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

Abstract

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 AsO33− 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/tAs to 0.022 Nm3/tAs, 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 AsO33− 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.