Contrasting sorption behavior of arsenic(III) and arsenic(V) in suspensions of iron and aluminum oxyhydroxides

United Kingdom It has been widely observed that the sorption of arsenic (As) as As(III) and As(V) on iron (Fe) oxyhydroxides is comparable as is the sorption of As(V) on Fe and aluminum (Al) oxyhydroxides. However, quite different sorption behavior has been observed for As(III) on Fe and Al oxyhydroxides. Here, surface complexation modeling is used to show that recent reports of As(III) sorption onto Al oxyhydroxides are consistent with previous observations of negligible sorption under conditions relevant to water treatment. This modeling exercise also demonstrates that the level of protonation of surface species is not well constrained by commonly-reported pH edges and that the possibility of distinguishing between mononuclear and binuclear surface complexes depends on the level of surface coverage. These issues complicate the integration of macroscopic sorption studies with spectroscopic studies and molecular modeling.