Grade Chromite Research Articles

Energy saving Chemical Beneficiation Method of Improving Low Grade Nigeria Chromite Ore for Use in Steel Industries

This study detailed how direct acid leaching can be used to extract high grade chromite from low grade chromite ore for utilization in the steel industry. The suggested method, which makes use of nitric acid, avoids using traditional pyrometallurgical processes because they use a lot of energy. The leaching procedure is adjusted in accordance with the circumstances that will maximize chromium recovery. In this context, the independent variables are the nitric acid concentration (0.5–4 M), temperature (28–80°C), liquid to solid ratio (L/S) (3–10 mL g–1), and leaching period (10–120 min). The three parameters that affect the leaching process most effectively are, in order, acid concentrations, temperature, and particle sizes. By doing this, 86.7% of the chromite in the lean chromite ore was recovered. Shirking core model examination of the kinetics of leaching reveals that internal diffusion reaction controls the rate of leaching, and the apparent activation energy calculated is 24.8 kJ.mol-1. This approach is successful and relatively inexpensive for chromite beneficiation. The gap is thus filled by the use of all-known inefficient acid dissolution procedures, which are less expensive and could serve as an alternate way of chromite beneficiation for use in iron and steel.

Mineralogical studies and optimization of tabling parameters of low grade chromite ore by box behnken design of experiments

Chromite ore is geologically associated with gangue materials which have lower density compared to pure chromite (FeO.Cr2O3). Gravity separation techniques are very suitable for beneficiation of low grade chromite ore. In the present study mineralogical analysis of the sample has been carried out by using Wavelength dispersive x-ray fluorescence (WDXRF), X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive X-ray (EDX). The beneficiation of low grade (Cr2O3% 26.88) chromite ore has been investigated using wilfley table. Optimization has been carried out using box-behnken statistical design (BBD). The experimental parameters selected are: tilt angle, water flow rate and pre-heat treatment of the chromite ore. It is observed that percentage recovery of Cr2O3 depends upon tilt angle, water flow rate and pre-heat treatment of chromite ore. Pre-heat treatment of chromite ore plays a vital role in gravity separation. The optimized tabling conditions suggested by BBD are 8° tilt angle, 4 L∙min-1 water flow rate and temperature for pre-heat treatment of raw chromite ore at 443.72℃. After tabling under optimized conditions, chromite concentrate contained 1.91 Cr/Fe ratio, 46.02% of Cr2O3 with 65.95% recovery.

Iron and Nickel Enrichment in Low Grade Chromite Overburden to Produce Ferronickel Alloys

Chromite overburden (COB), considered as a waste material with 46% Fe and 0.8% Ni, is the only source of nickel in India. Iron and nickel from COB were recovered through reduction roasting, magnetic separation and smelting. In sintering, maximum Ni% was achieved at 1.0% S, 10% C inside and 10% C outside of the COB pellet. Ni was, further, enriched by smelting the magnetic fraction of sintered COB. XRD, SEM–EDS and chemical analysis of the feed material and products confirmed enriched Ni content in the ferronickel alloy. With the optimized parameters such as 12 min time, 1.2 basicity and 10% reductant, ferronickel alloy contains 8% Ni and 89% Fe with recovery of 87% Ni. It was possible to produce different grades of ferronickel, varying from 2 to 10% Ni.

Feasibility of nickel extraction from Indian chromite overburden by solid state reduction and smelting route

The present work demonstrates the extraction of nickel from low-grade chromite overburden by using solid state reduction and direct smelting route. Goethite & Quartz are present as major phases whereas chromite, hematite were identified as minor phases in the mineral. Solid state reduction of pellets were carried out inside a horizontal tube furnace at 1000?C, 1200?C, 1400?C for 30, 60, 90 and 120 minutes respectively with creating reducing atmosphere. Pellets of varying basicity (i.e. 0.5, 0.6, 0.7, 0.8 and 0.9) were used directly in the EAF for smelting studies. Highest percent of nickel (2%) having ~ 91% recovery were obtained in solid state reduction route for pellets which was reduced at 1400?C for 120 minute. Similar recovery (~90%) of nickel was obtained inside the ingot (0.67% Ni ) by using pellets of 0.9 basicity through smelting route. From the present investigation, it could be concluded that the solid state reduction as well as smelting routes are feasible for the recovery of nickel from low grade chromite overburden. The production of nickel pig (low grade ferronickel) could also be feasible by smelting route.

