Recovery of Noble Metals from Spent Catalysts: A Review

In the past several decades, many technologies to recover platinum group metals (PGMs) and rhenium (Re) from electronic waste and spent catalysts have been developed and published. The reasons for the rising interest in this area are: (1) The abundance of these elements in the earth's crust is < 10(-3) ppm (similar to 6.6 x 10(4) tons worldwide); (2) global demand for PGMs is > 590 tons; (3) electronics and catalyst industries consume > 90 pct of precious metals (about 65 pct of Pd, 45 pct of Pt and 84 pct of Rh are used in catalytic converters); (4) properties of PGMs and Re (resistance to corrosion and oxidation, high melting temperatures, electrical conductivity and catalytic activity) are of great commercial interest. Even though several comprehensive reviews on the recovery of precious metals from spent catalysts have recently been published, several developments were not focused by the scientific community. The reviews divide the technologies into hydro- and pyrometallurgical ones. However, the variety of different approaches requires a more detailed classification. This article is an overview of the recently reported works and a comparison of different technologies in terms of extraction efficiency, environmental friendliness, and capital and operational expenditures. A new electrochemical method, which is now under development, is also presented.