism, which directly confirms the possibility of formation of yimengite and K-Cr-priderite and other titanates, the result of mantle metasomatism of upper mantle peridotite under conditions of the highest activity of potassium.

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Ostrander, Gary K., und Jack A. Ward. „The function of the pelvic fins during courtship and spawning in the orange chromide, Etroplus maculatus“. Environmental Biology of Fishes 13, Nr. 3 (Juli 1985): 203–10. http://dx.doi.org/10.1007/bf00000932.

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6

Escudero-Castejon, Lidia, Sergio Sanchez-Segado, Stephen Parirenyatwa und Animesh Jha. „Formation of Chromium-Containing Molten Salt Phase during Roasting of Chromite Ore with Sodium and Potassium Hydroxides“. Journal for Manufacturing Science and Production 16, Nr. 4 (01.12.2016): 215–25. http://dx.doi.org/10.1515/jmsp-2016-0023.

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AbstractChromium has a wide range of applications including metals and alloys manufacturing, pigments, corrosion resistance coatings and leather tanning. The production of chromium chemicals is based on the oxidative alkali roasting of chromite ores, which leads to the formation of water-soluble alkali chromates. Previous investigations reported that when chromite is roasted with soda-ash, a molten salt containing chromium, which is mainly composed of sodium carbonate and sodium chromate (Na2CO3-Na2CrO4 binary mixture), forms under typical roasting conditions. The physical properties of the liquid phase, which are dependent on the temperature, charge and gangue compositions, play an important role on the oxidation reaction and may limit the chromate recovery by hindering the oxygen transport to the reaction interface. This investigation focuses on the alkali roasting of chromite ore at 1,000 oC using NaOH and KOH, followed by water leaching. The influence of the alkali ratio on the chromium extraction yield is analysed, and the results obtained with both hydroxides are compared. Sample characterisation and thermodynamic analysis, including phase diagrams, equilibrium calculations and computation of liquidus curves, are combined with the purpose of studying the formation of the molten salt phase under different roasting conditions and its effect on the final chromium recovery.

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Lalomov, Alexander V., Ildar R. Rakhimov und Antonina V. Grigor’eva. „Chromite placer occurrences of the Volga-Ural basin – genesis, sources and industrial potential“. Georesursy 23, Nr. 3 (30.08.2021): 143–48. http://dx.doi.org/10.18599/grs.2021.3.17.

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Chromium is a strategic metal, but more than a half of Russia’s needs are met by imports, so new deposits of chromites, including unconventional placer deposits, are of industrial and scientific interest. Previous studies and current works of the authors of the article have established the chromite placer metal content of Permian-Jurassic deposits of the Volga-Ural basin, which has industrial and potential significance: within the Lukoyanovsky placer area (Nizhny Novgorod region), the industrial chromite content of Jurassic coastal-marine titanium-zirconium placers has been established; in the south-west of Bashkiria, chromite-bearing sands (Sabantuy occurrence) with increased contents, but not yet clear industrial potential. The study of the typomorphism of chromites indicate their close relationship with the chrome spinel of ophiolite associations. The assumed overthrust structure of chromite-bearing hyperbasites of the Urals suggests a wide distribution of chromite-bearing sands within the Upper Permian-Jurassic Volga-Ural paleobasin, in which the increased content of chromites was controlled by hydro- and lithodynamic conditions favorable for placer formation. Questions of the genesis of chromite placer occurrences in the Ural part of the East European Platform, their distribution and primary sources need further study.

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Bhat, Aadil, Anutosh Paria, A. Deepika, K. Sreedharan, M. Makesh, Megha K. Bedekar, C. S. Purushothaman und K. V. Rajendran. „Molecular cloning, characterisation and expression analysis of melanoma differentiation associated gene 5 (MDA5) of green chromide, Etroplus suratensis“. Gene 557, Nr. 2 (Februar 2015): 172–81. http://dx.doi.org/10.1016/j.gene.2014.12.028.

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9

Henry, Karen S., John C. Petura, Steven Brooks, Steven Dentico, Stephen A. Kessel und Mark Harris. „Preventing surface deposition of chromium with asphalt caps at chromite ore processing residue sites: a case study“. Canadian Geotechnical Journal 44, Nr. 7 (01.07.2007): 814–39. http://dx.doi.org/10.1139/t07-029.

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Caps were constructed on chromite ore processing residue (COPR) sites in the Kearny, New Jersey, area between 1989 and 1994 to prevent human exposure to hexavalent chromium (Cr(VI)). The caps comprise geotextile overlain by 100 mm of dense graded aggregate (DGA) and 100 mm of hot mix asphalt (HMA). Prior to constructing these "composite asphalt caps" (CACs), Cr(VI) was sometimes deposited on surface soils as chromate (salts) during evaporative periods. We initially thought the geotextile and DGA acted as a capillary barrier, stopping capillary water rise, but site inspection revealed that the DGA and geotextile were too moist to perform this function. Further study included a literature review, DGA capillary rise estimates, in situ measurement of soil-water content over 7 months at a representative COPR site, and numerical modeling of matric suction gradients induced by evaporation. The collective results reveal that the CACs eliminate upward matric suction gradients from the COPR–soil through the DGA, thereby precluding surface chromate deposition. Even during evaporative periods, the low unsaturated hydraulic conductivity of the HMA restricts upward movement of moisture and soluble chromate from underlying COPR–soil. In contrast, there are almost always upward matric suction gradients in uncapped COPR–soil.Key words: capillary rise, chromite ore processing residue, chromate, hexavalent chromium, composite asphalt cap, evaporation.

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Dey, Satarupa, Baishali Pandit und A. K. Paul. „Reduction of Hexavalent Chromium by Viable Cells of Chromium Resistant Bacteria Isolated from Chromite Mining Environment“. Journal of Mining 2014 (10.08.2014): 1–8. http://dx.doi.org/10.1155/2014/941341.

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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) during growth. Viable cells of these isolates were also capable of growing and reducing 100 μM Cr(VI) quite efficiently in Vogel Bonner (V.B.) broth under batch cultivation. Freshly grown cells of the most potent isolate, Arthrobacter SUK 1201, reduced 100 μM Cr(VI) in 48 h. Reduction potential of SUK 1201 cells 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 SUK 1201 was promoted in the presence of glucose and glycerol while the highest reduction was at pH 7.0 and 25°C. The reduction process was inhibited by divalent cations Ni, Co, and Cd, but not by Cu. Similarly, carbonyl cyanide m-chlorophenylhydrazone, N,N,-Di cyclohexyl carbodiimide, sodium azide, and sodium fluoride were inhibitory to chromate reduction, while 2,4 dinitrophenol promoted the process. Cells permeabilized by toluene increased the efficiency of Cr(VI) reduction and, thereby, indicate that Arthrobacter sp. SUK 1201, indigenous to chromite mining environment, could be used as an ideal tool for chromium bioremediation.

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Swaminathan, T. Raja, Wazir S. Lakra, A. Gopalakrishnan, V. S. Basheer, B. Khushwaha und K. A. Sajeela. „Development and characterization of a new epithelial cell line PSF from caudal fin of Green chromide, Etroplus suratensis (Bloch, 1790)“. In Vitro Cellular & Developmental Biology - Animal 46, Nr. 8 (25.06.2010): 647–56. http://dx.doi.org/10.1007/s11626-010-9326-y.

