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LEACH-SX-EW COPPER REVALORIZATION FROM OVERBURDEN OF ABANDONED COPPER MINE CEROVO, EASTERN SERBIA Z. Stevanović* # , M. Antonijević**, R. Jonović*, Lj. Avramović*, R. Marković*, M. Bugarin* and V. Trujić* *Institute for Mining and Metallurgy 19210 Bor, Serbia **University of Belgrade, Technical faculty in Bor, 19210 Bor, Serbia (Received 31 August 2009; accepted 19 September 2008) Abstract Hydrometallurgical processes for copper revalorization from overburden of abandoned mine Cerovo in Eastern Serbia were studied. Paper contain results of percolation leaching tests, performed with acidic mine waters accumulated in the bottom of the former open pit, followed by solvent extraction (SX) and electrowinning (EW) processes on achieved copper pregnant leach solutions. Usage of accumulated waste waters was objected to minimizing the environmental hazard due to uncontrolled leaking of these waters in nearby creeks and rivers. Chemical composition of acidic mine waters used for leaching tests was: (g/dm 3 ): Cu – 0.201; Fe – 0.095; Mn – 0.041; Zn – 0.026; Ni - 0.0004; pH value - 3.3. Copper content in overburden sample used for leaching tests was 0.21% from which 64% were oxide copper minerals. In scope of leaching tests were examined influence of leaching solution pH values and iron (III) concentration on copper recovery. It was established that for 120 hours of leaching on pH=1.5 without oxidant agents, copper concentration in pregnant leach solutions enriched up to 1.08g/dm 3 which was enough for copper extraction from solution with SX-EW treatment. As extraction reagent in SX circuit was used LIX-984N in a kerosene diluent. Cathode current density in electrowinning cell was 220Am -2 while electrolyte temperature was kept on 50±2 o C. Produced cathode copper at the end of SX-EW process has purity of 99.95% Cu. Keywords: Leaching; SX-EW; Overburden; Copper; Mine Waters; Abandon Mine. # Corresponding author: [email protected] DOI:10.2298/JMMB0901045S Journal of Mining and Metallurgy Journal of Mining and Metallurgy 45 B (1) (2009) 45 - 57

Leach-sx-ew Copper Revalorization From Overburden of Abandoned Copper Mine Cerovo

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Page 1: Leach-sx-ew Copper Revalorization From Overburden of Abandoned Copper Mine Cerovo

LEACH-SX-EW COPPER REVALORIZATION FROM

OVERBURDEN OF ABANDONED COPPER MINE CEROVO,

EASTERN SERBIA

Z. Stevanović*#, M. Antonijević**, R. Jonović*, Lj. Avramović*, R. Marković*,

M. Bugarin* and V. Trujić*

*Institute for Mining and Metallurgy 19210 Bor, Serbia**University of Belgrade, Technical faculty in Bor, 19210 Bor, Serbia

(Received 31 August 2009; accepted 19 September 2008)

Abstract

Hydrometallurgical processes for copper revalorization from overburden of abandoned mineCerovo in Eastern Serbia were studied. Paper contain results of percolation leaching tests,performed with acidic mine waters accumulated in the bottom of the former open pit, followed bysolvent extraction (SX) and electrowinning (EW) processes on achieved copper pregnant leachsolutions. Usage of accumulated waste waters was objected to minimizing the environmental hazarddue to uncontrolled leaking of these waters in nearby creeks and rivers. Chemical composition ofacidic mine waters used for leaching tests was: (g/dm3): Cu – 0.201; Fe – 0.095; Mn – 0.041; Zn –0.026; Ni - 0.0004; pH value - 3.3. Copper content in overburden sample used for leaching tests was0.21% from which 64% were oxide copper minerals. In scope of leaching tests were examinedinfluence of leaching solution pH values and iron (III) concentration on copper recovery. It wasestablished that for 120 hours of leaching on pH=1.5 without oxidant agents, copper concentrationin pregnant leach solutions enriched up to 1.08g/dm3 which was enough for copper extraction fromsolution with SX-EW treatment. As extraction reagent in SX circuit was used LIX-984N in a kerosenediluent. Cathode current density in electrowinning cell was 220Am-2 while electrolyte temperaturewas kept on 50±2oC. Produced cathode copper at the end of SX-EW process has purity of 99.95%Cu.

