Chromite Research Articles

Mechanical properties of (Ni, Fe)Cr2O4 polycrystal spinels studied by molecular dynamics simulations.

The elastic moduli and mechanical properties at the onset of crack in nanocrystalline and nanoporous (Ni, Fe)Cr2O4 compounds with a spinel structure are investigated by molecular dynamics simulations. The polycrystalline structures generated contain nanograins from 2.5 to 30nm in diameter. These structures are representative of the internal corrosion layer in nickel-based alloys. These simulations enabled us to establish the evolution of elastic moduli as a function of the composition, porosity, and grain size of the polycrystals. From this evolution, the initial database for the elastic properties of corrosion layers based on von Bertalanffy growth functions was determined. The onset of crack in polycrystals is also investigated via uniaxial tensile and shear deformation. Under shear deformation, flow stress as a function of grain size follows normal and inverse Hall-Petch regimes. The regime change occurs for grain sizes around 10nm. For grain sizes under this threshold, shear banding involving collective translation and rotation of nanograins dominates the plastic deformation. For grain sizes greater than 10nm, phase transition inside grains from a spinel to a post-spinel-like structure is observed as well. In that case, phase transition dominates the plastic deformation. Under uniaxial tensile deformation, intergranular decohesion occurs. The general law as a function of grain size for toughness, which is the material's capacity to absorb elastic and plastic energy prior to failure, is also established.

Diversities of chromite mineralization induced by chemo–thermal evolution of the mantle during subduction initiation

Ophiolites, mostly formed via subduction initiation at proto-forearcs, exhibit a unique variation of mantle-derived magmatism from MORB-like to low-Ti tholeiitic and bainitic-like affinities. Such variation was suggested to form chromite deposits spanning high-Al to high-Cr types. Nevertheless, the origin of diverse magmatism during subduction initiation and their linkages to different chromite deposits has long been enigmatic. Here we show elemental and Os isotopic compositions of different chromitites from the Zambales ophiolite, Philippines. Combined with data from ophiolites worldwide, high-Al and high-Cr chromitites are revealed to result from low-Ti tholeiitic and boninitic-like magmatism, respectively. Proto-forearc mantle had few chromitites generated during MORB-like magmatism, but afterwards, it was modified first by slab fluids and later by continuous asthenospheric upwelling in the context of slab densification and rollback. The latter modification elevated the geothermal gradient and replenished fertile components in the proto-forearc mantle progressively, inducing increasingly higher degrees of mantle melting and Cr-richer magmatism and chromitites.

STUDY OF THE MODES OF RECOVERY AND DESTRUCTIBILITY OF CHROME BRIQUETTES UNDER CURRENT AND THERMAL LOADS

For an objective assessment of the recoverability of the resulting oxidized materials and deciphering the physico-chemical characteristics of their reduction processes occurring during the smelting of carbonaceous ferrochrome, special studies are needed. In this regard, the kinetics of the briquette reduction process has been studied in this article, which is extremely important for understanding the mechanism of carbothermic reduction in order to improve metallurgical technologies using coated materials. During the study, 6 different variants of briquettes with chromium ore and various types of carbon reducing agents were studied, such as China coke, Shubarkolsky special coke, Borlinsky coal and Shubarkolsky coal. The degree of chromium reduction was studied in the Tamman furnace by thermogravimetric method at temperatures of 1200; 1300; 1400; 1500; 1600 ° C for 1 hour. This article also provides calculations to determine the degree of reduction of chromium and iron using the Yander and Gistling-Brownstein equations. Of the six briquette variants, the best results in studying the kinetics of reduction of chromium ore raw materials were obtained using briquettes № 1, 3, 5. The study emphasizes the critical importance of understanding the reduction and destructibility modes of chromium briquettes to optimize the melting processes of carbon ferrochrome. The conclusions from this study are key to the development of both scientific understanding and practical applications in the metallurgical industry. This article summarizes the main results and meanings of the authors’ research, emphasizing its contribution to improving the efficiency and quality of carbon ferrochrome production through the systematic study of reduction behavior in chrome ore briquettes. Keywords: ferrochrome, chrome briquettes, coal, coke, degree of reduction, Yander equation, Gistling-Brownstein equation.

