Geneva University, Department ofMineralogy April 2006 Short CoursebyR.W. Lehne (Script withSketches& Tables) AND BASEMETAL . TREATMENT AND MICROSCOPY OFGOLD

www.isogyre.com okn etrs35 32 29 34 30 33 31 25 24 28 18 26 21 23 19 Locking textures 27 Flowsheet ofaselective Pb-Zn flotation Flowsheet ofasimpleflotation process 14 Column 22 cell flotation 15 16 Design andfunctionofaflotationcell 17 Selection offlotationreagents Common Economically importantcopperminerals 20 10 Relation goldcontent/amountofparticlesinpolished section 9 7 Complexing ofgoldbythio-compounds Carbon inpulpprocess Heap flowsheet solubilitiesofselectedminerals Chemical reactionsofgoldleachingandcementation Pressure oxidationflowsheet Amalgamating mills(Mexican“”,Chilean“trapiche”) 11 concentrator spiral Humphreys Shaking table 7 7 Gravity concentrationofgold(“Long Tom”) 10 Gravity concentrationofgold(Agricola) Different waysofgoldconcentration 13 7 (Sketches & Tables) 2 3 4 5. Selected bibliography 2 (practicalexercises) 4.2 Microscopyofselectedbasemetaloresandmillingproducts 6 4.1 Specific tasks ofmicroscopicalinvestigations 4. Microscopyofbasemetaloresandmillingproducts 5 2 5 5 3.5 3.4 Column flotation 3.3 Principlesandmechanismsofflotation 3.2 Developmentoftheflotationprocess 3.1 Flotation 2 3. Basemetaloresandtheirbeneficiation (practicalexercises) 2.2 Microscopyofselectedgoldoresandproducts 2.1 Tasks andproblemsofmicroscopicalinvestigations 2. Microscopyofgoldoresandtreatmentproducts 1.6 Cyanideleachingvs.thio-compound processes extraction 1.5 processes Leaching 1.4 processes subsequent and Flotation 1.3 1.2 Amalgamation processes Gravity 1.1 1. Goldoresandtheirmetallurgicaltreatment (Script) CONTENTS page

www.isogyre.com The 1.2 Amalgamation Humphreys spiralconcentrator(p19). Gravity concentrationofgold, “Long Agricola (p16), Tom” (p17).Shakingtable (p18). and sizingofthefeedmaterialfollowedbyoneoretwostages ofgravimetricgoldrecovery. The flowsheetofagravityprocessisrathersimple.Itgenerallyconsistsconditioning settle asfastroundedgrains. of lessthan30micronssizecanhardlyberecoveredbygravityandtinyflakesdonot gravity concentrationaremainlydeterminedbythesizeandshapeofgoldparticles:Particles shaking tables,jigs,spirals,centrifugalconcentrators,anddrywashers.Thelimitsof concentration areinnumerable.Themostcommononesare:Sluiceboxes,rocker specific gravityofgoldthatamountsto19.3.Thedevicesdevelopedandusedfor Gravity concentrationistheoldesttechniqueforgoldrecovery. Itmakesuseofthehigh 1.1 Gravityconcentration concentration (p15). ores, however, requirerathersophisticatedrecoverytechniques. a straightforwardrecoverybyrelativelysimpleconventionaltechnology. Refractorygold flowsheet (p21). oxidation oxidic residuesthatcan beleached.Athirdalternativetodegradegold carriersis pressure oxidation have tobechemicallydestroyedliberatethegold. Thiscanbeachievedby solution andpermitthegoldtoberecovered.Ifthis isnotthecase,auriferoussulphides steps. Regrindingofanauriferoussulphideconcentrate cancreateaccessforaleaching refractory ores.Subsequentstagesofgoldrecovery mayrequireoxidationandleaching concentrate. Ingoldmetallurgyflotationisoften usedasapre-enrichmentprocessfor sulphides thatcontainfinelydisseminatedgold canbefloatedandrecoveredina The flotationprocessisdescribedindetailchapter 3.3.Nativegold,goldtellurides,and 1.3 Flotationandsubsequentprocesses(refractory oreprocessing) “arrastra”, Chilean“trapiche”(p20). a goldconcentratethatcanbesmelteddowntobullion. . Heatingofthefiltercakeevaporatesmercury, andtheremainingmaterialis elutriation (desliming),cycloningoranothergravityprocess.Filterpressingremovessurplus forminganamalgam.Thephysicalpropertiesofamalgampermititsrecoveryby which permitsgoldparticlestobewettedandenclosedexceedinglywellbytheliquid distinguished: The mineralogydeterminestherecoveryprocessofgold. Two typesofgoldores can be arsenopyrite. series ofmineralsthatcancarrygoldasaphysicalconstituentsuchpyriteand followed bygoldtellurides.Othercompoundsareeconomicallyirrelevant.Thereisa Only afewmineralsareimportantasgoldcarriers.Nativeisbyfarthemostimportant, 1. Goldoresandtheirmetallurgicaltreatment amalgamation process bymeansofThiobacillus andLeptospirillumbacteria. Non refractory thattransformleaching resistant goldcarriersintoporousoxidesor isbasedonthelowsurfacetensionbetweengoldandmercury, oresand refractory ores. Nonrefractorygoldorespermit Amalgamating mills:Mexican Different waysofgold Pressure oxidation bio- or

