2. 1 | P a g e
Table of Contents
Executive Summary ..............................................................................................2
Introduction ........................................................................................................3
Theory. ...............................................................................................................3
Results and Discussion ..........................................................................................9
Drying and sampling........................................................................................................... 9
Base line analysis process................................................................................................ 10
Results............................................................................................................................... 10
Flowsheet and implications............................................................................................. 11
Environmental Context .......................................................................................12
Global and Societal Context.................................................................................13
Conclusion.........................................................................................................13
Future Work ......................................................................................................14
References ........................................................................................................15
Appendix...........................................................................................................18
A........................................................................................................................................ 18
B........................................................................................................................................ 22
C........................................................................................................................................ 25
D....................................................................................................................................... 28
E........................................................................................................................................ 30
F........................................................................................................................................ 33
G....................................................................................................................................... 35
H....................................................................................................................................... 41
Acknowledgements ............................................................................................44
3. 2 | P a g e
Executive Summary:
Barrick Gold,the largestgoldminingcompanyinthe world,hastaskedthisdesignteamto analyze a
reserve of tailingstheyhave atone of theiroldestminestosee if the tailingscanbe profitably
concentrated, andif theycan, designaprocessto do so.Barrick believes thatwiththe currentprice of
goldand withadvancementsin mineral processing,the tailingsare now aviable source of gold. To
determine the amountof goldinthe tailings,the teamhasconducted three concentrationtechniques.
Magneticseparation,frothflotation,andgravityseparationwere all usedtoconcentrate the gold. Inthe
frothflotationconcentrationmethod,fourtestswere performed.The firsttestperformedshowedthe
presence of gold,butthe resultscouldnotbe repeated.Giventhe unreliabilityof thistest,the team
decidedthatfrothflotationwouldnotbe aviable optionforconcentratingthe goldinthe tailings.The
scope of the projectwasshiftedtowardsmagneticseparationandgravityseparation. The resultsof
gravityseparation were notbetteras a fire assaydeterminedthatthe grade of the concentrate wasless
than the initial grade of the tailingsmakingitaninaffective method. Magneticseparationtestinitially
seemedencouragingasthe grade of the tailingwasimprovedtenfold,puttingitabove the minimum
grade value that Barrickis willingtoprocess. Subsequenteconomiccalculationsshowedthattoomuch
moneywouldbe spentdryingthe tailingpriortoprocessing,meaningthatmagneticseparationasthe
teamperformeditwasuneconomical. Howeverourcontactat Barrack Goldprovidedinformationona
wetmagneticseparationtestthathe performedandthe economiccalculationsforthisversionof
magneticseparationprovedpromisingasthe NPV andIRR were foundto be about$390 millionand33%
respectively.
4. 3 | P a g e
Introduction:
It isa commonmisconception thatwhenamineral processingcompany isdone withanore bodythat all
of the valuable materialiscompletelyextracted. While itispossible toprocessthe ore until nearlyall of
the valuable material istaken,thisisalmostnevereconomicallyjustified.Itistypicallythe case that
initiallyalarge portionof the desiredmaterial canbe easilyextractedfromthe ore but, as lessmaterial
isavailable,the more costlyitbecomestoextractthe remainder,thusmakingituneconomical to
continue processingthe ore. However,astime movesforwardanddemandschange,the price forsuch
material mayincrease tothe pointthat itis economical tocontinue processingthe depletedore body
for the remainingmaterial.
Thisis whatBarrick gold wishestofindoutas theyhave 170 milliontonsof tailings fromtheirGoldstrike
mine.Barrick believeswiththe risinggoldprice thatthe tailingsmaynow be a viable ore source.The
team’sobjective istoanalyze samplesfromthe tailingsto measure the grade of the tailingsandthento
designflowsheetsthatwill maximizethe netpresentvalueandinitialrate of return. Thiswill determine
if it iseconomicallyfeasible forthe tailingsto be reprocessedforthe remaininggold. Barrickhas
requestedthatourgroupto be finishedcollectingandanalyzingdatabyFebruaryof 2015.
Theory:
The tailingsof anymineral processing operation will retain some amountof desiredmaterial. However
if it the value of the material increasesornewertechnologyallowsforeasierrecovery,thenfurther
processingmaybe justified. There are manywaysto concentrate ore bodiesandall of themtake
advantage of the ore’sphysical andchemical characteristics,thisisgenerallyknownasbeneficiation.For
thisdesignproject,the groupwill focusonconcentratinggoldbyemployingthe mostavailable and
commerciallyusedmethods,gravityseparation,frothflotation,andmagneticseparation.
Gravity Separation
The firstprocessusedto beneficiate the goldtailingsthatwill be considered,isgravityordensity
separation.Gravityseparationisanenvironmentallyfriendlyprocess,whichutilizessimple equipment
withfewmovingparts.(Abols) Goldpanningisasimple formof gravityseparationthathasbeenused
for centuries. Throughoutthe historyof mineral processing,manydifferenttypesof gravityseparation
deviceshave beenutilized,butthe one the teamwill use isa wave table. Gravityconcentration
processesrelyonthe principle thatgoldcontained withinanore bodyishigherinspecificgravitythan
the gangue. Elemental goldhasa specificgravityof 19.3, andtypical ore has a specificgravityof about
2.6. (Fast) Movementiscreatedbygravityconcentrationdevices betweenthe goldandhostrock
particlessothat the heavyparticlesare separatedfromthe lighterparticles. Onawave table,particles
will be fedontothe machine alongwithastreamof water.The bedof the table will begintoshake
resultingintwoevents,the formationof awave inthe waterandthe gradual forwardmovementsof the
particlestowardsatrough at the endof the table.While the particlesare incontactwiththe surface of
the table,the shakingwill cause them tomove forward. Whena wave passesoverthem, lessdense
5. 4 | P a g e
particleswill be movedbackwardswhiledensermaterial are eithernotmoved,ormove verylittle
resultinginaseparationof the particlesbytheirrespectivedensities. See Figure 1.
Figure 1: Wave Table wave velocity profile. Yellow is gold and black is gangue
To determine if gravityseparationisafeasibleprocessacommontechnique istocalculate the
concentrationcriterion.As shown inEquation1the concentrationcriterioniscalculatedbythe specific
gravityof the heavymineral subtracted bythe specificgravityof the fluiddividedbythe specificgravity
of the lightermineral subtractedbythe specificgravityof the fluid.Assumingagangue withadensityof
2650 kg/m3
goldhas a concentrationcriterionof 10.3 and hematite hasa criterionof 2.5. The other
majorfactor of determiningif gravityseparationispossible isdeterminingthe particle size of the
mineral thatisdesired.Below inFigure 2showsconcentrationcriterionversusthe sizeof mineral
particlesinmicronsshowingwhere separationispossible andimpossible (Guapta).Table 1alsobacks up
the data showedinFigure 2.
6. 5 | P a g e
Figure 2: Size limit curve for gravity separation
Table 1: Concentration criterion guide for gravity separation
Ideallygoldandgoldbearingmaterial will move intothe troughof the table butthe teamwill likely
collectall of the material closesttothe top fortesting.One disadvantage of gravityseparationisthat
ultrafine clayparticlesare noteasilyrejected (Honaker).Anotherdifficultywillbe the change togolds
specificgravitybyironoxide sludgeof maghemiteattachedtothe goldore.Finallythe small particlesize
of the gangue createsanotherobstacle todeal withif the teamdecidedtouse gravityseparationasa
concentrationmethod.
Froth Flotation
Froth flotationislargelyconsideredtobe one of the mostwidelyusedmethodsinmineral processing.
The processwas inventedbyFrankElmore in1896. Elmore had justpurchasedthe Glasdircoppermine
whichhad a notorioushistoryof havingdifficultore toworkwith. The mine hadbeensoldseveral times
inits lifetime. Elmore experimentedwithusingoil asa collector.The processwasa huge success.The
mine hasable to collectnearly70%of the ore’scoppercontent.To give a basicdescription,froth
flotationessentiallyutilizesamineral’saffinityforwaterinorderto create a separation.Due tothe
process’ssimplicityandhistorical success,the Barrickdesignteamwill be evaluatingfrothflotationasa
7. 6 | P a g e
possible concentrationtechniqueforthe goldstrikemine’stailings. Inorderto give the designgroup
and anyother readersa betterunderstandingof the process,the followingsectionswill coverhowthe
processworks,andhow itis commonlyperformed.
How does it work?-Asstatedabove,frothflotationexploitsthe factthatsome mineralsare hydrophilic
(likeswater) andsome are hydrophobic(hateswater). Thisisthe basisof creatinga goodseparation.
The ore ismixedintoa slurryandthenintroducedintoaflotationcell where theyare agitated. Airis
pumpedintothe bottomof the cell inthe form of small bubbledtypicallyof aboutone totwo
millimeters.If amineral particle ishydrophobic,itwill attachonto a bubble andfloattothe surface of
the slurrywhere itcan be skimmedoff. Those particlesthatare hydrophilicwill notattachto air
bubblesandwill remaininthe slurry.
What makesdifferentmineralparticleshydrophobicornotcomesdownto the surface chemistryof the
particle. The surface of any particle can be splitintotwolayers:the sternlayerandthe diffuse layer.
These twolayersare oftencalledthe electrical double layer.The sternlayerisasmall layerdirectlyon
the particle’ssurface thattendstoaccumulate ionsof the opposite charge of the surface.Forinstance a
particle withanegative surface charge will accumulate positivelychargedionsinthe sternlayer.The
diffuse layerisa muchlargerlayeroutside the sternlayerthatcontainsa mixture of positive and
negative ionsandessentiallyzeroesthe total charge tothe surroundings(Figure 3).Twoimportantvalue
inflotationisa mineral’szetapotential.The zetapotential isthe charge justoutside the sternlayer.
Differentsolutionshave differentpHvaluesandthereforedifferentamountsof positive (H+
) and
negative (OH-
) ions.VaryingpHscan change the zetapotential of a particle.The pHvalue where the zeta
potential of aparticle isequal tozero iscalledthe point-of-zero-charge(PZC) (Figure 4).Bymakingthe
zetapotential negativeorpositive,one canthenaddchemicalsthatwill adhere tothe surface of select
particlesandrenderthemhydrophobicallowingthemtofloat.