STUDY OF FERROCHROME SMELTING TECHNOLOGY USING BRIQUETTES WITH VARIOUS CARBONACEOUS REDUCERS

This study explores the ferrochrome smelting technology using briquettes with various carbonaceous reducers. The research addresses the significant challenge of dust and fine fractions of raw materials generated during the metallurgical industry's crushing, beneficiation, storage, and transportation processes. Briquettes were produced and tested by agglomerating chrome ore dust with carbonaceous reducers for their mechanical properties and effectiveness in smelting processes. The study concludes that carbonaceous reducers' ash content significantly affects the chrome ore-containing briquettes' thermal stability and electrical conductivity. Low ash content was associated with better performance in the smelting process. Using briquettes with various carbonaceous reducers offers a flexible approach to charge composition, depending on specific production needs and the availability of reducers. The results highlight the potential for improved environmental impact, reduced material losses, and enhanced efficiency in ferrochrome production.

Sustainable chromium ore processing residue (COPR) waste treatment with black soldier fly larvae (BSFL)

Chromium elements are prevalent in daily life, and millions of tonnes of Chromium Ore Processing Residue (COPR) remain untreated in China, posing significant environmental risks. In search of a cost-effective and environmentally friendly treatment method, this study investigated the potential of black soldier fly larvae (BSFL) as a biological treatment for COPR. Experiments were conducted using BSFL to treat 100 % COPR and a mixture of 50 % COPR with 50 % wheat bran. Post-treatment analysis using ICP-MS, X-ray diffraction (XRD), and scanning electron microscopy revealed a significant reduction of approximately 43 % in COPR dry mass and a decrease in total hexavalent chromium content from 5636 ppm to 563 ppm. The optimal treatment conditions involved mixing 50 % COPR with 50 % wheat bran. The results suggest that BSFL can serve as a sustainable and economically viable biological treatment for hazardous waste such as COPR, offering potential benefits for both the environment and the economy. Further research is needed to explore the mechanisms and effects of BSFL on hazardous waste treatment.

Discovery and Significance of Layered Chromite Mineralization in Mafic-Ultramafic Rocks from the Gayahe Area of the East Kunlun Orogenic Belt, Northwestern China

Discovery and Significance of Layered Chromite Mineralization in Mafic-Ultramafic Rocks from the Gayahe Area of the East Kunlun Orogenic Belt, Northwestern China

Thermodynamic Diagram Analysis and Smelting of Complex Fe-Cr-Mn-Si Ferroalloy

A state diagram of the Cr-Mn-Si-Fe metallic system, which simulates the compositions of complex chromium-manganese-silicon-containing ferroalloy (Fe-Cr-Mn-Si), has been constructed using thermodynamic-diagram analysis. Theoretical investigations have determined that the system comprises eight elementary tetrahedra. The sum of the relative volumes of the elementary tetrahedra equals one (1.00000), confirming the accuracy of the tetrahedration conducted. Analytical expressions for each tetrahedron have been derived. Calculations have determined the tetrahedron characterizing the phase composition of the ferroalloy. This tetrahedron is identified as the most voluminous phase triangle in the Cr-Mn-Si-Fe metallic system, implying that its significant volume facilitates the smelting process of chromium-manganese-silicon-containing ferroalloy, i.e., there is the possibility of freely regulating the charge compositions to achieve the required alloy grade. Based on the obtained results, an experimental smelting of the Fe-Cr-Mn-Si ferroalloy was conducted using a charge composed of chromium ore, low-grade manganese ore, and coke, resulting in a sample with the following composition, %: 44.07 Cr, 13.97 Fe, 12.48 Mn, 9.48 Si, 4.45 C. The microstructure comprises a complex silicide (Cr, Fe, Mn)3Si and Cr3C2 carbides.

