Recovery of Elemental Arsenic from Acidic As-Containing Wastewater by a Hypophosphite Reduction Process

Abstract

Biological oxidation is a low-carbon technology for the treatment of As-containing gold ores, but it causes a large amount of acidic As-containing wastewater that is harmful to the environment. This paper proposed a novel, eco-friendly method to treat this wastewater. Thermodynamic analysis, H2PO2− reduction, and wastewater recycling tests were conducted. Thermodynamic analysis indicates the feasibility of the reduction of As(V)/As(III) by H2PO2− or H3PO2 to As0 under acidic conditions. Experimental results confirmed the thermodynamic prediction and showed that H2PO2− could efficiently convert the As (i.e., As(V)/As(III)) in the wastewater to high value-added As0. Under the optimal conditions, 99.61% of As precipitated out, and the obtained As0 had a high purity of 98.5%. Kinetic results showed that the reaction order of H2PO2− concentration was 0.6399, and the activation energy of the H2PO2− reduction process was 34.33 kJ/mol, which is indicative of a mixed-controlled process (20–40 kJ/mol). Wastewater recycling results showed that after recovering As, the wastewater could be reused as a bacterial culture medium. Based on the thermodynamic analysis and experimental and analytical results, hypophosphite reduction mechanisms for removing and recovering As from its acidic wastewater were proposed. The results presented in this paper suggest the feasibility of this one-step H2PO2− reduction approach, which may be promising in treating acidic As-containing wastewater.