Chromite Research Articles

Phase transformation of Cr(VI) host-mineral driven by citric acid-aided mechanochemical approach for advanced remediation of chromium ore processing residue-contaminated soil

The slow release of Cr(VI) from chromium ore processing residue-contaminated soil (COPR-soil) poses a significant environmental and health risk, yet advanced remediation techniques are still insufficient. Here, the slow-release behavior of Cr(VI) in COPR-soil is observed and attributed to the embedded Cr(VI) in the lattice of vaterite due to the isomeric substitution of CrO42- for CO32-. A citric acid-aided mechanochemical approach with FeS2/ZVI as reductive material was developed and found to be highly effective in remediating COPR-soil. Almost all Cr(VI) in COPR-soil, including Cr(VI) embedded in the minerals, are reduced with a reduction efficiency of 99.94%. Cr(VI) reduction kinetics indicate that the Cr(VI) reduction rate constant in the presence of citric acid was 4.8 times higher compared to its absence. According to the Raman spectroscopy, X-ray diffraction (XRD), and Electron Probe X-ray Micro-Analyzer (EPMA) analysis, the reduction of Cr(VI) embedded in vaterite was mainly attributed to the citric acid-induced protonation effect. That is, under the protonation effect, the embedded Cr(VI) could be released from vaterite through its phase transformation to calcite, whose affinity to Cr(VI) is low. While the reduction of released Cr(VI) could be promoted due to the complexation of citric acid with disulfide groups on FeS2/ZVI. The results of long-term stability tests demonstrated that the remediated COPR-soil exhibited excellent long-term stability, which may also be associated with improved utilization of available carbon and electron donors by the Cr(VI) reducing bacteria (Proteobacteria)-dominated microbial community in the presence of citric acid, thereby promoting to establish a stable reducing microenvironment. Collectively, these findings will further our understanding of the reduction remediation of COPR-soil, especially in the case of Cr(VI) embedded in minerals.

Oxidation behaviour of Ni-base superalloy 617 in simulated Advanced Ultra Supercritical (AUSC) steam

Alloy 617 was exposed in a simulated Advanced Ultra Supercritical (AUSC) steam oxidation test loop at 650–710 ℃, 31 MPa for 600 h. Detailed characterization of the oxide scales was carried out using Transmission Electron Microscopy coupled with Precession Electron Diffraction. The alloy 617 showed insignificant weight gains with super-parabolic kinetics. The oxide scale formed on the alloy consisted of a thin inner Cr2O3 layer and outer islands of (Mn,Ni,Fe)Cr2O4 spinel with negligible internal oxidation zone comprising Al2O3. The mechanistic aspect of AUSC steam oxidation is discussed.

Highly efficient Cr (VI) removal from electroplating wastewater by regenerable copper sulfides: Mechanism and magical induction effect for Cr resource recovery

The current sorbents used to remove Cr (VI) from electroplating wastewater are faced with some challenges including the difficulty in separating, regenerating, and safely disposing of adsorbed Cr species. To address these challenges, CuSx/TiO2 was developed to recover Cr (VI) from electroplating wastewater. CuSx/TiO2 had superior performance in removing Cr (VI), with the rate and capacity of approximately 9.36 mg g−1 h−1 and 68.8 mg g−1 at initial pH 4.0, respectively. Additionally, Cu2+ released from CuSx/TiO2 during Cr (VI) removal would come back to its external surface as the Cu(OH)2 precipitate at initial pH 4.0, which helped to prevent the generation of secondary pollution. The Cu(OH)2 precipitate would be decomposed into CuOx after calcination, which would then be transformed back into CuSx by re-sulfuration for regeneration. Hence, CuSx showed a magical induction effect on Cr (VI) recovery, and Cr (VI) from electroplating wastewater might be gradually enriched as Cr2O3 in the sandwich between CuSx and TiO2 through multiple regenerations and removals, which could be considered as a chromium ore resource for industrial applications when the amount of enriched Cr2O3 reached more than 30 wt%. Overall, CuSx/TiO2 showed great potential as a promising sorbent for Cr (VI) removal from electroplating wastewater.

Research on the Production of Pigments Based on Composite Pellets in the Recycling of Industrial Waste

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.

