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Scandinavian Journal of Metallurgy 2003 32 289 295 CopyrightC Blackwell Publishing 2003 Printed in Denmark All rights reserved SCANDINAVIAN JOURNAL OF METALLURGY Chemical technological processing of the complex barite sulphide ore Rajko Vracar1 Labud Saljic2 Miroslav Sokic2 Vladislav Matkovic2and Slobodan Radosavljevic2 1Faculty for Technology and Metallurgy 2Institute for Technology of Nuclear and other Mineral Raw Materials Belgrade Yugoslavia The investigation results of the processing possibilities of the complexbarite sulphideorefrom Bobija deposit Serbia for the sake of lead zinc and copper extraction are presented in this paper Through x ray diffraction and microscopic examination it is concluded that a it is not possible to en rich the ore for obtaining any selective or a collective sul phide concentrate using the conventional methods of mineral processing and b it is necessary to include chemical and technological procedures for ore processing Examination of reduction roasting with carbon addition for the barite BaSO4 reduction into good soluble BaS is performed After water leaching of BaS from the calcined ore the solid residual is submitted to the magnetic separation procedure for the pyrrhotite Fex 1Sx separation which is formed after pyrite FeS2 dissociation and for obtaining a collective sulphide concentrate Pb Zn Cu Finally the sulphide concentrate is leached with the solution of H2SO4in the presence of oxy gen at elevated temperatures and pressures in an autoclave Through their sulphide oxidation zinc copper and iron were dissolved while lead sulphide remained as insoluble in the solid residual after leaching The infl uence of the working pa rameters on the degree of leaching of zinc copper and iron is examined Key words complex barite sulphide ore leaching magnetic separation reduction roasting C Blackwell Publishing 2003 Accepted for publication 12 November 2002 Thedepositofthecomplexsulphide bariteore Bobija is located in Western Serbia It consists of a number of ore bodies of different morphological and structural textural characteristics In the deposit the following mineral paragenesis occurs the barite barite quartz pyrite and pyrite polymetallic paragenesis 1 4 Be sides this mineral paragenesis is integrated giving more complex mineral paragenesis with very compli cated structural textural relationships The barite mineral paragenesis consists of 80 95 of barite with lesser proportions of pyrite and quartz The barite is of good quality here so portions of these clean batches can be selectively exploited The barite quartz pyrite mineral paragenesis is less represented and occurs as an interbedded layer be tween the barite and pyrite polymetallic paragenesis with barite Thepyrite polymetallicmineralparagenesisis formed mainly of sulphides with a high pyrite content Inadditiontopyriteandbarite inthismineralparagen esissulphidesoflead zincandcopper withadmixtures ofarsenic antimony silver bismuthandcalciumminer als and further the rare earth minerals such as indium gallium vanadium tungsten selenium and tellurium prevail Leaching of the sulphide minerals as the ingredients of the polymetallic ores has been the subject of many in vestigations 5 12 Theseinvestigationsincludedleach ing under high pressure and atmospheric pressure It is not possible to process this type of polymetal lic complex concentrates using existing technologies without the total loss of some metal presented Because of this and the high content of lead zinc copper and barite the investigations were aimed at ascertaining a technical and technological solution which would enable the use of all valuable components from the deposit Experimental procedure Chemical 13 and mineralogical qualitative and quan titative examinations 14 were performed on prepared samples of barite sulphide ore Mineralogical investigations were carried out using a Carl Zeiss Jena Jenapol U polarization microscope for reflected and transmitted light and Ozaria 2 5 the 289 Vracar et al microphotographyandquantitativemineralogicalanal ysis program Since the chemical and mineralogical examinations confirmed the high pyrite barite sphalerite galena tetrahedrite and quartz content in the ore as well as their fine grained structure which makes difficult their separation further work was directed to investigate the possibilities of the applications of chemical and techno logicalprocedurestoenrichthevaluablemineralsinthe ore These