Electrochemical Method for Remediation of Arsenic-Contaminated Nickel Electrorefining Baths

At only ppm concentrations, arsenic is incompatible with the deposition of pure nickel at the cathode of a nickel electrorefining bath. We report an electrochemical method for the removal of arsenic. At a Ti/IrO2 anode, chloride ion in the bath is oxidized to HOCl, which effects the chemical oxidation of As(III) to As(V). HOCl also reoxidizes any As(III) that might be formed by back-reduction at the pure nickel cathode, preventing cathodic reduction of As(III) to elemental arsenic or to the toxic gas arsine, AsH3. If, alternatively, a pure copper cathode is employed, the cathode potential can be controlled to electroseparate copper from nickel during the remediation of the bath, while achieving complete oxidation of As(III). After pH adjustment to ~4, arsenic is removed with added Fe(III) as a chemisorbed arsenate-ferrihydrite precipitate, leaving the bath essentially free of both iron and arsenic.