Figure 6. Proposed mechanism of As(III)-nZVI reactions. The process includes (1) rapid adsorption of aqueous As(III) at the oxide surface, (2)
reduction of As(III) complexes at the surface, (3) translocation of arsenic across the oxide shell accompanied by further breaking of As−O bonds,
and (4) diffusion into the Fe(0) core. Arsenic prefers to accumulate at the surface of Fe(0) forming a thin layer of Fe−As intermetallic, thus the
amount of reduced arsenic depends on the amount of nZVI used. As* denotes intermediate states between As(III) and Fe−As intermetallic.