Recycling of Palladium from Spent Catalysts Using Solvent Extraction—Some Critical Points

Electrical and electronics equipment and automotive and industrial catalysts are some examples of top technological devices whose functioning rely on the use of platinum-group metals (PGMs). The PGMs’ high economic value and difficult to replace technological properties, together with their scarcity in the Earth’s crust, justify concerns about their critical condition and reinforce the importance of developing recycling practices for PGM end-of-life materials. This article presents and discusses recent advances regarding the use of hydrometallurgical solvent extraction to recover one PGM, palladium, from spent catalysts. Two different tendencies are implicit in the literature concerning Pd(II) extraction: a few groups focus on the adjustment and optimization of current commercial extractants, while others prefer to design new extracting compounds. Actually, the leach solutions obtained from the treatment of anthropogenic materials generally exhibit different compositions when compared to those coming from the primary resources. The pros and cons of both approaches are critically discussed, and the assumptions backing some of the reported achievements are also appraised.