Experiments using pilot size flotation Column as cleaner cell were conducted to evolve a suitable flow sheet for the production of bulk sulphide concentrates of Cu-Pb-Zn. The flotalion circuit consisting of roughing, scavenging, and two stage cleaning by conventional flotation machines

was compared with the circuit where two stage cleaning operation was replaced with single stage cleaning by flotation column. It is clearly demonstrated that a single stage cleaning by flotation column is more efficient and sufficient to obtain bulk concentrate suitable for further

processing. Of the two types of sparger systems used viz, TURBO and MICROCEL, the former was found to be better to achieve high quality concentrate

Bhaskar Raju, G

Prabhakar, S

Sankaran, C

Vora, S B

English

eprints@NML

Proceedings 01 the Inlernatlonal Conlerence on "Recenl Advances In Metatlurglcal Processes·Golden Jubilee Celebrations, Department 01Melallurgy, Indian Instllule 01Sclence, BangaloreEds. D.H. Sastry, E.S. Dwarakadasa, G.N.K. Iyengar and S. SubramanianNew Age International Publishers, New Delhi (1997) _'PILOT SCALE STUDIES ON THE BENEFICIATION OFCOMPLEX SULPHIDES BY FLOTATION COLUMNNational Metallurgical Laboratory, C SIR Madras complex,TTTI Taramani P.O, Chennai 600 113*Gujarat Mineral Development Corporation, AlunedabadExperiments using pilot size flotation COIUlTUlas cleaner were conducted to evolve a suitableflow sheet for the production of bulk sulphide concentrates of Cu-Pb-Zn. The flotalion circuitconsisting of roughing, scavenging, and two stage cleaning by conventional flotation machineswas compared with the circuit where two stage cleaning operalio" was replaced with singlestage cleaning by notation column. It is clearly demonstrated that a single stage cleaning byflotation colulTUl is more efficient and sufficient to obtain bulk concentrate suitable for furtherprocessing. Of the two types of sparger systems used viz, TURBO and MICROCEL, theformer was found to be better to achieve high quality concentrate,In recent years, column flotation has been receiving an increased attention both forplant improvemments and new installations [1-2). Industrial use of flotation columns haswitnessed a remarkable growth since the beginning of the eighties. The column hasoutperfonned mechanical cells especially for difficult separations involving fines [3-6].Based on the spectacular performance of column, over 2000 columns were installed allover the world for the beneficiation of different minerals. In India, Kudremukh Iron OreCompany Limited (KIOCL) and Tamilnadu Minerals Limited have successfullyimplemented column technology for the beneficiation of iron ores and graphiterespectively.By considering the advantages of flotation columns, it has been decided toinvestigate the amenability of column technology for the beneficiation of Cu, Pb and Zncomplex sulphide ores. This paper incorporates extensive R & D work conducted to evolvea suitable flOW-Sheet for the production of bulk concentrate of Cu-Pb-Zn suitable forsmelting operation. -MATERlALS AND METHODSMineralogy" .Ambaji nlUllimetal deposil.owned by Mis GMDC Ahmedabad contains 7 milliontonnes of demonstrated ore reserves at an average of 8,5'% of Cu-Pb-Zn, 1)1 addition there isapproximately I million tonnes of infelTed reserves. Mineralogical characteristics of thisore body is complex compared to the oth'er deposits of similar nature. Sulphides of copper,lead unu zinc are valuable minerals along with siliceous gangue, talc and mica. Theappropriate mineral suite is shown in Table.!. The mineralogical analysis suggests that theore is highly oxidised in nature and the gangue is fully liberated at a dao value of 75 fUll.Wei ht%1.153.257.4510.251.720.500.10EXPERlMENT ALGau ue MineralsWei ht%Pilot Column: The pilot column with the dia of 30 cm and a height of 10m was installedin the premises of the existing pilot plant test facility at Ambaji. The column shell is madeout of three flanged sections which are connected together with proper gaskets and bolls.The legs of the column shell were bolted to the ground after checking the verticality. Thedimensions of different zones of column viz, collection, cleaning and froth zones areshown in Fig 1.Sparger: The pilot column incorporates two alternative teclll1010gies for bubblegeneration, namely, Turbo type and Microcel type. Turbo type is high pressure and lowshear external bubble generator originally developed at the U S Bureau of Mines (Fig. 2).A mixture of air and