X-RAY-ABSORPTION SPECTROSCOPY INVESTIGATION OF SURFACE REDOX TRANSFORMATIONS OF THALLIUM AND CHROMIUM ON COLLOIDAL MINERAL OXIDES

Examination of the adsorption mechanism of Tl and Cr on selected miner al oxides was carried out by X-ray Absorption Spectroscopy (XAS) using synchrotron radiation. Information on the oxidation states of surface bound species was obtained from the low energy side of XAS spectra, t he XANES (X-ray Absorption Near Edge Structure) region. Surface precip itation of Tl2O3(S) was found to take place on delta-MnO2(s) as a resu lt of Tl(I) sorption and oxidation at the mineral surface. Adsorption of chromates on alpha-FeOOH(s) containing very small amounts of ferrou s ions was observed to be followed by partial reduction to Cr(III).