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

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 without addition 10 v/v% H2O2 solution. It was shown that situ generated headspace gas pressure-tight reactor elemental speciation spent catalysts influence leachability PGMs LREEs. The formation Cl2 provided system a suitable oxidizing environment to leach as soluble chloro?complexes. Indeed, containing prevalently oxidized PGM species leached best (93.9 ± 0.7% Pd, 98±3% Pt, 70.7 0.4% Rh). Whereas, moderately decreased efficiency due surface passivation by an oxide layer. However, other oxidizable substrates (e.g. Ce3+, zerovalent PGMs) give rise H2 evolution, compensated partially oxidation potential system. In such case, slightly improved (Rh 91.8 0.1% 96±4% 89.9 0.2% Among studied LREEs, Ce mainly affected Ce3+ through oxidation, thus absence lower initial concentration (87–94%). effect hydrogen peroxide negligible for La Nd, moderate towards Y leaching. these constrained their association Al Zr oxides, respectively.