procedures were performed in three stages 1 Barite sulphide ore reduction roasting for BaSO4re duction into BaS and subsequent water leaching of cal cined ore for BaS dissolving 2 Magneticseparationforpyrrotiteseparating whichis formed after pyrite dissociation during reduction roast ing and for obtaining a collective Pb Zn Cu sulphide concentrate 3 Autoclave oxidation leaching of collective Pb Zn Cu concentrate for zinc and copper separation from lead which remains in solid residual after leaching Reduction roasting Thermodynamic analysis by the calculation of the reac tions Gibbs energies of barite and adequate metal sul phides roasting shown in Table 1 has been done before reduction roasting experiments Copper in this ore is in the form of tetrahedrite Cu12Sb4S13 which can also be written as 5Cu2S 2CuS 2Sb2S3 When tetrahedrite is heated in the absence of air the same as chalcopy rite and other higher sulphides 12 it decomposes as follows Cu12Sb4S13 6Cu2S 2Sb2S3 So 1 During tetrahedrite decomposition at elevated tem peratures CuS will not be formed together with CuS2 because CuS is unstable at given conditions and im mediately dissociates to Cu2S and elemental sulphur Table 1 Reduction roasting reactions No Reaction 1BaSO4 2C BaS 2CO2 22BaS C 2Ba CS2 32PbS C 2Pb CS2 42ZnS C 2Zn CS2 5 x 1 FeS2 x 2 1 C Fex 1Sx x 2 1 CS2 6Fex 1Sx x 2 C x 1 Fe x 2 CS2 7 x 1 FeS2 Fex 1Sx x 2 S 82S C CS2 92Cu2S C 4Cu CS2 102CuS Cu2S S 112Sb2S3 3C 4Sb 3CS2 Fig 1 Dependence of G on temperature for reduction roasting reactions which will be shown in thermodynamic analysis This is the reason why in thermodynamic analysis for the roasting reaction at elevated temperatures Cu2S and Sb2S3were used instead Cu12Sb4S13 In calculations of the pyrite dissociation at reduction conditions it is as sumed that pyrrhotite of Fe0 877S type is formed which corresponds to Fex 1Sx at x 8 In order to clarify the occurrence probability and priority of quoted reactions 1 11 the Gibbs energy change was calculated within a temperature range from 100 to 1000 C and obtained values are showed in Fig 1 HSC Chemistry software and its database of thermo dynamic values of reaction participants were used in calculation Positive values of G for the reduction roasting reac tionsofsulphides PbS ZnS Cu2S Fex 1SxandSb2S3 up to 1000 C Fig 1 indicate great stability of the specified minerals in examination conditions Barite reduction reaction at the temperatures above 330 C has a negative G value while the reduction in the tem perature contributes to reaction proceeding Fig 1 In reduction conditions pyrite dissociates to pyrrhotite at 290 Processing the complex ore temperatures above 650 C Covellite as a tetrahedrite dissociation product at elevated temperatures is un stable above 320 C and turns into chalcocite with the release of sulphur Besides forming Sb2S3during tetre hedrite dissociation at elevated temperatures Cu2S is also formed and it is stable in reduction conditions up to 1000 C Itisnecessarytodeterminetheconditionsforthemax imum rate of BaSO4transformation in BaS in the re duction roasting stage For that purpose the samples of barite sulphide ore were roasted with reducer added and the calcined ore was water leached after cooling for dissolved BaS BaS dissolubility in water is high 373 5kg m3at80 C Sulphidesofothernonferrousmet als and iron remain precipitated considering they are insoluble in water Thereductionroastingforthebarite sulphideorewas carried out in a preheated electro resistant furnace in a graphite crucible putting together a homogenous mix tureoftheoreandareducer Thewoodcoalwasusedas areducent Afterthereductiontimeelapsed thecrucible was cooled in air till it reached room temperature and the crucible content was moved into the leaching ves sel Waterleachingwascarriedoutinaleachingagitator with intensive stirring The next step was filtration The solutionwasanalyzedtodeterminethebariumcontent based on which the degree of barium leaching is calcu lated Barium sulphide water solution was treated with azincsulphatewatersolutionaccordingtothisreaction BaS ZnSO4 BaSO4 ZnS s 2 The solid product obtained is called raw litophone which can be converted into commercial litophone by roasting at 800 C It is used in the colour industry as a white pigment with great covering ability Magnetic separation The sulphide residual after solution separating is rinsed dried and subjected to magnetic separation for theremovalofpyrrhotite whichisproducedfrompyrite dissociation in the