Intec Gold Process

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    Intec Ltd

    Engineering for Superior and

    Sustainable Metals Production

    Intec Gold Process

    March 2009

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    This brochure was carefully produced. Nevertheless, the authors do not warrant the information

    containedtobefreeoferrors.Readersareadvisedtokeepinmindthatstatements,data,illustrations,

    procedural

    details

    or

    other

    items

    may

    inadvertently

    contain

    inaccuracies.

    Allrightsreserved(includingtranslationinotherlanguages).Nopartofthisbookmaybereproducedin

    any form,nortransmittedortranslated intoamachine languagewithoutwrittenpermission fromthe

    publishers.

    IntecLtd,2009

    PrintedinAustralia

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    TableofContents

    1 Introduction.......................................................................................................................................... 4

    2 IntecGoldProcessFlowsheet............................................................................................................... 6

    3 IntecGoldProcessProcess................................................................................................................... 8

    3.1 ConcentrateGrindSize................................................................................................................. 8

    3.2 LeachReactions............................................................................................................................ 8

    3.2.1 Leachreactionsforarsenopyrite.......................................................................................... 8

    3.2.2 Leachreactionsforpyrite..................................................................................................... 9

    3.2.3 GoldstabilityintheIntecGoldProcessleachcircuit............................................................ 9

    3.3 GoldRecovery............................................................................................................................. 10

    3.3.1

    ActivatedCarbon

    .................................................................................................................

    10

    3.3.2 Resins.................................................................................................................................. 11

    3.4 ByProductRecovery................................................................................................................... 11

    3.4.1 Silver.................................................................................................................................... 11

    3.4.2 Copper................................................................................................................................. 12

    3.4.3 Elementalsulphur(seleniumandtellurium)...................................................................... 12

    3.4.4 Minormetals(zinc,cadmium,magnesium,manganese,etc)............................................ 12

    4 IntecGoldProcessAdvantages........................................................................................................... 13

    4.1 EnvironmentalAdvantagesoftheIntecGoldProcess................................................................ 13

    4.2 EconomicAdvantagesoftheIntecGoldProcess........................................................................ 13

    5 IntecExperience.................................................................................................................................. 16

    6 CapabilitiesofIntec............................................................................................................................. 17

    7 Conclusion........................................................................................................................................... 17

    8 References.......................................................................................................................................... 18

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    1 IntroductionThe major proportion of the worlds gold reserves are goldbearing refractory ores, which are

    dominatedby ironsulphides suchasarsenopyriteandpyrite.Thereareanumberof factors thatcan

    renderagoldbearingorerefractory,asshowninTable1.

    Table1.CausesofRefractoryCharacteristics

    Type CausesofRefractoryCharacteristics

    Locked Physicallockingorsubstitutioninsilicates,sulphides,carbon,etc.

    Passivation Passivationduetoformationofachemicallayer.

    Chemical Formationofauriferouscompoundse.g.goldtelluridesandaurostibnite.

    Adsorption Adsorptionofdissolvedgoldbyactivecarbonaceousmaterialintheorepulp.

    Currentconventionaltechnologiesrequireanoxidativepretreatmentstepsuchaspressureoxidationor

    biologicaloxidation

    to

    liberate

    gold

    from

    the

    concentrates.

    The

    oxidised

    residue

    is

    then

    leached

    using

    an

    alkalinecyanidesolution,followedbypurificationandgoldrecovery.

    Incontrast,theIntecGoldProcess(IntecGoldProcess)usesamixedhalide lixiviant(chloride,bromide

    and/oriodide),permittinggolddissolutiontooccurconcurrentlywithsulphidemineraloxidation.Once

    the gold is solubilised, it can be extracted from the solution onto activated carbon or ionexchange

    resins, either in the leach pulp (carboninpulp/resininpulp), or separately in columns (carbonin

    column/resinincolumn).Gold istypicallyelutedusingappropriatecomplexingagents,andtheneither

    electrowonasgoldmetalorcementedusingreductants(e.g.zincpowder).

