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The redox state of chromium ores of the main industrially significant types, developed in ultramafic rocks of the Rai-Iz–Voykar complex of the Polar Urals, was studied. The chromitites occurring in various geological settings—dunite–harzburgite complex and large dunite bodies metamorphosed to different degrees—have been investigated. For the first time, oxygen fugacity and temperature of the formation of chromium ores, based on olivine–spinel equilibrium, were studied in more than representative samples from the Rai-Iz and Voikar–Synya massifs. The Fe/(Fe + Mg) of minerals increases linearly from chromitites to their host ultramafic rocks at each of the studied objects. The temperature of olivine–spinel equilibrium in chromitites varies within 550–800°С. The oxygen fugacity in aluminous chromitites averages FMQ +0.5–1.5 log units; in medium chromium, FMQ +1.5–2.5 log units; in high-chromium ones, more than +2.5 log units relative to the FMQ buffer. The oxygen fugacity in densely disseminated chromitites is 0.5–1 log units higher than in poorly disseminated and rarely disseminated ones. The T–fO2 values correspond to the crustal conditions and are close to those established in the metaultramafic rocks of the studied massifs. The data obtained may indicate that the concentration of the ore component and the formation of chromium ore deposits occur not only in mantle or lower crustal conditions, characterized by fO2 values close to the FMQ buffer, but also as a result of ultramafic crustal metamorphism occurring in an oxidizing environment. [ABSTRACT FROM AUTHOR]

The mineral base state for Russian manganese and chromium ores does not allow our country in the foreseeable future to achieve complete self-sufficiency and to abandon imported raw materials. But the problem can be significantly mitigated due to the partial involvement in the operation of the proven ore reserves with relatively low quality. Based on the performed research, four main directions are formulated that would make it possible to put into operation a number of previously known but out-of-use (or poorly used) deposits of poor mineral raw materials for the ferroalloy production: (1) selective reduction of ore components divided into metal semi-products with a low main component content suitable for the smelting of the alloyed steel grades and an oxide product with a high content of Mn or Cr oxides suitable for the smelting of the high-grade ferroalloy grades; (2) rational additional charging of poor domestic ores to beneficiate imported ones to obtain standard grades of ferroalloys; (3) smelting of new alloys, including marketable high-carbon ferromanganese and ferrochrome with reduced main component content, high silicon content, and complex ferroalloys containing, in addition to the main, other elements necessary for the composition of a number of steel grades (silicon, manganese, titanium, etc.); and (4) production of limited grades of ferro-, silico-manganese, and chromium and their application in smelting of the ferroalloys refined grades. [ABSTRACT FROM AUTHOR]

Ferroalloy production is an important branch of metallurgy having a great impact on its development since the treatment of liquid metals by ferroalloys remains one of the main methods to regulate the quality of steel, cast iron, and nonferrous alloys. Manganese is the most essential element to treat ferrous and non-ferrous metals. A need for manganese alloys in Russia averages to 600-650 metric tons per year, but only a half of the quantity is satisfied by the domestic production. In contrast to manganese alloys, Russia provides itself with chromium ferroalloys obtained with the use of foreign raw materials. Domestic ores are used in limited quantities. Taking into account the strategic importance of ferroalloy industry and the necessity to create and include manganese and chromium ore bases, as well as the other basic problems, the achievement of the goals has to be implemented by enterprises with the help of the State. The output of ferrosilicon and crystal silicon in the Russian Federation exceeds its consumption in the country due to raw material reserves (quartzite, quartz), high productive capacity, and consumer demands. Ferroalloy enterprises in Russia produce ferrovanadium, ferromolybdenum, ferroniobium, ferrotungsten, ferrotitanium, and ferronickel. A traditional challenge for ferroalloy enterprises in Russia is improving the competitiveness at the expense of reducing production costs, improving the production quality, and solving the issue of import substitution for certain types of ferroalloys. [ABSTRACT FROM AUTHOR]

Experimental and industrial data are obtained about the heating rate and degree of Cr reduction for a vertical section of the workspace of an ore reduction electric furnace during treatment of a mixture of lean and rich chromium ores in relation to melting period. A scheme of proposed for the temperature fields and degree of chromium reduction in reaction zones of an ore reduction furnace using data about physicochemical characteristics of the ore raw material, determined under laboratory conditions. It is shown that the degree of Cr reduction in the lower levels of the furnace bath before tapping reaches 95%, and at the end of tapping it reaches up to 85%. [ABSTRACT FROM AUTHOR]