www.isogyre.com 2 Presuming idealconditionsthesolubilityrateofpuremetallic goldis3,25mg/cm isdefinitelybelow0.5%. a leachingoperationuneconomic.Theapproximatetolerablelevelforcyanidesoluble consumption; undercertainconditionscyanideconsumptioncanreachlevelsthatrender called cyanicidesorcyanidekillers(e.g.secondarycoppersulphides)increases tonne oforeisintheorder100–500g.Thepresencecyanidesolubleminerals,so flowsheet (p24). several weekstoafewmonths. Thegoldrecoveryhardlyexceeds70%. rial containedinaheapcanreachmorethan100.000 t.Theleachingtimerangesfrom pregnant solutioniscollectedandpumpedtoagold recoveryplant.Theamountofmate- cyanide solutionthatpercolatesthroughtheore dissolving thegold.Thegoldbearingor surface, asocalledleachpad.Asprinklersystem providesacontinuoussprayofalkaline low gradegoldore.Basicallytheoreispiledtoagiven heightonaninclinedimpermeable The cheapestbutslowesttechniqueis lies intheorderof70–80%. free circulationoftheleachingagent.The periodis2–4daysandgoldrecovery good permeability. Grainsizes of<2mmaredisadvantageous astheytendtoblockthe leaching theoreisnotagitatedintanksandonlycoarsematerialwarrantsa grain sizesof<1cmaremuchcoarserascomparedtoagitationleachingbecauseinvat A secondtechniqueis The goldrecoveryliesusuallyabove90%. special tanks(e.g.Pachucatanks).Theleachingperiodisgenerallylessthan24hours. an orepulpwithgrainsizesof<100micronsispermanentlyagitatedduringitsleachingin effective techniqueforwellleachablehighgradegoldoresis A cyanideleachingprocesscanbeconductedunderdifferenttechnicalconditions.An often combinedwithgravitycircuitsthatservefortherecoveryofcoarsegoldparticles. diameter goldparticlewouldneedalmost45hours.Thereforeleachingprocessesare such arategoldgrainof30micronssizewoulddissolvewithin9hours,150 levels aswellap The essentialrequirementsforagoodgoldrecoveryareadequatecyanideandoxygen solution byferroussulphate.Therathercommon washed outwithwater. The dissolvedgoldwaseventuallyprecipitated fromtheaqueous conducted throughwet,precrushedgoldoreformingsolublechloridethatcouldbe The relatively lowgoldgrades.Leachingprocesses,however, arenotlimitedtosuchores. deposits whichwouldelsebeuneconomicbecauseoftheirfinegolddistributionor Leaching isahydrometallurgicalmethodthatpermitsthebeneficiationofgoldoresfrom 1.4 Leachingprocesses leaching bysodiumcyanidearethefollowing: the selectivesolubilityofgoldinaweakcyanidesolution.Thechemicalprinciples chlorination process 4Au +8NaCN+O H –valuebetween10and12.Thenormalcyanideconsumptionper vat leaching , whichisobsoletebynow, usedchlorinegasthatwas Cyanidesolubilitiesofselectedminerals(p23). 2 +2H , whichalsorequireswellleachableores.Therequired 2 O → 4Na[Au(CN) cyanide leachprocess . Itisaprocessusuallyappliedto 2 agitation leaching ] +4NaOH

Heap leaching isbasedon . Thereby 2 /hour. At

www.isogyre.com 3 (Merrill-Crowe process). Cementation There areessentiallythreeprocessvarietiesthatusecarbonadsorption: . tonne ofcarbonisachievedleavingaslittle0,01ggoldpersolutioninthe value ofapprox.2ggoldpertonnesolutionacarbonloadingupto15kg regenerated byheatingitatapprox.600 which itcanberecoveredbyelectrolysis.Thedesorbedor“stripped”carbon carbon. Thegoldattachedtothecarbonisthendesorbedbyacyanidesolutionfrom carbon. Duringadsorptiontheentiregoldcyanidecomplexbecomesattachedto The zinc. Before smeltingthecementateiswashedwithacidinordertoremoveremainderof immediately precipitatedandthecementatecanbefiltratedmeltedtoagoldbullion. As soonasthezincdustisaddedalmostcompletegoldcontentofliquor by After dissolvingthegoldbyacyanidesolutionmetalcanbeextractedfromliquor 1.5 Goldextraction strip, andiftheyareselectiveeasytostriptheir loadingcapacityisverylow). spread use(theyareexpensive,mostofthem nonselectiveforgoldanddifficultto artificial resins. The disadvantages oftheexistingresins,however, preventedtheirwider In principleadsorptioncanalsobeaccomplished by technique thatareusedunderspecialconditions. The appear infractionsbetween1and3mm. sieving. Whereaspulpparticlesgenerallydonotexceed100microns,thecarbongranules grain sizebetweencarbonandpulpparticlespermitsaneasyseparationofthetwoby if thepulpinthisstageiscontactedwithunloadedcarbon.Theconsiderabledifference solution, andthereforethelowgoldconcentrationsinfinalstagecanbeadsorbedonly gold adsorbedonthecarbonisinequilibriumwithresidualconcentration counter currentcircuit.Theprincipleisimportantbecausetheamountof During the cementation adsorption CIL process - The - The - The CIP process carbon incolumn(CIC)process carbon inpulp(CIP)process carbon inleach(CIL)process of dissolvedgoldfromtheleachingsolutionisperformedbypulverisedzinc ofgoldfromcyanidesolutionmakesusethenaturalaffinityfor or and the adsorption 2[Au(CN) activatedcarbonparticlesareaddedtotheleachedpulpina CICprocessare 2 . ] - +Zn ° → C for30minutesinabsenceofair. Fromahead Carbon inpulpprocess(p25). 2Au+[Zn(CN) , essentiallyvariationsofthecarboninpulp and . ion exchangetechnology 4 ] 2- with

