Palladium removal from the simulated nuclear spent fuel solution using a silica-based SiPyR-N3 anion exchanger

The ERIX process consists of electroreduction and anion exchange for reprocessing spent nuclear fuels, in which Pd removal from spent fuel solution is necessary in the first step, since Pd can deposit at the electrode in the metallic state and interfere with the electroreduction. In the present work, the possibility in selective removal of Pd using a porous silica-supported anion exchanger, SiPyR-N3, containing a pyridine group has been studied. Adsorption behavior of Pd(II) from a simulated solution using a SiPyR-N3 packed column has been investigated. The elution of Pd(II) using 0.05 M DTPA and 0.2 M thiourea was examined and compared. The SiPyR-N3 resin showed a significantly strong adsorption for Pd(II) from HNO₃ solution. The unique adsorption was considered to result from the complex formation between Pd(II) and the resin which contains the soft-atom N with a lone pair of electrons. U(VI) and some typical simulated fission products, La(III), Pr(III), and Sr(II), showed almost no or very weak adverse impact on the Pd(II) separation, except for Re(VII) and Ru(III). The results of column experiments demonstrated that the Pd can be selectively removed from the nuclear spent fuel solution, though further work is needed to improve Pd elution.