The extraction of copper from dilute aqueous solutions using a liquid membrane process

A liquid surfactant membrane process is considered for the separation of copper ions from dilute aqueous solutions. The process is shown to work effectively, solutions ranging in concentrations from 2000 ppm copper as copper sulphate (typical of acid leach solutions) down to 100 ppm copper have been successfully processed. In the case of the very dilute solutions the copper concentration in the final raffinate can be taken down to less than 1 ppm in a single contact stage. The liquid membrane is made up of a chelating agent, in this work Shell SME 529, organic diluent and emulsifying agent. Factors influencing mass transfer, such as membrane composition, O/A ratio, pH of the aqueous feed solution and acid content of the strip solution, contacting condition etc., have been studied. Providing membrane breakdown is low the process can be represented as a pseudo first order rate process. It is shown that by using this form of facilitated transport transfer of copper ions against very adverse concentration gradients across the membrane can be achieved. Further pilot plant work is required to examine scale up features of this process. Compared with conventional solvent extraction the amount of solvent (reagent and diluent) required in the contacting stage(s) is very much reduced. In this work it is shown that successful extraction of copper can be achieved using over two orders of magnitude less solvent than with solvent extraction.