Electrochemical reduction of As(III) and As(V) in acidic and basic solutions

The removal of As(III) and As(V) from acidic and basic solutions by electrochemical reduction was studied using a reticulated vitreous carbon cathode and a IrO2/Ti anode in an electrochemical reactor that could be operated divided or undivided. By using a cascade of 7-9 plug flow reactors, residual concentrations of arsenic less than 20 ppb were achieved upon reduction of 100 ppm As(III) in either acidic or alkaline solutions and for 100 ppm As(V) in acidic solution. The reduction of As(V), generally considered electrochemically inactive in alkaline solutions, was proved possible, but was much less efficient. In all cases, the only product of electrochemical reduction was arsine. A moderate improvement in reduction efficiency was achieved under conditions of electrocatalytic hydrogenation using 5% Pd on alumina as catalyst.