www.isogyre.com 4 for thioureaorthiosulphatearetheirhighleachingratesthatcanreach250mg/cm it wasbelievedthatlesstoxicornon-toxicreagents areinvolved. An additionalargument minerals; carbonaceous matter) cyanide solublecopper minerals suchaschalcocite,digenite,covellite or stibnite;clay and oxygenconsuming minerals suchaspyrrhotite,marcasite,andmelnicovite ; The mineralassemblage(nativegold,goldtellurides, auriferoussulphides;acidgenerating particular: of theoredeterminesrecoveryprocess.The decisivemineralogicalfactorsarein assessment ofallrelevantparametersthatinfluence therecoveryprocess.Themineralogy The maintaskofgoldoremicroscopywithregard tometallurgicaltreatmentisthe 2.1 Tasks andproblemsofmicroscopicalinvestigations particles inpolishedsection(p27). or chemicallybondedgoldwillgenerallybedetected. microanalytical investigationsshouldbeconsidered.Byusingthesetoolssubmicroscopical can befoundafterthestudyofareasonableamountsections,electronopticaland looked afterinordertoobservemicroscopicgoldmoreeasily. If,however, nogoldminerals siliceous orferruginouspartsinzonesofmicrofracturing.Theseenvironmentscanbe concentrations orclusters,ofteninassociationwithspecificpropertiesoftheoresuchas submicroscopic form,e.g.insulphides.Oncedetectedweshallfindthattherearelocal first sectionofanhighgradeoremustnotleadtotheconclusionthatitoccursina and evenmoresoonmicroscopicscale.Thefactthatgoldcannotbedetectedinthevery Gold tendstoshowanirregulardistributionintheore.Thisiscaseonmacroscopic in thefrequentlysmallsizesofgoldparticles,whichrequireusehighmagnifications. only after timeconsumingstudiesofseveralsections. Another complicatingfactorconsists which makesitoftenhardtofindanygoldinpolishedsection.Thiscanbeachieved has itspeculiardifficulties.Aboveallrangestheusuallylowgoldcontentofores, microscopy becauseoftheirdistinctiveopticalproperties.Neverthelessgold Gold mineralsandespeciallynativegoldcangenerallybeidentifiedverywellbyore 2. Microscopyofgoldoresandtreatmentproducts into theecosystem.Inadditiontothisthioureaissuspectedbecarcinogenic. compounds generatesaseriesofpartlyhighlytoxicproductsthatmustnotbereleased compared tocyanideisonlyvalidregardingtheirlethaltoxicity. Decompositionofthio- is verylimitedifnotimpossible.Theseeminglylowtoxicityofthetwocompoundsas thio-compounds (p26). decomposing readilytosubstancesthatareunableleachgold. In recentyears 1.6 Cyanideleachingvs.thio-compound very sensitivetop compared tosodiumcyanide.Thegoldleachingreactionbythioureaandthiosulphateis factor arethehighcostsforreagentsbecauseofreagentconsumptionsas we seeveryfewoperationsthatapplythioureaasanalternativelixiviant.Anotheradverse thio-compound leachingprocess,however, impliesaseriesofproblemsandtherefore hour exceedingcyanidesalmostbyafactorof100.Thetechnicalimplementation thiourea andthiosulphateleaching H andredoxpotentialbothchemicalsareintrinsicallyunstable Thismeansthatprocesscontrolisdifficultandreagentrecycling gainedacertainattractivitybecause Relation goldcontent/amountof Complexing ofgoldby 2 per

www.isogyre.com 5 + abundantgold accessorygold tracesofgold +++ ++ + primary (pyrite)aswellinsupergene(quartzandlimonite). Sol deOro/Peru++ Salsigne /France+ Rheingold /Germany+++ Kotchbulak /Uzbekistan+++ intergrown withaccompanyingpyrite,arsenopyrite,andstibnite. Hillgrove /Australia+++ with pyrite,bothincoarselockingsandastinyinclusions. pyrite (2sections). Auriferous pyriteconcentrates(2sections);goldoccursintergrown El Callao/Venezuela +++ situ relicsofgoldinclusionsinformerpyrite. the goldindicateasimultaneousprecipitationofandironhydroxidesratherthanin with limoniteinwhichitoccursasrathersmallinclusions;isolatedcolloformtexturesof Callion /Australia++ 2.2 Microscopyofselectedoresandproducts iron oxidethatshieldsthegoldinclusionsfromcyanidesolutions. prior tocyanidation“flashroasting”mayconverttheenclosingsulphideintoanonporous in ordertodiscoverthereasonsforpotentialgoldlosses.Whenrefractoryoresareroasted It isoftenusefultostudytheintermediateproductsandtailingsofagoldrecoveryprocess sizes thatpermitgravityconcentrationorrequirealeachingprocess) Textures andparticle sizesofthegoldminerals(freeorlockedgold;nativeatgrain (3sections): (4sections):Auriferouscrudeore;goldoccursasinclusionsin (2 sections):Auriferouslimoniteconcentrate;goldisassociated (2sections):Auriferoussulphideconcentrates;goldoccurs (7sections):Goldinassociatedwithquartz(3sections)and (2 sections):Goldgravityconcentrate;flakesandgrains. (4 sections):Nativegoldandtellurides.

www.isogyre.com 6 The beginningsofflotation technologydatebacktothemiddleof19 3.2 Developmentoftheflotationprocess those finegrainedbasemetalsulphidesminedtodayatthemajorityofdeposits. flotation istheonlyprocessavailablethatpermitsproductionoforeconcentratesfrom widely usedinavarietyoffieldssuchasrecyclingplastics,paper, etc. At present Flotation isatechnologyfortheseparationoffineparticlesdifferentmaterials.It 3.1 Flotation Economically importantcopperminerals(p28).Commonzinc(p29). material whoseconventionaltreatmentwouldbeuneconomicortechnicallydifficult. Hydrometallurgical methodspermittheutilizationoflowgradeormineralogicallycomplex In recentyears best recoveredbyleachingandprecipitationwithscrapiron). porphyry copperdeposits e.g.contain suchmineralsas Antlerite orBrochantite whichare represent themainoreotherrecoverymethodsmayhavetobeapplied(manyimportant series ofoxidesandsulphatesthatpossesshighmetalcontents.Indepositswherethey method forbasemetalores.OfcourseitisnoremedyalltypesofTherea Flotation workswellwithmostsulphideoresandisdefinitelythewidespreadrecovery new typeofbasemetaldepositsbecamepossible. nature. Onlyaftertheinventionofanewtechnologycalled metal sulphidesminedtodaywouldhavebeenuselessbecauseoftheirfineandcomplex Those wereallfairlycoarseandeasytoseparatefrombarrengangue.Mostofthebase These simpletechniqueslimitedtheoresthatcouldbeusedbymankindtoafewtypes. In earlydaysofminingorescouldbeenrichedonlybyhandpickingandgravityconcentration. 3. Basemetaloresandtheirmetallurgicaltreatment remain themostcommonsulphidecollectors. replaced thedifferenttypesofoilwiththeirrather inconsistentproperties.Xanthatesstill as collectorsforsulphides.Thexanthatesarewell definedwatersolublereagentsthat United StatesofAmerica.Inthetwentiespast centuryKELLERmadeuseofxanthates The followingdevelopmentofflotationtechnology tookplacemainlyinAustraliaandthe in agraphiterichfoam. would thengetattachedtothebubblesandfloat surfacewheretheycouldberecovered grease washeatedtoboilinginordergeneratesteambubbles.Theoilygraphiteflakes deposit ofKropfmühl.Anaqueousslurrygroundgraphiteorewithadditivesoilor flotation. TheprocesshadbeendevelopedfortherecoveryofgraphiteminedatBavarian In 1877BESSELpatentedaprocessthatshowsalreadyalltheessentialsofmodern preferentially bywater(HAYNES, 1860). was realizedthatmetallicmineralsbecomepreferentiallywettedbyoilandgangue hydrometallurgy hasgainedagrowingimportanceinmineralbeneficiation. flotation thedevelopmentofa th century, whenit

