The treatment of mineral wastes in the form of slimes and its utilisation, for management of pollution and conservation of mineral wealth, have become very important now-a-days. Multi Gravity Separator (MGS) is the latest inclusion to various gravity separation machines developed far the treatment offines and ultrafines. In this paper, results of recent studies carried out at NML with MGS using slimes of chromite ore, iron ore, phosphatic soil etc. are discussed to evaluate the effectiveness of the equipment for the treatment of slimes. In most of the cases, three to four fold upgradations have been achieved even at very fine sizes

Bhattacharyya, P

Chakrabarti, D M

Chattoraj, U S

Ghosh, S R

Saha, P

Sarkhel, B R

English

The treatment of mineral wastes in the form of slimes and its utilisation,   for   management   of    pollution and conservation of   mineral   wealth,      have become very

important now-a-days. Multi Gravity Separator (MGS) is the latest inclusion to various gravity separation machines developedfor the treatment offines and ultraflnes. In this

paper, results of recent studies carried  out  at NML with MGS using slimes of chromite ore,   iron ore,   phosphatic soil etc. are discussed to evaluate the effectiveness of the equipment for the treatment of slimes. In most of the cases, three to four fold upgradations have been achieved even at very fine sizes

eprints@NML

PROCEEDINGS: NS-EWM 19960 NML, JAMSHEDPUR, pp.139-145Gravity separation at variable 'g' for managementof mineral wastes and pollutionP.BHATTACHARYYA, B.R. SARKHEL, D.M.CHAKRABARTI,P.SAHA, S.R.GHOSH AND U.S.CHATTORAJMineral Processing Division,National Metallurgical Laboratory, Jamshedpur - 831 007, IndiaABSTRACTThe treatment of mineral wastes in the form of slimes and its utilisation, formanagement of pollution and conservation of mineral wealth, have become veryimportant now-a-days. Multi Gravity Separator (MGS) is the latest inclusion to variousgravity separation machines developedfor the treatment offines and ultraflnes. In thispaper, results of recent studies carried out at NML with MGS using slimes of chromiteore, iron ore, phosphatic soil etc. are discussed to evaluate the effectiveness of theequipment for the treatment of slimes. In most of the cases, three to four foldupgradations have been achieved even at very fine sizes.INTRODUCTIONSlimes, produced during processing of ores/minerals and rejected as wastes,create environmental problems. Recovery of values from these slimes is gainingincreasing importance of late. Wastes generated by the mining, mineral processing andmetallurgical industries, totalling about 2 billion ton per annum, are to be disposed ofwith a minimum environmental degradation and at acceptable cost. Some of themetallic and mineral constituents of these wastes are valuable, and their recovery canlead to substantial conservation of mineral and metal resources. Researchers areidentifying ways and means to recover the valuable constituents from the wastes. Theultimate aim is, of course, to develop technology where every input into the plantdelivers products of commercial value leaving nothing to discard (zero waste technol-ogy)t'1.To upgrade slime is a difficult problem in Mineral Processing and particularlyin gravity separation where ultrafines pose special problem. For very fine particles (lessthan 75 microns), the force associated with the water flow becomes dominant over thatassociated with gravity. As a result, a large part of the valuable minerals contained inthese fine particles prove to be irrecoverable with traditional methods of gravityseparation. To overcome this problem, various gravity separation methods andmachines have been developed over the last few decades viz. Fines table, Multi-deckseparator, Cross belt concentrator etc. The new devices and processes, as compared to139P.BHATTACHARYYA et al.flotation of slimes, have