Copper(II) sulphate solutions treatment by solvent extraction with Na-Cyanex 272

Cyanex 272 (bis(2,4,4-trimethylpentyl)phosphinic acid) and its sodium salt were used as extractants to treat copper(II) sulphate solutions. Solvent extraction of Cu(II) is more efficient with Na-Cyanex 272 than with its acidic form, and a significant change in pH of the raffinate is observed after extraction. Two mol/dm3 H2SO4 is an effective stripping solution of Cu(II) from the loaded Na-Cyanex 272, and gives 75% of the stripped metal ions in one step. Adsorption parameters show that molecules of Na-Cyanex 272 are populated more densely at the saturated water/toluene interface than Cyanex 272 molecules. Equilibrium and dynamic interfacial tension measurements confirm the interfacial mechanism of Cu(II) extraction and high surface activity of Na-Cyanex 272. Diffusion coefficients estimated for Na-Cyanex 272 are two orders greater than with its acidic form. The differences between both FT-IR and UV/VIS spectra of metal–ligand complexes point out the presence of two types of complex structures depending on the metal–ligand molar ratio (probably planar for 1:1 and tetrahedral for 1:2). Finally, photostability studies show that both extractants are chemically resistant even after contact with H2SO4. The results presented in this paper confirm that conditioning of Cyanex 272 greatly improves the efficiency of Cu(II) extraction in comparison to its acidic form.

► Na-Cyanex 272 salt is an effective extractant of Cu(II) from sulphate solutions. ► Adsorption parameters confirm interfacial mechanism of Cu(II) extraction. ► Spectroscopic techniques explain interactions ligand–metal at various conditions. ► Tetrahedral configuration of Cu(II)–Na-Cyanex 272 after extraction is confirmed. ► High chemical resistance of both extractants is proved by photostability studies.