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12

Liu, Cheng Jun, Jie Qi und Mao Fa Jiang. „Experimental Study on Sulfuric Acid Leaching Behavior of Chromite with Different Temperature“. Advanced Materials Research 361-363 (Oktober 2011): 628–31. http://dx.doi.org/10.4028/www.scientific.net/amr.361-363.628.

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Utilizing Pakistan chromite as raw material, the rapid leaching of chromium and iron could be realized by the sulfuric acid leaching process on the condition of atmospheric pressure and the addition of oxidant A. And the leaching rate of chromium and iron would be 98.5% and 71.9%, respectively. The sulfuric acid leaching processes with different temperature were systematically studied by chemical analysis and phase analysis. The results showed that, with the increase of reaction temperature, the leaching rate of chromium would increase gradually, but the leaching rate of iron increased at first and then decreases and reached its maximum at 140°C. When the temperature > 160°C, the phases of the leaching residue were magnesium iron silicate and a few of silica, no chromohercynite, chrompicotite and magnesioferrite existed in the chromite. The leaching solution of sulfuric acid leaching process could be used for preparing the basic chrome sulfate, and there is no Cr6+ in the leaching residue and solution. The results would provide theoretical guidance for solving environmental pollution problem of Cr6+ in traditional chromate production process.

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Chaumba, Jeff B., und Caston T. Musa. „Geochemistry of the chromitite stringer at the contact of the mafic sequence and the ultramafic sequence in the Unki Mine area, Shurugwi Subchamber of the Great Dyke, Zimbabwe“. Canadian Mineralogist 58, Nr. 3 (01.05.2020): 313–33. http://dx.doi.org/10.3749/canmin.1900052.

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ABSTRACT Several models have been proposed to explain the origin of a chromitite stringer located at the contact between the Mafic and Ultramafic Sequences in the Unki Mine area of the Shurugwi Subchamber of the Great Dyke, Zimbabwe. A petrographic and geochemical study of this chromitite stringer was undertaken with the aim of constraining its origin. Forty-three chromite compositions were obtained from the studied chromitite stringer, which is characterized by a chromium number between 59.9 and 62.8 and a magnesium number which ranges from 37.8 to 46.4. The chromites at the contact zone in the Unki Mine commonly contains inclusions of sulfides, orthopyroxene, plagioclase, and/or amphiboles. The chromites likely formed early in the crystallization history of the Mafic Sequence, as they are commonly partially rimmed by sulfides and they occur as inclusions in plagioclase crystals. Unlike chromites from underlying Ultramafic Sequence chromitite layers, chromites at the contact zone contain low Cr2O3 contents which range from 39.4 to 42.6 wt.%. Furthermore, these chromites are enriched in Fe compared to most Great Dyke chromitites, which is interpreted to be a consequence of subsolidus exchange of Mg into orthopyroxene and Fe into the chromite. The absence of zoning in the chromites at this contact zone, and their low Mn, Fe contents, is consistent with attainment of equilibrium because the altered chromites often contain Cr-bearing magnetite rims. Two possible models for the formation of this chromitite stringer are mixing of relatively primitive and evolved magmas (i.e., ultramafic and anorthositic magma), possibly of different oxygen fugacities, and chemical diffusion across the contact between the Mafic and the Ultramafic sequences which resulted in melting at and below this boundary. The latter would have caused preferential loss of orthopyroxene from the underlying P1 Pyroxenite Layer, accompanied by re-precipitation of chromite at this contact.

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Lee, Yong M., und Claudia L. Nassaralla. „Heat capacities of calcium chromate and calcium chromite“. Thermochimica Acta 371, Nr. 1-2 (April 2001): 1–5. http://dx.doi.org/10.1016/s0040-6031(00)00755-3.

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15

Wang, Zhaolin, Jiayong Yan, Hejun Tang, Yandong Xiao, Zhen Deng, Guixiang Meng, Hui Sun, Yaogang Qi und Lulu Yuan. „Geochemistry and Mineralogy of Peridotites and Chromitites from Zhaheba Ophiolite Complex, Eastern Junggar, NW China: Implications for the Tectonic Environment and Genesis“. Minerals 13, Nr. 8 (13.08.2023): 1074. http://dx.doi.org/10.3390/min13081074.

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The Zhaheba ophiolite is an ocean relic of the Zhaheba-Aermantai oceanic slab, a branch of the early Paleozoic Paleo-Asian Ocean. The peridotites consist mainly of harzburgite, lherzolite and minor dunite, chromitite. This study describes the whole-rock geochemistry and mineral chemistry of the Zhaheba peridotite and chromitite for the purpose of constraining their tectonic environment and genesis. The major oxides and the trace element concentrations of the peridotites are comparable with abyssal peridotite, but fall outside the field of SSZ (suprasubduction zone) peridotite and the fore-arc peridotite. The massive chromites belong to the high-Cr group, with an average Cr# (Cr/(Cr + Al)) atomic ratio) value of chromian spinel of 0.77, whereas the average Mg# value is 0.60. The disseminated chromites give a lower concentration of Cr2O3 (38.96–42.15 wt.%, average 40.35 wt.%) and lower Cr# values (0.50–0.56, average 0.53), but slightly higher contents of MgO (13.23 wt.%) and Mg# (0.61) than the massive chromites. In the diagrams of Cr#-Mg#, NiO-Cr# and TiO2-Cr#, the massive chromites fall in the field of boninite, and the disseminated chromite in the peridotite plot fall in the field of abyssal peridotite and mid-oceanic ridge basalt (MORB). The massive chromitites, with high-Cr, display a boninite affinity, whereas the disseminated chromite plot in the high-Al and abyssal peridotite type field may be generated by the extension of the Zhaheba ocean in the MOR environment then experienced deep subduction and exhumation. The calculated degrees of partial melting for the massive chromites are 21%−22%, and for the disseminated chromites in peridotites the degrees are 17%−18%. The calculated values of fO2 for the massive chromites range from −1.44 to +0.20, and the values for the disseminated chromites range from −0.32 to +0.18. The inferred parental melt composition for massive chromitite falls in the field of boninite in an arc setting, whereas the disseminated chromite in peridotites are in the field of a MORB setting. This indicates that the parental magmas of the former were more refractory than the latter. A two-stage evolution model for the chromites was proposed, in which disseminated chromites were first formed in an MOR environment and then modified by later-stage melts and fluids, and formed massive chromites were formed in an SSZ setting during intra-oceanic subduction.

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Rani, M., K. Tariq, A. Younus, K. Batool, M. Sattar, R. Shafique, M. Bukhari, N. Akhtar und A. Mehmood. „Sol-gel Synthesis of Nanoscaled Spinels using 1, 2-ethanediol as a Gelation Agent“. Journal of Optoelectronic and Biomedical Materials 13, Nr. 3 (Juli 2021): 89–94. http://dx.doi.org/10.15251/jobm.2021.133.89.

