Removal of Ag(l), Cu(II) and Zn(ll) ions with a supported liquid membrane containing cryptands as carriers

Abstract

The interface behaviour in the facilitated co-transport of Ag(I), Cu(II) and Zn(II) ions through supported liquid membranes (SLMs) made of a flat-sheet polypropylene membrane support containing cryptands (2.2.2 or 2.2.1) as carriers was studied. The liquid-liquid extraction tests showed a maximum distribution coefficient when the carrier concentration was greaterthan 10 −4M. In transport experiments the transmembrane flux increased with increasing carrier concentration reaching a limiting value at greater than 10 −3M concentration. The calculation ofthe diffusion coefficients in membranes showed ahigherdiffusivityof2.2.2-metal complexes with respect to 2.2.1-metal complexes for silver ions. A sequence of diffusivity D(Ag+)>D(Cu 2+)>D(Zn 2+) was obtained, but carrier 2.2.1 showed a higher selectivity through copper ions. A sequence of diffusivity D(Cu 2+)>D(Zn 2+)>D(Ag +) was obtained. The diffusivity was significantly higher when using Celgard 2500 support compared to Celgard 2400 or 2402. Variable metal ion concentrations in the feed phase fluxes almost zero, at less than 10 −2 M concentration, were obtained. In the transient state of the transport through the SLM, different molar flow rates at the feed-membrane and membrane-strip interfaces were observed. The selectivity of the interfaces containing 2.2.2 in the separation binary mixtures of ions showed the following separation factors: SF AgZn = 2.50, SF AgCu = 1.64, SF cuZn = 1.42.