…or to put it another way, acid mine drainage, or AMD, or acid rock drainage, or ARD, or acid and metalliferous drainage, or AMD, or abandoned mine drainage, or AMD… It is arguably the world’s most significant mining environmental challenge, yet the semantics of its name are almost as tricky as the complexity of the phenomenon itself.
Chemical intricacy prevails, but this is not the place for a detailed technical discussion of AMD; suffice it to say that AMD is produced by the chemical weathering of fresh sulphide mineral surfaces exposed during mining (including processing) activities – particularly for coal and metal ores. Sulphide minerals react with oxygen and water to produce sulphuric acid, releasing iron and potentially toxic elements, such as copper, arsenic, etc. from their host minerals.
Acidic, metal-contaminated waters are found worldwide flowing from underground mine workings, or leaching from surface waste rock dumps or processing wastes. Ultimately ground and surface waters and soils can become acidic and contaminated/ polluted, and cleaning up the consequences can costs hundreds of millions of dollars per site. For more information please see any of the organisations below (just a sample of the gamut of excellent groups working to address the AMD challenge – their number and breadth reflecting the seriousness of the issue):
ADTI – Acid Drainage Technology Initiative, USA
CNAMD – Chinese Network for Acid Mine Drainage
IMWA – International Mine Water Association
INAD – Indonesian Network for Acid Drainage
INAP – International Network for Acid Prevention, an organisation of international mining companies
MEND – Mining Environment Neutral Drainage, Canada
PADRE – Partnership for Acid Drainage Remediation in Europe
SANAP – South American Network for Acid Prevention
WRC – Water Research Commission, South Africa
Etc.!
If sufficient appropriate AMD investigations are carried out during the early phases of mine planning, i.e. during the pre-feasibility/ feasibility phase and/or as part of the environmental and social impact assessment, mitigation and management activities and related costings can be more accurately included in a mine’s operational costs. Too often, though, insufficient effort is expended on such studies leading to much greater overall treatment costs during the mine lifecycle. The crunch, as with so many things, comes when the mine closes. After closure mines may continue to produce large quantities of AMD for many decades, or even longer, which needs to be treated to protect drinking and irrigation water supplies, soils and aquatic ecosystems. The total costs and effort, in such cases, are very difficult to calculate accurately leaving an ongoing liability that may need attention ‘in perpetuity’.
But there is an oft-overlooked, stark beauty to be found where industry and nature interact as illustrated in these three images of an abandoned metal mine in Cuba and a post-closure coal mine water treatment plant in the East Rand, South Africa.
To be continued…
AMD in abandoned open pit metal mine, Cuba
Post-closure coal mine AMD treatment on the East Rand, South Africa
