Effects of surface coating agents on pyrite oxidation : batch and field studies

Abstract

The acid mine drainage (AMD) is characterized by low pH, high concentrations of toxic heavy metal and SO42-. Amongst the sulphide minerals, pyrite is the most abundant in natural rocks and mine-wastes. In general, both active-treatment and passive-treatment system have been employed for treating the AMD. For reducing the volume and concentration of hazardous elements in AMD and employing less expensive materials, pretreatment technology was tested in this study. Surface coating agents could inhibit the oxidation of metal sulfide minerals existed in abandoned mine area in which AMD is originated. Two geological typical different mines, Young-Dong coal mine and the Il-Gwang gold mine, were examined by conducting experiments with laboratory scale and field tests. Powdered Peru pyrite as a standard sulfide mineral and rock samples from two mine outcrops were mixed with six coating agents (KH2PO4, MgO and KMnO4 as chemical agents, and apatite, cement and manganite as mineral agents) and incubated with oxidizing agents (H2O2 or NaClO). For the observed time period (8 days), Young-Dong coal mine samples exhibited the least sulfate (SO42-) production in presence of KMnO4 (16%) or cement (4%) while, for Il-Gwang mine samples, the least SO42- production was observed in presence of KH2PO4 (8%) or cement (2%) compared to control. Field-scale pilot tests at the Il-Gwang site also showed that addition of KH2PO4 decreased SO42- production from 200 to 13 mg L-1 and it also reduced Cu and Mn from 8 and 3 mg L-1, respectively to <0.05 mg L-1 (below ICP-OES detection limits). The experimental results suggested that the use of surface coating agents is a promising alternative for sulfide oxidation inhibition at acid mine drainage sites.