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The biomass valorization is of great importance as an alternative for the production of transport fuels and fine chemicals. Furfural hydrogenation to furfuryl alcohol is a prevailing industrial route for the utilization of hemicellulose component of biomass. The toxicity of the chromium species in commercial copper chromite catalyst for furfuryl alcohol production motivates the development of efficient chromium-free catalyst. Thus, a highly efficient silica supported copper catalyst is developed in this study. The catalyst is prepared by freeze drying of a gel precursor that is synthesized by ammonia evaporation, followed by calcination and H2 reduction. The catalyst exhibits higher furfural hydrogenation activity than oven dried catalyst, commercial copper chromite catalyst and a plant supplied commercial silica supported copper catalyst. The catalyst also shows good stability. The superior performance of the freeze dried catalyst has resulted from its developed pore structure and higher amount of Cu0 as well as Cu+ active sites.

The ferrite process can not only purify wastewater containing heavy metal ions but also recycle valuable metals from wastewater. Therefore, it is considered a promising technology to treat chromium-containing wastewater. However, the process has not been extensively applied in industry due to its high synthesis temperature. In this paper, the feasibility of chromite synthesis at room temperature was comprehensively studied. The effects of critical factors on the effluent quality and the crystallization behavior and stability of the synthetic products were investigated. Results showed that the removal ratio of chromium from wastewater was over 99.0%, and the chromium concentration in the supernatant reached the sewage discharge standard after undergoing the ferrite process at room temperature. Increases in the aeration rate, stirring rate, and reaction time were favorable for the formation of stable chromite. The particles obtained by the ferrite process at room temperature were characterized by a compact structure, and the maximum size of the particles reached 52 μm. Chromium gradually entered the spinel crystal structure during the synthesis process, and the molecular formula of the synthetic chromite might be Fe3-xCrxO4, in which x was approximately 0.30. The path of the microscopic reaction was proposed to illuminate the synthesis mechanism of chromite under room temperature conditions. The present study has laid the foundation for the industrial application of the ferrite process in the purification and utilization of chromium-containing wastewater.

To establish a cleaner production technology of chromium salt, the pressurized leaching process of chromite ore in 60 wt.% NaOH solution, subsequent separation of a chromium salt from the leached solution and Cr2O3 preparation from the intermediate product BaCrO4 were systematically investigated, and a new highly efficient and economical process for the production of Cr2O3 from chromite ore was established. The results showed that the decomposition of chromate ore could be significantly improved by increasing the temperature, and the Cr leaching rate reached 99% at 240 ℃ for 4 h. Meanwhile, the leaching process was controlled by surface chemical reactions with activation energy (Ea) of 34.3051 kJ/mol and a pre-exponential factor (A) of 6.9560. In the leached liquor, Na2CrO4 was transformed into BaCrO4 through its reaction with Ba(OH)2, Cr separation efficiency could reach as high as 89% in the undiluted leached liquor, while the separated alkali liquor could be effectively recycled for the leaching of chromite ore. Ultimately, a new method for the preparation of Cr2O3 from the intermediate product BaCrO4 was presented by the dissolution and reduction of BaCrO4 with HCl-CH3CH2OH as the reactant. The new cleaner process for Cr2O3 preparation from chromite ore provides an attractive alternative to upgrading the current chromate salt production processes.

Cerium-promoted silica supported copper chromite catalyst was synthesized from acid hydrolysis of sodium silicate by sol–gel method. The catalyst was characterized by Brunauer–Emmett–Teller (BET) method, field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD) and pyridine adsorbed Fourier transform infrared spectroscopy (Py-FTIR). Among cerium doped catalysts, 5 wt% of Ce promoted copper chromite supported by 40 wt% of silica (SiCuCr40–Ce5) shows the largest BET surface area. XRD analysis of the reduced form of the catalyst shows both CeO2/Ce2O3 redox system and CuO/Cu2O/Cu redox system. Py-Fourier shows the maximum number of Lewis acid sites for SiCuCr40–Ce5 than others. The highest acetol selectivity with analytical reagent (AR) grade glycerol conversion is observed for SiCuCr40–Ce5 at 200 °C for 3 h in a batch reactor at atmospheric pressure. Cerium promotion lowers the reaction temperature with enhanced glycerol conversion and increased acetol selectivity. Though the above catalyst shows higher conversion for laboratory reagent (LR) grade glycerol but it reduces acetol selectivity. The addition of glucose into the LR grade glycerol further reduces glycerol conversion and decreases the acetol selectivity to zero. This may be due to the presence of iron as impurity in LR grade glycerol. XRD analysis of spent catalyst shows the absence of redox catalytic system and the pore volume reduces identified by BET analysis. Raman analysis of the spent catalyst shows graphite-like carbon deposition in the spent catalyst.

The corroded microstructures of the Cr2O3–Al2O3–ZrO2 refractory brick in an industrial opposed multi-burner (OMB) coal water slurry gasifier were investigated. It was found that the chromite spinel isolation layer rich in iron and magnesium was formed on the surface of the corroded brick body. By comparing and analyzing the corrosion of different zones in the gasifier, the results indicated that the molten slag entered the brick through the gaps and generated the spinel layer along the edge of the gaps, causing the dense structures of the refractory surface destroyed. In addition, in the high chrome brick corrosion experiment conducted by HTSM, 3 μm sized spinel were observed covering on the surface. The FactSage calculation results showed that the amount of spinel produced would drop significantly as the slag penetrated.

Recently, there has been increasing interest in the synthesis and use of refractory oxide ceramics as a high-temperature electrode and also thermo-electric materials. These materials, such as perovskite type oxides, particularly, compounds like lanthanum chromite LaCrO3, usually exhibit hopping-type electrical conductivities approaching 30(Ω.cm)-1. The present work aims to synthesize and characterize rare-earth chromite oxides RECrO3 (RE: La, Yb, Gd, Pr), which have the orthorhombic perovskite structure that is apparently stable at 1000 °C calcination temperature. The synthesis of RECrO3 (RE: La, Yb, Gd, Pr) compounds was made by a citrate gel process, using rare-earth-nitrate salts as cation precursors, and followed by a heat-treatment at various temperatures (400 °C, 600 °C, 800 °C, and 1000 °C) for 4 h. The obtained powders were characterized by X-Ray diffraction (XRD), and scanning electron microscopy (SEM). Results show that all the products, especially calcined at 1000 °C have a high purity degree and good crystallinity and that this latter increases with the calcination temperature increasing which has “in contrast” a great effect on the agglomeration of the powders as is shown in the SEM’s micrographs.

We report the first zinc isotope data (expressed as δ66Zn relative to the JMC-Lyon standard) for chromian spinels (Cr-spinels) and coexisting olivines in oceanic peridotites. All spinel-olivine pairs fall on the 1:1 fractionation line in the diagram of δ66Znspinel versus δ66Znolivine, suggesting equilibrium isotope fractionation. Cr-spinels are always isotopically lighter than coexisting olivines (Δ66Znspinel-olivine = δ66Znspinel − δ66Znolivine = −0.50‰ to −0.33‰; n = 13), which is opposite to the positive Zn isotope fractionation between Al-spinel and olivine observed in cratonic peridotites. The “inverse” Zn isotope fractionation between Cr-spinel and olivine is unlikely to have been caused by low-temperature alteration of the oceanic peridotites, given the lack of correlation between Δ66Znspinel-olivine values and chemical indices of serpentinization and weathering (e.g., LOIs, MgO/SiO2). Ionic model calculation indicates that even considering that Zn occurs at both tetrahedral and octahedral sites in the crystal lattice of spinel, the magnitude of equilibrium fractionation is still inconsistent with the observed Zn isotope fractionation between Cr-spinel and olivine. We suggest a “chemical effect” in which the Zn O bond length (tetrahedral site) in spinel increases when Cr substitutes Al in octahedral site, which is corroborated by the striking negative correlation of δ66Zn with Cr# [molar Cr3+/(Cr3+ + Al)] in natural spinels. Therefore, Zn isotopic compositions of natural spinels can be highly variable depending on their chemical compositions. During magma differentiation, zinc is moderately incompatible in silicate minerals (olivine and pyroxene) but highly compatible in Cr-spinels/chromites that have Zn contents tens of times higher than those of basaltic melts. Given its light Zn isotopic composition, chromite crystallization–if any–can evidently elevate δ66Zn and lower Zn contents of the residual melts. Lunar mare basalts are typically characterized by higher δ66Zn and lower Zn contents relative to terrestrial basalts, but modelling suggests that chromite crystallization during magmatic differentiation is unlikely to account for Zn isotopic and elemental data of lunar mare basalts. Global ocean island basalts (OIBs) and some intraplate alkali basalts have systematically higher δ66Zn and higher Zn contents than those of the normal mantle-derived melts (e.g., mid-ocean ridge basalts; MORBs), which contradicts with a chromite crystallization model. Instead, such signatures can reflect recycling of surface carbonates into the Earth’s deep mantle, reinforcing the application of zinc isotopes as a tracer of deep carbonate recycling.

