Efficient gold recovery by microbial electrochemical technologies

The applicability of microbial electrochemical technologies for the recovery of gold was investigated. Two-chamber microbial fuel cells (MFC) with bioanodes buried in sediment were used in two operating modes. The cathodes (gold foil or graphitized paper), submerged in HAuCl₄, solutions, were short-circuited with the bioanodes, and thus for the first time, the microbial electrochemical snorkel (MES) was applied for gold recovery. Operation in MFC mode, where the cathode and the anode were connected through an external resistor equal to the internal resistance of the system was also implemented. The electrochemical results along with the microscopic analyses, XPS data, and the estimated rate constants show the better performance of the MES over the MFC and predict the putative mechanism of the cathodic gold deposition. The gold removal and recovery reached ca. 95% within a day and the cathodic efficiency approached almost 100%. 7% higher gold recovery and 5% higher gold removal were achieved in the MES mode, which reveals the advantage of the operation under short-circuit conditions. The deposited on the cathode gold is in its elemental state. The similar results obtained with the two types of cathodes justify replacing the gold electrodes with much cheaper graphitized paper to reduce the cost. In addition, it has been demonstrated that gold can be also recovered by MES from the aqueous solutions of its complex Na₃[Au(S₂O₃)₂], simulating leachates from printed circuit board waste, which expands the limits of its practical application.