Electrochemically-assisted intensification of As(III) removal through integrated alkalization and oxidation process

Abstract

In response to the need for trace arsenic removal and detoxification, an electro-assisted self-alkalization and oxidant-free processes (ESOP) cell was developed and investigated. It was found that the ESOP removed 90.3 % of arsenic and reduced the As(III) concentration from 150 µg L^-1 to less than 5 µg L^-1 in its cathode chamber. The As removal involved migration of As(III) and As(V) from the cathode to the anode driven by electrical current. In the ESOP cathode, As(III) was dissociated to As(III) oxyanions via alkalization and then oxidized into As(V) by H₂O₂. Nearly 80 % of As(III) migration could be attributed to the oxidation by H₂O₂ and approximately 20 % dissociation by pH alkalization. The voltage-controlled conditions (1.2 -1.5 V) achieved a peak cumulative H₂O₂ concentration of 10.9 mg L^-1. The ESOP demonstrated a high As(III) oxidation to As(V) conversion efficiency of 97.0 % as well as a low energy cost of 0.013 kWh m^-3 at 1.2 V. The migrated arsenic was stabilized onto the anode electrode through in-situ electro-oxidation of As(III) and electrosorption of As(III, V); this would help with the post-treatment waste disposal. Those results have provided important insights into an electrochemical approach for highly efficient arsenic detoxification.

Keywords: Arsenic detoxification; Arsenic oxyanions migration; As(III) dissociation and conversion; Simultaneous alkalization and oxidation.