Recovery of Platinum-Group Metals from an Unconventional Source of Catalytic Converter Using Pressure Cyanide Leaching and Ionic Liquid Extraction

The fast depletion of critical metals in natural reserves against their increasing demands in advanced technology application presents the necessity to exploit the end-of-life/waste materials as unconventional resources. Due to a higher accumulation of platinum-group metals (PGMs) in exhausted autocatalytic converters, their recycling through an integrative bio-solvo-chemical technique has been studied. PGMs were efficiently dissolved in bio-cyanide solution produced by Chromobacterium violaceum. The autoclave leaching was optimized in the conditions of temperature, 150°C; pO(2), 200 psi; and time, 120 min, yielding > 90% PGMs’ dissolution. PGMs’ separation from cyanide leach liquor was performed using an ionic liquid, Cyphos IL101. Under optimum conditions (i.e., ionic liquid concentration, 0.15 mol/L; extraction pH, 10.4; and temperature, 25°C), Pt and Pd were selectively stripping with > 99% efficiency in 0.1 mol/L (acidic) thiourea and 1.0 mol/L HNO(3) solution, respectively, leaving Rh in the raffinate.