roasting stage A magnetic separa tor SALLA was used with an intensity control of the magnetic field of 1000 G Separated iron concentrate magnetic fraction and the sulphide concentrate Pb Zn Cu nonmagnetic fraction were analyzed with bar ium lead zinc copper iron and silver Autoclave oxidation leaching Collectivesulphideconcentrateoxidationleachingwith sulphuracidsolutioninthepresenceofgaseousoxygen atelevatedtemperaturesandpressures wascarriedout in an autoclave The autoclave is made of stainless steel V 4A with an operating volume of 3 dm3 Maximal allowed temperature and maximal allowed operating pressure are 250 C and 50 105Pa The working vessel ismadeoftitanium Ti 99 99 whichisacidresistant and very reliable while working with very acidic pH 1 solutions The autoclave is heated with electro resistant heaters anditenabled 1 automatictemperatureregulationand its maintenance in the range of 1 5 C 2 oxygen in jection and PO2maintenance at the constant level with 100 KPa 3 stirring with propeller mixer with 100 400 rpm 4 sampling from the autoclave working ves sel in operating conditions The acid oxidizing leaching process under oxygen pressure in the autoclave is accomplished by inserting a determinedquantityoftheoreandsulphuricacidinthe working vessel before closing the autoclave The total loaded pulp quantity was half till two thirds of the total operating volume of the working vessel This quantity is accepted so as to r simplify the sampling from the autoclave r minimize the free operating volume in the auto clave and in that way to minimize eventual errors caused by solution evaporation r work with greater quantities which gives more re liable insight into the evaluation of the process After the sample was inserted the autoclave was closed and the operating temperature was reached Then gaseous oxygen was injected until a defined par tial pressure was reached This was the starting point for the measurement of the leaching time The operat ing temperature and the oxygen partial pressure in the autoclave were kept constant Solution stirring in operating conditions was accom plished using a mixer made of titanium After the reac tion time elapsed the sampling was carried out in the working conditions The samples were analyzed using conventionalvolumetricanalysismethodstodetermine the degree of leaching of copper zinc and iron Results and discussion The chemical composition of the examined barite sulphite ore is presented in Table 2 The presence of minerals barite pyrite sphalerite galena tetrahedrite marcasite covellite chalcopy rite pyrrhotite arsenopyrite natural silver bornite Table 2 Chemical composition of examined ore BaPbZnCuFeAg 28 303 923 750 8412 240 0087 291 Vracar et al Table 3 Quantitative mineral composition mass MineralsWt Galena4 53 Sphalerite6 10 Tetrahedrite1 84 Barite48 08 Pyrite26 23 Pyrrhotite0 30 Marcasite0 20 Covellite0 10 Arsenopyrite0 11 Bornite0 02 Natural silver 0 01 Limonite0 25 Cerussite0 04 Guange minerals12 57 Total100 00 cerussite limonite malachite calcite dolomite and quartz isdeterminedbymineralogicalanalysis Table 3 shows the quantitative mineral composition of the examined ore The mineral components mainly presented are pyrite and barite which are the main bearers of colloid struc tures in the deposit Sphalerite galena and tetrahedrite are intergrown with them in different ways and also mutually compositely intergrown Reduction roasting results Theinfluenceoftemperature 500 950 C andtheroast ing time 30 240 min on the degree of barite reduction were examined during the reduction roasting experi ments In all the roasting and leaching experiments the next operating parameters were constant Ore quantity2000 g Reducer quantity200 g Solid liquid ratio during leachingS L 1 2 Leaching temperature80 C Leaching time90 min Stirring speed400 rpm min Dependence of the degree of barite reduction on time and temperature is shown in Fig 2 These curves repre sent the logical and expected dependence in which the reduction degree increases with increases in tempera ture and time At the temperature of 850 900 C and the reaction time of 120 180 min 93 5 96 7 of the barite can be removed during leaching After reduction roasting water leaching and filtra tion the residual was dried The dependence of the residual chemical composition on the reduction tem perature at a reduction time of 240 min is presented in Table 4 and shows the decreasing effect of the barite Fig 2 Dependenceofthedegreeofbaritereductionontimeandtemperature