Efficient removal of AlN from secondary aluminum dross using binary fluoride: a theoretical and experimental study

Secondary aluminum dross (SAD) typically contains significant amounts of AlN, which is a major source of the toxic gases released from SAD. Converting AlN into more stable aluminum compounds is crucial for the safe disposal and resource recovery of SAD. In this study, the oxidative removal of AlN from SAD was investigated, and an efficient denitrification method is proposed. Theoretical and experimental results demonstrate that AlN oxidation forms a dense, ordered [Al-O] oxide layer on its surface, which hinders further oxidation. NaF, AlF₃, and Na₃AlF₆ were found to enhance SAD denitrification, and binary fluoride additives KF-Na₃AlF₆ provided further improvement. Roasting SAD at 800 °C for 60 min with 12 wt% KF-Na₃AlF₆ (6 wt% Na₃AlF₆ + 6 wt% KF) achieved 93% oxidation of AlN. The treated SAD showed low reactivity and released negligible gas in aqueous solution. The promoting effect of Na₃AlF₆-based additives is attributed to their ability to facilitate the transformation of the dense, well-ordered [Al-O] surface layer into β-alumina.