A new method for gravity separation: Vibrating table gravity concentrator

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.

An integrated approach for production of stainless steel master alloy from a low grade chromite concentrate

As an alternative process, the production of stainless steel master alloys in blast furnace (BF) exhibits high economic efficiency and great potential to use low-grade chromite resources. To produce desirable sinter products required by the blast furnace smelting process, sintering tests of ore mixtures made from a low grade South African chromite concentrate (Cr2O3/FeO = 1.99) and Chinese magnetite concentrate were performed in a sinter pot in terms of various sintering parameters including coke dosage, mix moisture, sinter basicity and proportion of magnetite concentrate, etc. An integrated process comprising “high pressure grinding rollers (HPGR) pretreatment, pelletizing, coke coating, pre-drying and non-fluxed sintering” steps was proposed based on the pellet-sintering technique. The quality of Cr-bearing sinters was evaluated. The results show that high quality Cr-bearing sinters can be obtained through the proposed process. Addition of 40% or more magnetite concentrate in ore blends promises to yield desirable sinters of proper chemical composition and good metallurgical properties required by the blast furnace smelting process. The smelting performance of the Cr-bearing sinter made from the 40% chromite and 60% magnetite mixture was assessed under simulated blast furnace smelting conditions. It is feasible to use the Cr-bearing sinters in blast furnace for stainless steel master alloy production. A stainless steel master alloy containing 71.75% Fe, 19.52% Cr and 7.84% C with phosphorus and sulfur contents (<0.015%) is obtained at Fe and Cr recovery rates of 92.55% and 87.53%, respectively, when smelting at 1550 °C for 60 min with slag compositions (10% Al2O3, 10% MgO and R2 = 1.0). The bonding mechanism of Cr-bearing sinters and the formation mechanism of liquid phase were further revealed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS). Both slag bonding (10 to 20% silicate) and solid bonding (recrystallization of spinel phase) contribute to the consolidation of the Cr-bearing sinters. Increasing the basicity of sinter made from 100% chromite concentrate or addition of magnetite concentrate in the ore blend at natural basicity lead to the formation of low-strength slag bonds, which generally reduces the sinter strength.

Mapping chromite deposits with audio magnetotellurics in the Luobusa ophiolite of southern Tibet

The exploration of podiform chromites in the Indus Yarlong Zangbo suture zone of southern Tibet has proved difficult because most known deposits pinch out and then reappear in the same direction. Several ground-based geophysical approaches such as gravity, magnetic, and controlled-source audio-frequency magnetotelluric (CSAMT) methods have been applied to explore for these chromite deposits but have mostly failed to delineate prospective areas. We have evaluated a successful podiform chromite exploration case history that is based on AMT. More than 8000 AMT stations were used in this study within a [Formula: see text] area of the ophiolite belt. Line separations were 80 or 40 m, and the station separation was 20 m. We implemented Bostick conversion and nonlinear conjugate gradient inversions for data interpretation, whereas 2D resistivity sections and 3D resistivity imaging were used to elucidate the inner structure and distribution of rock faces within the Luobusa ophiolite. Results from rock physics and drilling further indicate that resistivity-anomaly domains from these AMT results are correlated with rock faces in terms of fresh harzburgite, altered harzburgite and dunite, and they can thus be connected to concealed deposits. Therefore, we have developed three resistivity-anomaly models for chromite exploration, and we delineated several prospective regions containing exploitable deposits within the Luobusa ophiolite. Seven of the nine verified boreholes discussed in this paper intersected with chromite deposits; one comprises the largest and highest grade chromite deposit in China to date. Our AMT results provide the impetus for future chromite exploration in Tibet and enable a refined understanding of the structure and distribution of rock faces within the Luobusa ophiolite.

Optimization of Process Parameter for Smelting and Reduction of Ferrochrome

The increasing costs of electric energy and continuous depletion of quality raw material such as Chromite ore and coke for production of high grade Ferro-chrome imposed a big challenge for the Ferro- alloys industries. In order to sustain in the globalized market, an attempt have been made in the present investigation for production of high grade Ferro-chrome utilizing lean grade raw materials. Chromite ore having different Cr/Fe ratio were smelted in a 100 KVA submerge arc furnace (SAF) with low grade nut coke. The Cr/Fe ratio of the Chromite ore pellets were optimized with respect to the slag basicity and power consumption to yield high grade Ferro-chrome. The basicity of the slag and Cr/Fe ratio of the ore were optimized to produce high grade Ferro-chrome (Cr > 60%) with low power consumption. It was observed that high grade Ferro-chrome can be produced utilizing low grade Chromite ore having Cr/Fe ratio 2.4 at the slag basicity of 1.

