Assessment of synthetic zeolite Na A–X as sorbing barrier for strontium in a radioactive disposal facility

The retention of strontium onto synthetic zeolite Na A–X, candidate as backfill material in a near surface disposal facility, was studied using batch and column techniques. In order to investigate the sorption mechanism, the kinetic data were tested using pseudo-first-order, pseudo-second-order, homogenous particle, and intraparticle models. The suitability of the geochemical conditions was preliminarily assessed by conducting equilibrium sorption studies at different pH ranging from 2.0 to 9.0. To optimize the design of the barrier, the effect of the initial concentration on the retention of Sr2+ onto the proposed material at three temperatures was investigated. The sorption equilibrium data were analyzed using non-linear Freundlich, Langmuir, and D–R models to evaluate the sorption characteristics and the thermodynamic parameters such as changes in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) were calculated. To assess the effect of the utilized method to determine the retardation coefficients on the predicted concentration, a simple pulse analytical model was used.