Prediction of burden distribution and electrical resistance in submerged arc furnaces using discrete element method modelling

A computational model of a submerged arc furnace (SAF) used in the production of ferrochrome is presented. The model's intended use is to investigate the extent to which intrinsic and extrinsic properties of the raw materials affect burden distribution and electrical resistance within the furnace. The model is built on the discrete element method and calculates the mechanical interactions of particle distributions resulting from the flow motion of typical raw materials used in the smelting of chromium ore. This model excludes the effects of thermodynamics, furnace chemistry, and heat transfer. It illustrates how the consumption of materials (chromite pellets, flux, and reductant) is affected by changes in electrode length, reductant fractions, and reductant sizing and density during the formation of a reductant bed. The resistance calculation algorithm developed by Mintek was applied to construct networks developed from particle contacts, which can quantitatively generate estimates of the electrode-to-electrode and electrode-to-bath electrical conduction conditions.

Metagenomes from microbial populations beneath a chromium waste tip give insight into the mechanism of Cr (VI) reduction

Dumped Chromium Ore Processing Residue (COPR) at legacy sites poses a threat to health through leaching of toxic Cr(VI) into groundwater. Previous work implicates microbial activity in reducing Cr(VI) to less mobile and toxic Cr(III), but the mechanism has not been explored. To address this question a combined metagenomic and geochemical study was undertaken. Soil samples from below the COPR waste were used to establish anaerobic microcosms which were challenged with Cr(VI), with or without acetate as an electron donor, and incubated for 70 days. Cr was rapidly reduced in both systems, which also reduced nitrate, nitrite then sulfate, but this sequence was accelerated in the acetate amended microcosms. 16S rRNA gene sequencing revealed that the original soil sample was diverse but both microcosm systems became less diverse by the end of the experiment. A high proportion of 16S rRNA gene reads and metagenome-assembled genomes (MAGs) with high completeness could not be taxonomically classified, highlighting the distinctiveness of these alkaline Cr impacted systems. Examination of the coding capacity revealed widespread capability for metal tolerance and Fe uptake and storage, and both populations possessed metabolic capability to degrade a wide range of organic molecules. The relative abundance of genes for fatty acid degradation was 4× higher in the unamended compared to the acetate amended system, whereas the capacity for dissimilatory sulfate metabolism was 3× higher in the acetate amended system. We demonstrate that naturally occurring in situ bacterial populations have the metabolic capability to couple acetate oxidation to sequential reduction of electron acceptors which can reduce Cr(VI) to less mobile and toxic Cr(III), and that microbially produced sulfide may be important in reductive precipitation of chromate. This capability could be harnessed to create a Cr(VI) trap-zone beneath COPR tips without the need to disturb the waste.

Oxidation kinetics of typical high FeO ferrous spinels

In this study, the isothermal oxidation kinetics of magnetite (OM), high-Mg magnetite (MM), titanomagnetite (TM), and chromite (CM) were investigated by applying thermogravimetry (TG) analysis at temperatures ranging from 1073 K to 1223 K. The results show that different high-FeO spinels possess distinct oxidizability. The oxidation process of OM in the temperature range from 1073 K to 1223 K is faster than others, followed by MM and TM. While CM exhibits the poorest oxidizability, and generally undergoes complex phase transitions. In the initial stage of oxidation, high FeO spinels have a higher oxidation rate due to the surface oxidation of spinel particles. However, the oxidation rate gradually declines in the later stages of oxidation due to increased internal diffusion resistance. The results of oxidation kinetics indicate that the initial oxidation stage of four spinels can be described as random nucleation and subsequent growth mechanism. The average apparent activation energies of the initial oxidation stage of OM, MM, TM, and CM are 25.09 kJ/mol, 32.39 kJ/mol, 58.10 kJ/mol, and 82.42 kJ/mol, respectively.

Dissolution behavior of chromite mineral impurities in raw materials of glass production using scanning electron microscopy-energy dispersive spectrometer, X-ray fluorescence spectroscopy and Raman spectroscopy methods

Silica sand is an essential raw material for glass production. The specification of silica sand for each type of glass is the most important point, such as chemical purity, grain size, grain shape, and their impurities. Some of the impurities in the sand can be eliminated by processing yet some cannot be avoided. This paper indicates that as an impurity in the sand, chromite minerals dissolve in glass. 0.200 mm and 0.250 mm grain size chromite minerals were observed grain size change at 1350 °C − 1400 °C − 1450 °C. With increasing in temperature, the rate of size change in the grain diameter increased. Because of the chemical composition of chromite mineral, with increasing temperature, first of all, aluminum and magnesium content start to dissolve in soda lime silicate glass. Then, chromium content transforms into chromium oxide. The transformation rate depends on the mineral composition as well as the temperature and the residence time in the furnace. This paper concerns the chemical composition of the chromite by scanning electron microscopy equipped with energy dispersive spectrometer, the compositions of the raw material analyzed with X-ray fluorescence spectroscopy, inductively coupled plasma optical emission spectrometer and chromite characteristics analyzed by Raman Spectroscopy methods.

