Selective recovery of platinum from spent automobile exhaust catalysts via magnetite nanoparticles

The numerous applications and high cost of platinum group metals (PGMs), in addition to the scarcity of their sources and mines, has led the secondary sources of these metals to a high consideration. In this study, the hydrometallurgical recovery of platinum from spent catalysts was investigated. For this purpose, after the preparation and grinding, the catalysts were dissolved in HCl and HNO3, as an oxidant. Extraction of platinum from acidic solution was performed by magnetite nanoparticles. Firstly, the magnetite nanoparticles were synthesized by co-precipitation of ferrous and ferric salts in the presence of ammonium hydroxide. Because of the instability and tendency to agglomeration, the surface of nanoparticles was coated by tetraethyl silicate. Subsequently, the silica-coated nanoparticles were functionalized with diphenyl phosphine ligand, that had the ability to selective adsorption of Pt. Finally, in a time less than 15 minutes about 91% [PtCl4]2- was recovered from leach liquor.