Status and research progress on recovery of platinum group metals from spent catalysts

In China, the reserves of platinum group metals (PGMs) are scarce, but the consumption of PGMs is enormous, which has resulted in a high external dependence. As more than 90% of PGMs are used by the catalyst industry, spent catalysts are the most important secondary source. Therefore, recycling PGMs from spent catalysts is the most significant strategy for relieving the risk of shortage in the PGMs supply. In this review, the consumption distribution of PGMs and their recycling status were introduced and recycling technologies were discussed in detail. The volume of recycled PGMs has been estimated to be approximately 20%–30% of the global mine production and this trend is increasing. Sample analysis is considered to be crucial for determining the recovery efficiency of PGMs. Extensive studies have shown that pretreatment methods such as reduction, calcination, and mechanical milling can improve the efficiency of PGMs recovery. Compared with traditional cyanide leaching and aqua regia dissolution, more environmentally friendly leaching methods have been developed in recent years, including chlorination leaching, supercritical fluids extraction, and substrates leaching. However, although some hydrometallurgical processes have been industrialized, their disadvantages include the generation of wastewater, emission of hazardous gases, and low recovery efficiency of Rh, which must be carefully evaluated. Pyrometallurgical methods have been widely used to concentrate PGMs due to the generally low PGMs content in spent catalysts. Lead, copper, iron, and matte are good PGMs collectors, whereby the PGMs form alloys with the collector metals and supporting materials, then enter the slag phase. These melting collection methods were reviewed and their advantages and disadvantages were summarized. Based on the serious environmental problems and low recovery efficiency of PGMs by current technologies, future trends for PGMs recycling have been proposed, including activation pretreatments, co-recovery of valuable metals and carrier materials, base metals synergistic smelting, iron melting capture, and electrolysis. These recycling technologies may indicate the development directions and can serve as effective references for further research in this field.