Ferrochromium nitride is an important alloying additive for smelting nitrogen–containing steel. Preparing nitrides by using ammonia gas as reducing and nitriding agent is characterized by high–efficiency and carbon free. In this study, the reaction behavior between chromite spinel and ammonia gas was investigated. Thermodynamic analysis revealed that the reaction was feasible. The transformation of chromite spinel as well as the final products were dependent on reaction temperature, time and input fraction of ammonia gas. The experimental results proved the effect of reaction parameters on the reduction and nitridation process. Chromite spinel was reduced and nitrided to form metallic iron and CrN at temperatures below 950 °C, while metallic iron and Cr2N were the main products at 1000 °C. XPS analysis also proved the existence of CrN and Cr2N. Ferrochromium nitride with N content treater than 15 wt% was obtained when reducing above 950 °C for 3 h.

The present study investigates the recovery of chromite from a low-grade ferruginous ore through the carbothermic magnetization route using conventional and microwave heating sources. The carbothermic magnetization of ore is studied in both a horizontal tube furnace and a microwave oven by varying different process variables. The main objective of the study is to enhance the magnetic susceptibility of iron-bearing gangue minerals to enable the separation in a magnetic field. Alteration of crystalline structure and magnetic property of these minerals enables separation of low-grade ore by using magnetic separation. It is found that low-grade ferruginous chromite ore can be upgraded by reduction roasting, and 61.2% Cr2O3 was recovered with a chromium-to-iron ratio of 1.93 from a feed chromium-to-iron ratio of 1.01. The optimum result is achieved at a roasting temperature of 800 °C, with a roasting time of 60 min and a reductant dosage of 7.5%. Similarly, under microwave radiation, the chromium-to-iron ratio was upgraded to 1.81 with a recovery of 22%Cr2O3. The optimum result achieved under microwave radiation is at a microwave power of 900 W and exposure time of 7.5 min, with a reductant dosage of 10%. The findings of these two processing routes are discussed through characterization tools.

In this study, the properties of machinable glass-ceramic materials produced from basalt and chromite ore were investigated. Three different compositions by adding chromite ore in different ratios to the main composition produced from basalt and MgF2 were prepared. In this way, the effects on the machinable glass-ceramic of chromium and iron oxides in the chromite ore were investigated. Thermal degradation of chromite ore and the effect of its compounds on the crystallization of machinable glass-ceramics were investigated. The samples were subjected to machinability testing. Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were used for characterization. The results show that chromite addition has positive effects on crystallization and machinability. Also, crystallization kinetic studies were realized. It was seen that the effect of iron oxide in chromite ore on crystallization is higher than that of chromium oxide for the crystallization conditions that used chromite ore as a nucleating agent.

Catalysis of chromite spinel MCr2O4 (M = 3d metal etc.) depends very much on M but the reason is unclear. Herein, CO oxidation by cubic MCr2O4(1 1 1) (M = Mg, Co, Cu, and Zn) and tetragonal CuCr2O4(1 0 0) was investigated as one example, using DFT + U. Surface termination of these chromites is determined by available oxidation state of M. Catalytic activity of the most stable surface termination increases following the order cubic CuCr2O4(1 1 1)

Oxygen bottom-blown smelting technology (SKS) is a promising way to utilize the low-grade and complex multimetallic copper ores. To reveal the wear mechanisms of the furnace linings, a post-mortem study of the used refractories (fused-grain rebonded magnesia-chromite refractory) was carried out by chemical and microstructural analysis. The results showed that the chemical interaction at the bath-lining interface was particularly strong since thick corrosion layers (around 4.0 cm) were generated, where a continuously distributed phase of forsterite was identified. This was mainly owing to the high injection pressure and the presence of Cu-CuxO melts in the slag, which greatly accelerated the slag infiltration and periclase dissolution. In this case, fused grains with a high content of intergranular spinel were found more difficult to be corroded by the slag. The significant loss of direct bonds and the softening of refractory are considered as the main degradation mechanisms for the SKS furnace linings. The interaction between FexO in slag and chromite spinel was evident, but it only occurred in the areas near the hot face, showing limited effect on the corrosion behavior.

To better understand the role and extent of inter-mineral diffusion during subsolidus processes, we investigated the iron and magnesium isotopic compositions of olivine, orthopyroxene, and chromite separates from the Peridotite Zone of the Stillwater Complex. Olivine and orthopyroxene show limited Mg isotopic variations, with δ26Mg values ranging from −0.40 to −0.26‰ and from −0.29 to −0.22‰, respectively. In contrast, chromite displays extremely large Mg isotopic variations, with δ26Mg values ranging from −0.05 to +0.84‰. The δ56Fe values of olivine and orthopyroxene range from 0.00 to +0.17‰ and −0.04 to +0.06‰, respectively, whereas those of chromite range from −0.09 to +0.13‰. Most olivine-orthopyroxene pairs in our samples show no clear Fe-Mg isotopic differences, whereas silicate and coexisting chromite pairs plot away from theoretically predicted equilibrium lines, indicating disequilibrium inter-mineral fractionation. Higher δ56Fe values in silicates than in chromite and significantly higher δ26Mg values in chromite than in silicates indicate that subsolidus re-equilibration is responsible for the observed disequilibrium Fe-Mg isotope fractionation. We develop a quantitative model based on the investigated olivine and chromite to reproduce the observed kinetic Fe-Mg isotope fractionations. Our model results indicate a systematic difference between the Fe and Mg isotope fractionation factors, β, of olivine (βFe ≈ 0.27 and βMg ≈ 0.16) and chromite (0.03

We investigated thermoelectric and magnetic properties of polycrystalline CuCr1-xMgxO2 (x = 0; 0.002; 0.008; 0.015; 0.030) ceramic samples, synthesized by a special chemical homogenization method (nitrate synthesis). Temperature dependencies of magnetization were measured in magnetic field H = 1000 G. Transition temperature do not noticeably shift with variation of Mg content. Seebeck coefficient S increases with temperature for all investigated samples. At room temperature S decreases from nearly 700 mV/K in pristine material to about 250 mV/K for the copper chromite with 3at.% Mg. Heat conductivity k of all investigated samples is close to the heat conductivity of undoped CuCrO2 crystals. Resistivity of investigated samples decreases several orders of magnitude with increase of Mg content up to 3%. Temperature dependence of resistivity and Seebeck coefficient was interpreted by hopping conductivity in the presence of the Coulomb (parabolic) gap in the density of states.

In this contribution an overview of oceanic lithosphere, associated ore deposits (sulphides, Fe and Mn oxides, chromitites) and their final destination in ophiolitic rocks are presented. This is followed by a discussion on massive sulphide mineralisation formed at mid-ocean ridges (MOR) and/or supra-subduction zones (SSZ). The geological characteristics and the genesis of the Cu-rich massive sulphide deposits of Cyprus and of the Oman ophiolite are discussed based on an extensive review of the published literature. This is followed by a synopsis of the ophiolitic terranes and associated mineral system in the Urals. We also present an overview of the ophiolitic belts and sutures of the Tethyan orogens, focussing on the podiform chromite deposits that they typically host, with a special focus on the ophiolitic chromitites of Turkey. A final section deals with possible ophiolites of Proterozoic and Archaean ages and, where applicable, associated chromitites. In the concluding remarks a brief note is made of some specific ancient seafloor hydrothermal constructs that have been interpreted as black chimneys in volcanogenic massive sulphide (VMS) deposits now hosted in ophiolitic sequences.

co-auteur étranger; International audience; Transition metal isotopes are particularly useful for understanding the conditions under which magmatic processes occur. Moreover, those with more than one oxidation state (e.g. Cr2+, Cr3+ and Cr6+) may also provide powerful constraints on the evolution of the redox state of the mantle over time. By investigating the Cr isotopic compositions in both magnesiochromite and silicate melts during experiments performed at 1300 °C and under controlled redox conditions (−12 −6) are much lighter than those of melts equilibrated with magnesiochromite at lower oxygen fugacity. The observed variations can be explained by changes in bonding environment for Cr under oxidised conditions in the silicate melts and/or in the magnesiochromite grains. Similarly, the second set of experiments designed to study fractional crystallisation (series B) suggest that Cr isotope fractionation is larger under oxidising conditions.

Understanding the mechanisms of the breakage of ore particles is important to predict the particle size distribution in size reduction operations. This paper aims to show the presence of common breakage modes in impact breakage and ball milling of the cement clinker and chromite samples. For that purpose, narrow size fractions of the two samples were broken in a drop-weight tester or ball mill by changing the degree of applied energy. Then the resultant size distributions were evaluated to seek evidence for the common breakage modes. The results showed that increasing the breakage energy will produce a systematic change in the shapes of the size distributions, suggesting a sequential set of breakage modes. The breakage is initially due to tensile stresses at low breakage energies and compressive stresses at high breakage energies. Further studies should be done to assess if these breakage modes occur at size-reduction of different ores.

