Modification of natural zeolite with iso-polyanions for the separation of cesium and strontium from aqueous solutions

Cesium (۱۳۷Cs) and Strontium (۹۰Sr) are among the most dangerous isotopes present in nuclear waste. These radionuclides can be adsorbed using synthetic zeolites such as type A[۱], as well as natural zeolites like mordenite and clinoptilolite[۲]. One of the earliest applications of the ion exchange properties of zeolites is their use in the adsorption and separation processes of the radioisotopes ۹۰Sr and ۱۳۷Cs[۳]. Among these zeolites, clinoptilolite is a suitable option due to its abundance and accessibility.In the present study, different techniques for modifying zeolites with zirconium molybdate iso-polyanions were investigated. The optimal modification method was chosen based on the adsorption capacity of strontium (II) and cesium (I) ions after the characterization of the adsorbents. The modified adsorbent demonstrated a ۲۶% enhancement in strontium (II) ion capacity, increasing from ۳۲ mg/g to ۴۰.۴ mg/g, while it had negligible impact on cesium (I) ion adsorption. Adsorption tests revealed that calcination of the adsorbent during any stage of modification decreases its adsorption capacity. Increasing the amount of iso-polyanion used in the zeolite modification stage also increases the adsorption capacity but raises the cost of the modified adsorbent. Therefore, the weight ratios of zirconium to zeolite and molybdate to zirconium-modified zeolite were selected as ۰.۳۸ and ۰.۵۸, respectively. Finally, the effects of pH and the concentration of strontium and cesium ions were examined. The maximum adsorption capacities for strontium ions by natural and modified zeolite adsorbents occurred at pH ۶.۸ and ۶.۷, respectively, and for cesium at pH ۶.۹ and ۶.۲. Increasing the initial concentration of metal ions in the solution led to an increase in adsorption capacity.

کلیدواژه ها:

Clinoptilolite ، Modified zeolite ، Cesium ، Strontium ، Zirconium ، Molybdate