Control of pyrite oxidation by phosphate coating

Abstract

Several techniques are currently being investigated for the treatment and abatement of acid mine drainage (AMD). While some of these methods are directed towards the treatment of the resulting drainage, others are directed towards prevention of acid mine drainage at source. Conventional methods of controlling acid mine drainage have primarily been limited to collecting the drainage and neutralizing with alkaline materials which do not provide a permanent solution to the AMD problem. Since the oxidation of pyrite in acid media is initiated by preferential release of iron ions into solution, the mechanism of pyrite oxidation can be likened to the corrosion of metals, and therefore could potentially be protected by metal phosphating techniques. In this communication, the application of low and high temperature phosphating of pyrite to control its rate of oxidation was investigated. The phosphate coated pyrite was tested in an accelerated oxidation column and in an autoclave. The results show that phosphate coating reduces the rate of pyrite oxidation significantly. Phosphating at higher temperatures appears to produce thicker coatings, but did not improve the oxidation stability of the pyrite by any significant amount.