High-affinity ion-complexing polymer-supported reagents: Immobilized phosphate ligands and their affinity for the uranyl ion

The complexation of uranium(VI) by polymer-supported phosphonate and phosphate diester ligands has been studied in acid solutions up to 4 N. Hydroxy groups proximate to the phosphoryl oxygen increase its basicity which enhances uranium(VI) sorption, particularly in low acid solutions. The mechanism of complexation entails coordination of UO22+ in low acid solutions and anion exchange of UO2Xn− in high acid solutions. Counterions affect the complexation, especially as solution acidity increases, with uranium distribution being preferred in the order HNO3 > HCl > H2SO4. The different behavior of the counterions is due to their free energies of hydration.