Sequential precipitation of Cu and Fe using a three-stage sulfidogenic fluidized-bed reactor system

The exposure of sulfides, such as pyrite (FeS2) to water and air leads to the formation of acidic metal and sulfate containing waters, generally referred to as acid mine drainage (AMD). Under anaerobic conditions and in the presence of a suitable electron and carbon source, sulfate-reducing bacteria (SRB) can reduce sulfate to hydrogen sulfide which can precipitate metals as low-solubility sulfides. In the present study, a three-stage fluidized-bed reactor (FBR) system was operated at 35 °C with ethanol as an electron and carbon source for SRB to sequentially precipitate Cu and Fe from synthetic AMD. The system consisted of two pre-settling tanks before a sulfidogenic FBR for the sequential precipitation of Cu and Fe with biogenic H2S gas and HS− containing effluent, respectively. Cu and Fe precipitation efficiencies were over 99% and sulfate and COD removals 60–90%. Biologically produced alkalinity increased the initial pH of the AMD from 3.0 to neutral values.