    Therefore,the

    Intec

    Gold

    Process

    differs

    from

    all

    current

    commercial

    practices

    for

    treatment

    of

    refractorygoldconcentrates,wheregoldisextractedfromtheoxidationresidueusingcyanide.Cyanide

    systemsrequireaseparatededicatedleachcircuitandcostlymeasuresforresidualcyanidedestruction.

    Importantly,however,theIntecGoldProcesscanberetrofittedtoexistingoperationswhereacyanide

    stripisemployedtorecovergoldfromactivatedcarbon,priortoanelectrowinningcircuit(Zadra(Zadra

    1951)orAngloprocesses).

    The Intec Gold Process has successfully treated concentrates containing the full range of minerals

    associatedwithgold(Table2).However,highlycarbonaceousfeedsthatcontainactivecarbonmaybe

    unsuitable fordirect treatmentusing the IntecGoldProcessdue toexcessivepregrobbingbehaviour

    duringleaching.

    In

    these

    cases,

    concentrate

    pre

    treatment

    or

    leach

    residue

    treatment

    techniques

    are

    recommendedtoattainhighgoldrecovery.

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    Table2.MineralsSuitableforTreatmentUsingtheIntecGoldProcess

    ClassofMineral TypicalMinerals ChemicalFormula

    Arsenides Arsenopyrite

    Enargite

    Tennantite

    FeAsS

    Cu3AsS4

    (Cu,Fe)12As4S13

    Sulphides Pyrite

    Pyrrhotite

    Chalcopyrite

    Stibnite

    FeS2FeS

    CuFeS2Sb2S3

    Tellurides Krennerite

    Hessite

    AuTe2Ag2Te

    Elemental Electrum

    Nativegoldandsilver

    AuxAgyAuandAg

    Antimonides Aurostibnite

    Tetrahedrite

    AuSb2(Cu,Fe)12Sb4S13

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    Golddepleted liquor issent to thepurificationcircuitwherebyproductsareprecipitatedwith slaked

    lime. The precipitated solids are separated by filtration where they are washed, and the filtrate is

    recycledtoleachingoperations.

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    3 IntecGoldProcess3.1 ConcentrateGrindSizeDuring conventional flotationand concentrationprocessing,particlesoforeare typicallyground toa

    sizerange

    of

    p80

    =70

    100

    m.In

    most

    cases

    leach

    kinetics

    are

    significantly

    enhanced

    when

    concentratesareregroundtoafinerparticlesize.Wherearsenopyriteisthesolegoldbearingmineral,

    asizeofp80=3040mhasprovenadequatetoachievegoodgoldextractionandanacceptableleach

    retentiontime.Wheregoldislockedinpyrite,thegrindsizewillprincipallydependonthereactivityof

    thepyrite. Forahighlyactivepyrite,thegrindemployedforarsenopyrite isused,butmorerefractory

    pyriteexamplescommonly require finergrinding. Thismayextend toanultrafinegrind (

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    TheoxidativeactionoftheCu2+/Cu+coupleissupplementedbytheFe3+/Fe2+couple,sincea background

    concentrationofironisalwayspresentintheprocessliquor. Thepotentialachievedundertheinfluence

    oftheCu2+andFe3+is~850mV(versusSHE)inthepresenceofoxygen.

    In thepresenceof ferric ion, thearsenicacid readily forms insoluble ferricarsenateaccording to the

    followingreaction:

    H3AsO4+Fe3+

    FeAsO4(s)+3H+ (5)

    Ferricarsenate(scorodite)formed inthehighchlorideelectrolyte,andundertheoperatingconditions

    usedintheIntecGoldProcess,istypicallycrystallineandstableinthenaturalenvironment.

