JRP CALL information
Supported By

European Commission

Short description of the work

This research project focuses on the sorption of the redox sensitive element neptunium by montmorillonite under geochemical conditions relevant for radioactive waste repositories. In the near-field, corrosion of steel containers produces large amounts of Fe(II), which may influence Np sorption by the engineered barrier system. The sorption of the reduced Np(IV) in the absence Fe(II) will be studied by batch sorption experiments to verify the chemical analogy with Th(IV) and to provide Kd values for the performance assessment. For the oxidized Np(V), we will measure sorption edges and isotherms in the presence and absence of dissolved Fe(II). These experiments aim at elucidating the sorption mechanism in the presence of dissolved Fe(II), i.e. competitive sorption as well as surface mediated redox reactions between sorbed Fe(II) and Np(V). The 2SPNE SC/CE sorption model is complemented with the derived surface complexation reactions and associated thermodynamic constants for Np(IV/V) and with redox reactions. X-ray absorption spectroscopy (XAS) is carried out on the Np(V)-Fe(II)-montmorillonite system to derive structural information on the surface complexes. The results provide hitherto neglected data for the performance system of anoxic radioactive waste repositories.

 
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