Keywords: Leaching; SX-EW; Overburden; Copper; Mine Waters; Abandon Mine.

# Corresponding author: [email protected]

DOI:10.2298/JMMB0901045S

J o u r n a l o f

M i n i n g a n d

M e t a l l u r g y

Journal of Mining and Metallurgy 45 B (1) (2009) 45 - 57

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1. Introduction

At present, there are basically two mainmethods used worldwide in order to processcopper ores for metal production. First one isthe "conventional" – pyro-metallurgicalmethod, comprised by numerous types ofshaft and flash technologies. Treatmentprocess is consisted of crushing, grinding,flotation, smelting-refining and electro-refining stages. This method is applied tosulphide copper ores and is economicallyfeasible for copper richer feeds [1,2].

A second method, “hydrometallurgical”,is applied to the rest of the world’s primarycopper production, objected mainly on oxideand/or low grade copper ores due tosignificantly lower operating costs [3,4,5].Treatment chain in hydrometallurgyprocesses are usually consisted of crushing,leaching (non-oxidative leaching,atmospheric leaching or pressure leaching),solvent extraction and electrowinning.Hydrometallurgical processing can beeffectively applied for oxidized ores,containing CuO, Cu2O, carbonates and somesilicates, and rarely for sulphide ores withchalcocite and covellite as predominantcopper minerals [6, 7]. Hydrometallurgicalmethods are used in countries having readilyavailable deposits with low copper contentand with surplus of oxidized forms at thesame time (USA, Chile, Australia, and Peru).The most important development in copperhydrometallurgy, with respect to the growingnumber of its applications as well as for itsfuture potential, has been solvent extractionprocess. It became the achievement whichrevolutionized copper production all over theworld and enabled to introducehydrometallurgy for industrial scale [8].

Beginning of solvent extraction processdevelopment, objected on metal extraction

from leach solutions, date from the late 60'sof last century. Beforehand, solventextraction processes were used in analyticalchemistry assaying [9], while large scaleusage was mostly for uranium extractionfrom sulphuric acidic leach solutions [10].Achieved experiences in uranium extractionprocesses initiated some of leading miningCompanies to start researching of copperextraction from different solutions by solventextraction process usage. One of them wasGenerally Mills which already haddeveloped and commercialized ALAMINE®336, as an SX reagent for the recovery ofuranium from sulphuric acid leach liquors,[11] and believed that a similar technologyfor copper recovery would be welcome.However, pioneering operations of theBluebird Mine and Bagdad Mines inArizona, USA in the late 60's of last century,which used selective organic extractionreagents for metal concentration from leachsolution in order to make possible thecommercial production of pure copper metalby electrowinning processes, represent thebeginning of the SX-EW technology as weknow it today [12].

Mining & Smelting Complex Borrepresent largest copper producer in Serbiawhere mining and processing of copper andother precious metals have history of overone century. Mining production started in1903 with the exploitation of theunderground mine, followed by opening of 3open pits in the Bor area (from 1912, 1979and 1991 – Bor, Veliki Krivelj and Cerovorespectively). The industrial activities in Bor,in particular those by the mining and smeltercomplex, have resulted in negative impactson the environment of the region (includingair, water, and soil) as well as having raisedserious concerns about associated healtheffects of the pollution at large [13]. From

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the influence width point of view, waterpollution certainly represents one of thestrongest environmental impacts whichfurther induce water and soil pollution inwider area.