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In the present work sodium chromite (NaCr2O4) based pigment was synthesized using sol gel technique. From XRD analysis, it is clear that all samples manufactured by sol gel technique have spinel structure crystallization. Also chromites with a chromium concentration (max) shows black color and Na- substituted shows green color. The samples were annealed at different temperature from 600˚C to 700˚C. The obtained nano particles were characterized by other different techniques as well such as Scanning electron microscopy, Raman spectroscopy, Photoluminence and Energy dispersive spectroscopy. The particle size of parent compound is ranging from 4.4nm to 11nm determined from SEM. The tendency of particles to form the aggregates with the increasing annealing temperature has been observed. The optical characterization of the compound shows that the sol gel attained material is strongly persuasive sodium chromite.

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Tripathy, Sunil, Y. Murthy, Veerendra Singh, Saeed Farrokhpay und Lev Filippov. „Improving the Quality of Ferruginous Chromite Concentrates Via Physical Separation Methods“. Minerals 9, Nr. 11 (29.10.2019): 667. http://dx.doi.org/10.3390/min9110667.

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The low chromium-to-iron ratio of chromite ores is an important issue in some chromite deposits. The value of the chromite ore is indeed dictated in the market by its iron, as well as its chromium content. In the present study, a chromite concentrate was reprocessed by gravity (spiral concentrator) and magnetic separation to enhance the chromium-to-iron ratio. Also, detailed characterization studies including automated mineralogy were carried out to better understand the nature of the samples. Enhancing the chromium-to-iron ratio was achieved by using advanced spiral separators which will be discussed in this paper.

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Nasr, Ahmed Ibrahim. „Conversion of Chromium Shaving Waste from Leather Processing into Activated Carbon“. Textile & Leather Review 6 (03.08.2023): 343–59. http://dx.doi.org/10.31881/tlr.2023.079.

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This study aimed to convert chrome shaving waste (CSW) generated from leather processing into valuable materials, such as de-chromed activated carbon and basic chromium sulphate. CSW was de-chromed using three levels of leaching solution of potassium carbonate, hydrogen peroxide, and water (0.25:0.1:5, 0.5:0.2:5, and 0.75:0.3:5, respectively), and the resulting potassium chromate was converted into basic chromium sulphate using sugar reduction method. De-chromed shaving waste (DSW) was pyrolyzed at three temperatures levels (400, 500, and 600 °C) to obtain de-chroming shaving ash (DSA), which then was chemically activated using three levels of potassium hydroxide (3:1, 2:1, and 1:1 of DSA: KOH, respectively). The results showed that up to 21% of de-chroming activated carbon (DAC) was produced, containing 71.22% carbon with a surface area of 731 m2/g, total pore volume of 0.385 cm3/g, and an average pore diameter of 2.106 nm. The produced basic chromium sulphate was suitable for reuse in leather processing. Therefore, this study provides an effective way to convert CSW into valuable materials, reducing the environmental impact of leather processing and promoting sustainability.

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Kanari, Ndue, Eric Allain, Lev Filippov, Seit Shallari, Frédéric Diot und Fabrice Patisson. „Reactivity of Low-Grade Chromite Concentrates towards Chlorinating Atmospheres“. Materials 13, Nr. 20 (09.10.2020): 4470. http://dx.doi.org/10.3390/ma13204470.

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The most economically important iron-chromium bearing minerals is chromite. In natural deposits, iron(II) is frequently substituted by magnesium(II) while chromium(III) is replaced by aluminum(III) and/or iron(III) forming a complex chromium bearing material. The majority of mined chromite is intended for the production of ferrochrome which requires a chromite concentrate with high chromium-to-iron ratio. Found mostly in the spinel chromite structure, iron cannot be removed by physical mineral processing methods. In this frame, the present work deals with the reaction of chlorine and chlorine+oxygen with selected samples of chromite concentrates for assessing the reactivity of their components towards chlorinating atmosphere, allowing the preferential removal of iron, hence meeting the chromite metallurgical grade requirements. Isothermal thermogravimetric analysis was used as a reliable approach for the kinetic reactivity investigation. Results indicated a wide difference in the thermal behavior of chromite constituents in a chlorinating atmosphere when considering their respective values of apparent activation energy oscillating from about 60 to 300 kJ/mol as a function of the sample reacted fraction. During the chromite treatment by chlorine in presence of oxygen, chromium was recovered as liquid chromyl chloride by condensation of the reaction gas phase.

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Fedortchouk, Yana, und William LeBarge. „Sources of placer platinum in Yukon: provenance study from detrital minerals“. Canadian Journal of Earth Sciences 45, Nr. 8 (August 2008): 879–96. http://dx.doi.org/10.1139/e08-032.

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Source rocks for the platinum group minerals (PGM), historically reported in a number of Yukon placers, remain either unknown or poorly understood. A study of heavy-mineral samples from five creeks draining bedrock in west and central Yukon was undertaken to confirm the presence of placer platinum, to determine which mafic–ultramafic rock is the source of PGM in Kluane area, southern Yukon, and to explain platinum occurrences in Canadian and Florence creeks, central Yukon, where no known mafic–ultramafic rocks are present. Diverse composition of chromian spinel and clinopyroxenes from three creeks in the Kluane area indicate several sources of ultramafic rocks, including fragments of Alpine-type peridotites formed in back-arc basin and mid-ocean-ridge settings, and a source rock for zoned zinc-rich chromites of unknown origin. The Kluane ultramafic sills are the most likely source of PGM in this area. The heavy-mineral sample from Canadian Creek returned one PGM grain, no chromite, and abundant ilmenite and titanomagnetite. A group of chromium-rich magnesian ilmenites (∼4 wt.% MgO) closely match the composition of ilmenites from continental mafic intrusions produced during continental rift magmatism. This supports the continental rifting event recently proposed for this part of Yukon and indicates the economic potential of the Canadian Creek platinum occurrence. Composition of spinel from Florence Creek sample indicates an Alaskan-type intrusion as the source of PGM.

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Hu, X., H. Wang, L. Teng und S. Seetharaman. „Direct chromium alloying by chromite ore with the presence of metallic iron“. Journal of Mining and Metallurgy, Section B: Metallurgy 49, Nr. 2 (2013): 207–15. http://dx.doi.org/10.2298/jmmb120815015h.

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Direct chromium alloying by chromite ore in EAF operation is a promising process in stainless steel production, which has the advantage of resource-saving, energy-saving, and environment-friendly. In the present investigation, iron, carbon, and chromite ore mixture (Fe+C+FeCr2O4) were chosen as the precursor for direct chromium alloying. Thermogravimetric Analysis (TGA) experiments were carried out to investigate the effect of iron content on the reduction kinetics, and the results show that the presence of metallic iron in the precursor will increase the reduction rate of chromite. Up-scaling experiments (100 g and 500 g scale) have been carried out in the induction furnace to further test the effectiveness of using industrial chromite ore for direct chromium alloying. The induction furnace tests confirmed the necessity of adjusting composition of the slags to ensure high yield of chromium in the final products; and chromium yield can reach 90%.

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Xiao, Y. Y., L. J. Wang, S. Y. Liu, X. B. He und K. C. Chou. „Kinetic mechanism of FeCr2O4 reduction in carbon-containing iron melt“. Journal of Mining and Metallurgy, Section B: Metallurgy, Nr. 00 (2023): 10. http://dx.doi.org/10.2298/jmmb230215010x.

