Efficient photochemical recovery of rhenium from aqueous solutions

Recovery of rhenium from aqueous solutions by photoinduced-electron transfer from an electron donor to excited-state ReO4− is reported for the first time. Specifically, irradiation of aqueous ReO4− in the presence of 2-propanol as the electron donor efficiently decreased the ReO4− concentration in the solution and resulted in formation of a precipitate consisting of amorphous ReO2 and ReO3 and formation of acetone by oxidation of 2-propanol. After 19 h of irradiation, ReO4− had completely disappeared, and 89.1% of the initial rhenium content was recovered in the collected precipitate. Although an induction period prior to the decrease in the ReO4− concentration was observed, the induction period could be eliminated by introduction of acetone to the reaction system, which afforded 94.7% recovery of rhenium within 6 h of irradiation. The acceleration of the reaction induced by acetone could be explained by an increase in the light absorption of ReO4− via precomplexation with acetone, which resulted in an increase in the emission intensity from the excited rhenium species.