Sorption and Colloidal Behavior of Np(IV) in a Bentonite-Carbonate Solution System

Abstract

Abstract Sorption of Np(IV) on bentonite in the presence of carbonate was studied by a batch method. The sorption was considered mainly due to Np(OH)2(CO3)2 2- and Np(OH)4(CO3)2 4- The distribution coefficient (Kd of Np(OH)2(CO3)2 2- and Np(OH)4 (CO3)2 4- was determined to be 104.01±0.24 ml/g and 103.93±0.37 ml/g respectively. The increasing Kd at high pH was attributed to the sorption of NpO2(OH)-2 with the Kd of 105.82±0.39 ml/g The formation of colloidal species was observed under a reducing condition. By assuming Np(OH)4 as the colloidal species, the formation constant was evaluated to be βc≤1053.85 Under an oxidizing condition, the formation of the colloidal species was less observed possibly due to the transformation of Np(OH)4 to NpO2OH.