Particle sorting to improve the removal of fluoride and aluminum nitride from secondary aluminum dross by roasting.

Abstract

It is important to remove active substances from secondary aluminum dross (SAD) to meet the reuse of SAD. In this work, the removal of active substances from different particle sizes of SAD was studied using roasting improvement with particle sorting. The results showed that roasting after particle sorting pretreatment can effectively remove fluoride and aluminum nitride (AlN) from SAD, while getting the high-grade alumina (Al2O3) crude materials. The active substances of SAD mainly contribute to AlN, aluminum carbide (Al4C3), and soluble fluoride ions. AlN and Al3C4 mainly exist in particles of 0.05-0.1mm, while Al and fluoride are mainly in particles of 0.1-0.2mm. The SAD of particle size ranging 0.1-0.2mm has high activity and leaching toxicity; the gas emission was reached 50.9mL/g (limit value of 4mL/g), and the fluoride ion concentration in the literature was 137.62mg/L (limit value of 100mg/L) during the identification for reactivity and leaching toxicity according to GB5085.5-2007 and GB5085.3-2007, respectively. Roasting at 1000°C for 90min, the active substances of SAD were converted to Al2O3, N2, and CO2; meanwhile, soluble fluoride converted to stable CaF2. The final gas release was reduced to 2.01mL/g while soluble fluoride from SAD residues was reduced to 6.16mg/L, respectively. The Al2O3 content of SAD residues was determined at 91.8% and has been classified as category I solid waste. The results suggested that the roasting improvement with particle sorting of SAD can meet the reuse of valuable materials at full scale.