Uranium (IV)-(VI) electron exchange reactions in anion exchange resin, tri-n-octyl amine and tri-butyl phosphate

A study has been made of the U(IV)-U(VI) electron exchange reactions taking place between natural U(IV) and depleted U(VI) in anion exchange resin, as well as in TnOA/benzene and TBP/benzene systems. The exchange rate in the anion exchange resin was smaller than the corresponding rates in 8∼10 M HCl, which might be explained by considering that the diffusion of the exchangeable species is much slower in the anion exchange resin than in 8∼10 M HCl. The exchange rates in TnOA/benzene and in TBP/benzene were accelerated by decreasing the concentration of TnOA or TBP in benzene. The reason may be that TnOA and TBP, including the exchangeable species, is more easily diffused in dilute than in concentrated solution. Based on activation energy values, the mechanism of exchange in the anion exchange resin was estimated to be similar to that in 8∼10 M HCl solution, and the corresponding mechanism for TBP/benzene similar to that for the cation exchange resin. In the case of TnOA/benzene, the exchange process was presumed to resemble that of the anion exchange resin, judging from the similarity of ionic species extracted thereinto. (author)