The modelling of equilibrium data for the liquid-liquid extraction of metals part III. An improved chemical model for the copper/LIX 64N system

New data are presented for the copper sulphate—sulphuric acid/LIX 64N—Escaid 100 solvent extraction system, and it is shown that these data do not exhibit the anomalous features of Robinson's (1971) results. The data are modelled using equations based on the thermodynamics of the Cu²⁺, CuSO₄, H⁺, HSO₄^?, SO₄^2? aqueous system and the HR, (HR)_n, CuR₂ organic sytem (where HR represents the active β-hydroxyoxime in LIX 64N). Although the values of the two aqueous and the two organic equilibrium constants cannot be held to have thermodynamic significance, the best models are capable of predicting the organic copper concentrations of the 86 data points at four different concentrations of LIX 64N (5–50 vol.%) from the aqueous phase analyses with average errors as low as 7%. Isotherms for desired aqueous feedstocks and desired concentrations of our batch of LIX 64N in Escaid 100 at 25–26°C can be calculated.