Hydrogeological evaluation and sorption process of contaminants onto clay and sand as multi-barrier of a radioactive disposal site

This study investigates the hydrogeological and sorption characteristics of clay-sand mixtures as barrier layers in nuclear waste disposal facilities. The primary objective is to evaluate geotechnical properties and the immobilization behavior of strontium (Sr²⁺) and cobalt (Co²⁺) on clay and sand layers under simulated contaminant release scenarios from disposal packages. Saturated hydraulic conductivity (Ks) values for brown clay and brown sand were 3.78 × 10⁻⁸ and 1.02 × 10⁻ 3 cm/s, respectively demonstrating strong resistance to water flow and contaminant migration. Simulated acid water flow significantly increased Ks in brown clay but not in white clay, attributed to kaolinite’s chemical inertness (aluminum silicate-rich) in the latter versus illite, interlayer cations, calcite, and weathering in the former. Batch adsorption experiments and kinetics at pH 6 revealed superior Sr²⁺ and Co²⁺ uptake in brown clay compared to white clay and brown sand. Experimental and modeled adsorption capacities aligned best with the pseudo-second-order kinetic model, outperforming the pseudo-first-order model across all samples.