In order to promote the recycling of by-product from Si wafer manufacturing process and to develop environment-friend and low cost process for ferrochrome alloy production, a basic study was performed on the preliminary reduction reaction between chromium ore and the Si sludge, comprised of SiC and Si particles, which is recovered from the Si wafer manufacturing process for the semiconductor and solar cell industries. Pellets were first made by mixing chromium ore, Si sludge, and some binders in the designed mixing ratios and were then treated at different temperatures in the 1116 °C-1388 °C range in an ambient atmosphere. Cordierite and SiO2 were confirmed to be formed in the products after the reduction. Additionally, metal particles were observed in the product with Fe, Cr, and Si components. It is found that temperatures above 1300 °C are necessary for the reduction of the chromium ore by the Si sludge. The reduction ratio for Fe was evaluated quantitatively for our experimental conditions, and the proper mixing ratio was suggested for the pre-reduction of the chromium ore by the Si sludge. This study provides basic information for the production of ferrochrome alloys on the pre-reduction of chromium ore using Si sludge. [ABSTRACT FROM AUTHOR]

It has been shown that EPA Method 3060A does not adequately extract Cr(VI) from chromium ore processing residue (COPR). We modified various parameters of EPA 3060A toward understanding the transformation of COPR minerals in the alkaline extraction and improving extraction of Cr(VI) from NIST SRM 2701, a standard COPR-contaminated soil. Aluminum and Si were the major elements dissolved from NIST 2701, and their concentrations in solution were correlated with Cr(VI). The extraction fluid leached additional Al and Si from the method-prescribed borosilicate glass vessels which appeared to suppress the release of Cr(VI). Use of polytetrafluoroethylene vessels and intensive grinding of NIST 2701 increased the amount of Cr(VI) extracted. These modifications, combined with an increased extraction fluid to sample ratio of ≥900 mL g-1 and 48-h extraction time resulted in a maximum release of 1274 ± 7 mg kg-1 Cr(VI). This is greater than the NIST 2701 certified value of 551 ± 35 mg kg-1 but less than 3050 mg kg-1 Cr(VI) previously estimated by X-ray absorption near edge structure spectroscopy. Some of the increased Cr(VI) may have resulted from oxidation of Cr(III) released from brownmillerite which rapidly transformed during the extractions. Layered-double hydroxides remained stable during extractions and represent a potential residence for unextracted Cr(VI). [ABSTRACT FROM AUTHOR]

Electrokinetics (EK) was investigated as a possible technique for in-situ treatment of leachable chromium at a built site contaminated with chromium ore processing residues (COPR). A preliminary EK experiment was carried out at the laboratory scale on an undisturbed COPR core sample. Methods applied for material and pore water characterization before and after EK treatment addressed physical aspects by laser diffraction granulometry, pycnometry and pore water content, mineralogical aspects by X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and chemical aspects by inductively coupled plasma-atomic emission spectroscopy and atomic absorption spectroscopy for elemental composition, spectrophotometry for Cr(VI) analysis, and potentiometry for pH determination. EK was run at 1 V/cm with no external constraints on current intensity. The EK experiment reached an extraction of 72% of the total leachable Cr(VI) after only 10 days of treatment and 84% after 20 days. Material texture, composition, and pH remained similar. These results indicate that EK presents a potential solution for extracting leachable Cr(VI) from COPR sites. The impounded COPR material appeared to be heterogeneous in composition at all scales, from field to lab sample, adding to the challenge of in-situ treatment. [ABSTRACT FROM AUTHOR]

