During the first phase of the study, laboratory size

flotation column was installed within the premises

of flotation plant of M/s BGML to study the

amenability of column technology for the benefIciation of gold. Encouraged by the results,  semi-commercial flotation column designed and developed by NML Madras Centre was installed in the flotation circuit to evaluate its performance and also to instil confidence. The results obtained both by laboratory and semi-commercial size

flotation columns clearly indicated that the

columns can perform better than the conventional

cells. It was observed that high quality

concentrates assaying 40 to 50 ppm of gold could

be achieved by flotation column, whereas

conventional cells could produce hardly 10 to 15

ppm of gold concentrates

Bhaskar Raju, G

Prabhakar, S

Sankaran, C

Subba Rao, S

English

eprints@NML

Proceedings of theINTERNATIONAL SYMPOSIUMONBENEFICIA nON IAGGLOMERAnONANDENVIRONMENT(January 20-22,1999)BhubaneswarConvenorD.N.DEYEditorsS.R.S. SASTRISWATIMOHANTYB.K.MOHAPATRAOrganised byRegional Research Laboratory(Council of Scientific and Industrial Research)Bhubaneswar - 751 013, India1£1ALLIED PUBLISHERS LIMITEDNew Delhi • Mumbai. Calcutta • Lucknow • ChennaiNagpur • Bangalore • Hyderabad • AhmedabadBeneficiation of Gold Ore by Flotation Column:A Pilot Scale StudyG. BhlUkR.rRR.ju, S. PrabhakR.r, S. Subba RJuJand C. SankR.ranNatitnuzlMetallurgical Laboratory (Madras Centre))CSIR Madras Complex) Taramani (P.O.))Chennai 600 113IndiaDuring the fIrst phase of the study, laboratory sizeflotation column was installed within the premisesof flotation plant of Mis BGML to study theamenability of column technology for the'benefIciation of gold. Encouraged by the results, .-semi-commercial flotation column designed anadeveloped by NML Madras Centre was installedin the flotation circuit to evaluate its performanceand also to instil confIdence. The results obtainedboth by laboratory and semi-commercial sizeflotation columns clearly indicated that thecolumns can perform better than the conventionalcells.-- It was observed that high qualityconcentrates assaying 40 to 50 ppm of gold could-be-achieved by flotation column, whereasconventional cells could produce hardly 10 to 15ppm of gold concentrates.Kolar Gold Fields owned by Mis. BharatGold Mines Ltd. (BGML) is well known for itsgold reserves for the past 100 years. Since itsinception, gravity methods were followed to enrichgold. As the characteristics of the gold ore changedover the time, the losses of gold were found to besevere by gravity methods. During 1983 detailedmineralogical analysis was conducted in order tounderstand the mineralogy and nature of goldlosses in tailing. It was established that very fInegrained gold particles locked with gangue mineralsas well as the unliberated gold particles inarsenopyrite are the main reasons for gold .loss intotailings. It was also found that the gold values incyanide residue were due to incompletecyanidation of gold locked up in arsenopyrite.These gold inclusions along with fine specs of goldlocked in sulphides were estimated to be around20%. It is known that gravity methods"· are .-inadequate to recover micron size gold particles.Hence Mis. BGML decided to introduce flotationcircuit during 1990. The flowsheet of presentoperatiml consiSts of usual crushing, grinding,classification, gravity concentration, flotation inaddition to leaching, elution, electtowinning,smelting and· bullion. Tailings generated fromflotation .and leaching are subjected toclassification. The cyclone overflow is dumped intailing dam whilst underflow is utilised for minefIlling.In order to sustain the impact ofglobalisation, Mis. BGML have identifIed variousoptions. Replacement or total elimination ofineffective and age old equipments with latesttechnologies, simplifIcation of flowsheet withbetter ·control strategy and steep increase in millingcapacity are a few among various measures aimedto cut down the production costs. In order to meetthe increased tonnage of milling, it was decided toexpand the existing flotation circuit by columntechnology .Since part of the gold is distributed insulphides, incorporating flotation column in theexisting flotation circuit was considered to be the "best choice to derive better metallurgical results.The technology of column flotation is rapidlygaining attention due to its distinct advantages ov~conventional flotation technology. Increase Inconcentrate grade, product