A novel route to denitrify, recover chlorines and prepare pre-melted refine slag of 12CaO·7Al2O3 (C12A7) from secondary aluminum dross (SAD)

Abstract

Secondary aluminum dross (SAD) containing toxic elements, such as N, Cl, F, Na, and K, is a typical hazardous substance in the process of recycling aluminum. Numerous studies have reported the detoxification of SAD by hydrometallurgical technologies; nonetheless, those methods were always inefficient due to the long process. In this study, a novel process for detoxification, recycling and high-value utilization of SAD was investigated. Thermodynamic analysis revealed that hazardous substances of AlN, Al4C3, and Al can be easily oxidized to Al2O3, while Cl, K, and Na can be volatilized above 1000 °C. The experimental results confirmed that more than 99.7% of nitrogen in AlN could be transformed into the harmless N2 under the optimal air roasting conditions (Ca/Al mole ratio of 1.7, roasting temperature of 1400 °C and roasting time of 120 min). Na, K, and Cl were recycled efficiently as the volatiles with recovery rates of 95.3%, 99.5% and 95.9%, respectively. During the roasting process, high purity C12A7 was prepared successfully, and most fluorine in SAD was solidified in the calcium aluminates, which can be used as a steel refining desulfurization agent. This study provided a zero hazardous waste thought for the utilization of SAD.