Ion-exchange membranes in extraction processes

Extraction processes aided by ion-exchange membranes are reported. Extraction of metal cations was carried out with a cation-exchange membrane separating the feed from the extractant. It is shown that the components of the extraction medium are very well retained in the organic phase. Stripping was carried out either through a second, identical, membrane, or by direct re-extraction. In the extraction of copper by LIX the ion transport is sensitive to the rate of stirring in the organic extractant phase. In a flow cell the copper transport is 5.6 × 10^-9 mol/cm²-sec from a mixture of copper and nickel salt, 4.5 mM each. No nickel transfer was observed. Silver was selectively extracted by di(2-ethyl-hexyl)dithiophosphoric acid from a solution containing an excess of sodium thiosulfate. Extraction of acid with a long chain amine was carried out with an anion-exchange membrane separating the feed and the extractant and a second anion-exchange membrane separating the extractant and receiving solution in a three compartment cell. The aqueous solutions were not contaminated by the amine. Flux of acid was 4.7 × 10^-9 mol/cm²-sec from an 0.57 M solution of sulfuric acid.