Many differentchemicalsmaybe addedtoa mineral slurrytochange how theyreact withwater.Those
that change the hydrophobicityof aparticle are knownas collectorsorsurfactants.Collectorscanbe
eitheranionicorcationicdependinguponwhatthey adhere to. Anioniccollectorswill adhere to
positivelychargedparticles,while cationiccollectorswilladhere tonegativelychargedparticles.Inthis
way,differentcollectorscanbe usedtotarget particleswithdifferentcharges.Chemicalscanalso be
usedto alterthe pH of a solutioninordertoisolate amineral forflotation.Forinstance,if one wanted
to floatironoxide (PZC6.7) from silica(PZC2) withan anioniccollector,the pHcouldbe loweredtofive
to renderhematite positivelychargedandsilicanegativelycharged. The anioniccollectorwill then
attach to the iron oxide,makingithydrophobic,causingittofloatwhile leavingsilicabehind.Additional
chemicalscalledfrothersmayalsobe usedinordertocreate a more resilientfrothlayer.
8. How is flotationperformed-Before flotationcanoccur,ore typicallyhastobe reducedto fine particles
usinganynumberof comminutiontechniques.Typicallyflotationisperformedwithparticlesof around
0.1 mm butcan sometimesrequireevensmallerparticle sizes. The groundore isthenmixedwithwater
to forma slurrybefore the additionof pHalteringchemicalsandsurfactants. The slurryisthen
introducedintoaflotationcell where itisaeratedandallowedtofloat. The frothcan thenbe removed
as concentrate.Those particlesleftbehindmaybe pumpedoutof the cell as tailings.One advantage of
frothflotationisthatit iseasilyscalable fromsmall laboratorycellstolarge industrialcellsthatmaybe
linkedtogethertoobtainthe mostout of the process.
The Barrick designteamperformedsome basicflotationtestsonthe ore receivedfromthe Goldstrike
mine.Underthe suggestionthatgoldwastrappedwithironoxide fromthe group’sadvisoratBarrick,it
was decidedthatanattemptto floatthe ironoxide wouldbe made.Frommineralogyreportsperformed
on the tailings,the groupwasable todetermine thatalarge portionwas carbonaceousmaterial.This
suggestedthata goodseparationmightbe possible.The grouppreparedfourrepresentative samples
fromthe tailing,andutilizedoleicacid(anioniccollector)aswell asanunidentifiedfrothertotest
differentflotationcombinations.Fourtrialswouldbe run:anatural floatwithnoadditives,asecond
trial withan addedfrother,the thirdwoulduse three drops of oleicacid,the lasttrial usedbotholeic
acid anda frother.Waterand the tailingssample werefirstintroducedintothe flotationcelland
allowedtoconditionwithaironforone minute.Whatwas collectedwasreturnedtothe cell. Thisinitial
step’spurpose istoproperlymix andcreate a uniformslurry.The cell wasthenturnedbackon and
allowedtorunfor three minutes.Concentratesweredriedandthenscorificationassayswere runto
determine goldgrade.
Figure 3: Diagram of a particle showing the
electrical double layer
Figure 4: Graph of zeta potential versus solution pH. PZC
equals 9.5
9. 8 | P a g e
MagneticSeparation
Magneticseparationisa popularandlow-costmethodof recoveringmetals. Magneticseparationis
usedprimarilybyminingindustries,butisalsowidelyusedinthe recyclingindustry.Magnetic
separationusesamagneticfieldtoseparate magneticmaterialsfromnon-magneticones.
Explanation- Whenmineralsare placedina magneticfield,thereare three reactionsthancanoccur.
Attractionto the magneticfield,repulsionfromthe magneticfield,ornoreactionat all. The particles
that are attractedto the magneticfieldare calledmagnetic.These particlesare subdividedintotwo
classifications;stronglymagneticparticlescalledferromagneticandweakermagneticparticlescalled
paramagneticparticles.Ferromagneticparticlesmaybe easilyseparatedwithaseparatorhavinga low
intensitymagnetic.However,paramagneticparticlesrequire ahigherintensitymagneticfieldto
separate them.
Particlesthatare repulsedbyamagneticfieldare calleddiamagnetic.EddyCurrentSeparators,take
advantage of the diamagneticparticles,separatingthemfromothermaterial.EddyCurrentSeparators
are largelyusedinthe recyclingindustry.Here,wire andmetalsmade fromcopperandaluminumare
separatedfromplastics.Whenaproduct,such as aluminum, passesoverthe eddy current,amagnetic
fieldformsaroundthe piece of aluminum.The polarityof the magneticfieldof the aluminumisthe
same as the rotatingmagnets,causingthe aluminumtobe repelledawayfromthe separator.Plastic,
glass,or otherprocessmaterialssimplyfalloff the endof the separator.Aneddycurrentisdefinedas
the currentscausedby voltagesinducedbychangingflux,andtendtooppose the change of the flux.
Non-magneticparticles,suchasgold,quartz,andpyrite,are not susceptible to magneticseparation,but
some magneticmaterial maybe removedfromthe feed.Forinstance,inafew situations,plantsusing
gravityconcentrationforrecoveringgold,usedmagneticseparatorstoremove the highconcentration
of magnetite thatwasrecoveredwiththe gold,priortofurtherprocessing.
Magneticseparationisgenerallyalowcostmethodof recovery,unlesshighintensityseparatorsare
required.The electro-magnetichighintensityseparatorsthatproduce 20,000 gauss,tendto be
expensive. However,the rare earthmagneticseparatorsare relativelyinexpensive andcanproduce
magneticfieldsaround6,000 gauss.So,whenlookingfora processto recovervaluable minerals,
magneticseparationshouldnotbe overlooked,if some of the material is magneticorpara-magnetic.
(Kinsack)
Whenconsideringusingmagneticseparationprocessitisimportanttoevaluate amaterial’smagnetic
susceptibility.Magneticsusceptibilityisavalue giventoamaterial basedonhow magneticitis per
volume andis measuredbyweighingasample andthenturningonan electromagnettosee how the
weightisaltered.A material likepure goldhasa negative magneticsusceptibilitymakingitdiamagnetic
so usingmagneticseparationmethodonitwouldnotyieldanyresults.
The process-There are differentsortsof magneticseparators,butthe mostcommonis the drum
separator.(See figure 5) Essentially,astreamof material isdroppedontothe beltof a magneticdrum.
10. 9 | P a g e
Non-magneticorweaklymagneticparticlesbounce orfall off of the drum.The remainingmagnetic
particlessticktoit until theyare scrapedoff. The speedof the beltas well of the intensityof the
magneticfieldwill bothhave aneffectonhow muchof the magneticmaterial isattractedtothe belt.
(Osbourne)
Figure 5: Drum Separator
In additiontothe drummethod,manyothertypesof separatorsexist.These include,butare not limited
to, pulleys,discs,beltsandrings.Magneticseparatorscanbe usedeither"wet"or"dry"and come in
countlessshapes andsizes.
Magneticseparation for our project-Withthe majorityof the goldbeingtrappedinsome formof iron
oxide,magneticseparationwill mostlikely,prove tobe veryuseful. A BarrickGoldrepresentative
informedthe teamthatthe entire tailing’smasswasonlycomposedof about3-5% ironoxides,sothe
resultsfromthe team’sattemptneededtobe nearthisrange.Ironoxide hasa veryhighmagnetic
susceptibilitymakingitparamagnetic.If the goldisimbeddedinthe ironoxidemagneticseparation
shouldbe a viable processingoption.
The resultsof the magneticseparationperformedbythe teamdidnotmatch that of the data from
Barrick. Barrickwas able to performthe magneticseparationusingawetmethod.Giventhe resources
available atSouthDakotaSchool of MinesandTechnology,the teamwasunable torun a wetmagnetic
separationtest.
While there are manywaysof beneficiatingthe gold,these threeprocessesare most readilyavailable.
Each methodhas itsownadvantagesanddisadvantages.Usingacombinationof these complimentary
processescanimprove the overall recoveryof goldfromthe tailings.Eachmethodworksbestincertain
situationsandundercertainconditions.Withthe rightknowledge of the tailingsmineralogyand
chemical composition,the recoverycanbe maximized.
11. 10 | P a g e
Results andDiscussion:
Drying and sampling- The sample arrived inaslurryform so,before itcould be processed,itmustbe
dried. The sample wasgivenafewdaysto sit,thus allowingthe particlestosettle tothe bottomof the
shippingbarrel. Withthe particlessettled,the toplayerof waterwasremovedusingabucketuntil the
movementof the watercausedbythe bucketbeganto disturbthe particles. The particleswere then
allowedtosettle again. Once settledawet-dry-shop-vacuumwasthenusedtogentlyremove the rest
of the surface water.
As the sample slurrywasbeingpumpedintothe 55 gallondrumitarrivedin,it can be assumedthatthe
slurrywas thoroughlymixedfromthe violentmotionsimpartedonitduringthe time itspentmoving
throughthe pipingsystemandthe initial agitationlikelyusedtoloosenupthe tailingsduringthe
acquisitionfromthe tailingdam. Therefore,if the slurrywasthoroughlymixedinthe drumitcan be
furtherassumedthatthe settlingof the particle inthe waterallowedforarelativelyuniform
dispersement,because whileindividual particlesprocesseddifferentsettlingvelocitiesthe initial
uniformdispersementinthe fluidshouldsufficientlyoffsetanysettlingtrends. Inthisregard, a sample
takenby a coringmethod shouldbe representative of the entire tailingssample. Sothe teamuseda
PVCpipe tocore and remove arepresentative sample. Thiscore wasthenplacedinan ovento dry.
Once the core was dried,the particlesfusedintolarge agglomerates,necessitating breakingthe
agglomerates usingamortarand pestle. Afterthiswascompleted,analysisof the tailingsbegan usinga
riffleralongwiththe cone andquarteringtechniquetoseparate representativesamplesforvarious
tests.
