Sustainable recovery of nickel and aluminum from spent NiAl2O4 catalysts via soda roasting-water leaching: Disruption of NiAl2O4 and leaching kinetic

The widespread use of NiO/Al₂O₃ catalysts in the petrochemical industry generates hazardous spent materials due to the formation of refractory nickel-aluminum spinel (NiAl₂O₄), which complicates metal recovery and exacerbates resource inefficiency. Traditional direct acid and alkali leaching cannot recover Ni and Al due to excellent stable structure of NiAl₂O₄. Here, we propose a simple soda roasting-water leaching strategy to disrupt the spinel lattice and recover Ni and Al with high efficiency. By roasting spent catalysts with Na₂CO₃ at 1000 °C, Na ⁺ ions substituted Al³⁺ in the octahedral sites, which destroyed the spinel framework and converted Al₂O₃/NiAl₂O₄ into water-soluble NaAlO₂. Over 98.31 % of Al was selectively leached at 90 °C, followed by pH-controlled precipitation and calcination at 600 °C to regenerate γ-Al₂O₃ with the purity of 98.21 %. Residual NiO was recovered via 2 M H₂SO₄ leaching, with Fe impurities removed through pH-selective precipitation. The kinetic analysis revealed a chemically controlled leaching mechanism (E_a = 47.61 kJ/mol). Final Ni(OH)₂ through calcination at 400 °C yielded reusable NiO. This approach achieved >98 % metal recovery, minimized waste, and aligned with circular economy principles by transforming hazardous spent catalysts into high-purity industrial feedstocks.