Utilisation of pre-oxidised ore in the pelletised chromite pre-reduction process

Ferrochromium is a vital alloy mostly used for the production of stainless steel. It is produced from chromite ore, the only economically exploitable natural chromium resource, through carbothermic smelting in submerged arc or direct current furnaces. The pelletised chromite pre-reduction process is currently the industrially applied ferrochromium production process with the lowest specific electricity consumption. Results obtained from this study proved that the pre-oxidation of chromite ore prior to milling, agglomeration and pre-reduction significantly enhances the level of chromite pre-reduction achieved in the pelletised chromite pre-reduction process. The optimum pre-oxidation temperature was established as the temperature where a balance was achieved between maximising iron (Fe) migration to the surface of ore particles that were pre-oxidised, while avoiding the formation of free eskolaite (Cr2O3). For the case study metallurgical grade chromite ore considered, the optimum pre-oxidation temperature was found to be 1000°C. Utilising such pre-oxidised ore could theoretically lead to an improvement of approximately 8.5% in the specific electricity consumption and a 14% decrease in the lumpy carbonaceous material required during submerged arc furnace smelting of pelletised chromite pre-reduced feed.

Smelting characteristics of fluxed chromite sinter and its performance assessment in electric arc furnace to produce high carbon ferrochrome

More than 80% of the high grade chromite ores are fragile and tend to form fines during their handling. In order to utilise these chromite ore fine, in ferrochrome production, agglomeration is necessary. In the present study, the direct sintering of chromite ore fines in the presence of coke breeze has been carried out, which does neither require further grinding of ore fines ( − 10 mm) nor binder. It uses suitable fluxes and coke breeze as heat source to raise temperature up to 1600°C and produces a semifused mass (20% molten phases) with good strength. The developed sinter showed very good strength properties suitable for cold handling. Since it contains higher amount of fluxes than conventional pellet, the study on its smelting characteristics is necessary to assess its suitability in Fe–Cr production. In the present paper, smelting reduction characteristics and assessment of its performance with respect to the lump ore in a 50 kVA electric arc furnace have been studied in 10 kg scale. Different smelting parameters such as coke and flux requirement, energy consumption, etc. has been optimised through both thermodynamically and experimentally to get maximum extent of reduction, metallic yield and chromium recovery. Coke (21%), quartzite (7.52%) and bauxite (10%) addition with 45 kWh of heat input was found to be optimum to achieve 76% metallic yield and 91%, chromium recovery. In the comparative study in identical condition, the chromite sinter showed much better metallic yield (76%) and higher chromium content (54.6%) in the produced ferrochrome than the lump ore (70 and 51. 9% respectively) of the same grade.

Direct chromium alloying by smelting reduction of mill scale and low grade chromite ore

Direct alloying is the process in which all of the elements needed for alloying can be reduced from their oxides in a furnace or a ladle. This process is one way of reducing the amounts of energy and materials, reducing the loss of alloying elements, and improving working condition. Mill scale produced in rolling mills is considered a rich iron source (> 67% Fe) with minimum impurities. In this paper, iron high-Cr alloy was produced by a direct alloying with chromium in carbo- thermal reduction using fine of low grade chromites ore and mill scale. The smelting experimental heats were carried out in a 5 kg pilot plant submerged electric arc furnace. The charging materials and reduction parameters were varied and the optimum conditions for obtaining alloy with the highest metallic yield and the highest iron and chromium recovery were determined. When using coke as the reducing agent in stoichiometric amounts, for a mixture of mill scale (55%) and chromite ore (45%), 89.1% of the iron and 72.5% of the chromium were recovered, producing iron high-Cr alloy containing 17.9%Cr, 3.73%C, 0.46%Mn and 1.47%Si. The maximum iron and chromium recoveries obtained were 99.3% and 72.5%, respectively when using excess carbon. The present study clarifies the possibility of using a mixture of chromite ore , mill scale and coke as the precursor for direct chromium alloying. This method offers an alternative process route with cheaper raw materials and fewer process steps (by avoiding the step of ferrochrome production) for producing high chromium iron or steel alloys.

