Adsorptive Removal of Strontium by Binary Mineral Mixtures of Montmorillonite and Zeolite

The adsorption characteristics of montmorillonite and zeolite minerals and their mixtures for Sr removal have been studied by means of a radiotracer technique using the Sr-90 isotope. Experimentally measured distribution coefficients for both single and binary adsorbent systems are in agreement with mathematically calculated values. Adsorption capacities for Sr calculated from Dubinin-Radushkevich isotherm parameters increase with increasing zeolite fraction in binary mixtures, whereas they decrease in the presence of NaCl with respect to pure SrCl2 solutions. Thermodynamic parameters have been estimated from the temperature dependency of the adsorption equilibrium constants evaluated from the selectivity coefficients in brines. Results show that Sr adsorption is an endothermic process, but the spontaneity of adsorption increases with increasing zeolite fraction and temperature. A site distribution function has been mathematically calculated by using the Freundlich isotherm parameters, which gives valuable information about the affinity of exchange sites on the adsorbents for binary exchange between Sr and Na.