The spent automobile catalysts (SAC) is the major secondary source of palladium and the production of SAC is increasing rapidly over years. The price of palladium keeps rising over the years, which demonstrates its preciousness and urgent industrial demand. Recovering palladium from the spent automobile catalysts benefits a lot from economic and environmental protection aspects. This review aims to provide some new considerations of recovering palladium from the spent automotive catalysts by summarizing and discussing both hydrometallurgical and pyrometallurgical methods. The processes of pretreatment, leaching/extraction, and separation/recovery of palladium from the spent catalysts are introduced, and related reaction mechanisms and process flows are given, especially detailed for hydrometallurgical methods. Hydrometallurgical methods such as chloride leaching with oxidants possess a high selectivity of palladium and low consumption of energy, and are cost-effective and flexible for different volume feeds compared with pyrometallurgical methods. The recovery ratios of palladium and other platinum-group metals should be the focus of competition since their prices have been rapidly increased over the years, and hence more efficient extractants with high selectivity of palladium even in the complexed leachate should be proposed in the future.

A comprehensive recovery process for the selective separation and enrichment of copper, zinc and iron minerals from a polymetallic ore was developed, which consisted of copper flotation, zinc flotation, and iron magnetic separation, and the adsorption mechanism of the copper collector Z-200 (O-isopropyl-N-ethyl thionocarbamate) was also studied in this work. The contents of the main valuable metallic elements of Cu, Zn and Fe in the ore were respectively 0.61%, 1.68% and 14.17%, and they mainly existed as chalcopyrite, sphalerite and magnetite, whose dissemination relationship was complex. Under the optimal conditions of this process, the recoveries of Cu, Zn and Fe in their respective concentrates reached 86.1%, 87.6% and 77.8%, and their grades were separately 20.31%, 45.97% and 63.39%. This process realized the selective separation and beneficiation of copper, zinc, and iron minerals from the ore, and had promising industrial application prospects. The adsorption configuration analysis demonstrated that the steadiest adsorption configurations of Z-200 on the surfaces of chalcopyrite, sphalerite and magnetite were the simultaneous adsorption of carbonyl S together with the O atom. Compared with sphalerite and magnetite, Z-200 was more prone to adsorb on the chalcopyrite surface. The Mulliken charge population and bond length analyses manifested that Z-200 chemically adsorbed on the chalcopyrite surface by forming a normal covalent bond and a back donation covalent bond, and the normal covalent bond played a leading role. The chemisorption of Z-00 was supported by the FTIR spectrum analysis result.