The photochemical oxidation of arsenite [As(III)] on birnessite was investigated as a function of pH. Irradiation of As(III), birnessite suspensions with visible light led to the oxidation of As(III) at a rate that was approximately two times faster than in the absence of light. At pH 5 the majority of the arsenate product, Mn(II) was released into solution. At pH 7.4 Mn(II) did not partition into the aqueous phase, instead adsorbed and went into the interlayers of the birnessite. In the absence of O2 and presence of light, As(III) oxidation was similar to the As(III) oxidation by birnessite in dark. OH� and H2O2 produced in the presence of O2, birnessite, and light, were responsible for this additional As(III) oxidation. TEM of the post-reaction birnessite particles showed that the particles were smaller, edges are rounded compared to the pre-reaction birnessite particles, consistent with the dissolution of the particles during As(III) oxidation.

Oxidation of arsenite to arsenate on birnessite in the presence of light

244th National Meeting (2012)

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