Application of PEG based aqueous biphasic systems in extraction and separation of no-carrier-added 183Re from bulk tantalum

Abstract

Abstract No-carrier-added (nca) rhenium isotopes (182,182m,183Re) were produced by irradiation with 30 MeV α particles on natural tantalum target. The short-lived 182,182mRe were allowed to decay and long-lived nca 183Re was separated from bulk tantalum matrix by aqueous biphasic system (ABS) using 2 M solutions of nine different salts, namely, Na2SO4, Na2SO3, NaHSO3, Na2S2O3, Na2HPO4, Na2CO3, Na-citrate, Na-tartrate, and (NH4)2SO4 as salt rich phases against 50% (w/w) PEG-4000 as polymer rich phase at room temperature. The influence of temperature and thermodynamic parameters Δ Hº and Δ Sº were obtained for the partition of 183Re and tantalum in these systems. Nca 183Re was extracted in high amount in polymer rich phases irrespective of the salt rich phases. Bulk tantalum showed tendency to remain in salt rich phases. ABSs with PEG-4000 polymer rich phase in combination with Na2SO4, Na2SO3, NaHSO3, Na2HPO4, Na2CO3, Na-citrate and Na-tartrate as salt rich phases at basic pH and at ambient temperature (27 ºC) offered single-step separation between nca 183Re and bulk Ta. When Na2S2O3 and (NH4)2SO4 were used as salt rich phase, slight extraction of bulk tantalum was observed in PEG-4000 rich phase. The dynamic dissociation constant of 183Re-PEG-4000 complex was measured by dialysis of the PEG-rich phase against de-ionised water. The k dissociation value was found as low as 0.0185 min−1. Therefore, it is possible to have pure 183Re in de-ionized water immediately after the dialysis.