Abstract: |
Chromate adsorption on amorphous iron oxyhydroxide was investigated in dilute iron suspensions as a single solute and in solutions of increasing complexity containing CO2(g), SO42−(aq), H4SiO4(aq), and cations [K+, Mg2+, Ca2+(aq)]. In paired-solute systems (e.g., CrO42−–H2CO3*), anionic cosolutes markedly reduce CrO42− adsorption through a combination of competitive and electrostatic effects, but cations exert no appreciable influence. Additionally, H4SiO4 exhibits a strong time-dependent effect: CrO42− adsorption is greatly decreased with increasing H4SiO4 contact time. In multiple-ion mixtures, each anion added to the mixture ecreases CrO42− adsorption further. Adsorption constants for the individual reactive solutes were used in the triple-layer model. The model calculations are in good agreement with the CrO42− adsorption data for paired- and multiple-solute systems. However, the model calculations underestimate CrO42− adsorption when surface site saturation is approached. Questions remain regarding the surface interactions of both CO2(aq) and H4SiO4. The
results have major implications for the adsorption behavior of CrO42− and other oxyanions in subsurface waters. |