The cocrystallization coefficients of Cr, V, and Fe (D Me/Fe ) in magnetite and sulfide minerals (pyrite, chalcopyrite, and Fe-containing sphalerite) in multiphase associations are determined in hydrothermal-growth experiments with internal sampling at 450 °C and 100 MPa (1 kbar). The results are compared with previous data on D Mn/Fe . Magnetite and pyrite are characterized by the highest D Me/Fe values for both Cr (1.2 and 2) and V (6.6 and 1.1). These minerals also show the highest mineral/solution distribution coefficients of Cr and V. For V and Cr in chalcopyrite, much lower D Me/Fe values (0.03 and 0.04, respectively) were obtained, which, however, are slightly higher than those for Mn in magnetite (0.01). Although the deposition of magnetite and iron sulfides has no significant effect on the evolution of Mn in solution and Mn-Fe partitioning, crystallization of magnetite and pyrite favors a decrease in Cr and V contents relative to Fe content in solution. The data obtained can be used to reconstruct the chemical composition of paleofluids. Spinel minerals with close contents of Mn, V, and Cr can form through a hydrothermal process provided that the solutions are highly enriched in Mn relative to Fe and have V and Cr contents close to the Fe one. Such solutions seem to be exotic. Usually, a magnetite-forming hydrothermal fluid contains V and Cr as millionths of Fe, while the Mn content in it can be of the same order of magnitude as the Fe content. The data obtained may be of interest for reconstructing the evolution of the chemical composition of the World Ocean in different geologic periods. The study has shown that the bulk distribution coefficient of variable-valence elements between mineral and hydrothermal solution varies over a wide range of values even at constant pressure, temperature, and solution composition and can be used only for qualitative estimation of the element compatibility. In contrast, the bulk cocrystallization coefficient of chemically similar elements is less dependent on physicochemical conditions, has a nearly three times lower variation coefficient, and permits an element partitioning analysis in heterogeneous mineral-fluid systems. [ABSTRACT FROM AUTHOR]

In order to master the partition between metal and slag for high chromium vanadium titanium magnetite in ironmaking process, the same batch of sinter, pellet, hot metal and slag were investigated mainly from two viewpoints of phase composition change and distribution of valuable components in this study. Chemical analysis, XRD and SEM-EDS analysis, material balance and distribution of valuable components reveal that the total input-output amounts of valuable components are nearly balanced under the stable operation condition. 98.60% of iron, 86.71% of vanadium, 83.73% of chromium and only 6.48% of titanium have passed to hot metal. The distribution of titanium and silicon between hot metal and slag was investigated, which is in accordance with the previous studies in the laboratory condition. The phase composition change process of vanadium is V2O3 [V]. The reduction process of chromium oxide is Cr2O3 [Cr]. The titanium oxide is partially reduced into the hot metal in the hearth by the reaction: TiO2 [Ti], then the dissolved titanium can easily react with C and N2 forming Ti(C,N). [ABSTRACT FROM AUTHOR]

A greenhouse pot experiment was conducted to evaluate the feasibility of using a native ornamental plant, Mesua ferrea L. as phytostabilizer for chromium ore tailings (COT) and to assess the metal accumulation capacity. Different ratios of soil and COT were taken in pots and sowed with seeds of M. ferrea. Plants were harvested at various intervals and separated into roots and shoots for analysis of metal concentrations and physiological characteristics of the plants. The study revealed that the plant has great tolerance and stronger ability to accumulate Cr. The results suggested an increase in growth, chlorophyll content, antioxidant activities, as well as metal accumulation capacity of M. ferrea with increasing proportion of COT in the soil. This indicates the plant's efficiency to overcome any stress generated due to excess of chromium as well as other heavy metals. The order of accumulation of heavy metals was observed to be Fe>Cr>Ni>Cd>Co. The accumulation of Cr was higher in root compared to that in shoot. M. ferrea has found to be potential as a native species candidate for phytostabilization of chromiummine tailings. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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Cr(VI) is an important contaminant found at sites where chromium ore processing residue (COPR) is deposited. No low cost treatment exists for Cr(VI) leaching from such sites. This study investigated the mechanism of interaction of alkaline Cr(VI)-containing leachate with an Fe(II)-containing organic matter rich soil beneath the waste. The soil currently contains 0.8% Cr, shown to be present as Cr(III)(OH) 3 in EXAFS analysis. Lab tests confirmed that the reaction of Cr(VI) in site leachate with Fe(II) present in the soil was stoichiometrically correct for a reductive mechanism of Cr accumulation. However, the amount of Fe(II) present in the soil was insufficient to maintain long term Cr(VI) reduction at historic infiltration rates. The soil contains a population of bacteria dominated by a Mangroviflexus -like species, that is closely related to known fermentative bacteria, and a community capable of sustaining Fe(III) reduction in alkaline culture. It is therefore likely that in situ fermentative metabolism supported by organic matter in the soil produces more labile organic substrates (lactate was detected) that support microbial Fe(III) reduction. It is therefore suggested that addition of solid phase organic matter to soils adjacent to COPR may reduce the long term spread of Cr(VI) in the environment. [ABSTRACT FROM AUTHOR]

