Experimental study on modeling of Pu sorption onto quartz

Plutonium(IV) sorption onto quartz in carbonate solutions was systematically investigated under anaerobic conditions to analyze the sorption behaviors of Pu(IV) with a non-electrostatic model (NEM). Pu(IV) sorption data was obtained from batch sorption experiments as a function of pH and carbonate concentration. The Pu(IV) sorption onto quartz showed similar tendencies to Th(IV), which is considered to be chemically analogous as a tetravalent actinoid. The distribution coefficient, K${}_d$ , of Pu(IV) onto quartz showed inverse proportionality to the square of the total carbonate concentration under the investigated pH conditions of 8–11. The modeling study, however, revealed a Th(IV) sorption model, which is ≡SOTh(OH)${}_4$${}^{-}$ and ≡SOThOH(CO${}_3$)${}_2$${}^{2-}$ , could not be applied to simulate the Pu(IV) sorption onto quartz. It was inferred that the electrostatic repulsion between negatively charged ligands limited the formation of ≡SOM(OH)${}_4$${}^{-}$ and ≡SOMOH(CO${}_3$)${}_2$${}^{2-}$ for Pu(IV) with smaller ionic radii than Th(IV). The Pu(IV) sorption model was developed as ≡SOPu(OH)${}_3$ and ≡SOPu(OH)${}_4$${}^{-}$. In addition, data of Pu(IV) sorption onto muscovite was obtained in order to be compared with data for quartz.