A new technique for extraction of platinum group metals by pressure cyanidation

Abstract

At room temperature and pressures, the reaction between sodium cyanide and platinum group metals (PGMs) does not occur because of poor kinetics. However, at elevated temperatures between 120 and 180 °C, PGMs can be leached by sodium cyanide like the reaction of gold. In this work, a new technique to treat Pt–Pd sulfide flotation concentrates and spent auto-catalysts by pressure cyanidation is put forward, and the results of 5 kg-scale batch experiments in a 50 L autoclave are reported for process development. The cyanide leaching reaction mechanism is also discussed. For flotation concentrates containing about 80 g/t Pt and Pd, after pre-treating by pressure acid leaching, followed by two steps of pressure cyanide leaching, up to 90–94% Pt and 99% Pd extraction could be achieved. Final concentrates obtained from cyanide leaching solution using zinc cementation contained 70–90% of precious metals. For spent auto-catalysts containing ≈ 1000–2000 g/t Pt + Pd + Rh, after a pre-treatment process to remove the wrapping of the catalyst carrier and to rid surface accumulated carbon and gasoline contaminants, followed by two steps of pressure cyanide leaching, the recoveries of Pt, Pd and Rh were 95–96%, 97–98% and 90–92%, respectively.