www.isogyre.com 7 depressors, p flotation ofparticularminerals. Theregulatorsaresubdividedinto are usedtoenhanceordiminishthefloatabilityof minerals therebypermittingtheselective Finally thereareaseriesofchemicalreagents known as ranges between10and100gpertonneofore. Common frothersarepineoil,alcohols,andcertain soaps.Theconsumptionofpineoil water interfacereducingthesurfacetensionand therebystabilisingtheairbubbles. flotation cell.Generally, frothersaresurfaceactiveagents thatareadsorbedtotheair- and toproduceafrothstableenoughcarrythe loadoffloatedmineralsatthetop In additiontocollectors between 20and200g. its surfacewithathinfilm.Theconsumptionofxanthatecollectorpertonneorelies bubble. Therearealsononpolarcollectorsthatrenderamineralhydrophobicbycovering achievesawaterrepellentcharacteristicandgetseasilypickedupbyrisingair the polarmineralsurfaceleavingnonendtowardwater. Sotheconditioned chemicals thatusuallypossessapolarandnonend.Theendisadsorbedto are addedtothepulpinspecialconditioningtanks.Collectorscomplexorganic reagents, socalled More orlesspolarmineralssuchasmostsulphideshavetobeconditionedbychemical hydrophilic attached toairbubblesarewaterrepellentor ability iscontrolledbythesurfacepropertiesofmineral.Mineralparticlesthatgetreadily The floatabilityofamineralmainlydependsfromitsabilitytoadhereairbubbles.This more anddominant. called “slimes”,tendtoloosetheirchemicalidentityinfavourofphysicalforcesthatbecome 10 micronstherearephenomenathatstronglyaffectflotation:Extremelyfineparticles,so generally obtainedwithparticlesizesrangingfrom10to100microns.Withparticlesbelow limit rarelyexceeds500micronsandisusuallybelow300microns.Optimumresultsare certain dimensions,whichdependonthespecificgravityofmineral.Theuppersize defy thelawsofgravitywithhelpanairbubbleamineralparticlemustnotexceed Before submittinganoretoflotationithasbegroundfloatablegrainsizes.Inorder are removedfromthetopofcell. bubbles havetoformastablefroththatcancarrythefloatedmineralparticlesuntilthey certain mineralshavetoattachthebubbleswhichtakethemsurface.There stream ofairbubblesrisesfromthebottomtotopcell.Formineralseparation are maintainedinsuspensionbyagitators orimpellers. At thesametimeacontinuous particles. Theprocesstakesplaceinflotationcells.Inthosecellsthefinegrainedsolids A flotation systemconsists ofthreedifferent phasesrepresented bywater, air, andsolid reagents. minerals. Flotation isbasedondifferencesinthephysico-chemicalsurfacepropertiesof Principlesandmechanisms offlotation 3.3 Thesepropertiesareeitheralreadyexistentortheyinducedbycorresponding . H -regulators collectors frothers and , beforetheycanberecoveredbyflotation.Thecollectors havetobeaddedthepulpcreatepersistent bubbles deflocculants. Design andfunctionofaflotationcell(p31). hydrophobic regulators , thosethatdonotattachare or activators modifiers and that

