Effect of Dopants on Strontium-Adsorption Performance of Metal-Doped Antimony Ion Exchangers

抄録

Radioactive strontium-90 (⁹⁰Sr) is one of the heat-generating nuclides generated by nuclear reactions in reactors, and selective separation of strontium is an efficient treatment method. It was demonstrated that some metal-doped antimony silicates showed high strontium-adsorption performance under acidic condition. The effects of ionic radii and acidity of dopants, namely, tungsten, vanadium, tantalum, and zirconium, on the strontium-adsorption performance of antimony silicates under acidic condition and a solution containing sodium ions were investigated. The results of the investigation revealed that the ion-exchange capacity of metal-doped antimony silicate was 2.4 mEq/g for vanadium, 1.8 mEq/g for tungsten and tantalum, and 1.3 mEq/g for zirconium; basically, it decreased as a function of the ionic radius of the dopant. The tungsten-, vanadium-, and tantalum-doped antimony silicates had high distribution coefficients for strontium (Kd_Sr) of over 10³ L/kg in deionized water, chloride solution, and nitric acid solution under various pH conditions. Kd_Sr under acidic condition increased with increasing acidity of the dopants. At various sodium concentrations, Kd_Sr of tungsten-, vanadium-, and tantalum-doped antimony silicates was greater than Kd_Ca. The selectivity coefficient of strontium over sodium (K_Sr–Na) was found to depend on the ionic radius of the dopant. These results indicate that the ionic radii and acidity of the dopants affect the total number of adsorption sites and activation of individual adsorption sites; that is, larger ionic radii of dopants cause collapse of the pyrochlore structure of the antimony silicates, thereby decreasing the ion-exchange capacity, and dopants with high acidity support the formation of cationic-exchange groups that increase Kd_Sr for antimony silicates under acidic conditions.