Impact of the degradation leachate of the polyacrylonitrile-based material UP2W on the retention of Ni(II), Eu(III) and Pu(IV) by cement.

The uptake of 63 Ni(II), 152 Eu(III) and 242 Pu(IV) by hardened cement paste (HCP, CEM I) in the degradation stage II (pH ≈ 12.5, [Ca] ≈ 0.02 M) was investigated in the presence of a degradation leachate of UP2W, a polyacrylonitrile-based (PAN) material used as a filter aid in nuclear power plants. The degradation leachate with a concentration of dissolved organic carbon of ∼40 ppm was obtained from the degradation of UP2W in portlandite-buffered solutions for ca. 1100 days. Redox conditions in the Pu systems were buffered with hydroquinone, which defines mildly reducing conditions (pe + pH ≈ 10) where Pu(IV) is the predominant oxidation state. The degradation leachate investigated in this work is moderately sorbed by cement, with distribution ratios ( R d ) of (0.35 ± 0.15) m 3 kg -1 . These values are 30 to 100 times greater than distribution ratios previously reported for proxy ligands of PAN degradation products, i.e. , glutaric acid, α-hydroxyisobutyric acid and 3-hydroxybutyric acid. The presence of the degradation leachate induces a moderate decrease in the uptake of 63 Ni(II), 152 Eu(III) and 242 Pu(IV) by cement, as compared to the sorption in the presence of the proxy ligands. Nevertheless, retention in the presence of the degradation leachate remains high for all investigated radionuclides, with R d ( 63 Ni(II)) ≈ 2 m 3 kg -1 , R d ( 152 Eu(III)) ≈ 100 m 3 kg -1 and R d ( 242 Pu(IV)) ≈ 30 m 3 kg -1 . These observations possibly reflect that the multiple functionalities (-COOH, -OH, amide groups) expected in the macromolecules (10-15 kDa) present in the degradation leachate, can offer further binding/chelating capabilities compared to the small organic proxy ligands with at most bidentate binding.