Extraction of metal–dye ion-association complexes by thin ether-type polyurethane membranes

The extraction and transport of various gold(III) chloride–organic dye ion-association complexes in aqueous solution through thin ether-type polyurethane membranes have been studied. The effects of the presence of salt, acid, different starting and receiving solution compositions, and temperature on the sorption process were investigated. Methylene Blue, Rhodamine B and Brilliant Green, which represent organic dyes from the thiazine, xanthene, and triphenylmethane groups, respectively, were used for this study. Gold(III) chloride and the individual organic dyes were extracted and transported through the membrane only if the solution conditions favored the formation of a neutral species. The ion-association complexes of gold(III) chloride with Methylene Blue and Rhodamine B were extracted and transported by the polymer only when the formation of the complex was more efficient than the individual extraction and transport of each of the species. The extraction of Brilliant Green under all conditions studied was very high, however, no transport occurred. The overall sorption of this dye was found to be independent of the presence of gold regardless of solution composition. High temperature resulted in a very high rate of transport of the gold(III) chloride–organic dye ion-pair.