Solid-solution reactions in As(V) sorption by schwertmannite

Fukushi, Keisuke*; Sato, Tsutomu*; Yanase, Nobuyuki

The mechanism of As(V) sorption on schwertmannite was investigated by a batch sorption experiment as a function of solution As(V) concentration under acidic conditions (pH 3.3 0.1) at 25 C. The reacted solution chemistry and mineralogy showed that the mechanism of As(V) sorption was ligand exchange with solid phase SO in schwertmannite. Two processes presumably occur simultaneously within the reaction period. i.e., ligand exchange of As(V) with surface site SO and subsequent transfer of As(V) to the structure and ligand exchange with tunnel site SO. The exchange ratio between As(V) sorption and SO release, and the SO coordination environment in schwertmannite indicates that monodentate As(V) coordination occurs in surface sites while bidentate binuclear As(V) coordination occurs in tunnel sites. Sorption modeling that considers the different types of reactive sites successfully described the observed As(V) sorption behavior.