Oxygen side-blown reducing smelting is an efficient and environment-friendly technology to directly process the liquid high-lead slag, but it shows high refractory wear during industrial practice. To understand the specific degradation mechanisms, a post-mortem analysis of magnesia-chromite refractory bricks (fused-grain rebonded type) taken from the tuyeres of the furnace was performed by SEM and phase diagram. According to the results, typical reaction zone and infiltrated zone were formed between the hot face and the original refractory. The fast and deep infiltration of PbO-containing fayalite slag under turbulent conditions was responsible for the significant dissolution of periclase grains, which caused the development of a continuous and thick forsterite layer. Meanwhile, the components of FeO and ZnO in the slag were mainly absorbed by the chromite grains. Then the increased CaO/SiO2 of the slag resulted in the large formation of monticellite in the infiltrated zone. Based on these results, the key reasons for the high wear of refractory lining were revealed and several possible solutions were also proposed.

The effective extracting Cr(VI) from chromite ore processing residue (COPR) is the key to achieve COPR detoxification and recovery. We developed an effective method to extract Cr(VI) from COPR via controlling the phase transformation of Cr(VI)-containing minerals. Characteristic analysis showed that Cr(VI) was mainly incorporated in the hydrocalumite (NaCa4Al2O6(SO4/CrO4)1.5⋅15H2O) in COPR, which was a layered-double hydroxide (LDH) with multilayer structure. In the hydrothermal treatment experiments, the Na2CO3 solution showed significant extraction effect of Cr(VI) and detoxification effect of COPR. After treatment, 95% of Cr(VI) was removed and the Cr(VI) concentration in the leachate was decreased to 1.6 mg/L by the toxicity characteristic leaching procedure (TCLP), within the regulatory limit disposal standard (HJ/T 301–2007, 3 mg/L). Further study revealed that, during the treatment, hydrocalumite transformed into calcite (CaCO3) under the effect of mineralizer, therefore, the layered structure collapsed and the incorporated Cr(VI) was released to the supernatant. Meanwhile, the Cr(VI) desorbed from calcite with the calcite particles grew into large size with smooth surface. Stir-flow experiment revealed that the amount of chromium released from CORP to the environment was significantly reduced after treatment, and it is safer for landfill disposal. This work will provide an instructive guidance for the detoxification and recovery of COPR.

Dissimilatory Iron Reducing Bacteria (DIRB) in specific has found wide range of application in bio-beneficiation for removal of iron impurities from different ores and in bioremediation for detoxification of heavy metals, hazardous pollutants, etc. Numerous research works have been reported for bio-beneficiation of kaolin, bauxite by IRB. This study aims at studying effect of anaerobic dissimilatory iron (III) reducing bacterial consortium on different phases of iron present in lateritic nickel ore. Such conversion in lateritic nickel ore is helpful in better recovery of sorbed metal values like Ni and Co by subsequent bioleaching or acid leaching. Over the past decade, the global demand-supply chain of nickel is constrained due to depletion of sulphidic nickel ores. However, with anticipated boom in electric vehicles (EVs), the forthcoming decade for battery demand is very bullish for nickel. Hence, there is an urgent need to extract nickel from lateritic nickel ores to meet its high demand. Application of conventional methods for nickel extraction from lateritic ores is challenging from metallurgical and technical viewpoint and requires high capital investments. There is ongoing search for alternative nickel extraction methods from lateritic ores to meet the high nickel demand loom. In India, nickel metal is concentrated in the Chromite overburden (COB) dumps of Sukinda Valley Jajpur, Odisha. The nickel metal is ingrained within the stable goethite matrix (oxidic mineral phase) which requires stringent actions (high energy and/or chemical attack) for its dissociation. 70% Ni and 81% Co was recovered on acid-leaching of DIRB-treated ore whereas only 54% Ni and 57% Co was recovered on acid leaching of untreated COB Hence, pre-treatment of COB with DIRB can enhance the recovery of nickel. Exploitation of competent indigenous microorganisms can thus formulate an eco-friendly approach for nickel extraction. This work discusses the various aspects of microbial application for nickel recovery from lateritic nickel ores.

Olivine chemistry has been widely used to track the petrogenesis of mafic and ultramafic magmas from their mantle source to eruption at the surface. A major challenge in these studies is deciphering crystal growth versus diffusion controlled zoning. Here we report a multi-element approach using high-precision electron microprobe techniques to evaluate crystal growth versus diffusion in kimberlitic olivine from the Benfontein kimberlite, South Africa. These results have implications for both the petrogenesis of kimberlite magmas and the understanding of crystal growth and diffusion-based zoning in igneous olivine in general. The Benfontein olivine contain multiple phosphorous (P)-rich and P-poor zones. Core zones are characterized by homogenous low-P ( Multiple P-poor (100–150 ppm) and P-rich (200–450 ppm) concentric, oscillatory zones with inclusions of kimberlitic oxide phases are observed surrounding the low-P xenocrystic cores. Oxide phases change from chromite in the inner zones to ilmenite in the intermediate zones to magnetite-rich spinel in the outer zones of the olivine. The P-zoning corresponds with changes in Fo content implying that stages of crystal growth was preserved by both fast and slow diffusing elements rather than diffusion processes. Elements compatible with olivine (±chromite) crystallization (i.e., Ni and Cr) display a constant decrease across all zones, suggesting that magma mixing is unlikely a controlling process for P-zoning. We interpret P-rich zones to result from stages of solute trapping related of rapid disequilibrium growth driven by extrinsic factors such as changes in pressure-temperature during kimberlite evolution. In contrast, P-poor zones represent stages of equilibrium crystal growth. The outer olivine zones are characterized by an increase in Fo contents up to Fo96, and in conjunction with a change to more Fe3+-rich oxides, suggest late stage increase in fO2. Correlated Fo and P changes in the Benfontein olivine suggest that major element zonation represents an example where crystal growth-induced Fo zoning has been preserved in olivine. Furthermore, P-rich olivine zones preserve evidence for concentric growth rather than common dendritic structures seen in other occurrences. These results have implications for understanding the effect of magma dynamics and changes in pressure-temperature-fO2 conditions on olivine growth in igneous rocks.

Ageing is an irreversible process during which, the material undergoes a series of slow chemical degradation/oxidation reactions. The aim of this paper is to study the effect of ageing of ammonium perchlorate-copper chromite (AP-CC) pellets on the burn rate. It also focuses on any change in CC properties due to direct contact with an oxidizer (AP). Accelerated ageing with cyclic temperature profile has been used to replicate the natural ageing. The effect of ageing of individual ingredients on the burn rate was studied. The burn rate of AP-CC pellets was found to reduce when AP-CC were aged together. X-ray diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) analysis were used to identify the change in properties of copper chromite during ageing.

Chromium isotope data were obtained from olivine, orthopyroxene and chromite separates of the Kizildag ophiolite, SE Turkey, to investigate the effects of high temperature magma processes on Cr isotope fractionation. Harzburgite in the Kizildag ophiolite has the δ53Cr values of −0.14 to −0.12‰ in chromite, and −0.08 to −0.01‰ in bulk rocks. These Cr isotope fractionations could be driven by partial melting and metasomatism. The dunite and chromitite samples from the mantle-crust transition zone of the Kizildag ophiolite are cumulates, and their chromite and olivine have δ53Cr values of −0.29 to −0.06‰ and −0.11 to 0.41‰, respectively. The δ53Cr values of chromite are negatively correlated with the chemical indices of fractional crystallization (e.g., Fe# of chromite), suggesting that Cr isotopes were fractionated during fractional crystallization. In the chromitite, the degree of Cr isotope fractionation increases with fractional crystallization, with 0.23‰ Cr isotope fractionation occurring at mineral scale. During fractional crystallization, solid phases preferentially incorporate Cr, particularly heavy Cr isotopes, driving the depletion of Cr and enrichment of light Cr isotopes in the evolved melts. The δ53Cr values of olivine are higher than the coexisting chromite, which could be explained by the fact that the olivine grains were probably formed earlier than the chromite. The Cr isotopic features of chromite in the podiform chromitite (−0.22 to −0.04‰) from the mantle sequence are consistent with the modelled fractional crystallization trend, confirming the magmatic origin of the podiform chromitite. Therefore, a significant Cr isotope fractionation at chromite from the Kizildag ophiolite could be induced by the high-temperature fractional crystallization.