www.isogyre.com 8 that produces plant. Thesecondoptiontorecoverdifferentmineralsfromoneoreisa superior processcontrol. column flotationpossesses significantlylowercapitalandoperationcosts andpermitsa higher gradeproduct.In addition tothisdistinctadvantageoverconventional technology flotation, whereitsability towashthefrothoffentrainedgangueparticles resultsina alternative toconventionalflotation.Itismainlyused inthecleaningapplicationsofsulphide Column flotation 3.4 Columnflotation first, followedbytheflotationofmineralsthatare moredifficulttofloat. by one.Insulphideflotationthemosthydrophobic ortheeasiesttofloatarerecovered sophisticated installations.Usuallythevaluableminerals arerecoveredinsequence,one ore pulpisthenpumpedtothe one singleproductcalled two options.Thefirstistorecoverallthevaluablecomponentsby If theorecontainsmorethanonetypeofvaluablemineralwecanusuallydecidebetween recovery. This isdonetoproduceaconcentrateascleanpossibleandminimizelossesinore concentrate isobtainedthepulphasoftenpassedseveralcleanerandrecleanerstages. which thefeworeparticlesstillremaininginpulpcanberecovered.Untilafinal tailings ofthecleanerstagecanbepassedthroughanadditional particlesthatfloatedwiththeoremineralsaredepressedtotailings.The impure preconcentrateoftheroughercellsthengetstoa only ganguemineralsremaininthepulpwhichispumpedtotailings.Therelatively last flotationcelloftherougherstagebecausetheyarefloatedineachcell.Theoretically recovered. Theportionofhydrophobicmineralsinthepulpdecreasesfromfirstto grain sizegetstoa Flotation isacontinuousprocess.Thecrudeorewhichhasbeengroundtoanappropriate Flowsheet ofasimpleflotationprocess(p33). range fromseveralgramstoafewkilograms. The amountsofmodifiersusedpertonneorevaryaswidelytheirapplications;they consumption offlotationchemicalsbyadsorbingthemtotheirlargespecificsurfaces. floated andaffecttheselectivityofaflotationprocess.Additionallytheywouldincrease (“slimes”). Theseslimeswouldotherwiseadsorbonthesurfacesofmineralstobe Dispersing agentsordeflocculantsareusedtocontrolanaccumulationofultrafineparticles acid provideanoptimump In selectiveflotationastrictp mineral becomesunfloatable. inactive toacollectorbyformingcoatingonit.Thusthecannotconnectand Depressors preventundesiredmineralsfromfloating.Theyrenderamineralsurface sphalerite duetoitscopperionsduringflotationwithxanthates. are generallysolublesaltswhichioniseinsolutione.g.coppersulphatethatactivates Activators makeamineralsurfacemoreamenabletotheadsorptionofcollector. They Generally thereisacriticalp Flowsheet ofaselectivePb-Znflotation (p34). selective concentrates isspecialtechniquethathasbeendeveloped fairlyrecentlyasan conditioner Columncellflotation(p32). bulk concentrate H environmentthatisneededforflotationofaparticularmineral. H H abovewhichamineralwillnotfloat. controlisessential.P whereflotationchemicalsareadded.Theconditioned rougher flotation . Suchanoperationrequiresmuchmore . Thiscanoftenbedonebyasimpleflotation Selection offlotationreagents(p30). H inwhichallfloatablemineralsare -regulators suchaslimeorsulphuric cleaner flotation scavenger flotation collective flotation selective flotation in which in in

www.isogyre.com 9 Teck-Cominco developedanew, lowcostprocess sulphide ores,goldbearingpyritesandarsenopyrites. action liberatesmetalionsfromtheore.Bio-leachinghasbeensuccessfullyappliedto oflow-gradeoresisanotherexamplehydrometallurgy. Inthiscasebacterial required metalisisolatedandcanbeextracted. in anaqueoussolution. After purifyingthesolutiontoremovedeleteriouselements leaching themetalcontentfromore,aconcentrateorprocesssideproducts Hydrometallurgical processesarebecomingmoreandimportant.Theyinvolve 3.5 Hydrometallurgy feed material. i.e. thetailingsstreamflowthatleavescellatbottomisgreaterthaninflowof water isaddedtoensurethattheflotationprocessperformedundera gangue particlesthatmayhavegottothecleaningzone.Itisessentialsufficientwash flowing streamofwashwater. The washwaterremovestherestofundesiredhydrophilic minerals riseintothe solids andcontact ismadeinthe the column. As thebubblesriseupthroughpulptheygetincontactwithdescending an internalsparger oranexternalbubblegenerator. The orepulpisfedintheupperpart of agitates thepulpanddispersesair, airisintroducedatthebottomofcelleitherby can measureover10minheightand3mdiameter. Insteadofanimpellerthat Column flotationiscarriedoutintowerlikecells.Thecellsareusuallyroundand The environmentally soundwithnosulphurdioxideemissionsinvolved. grinding andflotation.Itisapplicabletoavarietyofzincoresand,lastnotleast,it and .Theprocessisadirectoretometalprocedure,whichdoesnotrequire in heapswithnaturallyoccurringbacteria,followedbyneutralization,solventextraction extraction ofzincmetalfromsulphideores.Thenewprocessinvolvesbio-leachingore gold andsilverare90-95%. Base-metal recoveriesfor the Albion processaretypicallyinexcessof95%,andthosefor solvent-extraction andelectrowinningtorecover suchascopper, zincandnickel. and sentforcyanidationgoldsilverrecovery. The filtrateundergoesconventional filters areusedtoproduceafiltercake.The cake isthenconvertedbackintoaslurry solids asferricarsenate.Theneutralisedslurry is subsequentlythickened,andvacuum to produceagoethiteresidue.Harmfulimpuritiessuch asarsenicarefixedintheneutralised acid inleachingtanksandtheleachedslurryisneutralisedtoprecipitateimpurities,ideally sustaining andneedsnoexternalenergy). After oxidationtheslurryisleachedwithsulfuric open agitatedtanks(theoxidationofsulphidemineralsasanexothermicprocessisself- of 80%lessthan20microns.Theresultingslurrythenundergoesautothermaloxidationin Territory. The processrequiresultrafinegrindingofanoreorconcentratetoparticle sizes from theextremelyfine-grainedoreofMcArthurRiverdepositin Australia’s Northern Albion Process cleaning zone was developedbyMountIsaMinesinordertooptimisemetal recovery collection zone , wherethemineralisedfrothiscleanedbyadownward . After attaching tothebubblesore (HydroZinc Process) positive bias forthedirect ,

