Retention of redox sensitive elements in aquifers—the case of neptunium

An original development based on a surface complexation model allows Kd calculations as a function of the redox potential. Neptunium is studied because its redox chemistry is complex due to the presence of various valence states ranging from Np(III) to Np(VII). Its sorption on SiO2, FeOOH and A12O3 is calculated as a function of the redox potential for different pHs using a simplified surface complexation model. Calculated Kd values are consistent with the experimental Kd data from the literature for Np or analogous species (Am(III), Th(IV), U(VI)) at pH8. The neptunium retention in aquifers may then be evaluated on the basis of their porosity properties.