Environmental Aspects of Phosphate and Potash Mining

ExtractionEnvironmental Aspects of Phosphate and Potash Miningreducing the need for more intrusive exploration techniques.ConstructionConstruction activities have significant potential tohave adverse environmental impacts. During thisphase, often a large transient workforce is employed,workforce numbers tend to peak and material andequipment movements tend to be large. Impacts aretypically related to land disturbance caused by earthworks,air emissions from dust, noise from equipmentand construction activities and heavy volumes of trafficon access roads.In many cases, specialized third party companies andconsultants conduct mine construction activities.‘Turn key’ construction contracts are commonlyawarded. The ability of the mine site's owner to controlenvironmental impacts can be maintained tosome extent by considering potential issues andexplicitly addressing them in the drafting of the tenderand contract.3.3 ExtractionSurface mining methods, by nature, tend to affect awide area of land and could result in a variety ofeffects such as: land surface disturbance, contaminationor depletion of ground and surface water, and areduction in air quality. Currently, most phosphaterock and a small quantity of potash ore are sourcedusing surface mining.Figure 3.3.1Potential environmental effects : ore extractionOverburden removalor orebody accessOre extractionLand surface disturbanceWater contaminationWater table loweringAir emissionsTopsoil degradationVegetation and wildlifedisruptionNoise and vibrationmay become contaminated or deplete overlyingaquifers. Underground mining methods are used tosource potash ore from deeply buried marine evaporitepotash deposits. A lesser quantity of phosphaterock is sourced using underground methods.Land Surface DisturbanceExtraction activities disturb the land surface throughclearing of vegetation, removal of topsoil, excavationof ore and overburden and the construction of overburdendumps or solar evaporation ponds.Removal and stockpiling of topsoil for subsequentrehabilitation is carried out at many mining operations.In a number of cases, topsoil is removed andplaced directly on landscaped reclaimed areas. Thisavoids the cost of re-transporting topsoil from stockpilesand the possible reduction of biodiversity.Moreover, close coordination and planning is requiredbetween the mining and rehabilitation operations toensure that areas are prepared in a timely manner. There-planting of small trees from areas to be mined andthe placement of dead trees on rehabilitated areas hasbeen used to accelerate the establishment of vegetationand provide a wildlife habitat.Generally, overburden (4) is either dumped directlyinto the adjacent mined-out areas or placed in speciallydesigned overburden dumps. On closure, thismaterial is landscaped, covered with a layer of topsoiland revegetated. These activities are discussed furtherin Section 3.7 “Rehabilitation”.The costs associated with transporting and landscapingoverburden are minimized in many cases bydesigning and managing overburden dumping operationsso as to ensure that they are placed as close aspossible to the final desired location and to the finalshape. Bucketwheel excavator operations are particularlyflexible, allowing selective placement of theoverburden in the order of extraction and the creationof a flat final landscape. This has advantages for laterrehabilitation.Underground mining methods tend to create fewerenvironmental problems, the major issue being possiblesurface subsidence. This is induced by the removalof extensive flat-lying ore deposits, followed by thesubsequent collapse of overlying rock. Some minorenvironmental effects may be associated with the disposalof rock removed to access the orebody. Also,ground water inflow into the underground openings(4) The term overburden is usually applied to the barrenmaterial (clay, sand, or rock) removed to expose the ore insurface mines. Underground mines produce a far more limitedvolume of barren waste rock during excavation of theaccess ways such as shafts and tunnels. Finally, processingoperations generally produce a number of solid wastes such assalt tailings, sands, and clays. The term overburden will beapplied to all barren material stripped from the surface toallow the ore to be extracted.