It is shown that ortho- and clinopyroxenes in mantle peridotites, which host different-scale chromite deposits, are marked by significant differences in the structure of rocks, composition of olivine and chromian spinel, and, primarily, content and distribution of the major ore-forming oxides therein. Enstatites and diopsides in peridotites from the southern Kempirsai Massif are notably depleted in the major oxides as compared to minerals in harzburgites from the Voykar-Synya Massif. The central portion of some large enstatite grains in peridotites from the Kempirsai Massif is marked by high contents of chromium oxide and alumina. Correlation of the prominent strain-mediated zonation in large relict pyroxene grains with decrease in CrO and AlO at their rims suggests an initially high content of these components in pyroxenes. Extremely narrow variation range of the composition of high-Mg olivine in harzburgites from the Kempirsai Massif and its relatively small grain size as compared to harzburgites from the Voykar Massif were also provoked by the high-temperature recrystallization of mantle rocks accompanied by the transition of Cr and Al from silicates (pyroxene) into ore mineral (chromian spinel). Redistribution of components and recrystallization of peridotites were likely caused by the emplacement of harzburgites by a large volume of fluid/melt, which reacted with the host rocks, and by the high rate of mantle deformation (contraction of olivine grains) during this process. Components (Cr, Al, Fe) needed for the formation of chromium ores were extracted from both rock-forming silicates and migrating melts. [ABSTRACT FROM AUTHOR]

A new metallurgical process for extracting chromium from chromite ore is proposed to overcome the severe chromium (VI) pollution in chromate production industry. When the 60 wt.% KOH solution was used to decompose chromite ore, the chromium and iron ions in chromite ore were oxidized into soluble K 2 CrO 4 crystal and insoluble KFe 3 O 5 particle, respectively. The chromium levels in the new residue meet the emission standard of chromium-containing waste due to the KFe 3 O 5 crystal's compact appearance, hence the pollution problem of chromite ore process residue is thoroughly resolved. The effect of the main variables on this clean metallurgical process was systematically investigated. Under the condition of leaching temperature 200 °C, oxygen partial pressure 2.0 MPa, and particle size 0.045–0.063 mm, the chromium extraction reached up to 99.4% after 5 h reaction. There is no product layer existing during the leaching process, and the reaction rate is controlled by the surface reaction. The resistances of oxygen transport during the leaching process were calculated step by step, and the surface chemical reaction was the main resistance factor that was consistent with the kinetics study. [ABSTRACT FROM AUTHOR]

The article focuses on a study which discusses compositions of peridotites in massifs of chromite chromium ores in ophiolites. According to the study, compositions of olivine, pyroxenes and chrome spinellide from different ophiolite massifs of the Urals, Kempirsai and Voykar–Synyin were analysed. The study predicts differences in the concentration and distribution of ore forming oxides between ortho and clinopyroxenes in mantle complexes with olivine and chromite deposits with ores.

Purpose: Wastes of unknown composition derived from the production of trivalent chromium (Cr(III)) salts used as tanning agents are deposited in the area of Kanpur, India. The questions of whether these samples are chromite ore processing residue (COPR) and whether Cr occurs in its toxic hexavalent form (Cr(VI)) arise. Materials and methods: Twenty-one samples from two disposal sites and surrounding soils were analyzed, specifically examining their elemental and mineralogical composition. Additionally, aqueous eluates with different liquid-to-solid ratios were performed and analyzed for Cr(VI). Results and discussion: The samples were classified in accordance to the sum of silicon and aluminum and the sum of calcium and Cr contents: uncontaminated, moderately contaminated, and highly contaminated material. Highly contaminated material exhibited extremely alkaline pH values up to 12.5 and total Cr contents ranging from 65.7 to 110 g/kg, whereas uncontaminated material had comparatively moderate pH values and Cr contents <1 g/kg. In total, seven crystalline phases commonly found in COPR were identified in the contaminated samples, of which five phases (brownmillerite, hydrocalumite, hydrogarnet, magnesiochromite, and periclase) are known to be able to accommodate Cr whereas hydrogarnet and hydrocalumite are the main host phases for Cr(VI). Batch tests showed that dissolution controlled the Cr(VI) concentrations in the eluates. Conclusions: Six samples were clearly identified as highly Cr-contaminated COPR. Leaching of Cr(VI) and resulting contamination of soils and water bodies is a key environmental risk arising from these COPR sites especially during the monsoon season. This situation is of particular concern as the local population use the highly Cr(VI)-contaminated water not only for the needs of livestock and irrigation but also as drinking water due to the absence of alternative water resources. [ABSTRACT FROM AUTHOR]