    3.2.2 LeachreactionsforpyriteTheoxidationofpyrite(FeS2) intheIntecGoldProcess isachievedviathesameseriesof intermediate

    reactionsasemployedforarsenopyriteoxidationaccordingtothefollowingoverallreaction:

    4FeS2(s)+15O2(g)

    +2H2O

    8SO42

    +4Fe3+

    +4H+

    (6)

    It should be noted that the pyritic sulphur is oxidised all the way to sulphate in contrast to the

    arsenopyriticsulphur that isonlyoxidised to theelementalstate.Thushigheramountsofoxygenare

    consumedinleachingpyritecomparedtoarsenopyrite.

    Pyrite ismorerefractorythanarsenopyrite,typically requiringa finergrindsizetoachieveacceptable

    reaction kinetics. However, individualpyrite samplesexhibitvariable reactivity that is thought tobe

    influencedbyarsenicsubstitutionforaportionofthesulphurinthecrystallattice. Suchpyriteisoften

    termed arsenical pyrite, and the higher the arsenic contamination the more the pyrite reactivity

    approaches thatof true arsenopyritewith anAs/S ratioofone. Forparticularly refractory (lowAs)

    examplesofpyrite,ahigheroxidationpotential than isachievablewithairmaybeneeded,andpure

    oxygencanbeused.

    Tomaintainastablebackgroundirontenorintheprocessliquor,ferricisprecipitatedashematitebythe

    additionoflimestoneatapHofapproximately11.5accordingtothefollowingreaction:

    2Fe3++3H2OFe2O3(s)+6H+ (7)

    The sulphate precipitates as calcium sulphate (crystalline anhydrite) due to the presence of calcium

    chlorideinthebrinematrix,accordingtothefollowingreaction:

    2H+

    +SO4

    2

    +CaCO3(s)

    CaSO4(s)

    +H2O

    +CO2(g)

    (8)

    3.2.3 GoldstabilityintheIntecGoldProcessleachcircuitLeachinggoldintoanacidicsolutionrequireshighlyoxidisingconditions,otherwisethegoldremainsas

    an insolublemetal.Active sulphides (e.g. pyrite) or inorganic carbonaceousmaterialsmake leaching

    difficultastheunleachedmattercanreducesolubilisedgoldbacktothemetallicstate.Thetermcoined

    for this phenomena is pregrobbing.As a consequence, historically gold operationshave employed

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    alkalicyanide treatments for recoveryofgold from leach residues.While thegoldcyanidecomplex is

    extremely stableacrossa rangeofconditions,cyanide isahighly toxicsubstanceand itsuse isbeing

    restrictedworldwide.

    Analternativesystemtocyanideistousehalides.Thestabilityofgoldhalidecomplexesisgivenbelow,

    andclearly

    the

    gold

    complexes

    become

    more

    stable

    as

    the

    halide

    changes

    from

    chloride

    to

    bromide

    to

    iodide:

    Au+2Cl AuCl2

    +e E=+1.00(V)vsSHE (9)

    Au+4Cl AuCl4

    +3e E=+0.92(V)vsSHE (10)

    Au+2Br+Br2 AuBr4

    +e E=+0.80(V)vsSHE (11)

    Au+2I+I2 AuI4

    +e E=+0.55(V)vsSHE (12)

    Gold recovery processes using only a single halide are difficult, and no commercial processes are

    available

    (Marsden

    and

    House

    2006).

    This

    is

    due

    to

    chloride

    complexes

    being

    insufficiently

    stable

    to

    preventpregrobbing,andcircuitsusingjustbromideoriodidestruggletolimitthelossoftheexpensive

    halide.Incontrast,Intechasdevelopedandpatentedtheuseofmixedhalidesystemsfortherecovery

    ofbaseandpreciousmetalsfromsulphideandoxidefeedstock.Thekeyadvantageofamixedsystemis

    thatthemajorhalidecanbechloride,andonlytraceamountsofthegoldstabiliserhalide(bromideor

    iodide) need to be used. In this manner, the circuit is economically viable and achieves excellent

    recoveryofgold.

