Sorption of strontium onto illite/smectite mixed clays

Radioactive strontium is a by-product of the fission of uranium and plutonium and its mobility in the environment is largely dominated by sorption onto soil minerals, especially clays. In this study, the sorption behaviour of Sr in illite/smectite mixtures was analyzed from a mechanistic point of view. Sorption of Sr onto smectite and illite, previously homoionised in Na, was studied under different pHs, ionic strengths and radionuclide concentrations. Sorption experiments were also carried out with smectite and illite, mixed in two different proportions: 50–50% and 75–25%. Sr sorption data that were obtained from the single mineral systems were modelled considering both ionic exchange and surface complexation and using a non-electrostatic model. The selectivity coefficients and complexation constants obtained for the individual minerals were incorporated into a model to predict the adsorption of Sr in binary adsorbent systems and the model predictions were consistent with Sr experimental adsorption data.