To investigate chromium diffusion kinetics in ultramafic cumulate minerals, we analyzed the Cr elemental and isotopic compositions of olivine, orthopyroxene, and chromite from the Stillwater layered intrusion. Core-to-rim compositional profiles reveal that Cr elemental concentrations decrease from 60 to 20 ppm in olivine and from 5000–4600 to 2700–2400 ppm in orthopyroxene. These zoned Cr distributions in olivine and orthopyroxene suggest that Cr was lost by diffusion into the melt. Olivine and orthopyroxene have δ53Cr values ranging from –0.09 to 0.25‰ and from –0.11 to 0.07‰, respectively, higher than the values of coexisting chromite (–0.23 to –0.07‰). This isotopic disequilibrium can be explained by diffusion-driven kinetic fractionation during cooling. The preferential diffusion of light Cr isotopes from silicate minerals to the melt resulted in isotopically heavier olivine and orthopyroxene, but the kinetic diffusion between chromite and melt negligibly affected the isotopic compositions of chromite grains due to their high Cr concentrations. Modeling results based on the observed Cr contents and isotopic compositions of silicate minerals constrain the cooling time of the Peridotite Zone in the Stillwater magmatic system to have been 10–100 kyr.

This paper deals with the low pressure deflagration limit (LPDL), which is the minimum pressure below which burning of a propellant ceases without the assistance of an external energy source. The LPDL of AP monopropellant reported in literature is around 20 bar and it is reported to shift to different higher pressures with the addition of small fraction of impurities or additives. Most of these additives (such as iron oxide and copper chromite) are known to catalyze AP combustion, but yet their reported LPDL is significantly higher than the LPDL of AP itself. In present study, reasons for this behavior have been explored experimentally. Three additives (each of 1% by mass) namely iron oxide (IO), copper chromite (CC) and activated charcoal (AC) were used. The LPDL of AP with these additives was determined using three methods. Two of these methods (method I and method II) include the effect of ignition dynamics on LPDL while in method III (slow depressurization) ignition dynamics does not play a role. In method I, hot nichrome wire was used for ignition, while in method II, nichrome wire ignition in conjunction with an in-situ propellant was used to ignite the pellets. The effect of convective heat loss on LPDL was studied with the use of silica grease whose role through carefully thought out experimentation has been identified as an insulation on sides of pellet. The LPDL of AP with additives was found to be higher for method I compared to method II. Lastly, method III (slow depressurization) was found to result in lowest LPDL for these additives. The LPDL of pure AP, which has been reported as around 20 bar, was revisited and method III along with the use of silica grease has lowered the LPDL of pure AP to 14 bar.

We have reconstructed the distribution of extraterrestrial chrome spinels in a marine limestone section across the Frasnian-Famennian stratotype section at Coumiac in southern France, providing the first insights on the types of micrometeorites and meteorites that fell on Earth at this time. The data can test whether the small cluster of roughly coeval, large impact structures is related to an asteroid breakup and shower with possible bearings also on the late 26 Devonian biodiversity crisis. A total of ~180 extraterrestrial spinel grains (>32 microns) were recovered from 957 kg of rock. Noble-gas measurements of individual grains show high solar-wind content, implying an origin from decomposed micrometeorites. Element analyses indicate a marked dominance of ordinary chondritic over achondritic grains, similar to the recent flux. The relation between H, L and LL meteorites is ~29-58-13%, similar to the late Silurian flux, ~31-63-6%, but different from the distribution, ~45-45-10%, in the recent and the Cretaceous flux. Our data show no indication of a generally enhanced late Devonian micrometeorite flux that would accompany an asteroid shower. However, in a single limestone bed that formed immediately before the Upper Kellwasser horizon, that represents the main end-Frasnian species-turnover event, we found an enrichment of ~10 ordinary chondritic grains (>63 microns) per 100 kg of rock, compared to the ~1-3 grains per 100 kg that characterize background. The anomalously abundant grains are of mixed H, L and LL types and may be related to an enhanced flux of extraterrestrial dust during postulated minima in both the 405 ka and 2.4 Ma Earth-orbit eccentricity cycles at the onset of the Upper Kellwasser event. In the present solar system the dust accretion at Earth is the highest at eccentricity minima because of the spatial distribution of dust bands of the zodiacal cloud. Besides this small grain anomaly the data here and in previous studies support a stable meteorite flux through the late Silurian and Devonian, in contrast to the mid-Ordovician, when achondritic meteorites that are rare on Earth today were common, followed by the influx of a flood of debris related to the breakup of the L-chondrite parent body. Our accumulated data for six time windows through the Phanerozoic indicate that the ordinary chondrites make up a major fraction in the meteorite flux since at least the mid-Ordovician. We note that the sources in the asteroid belt of the H and L3 meteorites, the two most common types of meteorites today and through much of the Phanerozoic, remain elusive.

Carbonatite metasomatism plays an important role in modifying the composition of Earth's mantle, however, its effect on mantle Mg isotopic composition is poorly constrained. Here, we report high-precision mineral Mg isotope data for three suites of mantle peridotite xenoliths that experienced variable degrees of carbonatite metasomatism. The δ 26 Mg values of minerals in these xenoliths are variable and range from −0.32 to −0.11‰ in olivine, from −0.28 to −0.09‰ in orthopyroxene, from −0.27 to −0.05‰ in clinopyroxene, from 0.06 to 0.44‰ in spinel and from −0.61 to −0.37‰ in garnet. Calculated bulk-rock δ 26 Mg values of the peridotites vary from −0.27 to −0.10‰, falling within and slightly higher than the normal mantle range (−0.25 ± 0.07‰). The coexisting minerals are in isotopic equilibrium, with clinopyroxene δ 26 Mg values correlated with the carbonatite metasomatic indices such as MgO and Na2O in orthopyroxene. These results suggest that carbonatite metasomatism does not produce light Mg isotopic signature in mantle peridotites as previously suggested, instead it might slightly elevate their δ 26 Mg values. Therefore, carbonatite-metasomatized peridotites in the mantle cannot be the primary source rocks of low- δ 26 Mg mantle-derived magmas. Instead, fractional crystallization and accumulation of chromite during ascent of the basaltic magmas may explain the isotopically light basalts, as supported by the covariations of δ 26 Mg with chemical indices of chromite crystallization (e.g., Cr, V, Fe and Ti). Consequently, chromite crystallization may significantly influence the physiochemical processes on the genesis of basalts, which would require comprehensive evaluation in future studies.

This work is a post-mortem study of the magnesia-chromite refractory lining of the gas area of a Submerged Arc Furnace (SAF) used for slag-cleaning at the Atlantic Copper Smelter (Spain) after a six-year working campaign. A Scanning Electron Microscope (SEM) equipped with an Energy Dispersive Spectroscopy (ESEM-EDS) system was used to identify the phases and for chemical analysis.Almost nothing on Submerged Arc Furnace operations in the copper-making industry is found in literature, and none has focused on the interactions of the magnesia-chromite refractory used in the area in contact with gases.In this work, refractory brick samples were collected from the gas area of a Submerged Arc Furnace that processed fayalitic slag after a six-year campaign. These bricks had been penetrated by gases. Lead and zinc from the gases were found on the hot face of the refractory. The post-mortem analysis was supported by thermochemical calculations using FactSage® databases. Resumen: Este trabajo está enfocado al estudio post mortem del refractario usado en la zona de gases de un horno eléctrico de arco sumergido (SAF) donde se han llevado a cabo las operaciones de limpieza de escoria durante seis años de campaña en Atlantic Copper (España). Para la identificación de las fases y los análisis químicos de las mismas se ha usado un microscopio electrónico de barrido (SEM) equipado con un espectrómetro (ESEM-EDS).En la literatura no se encuentra casi nada publicado referente a operaciones de hornos eléctricos de arco sumergido en la industria del refino del cobre y nada referente a la interacción de los gases de este proceso con el refractario de magnesia-cromita usado en los mismos.Para este trabajo se han tomado ladrillos de muestra de la zona, de gases de un horno eléctrico de arco sumergido después de seis años de operación de limpieza de escorias fayalíticas (recuperación de cobre). Estos ladrillos refractarios se han encontrado infiltrados por gases. En la cara caliente de lo refractario se ha encontrado plomo y zinc procedente de las fases contenidas en los gases de proceso. El análisis post mortem ha sido complementado con cálculos termodinámicos usando las bases termodinámicas de FactSage®. Keywords: Refractory, Magnesia-chromite, Submerged Arc Furnace, Post-mortem, Gas, Palabras clave: Refractario, Magnesia-cromita, Horno de Arco Sumergido, Post-mortem, Gas

