Catalytic Oxidation of Arsenite By Polyoxometalate in the Presence of Aluminum Metal and Ferrous Ion.

Arsenic (As) consists of two major inorganic forms of As(III) and As(V) in the natural environments. Both As are toxic and carcinogenic, and thus, a maximum As level of 10 μg/L in drinking water have been suggested by the World Health Organization (WHO). To meet the criteria, zero-valent iron (ZVI) metals have been used as a precursor of OH radicals to convert more toxic As(III) to As(V), followed by As(V) removal on iron hydro(o)xides to eliminate the possible impacts of As derived from either anthropogenic or geological sources. However, the efficiency of ZVI as As scavengers is low due to the presence of oxide layers on the surfaces of ZVI which inhibit greatly the electron-transferring between reactants. In the current study, zero-valent aluminum (ZVAl) metals and polyoxometalate (POM), an anionic cluster, were used to provide a better efficiency for As removal because ZVAl exhibits a higher reduction potential and POM can serve as a bronsted acid and an electron shuttle for removing oxide layers and promoting electron transfer, respectively. Results showed that 78 and 30 mM H₂O₂ at pH 1 and 2, respectively, would be produced when 0.1 mM POM reacted with 1 g ZVAl in the presence of O₂. Upon H₂O₂ formation, the presence of 0.25 mM ferrous ions would lead to OH radical productions through a Fenton-like reaction. As a result, 16 mg/L As(III) could be oxidized, and the generation of OH ions from Fenton-like reaction would lead to the formation of Al hydr(o)oxides for As(V) removal. The recycle and reuse of POM will be our next approach to allow developing a cost-effective technique for As removal.