    3.3 GoldRecoveryExtractionofgoldfromthemixedhalideliquorcanbeachievedusingactivatedcarbonorionexchange

    resins.Both

    techniques

    have

    been

    successfully

    tested

    by

    Intec

    and

    third

    parties.

    3.3.1 ActivatedCarbonActivated carbon is the most widely used adsorbent for the recovery of gold from cyanide leach

    solutions. Either the Zadra (Zadra 1951)orAngloprocesses areused, and are known tobe reliable,

    simpleandcosteffective. Inthesesystems,goldcyanidecomplexesare loadedontoactivatedcarbon,

    andthenstrippedusingacombinationoftemperature,pressureandalkalicyanidesolutions.

    ThegoldhalidecomplexesusedintheIntecGoldProcessarealsoreadilyloadedontoactivatedcarbon.

    Extensive testingby Intecand theAJParkerCentre forHydrometallurgy,Australia,hasdemonstrated

    thefulllifecycleperformanceofactivatedcarbon.Repeatedloadingofgoldhalidesandstrippingtests

    usingcyanidesolutionsweresuccessfullycompleted.

    Retention time for gold adsorptionwas 1015minutes,which is similar to conventional practice for

    cyanidesystems.Gold loadingontothecarbonwastypically25%w/wduetotherelativelyhighgold

    concentrations insolutions typically10100mg/l.Thetestingconcludedthatgoldcouldberecovered

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    byconventionalelutionorbyburningofthecarbon,withthechoicedependingontheeconomicsofthe

    individualsituation.

    However,therearetwomajor limitationstocarbonsystems.The first isthatactivatedcarbon isnon

    selective forgold,withcoloadingofcopperandtheformationof ironprecipitatesobserved.Astrong

    hydrochloricrinse

    of

    the

    carbon

    is

    sufficient

    to

    remove

    copper

    and

    iron

    prior

    to

    gold

    stripping,

    but

    this

    clearlyadds costandcomplexity to theoperation.The second limitation is thatactivatedcarbon isa

    reductantandcanreducesolutionpotentialstotheextentthatelemental/colloidalgoldcanbedirectly

    cementedontothecarbon.Thiscan leadtodepositionofgoldalongsurfacesofequipment,reducing

    theoverallefficiencyofthesystem.

    Nevertheless, direct integration of the Intec Gold Process with existing carbon treatment circuits is

    viable.

    3.3.2 ResinsIn

    recent

    years,

    ion

    exchange

    resins

    have

    been

    widely

    used

    across

    all

    metal

    industries.

    However,

    industrial use of resins for recovery of gold has predominantly been confined to Eastern European

    countries,wheregoldthiosulfatechemistryhasprevailedinsteadofgoldcyanidechemistry.Resinshave

    been developed due to the well documented inability of goldthiosulfates to load onto carbon

    (Gallagheretal.1990;Navarroetal.2006).

    In Intecprocess liquors, resinshavebeenshown tobemoreselective forgold loading thanactivated

    carbon.Also,unlikecarbons,resinsdonotneedtoberegeneratedviaathermalprocess,whichmeans

    theinitialcapitalandthesubsequentoperatingcostsaresubstantially lowerthantheactivatedcarbon

    technology. Loaded resinshavebeen successfully strippedwith thiosulfateand/or thiourea solutions,

    whichcan

    be

    readily

    forwarded

    directly

    to

    electrowinning

    or

    zinc

    cementation

    circuits.

    3.4 By-ProductRecovery3.4.1 SilverSilveriscommonlyassociatedwithgoldconcentrates.However,highcyanideconcentrations(>0.5g/L)

    areoftenrequiredtoenablesilversolubilisation,andrecovery isgenerally limitedtozinccementation

    circuitsinsteadofactivatedcarboncircuitsduetopoorsilverloadingcharacteristics.