Baseline analysisprocess- A baseline analysis of the tailings todetermine suchthingsasmineralogy and
particle size distributionwas conductedsince characteristicssuchasthese will influence how a
concentrationmethodwillperform. A sample was processedand/oranalyzedineachof the following
ways:
Usedto performa fire assay(see Appendix B) bya memberof the team. Thiswill give aresult
regardingthe tailingscurrentgoldgrade thatis representative.
Digestedinaquaregiaor anotheracidsolutiontobringthe goldpresentintosolution. Use AAS
to determine the concentrationof goldinthe solutiontothenbackcalculate the grade of the
ore. This methodmaynot be as accurate as the fire assaybut can be performed quicklyfor
multiple samples,thusthismethodwill be done frequently.
Sentto EngineeringandMiningExperimentStationpersonnelfor SEManalysis.Thisalongwith
othermethodswill helptodeterminethe mineralogyof the tailings.
Takento EngineeringandMiningExperimentStationpersonneltohave X-raydiffraction(XRD)
performed. Thisisa greattechnique fordeterminingmineralogy.
Results- Asof now the teststhat have beenperformedinclude SEMandXRD analysis,fire assay, AAS,
magneticseparation andpreliminaryfrothflotation.
12. 11 | P a g e
The SEM gave a roughelemental compositionof the sample.Forthe SEManalysis,agrab sample from
the top of the sample wasusedinsteadof arepresentative sample.The highpeaksof the graphshow
the presence of silicates inthe sample.(SeeAppendix A andD)
The XRD showedmanyof the minerals withinthe sample andwasperformedafterdifferentprocesses.
ResultsfromXRDdidnot change much evenaftermagneticseparation,XRDshowedthe presenceof
quartz, gypsum,dolomite,andcalcite (see Appendix A) butnotmuchelse.The expectationwasthat
aftermagneticseparation, ironoxidewouldbe found,butthatwasnot the case. The team later
discoveredthatthe ironoxide wasmaghemite,anoxidationstage betweenhematite andmagnetite,
and itwas not detectedbecause the XRDequipmentwasnotcalibratedtodetectit.
Table 2: Grade and recovery results
Fire Assayand AASwere performed before anyconcentration toreveal the initial average value of the
goldwithinthe sample. Bothresultswereverysimilarwiththe average valueforfire assaybeing 0.038 t
Oz/tonand the average value forAASbeing 0.035 t Oz/ton.These valuesare abouthalf of Barrick’s
requirementof aconcentrate grade of 0.08 t Oz/ton.
The firstconcentration methodcompleted wasmagneticseparation. The groupwasinformed byBarrick
personnel thatthe majorityof the goldleftinthe tailing istrappedinmaghemite.Furthermore,
maghemite comprisedabout3-5wt% of the tailing.The team’smagneticseparationreflected this
expectation withamagneticconcentration of justunder7 wt% of the tailingssample. ResultsfromAAS
showedthatthe magneticconcentratesfromthe separationhad a grade of 0.17 t Oz/ton. Thisvalue is
nearlytwice Barrick’s minimumrequiredgrade. Later,a fire assayshowedthatthe actual grade was
around0.48 t Oz/ton.
Flotationsof the tailingswere performed on500 gram samplesinanattemptto determine how much
goldcouldbe floatedoutof the naturallyhydrophobic, carbonaceous material presentinthe tailings by
floatingwithnoadditives,oleicacid,afrotherand botha frotherand oleicacid. All floatswhere
performedata pH around 8, withabout2.6 litersof waterand anyadditiveswhere addedat0.268
lbs/ton. The frothercollectedthe most witharound16.4wt%collectedwhile oleicacidcollectedthe
leastwitharound5.18wt% collected. Howevernone of the flotationsmanagedtoconcentrate any
significantamountof gold. The resultsof the fire assaysshowedthatonlythe flotationwithnoadditive
had collectedanygoldbutthe goldthat wascollectedwasbelow the lowerlimitof the scale (limitof
scale is.00002 grams). Meaningthat the highestpossible grade wouldhave been0.018 t Oz/ton,this
beinglessthanthe initial grade of the tailings.
Initial Magnetic
concentrates
Unrepresentative
floatation (natural)
Unrepresentative
flotation(w/oleic acid)
Natural
flotation
Oleic Acid
flotation
Frother
flotation
Oleic+frother
flotation
Gravity
FireAssay
(t Oz/ton)
0.038 0.48 3.89 LOST >0.018 0 0 0 >0.018
Recovery
(%)
NA 88 NA NA NA 0 0 0 NA
13. 12 | P a g e
The last concentrationmethodwasgravityseparationperformedonawave table. Beingthatthe
particle sizes were sofine,the lowestsettingonthe table was used. 2004.6 grams of tailingswere
separatedand 91.2 grams were collectedwhichisaround4.55wt%. Unfortunatelythe resultswere not
promisingasagainthe goldfrom the fire assaywas below the lowerlimitof the scale makingitshighest
possible grade around0.018 t Oz/ton.
Flowsheetandimplications- Thiswas the laststepof the design project.Basedonthe resultsof the
concentrationmethodsaflowsheetyieldingthe greatestprofit wasconstructed aroundthe magnetic
concentrationmethodasthiswasthe onlymethodtoshow promisingresults. Usingthe estimated
valuesforcapital,horse power,costperton of concentrated,andvariousotherfigure eitherprovided
by the team’scontact at Barrick Goldalongwithotherfigurescalculatedfromresearch(seeAppendix F
for all economicinformation) aflowsheetwasconstructed. However,asitispossible toperformthe
concentrationeitherwetordrya flowsheetforbothmethodsmustbe done andshownbetweenthe
twowhichis more profitable bycalculatingbothflowsheet’sNPV andIRR. Flowsheetsforbothwetand
dry processingisshowninfigure 6below while the NPV andIRRforbothare shownintable 3.
Figure 6: Flowsheets for process. Top is wet and bottom is dry.
Table 3: NPV and IRR
NPV IRR
Wet process $390 million 33.1%
Dry process -$166 billion -5.27x1021
%
Tailing
dam
Dredger
Gold
recovered
AutoclaveMagnetic
separator
Acid
leach
New
tailings
dam
Tailings
Dredger
Gold
recovered
AutoclaveMagnetic
separator
Acid
leach
Tailings New
tailings
dam
Tailing
dam
Fluidbed
dryer
14. 13 | P a g e
Environmental Context:
One majorhurdle forthe designteamonce a concentrationmethodhasbeendecideduponwill be how
to fitthe processingplantintoBarrick’sexistingstructuresatthe Goldstrike site.Ideally,the
concentrationsite wouldbe asadjacentaspossible tothe damwhere the tailingsare currentlylocated.
Thispart of the designprojectwill cause the teamtoevaluate geographical limitationsof the site fora
newconcentrationfacility,andisbeyondthe scope of thisproject.Fromwhatthe designteamhas
decidedonfora flowsheet (Figure 6) thoughthe environmentaleffectshouldbe minimal.Justlooking
at the wetflowsheetthe onlyone newfacilitywill have tobe constructedtoaccommodate the new
process.
Anothermajorenvironmental issue wouldbe the effectof runoff from thisnew concentrationfacility.
The chemicalsinthe tailingsrightnoware alreadya hazard to the environmentandadditional
dangerouschemicals maybe needed toconcentrate the tailings.Thispotentiallycouldcreate arunoff
that couldbe exceedinglyharmfultothe environmental.Topreventanyenvironmentdamage the team
will have todetermine if the tailingsfromthe concentrationfacilitywill be able tomix withthe tailings
Barrick will alreadyhave comingoff theirmainprocess.If notthe teamwill have todetermine awayfor
Barrick to safelydisposeof thisrunoff withoutanydamage tothe environment.
Whenconsideringthe three concentrationmethodsthe designteamtestedtheyall have theirown
environmental effects.Firstfrothflotationprobablyhasthe worstenvironmental effectsof the three.
Froth flotationprocessoftenusessome type of chemical tocollectcertainelementsorcause frothing.
Froth flotationalsohasahighwater usage. Gravityseparationandmagneticseparationare muchmore
kindto the environment.Neitherrequire anychemical additionstothe elementswhichmakesthe
disposal of the tailingsverysimple.Inthe processthe designteamdecidedonusingawetmagnetic
separatorisfairlyenvironmental friendly.The processusesnoharmful chemicalstohelpconcentrate
the gold,and the concentrate will notrequire anyotherprocessesthatBarrickisnotalreadyconducting.
The major environmental take awayisthatthe processdesignedbythe teamisnotcreatingany
environmental threats.
Global and Societal Context:
On a global scale thisdesignprojectcouldhave huge implications.The mostnotable one couldbe the
change of goldprices.The price of gold, isdetermined bysupplyanddemand.If thisdesignprojectis
successful thenthere will be animmediateboosttothe supplyof goldwhichmaycause the price of gold
to drop. Anotherglobal implicationthisdesignprojectmayhave or influence isBarrickandothermine
companiescould mimicthe processingstrategydevelopedhereinandimplicate it attheirolderminesto
extractgoldfrom theirtailings.
15. 14 | P a g e
There are some societal effectstobe considered if thisdesignprojectissuccessful.Mineshave afinite
amountof ore,and when shutdown, canhave amajor economicblow onthe local community.If this
designprojectissuccessful, thenitcouldincrease the lifeof the Goldstrikemine,whichmeansthata
great employerforthe communitywill staylongercreatingmore jobs.
Conclusion:
Barrick initiallyapproachedthe designteamwiththe taskof analyzingthe economicfeasibilityof the
170 milliontonsof tailingsfromtheirGoldstrike mine,locatedinnorth-eastNevada.Barrickprovideda
sizable representativesample of approximately200 poundsof solidsina slurry,shippedina55 gallon
drum. Arsenic,mercuryandcyanide were listedonthe shipping label asbeinginthe sample prompting
a meetingwith Ms. JerilynRobertsof campusEnvironmental HealthandSafetytodiscussthe safe
handlingof the sample. The teamsetthe goal of havinginitial labresultscompletedbythe endof the
semesterwithconcentrationteststofollow inthe spring.
