ADSORPTION ON HYDROUS OXIDES. IV. MECHANISMS OF ADSORPTION OF VARIOUS IONS ON GOETHITE

Abstract

Summary Infrared spectroscopy has been used to investigate the complexes that are formed when acids are evaporated onto goethite. It is probable that, like HPO 2− 4 , the anions SO 2− 4 , SeO 2− 3 , and oxalate are adsorbed by ligand exchange and form binuclear bridging complexes where two singly coordinated A‐type OH groups are replaced by two oxygen atoms of one ligand. There is evidence that HPO 2− 4 and oxalate are likely to be present in this form in wet environments, and this is probably also true for SO 2− 4 and SeO 2− 3 . Fluoride ions can completely replace the singly coordinated A‐type OH groups but do not replace C‐ or B‐type OH groups that are coordinated, respectively, to two and three Fe 3+ ions. The other halides, nitrate, and benzoate partially replace the A‐type OH groups, benzoate being adsorbed as a monodentate ligand. Copper ions do not appear to react with A‐type OH but zinc ions are probably adsorbed on the goethite (100) face in conjunction with carbonate or bicarbonate.