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Direct alloying of chromium by chromite attracts a lot of interest for its superiority in energy-saving and process simplification. The knowledge of chromium alloying by reduction of FeCr2O4, the main component of chromite, is key to understanding the mechanism of chromium alloying from chromite. The effect of melt composition (carbon and chromium addition) and temperature on the reduction of FeCr2O4 by carbon-containing iron melt was studied. The higher the carbon content is in the melt, the higher chromium recovery is obtained. Similarly, the higher temperature is favourable for the reduction of FeCr2O4. The reduction of FeCr2O4 was impeded by chromium addition due to the lower activity of carbon resulting from the strong attraction between carbon and chromium. The kinetics of FeCr2O4 reduction by carbon dissolving in iron melt were investigated, and the results indicated that the controlling step is the chemical reaction at the FeCr2O4/melt interface at 1823K. And the calculated activation energy for the chemical reaction is 392.82 kJ/mol.

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Starks, Courtney M., Russell B. Williams, Vanessa L. Norman, Stephanie M. Rice, Mark O’Neil-Johnson, Julie A. Lawrence und Gary R. Eldridge. „Antibacterial chromene and chromane stilbenoids from Hymenocardia acida“. Phytochemistry 98 (Februar 2014): 216–22. http://dx.doi.org/10.1016/j.phytochem.2013.11.012.

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Liu, Yan, Mao Fa Jiang und De Yong Wang. „Reduction Feature and Selection Principle of Chromium Ore for Stainless Steelmaking in a Smelting Reduction Converter“. Applied Mechanics and Materials 142 (November 2011): 161–64. http://dx.doi.org/10.4028/www.scientific.net/amm.142.161.

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This paper starts with the mineral structure, reducing properties of chromium ore and the physical and chemical properties of chromium oxide and discusses the requirements of the chemical composition of chromite and confirms the selection principle of chromium ore and reducing agent of chromium ore smelting reduction. The chemical compositions of the available chromite request the relatively high contents of chromium and iron, the lower contents of Al2O3, MgO and P in gangue and the lower Cr/Fe ratio in keeping with the case of high chromium. Chromoium ore in South Africa is considered to be suitable for smelting stainless steel crude melts in a smelting reduction converter. From the reducing power and economy angle, carbon as a reducing agent is more suited to reducing chromium ore.

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Kokkaliari, Maria, Karen St Seymour, Stylianos F. Tombros und Eleni Koutsopoulou. „Study of the chromite mineralization associated to ophiolites from Tinos Island, Attico-Cycladic Massif“. Bulletin of the Geological Society of Greece 55, Nr. 1 (14.11.2019): 185. http://dx.doi.org/10.12681/bgsg.20777.

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This paper aims to study the chromitites, as well as their host rocks (meta-peridotites, meta-dunites and serpentinites) of the ophiolite complex of Mount Tsiknias, in Tinos Island. Recognition of their mineralogy and their textural features was carried out through detailed petrographic study. The mineral chemistry analysis contributed to the evaluation of the analyzed chromites, the chemical composition of which provides important information about the petrogenetic evolution of the chromitite ores. The chromites were in equilibrium with boninite melts derived from Supra-Subduction Zone, e.g., a depleted mantle wedge. In the binary classification diagram for spinels, the Tinos samples extend in the fields of Mg-chromite and chromite sensu strictu. In the TiO2 vs Al2O3 diagram, the chromites plot in the field of Supra-Subduction Zone (SSZ) peridotites and partly overlap the field of chromites in Back-Arc Basalts (BABB), however the same samples plot in the field of chromite of boninites. In the Al2O3 vs Cr2O3 diagram both groups of Tinos chromites plot in the field/extremity of “mantle chromites”.

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Demir, Orhan, und Rauf Hurman Eric. „Rate and Mechanism of Reduction-Dissolution of Chromite in Liquid Slags“. High Temperature Materials and Processes 32, Nr. 3 (14.06.2013): 255–63. http://dx.doi.org/10.1515/htmp-2012-0133.

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AbstractThe dissolution of chromite from the Bushveld Complex of South Africa in liquid slags was studied in the temperature range 1550° to 1665°C under argon gas. The slag compositions were similar to those of ferrochromium production and stainless steel making. Empirical relations between the slag composition and the dissolution of chromite were established through the use of a statistical model. The dissolution process was investigated by using the rotating cylinder technique and measured by the chemical analysis of the samples taken from the melt and the SEM-EDAX analysis of the reacted chromite cylinder samples. The chromite grains were depleted in iron and chromium as the dissolution progressed, leaving behind an alumina and magnesia rich spinel. The experimental data was evaluated by using kinetic models and mass transfer coefficients of chromium, iron and oxygen ions through the phase boundary between the solid chromite cylinder and the liquid slag were determined.The dissolution of chromite in liquid slags increases with increasing stirring rate. SEM-EDAX studies on the reacted chromite cylinders showed that coring took place within the chromite grains subjected to dissolution for sufficient length of time. Chromium and iron concentrations in the chromite were decreasing from the centre towards the surface of the grains while aluminum and magnesium contents were increasing at the edges compared to the centre of the chromite grains. Furthermore, the slag rich in alumina and magnesia diffuses in bulk into the chromite with a net result of increase in the concentration of these elements.The rate of dissolution of chromite in liquid slags was found to be controlled by the mass transfer of oxygen ions (O2−) through the liquid phase boundary between the solid chromite and the liquid slag. The activation energy for the mass transfer of O2− ions was calculated as 30.61 kCal/mol (128.07 kJ/mol).

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Song, Xie-Yan, Kai-Yuan Wang, Stephen J. Barnes, Jun-Nian Yi, Lie-Meng Chen und Louise E. Schoneveld. „Petrogenetic insights from chromite in ultramafic cumulates of the Xiarihamu intrusion, northern Tibet Plateau, China“. American Mineralogist 105, Nr. 4 (01.04.2020): 479–97. http://dx.doi.org/10.2138/am-2020-7222.

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Abstract Chromite is one of the earliest crystallized minerals from mafic melts and has been used as an important “petrogenetic indicator.” Its composition may be modified by interaction with intercumulate melt and adjacent minerals. Thus, chromite in mafic-ultramafic rocks contains clues to the geochemical affinity, evolution, and mantle source of its parent magmas. The Devonian Xiarihamu intrusion, located in the East Kunlun Orogenic Belt in the northern Tibet Plateau, China, hosts a very large disseminated Ni-Co sulfide deposit. This study focuses on geochemistry of the chromite enclosed in olivine of ultramafic rocks of the intrusion. Enrichments in Mg and Al in the rim of the chromite indicate only minor effects of alteration on the compositions of the chromite. The chromites enclosed in the olivines with forsterite percentage (Fo) lower than 87 are characterized by large variations in major and trace elements, such as large ranges of Cr·100/(Cr+Al) (Cr# = 15–47), Mg·100/(Mg+Fe2+) (Mg# = 41–65), and Al2O3 (= 26–53 wt%) as well as 380–3100 ppm V, 70–380 ppm Ga, and 1100–16300 ppm Zn. The chromites display positive correlations between Cr/(Cr+Al) and Ti, Mn, V, Ga, and Sc, inconsistent with fractional crystallization but indicative of an interaction between the chromites, intercumulate melts and hosting minerals. In contrast, chromites hosted in olivine with Fo > 87 in harzburgite have small variations in Cr# (ranging from 37 to 41), Mg# (48 to 51), and Al2O3 (30 to 35 wt%) as well as restricted variation in trace elements, indicating relatively weak interaction with trapped liquid and adjacent phases; these compositions are close to those of the most primitive, earliest crystallized chromites. The most primitive chromite has similarities with chromite in mid-ocean ridge basalt (MORB) in TiO2 and Al2O3 contents (0.19–0.32 and 27.9–36.3 wt%, respectively) and depletion of Sc and enrichment of Ga and Zn relative to MORB chromite. The geochemistry of the chromite indicates a partial melting of the asthenospheric mantle that was modified by melts derived from the subduction slab at garnet-stable pressures.

