Utilizing γ- and θ-Alumina from Aluminium Black Dross for Catalytic Applications: Hybrid Sustainable Pyro-Hydrometallurgy and Residue Heat Utilization

This study is aimed at extracting gamma- and theta-alumina from recycled black aluminium dross for catalytic applications, employing a novel hybrid pyro-hydrometallurgical approach as a waste management technique. The process begins with the extraction of elements from aluminium black dross, controlled heating at 680 degrees C leverages residue heat resources, essential in optimizing resource utilization. Further alkali metal halides addition is done to significantly enhance efficiency in melting aluminium-low magnesium (<= 1%) scraps. Optimization in filtration was conducted at 900 RPM and temperatures near 50 degrees C to refine the purification process and eliminate impurities. Slow calcination was done at 100 degrees C for over 40 min, the salt cake allowing dissolution in a 3 M NaOH solution to achieve a critical pH value of 11.72. The precise pH neutralization was done by using a 3:1 H2SO4 solution to form aluminium hydroxide through the precipitation method at a pH level of 7, a pivotal precursor in alumina extraction. A detailed analysis of post-low-temperature calcination, ranging from room temperature to 800 degrees C for 10 min, was done. Furthermore, a thorough examination of residues and extracted gamma- and theta-alumina was done using XRD, SEM-EDS, and ICP-OES techniques. About 79% of alumina was recovered from black aluminium dross. The proposed technique extracted alumina with a purity of 94.9% with a particle size of 318 nm.