Separation and concentration of Pd, Pt, and Rh from automotive catalytic converters by combining two hollow-fiber liquid membrane systems

A new system combining two hollow-fiber-supported liquid membranes (HFSLMs) for the separation and concentration of platinum, palladium, and rhodium. is presented. The best results were obtained when the feed solution was recirculated through a first module containing Cyanex 471 as the solvating extractant and then the depleted feed solution was recirculated through a second module containing the anion exchanger Aliquat 336 as the carrier. Under these conditions, palladium was selectively recovered in the stripping solution of module I, while platinum was recovered in the receiving phase of module II, and rhodium remained in the feed solution. It was observed that low concentrations of thiocyanate in the feed solution favored the permeability of platinum. This separation scheme was applied to the recovery of platinum-group metals from the leaching solutions of spent automotive pellet-type catalysts. Palladium and platinum were effectively separated and enriched, and only small amounts of aluminum were cotransported through the liquid membrane systems.