A smallerrepresentative sample wasacquiredbyfirstdecantingthe sample andthentakingacore using
a PVCpipe fromthe middle of the drum. This sample wasconedandquarteredtocreate smaller
samplesforvariousothertasks,these includedAAS, SEM,XRDand fire assays. The goal of these tasks
was to learnpropertiesof the tailings suchasmineralogyand goldore grade.
Mineralogywaslargelydeterminedthroughthe use of XRD whichindicatedhighpercentagesof silicates
as well ascalciumand magnesiumcarbonatesinthe formof dolomite inadditionto trace amountsof
othercompounds. Determinationof currentgoldore grade wassuccessful,utilizingbothAASandfire
assaymethods. AASresultscame backwithan ore grade of 0.036 t Oz/ton. Thisissupportedbythe fire
assayresultsof 0.038 t Oz/tonmeaningof the 170milliontonsof tailings about6.46 milliontroyounces
of goldispresent,thishavinga presentestimatedvalue of $8.4billion. However,inorderforthe
tailingstobe profitable toBarrick,the ore grade needstobe nearly doubled.
Magneticconcentrationproved tobe the most efficientmethodof beneficiatingthe tailingsincreasing
the grade to 0.48 t Oz/tonwithan 88% recovery. Howeverperformingthe processdryisnot
economically feasibleasmoneyspentdryingthe tailingsexceedanyprofitmade.Butwithexperimental
detailsprovidedbythe team’scontactat Barrick gold,itis possible toturna profitbymagnetically
separatingthe tailingwet,thoughthislowers the recoveryfrom88% to 26%, for thisprocess the
calculatedNPV andIRR forthisprocesswere about$390 millionand33% respectfully.
16. 15 | P a g e
Future Work:
The overall projectistechnicallyfinishedbutwiththe limitedtime the teamhad,some of the testing
was notdone as thoroughlyastheycouldhave been. The magneticseparationthatthe teamperformed
was done drybut performingitwetwasalsoa desiredtaskasthe team’scontactat barrack goldhad
done thisveryidea. The flotationsperformedshowedthatverylittlegoldwastrappedincarbonaceous
material butflotationscouldhave beendone toisolate the maghemite thatthe goldwastrappedinand
as thismethodiscommonlyusedtoconcentrate large amountsof low grade ores,like copperores,this
couldhave provide verypromisingresults. If more time wasgiventhese tooideaswouldhave been
exploredmore completely.
17. 16 | P a g e
References:
Abols,J. A. P.M Grady, and P.M Grady. "MaximizingGravity Recovery through the Application of MultipleGravity
Devices." (n.d.): n. pag. Gekkos.com. Web.
"About Us." Barrick Gold Corporation.N.p., n.d. Web. 05 Dec. 2014.
"Arsenic and Gold Mine Tailings FAQ." Arsenic in Historic Gold MineTailings(n.d.):n. pag. Arsenic and Gold Mine
Tailings FAQ.Nova Scotia.Web. 5 Dec. 2014.
Brennan, Ed. "History of Fire AssayingWhich Determines Precious Metal Content in Ores." History of Fire
Assaying Which Determines Precious Metal Content in Ores. Assay One. Web. 21 Nov. 2014.
<http://www.assayone.com/fire-assaying.html>.
Bugbee, Edward Everett. A Textbook of Fire Assaying,. 3d ed. New York: J. Wiley & Sons;, 1940. Print.
"Chemical SamplingInformation | Cyanide (as CN)." Chemical Sampling Information | Cyanide(as CN).N.p., n.d.
Web. 05 Dec. 2014.
"Cyanide Poisoning:Get Facts About Effects and Treatment."EMedicineHealth. N.p., n.d. Web. 05 Dec. 2014.
"Environmental Health and Medicine Education." Arsenic Toxicity Case Study: WhatAre the Standards
and Regulation for Arsenic Exposure?N.p., n.d. Web. 05 Dec. 2014.
Fastand Associates LLC. "Gold MiningProcess Development." Denver Mineral Engineers. N.p., n.d. Web.
14 Dec. 2014.
Gupta, A. Yan, D. S.. (2006). Mineral ProcessingDesign and Operation - An Introduction.Elsevier.3 March 2015
Han, Kenneth, and Yuhong Chen. "UsingFlotation to Separate Carbon Material fromCarlin Ore."(n.d.): n
. pag. OneMine.org. Web.
Honaker, R.Q. "A Fine Coal Circuitry Study UsingColumn Flotation and Gravity Separation." SciTech (1995):
n. pag. Osti.gov. Web.
Kellar,Jon. Met/EnvE 220 Mineral Processingand ResourceRecovery text part 15. Web. 9 Dec. 2014.
<http://www.hpcnet.org/upload/attachments/425768_20080331055541.pdf>.
"REGULATIONS AND ADVISORIES." 7. REGULATIONS AND ADVISORIES (n.d.): n. pag. Web. 5 Dec. 2014.
Abols,J. A. P.M Grady, and P.M Grady. "MaximizingGravity Recovery through the Application of
MultipleGravity Devices." (n.d.): n. pag. Gekkos.com. Web.
Fastand Associates LLC. "Gold MiningProcess Development." Denver Mineral Engineers. N.p., n.d. Web.
14 Dec. 2014.
Han, Kenneth, and Yuhong Chen. "UsingFlotation to Separate Carbon Material fromCarlin Ore."(n.d.):
n. pag. OneMine.org. Web.
Honaker, R.Q. "A Fine Coal Circuitry Study UsingColumn Flotation and Gravity
Separation." SciTech (1995): n. pag. Osti.gov. Web.
Richard A. Clarke. "Magnetic properties of materials".Info.ee.surrey.ac.uk. Retrieved January 15th,2015.
18. 17 | P a g e
Ramsaywok, P. "Influence of SalineWater on Electrostatic/High Tension Separation." Eighth International Heavy
Minerals Conference. 2011.263-269.Print.
Bittner, James. "TRIBOELECTRIC BELT SEPARATOR FOR BENEFICIATION OF FINE MINERALS." Metsco Proceedings
2013.Needham: Separation Technologies,LLC, 2013.1-10. Print.
Oberrauner, A. "NEW DEVELOPMENTS ON ELECTROSTATIC SEPARATION OF FINES." XXVI International Mineral
Processing Congress (IMPC) 2012 Proceedings. NEW DELHI: IMPC, 2012.Print.
"Electrostatic Separation."Electrostatic Separation. MINE-ENGINEER.com. Web. 30 Jan. 2015.
<http://mine-engineer.com/mining/minproc/elstat1.htm>.
Weiss,Norman L. "Section 6: Electrostatic and Magnetic Separation." SME Mineral Processing Handbook. Vol. 1.
New York, N.Y.: Society of MiningEngineers of the American Institute of Mining,Metallurgical,and
Petroleum Engineers, 1985. 6.2-6.10. Print.
Young, Courtney, and Gerald Luttrell. "Separation Technologies for Minerals,Coal,and Earth Resources." Google
Books. N.p., n.d. Web. 17 Apr. 2015.
19. 18 | P a g e
Appendix A
Figure 7: Colored image created using EDS showing areas of similar elemental composition.
Figure 8: Separate colors representing different elements filtered out of figure 7.
20. 19 | P a g e
Figure 9: Overall spectrum of figure 7 image.
Figure 10: Spectrum 7, BSE spectrum of a dolomite particle.
21. 20 | P a g e
Figure 11: Spectrum 12, BSE spectrum of an iron oxide particle.
Figure 12: Spectrum 10, BSE spectrum of an aluminum silicate particle.
22. 21 | P a g e
Figure 13: XRD scan of representative Barrick tailings
Table 4: Mineral names and formulas
Mineral Name Chemical Formula Mineral Name Chemical Formula
Quartz, silica SiO2 Sodium silicate Na2(SiO2)nO
Calcite Ca(CO3) Sodium carbonate Na2CO3
Gypsum CaSO4·2H2O Litharge, Lead(ii)Oxide PbO
Dolomite CaMg(CO3)2 Borax, Sodium borate Na2B4O7 · 10H2O
Hematite Fe2O3
Magnetite Fe3O4
Maghemite γ-Fe2O3
23. 22 | P a g e
Appendix B
Fire Assays
Thoughthe processof Fire Assayingismanycenturiesold,withoriginsthatcanbe tracedas for back to
the bible (Jeremiah6:27-30),it haschangedverylittle butisstill heldasthe mostaccurate methodfor
determiningthe amountof goldinan ore sample. Infact, thismethodof analysisisheldwithsuchhigh
regardthat it isconsideredthe “GoldStandard”of measuringgoldinoresand alloys. Toput itsimply
thismethodisoftenusedbyanyone whowishestodetermine the amountof goldina particulargold
baringsample. Because the BarrickGoldstrike teamof 2013-14’s entire designprojectrevolvesaround
findingouthowmuchgoldis ina particularsample,itisimportantformembersof the teamto learn
howto do thisanalysisina timelymanner. Sothe questionsof,“How doesitwork?How is it
performed?”,will be answered,withrespecttohow the teamperformedit,inthe followingpassages.
How does it work?
Fire Assayingcomesinmanyformsbutthe teamdecidedtogowiththe crucible assaymethodasthisis
the most commonform. The general theoryof thisprocessstartswiththe understandingthatthe
majorityof ores,forthe mostpart, cannotbe fusedbutif the ore’saverage particle size issufficiently
reducedandmixedwiththe rightratiosof appropriate reagents,the mixture will fuse ataneasily
obtainable temperature.Next,itisassumedthatthe ore particlesare incontact withone or more
particlesof litharge andreducingagent. Asthe temperature of the mix increasestoaround500o
C, the
litharge will begintobe reducedbythe carbon1
inthe mix and these reducedglobulesof leadcollectthe
goldand silverformthe surroundingparticlebyalloyingwiththem.
