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Total recycling of all the components from spent auto-catalyst by NaOH roasting-assisted hydrometallurgical route
- Trinh, Ha Bich, Lee, Jae-chun, Srivastava, Rajiv R., Kim, Sookyung
- Journal of hazardous materials 2019 v.379 pp. 120772
- X-ray diffraction, aluminum, aluminum oxide, automobiles, catalysts, ceric oxide, cordierite, hydrochloric acid, leaching, magnesium, models, phase transition, purification methods, recycling, roasting, sodium chlorate, sodium hydroxide, sulfuric acid, temperature
- Total recycling of all valuable metals such as PGMs, Ce, Al and Mg from the spent automobile catalysts has been explored. The alkali roasting was performed under NaOH, 0.5–3.0 g; temperature, 300–800 °C; and time, 10–60 min. The phase transformation from cordierite to the soluble products (NaAlO2, Na2MgSiO4) was influenced by the temperature, following the diffusion-controlled model (Ea(roasting), 6.4 kJ/mol). XRD analysis of the roasted mass revealed that the refractory phases of cordierite and γ-alumina could be eliminated at ≥600 °C at sample-to-NaOH mass ratio, 1:1. The leaching of the roasted mass followed an intermediate-controlled mechanism for aluminum leaching with (Ea(Al-leaching) value of 20.3 kJ/mol), while it was diffusion-controlled for magnesium leaching (Ea(Mg-leaching), 8.9 kJ/mol). At the optimum leaching condition (1.0 M H2SO4, 90 °C, 60 min, yielding >95% aluminum and magnesium), a significant amount of PGMs was also leached. Thereafter, the cementation process was investigated with Al0-powder that could precipitate >99% PGMs within 15 min at 90 °C. The yielded concentrate of PGMs and CeO2 was subsequently leached in 6.0 M HCl with 2.0 M NaClO3 that dissolved >97% PGMs, leaving the residue as the CeO2 concentrate. Individual metals can be recovered by following established separation and purification techniques.