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 Co(2+) or Ni(2+) are by far higher than those of tricaprylmethylammonium sulfate (A336SO(4)), sec-octylphenoxy acetic acid (CA-12), mixture of A336SO(4) and CA-12 at the acidities from 1x10(-5) mol L(-1) to 1x10(-3) mol L(-1). The synergy coefficients of [A336][CA-12] for Co(2+) are higher than the synergy coefficients of [A336][CA-12] for Ni(2+), which can be used for the Co(2+) and Ni(2+) separation. Some thermodynamic properties of the inner synergistic extraction using [A336][CA-12] for Co(2+) and Ni(2+) are also studied, such as influence of temperature, thermodynamic functions, extraction mechanism, separation factors and stripping properties.