Arsenite Oxidation Coupling With Arsenate Removal in An Aerated Zero-Valent Aluminum System With Fe(II).

Arsenite oxidation coupling with arsenate removal in an aerated zero-valent aluminum system with Fe(II)

Yu-Min Tzou   C.E. Hwang

Abstract

Groundwater from a number of aquifers worldwide has been identified as having high concentrations of arsenic (As), mainly As(III) and As(V). Mining-related activities, leading to the release of As with extremely acidic solutions (pH < 2) into surface or ground waters, have also been recorded in many parts of the world. Although As(III) treatment by zero-valent iron (ZVI) is a promising technique, the choice of alternative zero-valent metals is still needed because ZVI may not be readily obtained by people currently struggling with As problems. In this regard, aluminum alloys/foils, such as aluminum beverage cans (consisting of more than 95% aluminum) or zero-valent aluminum (ZVAl), may be a potential substitute for ZVI because these materials can be readily recycled and because aluminum metal is more efficient at providing the thermodynamic driving force for electron transfer. Results showed that in an aerated system with Al beverage cans or ZVAl, As(III) oxidation did not occur; however, Fe(II) (0.1-0.4 mM) could promote As(III) oxidation and the reaction increased with an increase of Fe(II) concentrations. As(III) oxidation was more favorable at lower pH, and the oxidation was best described by zero-order reaction. The productions of OH radicals through the reactions of H₂O₂ (derived from the interactions of O₂ with Al) and Fe(II) are responsible for As(III) oxidation. Upon the oxidation of As(III) to As(V), the redox products of metal ions, such as Al³⁺ and Fe³⁺, could be co-precipitated or could serve as adsorbents for As(V), and thus, As could be completely removed in a cost-effective manner.