The redox state of chromium ores of the Polar Urals

The redox state of chromium ores of the Polar Urals

Current supply status, demand trends and security measures of chromium resources in China

Chromium, a strategic mineral resource in China, is widely used in high-precision equipment manufacturing. As the world’s leading consumer and importer of chromite, China’s external dependence exceeds 99%. The significant imbalance between domestic supply and demand seriously threatens national economic security. This study discusses the state of China’s chromium resource supply from four aspects: the overview of domestic and global chromium resources, China’s chromite production and import volume, the sources of imported chromite, and risk analysis. Considering the chromium industrial chain and factors such as production, consumption, and recovery tendency of chromium-bearing stainless steel, it is forecasted that China’s demand for chromium ore will decline by 2040. This could considerably reduce the security situation of chromium resources. This study proposes five strategies for securing chromium resources: technological innovation, enhancing international cooperation and acquiring overseas resources, constructing a new pattern of “dual circulation” resource guarantee for sea–land transportation, encouraging chromium recycling, and building an emergency management system and strategic reserve mechanism for chromium resources.

Processing of stale slurry tailings from chrome ore processing plants to obtain standard chrome concentrate

Processing of stale slurry tailings from chrome ore processing plants to obtain standard chrome concentrate

DETERMINATION OF THE MASS BALANCE OF HIGH-CARBON FERROCHROME IN A SUBMERGED ARC FURNACE

In this study, it is aimed to establish one-day mass balance of the materials entering into and leaving from a submerged arc furnace (SAF) where high-carbon ferrochrome is produced in it. The SAF is used in a plant located in Elazig, Turkey. For this purpose, measurements were taken from the SAF during one month by obtaining the necessary permits from the plant. In addition to these measurements, chemical reactions in the SAF are defined based on the information obtained from the literature and the plant. Chrome ore and rich slag are raw materials for furnace; as auxiliary raw materials, coke, coal, electrode paste, quartzite, and bauxite are fed. The product and the waste coming out of the SAF are high-carbon ferrochrome, slag, flue gas, and fly ash. Samples were taken from each raw material and auxiliary raw materials fed into the SAF and the products, then the chemical composition analysis was carried out by using an X-ray fluorescence (XRF) device. The reactions that take place in the SAF are carbothermic reduction reactions. Metal oxides (Cr<sub>2</sub>O<sub>3</sub>, Fe<sub>2</sub>O<sub>3</sub>, Al<sub>2</sub>O<sub>3</sub>, etc.) react with carbon and are reduced as MO + C = M + CO (M = metal). As a result of this study, the mass amounts of the materials entering into and leaving from the SAF established a balance.

Trends in the Unit Cell Parameter for Kimberlitic Versus Non-Kimberlitic and Diamond-Indicating Chromite

