Introduction of bifunctionality into the phosphinic acid ion-exchange resin for enhancing metal ion complexation

In nuclear industry the role of conventional strong cation exchange resins is limited as they function less in high acid media. The phosphorous group that has got more affinity towards actinide elements is chosen as a chelating group and the phosphinic acid ion exchange resin was synthesized. The extraction ability of the phosphinic acid resin for plutonium (Pu) from HNO3 medium as well as from H2SO4 medium was studied. Though the resin shows better extraction for Pu than the strong cation exchanger resins at higher acidities, its kinetics is slow. In order to enhance the kinetics as well as to improve upon selectivity, a sulphonic group is introduced into the phosphinic acid resin. To verify the effect of bifunctionality extraction studies have been carried out with Pu from different acid media of varying concentrations. Sulphonated phosphinic acid resin shows a 2-fold increase in distribution coefficient (kd) as well as it reached equilibrium very fast compared to the phosphinic acid resin. It is postulated that the sulphonic acid ligand provides an access mechanism for the metal ions into the polymer matrix while it is the phosphinic acid group that is responsible for selective coordination of metal ions. Thus bifunctionality is coupling of an access mechanism to a recognition mechanism. The experiments carried out demonstrated the applicability of sulphonated phosphinic acid resin in the nuclear industry.

The increase in the capacity and kinetics of sulphonated resin is because of coupling of an access mechanism with a recognition mechanism. The access mechanism can be nonselective and it allows all ions into the proximity of the polymer matrix, while it is the recognition mechanism which selectively complexes the targeted metal ion. Here sulphonic acid ligand acts as the access Fig. 5. Kinetics of Pu (IV) extraction from HNO3 (1 M and 6 M) by phosphinic acid resin and sulphonated phosphinic acid resin.