theadvantages of adaptability, low costand less environmentalpollutiont2'3J. Very recently, Multi-gravity separator (MGS) has appeared in themarket and seems to be very promising in tackling the problem of fines andultrafines . This equipment can be operated at variable 'g' depending on the charac-teristics of the slurry to be treated. The potential and limitations of MGS, however,are yet to be fully understood'"t.Since installation of the MGS at the National Metallurgical laboratory in1992, several studies have been carried out on samples of Indian and foreign originsviz. lean tungsten ore, iron ore, chromite ore, phosphatic soil etc. varying differentdesign and operating variables. Some of the results of those studies are presented inthis paper. MGS studies on chromite ore slime at 100% -60 micron size resulted inabout fourfold upgradation of Cr2O3 content in the concentrate. For the slime ofphosphatic soil at 80% - 8 microns size, a concentrate of comparable upgradation inquality could be obtained. Similarly, for an iron ore slime at - 147 microns size, aconcentrate assaying 65.58% Fe, 2.0% A1203 and 1.52% SiO 2 could be producedfrom a feed assaying 55.51% Fe, 7.49% AI2O, and 4.24% SiO2.Multi -Gravity SeparatorThe MGS is used to separate two minerals from each other or to separate agroup of heavy minerals from lighter minerals provided there is a reasonabledifference in specific gravities. It consists of a slightly tapered open ended drum thatrotates in a clockwise direction and is shaken sinusoidally in an axial direction. Thereis a scraper assembly, inside the drum, which rotates in the same direction but at aslightly faster speed. Feed slurry is fed midway onto the internal surface of the drumvia an accelerator ring launder . Wash water is added via a similar launder positionednear the open end of the drum. Due to high centrifugal forces, the dense particlesfrom a semi solid layer against the wall of the drum and are conveyed towards theopen end of the drum by the scrapers when it discharges into the concentrate launder.The less dense minerals are carried by the flow of wash water towards the rear of thedrum to discharge into the tailing launder.The design and operating parameters which affect separation are rotationalspeed, frequency and amplitude of the shake, slope of drum with the horizontal, washwater flow rate, feed rate and feed pulp density. The specially significant parameterof variable 'g' is obtained in the MGS by changing the RPM of the drum and isempirically given by the following equation :g = 5.6x 1W xDN2where D is the diameter of the drum (in m.) and N is the rotational speed ofthe drum (in RPM). Therefore, drum speeds of 160 to 240 RPM, with a diameter of0.5 m produce 'g' values of 7 to 16.140P.BHATTACHARYYA et al.Experiments and observationsTo evaluate the effectiveness of the Multi-gravity separator, experimentswere performed using slimes generated after processing of low grade chromite ores,washing of iron ore and beneficiation of phosphatic soil. In each case, effects ofvariation of different design and operating parameters were studied to obtainoptimum combination.Chromite ore slimeDuring beneficiation of low grade chromite ores a large amount of slime isgenerated which still contains certain amount of mineral values. Recovery of anyportion of this mineral value, otherwise rejected as wastes, is of great significancein terms of overall economy of the process and conservation besides wastemanagement.The chromite slime sample analysed 10.52% Cr2O3, 29.68% Fe (T), 33.6%Si02 and 13.13% Al20,. It was treated on MGS varying the design and operatingparameters. The sample was 85% - 20 microns in size, as presented in Table-1.Results of MGS studies are plotted in figures 1-4. All the figures represent gradesof Cr203 and Fe (T) in the concentrates. While figures 1 and 2 show the effect ofvariation of design variables viz, rotational speed and tilt angle (slope) in separatingthe mineral values from the gangue minerals, figures 3 and 4 represent the effect ofvariation of wash water flow rate and feed pulp density. From figures 1 and 2, it isobserved that with increasing rotational speed Cr203 content decreases but increasein tilt angle initially improved the grade substantially though further increase onlyresulted in marginal improvement. On the other hand, increase in wash water flow-^wiv3 l I.. C.