Technetium(IV) oxide colloids produced by radiolytic reactions in aqueous pertechnetate solution

We report the reduction of pertechnetate (Tc(VII)O4−) to Tc(IV) species by bremsstrahlung irradiation of an aqueous solution of TcO4− at different pHs of the solution. When the TcO4− solution at pH 1.8 acidified with sulfuric acid was irradiated, soluble Tc(IV) species, which was proposed as polymeric Tc(IV) species, was formed. Amounts of the polymeric Tc(IV) species increased with an increase of absorbed dose and 80% of TcO4− was converted to the polymeric Tc(IV) species at 6.5 kGy. By the irradiation of the TcO4− solution at pH 2.7, technetium(IV) oxide (Tc(IV)O2·nH2O) colloids were formed in addition to the polymeric Tc(IV) species. At pH 4.1, only the Tc(IV)O2·nH2O colloids were observed in the irradiated solution. The colloid particle was found as an aggregate (30–130 nm) of tiny particles of 2–3 nm in diameter. The polymeric Tc(IV) species was not filtered off with an ultrafilter (NMWL 10,000) and changed to TcO2·nH2O colloids as the pH of the solution increased, suggesting that the polymeric Tc(IV) species was a precursor of TcO2·nH2O colloids. The reduction of TcO4− in acidic media proceeds through a bimolecular reaction with hydrogen radicals (a product of water radiolysis) followed by successive disproportionation reactions of Tc(VI) and Tc(V).