Extraction enhancement of zinc(II) in ammoniacal media through solvent and synergistic effects: A structural and mechanistic investigation

Solvent and synergistic effects on the zinc extraction in ammoniacal media have been investigated where 4-ethyl-1-phenyl-1,3-octadione is used as extractant. The structure of the extracted zinc complexes has been determined by use of FT-IR spectroscopy and X-ray absorption spectroscopy. And the interactions of the extracted species with water, ammonia and ligand molecules in the organic phase have been studied to elucidate the extraction mechanism. The extraction efficiency of zinc at pH 7.3 is more than 90% for octanol solvent system and for both trioctylphosphine oxide (TOPO) and tributyl phosphine (TBuP) synergistic systems, indicating that the polar solvent and neutral ligands containing phosphine can evidently enhance the extraction efficiency of Zn(II) in ammoniacal media. The solvent effect should be mainly attributed to the stabilization of hydrated and ammonia-solvated zinc complexes in polar solvent by intermolecular hydrogen bonding, whereas the synergistic effect could result from the formation of more hydrophobic and stable zinc adducts, which promote the distribution of zinc extracts.

• Solvent and synergistic effects on zinc extraction in ammoniacal media are studied.
• Zinc extraction depends on the solvent polarity and the type of ligands.
• The coordination of zinc extracts with water and ammonia depresses zinc extraction.
• The coordination structure of zinc extracts has been determined by EXAFS spectra.