Plutonium retention in the isosaccharinate – cement system

Abstract

Uptake of plutonium by Portland cement in degradation stage II was investigated in the presence of α-D-isosaccharinic acid (ISA) under reducing conditions set by hydroquinone, Sn(II) or Na2S2O4. Sorption experiments were performed at log [Pu]in = −6 to −9, log [ISA]tot = −6 to −2 and with solid to liquid ratios (S:L) of 0.1–50 g⋅dm−3. ISA sorbs strongly on cement, causing a significant decrease in the ζ potentials of cement particles above log [ISA]tot ≥ −3.5 at S:L ≤ 4 g⋅dm−3. Sorption of Pu significantly decreases above log [ISA]tot ≥ −4.5 due to the competing formation of aqueous Ca(II)–Pu(IV)–ISA complexes. The increased retention of Pu observed above ∼25% of surface coverage by ISA is attributed to the co-adsorption of Pu(IV) with ISA. The impact of the order of addition of individual components on Pu sorption kinetics can be on the scale of several years.