Efficient extraction of platinum(IV) using tertiary-amine groups functionalized thiacalix[4]arene as extractant

Abstract

In the present study, the extraction performance and complexation mechanism of p-di-ethyl-amino-methyl-thiacalix[4]arene (L) toward Pt(IV) in a hydrochloric acid system were investigated. The effects of various parameters including solution pH, L to Pt(IV) mole ratio, Cl− concentration, acidity and reaction time on the complexation process of L with Pt(IV) were systematically investigated. The experimental results indicated that L has excellent complexation ability toward Pt(IV) that about 90 % of Pt(IV) could be extracted within 2 min under the optimal conditions. Moreover, L could selectively extract Pt(IV) from the HCl system containing multiple competing ions such as Ce(III), Zr(IV), La(III), Fe(III), Ni(II), Mg(II), and Al(III). The complexation mechanism between L and Pt(IV) was further clarified by slope analysis, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), and proton nuclear magnetic resonance (1H NMR) titrations. Theoretical analysis of thermodynamics, complexation structure and intermolecular interactions between L and Pt(IV) during the solvent extraction process were performed through density functional theory (DFT) calculations. The results showed that the protonation of L occurs first to form the complex of L·2HCl, which further reacts with PtCl62− forming the complex of L·2H+·PtCl62− through anion-exchange, achieving the efficient and selective extraction of platinum.