    SilverisreadilysolubilisedintheIntecGoldProcessduetothemixedhalidebrine.Ifthesilvercontentin

    theconcentrate

    is

    high

    compared

    to

    the

    gold

    content,

    then

    selective

    recovery

    onto

    resins

    or

    solvent

    extraction is preferred. High purity silver chloride is precipitated from the hydrochloric acid strip

    solutions,andthenmeltedtoyieldsilvermetal.

    On theotherhand, if the silver content is lowor similar to the gold content, simultaneous recovery

    throughtoelectrowinningamixedsilver/goldproductisalsoaviableoption.

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    3.4.2 CopperManycopperconcentratescontaingold.Dependingon thesizeof theproject, the IntecGoldProcess

    flowsheet can be modified to recovery copper as metal via electrowinning, copper sulphate

    pentahydratecrystalsviasolventextractionandcrystallisation,orcopperoxychlorideviaprecipitation.

    3.4.3 Elementalsulphur(seleniumandtellurium)The leach residue from the Intec Gold Process contains elemental sulphur. Intec has successfully

    recovered the sulphur by differential flotation from the residue, as the other components are iron

    oxides (hematite), calcium sulphate,andanyunreactedminerals.Givenappropriatemarkets, sulphur

    canbesold,orburntforenergyandsulphuricacidproduction.

    Thecrystalstructureofelementalsulphurisaneightmemberring(S8).Seleniumandtelluriumarewell

    known to substitute into these rings, and this is the case when the Intec Gold Process treats

    concentrates rich ineithermetal.TheSe/Terich sulphurcanbe separated from the leach residueby

    flotationand

    re

    processed

    by

    third

    parties

    for

    recovery

    of

    these

    important

    and

    valuable

    trace

    metals.

    3.4.4 Minormetals(zinc,cadmium,magnesium,manganese,etc)Thepresenceof impurities in the feedconcentrate (e.g.zinc,cadmium,manganese,magnesium,etc)

    hasnodetrimentaleffectoneither the leachingorarsenicprecipitationoperations. Nevertheless, a

    methodforthemanagementofimpuritiesisrequired.

    Firstly,limestoneisaddedtothegolddepletedbleedtoprecipitateresidualironandcopperatpH3.5.

    Thesolidsareremovedbyfiltrationandrecycledtothe leach. Impuritiesarethenremovedviaslaked

    limeadditionatpH9toforminsolublehydroxidesthatarerecoveredbyfiltrationfordisposal,according

    tothefollowingreaction:

    MCl2+Ca(OH)2(s)M(OH)2(s) +CaCl2 (13)WhereM=Zn,Cd,Mg,Mn,etc.

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    4 IntecGoldProcessAdvantages4.1 EnvironmentalAdvantagesoftheIntecGoldProcessTheinherentenvironmentaladvantageoftheIntecGoldProcessaresummarisedassuch:

    Nocyanideisusedintheleachingprocess,andwhenusingresinsnocyanideisrequiredforthe

    goldrecoverycircuit.

    Arsenic is converted into a stable and benign ferric arsenate (FeAsO4 scorodite), enabling

    successfultreatmentofconcentratescontaining>10%arsenic.Thiscomparesfavourablywith

    roastingtechnologieswhichcreatetoxicarsenictrioxide(As2O3),whichmustbecarefullystored

    andeventuallydisposedofatconsiderableexpense.

    Noliquideffluents

    Nonoxiousgaseousemissions

    Low carbonfoot print due to low energy consumption relative to other minerals processing

    technologies(POX,

    roaster,

    etc)

    Underappropriateprojectconditions,azerowasteprocesscanbeimplemented

    High overall metal extraction from feedstock (typically > 98%), resulting in stable iron oxide

    (hematite)/elemental sulphur/calcium sulphate leach residues with little trace/toxic metals

    present.

