Use of polyethylene glycol (PEG) based aqueous biphasic system (ABS) for the extraction of Pu(IV), Pu(VI) and Am(III) with 18-crown-6: A thermodynamic study

Extraction of pu(IV), Pu(VI) and Am(III) using PEG-2000/ (NH4)(2)SO4 (40% w /w of each) ABS with 18-crown-6 (18-C-6) as the extractant was studied at f our fixed temperatures in the range 288 to 318 K. The distribution ratios f ollow the order: Pu(VI) > Pu(IV) > Am(III). The species extracted were iden tified to be [Pu . 2(18-C-6)1(SO4)(2), [PuO2.(18-C-6)]SO4 and [Am . 2(18-C- 6)](SO4)(1.5) for Pu(IV) Pu(VI) and Am(III), respectively, The equilibrium constants (K) evaluated for the extraction reactions follow the order, K-Pu (iV) > K-Pu(IV) > K-Am(III) as expected in accordance with the axial charge experienced by the incoming ligand (18-C-6). The thermodynamic parameters evaluated at 298 K showed the reaction to be stabilized by the decrease in enthalpy and counteracted by the decrease in entropy in all the three cases . The large decrease in the enthalpy observed in all the cases showed that there is direct bonding of crown ether to the central metal atom (i.e., the formation of inner sphere complex).