China Nonferrous Metallurgy

This study proposes a novel high-temperature sintering-hydrometallurgical leaching process for the separation and recovery of aluminum (Al) and palladium (Pd) from spent automotive catalysts. In this process, sodium carbonate (Na₂CO₃) and calcium carbonate (CaCO₃) are mixed with the raw material for sintering, and the crystalline phase formation mechanism during the sintering process is systematically investigated. Na₂CO₃ preferentially reacts with cordierite to form sodium aluminosilicates and other products; Na⁺ ions can inhibit the phase transformation of β-2CaO·SiO₂ to the γ phase and enhance its stability, while excessive Ca²⁺ ions tend to form refractory 3CaO·Al₂O₃ with low leachability. The optimal roasting parameters are determined as N/A 1.0-1.35 and C/S 2.0 ~ 2.16, and the main crystalline phases of the sintered clinker are γ-2CaO·SiO₂, β-2CaO·SiO₂, CaO·ZrO₂, Na₂O·Al₂O₃, and MgO. Alkali leaching at 80℃ with 10 g/L caustic lye for 30 minutes results in an Al leaching efficiency of over 95%. Subsequent acid leaching with 1 mol/L hydrochloric acid (HCl) at 50 ~ 70℃ for 40 minutes can effectively remove magnesium (Mg) with negligible Pd loss; the mass fraction of PdO in the acid leaching residue is upgraded from 0.043 4% to 0.314%, achieving nearly tenfold Pd enrichment. The proposed process not only enables efficient recovery of Al from spent catalysts but also effectively reduces the Mg content, thereby lowering the smelting temperature required for the subsequent pyrometallurgical recovery of Pd, which provides a new technical approach for the resource recycling and valorization of spent automotive catalysts.