In-situ production of iron flocculation and reactive oxygen species by electrochemically decomposing siderite: An innovative Fe-EC route to remove trivalent arsenic.

The removal of trivalent arsenic (As (III)) from water has received extensive attention from researchers. Iron electrocoagulation (Fe-EC) is an efficient technology for arsenic removal. However, electrode passivation hinders the development and application of Fe-EC. In this work, an innovative Fe-EC route was developed to remove As (III) through an electrochemical-siderite packed column (ESC). Ferrous ions were produced from siderite near the anode, and hydroxide was generated near the cathode during the electrochemical decomposition of siderite. As a result, an effect of Fe-EC-like was obtained. The results showed that an excellent removal performance of As (III) (>99%) was obtained by adjusting the parameters (As (III) concentration at 10 mg/L, pH at 7, Na2SO4 at 10 mM and the hydraulic retention time at 30 min) and the oxidation rate of As (III) reached 84.12%. The mechanism analysis indicated that As (III) was oxidized to As (Ⅴ) by the produced active oxide species and electrode, and then was removed by capturing on the iron oxide precipitates. As (III) was likely to be oxidized in two ways, one by the reactive oxygen species (possibly •OH, Fe(IV) and •O2- species), and another directly by the anode. The long-term effectiveness of arsenic removal demonstrated that ESC process based on the electrochemical-siderite packed column was an appropriate candidate for treating As (III) pollution.