Radiopharmaceutical and Hydrometallurgical Separations of Perrhenate Using Aqueous Biphasic Systems and the Analogous Aqueous Biphasic Extraction Chromatographic Resins

Poly(ethylene glycol) (PEG)-based aqueous biphasic systems (ABS) and the analogous aqueous biphasic extraction chromatographic (ABEC) resins have been investigated for the separation of perrhenate (ReO 4 - ) from tungstate (WO 4 2- ) in alkaline tungstate media for radiopharmaceutical application and for the separation of perrhenate from molybdate (MoO 4 2- ) in hydrometallurgical application. Salts of the water-structuring anions OH -, WO 4 2-, and MoO 4 2- form ABS by salting-out PEG, while chaotropic anions such as ReO 4 - and the similar TcO 4 - quantitatively partition to the PEG-rich phase in such ABS. Perrhenate can thus be separated from solutions high in WO 4 2- and OH - concentration, and the separation factors improve with an increase in the tungstate or hydroxide concentration. In addition, the ReO 4 - anion can be separated from load solutions high in MoO 4 2- and SO 4 2- . Perrhenate can also be separated under similar conditions using ABEC resins in both batch and chromatographic modes. The retained ReO 4 - can be eluted from the column with a simple water strip. The chromatographic separation of ReO 4 - from WO 4 2- provided 97% of the loaded ReO 4 - in 20 mL. Unlike traditional technetium generators which are adversely affected by high parent ion concentrations, higher concentrations of the parent anion improve the retention of ReO 4 - onto ABEC resins. After exposure of the ABEC resins to radiation doses as high as 500 Mrad, an acceptable level of performance was maintained, although degradation of the resin (monitored using differential scanning calorimetry) was obvious.