Abstract
Five clays from four different deposits in the Ivory Coast (Adattie, Nieki, Grand-Bassam, Nigui-Saff) were studied by Fe-57 Mossbauer spectroscopy and electron paramagnetic resonance (EPR) at room temperature. Their chemical compositions were determined by X-ray fluorescence and the most important crystalline phases were identified by X-ray diffraction. In these natural clays, kaolinite is the dominant mineral phase with minor amounts of other minerals including quartz, haematite, goethite, lepidocrocite and illite. Room-temperature Fe-57 Mossbauer spectra of the samples from Nieki, Adattie and Nigui-Saff show mainly a broad quadrupole-split doublet which indicates that iron is essentially present as Fe(III). Samples from Grand-Bassam contain important amounts of goethite (alpha-FeOOH) and lepidocrocite (gamma-FeOOH). Some samples from Nigui-Saff contain large amounts of haematite. Clays from Nieki and Adattie are characterised by very low concentrations of iron oxides or hydroxides, and by small amounts of structural Fe(II) in the kaolinite lattice. Oxidation states and lattice sites of structural iron in the kaolinites were determined by Fe-57 Mossbauer spectra recorded after iron extraction with dithionite-citrate-bicarbonate (DCB). The results were confirmed by electron paramagnetic resonance (EPR) measurements