Remediation of As-contaminated soils using citrate extraction coupled with electrochemical removal

Arsenic (As) pollution of soils poses serious threats to the ecological environment. In this study, organic acid (citrate) washing and electrochemical removal (manganese oxide cathode) were combined to remediate highly As-contaminated soils, and the effect of voltage was investigated as well. Citrate could extract the As bound to iron and aluminum oxides and enhance As mobility by indirectly reducing As(V) to As(III) in the soils. During the electrochemical removal of As, the rhodochrosite produced from the reduction of birnessite at the cathode, the birnessite generated from the re-oxidation of released Mn(II) and the ferrihydrite formed from the hydrolysis of Fe(III) at the anode together contributed to the adsorption and fixation of As in the leachate. After three successive rounds of combined remediation by citrate (0.1 mol L^-1) washing and electrochemical removal with birnessite electrode at 1.5 V, the As was totally removed in the leachate and the content of As bound to iron and aluminum (hydr)oxides was reduced by 84.2% in soils. Correspondingly, the contents of total and bioavailable As in the soil decreased from 1981.4 and 242.0 to 563.2 and 86.0 mg kg^-1, respectively. The As removal efficiency from the leachate and soil increased with increasing voltage from 0 to 1.5 V. This study provides a new method for the effective treatment of As-contaminated soils.