Hydrometallurgical recovery/recycling of platinum by the leaching of spent catalysts: A review

Platinum is one of the precious metals with many applications, including in catalysis, electronic devices and
jewelry. However, its limited resources are becoming depleted. To meet the future demand and conserve
resources, it is necessary to process spent platinum-containing materials, such as catalysts, electronic scraps
and used equipment. These materials are usually processed by pyro/hydrometallurgical processes consisting of
thermal treatment followed by leaching, precipitation or solvent extraction. This paper reviews platinum
leaching fromsuch resources using acidic and alkaline solutions in the presence of oxidizing agents, such as nitric
acid and hydrogen peroxide, sodium cyanide and iodide solutions. The results of the study are described with
respect to the recovery of platinum and other metals under the optimized conditions of leaching with lixiviants.
Previous studies have achieved platinumrecovery using aqua regia and acidic solution in the presence of chlorine
to produce platinum from spent catalysts on a commercial scale; however, the process generates toxic nitrogen
oxide and chlorine gases. This paper reports the salient findings of efforts to replace the aqua regiawith hydrogen
peroxide in acidic solution, chloride salts, sodium cyanide and iodide solution to improve the economics of the
existing processes and reduce the environmental pollution.