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Automated analysis of Merril Crowe Gold precipitation tailings solutions
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  PAPERTO BEPRESENTED -t SYI4POSIUM ONTHEASSAYING OFPRECIOUS METALS organisedby SOUTH AFRICANINSTITUTEOF ASSAYERS& ANAIYSTSat Johannesburgon 16 Sentember1986AUTO}4ATED SOLUTIONTAILS ANALYSISON IIARMONY GOLD MINE by E.KIRBY,* BSc(Hons)PhD *MetallurgicalSuperintendent,Services,HarmonyGoldMiningrCompany Limited  AUTOMATED SOLUTIONTAILSANALYSIS ODJ HARI4ONYGOLD MINEINTRODUCTION a .rificalqi-enin theCrowe-Merrilrecoveryprocessis theprecipitation ofgoldfromd.eaeratedcyanide solution.Ttrisoperationisgenerallyreliablebutchemicalormechanicalproblemscaqresult i:r hiqh value tailssolutions.Inrecentyearsthekeytopreventj-ngsuch losses has beentheinstallationofautomatic solution tailsanalysers.T'hefirstautomatic goldanalyserwasdeveloped byRand MinesCorperHouse\'T:Eboratoriesjl'theperiod1965 to 1969-.A nurnberofunits were installedonvarious SouthAfrican plants.Extensively modifiedversions of the srcirtalanalyser arestill workingat theERPMandBlyvooruitzichtGoldt4ines,Furtherdevelopmentby AngloArnericanResearch Laboratories(AARL)resultedin anjnnrnrraA:n:1rrca1.Ttreirf irstj_nstallationwasj11Novernlcer 1978 at the Ergo)GoldPlant-.Conti-nuedwork led tothecornmericalavailability of theOLGAseriesofanalysers in 1983.All oftheseunitswere desi,gnedaround flameatomisationatomic absorptionequipment. Goldpreconcentrationby solvent extractionwasnecessary toachievethedesiredsensitivityof0,01ppmAuj.nsolution. The firstanalysertouseelectrothermal atomisationwasdevelopedbyIvlrttekin 2 7982'.Increased sensltivityeliminated ttreneedforthetroublesome hro-^n^an Fr:l- i an cl- a^ Tlar^rorrar l- h iq:Arranl- arvire. e!,*u *,-agewasprobabLy of fset by mechanical difficultieswithsamplepresentation.Durilg 1983Mj-ntekpersonnelwere discussingtheuse ofthe newVarian GTA95 Graph.iteT\rbeAtomiserto overcome suchproblems.Latei-rr1983 it was decided tojrtstallan autorlaticanalyseron theMerriespruitGoldPlant ofHarmonycold Miling CompanyLimited..Afterconsidering variousalternatives,thei-n-housed.evelopmentof a newsyst.emwasaFproved. DESfQ'l/.. .  DESIGNOFTHEAUTOMATEDSOLUTIONTAILS A}]ALYS]S(ASTA)SYSTEMAMintekdemonstrationofVarianprod.uctsshowed.theirsuita-bilityforon-Iineinstallation.The analysiseguiproentcouldbe fittedwithaninterfaceandlinkedto amicro-computer,thus allowingremotecontrolanddata collection.Atthe sametime,thecoryuterwould. havesufficient.capacitytomonitorandcontrolotherequipmentProposalsforthenewanalysertookad.vantageofthe availalriJ-ityoftheseproducts-Theconceptjlvolvedthecouputermoni-torJlgofplantoperatj-ngcond,itions(precipj-tationunitsonline,off lj-neor circulating),togretherwith controlof sampling,the atomicabsorption (AA)machll.e,andthegraphitetube atomiser(GTA).The frequencyandsequenceofanalyseswouldbedependantonStellarfilter(precipitationunit)operationsand.ontailsvalues-AflexjJclesystem,withartificialintelligenceprovidedbycomputersoftware'was eivisaged.Atthesametime,a L4zcapitalcost advantageoverpurchasinganOLGAsystem fromAARLwas estirna1.6.Ani-mportantpartofthedesign philosophywas