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 from such 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 platinum recovery 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 regia with 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.