Enhanced adsorption removal of arsenic from mining wastewater using birnessite under electrochemical redox reactions.

• Arsenic is electrochemically adsorbed by birnessite from mining wastewater. • Electrochemical redox reactions of birnessite contribute to arsenic adsorption. • H 2 O 2 formation and high potential of birnessite anode facilitate As(III) oxidation. • Mn2+ in wastewater can also be effectively removed during arsenic adsorption. • Cell voltage reversal facilitates the continuous use of birnessite electrode. Manganese oxides have been extensively investigated for arsenic (As) adsorption from aqueous solution. However, the effect of electrochemical redox reactions on the adsorption performance and underlying mechanism remain elusive. Herein, birnessite was used for electrochemical adsorption of As from mining wastewater at a constant cell voltage, and the effect of cell voltage and the continuous use (without desorption) performance of birnessite electrode were also evaluated. At 1.2 V for 24 h, the concentrations of total As (As(T)) and As(III) in wastewater decreased from 3808.7 to 73.7 μg L−1 and 682.8 to 21.4 μg L−1, respectively. The As(T) removal ratio increased with increasing cell voltage and reached 98.1% at 1.2 V, which was higher than that at open circuit (84.1%). The Mn2+ concentration also significantly decreased in wastewater during As adsorption. The high potential of birnessite anode and the generation of H 2 O 2 on cathode facilitated As(III) oxidation, and the electrochemical redox reactions of birnessite contributed to the enhancement of As(T) removal. The application of cell voltage reversal could improve the utilization rate of birnessite electrodes by dissolution-recrystallization during continuous use, and the As(T) removal ratio was increased from 73.5% to 85.1% after five cycles of voltage alteration. The present work indicates that birnessite is a promising absorbent for the electrochemical adsorption of As from real wastewaters. [ABSTRACT FROM AUTHOR]