Electrocatalytic reductive removal of arsenite from nonferrous smelting waste acid on copper electrode

Abstract

Nonferrous smelting waste acid containing a high concentration of arsenite (As(III)) may pose a serious contamination to local ecosystems and a threat to human health. The direct electrocatalytic reduction of highly toxic As(III) to elemental arsenic (As(0)) in waste acid represents a promising green strategy for As removal. However, several obstacles remain to be overcome. In this study, we investigated the electrocatalytic reduction of As(III) to As(0) in simulated and real waste acid using an H-type cell at room temperature. The effects of diverse parameters, including cathode materials, potential, pH, and coexisting ions, on the reduction efficiency of As(III) to As(0) were examined. The selection of copper foam as the electrocatalyst was based on the findings of linear sweep voltammetry (LSV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). These measurements indicated that the Tafel slope and resistance of the copper foam were comparatively lower, thereby rendering it a suitable candidate for the desired application. The findings indicated that a lower pH was more conducive to the reduction of As(III), whereas the presence of co-existing cations impeded the reduction of As(III). The removal efficiency of As(III) was observed to reach 98 % within a 4 h period at an electrode potential of −1.25 V (vs. Hg/Hg₂SO₄) and pH 0.34. The XPS, SEM, and EDS results show that the solid precipitates are mainly composed of As(0) with a small amount of As(III). Electron paramagnetic resonance (EPR) analysis and radical scavenging experiments indicate that both direct electro-reduction and H• contribute significantly to the reduction of As(III). Our results provide a promising method for the direct removal and recovery of As(0) from nonferrous smelting waste acid.