Optimizing a method for leaching PGMs from simulated spent autocatalyst material using ozone & hydrochloric acid

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dc.contributor.advisorBradshaw, Steven Martinen_ZA
dc.contributor.advisorAkdogan, Guvenen_ZA
dc.contributor.advisorvan Wyk, Andries Pieteren_ZA
dc.contributor.authorKnight, Marcus Alexanderen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.en_ZA
dc.date.accessioned2024-03-05T08:10:50Zen_ZA
dc.date.accessioned2024-04-26T21:17:36Zen_ZA
dc.date.available2024-03-05T08:10:50Zen_ZA
dc.date.available2024-04-26T21:17:36Zen_ZA
dc.date.issued2024-03en_ZA
dc.descriptionThesis (MEng)--Stellenbosch University, 2024.en_ZA
dc.description.abstractENGLISH ABSTRACT:Catalytic converters are present in all modern vehicles and contain the PGMs Pt, Pd, and Rh. These PGMs act as catalysts for the oxidation of C, H, and O to CO2 and H2O; and the reduction of NOx to N2, H2O, CO2, and NO. Mining is the primary source of these metals, but much research and development has been conducted into recovery from secondary sources such as e-waste and scrap. Pyrometallurgical methods are most popular for large scale recycling but produce toxic fumes such as sulphur oxides and have a significant electrical requirement. Hydrometallurgical methods show good extraction efficiencies, especially on a smaller scale, but trade the high energy requirements and toxic emissions of pyrometallurgical processes for increased reagent requirements. A need is present for continued investigation into optimizing processes for recovering these PGMs from spent auto-catalysts using more environmentally benign hydrometallurgical methods. The use of ozone as an oxidant in chloride leaching is one option. The gas has a high oxidising potential and is safer and less aggressive when compared to other popular oxidants such as chlorine gas. Therefore, the aim of this investigation was to develop a process for leaching Pt, Pd, and Rh from simulated spent autocatalyst material using ozone and hydrochloric acid. Development of the chosen process was carried out through kinetic and statistical analyses. Experimentation was divided into two stages: Leach 1 and Leach 2. Both leaches were carried out using a Box-Behnken experimental design. The O3 mass flow, initial HCl concentration, and temperature were varied at factor levels of 3.34, 5.01, and 6.68 g/h; 1.0, 3.0, and 5.0 M; and 30, 60, and 90oC respectively. Fifteen runs were conducted with a centrepoint triplicate for each leach. From the results and a statistical analysis, it was concluded that when maximizing the overall PGM extraction the leach was optimized at 5.01 g/h O3, 5.0 M HCl, and 90oC with Pt, Pd, and Rh extractions of approximately 80%, 85%, and 42%. However, at these conditions a significant degree of impurity extraction was observed at 67% and 68% for Al and Mg. Due to the high dependency of Rh and these two impurities on temperature, a desirability analysis determined that adjusting the factor setpoints could potentially facilitate the selective extraction of Pt and Pd (at values >80%) while minimizing the extraction of Rh and impurities. This was the basis for Leach 2. The second leach was conducted at the same O3 mass flows, HCl initial concentrations of 4.0, 5.0, and 6.0 M, and temperatures of 25, 30, and 35oC. The analysis from this leach indicated optimum conditions of 3.34 g/h, 5.0 M, and 25oC. The extractions at these conditions were 64% for Pt and Pd, and Rh, Si, Al, and Mg extractions were 1.3%, 2.6%, 2.8%, and 4.1%. Therefore, the minimization of the Rh and impurity extraction was successful. However, throughout experimentation a decrease in the extractability of the PGMs was observed over time. This is highlighted by the difference in the optimum results for Pt and Pd between Leach 1 and 2, and the similar conditions used to facilitate these extractions. A possible cause of this decrease is the gradual hydroxylation of the PGM oxides as a result of their exposure to humid air. However, further investigation is required to establish exactly what decreased the PGM extractability over time.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.af_ZA
dc.description.versionMastersen_ZA
dc.format.extent205 pages : illustrationsen_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/130539en_ZA
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshAutomobiles -- Catalytic convertersen_ZA
dc.subject.lcshHydrometallurgyen_ZA
dc.subject.lcshHydrochloric aciden_ZA
dc.subject.lcshLeachingen_ZA
dc.subject.lcshPlatinum groupen_ZA
dc.titleOptimizing a method for leaching PGMs from simulated spent autocatalyst material using ozone & hydrochloric aciden_ZA
dc.typeThesisen_ZA
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