Modelling of zinc (II) transport through a PC-88A supported liquid membrane

Zinc has been permeated through a flat-sheet supported liquid membrane, using 2-ethylhexylphosphoric acid mono-2-ethylhexyl ester (PC-88A) in kerosene. Liquid–liquid experiments were conducted as a function of aqueous pH (1–6) to establish optimum conditions for both extraction and stripping of the metal. A mass-transfer model was developed to predict the extent of Zn(II) permeation through the supported liquid membrane (SLM) under different experimental conditions. The effect of stirring rate, carrier concentration and temperature upon metal transport has been evaluated. The metal flux has been derived taking into account stagnant layer aqueous diffusion and liquid membrane diffusion as controlling factors. The overall transport evaluated from the proposed resistances model was in reasonable agreement with those obtained from experimental data. Under the studied experimental conditions the resistance of the intrinsic organic phase is masked by the aqueous stagnant layer resistance; therefore the Zn (II) transport through the liquid membrane is mainly controlled by the hydrodynamic of the system.

Transport of zinc(II) from aqueous solutions through SLM containing PC-88A in kerosene was investigated. The results obtained in this study provide important information about the adequate experimental conditions for Zn(II) transport through a SLM. The experimental results indicate that the highest Zn(II) extraction occurs when the pH of the feed and stripping solutions are adjusted to a value of 4 and 2 respectively. The interfacial chemical reactions between Zn(II) and PC-88A extractant [Eq. (1)] was corroborated by liquid–liquid extraction experiments. From these experiments an expression was obtained, which gives the temperature dependence of the equilibrium constant. The effect of carrier concentration, stirring rate and temperature on Zn(II) transport through the SLM was analyzed. It was found that increasing the impeller rotation and the system temperature produces an increase on metal transport, whereas the carrier concentration effect was negligible. A mass transfer model to predict the extent of Zn(II) permeation through the SLM was proposed. From this, a general expression of Zn permeation rate taking into account aqueous stagnant layer and organic resistances as controlling factors was derived. The evaluated resistances were in reasonable agreement with the overall resistance evaluated from experimental data. It was shown that for the studied operating conditions aqueous stagnant layer resistances mainly controlled the Zn(II) transport using PC88A in high concentrations, a similar behavior was found for special conditions of Zn(II)D2EHPA transport ([Zn] # 1.74×10!3 M, [H+] # 1.6×10!3 and [(RX)2] # 2.66×10!2 M) [21].