Efficient thiacalix[4]arenes for the extraction and separation of Au(III), Pd(II) and Pt(IV) metal ions from acidic media incorporated in membranes and solid phases

The complexation of noble metal chloro complexes with thiacalix[4]arene derivatives bearing or not bearing functional groups was studied by liquid–liquid extraction. Among the four tested thiacalixarenes dissolved in chloroform, it was found that the derivative bearing amide groups (macrocycle 1) effectively extracted gold, palladium and platinum from chloride aqueous media via an ion-exchange mechanism, and its affinity was ranked according to Au > Pd > Pt. Moreover, the thiacalix[4]arene (macrocycle 4) selectively extracted palladium. In all cases, a solution of 0.5 M thiourea in 1 M HCl effectively eluted the extracted metals. Based on these results, different membrane systems (supported liquid membranes and polymer plasticized membranes) were designed for the selective transport of Au(III) and Pd(II). A new solid phase extraction (SPE) support was also prepared by adsorption of macrocycle 1 or 4 onto commercially available supports. It was found that the extraction ability of these supports towards noble metals was markedly enhanced, showing higher affinity for gold(III) and palladium(II) due to the presence of thiacalixarenes.