Electro-removal of arsenic(III) and arsenic(V) from aqueous solutions by capacitive deionization

The feasibility of the electro-removal of arsenate (As(V)) and arsenite (As(III)) from aqueous solutions via capacitive deionization was investigated. The effects of applied voltage (0.0-1.2 V) and initial concentration (0.1-200 mg L−1) on arsenic removal were examined. As evidenced, an enhancement of arsenic removal can be achieved by capacitive deionization. The capacity to remove As(V) at an initial concentration of 0.2 mg L−1 on the activated carbon electrode at 1.2 V was determined to be 2.47 × 10−2 mg g−1, which is 1.8-fold higher than that of As(III) (1.37 × 10−2 mg g−1). Notably, the possible transformation of arsenic species was further characterized. The higher effectiveness of As(V) removal via electrosorption at 1.2 V was attributed to the formation of an electrical double layer at the electrode/solution interface. The removal of As(III) could be achieved by the oxidation of As(III) to As(V) and subsequent electrosorption of the As(V) onto the electrode surface of the anode. The presence of sodium chloride or natural organic matter was found to considerably decrease arsenic removal. Single-pass electrosorption-desorption experiments conducted at 1.2 V further demonstrated that capacitive deionization is a potential means of effectively removing arsenic from aqueous solutions.