Significant part of water pollution arisesby Acid Mine Drainage (AMD) originatedby percolation of atmospheric watersthrough dumped overburden. Afterexcavation and delaying of overburden,present sulphide mineralization has beenexposed to influence of air and atmosphericwhich have as a result oxidation processes,especially of pyrite, and making AMD`s.Generally, the oxidation of pyrite frommining wastes under weathering conditions,and further formation of iron (III) could berepresented by the following reactions [14-16]:

FeS2 + 31/2O2 + H2O → FeSO4 +H2SO4 . . . ( 1 )

2FeSO4 + H2SO4 + 1/2O2 →Fe2(SO4)3 + H2O . . . ( 2 )

Products of pyrite oxidation are sulphuricacid and iron (III) which further induceoxidation of other sulphide minerals andgeneration of contaminated Acid MineDrainages (AMD) with low pH value (2.5-4.5) and increased content of SO4 and metalsions (Cu, Zn, Pb, As, Cd, Ni i Mn),metalloids, etc. [17, 18]. Originated AMD`smobilize and disseminate metals ions innearby rivers making strong negativeenvironmental impact, reflected throughlong term contamination of surrounding soil,as well as surface and underground watersystem.

Main sources in scope of Mining andSmelting Complex Bor for AMD originationfrom overburden are three open pit mines(Cerovo, V. Krivelj and Bor) located asillustrated on Fig.1.

Copper mine Cerovo is the youngest minein scope of Mining and Smelting ComplexBor, opened in 1991 and include open pitmining and processing plant with crushingstage (three stadiums), grinding stage (twostadiums) and formed pulp thickening up to36% of solid contents. The thickened pulpwas pumped by three serial linked slurrypumps through steel pipeline up to the Borflotation plant, which is located 13.3 km faraway from Cerovo mine. Operating period ofCerovo mine was very short, from 1991 up to2002 and during this time, all wastewatersfrom open pit and Cerovo processing plantwere collected into “ecological dam” andfrom it, used back as technological water inprocessing plant. Since mine closure in 2002,atmospheric waters was continued to flowinto the area of open pit making water

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Fig. 1. Locations of open pit mines in scope ofMining & Smelting Complex Bor

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accumulation in the bottom of open pit withabout 400 m3 of water characterized by lowpH value and high concentration of residualmetals and metalloids. Existing “ecologicaldam” does not preserved a sufficiently highprotection for surroundings soil and waterstreams from further pollution, mainlybecause of huge average atmosphericprecipitation on annual level, calculated ataverage of around 550 m3 per day whichflow into open pit area. Whereas mineCerovo is the first spot from the North side,in scope of Mining and Smelting ComplexBor (Fig.1), where was mining activities,surrounding cricks (Valja Mare and CerovaRiver), as illustrated on Fig.2, have upstreamwater quality of I and II category anddownstream are highly polluted by AMDsthrough disorganized natural system ofsurface and underground water system.

Owing to dumped overburden quantity ofaround 25.000.000 tons with average coppercontent of 0.21% and increased content ofpyrite, it could be expected that AMDorigination will last very long time causing alot of environmental problems. However,

apart from being the source for AMD`sorigination and pollution, overburden alsocould be source for copper revalorizationbecause AMD`s have some appearance withcopper content of over 1g/dm3, which couldbe extracted by usage of up to date SX-EWprocesses. Therefore, the aim of this paperwas to make a contribution to definingpossibility for environmental protection onCerovo location with making economicbenefits through copper revalorization byleaching and SX-EW technologies usage.

According to proposed aim, we performleaching experiments of overburden sampleusing adjusted mine waters from Cerovoopen pit accumulation followed by SX-EWtreatment of pregnant leach solution objectedto metal copper producing. The intention wasto determine optimum process parametersfor eventual large scale process on mine sitewhere all mine waters will be collected andtreated.

