Separation of palladium and platinum by liquid surfactant membranes with a sulfur-containing carrier

Separation of palladium and platinum from a hydrochloric acid solution was conducted with liquid surfactant membranes (LSMs) containing didodecylmonothiophosphoric acid (DDTPA) as a carrier and a synthesized surfactant as an emulsifier in a stirred tank. The extraction behavior of palladium and platinum in liquid-liquid extraction was examined, along with the LSM experiments. At high concentration of hydrochloric acid, palladium was extracted selectively over platinum by DDTPA, while platinum was extracted at low chloride concentration. Synthetic surfactants themselves have the ability to extract the two metals. In a LSM with DDTPA as a carrier, palladium was found to be extracted rapidly and selectively over platinum from the feed solution into the liquid membrane phase and could be concentrated in the recovery solution. Using ionic surfactants which have a quaternary ammonium group in their structures, the extraction rate of palladium became fast compared to that with a nonionic surfactant.