The importance of organic phase diffusion in the solvent extraction of copper by LIX 64N — Experiments with a static interface cell

Abstract

Previous studies have suggested that the extraction of copper by hydroxyoxime extractants involves mass transfer with chemical reaction. This paper reports the results of experiments where an aqueous copper solution (4.94 g dm −3 copper, 5.26 g dm −3 H 2SO 4) is contacted with a 5% v/v LIX 64N solution in Escaid 100, in a diffusion cell with a stagnant interface. The concentration-distance distribution of the diffusional band of copper complex which appeared in the organic phase was measured at various times, and the results can be modelled by equations based on diffusion about an interface with and without interfacial resistance. If the previously measured diffusion constants for copper in the aqueous and organic phases were used in the model, then an unrealistically high resistance (200,000–300,000 s cm −1) would have to be chosen to obtain a correlation. If a low resistance (1,000 s cm −1) is assumed and the previously measured diffusion constants for copper in the aqueous phase (5.2·10 −6 cm 2 s −1) and copper in the organic phase (5.0·10 −6 cm 2 s −1) are taken, then it is necessary to reduce the organic phase diffusion constant to 2·10 −6 cm 2 s −1 to obtain correlation of the model with the data. It is proposed that as the organic product film develops, the diffusivity of the copper complex is reduced.