Challenges and threats to modern subsoil use using the example of the Ural Federal District

Relevance. Environmentally sustainable subsoil use requires full coordination of socio-economic and environmental subsystems. The growing economic problems, the deterioration of international relations, the approaching environmental crisis are causing challenges and threats that provoke disruptions in the operation of enterprises in the industry, which makes it necessary to identify threats and challenges in order to take systemic measures to mitigate the consequences or prevent them. The purpose of the study is to identify challenges and threats that pose a danger to subsoil use (using the example of the Ural Federal District). Research methods – generalization and analysis, methods of analogy, groupings, logical analysis, expert assessments. Results. The conceptual and categorical tools of the study have been clarified, the main challenges and threats that provoke the occurrence of adverse events for subsoil use, including the emergence of economic, social and environmental threats with a decoding of their characteristics, have been identified. Using the Delphi method in a lite variation by D. Peskov, three basic threats to the subsoil use of the Ural Federal District were identified with the involvement of 26 experts for evaluation. A detailed analysis of each of these threats has been carried out. The depletion of the mineral resource potential within the Ural Federal District and the need to meet the demand for raw materials through external and internal supplies were confirmed. Among the solid minerals are coal, manganese and chromium ores, copper raw materials, etc. An insufficient level of funding for geological exploration has also been determined. The analysis of the threat associated with the dependence of the industry on foreign IT products was performed in great detail. Data on the assessment of the current situation at enterprises engaged in subsoil use in the Ural Federal District are given. Possible ways out of the current critical situation are considered. Conclusions. The consequences of the identified threats for subsoil use are formulated. The need to reduce the impact of threats is substantiated: the depletion of the mineral resource potential, the reduction in funding for geological exploration and the dependence of the industry on foreign IT products.

Association of Fe–Ti oxides in subalkaline dolerites of the Rai-Iz massif (Polar Urals)

The relevance of the research. Subalkaline dolerites, Fe–Ti oxides of which were studied in this work, occur within the largest deposits of chromium ores of the Rai-Iz massif. The study of the material composition and age of these rocks was carried out by the authors for the first time. The purpose of the research is to reveal the patterns of changes in the chemical composition of the main accessory minerals of rocks – titanomagnetite and ilmenite, and on the basis of the obtained data to evaluate the conditions for the formation of subalkaline dolerites of the massif. Research methodology. The chemical compositions of minerals were determined using microprobe analysis on a CAMECA SX 100 and scanning electron microscopy on a Jeol JSM-6390LV setup with an INCA Energy 450 X-Max 80 energy dispersive attachment. Raman spectra were obtained on a LabRam HR 800 Evolution spectrometer equipped with an Olimpus BX-FM microscope. The studies were carried out at the “Geoanalyst” сenter for the collective use of scientific equipment of the IGG, UB RAS. Results. The typomorphism of the chemical composition of titanomagnetite and ilmenite has been established for petrographic varieties of dolerites allocated on the massif. The T–fO2 parameters of dolerite formation were estimated and compared with metaultramafites. It is shown that titanomagnetite in amphibole dolerites undergoes maghemitization. The highest temperatures (1076–1126 °C) are recorded in pyroxene dolerites. The oxygen fugacity in these rocks is FMQ +0.6–+1 units. Hyalodolerite from the chilled margin of the pyroxene dolerite dike gives a temperature of 811–818 °C and an oxygen fugacity of 1.8 units above FMQ. The compositions of the associated ilmenite and titanomagnetite from amphibole dolerites correspond to fO2 = –2–0 units relative to FMQ and temperature 580–720 °C. The trend of change in T–fO2 parameters shows that the injection of the mafic melt occurred under conditions of metamorphism of ore-bearing ultramafic rocks. Conclusions. The formation of dolerite veins occurred under conditions of ultramafic rock metamorphism. The increased fugacity of oxygen at a relatively low temperature led to the maghemitization of titanomagnetite, rather than to the redistribution of components in the magnetite-ilmenite paragenesis.

