Mechanism of zero-valent lead reduction for removing high concentration of arsenic from waste acid of lead smelting system

Abstract

Lead metal smelting waste acid containing high concentrations of arsenic and sulfuric acid threaten human health and pose huge potential environmental risks due to its possible leakages during storage and disposal. In order to remove arsenic in smelting waste acid, a new method for arsenic removal by adding zero-valent lead and CuSO4 is proposed. The substitution reaction between zero-valent lead and CuSO4 to generate Cu0, and form a Pb-Cu galvanic cell system with zero-valent lead. Through the reduction of zero-valent lead, As(III) was reduced to As(0) and reacted with Cu0 to produce Cu3As precipitation. As the pH of waste acid changed, AsO2- will produce As2O3. When the molar ratio of Pb to As (Pb/As) was 6, CuSO4 concentration was 7 g/L, 25 °C, and 240 min, the arsenic concentration sharp decreased from 4706.4 mg/L to 35.21 mg/L, arsenic removal efficiency reached 99.25%. The arsenic removal process could be described by the shrinking core model which was controlled by a diffusion process. XRD, SEM-EDS, and XPS were used to characterize the phase, morphology, and elemental valence of the arsenic-containing precipitates. Based on the above analysis and combined with thermodynamic analysis, the mechanism of arsenic removal by zero-valent lead combined with CuSO4 was revealed.