+Nw1wT.) YFy)/o00 40b peo tob 10^Gry [* IT)O160 24c• CYto'J C 2.. Ca.cawt-ta)♦o -st o4scope (s,..VaFig.] : Effect of variation of rotational Fig.2 : Efect of variation of slope onspeed on chromite ore slime chromite ore slime141P.BHATTACHARYYA et al.rate was found to improve grade linearly (Fig.3) and similar trend prevailed in the caseof increase in feed pulp density. In all the above cases three to fourfold increase in Cr2O3content was observed but change in Fe content with respect to feed was marginal.Table-] : Size distribution of chromite ore slimeSize (Micron) Wt. (%)-60+50 1.5- 50+40 2.0- 40 + 30 3.830 + 20 7.6- 20+10 19.0- 10+5 8.95+ 1 21.01+0,5 12.70.5 23.5Iron ore slimeThe iron ore washing plants generate slime on an average of 10-20% byweight of the ore and is wasted. About 12 million tonnes of iron ore slimes aregenerated in India every year analysing 50-60% Fe. Apart from loss of resource, theseslimes pose problem of disposal and consequent damage to environment. Attemptswere made earlier to develop suitable methods to recover the metal values by usinghydrocyclone, magnetic separator etc., to increase productivity and also to controlenvironmental degradation'-,1. Recently, at NML, MGS was employed on an iron oreslime analysing 55.51 % Fe, 7.49% A12O3 and 4.24% 5102 at 100% - 147 microns size(Table-2) to study its effectiveness in reducing the alumina content. The experimentswere carried out by varying different parameters to obtain the optimum combination'51.Table-2 : Size distribution of iron ore slimeSize (Micron) Wt. ( %)- 147+105 7.9- 105+74 8.8- 74 + 63 3.8- 63+44 11.8- 44 67.7Results obtained were, indeed, encguraging. Effects of changcof shake intensityi.e., shake frequency and amplitude are plotted in Figs 5 and 6. While Fig. 5 shows thatincrease in frequency diminishes A1203 content, at maximum amplitude there occurs142P.BHATTACHARYYA et at.a sharp fall in the value of alumina content in the concentrate (Fig.6).Phosphatic soil slimeA phosphatic soil slime, assaying 7.33% P2O5, 16.68% Fe, 22.4% SiO2 and21.4% AI2O, at 95% - 30 microns (as presented in Table-3), was generated duringdesliming of a phosphatic soil sample (10.28% P205). MGS studies on this slimeshowed that a concentrate assaying 25% P2O5 could be produced.Table-3 : Size distribution of phosphatic soil slime.Size (Micron) Wt. %- 80 + 60 0.8- 60+50 0.9-50+40 1.2-40+30 2.0-30+20 4.1- 20 + 10 10.5- 10 + 5 4.6- 5+ 1 29.8- 1 46.1DISCUSSIONFrom the above study it is clear that different design and operating parametersaffect the performance of MGS in different manner (Figs. 1-6). For any particularapplication, depending on the nature of the material to be treated and the specifica-tions of the concentrate to be produced, optimum combination of parameters is to bechosen. In general, when the rotational speed of the drum increases, all othervariables remaining constant , the 'g' value acting on the mineral particles increases;the effect of shake is to impart the additional shearing action on the particles whichaids the separation process. Increasing slope angle increases the throughput a littlebut larger slope angle tends to reduce heavy mineral recovery. Wash water cleansthe concentrate by carrying away lower density minerals released by the ploughingaction of the scrapers. Feed pulp density can varied within the range of 10 to 50%solids w/w. However, higher feed densities should be counter