tornaximisetheuseofstandardcomponents.Itwas thoughtthatthiswouldminimised.evelopmenttimean6allow goodavailabil-ityofmainlsnancespares.Asitturned.out,theonlyspeciallyrnade partv/as aplasticsamplingweir.Thiswasrnachinedfrompolyethylenej-ntheCarpentersrworkshoponthelrine. Furtherdetailsoftheitemswhichrake up thejl.stallationarecoveredfur aprevj_ou=p.p.r4.DEVELOPMENTOF ASTAThesystemwasdeveloped,i_n astepwiseyear.The AAandGTAwereacquired,lateinthelaboratory,theywerej_nstalled1984.Initiallythesamplingvalvesandby asequencecontroller.fashionoveraperiodofah'outoneir Novernber1983.Afterbench testingon lileatMerriespruitinJanuarythe analysisequj_pmen!wereoperated.The nextdevelopmentwasthearrivalofthe computerjll4ay1984.Aftersomeprogrammjng,thistookoverfromthesequencecontrollerinJune|gg4.Pressureswitchesweretheninstalled,onpneurnatj-cvalveactuatinglines,tomonitorthe statusofstellarfilters.signalsfromthesewerecorruunicated,tothecomputerjISepteiulcer1984andthesoftwareextendedto allowASTAtorespond.Bytheendof1984thecontrolsoftwarehad.developed.virtuallytoitsfi'.alversion.Alrofthedesignconceptsweresatisfied..Inj-tially/...  InitiallyLhemachine wasstandardised witha0,020ppmgoldsolution. Atthis value theanalysis sequence usedgaveameasuredatomicabsorbance ofabout 0,6. Ttre time takenforeachanalysis, caliJcrationar zerocheckwasabouttwominutes.Reasonablyaccurateanalyses in the rangeO,OO2to0,020ppmAuwerepossjlcle.However, thearrangementwasnotpopularwithprocessmanagement; inLimes of troubleallvalues werewellabove theupperlimitfbr ^--1---i ^ T+ -. qrrqlyrrr.ruwdsth€DimpossiJcleto tell if controlactionswerehaving anyThernachineis now standardised withaO,10ppm. goldsolution, allowinganalyses in the range0,01to0,11ppm.The new analysis sequence usesshorLer dryingand ashj-ng times and ind.ividual analyses take about onemj-nuteeach. At0,10ppmAu, thepeakabsorbancemeasuredis about0r9.Althoughpoorerinprecision,the newprogramcomescloserto saLisfying Lhe.needs of\.the operatino staff. OPERATING EXPERIEI{CE WITH ASTA The system hasoperatedcontinuously since January1984 with an averageavailabilityofbetterthan94%. Achieving LhisLevelofavailability wasagrj-m struggle.Earlyoperationsweredisturbed byacollectionofsoftwarefaults whichcaused frequent stoppages.MaintenancerequirementsfortheGTAandAAmachinewerelearnedbytrialand error, althoughtechnicalsupportfrom the supplierswasgood.Whatwasthought tobethe finalsoftwarebugactually turned out tobeanintermittentfault in theAAmachine. Thiswasonly rectifj-ed at theendof1985 whenthe keyboardmodule wasreplaced.Since thenthemaintenancecall-outfrequency hasd.ecreased.toanacceptableleveloflessthanonce perweek.Inthe lasttwoand ahalfyears,ASTAhas averted a nunber ofrnjor incidentswithgold precipitation.Onat leastone occasion theresultilg savingwouldhave easily covered the capital costof the installati-on.Thereare alsoworthwhile benefits toroutinepLantoperation.Whenprecipitationunitsarebeingcirculated turpreparation forbeingputonline,ASTArepeated.Iy checkstheir barrenvalues.Tttisallowsthemtobe broughton lj-nefasterandwithgreaterconfidence.Many minorincidentswiLhprecipitationare averted by cfral | /
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