The Mechanism of Sulfate Adsorption on Iron Oxides

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Abstract
Adsorption isotherms were determined for sulfate adsorption on iron oxides under acid conditions. The product of the surface reaction between the iron oxides and sulfate ions was examined by infrared spectroscopy which showed four bands in the v S‐O stretching region. Thus a structural model could be obtained for the reaction. Two surface hydroxyl groups (or OH2+ ions) are replaced by one sulfate ion, and two oxygen atoms of the sulfate ion are coordinated each to a different Fe3+ ion, resulting in the binuclear bridging surface complex Fe‐O‐S(O2)‐O‐Fe. The complex is formed on the surfaces of goethite (α‐FeOOH), akaganéite (β‐FeOOH), lepidocrocite (γ‐FeOOH), hematite (α‐Fe2O3) and amorphous ferric hydroxide.