Economical and efficient recovery of Pd and Al2O3 from spent Pd/Al2O3 catalyst with integrated sodium roasting−reductive leaching process

An integrated sodium roasting−reductive leaching process was developed to recover Pd and Al2O3 from spent Pd/Al2O3 catalyst. The thermodynamic analysis of sodium roasting indicated that NaOH, Na2CO3 and Na2C2O4 could completely react with Al2O3 to form NaAlO2 at the optimal Na2O/Al2O3 molar ratio and temperature. The Al2O3 leaching ratios were 99.6%, 61.0% and 55.3%, respectively, when the roasted residues from NaOH, Na2CO3 and Na2C2O4 roasting were subjected to water leaching. Mechanical activation−dry NaOH roasting process avoided the consolidation of roasted residue, and high Al2O3 leaching ratio could be obtained. Reductive leaching with N2H4·H2O averted Pd dissolution loss during water leaching, and 99.7% of Al2O3 in the catalyst was leached. NaAlO2 leachate and Pd-enriched residue were finally obtained, and the valuable Al and Pd can be further recovered.