Modeling of Equilibria for the Solvent Extraction of Ammonia with LIX84I

Solvent extraction of valuable metals such as copper and nickel is often carried out from ammoniacal alkaline solutions with chelating extractants, during which coextraction of ammonia is inevitable. In the present study, as a basis of modeling of the whole ammoniacal extraction process, the equilibrium distribution ratios of ammonia between a 3 mol L-1 ammonium nitrate solution and LIX84I (the active component of which is 2-hydroxy-5-nonylacetophenone oxime, HR) dissolved in a nonpolar diluent were measured as a function of pH and LIX84I concentration at 298 K. We successfully modeled the measurement results by assuming the formation of two associated species, (HR)n・(NH3) and (HR・NH3)n, the aggregation of HR, and the dissociation of NH4. Fourier transform infrared spectroscopy results suggested that ammonia was extracted via hydrogen bonding with HR, and these results were in accord with the proposed equilibrium model.