Surface complexation modelling of uranium sorption data obtained by isotope exchange techniques

Uranyl sorption on samples from the vicinity of two uranium ore deposits was studied using a batch adsorption technique, and the results modelled using the surface complexation approach. The use of a synthetic groundwater spiked with an artificial uranium isotope (236U) enabled adsorption to be measured together with desorption of the natural uranium in the samples. The amount of 238U taking part in sorption interactions was estimated from the isotope exchange between 236U and 238U. This 'accessible' fraction comprised approximately 20 per cent of the uranium in the samples, and the use of this amount rather than the total uranium content was more realistic for modelling purposes. Although the surface complexation model was only applied to sorption on the amorphous iron component of these complex samples, it gave a reasonable description of experimental results. (orig.)