Treatment of acidic mine drainage in up-flow sulfidogenic reactor: Metal recovery and the pH neutralization

Abstract

Acidic mine drainage is known to have a low pH and contain high concentrations of heavy metals and constitute a serious risk for the receiving environment. Because of the fact that factors affecting the formation and mineralogy of acidic mine drainage vary a lot, treatment of it is difficult and costly. In this study, the treatment of acidic mine drainage together with the pH neutralization and metal precipitation (Fe, Cu, Co, Mn, Zn, Ni) in two stage ethanol fed up-flow anaerobic sulfate reducing bioreactor were investigated. The reactor was operated in a temperature controlled room (30 °C) at a HRT of 1 day for 245 days. The COD/SO42− mass ratio was 0.67–0.87. Sulfide and alkalinity produced in the reactor were recycled to a pre-treatment unit where pH was neutralized and metals were precipitated. Throughout the study, up to 4000 mg/L sulfate was added to feed and the effluent sulfate was 325 ± 9.75 mg/L, corresponding to 91.25% removal. The feed was contained 400 mg/L Fe, 200 mg/L Cu, 50 mg/L Co, Mn, Zn and Ni and over 87% Fe, over 98% Cu, Co, Zn and Ni and 49% Mn removals were achieved in the pre-treatment unit. The remaining metals were also filtered in the sulfidogenic reactor. This study demonstrated that by setting a reactor configuration, pH neutralization, metal precipitation as well as sulfate reduction can be achieved in two stage reactor system.