ION-EXCHANGE MEMBRANES IN EXTRACTION PROCESSES

Extraction processes aided by ion-exchange membranes are reported. Ext raction of metal cations was carried out with a cation-exchange membra ne separating the feed from the extractant. It is shown that the compo nents of the extraction medium are very well retained in the organic p hase. Stripping was carried out either through a second, identical, me mbrane, 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 X 10(-9) mol/cm2 -sec from a mixture of copper and nickel salt, 4.5 mM each. N o nickel transfer was observed. Silver was selectively extracted by di (2-ethyl-hexyl)dithiophosphoric acid from a solution containing an exc ess of sodium thiosulfate. Extraction of acid with a long chain amine was carried out with an anion-exchange membrane separating the feed an d the extractant and a second anion-exchange membrane separating the e xtractant and receiving solution in a three compartment cell. The aque ous solutions were not contaminated by the amine. Flux of acid was 4.7 X 10(-9) mol/cm2-sec from an 0.57 M solution of sulfuric acid.