The preparation and characterisation of four chromium ore reference materials are described in this paper. The sample material for GCr-1, GCr-3 and GCr-4 was collected from chromite deposits in Tibet, Qinghai province and Inner Mongolia. GCr-2 is a composite sample from GCr-1 and GCr-4. Sample homogeneity was tested by WD-XRF and the relative standard deviations were < 1.0%. An F-test showed that all four materials were homogeneous. Thirteen laboratories involved in the inter-laboratory programme provided 672 determinations (eighteen oxides and elements). Sixteen components were characterised as certified values, of which Cr2O3 ranged from 17.59 to 57.80% m/m. The contents of FeO and CO2 were taken as reference values. [ABSTRACT FROM AUTHOR]

Abstract: Incidental ingestion of Chromite ore processing residue (COPR) particles poses a potential health risk. The purpose of this study was to determine the Cr bioaccessibility from COPR using the in vitro gastrointestinal (IVG) procedure. The bioaccessible Cr(VI) was 53.8% and 42.9%, respectively, in the gastric and intestinal phases from a total of 19490mgkg−1 Cr(VI) in COPR. Food intake including milk, dough, and ascorbic acid resulted in a significant decrease in Cr(VI) bioaccessibility. Some organic acids such as lactic, malic, and citric acid moderately reduced Cr(VI), while acetic acid exhibited no capacity for Cr(VI) reduction. The integrated area under the concentration–time curve (AUC) of the IVG extraction was used to calculate bioaccessibility. Compared with the bioaccessibility conventionally estimated using concentrations at the end of the extraction (CEP), the AUC technique should be implemented to confirm the accuracy of the IVG method when reduction of Cr(VI) occurs during the extraction. The absence of Cr(VI) phases in extracted residues as evidenced by XANES and XRPD analysis confirmed the Cr(VI) release and Cr(VI) reduction by food and ascorbic acid. With readily bioaccessible Cr(VI) and rapid human uptake, reduction of Cr(VI) might not be as effective a detoxification pathway as initially thought. [Copyright &y& Elsevier]

Chromatite (CaCrO4, tetragonal) is mainly known from Cr6+-contaminated soils associated with chromium ore processing residue. This extremely rare mineral was found at the Nabi Musa locality (Judean Desert, Israel), in a peculiar rock complex of the Mottled Zone. We have explored the possible mechanisms responsible for leaching Cr6+ from natural rocks, by means of field observations, batch experiments, thermodynamic modeling, and mineralogical analyses of the Nabi Musa rocks (XRPD, EMPA, SEM, FTIR, and optical microscopy). A remarkable feature of the Mottled Zone rocks is a broad occurrence of high- and ultrahigh-temperature combustion metamorphic rocks, with Cr3+ accumulated mainly in opaque minerals such as Fe-spinel, brownmillerite, and perovskite. Another feature of the Mottled Zone sequence is abundant Cr3+ (bentorite and volkonskoite) and Cr6+ mineralization (Cr6+-bearing ettringite and baryte-hashemite solid solution) in low-temperature hydrothermal veins. Field, mineralogical, and thermodynamic modeling data suggest that Cr was leached from Cr3+-bearing opaque minerals during late hydrothermal alteration of combustion metamorphic rocks by unusual hyperalkaline waters (pH up to 12). The Cr3+ was then oxidized to Cr6+, and subsequently partially immobilized in Cr6+-bearing ettringite. As a consequence of the highway construction across Nabi Musa hill in 2006, the buried veins filled by Cr6+-substituted ettringite were exhumed and exposed to supergene alteration. The ensuing decomposition of Cr6+-bearing ettringite was followed by Cr6+ release into pore waters in rainy seasons, and then by precipitation of chromatite on the evaporation barrier under the hard desert insolation in dry seasons. The chromatite formation has been due to both unique rock and water chemistry of the Mottled Zone sequence and to the arid climate of the Judean Desert. [ABSTRACT FROM AUTHOR]