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Rakhimov, Ildar R., Dmitri E. Saveliev, Mikhail A. Rassomakhin und Aidar A. Samigullin. „Chromian Spinels from Kazanian-Stage Placers in the Southern Pre-Urals, Bashkiria, Russia: Morphological and Chemical Features and Evidence for Provenance“. Minerals 12, Nr. 7 (01.07.2022): 849. http://dx.doi.org/10.3390/min12070849.

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Six minor alluvial chromite placers (Kolkhoznyi Prud, Verkhne-Yaushevo, Sukhoy Izyak, Bazilevo, Novomikhaylovka, Kiryushkino) and one major littoral placer (Sabantuy) were found in sandy sediments of the Kazanian stage of the Permian System (Late Roadian and Wordian Stages) in the Southern Pre-Urals. It is shown that the morphological features of chromian spinels are diverse, which is not evidence of the heterogeneity of the source. The bulk chemical composition of chromian spinels from all placers is similar and generally correlates with compositions of chromian spinels from the Kraka ophiolitic complex in the Southern Urals. The morphological diversity of grains, varied chemical composition and presence of melt inclusions in Ti-high octahedral grains of chromian spinels comply with the ophiolitic nature of the source. Thus, there is no need to refer to other sources for chromite ores but ophiolitic. The new placers expand the dissemination area of chromite-bearing deposits on the east edge of the East-European Platform and offer a prospect to discover new placers.

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Ge, X., S. Jin, M. Zhang, X. Wang und S. Seetharaman. „Synthesis of chromium and ferrochromium alloy in molten salts by the electro-reduction method“. Journal of Mining and Metallurgy, Section B: Metallurgy 51, Nr. 2 (2015): 185–91. http://dx.doi.org/10.2298/jmmb141222022g.

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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.

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Ye, Jin Ling, und Feng Ye. „Effects of Strong Carbide-Forming Elements on Low Temperature Salt-Bath Chromizing“. Advanced Materials Research 214 (Februar 2011): 646–50. http://dx.doi.org/10.4028/www.scientific.net/amr.214.646.

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The microstructure, phase structure, white layer thickness and chromium concentration, microhardness of the chromized layer of T10 steel and 3Cr2W8V steel by low temperature salt-bath chromizing with plasma nitriding are contrasted. The chromizing process is investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD). Results show that the strong carbide-forming elements (Cr, W, V) obstruct the diffusion of chromium and carbon, the white layer thickness and microhardness, surface chromium concentration of the chromized layer are reduced. A chromized layer of T10 steel with average 7.3μm in thickness, 84.47% in surface chromium concentration and 1300HV-1400HV in microhardness is formed on the substrate by chromizing at 610°C for 6h, as compared to the chromized layer of 3Cr2W8V steel with average 3.3μm in thickness, 74.27% in surface chromium concentration and 1200HV-1300HV in microhardness.

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Barber, Kevin N., Cory K. Perkins und Allen W. Apblett. „Reduction of chromate by molybdenum hydrogen bronze“. Canadian Journal of Chemistry 94, Nr. 4 (April 2016): 401–5. http://dx.doi.org/10.1139/cjc-2015-0381.

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Molybdenum hydrogen bronze, H0.57MoO3, is capable of removing up to 80 mequiv./g chromate from aqueous solution. The redox process is accompanied by adsorption of the reduced chromium species so that the chromium is completely removed from solution. Chromate removal was only weakly dependent on pH, being slightly favored at acidic pH. The kinetics appear to involve the rapid adsorption of chromate in an equilibrium process that is followed by reduction of the chromium(VI). The rate constant was found to be first order in chromate and the amount of suspended H0.57MoO3 with a rate constant of 1.40 L g−1 min−1.

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Atasoy, Ahmet, und F. R. Sale. „An Investigation on the Solid State Reduction of Chromite Concentrate“. Solid State Phenomena 147-149 (Januar 2009): 752–57. http://dx.doi.org/10.4028/www.scientific.net/ssp.147-149.752.

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In this article, Turkish chromite concentrate was reduced with metallurgical coke at temperature between 1000-1500 °C with variables reducing times. The reduction mechanism and the microstructure of the reduced chromite were investigated. There were closer relationships between the reduction of chromite and the sample morphology, such as, the surface area and the porosities and cracks of the particle have positive effect on the metallization of iron and chromium oxides. The reduction of the iron chromite spinel started at 1000 °C, but picrochromite started to reduce at temperature around 1300 °C. At lower temperature, the formation of iron carbide phases was affected on the formation of ferro alloy and accelerates the reduction of chromium. The formation of carbon monoxide was also affected on the reduction of chromite spinel, especially around imperfections of grain where porosity, cracks and fractures act as diffusion channel for the reducing gas. For the charecterisation of the reaction products, X-ray diffraction techniques, SEM and EDAX were used.

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Turakulov, Bakhriddin, Kurmanbek Zhantasov, Alexandr Kolesnikov, Bakyt Smailov und Yury Liseitsev. „Research on the Production of Pigments Based on Composite Pellets in the Recycling of Industrial Waste“. Journal of Composites Science 7, Nr. 7 (13.07.2023): 289. http://dx.doi.org/10.3390/jcs7070289.

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This article presents the complex processing of low-grade and substandard chromium ores, as well as sludge tailings, with the production of composite chromium-containing materials and pigments, while improving environmental performance in the Republic of Kazakhstan through the utilization and processing of technogenic raw materials. In this work, to study the physicochemical properties of the starting materials, modern analytical, thermodynamic, chemical, granulometric, as well as computational, mathematical, laboratory, and experimental methods were used. In particular, studies of a method for producing composite pellets for chromite pigments based on industrial technogenic waste of the Republic of Kazakhstan are presented. Based on the results of the experimental studies, composite pellets were obtained, having a compressive strength of 150–220 kg/pellet and containing 49.7% of chromium oxide and 0.5–1.0% of carbon in its composition. The resulting chromite pigment based on the composite pellets is a modification of chromium oxohydroxide with the formula γ-CrOOH. The density of the resulting pigment is 3.4 kg/m3. The chromite pigment based on the composite pellets is recommended for use in various coloring compositions, including using it for printing on cotton and mixed fabrics intended for sewing outerwear.