International audience; This work provides the first comprehensive petrological and multi-scale structural investigation of a suite of ultramafic bodies and enclosing metasediments from the Late Paleozoic accretionary prism of South-Central Chile. The targeted outcrops are located in the La Cabaña area and are characterized by the presence of three main types of ultramafic rocks: (1) partially serpentinized massive peridotites, (2) antigoritic schistose serpentinites, and (3) antigoritic mylonitic serpentinites. Partially serpentinized massive peridotites and schistose serpentinites recorded a common first hydration event with the formation of Fe2+ porous rim in chromites (at ~500 °C), followed by static partial transformation of olivine to lizardite (below ~300 °C) and formation of rims of Fe3+-rich chromite and magnetite around chromites. A second event of serpentinization linked to fluid passage through zones with focused deformation resulted in the partial transformation of partially lizarditized massive peridotites into antigoritic schistose serpentinites (at ~320–400 °C). This second event took place within the shallower portion of the serpentinitic subduction channel, near the base of the accretionary prism and was characterized by the formation of tubular folds made up of lenses of olivine-lizardite massive rocks embedded in a matrix of schistose serpentinites. Antigoritic mylonitic serpentinites encountered in the matrix of schistose serpentinites may locally contain metamorphic olivine (i.e., olivine-bearing mylonitic serpentinites), registering higher temperature conditions at medium pressures (~600 °C, 11 kbar) that prevailed during the initial immature stage of development of the subduction system. Moreover, some mylonitic serpentinites containing Ti-clinohumite, Ti-chondrodite and metamorphic olivine still record higher pressure conditions (>15 kbar, i.e., >50 km depth for ~500 °C), which are related with a deformational event taking place when the subduction system had already cooled. These medium- and high-P mylonitic serpentinites preserved kinematic indicators of burial, whereas their exhumation along the subduction channel towards the shallower schistose serpentinites near the base of the accretionary prism could take place through discrete shear zones possibly aided by large sheath folds. Once incorporated in the accretionary prism (c. 285 Ma ago), the serpentinites shared metamorphism and deformation with the enclosing metasediments. Subvertical shortening related to uplift processes within the accretionary system took place in the stability field of antigorite (>300 °C) and, later, a subhorizontal E-W shortening prevailed in more superficial conditions.

Reductive dissolution of corrosion product oxides relevant to nuclear power plants such as haematite (Fe2O3), nickel ferrite (NiFe2O4), iron chromite (FeCr2O4) and mixed oxides (NiFe2-xCrxO4; x = 0.4, 0.8, 1.2 and 1.6) were carried out in ethylene diamine tetra acetic acid (EDTA) and nitrilo tri acetic acid (NTA) based chemical formulations. Of all the reducing agents investigated, Cr(II)-complexes were found to be effective in dissolving these oxides. The results showed no preferential dissolution of a metal ion from the oxide lattice and the rate of dissolution was influenced by the concentration of Cr(II)-complex in solution, chromium content in the oxide lattice and pH of the formulation.

We report here for the first time aluminous Ca-amphibole exsolution lamellae in an anhydrous chromite host of podiform chromitite from the Nakhl massif of the Semail Ophiolite. Transmission electron microscopy observations show that the Ca-amphibole lamellae have a crystallographic topotaxy and d-spacing relationship with the host chromite, i.e., [103]am//[11 8 _ ]chr, (020)am//(2 2 _ 0)chr and d060am ≈ d220chr, that indicate an exsolution origin. The presence of Ca-amphibole exsolution implies the incorporation of Si4+ and Ca2+ cations and hydroxyl in the host precursor chromite. The reconstructed precursor chromite had SiO2 concentrations of 0.33–0.58 wt%, suggesting upwelling from a minimum pressure of 8 GPa (depth of ~250 km). Hydroxyl groups occupy octahedral vacancies, which can be introduced in high-pressure chromite by substituting 4 Cr3+ by 3 Si4+ and a vacancy. During upwelling, vacancies decrease when Si4+ cations exsolve stepwise from chromite. It leads to a coupled decrease of OH occupied vacancies and exsolution of Ca-amphibole lamellae at pressures below 3 GPa. Our results provide new evidence for a deep origin of the chromitite-bearing mantle section of the Semail ophiolite.

Liberation of the valuable minerals of an ore from its gangue is a prerequisite for the economic recovery of the valuable minerals to concentrates. Mineral liberation is achieved by reducing the size of ore particles in various crushing and grinding devices. The fineness to which the ore must be ground, so as to yield sufficient degrees of liberation, increases if the valuable minerals with small grain sizes are disseminated throughout the gangue. Intensive fine grinding, however, increases energy costs and can lead to the loss of very fine untreatable particles into the tailings. Therefore, research should be oriented toward developing methods to foster breakage through the mineral grain boundaries to accomplish liberation at relatively coarser grinds. The purpose of this study is to determine if the pretreatment of the samples of a chromite ore with aqueous solutions of some salt and surfactant additives could improve the liberation by promoting preferential fracturing at the grain boundaries between the chromite and silicate minerals in the ore. For this purpose, untreated and pretreated samples of −9.53 + 6.35 mm size fraction of the ore were broken in a drop-weight tester, and the liberation spectra and the mass distribution of the resultant progenies were measured and compared. Optical and scanning electron microscope images and spectroscopic tools were used to find evidence for grain-boundary fracturing in the breakage progeny fragments. Results support the promoting effect of hydrolysis on grain-boundary fracturing. Aqueous salt and surfactant species enhance grain-boundary fracturing by forming surface complexes and dislocating aluminum atoms at the grain boundaries. Grain-boundary fracturing yields exposed chromite surfaces and enriched chromite content in the coarse progeny particles. The grain-boundary weakening is associated with slight hardness variation along the boundary.

Considering the simplicity and flexibility of thermal treatment method for preparing fine nanocrystalline oxide, the present work reports up-scalable synthesis of nanosized nickel cobalt chromite spinel. The effect of calcination temperatures on the final properties of obtained materials was carefully examined using various characterization techniques. The XRD and FT-IR spectra confirmed the formation of nickel cobalt chromite spinel phase in the calcination temperature of 550–850 °C. The estimated average sizes from TEM images increases from 10 nm at 550 °C to 51 nm at 850 °C, which are in good agreement with determined crystallite size from XRD analysis. The calcined samples at 650 and 850 °C showed paramagnetic behavior with g-factor of 1.93 and 2.19, peak-to-peak line-width of 2053 and 8905 A/m, and resonance magnetic field of 27089 and 23755 A/m, respectively. Variation in the value of g-factor, peak-to-peak line-width and resonance magnetic field may be attributed to the dipole-dipole and super exchange interactions.

Combined Fe isotopic and olivine fabric analyses have been conducted on the nodular chromitites from the Luobusa ophiolite, Tibet, to study the physico-chemical effects of plastic flow in modifying chromitites and their associated mantle peridotites below spreading centers. The Luobusa nodular chromitites are generally composed of fresh dunitic matrices and well-aligned chromite nodules. Olivine grains in both the dunitic matrices and chromite nodules underwent pressure solution, and those in the dunitic matrices have prevalent Fe-rich stripes parallel to their kink bands and sometimes show lattice dislocation-induced preferred orientations of (1 0 0). Chromite grains in the chromite nodules have Cr# ∼ 75–80 and δ56Fe values from −0.122 to 0.067. The Fo and δ56Fe values of olivine in the dunitic matrices vary from 96 to 99 and 0.165 to 0.294, respectively, distinguishably higher than those of olivine in ordinary ophiolitic dunites (mostly 90–95 and 0.050–0.150). The calculated Mg-Fe exchange temperatures between olivine in the dunitic matrices and chromite in the chromite nodules range from 700 to 900 °C, overall higher than those for ordinary dunites and chromitites (∼600–800 °C). Combined with numerical modeling of diffusion of Fe in olivine, our study reveals that the abnormally high Fo and δ56Fe values of olivine in the dunitic matrices of nodular chromitites were not controlled by their parental magmas but caused by significant loss of Fe from olivine under subsolidus conditions. Intensive plastic deformation in nodular chromitites largely promoted the migration of Fe from olivine and facilitated the Mg-Fe exchange between the chromite nodules and dunitic matrices, maximizing the Fo and δ56Fe values of olivine. However, such an effect is expected to be negligible in chromite-barren dunites and harzburgites because such rocks do not have enough chromite to generate effective chemical-potential gradients for Fe migration. The high Fo values of olivine in nodular and massive chromitites require fast cooling rates (∼0.05–0.1 °C/yr) in the surrounding mantle, consistent with settings below intermediate-fast spreading ridges. Boudinization of small chromitite bodies in less competent dunites under 900–1200 °C is a potential mechanism for generating the nodular texture, also accounting for the en-echelon or bead-like occurrences of chromitite bodies in ophiolites. Effective mantle flow below spreading centers plays an important role in shaping the textures and compositions of mantle rocks, explaining the absence of deformation-related nodular chromitites in layered mafic-ultramafic intrusions.

