Behavior of As(V) with ZVI–H2O System and the Reduction to As(0)

The interaction of As(V) with zerovalent iron (ZVI) and H2O system was studied under oxic and anoxic conditions. XRD and XPS analysis of the ZVI confirmed the core–shell Fe0structure with an outer coating of iron oxide/hydroxide. Batch experiments showed that the rate of removal of As(V) was very fast for oxic compared to anoxic condition. Under open atmospheric environment, the analysis revealed that ZVI spontaneously reacts with water and oxygen to form a number of iron oxide/hydroxides and the As(V) is removed from the solution by sorption/coprecipitation onto these corrosion products. However, reduction of As(V) did not take place in such experimental conditions. On the other hand, in anoxic conditions, reduction of As(V) to As(III) and As(0) was demonstrated via XPS analysis. Electrons, Fe2+(s), and H(s)formed from Fe0oxidation were thought to be the reducing agents for such reduction process. Therefore, the inherent oxide/hydroxide layer on the ZVI surface plays an important role and helps in the indirect reduction of As(V). Thus, the present study delineates the possible mechanism of As(V) reduction with ZVI-H2O system where the formation of As(0) is important in view of arsenic immobilization.