First-principles calculation study of mechanism of cation adsorption selectivity of zeolites; A Guideline for effective removal of radioactive cesium

Nakamura, Hiroki  ; Okumura, Masahiko   ; Machida, Masahiko  

Zeolites have attracted attention in reprocessing of radioactive nuclear wastes because of their high selective affinity for radioisotopes of Cs. Very recently, the useful property has been widely utilized in decontamination after the accidents at Fukushima Daiichi Nuclear Power Plants. In this paper, we study the high selectivity in Cs adsorption of zeolites by using first-principles calculations and clarify mechanism of the cation selectivity. We obtain energy surfaces on any captured locations for Cs/Na ion inside the micropore of a zeolite, "mordenite" and find three crucial conditions for high ion selective exchange of Na for Cs as (1) micropore whose radius 3 , (2) moderate Al/Si ratio, and (3) uniform distribution of Al atoms around the micropore. These insights suggest a guideline to develop zeolites with high Cs selectivity and to enhance the cation selectivity in more general situations.