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Bjerg, Ernesto A., Milka K. De Brodtkorb und Eugen F. Stumpfl. „Compositional zoning in Zn-chromites from the Cordillera Frontal Range, Argentina“. Mineralogical Magazine 57, Nr. 386 (März 1993): 131–39. http://dx.doi.org/10.1180/minmag.1993.057.386.13.

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AbstractSerpentinised ultramafic bodies containing zoned chromite grains occur in the Cordillera Frontal Range, western Argentina. Chromites show Zn-rich Al-chromite cores (4.04 wt.% ZnO) surrounded by ferritchromite rims (1.3 wt.% ZnO) and outer Cr-magnetite rims. In intensely altered chromites which are spatially related to sulphide mineralisation, the primary chromite cores have been replaced by Zn-rich ferritchromit (7 wt.% ZnO) and they are rimmed by Cr-magnetite. In the Al-chromites the mean [Cr/(Cr + Al] ratio is 0.53 and the [Mg/(Mg + Fe)] ratio is 0.53; they plot in the field of Alpinetype intrusions. Ferritchromit has a mean [Cr/(Cr + Al)] ratio of 0.93 and [Mg/(Mg + Fe)] ratio of 0.4. In Cr-magnetites the mean [Cr/(Cr + Al) is 0.98 and the [Mg/(Mg + Fe)] ratio is 0. Ferritchromit is always surrounded by a Cr-magnetite rim and it was formed as a reaction product owing to the irreversible dissolution of primary chromite cores. The dissolution of these cores provided the essential components for ferritchromit growth. Zn was introduced into the chromite cores and ferritchromit rims during the formation of the latter. Step-scan profiles have shown that the Zn content in the cores increases from the centre to their outer border, where they show the highest Zn values. It is suggested that Zn was introduced by the fluid phase involved in the alteration process that affected the cores and lead to the formation of the zoned chromite grains. This alteration process was also responsible for the changes in [Cr/(Cr + Al)] and [Mg/(Mg + Fe)] ratios.

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Jacob, K. T., G. M. Kale und K. P. Abraham. „Electrochemical Determination of Gibbs Energies of Formation of Calcium Chromite and Chromate“. Journal of The Electrochemical Society 139, Nr. 2 (01.02.1992): 517–20. http://dx.doi.org/10.1149/1.2069248.

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Matern, K., und T. Mansfeldt. „Chromate adsorption from chromite ore processing residue eluates by three Indian soils“. Environmental Chemistry 13, Nr. 4 (2016): 674. http://dx.doi.org/10.1071/en15147.

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Environmental context Chromate (CrO42–)-containing waste is illegally dumped in some places in the state of Uttar Pradesh, north India, although CrO42– is known to be toxic and carcinogenic. Because CrO42– is leached from the landfills, this study investigated the adsorption of CrO42– by soils. The results indicated that CrO42– is highly leachable and adsorption is inhibited, which leads to contamination of the groundwater and drinking water in this area. Abstract Chromite ore processing residue (COPR) is a harmful waste of the chromate (CrO42–) extraction roasting process. Nevertheless, deposition of COPR in uncontrolled surface landfills is still common practice in some countries. Leaching of carcinogenic CrO42– and contamination of groundwater is a key environmental risk arising from COPR sites. The objective of this study was to evaluate the adsorption behaviour of CrO42– from COPR eluates by soils. Prior to the adsorption experiments, batch studies at varying solid-to-liquid ratios were performed to evaluate the solubility of CrO42– from COPR. Chromate adsorption experiments were carried out in a batch system with eluates obtained from two different Indian COPRs to assess potential groundwater contamination by CrO42–. Three soils that originate from the surroundings of COPR dumping sites were chosen in order to provide realistic adsorption conditions. The data were evaluated with the Freundlich and Langmuir equation. Chromate adsorption was inhibited because of the high pH of both of the soils (pH 6.7 to 7.2) and the eluates (pH 12.3) as well as the high carbonate concentration of the eluates. The extent and behaviour of CrO42– adsorption from both eluates was similar. The main difference between the eluates was the solubility of CrO42– from COPR and thus the initial CrO42– concentration. The results presented in this study provide an improved understanding of the mobility of CrO42– in the affected area, which is important because the local population uses the groundwater not only for the needs of livestock but also as drinking water.

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Dyussenova, S., B. Kenzhaliyev, R. Abdulvaliyev und S. Gladyshev. „The method of processing technogenic tailings of chromium“. Journal of Mining and Metallurgy A: Mining 56, Nr. 1 (2020): 15–22. http://dx.doi.org/10.5937/jmma2001015d.

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Taking into account the existing demand for chromium concentrates, the extraction of chromium from technogenic formations of sludge storages of the tailings of chromium ore beneficiation is an important practical task. The comprehensive utilization of beneficiation sludge will increase the profitability of production and solve the environmental problems of the region. The importance of solving the problem of involving in processing tailings is connected not only with the environment but also with the need to increase the production of chromium. Modern gravity enrichment technologies make it possible to efficiently produce chromium concentrates from large and medium fractions of chromite-containing ores, while finely divided sludge is practically not extracted due to the difficulty of separating complex minerals into concentrates and waste rock. This paper presents the results of studies on the gravity processing of tailings. The technology includes the enrichment of the fine fraction-0.2+0 mm of tailings of the dressing plant of chromite-containing ores by gravity methods using a KNELSON centrifugal separator. In technology, the efficiency of the operation of gravity enrichment is provided by the preliminary activation of the fine fraction in a solution of sodium bicarbonate (NaHCO3). With gravitational enrichment, the total chromite concentrate was obtained containing 51.3% Cr2O3. The output of concentrate was 41.7%. The extraction of Cr2O3 in the concentrate was 68.1%.

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Iwata, Naoki, und Susumu Kitanaka. „New Cannabinoid-Like Chromane and Chromene Derivatives from Rhododendron anthopogonoides“. CHEMICAL & PHARMACEUTICAL BULLETIN 59, Nr. 11 (2011): 1409–12. http://dx.doi.org/10.1248/cpb.59.1409.

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Christiansen, F. G., und N. Ø. Olesen. „Large skeletal chromites in the Vourinos ophiolite, Greece“. Bulletin of the Geological Society of Denmark 38 (25.04.1990): 33–42. http://dx.doi.org/10.37570/bgsd-1990-38-03.

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Exceptionally large skeletal chromites, up to several cm across, from harzburgite veins in the Vourinos ophiolite, Greece have been described in detail using microstructural and fabric methods of silicate minerals combined with S. E. M. studies of chromite. Inferred from olivine fabric data, the harzburgite veins with the skeletal chromites have suffered only minor deformation (both in the ductile and brittle regime) compared to the highly deformed dunite host rock. The S. E. M. observations (electron channeling patterns) demonstrate (1) the large grain size of the chromite and (2) that the numerous grain facets are dominated by {111} lattice orientations. Furthermore the chromite displays local plastic deformation and it is highly fractured and typically displays tilts/rotations -1 ° of the lattice across the fractures. The harzburgite veins formed during a late-tectonic stage of mantle flow. A metamorphic segregation model, where the skeletal growth of chromite was caused by super-saturation of Cr during diffusion, is the most likely mode of formation.

