Sorption equilibrium and kinetics of NpO2+ on dispersed particles of Na-montmorillonite

Sorption equilibrium and kinetics of NpO2+ on dispersed particles of Na-montmorillonite were experimentally investigated by using a batch technique and a spectroscopic method, respectively. Considering the heterogeneity of sorption sites, we investigated the affinity spectra for the sorption of NpO2+. It was found that the spectrum for NpO2+ was monomodal but asymmetrical and that the half-width at half-maximum of the spectrum was relatively broad, indicating that the sorption sites of surface of Na-montmorillonite are strongly heterogeneous. From the kinetic spectrum for NpO2+, two sorption processes could be distinguished. It was considered that the fast process is attributable to the sorption of NpO2+ on the easily accessible outer surface of Na-montmorillonite particles and that the slower process is assigned to the sorption on the interlayer surface. Mean apparent activation enthalpies for the fast and the slow processes were evaluated as 19±2 kJ/mol and 23±3 kJ/mol, respectively. (orig.)