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

Abstract

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; p O 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.

Sustainable Recovery of Platinum Group Metals from Spent Automotive Three-Way Catalysts through a Biogenic Thiosulfate-Copper-Ammonia System

“…The critical role played by the pH level in PGM leaching processes has been reported by other authors [17,[54][55][56][57]. The optimal pH for leaching PGMs can vary significantly depending on the specific leaching process and conditions.…”

“…The choice of pH level is crucial in designing effective PGM leaching processes. Ilyas and Kim [56] document an upward trend in the extraction of Pt and Pd as the pH of the leach liquor decreases from 11.2, resulting in 96.4% Pt and 92.7% Pd extraction, to 10.4, where extraction rates reach 98.2% for Pt and 97.6% for Pd. Bax et al [55] reported a substantial increase in the recovery of Pt and Pd at pH 1, achieving a 99.7% recovery for Pt and 96.3% for Pd.…”

Separation of Palladium from Alkaline Cyanide Solutions through Microemulsion Extraction Using Imidazolium Ionic Liquids

“…These disadvantages of the above processes make them unsuitable for large-scale metal cyanide removal. By comparison, solvent extraction can be used to remove metal cyanides and recover valuable metals due to its large processing capacity and high selectivity [ 25 , 26 , 27 ].…”