Membrane-assisted liquid phase extraction of Lu(III) in U-shaped contactor with a single hollow fibre membrane under recirculation mode of operation

Extraction of Lu(III) from an aqueous LuCl3 solution at pH 3.5 into an organic phase containing 5% (v/v) di(2-ethylhexyl)phosphoric acid (DEHPA) in di-n-hexyl ether (DHE) immobilized within a polypropylene hollow fibre membrane and a simultaneous back-extraction of Lu(III) into 2 mol dm-3 HCl solution has been investigated using two miniaturized supported liquid membrane (SLM) systems: (i) a single hollow fibre membrane, with stagnant acceptor phase in the lumen, immersed into a donor phase reservoir; (ii) U-shaped module containing a single hollow fibre membrane with a closed-loop recirculation of aqueous phases through the module. In the stagnant SLM system, the maximum extraction efficiency was 8.8% due to limited acceptor volume and absence of flow within the lumen. In recirculating SLM system, after 80 min of operation at the donor phase flow rate of 5.3 cm3 min-1, the acceptor phase flow rate of 0.4 cm3 min-1 and the donor-to-acceptor phase volume ratio of 6.7, the equilibrium removal efficiency of Lu(III) reached 88% and less than 5% of Lu(III) extracted from the feed solution was kept in the organic phase. For shell side flow of the donor phase at the Reynolds number of 3−34, the overall mass transfer coefficient was proportional to the donor flow rate raised to the power of 0.63 and increased from 2.3 to 8.8 × 10-5 m s-1. The rate-limiting step was the mass transfer of Lu(III) within the boundary layer of the donor phase adjacent to the outer wall of the hollow fibre.