Acid Mine Drainage Treatment Using a Sulfidogenic Bioreactor and Selective Two-step Precipitation of Multiple Metal(loid)s

Abstract This study investigated the treatment of acid mine drainage (AMD) and the precipitation of metals and metalloids using sulfur species delivered in gaseous and liquid forms. An up-flow sulfidogenic reactor was operated for 58 days to obtain stable sulfate-reducing conditions. Under the final operating conditions, the bioreactor reached maximum sulfate and COD removal efficiencies of 95% and 92%, respectively, with peak alkalinity and sulfide concentrations of ≈ 2010 mg CaCO₃/L and 326 mg/L. Using the generated sulfide and alkalinity, precipitation tests were conducted on a synthetic AMD solution containing various metal(loids) (Fe, Pb, Zn, Cu, Ni, Sn, Co, Cr, Cd, V, Mn, Sb, As, and Se), with H 2 S gas and HS⁻/HCO 3 ⁻ liquid phases as the precipitating agents. Consequently, Pb, Sn, As, Cu, and Se precipitated at low pH via H 2 S gas, while Zn, Cd, Fe, Co, and Ni precipitated at high pH via HS⁻/HCO 3 ⁻ liquid phases. XRD analysis of the precipitates obtained from the liquid-phase sulfide process at a pH of 5.5 ± 0.2 revealed distinct 2θ peaks between 35° and 65°, confirming the presence of Zn, Ni, Co, and Fe in the precipitates. The results of this study demonstrate that sulfidogenic reactors are an effective tools for both the remediation of AMD and the selective precipitation of metals and metalloids.