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Some of the main features of the IHC bucket wheel are: ~Thebottomandcurvedbackoftheconventionawlheelbuckethavebeencompletelyomittedtoavoid accumulation of the material and plugging of the suction passage, ~ Theouteredgeofthebucketisspeciallyshapedtoguidethematerialintothesuctioninlet. ~ Thespacebetweenthebucketsissmallerthanthesizeofthematerialentering,thereforepreventing obstruction of the suction and discharge line or the pump. Thequestfortheeconomicdredgingofmineraldepositshasledtotheimprovemenotftheexistingdredges for usein specificlocalconditions Dieperink,1978;Anon,1981and1982;LimCheWan,1983;Houston, 1983; Woodsend, 1984; Lewis, 1984!, New concepts have also been proposed for deeper dredging, such as continuous-draglinedredgeanda multi-grabdredge Hewitt,1978!. Recovery Techniques ancf Developments The processingof mineralsevolvedas a necessityto recoverthe valuablemineralsfrom a mineddeposit and producea requiredmarketableconcentrate.The recoveryoperationdependson the amenabilityof the mineralsto a treatmentprocessand it is basedon the differencesin the physicalpropertiesof the minerals, such as particle size, shape, specific gravity, magnetic and electric properties, surface wetability and other properties, Screeningandgravityseparationarethe mostcommonmethodsto recoverplacergoldandheavyminerals from alluvial deposits,whereas the magneticand electrostaticseparationsare used mainly in cleaning processesandto separatespecificheavymineralsfrom eachother.The ditferencesin surfacewetabilityof the mineralsis appliedin the flotationprocessto recoverfine and ultra fine particles. Earlyinlanddredgeminingoperationsusedsluicesandtablesas gravityconcentrationdevicesto recover goldfromsandandgraveldeposits.Withdeclininggrades,Humphreysspiralsandvarioustypesofjigsof higher treatment capacity were introduced, Technologicadlevelopmentsintheprocessingoflow-grademineralshasledtomoreefficientsystemsand equipmenwthichcouldalsobeapplicabletotherecoveryofmarinepiacerminerals.Majoracheivernentswere madeinprimarygravityconcentratorfsormineraslandsinAustraliaWhite,1984!.TheWrightImpactPlate SeparatorpsrovedefficienftortherecoveryofbeachmineralsfromseverabllacksanddepositsinAustralia andWestAfricaMacdonald1,983!.TheWrightImpacPtlateseparatordsifferfromothertypesofsluicesby thepresenceofanimpacptlatewhichdividestheslurryflowintotwostreamsT.heangleoftheimpactrelative to the slurryflow determinesthe recoveryrate. MineraDlepositsLtd.,Australiad,evelopedoubleconeconcentratortosimprovetheefficiencoyftheearly ReicherctonesystemsT.heconeshaveanaveragetreatingcapacityof80t/handcanachieveseparations ofparticlesasfineas40micronsBurt,1984!.SierraRutileLtd.hasrecentlybeenusingtheconesseparation systemonitsdredgingoperationsto recoverrutiledepositsfromalongtheSierraLeonecoast,WestAfrica Anon,1981!.ReicherctoneshavealsobeenusedbydredgingoperationisnNewZealandBuistetal.,1978! andat RichardsBay,SouthAfrica Anon,1976!. In an effortto improvethe recoveryof finegoldandotherheavymineralsandto increasethetreatment capacityoftheconventionajigl cellunits,IHCHollandevelopedtheradiajlig,originallypatentedin1967as the circularjig by N. ClevelandIHCHolland,1983!.Unlikethe conventionajilgs,the IHCradialjig works withoutbackwateardditionorwitha limitedamountT.heIHCjigusesa specifidcrivesystemtoinducea fast upstroke and a slow downstrokewave pattern, "saw tooth" wave, rather than a harmonic wave as in a conventionjiagl Figure2!,Theshorts,harpulsatiomninimizethsefineslossandallowtsheirecoverdyuring longer, gentle suction. Toovercomtehedifficultieisnhandlingandtransportationfthestandardcirculajrigs upto7.5min diameter!a, module-jicgoncepwt asdevelopedT. hetreatmenct apacityof a modulerangesfromapproxi- mately40to83m/hsolidsandcanbeassembleindanynumbertw,elvemodulebseingrequirefdora completecircle,TheIHCradiajligshavebeenappliedrecentlybysomeoffshoredredgingoperationisnSouth EasAtsiafortherecoveroyfcassiteriteKrarne1r,984!i,nAlaskafortherecoveroyfgoldAnon1,985!i,n Brazial ndothercountriesIHCHolland1,985!F. igure3 presenatscomparisboentweetnheIHCradiajlig, conventionajigl,tablesandriffledsluicefortherecoveryoffinegoldparticles. Therecovereyfficiencoyfvarioutsypesofhydrocyclonaensdcentrifugsaelparatoorsndredgeplantshave beeninvestigatedby the Soviets Anon,1981!.Thewideangleconcentratinhgydrocyclonreeportedthe 17PDF Image | Dredging Applications of High Density Polyethylene Pipe
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