recovery, decrease in~_ number of flotation stages re~ired to - achieveproduct grade or a combinatJ~af these effectshave been reported on many orCS' [1-4]. Columnflotation was adopted td process sulphidic gold oreat the Harbour Lights mine in Leonora, WesternAustralia to produce a final gold bearing sulphideconcentrate in a single stage [5]. The Three MileHill gold deposit of Goldfan Ltd. located nearCoolgardie also adopted column as rougher for thebeneficiation of gold mostly associated withsulphides. Column cells have been installed in goldrecovery circuits at the Austin Gold Venture inNevada, Asamera's Cannon Mine in Washingtonand Echo Bay's McCoy Mine in Nivada. In all thecases, column cells were used for cleaning rougherflotation concentrate [6]. The· column technologywas proved to be superior over conventinal cells inmany operations through out the world.Detailed column flotation tests wereconducted by 0.074 metres dia. labora~ry flotationcolumn to establish the amenability of flotationcolumn for the beneficiation of gold ores at MIs.BGML [7]. Encouraged by the results, semi--commercial size (0.5 metre- dia.) flotation columnwas installed to confirm the reproducibility ofresults obtained by laboratory size. In the presentpaper, results obtained by the semi-commercial sizecolumn are discussed and compared to that oflaboratory size column.Detailed mineralogical assay ofNundydroog ore of KGF reported by MineralExploration Corporation, Nagpur revealed that theore is semi-refractory containing both free andrefractory gold approximately in the ratio of 80:20.In the refractory ore, about 85-90% of gold Waltobserved to be locked in arsenopyrite and loellingitegrains. Though the grain size of g~ld particlesranges from one micron to hundred microns, mostof the particles were found to be 0 in t,he range of 2 too20 microns. The free gold occunng In the gangue IScoarser i.e. 10-100 microns. Based on their modalabundances, different ore minerals were grou~ed as:Major Minerals(> 5% by volume)Pyrrhotite, Ilmenite,Sphene andArseno °teMagnetite, Loellingiteand Chalco °teSphalerite, Pyrite andMarcasiteGold, native Bismuth,Petlandite, Graphite'and Platinoid mineralsThe column shell with an ID of 0.5 metre isfabricated out of mild steel. It comprises severalflanged sections with suitable fixtures for feedinjection, air sparging, launder and housing for levelcontroller. The feed injection point is located at aheight of 5 metres from the bottom of the column.The height of the column is further extended to 3.5metres for cleaning froth zones measuring 3 metersand 0.5 meters respectively. The top section isconnected to a launder with sufficient-slope so thatthe froth falling from the column is effectivelydrained through a pipe.Air spargerslbubble generators withdifferent porosities designed at NML MadrasCentre were used. The gas hold up of the columnwas found to vary from 10-15% depending on theair rate, frother dosage and solids: A single loopcontroller connecting differential pressuretransmitter (OPT) and the tailing discharge valveis adopted to maintain the interface between frothand slurry. The discharge valve is actuated by asignal 4-20 mA generated by OPT. Under steadystate conditions, the interface level could bemaintained within . ± 50 mm. Magnetic flowmeters are used to measure slurry flow rates.Digital display meters were incorporated tomeasure flowrates and total volume of air andwater. Online electro-pneumatic valves with timerare also installed for automatic sample collection.The schematic diagram of flotation columninstalled in the circuit is shown in Fig.I. Thecolumn was installed as rougher cum cleaner.Conventional cells were utilised for scavenging.1.Control Panel2 "DPT3.Sparger4.Compressor5.Control Valve6.Auto Sampler11 27-0-:1,.000.mp. - I I.12···~ '7. Conditioner8. Mag. Flow meter9. Wash water flow meterio. Wash Water Distributor11. Cleaning zone12. ColIection zoneFig.1: Schematic diagram of Semi-commercialflotation columnThe column was run on a continuous basis for aperiod of 3 months. The standard test procedureestablished by Finch eta\. [8] was adopted throughout the work.During the first phase, 0.074 metre dialaboratory size flotation columri was instalIedwithin the plant premises and the amenability ofthe flotation column as " rougher cum cleaner wasstudied. Entire amenability test work wascondqcted on a sample collected directly frommill cyclone overflow which is free from reagentsand recirculation