Recovery of rhenium from aqueous mixed metal solutions by selective precipitation: A photochemical approach

Abstract Selective precipitation recovery of rhenium from aqueous solutions containing a coexisting metal (molybdenum, tungsten, or aluminum) by means of UV–visible light irradiation in the presence of 2-propanol and acetone was investigated. When the pH of the rhenium–molybdenum solutions (initial concentration 10.4 mM for each metal) was in the range from 6.3 to 12.5 and the irradiation time was 6 h, the rhenium in the initial solutions was efficiently recovered in the precipitates (92–99%), and the rhenium selectivity was high (the rhenium recovery ratio was 9.2–21 times that of molybdenum). The high selectivity for rhenium was also observed at different molybdenum concentrations (4.8–15.7 mM) and at a higher rhenium concentration (17.5 mM). Rhenium was also recovered efficiently and selectively from rhenium–tungsten solutions (initial concentration 10.4 mM for each metal): when the pH ranged from 7.0 to 12.0 and the irradiation time was 6 h, the rhenium recovery was 90–95% and the rhenium recovery ratio was 7.3–45 times that of tungsten. In contrast, when the coexisting metal was aluminum (initial rhenium and aluminum concentrations, 10.4 mM and 8.6 mM, respectively; pH 11.2), 95% of the rhenium was recovered in the precipitate after 6 h of irradiation; however, aluminum was somewhat unstable in the basic solution and the rhenium recovery ratio was 3.2 times that of aluminum. Unlike molybdenum and tungsten, aluminum tended to coprecipitate with rhenium.