The present work is part of an investigation towards the development of a process route for the extraction of metal values from slag, low grade ores and other oxidic materials such as spent refractories using molten salts in the temperature range 800–950°C. The present paper focuses on the recovery of metal values, primarily Cr and Fe, from electric arc furnace slag and chromite ore. The impact of different factors to the dissolution of slag, such as temperature, holding time, flux content and weight ratio of flux/slag was studied. Based on the optimised experimental factors, the salt bath containing metal values extracted from the slag/ore was electrolysed under an applied voltage of 2·8 V. The cathode deposit was subjected to SEM/EDS and XRD analyses, which confirmed the formation of CrFe alloy. The process was also extended towards the production of CrFe alloy directly from chromite ore. The results show that the molten salt extraction process offers a promising route towards the recovery of metal values from slags and low grade ores. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports an investigation into the possible fate of Cr(VI) that is migrating downwards from a chromium ore processing residue (COPR) tip into the underlying soils. This waste was deposited at a site in the north of England more than 100 years ago and is currently a cause for environmental concern because groundwater emerging from the waste is alkaline, visibly yellow and has an elevated Cr(VI) concentration. Sandy clay from immediately beneath the waste (assumed to be the topsoil layer prior to waste tipping) contains between about 600 and 3000mgkg−1 of Cr, and around 60% of 0.5N HCl extractable iron was present as reduced Fe(II). DNA fragments from soil bacteria were extracted from this soil, and microcosm experiments where the pH was adjusted to more neutral values showed that it contains a viable bacterial population capable of iron-reduction. This sandy clay layer, despite a pH value of 10.5, appears to be acting as a natural reactive zone beneath the waste as it is accumulating chromium. It is thought that the mechanism of Cr(VI) reduction is most likely to be an abiotic reaction with the Fe(II) present in the soil, and that Fe(II) in the soil is being replenished by microbial iron-reduction (although the rate of replenishment is unknown). [Copyright &y& Elsevier]

Knowledge of thermodynamic properties of chromium oxides in molten slags is very important for the optimization of the steel making processes of stainless and high-alloying steels as well as the processes of chromium ores. Despite this importance, the thermodynamic data for chromium oxides at steel making temperatures are still too scarce to meet the demand. Only a few experimental studies are found in the literature.[–] Chromium exists in the form of ions, namely, Cr2+, Cr3+, and even Cr6+ in oxide solutions. The fractions of these irons depend not only on temperature but also on the chemical potentials of chromium and oxygen in the system. In the slags of steel making, chromium would mostly take the form of Cr2+ and Cr3+. The difficulties associated with maintaining the fractions of these ions and accurate determination of the same are among the main reasons for the scarcity of thermodynamic data. For example, Cr2+ easily reacts with lixiviating impregnant and forms intermediates in wet chemical analysis due to its unstable nature. [ABSTRACT FROM AUTHOR]

This article discusses how erroneous sample preparation can alter conclusions drawn from qualitative and quantitative X-ray powder diffraction analyses of environmental samples. The authors suggest that mechanical pulverization using non-polar fluids, namely cyclohexane, was the optimal method in determining the reactive potential of chromite ore processing residue (COPR), by reliably quantifying the brownmillerite content, the major unstable mineral phase in COPR. Using water during milling caused extensive hydration reactions and yielded nonrepresentative results for COPR mineralogy. Complementary hand pulverization proved necessary to preserve softer minerals. Similar effects may occur in most reactive environmental media.

The article provides information on the crocoite mineral. The chromium-essential minerals of interest to the collector include the colorful species vauquelinite, phoenicochroite, uvarovite, and crocoite. It is essentially unique in appearance, occurring most commonly in brilliant red to red-orange prismatic crystal groups of decided beauty and delicacy. It is an uncommon secondary mineral formed in the oxidized portions of lead deposits contiguous to or hosted in chromium-bearing rocks.