Abstract Spinel-group minerals are among the best-known and widely used minerals in diamond exploration due to their ubiquity, resistance to weathering, and utility as petrogenetic indicators. The kimberlite indicator mineral chromite is investigated in this study using micro-X-ray diffraction (µXRD) to measure chromite unit cell parameter ao. We used epoxy-mounted chromium-rich spinel (henceforward called ‘chromite’) mineral separates with known chemical composition from kimberlitic and non-kimberlitic sources to evaluate structural-chemical correlations for potential use in diamond exploration. Chromite grains of <300 µm size from the Koala, Misery, and Sheiba kimberlites in the Ekati property (Northwest Territories, Canada), as well as from exploration programs in Botswana and Gabon, Africa, were examined in situ, as mounted for standard electron probe microanalysis (EPMA). Unit cell parameter ao was measured by µXRD for several natural kimberlitic and non-kimberlitic chromite grains, and these data have been correlated with chemical composition as determined by EPMA on a grain-by-grain basis. Conventional chemical discrimination plots with unit cell size denoted by color demonstrate clearly discernable unit cell trends that are useful for classification. Two kimberlitic chromite compositional trends can be discriminated by chromite unit cell size. The kimberlitic phenocryst trend is delineated by a distinct increase in unit cell size (ao > 8.336 Å), whereas the kimberlitic xenocryst trend is delineated by a distinct decrease in the unit cell (ao < 8.322 Å). The latter trend is also followed by the Gabon non-kimberlitic samples. Notably, the unit cell parameters for chromite in the diamond-indicating field have a tightly determined value of ao = 8.329 (± 0.007) (or 8.322–8.336 Å). This field partially overlaps with the unit cell values for some non-kimberlitic chromites (e.g., Botswana). Unit cell values of chromite grains recovered from heavy mineral concentrates could serve as a preliminary screening technique for identifying diamond-indicating chromites prior to chemical analysis if their kimberlitic provenance is known. More broadly, the μ-XRD unit cell technique is a useful, non-destructive tool that shows promise for application to other kimberlite indicator minerals.

Emplacement and ore potential of the Permian Pobei mafic–ultramafic complex, NE Tarim, NW China

A number of mafic–ultramafic intrusions with variable degrees of Ni-Cu sulfide mineralization occur in the northeastern Tarim Block and East Tianshan Orogenic Belt (NW China). Among them, the Pobei complex is composed of a gabbro body intruded by several ultramafic bodies including Poyi and Poshi. These bodies have similar mineralogy and chemical compositions and were derived from a common magma. Olivine crystals from the Poyi and Poshi bodies generally have high Fo contents with the highest Fo value of 89.5 and Ni up to 3300 ppm Ni, indicative of crystallizing from Ni-undepleted, high-Mg basaltic magmas. Sr-Nd-Pb isotopic compositions show that more mafic rocks show relatively low degrees of crustal contamination, whereas more evolved rocks experienced higher degrees of contamination, especially in the upper part of the complex. Olivine crystals from both the Poyi and Poshi bodies show sharp decrease of Ni with decreasing Fo values, indicating sulfide segregation in these two bodies. Gabbros may have potential of reef-type chromite mineralization at the deep level, and V-bearing magnetite mineralization at higher stratigraphic level corresponding to the current surface level, but the potential of PGE mineralization is low. We propose that the ultramafic bodies of the Pobei complex may have been formed from the injection of olivine- and sulfide-laden crystal slurry from the bottom of a large magma chamber. The Ni-Cu mineralization was triggered by the crustal contamination. The Pobei complex was formed by the multiple intrusions of magmas to form the current complex.

Efek Pre-Roasting Terhadap Parameter Kinetika Leaching Cr dari Limonit

Hydrometallurgical processes such as leaching of limonite ore to extract valuable metals including Ni and Co are often non-selective, including other metals in the leachate product. The leaching behavior of Cr from the chromite mineral contained in limonite ore is of concern due to the high Cr content of the leachate effluent. The pre-roasted process is frequently used to pre-treat limonite to increase the precious metal content. This study aims to determine the leaching behavior of Cr and the effect of pre-roasting on its kinetic parameters. The pre-roasting process was carried out at 280 and 610 oC for 4 hours. Observation of Cr leaching behavior was carried out in the leaching temperature range of 30-90 oC for 0-120 minutes using sulfuric acid solvent. The highest Cr recovery was achieved in pre-roasted ore leaching at 610 oC with leaching operating conditions of 2 M sulfuric acid, solid-liquid ratio of 5 g/50 mL, 200 rpm, for 120 minutes, at a leaching temperature of 90 oC, under these conditions Cr recovery reached 53.16%. The higher the roasting temperature, the lower the activation energy required for the leaching process. Cr leaching from raw and pre-roasted ore is controlled by the diffusion process through the ash layer with activation energies (EA) of 21.41, 18.64, and 14.71 kJ/mol for raw ore, pre-roasted ore 280 oC, and pre-roasted ore 610 oC, respectively. The comparison of kinetics data from several roasting products for atmospheric leaching feeds will provide industry with information to integrated pyro-hydrometallurgical process to increase Cr production from laterite.

