Solvent extraction equilibria of nickel from ammonium nitrate solution with LIX84I

The equilibrium distribution ratios of nickel(II) ion between LIX84I (active component 2-hydroxy-5-nonylacetophenone oxime (HNAPO)), dissolved in a non-polar diluent and 3 kmol m− 3 ammonium nitrate solution are measured in the pH range 2–10 at 298 K. The effect of pH on the distribution ratio of nickel is analyzed based on the extraction equilibrium model assuming that the extracted complex has the stoichiometry of 1:2 (Ni:HNAPO). The successive aggregation of HNAPO in the organic phase and the nickel-ammine complex formation in the aqueous phase are considered, where the acid dissociation constant of ammonium ion, measured by the half-neutralization method, is used. The equilibrium constants for the extraction, successive aggregation, and distribution of the nickel extractant complex between the aqueous and organic phases are determined to be 4.90 × 10− 5, 9.9 (kmol m− 3)− 1 and 1 × 10− 4, respectively. These constants reproduce the experimental distribution data with good accuracy.

Research Highlights► Quantitative equilibrium model for Ni SX from ammnoniacal solution with LIX84I. ► Linear relationship between the pKa value of NH4+ and Conc. of NH4NO3. ► Eq. Const. for Ni Extr., aggregation of LIX84I, and Ni-LIX84I complex Ditr.