balanced by theaddition of more wash water.From Fig.1 it is observed that nearly fourfold upgradation of Cr2O, valuecould be achieved at 160 RPM but an higher RPM's the Cr2O3 content of theconcentrate decreased sharply with a little increase in the Fe-value. Apparently, under143P.BHATTACHARYYA et%CY203 C in Co., c^nt ramie) •G Fe(s )_ sob0^t^3 ( In Coneenl.eeke ) %Fe(T)50 50•O40 40 403030 - 30 302020 2000 I0 1 IaA&-Cr203 --0- PQ(T)0 0fC.203 --OI-pe(T)03 5 7 15 25 35woSl v.ler (I/wNn) Feed Pulp denO7 (%Solid)Fig.3 : Effect of variation of wash water Fig,4 : Effect of variation offeedpulpon chromue ore slime density on chrornite ore slime0/a Fe-?s-7065605550(T, Co nc. v'-4rei`e) -/ .Al2O3 S4 -701-3 652 605 51-4.0f Fe -o-A1203A.eFre.tu.ney(cpS)6r0 5o'Co,ca^4y 4e )4-Fe -'0-At 2.03%Al20^11.7 14.0 25.4Ainplit ude Onw )Fig. 5 : Effect of variation of shake speed Fig .6 : Effect of variation of shakeon iron ore slime amplitude on iron ore4320144P.BHATTACHARYYA et at.conditions of higher'g' minerals heavier than chromite (e.g. magnetite, hematite etc.)are being transported to the drum wall in preference to chromi te. The same trend would,of course, be observed in the case of locked particles also - containing chromite andheavier iron bearing minerals. Fig.3 clearly depicts the cleansing effect of wash wateron the concentrate; while the very heavy Fe-minerals steadily adhere to the drum, therelatively lighter chromite gets more and more clean as increasing wash water removemore and more lighter gangues. Similarly, the beneficial effect of the shake intensityto eliminate lightergang ues is apparent from Figs.5 and 6. It is observed that as the shakeintensity increases, i.e., as the separating layer gets more agitated more gangue mineralsget released and eliminated. It is significant to note that by employing MGS thedetrimental alumina content of the slime is brought down from 7.49 to 2.0%. Besidesrevealing significant characteristics of the slimes as discussed above, the studies alsoindicate that it is possible to salvage useful components from these slimes which wouldhave been otherwise wasted and added to pollution problems.However, a few constraints on the use of MGS must be mentioned, especiallywhen dealing with slimes. A clear understanding of the mineralogy and mineragraphyof the slime is required to select parameter setting of the equipment. Conventionaloptical microscopy is ineffective in most cases to provide above mentioned informationfor the slimes because of their very fine sizes (please see from Table-I to 3). Electronmicroscopic techniques (EMPA and SEM) are helpful in this regard but are expensiveand notavailable easily. Further, the equipmentis yet to be developed for true large scalecontinuous operation, Notwithstanding, these constraints, the MGS can be gainfullyemployed to recover high value concentrates like precious metals, minerals etc. fromwasted slimes. This, of course, is in addition to more conventional use of the equipmentfor the treatment of ores, heavy mineral sands etc.ACKNOWLEDGEMENTThe authors are thankful to Director, National Metallurgical Laboratory,Jamshedpur for his kind permission to present this paper . Thanks are also due to othercolleagues who contributed to generate the data discussed in this paper.REFERENCES[1] G.M. Rao and S.K.Choudhuri, Proc. Int. Sem . on "Mineral Sector in India" , held at Hyderabad,India, 1 993, 444.[2] G.D. Player, Proc. Int. Conf. on "Mineral Processing and Extractive Metallurgy" held in PeoplesRepublic of China, 1984, 245.[3] LShangxian. L.Gi and D.Tiyao. Ibid. 491.[41 P.Tucker , S.K.Chan, R.H. Mozley and G .J.C. Childs, XVII Int. Min . Process . Congress,Vol.IIl(1991),77.[5] K.K.Bhauacharyya, B.R.Sarkhel. P. Saha, S.R. Ghosh et.el. NML IR.No. 12325084. 1994.161 A.Traore et.al. Mineral Engg . Vol-8 (No.7), 1995, 767.[7] U.S. Chauoraj. P.Bhauacharyya. et.al. NML IR No. 12620030. 1990.145

