Sodium citrate enhancing electrodeposition of metallic arsenic from toxic trivalent arsenic and the mechanism understanding

Electrochemical conversion of hypertoxic trivalent arsenic to value-added metallic arsenic can not only contribute to pollution abatement, but also resources reutilization, therefore being widely explored. Electrochemical reduction of trivalent arsenic as a promising way is widely explored. However, the high efficiency conversion is retarded by the sluggish reduction kinetics of AsO₃^3- and fierce evolution of side products of both H₂ and toxic AsH₃. Herein, by using the sodium citrate as the additive, the current efficiency for metal arsenic production is increased greatly from 60% to 91%, with the accompanied evolution of hypertoxic AsH₃ being restrained from 0.15 Nm³/t_As to 0.022 Nm³/t_As, promising a high-efficiency and green process. The electrochemical tests and electrode surface characterizations as well as DFT calculations indicate that the added sodium citrate promotes both the diffusion of reactive AsO₃^3- towards the cathode and its subsequent adsorption on the Ti cathode, contributing to smoother reduction for generating metal arsenic, with the evolution of toxic AsH₃ being hindered at the same time. The results can provide new insights for the high-efficiency and greener conversion of hypertoxic trivalent arsenic to value-added metallic arsenic.