Environmental Problems Related to Pyrite Oxidation from an Active Coal Washing Plant, Alborz Sharghi, Iran

The low grade wastes produced by coal washing plant often contain pyrite which may be oxidised and produce acid mine drainage (AMD) if it is exposed to the atmosphere. AMD is characterised by high concentrations of iron, high sulphate and low pH and it is considered to be a major cause of long-term poor water quality and the source of many environmental problems. In this study, the pollution problem associated with the wastes (which cover an area of about 1 km2) produced by Alborz Sharghi coal washing plant, at Shahrood, Iran, was investigated by mineralogical and geochemical techniques. Mineralogical analysis indicates the presence of pyrite in the unoxidised waste and its depletion in the oxidised zone. Geochemical analysis of samples taken from different depths over the coal wastes dump up to 2 metres show that pyrite oxidation in the upper 75 cm of the dump has resulted in a peak concentration of sulphate, low pH and high concentrations of metals (pH<3.5, 349 mg/