Title of Invention

"A METHOD OF RECOVERING CHROMITE FROM TAILINGS OF CHROME ORE BENEFICATION (COB) PLANT"

Abstract

This invention relates to a method of recovering chromite from tailing of chrome ore beneficiation (COB) plant comprising the steps of; (a) obtaining coarse scavenger tilings (-0.5+0.1)mm (CST) , fine seavenger tailing (-0.l+0.038)mm (FST) and slime (-0.038mm to 0.025mm) form chrome ore beneficiation plant tailings; (b) subjecting said CST to classification to get coarser fraction (+0.15mm) and finer fraction (below 0.15mm); (c) combining the finer fraction (from above below 0.15mm) with said FST and slimes for further processing; (d) passing the combined material form step (c) through bydrocyclones for separation at 0.015 mm into coarser and finer fractions (below 0.01mm); (e) subjecting the coarse fraction to gravity separation in two stages, concentrates (+0.015mm) from first stage being further upgraded in two stages; (f) treating the concentrate (heavier fraction) from said second stage of gravity separation to a magnetic separation for reducing the iron content; (g) collecting the non-magnetic fraction from the magnetic separator for obtaining the final product of 46% to 48% Cr2 O3.

Full Text

The present invention relates to a method of recovering additional marketable grade chromite values from tailings of chrome ore beneficiation (COB) plant. Chromite-resources from mines like Sukinda in the Slate of Orissa (mined at about. 4.5 million tones per annum) are mostly enriched with'ferruginous type ore. These are different in many respects with other leading world chromite resources particularly in terms of higher near density iron minerals matrix and friability due to varied degree of weathering. During mining operation for marketable grade ores, low grade ores are generated from the mines which are treated in conventional gravity circuits at the chrome ore beneficiation (COB) plant for producing different marketable grade concentrates of below 500 micron size to meet the requirement of different customers. The beneficiation process produces approximately 17% Cr2 O3 grade tailings and rejected. The beneficiation plant primarily consists of crushing and grinding circuit to reduce the run-of-mine ore from 300 mm to beiow 0.5 mm. The classification circuit consisting of hydrocyclones to classify -0.5 mm fraction into coarse (0.5 to 0.1 mm), fine (0.1 to 0.038 mm) and slime (-0.38 mm) fractions. The beneficiation circuit consisting of 4 stage spirals in coarse circuit and 3 stage spirals and tables in fine circuit to produce -2- Marketable grade concentrates. In this process, 3 types of tailings i.e., coarse scavenger tailings (CST) with 14-18% Cr2 O3, fine scavenger tailings (FST) with 20-25% Cr2 O3 and slimes mostly - 0.038 mm fraction with 11-13% Cr2 O3 are generated. The analysis of the total tailings comprising all the above mentioned three types of tailings show about 15-23% Cr2 O3 These tailings on an annual average show about 17% Cr2 O3 which is considered to be high. The primary objeci of the present invention therefore, is to provide 3 method of recovering additional marketable grade chromite values from the chrome ore beneficiation plant tailings. The present invention provides a method of recovering chromite from tailings of chrome ore beneficiation (COB) plant comprising the steps of: A method of recovering chromite from tailing of chrome ore beneficiation (COB) plant comprising the steps of: (a) obtaining coarse scavenger tailings (0.5 to 0.1 )mm (CST), fine scavenger tailings (0.1 to 0.038)mm (FST) and slime (0.038mm to 0.025mm) from chrome ore beneficiation plant tailings; (b) subjecting said CST to classification to get coarser fraction coarser than (0.15mm) and finer fraction (below 0.15mm); (c) combining the finer fraction (from above below 0.15mm) with said FST and slimes for further processing; -3- (d) passing the combined material from step (c) through hydrocyclones for separation at 0.015 mm into coarser and finer fractions (below 0.01mm); (e) subjecting the coarse fraction to gravity separation in two stages, concentrates (+0.015mm) from first stage being further upgraded in two stage; (f) treating the concentrate (heavier fraction) from said second stage of gravity separation to a magnetic separation for reducing the iron content; (g) collecting the non-magnetic fraction from fee magnetic separator for obtaining the final product of 46% to 48% Cr2 O3. From a study of the total tailings of the chrome ore beneficiation plant it has been found that the coarser fraction (+0.15 mm) of total tailings contains chromite mostly locked with gauge particularly with iron minerals. The iron minerals include, hermatite, martite/magnetite, goethite, ferrian-chromite and limonite. This indicates, that during gravity separation these iron minerals also report along with chromite and thereby contributing to a lower