www.isogyre.com 10 that requiresimmediate action. tests oremicroscopyformsanintegralpart ofthe studying allits intermediate andfinalproducts. Together withmetallurgical benchscale not belimitedtocrudeoresormillfeedsbutaccompanythewholetreatmentprocessby mineralogical, particularlyoremicroscopicalinvestigations.Ofcoursemicroscopymust The systematictreatmentofanunknownoreisimpossiblewithoutaccompanying 4.1 Specifictasksofmicroscopicalinvestigations replaced becausenoothermethodallowsustorecognisemineralsintheirnaturalform. investigation suchasX-raydiffractometry, spectographyormicroanalysisbutitcannotbe microscopic examination.Microscopymaybecomplementedbyothermethodsof The mineralogicalcompositionandtextureofasamplecanbeobtainedonlybyits 4. Microscopyofbasemetaloresandmillingproducts microscopy basesessentiallyonthedeterminationof feasibility ofaminingprojectandtoselectanappropriateoredressingprocess.Thereby microscopy playsadecisiveroleingeneratingparametersthatareneededtodecidethe foresee themetallurgicalbehaviourofanoreandqualityitsconcentrates.Thus mineral texturesandlockings oxidation processdramatically withtheeffectofasteepdropinp generation oflargesurfaces duringthecomminutionoforeoftenaccelerates this as melnicovitepyritetendtodecayrapidlyintosulphates after beingexposedtoair. The There aremineralsthataffectabeneficiationprocess: Certaintypesofpyrrhotiteaswell emissions. higher orlower, afactthatisimportant forsmeltersthathavetocontroltheirsulphurgas containing over40%copper. Relativetothecoppercontents thesulphurcontents are concentrate hardlyexceeds30%whereaswithbornite oneeasilyobtainsaconcentrate Although bothmineralsaretreatedbythesameprocess thecoppergradeofachalcopyrite It makesadifferencewhetherthecoppercarrier of anoreischalcopyriteorifitbornite. monomineralic ones. recovery fromcomplexpolymetallicoresdifferssubstantiallythatofsimple other treatmenttechniquesthanoxideores. And itisalsounderstoodthatthemetal behaviour ofmineralsduringtherecoveryprocess.Itisclearthatsulphideoresrequire It isobviousthatalterationphenomenaaffectthesurfaceandthereforespecific The importanceofapropermineralinventorycanbestbeexplainedbyfewexamples: represent asubstantialreductionintherevenuesofminingoperation. penalties. by metallurgicalmeasuresoriftheywillreporttotheconcentratesattracting elements. Itshowswhetherdeleteriouselements suchas As, Bi,andHgcanbeeliminated elements occurinanore,microscopyshowsthemineralsthatareformedbythese and explainthechemicalanalysis.Whileaanalysisdoesnottellhowanalysed alone cannotprovide.Onthecontrary, amineralinventoryisindispensabletounderstand parameters thathaveanimpactonthemetallurgicaltreatment,whichachemicalanalysis first thingtodowheninvestigatinganunknownore.Itallowsestablishimportant The determinationofthemineralogicalcompositionor The penaltiesaredeductionsfromtheoriginalconcentratevaluewhichmay of anoreanditstreatmentproducts. predictive metallurgy mineral inventory mineral inventory H valueoftheorepulp iscertainlythe , whichtriesto andthe smelter

www.isogyre.com 11 The determinationof with copperinthesameminerale.g.asenargiteortennantite. bound toarsenopyritethatcanbedepressedduringcopperflotationoritmayoccurtogether corresponding zincconcentrate.Thesameistrueforarsenicincopperores;itmaybe case theycannotbeeliminatedbymeansofflotationandwillreducethevalue pyrite, pyrrhotite,andmagnetiteormaybeanintegralpartofthesphaleritelattice.Inlatter flotation: Ironcontentsinzincorese.g.mayoriginatefromindependentmineralssuchas Certain elementsreducethequalityofmillproductsiftheycannotbeeliminatedduring or not. and inextremecasesoremicroscopycanevendecide ifanoreisamenabletobeneficiation avoid unpleasantsurprisesbyidentifyingmetallurgical problemsatanearlyprojectstage, enabling himtoelaborateanoptimumtreatmentprocessforagivenmaterial.Ithelps quality oftheplannedproducts.Itcangivespecificrecommendationstometallurgist make veryconcretepredictionsonthemetallurgicalbehaviourofmineralsand indispensable andeffectivetoolfortheevaluationofanoreitsmillingproducts.Itcan Summing upthefactsandexamplesjustgivenitcanbestatedthatoremicroscopyisan ore pulpwithallsorts ofmetal ionsthatleadtoanerraticflotation behaviour. crystallised sulphidesthattendtodecayduringtherecoveryprocesscontaminating Whenever colloformmineraltexturesappearwehavetoenvisageproblemsduepoorly to painfulsmelterpenaltiesfortheaffectedconcentrates. often occurintheformofmillingresistantinclusionswithingalenaorchalcopyriteleading Another examplethatshowsthelimitsofgrindingareaccessorybismuthminerals responsible forcopperlossesinthezincconcentrate. grinding. Itmakesthesphaleriteinclinedtofloatwithcoppermineralsanditis disease” anditcannotbecuredbecausethechalcopyriteinclusionsareresistantto in sphaleriteforminganemulsion-liketexture.Inmetallurgythistextureiscalled“chalcopyrite A wellknownandfrequentphenomenoninoremicroscopyaretinychalcopyriteinclusions The followingexamplesillustratethemetallurgicalimpactofmineraltexturesandlockings: textures (p35). of agrindingprocessandtowarrantitspermanentcontroloptimisation. mineral lockingsistheonlyappropriatetooltoevaluatedirectlyefficiencyandeconomy the oremustnotbegroundanyfurther. The quantitativemicroscopicalassessmentof the requiredsupervision.Onceanoptimumliberationformineralseparationisobtained fine asnecessaryandcoarsepossible, grinding. Oregrindingwhichisexpensive,bestperformedaccordingtotheprinciple microscopy. Itindicatesthe mineral texturesandlockings liberation size ofamineralwhichisthekeyparameter inore anditistheoremicroscopythatprovides isthesecondimportanttaskofore Locking as

www.isogyre.com 12 Neves Corvo/Portugal Ok Tedi /PapuaNG Ertsberg /Indonesia Escondida /Chile tailings. Sotiel /Spain fractioned. Song Toh /Thailand crushing andgrinding. Sta. Lucia/Cuba Gataga Project/Canada Cayeli /Turkey Castellanos /Cuba Bou Grine/Tunisia Bo Yai /Thailand concentrate, tailings. Artjomovskoje /Kazakhstan exercises) 4.2 Microscopyofselectedbasemetaloresandmillingproducts(practical (24 sections):Orefeed,Cu-conc,Pb-conc,Zn-conc,pyriteconcentrate, (18sections):Cu-Zn-Pbore. (2sections):Zn-Pbore;fraction75-63micron:comparisonbetween (13 +8sections):Pb-Znore.Zn&mixconc,sizefractioned. (2 sections):HighgradeCu-conc. (5+5sections):Zn-Pbore,sizefractioned;Znconc,fractioned (31sections):Zn-Pb-Cuore. (16+11 sections):Pb-Znore.Pb,Zn&mixconc,size (2 sections):MediumgradeCu-conc. (2 sections):HighgradeCu-conc. (10sections):Zn-Pborewithabundantglobularpyrite. (2 sections):LowergradeCu-conc. (6 sections):Orefeed,Cu-conc,Pb-conc,Zn-conc,pyrite