PROMISING MULTIFUNCTIONAL ANIONITES FOR THE EXTRACTION OF CHROMIUM (VI) IONS

30% of the chromium ore reserves in the world are concentrated in Kazakhstan, during the processing of which large volumes of wastewater containing toxic chromium salts, are formed. Сhromium is one of the priority components both in terms of emission and toxicity (for Cr(VI), the maximum permissible concentration is 0.05 mg/l). The compounds of chromium (III) and especially chromium (VI) have a general toxic, allergenic, carcinogenic, mutagenic effect on the human body, and are among the most dangerous pollutants for the environment. The aim of this work is to develop a technological scheme for the extraction of Cr (VI) ions by multifunctional ion exchangers. Methods. Anionite, based on diglycidyl ether of dioxyphenylpropane, allylglycidyl ether and polyethylenimine – Ionite No. 1 has been synthesized by polycondensation, and epoxyamine has been synthesized from benzylamine and epichlorohydrin, by the condensation of which Ionite No.2 has been obtained with polyethylenimine. The sorption of chromium ions on newly synthesized anionites has been studied, using model solutions with the concentrations of 25, 50, 75 and 100 mg/l Cr (VI). Results and discussion. It has been established that Ionite No.1 exhibits greater affinity for Cr (VI) ions. So, its maximum sorption capacity is 13.5, and that of Ionite No.2 is 11.7 mg/g. Conclusion. We have proposed a basic technological scheme of a desalination plant, consisting of modular units: reagent-mechanical, sorption, membrane, ion exchange and bacterial purification. It has been established that reagentmechanical purification is the initial stage of water treatment, designed to isolate insoluble coarse- and fine-dispersed impurities.

Origin of chromitites in the Norilsk-1 intrusion (Siberian LIP) triggered by assimilation of argillaceous rocks by Cr-rich basic magma

Сhromite-rich rocks and monomineralic chromitites occur in mafic-ultramafic layered intrusions worldwide, and are economically important as they host major resources of chromium and platinum group elements. One of the acknowledged genetic concepts for such mineralization advocates bulk chromite crystallization in a response to hybridization of Cr-rich basic magma with felsic melts, derived from partial melting of the wall rocks. However, there has been lack of direct insights into this process and its details have been remaining largely obscured. In this study, we report data on chromite-rich assemblages of the Noril'sk-1 intrusion (Siberian LIP), with a particular focus on chromite-hosted multiphase inclusions. Composition of the latter is different from the rocks of the Noril'sk-1 intrusion and inherits geochemical fingerprints of the wall rock argillites and, therefore, represent snapshots of the heavily-contaminated medium of the magma-wall rock reaction front. Mineral relationships in chromite-rich breccias with fragments of the wall rocks also provide valuable insight into chromite mineralization mechanisms. Our results, along with geological evidence and data on other Noril'sk-type intrusions, indicate that bulk crystallization of chromite, aided by partial suppression of silicate crystallization, occurred in the hybrid medium during digestion of the wall rocks by ascending and emplacing basic magma. Continuous flow of the magma around outshoots of the wall rocks or through a “magmatic karst” in the wall rocks, allowed for a continuous precipitation of chromite. Concentration of chromite grains to form dense mineralization apparently occurred due to formation of chromite-rich blobs around the wall rock fragments, and selective collection and transport of chromite by fluid bubbles, which formed via degassing of wall rocks and then carried chromite and relics of the wall rocks (xenoliths) to the upper parts of the pluton. We propose that assimilation-driven formation of chromite-rich lithologies in intrusions requires: (1) sufficient Cr contents in magma, which allow for its oversaturation in Cr-spinel only by a sudden cooling and addition of SiO2, K2O or/and H2O; (2) efficient disintegration and digestion of the host rocks, releasing considerable amounts of these components to the magma, and (3) a mechanism ensuring accumulation of excess chromite within a small volume (e.g. continuous reaction of Cr-rich magma with the products of the host rocks' assimilation or/and mechanical concentration of chromite).

Recycling of Chrome-Containing Waste from a Mining and Processing Plant to Produce Industrial Products

Prolonged development of ore deposits, ore beneficiation and metallurgical smelting of concentrates result in the accumulation of wastes, forming large-scale dumps and sludge ponds negatively affecting the environment and human health. The creation and introduction of industrial waste treatment technologies will make it possible to dispose of them with the production of valuable commercial products and improve the environmental situation. In a research article on chemical beneficiation with the subsequent gravitational beneficiation of chrome-containing slurry tailings of Donskoy Ore-Mining and Beneficiation Plant (DOMBP), which processes chrome ore of the Kempirsay deposit in the Republic of Kazakhstan, Aktobe region, having considerable stocks of such waste is presented. The chromium-containing slurry tailings were heat-treated at 1100 °C, sintered with ammonium sulfate, water and sulfuric acid in a defined ratio at 300 °C, and then the resulting sinter was leached with water at 90 °C. The cake was washed to separate the liquid part from the solid part. The solid precipitate is the chromium-containing cake, which is upgraded by gravity concentration to a grade concentrate for ferroalloy production. When the solution is evaporated, magnesium sulfate with ammonium sulfate forms the Tutton’s salt ammoshenite. High-throughput chromium oxide extraction of 93.9% was achieved as a result of the research, and three products were obtained: (1) standard chromium concentrate with 49.48% Cr2O3 content, (2) ammoshenite used as a nitrogen–magnesium fertilizer and (3) forsterite, which is concentrated in gravity concentration tailings and can be used in the production of refractory minerals.

