Removal of antimony (III) copper in sulphuric acid solutions by solvent extraction with LIX 1104SM

Ž.Hydrometallurgy531999121–131www.elsevier.nl r locate r hydrometž/Removal of antimony III from copper in sulphuric acid solutions by solvent extraction with LIX1104SMP.Navarro a,J.Simpson a,1,F.J.Alguacil b,)a Departamento de Ingenierıa Metalurgica,Facultad de Ingenierıa,UniÕersidad de Santiago de Chile,AÕda.´´´Libertador B.O’Higgins3363,Casilla10233,Santiago,Chileb()Centro Nacional de InÕestigaciones Metalurgicas CSIC,AÕda.Gregorio del Amo8,Ciudad UniÕersitaria,28040Madrid,SpainReceived15January1999;received in revised form7April1999;accepted8May1999 AbstractAntimony is not a desirable component in copper electro-refining streams although it is an element often found in normal plant practice.The present work presents data on the extraction of Ž.Sb III with LIX1104SM in Escaid103.The extraction system is studied in terms of:extraction and stripping kinetics,temperature,antimony loading,stripping and selectivity of the system.OnŽ.Ž.the basis of results obtained,a continuous run on Sb III–Cu II–H SO synthetic solution has24been performed.q1999Published by Elsevier Science B.V.All rights reserved.Keywords:Antimony;LIX1104SM;Sulphuric acid1.IntroductionThe production of copper from sulphide raw materials by pyrometallurgical process-ing leads to the preparation of impure copper anodes which need to be electro-refined.In the electrolytic refining of copper,impurities such as antimony are introduced into the electrolyte from the anodes.As the operation proceeds,the impurities are released into the solution and their concentration gradually increases,causing them to be deposited on the copper cathode.)Corresponding author.E-mail:fjalgua@cenim.csic.es1E-mail:jsimpson@ach.cl.0304-386X r99r$-see front matter q1999Published by Elsevier Science B.V.All rights reserved.Ž.PII:S0304-386X9900033-X()122P.NaÕarro et al.r Hydrometallurgy531999121–131The antimony in the anode is dissolved into the electrolyte in the trivalent state,and mostly exists in this oxidation state in the electrolyte during the copper electro-refiningw xdue to the very slow oxidation to the pentavalent state by dissolved oxygen1.Conventional purification of the electrolyte is shown in Fig.1,which presents a number of drawbacks,e.g.,high energy consumption and evolution of toxic arsine gas w x2.Electrolyte impurity treatment has been addressed by various procedures;in the case of antimony removal,the proposed technologies have been:ion exchange,molecular recognition and solvent extraction.The use of amino-methylene-phosphonic acid ion exchange resins and other reagents for the removal of antimony from tankhouse electrolytes is practiced in several Japanesew x w x refineries,e.g.,using the Unicellex UR-33002,3or the Eporoux MX-24resins.In addition,a number of ion exchange resins suitable for the removal of antimony fromw xcopper electrolytes have been surveyed5.Recently,a process has been described forŽ.the removal of antimony and bismuth from copper electrolyte at Amarillo Copperw x Refinery using ion exchange technology coupled with a novel stripping system6.Fig.1.Schematic flow-sheet of conventional purification process.()P.NaÕarro et al.r Hydrometallurgy531999121–131123Molecular recognition products are macrocycles affixed to silica supports and arew x known to be very selective for the element of choice,e.g.,bismuth or antimony7.In addition to these,solvent extraction practice has been proposed for the removal of antimony,among other contaminants,from copper electro-refining solutions using various reagents.Previous studies have demonstrated that various grades of DEHPA could be used,although the reagents used had very poor stability and rapidly lost the ability to load antimony.A mixture of Kelex100and DEHPA has been reported to bew xefficient for the removal of antimony from such electrolytes8.A mixture of mono-2-Ž.