loads.Batch type experiments related tooptimisation of various reagents and columnparameters were conducted by the laboratory sizeflotation column. The optimum conditions thusobtained are tabulated below:Soda ash:Sodium SilicateCopper SulphateAmyl xanthatePine oilpHAir velocityWash water velocityFeed velocityFroth depthResidence timedao1.00 kglt0.50 kglt0.40 kglt0.04 kglt .0.015 kg/t8.01.16 cm/s0.Q78 cmls1.1 cm/s40cm400 see75 J.LCuSO. is used as an activator to enhancethe flotability of arsenopyrite. GeneralIy. the.flotability of iron containing sulphides likepyrrhotite and arsenopyrite is sluggish and needsan activator like CuSO. to obtain betterrecoveries using xanthates- as .colIectors. H isknown that metal xanthates of arsenic and iron areless stable and more soluble compared to copperxanthates. -Typicaliy a froth dep~ ~of 1. metre ispreferred in most of the operations: Froth depthhas practical advantage of dampening down theentrainment. However, in this particular case dueto very high density of concentrate and lowmineral content, froth depth was deliberatelymaintained to a maximum of 0.5 metres to obtainbetter recoveries. While floating heavy goldminerals, froth zone density may exceed thedensity of slurry due to the pressure exerted bycoarse and high density solids. Consequently thefroth may sink through lower density regionsbelow. This phenomena would adversely affectsthe recoveries. Hence low froth depths rangingfrom 0.3 - 0.5 metres are preferred to achievebetter recoveries.Slurry feed rate and % solids areimportant variables to establish the residence timeand column throughput. By increasing the feedrate, the particle residence time is reduced andthere by the recovery. Effect of feedflowratelslurry residence time on grade andrecovery' of gold is shown in Table 1.prevailing in flotation column. Due to countercurrent flow of particles and air bubbles. thecollision efficiency is high in flotation columnsand intum the recovery. Column throughput canbe increased simply by increasing the feed solidsupto a point where SUfficientbubbles are availableto lift the particles. Generally 20% solids ispreferred in cleaning operations. In this particularcase, since the valuable material which is to befloated is very 'less, thorougli separation can beachieved even at 40% solids.After optimising all the parameters a fewruns were carried out for a longer duration rangingfrom 6 to 8 hours and the samples were collectedfrom the column and the plant simulumeously.The results of the same are shown in Fig.2. Highgrade concentrates assaying 30-50 ppm of gold81., Slurry residence Cone. Gold Assay (ppm) Recovery .No. time (Sec.) Wt(%) (%)Feed Cone. Tails1 1458 6.7 2.15 23 0.42 80.72 1068 7.5 2.15 30 0.40 82.53 1008 5.5 2.10 23 0.40 82.44 858 7.4 2.20 ,30 0.40 82.95 714 8.8 2.15 30 0.40 82.56 432 4.7 2.20 60 0.50. 80.07 324 3.7 2.15 65 0.55 75.1It is apparent that slurry residence time of8 minutes is fou"d to be sufficient to achieve thetarget recovery. The residence time to achieveequivalent recovery by conventional flotation cellsis observed to be 15 minutes. The results clearlyindicate that the kinetics of flotation of goldbearing minerals in column are superior comparedto conventional cells. The better flotation kineticsare attributed to better hydrodynamic conditionswas obtained by flotation column whereasconventional cells have yielded hardly 5-10 ppmof gold concentrates. The recoveries were found tobe more or less same in both the cases. It may benoted that plant recoveries mentioned areinclusive of scavenging operation whereascolumn recoveries reported are withoutscavenging. Also, it is apparent that around 40 %of the solids report to concentrate in conventionali;100 100CONVENTIONAl CElLS (Plant) lABORATORY COLUMN90 90- ~80C 80 •~ ~CIl CIl> >!70 8~ 7060 6050o 5 10 15Grade (ppm)50o 20 40 60Grade (ppm)Fig. 2: Comparison of metallurgical preformancebetween Conventional cells and Columnflotation, resulting in poor grades, whereas weightof the float is below 10% in flotation column.Apparantly, the cost of down stream operationscould be minimised by rejecting most of thegangue during the flotation stage.Encouraged by the performance of thelaboratory column over the conventional flotationit was decided to confinn the same on a largescale operation. Accordingly a semi-commercialcolumn was installed in the flotation circuit andallowed to run at the optimum conditions alreadyestablished by laboratory size flotation column.The