Environmental Aspects of Phosphate and Potash Mining

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Overview of Phosphate Rock and Potash Mining and Beneficiation12Figure 2.2Common potash mining processes and equipmentExtractionHandlingUndergroundSolutionSurfaceBeneficiation / concentrationSize reductionDeslimingConcentrationDewateringDryingCompactionGranulationStorageContinuous miningmachineLongwallLoad-haul-dump (LHD) unitsDrill and blastInjection wellsRecovery wellsEvaporation pondsShuttle carsConveyorsFeed binsShaft or decline haulageBrine pipelinesCooling pondsCrushingGrindingScreeningHydrocyclonesAttrition scrubbingHydrocyclonesFlotationThermal dissolution--crystallizationElectrostatic separationHeavy-media separationFiltersThickenersCentrifugesRotary ovensFluidised bed dryersRotary compactorGranulatorConveyorsShedsAlthough it is not strictly mining, the concentration ofbrine in solar evaporation ponds is another method ofproducing potash ore. The method relies on the evaporationof brine through a series of shallow ponds.The initial ponds are used to precipitate halite (NaCl)and concentrate the desired minerals, the brine is thenpumped into a second series of ponds in which thepotash ore, mostly carnallite, is precipitated. The carnalliteis harvested and pumped as a slurry tobeneficiation facilities for processing.Potash BeneficiationThe processing of potash generally involves a series ofsteps including: Size reduction; Desliming; Separation; Drying; Compaction and granulation; Disposal of the waste streams.The specific process employed will depend on factorssuch as the characteristics and constituents of thepotash ore and the market specifications.Generally, the ore is reduced in size using a system ofcrushing and grinding to liberate the different mineralsfrom each other. This is usually followed bydesliming by intense agitation followed by flotation orhydrocyclones to separate the fines consisting of clays,dolomite and sand from the potash ore.Four basic techniques are used to separate the wasteminerals or by-products such as salt and concentratethe potash; flotation, electrostatic separation, thermaldissolution-crystallization, and heavy media separation.Several of these may be used together to enhancerecovery.Flotation is the most widely used technique, relying onthe difference in surface properties between mineralsto selectively float the desired mineral. Electrostaticseparation is a dry process in which the minerals areseparated using their different electrical conductivities.Thermal dissolution-crystallization relies on thesame principle as solution mining, whereby a heatedbrine preferentially dissolves potassium chloride.Heavy media separation relies on the difference in specificgravity between sylvite and halite to selectivelyfloat and remove the lighter sylvite particles.
Environmental Aspects of Phosphate and Potash MiningAfter concentration, the potash concentrate is generallydried in a rotary or fluidized bed dryer to reduce themoisture content. Depending on market requirements,this may be followed by compaction at highpressure between rollers and then granulation to producea uniform size potash product.Three major waste streams are produced during beneficiation;brines, fines, and salt tailings. A variety ofdisposal methods are currently used, including: Stacking of the salt tailings on the surface; Retention of the fines and brines in surface pondsfor solar evaporation; Deep well injection of brines into confined permeablegeological strata; Backfilling of mined underground openings withsalt tailings, fines and brines; Release of wastes to water bodies such as rivers orseas.Filtering potash before drying - Kali und Salz GmbH,GermanyThese are discussed in greater detail in Chapter three.Figure 2.3Typical potash beneficiation processKali and Salz GmbH, GermanyMinePrimary crushingFine grindingFlotationHot leachingPotash rotary drier - Potash Corporation of Saskatchewan(PCS), CanadaClassificationCrystallizationDryingWashing processGranulationDryingDustfreeGranularKCl 99Storage / shipmentStorage / shipmentPotash compaction rollers - Potash Corporation ofSaskatchewan (PCS), Canada
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Page 4 and 5: AcknowledgementsA number of people
Page 6 and 7: PrefaceThis report on the environme
Page 8 and 9: Introduction2During recent decades,
Page 10 and 11: Introduction4Figure1.2The mineral f
Page 12 and 13: Overview of Phosphate Rock and Pota
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Page 42 and 43: ClosureThe Environmental Approach o
Page 44 and 45: RehabilitationThe Environmental App
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