    4.2 EconomicAdvantagesoftheIntecGoldProcessInadditiontohavingsignificantenvironmentalbenefitswhencomparedtoalternativetechnologies,the

    IntecGoldProcessalsohassuperioreconomics.Acomparisonofthe IntecGoldProcesstoarangeof

    existingprocess

    technologies

    with

    respect

    to

    plant

    capital

    and

    operating

    costs

    is

    provided.

    The

    data

    is

    based upon comparative cost analysis commissioned by Intec in 2004 and compiled by J.R. Goode

    (Goode 2005) and HG Engineering (HG Engineering 2005). Further costing data is referenced from

    MarsdenandHouse2005(MarsdenandHouse2006).

    Thefollowingassumptionswereusedforthecomparison;

    PlantlocatedinNorthAmerica

    Costsexcludetailingsdisposal,effluenttreatmentandoreminingcosts

    Costsincludeflotationandgrindingcircuitswherenecessary

    Goldconcentratethroughputofapproximately50,000tpa(at60g/tgold)

    Intec

    Gold

    Process

    oxidation

    circuit

    assumes

    the

    use

    of

    air

    as

    asource

    of

    oxygen

    Costshavebeen inflated to2009 levelsusingaMarshall&Swift/Mine&Millcostescalation

    index

    Thecomparisonsareonlyindicative,asvariationsinoremineralogyandspecificprojectconditionsand

    requirementsmayrendersomeprocessesunsuitable.Sixteenprocessoptionswereincludedinthecost

    comparisonassummarisedinTable3;

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    Table3GoldProcessingOptions

    LeachProcess ProcessOption PretreatmentStep Recovery

    DumpLeach 1 None CarboninColumn,Electrowinning

    ROM

    Ore2 CoarseCrushing CarboninColumn,Electrowinning

    3 MediumCrushing CarboninColumn,Electrowinning

    4 MediumCrushingCarbon

    in

    Column,

    ZnPrecipitation

    5Fine

    Crushing,AgglomerationCarboninColumn,Electrowinning

    FreeAucon 6* Grinding,Flotation CarboninPulp

    Gr

    oundOre

    7 Grinding,Biooxidation CarboninPulp,Electrowinning

    8 Grinding,Roasting CarboninPulp,Electrowinning

    9 Grinding CarboninPulp,Electrowinning

    10+ Grinding,Flotation CarboninPulp+

    11

    Grinding,Pressure

    Oxidation

    Carbon

    in

    Pulp,

    Electrowinning

    12 GrindingCountercurrentdecantation

    ZnPrecipitation

    LockedGold

    Concentrate

    13Grinding,Flotation,

    RoastingCarboninPulp,Electrowinning

    14Grinding,Flotation,

    BioOxidationCarboninPulp,Electrowinning

    15Grinding,Flotation,

    PressureOxidationCarboninPulp,Electrowinning

    16 Grinding,Flotation ResinColumns,Electrowinning

    *Freegoldconcentratesonly+Saleofconcentrate

    Figure2highlightstheadvantageoftheIntecGoldProcessintermsofcapitalcostswhencomparedto

    the15otherprocesstechnologies.Whilethe IntecGoldProcesscapitalcost issignificantly lowerthan

    processoptions515,italsocomparesfavourablytoheapanddumpleachoperationsfortreatmentof

    ore.Somefeedstocksareunsuitableforheapordump leaching,andtheseareparticularlysuitablefor

    treatmentusingtheIntecGoldProcess.

    Figure3highlights theadvantageof the IntecGoldProcess in termsofoperatingcosts.Asexpected,

    apart from thecheaperheapordump leachoperations, the IntecGoldProcessoperating cost is the

    lowestofallotheravailabletechnologies.

    As shown through this indicative cost comparison, the Intec Gold Process has a significant cost

    advantageinbothcapitalandoperatingcosttoallotherstandardgoldprocessingtechnologies.