Cr/Fe ratio. By gravity methods it is possible to produce finer (-0.5+ 0.015 mm) concentrates analyzing less than 2% SiO2 with around 46% Cr2 O3 and 1.6 Cr/Fe ratio at a yield of about 22 % from total tailings. The hand magnetic tests with 4.03 sink product indicated that certain iron minerals can be removed by magnetic separation and it is possible to increase Cr/Fe ratio by 0.3 units. -4. On the whole, such characterization studies indicated that by treating total tailings it is theoretically possible to get more than 46% Cr2 O3 concentrates by gravity separation and simultaneously tailings with about 12% Cr2 O3 . On the basis of the above characterization studies further beneficiation studies were carried out for a process developing for recovering additional marketable grade chromite of chrome ore benefication (COB) plant. Hydrocycloning optimisation studies to classify below 0.15 mm feed at 0.015 mm size indicated that it is possible to get 16- 32% material analysing 7 - 9.5 55 Cr2 O3 .The misplacement of -0.015 mm fraction in Under Flow is 13% and contains mostly chromite and iron materials. This indicates these misplaced particles have reported to Under Flow due to gravity. Two stage gravity separation in a multi gravity separator (MGS) test results indicated that it is possible to get not only marketable grade concentrate but their yield would be high and tailing losses less than 12% Cr2 O3 but the concentrate Cr/Fe ratio will be relatively low ( 2). Magnetic separation test results of MBS concentrates indicated at 1000 Gauss magnetic intensity, that it is possible to increase Cr/Fe ratio to 2.6. The magnetic fraction contains mostly marite/magnetite and ferrian-chromite . -5- The concentrates produced in spirals and MGS analysed invariably MgO 9% and SiO2 l.2 to 1.6%. The present invention will be better explained in the accompanying drawing in which Fig. 1 is a flow sheet showing schematically the steps of the method of recovering additional marketable grade chromite values from tailings of chrome ore beneficiation (COB) plant, showing me percentage material balance obtained at various stages of me method steps. COB Plant tailings consists of coarse circuit tailings i.e. coarse scavenger tails (CST), fine circuit tailings-fines scavenger tails (FST) and Slime. Out of the 3 types of tailings, the coarse circuit tailings (CST) is subjected to classification using either a screw classifier or a sieve bend to get two products. The coarser fraction (+0.15 mm) which contains low Cr2 O3 is rejected. The finer fraction (-0.15 mm) from screw classifier or a sieve bend is combined with other two types of tailings of COB plant, i. e. FST and slimes and processed further for recovery of concentrate. The combined material which contains about 18% Cr2 O3 is passed through a set of -4"or 5" hydrocyclones for separation at 0.015 mm into two size products. The finer fraction i.e. O/F (-0.015 mm) containing low Cr2 O3 is rejected. The coarser fraction i.e. U/F (+0.015 mm) is subjected to gravity separation in 2-stages in a multi gravity (MGS). The concentrate obtained in first stage MGS is used as a feed to the second stage MGS for further up gradation. -6- The heavier fraction of second stage MQS i.e. concentrate is finally treated for magnetic separation to reduce iron content of the product, in a wet magnetic separator. The non-magnetic fraction from the magnetic separator containing about Cr2 O3 is obtained as a final product The product containing more than 46% Cr2 O3 is marketable, Thus by treating tailings generated at chrome ore beneficiation (COB) plant which contain about 17% Cr2 O3 on an average can be up graded to produce a marketable grade product containing more than 46% Cr2 O3 using a set of classification (size separations) units e.g. sieve bend/screw classifier/hydrocyclones, then 2-stage gravity separator units (MGS) and finally wet magnetic separator. The weight recovery of the final product is about 12% of the total tailings being processed. The invention is herein illustrated by the following example for beneficiation of chromite from tailing of chrome ore. Example -1 (a) The coarse scavenger tailings (CST), Fines Scavenger tailings (FST) and slimes (- 0.025 mm size fraction) or any other tailings/rejects generated from regular chrome ore beneficiation plant are collected individually to different locations called "sumps'. (b) The CST is fed to screw classifier for classifying it into coarser (+0.l5mm) and finer (below 0.15 mm) fractions. The coarser fraction will be directed to reject pond as one of the stream of total reject (c) The finer fraction (-0.15 mm) of the screw classifier product is pumped to either to FST sump or slimes sump. This pumped finer fraction of screw classifier CST, FST and slimes will become a feed and pumped together for further processing. -7- (d) The combined feed (This pumped finer fraction of screw