Comparison of interfacial behavior and silver extraction kinetics with various types calix[4]arene derivatives at heterogeneous liquid-liquid interfaces

Various p-tert-octylcalix[4]arene derivatives as hydrophobic extractants have been prepared to investigate Ag(I) extraction efficiency in a batch-wise process in nitric acid media. The influence of the functional groups of the hydrophobic extractants on the interfacial behavior and Ag(I) extraction efficiency in nitric acid media has been investigated using the drop-volume method. Fitting of the interfacial tension isotherms to the Gibbs and Szyszkowski equations has provided parameters characterizing the interfacial activity of the extractants, in particular the Gibbs free energy of adsorption at the interface, the interface excess on saturation (Г∞) and the average area per the adsorbed extractant molecule (Amin). The amido-type p-tert-octylcalix[4]arene derivatives have strong interfacial activity and fast extraction rates. The interface excess at saturation (Г∞) increased with the type of functional groups in the following order: methyl ketonic < phenyl ketonic < dibenzyl amido < diethyl amido < quinolyl < pyridyl. The relationship between the interfacial activity and the dependence of the Ag(I) extraction efficiency on the different functional groups is discussed. The interfacial behavior of the extractants affected both the solvent extraction equilibrium and the kinetics and the overall results are consistent with a mass transfer mechanism at the heterogeneous liquid-liquid interfaces.