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    Figure2ComparisonofPlantCapitalCosts(USDmillions)

    Figure3ComparisonofPlantOperatingCosts(USDpertonneROMore)

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    5 IntecExperienceOverthe last10years Intechassuccessfullycarriedouttestwork forexternalclientstoevaluateand

    prove the IntecGoldProcess technical feasibility,economicandenvironmentaladvantages.Testwork

    hasrangedfromproofofconceptstudiestopilotplantcampaigns.Ithasalsoverifiedtheprocessata

    demonstrationplant

    scale

    in

    Burnie,

    Tasmania.

    Examples

    of

    testwork

    are

    provided

    in

    Table

    4:

    Table4.ExamplesofsuccessfulapplicationofIntecGoldProcesstorefractorygoldconcentrates

    ProjectTitle OreTypeAuhead

    grade(g/t)Extraction

    Recoveryfrom

    solution

    OtherMetalsin

    Concentrate

    LaboratoryBenchScaleTests:

    Furteigoldproject,

    Sardinia

    Enargite,Cu3AsS4Pyrite,FeS2

    38.7 85%

    >98%using

    resinsfrom0.3

    ppmsolution

    10% As,28%Cu,

    190g/tAg,1860g/t

    Te,750g/tHg

    SamplefromPolyus,

    Russia

    Arsenopyrite,FeAsS

    Pyrrhotite,FeS

    Antimonite,

    Chalcopyrite,CuFeS2

    Pyrite,FeS2

    91.8 90%>95%

    using

    carbonfrom10

    ppmsolution

    6%As,4%Sb,3%C

    SamplefromBarrick,

    SouthAmerica

    Enargite,Cu3AsS4Arsenopyrite,FeAsS

    Pyrite,FeS2

    48.1 87%

    >98%using

    resinfrom

    2ppmsolution

    4.4%As,11.2%Cu,

    1.4%C,175g/tTe,

    705g/tAg

    Samplefrom

    GoldCorp

    Arsenopyrite,FeAsS

    Pyrite,FeS2170 95% notcompleted

    15%As,9.8%Si,

    1.5%C

    PilotplantScaleTest:(closedloopcontinuousoperation)

    SamplefromBarrick,

    Australia

    Arsenopyrite,FeAsS

    Pyrite,FeS258.6 >95%

    >98%using

    carbonfrom10

    ppmsolution

    0.5%As

    In 2004, Intec successfully operated a pilot plant using the Intec Gold Process to treat 30kg/day of

    refractory gold concentrateprovidedbyBarrick,Australia.Gold leach extractionobtainedwasup to

    96.5%usingasingleleachcircuitandmildgrinding(70m).Goldrecoveryontocarbonwasveryhigh,as

    wasplantavailabilityat99%. IntecGoldProcessgoldrecoverywashigherthanthatobtainedbyusing

    ultrafinegrinding(10m)followedbycyanideleaching(9092%)inaconventionalcircuit.Thefullscale

    ultrafinegrindingoptionwaschosenbyBarrick inearly2001asthemostcosteffectivealternativeto

    roastingwhen

    compared

    to

    an

    acid

    plant,

    pressure

    oxidation,

    and

    bacterial

    oxidation.

    However,

    this

    optionstill involvesveryhighcostsassociatedwithenergyconsumption levelstoachievetherequired

    particlesize,upto 120kWh/tofconcentrateforagrindsizeof10m(EllisandGao2002). IntecGold

    Process performance for this sample concentrate suggests that the Intec Gold Process is a more

    economic andenvironmentaloption thanultrafine grinding in conjunctionwith cyanide leaching for

    thisparticularcase.

