Environmental Aspects of Phosphate and Potash Mining

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The Environmental Approach of the Phosphate Rock and Potash Mining IndustryThe waste slimes and brine are transferred undergroundthrough a slurry pipeline and discharged to theexcavated salt rooms. Generally, two or three salt roomsare filled simultaneously. Deposition and settling of theslimes occurs in one room, while the clarified brineoverflows into the second and/or third.The clarified brine is recovered from the salt rooms andreturned to the processing plant where it is evaporatedto produce both a fresh water condensate, and a concentratedbrine. The fresh water condensate is usedlargely as an input to the process with excess releasedthrough the holding pond. The concentrated brine isreturned to the crystallization circuit for recovery ofresidual potassium chloride.The water balance of the operation is essentiallyclosed. Water released from the site is related to eitheron-site rain or snowfall or the excess fresh water condensatefrom the processing facility. Both of thesesources are retained in a continuously monitored holdingpond prior to release to the local river.The adoption of the closed circuit waste loop, demonstratessome of the benefits that arise from an effectivepollution prevention program. The potential sources ofpollution in the form of the three major waste streamshave been integrated into the mining process. The salttailings have become an essential component of the cutand fill mining method, recycling of the brines hasincreased product recovery and eliminated the need forcontaminated discharges, and the slimes and somebrine are effectively disposed of in the salt rooms.The major environmental benefit of the approach is thesmall surface impact of the operation. The lack of anysurface salt tailings stack, slime and brine ponds hasreduced the potential for surface environmentalimpacts to negligible levels.The approach does incur an additional cost in comparisonto conventional surface waste disposal methods. Inthe case of the New Brunswick operation, this has beenpartially offset by greater recovery of the potash oreresource, lower product transportation costs due to theoperations location with respect to markets and apotentially a lower future rehabilitation cost duringoperation closure.32Treatment of the Clay Fines to Remove SaltsThe IMC Potash Colonsay operation in Saskatchewan,Canada is developing a process to remove salt andbrines from the clay slimes waste. Removal of the saltallows the insolubles to be disposed of without specialprecautions.The process involves a number of steps: Separation of the slime component by thickening toremove brine; Washing of the slimes with water to dissolve anyresidual salt; Cycloning to remove brine; Filtering with the addition of fresh water to produce arelatively dry, desalinated product.The filtered slurry forms small, stable, agglomeratedparticles, facilitating handling and reducing the likelihoodof dust problems.Results from earlier trials are being used to improve theprocess.This method removes the need for large areas to be setaside for clay slimes settling ponds. The slimes areinstead converted into an environmentally benign, easilydisposed product that may possibly be sold as a claysubstitute for brick and pottery or a water retentionamendment for sandy soils.Figure 3.6.5Flowsheet of the slimes desalination anddewatering process. IMC Potash, Canada.FreshwaterClay, salt finesand brineCold slimesthickenerFilterFlocculantBrackish waterDesalinated and dewatered clay(75 - 80% solids)WashingCycloneClayandbrine
Environmental Aspects of Phosphate and Potash MiningWater Management and TreatmentThe Foskor Ltd. operation at Phalaborwa is located inthe semi-arid northeast of South Africa, adjacent to theSelati River and upstream from the Kruger NationalPark.The processing operation uses 250 million litres ofwater per day, the majority of which is recirculated.Excess water is transferred to the tailings dam beforerelease to the Selati River. The tailings water is high inboth total dissolved solids (TDS) and sulfates. The sulfatesare largely introduced with tailings sourced fromthe adjacent Phalaborwa Copper mine, which currentlysupplies about 40% of the phosphate ore feed for theFoskor beneficiation plant.Concerns by Kruger National Park management aboutthe potential effect of contaminated water on thedownstream aquatic ecosystem led to the implementationof a water treatment system.After consideration of the most suitable water treatmentprocesses on the market, the ‘Paques’ process wasselected. This bacterial process converts sulfates in thetailings water to sulfur.The sulfur is subsequently recoveredand sold to the adjacent fertilizer processingcomplex for use in the production of sulfuric acid.The process is used to treat about 40 to 50 mega-litresper day. Monitoring of the release is conducted as partof a comprehensive surface and ground water monitoringsystem for the site that includes biologicalmonitoring points located on the Selati River.The water treatment system protects the downstreamaquatic ecosystem and the natural values of the KrugerNational Park. Additionally, the sulfur by-product can besold to recover a portion of the operating costs.Selati River flowing adjacent to the tailings dam - FoskorLtd, South AfricaWater ContaminationSurface and ground water contamination may occurthrough the release or seepage of tailings effluent andbrines from dams, ponds and stacks. Contaminantsmight include clay fines, chemical reagents, sulfates,salt and magnesium chloride. In addition, rainfall maydissolve salt tailings or cause erosion and mobilizefines.Depending on the operation, water releases arerequired to maintain the water balance of the operationsstorage facilities. In most countries, this watermust meet established water quality standards. Toachieve this, excess water is treated through a systemof dams and wetlands to clarify and remove contaminants.Where possible clean water and contaminated wateron the mine site are kept separate and handledthrough different systems, to reduce the quantity ofwater that must be treated before release.Aquatic species are sometimes used as an indicator ofthe performance of the waste management system.Monitoring the biodiversity of aquatic species downstreamfrom release points provides an indicator ofenvironmental response.The leakage of liquid wastes such as brines from storageand disposal ponds is controlled to a large extentby containment techniques such as plastic or clay liners,ditches, drains and containment pumping wells.Landscape DisturbanceThe construction and operation of surface waste storagefacilities typically disturbs a significant area ofland. Some operations have reduced the area affectedby stacking wastes higher. In other cases, wastes aredisposed of to mined-out areas, avoiding impacts onundisturbed areas.Rehabilitation of disposal areas to mitigate environmentaleffects is discussed in Sections 3.7 “Closure”and 3.8 “Rehabilitation”.Tailings Stability and FailureThe potential for accidental failure of waste disposaldams and ponds is of concern. This can cause rapid,extensive and widespread impacts on the surroundingenvironment. The installation of monitoring systems,preparation of emergency response plans and procedures,and the regular auditing of performance assist
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Page 4 and 5: AcknowledgementsA number of people
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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
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