Results of presented investigations haveto route direction of further steps for definingpossibilities of this issue resolving and alsoto induce Mining and Smelting Complex Bormanagement to consider implementation ofSX-EW processes on other similar resourcesin scope of Bor Copper Mines.

2. Experimental

2.1. Particle sizes determination andchemical analyzing

Overburden sample particle sizesdetermination was performed on standardTyler sieve series by dry method. Chemicalanalyzing was performed on overburden andmine waters samples as well as on pregnantleach solutions, SX-EW solutions andproduced cathode copper.

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Fig. 2. Cerovo open pit Mine area withsurrounding rivers

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Analyzing elements in overburden sampleand mine waters samples were firstly heavymetals with limitation concentration for soilsand waters by law regulations of SerbiaRepublic (Gazette 23/94). All chemicalanalyzes was determined by AES method onAtomic Emission Spectrometer with InducedCoupled Plasma (ICP-AES). Overburdensamples are firstly homogenized by standardmixing procedure from which is afterwardtaken smaller sample quantity in mass of20g, by “chess field” method. Reducedquantity of samples was homogenized onemore time after which was taken samples inquantity of 0.5g for respective chemicalanalyses. Samples for chemical analyzingwere dissolved by using 10ml(HCL:HNO3=3:1) solution. Dissolvedsamples were transferred in normal vessel of25ml volume which is afterwardsupplemented with redistilled water up to themark of 25ml. Solutions prepared bydescribed procedure were, by peristalticpump, introduced in induced coupled plasmaflame (T=7000K) of ICP where is performedatomization and ionisation of elements.Finally detection of elements concentrationswere done through CCD detector of ICP.Mine waters and pregnant leach solutionssamples were analyzed on same equipmentand by same procedure but directly withoutpreparation due to already homogenizecharacteristics of solutions.

Solution samples from SX-EW circuitwere taken in quantity of 10ml by measuringflask and afterward supplemented withredistilled water up to the 50ml. Copper was

analysed by Gravimetric method (G),sulphuric acid by titration standardprocedure (VT) and iron by AtomicAbsorption Spectrophotometer (AAS)(Perkin-Elmer – 403). Cathode copperdeposit obtained during the electrowinningprocess was analyzed by Atomic AbsorptionSpectrophotometer (AAS) (Perkin-Elmer –403) according to Standard BS 6017requirements.

2.2. Cerovo overburden samplecharacteristics

During operating period between 1991-2002 Cerovo copper mine produced19.950.000 tons of copper ore and24.800.000 tons of overburden. Copper orewas treated in Bor flotation plant whileoverburden (open pit tailing) was dumped onwest - southwest side of the open pit Cerovo.

Overburden sample was taken on westside of the open pit in total quantity of200kg. Due to easier manipulation, entiresample was crushed up to 85% -30mm.Overburden sample chemical compositionand particle sizes characteristics arepresented in Table 1 and Fig.3 respectively.

2.3. Cerovo mine waters samplecharacteristics

Mine waters in the accumulation on thebottom of open pit Cerovo, with total volumeof 400m3, are collected from undergroundwaters and surface waters which areoriginated from atmospheric precipitations

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Table 1. Chemical composition of overburden sample

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and gravitate into Cerovo open pit area. Dueto geographical position of open pit Cerovo(Fig.2), surface waters from north, west andsouthwest side gravitate into open pit whilesurface waters from east and southeast sideflow into Cerova River. Image of wateraccumulation on the bottom of open pitCerovo, generated by using GEMCOM v.6.2software tools, is presented on Fig.4.

Mine water sample, used for leachingsolutions preparation, was taken fromdescribed accumulation in total volume of150dm3. Characteristics and chemicalcomposition are presented in Table 2.

2.4. Experimental setup

2.4.1. Leaching

Equipment for leaching experiments wasconsisted of Plexiglas column with diameter150mm and height of 900mm, 5dm3 volumedosing tank with flow regulation valve, 15dm3 volume collecting tank for enriched

solution and peristaltic pump. Experimentalsetup of leaching tests is illustrated on Fig.5.