We investigate magnetic properties of mixed crystals of spinel oxides Zn(Cr1−xFex)2O4 and Cd(Cr1−xFex)2O4 to study Cr-site substitution effects on the geometrically-frustrated magnetism of chromite spinels ZnCr2O4 and CdCr2O4. Zn(Cr1−xFex)2O4 and Cd(Cr1−xFex)2O4 with above x ∼ 0.1 exhibit spin-glass-like behavior below ∼10 K which is suppressed by magnetic field H > 1 kOe. Moreover, the Fe concentration x dependence of Weiss temperature ΘW in Zn(Cr1−xFex)2O4 (Cd(Cr1−xFex)2O4) exhibits the sign change of ΘW from negative below x ∼ 0.4 (x ∼ 0.1) to positive above x ∼ 0.4 (x ∼ 0.1). This suggests that, in Zn(Cr1−xFex)2O4 and Cd(Cr1−xFex)2O4, the competition of antiferromagnetic and ferromagnetic interactions (bond frustration) becomes stronger with increasing the Fe concentration x, while the geometrical frustration becomes weaker with increasing x.

Non-invasive methods including micro-Raman spectroscopy (μ-Raman), micro X-ray fluorescence (μ-XRF), fibre optics reflectance spectroscopy (FORS) and environmental scanning electron microscopy (ESEM) were used to study thirty-five ceramic shards from Afrasiyab and forty-seven potshards from Nishapur. These shards are dated from the ninth to the tenth century AD and include various types of underglaze and inglaze decoration. Non-invasive scientific studies indicated that tin oxide was employed as a white opacifier in both sites while silicates including quartz, olivine, diopside and feldspar served as opacifier in Afrasiyab shards thus demonstrating a technological connection with the pre-Islamic tradition of glaze opacification. The white slip of most of the wares excavated at Nishapur contained dehydrated pyrophyllite which may be indicative of local production. Furthermore, while a dense distribution of chromite was found in the black underglaze decoration of the so-called yellow staining black ware from Nishapur, a diluted chromite probably obtained from a different source was used in the imitated lustre wares from Afrasiyab. Mixtures with different proportions of manganese oxide and black haematite were utilised as the black colouring agents. Taking all of these findings into account, it is proposed that a consistent ceramic technology and production is represented by the entire set of the shards from Afrasiyab while different materials and technologies are evinced in the Nishapur ceramics.

The Bushveld Complex, the largest layered mafic-ultramafic intrusion worldwide, is host of numerous, laterally continuous and chemically similar chromitite layers. Based on their stratigraphic position the layers are subdivided into a lower, middle and upper group (LG, MG and UG). Within these groups the layers are numbered successively – from the base to the top of each group. Attempts of discriminating between single layers based on their composition have failed – mainly due to the significant overlap of compositional fields, e.g. of chromitite mineral assemblages and chromite mineral chemistry between (neighboured) layers. In this contribution a tailored and easy to use multivariate classification scheme for the chromitite layers is proposed, based on a comprehensive classification routine for the LG and MG chromitites. This routine allows a clear attribution with known uncertainty of eight distinct chromitite layers. The study was carried out at the Thaba Mine, a chromite mine located on the western limb of the Bushveld Complex. The classification is based on a large geochemical database (N = 1205) from Thaba Mine. It comprises of a hierarchical discrimination approach relying on linear discriminant analysis and involves five distinct steps. Using default homogeneous prior probabilities, classification results are excellent for the first discrimination steps (LGs vs. MGs, 97 %; LG-6 vs. LG-6A, 94 %) and very good for the following steps (MG-1/2 vs. MG-3/4, 86 %; MG-1 vs. MG-2, 92 %; MG-3 vs. MG-4, 93 %; MG-4 vs. MG-4Z, 97 %; MG-4 vs. MG-4A, 88 %). The classification scheme was tested using the same sample set as a training set with unknown composition. Overall classification results for unknown samples belonging to one of the layers are 81 %. Hence, the classification scheme is at least valid for the Thaba mine. The approach may, however, be extended across the entire Bushveld, provided that an appropriate geochemical data set is available.

This paper focuses on formation of subcalcic Cr-rich garnet (up to 14.25 wt% Cr2O3) in the model ultramafic system corresponding to natural harzburgite with the presence of REE-bearing fluid phase. The experiments were carried out using a “split-sphere” type multi-anvil high-pressure apparatus (BARS) at a pressure of 5 GPa and a temperature of 1300 °C. Natural serpentine, chromite, corundum and REE-carbonatite were used as starting components. Crystallization of garnet occurred in subsolidus conditions by the reaction of orthopyroxene and spinel in the presence of fluid phase. Composition of fluid was controlled by interaction of water released by decomposition of serpentine with carbonate. By using different amounts of carbonatite (0.5 and 1.5 wt%) as a source of calcium and REE, subcalcic Cr-rich garnets with up to 3.5 wt% CaO were crystallized, which are typical for inclusions of harzburgitic paragenesis in natural diamonds. The experiments demonstrated that the rare earth elements (REE) released from the initial carbonatite were transported by the fluid and were incorporated into the newly formed garnet. The distribution of REE in garnet revealed a vivid enrichment toward the heavy REE (HREE), showing the pattern with a very steep slope. These results confirmed high partitioning of HREE into garnet. The present study indicates that the mantle carbonatites, which contain very high proportions of light REE (LREE) to HREE, can play an important role as source material in formation of REE-rich fluids to crystallize garnets with typical REE patterns in mantle peridotites.

The Songshugou dunites are part of the ultramafic sequence of the Songshugou ophiolite within the Qinling Group metamorphic rocks, which are distributed in the northern part of the Shang–Dan Suture Zone (SDSZ) in central China. The dunites include lenses of coarse- and medium-grained dunite set in a fine-grained dunite host. Disseminated chromite within these dunites can be classified into three microstructural types: (1) partly altered chromite with primary cores surrounded by porous chromite rims; (2) porous chromite with abundant pores that are filled with chlorite; and (3) homogeneous chromite. The primary magmatic cores of the partly altered chromite (Chr) is depleted in Cr and enriched in Al and Mg. Porous chromite includes Cr-rich Chr and ferritchromite (Fe-Chr) that is enriched in Fe2+ but depleted in Al. Homogeneous chromite is mainly Cr-magnetite (Cr-Mag) that is enriched in Fe3+ and extremely depleted in Al. The primary Cr-poor chromite was gradually transformed to porous Cr-rich Chr and/or by Fe-Chr during metamorphism. Reaction of Cr-poor Chr with olivine (Ol) produces chlorite (Chl) and secondary Chr enriched in Cr and Fe2+. Mg and Al diffuse away from primary Chr, leaving a residual Al- and Mg-depleted, Cr-rich Chr and Fe-Chr. Porous Chr is enriched in Zn, Co, Mn, but depleted in Ga, Ni, and Sc, due to the fluid-assisted formation of Chl within the pores of porous chromite. Zn, Co, and Mn from the metamorphic fluids diffuse toward the cores of chromite. The elements Sc, Ti, V, and Ni diffuse from Cr-poor Chr core to Cr-mag rim with increasing Fe3+/(Fe3+ + Fe2+). Late precipitation of Cr-mag occurred under oxidizing and hydrous conditions. The infiltration of fluid produced non-porous Fe3+-rich Chr or Cr-mag along grain boundaries or fractures within chromite. These fluids further promoted the reordering of octahedral sites, enhancing higher mobilization and enrichment of Ga, Ni, Sc, V, and Ti. The infiltration of high oxygen fugacity fluids promoted diffusion of Ga, Ni, Sc, and Ti toward the rims, and diffusion of Zn, Co, and Mn toward the cores. All chromite grains from the Songshugou dunites have low Mg# [molar 100 × Mg/(Mg + Fe2+)] values, and high Cr# [molar 100 × Cr/(Cr + Al)] and Fe3+/(Cr + Al + Fe3+), similar to metamorphic chromite formed under amphibolite-facies conditions. The observed positive Zn–Co–Mn anomalies and negative Ga–Ni–Sc anomalies in chromite, and the crystallization of Chl, are fingerprints of amphibolite-facies metamorphism. The compositions of chromite, the inferred mineral assemblage in which it occurs, and mineral equilibria modeling of the assemblage all suggest amphibolite-facies metamorphic temperatures ranging from 600 °C to 700 °C.

Ultramafic and mafic rocks of the Variscan Śleza ophiolite (Bohemian Massif, Sudetes, SW Poland) contain abundant Cr and Fe-Ti mineralizations. The occurrence of chromitites is related with serpentinites of refractory harzburgitic protoliths. Chromite I from chromitites has variable Cr and Mg numbers (Cr# = 0.41 – 0.58, Mg# = 0.62 – 0.83) and low TiO 2 contents ( 2 , Al 2 O 3 and V 2 O 3 contents (0.19 – 9.82 wt%, 0.13 – 1.67 wt% and 1.08 – 1.61 wt%, respectively). It forms xenomorphic grains with trellis or sandwich exsolutions of ilmenite, as well as aggregates with individual ilmenite grains. The moderate Cr# of chromite I points to an its origin from a MORB-type melt. The occurrence of hydrous inclusions and nodular textures indicates chromitite formation and alteration under low pressure conditions. Primary sulfide, phlogopite and pargasite inclusions suggest that the parental melt was moderately hydrous and sulphur-rich. Water in the magmatic system originated supposedly from interaction of primary MORB melt with hydrothermal fluids and a significant influence of fluids on chromite composition is expressed by its very low Ti content. Metagabbros containing abundant Fe-Ti oxide mineralization may be classified as ferrogabbros. High V and Ti contents in magnetite indicate a magmatic origin. Its xenomorphic and intragrain mode of occurrence suggest crystallization between pre-existing gabbroic minerals like pyroxene and plagioclase. Ilmenite exsolutions indicate its growth at the expense of magnetite under oxidizing conditions. Occurrence of chromitites in harzburgites and ferrogabbros related to isotropic gabbros may suggest various spreading conditions during formation of the mafic and ultramafic members of the Śleza ophiolite.

