Kemija u Industriji (Sep 2008)
Extraction and Separation of Cobalt and Nickel with Extractants Cyanex 302, Cyanex 272 and Their Mixture
Abstract
The extraction and separation of cobalt(II) and nickel(II) from sulphate solutions with different initial volume fractions of commercial organophosphorus extractants Cyanex 302, Cyanex 272 and their mixture, in kerosene as diluent, were investigated. Prepared samples contained the mixture of cobalt(II) and nickel(II) in mass concentrations chosen to approximate the mass concentrations of the two metals in solutions obtained by leaching typical low-grade ores or waste materials with sulphuric acid. The experiments were carried out at two concentration ratios of nickel to cobalt(ζNi/Co), 25 and 125. The latter ratio was chosen as model for the solutions of naturally occurring ores and other materials in which the concentration of nickel is much higher than that of cobalt. In all cases, the concentration of cobalt was approximately y= 0.15 g L–1, and the concentration of nickel was approximately g= 3.80 g L–1 (at ζNi/Co = 25) and 18.80 g L–1 (at ζNi/Co = 125). Other initial values were based on conditions found to be optimal in previous investigations, and kept constant in all experiments: pH0= 8, θ0 = 25 °C, phase volume ratio organic to aqueous ψ = 1 and 0.5, contact time 2 minutes.The tested fractions of extractants (Cyanex 302 or Cyanex 272), diluted in kerosene, were j = 2.5, 5.0, 7.5 and φ = 10 %. The studies of the mixture of extractants were carried out at two sets of fractions. In the first set, the fraction of Cyanex 302 was kept at φ = 10 %, and Cyanex 272 was varied in the range φ = 2.5 –10 %. In the second set, the mass concentration of each of the two extractants was varied in the range φ = 2.5–10 % so that the total fraction of the two extractants always added up to φ= 10 %.The obtained results describe the influences of type and initial volume fraction of extractant on the separation and extraction of cobalt and nickel. Under the investigated range of conditions, Cyanex 302 outperformed Cyanex 272 in cobalt-nickel separation, which is obvious from the distributionratios for cobalt (Figs. 1 and 2) and nickel (Figs. 3 and 4) as well as from the cobalt-nickel separation factors (Table 1).In the extraction of cobalt and nickel with different mixtures of Cyanex 302 and Cyanex 272, no evidence for any synergistic effects were found, as indicated by the obtained synergistic coefficients (Table 2 and 3) and separation factors for cobalt and nickel (Table 4).In the follow-up work to this study, we plan to investigate new mixtures of extractants for their ability to separate cobalt from nickel in solutions with properties similar to those encountered in the extraction industry.
