ADSORPTION ON HYDROUS OXIDES I. OXALATE AND BENZOATE ON GOETHITE

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Abstract
Summary: The adsorption of oxalic acid on synthetic goethite (α‐FeOOH) was studied using adsorption isotherms. Infrared spectra were obtained for goethite‐oxalate complexes at several points on the isotherms. On a goethite preparation with a phosphate sorption capacity of 200|μmolg−1 the amounts of oxalate strongly adsorbed varied from near zero at pH 8 to about l00μmolg−1 at pH 4 and below. At pH 3.4, the first l00μmolg−1 of oxalic acid added was strongly adsorbed as a binuclear complex (FeOOC–COOFe), replacing two singly‐coordinated OH groups by ligand exchange. At higher concentrations a further 200 μrnol g−1 of oxalic acid formed a monodentate complex (FeOOC–COOH) so that more oxalate could be accommodated.Benzoic acid was weakly adsorbed on goethite with one benzoate oxygen replacing one singly‐coordinated OH. The other oxygen of the COO group fitted into the goethite surface so that the benzene ring was at a high angle to the (100) face.

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