At about560o
C,the borax of the charge beginstomeltand to formfusible compoundswithsome of the
basesof the flux andore charge. Once thisbeginsthe slagbeginstoformrapidly. Forthe processto
workproperly,the temperature of the slagshouldremainlow enoughthatitsdensityisgreaterthan
lead, 10.66 grams percubic centimeter,andheldatthistemperature longenoughthatore particlesare
thoroughlydecomposedandeveryparticleof goldandsilverhasbeencollectedbyanearbysuspended
globule of lead. Once thishasoccurredthe temperature canbe raisedto a pointthat the slag’sdensity
islessthan thatof lead,allowingthe denserglobulesof leadtosettle atthe bottomforminga single
leadmass,calleda button.Itis presumedthatthe buttoncontainsnearlyall of the preciousmetal inthe
ore.
To separate the preciousmetalsfromthe lead,the buttonmustundergoaprocesscalledcupellation.
The processof cupellationisverysimple,afterthe leadbuttonhasbeenbrokenoff fromthe slagandall
of the slaghas beenremovedfromthe surface of the button,the buttonisplacedina furnace along
witha preheatedcupel. At327o
C the leadwill begintomeltandformleadoxides,mostof the lead
oxide isthenabsorbedbythe cupel,whilethe restare vaporized.Thisprocesswill leave behindasmall
beadmade of silverandgoldasthese twoelementsare notsoeasilyoxidized.
The last twostepsbefore ameasurable amountof goldcan be obtaininvolve partingthe silverfromthe
goldand annealingthe gold. Topart the silverfromthe gold,nitricacidisthe preferredchoice assilver
2 Carbon can come in many forms, for our project all-purposeflour was the carbon source
24. 23 | P a g e
iseasydigestedinthisacidwhile goldremainsstable. Once the silverhasbeenfullydissolvedandthe
remaininggoldflake hasbeenwasheddried,the final stepisannealingthe gold.Thisstepdoesnothing
more than make the goldeasiertohandle as the formthat it isinbefore annealingisverybrittle.
Withthisfinal goldflake the fire assayiscomplete andthe goldcan be weighedtodetermine the
equivalentTroyouncespertonbasedon equationtwobelow:
Eq(1)
Where: Mgold is the massof the goldfoundafterFire Assaying
Msample is the massof the ore thatwas usedinthe Fire Assay.
How is it performed?
Onlyone fire assayhas beenperformedasof thistime sothisprocedure is onlyrelevanttothe
measurementof the initial tailings.
To performan intelligentfire assaythe ore’smineralogymustbe understoodtoadegree,inthe team’s
case it’sthe tailing’smineralogythatmustbe understood. Because the ultimatesuccessof afire assay
dependsonthe formationof slag. Thisreferstothe part mentionedearlierthatthe particlesbecome
fusible ata relativelylowtemperatureaswell aspropertiesbasedonthe nature of the slag. A desirable
slagwill be neutral innature as opposedtoacidicor basic. To accomplishthisgoal itmustbe first
determine if the tailingswerecomposedof acidicorbasiccomponents,thenneutralizethemwithan
opposingmix. FromX-rayDiffraction(XRD) analysis,itwasfoundthatthe tailingscontainedalarge
portionof dolomite,whichisverybasicinnature. Knowingthis,E.Bugbee’s A TextbookforFire Assays
was referencedtofindastartingmix that wouldbe appropriate fora basicore. A startingmix would
usuallybe justthat,a mix youstart withand adjustuntil the resultsof the pourgave desiredresultslike
a large leadbutton. By chance howeverthe initial mix workedquitewell. The mix calledforthe
followingora 1 Assayton(30g ore sample):
Figure 14: Charge mix for basic ore.
Afteraddinga small beadof silvertothischarge,as the collectionof goldwiththe leadisbetterwith
silverpresent, the charge wasallowedtoheatto 800o
C for 45 minutes. The temperature wasthen
raisedto 1050o
C for an hour. The moltenassaywasthenpouredintoa cast iron mold,andallowedto
solidify. Once cooledthe buttonwas brokenoff withthe use of a hammer,the hammerwasthenused
to poundthe leadbuttonintoa cube so as to remove as muchslag as possible. Nextthis cube of lead
was placedincupel thatwas sittingina 925o
C furnace. 45-50 minuteswaslongenoughforthe leadto
be oxidizedandabsorbedbythe cupel. The silverbeadthatwasleftinthe cupel wasthenallowedto
cool before beingaddedtoa crucible of nitricacidfor parting. The acid was changedoutperiodically
29167 gold
sample
M
M
25. 24 | P a g e
until the liquidnolongerturnedyellowasa resultof the silver. The final flake of goldwasthenrinsed,
driedandannealed. The goldflake thatwasrecoveredfromthe original 154 grams hada massof about
0.0002 grams, whichwouldgive the initial tailingsagrade of 0.038 Troy ouncesperton. (See Appendix
A forall mineralsandcompoundsmentioned)
26. 25 | P a g e
Appendix C
Safety Guidelines
Abstract
In thisdesignprojectthere isaconcernabout the hazardousmaterial intailingsatthe Goldstrike mine.
Thisreportwill firstdiscussthe levelsof arsenic,mercury,andcyanide andhow the levelsof these
tailingscompare toOSHA’sacceptable levels. Secondly,thisreportwill coverthose concernsof these
hazardousmaterial andpossible waysthatsomeonecouldgetthese hazardouschemicalsintotheir
system.
Introduction
Safetyisan importantissue intoday’sworkplace.If youneedproof youneed notlookfartherthana
company’swebsite.Everycompanynowadays hasa safetysectionwhere theypreachtheir
commitmenttosafetyandhowtheyare takingcare of theiremployee’s.Forexample,here iswhat
Barrick itself saidonitswebsite:“Usingbothqualitativeandquantitative methods,risks,suchasthose
impactingthe health,safetyandsecurityof ouremployees,ourneighboringcommunitiesandthe
environmentinwhichwe operate,aswell asouroperational andfinancialperformance are assessed
and appropriate solutionsimplemented(1).”Soforthisdesignprojecttosucceedeffortsneedtobe
made to limitanysafetyincidents.Thatiswhythisreporton the potential risksandhow to avoidthose
riskswhenworkingwiththe tailingsfromthe Goldstrike mine.
Arsenic
Arsenicisa notoriouslypoisonousnaturallyoccurringelement.Arsenicusuallyoccursinthe
environmentinalloyswithsulfurandmetalsandasa pure elemental crystal.Groundwater
contaminationbyarsenicisa majorproblemthat affectsmillionsof peoplearoundthe world(3).
In the Goldstrike tailingsarsenichasthe highestconcentrationof the three hazardouschemicalspresent
at approximately800ppm.The arsenicwouldnothave beenaddedduringthe mineral processingsoit
can be assumedthatthe ore source at Goldstrike hassome arsenicinthe ore.Thismakessense
consideringarseniciscommonwithgolddepositcontainingsulfideminerals.
OSHA has specificguidelinesonwhatisanacceptable amountof arsenicinthe work place.Inthe
general workplace OSHA says,“The permissible exposure limitforarsenicisnogreaterthan 10
microgramsof inorganicarsenicpercubicmeterof air,averagedoverany 8 hour periodfora 40 hour
workweek(2).”The sample of tailingscame in a 55 gallondrumwhichisapproximately0.21m3
.
Calculatingitoutthere couldpotentiallybe 10.5 microgramsina lab room, but consideringa
considerable amountof arsenicwasremovedduringdrainingthe slurry,andthe designteamisnot
workingwith the whole tailingsatone time.
There are some concernswhenworkingwitharsenicina labsetting.Arsenicisonlydangeroustoa
personwhenitisingested.Inmostcasesof poisoningthe arsenichasfounditswayintothe ground
27. 26 | P a g e
waterand poisonedthe people whowere drinkingfromthatwatersource (3). Ina labsettingsomeone
workingwitharsenicstill hastobe verycareful.Whenworkingwitharsenicitisimportanttowear
gloves,longsleeves,pants,longpants,andabreathingmask.The breathingmaskwill stopanydust
particlesof arsenicfrombeingingested.If someone doesgetthe slurryontheirskinthe arsenicwill not
be a problem,butitisimportantto washthe area thoroughlybecause if the arsenicgetsonyourhands
it can laterbe transferredtofoodwhenyouare eating.
Mercury
Mercury isanothernatural occurring elementlike arsenicthatcan be justas dangerous.Mercuryis used
withcyanide ingoldprocessingtoseparate the goldfromthe otherelementsthatare in the ore.
Mercury poisoninghappenedoftenbefore people understoodthe dangersof it.Incurrenttimesmost
mercurypoisoningoccursmostlybecause of mercuryinfish.
Mercury has one of the smallestconcentrationinthe tailingsat4 ppm. Mercury wasusedfor gold
processinginthe earlyyearsof mineral processing,buttodayall mercuryintailingswouldcome from
the ore.The concentrationisprobablyaslow as itis because Barrickwouldhave tosafelydispose of so
much of theirmercuryto avoidrun off of dangerouschemicalsintothe environment.
Like arsenicOSHA has standardsforwhat isan acceptable Mercuryis dangeroustoingest,butunlike
arsenicitcan be absorbedthroughthe skin.OSHA onlyallowsaconcentrationof 0.1 mg/m3
(4).
Consideringthe areathe teamwill be workinginisaround16 m3
there isa potential riskof 0.25 mg/m3
inthe lab.The actual concentrationof Hg inthe air will be lowerthanthat.The level shouldnotbe in
the dangerzone,but toavoidany riskof breathing,ingesting,orabsorptionthe teamwill follow the
same skinprotectionasfor arsenicanda face mask.
Cyanide
Cyanide isa compoundthatlike the othertwoelementsdiscussedinthisreportishazardousand
extremelydangerousif notproperlyhandled.Like mercury,cyanide isusedformineral processing
specificallypreciousmetalslike goldandsilver.Cyanide iscombinedwitharichore source andthe
cyanide anionsattackthe ore creatinga pregnantheapleach.
Cyanide’sconcentrationcouldnotbe determinedexactly,but the concentrationislessthan20 ppm.
