Adsorption/Desorption Characteristics of Cesium Ions on Natural and Synthetic Minerals

Geochemical reference samples, a natural zeolite, synthetic zeolites, vermiculite, and bentonite were tested for their adsorption and desorption characteristics of cesium. Large amounts of cesium were adsorbed on bentonite and natural zeolite because of their pore sizes or lamellar structures and their large numbers of exchangeable cations. In the geochemical reference samples, the adsorption behavior of cesium was affected by the exchangeable cation content and the soil corrosion product content. The desorption ratios of cesium from the minerals were influenced by the amounts of cations in the solution. The desorption ratios of cesium from the natural and synthetic zeolites were 5.4% and 70% to 75%, respectively, with 0.1 mol/L of hydrochloric acid. The amounts of aluminum ions eluted from the synthetic zeolites due to structure collapse was approximately 30-fold higher than that from the natural zeolite. Cesium adsorption ratios onto the minerals and the desorption ratios from the minerals decreased as the calcination temperature increased. X-ray diffraction and scanning electron microscopy confirmed that the mineral surface was melted by heating. The desorption of cesium ions was inhibited by cement hardening treatment of the minerals because the cement hydrates that coated the mineral particle surfaces could adsorb cesium.