Enhancing the Utilization Potential of a Low Grade Chromite Ore through Extensive Physical Separation

Low grade chromite ore with less than 30% Cr2O3 was investigated with a view to enhance its utilization potential. The ore contained olivine, serpentine, and chrysotile as the gangue minerals. The chromite mineral contained alumina, magnesia, and FeO in its lattice. Critical mineralogical assessment indicated that enrichment to a level of 39-43% Cr2O3 may be possible. Beneficiation of the ore was undertaken using gravity based methods. Inadequate liberation prevented any significant enrichment at 0.9 mm top size. At 0.3 mm top size, the spiral concentration generated a concentrate with 40.5% Cr2O3 from the coarser fraction. The finer fraction was treated in a shaking table to generate another concentrate with 41.6% Cr2O3. The final combined concentrate assayed 41.2% Cr2O3 with a Cr/Fe ratio of 2.27. The middling from both treatments were rich in chromite content and were recommended to be included in the concentrates. Chromite recovery from the coarse reject was also beneficial. It was recommended that 8-10% solids content of the reject stream with 0.02 kg/t of Magnafloc flocculant may be used to achieve best settling characteristics of the reject fines.

Modelling and optimization of process parameters for beneficiation of ultrafine chromite particles by selective flocculation

Chromite tailings are generated from chrome ore beneficiation plants, containing substantial quantities of ultrafine particles. Generally these ultrafine particles of chromite cannot be treated effectively using conventional beneficiation methods, because of limitations in particles size being treated by these processes. Selective flocculation process could be one of the alternative physico-chemical methods for treating these ultrafine particles. Here an attempt was taken to establish selective flocculation process for treating chromite particles using synthetic mixture of high grade chromite ore and kaolin. Box Behnken experimental design was applied to study the significance of operating parameters like flocculant dose, dispersant dose and pH on responses of selective flocculation process. Both pH and flocculant dose significantly affect selective flocculation process. Further, an optimization of process parameters were also carried out and optimized response was found to be 41.86% grade of Cr2O3 in concentrate with 69.73% recovery.

On the Flotation of a Low Grade Chromite Ore

This study is concerned with the processing of low grade chromite ores, Ingassena Hills by froth flotation techniques. For this purpose, representative samples were taken from four different mines. Mineralogical examinations indicated that, the major minerals are chromite and serpentine .Olivine, iron oxides and talc have been identified as minor minerals. Adequate degree of liberation of chromite was obtained by grinding the ore to minus 177µm. Froth flotation was used to upgrade that particular chromite ore. Oleic acid was used as collector. Several operating parameters influencing the floatability of both high grade chromite and serpentine were investigated. These include the concentrations of the collector and depressant, pulp pH and conditioning time. From an ore feed grading 20.27% Cr2O3, a chromite concentrate of 28.71% Cr2O3 with recovery of 94.54 % could be obtained by flotation at collector dosage of 0.300 kg /t , neutral pulp (pH 9) ,conditioning time ,2min ,and pulp density, 20%.

Carbothermic smelting of high carbon ferrochromium alloy from low and high grade chromite ores

The objective of this study is to investigate some of the parameters affecting the possible utilisation of Egyptian chromite ores for the production of high carbon ferrochromium. Pilot plant experimental heats were carried out to determine the optimum condition to get the highest recovery and metallic yield using the carbothermic smelting process in 100 kVA submerged electrical furnace. Different amounts of nut coke, as well as different fluxes, were used in these melts. Chromium recovery and metallic yield were related to the excess reductant and slag composition. The results showed that 50% of coke in excess of the stoichiometric amount should be added. Both MgO/Al2O3 and slag basicity must be controlled by flux addition. Acidic slag having (CaO+MgO)/(SiO2+Al2O3) weight ratio equal to 0·74 and MgO/Al2O3 weight ratio in the range of 0·9–1·1 ensure higher chromium recovery and metallic yield. With the optimum reductant addition and slag condition, chromium recovery and metallic yield of ∼82% can be attained, and ferrochromium alloy containing 66% chromium and 7% carbon can be produced from these chromite ores without concentration.

An efficient process for the beneficiation of a low grade chromite ore

The applicability of centrifugal force multigravity separator (MGS) to concentrate fine fractions (–0·1 mm) of a low grade chromite ore assaying 9·3%Cr2O3 was investigated. The metal screen analysis revealed that 83·92% of the material prepared for tests was in the +0·106 mm fraction containing 8%Cr2O3 and that 16·08% was in the –0·106 mm size fraction containing 16·12%Cr2O3. The +0·1 and –0·1 mm fractions of the ore was used as feed for shaking table and MGS tests respectively. The results gathered from shaking table test were not satisfactory due to low Cr2O3 recoveries. However, a chromite concentrate with 46·22%Cr2O3 grade and 66·1 wt-%Cr2O3 recovery was obtained by the combination of shaking table and MGS. It was clearly demonstrated that MGS is an ideal beneficiation equipment for fine fractions of a low grade Cr2O3 ore. Based on the experimental results, a principal flowsheet for the enrichment plant was proposed.

