Synergistic effect of Cyanex 272 and Cyanex 302 on separation of cobalt and nickel by D2EHPA

Synergistic effects of Cyanex 272 mixed with D2EHPA and Cyanex 302 mixed with D2EHPA were investigated for the separation of cobalt and nickel from a dilute sulfate media with the aim of reducing the reagent cost. Selective extraction of cobalt over nickel improved with respect to D2EHPA, but worsened with respect to Cyanex 272. By the application of the slope analysis method, the stoichiometric coefficient of the extractant was found to be four for cobalt and five for nickel, in a mixture of D2EHPA with Cyanex 302. However, it was four for both cobalt and nickel in a mixture of D2EHPA with Cyanex 272. Fourier Transform Infrared Spectroscopy (FT-IR) was utilized to examine the organo-metallic complexes containing cobalt and nickel. Increasing the ratio of Cyanex 272 or Cyanex 302 to D2EHPA did not reveal a significant effect on the extraction curve of cobalt, but caused an increase in pH of the nickel extraction curve. Increasing the ratio of Cyanex 272 or Cyanex 302 to D2EHPA increased the pH50 difference (ΔpH50(Ni-Co)). Optimum separation was found with a Cyanex 302 to D2EHPA ratio of 0.3:0.3 when the pH50 difference (ΔpH50(Ni-Co)) was 0.9. Results showed that extraction of cobalt is more endothermic than that of nickel. Improved separation was hence achieved with a warm mixture.