Microwave chloride leaching of valuable elements from spent automotive catalysts: Understanding the role of hydrogen peroxide

•PGM and LREE microwave leaching from autocatalysts was satisfactory in 6 M HCl.•In situ generated Cl2 provides additional oxidizing power to leach PGMs in 6 M HCl.•The headspace gas and pressure build-up at 150 °C affected the PGM and LREE leaching.•The effect of H2O2 addition on PGM leaching was m...

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Veröffentlicht in:Resources, conservation and recycling conservation and recycling, 2021-03, Vol.166, p.105349, Article 105349
Hauptverfasser: Abo Atia, Thomas, Wouters, Wendy, Monforte, Giuseppe, Spooren, Jeroen
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Sprache:eng
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Zusammenfassung:•PGM and LREE microwave leaching from autocatalysts was satisfactory in 6 M HCl.•In situ generated Cl2 provides additional oxidizing power to leach PGMs in 6 M HCl.•The headspace gas and pressure build-up at 150 °C affected the PGM and LREE leaching.•The effect of H2O2 addition on PGM leaching was marginal.•The oxidation states of Rh and Ce in the autocatalyst influenced their leaching. This study reports on the microwave-assisted leaching behavior of platinum group metals (PGMs) and light rare earth elements (LREEs) from two representative end-of-life automotive ceramic catalyst materials in 6 M HCl at 150 °C with and without the addition of 10 v/v% H2O2 solution. It was shown that the in situ generated headspace gas in the pressure-tight reactor and the elemental speciation in the spent catalysts influence the leachability of PGMs and LREEs. The formation of Cl2 in the headspace provided the 6 M HCl system with a suitable oxidizing environment to leach PGMs as soluble chloro‑complexes. Indeed, spent catalyst containing prevalently oxidized PGM species leached best in 6 M HCl (93.9 ± 0.7% Pd, 98±3% Pt, 70.7 ± 0.4% Rh). Whereas, H2O2 addition moderately decreased the PGM leaching efficiency due to surface passivation by an oxide layer. However, spent catalyst containing other oxidizable substrates (e.g. Ce3+, zerovalent PGMs) that give rise to H2 evolution, compensated partially the oxidation potential of the HCl system. In such case, H2O2 addition slightly improved the PGM leachability (Rh 91.8 ± 0.1% Pd, 96±4% Pt, 89.9 ± 0.2% Rh). Among the studied LREEs, Ce leaching was mainly affected by the passivation of Ce3+ through oxidation, thus in the absence of H2O2 and at lower initial Ce3+ concentration Ce leached best (87–94%). The effect of hydrogen peroxide was negligible for La and Nd, and moderate towards Y leaching. The leaching of these elements was constrained by their association with Al and Zr oxides, respectively.
ISSN:0921-3449
1879-0658
DOI:10.1016/j.resconrec.2020.105349