Separation of zinc and nickel ions in a strong acid through liquid-liquid extraction

Many solid wastes contain both zinc and nickel at the same time. For recycling or recovery of metals, it is essential to separate materials. Among those materials, zinc and nickel are very difficult to be separated because there is not so much difference in the chemical and physical properties. This paper focuses on the separation of zinc and nickel ions in a diluted aqua regia solution. Liquid-liquid extraction by TBP, Cyanex 272 and Cyanex 301 was used and a distribution coefficient (D), a separation factor (S) and a relative purity (R) were induced to evaluate the degree of separation. All of the extractions were proportional to the concentration of the extractants, and zinc ions were extracted more easily than nickel ions. Among the extractants, Cyanex 301 showed the best characteristics regarding Zn/Ni separation. In particular, the extraction of zinc ions in the range of pH ≤ 6 was constantly over 99 wt.%, whilst that of nickel ions was less than 20 wt.%, when 100 vol.% Cyanex 301 was used. The maximum SZn,Ni value was about 21,700 at pH 6.0 and the highest relative purity (R) of zinc was about 99 wt.% without a pH control, pH −1.1.