www.isogyre.com 13 Heinemann, Oxford,856p. WILLS, B. A. (1997). Mineral processingtechnology. 6thedition,Butterworth- VASSILIOU, A. H.etal.,eds.(1987).ProcessmineralogyVII.Proceedings, AIME, 649p. Journal,August,p23–34. SUTTILL, K.R.(1991).Atechnicalbuyersguidetominingchemicals.Engineering& Minerals, February, p47–59. SKILLEN, A. (1993).Frothflotation, newtechnologiesbubblingunder. Industrial Sortierprozesse. Dt.Verlag Grundstoffindustrie, Leipzig,580p. SCHUBERT, H.(1996). Aufbereitung festermineralischerRohstoffe. 4. Aufl., Bd.2, survey. MineralsScienceEngineering,vol12,no2,p85–99. McDOUGALL, G.&HANCOCK,R.D.(1980).Activatedcarbonsandgold–aliterature p 40–45. McDONALD, G. W. (1989).Demonstrationheapleaching.CIMBulletin82,no926, MATIS, K. A. (1994).Flotation scienceandengineering.Dekker, New York, 558p. Metallurgy, Johannesburg,268p. KING, R.P. ed.(1982).Principlesofflotation. South African InstituteofMiningand JAIN, S.K.(1987).Oreprocessing.Balkema,Rotterdam,518p. Minerals ScienceEngineering,vol7,no4,p289–311. HENLEY, K.J.(1975).Gold-oremineralogyandits relationtometallurgical treatment. p 108–114. HABASHI, F. (1987).Onehundredyearsofcyanidation.CIMBulletin80,no905, technical aspects, worksafety, andenvironmental safety. DEGUSSA AG, 13p. GOS, S.&RUBO,A.(2002).Therelevanceofalternativelixiviantswithregardto CIM Bulletin76,no851,p144–153. GASPARRINI, C.(1983). The mineralogyofgoldandits significanceinmetal extraction. 5. Selectedbibliography

www.isogyre.com 14 GOLD ORE

COMMINUTION (crushing, grinding)

GRAVITY CONCENTRATION (coarse gold)

FLOTATION AMALGAMATION (auriferous sulphides, tellurides)

REGRINDING ROASTING BIO-OXIDATION PRESSURE OXIDATION

RETORTING LEACHING PROCESS (heap l., agitation l., vat l.)

DIFFERENT WAYS OF GOLD CONCENTRATION EXTRACTION PROCESS (precipitation, adsorption)

GOLD CONCENTRATE

www.isogyre.com 15 intervals. changing andwashingtheclothat certaintime for tinygoldparticles.Theparticles arerecoveredby A sluiceboxiscoatedwithacloth servingasatrap GRAVITY CONCENTRATION OFGOLD(Agricola,1556)

www.isogyre.com 16 water inflow

ore feed

GRAVITY CONCENTRATION OF GOLD recovered gold

“Long Tom”, a sluice box used by the Californian “Forty-Niners”

www.isogyre.com 17 GRAVITY CONCENTRATION OF GOLD Working principle of a shaking table (table sizes of approx. 50x100cm - 200x500cm)

ore feed

water flow drive shaft

eccentric spring buffer

slimes tailings middlings concentrate

jog (1- 3cm, 200- 400 cycles/min)

www.isogyre.com 18 by I.B.Humphreys (1943) Sketch fromtheoriginal patent HUMPHREYS SPIRAL CONCENTRATOR

www.isogyre.com 19 Source: EisenbibliothekSchaffhausen PRIMITIVE AMALGAMATINGMILLS Mexican “arrastra” Chilean “trapiche”

www.isogyre.com 20 steam

gold bearing water 4

sulphide concentrate 8 3 8 8 8 8 8

1 8

oxygen

water 2

8 5 5 8 waste water

22 SULPHIDE BREAK-UP BY PRESSURE OXIDATION (SHERRITT-GORDON PROCESS) lime 1 Acid pretreatment of sulphide concentrate 2 Thickener 6 3 Autoclave (sulphide oxidation at approx. 200 °C, 21 bar) 8 gold leaching 4 Flash tank 5 Countercurrent washing circuit for oxide pulp 6 Neutralisation of oxide pulp

www.isogyre.com 21 CHEMICAL REACTIONS OF GOLD DISSOLUTION AND PRECIPITATION

1. Dissolution of gold by sodium cyanide

4Au + 8NaCN + O2 + 2H2O 4Na[Au(CN)2] + 4NaOH

2. Cementation of gold from solved cyanide complex by zinc dust (Merrill-Crowe process)

- 2- 2[Au(CN)2] + Zn 2Au + [Zn(CN)4]

www.isogyre.com 22 aaht Cu Malachite opr(aie u90,0(100) Cu Cu Cu Chalcocite (native) Copper formula Chemical Tetrahedrite Chalcopyrite Mineral OF COPPERMINERALS CYANIDE SOLUBILITY zrt Cu Cu Cu *) Leachingparameters:Mixtureofcoppermineralandquartz Cu Azurite Cuprite Bornite Enargite Chrysocolla Leachingtime24h Leachingtemperature23°C(45°C) Pulpdensity9% Agitatedsolutioncontaining0,1%NaCN Coppergradesbetween0,2and0,3% <150microns CuFeS CuSiO 3 2 2 2 12 5 3 (OH) (OH) 85,5(100) O 90,2(100) S FeS AsS Sb 3 4 2 +a.11,8 (15,7) aq. + 4 4 S 2 2 [CO CO 13 (Leaver&Woolf,1931) 3 3 ] 2 94,5(100) 90,2(100) 70,0(100) 65,8(75,1) 21,9(43,7) 5,6(8,2) Extraction [%]*)

www.isogyre.com 23 SIMPLIFIED FLOWSHEET OF A HEAP LEACHING OPERATION

sprinklers barren solution

pregnant solution ore pile gold recovery plant impermeable leach pad

pregnant barren pond pond

www.isogyre.com 24 CARBON IN PULP gold bearing PROCESS pulp addition of activated carbon 1 Adsorption agitators 2 Desorption unit 3 Electrolytic cells 1 4 Carbon regeneration barren 1 pulp 1 1 loaded carbon 2