Ž. ethylhexylphosphoric acid M2EHPA and di-2-ethylhexylphosphoric acid2EHAPO4w xhas also found to be promising for removing antimony from electrolytes9,but there are major problems identified with the use of M2EHPA such as its hydrolytic stability in the high acid concentration of the electrolyte.To improve the stability characteristics of these monophosphate ester reagents,the DS5834extractant was developed and its performance in the removal of antimony has w xbeen described10,11.The active group of the extractant isThe use of this reagent under the name of SBX-50has been used at the San Manuel w xRefinery in Arizona12.It is well known that hydroxamic acids form stable compounds with a number of metal ions,thus,a commercially available reagent LIX1104was developed to controlw ximpurities levels in copper tankhouse electrolytes13.Further,LIX1104SM reagent which is a special modified version of the early reagent was produced to improve the stripping performance of LIX1104.w xLiterature on these two extractants is limited5,14.The present paper deals with the Ž.extraction of Sb III from sulphate solutions using LIX1104SM in terms of the effect of different variables on the extraction system.Furthermore,a process flow-sheet for the elimination of this element from copper electrolyte is proposed.2.ExperimentalThe extractant LIX1104SM supplied by Henkel was used as such.The active substance of the reagent is a hydroxamic acid,with a structure as shown belowwhere R,R and R are mixtures of C–C branched chains.1231019()124P.NaÕarro et al.r Hydrometallurgy531999121–131Escaid103,obtained from Esso Chile Petrolera,having the following specifications;Ž.3 boiling range205–2498C,flash point798C,aromatics10%,density208C810kg r mwas used as diluent.Ž.Antimony III stock solution used throughout the present investigation was preparedŽ.by the following procedure:pure antimony metal1g was heated in25ml of concentrated sulphuric acid and transferred to1l flask and dilute sulphuric acid Ž.typically1q6was added.All other chemicals were of AR grade.Measured volumes of the aqueous and organic phases at the desired O r A phase ratio were placed in separatory funnels provided with mechanical shaking and thermostatted at the required temperature.After settling,the antimony content in the equilibrated aqueous solutions was analysed by AAS.Analysis of the metal ions was carried out following the same methodology.Metal concentrations in the organic phases were estimated by mass balance.The acid concentrations were measured by titration with NaOH solutions.No sulphuric acid determinations were carried out on raffinates as previous experimentsdemonstrated that LIX1104SM does not extract H SO to any extent.24Continuous experiments were conducted in a unit of three mixer–settlers.The unit had a maximum flow capacity of100ml r min for each phase,mixing and settling volumes were200and700ml,respectively.3.Results and discussion3.1.Extraction3.1.1.Influence of contact time and temperatureExperiments on the influence of contact time on antimony extraction have beenŽ.carried out by shaking aqueous phase of0.3g r l Sb III and180g r l H SO with24 organic solution of20%v r v LIX1104SM in Escaid103at258C for various lengths of time.Results obtained showed that the system reaches99.7%extraction at1min and 99.9%at5min of contact.Further,the relationship between antimony extracted into the organic phase and the temperature was studied using an organic phase of12%v r v LIX1104SM in Escaid103Ž.and an