Analysis of liquid membrane extraction of binary Zn(II) and Cd(II) from chloride media with Aliquat 336 based on thermodynamic equilibrium models

The transport and separation of binary Zn(II) and Cd(II) from chloride media in a supported liquid membrane (SLM) containing Aliquat 336 in 4 vol.% n-decanol and kerosene was studied. Batch solvent extraction (SX) experiments were conducted to determine reaction stoichiometries. Experiments were performed at various total metal concentrations (1.7–10.4 mM), concentration ratios of Zn(II) to Cd(II) (0.4–7.6), and Aliquat 336 concentrations (0.05–0.2 M). A simplified thermodynamic relationship was presented to describe SX equilibrium, in which the non-ideality in the aqueous or organic phase was considered. It was shown that a proposed SLM mass transfer model, which takes into account diffusion in aqueous feed and strip stagnant layers as well as in the membrane, was satisfactorily applicable for binary metal systems (standard deviation, 5%). The separation factors of Cd(II) over Zn(II) with Aliquat 336 under equilibrium (batch SX) and non-equilibrium (SLM) conditions were also evaluated and discussed.