AMD. THE GLOBAL CRISIS
effects acid mine drainage
Acid Mine Drainage
how to treat acid water
Acid drainage is a little-known global crisis. The UN has labelled AMD as the second biggest problem facing the world after global warming. In the US, an estimated 22,000km of streams and 180,000 acres of freshwater reservoirs are affected by acid mine drainage. Rivers and lakes in Arizona, Patagonia, Guangdong (China), Ontario, Papua New Guinea and at Rio Tinto in Spain, to name just a few, have all been polluted by AMD. In South Africa, the problem is disastrous, with more than 36 million cubic meters of AMD leakages a day imploding into the regions water.
The cost of AMD remediation at abandoned mines alone has been estimated to be in the tens of billions USD.
“Source for costs - Dr Michael Short, School of Natural and Built Environments – UniSA, January 2016”
PINS REPRESENT MULTIPLE SITES
18,000 AMD producing mines in Australia alone, with over 600 mines in critical need of a total acid management solution, Australia represents just 2% of the global AMD issue.
WHAT IS AMD?
AMD is a form of water pollution that occurs when rain, runoff, or streams come into contact with rock that is rich in sulphur. As a result, the water becomes very acidic and damages downstream aquatic ecosystems. It mostly occurs where mining is done to extract coal or metals from sulphur-bearing rocks. Silver, gold, copper, zinc, and lead are commonly found in association with metal sulphates, therefore their extraction can cause acid mine drainage. Long after those mines are closed, the effects of acid mine drainage continue to manifest and contaminate waters as well as ecosystems.
The acronym ‘AMD’ is defined here as acidic and metalliferous drainage and includes acidic drainage, pH neutral metalliferous drainage (NMD), and saline drainage (SD) generally caused by the oxidation of sulphide minerals.
AMD (as manifested by NMD or SD) can still be an issue even if a site assessment concludes that drainage with a low pH is unlikely to develop. The potential for self-heating and auto-ignition of sulfidic waste materials must be considered and assessed where needed.
It is the total load (the product of concentrations and flow), not concentrations alone, of acid, metals/metalloids and salts in the source mine drainage that influences the magnitude of downstream impacts and the cost of treatment.
AMD sources can include waste rock dumps (WRDs); ore stockpiles; tailings storage facilities (TSFs) and tailings dams; roadways and embankments constructed with sulfidic material; open cuts and mine pits; underground mines; heap and dump leach piles; and acid sulphate soils.
During mining, pyrite is exposed to oxygen
Ground water seeps into the mine
Oxygen, water and pyrite react to form sulphuric acid and in turn dissolve metals from the rocks
Water drains out of the mine
Dissolved metals react and fall out of solution into stream water, turning a bright colour
Aquatic animals and plants are killed by the AMD
Drinking water becomes contaminated. Groundwater can be affected, impacting local water wells.
Water with a very low pH can support only severely reduced animal and plant diversity. Fish species are some of the first to disappear. In the most acidic streams, only some specialised bacteria survive.
Due to its corrosive nature, acidic stream water damages infrastructure such as culverts, bridges, and storm water pipes.
Recreational activities, e.g. fishing, swimming and scenic value for streams or rivers affected by acid mine drainage are greatly reduced.
“Acid Mine Drainage (“AMD”) is a little-known global crisis. The UN has even labelled it the second biggest problem facing the world after global warming.”