Gravity Separation at Variable 'g' for Management

of Mineral Wastes and Pollution

PROCEEDINGS: NS-EWM 1996® NML, JAMSHEDPUR, pp.139-145Gravity separation at variable 'g' for managementof mineral wastes and pollutionP.BHATTACHARYYA, B.R. SARKHEL, D.M.CHAKRABARTI,P.SAHA, S.R.GHOSH AND U.S.CHATTORAJMineral Processing Division,National Metallurgical Laboratory, Jamshedpur - 831 007, IndiaABSTRACTThe treatment of mineral wastes in the form of slimes and its utilisation, formanagement of pollution and conservation of mineral wealth, have become veryimportant now-a-days. Multi Gravity Separator (MGS) is the latest inclusion to variousgravity separation machines developed for the treatment offines and ultrafines. In thispaper, results of recent studies carried out at NML with MGS using slimes of chromiteore, iron ore, phosphatic soil etc. are discussed to evaluate the effectiveness of theequipment for the treatment of slimes. In most of the cases, three to four foldupgradations have been achieved even at veryfine sizes.INTRODUCTIONSlimes, produced during processing of ores/minerals and rejected as wastes,create environmental problems . Recovery of values from these slimes is gainingincreasing importance of late. Wastes generated by the mining, mineral processing andmetallurgical industries, totalling about 2 billion ton per annum, are to be disposed ofwith a minimum environmental degradation and at acceptable cost. Some of themetallic and mineral constituents of these wastes are valuable, and their recovery canlead to substantial conservation of mineral and metal resources. Researchers areidentifying ways and means to recover the valuable constituents from the wastes. Theultimate aim is, of course, to develop technology where every input into the plantdelivers products of commercial value leaving nothing to discard (zero waste technol-ogy)I"•To upgrade slime is a difficult problem in Mineral Processing and particularlyin gravity separation where ultrafines pose special problem. Forvery fine particles (lessthan 75 microns), the force associated with the water flow becomes dominant over thatassociated with gravity. As a result, a large part of the valuable minerals contained inthese fine particles prove to be irrecoverable with traditional methods of gravityseparation. To overcome this problem, various gravity separation methods andmachines have been developed over the last few decades viz. Fines table, Multi-deckseparator, Cross belt concentrator etc. The new devices and processes, as compared to139P.BHATTACHARYYA et at.flotation of slimes, have the advantages of adaptability, low costand less environmentalpollution' 1. Very recently, Multi-gravity separator (MGS) has appeared in themarket and seems to be very promising in tackling the problem of fines andultrafines. This equipment can be operated at variable 'g' depending on the charac-teristics of the slurry to be treated. The potential and limitations of MGS, however,are yet to be fully understoodt"'.Since installation of the MGS at the National Metallurgical Laboratory in1992, several studies have been carried out on samples of Indian and foreign originsviz. lean tungsten ore, iron ore, chromite ore, phosphatic soil etc. varying differentdesign and operating variables. Some of the results of those studies are presented inthis paper. MGS studies on chromite ore slime at 100% -60 micron size resulted inabout fourfold upgradation of Cr2O3 content in the concentrate. For the slime ofphosphatic soil at 80% - 8 microns size, a concentrate of comparable upgradation inquality could be obtained. Similarly, for an iron ore slime at - 147 microns size, aconcentrate assaying 65.58% Fe, 2.0% AI2O3 and 1.52% SiO2 could be producedfrom a feed assaying 55.51% Fe, 7.49% A12O3 and 4.24% SiO2.Multi-Gravity SeparatorThe MGS is used to separate two minerals from each other or to separate agroup of heavy minerals from lighter minerals provided there is a reasonabledifference in specific gravities. It consists of a slightly tapered open ended drum thatrotates in a clockwise direction and is shaken sinusoidally in an axial direction. Thereis a scraper assembly, inside the drum, which rotates in the same direction but at aslightly faster speed. Feed slurry is fed midway onto the internal surface of the drumvia an accelerator ring launder. Wash water is added via a similar launder positionednear the open end of the drum. Due to high centrifugal forces, the dense particlesfrom a semi solid layer against the wall of the drum and are conveyed towards theopen end of the drum by the scrapers when it discharges into the concentrate launder.The less dense minerals are carried by the flow of wash water towards the rear of thedrum to discharge into the tailing launder.The design and operating parameters which affect separation are rotationalspeed, frequency