aqueous solution containing1g r l Sb III and180g r l H SO.Fig.2shows the24variation of log D vs.1000r T.The increase of temperature decreases antimony SbŽ. extraction indicating that the reaction is exothermic D H8sy159kJ r mol.3.1.2.Reagent concentration dependence and estimation of the antimony extraction reactionAntimony maximum loading on organic phases of LIX1104SM in Escaid103wasŽ.studied using extractant concentrations of5,10and20%v r v and aqueous solutions of Ž.0.17g r l Sb III and180g r l H SO for five cycles.Temperature was kept at258C and24a contact time of5min was maintained.()P.NaÕarro et al.r Hydrometallurgy531999121–131125Fig.2.Arrhenius plot for antimony extraction using LIX1104SM in Escaid103.Dotted line shows95% confidence interval.Fig.3plots the variation in the concentration of antimony loaded in the organic phase Ž.accumulated vs.number of cycles.It can be seen that only with the lower extractant concentration is it possible to completely saturate the extractant,whereas with the other two,antimony loading occurs slowly,this may be due to the use of a low initial antimony concentration in the aqueous feed.From experimental data,it is estimated thatwŽ.x w xat maximum loading the Sb III r LIX1104SM ratio in the organic phase is near1.Fig.3.The effect of LIX1104SM concentration on antimony loading.A r O phase ratio2.()P.Na Õarro et al.r Hydrometallurgy 531999121–131126An antimony extraction equilibrium isotherm was obtained by shaking different volumes of organic solutions of LIX 1104SM 12%v r v in Escaid 103and aqueous Ž.Ž.solutions containing 0.3g r l Sb III and 180g r l H SO at 258C Fig.4.Again,at 24maximum loading a metal:extractant concentration ratio of near 1is obtained.The equilibrium isotherm curve can be mathematically represented by the following equation:w x 1.7Sb aqw x Sb s 1Ž.org w x 0.02q Sb aq w x w x where Sb and Sb represent the respective metal concentrations in the organic and org aq aqueous solutions at equilibrium.ŽBased on experimental evidence taking into account that at these high acid concen-Ž.q w x w x .trations Sb III is found as SbO 15and that LIX 1104acts as cation exchanger 14,it is logical to propose that LIX 1104SM having the same active substance follows the extraction of antimony by the equation:SbO q q HL °SbOL q H q2Ž.aq org org aq where HL represents the extractant and aq and org shows the aqueous and organic phases,respectively.()3.1.3.The selecti Õity of the system Sb III –LIX 1104SM Õs.other metallic speciesDue to the composition of the anodes,copper electrolytes contain a number of elements,thus,in the present case,the selectivity of the present extraction system was studied using an organic phase of 12%v r v LIX 1104SM in Escaid 103and aqueous Ž.Ž.Ž.Ž.phase containing 0.3g r l Sb III ,3.0g r l As V ,4.2g r l Fe III ,32g r l Cu II andFig.4.Antimony loading isotherm.()P.NaÕarro et al.r Hydrometallurgy531999121–131127ŽŽ.180g r l H SO no Bi III was added to the aqueous feed,as the Chilean electrolytes 24.w xusually contains very low bismuth concentrations.Literature data9,11,12show that Ž.Ž.Sb III and Bi III perform similarly in many solvent extraction systems,thus,if Bi Ž.III is present in the aqueous feed,its behaviour is expected to be very similar to that of Ž.Sb III.Temperature and contact time were258C and10min,respectively.Table1shows the distribution ratios and separation factors obtained from theseŽ.experiments.At this high acid concentration,Sb III distribution ratio is markedly higher than those obtained for the other metals,thus,an extraction order can beŽ.Ž.Ž.