Application of simplified desorption method to study on sorption of neptunium(V) on montmorillonite-based mixtures

Kozai, Naofumi   ; Yamasaki, Shinya; Onuki, Toshihiko

To elucidate migration behaviors of radionuclides in the subsurface environment, this paper investigated sorption-desorption behavior of neptunium(V) on montmorillonite -based two-mineral systems. In montmorillonite-calcite system, the sorption on the montmorillonite moiety decreased with increasing calcite content due to interference by the calcium ions dissolved from the calcite moiety, while Np was not accumulated to the calcite. Total Np sorption on montmorillonite-apatite system was larger than that on apatite-free montmorillonite, but the sorption on the montmorillonite moiety in this system was less than that on apatite-free montmorillonite. Under weakly acid and neutral pH conditions, Np accumulated on the apatite moiety. At final pH 4, though the apatite moiety completely dissolved, the sorption increased with time and the increased Np was was not cation exchangeable. This increase of the unexchangeable sorption cannot be explained by the knowledge accumulated so far.