and amplitude of the shake, slope of drum with the horizontal, washwater flow rate, feed rate and feed pulp density. The specially significant parameterof variable 'g' is obtained in the MGS by changing the RPM of the drum and isempirically given by the following equation :g = 5.6x10''xDN2where D is the diameter of the drum (in m.) and N is the rotational speed ofthe drum (in RPM). Therefore, drum speeds of 160 to 240 RPM, with a diameter of0.5 in produce 'g' values of 7 to 16.140P.BHATTACHARYYA el al.Experiments and observationsTo evaluate the effectiveness of the Multi-gravity separator, experimentswere performed using slimes generated after processing of low grade chromite ores,washing of iron ore and beneficiation of phosphatic soil. In each case, effects ofvariation of different design and operating parameters were studied to obtainoptimum combination.Chromite ore slimeDuring beneficiation of low grade chromite ores a large amount of slime isgenerated which still contains certain amount of mineral values. Recovery of anyportion of this mineral value, otherwise rejected as wastes, is of great significancein terms of overall economy of the process and conservation besides wastemanagement.The chromite slime sample analysed 10.52% Cr203, 29.68% Fe (T), 33.6%SiO2 and 13.13% A1203. It was treated on MGS varying the design and operatingparameters. The sample was 85% - 20 microns in size, as presented in Table-1.Results of MGS studies are plotted in figures 1-4. All the figures represent gradesof Cr2O3 and Fe (T) in the concentrates. While figures 1 and 2 show the effect ofvariation of design variables viz, rotational speed and tilt angle (slope) in separatingthe mineral values from the gangue minerals, figures 3 and 4 represent the effect ofvariation of wash water flow rate and feed pulp density. From figures 1 and 2, it isobserved that with increasing rotational speed Cr203 content decreases but increasein tilt angle initially improved the grade substantially though further increase onlyresulted in marginal improvement. On the other hand, increase in wash water flow(1..-4 114N soweEC4010to0tC, O3 -o-^e(r)200RIM240So Crava (7n Cone.2s._e.a +6 K*> so4a.o. (d.y..yFig.] : Effect of variation of rotational Fig.2 : Effect of variation of slope onspeed on chromite ore slime chromite ore slime141P.BHATTACHARYYA et al.rate was found to improve grade linearly (Fig.3) and similar trend prevailed in the caseof increase in feed pulp density. In all the above cases three to fourfold increase in Cr2O3content was observed but change in Fe content with respect to feed was marginal.Table -1 : Size distribution of chromite ore slimeSize (Micron) Wt. (%)- 60 + 50 1.5- 50 + 40 2.0- 40+30 3.8- 30+20 7.6- 20+10 19.0- 10+5 8.9- 5+ 1 21.0- 1+0.5 12.7- 0.5 23.5Iron ore slimeThe iron ore washing plants generate slime on an average of 10-20% byweight of the ore and is wasted. About 12 million tonnes of iron ore slimes aregenerated in India every year analysing 50-60% Fe. Apart from loss of resource, theseslimes pose problem of disposal and consequent damage to environment. Attemptswere made earlier to develop suitable methods to recover the metal values by usinghydrocyclone, magnetic separator etc., to increase productivity and also to controlenvironmental degradation''1. Recently, at NML, MGS was employed on an iron oreslime analysing 55.51% Fe, 7.49% A1203 and 4.24% SiO2 at 100% - 147 microns size(Table-2) to study its effectiveness in reducing the alumina content. The experimentswere carried outby varying different parameters to obtain the optimum combination(s).Table-2 : Size distribution of iron ore slimeSize (Micron ) Wt. (%)- 147 + 105 7.9- 105+74 8.8- 74+63 3.8- 63+44 11.8- 44 67.7Resultsobtained were, indeed, encouraging. Effectsofchangeofshakeintensityi.e., shake frequency and amplitude are plotted in Figs 5 and 6. Whi le Fig. 5 shows thatincrease in frequency diminishes A1203 content, at maximum amplitude there occurs142P.BHATTACHARYYA et al.a sharp fall in the value of alumina content in the concentrate (Fig.6).Phosphatic soil slime. A phosphatic soil slime, assaying 7.33% P2O5, 16.68% Fe, 22.4% SiO2 and21.4% A12O3 at 95% - 30 microns (as presented in Table-3), was generated duringdesliming of a phosphatic soil sample (10.28% P2O5). MG S studies on this slimeshowed that a concentrate assaying 25% P205 could be produced.Table-3 : Size distribution of phosphatic soil slime.Size (Micron) Wt. %- 80 + 60 0.8- 60 + 50 0.9-50+40 1.2-40+30 2.0-30+20 4.1- 20 + 10 10.5- 10 + 5 4.6- 5 + 1 29.8- 1 46.1DISCUSSIONFrom the above study it is clear that different design and operating parametersaffect the performance of MGS in different manner (Figs. 1-6). For any particularapplication, depending on the nature of the material to be treated and the specifica-tions of the concentrate to be produced, optimum