Cloud Point Extraction of Platinum Group Metal solutions: Key factors in metal extraction and selective elution at low concentrations

This is the authors' abstract. We don't add key points for this paper.

Platinum group metals are leached from spent autocatalytic converters and other end-of-life products, producing Platinum group metal concentrations below 500 ppm compared to 15,000 ppm from commercial concentrates. Conventional solvent extraction and precipitation methods are inefficient for processing end-of-life leachates, but Cloud Point Extraction shows promise for recovering trace Platinum group metals with minimal environmental impact. However, literature on Platinum group metal Cloud Point Extraction is limited, particularly regarding methods to elute Platinum group metals or remove co-extracted impurities from the surfactant phase. This study used design of experiments to investigate how initial solution pH, surfactant volume (10 % w / v Triton X − 100), complexing agent volume (1 % w/v 2-mercaptobenzothiazole, 2-MBT), metal ion concentration, and contact time affect Platinum Group Metal extraction from spent autocatalytic converters chloride leachate. Leach solutions contained 82–165 ppm PGMs and 2153–4348 ppm matrix elements. Key factors were identified to be the initial solution pH, metal ion concentration, and complexing agent volume. Interactions between initial solution pH and metal ion concentration, as well as 2-MBT and metal ion concentration, enhanced Pt, Pd, and Rh recovery, while initial solution pH–2-MBT interactions reduced Pd and Rh recovery. An increase in metal ion concentration resulted in all matrix elements being extracted to the surfactant phase. Elution of Pt and Pd from the surfactant phase with 1.0 M thiourea in 0.5 M HCl achieved 66 % and 62 % recovery, respectively, while 6.0 M HCl eluted 68 % of Rh. Attempts to achieve selective Platinum group metal elution were unsuccessful, prompting impurity scrubbing tests. Aluminium and magnesium were removed, but iron remained. These findings highlight key factors influencing Cloud Point Extraction performance and offer insights for optimizing Platinum group metal recovery by Cloud Point Extraction. • Applied fractional factorial design to optimize cloud point extraction of PGMs from spent autocatalytic converter leachate. • Identified initial pH, 2-MBT volume, and metal ion concentration as critical factors influencing PGM extraction efficiency. • Achieved over 60 % recovery of PGMs via thiourea/HCl elution, though selective separation remains challenging. • Developed impurity scrubbing methods effectively removing Al and Mg, with Fe removal remaining problematic. • Study offers insights into optimizing PGM recovery from complex leachates via cloud point extraction.