Globally, bauxite mining disturbs a relatively small area of land compared to other types of open cast mining. Around one square metre of land is newly opened up each year to produce one tonne of aluminium, with the same area annually rehabilitated.
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The area of mined land rehabilitated every year globally is equivalent in size to the area newly mined.
Bauxite mining operations aim to restore the pre-mining environment and respective conditions; returning the original ecosystem as close as possible, in terms of structure, function and dynamics and creating a land-use to benefit the local community. Most operations rehabilitate used areas progressively as mine pits are closed.
Mining leases and concessions are linked with rehabilitation conditions and the obligation to comply with government regulations. Many operations make rehabilitation the responsibility of individual production staff by including rehabilitation targets in their performance appraisals. All operations reporting to the International Aluminium Institute have clearly defined rehabilitation objectives, fully integrated rehabilitation programmes, and written rehabilitation procedures. Most have made considerable financial provisions; devoting human resources, knowledge, material and equipment for the rehabilitation of land that was used for mining and associated infrastructure, final decommissioning and mine closure.
Specific rehabilitation processes are very much dependent on the mine site and the ecological, social and geological conditions. A general process involves first landscaping the mined area to reshape the pit, burying large rocks and removing pit faces. Operators take the opportunity to improve drainage; heavy vehicles used during the mining process can compact the ground, making it difficult for roots and water to penetrate. Mechanical ripping of the surface helps to alleviate this problem and forms a well drained foundation for subsequent layers.
Next the overburden and topsoil layers, which were removed during the first stages of mining, are returned to the pits. Due to the essential nutrient and seed contents of these layers they are carefully stored until they are needed. Often native plant species, based on collected seeds and saplings, are cultivated in nurseries for colonisation of the replaced earth. Habitats are created using original rocks and timber material, encouraging invertebrates, insects and other fauna to recolonise the area.
Reshaping of mined land blends mined areas into the surrounding landscape, reduces the likelihood of erosion, by reducing slope angles and lengths, and allows natural drainage patterns to be re-established. Despite being located in areas with heavy seasonal rainfall, most operations rate the erosion risk at their mines as low. This is due to effective mitigation measures, which prevent soil loss during clearing, mining and stockpile storage.
- Building of structures to retain and control runoff water;
- Storage of topsoil and overburden on areas with shallow side slopes to prevent erosion and soil degradation;
- Quick revegetation of used/backfilled areas and soil stockpiles with soil binding species such as lemon grass;
- Vegetation cover through mulching;
- Soil handling at times of the year with lower erosion potential.
Once rehabilitation has taken place it is important to monitor the ecological development of the rehabilitated areas, highlighting areas which need further reworking and providing useful feedback for future rehabilitation programmes.