Selective thiacalix[4]arene bearing three amide groups as ionophore of binary Pd(II) and Au(III) extraction by a supported liquid membrane system

Thiacalix[4]arene derivatives are considered as specific ligands for metallic species in molecular recognition processes. In the present study, a new macrocyclic compound based on thiacalix[4]arene bearing three amide substituents is investigated for the extraction of gold and palladium in chloride media, and results are compared with those obtained with a similar ligand containing four amide substituents. Results obtained from liquid–liquid extraction experiments show that the new compound effectively extracts both Au and Pd, improving in the case of Pd the results obtained when using the more substituted ligand. Based on these results, a solid supported liquid membrane system has been developed for Pd and Au permeation containing the new ligand dissolved in NPOE as organic phase, and using 0.5 M NaSCN at pH 2 as stripping agent. Several parameters affecting liquid membrane performance have been investigated such as the chloride content in the feed solution and the chemical nature of the polymeric support used to immobilize the liquid membrane. Finally, the selectivity of the designed liquid membrane system has been evaluated under competitive metal transport conditions using as feed solutions a mixture of Pd and Au alone or in the presence of base metals.