This paper discusses recently developed gravity concentration equipment, namely vibrating table, and reports detailed descriptions of the equipment in terms of principles of design and their effects on operational parameters. Vibrating table originally combines the known physical phenomena of a teetered bed, resistance to water flow, vibration, and density differences. The resulting effect of these combined forces can also be manipulated by integrated settings of feed rate, solid %, plate inclination, and water rate. Following the detailed description of the equipment, mineral separation tests with two different chromite ores obtained from industrial applications were performed in order to investigate the performance of the laboratory scale vibrating table. While former chromite ore had low grade with complex mineralogy and inadequate liberation, the latter had high grade consisting of liberated lumpy chromite particles. Experimental studies were focused on investigating the effect of plate inclination, removal of slimes, ore type, size classification, and particle size on separation performance. Within the tests performed with −600 µm, −800 µm, and −1000 µm high grade chromite ores under certain conditions, it was observed that increase in particle size results in a dramatic increase in recovery, while % grade decreases slightly. In another test with high grade chromite ore, sustainable product qualities were achieved up to a recovery of 93.22% in comparison with the 66.08% achieved with a conventional shaking table, within and approx. 47–48% final grade level. Additionally, product grades and recoveries up to 50.20%–58.36% with deslimed −400 µm low grade chromite feed and 53.68%–67.45% with deslimed −200 µm low grade chromite feed were obtained, respectively.

Three different residues from Pb recovery (lead slag - LS) and Cu smelting (shaft furnace slag - SFS, and granulated slag - GS) in Cu foundries, located in the SW Poland, were examined with respect to chemical and phase composition. The examined materials reveal distinct mineral composition. The LS slag exhibits crystalline structure, and main phases observed in this slag were sulfides (nukundamite, idaite, sphalerite, troilite), spinel oxides (magnetite and chromite), intermetallic compounds (Cu, Pb and Fe) and non-stoichiometric olivines. The SFS slag and the GS slag are amorphous apart from the presence of some crystalline phases such as spinels and sulfides in the SFS sample. Both SFS and GS slags have metallic Cu and Pb inclusions. The samples are abundant in potentially toxic elements such as Cu, Pb and Zn, as well as critical elements such as REE, Co, Mo and V (up to 308, 1445, 773 and 1228 mg kg−1, respectively). Two standardized leaching protocols were applied to illustrate the leaching potential of selected metal(loid)s. The slags were found chemically resistant to leaching by simulated rainfall or water. Six-step sequential extraction revealed that labile forms of metals are present in granulated slag, that exhibits mainly vitreous texture.

The Ulsan Fe–W skarn deposit is located within the Cretaceous Gyeongsang Basin in the southeastern part of the Korean Peninsula. The skarn and mineralization formed along contacts between the Paleogene Gadaeri granite, limestone, partially serpentinized ultramafic rocks (dunite and harzburgite), and hornfelsed volcanic and siliciclastic rocks. These various country rock types produced a system with multiple types of skarn. Typically, skarn within limestone occurs as clinopyroxene–magnetite skarn, clinopyroxene–garnet skarn, and garnet skarn, but the unique host rocks (ultramafic rocks + albitite) at Ulsan also produced unusual skarn types such as a sodic–calcic skarn system. Na–Ca skarn formed by chemical interactions between albitized granites and adjacent ultramafic rocks. This Na–Ca skarn contains unusual Na-rich clinopyroxene (acmite), Na-rich amphiboles, Cr-rich clinopyroxene, Cr-rich amphiboles, Sr-bearing plagioclase, and Ba-bearing K-feldspar. Clinopyroxene and amphibole have Na2O concentrations up to 6.5 wt%, and these minerals contain up to 12.1 and 2.5 wt% Cr2O3, respectively. Na was derived from albitite, and the formation of Cr-bearing acmite (kosmochlor) and Na-amphibole (richterite) appears to have been related to the release of Cr into the fluid phase by the breakdown of chromite in ultramafic rocks during prograde skarn formation. K-feldspar K–Ar dating yields an age of 50.3 ± 1.7 Ma for the prograde garnet skarn. The related Gadaeri granite exhibits a high-K calc-alkaline signature and a weakly metaluminous to peraluminous I-type affinity with a total alkalinity (Na2O + K2O) of 8.5–8.8 wt%. The Gadaeri granite shows an enriched REE pattern compared with albitite, as well as negative Eu anomalies, which together with the K/Rb values (200–500) are suggestive of a highly evolved magma from a continental-margin setting.

Chromitites in the Kizildag ophiolite mostly occur in the mantle harzburgites and some of them in crustal cumulate dunites. Olivine in both the dunites and chromitites is highly magnesian (Fo = 90.5–92.8 and 90.2–96.1, respectively), while the coexisting chromite varies widely in composition (Cr# = 52.9–68.6 and 57.1–76.2, respectively), placing it between high-Al and high-Cr varieties. Concentrations of Ni, V and Ga in the chromite (Ni: 741–1310 ppm; V: 521–1227 ppm; Ga: 20–51 ppm) are also highly variable, straddling the range of high-Al and high-Cr chromite. Olivine in the dunites and chromitites has a large range of Li concentrations (0.27–2.47 ppm) and δ7Li values (−7.20–29.90‰). Based on the calculated Al2O3 (12.1–17.2 wt.%) contents, FeO/MgO values (0.92–1.57) and trace element concentrations of the parental magmas of the dunites and chromitites, it is suggested that they are transitional between MORB and boninitic melts, and should have been derived by mixing of geochemically and spatially distinct magmas generated by partial melting of different sources. The Li isotopic compositions of olivine from the dunites and chromitites (except KZ14-38 and KZ15-38) are neither controlled by diffusion nor fractional crystallization, and thus may be intrinsic features of their parental melts. The range of δ7Li values of olivine in the dunites and chromitites is analogous to that of arc lavas and marine sediments, indicating that the chromitites record various degrees of melt penetration. The wide range of Li isotopic variations in olivine and chemistry in chromite from the Kizildag chromitites suggest that the parental melts were originated in a proto-forearc mantle during subduction initiation.

Aluminum spent potlining (SPL) was employed as both the fluxing agent and a source of carbonaceous reductant for the carbothermic reduction of chromite, aiming to allow effective separation of alloy from the slag component. The experimental results show that the carbonaceous component of the SPL is more reactive towards chromite reduction compared to graphite. The formation of refractory spinel (MgAl2O4) on chromite particles hinders further reduction and alloy growth. The slag-making components of the SPL (e.g. nepheline and NaF) form molten slags at low temperatures (∼1300 °C) and partly dissolve the refractory spinel as well as the chromite. Destruction of the spinel layer with enhanced mass transfer greatly improves the alloy growth, which can be further promoted by reduction at a higher temperature (e.g. 1500 °C). Ferrochrome alloy particles grow large enough at 1500 °C in the presence of SPL, allowing effective separation from the slag component using elutriation separation.

To determine the chemical composition of minerals on planetary surfaces from spectroscopic data, it is required to establish the link between mineralogy, spectroscopy and chemical composition of rock forming minerals on Earth. To meet this requirement, we performed integrated mineralogical and spectroscopic (Visible-Near Infrared and micro Raman) characterisation of chromite from the chromitite layer in the mantle section of the Nidar ophiolite complex, SE Ladakh, J&K, India. Chromite commonly occurs as monominerallic chromitite layers (up to 1 meter wide) and disseminated grains within the dunites and harzburgites. The Cr2O3 content is generally high (>60 wt%) and chemically homogeneous across the grains. The X-ray Diffraction (XRD) analyses show highest peak intensity at ∼36° 2θ, followed by other diagnostic peaks for chromite. Micro-Raman of chromite yields very strong diagnostic Raman active vibrational modes at 685 cm−1 (A1g), followed by 520 cm−1 (F2g(2)). The other peaks, viz. 446 cm−1 and 610 cm−1 are rather weak and correspond to Eg and F2g, respectively. VNIR (0.4μ to 2.4μ) reflectance spectroscopy of chromite suggested strong absorption near 2 μm and could be useful to quantify the chemical composition (especially Cr2O3, Al2O3 and Cr#). We found a good correlation of VNIR absorption and chemical composition of chromite (e.g. band positions versus Al2O3 and Cr# are well within 95% correlation interval). The intense Raman peak at 685 cm−1 corresponds to higher Cr content. This study, therefore, implies a significant understanding in determination of mineral chemistry (especially Chromites) by VNIR and micro Raman spectroscopy, which could be a useful tool for the future planetary exploration.

