The interaction of extractants during synergistic solvent extraction of metals. Is it an important reaction?

Abstract

The enhancement of the synergistic solvent extraction of metallic species may depend on the nature and strength of the possible interaction between the two ligands. The prediction of the extraction systems properties remains a difficult task due to a lack of knowledge about the behaviour of the acidic/neutral or acidic/cationic couples. The use of multiple analytical techniques (NMR, FT-IR, UV-vis, ESI-MS) gives more insight into the structure of the formed adducts in the organic phase responsible for the weakened extraction process and destruction of synergism. The increased acidity of the acidic extractant and the basicity of the neutral ligand lead to a stronger tendency to react with each other forcing the consumption of extractants liable for antisynergism. Major conclusions on the role of such intermolecular interactions towards the extraction mechanism and yields are additionally provided. This information could be useful nowadays when developing new synergistic extraction systems includes ionic liquids as innovative organic media instead of VOCs, despite the complicated chemical environment provided by these modern alternative diluents. This article gives an overview on some investigations as well as on our own contributions on this topic.