Modified Double Potential Step Chronoamperometry (DPSC) Method for As(III) Electro-oxidation and Concomitant As(V) Adsorption from Groundwaters.

Constrained by low energy efficiency and ineffectiveness in As(III) removal under circumneutral pH conditions by many exsiting technologies, As(III) removal has become an issue. In this work we present proof of concept of a modified double potential step chronoamperometry (DPSC) method of As(III) oxidation and concomitant As(V) electro-sorption from aqueous solution. Results show that in situ anodic As(III) oxidation, As(V) electro-sorption, and As(V) electro-desorption are affected by aqueous pH with high oxidation and sorption/desorption rates observed at the elevated pH. We particularly show that effective As(III) oxidation and concomitant As(V) adsorption are related to (i) the rapid oxidation of the deprotonated species compared to the protonated species and (ii) stronger electrochemical interaction between the multicharged As(V) species and the electrodes. At 1.2 V and an electric energy consumption of 0.06 kWh m, the total As concentration can be reduced from 150 to 15 μg L using an electrochemical cell with electrode area of 10 × 8 cm and electro-sorption time of 120 min. On the basis of the experimental results, we have developed a mathematical model to describe the kinetics and mechanism of arsenic removal by the modified DPSC method with this model of use in predicting, and potentially optimizing, process performance under various conditions.