Abstract: Chromite ore processing residue (COPR) waste from a former chromium chemical works (1830–1968) is still contaminating groundwater in Glasgow, Scotland, with carcinogenic hexavalent chromium, Cr(VI). An integrated analytical, experimental and modelling approach has identified and accounted for mineral phases and processes responsible for the retention and release of Cr(VI) under prevailing field conditions. Both the nature of mineral phase retention and the buffered high pH of the sites, however, militate against direct remediative treatment of the source material, for example by the application of generic methods (e.g. FeSO4) that have been successfully employed elsewhere for the reduction of Cr(VI) to Cr(III) in other matrices. The interception and treatment of groundwater to remove Cr(VI) and the capping of sites to reduce human exposure to airborne Cr(VI)-contaminated dust may well be more realistic and effective, at least in the short to medium term. [Copyright &y& Elsevier]

Chromium has been widely used in many industrial applications. As a result of chromite ore processing, large amounts of chromite ore processing residue (COPR) material that can be classified as hazardous have been produced and released into the environment. Therefore, knowledge of migration behavior and leaching rates of chromium through waste materials are of primary concern for environmentally sound management of hazardous wastes. Leaching rates of total Cr and Cr(VI) were studied experimentally using laboratory columns packed with COPR material produced by a sodium chromite plant. Based on the experimental results, the present study aims, through mathematical modeling, to understand the dissolution kinetics of chromium during leaching of COPR material and to investigate the effectiveness of intermittent leaching, which involves a sequence of batch (dissolution) and mass flushing (leaching) operational modes. Modeling results show that a coupled system of two first-order differential equations was able to capture the essential characteristics of leaching behavior of COPR material. In addition, the kinetics of chromium dissolution from COPR appeared to be controlled by the difference between aqueous phase concentration and saturation concentration (effective solubility), by the mass fraction of dissolvable chromium remaining in the solid phase, and finally, by the contribution of a constant dissolution rate manifested as a steady-state tailing behavior. As a result of performed simulations it was seen that intermittent leaching could be 65 and 35% more effective than continuous leaching for total Cr and Cr(VI) removal, respectively. [ABSTRACT FROM AUTHOR]

Pseudo-ternary compounds of LiO0.5–X–TiO2 (X: FeO1.5, CrO1.5 and NiO) system were prepared using a fully automatic combinatorial robot system with the following functions: weighing and mixing of starting materials, heat treatment, and X-ray diffraction analysis. The following crystal structures were obtained by means of heat treatment at 1373 K: ramsdellite, spinel, pseudobrookite, rock salt, hematite and rutile. Furthermore, the composition range of the products with a ramsdellite-type structure in LiO0.5–X–TiO2 (X: FeO1.5, CrO1.5 and NiO) system was considered to have a relationship to the ionic radii of the substitutional transition metals Fe3+, Cr3+ and Ni2+ for Ti4+ in octahedral site. It was found that solubility limits of 3d elements in lithium titanium oxide with ramsdellite structure were investigated in a shorter time by combinatorial method. [Copyright &y& Elsevier]

The effect of dispersion and ensembling mode of chromium oxide nanocrystals in bulk xerogels and aerogels on their performance as well as efficiency of high surface area chromia aerogel as catalysts support were investigated in complete ethylacetate (EA) oxidation. Two series of chromia catalysts with a structure of α-Cr2O3 (7–110 m2 g−1) and α-CrOOH (230–735 m2 g−1) were tested in EA complete oxidation as a model reaction for VOC combustion. For α-Cr2O3, the specific activity increased 3.3 times with decreasing the crystal diameter from ∼100 to 13 nm. For α-CrOOH materials, where the surface area was determined by the different packing mode of primary nanoparticles of the same size (3–5 nm), the similar specific rate constants were measured with all the tested samples. The activity of the chromia aerogel (α-CrOOH, 630 m2 g−1) was four times higher compared with 0.5% Pt/Al2O3 and 30 times higher relative to 30% Cr2O3/SiO2. Oxidative treatment (O2) at elevated temperatures converts both phases to CrO2, in case of α-Cr2O3—only in the crystals surface layer. In both reduced and oxidized states, high concentration of surface oxygen vacancies were detected in α-Cr2O3 and α-CrOOH catalysts. A redox cycle Cr(III)[ ]OH↔Cr(IV)[O]O which determines the catalysts performance at the surface of both types of bulk chromia materials was proposed. Promotion of high surface area chromia aerogel with Pt, Au, Mn and Ce increased its activity in EA complete oxidation by a factor of 1.25–2.7. Addition of Pt, Mn to ceria-promoted chromia aerogel has a significant effect, yielding a high specific rate constant. Promotion with Ce- and Mn-additives improved the efficiency of redox cycle in Cr-aerogel and increased the concentration of surface oxygen vacancies. [Copyright &y& Elsevier]