Three bond modes of basic refractories used for Ruhrstahl Heraeus degassing process

AbstractMagnesia–spinel brick and unburnt periclase–spinel–Al brick are being employed as a substitution of traditional magnesia–chrome brick in the chromium‐free campaign of lining materials in Ruhrstahl Heraeus (RH) degasser. These three materials are investigated, in terms of physical properties, corrosion resistance and flexibility by wedge splitting test. Tracking their physical alterations and chemical reactions through burning or heating, three bond modes are discovered. Magnesia–chrome brick is subject to a series of phase transformation with rising temperature to yield a liquid envelop around chromite‐ore particles, to further form porous rim while liquid is gradually absorbed by surrounding magnesia and eventually to precipitate secondary chromite spinel lied between magnesia particles by thoroughly dissociating chrome ore. The precipitated chromite spinel functions as the featured bond that enhances hot strength and corrosion resistance to slag, and additionally liquid coexistence improves the flexibility. The direct bond mode of magnesia particles in magnesia–spinel brick endures slag penetration by immanent character of MgO. Spinel incorporation in magnesia effectively improves thermal shock resistance. Due to minor negative value of permanent linear change after reheating, further sintering (densifying) in using at high temperature would bring a risk of loosening and open joints of magnesia–spinel lining. While used in RH degasser, unburnt periclase–spinel–Al bricks undergo a miraculous process of metallic Al melting, gaseous AlN and AlON formation, MgAlON whiskers germination combined with gaseous Mg reduced, and micron‐size whisker network bond domination in their matrix. Such a whisker‐network bond renders the material a successful eco‐friendly alternative to magnesia–chrome refractory.

Immobilization of chromium ore processing residue by alkali-activated composite binders and leaching characteristics.

Chromium ore processing residue (COPR) is classified as hazardous solid waste because of the leachable Cr(VI). Cementitious materials are often used to solidify and stabilize heavy metals. However, most of them focus on the leaching concentration of particles after solidification and stabilization and lack research on leaching characteristics. This study investigated the leaching characteristics of heavy metals in three simulated environments (HJ557-2010, HJ/T299-2007, TCLP) after immobilizing COPR with composite binders. Industrial solid waste coal fly ash and lead-zinc smelting slag are used to prepare composite binders through alkali activation technology. Compressive strength, particle leaching toxicity, acid neutralization capability, and semi-dynamic leaching test are used to evaluate the performance of the solidified body. The solidified body can be applied to building materials or treated as general industrial waste. Heavy metals are mainly released from the matrix by surface washing at a low rate. The analysis results, including XRD, FTIR, and SEM-EDS, show that chemical binding and physical encapsulation are the main immobilizing mechanisms to realize the coordinated disposal of Zn and Cr(VI).

Development and Characterization of Natural Chromite Coating on Metal Substrate Using the Plasma Spray Process.

Natural materials are gaining interest as coating feedstock because their "quality to cost" ratio is better and they are more environmentally friendly than most of the synthetic ceramics. They give sufficient protection to metal surfaces against harsh conditions such as corrosion, wear, and high temperature. In the current study, chromite mineral was beneficiated and reduced to two different sizes to be used as feedstock material for thermal spray coating. Powders were upgraded by gravity and magnetic separation, respectively, and thermally sprayed onto mild steel samples by using atmospheric plasma spray (APS) equipment. Morphology, structure, phases, elemental distribution of chromite powder, and coatings were studied using field emission scanning electron microscopy, X-ray diffraction, X-ray fluorescence spectroscopy, and energy-dispersive X-ray spectroscopy. Tribological properties of APS chromite coatings were investigated by using a ball-on-disk tribometer, and corrosion resistance properties were evaluated by carrying out potentiodynamic polarization testing in 3.5% NaCl solution. It is observed that the coating has better wear and corrosion resistance and is worn by abrasive wear that includes scratching and particles pull out. Coating efficiency, surface morphology, and microhardness of the coating developed by fine powder were better than those of coarse powder coating.