While cyanide poisoningcanoccur throughinhalationitwouldtake alarge amountof cyanide tofeel
any immediateeffects.Cyanide isanatural occurringchemical intobacco socigarettesliberate cyanide
duringsmoking(6).The mainriskfor cyanide isabsorbingtoomuchof the compoundthroughyourskin,
or throughinhalationinthe gaseousform.
OSHA doesnot have any standardsforan air mediumforcyanide,buttheydohave an allowable limit
for skincontact.The allowablelimitforcyanide is5 mg/m3
(5).Assumingthe concentrationof cyanide is
20 ppm ina 0.21 m3
containerthenthe concentrationwouldbe 95.2 mg/m3
.So withthatpossible
concentrationglovesandproperclothingatall timesisamust whenhandlingthe tailings.
28. 27 | P a g e
Conclusion
Withsafetybeingsucha major concernintoday’ssocietyitisimportantto do everythingtoreduce risk
inthe workplace.Inthisreport the three hazardouschemicalsinthe tailingswere examinedand
explainedhowtheycanaffecta person.The OSHA safetystandardswere consideredalsoandexamined
if the team wouldbe at riskof any of these materials.The guidelinesforthose three materialswere laid.
The basics of the safetyguidelinesare toweargloves,appropriateclothing,andabreathingface mask.If
these guidelinesinplace the designteamcanruntestssafelyworkingwiththe tailingswithoutworryof
personal safety.
29. 28 | P a g e
Appendix D
Mineralogy of Goldstrike Tailings
(see Appendix A for relevant figures)
Introduction
The mineralogical makeup of the tailings body is extremely important information to
have for this project. Depending on what makes up the tailings largely effects the specific
concentration techniques used and as well as the parameters of these techniques. The tests
that we performed included using a scanning electron microscope (SEM), and x-ray diffraction
(XRD). The group has samples prepared for use with micro-focused x-ray computed
tomography (MXCT) and is expected to get results early next semester. Most of what has been
found thus far is purely qualitative.
SEM
SEM was the first test the group performed on the tailings. A small amount was dried and then
mounted on carbon tape to be examined. SEM uses beamed electrons to gain information
about a sample’s topography. It also has the ability to use energy-dispersive x-ray spectroscopy
(EDS) to create colored images showing particles of similar elemental composition (figure 7).
The image can then be filtered by color layer for ease of viewing. As can be seen in figure 8 and
9, the main elements detected were aluminum, calcium, iron, magnesium, oxygen, potassium,
silicon and sulfur. Carbon is skewed due to the carbon tape the sample is mounted on. The
carbon tape also nulls the Wt. % measurements given by the spectrums. One thing to note is
the two distinct iron particles as well as the large presence of particles with both calciumand
magnesium. The EDS scans also indicated fair amounts of gypsum and silicates. As can be seen
on figure 3, individual point scans were taken and used to create elemental spectrums (Figures
10-12) using back-scattered electrons (BSE). Spectrums 8, 9 and 11 all hit the carbon tape
resulting in a skewed spectrum and were not included on this report. Spectrum 7 was placed
one of the particles that was high in calcium, magnesium and oxygen, most likely a dolomite
particle (CaMg(CO3)2). Spectrum 10 had high amounts of silicon, aluminum and oxygen
suggesting an aluminum silicate (Al2SiO5) particle. Spectrum 12 was placed on the particle that
scanned high in iron. SEM is great for qualitative elemental data but fails to provide a true
quantitative mineralogical breakdown. The second test we performed for mineralogy is an XRD
scan.
30. 29 | P a g e
XRD
XRD uses similar technology to SEM but instead of electrons being used, x-rays are used.
Beams of x-rays are shot at the sample and will diffract in different directions. By measuring
the angles of diffractions as well as the intensities, an overall spectrum is obtained and minerals
can be identified. An initial grab sample was taken before the tailings could be divided into
representative parts. It indicated that quartz was in the largest concentration followed by
gypsum, mica and dolomite. The results of the XRD coincide with what was found with the
SEM. Later in the semester, when several smaller representative samples were prepared,
another XRD scan was performed (figure 13). Dolomite appeared in the largest quantity
followed again by quartz and calcite. A new mineral also appeared in this scan, pseudobrookite
(Fe2TiO3). Curiously, no iron-oxide particles such as magnetite or hematite were detected,
raising questions about the magnetism of the tailings.
Challenges
One of the group’s current concerns that eludes the project is why the tailings are so magnetic.
An initial magnetic separation test returned almost 90% weight of magnetic concentrates.
According to Barrick, only 3-5% Wt. % of the tailings should be magnetic. Using SEM the group
was able to observe particles that contained iron-oxide particles. These iron-oxide particles did
not show up in XRD scans. A theory to this discrepancy is that the iron minerals are amorphous.
Due to the lack of a consist shape, XRD is not reporting them in high concentrations. The use of
MXCT early next semester will hopefully answer these questions about the iron in the tailings.
This will be useful as magnetic separation could be an effective concentration process.
Conclusion
The mineralogy of the tailings is invaluable data to have when designing a concentration
flowchart. Using technologies such as SEM and XRD, as well as MXCT in the future, the group
has identified what makes up the majority of the sample body. Most of the data collected thus
far has been qualitative in nature. The mineral in the highest concentration is quartz followed
by dolomite. Other silicates, carbonates and sulfides make up most of the rest with iron based
minerals supposedly in low concentrations. Samples have been prepared for use with MXCT
and are scheduled to be run early next semester.
31. 30 | P a g e
Appendix E
Processing Gold Tailings
Introduction
The tailings of any mineral processing will retain some amount of desired material, however the
amount left over does not hold enough value to justify further recovery, but if it the value of
the material increases or newer technology allows for easier recovery, then further processing
may be justified. However, the tailings will have a majority of undesired material, and any gold
that is left, will be sporadically dispersed throughout the ore, or trapped in another material.
For this reason, it becomes necessary to concentrate the desired material, reducing time and
money wasted on the portion of the tailings containing little to no gold. There are many ways
to concentrate ore bodies and all of them take advantage of the ores physical and chemical
characteristics, this is generally known as beneficiation. For this design project, the group will
focus on concentrating gold by employing the most available and commercially used methods,
gravity separation, froth flotation, and magnetic separation.
Gravity Separation
The first process used to beneficiate the gold tailings that will be considered, is gravity or
density separation. Gravity separation is an environmentally friendly process, which utilizes
simple equipment with few moving parts. (Abols) Throughout the history of mineral processing,
many different types of gravity separation devices have been utilized, but the one the team will
use is a wave table. Gravity concentration processes rely on the principal that gold contained
within an ore body is higher in specific gravity than the material it is trapped in. Elemental gold
has a specific gravity of 19.3, and typical ore has a specific gravity of about 2.6. (Fast)
Movement is created by gravity concentration devices between the gold and host rock particles
so that the heavy particles are separated from the lighter particles. On a wave table, particles
will be fed onto the machine along with a stream of water. The bed of the table will begin to
shake resulting in two events, the formation of wave in the water and the gradual forward
movements of the particles towards a trough at the end of the table. While the particles are in
contact with the surface of the table, the shaking will cause them to move forward. When a
wave passes over them, less dense particles will be moved backwards while denser material are
either not moved, or move very little resulting in a separation of the particles by their
respective densities. See Figure 1 in report. Ideally gold and gold bearing material will move
into the trough of the table but the team will likely collect all of the material closest to the top
for testing. One disadvantage of gravity separation is that ultrafine clay particles are not easily
rejected. (Honaker)
32. 31 | P a g e
Froth Floatation
The flotation process consists of producing a mineral concentrate through the use of chemical
conditioning agents followed by intense agitation and air sparging of the agitated ore slurry to
produce a mineral rich foam concentrate. Specific chemicals are added to either float specific
minerals or to depress the flotation of other minerals. Several stages of processing are general
involved with rough bulk flotation products being subjected to additional flotation steps to
increase product purity. Generally, the flotation process does not float free gold particles, but it
is very effective when the gold is associated with sulfide minerals. Highly oxidized ores usually
do not respond well to the process. An advantage of the flotation process is that the gold is
usually liberated at a coarse particle size, near 28 mesh, reducing the grinding cost. Also, the
chemical reagents are generally not toxic allowing for easy disposal. (Fast)
A majority of the gold within the tailings received from Barrick are trapped in iron oxide and
carbonaceous material. The tailings come from Barrick’s Goldstrike mine which is located on the
Carlin Trend in Nevada. With this knowledge, a specialized process can be used with a specific
collector and dispersing agent. Dr. Kenneth Han and Dr. Yuhong Chen, performed a study on how
to remove the carbonaceous material from Carlin ore. The results of this investigation showed
that it is possible to use froth flotation, and that a Philips aromatic oil served to be the best
collector. One of the reasons for poor flotation recovery was due to oxidation of the
carbonaceous material. Therefore, flotation recovery was significantly improved by subjecting
the oxidized ore to reduction before flotation. Sodium silicate proved to be an effective
dispersing reagent for the Carlin gold ore. The effect of pH on flotation was insignificant. The
flotation response at room temperature was as good as any other temperature between 15° and
60° C. (Han)
This study will prove to be very beneficial to the team moving forward. With the knowledge of
the specific collector and dispersing agent, the floatation of the tailings can be greatly improved.
Magnetic Separation
With the majority of the gold being trapped in some form of iron oxide, magnetic separation
will most likely, prove to be very useful. The concept of magnetic separation is a very simple
process. A feed stream is passed through magnetic field, the magnetic attraction force between
the magnet and magnetic particles will then pull these particles, separating them from the rest
of the stream. See Figure 3 in report for illustration. Additionally because materials are either
very magnetic (ferromagnetic), slightly magnetic (paramagnetic) or non-magnetic
(diamagnetic), a feed stream can be effectively beneficiated by either adjusting the strength of
the magnetic field, the speed at which the particles pass through the magnetic field or both.
However information about the tailings suggested that the entire mass was only composed of
about 3-5% iron oxides, so the results from the team’s attempt should be near this range.
33. 32 | P a g e
Conclusion
While there are many ways of beneficiating the gold, these three processes are most readily
available. Each method has its own advantages and disadvantages. Using a combination of
these complimentary processes can improve the overall recovery of gold from the tailings. Each
method works best in certain situations and under certain conditions. With the right knowledge
of the tailings mineralogy and chemical composition, the recovery can be maximized.
