The chrome ore beneficiation processes include gravity separation, flotation, magnetoelectric separation and chemical beneficiation, etc. Because of the chrome ore composition that composed of one or more silicate, and the density difference between the chrome and silicate, the research both in home and aboard about chrome beneficiation process mainly focuses on the gravity separation process. However, using a single gravity separation process can improve the chrome grade, but fail to recover it effectively. In this paper, try to find a better way by using a combined beneficiation process of gravity and magnetic separation.
X-ray diffraction analysis The main mineral ores in the chrome sample are chromite, enstatite, anorthite, hopfnerite, diopside, albite, biotite, etc. Physical analysis The metallic minerals in the chrome samples are mainly chromite, the gangue minerals are mostly enstatite and anorthite, followed by tremolite, diopside, quartz and albite, and a small amount of biotite, serpentine and chlorite, trace amounts of calcite, chalcopyrite, sphene, etc.
Cr2O3 is found in the form of individual minerals, mostly in chromite, few in enstatite. Therefore, chromite is the target minerals to be recovered in this experiment. The following is a systematic grain size grade of chromite and enstatite. As shown in the table above, the chromite material particle mainly of middle-fine of finesse, cover in the range of 0.02-0.104mm. In which, the particle of +0.074mm account for 31.56%, -0.043mm account for 44.9%, -0.010mm only account for 1.76%. Concentrated distribution same as the chromite, the particle of enstatite mainly in 0.020mm-0.147mm, -0.010mm only account for 0.13%.
The dissociation degree of chromite monomer in the sample is 95.11%, the magnetism can be used to separate the chromite from the nonmagnetic ores. The gangue minerals, such as enstatite, tremolite, diopside, biotite, also have weak magnetism, affect the grade of magnetic concentrate. It is better to separate it by using gravity separation. In this experimental, we adopt a strong magnetic process, roughing- concentration- scavenging, to remove the impurity preliminary, then to separate the chromite from nonmagnetic ores. at next, using gravity separation process to refine the chromite concentrate and scavenging tailings, meanwhile, improve the grade and recovery rate. Chrome process equipment is wet type strong magnetic separator, and spiral chute (chrome spiral plant) of gravity separator.
The chrome raw ore is a flotation tail ore, which is mainly formed in the chromite, and the chromite is the target recovering mineral. The dissociation degree of ferrochromium ore is low, and it has a weak magnetic property. First of all, magnetic separation processing to separate chromite. Besides, the grain size is fine, so there is no need for grinding, the grading result shown in the below. Raw ore process flow: roughing- concentration- scavenging. the Cr2O3 mainly in the fine particle ore, in order to ensure the grade and recovery rate, take the roughing experimental under the high gradient separation condition, results as follows.
The results of this study show that, after the first rough separation, the grade of chromite concentrate Cr2O3 is 32.06%(13% higher than the grade of raw ore), the productivity of that is 48.88%, and the recovery rate of that is 83.04%. In order to know the Cr2O3 distribution among the concentration and tailings, make a grade sieving in the roughing concentration and tailings respectively.
As can be seen from the above table, in the concentration, the Cr2O3 mainly in the fine particle grade; in the tailings, the Cr2O3 distribute evenly. strong magnetic separation can recover the valuable minerals, but dont increase the chromite mineral grade to the metallurgical grade, that is, the Cr2O3 higher than 38%.
After the advanced concentrate process, the grade of concentrate Cr2O3 is 38.5%, reach the smelting grade, and that of tailings is 24.28%. After the scavenging process, the grade of concentrate Cr2O3 of roughing tailings is 15.07%, that of tailings is 2.4%. It turns out that the roughing process tailings and scavenging process concentrate have recovery value.
The density of chromite ore is slightly higher than that of its other magnetic gangue ore. Therefore, the separation of ferrochromium from other minerals can be realized by gravity separation. Use spiral chute to separate the concentrate process tailings and the scavenging process concentrate respectively. As shown in the gravity beneficiation process result, both of the grade of concentrate process tailings and scavenging process concentrate higher than 40%, the productivity of that is up to 70%. In conclusion, gravity separation technology can purify the chromite significantly.
As for the chrome beneficiation processes, the single gravity separation process can obtain the qualified grade but does not ensure the productivity and recovery rate. The combination of magnetic process and gravity separation can ensure all indexes of grade, productivity and recovery rate.
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Experience indicates that chrome ores are concentrated to best advantage by gravity methods. Since recoveries are generally very poor in the fine sizes, the gravity flowsheet must be designed to remove the chrome as soon as liberated by crushing and grinding. For example, if the chrome is not entirely freed until the ore is minus 16 mesh, it is obvious that the plus 16 mesh particles should be removed after stage crushing and grinding to prevent further reduction of the chrome and consequent loss in the fine sizes.
The crushing section for this 250 ton per day chrome mill consists of a coarse ore grizzly, a coarse ore bin with pan feeder to a 18 reduction crusher and a crusher discharge conveyor to a crushed ore bin. On this particular ore, we find that there is no chrome liberated in sizes larger than .
The 36x 8 Adjustable Stroke Ore Feeder is used to accurately control feed of crushed ore to the grinding section. Before it is fed to the 4x 8 Peripheral Discharge Rod Mill, the minus chrome ore is removed from the grinding circuit by means of a 4x 12 Dillon Vibrating Screen. This minus product is then ready for concentration in the Mineral Jigs.