After homogenization and quantityreducing, overburden sample in mass of8.3kg with copper content of 0.21% wereplaced in column. Over the sample wasmount inert silicon dioxide bed, thickness ofabout 1cm, due to uniform distribution ofleaching solution. Below the sample, in thebottom of column, was placed linen for veryfine particles filtration.

Volume of leaching solution forexperiment was 15dm3 with introductionspeed in column of 0.300dm3/h which wascalculated based on solutions flow throughporous media during copper ores leaching[19,20]. pH values were adjusted by additionof sulphuric acid to leaching solutions beforeexperiments and to output solutions beforerecirculation. In experiments with oxidant,iron (III) sulphate was only added inleaching solution after pH value adjustmenton the beginning of experiment. Total time ofexperiment was 120h with recirculation ofleaching solution.

Z. Stevanović / JMM 45 (1) B (2009) 45 - 5750

Fig. 3. Particle sizes characteristics ofoverburden sample

Fig. 4. Water accumulation on the bottom ofthe open pit Cerovo

Table 2. Mine water characteristics and elements content

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In scope of leaching tests were performedtwo experiments series for examination ofleaching solution pH values and iron (III)concentration influence on copper recovery.pH influence on copper recovery wasexamined with following values (pH=1;pH=1.5; pH=2). During analyzing theinfluence of iron (III) in leaching solutionwith pH=1.5 (source of iron is iron (III)sulphate), concentrations of Fe3+ ions were1.0, 5.0 and 10.0 g/dm3. All experimentswere performed at atmospheric conditions.Copper pregnant leach solution, fromleaching process with selected optimalparameters at the end of leachingexaminations was treated by SX-EWprocess.

2.4.2. SX-EW

SX-EW equipment was consisted oflinked solvent extraction and electrowinning

laboratory units. SX unit was Mixer – SettlerPOLUX C Type with mixer volume of85cm3 and settler volume of 175 cm3. EWunit was rectangular electrolytic cell, with1.5 dm3 capacity, made from Polypropylene.The cap of the cell was also rectangular withkerfs witch permitting the parallelarrangement of the electrodes and holes forinflow and overflow of electrolyte. Thesupply glass reservoir with volume of 1dm3

was equipped with flow regulation valve andpipe heater. Electrolytic cell was connectedby busbar to the galvanostate, model 5B(IRM-Bor, Serbia), with characteristics:max. electrical current 5A and max. voltage5V. Flow rate of linked SX-EW equipmentwas 1dm3/h. Schematic illustration of SX-EW experimental setup is given on Fig.6.

Due to closing linked SX-EW circuit atthe experiments beginning was preparedsynthetic CuSO4 solution as spentelectrolyte with contents of copper (31g/dm3) and sulphuric acid (198 g/dm3).

Pregnant leach solution from leachingstage with pH=1.5, contents of copper (1.08g/dm3) and iron (1.11 g/dm3) wasintroduced into SX unit by peristaltic pump.Owing to high selectivity characteristics ofcopper over iron in high acidic media(pH=1.8) and faster kinetics (rate ofreaction) [21], as extraction reagent inextraction circuit was used LIX-984N (5%)in kerosene diluents. SX circuit wereconsisted of two extraction stages and onestripping stage. Organic-Aqueous ratio inextraction stage was 1:1, while in strippingstage was 5:1 [22]. Organic and aqueousphases are mixed in mixers until equilibriumis reached and then separated in settlers.After the extraction and stripping stageswere performed sampling of aqueous phasesfrom settler overflow and analyzed oncopper, iron and sulphuric acid content.