combination of parameters is to bechosen. In general, when the rotational speed of the drum increases, all othervariables remaining constant, the'g' value acting on the mineral particles increases;the effect of shake is to impart the additional shearing action on the particles whichaids the separation process. Increasing slope angle increases the throughput a littlebut larger slope angle tends to reduce heavy mineral recovery. Wash water cleansthe concentrate by carrying away lower density minerals released by the ploughingaction of the scrapers. Feed pulp density can varied within the range of 10 to 50%solids w/w. However, higher feed densities should be counter balanced by theaddition of more wash water.From Fig.1 it is observed that nearly fourfold upgradation of Cr203 valuecould be achieved at 160 RPM but an higher RPM's the Cr2O3 content of theconcentrate decreased sharply with a little increase in the Fe-value. Apparently, under143P.BHATTACHARYYA et at.%C1203 ( rn Lonesr^trate) ^^ FQ(T) ^^C>IL03_ _ 5040302010O-♦ C1r2O3 --O-Fe(T)3 5Wash Wa1*?, ( VM;N)740 A3O 320 20Ir Coneenfuke) Fe(T)510 100 0`-411-Cla03 -1 Pe(T)15 75Fe.d pulp dM+s14r (%6 Iid)O35Fig.3 : Effect of variation of wash water Fig.4 : Effect of variation offeedpulpon chromite ore slime density on chromite ore slime%,Fe7Cr- Con ca .+Ardha) % A1s03 S 9e F! ( Sn Con ca nl .o{e ) Jo 121754 7010656055A.0-Fe - A1a,0313 652jO50A.eFregp.ncy(cP6)676055So411-Fe -O-AI20312.7 19.0 25.4Amplitude (MM)Fig. 5 : Effect of variation of shake speed Fig.6 : Effect of variation of shakeon iron ore slime amplitude on iron ore144P.BHATTACHARYYA et al.conditions of higher 'g' minerals heavier than chromite (e.g. magnetite, hematite etc.)are being transported to the drum wall in preference to chrom ite. The same trend would,of course, be observed in the case of locked particles also - containing chromite andheavier iron bearing minerals. Fig.3 clearly depicts the cleansing effect of wash wateron the concentrate; while the very heavy Fe-minerals steadily adhere to the drum, therelatively lighter chromite gets more and more clean as increasing wash water removemore and more lighter gangues. Similarly, the beneficial effect of the shake intensityto eliminate lightergangues is apparent from Figs.5 and6. Itis observed that asthe shakeintensity increases, i.e., as the separating layergets moreagitated moregangue mineralsget released and eliminated. It is significant to note that by employing MGS thedetrimental alumina content of the slime is brought down from 7.49 to 2.0%. Besidesrevealing significant characteristics of the slimes as discussed above, the studies alsoindicate that it is possible to salvage useful components from these slimes which wouldhave been otherwise wasted and added to pollution problems.However, a few constraints on the use of MGS must be mentioned , especiallywhen dealing with slimes . A clear understanding of the mineralogy and mineragraphyof the slime is required to select parameter setting of the equipment . Conventionaloptical microscopy is ineffective in most cases to provide above mentioned informationfor the slimes because of their very fine sizes (please see from Table-I to 3). Electronmicroscopic techniques (EMPA and SEM) are helpful in this regard but are expensiveand notavai lable easily . Further, the equ ipment is yet to be developed for true large scalecontinuous operation . Notwithstanding these constraints , the MGS can be gainfullyemployed to recover high value concentrates like precious metals, minerals etc. fromwasted slimes . This, of course , is in addition to more conventional use of the equipmentfor the treatment of ores , heavy mineral sands etc.ACKNOWLEDGEMENTThe authors are thankful to Director, National Metallurgical Laboratory,Jamshedpur for his kind permission to present this paper. Thanks are also due to othercolleagues who contributed to generate the data discussed in this paper.REFERENCES[1] G.M. Rao and S.K.Choudhuri, Proc. Int. Sere. on "Mineral Sector in India" , held at Hyderabad,India. 1993, 444.[2] G.D. Player, Proc. Int. Conf. on "Mineral Processing and Extractive Metallurgy " held in PeoplesRepublic of China, 1984, 245.[31 L.Shangxian, L.Gi and D.Tiyao. Ibid. 491.[41 P.Tucker, S.K.Chan, R.H. Motley and G.J.C. Childs, XVII Int. Min. Process . Congress,Vol.]II(1991).77.[51 K.K.Bhattacharyya, B.R.Sarkhel, P. Saha, S.R. Ghosh et.el. NML IR.No. 12325084,1994.[6] A.Traore et.al. Mineral Engg. Vol.8 (No.7), 1995, 767.[7] U.S. Chanoraj, P.Bhattacharyya, et.al. NML IR No. 12620030, 1990.145

Gravity separation at variable 'g' for management of mineral wastes and pollution

http://eprints.nmlindia.org/1540/1/139-145.PDF

Gravity separation at variable 'g' for management of mineral wastes and pollution

Abstract

Similar works

Full text

Available Versions

eprints@NML

eprints@NML