Exploring Chromium Ore Consumption: New Perspectives from Hybrid CEEMDAN–S-Curve Modeling

Exploring Chromium Ore Consumption: New Perspectives from Hybrid CEEMDAN–S-Curve Modeling

Isotopic (Sm–Nd) and Geochemical (Nb/Y–Zr/Y) Systematics of the Sikhote-Alin Basic-Hyperbasic Complexes

The paper demonstrates the possibility of application of the 143Nd/144Nd–Sm/Nd and Nb/Y–Zr/Y diagrams to systematics of basic–ultrabasic complexes of different age: Paleozoic Kalinovsky, Cambrian Sergeevsky and Vladimiro-Aleksandrovsky, and Jurassic and Paleocene ones. The position of data points of the Kalinovsky, Sergeevsky, and Vladimiro-Aleksandrovsky complexes in the diagrams indicates their derivation from a primitive mantle-type (BSE) source, the derivatives of which are frequently associated with Cu, Ni, Co, and PGE mineralization. The position of data points of metabasic rocks of the Avdokimovsky complex and peridotite rocks of the Dalny Kut massif in these diagrams suggests that they have originated from depleted mantle and are promising for the discovery of PGE-bearing chromite mineralization. Data points of Paleocene explosive structures of Sikhote-Alin in the Nb/Y–Zr/Y diagram fall on the trend of recycled crust as a source. This explains the alkaline (to subalkaline) type of magmatism and the high gas saturation of magmas. The explosive structures resemble lamproite pipes, while their rocks are geochemically and mineralogically close both to lamproites and kimberlites.

Water/acid/reductive biomass leaching of Cr(VI) in chromium ore processing residue (CORP) for safe discharge of effluent and to recover Cr(III) and gypsum

The hydrolyzed biomass, a green and renewable resource, was used as a reducing agent to achieve the harmless treatment of chromium ore processing residue (COPR). This paper proposes a detoxification process of two-stage sulfuric acid leaching accompanied by biomass reduction of hexavalent chromium and a one-step combined leaching and reduction process. The orthogonal tests and single factor tests allowed to propose the most suitable operating conditions of different stages such as biomass hydrolysis, two-stage acid leaching, reduction of the acid leachate and combined leaching and reduction. The Cr(VI) content in both the leach residue and reduction solution reached the discharge criterion. The FTIR and XPS measurements showed that the reducing sugars produced by the hydrolysis of biomass reacted with the leached Cr(VI) to generate chromium sulfate adsorbed on the surface of COPR. In addition, XRD, SEM-EDS showed that the gypsum was generated after COPR detoxification, which can be used for resource utilization, providing a new idea and reference for the harmless treatment of COPR producing Cr(III) and gypsum.

Thermodynamic Analysis of the Chromium Reduction Process Using the Cr-C-O System During Metallization of Chromium Ores

The aim of the work is to determine the optimal temperature regime for firing chromium ore and the consumption of solid carbon, which ensures the recovery of chromium. The process of chromium reduction was investigated on a model elementary system by reducing chromium from ore with solid carbon. The areas of redox conditions in the Cr-C-O system were identified, the boundaries of the reduction, transition and oxidative regions were revealed. The temperature required for the recovery process was determined by calculating the equilibrium compositions of the Cr2O3 + nC system in the temperature range 1100-1900 K at n = 1, 2, 3, 4 and 5 moles.

Psychological support algorithms for underground miners to assess hypertension development risk

Objective. To study the psychovegetative status of underground miners and form psychological support algorithms to identify the risk for developing hypertension. Hypertension occupies a leading place in the structure of cardiovascular diseases, and determining the risk of its development is of great preventive importance for professional longevity. The study of the psychovegetative status to identify the risk of this pathology corresponds to modern diagnostic approaches within the framework of industrial corporate programs.
 Materials and methods. There were examined 109 male underground miners of the enterprise for the extraction of chromium ore. The patients were divided into two groups: the main group 60 men working in underground conditions, whose work is classified as "harmful" (class 3.33.4); the comparison group 49 men engaged in ground works, the conditions of which are classified as class 3.2. The main group was divided into two subgroups: I workers under 45 years old (n = 20, age 38.45 2.95 years), II over 45 years old (n = 40, age 50.90 1.46 years.); the comparison group was divided accordingly (23 employees, aged 38.0 2.8 years, experience 9.3 1.5 years; comparison group 45 years and 26 employees, aged 49.2 2.1 years, experience 24.0 1.8 years; comparison group 45 years). A complex of research methods was used: analytical (analysis of special assessment cards of working conditions, sociodemographic questionnaires), psychophysiological, functional and clinical and laboratory diagnostics, mathematical statistics (ROC analysis, multivariate logistic regression).
 Results. In two subgroups, two phenotypes were identified; in group I, there was a correlation of psychovegetative indicators with age and experience, and in group II a negative correlation. It has been proved that, depending on age, the psychologically realized adaptive phenotype is transformed into a psychosomatic one.
 Conclusions. Diagnostics of phenotype transformation formed the basis of the developed algorithms for psychological support, which makes it possible to assess the risk for developing arterial hypertension.