Z. Stevanović / JMM 45 (1) B (2009) 45 - 57 51

Fig, 5. Leaching experiments setup

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Electrowinning of pregnant electrolytefrom stripping stage was performed inelectrolytic cell with maintaining electrolytetemperature on 50±2oC. Pregnant electrolyteworking volume for EW stage was 15 dm3

with flow rate of 1dm3/h. Concentration ofthe main components in pregnant electrolytefrom stripping stage was (g/dm3): Cu – 36.1,H2SO4 - 182.41 and Fe – 0.015. In order toreduce corrosion of the lead anode and due tolower lead content in the copper cathode wasadded cobalt sulphate. Two starter cathodesheets and three anodes were inserted intothe cell with 20 mm interraxial distancebetween two various electrodes. Electrodeorganization was anode – cathode – anode.Starter cathode sheets was prepared fromcathode copper plate, produced in Miningand Smelting Complex Bor - ElectrolyticRefinery Plant with following content (ppm):As < 3; Sb < 2; Bi < 1; Fe < 5; Pb < 2; Ni <1; Si < 9; Ag < 5; Te < 0.1; Sn < 2; Zn < 5;Al < 10; Se < 0.7 and Cu = 99.95 %. Totalactive surface of all cathodes which wereimmersed into the electrolyte was 0.0225m2.Cast antimonial lead anodes (6 % antimony)were used as anode material in a form ofplate. Anode and cathode dimensions weresimilar. The EW test was carried out ingalvanostatic operations at cathodic currentdensity of 220Am-2 and I=4.95A and thisvalue was function of specified Cu content inspent electrolyte [23]. Corresponding cellvoltage was measured with differential

electrometer. The solution samples weretaken on each 60 minutes from the celloverflow due to analyzing of Cu, Fe andsulphuric acid concentrations. Cathodecopper deposit obtained during theelectrowinning process was analyzed oncopper purity at the end of experiment. Spentelectrolyte was returned in a SX unit forcopper striping from the loaded organic.

3. Results and discussion

3.1. Leaching

3.1.1. The effect of leaching solution pHvalue

Obtained results from examination of pHsolution value (pH=1.0, pH=1.5 and pH=2.0)influence on Cu and Fe leaching rate fromoverburden samples are presented on Figs. 7,8 and 9 respectively. Experiments wereperformed without oxidants addition atatmospheric conditions.

By increasing the pH value of leachsolution in range of 1.0–2.0, after 120 hoursof leaching, copper content in outputsolutions was increased from 0.99g/dm3 to1.11g/dm3 with copper recoveries from 68%to 79% respectively. Although oxidants werenot added during the experiments, except forthe oxygen from the air, a relatively highcopper dissolution values were achievedindicating the presence of readily leachable

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Fig. 6. Schematic illustration of SX-EW experiments setup

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copper oxides in the overburden. Sinceoverburden have been exposed to weatheringfor over 10-15 years, and knowing from theother side that copper deposit on Cerovolocation was consisted partly from oxidecopper minerals, oxidation of some coppersulphides and formation of secondary copperminerals such as:

cuprite Cu2O, tenorite CuO, chalcanthiteCuSO4

.5H2O, azurite 2CuCO3.Cu(OH)2,

malachite CuCO3.Cu(OH)2 and chrysocola

CuO.SiO2.2H2O which are easy leachable is

expectable.At pH 2 (Fig.9), copper content is the

lowest (0.99g/dm3) which could beconsequence of iron hydroxide formation onhigher pH values and reducing of Fe(III)concentration who represent main oxidantagent for sulphide oxidation and H+ ionsgeneration [24,25].

Also, H+ ions concentration increasingsensibly correlates with the iron dissolution,at pH 2 iron concentration after 120 hoursleaching reached 0.54g/dm3 (Fig.9), while atpH 1 iron concentration increased up to2.28g/dm3 (Fig.7) which could be obstacleduring solvent extraction stage.

Consequently, leaching solution ofacidity pH 1.5 can be selected as optimal onefor further investigations considering theobtained results (Fig. 8). Copperconcentration of 1.08g/dm3 with recovery of76% is slightly lower than at pH 1.0(1.11g/dm3) with copper recovery of 79%(Fig.7), but however, iron concentration issignificantly lower (1.11g/dm3) than at pH1.0 (2.28g/dm3) which is advantage forpregnant leach solution treatment in SXcircuit.