The salt extraction process: a novel route for metal extraction Part I – Cr, Fe recovery from EAF slags and low grade chromite ores

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

Las cromititas del Complejo Ofiolítico de Camagüey, Cuba: un ejemplo de cromitas ricas en Al

The Camaguey Ophiolitic Complex extends along the central-eastern region of Cuba. This ophiolitic complex contains several deposits of Al-rich chromite [Cr/(Cr+Al) = 0.31-0.6] very enriched in TiO 2 (up to 1 wt%) and represents the second most important mining district for refractory grade chromite in Cuba. The chromite deposits are hosted by dunite and harzburgite, spatially associated with feldspatic rocks (gabbro dikes and/or sills, troctolites and/or anorthosites) in close proximity to gabbroic cumulates at the base of the plutonic crust. The texture observed in the chromite deposits is predominantly massive, although fine disseminated, nodular and brecciated textures are also present. The interstitial silicate matrix of the chromitite consists principally of olivine and to a lesser extent pyroxenes and plagioclase. Often these silicates are altered to other secondary minerals such as serpentine, chlorite, magnetite and uvarovite-type garnet. The chromite crystals usually host small solid inclusions of the same silicates that form the matrix, Fe-, Ti- and/or Zr-rich oxides, and Fe-Ni-Cu sulphides and alloys. The above mentioned metallic minerals also occur in the interstitial silicate matrix where they record variable alteration. The structural, petrological and geochemical characteristics of the chromitites suggest formation from melts generated after reaction of basaltic melts with upper lithospheric mantle peridotites or, alternatively, as result of the assimilation of pre-existing feldspatic rocks (gabbros and troctolites) located in the shallowest upper mantle.

Studies on bioleaching of silica from Indian chromite ore by a silica tolerant Aspergillus niger AB200 : Characterisation of some physical parameters and scanning electron microscopic studies

The bioleaching of silica from chromite ore was studied to remove silica from low grade chromite ore and therefore increase the percentage of chromium in the ore. Three microorganisms Bacillus circulans, Saccharomyces cerevisiae and Aspergillus niger were used for bioleaching studies. The results showed that Aspergillus niger has higher potency of silica bioleaching (30%) from chromite ore, followed by Saccharomyces cerevisiae (20.3%) and Bacillus circulans (17.8%). The organisms were then grown in their respective growth media along with silica for development of silica tolerant strain. The silica adapted organisms were used for bioleachig studies. Silica tolerant Aspergillus niger grown with 90 mg/100 ml silica concentration in the growth media showed maximum bioleaching of silica (53%) from chromite ore. It was named Aspergillus niger AB 200 and selected for further studies. The structural changes in the ore after bioleaching was studied along with morphological changes in Aspergillus niger during the process of bioleaching by scanning electron microscope. Physical parameters are optimized for proper cellular growth and effective silica bioleaching from chromite ore. The optimized bioleaching process was carried out at 33 °C for 7 days with 6 ml inoculum having 1.5 × 10 6 spores/ml. The initial pH of the fermentation media was maintained at 4.5.

An investigation of the mineralogical properties of chemical grade chromite minerals

The chemical grade chromite ores are used extensively for the production of sodium chromate. The mineralogical properties, which pose a major limitation in utilising a wide variety of chemical grade chromite ores from different origins, determine the yield of sodium chromate in the soda‐ash roasting process. In this paper, the mineralogical properties of chemical grade chromite ores from 5 different countries, namely South Africa, India, Philippines, Indonesia and China are reported. The physical and chemical properties of the chromite ores were investigated using the atomic absorption spectroscopy (AAS), X‐ray fluorescence spectroscopy (XRF), X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques. The results obtained from the X‐ray diffraction of phases and their scanning electron microscopic analyses were used for explaining the properties of chemical grade chromite ores. The research is aimed at improving the efficiency of extraction of chromium from chromite minerals from different origins, and thereby reducing the amount of chromium lost in the waste stream after the extraction process.