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    6 CapabilitiesofIntecTheprocessanddesignengineering teamat Intec isable toprovideprocess flowsheetdevelopment,

    flowsheet modelling, inhouse process evaluation testwork (laboratory, piloting and demonstration

    scale), scoping/feasibility studies, and financial modelling for hydrometallurgical minerals processing

    projects.In

    many

    cases,

    acombination

    of

    common

    base

    and

    precious

    metal

    hydrometallurgical

    circuits

    canbeintegratedwithproprietaryIntectechnologycircuits,e.g.theproductionofzincsulphatecrystals

    would involve an Intec halide leach, solvent extraction, and then crystallisation from sulphuric acid

    brine.

    TheIntecteamhasgatheredsignificantexperienceintestinganddevelopingover50projectsinthepast

    10 years, for extraction and recovery of gold, copper, silver, lead, zinc, nickel, cobalt, indium, and

    platinum. Thetestinghas focusedonagitated leachingcircuits,purificationtechniques (cementation,

    solvent extraction, ion exchange resins, and precipitation), and product recovery (electrowinning,

    sulphidisation, and precipitation). Two continuous closedloop demonstration plants have been

    designed,built,

    and

    operated,

    with

    the

    $10M

    (AUD)

    Burnie

    Research

    Facility

    available

    for

    testwork

    and

    projectdemonstrationinTasmania,Australia.

    TheIntectechnologyisnowcommerciallyavailable.Intecpursuesaflexibleclientperclientapproachto

    licensing, royalties, equity participation, orother forms of investment. Exclusive access rights to the

    technologyareavailableonageographicalbasis.

    7 ConclusionThe IntecGold Process represents anew approach to the recoveryof gold from refractory sulphide

    deposits.Theprocesshasbeenproventodeliverhighgoldextractionsandrecoveries,whichcompare

    favourablyagainstothertechnologies.Thecapitalcostsandoperatingcostsarerelatively low,making

    theIntecGoldProcessattractivetonewoperations.Expansionprojectsshouldalsoconsideremploying

    theIntecGoldProcess,asitcaneasilybecombinedwithexistingcarbonorresingoldrecoverycircuits.

    Theenvironmentalbenefitsof theprocessareunparalleled,with theeliminationofcyanide from the

    leachcircuitandconversionofarsenic intostableferricarsenatebeingcriticalpointsofdifferentiation

    withallothertechnologiesforgoldprocessing.

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    Intec Gold Process Page 18

    8 References

    Ellis, S. and Gao, M. (2002). "The Development of Ultra Fine Grinding at KCGM". Conference

    Proceedings:SME

    Annual

    Meeting

    Phoenix,

    Arizona.,

    vol,

    p,

    Ed.

    Gallagher, N. P., et al. (1990). "Affinity of activated carbon towards some gold(I) complexes."

    Hydrometallurgy25(3):305316.

    Goode,J.R.(2005).CapitalCostIntecGoldProcess,Pox,Box.

    HG Engineering (2005). Barrick Gold Corporation: Review of Cost Estimate of Intec Refractory Gold

    Process.

    Marsden,J.O.andHouse,C. I.(2006).TheChemistryofGoldExtraction.Colorado,SocietyforMining,

    Metallurgy,andExploration,Inc.

    Navarro, P., et al. (2006). "The adsorption of gold on activated carbon from thiosulfateammoniacal

    solutions."GoldBulletin39(3):9397.

    Zadra,J.B.(1951),Patent:US2,579,531.Processforextractinggoldandsilver.

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    Intec LtdEngineering for Superior and

    Sustainable Metals Production

    orpora e ea quar ers

    Level 3, 2 Elizabeth Plaza

    North Sydney NSW 2060 Australia

    PO Box 1507

    North Sydney NSW 2059 Australia

    Telephone: (+61 2) 9925 8170

    Facsimile: (+61 2) 9925 8110

    Website: www.intec.com.au

    Email: [email protected]

    Contact Names: Dr Andrew TongProject Manager& Senior Research Metallurgist

    Philip WoodManaging Director

    & Chief Executive Officer