3.1.2. The effect of Fe (III) concentration

Z. Stevanović / JMM 45 (1) B (2009) 45 - 57 53

Fig. 7. Dependence of copper and ironconcentrations on time during leaching at pH=1

Fig. 9. Dependence of copper and ironconcentrations on time during leaching at pH=2

Fig. 8. Dependence of copper and ironconcentrations on time during leaching atpH=1.5

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Even it is known that increasedconcentration of iron in pregnant leachsolution can balk solvent extraction processwe performed preliminary experiments ofiron (III) concentration influence on copperrecovery. Intention was only to determine isit possible to make significant increasing ofcopper recovery and concentration inpregnant leach solution by oxidants, whichwill indicate on presence of easier leachablecopper sulphide minerals. Obtained resultsfrom examination of Fe (III) concentration atvaried concentrations (Fe3+ = 1.0, 5.0 and10.0 g/dm3) influence on copper leachingrate from overburden samples are presentedon Fig. 10. Experiments were performed atpH 1.5 and at atmospheric conditions.

The presented results indicate that thepresence of Fe3+ ions in the leach solutionhas very small effect on copper dissolution.The obtained copper concentrations for 120hours of leaching are approximately thesame and differ for only ±0.03g/dm3

(Fig.10) or by only ±3% from the copperrecovery point of view (76%-79%). Possiblereason for achieved results could be thatpresent iron in overburden, released duringpyrite and other iron minerals oxidation, isenough for leaching of available copperoxides, so introduction of additional Fe (III)have no significant effect.

From the other side, achieved copperrecoveries of over 75% mean that presentoxide copper in process feed (64%, Tab.1)and partially sulphides were recovered.Among all copper sulphide minerals onCerovo deposit chalcopyrite is dominant,and knowing that chalcopyrite oxidation ratewas marginally dependably on theconcentration of iron (III) [26-27], presentedresults could be quite logical andsatisfactory, even without the addition ofoxidants. Therefore, pregnant leach solution

for SX-EW circuit was prepared by leachingat pH 1.5 without oxidants addition.

3.2. Solvent extraction

Pregnant leach solution from leachingstage has copper concentration of 1.08g/dm3with copper recovery of 76%, ironconcentration of 1.11g/dm3, and pH value of1.5. SX circuit were consisted of twoextraction stages and one stripping stagewith usage of LIX 984N (5%) in kerosenediluents as extraction regent.

Extraction stage parameters were:• aq/o ratio= 1/1• Aqueous phase: Pregnant leach solution

Cu=1.08g/dm3, Fe=1.11g/dm3, pH=1.5• Organic phase: LIX-984N (5%) in

kerosene• Stages: 2• Copper recovery: 98%Stripping stage parameters were:• aq/o ratio= 1/5• Aqueous phase: Spent electrolyte

Cu2+=31g/dm3, H2SO4=198g/dm3

• Organic phase: Loaded organic • Stages: 1Obtained pregnant electrolyte for EW

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Fig. 10. Dependence of copper concentrat-ions on time during leaching at various Fe (III)concentrations

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process has content of Cu2+=36.1g/dm3, Fe3+=0.015g/dm3 andH2SO4=182.41g/dm3.Presented SX results indicate that LIX

984N, as extraction reagent in this case,show good performances in point of highselectivity of copper over iron and acidsduring the extraction process, high transfercapacity of the copper on the extractant, fastkinetics and good phase separation aftermixing. Therefore, our sense is that LIX984N would be quite suitable for theeventual industrial scale process whichnaturally should be confirmed throughfurther researching or pilot plant testing.

