Two-phase extraction of metal ions using a water-acetonitrile-ethyl acetate ternary mixed-solvent separation system.

A ternary mixed-solvent solution of water-acetonitrile-ethyl acetate changes from a homogeneous (single-phase) to a heterogeneous (two-phase) system with temperature and/or pressure changes. In this study, we used this system in a batch vessel to extract metal ions. Water-acetonitrile-ethyl acetate at a volume ratio of 3:8:4 containing 8-hydroxyquinoline was used as a ternary mixed-solvent solution, changing from homogeneous at 25°C to heterogeneous after 30 min at 0°C. The two-phase system comprised an upper (organic solvent-rich) phase and a lower (water-rich) phase at a volume ratio of 6:1. Fe(III), Co(II), and Ni(II) were used as model metal ions dissolved in the homogeneous solution at 25°C. The distribution constants and the extraction percentages were determined by measuring the metal ion concentrations in the upper and lower phases with inductively coupled plasma atomic emission spectroscopy. The metal ions were extracted through complexation with 8-hydroxyquinoline in the organic-rich phase with distribution constants and extraction percentage values, respectively, of 0.47 and 74 for Fe(III), 0.15 and 47 for Co(II), and 0.08 and 32 for Ni(II).