water is injected under high pressure (5-6 bars) through injectiontubes with distributed nozzles. Bubble size is controlled by manipulating air and waterpressure, air and water ratio and frother addition in the water line if necessary. TheMicrocel type is a low pressure and high shear bubble generator developed at VirginiaPolytechnic Institute (U S A). The sparger consists of one static on-line mixer and acentrifugal pump as illustrated in Fig 3. Slurry from the column (tailings) is sucked andpumped again to the column through the in-line static mixture where air and slurry <Iremixed under high shear conditions to create the bubble dispersion. The bubble slurry mixeris introduced at the column base and the bubbles rise through the column collection zone.A frother pump allows the addition of frother to cqntrol the average bubble size.Level Control: DifTerential pressure cell was used to control the level of the pulp/frothinterface· by manipulating the tailings flow. Depending on the level of the interface withreference to"set point, DP cell delivers an input signal' (4-20mA) to a PID controller. Thecontroller sends out an output signal (4-20 lOA) to a proportional electropneumatic controlvalve which changes the tailings fl.ow in order to keep a constant pulp level in the column.The desired pulp level is directly entered in the PID controller as the set point. By changingthe set point of the pulp/froth interface, froth depth can be varied behveen 20 em to 120cm.Wash Water: The purpose of wash water is to remove entrained gangue minerals frol11 thefroth and improve the concentrate grade. It also enhances the froth stability. A flowmelerindicating flow rate and totallizer was installed for measurement purpose.lunao.~I<t~ocnr-ig.2. Schcmalic alTangcment for theTMTurbo air systemStjEAR AIRELEMENT 1~~VALVE--SLURRYSTATIC;: MIXEnFig 3. Principle ofMicrocel™ bubble generation systemSlurry flo,w: Slurry flow rales were measured by installing magnetic flow meters in thepipe lines o'f feed, tails and concentrate.Proccdu rc: Pilot plant test runs were conducted over a period of one month. Beforeslarting,!~e plant, column was filled with water and stabilised at required froth depth andwash water addition. Rougher concentrate generated from the rougher circuit was pumpeddirectly to the column. Necessary reagents for cleaning were added in rougher concentratelaunder itself. Column tailings were directed to an appropriate location of the circuit forrecirculation. All the parameters were noted just before collecting the sample. Due tolimitations of ball mill capacity, ROM was varied between 1..3 - 2.0 TPH. The percentageof solids of rougher concentrate was maintained by adjusting the launder water. Sampleswere collected at every half-an-hour interval, after allowing the circuit to nll1 conlinouslyfor a period of four hours. The, collected samples are processed to determine % solids priorto chemical analysis. Analyses of Cu, Pb, Zn, Fe and Mg were conducted by atomicabsorption spectrophotometer. Sta~ard gravimetric methods were adopted for theestimation of silica and insoluble material.Gas Hold up measurement: Volumetric fraction of the slurry displaced by gas is called"Gas holdup". Water manometers wert"connected to the column, at different points. Theactual gas holdup was evaluated by using the following equationtJ.p£ = 1----g Ps,gMwhere PsI = density of slurry, g = gravitational acceleration, tJ. L = distance betweentwo pressure taps.on the column and tJ. P = pressure difference between the two points.Pilot plant: Multi purpose pilot plant comprising ore bin, crusher, grinding mill classifier,conditioning and flotation units with the capacity of 2 tonnes per hour is available atAmbaji project site. It has attained an unique status in India by installing flotation column.The entire test work has been conducted at Ambaji m~lti metal project site.RESULTS AND DISCUSSIONPreliminary tests were conducted both on laboratory and pilot plant scale to study theeffect of various reagents and to optimise reagent schedule to obtain the final concentratewith required grade and recovery. Sodium silicate, NaCN and starch were used asdepressants for silica, pyrite, mica minerals and talc respecti vely. CuS04 was used toactivate sphalerite and isopropylxanthate as collector. Since the ore is highly oxidised innature, sulphidization prior to flotation was found to be essential to obtain betterrecoveries. Na2S was used for this purpose. Reagent schedule thus optinlised (Table II) wasadopted during the pilot plan runs.Systematic experiments were conducted for the individual separation of Cu, Pb andZn by differential flotation and found to be not ,encouraging. Attempts made to separatetalc by using MISC has resulted in 30% loss of galena. Thus the contamination of talc withlead and considerable loss of lead makes the process not attractive. Further set ofexperiments were conducted to separate sphalerite from chalcopyrite and galena.Table II. Pilot Plant: Reagent ScheduleReagent Soln Ball Rougher Scaven- Cleaner Cleaner Total (kglI )% Mill gel' -1 -2Lime 8.75 1600 - 400 Nil Nil 2000 5.25CUS04 3.75 Nil 540 450 Nil Nil 990 1.11Na7S -. 