Progress in recycling of precious metals in automobile catalysts

Platinum group metals (PGM) (Pt, Pd, Rh) were widely used in automobile catalysts. With the rapid industrial development and increasing demand for precious metal jewelry, the PGM demand increased. Scrapped automobile catalysts became the most important PGM secondary resources, so the recycling of PGM from spent automobile catalysts was particularly important. The methods of recovery of PGM from spent automobile catalysts were reviewed, including the crude extraction process, various hydrometallurgical and pyrometallurgical methods. Hydrometallurgical process included carrier dissolution, active component dissolution, total dissolution and pressure cyanidation, and pyrometallurgical process included plasma fusion, metal collection and dry chlorination. The advantages and disadvantages of these processes were compared, and the advancement of the technologies in recent years was briefly presented. Hydrometallurgical process had the advantages of simple technology, low cost, short process, and became the most common method for PGM recovery from car catalysts. The main drawbacks were that the PGM content in insoluble residue was still high, the leaching rate was not stable, and low recovery rate (especially Rh). Pyrometallurgical process had the advantage of large capacity, less waste water emissions, and high PGM recovery rate. However, the process required a lot of base metals for trapping agent, while the complex process, large investment, high energy consumption, long recovery period, and pollution control were the main problems in application. Finally, the development direction of automotive catalyst recycling technology was concluded as improving the level of technique, developing new technologies, being efficient and environment-friendly.