Chromite ore processing residue (COPR), derived from the so-called high lime processing of chromite ore, contains high levels of Cr(III) and Cr(VI) and has a pH between 11 and 12. Ferrous sulfate, which is used for remediation of Cr(VI) contamination in wastewater and soils via reduction to Cr(III) and subsequent precipitation of iron(III)/chromium(III) hydroxide, has also been proposed for remediation of Cr(Vl) in COPR. Instead, however, addition of FeSO[sub 4] to the infiltrating solution in column experiments with COPR greatly increased leaching of Cr(VI). Leached Cr(Vl) increased from 3.8 to 12.3 mmol kg[sup -1] COPR in 25 pore volumes with 20 mM FeS0[sub 4], reaching solution concentrations as high as 1.6 mM. Fe(II) was ineffective in reducing Cr(Vl) to Cr(III) because it precipitated when it entered the column due to the high pH of COPR, while Cr(VI) in solution was transported away with the infiltrating solution. The large increase in leaching of Cr(VI) upon infiltration of sulfate, either as FeS0[sub 4] or Na[sub 2]SO[sub 4], was caused by anion exchange of sulfate for chromate in the layered double hydroxide mineral hydrocalumite, a process for which scanning electron microscopy with energy-dispersive X-ray microanalysis provided direct evidence. [ABSTRACT FROM AUTHOR]

The article presents an overview of chromium contamination issues in the South-East of Glasgow and the potential for remediation. Chromite ore processing residues arising from the works were used as infill material across large tracts of south-east Glasgow. Glasgow City Council (GCC) identified 15 sites where elevated concentrations of hexavalent chromium extended to depths of 10m in places. The investigation of remedial options for the Glasgow sites followed on from this series of investigations, which were undertaken by Dames and Moore on behalf of GCC in 1993.

The article focuses on the leaching characteristics of chromite ore processing residue. Chromite ore processing residue is produced during the manufacture of chromates and dichromates. It will be shown that chromium release is dominated by a small proportion of soluble chromium phases, independent of the bulk chromium content of the material. Chromite ore processing residue from a site in England has been investigated using XRF, SEM and EDX analysis, batch tests and geochemical modelling.

The article presents analytical characterisation of solid and solution-phase chromium species at chromite ore processing residue (COPR)-contaminated sites. The solid phases present in COPR from three of the sites investigated were identified and quantified using X-ray powder diffractometry and scanning electron microscopy combined with energy dispersive X-ray microanalysis. The valency of the constituent ions is not obtained directly from the electron microprobe analysis but is derived from the stoichiometry and the known mineral structures.

The article focuses on the modelling of chromium behaviour and transport at sites contaminated with chromite ore processing residue. The presence of approximately 2.5 million tonnes of chromite ore processing residue on several sites in the vicinity of Glasgow has led to concern about the leaching of the known toxin, Cr(VI), into surface and ground waters and ultimately, into the River Clyde. Examination of the modelled mineralogical composition as a function of pH shows that the hydrogarnet dissolves first followed by the hydrocalumite in the pH range 11.5-10.5.

The article focuses on the variability in chemical properties of a chromite ore processing residue (COPR)disposal site and assessment of potential toxicity using a biosensor. Approximately two million tonnes of COPR have been used as infill in several urban sites in SE Glasgow. Marine luminescent bacteria have been used in the past to determine the toxicity of pure chromium solutions. The toxicity measured on pure chromium solutions may, however, differ from that of field samples, where matrices can be more complex and several factors can contribute to the overall toxicity.

A review of the iron and steel industry in the former Soviet Union for 1992 is presented. The industry had a bad year with many problems, including shortages of coking coal and scrap, a liquidity crisis, and a contraction in demand for its products. Output of crude steel delined by 11.3%, rolled steel 13.6%, steel pipe 18.25 and marketable ore 11.6%. Production of ferrous alloys, manganese and chromium also fell; manganese by 12.8% and chromium by 2.6%. The problems in the coking industry were largely financial.