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Setthayanond, Jantip, Porntip Sae-Bae, Podjanalak Chaiyapongputti und Phussadee Lim. „Chromium (VI) Adsorption Study Using Bio-Adsorbent Material Derived from Tamarind-Seed Testa“. Key Engineering Materials 723 (Dezember 2016): 534–39. http://dx.doi.org/10.4028/www.scientific.net/kem.723.534.

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In this research, the chromium (VI) adsorption in potassium chromate (K2CrO4) and potassium dichromate (K2Cr2O7) was studied with the low-cost adsorbent derived from sweet tamarind seeds obtained from the food processing industry in Thailand. The tamarind-seed testa was prepared by decoloring the tamarind-seed husks in boiling water and 1% NaOH solution followed by bleaching in H2O2 solution. The major components found in the tamarind-seed testa were alkali hydrolysable, low molecular-weight carbohydrates. The study found that the adsorbent material derived from tamarind–seed testa could well adsorb chromium ions in both chromium compound solutions at pH 2. The adsorption took place rapidly within the first 4 hours and then gradually declined until reaching adsorption equilibrium in 12 hours. Adsorption of chromium (VI) from potassium chromate solution was superior to that from potassium dichromate. Chromium adsorption at pH 2 fitted well with Langmuir and Freundlich isotherms. The adsorption mechanism in both solutions was a monolayer chemical adsorption rather than multilayer physical adsorption. The adsorbent could almost completely remove chromium in potassium chromate (90% removal) while it could remove 57% chromium from potassium dichromate solution when the initial chromium concentration of 100 mg/l was employed.

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Memon, Shahabuddin, D. Max Roundhill und Mustafa Yilmaz. „Remediation and Liquid-Liquid Phase Transfer Extraction of Chromium(VI). A Review“. Collection of Czechoslovak Chemical Communications 69, Nr. 6 (2004): 1231–50. http://dx.doi.org/10.1135/cccc20041231.

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Chromium(VI) is a widely used industrial chemical, and is generally considered to pose a greatest human health risk because it is more toxic, more soluble, and more mobile than chromium(III). Workers in industries that use chromium, in particular stainless steel welding, chromate production, chromium plating, and chrome pigment industries, where exposure via inhalation of aerosols is primarily to hexavalent chromium, are at increased risk of chromium effects. In this article we demonstrate various studies regarding remediation methods in particular liquid-liquid extraction of chromate and dichromate anions with various functionalized calixarenes. This review article briefly discusses various molecular designs of calixarene-type macrocycles for chromium(VI) oxoanion recognition, and gives examples on the relationship between structure and selectivity. The article does not, however, attempt to cover all of the different approaches to chromium(VI) extraction. A review with 73 references.

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Saeed, Muhammad, Malika Rani, Kiran Batool, Hafiza Batool, Aisha Younus, Sikander Azam, Arshad Mehmood et al. „Synthesis and Fabrication of Co1−xNixCr2O4 Chromate Nanoparticles and the Effect of Ni Concentration on Their Bandgap, Structure, and Optical Properties“. Journal of Composites Science 5, Nr. 9 (14.09.2021): 247. http://dx.doi.org/10.3390/jcs5090247.

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In the present work, cobalt-chromite-based pigment Co1-xNixCr2O4 chromate powder and nanoparticles with various transition metal concentrations (x = 0.2, 0.4, 0.6, and 0.8) were manufactured by applying aqueous synthesis approaches and sol–gel synthesis routes. XRD analysis of the powder shows that all samples formulated by the sol–gel method were crystalline with a spinel structure. Chromites show green color with a higher nickel concentration, while Co-substituent shows blackish pigments. Samples were annealed at distinct temperatures ranging from 600 °C to 750 °C. The nanoparticles obtained were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (RS), photoluminescence (PL), and energy-dispersive X-ray spectroscopy (EDS). The particle size of the parent compound (CoCr2O4) ranges from 100 nm to 500 nm, as measured by SEM. The tendency of particles to form aggregates with increasing annealing temperature was observed. These compounds may be successfully used as an effective doped nickel-cobalt ceramic pigment.

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V. H. Martirosyan, M. E. Sasuntsyan und V. V. Savich. „OBTAINING OF FERROSILICOCHROMIUM POWDER ALLOY BY SILICOTHERMIC REDUCTION AND STUDY OF THE MECHANISM OF THIS PROCESS“. International Academy Journal Web of Scholar 1, Nr. 1(31) (31.01.2019): 11–17. http://dx.doi.org/10.31435/rsglobal_wos/31012019/6307.

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The process of obtaining a powder ferrosilicochromic alloy by the method of silicothermic reduction of local chromites and slags of copper smelters was investigated. The mechanism of this process has been studied. It is established that the best results are obtained in the case of slag / chromite ratio = 1: 1, when an alloy with microdispersed structure and high strength is obtained. The optimum composition of the resulting alloy is as follows: 35,1% Fe; 36,35% Si and 28,53% Cr, with a metal yield of 98,4%. The obtained alloy powder can be used as an acidified and alloying additive to chromium- and silicon-containing stainless composite materials. The aspects of the process for obtaining FeSiCr alloy have been developed. The maximum temperature (Tc) and the linear propagation velocity of the combustion wave (Uv) are determined graphically. The mechanism of the formation of FeSiCr in the SHS process is explained.

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Fujie, Koichi, Tomohiko Tsuchida, Kohei Urano und Hisao Ohtake. „DEVELOPMENT OF A BIOREACTOR SYSTEM FOR THE TREATMENT OF CHROMATE WASTEWATER USING ENTEROBACTER CLOACAE HO1“. Water Science and Technology 30, Nr. 3 (01.08.1994): 235–43. http://dx.doi.org/10.2166/wst.1994.0110.

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A novel bioreactor system was developed for tbe simultaneous treatment of toxic and mutagenic hexavalent chromium (chromate) and high strengtb organic pollutants by introducing chromate-resistant and chromatereducing bacteria Enterobacter cloacae strain HO1. Growth and chromate reducing characteristics of E. cloacae HO1 were extensively investigated to setup the bioreactor system and to clarify the optimal operating conditions of it. To enrich active E. cloacae HO1 in the bioreactor, the aerated cultivation with oxidation-reduction potential (ORP) control was successfully applied. Chromate and organic substrates in the artificial wastewater and in the metal plating wastewater were satisfactorily removed in the bioreactor. The reduced chromate was removed by precipitation as chromium hydoxide from the wastewater. The rate of chromate reduction was as high as 500 mg-chromate/g-microbes as particulate organic carbon and 10-60 gchromate/m3.h in the bioreactor.

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Fébel, Hedvig, B. Szegedi und Szilvia Huszár. „Absorption of inorganic, trivalent and hexavalent chromium following oral and intrajejunal doses in rats“. Acta Veterinaria Hungarica 49, Nr. 2 (April 2001): 203–9. http://dx.doi.org/10.1556/004.49.2001.2.10.