34. 33 | P a g e
Appendix F
Table 5: Economic details
discountrate (I) 0.05
numberof years 10.78
$/kWh 0.06
operates80% of year 0.8
Tailings(tonage/day) 54,000
Concentrateswt%/100 0.05
kW/hp 0.75
personel 8
ore grade gold(tOz/ton) wet 0.2
goldrecovery%/100 0.75
goldprice $/troy 1,300
Facitity'shp 1,500
Dredgerhp 8,500
autoclave & acid$ /ton 90
personel salaraies/year 150,000
Maintenance %total cost/100 0.05
AC powerkWbasedon square footage 8,900
lightingpowerconsumption 120,000
square footage 2,000,000
dryerhp 5
Dryer PowerBTU 1E+12
BTU/ton coal 24,000,000
$/ton coal 70
ore grade gold(tOz/ton) dry 0.48
35. 34 | P a g e
Figure 15: Spreadsheet for wet process
Figure 16: Spreadsheet for dry process
Initial Costs $ Annual costs $ Annual prophits
Facity construction 210000000 Autoclave and acid 70956000 Gold 153738000
Dredger 2000000 Facitity's hp 470327.8233
personel salaries 1200000
Dredger hp 2660958.048
maintenance 983181.1769
Lighting 117761.28
AC 3751392.505
total 212000000 80139620.83 153738000
Wet process
NPV ($390,107,433.16) $0.00
IRR 0.331286996
Initial Costs $ Annual costs $ Annual prophits
Facity construction 210000000 Autoclave and acid 70956000 Gold 307476000
Dredger 2000000 Facitity's hp 470327.8233
Fluid bed dryer 21875000 personel salaries 1200000
Dredger hp 2660958.048
maintenance 1084629.706
Lighting 117761.28
AC 3751392.505
Dryer hp 39193.98527
Dryer power 20440000000
Total 233875000 20520280263 307476000
Dry process
NPV -$165,594,577,635.91 #NUM!
IRR -5.26879E+23
36. 35 | P a g e
Appendix G
Electrostatic Separation
Accordingto the SME Mineral ProcessingHandbook,electrostaticseparationisdefinedasthe selective
sortingof solidspeciesbymeansof utilizingforcesactingonchargedor polarizedbodiesinanelectric
field. Thisdefinition,atface value,sounds alotlike magneticseparation. Infact if someone were to
watch bothof these typesof separatorsinactionhe maybelieve theywere the same. Despitethe visual
similaritiesthese processingdevicesmaysometimesshare,the onlyreal similaritytheypossessisthat
theybothtake advantage of electrons. Whilemagneticseparationusesthe differingmagnetic
propertiescreatedbythe numberof spinningunpairedelectronsalreadypresentinthe material to
cause a separation,electrostaticseparationusesthe diffingelectrical chargescreatedfromthe number
of and/orpositionof electronsonamaterial tocause separation. Howeversince the forcescreated
fromthe attractionof opposingelectrical chargesare normallymuchweakerthanthose producedby
magnetismthe effectiveparticle size forelectrostaticseparationismuchsmallerthanmagnetic
separation2
soitis notnormallyusedasa primaryseparationmethodbutratherasa recoverymethod
followingmostmineral processingandendproductproducingsteps. Inthe followingsectionsthe
conceptsbehindhowelectrostaticseparationworksalongwithtypical designsandapplicationswillbe
discussedingreaterdetail.
Theory BehindElectrostatic SeparationandBasic Components
The primaryforce usedinelectrostaticseparationsisbasedonCoulomb’sLaw whichstatesthat,
1 2
2
4
o
o
q q
F r
r
ur r
EQ 2
where:q1 and q2 are magnitude of the twocharges,in coulombs.
r the distance betweenthe twocharges,inmeters.
or
r
isa unitvectoralong r
r
.
o is knownasthe permittivityof free space withavalue of 8.85 X 10-12
farads/meter.
F
ur
is expressedinNewtons.
Since the force betweentwochargedbodiesdependontheirmagnitude,itbecomesconvenientto
define anelectricfieldintensity,E
ur
withunitsof volt/meters,asthe force perunitcharge exertedbyone
charge onanotherand withEQ 2 thiscan be expressedas,
1
2
2 4
o
o
q rF
E
q r
rur
ur
EQ 3
Withthisequationitispossible todefineaunitof work perunitcharge involvedinmovingone movinga
charge fromone pointinan electricfieldtoanother. Thisunitof workperunitcharge inknownas the
2 Effective particlesizefor electrostatic separation is 200-40 microns,magnetic separation istypically used for
particlesizes of 152-.5 mm or greater.
37. 36 | P a g e
difference inelectrostaticpotentialandissymbolizedby V andexpressedaccordingtothe following
equation,
V E dr
ur r
EQ 4
where the negative signmeanthe V isincreasingwhenworkisdone onthe charge. For a conductive
material EQ 4 can be expressedas,
2
1
2
0 0 1 2
1 1
4 4
r
r
q dr q
V
r r r
EQ 5
But for nonconductinganddielectricmaterialEQ5 can be simplifiedtoeitherof the followingequations
dependingonwhatconditionisconsidered.
04
q
V
r
EQ 6
0
1
4
rq dr
V
r
EQ 7
Where EQ 6 isvalida reference pointisconsideredinfinitelyfarawayandEQ 7 isvalidif charge q is due
to distribution—thatistoa charge rq (C/m3
).
Nowthat the theorybehindelectrostaticseparationhasbeenexplainedlet’sfocusonthe basic
componentsof the methodof separation. All electrostaticseparationsystemshave atleastfourbasic
components,those beingacharging-dischargingmechanism, anexternalelectrical field,anonelectrical
particle trajectoryregulatingdevice andafeeding/productcollectionsystem.
A charging-dischargingmechanism
Perhapsthe mostimportant component,the mechanismbywhichthisbeneficiationmethodcharges
and/ordischargesitsparticleswill resultinone of the followingcategoriesof charge distribution:
1. Particlesof twodifferentspeciesenteranelectricfieldinaseparatingzone bearinganelectric
charge of opposite sign.
2. Particlesof twodifferentspeciesenteraseparatingzone where onlyone type of particle bears
a significantelectrical charge.
3. Particlesenterthe separatingzone,suchthatparticlesof differentspeciesbearthe same sign
charge,but the magnitudesof the electricchargesare significantlydifferent.
4. Particlesof differentspeciesenterthe separatingzone withsignificantlydifferentdipole
moments.
An external electrical field
For thisseparationmethodtoevenbe possible anelectricfieldisrequired. The electrical potentialsof
these fieldsvarygreatlybuttypicallyrange from10 to 100kV andare normallyunidirectional.The fields
themselvesrange from400kV/mto the breakdownstrengthof airwhichisaround3000kV/m.
A nonelectrical particle trajectory regulatingdevice
The physical separationof twodifferenttypesof particlesisalwaysmade byadjustingthe forcesand
time overwhichthe forcesact on a particle,suchthat at a predeterminedtime the trajectoriesof the
38. 37 | P a g e
twoparticle typeswill have differenttrajectories. Howeverinadditiontoelectrical forcesitmaybe
advantageoustoutilize otherforcessuchasgravity,andfrictiontoaid inthe selective sorting.
A feeding/productcollection system
Thisis a feature commontoall separators.A separatormusthave some meansof conveyingthe feed
material tothe separationzone inadditiontoa methodof cuttingthe streamof particlesata desired
pointso thatdifferentparticletypescanbe collectedandconveyedtoa followingseparationdevice or
productstorage tank.
Typical Designs andApplications
As mentionedbeforethe charginganddischargingmechanismispossiblythe mostimportant
componentof an electrostaticseparatorasthiswill dictate the machinesoverall designandapplication.
There are manywaysto electricallycharge particlesforseparation,butonlychargingby contactand
frictional electrification,ion or electron bombardment andconductiveinduction are usedcommercially.
Howeveritshouldbe made clearnowthat these mechanismsare notmutuallyelusive foreachdesign,
infact it’smore thanlikelythatatleasttwo of these mechanismsare presentatanygiventime foreach
separationdesign,the distinctioncomesfromwhichchargingmethoddominates.
Contact electrification
Chargingby frictionand/orcontactelectrificationisthe mostfrequentlyusedmechanismforseparating
twospeciesof dielectricmaterial.Some of the typical examplesbeingfeldsparfromquartz,quartzfrom
apatite andhalite fromsylvite.Butthisis notto sayconductive material wontcharge thisway,because
theywill,it’sjustthatsince theyare conductive itismore likelythatthese particlewillrelinquishtheir
charge before theyare separatedfromthe feedstreamnegativelyeffectingthe results.
The theorybehindexactlyhowchargingaparticle bycontact isverycomplex andis not fully
understood,butconceptuallyit’srelativelyeasytoexplain. If yourememberbacktowhenyouwere a
childandyou wouldruban inflatedballoonagainstyourheadthenlifteditawaytosee your hairnow
standingonendtryingto followthe balloon,wellthat’sbasicallywhatishappeningbetweenthe
particlesof thischargingmechanism.Yousee some dielectricparticleswill more readilygive uptheir
surface electronstoanotherdielectricparticle once contacthasbeenmade leadingthemnow to
become positivelyandnegativelycharged. Thoughthese particle are now oppositelychargedthe
coulombicforce betweenisstill weakenoughthatmomentumfromthe initiallycollisionwill separate
themand/orthe coulombicforcesbetweenthe particlesandthe electrical fieldgivenoff bythe
electrodeswill attractthe oppositelychargedparticle whilesimultaneouslyrepellingthe likecharged
particle leadingtothe desiredseparation.
A typical designisthe Free-Fall separatorasseeninfigure 16 below.
