The selective dissolution of alumina, cobalt and platinum from a calcined spent catalyst using different lixiviants

It was found that the selective dissolution of aluminium species with sodium hydroxide solution under leaching conditions from the spent cobalt-containing catalyst was effective. Approximately 89% of the aluminium species present in the calcined spent catalyst was selectively dissolved in sodium hydroxide solution (6.25 M) when using elevated pressure (about 9 bar) and temperature (170 °C) during two consecutive leaching steps. As expected, platinum species still remain insoluble in the sodium hydroxide solution. During the leaching step, both aluminium and cobalt species dissolved simultaneously in the mineral acids such as HCl, H2SO4 and HNO3 to form metal salts in the leach liquor. In conclusion, almost all of Al, Co and Pt species present in the original spent catalyst were respectively dissolved in the aqueous phase during the sodium hydroxide-nitric acid-aqua regia leaching process.