The Vibrating Screen oversize is ground in the Steel Head Rod Mill. A rod mill with the peripheral discharge feature is preferred for this application because the rapid-pass design produces a minimum of the undesirable fines. The discharge from the rod mill returns to the Dillon Vibrating Screen by means of a Belt Bucket Elevator, so that a closed circuit grinding arrangement is obtained.
The minus undersize from the Vibrating Screen is divided to feed two identical, parallel jigging circuits, each consisting of l6x 24 Duplex Mineral Jig used for roughing and a I6x 24 Duplex Mineral Jig used as a scavenger. Automatic Density Discharge Control Valves on the hutches of the scavenger Mineral Jig provide a controlled, continuous, high-density feed to a l6x 24 Duplex Mineral Jig used for final cleaning.
A final, cleaned concentrate is produced by the two cleaner Mineral Jigs and also a middling product which is re-circulated back to the scavenger jigs. This procedure is preferable to the immediate regrinding of the middlings as it avoids the further reduction of relatively pure chrome particles which are bound to be present.
The tailing from the scavenger Mineral Jig is directed to a 30x 13 Simplex Cross-Flow Classifier which discards a waste product as a final tailing at minus 65 mesh and the sand product is returned to the rod mill for further grinding. A SRL Sand Pump is used to pump the Mineral Jig Tailings to the Cross-Flow Classifier.
This flowsheet is very effective due to the ability to remove the high grade chrome with very littlegrinding on each pass through the mill. In this way, grinding takes place with a large number of small reductions followed byimmediate removal of the liberated chrome into a high grade concentrate.
In the concentration of certain chrome ores, high grade chrome particles are sometimes liberated at sizes larger than , For the concentration of these large size chrome particles, the Improved Harz Type Jig is indicated.
In the flowsheet described here, there is a minimum amount of valuable chrome in the classifier overflow and accordingly this product is sent to waste. However, conditions may justify the installation of slime concentrating tables and Tilting Concentrators.
Supply of world chromite (chrome ore) has come under severe pressure over the past year driven by strong demand for ferrochrome used in ferroalloy production for making stainless steel. Many of the strategic minerals are inputs into products in fast-changing markets. This article reviews the major process flow sheets in practice for the recovery of chromite values from various types of ores and critical issues related to chromite ore beneficiation. The comprehensive condensation of pertinent facts is intended to provide a single reference source rather than the reader perusing many articles. Emphasis is placed on different processes developed in identifying and solving critical plant problems.
This article reviews the major process flow sheets in practice for the recovery of chromite values from various types of ores and critical issues related to chromite ore beneficiation. Emphasis is placed on different processes developed in identifying and solving critical plant problems.Download : Download full-size image
High tailing losses from the existing chromite plants (920% Cr2O3). Accumulation of huge amount of low and sub-grade fines (1030% Cr2O3). Utilization of stockpiled tailings containing chromite values. Concentrate with required Cr2O3 content and Cr/Fe ratio. Unrecoverable ultrafine chrome particles.
The low-grade siliceous chromite ore from Ghutrigaon, Odisha, India, containing ~16% Cr2O3, with Cr/Fe ratio of 1.97 and ~55% of SiO2, does not find any use in metallurgical industry and hence considered as waste. Mineralogical investigation indicates the presence of chromite and quartz as major minerals with minor fuchsite and kaolinite. The beneficiation studies reveal that the product can be enriched to a Cr/Fe ratio of 3.35 and 3.02 by gravity concentration (wet shaking table) and wet high intensitymagnetic separation, respectively. Tiny Cr-grains within quartz and fine silica dusts within chromite inhibit liberation of chromite resulting in poor response to physical beneficiation. As an alternative, processing of ore through pyro-metallurgical route was evaluated. Chromite fines mixed with carbon and lime in the form of pellets/granules was charged to a plasma reactor. In about ten minutes, the metal globules/prills were separated from the slag in 1:6 ratio. The metal, examined through XRD and optical microscope, was found to be ferrochrome alloy. In situ EDAX analysis indicated the metal to have 61.51% Cr, 26.52% Fe and 13.1% C with minor silica (2.42%), and the slag was composed of Ca2Al2SiO7 which revealed that both metal and slag so obtained could suitably be used in different industries.
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Meegoda JN, Hu Z, and Kamolpornwijit W, Conversion of Chromium Ore Processing Residue to Chrome Steel. Final Report, New Jersey Department of Environmental Protection, New Jersey Institute of Technology (2007), p 19.
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The authors wish to thank the Council of Scientific & Industrial Research (CSIR) for the financial support to one of the authors (AKD) in the form of JRF[09/1036(0014)/2019-EMR I]. The authors would like to thank The Director of Institute of Minerals and Materials Technology (IMMT)-CSIR for providing necessary facilities to carry out the various experiments. The authors would also like to acknowledge Ravenshaw University for providing necessary laboratory facilities for carrying out the work.
Das, A.K., Khaoash, S., Das, S.P. et al. Processing of Low-Grade Chromite Ore for Ferroalloy Production: A Case Study from Ghutrigaon, Odisha, India. Trans Indian Inst Met 73, 23092320 (2020). https://doi.org/10.1007/s12666-020-02032-5