Surface complexation of Ca and competitive sorption of divalent cations on montmorillonite under alkaline conditions

アルカリ条件下におけるモンモリロナイト上でのCaの表面錯体形成および2価陽イオンの収着競合

杉浦 佑樹  ; 石寺 孝充 ; 舘 幸男  

Sugiura, Yuki; Ishidera, Takamitsu; Tachi, Yukio

In the geological disposal system, increase of Ca concentration with the alteration of cementitious materials would affect the retention of other radionuclides by competitive sorption. Batch sorption experiments were performed to investigate sorption behavior of Ca and competition with other divalent cations (Sr and Ni) on the edge site of montmorillonite under alkaline conditions. Ca and Sr formed surface complexation with the edge site at higher pH region compared to Ni. Sr sorption decreased with Ca concentration in alkaline pH region, whereas Ni sorption was not affected by Ca concentration. These results indicate that Ca and Sr sorb onto the same site while Ca and Ni sorb onto different sites, and competitive sorption depends on the chemical similarity such as hydrolysis behavior. Sorption model parameters obtained from the single element batch sorption experiments successfully reproduced the results of competitive sorption experiments.