Abstract
Calcite (CaCO 3) was treated with uranyl solutions of different concentrations in perchlorate medium at an initial pH of 6. X-ray photoelectron spectroscopy (XPS) measurements showed that there is no physi- or chemisorption of uranyl perchlorate molecules at the mineral surfaces and no diffusion of ClO 4 − anions into the mineral grains. We conclude this, because no chlorine atoms could be detected by XPS measurements. A significant amount of uranyl hydroxides is formed at the mineral surfaces. In addition, up to 20% of the calcium ions are exchanged by uranyl ions at the calcite surface. The inter-atomic uranium-oxygen distances of the reaction products at the mineral surface were determined using extended X-ray absorption fine structure (EXAFS) spectroscopy. In addition, the contacting solutions were studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). A new uranyl species was found in solution, which is also present in seepage waters from mine-tailing piles.
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