Hydrometallurgical Processing of Aluminium Drosses Using Alkaline and Acidic Leaching Media

Abstract

Aluminium dross represents an important secondary raw material containing significant amounts of metallic and oxidised aluminium. The present study investigates the hydrometallurgical processing of two aluminium drosses originating from secondary aluminium alloy production, namely rotary furnace dross and post-refining dross, representing two technologically different aluminium dross streams. The materials were characterised using X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS), and digital microscopy. Leaching experiments were performed using 5 wt.% NaOH, 5 wt.% KOH and 5 wt.% H2SO4 solutions at laboratory temperature. Aluminium concentrations in the leachates were determined by ICP-AES, while the solid residues were analysed by ED-XRF, XRD and SEM/EDS. The highest aluminium concentrations in the leachates were achieved using sodium hydroxide, reaching 21 800 mg·L-1 for rotary furnace dross and 25 000 mg·L-1 for post-refining dross. Lower aluminium concentrations (7 930–10 400 mg·L-1) were obtained for potassium hydroxide and sulphuric acid. XRD analysis revealed the presence of stable phases including AlN, MgAl2O4, Al2O3, CaAl12O19 and CaF2 after leaching, indicating incomplete dissolution of the original dross constituents. SEM observations confirmed substantial microstructural changes associated with partial dissolution of aluminium-bearing phases. The results indicate that, under the investigated conditions, alkaline leaching, particularly using NaOH, provides the most favourable conditions for aluminium recovery from the investigated drosses and confirms their potential as secondary raw material sources for hydrometallurgical processing.