Chromate Adsorption on Amorphous Iron Oxyhydroxide in the Presence of Major Groundwater Ions

Authors

• John M. Zachara, Pacific Northwest National LaboratoryFollow
• Donald Girvln, Pacific Northwest National Laboratory
• Ronald Schmidt, Pacific Northwest National Laboratory
• C. Thomas Resch, Pacific Northwest National Laboratory

Date of this Version

1987

Citation

Environ. Sci. Technol. 1987, 21, 589-594

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), SO₄^2-(aq), H₄Si0₄(aq), and cations [K⁺, Mg²⁺, Ca²⁺(aq)]. In paired-solute systems (e.g., CrO₄^2- =H₂CO₃*), anionic cosolutes markedly reduce CrO₄^2- adsorption through a combination of competitive and electrostatic effects, but cations exert no appreciable influence. Additionally, H4Si04 exhibits a strong time-dependent effect: CrO₄^2- adsorption is greatly decreased with increasing H₄SiO₄ contact time. In multiple-ion mixtures, each anion added to the mixture decreases CrO₄^2- 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 CrO₄^2- adsorption data for paired- and multiple-solute systems. However, the model calculations underestimate CrO₄^2- adsorption when surface site saturation is appr6ached. Questions remain regarding the surface interactions of both CO₂(aq) and H₄Si0₄. The results have major implications for the adsorption behavior of CrO₄^2- and other oxyanions in subsurface waters.