Separations of metal ions using ionic liquids: The challenges of multiple mechanisms

Ionic liquids are a distinct sub-set of liquids, comprising only of cations and anions, often with negligible vapor pressure. As a result of the low or non-volatility of these fluids, ionic liquids are often considered in liquid/liquid separation schemes where the goal is to replace volatile organic solvents. Unfortunately, it is often not yet recognized that the ionic nature of these solvents can result in a variety of extraction mechanisms, including solvent ion-pair extraction, ion exchange, and simultaneous combinations of these. This paper discusses current ionic liquid-based separations research where the effects of the nature of the solvent ions, ligands, and metal ion species were studied in order to be able to understand the nature of the challenges in utilizing ionic liquids for practical applications.