Ž.established for these metals:Sb III)As V)Fe III,Cu II not being extracted.It is also expected that the load of arsenic and iron would be minimized operating at conditions of full antimony loading of the organic solution,e.g.,by the use of a suitable O:A volumes phase ratio or by recirculation of the organic solution.3.2.StrippingPrevious experiments carried out in this investigation have shown that antimony cannot be stripped from LIX1104SM loaded phases using sulphuric acid,thus further investigations were carried out using a strong antimony complexing agent,i.e.,hydro-chloric acid.3.3.Influence of HCl concentrationŽ.Experiments were carried out with12%v r v LIX1104SM in Escaid103loaded Ž.Ž.with1.2g r l Sb III and various concentrations of hydrochloric acid Table2.Contact time of10min and temperature258C was maintained.It can be seen that antimony stripping is improved with HCl concentrations of6M.3.4.Influence of contact timeInfluence of contact time was studied using the same experimental conditions as described above using8M HCl.Results showed that equilibrium is reached within3Ž.min92.9%stripping.Table1The extraction of some metals using LIX1104SM in Escaid103aElement Concentration D belement Sb r element Ž.Sb III0.3299Ž.As V0.90.42712Ž.Fe III0.50.122492Ž.Cu II––infinitea Concentrations in the organic phase,all values in g r l.()128P.NaÕarro et al.r Hydrometallurgy531999121–131Table2Ž.The effect of HCl concentration on Sb III strippingŽ.HCl mol r l%stripping10.32 3.4433.1675.5892.53.5.Effect of O r A phase ratioThe effect of varying the O r A phase ratio from1to8on antimony stripping was studied using8M HCl for5min contact time.Results are shown in Fig.5and it can be seen that antimony stripping is favoured using low O r A phase ratios.3.6.SelectiÕity of stripping stageIn the event that some metal co-extraction occurs,e.g.,operating at conditions far from complete antimony loading,the behaviour of such impurities on antimony stripping was also studied.In this case,the organic phase of12%v r v LIX1104SM in Escaid103Ž.Ž.Ž.loaded with0.29g r l Sb III,0.89g r l As V and0.45g r l Fe III and the aqueous stripping solution containing8M HCl was used.Experiments were carried out at258C and5min equilibration time.Ž.The results are presented in Table3.Arsenic V is poorly stripped by8M HCl;Ž.however,As V can be stripped from LIX1104SM organic phases using containing-Fig.5.The effect of O r A phase ratio on antimony stripping.()P.NaÕarro et al.r Hydrometallurgy531999121–131129Table3The selectivity of stripping using HClElement%strippingŽ.Sb III90.6Ž.As V0.5Ž.Fe III55.0Ž.Ž.copper II–sulphuric acid pH2.2solutions.On the other hand,approximately half of Ž.the Fe III loaded in the organic solution is stripped using8M HCl solution,thus,to Ž.avoid Fe III co-stripping,it is better to operate in conditions of complete antimony load of the LIX1104SM organic solution.3.7.Antimony final recoÕeryŽ.The treatment of an antimony stripped solution Sb1.1g r l,HCl7.5M was carriedout using a NaHS aqueous solution in order to precipitate Sb S.Experimental23conditions were250g r l NaHS solution,15min of reaction at258C and using an antimony stripped solution r precipitation solution volume ratio of150.Under theseŽ.Ž.Fig.6.Quantitative flow-sheet for the removal of Sb III from a Cu II–H SO solution.24()130P.NaÕarro et al.r Hydrometallurgy531999121–131Fig.7.Schematic flow-sheet for the removal of impurities from a copper electrolyte.Conditions of Sb Ž.