1.25._ 1300 Nil Nil Nil Nil 1300 0.50 -Starch 2.00 Nil 340 340 170 170 1020 0.60NaCN 0.50 Nil 270 270 135 70 745 0.11Xanth 0.50 Nil 450 270 135 Nil 855 0.13MIBC Cone Nil 1.50 1.30 Nil Nil 2.80 0.068Generally, the floatability of sphalerite is very weak in the absence of an activator.Quite contrary to its usual behaviour, floatability of sphalerite was found to be very highinspite of high dosages of depressants like ZnS04 and NaCN(Table III). This unintentionalactivation of sphalerite is attributed to weathering action. CuS04 is f0Il11ed in solution as aresult of oxidation and dissolution of the chalcopyrite and pyrite in the upper regions of theIdeposil. These solutions percolate down to the water table, where they react withchalcopyrite to form the rims of the secondary copper sulphides namely covelite andchalcocite. The copper sulphate also reacts with sphalerite, depositing copper ions on thegrain surfaces [7]. .- •2+ 2+Cu (oq) + ZnS (su;!) = CUS(SUrl)+ Zn (oq)2+ . 2+ 02 Cu + 2 ZnS(Sur!) = CU2S + 2 Zn + S (Sur!)Table.IlI. Activation of sphalerite by dissolved metal ions'·Conditions: Sod. silicate: 1 kg/I; Starch:0.2 Kg/t Xanthate:0.15 Kg/t MIBC :0.05 Kg/t;:pH of slurry 9Depressants (Kg/t) Float Assay Recovery(wt%) % %ZnSO NaCN Cu Pb Zn Cu Pb Zn1.00 0.05 17.9 150 4.19 11.20 60.2 55.8 67.52.00 005 18.1 151 4.99 12.60 63.7 59.8 70.63.50 0.10 18.2 1.48 5.30 12.10 69.6 62.1 69.6Because of oxidation, the concentration of metal ions in slurry increases beyond thesolubility product of individual minerals. Metal ions released into the pulp due to oxidationin turn absorb on sphalerite and activate the same according to the following mechanism.2+ +ZnS(Surl) + Cu· (aq)+ 21120 = ZnS CU(OH)2 (surl)+ 2HCu(OHh(aus) + ZnS(Surl) = CuS(surf) = Zn(OHh (ads)o2Cu(OHh (aus)+ 2 ZnS(surl) = CU2S(Surf)+ 2Zn(OH)2 (ods)+ S (surf)Thus, oxidation appears to have an important bearing on the beneficiation. Secondarycopper sulfides rims of covel lite and chalcocite thus formed on the surface of sphaleriteparticle activate its flotation. Under such circumstances it is extremely difficult to produceclean and separate concentrates of chalcopyrite, galena and sphalerite. Hence, attention waspaid to produce bulk concentrate of Cu-Pb-Zn.Two types of bubble generation syslems viz, TURBO and MICROCEL were studicdand the results of the same are shown in Table IV. It is evident that the overall recovery isbetter in Microcel where as Turbo type yields be tIer quality concentrate. Higher recovcryin Microcel could be attributed to high air holdup values.Table.IV Difference in performance of Turbo and Microeel spargersType of.Cone Assay(%) Column Recovery'. ,Sparger,_ Cu Pb Zn Cu Pb ZnTurbo 2.56 16.40 32.00 65.78 55.24 62.00Micrpcel 1.64 13.10 32.10 ,'" 48.34 68.39 73.75Microcel system produces much finer bubbles than the Turbo system. Consequently,the air bubble surface area 'available in the collection zone is greater with Mierocel.Furthermore, while the slurry is recycled through static mixture (for bubble generation)where the air is introduced cocurrentlY,it enhances the collection process in the spargingzone. During this process, unattached hydrophobic particles make contact with air bubbles.Thus the overall recovery is enhan£.cd by adopting microcel sparger system. However, ifthe hydrophobic particles are gangue minerals the quality of the concentrate is drasticallyaffected. Microcel sparger may cause adverse effect especially in the case of Ambajideposit where the gangue is dominated by naturally hydrophobic minerals like talc andmica. Comparatively high recoveries of lead and zinc in Microcel are due to fine bubblessuitable to the fine particles of lead and zinc. .The perfonnance of conventional1Jotation cells with column is compared in Table V.In the 1st case, flotation circuit consisting of roughing, scavenging