Roasting Extraction of Lithium from Fly Ash: A Study of Influential Parameters and Mechanisms

Fly ash consists of significant amounts of lithium, which is an essential resource for developing batteries. This study proposed an efficient method for extracting lithium from fly ash. First, we explored the parameters affecting the activation effect of sodium carbonate roasting and the leaching efficiency of lithium using acid leaching. Additionally, ultrasonic pre-treatment was applied to enhance activation. A further mechanism for the roasting extraction of lithium was symmetrically analyzed. The results showed that ultrasonic treatment at 200 W for 1 h under alkaline leaching conditions (sodium hydroxide solution 4 mol/L, reaction temperature 80 °C, leaching time 2 h, solid–liquid ratio 1 g:30 mL) achieved a lithium leaching rate of 90.74%, surpassing the 84.72% with traditional roasting–alkaline leaching. Under optimal acid leaching conditions (850 °C for reaction of 2.5 h, fly ash-to-sodium carbonate ratio (R_fs) 1:2, sulfuric acid 2 mol/L, reaction temperature 80 °C, solid–liquid ratio 1 g:30 mL, and leaching time 1.5 h), the leaching rate reached 96.62%. With ultrasonic pre-treatment and acid leaching, the highest leaching rate of 98.68% achieved under optimal conditions: reaction temperature 850 °C for 2.5 h, mass R_fs at 1:1.5, sulfuric acid 2 mol/L, reaction temperature 80 °C, solid–liquid ratio 1 g:35 mL, and leaching time 120 min. The study demonstrated that ultrasonic pre-treatment outperforms the traditional method, achieving a higher leaching rate with fewer roasting additives and lower energy consumption.