(637d) Pyrite Oxidation in a Packed Bed Configuration

Pyrite is one of the more common minerals found in mining operations and is one of the major minerals involved in the formation of acid rock drainage.  The oxidation and the formation of acid rock drainage is a very complex process occurring in rock piles that depends on oxygen levels, temperature, pH, redox potentials, ionic concentrations and bacteria concentrations.  Abiotic oxidation of pyrite can occur with oxygen or with ferric ion and is strictly chemical but biotic oxidation requires the presence of iron-oxidizing and/or sulfur-oxidizing bacteria, the two more common species being acidothiobacillus ferrooxidans and leptospirillum ferrooxidans.  Despite numerous studies and publications, the mechanism of pyrite oxidation, both abiotic and biotic, is still somewhat controversial and terms such as “direct” and “indirect” oxidation have been used to describe the process.  This paper discusses the oxidation of pyrite under controlled conditions in a packed bed configuration. Experiments were conducted with pyrite crystals in a packed bed of glass beads over time periods of several weeks and results showed that oxidation rates varied with leaching pH and composition. Acidic conditions with 100 mg/L Fe⁺³ under water saturated conditions displayed the most rapid rates.