High performed new heavy concrete samples were designed and produced that absorption parameters were determined for gamma and neutron radiation by using Monte Carlo Simulation program GEANT4 code. In the sample production, many different materials were used such as; chromite (FeCr2O4), wolframite [(20Fe,80Mn) WO4], hematite (Fe2O3), titanium oxide (TiO2), aluminum oxide (Al2O3), limonite (FeO (OH) nH(2)O), barite (BaSO4), materials. Furthermore, calcium aluminate cement (CAC) was utilized for high temperature resistant. In the current study, five different new heavy concrete samples were produced then physical and chemical strength of them tested. High-temperature-resistant tests were made at 1000?C and good resistance against high temperature was observed. Neutron equivalent dose measurements were made for by using 4.5 MeV energy Am-241-Be fast neutron source. Results compared with paraffin and conventional concrete. It was found that the new heavyweight concretes had the better absorption capacity than paraffin and conventional concrete. Gamma radiation absorption measurements also were carried out at the energies of 160, 276, 302, 356, and 383 keV by using Ba-133 point radiation source. It has been suggested that the new produced concretes can be used for radiation safety in the nuclear applications., University of Agri Ibrahim Cecen [MYO.18.001-19.001], This work is financially supported by University of Agri Ibrahim Cecen with Grant no. MYO.18.001-19.001.

High MgO content and the dehydroxylation of laterite ore particles lead to poor compressive strength of fired chromium-nickel bearing iron ore pellets at natural basicity. For improving the compressive strength of the fired chromium‑nickel bearing iron ore pellets, burnt lime was applied as the additive to improve the pellet structure. Results showed that with an increase in quaternary basicity, the compressive strength of fired pellets was enhanced obviously. The optimum basicity of fired chromium-nickel bearing iron ore pellets is suggested at 1.15. Under the optimal test conditions, the compressive strength of fired pellets with natural basicity is only 607 N/pellet, but the compressive strength of fired pellets reaches 1991 N/pellet at basicity of 1.15. The structure of fired chromium-nickel pellets at 1.15 basicity greatly depends on the liquid bonding phases among chromite, hematite and enstatite particles, which are composed of kirschsteinite, SFCA and glass, and amount to 19.27% in fired pellets. The liquid bonding phases fill in the voids among mineral particles and interconnect them to form the intertwined structure, which increases the shrinkage and significantly improves the compression strength of fired pellets.

The Mesoarchean Sukinda Massif in the Singhbhum craton is the largest chromite ore deposit in India that contains ≈95% of Indian Cr resources. The Sukinda Massif consists of an elongated layered ultramafic unit (≈25 km × 400 m) that occurs within the 3.5 Ga supracrustal sequences of the Tomka-Daitari-Mahagiri greenstone belt in eastern India. The ultramafic unit comprises serpentinized dunite, orthopyroxenite and chromitite. There are six chromitite seams which are present within the serpentinized dunite. All ultramafic rocks are extensively weathered and capped by laterites (≈30 m thick). In the southwestern part of the Sukinda Massif, in the Katpal area, chromitite seams and the host ultramafic rocks are fragmented, forming breccias cemented by the gabbroic to granodioritic rocks. Whole-rock major, trace and platinum-group elements (PGE) geochemistry indicates that the ultramafic unit and the gabbro, including the cementing matrix materials of the breccias, are cogenetic. The ultramafic rocks formed by fractional crystallization of a parental boninitic or high-Mg siliceous magma. The cementing gabbroic rocks formed from an evolved boninitic magma generated from fractionated boninite or high-Mg siliceous basalt. The positive correlation between MgO and Ni, and MgO and Cr is due to fractionation of early cumulus like olivine and chromite from the high-Mg parental magma. The correlation between Zr and Cu suggests that the parental boninitic magma was S-undersaturated. However, the matrix gabbro shows a flatter trend with increasing Zr and Cu, indicating sulfide saturation occurred later in the evolved boninitic magma. In Sukinda, the concentrations of PGE in the massive chromitites (≈176–875 ppb) from the main ultramafic unit and in chromitite fragments (≈61–279 ppb) from the breccias are higher than in serpentinite (≈19–71 ppb), orthopyroxenite (≈14–19 ppb) and gabbro (≈3–11 ppb). Three samples of the massive chromitites from the main ultramafic unit have significant PGE concentrations (PGEtotal ≈ 651–875 ppb) with IPGE (Ir, Os, Ru) ≈ 528–634 ppb, much higher than PPGE (Pd, Pt, Rh) ≈ 93–332 ppb. Detailed PGE mineralogical studies of these samples revealed presence of IPGE-bearing platinum-group minerals (PGM) dominated by Os-Ir-Ru alloys (containing minor Pt) enclosed in chromite grains. Other PGMs are laurite present as composite grain within chromite plus irarsite which are associated with cracks in chromite grains and a small sperrylite grain attached to an Os-Ir-Ru alloy. All the As-bearing PGM are associated with cracks in the chromite suggesting introduction of As during alteration of primary PGM to PGM-arsenides. The positive correlation between IPGE (Os, Ir, Ru) and MgO or Cr indicates they are fractionated during the early stage of magmatic differentiation from a S-undersaturated boninitic magma. The low Ir of the silicate rocks indicate prior removal of Ir-bearing alloys from the parental boninitic magma which would account for the occurrence of Os-Ir-Ru alloys in massive chromitites. The results suggest that Os-Ir-Ru alloys from the Sukinda chromitites crystallized at relatively high temperature and low fS2 condition within a S-undersaturated boninitic magma ascending from the upper mantle where they entrapped by the growing chromite crystals. Overall, the initial PGE analysis from the Sukinda breccias, presented herein, indicate similarities with the Nuasahi breccias in the Singhbhum craton, and highlight the potential for mineralization in this area.

The Benfontein kimberlite is a renowned example of a sill complex and provides an excellent opportunity to examine the emplacement and evolution of intrusive kimberlite magmas. We have undertaken a detailed petrographic and melt inclusion study of the Benfontein Upper, Middle and Lower sills. These sills range in thickness from 0.25 to 5 m. New perovskite and baddeleyite U/Pb dating produced ages of 85.7 ± 4.4 Ma and 86.5 ± 2.6 Ma, respectively, which are consistent with previous age determinations and indicate emplacement coeval with other kimberlites of the Kimberley cluster. The Benfontein sills are characterised by large variations in texture (e.g., layering) and mineral modal abundance between different sill levels and within individual samples. The Lower Sill is characterised by carbonate-rich diapirs, which intrude into oxide-rich layers from underlying carbonate-rich levels. The general paucity of xenogenic mantle material in the Benfontein sills is attributed to its separation from the host magma during flow differentiation during lateral spreading. The low viscosity is likely responsible for non-explosive emplacement of the Benfontein sills, while the rhythmic layering is attributed to multiple magma injections. The Benfontein sills are marked by the excellent preservation of olivine and groundmass mineralogy, which is composed of monticellite, spinel, perovskite, baddeleyite, ilmenite, apatite, calcite, dolomite along with secondary serpentine and glagolevite [NaMg6[Si3AlO10](OH,O)8•H2O]. This is the first time glagolevite is reported in kimberlites. Groundmass spinel exhibits atoll-textures and is composed of a magnesian ulvospinel – magnetite (MUM) or chromite core, surrounded by occasional pleonaste and a rim of Mg-Al-magnetite. We suggest that pleonaste crystallised as a magmatic phase, but was resorbed back into the residual host melt and/or removed by alteration. Analyses of secondary inclusions in olivine and primary inclusions in monticellite, spinel, perovskite, apatite and interstitial calcite are largely composed of Ca-Mg carbonates and, to a lesser extent, alkali-carbonates and other phases. These inclusions probably represent the entrapment of variably differentiated parental kimberlite melts, which became progressively more enriched in carbonate, alkalis, halogens and sulphur during crystal fractionation. Carbonate-rich diapirs from the Lower Sill contain more exotic phase assemblages (e.g., Ba-Fe titanate, barite, ancylite, pyrochlore), which probably result from the extreme differentiation of residual kimberlite melts followed by physical separation and isolation from the parental carbonate-rich magma. It is likely that any alkali or halogen rich minerals crystallising in the groundmass were removed from the groundmass during syn−/post-magmatic alteration, or in the case of Na, remobilised to form secondary glagolevite. The Benfontein sill complex therefore provides a unique example of how the composition of kimberlites may be modified after magma emplacement in the upper crust.