Efficient separation of Re(VII) by radiation-induced reduction from aqueous solution

Rhenium (Re) is a good nonradioactive alternative of technetium-99 (Tc-99), which is a beta emitter causing long-term radioactive toxicity due to its long half-life and high yield in nuclear reactors. TcO4-, the dominant form of Tc-99, is very easy to migrate in the environment because of its high solubility. In this work, gamma irradiation was applied to separate rhenium from aqueous solution in the presence of isopropanol. Re(VII) was reduced by hydrated electrons (e(aq)(-)) generated from gamma-adiolysis of water, leading to the formation and precipitation of Re (0) and rhenium oxides (ReO2 and ReO3) nanoparticles. It was the first time that Re(0) was observed in the reduction products of Re(VII) by gamma irradiation, which was confirmed by HR-TEM, EDX, XPS and XRD. The reduction of Re(VII) by gamma irradiation was very fast and efficient in alkaline condition, whose separation ratio reached 93.6% after 2-h irradiation and the final separation ratio was as high as 98.1%. Increase in absorbed dose rate, isopropanol concentration, and pH, was conducive to the separation of Re overall. Further studies on the transient species by pulse radiolysis revealed that OH- might coordinate with the intermediate Re(VI) forming different complexes with different concentrations of OH- thus affecting the reduction of Re(VII). This work not only demonstrates that y irradiation could be a promising method for the efficient separation of Re (VII), but also gives a better understanding in the reaction mechanism.