Extraction and Optimization of Tanning Material from Osyris lanceolata Barks: Cleaner Leather Tanning Processing

Tanning is a processing mechanism that prevents the collagen fibers from putrefaction to maximize the hydrothermal stability of leather. Tannin agents extracted from plants were used in leather production in a process called vegetable tanning. Vegetable tanning is an eco-friendly tanning method when compared to chrome tanning. Chrome tanning is the most common method of tanning hides. Currently, chrome tanning, which is extracted from chrome ores, is used in more than 80–90% of the leather tanning industry, but the most serious environmental issue associated with tanneries is chromium. This implies that the presence of chromium both in wastewater and in leather waste has a significant environmental impact and a high cost for landfills. However, currently, vegetable tanning and other tanning materials take up a 10–20% share of the leather tanning industry. Even today, most commercial vegetable tanning is a mimosa. In this study, a new alternative material and chrome-free tanning process using the barks of the Osyris lanceolata plant barks which reduces the environmental pollution load in terms of wastewater and solid wastes would be introduced. The study also aimed to improve the extraction and optimization mechanisms of tannin material from the bark of the Osyris lanceolata plant, which grows in Dera Hamusit Woreda in Ethiopia’s south Gonder Amhara region. In addition to these, the chemical and physical properties of experimentally treated leather were analyzed. This study’s results show that the bark of Osyris lanceolata contains (18.72%) tannin with 96% tanning strength (96%), and 49 percent purity. Also, leather treated with this tannin showed good shrinkage temperature (84.5°C), and organoleptic properties results such as tensile strength, tear strength, and elongation were 7.1 N/mm2, 19 N, and 45%, respectively. Besides that, the FTIR analysis shows that the bark of the Osyris lanceolata plant has a phenolic compound that is used for tanning purposes. This study clearly shows that extracted tannin from Osyris lanceolata has the potential to be used as an alternative tannin material in the leather tanning industry.

Solubility product of chromate analogue of hydrogarnet (Ca3Al2[CrO4]0.12[O4H4]2.88(s)) at 25 °C

Chromium (Cr)-hydrogarnet (Ca3Al2 [CrO4]0.12[O4H4]2.88(s)) is a critical host of hexavalent chromium [Cr(VI)] in cementitious and alkaline solids such as chromium ore processing residue (COPR). Leaching from COPR often results in Cr(VI) contamination of soil and groundwater. Although Cr-hydrogarnet has been synthesized and characterized previously, its solubility product (Ksp) is poorly constrained. Accurate determination of this thermodynamic parameter is critical to quantify the extent of Cr(VI) dissolution from COPR in water. In this contribution, the Ksp of Cr-hydrogarnet was determined by (i) hydrothermal synthesis of the solid at 150 °C in alkaline conditions in two batches; and (ii) batch equilibration experiments over 745 d from undersaturation and over 60 d from supersaturation. For each synthesized batch of solids, Cr-hydrogarnet solubility in ultrapure water at 25 °C in triplicate reactors was measured. Time-dependent aqueous samples were collected, and concentrations of Cr(VI) and co-solutes and pH were measured until a steady state was attained from undersaturation, after which the state was perturbed by the addition of 7× Cr(VI) to trigger the supersaturation experiment. X-ray diffraction and SEM-EDS analyses on the reacted solids confirmed the presence of Cr-hydrogarnet and its constituent elements, respectively. In addition, calcite and aluminum oxyhydroxides were formed as minor secondary phases. The log ion activity products at steady states attained from undersaturation and supersaturation were 72.36 ± 0.86 and 72.75 ± 0.14, respectively. A mean log Ksp of 72.55 ± 0.87 at 25 °C for the reaction Ca3Al2 [CrO4]0.12[O4H4]2.88(s) + 11.52H+ ↔ 3Ca2+ + 2Al3+ + 0.12CrO42− + 11.52H2O was proposed. Furthermore, the new thermodynamic constant was used to analyze data from two previous COPR equilibration studies in water and identify the governing mechanisms of Cr(VI) release.