Application of Satellite Remote Sensing, UAV-Geological Mapping, and Machine Learning Methods in the Exploration of Podiform Chromite Deposits

The irregular and sporadic occurrence of chromite pods in podiform chromite deposits (PCD), especially in mountainous terranes with rough topography, necessitates finding innovative methods for reconnaissance and prospecting. This research combines several remote sensing methods to discriminate the highly serpentinized peridotites hosting chromite pods from the other barren ultramafic and mafic cumulates. The case study is the area of the Sabzevar Ophiolite (NE Iran), which hosts several known chromite and other mineral deposits. The integration of satellite images [e.g., Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite sensor, Landsat series, and Sentinel-2] coupled with change detection, band rationing, and target detection algorithms [including the Spectral Angle Mapper (SAM)] were used to distinguish potential lithological units hosting chromites. Results have been verified by an initial on-field checking and compared with the high-resolution (GSD ~6 cm) orthomosaic images obtained by the processing of photographs taken from an Unmanned Aerial Vehicle (UAV) at a promising area of 35 km2. The combination of visual interpretation and supervised classification by machine learning methods [Support Vector Machine (SVM)] yielded the production of a geological map, in which the lithological units and structures are outlined, including the crust-mantle transition zone units, mafic cumulates, crosscutting dykes, and mantle sequences. The validation of the results was performed through a second phase, made up of field mapping, sampling, chemical analysis, and microscopic studies, leading to the discovery of new chromite occurrences and mineralized zones. All ultramafic units were classified into four groups based on the degree of serpentinization, represented by the intensity of their average spectral reflectance. Based on their presumed protolith, the highly serpentinized ultramafics and serpentinites were classified into two main categories (dunite or harzburgite). The serpentinite with probable dunitic protolith, discriminated for a peculiar Fe-rich Ni-bearing lateritic crust, is more productive for chromite prospecting. This is particularly true at the contact with mafic dykes, akin to some worldwide chromite deposits. The results of our work highlight the potential of multi-scale satellite and UAV-based remote sensing to find footprints of some chromite mineral deposits.

Silicate mineral inclusions in chromite from the Eastern Bushveld complex: Implications for the origin and evolution of hydrous melt during chromite mineralization in the Critical Zone

Silicate mineral inclusions in chromite from the Eastern Bushveld complex: Implications for the origin and evolution of hydrous melt during chromite mineralization in the Critical Zone

Archaeology and alchemy applied: Experimental reproduction of Persian chromium crucible steel making

In a recent publication, we presented the earliest archaeological evidence for high-carbon steel alloyed with c. 1–2 percent by weight chromium, dating to the early 2nd millennium CE, and postulated that this ‘Chahak process’ was based on the addition of dried organic matter and chromite mineral as part of the charge of a closed crucible which was then fired to c. 1350 °C to produce steel. Here, for the first time, we present experimental proof that the direct reduction of chromite sand in the presence of liquid steel using common organic matter as reductant can lead to the addition of several percent by weight of chromium to the steel. In contrast, manganese oxide remains largely unreduced in the slag, despite forming a much larger part of the total crucible charge. This is in accordance with the lower reducibility of this oxide. We report the necessary operating conditions and highlight some of the constraints limiting the success of the process, and document the composition of the resulting slag and chromium-containing high-carbon steel. Our controlled crucible steel making experiments for the scientific reconstruction of the Chahak process are based on the combination of alchemical (Biruni’s crucible steel making recipe), archaeological and analytical evidence. We found the results support the alchemical recipe ingredients, and closely match the archaeological production remains, and the composition of the only currently known early Islamic chromium-rich steel artefact.