Environmental Aspects of Phosphate and Potash Mining

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The Environmental Approach of the Phosphate Rock and Potash Mining IndustryOpen Cut BackfillingThe Rasmussen Ridge mine, located in mountainous terrainin southeast Idaho, is owned and operated byAgrium, Inc. Open pit mining methods are used toextract two closely spaced, steeply dipping ore bodiesusing shovel, front-end-loaders and trucks. The pit isaround 100 metres deep, and will ultimately be minedaround 3,000 metres along the strike of the orebody.The mine and reclamation plan sequences the pit, whichis to be mined to its final depth progressively along thestrike. Once a sufficient length of pit has been mined,backfilling with overburden removed from the activemining area is carried out. External overburden dumpsare thus only required during the initial stage.The backfilled pit is landscaped to blend in with the naturalmountainous topography, re-establishing surfacedrainage patterns while minimizing the potential forerosion.Topsoil, generally from clearing in front of the pitface, is applied, followed by seed and fertilizer applicationto re-establish vegetation.This approach significantly reduces the area of land disturbedby external overburden dumps, and reduces thevolume of pit left empty on completion of mining operations.This in turn prevents the formation ofpost-mining pit lakes and the safety risk of exposedsteep pit walls.An additional benefit is the isolation of selenium-contaminatedoverburden. Selective placement at thebottom of the pit prevents selenium leaching into surfacewaters, potentially causing toxicity in livestock andfauna downstream. The development of best managementpractices for selenium control is discussed furtherin Section 3.9 “ Environmental Management”.Landscaped pits with snow, Conda, USA - Agrium Inc., USA18Open pit mining, Conda, USA - Agrium Inc., USALandscaped overburden dump with transplanted trees indistance, Conda, USA - Agrium Inc., USAThe wide area of land surface disturbed by surfacemining operations could require relocation and compensationof people living above the orebody.In some instances, surface subsidence induced byunderground mining may alter river and streamdrainage patterns, disrupt overlying aquifers, anddamage buildings and infrastructure. The degree ofsubsidence depends on factors such as orebody thicknessand geometry, the thickness of the overlying rockand the amount of ore recovered. The effects of subsidencehave been reduced to some extent, througheither:The design of the ore extraction layout so as toreduce the rate and extent of subsidence, orBy backfilling openings with processing wastessuch as salt tailings, to reduce or prevent subsidence.Where subsidence occurs, there is potential for damageto overlying buildings or infrastructure. To avoidsafety risks and property damage, close coordinationand communication is required between the companyand relevant government bodies, other companies andcommunities. This needs to be supported by a welldefinedsystem for reporting and repairing damage, or
Environmental Aspects of Phosphate and Potash MiningLand RentalThe phosphate rock orebody in Togo being extractedby the Office Togolais des Phosphates (OTP) is locatednear the coast in an area of intensive small-scale farming.Surface mining methods are used to remove theoverburden and extract the phosphate rock ore. Thisrequires the progressive relocation of farmers and villagecommunities as mining occurs. In compensation,the company pays farmers a rental for the land disturbedduring the mining process. New villages areconstructed in advance outside the mining area, to rehousedisplaced villagers. The land rental continuesuntil rehabilitation is completed and the land is onceagain suitable for farming.for providing compensation to avoid conflict.Solarevaporation ponds used to extract potash from surfacebrine deposits usually cover a wide area of land,with operations in the region of 90 square kilometres.The precipitation and build up of salt in the pondsover time presents an issue.Water ConsumptionIn some locations, water consumption during extractionactivities may lead to a lowering of the surroundingwater table.Water inflow is a common problem where open pitsand underground openings intersect aquifers.Generally, water is pumped from the excavations orfrom nearby wells to maintain a dry, safe and efficientoperating environment for the equipment. This maypotentially lead to the lowering of the surroundingwater table and the depletion of nearby surface waterbodies. In some locations, measures have been takento confine the area affected by water table depressionand protect the surrounding ecosystem.Ecosystem Protection Through the Use ofPerimeter DitchesThe elevated water table is a prominent feature of theFlorida ecosystem. Frequent surface appearance ofthe aquifer has produced a patchwork of wetlands,streams, rivers and lakes.This presents an issue for theefficient extraction of the phosphate rock deposit bydraglines. If the opencast pit contains water, draglineoperators have difficulty identifying the boundarybetween the ore and overburden, potentially resultingin the loss of ore or dilution by barren rock. Tomaintain dry excavations and an efficient operatingenvironment, the water table may be depressed to alevel below the ore by pumping from wells or sumps.However, this may lead to negative effects on the surroundingwater-sensitive ecosystem. To overcomethis, companies such as IMC Phosphate and CargillFertilizers Inc have implemented protection systems,using a perimeter ditch to confine the impact on thewater table to the immediate mining area.Before pumping commences, a perimeter ditch isexcavated around the mining area to a depth belowthe water table. The ditch is filled with water that ismaintained at a level consistent with the originalwater table, using a series of weirs and pumps. Whenthe water table is depressed by mining activities,recharge occurs from water in the ditch.Performance of the system is monitored by both dailyvisual inspection of the ditches and by weekly measurementsof the water table, through a series ofpiezometers located outside the perimeter ditch.The effectiveness of the method has been improvedby reshaping the overburden immediately adjacent tothe perimeter ditch as soon as possible on completionof mining. This allows the water table to partiallyreestablish itself inside the perimeter ditch.The application of this approach protects the surroundingwater-sensitive ecosystem by confining thedepression of the water table to the area delineatedby the ditch.Waste water produced during the extraction stage canbe used for downstream processing operations, reducingthe demand on other sources. In some places,water of suitable quality has been used for the irrigationof local farming operations. This is of greaterimportance in arid climates where water resources arelimited.Water ContaminationExcavation activities may contaminate surface waterthrough the release of fines generated during clearing,blasting and excavation operations, the weathering ofoverburden contaminants susceptible to leaching andthe release of salt from brines and potash ore.Perimeter ditch - IMC Phosphate, USA
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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
Page 20 and 21: BeneficiationHandling Extractiondev
Page 22 and 23: The Environmental Approach of the P
Page 28 and 29: HandlingThe Environmental Approach
Page 30 and 31: BeneficiationThe Environmental Appr
Page 42 and 43: ClosureThe Environmental Approach o
Page 44 and 45: RehabilitationThe Environmental App
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Page 60 and 61: AppendicesAppendix C. Australian Mi
Page 62 and 63: AppendicesAppendix D. Glossary of F
Page 64 and 65: AppendicesAppendix E. AcronymsAcron
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