Technological watch

Metal-bearing solid wastes are an important secondary source of metals. Compared to mining from ores, the recovery of metals, especially precious metals from rich secondary sources are more economical and sustainable. Spent automotive catalyst (SAC) is a rich source of platinum group metals [PGM: platinum (Pt), palladium (Pd), and rhodium (Rh)] which contains higher concentrations of PGM than found in natural ores. This paper presents a critical review of conventional recycling technologies used for the recovery of PGM from SAC, and highlights some of their shortcomings. A discussion on sample characterization, pretreatment techniques, metal mobilization, and immobilization of the soluble metal ions is presented. Bioprocesses are generally recognized as sustainable alternatives for the recovery of heavy metals. The intrinsic capability of some microorganisms to mobilize metals via processes such as bioleaching, and subsequent biosorption, bioaccumulation, bioreduction and biomineralization may provide a more sustainable pathway for the recovery of these metals.