Shouldn’t We Be Putting Our Sulphide-Rich Mine Tailings in the Ocean or in Lakes Rather than on Land?

Abstract

Acid rock drainage (ARD) is arguably one of the major environmental insults faced by all countries that mine sulphide ores. This reflects the fact that pyrite (FeS₂) and other metal sulphides are common constituents of mill waste (tailings), and being reduced substances they are ideal candidates for oxidation. The oxidation rate of such minerals is greatly enhanced by the catalytic activities of acidophilic bacteria, which are abundant in tailings deposits provided that oxygen and some moisture is present. Thus, the exposure of tailings and waste rock to air and water, a common condition in many historic and current mining operations, typically produces a variety of chemical oxidation products including sulphuric acid. The acid in turn dissolves various other mineral phases, yielding a low pH, metal-rich, and typically quite toxic solution that can readily contaminate surface waters. Such contamination has occurred historically in many mining regions and has caused often severe environmental degradation.