3.3. Electrowinning

During EW process, copper wasdeposited by using constant galvanostaticpuls from actual pregnant electrolyte at50±2°C at the current value of I=4.95A andconstant flow rate of 1 dm3/h. Dependenceof copper concentration on process durationis presented on Fig.11.

From the Fig. 11 could be seen that duringall the time of process Cu concentration inspent electrolyte was in a range of 30.83-32.65g/dm3 which was lower than thestarting value of 36.1g/dm3.

Calculated theoretical mass of cathodecopper for process duration of fifteen hoursis mo=88.06g while measured mass ofproduced electrowon copper has value ofm=82.78g. Current efficiency which iscalculated in relation to difference of copperdeposit masses from beginning to end of testis ø = 94%.

Dependence of sulphuric acidconcentration on process duration ispresented on Fig.12.

Results presented on Fig. 12 shows that

H2SO4 concentration is higher than startingvalue of 182.41g/dm3. Sulphuric acidconcentration in spent electrolyte samplesduring time was in range of 193.6-194.6g/dm3 which is in accordance with thevalues for the Cu concentration in electrolyte(Fig. 11). For the lower value of copperconcentration, value for sulphuric acid ishigher. Iron concentration was constantduring the process.

Values of cell voltages, measured withdifferential electrometer during time, wereused for average value calculation (averagecalculated=2.34V). This value was used forthe calculation of specific energyconsumption Es (kW h kg−1) according to

Z. Stevanović / JMM 45 (1) B (2009) 45 - 57 55

Fig.11. Cu concentrations in spent electrolyteduring time

Fig. 12. H2SO4 concentrations in spentelectrolyte during time

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the following equation [28]:

Es=100 x q x Ecell / m x ø

= 2.23kW h kg−1 . . . ( 3 )

Where are:q: Electric charge (kA h); Ecell: Cell voltage (V); m: Weight of deposited metal (kg) andø: Current efficiency (%).Final chemical analyzes of electrowon

copper confirmed that copper purity is inaccordance with standard BS 6017 [29].

4. Conclusion

On the basis of the results presented inthis work, the following conclusions can bedrawn:

• pH value of leaching solution has effectson the copper recovery from Cerovooverburden. By acidity increasing from thepH value of 2.0 to 1.0, after 120 hours ofleaching, copper recovery increased from68% to 79%.

• H+ ions concentration increasingsensibly correlates with the iron dissolution.At pH 2 iron concentration after 120 hoursleaching reached 0.54g/dm3, while at pH 1iron concentration increased up to2.28g/dm3 (Fig.7).

• Addition of Fe (III) as oxidant in theleach solution has no significant effect oncopper dissolution. Differences in copperconcentration with 10g/dm3 of Fe (III) andwithout oxidants are 0.03g/dm3 or only 3%from the copper recovery point of view(76%-79%) which indicate on significantpresence of chalcopyrite among sulphidecopper minerals.

• As extraction reagent, LIX 984N showgood performances in solvent extractioncircuit with achieved copper recovery of

98% from pregnant leach solution.• Current efficiency in electrowinning

stage was 94% with produced electrowoncopper in accordance with standard BS 6017.

• Copper recoveries through leaching andSX-EW processes were 76%, 98% and 94%respectively, resulting with total copperrecovery for entire process of 70% whichindicate on possible industrial scale processwith positive economic results.

• Achieved total copper recovery of70%, and possibility for solving problem ofwater system pollution by AMDs on Cerovolocation, induce necessity for performingpilot scale tests objected to copperrevalorization and environmental protectionwhich will contribute to sustainabledevelopment of mine activities in scope ofMining and Smelting Complex Bor.

Acknowledgement

Leach-SX-EW copper revalorization fromoverburden of the abandoned copper mineCerovo, Eastern Serbia has been made throughthe project Integral Treatment of Mine Watersand Low Grade Parts of Copper Deposits inscope of Copper Mines Bor supported by theMinistry for Science, Republic of Serbia - TR21008.

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