Arsenite Oxidation by a Poorly-Crystalline Manganese Oxide. 3. Arsenic and Manganese Desorption

Arsenic (As) mobility in the environment is greatly affected by its oxidation state and the degree to which it is sorbed on metal oxide surfaces. Manganese oxides (Mn oxides) have the ability to decrease overall As mobility both by oxidizing toxic arsenite (AsIII) to less toxic arsenate (AsV), and by sorbing As. However, the effect of competing ions on the mobility of As sorbed on Mn-oxide surfaces is not well understood. In this study, desorption of AsV and AsIII from a poorly crystalline phyllomanganate (δ-MnO2) by two environmentally significant ions is investigated using a stirred-flow technique and X-ray absorption spectroscopy (XAS). AsIII is not observed in solution after desorption under any conditions used in this study, agreeing with previous studies showing As sorbed on Mn-oxides exists only as AsV. However, some AsV is desorbed from the δ-MnO2 surface under all conditions studied, while neither desorptive used in this study completely removes AsV from the δ-MnO2 surface.