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Report No.

Migration behavior of actinide colloids in near-field

Nagasaki, Shinya*

Equilibrium and kinetics of sorption of NpO$$_{2}^{+}$$ on illite were investigated at pH = 6 by using the differential pulse anodic stripping voltammetry method and the spectroscopic method, respectively. It was found that the sorption isotherm obtained was fitted better by the Langmuir-Freundlich type equation than by the Langmuir equation. The heterogeneity coefficient was 0.89 $$pm$$ 0.05 and the half width at half maximum (HWHM) of affinity spectrum was 0.19 log unit, indicating that the surfacc of illite used has a low degree of heterogeneity. The kinetic spectra indicated that the sorption of NpO$$_{2}^{+}$$ occurs only at the outer surfacc. The mean HWHM of the kinetic spectra was 0.18 log unit. This also proves that the sorption kinetics of NpO$$_{2}^{+}$$ on the illite used is controlled by the same heterogeneity of the sorption sites. From the dependence of mean rate constants on temperature, a mean apparent activation enthalpy and a mean apparent activation entropy were evaluated at 37$$pm$$3 kJ/mol and - 69 $$pm$$ 7 J/K$$cdot$$mol, respectively. This value of enthalpy suggests that the sorption is not controlled by diffusion through the hydrodynamic film around the illite. Equilibrium and kinetics of sorption of NpO$$_{2}^{+}$$ and Np(V) carbonate complexes (mainly NpO$$_{2}$$CO$$_{3}$$) on Na-montmorillonite were also examined by using same technique.



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