column was op~ted simultaneously with theflotation plant by drawing a separate stream fromthe conditioner. The-results obtained by semi-commercial column (Figs. 3 & 4) are compared tothat of the laboratory flotation column andconventional cells. Fig.3 shows the comparison ofthe grade-recovery profile in both laboratory andsemi - commercial scale columns. Slightly better,recoveries observed in the semi-commercialcolumn were due to close circuit operation wherein scavenging concentrate is recirculated. A goodagreement of the results is seen from the contoursdrawn for the set of tests. In both the cases, goldconcentrates ranging from 35-60 ppm of gold witha recovery of 70-90% is achieved. A similaragreement of results could be seen from Fig. 4. where concentrate weight is compared with goldrecovery. The weight of the concentrates obtainedby column flotation is 2 - 10% which is very lesscompared to conventional flotation where theconcentrate weight was observed to fluctuatebetween 40-50%. Flotation columns were found toyield better concentrates with minimum gangue.The wash water introduced from the top of thecolumn could effectively displace the entrainedhydrophilic gangue particles from the froth phase.This reduction in concentrate weight will benefitthe . downstream operations particularly in the100 100lA8ORATO~YColUMN"SEJ,lI.t._RCIAl COLUMN90 90..- -~80';fl. 80-~ ~G)G)>>0 81 +u~ 70 ~ 7060 6050~ ~ ~ 00 0 ~ ~ ~ ~Grade (ppm) Grade (ppm)Comparison between Laboratory and Seml-commercial "otation columns. __ ._0100 COtMM11ONAl CELLS. SEMI-COMMERCIAl COLUMN90-~80 •~~ " .~ 70 • •a::6050o90- ,~80~~.~ 70 •a::6050 o 10 20 30 40 50 60Concentrat. Weight (%)50 o 4 8 12 16ConcentrateWeight (%)Fig. 4: Concentrate Weight va Recovery - Comparison betweenSemi-commercial column and Conventional cellireduction of cynaide consumption which intumwill reflect on the overall economics of the plant.The results obtained both by laboratoryand semi-commercial flotation columns clearlyindicate that the flotation columns are amenablefor beneficiation of gold ores of BGML. Grade-recovery profiles are almost identical in both theinstances. The quality of concentrate generated byflotation column. is superior compared toconventional cells. Nearly 90% of the gangue iseliminated by flotation column whereas hardly50% is rejected by the existing conventional cells.High grade concentrates with less ganguegenerated by flotation column is expected toconsume less cyanide during cyanidation stage.The significant reduction is cyanide consumptionalong with usual benefits of flotation column cancertainly improve the overall economics of theplant.-:..--- The authors. wish to acknowledgeProf.P.Ramachandra Rao, Director, NML for hiskeen guidance and permission to publish thiswork. The technical suppot rendered by Mr.TVKDas of NML Madras Centre is alsoacknowledged. Our thanks are also due to MIs.BGML for sponsoring the project1. Bhaskar Raju, G., Prabhakar, Sand Sankaran,C., Beneficiation of Iron Ores by ColumnFlotation. Trans. IMM., 102, C132-135, 1993.2. Prabhakar. S., Bhaskar Raju, G and Sankaran,C., Quality Improvement of Copper Concentratesby Column Flotation, Trans. lIM., 47, 89-101,1994.3. Michael J.• Brookes and lan, T.R. Fleming,Modemisation of the Nchanga Flotation Plant: AComparison of Flotation cells and Columns,Mining Magazine, July, 34-39. 1989.4. Donald J. Murdock and Harold E. Wyslouzil,Large Diameter Column Flotation Cells takeshold, E&MJ, Aug., 40-42,1991.5. Subramanian, K.N., Connelly, D.E.G andWong, K.Y., Commtrcialisation of a ColumnFlotation Circuit for Gold Sulphide Ore. inColumn Flotation "88, K.V.S.Sastry, Ed., pp 13-19, Society of Mining Engineers Inc., Littleton,1988.6. Marsden, J.O., Mansanti, J.G. and Sass, S.A.,Innovative Methods for Precious Metal RecoveryIn North. America, Mining Engineering, Sept.,1144-1151,1993 ..7. Prabhakar, S., Bhaskar Raju, G., Das, T.V.K.and Sankaran, C., Amenability of FlotationColumn for the Beneficiation of Gold Ore, AReport,National Metallurgical Laboratory-MadrasCentre, April, 1995.8. Del Villar, R., Finch, J.A., Gomez, C.O. andEspinosa-Gomez, R, Flotation ColumnAmenability. and Scale-up Parameter EstimationTests, Minerals Engineering, Vot5, No.2,pp 169-182,1992.

Beneficiation of Gold Ore by Flotation Column: A Pilot Scale Study

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Beneficiation of Gold Ore by Flotation Column: A Pilot Scale Study

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