39. 38 | P a g e
Figure 3: Free-Fall Separator
As seenfromthe figure,aFree-Fall separatorconsistsof ahopperanda vibratingfeederwheremuchof
the change of charge throughcontact will occur.The feedwill thenemptyintoachute thatleadsto an
emptycolumnsurroundedbychargedelectrodes. While gravityisthe force movingthe particles
throughthe machine the coulombicforcesfromthe chargedelectrodescause the separationbypulling
the oppositelychargedparticleduringtheirfall.Howeversince the effectivenessof separationcanvary
drasticallydependingonmaterial of feed,particle sizes,temperatureandpressure,aFree-Fall separator
isoftencustomizedaccordingtothese variablesbychangingthe feedrate,electricfieldintensityand/or
lengthof fall betweenthe electrodes.
Charging by corona
Chargingby ionor electronbombardmentisoftendone withacoronadischarge. These typesof
separatorsare bestsuitedfororeswitha mixture of conductive andinsulatingmaterial. Common
applicationincludeseparatingrutileandilmenite frombeachsandbutanothercommonuse isto
recovervaluable finesfromvariousmineral processingandfabricationplantsthatescape intothe air.
To charge bycorona solidsmustpassthrougha corona discharge froma wire electrode toagrounded
surface. A corona discharge occurswhenthe electrical potential of anelectrode israisedtothe point
that the electrical fieldinthe immediate areaexceedsthe electrical breakdownstrengthof air,this
internscreateschargedionswhere half are repelledbythe electrode andbombardthe feedparticles
thuscharging them.The mosttypical designforthistype of electrostaticseparationiselectrodynamic
separatoror as it ismore commonlyknownasthe High-Tensionseparatorwhichcanbe seeninFigure
17 below.
40. 39 | P a g e
Figure 4: High-tension separator.
Diagram of separation in progress is also shown
How thistype of machine causesa separationconceptuallyspeakingismoderatelysimple. Thismachine
takesadvantage of three forcesgravity,centripetalandcoulombic.The particle are feedontoaroller
that iselectricallygroundedwheretheyare chargedbya corona. The conductive material quickly
transfertheirelectrical charge tothe groundedrollerandwithnocoulombicforce tokeepingitattached
to the rolleristhrownoff ina predictable trajectorywhere itiscollected. The nonconductive material
will give theircharge tothe groundedrollertoobutat a much slowerrate meaningthese particle will
remainattachedto the rollerwithcolumbicforce until the charge decreasesenoughforgravityand
centripetal forcesbreakthe connectionorthe particlesare brushoff at the backof the roller.These
particle alsofollowasomewhatpredictabletrajectorysotheyare collectaccordingly. The collectionbin
that isdesignatedtocollectbothnonconductive andsmallerconductive material will be processedagain
at a differentrate toimprove separation.
Charging by conduction
Whenseparationisdesiredforamixture of conductive anddielectricmaterialschargingbyconduction
isoftenpreferred. Thismethodistypical usedasafollowingseparationstepforthe conductivematerial
collectedbythe coronamethodwhile processingbeachsand.
As the name suggestmaterials are chargedbyconductionmeaningthatthe particle mustcome in
contact witha chargedsurface.Thisis the beginningof the separationprocessusingthismethod. As
the particlesare chargedtheyare simultaneouslypassingthroughanelectricfield. The conductive
material will charge almostinstantlyandthiswhenthe coulombicforcesof the electrical fieldtake over
causingthe separation. The dielectricparticle will charge byconductionbutat a much slowerrate so
before theyare sufficientlychargedtheycome outof contact withthe conductingsurface andare thusly
unaffectedbythe electricfield. Twoof the more common designsforthismethodare Roll-type
separatorand the Tobogganseparatorseeninfigure 18 below.
41. 40 | P a g e
a) b)
Figure 5: a) Roll-type separator. b) Toboggan separator
For the Roll-type separatorthe conductingsurface isthe rollersothisdesigntake advantage of gravity,
centripetal andcoulombicforcestocause a separation,while the Toboggandesignhasaconducting
plate initscute where the particle descend meaningthatonlygravityandcoulombicforcesare usedto
cause a separation. Asyoucan image withthese designalotof chargingby contact ispossible sothe
actual chargingmechanismiscomplex anddifficulttopredictbutsince the conductionwasthe only
intendedmechanismandthe predominantone these designsare notconsideredacontact
electrificationmethod.
42. 41 | P a g e
Appendix H
Gravity Seperation
INTRODUCTION
Gravityseparationisa commonextractive technique forfreeinggoldfromitsgangue.Whenconsidering
gravityseparationyouhave tofigure outthe specificgravityof the desiredelementandthe surrounding
gangue.Gravityseparationwasone of the possible extractive techniquesthatcouldbe usedtoprocess
the tailingsatthe Goldstrike Dam.To determine if the goldinthe tailingscanbe recoveredusinggravity
separationthe teamhasto determine concentrationcriterionusingthe specificgravityof the goldand
the gangue.Thispaperwill alsocoversome of the historyof gravityseparation,the benefitsand
disadvantagesof gravityseparationconcentration,andcommonwaystouse gravityseparationfora
large scale miningoperation.
HISTORY
Gravityseparationisone of the oldestformsof ore concentrations.The ancientEgyptiansdepicted
gravityseparationin3,000 BC. Theynoticedhow weatheringcausedbywaterthatcreatedalluvial
depositsof metal andgemstones.Excavationshave alsounveiledthatmultiple ancientcivilizationshad
miningoperationsusinggravityseparation(Guapta).Anothercommontype of gravityseparationisgold
panning.Panningwasasimple techniquethatdrove manysettlerstoCaliforniainthe 1849 goldrush.
Panningobviouslyisnotusedinlarge scale miningoperationswithmore effective andchemical
techniquesbecomingmore available.Gravityseparationhasobviouslyhadamajor effectonhow the
worldtodayhas beenshapedbypreviousgenerations.
BENEFITSAND DISADVANTAGES
Gravityseparationisa concentrationmethodwithmanybenefitsanddisadvantages.Inideal ore
sourcesgravityseparationisthe bestmethod.Whenanore source containsfree goldparticleswitha
gangue that has a lowerspecificgravitythangold.However,manyof these ore sourceshave been
depletedbelow economicfeasiblelevels.There are betterrecoverymethodslike goldleaching,but
these concentrationmethodsuse harmful chemicals.Dealingwiththese harmful chemicalslikecyanide
are hard andexpensivetogetridof them.Gravityseparationonthe otherhanddoesnot needany
chemicalsinorderto separate goldfromthe gangue.
LARGE SCALE OPERATIONS
43. 42 | P a g e
There have beenrecentdevelopmentsingravityseparationtomake ita more feasible forlarge scale
miningoperations.One of these advancementsisthe KelseyCentrifugal Jig(KCJ).KCJcombinesjigging
technologywithcentrifugal forcesthatgreatlyimprovesongravityseparation.The KCJusesarotating
wedge wire screenwithabedof raggingmaterial onthe screen.The range of feedfora KCJ is10 to 500
micrometerswithdifferentmineralslike gold,tin,chrome,andiron(Luttrell,Young).Another
developmentwasthe KnelsonBatchCentrifugalConcentrator(KBCC).The KBCCisan outwardlyinclined,
walls-spinningcentrifugebowl withriffles.The spinningbowl spinsthe feedslurryandthenseparates
and recoversminerals.The KBCCisable toseparate 10 to 10,000 tonnesperhourdependingonthe
feed.The KBCChas beenusedtoseparate gold,platinum,andgold-copperores(Luttrell,Young).With
these andmanyother advancementsgravityseparationhascome alongway fromgoldpanningand
offersthe optionforlarge scale miningoperations.
DETERMING FEASABILITYOFGRAVITY SEPERATION
In orderto determine if gravityseparationisapossible concentrationmethodthe designteamneedsto
take a fewthingsintoconsideration.The firstthingtoconsideristhe concentrationcriterion.The
calculationforconcentrationcriterion(CC) isshownbelow inFigure 19.Giventhe gangue of density
2650 kg/m3
goldhas a CC of 10.3 and an ironore like hematitehasaCC of 2.5 (Guapta).However,the
goldmineral inthe tailingsare coveredinanironoxide knownasmaghemite.Sogiventhatfactitis
unlikelythatthe goldmineral wouldhave ahighenoughCCthatwouldallow forgravityseparationand
withan ironoxide combinedwiththe golditismuchlikelierthatmagneticseparationwill be amore
successful concentrationmethod.
Figure 19: Calculation for Concentration Criterion (Guapta)
To testif gravityseparationwaspossible the teamusedthe wave table inthe MIBuildingatSchool of
Mineson a sample of tailingstosee howmuchgoldcouldbe recovered.ShowninFigure 20 isa
representationof howawave table usesthe specificgravitytoseparate goldfromthe gangue.Asthe
wave table shakesbackand forththe table movesthe goldforwardwhile the watermovesthe gangue
back creatinga separationof the two.Whentestingthe teamwasable to recover4.55 wt%of the
testedsample of tailings.Howeveronfurtheranalysisusingfire assaythe goldamountwasbelowthe
lowerlimitsof the test.
44. 43 | P a g e
Figure 60: Representation of wave table. Yellow dots show gold and black shows gangue movement
CONCLUSION
Gravityseparationisa verysimple concentrationmethod,butunderthe rightcircumstancescouldbe
veryeffective.The technique of usingthe specificgravityof a mineral toconcentrate ithasbeenused
for hundredsof yearsandhas done a lotto shape the worldwe know today.Overthe years
advancementshave beenmade inthe conceptof gravityseparationwhichhasallowedaccesstomore
and more mineral sources.Throughsimplethinkingandcommontestproceduresthe designteamhas
shownthat gravityseparationtechnique wouldbe difficulttouse forconcentratingthe goldtailings.
Therefore,ithasbeendecidedthatdespite possible benefitsof gravityseparation,itwouldnotbe the
bestconcentrationmethod.
45. 44 | P a g e
Acknowledgments:
A special thankstothe followingpeople anddepartments:
Dr. Ed Duke for runningthe SEM ontailings.
Dr. Jon Kellarforadvisingthe team.
Alex Wulff forMXCTanalysisontailingparticles.
RussLingenfelterforperformingthe XRDanalysisandteachingmembersof the teamhowto
performfire assays.
