Within the H2020 PLATIRUS project (https://www.platirus.eu/), KU Leuven researchers developed a process for the refining of palladium, platinum and rhodium using solvent extraction. The process was validated using a battery of mixer-settlers.
Evaluating the viability of scaling up continuous solvent extraction processes is crucial. Currently, there is not so much publicly available information regarding the operation of counter-current solvent extraction equipment and addressing potential issues that may arise when using these contactors with real feed materials.
In this study, we assessed the performance of a solvent extraction process for the purification of palladium, platinum and rhodium. The extractant, Aliquat 336 iodide, was synthesized in mixer-settlers by contacting commercially available Aliquat 336, diluted in p-cymene, with an aqueous solution of potassium iodide, in counter-current mode. Aliquat 336 iodide was used to extract palladium(II) and platinum(IV) from a highly impure pregnant leach solution originating from spent automotive catalysts. Selective stripping was achieved using aqueous ammonia and thiourea solutions. In total, 12 liters of pregnant leach solution from spent automotive catalysts were processed using two stages for the extraction of palladium(II) and platinum(IV), and four stages for each stripping step. The chosen organic-to-aqueous (O/A) ratios allowed to enrich palladium and platinum solutions by approximately 6 and 2.5 times, respectively, while rhodium remained in the raffinate.
Following the solvent extraction, the output solutions were treated downstream to obtain highly pure (>99%) platinum group metal (PGM) nitrate solutions. This study critically addresses the challenges encountered when running a solvent extraction process at a minipilot scale.
Full reference paper:
Refining of Palladium, Platinum, and Rhodium from a Pregnant Leach Solution of Spent Automotive Catalysts by Continuous Counter-Current Solvent Extraction with Ionic Liquids in Mixer-Settlers. Viet Tu Nguyen, Koen Binnemans, and Sofía Riaño, Industrial & Engineering Chemistry Research 2023 62 (24), 9549-9562, DOI: 10.1021/acs.iecr.3c00851
The research leading to these results received funding from the European Union’s Horizon 2020 Research and Innovation program under Grant Agreement No. 730224 (PLATIRUS). This publication reflects only the authors’ view, exempting the Community from any liability. The authors thank Jeroen Spooren and Thomas Abo Atia from VITO (Belgium) for providing the pregnant leach solution within the frame of the PLATIRUS Project.