Leaching platinum-group metals in a sulfuric acid/chloride solution

A leaching process was established based on the ability of platinum-group metals to form stable chloro-complexes in acidic chloride solutions. Industrial catalyst losses were examined for the recovery of platinum, palladium, and rhodium by leaching with a mixture of sulfuric acid and sodium chloride to avoid using aqua regia or autoclave conditions. Extraction of platinum and rhodium in 60% H₂SO₄ at 135°C steadily increased with increasing NaCl concentrations reaching 95% and 85%, respectively, at 0.1 M NaCl after two hours. By comparison, palladium was dissolved more quickly but also reached 85% under the same conditions. Extraction of each metal increased with temperatures up to 125°C but plateaued at higher temperatures. Similar behavior was observed with increasing H₂SO₄ concentrations up to 60%. More than 99% extraction of each metal was obtained after ten hours using 0.1 M NaCl and 60% H₂SO₄ at 125°C. For more information contact Mohamed Hesham Hassan Mahmoud in the Extractive Metallurgy Department, Central Metallurgical R&D Institute, P.O. Box 87, Helwan, Cairo, Egypt; (202)5010642, Ext. 213; Fax (202)5010639; e-mail mheshamm@hotmail.com