Competitive sorption of divalent cations onto montmorillonite under high pH condition

Sugiura, Yuki  ; Ishidera, Takamitsu ; Tachi, Yukio  

We measured the sorption of Ca and its competitive sorption with Sr and Ni at high pH and ionic strength conditions. Sorption data were then evaluated using a thermodynamic sorption model. values of Ca increased with increasing pH values in alkaline pH region and the tendency was more pronounced at high ionic strength, indicating sorption onto edge sites. Fitting analyses show that Ca sorbs onto SOH sites, with CaOH sorption onto planar sites contributing at high alkaline pH regions. In competitive sorption experiments, Sr sorption onto the edge site decreased with increasing Ca concentration. In contrast, Ni sorption onto the edge site was independent of Ca. These results indicate that Sr sorbs onto the same edge sites (SOH) as Ca, while Ni sorbs onto different edge sites (SOH). Model calculations using the obtained sorption parameters reproduce the results of competitive sorption experiments.