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The intestinal absorption of trivalent and hexavalent chromium (Cr) given orally (experiment I) or infused in the intestine (experiment II) was investigated in rats. The nonabsorbable form of chromium (51Cr2O3) and water-soluble and more absorbable Na251CrO4 (the hexavalent form of Cr) were compared. Total retention of chromium given orally ranged around 15 percent of the dose, regardless of the chromium compounds applied. The absorption rate of chromic oxide, which is considered a nonabsorbable compound, was 14.4 as a percentage of chromium intake. This result indicates that some loss of chromium has to be taken into account in metabolic trials made by the indicator method. In isolated rat intestine, from the injected Cr 2.5% of chromic oxide and 43.2% of sodium chromate were absorbed during an hour (experiment II). The absorbed chromium was transferred to the liver where the liver tissue retained 10.9% of chromic oxide and 51.1% of sodium chromate. Radioactivity of v. cava caudalis following intestinal injection of Na2CrO4 was thirtyfold greater than after Na2CrO4 dosing. This phenomenon can be explained by the lower blood clearance of chromate. Different absorption rate of chromate depending on the route of administration could be due to the fact that the hexavalent form given orally was reduced to Cr3+ in the acidic environment of the stomach. When Na2CrO4 was infused directly in the intestine of rats, such reduction could not occur. This means that the acidic gastric juice might play a role in inhibiting the intestinal absorption of Na2CrO4 when this compound is given orally.

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Salarzadeh, I., und SA Tariq. „The Reactions of 11 Compounds of Copper, Silver and Chromium With the Molten Lithium-Sodium-Potassium Carbonate Eutectic“. Australian Journal of Chemistry 39, Nr. 7 (1986): 1119. http://dx.doi.org/10.1071/ch9861119.

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The reactions of Cu2Cl2, CuCl2, AgCl , AgNO3, CrCl2, CrCl3, Cr2O3, K2CrO4, K2Cr2O7, K2Cr3O10 and CrO3 with the molten lithium-sodium-potassium carbonate eutectic were investigated under argon as well as carbon dioxide atmospheres. Copper(I) and copper(II) chlorides reacted to produce CuO with the evolution of CO and CO2 respectively. The silver compounds reacted to produce silver metal and a mixture of O2 and CO2. Chromium(II) and chromium(III) chlorides and Cr2O3 were converted into alkali-metal chromate(III) species. Potassium chromate(VI) was found to be stable in the eutectic. Chromium(VI) oxide, dichromate(VI) and trichromate (VI) accepted oxide ions from the carbonate eutectic, and were ultimately converted into chromate(VI). Carbon dioxide was evolved in all the reactions of the chromium compounds; however, the CrCl2 reaction produced a mixture of CO and CO2. The temperature ranges of the reactions and their stoichiometries were established.

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Colás, Vanessa, Ignacio Subías, José María González-Jiménez, Joaquín A. Proenza, Isabel Fanlo, Antoni Camprubí, William L. Griffin, Fernando Gervilla, Suzanne Y. O’Reilly und Monica F. Escayola. „Metamorphic fingerprints of Fe-rich chromitites from the Eastern Pampean Ranges, Argentina“. Boletín de la Sociedad Geológica Mexicana 72, Nr. 3 (28.11.2020): A080420. http://dx.doi.org/10.18268/bsgm2020v72n3a080420.

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Chromitites hosted in the serpentinized harzburgite bodies from Los Congos and Los Guanacos (Eastern Pampean Ranges, north Argentina) record a complex metamorphic evolution. The hydration of chromitites during the retrograde metamorphism, their subsequent dehydration during the prograde metamorphism and the later-stage cooling, have resulted in a threefold alteration of chromite: i) Type I is characterized by homogeneous Fe3+- and Cr-rich chromite; ii) Type II chromite contains exsolved textures that consist in blebs and fine lamellae of a magnetite-rich phase hosted in a spinel-rich phase; iii) Type III chromite is formed by variable proportions of magnetite-rich and spinel-rich phases with symplectitic texture. Type I chromite shows lower Ga and higher Co, Zn and Mn than magmatic chromites from chromitites in suprasubduction zone ophiolites as a consequence of the redistribution of these elements between Fe3+-rich non-porous chromite and silicates during the prograde metamorphism. Whereas, the spinel-rich phase in Type III chromite is enriched in Co, Zn, Sc, and Ga, but depleted in Mn, Ni, V and Ti with respect to the magnetite-rich phase, due to the metamorphic cooling from high-temperature conditions. The pseudosection calculated in the fluid-saturated FCrMACaSH system, and contoured for Cr# and Mg#, allows us to constrain the temperature of formation of Fe3+-rich non-porous chromite by the diffusion of magnetite in Fe2+-rich porous chromite at <500 ºC and 20 kbar. The subsequent dehydration of Fe3+-rich non-porous chromite by reaction with antigorite and chlorite formed Type I chromite and Mg-rich olivine and pyroxene at >800 ºC and 10 kbar. The ultimate hydration of silicates in Type I chromite and the exsolution of Type II and Type III chromites would have started at ~600 ºC. These temperatures are in the range of those estimated for ocean floor serpentinization (<300 ºC and <4 kbar), the regional prograde metamorphism in the granulite facies (800 ºC and <10 kbar), and subsequent retrogression to the amphibolite facies (600 ºC and 4-6.2 kbar) in the host ultramafic rocks at Los Congos and Los Guanacos. A continuous and slow cooling from granulite to amphibolite facies produced the exsolution of spinel-rich and magnetite-rich phases, developing symplectitic textures in Type III chromite. However, the discontinuous and relatively fast cooling produced the exsolution of magnetite-rich phase blebs and lamellae within Type II chromite. The P-T conditions calculated in FCrMACaSH system and the complex textural and geochemical fingerprints showed by Type I, Type II and Type III chromites leads us to suggest that continent-continent collisional orogeny better records the fingerprints of prograde metamorphism in ophiolitic chromitites.

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48

Prasad, Sanjay, Manoj Kumar und N. S. Randhawa. „Processing of Chromite Overburden by Soda Roasting to Recover Chromium as Sodium Chromate“. Transactions of the Indian Institute of Metals 74, Nr. 9 (17.06.2021): 2221–30. http://dx.doi.org/10.1007/s12666-021-02320-8.

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49

Yildiz, Kenan, und I. Ayhan Sengil. „Investigation of efficient conditions for chromate production from chromite concentrate by alkali fusion“. Scandinavian Journal of Metallurgy 33, Nr. 4 (August 2004): 251–56. http://dx.doi.org/10.1111/j.1600-0692.2004.00694.x.

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50

Wang, Y., L. Wang, J. Yu und K. C. Chou. „Kinetics of carbothermic reduction of synthetic chromite“. Journal of Mining and Metallurgy, Section B: Metallurgy 50, Nr. 1 (2014): 15–21. http://dx.doi.org/10.2298/jmmb130125008w.

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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, thus, kinetic investigation of synthetic FeCr2O4 with different amount of carbon were carried out in the temperature range of 1473K to 1673K under both isothermal and non-isothermal mode. The iron can be easily reduced compared with chromium. And higher reduction degree of chromite can be achieved by increasing temperature and carbon content. With the supporting of X-ray Diffraction and Scanning Electron Microscope methods, the formation of metallic products followed the sequence: Fe-C alloy, (Fe,Cr)7C3and Fe-Cr-C alloy. Kinetics analysis showed that the first stage was controlled by nucleation with an apparent activation energy of 120kJ/mol, while the chromium reduction was controlled by crystallochemical transformation with an apparent activation energy of 288kJ/mol.

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