Chemistry of rhenium as an analogue of technetium: Experimental studies of the dissolution of rhenium oxides in aqueous solutions

Abstract

Summary The migration of fissiogenic Tc into the environment can be predicted by studying the dissolution behavior of Re, a chemical analogue of Tc, avoiding the use of a radioactive element at high concentration. We developed a series of experimental studies of the solubility of Re oxides under various oxidation states (+VII, +IV, and +III), in oxidizing and anoxic media, so as to verify the validity of the available thermodynamic data concerning Re. The experimental results confirm that the predictable solubility of Re, under the conditions found in radioactive wastes storage, is very high when in the form of {ReO4 -}, an analogue of {TcO4 -}. The Re(III) oxide, Re2O3, is not stable in aqueous solutions and therefore the existence of Re(III) in surface conditions is not much likely. The Re(IV) oxide, ReO2, is weakly soluble. Its solubility is in the range 4×10-7-10-6mol L-1, which suggests that Re(IV) can be found in noticeable concentrations in aqueous solutions even in anoxic media; similar result is expected for Tc.