Ž.III–As V co-extraction and selective stripping.conditions,a hydrochloric acid solution,containing0.001g r l antimony,and a precipi-tate of Sb S are obtained.The HCl solution can be recirculated,after the corresponding 23Žmake-up,to the stripping stage and the Sb S can be marketed to produce Sb O at a2323w x.price of around US$2100r ton16.3.8.Process flow-sheetTo complete the information available,experiments of extraction–stripping–precipi-tation were carried out on a continuous basis.The continuous operation was run for50h at25"38C.Two stages were used for extracting antimony from a synthetic solution of Ž.0.3g r l Sb III by a solution of LIX1104SM12%v r v in Escaid103and one stage of stripping with a solution of8M HCl.Fig.6presents the average mass balance flow-sheet of the process.Fig.7summarizes a possible flow-sheet for a solvent extraction procedure to remove metal impurities from a copper-refining electrolyte stream using LIX1104SM in Escaid103.4.ConclusionsŽ.LIX1104SM reagent is an effective extractant for removing antimony III fromŽ. sulphuric acid solution,the extraction reaction being exothermic D H8sy159kJ r mol. The selectivity of the system against other metallic species is good,with an extraction Ž.Ž.Ž.Ž.order:Sb III)As V)Fe III.Neither copper II nor sulphuric acid are extracted. The co-extraction of arsenic and iron should be minimized by high antimony loadings inŽ.the organic phase.Antimony III cannot be stripped from loaded LIX1104SM in Escaid103using sulphuric acid;the stripping is possible using HCl at low O r A phase()P.NaÕarro et al.r Hydrometallurgy531999121–131131Ž.ratios.Antimony III can be precipitated from stripped solutions as Sb S.The validity23Ž.of the scheme has been proven in a continuous trial using synthetic Sb III–Cu Ž.II–H SO solution.24AcknowledgementsŽ.Ž.The authors are grateful to the CSIC Spain and USACH Chile for supporting thisŽ.work.Thanks are also due to Henkel through its Chilean branch for LIX1104SM gift sample.Referencesw xŽ.Ž.1 F.Noguchi,M.Yano,T.Nakamura,Y.Ueda,Metall.Rev.MMIJ112199438–52.w xŽ.2R.Shibayama,T.Nagai,in:T.Sekine Ed.,Solvent Extraction1990,Elsevier,Amsterdam,1992,pp.1193–1198.w x3T.Shibata,M.Hashiuchi,T.Kato,in:J.Hoffman,R.G.Bautista,V.Ettel,V.Kudryk,R.J.Wesely Ž.Eds.,The Electrorefining and Wining of Copper,TMS-AIME,Warrendale,1987,pp.99–116.w x4Y.Sasaki,S.Kawai,Y.Takasawa,S.Furuga,Hydrometallurgy and electrometallurgy of copper,in:Ž.W.C.Cooper, D.J.Kemp,gos,K.G.Tan Eds.,Proc.Copper’91r Cobre’91,Pergamon, Elmsford,1991,pp.245–254.w xŽ.5 D.B.Dreisinger,B.J.Y.Leong,I.Grewal,in:B.Harris,E.Krause Eds.,Impurity Control and Disposalin Hydrometallurgical Processes,The Metallurgical Society of the CIMMP,Montreal,1994,pp.71–89. w xŽ.6R.M.Cunningham,J.V.Calara,M.G.King,in:B.Mishra Ed.,EPD Congress1997,TMS,Warrendale, 1997,pp.453–460.w x7R.M.Izatt,J.S.Bradshaw,R.L.Bruening,B.J.Tarbet,K.E.Krakowiak,in:kshmanan,R.G.Ž.Bautista,P.Somasundaran Eds.,Emerging Separation Technologies for Metals and Fuels,TMS-AIME, Warrendale,1993,pp.67–75.w xŽ.Ž.8G.P.Demopoulos,D.L.Gefvert,Hydrometallurgy1231984294–315.w xŽ.9 D.B.Dreisinger,B.J.Y.Leong,B.J.Balint,M.H.Beyad,in:D.H.Logsdail,M.J.Slater Eds.,SolventExtraction in the Process Industries,Vol.3,Elsevier for SCI,London,1993,pp.1271–1278.w x10 D.C.Cupertino,P.A.Tasker,M.G.King,J.Jackson,123rd SME Annual Meeting,Albuquerque,NM,USA,February1994.w x11 D.C.Cupertino,P.A.Tasker,M.G.King,J.S.Jackson,Hydrometallurgy’94,Chapman and Hall forIMM-SCI,London,1994,pp.591–600.w xŽ.12 D.K.Kim,T.A.Leese,M.P.Neild,B.R.Saito,S.K.Young,C.J.Weidner,in:B.Mishra Ed.,EPDCongress1998,TMS,Warrendale,1998,pp.301–315.w xŽ.13W.Schwab,H.Kroke,in:R.G.Reddy,J.L.Hendrix,P.B.Queneau Eds.,Arsenic Metallurgy Fundamentals and Applications,TMS-AIME,Warrendale,1988,pp.249–262.w xŽ.14 B.K.Tait,K.E.Mdlalose,I.Taljaard,Hydrometallurgy3819951–6.w xŽ.Ž.15P.Navarro,F.J.Alguacil,Rev.Metal.Madrid3041994213–226.w x16J.A.Saenz-Diez,Memoria de Tesis de Ingeniero Civil Metalurgista,Departamento de Ingenierıa´´´Metalurgica,Facultad de Ingenierıa,Universidad de Santiago de Chile,Santiago,Chile,1998.。