Separation of cobalt and nickel using inner synergistic extraction from bifunctional ionic liquid extractant (Bif-ILE)

The inner synergistic extraction of [tricaprylmethylammonium][sec-octylphenoxy acetate] ([A336][CA-12]) is studied for cobalt and nickel separation. Distribution ratios of [A336][CA-12] for Co2+ or Ni2+ are by far higher than those of tricaprylmethylammonium sulfate ([A336]2SO4), sec-octylphenoxy acetic acid (CA-12), mixture of [A336]2SO4 and CA-12 at the acidities from 1 × 10−5 mol L−1 to 1 × 10−3 mol L−1. The synergy coefficients of [A336][CA-12] for Co2+ are higher than the synergy coefficients of [A336][CA-12] for Ni2+, which can be used for the Co2+ and Ni2+ separation. Some thermodynamic properties of the inner synergistic extraction using [A336][CA-12] for Co2+ and Ni2+ are also studied, such as influence of temperature, thermodynamic functions, extraction mechanism, separation factors and stripping properties.