Table4 Chemicalcompositionofthesulphideresidualafterreductionroast ing and water leaching T C BaPbZnCuFeAg 50026 013 993 760 8712 380 0087 60025 844 033 780 8912 420 0088 70024 414 133 870 9112 780 0091 75019 884 494 311 0114 020 0099 8005 676 386 101 4320 010 0141 8502 007 297 081 6223 090 0159 9001 357 547 301 7024 120 0166 9501 297 567 331 7024 180 0168 10001 277 597 321 7124 170 0168 Magnetic separation results After decrease in the barite content the residuals with thechemicalcompositionpresentedinTable4weresub jected to magnetic separation The results of iron sepa ration are listed in Table 5 It can be seen that the iron content of 23 09 24 18 in sulphide residuals obtained at reduction temperatures 850 900 C Table 4 can be decreased to 6 24 4 40 us ing magnetic separation At the same time the other valuable components are being enriched Table 5 Table5 Chemicalcompositionofthesulphideresidual nonmag netic fraction after magnetic separation as a function of reduction temperature T C BaPbZnCuFeAg 50026 014 003 750 8712 400 0089 60025 874 073 790 8912 350 0090 70024 854 233 920 9211 800 0092 75021 614 734 511 0711 000 0106 8006 677 467 151 6810 900 0170 8502 789 969 672 216 240 0224 9001 9411 0510 592 424 400 0241 9501 9111 1210 682 484 350 0250 10001 8611 1410 692 494 350 0252 292 Processing the complex ore Table 6 Chemical composition of the magnetic fraction after magnetic sep aration ore roasting temperature 900 C FeSPbZnCuSiO2Ba 58 2233 231 271 550 502 000 006 The chemical composition of the magnetic fraction Table 6 indicates that considering high sulphur and lowarseniccontent thisfractionisappropriaterawma terial for sulphuric acid production Autoclave leaching results of the sulphide concentrate of Pb Zn Cu Collective Pb Zn Cu sulphide concentrate nonmag netic fraction is subjected to oxidizing acid auto clave leaching The literature investigations report that the sulphide minerals of zinc copper and iron in the reported conditions are dissolved in the sulphate form while lead mineral in the form of lead sul phate remains as a precipitate being a low soluble compound Fig 3 The leaching temperature and time infl uence on the degree of leaching of zinc copper and iron The temperature and time influence on the degree of leaching of zinc copper and iron were investigated at temperaturesbetween150 210 C atimerangebetween 30 and 240 min oxygen partial pressure PO2 10 105Pa solid liquid ratio S L 100 g dm3and the ini tial sulphuric acid concentration of 50 g dm3 The re sults calculated on the basis of a chemical analysis of solutions and precipitates after leaching are shown in Fig 3 The difference in the degree of leaching of zinc cop per and iron is appreciable at lower temperatures and shorter leaching times Copper has the lowest degree of leaching while iron has the highest which is reason able considering that in the sulphide concentrate iron is in the form of pyrrhotite which is easily oxidizable The increase in temperature and leaching time con tributes to an increase in the degree of leaching of all three metals and their difference becomes less signifi cant They reach their maximal values at the tempera ture of 210 C and leaching time of 240 min and their values are for zinc 97 85 for copper 95 36 and for iron 96 25 293 Vracar et al Fig 4 Oxygen partial pressure infl uence on the degree of leaching of zinc copper and iron RP t 190 C 240 min Figure 4 presents the oxygen partial pressure influ enceonthedegreeofleachingataleachingtemperature of 190 C and time of 240 min The oxygen partial pres sure interval is chosen according to the literature and apparatus possibilities where the total operating pres sure at a determined temperature is a limiting factor It canbeconcludedfromthepresentedresultsthattheop timal partial pressure of oxygen is 10 105Pa and its furtherincreaseslightlyincreasesthedegreeofleaching of each metal Based on the investigation of the autoclave leaching process and a chemical analysis of the solutions and solid residual after leaching it is confirmed that lead in the form of lead sulphate remains in the precipitate whilezinc copperandironaredissolved Suchaprecip itate withoutzincandcopper istheproperrawmaterial forleadproduction Intheprimaryleadproductiondur ing the roasting process the lead concentrate contains at least 47 of lead Since this content is important the ob tained solid residue from the leaching process can be added in the corresonding ratio to the lead concentrate Therefore lead reco