and two stage cleaningby conventional flotation cells (Fig 4) was rUIl on three different ore samples. In the 2ndcase, two stage cleaning by conventional cells was replaced by single stage colul11noperation as depicted in Fig 5.Table V Perfonnance of conventional machines and column cellType Conventional Columnof Grade (%) Recovery (%) Grade (%) Recovery (%)ore eu Pb Zn Cu Pb Zn Cu Pb Zn Cu Pb ZnLean 2.53 10.4 16.4 84.2 69.9 86.1 1.98 11.20 34.42 88.4 76.9 61.2Deri 2.12 16.6 35.5 92.9 73.1 88.8 2.50 17.25 36.20 89.4 93.3 96.6Mix 2.37 17.2 29.6 80.5 79.8 87.0 2.96 25.10 25.00 82.5 80.8 82.4FigA Bulk notation circuit of Cu-Pb-Zn". "--Fig.5 Bulk flotation circuit of Cu-I'b-Znconcentrate column as cleanerIt is apparent from Table.V that the quality of the concentrate obtained by coluillnoperation is superior compared to that of the conventional cells. A single stage cleaning bycolumn "was found-to be enough to obtain much cleaner concentrate. The entrainmcnt offine gangue material in the fr.oth product is a serious drawback with conventionalmachines. Due to high turb't.dent conditions prevai ling in the conven.tiolial cells, finegangue particles could be easily carried into the froth by getting either entrained in theliquid or mechanically entrapped. with the particles being floated affecting the quality ofthe concentrate. The absence of turbulence at the interface of the column minimises thechances of physical 'entrapment of unwanted gangue minerals. As the mineralized frothenters the cleaning zo~e, it immediately encounters a blanket of water spray which washestlown the entrapped gangue. Finch and Dobby (8) reported that less than I% of processwater reaches the concentrate product during the steady stale column flotation operation.The net effect is an improved selectivity resulting in a high grade concentrate product. Thisirtllercnt cleaning action is a main reason that the notation column finds its applicationmostly in cleaning operations,Thus, ilTespective of the fluctuations in feed grade, the quality of the concentratecould be maintained uniformly by introducing notation column in the circuit. Also,recirculation loads, circuit complexity could be minimised by replacing two stage cleaningby conventional cells with single stage cleaning by column. Other attendant benefits likelow maintenance, less power consumption etc can be reaped.Pilot scale test was conducted to evolve a suitable now sheet for the bencficiation ofcomplex sulphides multimetal deposit at Ambaji. The possibility of obtaining individualconcentrates of copper, lead and zinc was found to be a difficult task due to the weathcringaction. However, production of bulk concentrate of Cu-Pb-Zn suitable for smelting can beachieved by adopting simple notation circuit consisting of roughing, scavenging(conventional machines) and single stage cleaning .by flotation coluIlln. Flotation circuitconsisting of roughing, scavenging and two stage cleaning by conventional cells wascompared with the circuit where two stage cleaning operation was replaced with singlestage cleaning by flotation column. ]( was proved beyond doubt that the flotation circuitinvolving column is more efficient to derive better Illetallurgical benefits, Of the two typesof sparger systems tried, Turbo type was found more suitable to obtain high qualityconcentrates.The authors wish to acknowledge Prof. P Ramachandra Rao, Director, NationalMetallurgical Laboratory, Jamsheclpur for his keen guidance, constant encouragement andpcmlission to publish this work.I. Michael, J Brookes and Ian T R Fleming, Mining Magazinc, July (1989( 342. Donald J Murdrock and I-brold E Wyslouzil, E & MJ, Aug (1991) 40J. furtado J R V and Percs A E C, in Froth Flotation, Eds, Scrgio II Clslro Flores ct alElscivcl', Amsterdalll,p 109 (1988). 4. I'rabltakar S, Bhaskar Raju Ganci Sankaran C, Trans JIM. 47 (1994) 895. Bhaskar Raju G, Prabhakar Sand Sankaran C, Trans IMM, 102 (1993) C 1326. Reddy P S R, Kumar S G, Bhaltucharyya K K, Sastri S R S and Narasimhan K S, lnt. JMiner. Process, 24 (1988) 1617. Xianghuai Wang, Doctoral thesis, Lulea University ofTccllllology, Sweden (1989)8. f7inch J A and Dobby G S,."Column flotation" Pergamon Press, Oxford, p 86 (1990)

Pilot scale studies on the beneficiation of complex sulphides by flotation column

http://eprints.nmlindia.org/4050/1/RAMP_1997.pdf

Pilot scale studies on the beneficiation of complex sulphides by flotation column

Abstract

Similar works

Full text

Available Versions

eprints@NML