Acid mine drainage treatment and sequential metal recovery by means of bioelectrochemical technology

Abstract

BACKGROUND: This work studied the treatment of and metal recovery from a synthetic acid mine drainage (AMD) containing 500 mg L−1 copper (Cu2+) and iron (Fe+3), and 50 mg L−1 nickel (Ni2+) and tin (Sn2+) by using a bioelectrochemical system (BES). The presence of electroactive bacteria improved the performance of such reactor configuration, by contrast with systems with abiotic anodes. RESULTS: Operating as a microbial fuel cell (MFC), all of the Fe3+ was reduced to Fe2+ in about 24 h and Cu2+ was electrodeposited onto the cathodic surface, a Cu electrode, obtaining pure Cu0. Almost all of the Cu in the catholyte was recovered after four days. The maximum current density and power attained in this stage were 0.136 mA cm−2 and 0.0134 mW cm−2, respectively. Subsequent operation as a microbial electrolysis cell (MEC) allowed simultaneous recovery of the Fe2+, Ni2+ and Sn2+ by fixing the cathode potential at −0.7 V versus Ag/AgCl. The electrode material in this stage was titanium. The tin was completely deposited onto the cathodic surface after one day of electrolysis. After three days, 77% and 60% of Ni and Fe, respectively, was recovered. CONCLUSION: It was possible to recover Cu0 while generating electricity at the same time using a BES. The cell voltage required for the metal electrodeposition of Fe2+, Ni2+ and Sn2+ was low in the case of the BES because of the contribution of the electroactive bacteria. Sequential metal deposition is possible by adjusting the operating parameters of the BES reactors.