Oxidation of acetaminophen at boron-doped diamond (BDD) and at Ti/SnO 2 anodes in a plug-flow divided electrochemical reactor led to electrochemical combustion, whereas at Ti/IrO 2 benzoquinone was the exclusive product except at very long electrolysis times. The difference is explicable in terms of the different mechanisms of oxidation: direct oxidation at the anode for Ti/IrO 2 vs. indirect oxidation involving electrogenerated hydroxyl radicals at BDD and Ti/SnO 2 . At BDD, at which the efficiency of degradation of acetaminophen was greatest, the rate of electrolysis at constant concentration was linearly dependent on the current, and at constant current linearly dependent on the concentration. Current efficiencies for mineralization up to 26% were achieved without optimization of the cell design.

Acid mine drainage (AMD), which is caused by the biological oxidation of sulfidic materials, frequently contains arsenic in the form of arsenite, As(III), and/or arsenate, As(V), along with much higher concentrations of dissolved iron. The present work is directed toward the removal of arsenic from synthetic AMD by raising the pH of the solution by electrochemical reduction of H+ to elemental hydrogen and coprecipitation of arsenic with iron(III) hydroxide, following aeration of the catholyte. Electrolysis was carried out at constant current using two-compartment cells separated with a cation exchange membrane. Four different AMD model systems were studied: Fe(III)/As(V), Fe(III)/As(III), Fe(II)/As(V), and Fe(II)/As(III) with the initial concentrations for Fe(III) 260 mg/L, Fe(II) 300 mg/L, As(V), and As(III) 8 mg/L. Essentially quantitative removal of arsenic and iron was achieved in all four systems, and the results were independent of whether the pH was adjusted electrochemically or by the addition of NaOH. Current efficiencies were approximately 85% when the pH of the effluent was 4-7. Residual concentrations of arsenic were close to the drinking water standard proposed by the World Health Organization (10 microg/L), far below the mine waste effluent standard (500 microg/L).

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/IrO 2 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, AsH 3 . 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.