classifier CST, FST and slimes) is fed to hydrocyclones for separating the product in to coarser fraction (+0.015 mm size) as under flow and finer fraction (below 0.015mm size) as over flow. This over flow again directed to reject pond as another part of total reject. (e) the underflow of hydrocyclone (+0.Q15mm size) is fed to MGS (Multi gravity separation) unit with about 35% pulp density (the % of solids in the feed by adjusting the water content) and separated in to concentrate and tailings. Tlie tailings are directed to reject pond as another part of total rejects. The concentrate again to fed to another MGS to produce cleaner concentrate and tailings. The tailings are directed to reject pond and become another part of total reject pond. By this way two stage Multi Gravity Separation is done to produce the cleaner concentrates. (f) The cleaner concentrate obtained in 2nd stage MGS is used as a feed to Wet low intensity magnetic separator to reduce iron content of the product In this process 2 product are generated i.e. 1) Magnetic fraction and 2) nonmagnetic fraction. The magnetic fraction is directed to reject pond and become the another part of total rejects. (g) The non-magnetic fraction from the magnetic separator is the final marketable product and contains more than 46% Cr2 O3. The reject pond contains all rejects (Consist of CST coarser fraction, hydrocyclone overflow, MGS stage 1 and stage 2 tailings and magnetic fraction of magnetic separator) analysed 10-12% Cr2 O3 and is the another final product which can not be marketed and kept as reject The present invention as described and exemplified hereinabove should not be contemplated in a restrictive way as other embodiments are possible to be arranged within the scope and limit of the appended claims. -8- WE CLAIM 1. A method of recovering chromite from tailing of chrome ore beneficiation (COB) plant comprising the steps of: (a) obtaining coarse scavenger tailings (-0.5+0. l)mm (CST), fine scavenger tailings (-0.1+0.038)mm (FST) and slime (-0.038mm to 0.025mm) from chrome ore beneficiaiion plant tailings; (b) subjecting said CST to classification to get coarser fraction (+0.15mm) and finer fraction (below 0.15mm); (c) combining the finer fraction (from above below 0.15mm) with said FST and slimes for further processing; (d) passing the combined material from step (c) through hydrocyclones for separation at 0.015 mm into coarser and finer fractions (below 0.01mm); (e) subjecting the coarse fraction to gravity separation in two stages, concentrates (+0.015mm) from first stage being former upgraded in two stages; (f) treating the concentrate (heavier fraction) from said second stage of gravity separation to a magnetic separation for reducing the iron content; (g) collecting the non-magnetic fraction from the magnetic separator for obtaining the final product of 46% to 48% Cr2 O3. 2. The method as claimed in claim 1 wherein said classification of CST is carried out using a screw classifier or a sieve bend. -9- ¦10- 3. The method as claimed in claim 1, wherein said gravity separation is carried out in a two stage multi gravity separator (MGS). 4. The method as claimed in claim 1 wherein said magnetic separation is carried out in a wet magnetic separator. 5. A method of recovering chromite from a tailing of a chrome ore benefication (COB) plant substantially as herein described and illustrated This invention relates to a method of recovering chromite from tailing of chrome ore beneficiation (COB) plant comprising the steps of; (a) obtaining coarse scavenger tilings (-0.5+0.1)mm (CST) , fine seavenger tailing (-0.l+0.038)mm (FST) and slime (-0.038mm to 0.025mm) form chrome ore beneficiation plant tailings; (b) subjecting said CST to classification to get coarser fraction (+0.15mm) and finer fraction (below 0.15mm); (c) combining the finer fraction (from above below 0.15mm) with said FST and slimes for further processing; (d) passing the combined material form step (c) through bydrocyclones for separation at 0.015 mm into coarser and finer fractions (below 0.01mm); (e) subjecting the coarse fraction to gravity separation in two stages, concentrates (+0.015mm) from first stage being further upgraded in two stages; (f) treating the concentrate (heavier fraction) from said second stage of gravity separation to a magnetic separation for reducing the iron content; (g) collecting the non-magnetic fraction from the magnetic separator for obtaining the final product of 46% to 48% Cr2 O3.

Documents:

00512-cal-2002-abstract.pdf

00512-cal-2002-claims.pdf

00512-cal-2002-correspondence.pdf

00512-cal-2002-description(complete).pdf

00512-cal-2002-description(provisional).pdf

00512-cal-2002-drawings.pdf

00512-cal-2002-form-1.pdf

00512-cal-2002-form-18.pdf

00512-cal-2002-form-2.pdf

00512-cal-2002-form-3.pdf

00512-cal-2002-form-5.pdf

00512-cal-2002-letters patent.pdf

00512-cal-2002-reply f.e.r.pdf