Nickel and aluminium recovery from spent reforming catalyst through selective leaching, crystallization and precipitation

An attempt has been made to investigate and optimize the recovery of Ni and Al through sulphuric acid (3.0−5.5 mol/L) leaching under different operating conditions. From the leaching experiments, it was possible to extract 98.5% of NiO and 40.7% of Al2O3 under the conditions of 5.5 mol/L H2SO4, reaction time of 4 h, solid-to-liquid ratio 0.2 g/mL, temperature of 358 K, particle size <100 μm, 200−250 r/min with 5.0 g catalyst dosage. The leached liquor Al was separated by selective crystallization using 1.4 mol/L KOH and Ni was separated by selective precipitation using 0.3 mol/L H2C2O4. From the studies, it is possible to recover around 97.9% of NiO having 98.3% purity, around 25% of Al2O3 was also recovered as alum-(K) having 99% purity and 14.7% of Al2O3 as a salt of Al−K−C2O4−SO4.Sulphuric acid was found to be a suitable leaching agent for selective leaching and it was also observed that alum-(K) can be selectively crystallized from sulphate solutions. The study also indicated the effective extraction and recovery of nickel and aluminium which were well supported by characterization studies using TG-DTA/DTG and XRD techniques.