Hydrogeochemistry of Mine Water
Problems with mine drainage generally develop when ground and surface waters enter mine sites and come in contact with primary and secondary minerals under oxic conditions. During contact with those minerals, the water may dissolve components of the ore and rock-forming minerals. Most of the processes involved are controlled by the EH-pH conditions at the water-mineral contact. If even relatively small amounts of disulphides, as pyrite or marcasite, oxidise and dissolve, the acidity formed can dissolve other water contaminants. Because metal or coal deposits are so diverse, the metals and the composition of mine water are unique at every mine site. Commonly, carbonate minerals are present and neutralize (buffer) the acid, leading to neutral or even alkaline mine water, which might still be harmful to surface and ground waters in a catchment area. Barnes and Clarke (1964) nicely summarised the problem associated with disulphide oxidation: “if mine workings could have been isolated hydrologically, operators, who must pump as much as 23 t of water per ton of coal from the anthracite mines of Pennsylvania, could have saved a great amount of money”. That was in 1964 and even today, after nearly all of the questions discussed by Barnes and Clark have been resolved, we are still far away from being able to definitively stop acid mine drainage and metal leaching. These problems were, in fact, described by Agricola (1556), and clearly existed long before that.
KeywordsMine Water Radon Concentration Pyrite Oxidation Acidithiobacillus Ferrooxidans Excavation Disturbed Zone
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