4 stripped carbon pregnant recycled solution stripping solution

smelter 3

www.isogyre.com 25 COMPLEXING OF GOLD BY THIO-COMPOUNDS

1. Complexing of gold by thiourea

+ Au + 2CS(NH2)2 Au[CS(NH2)2]2 + e

2. Complexing of gold by thiosulphate

2- 3- Au + 2S2O3 Au(S2O3)2 + e

www.isogyre.com 26 210 - 105 8 000 < 0,01 (0,01) <0,01 0,01) (< <0,01 at agoldcontentof10ppm. 000 000 1 in mixturesofquartzandpyrite(valuesparentheses)respectively 500 000 125000 particle equivalentsexposedonthesurfaceofa2cmdiametersection 000 8 *) Thefiguresrefertothetheoreticalnumberofgoldparticlesor 32000 000 2 13-7 26 - 13 -26 53 53 - 105 105 - 210 210 - 420 Fraction [microns] Total numberofgrainsNumbergold*) NUMBER OFGOLDPARTICLES INPOLISHEDSECTION RELATION BETWEENGOLDCONTENT(10PPM) AND (Jones&Gavrilovic,1968) ,01,40 0,35 0,09 0,02 (2,60) (0,65) (0,16) (0,04)

www.isogyre.com 27 *) roundeddowntothenearestwholenumber Cu Digenite eoieCO80 Cu Cu CuO Atacamite 99 Malachite Tenorite Cu Coppercontent[%]*) Cu formula Chemical Chalcocite Copper (native) Mineral COPPER MINERALS ECONOMICALLY IMPORTANT oelt u 66 Cu Cu Cu Cu Cuprite CuS Cubanite Tennantite Enargite Bornite Covellite nlrt Cu CuSO Cu Cu Chalcanthite Antlerite Brochantite Chrysocolla Azurite erhdieCu Chalcopyrite Tetrahedrite CuFeS CuSiO CuFeS 2 3 3 4 2 9 12 12 2 2 3 5 Cl(OH) (OH) SO SO (OH) S O88 AsS FeS S79 Sb As 5 4 3 ·5H 4 4 4 4 3 2 +a.30 -36 aq. + (OH) (OH) S 4 4 S 2 2 [CO CO 13 13 3 2 O25 4 6 3 3 ] 2 30-45 42-52 23 34 48 63 78 53 56 59 55 57

www.isogyre.com 28 mtsnt ZnCO Smithsonite eiopieZn Hemimorphite iea Ceia oml formula Chemical Sphalerite Mineral COMMON ZINCMINERALS yrznieZn *) roundeddowntothenearestwholenumber Hydrozincite ilmt Zn ZnFe Willemite Franklinite Wurtzite ict n 80 ZnAl ZnO Gahnite Zincite α β ZS(e)48-67 (hex) -ZnS ZS(u)38-67 (cub) -ZnS 5 4 2 (OH) (OH) [SiO 2 2 O 3 O 4 4 2 6 ]58 4 [Si [CO 2 O 3 ] 7 2 ] ·5H ] 2 O54 Zinc content[%]*) 5-27 13-35 59 52

www.isogyre.com 29 oimslct - pH Organic colloids (dextrin, starch) - pH - pH Quebracho extract Sodium silicate (Di)chromate Sodium sulphide Copper sulphate Sulphuric acid Caustic soda Lime REGULATORS (modifiers) Frother, collector (cresols, xylenols) Aromatic alcohols (pine oil, eucalyptus oil) Cyclic alcohols (methyl isobutyl carbinol) Aliphatic alcohols FROTHERS Carbonate/oxide/sulphateflotation Alkyl ammonium salts Carboxylates (fattyacids,soaps) Dithiophosphates Xanth(ogen)ates COLLECTORS (promotors) SELECTION OFFLOTATION REAGENTS Activation ofoxidisedminerals Silicate/oxide flotation Sphalerite activation Depressor forgangueandslimes Sulphide flotation Sulphide flotation Depressor forquartzandslimes APPLICATION Depressor forsulphides Depressor forgalena Depressor forcalcite Frother Frother increase, dispersesgangue increase, depressorforpyrite decrease

www.isogyre.com 30 5 Agitator 4 Airsupply 3 Tailing 2 Oreconcentrate 1 Orepulpfeed DESIGN AND FUNCTIONOF A FLOTATION CELL

www.isogyre.com 31 COLUMN CELL FLOTATION pulp /frothinterface collection zone bubbling or cleaning zone froth or tailings wash water concentrate ore pulp air

www.isogyre.com 32 SIMPLE FLOTATION PROCESS FLOWSHEET OF A ore pulp recleaner rougher filter thickener cleaner scavenger tailings

www.isogyre.com 33 odtoes16 Filters flotation Zn-cleaner 13 Thickeners 15 flotation Zn-rougher 12 10Pb-cleaner flotation flotation Zn-recleaner 14 8 Conditioners 11 Pb-recleanerflotation 7 Hydrocyclone 6 Pumpfororepulp 9Pb-rougher flotation 5 Ballmill 4 Rodmill 3 Conecrusher 2 Sieve Jaw 1 Pb-Zn FLOTATION FLOWSHEET OFASELECTIVE lead concentrate zinc concentrate zinc lead concentrate run ofmineore tailings

www.isogyre.com 34 minerals according toAmstutz,1960 A geometricclassification ofbasicintergrowthpatterns of LOCKING TEXTURES 3c 2a 1c 1a 3a 1b 2b 3b 1d

www.isogyre.com 35