Siqi Jiang, Aimin Li
The efficient and low-cost recovery of metal in fly ash (FA) is crucial for its resource utilization. However, because metals were present in the structurally stable mullite, the recovery processes impose significant environmental and cost pressures. This study proposes a Li-mediated Flash Joule heating (Li-FJH) method to transform mullite into an amorphous glass phase and LiAlSiO4, thereby enhancing the leaching behavior of FA. First, the effects of Li2CO3 dosage, FJH temperature and time on the mullite Li-FJH were investigated. The FJH product was leached using eco-friendly citric acid. The optimal concentration was identified and the leaching kinetics were fitted. Second, the phase composition, microstructure, chemical bonding structure, and changes in the coordination states of Al and Si in the FJH products were analyzed using XRD, SEM, RS, FTIR, and NMR to elucidate the mechanism of mullite transformation. The content of metal in leachate was determined by ICP-MS to evaluate the recovery efficiency of valuable components and Li inducer. Finally, the advantages of this approach were assessed. The results indicate heating at 1800 °C for 8 s effectively induced the transformation of mullite into an amorphous glass phase and LiAlSiO4. 99.12 % of Al, 99.64 % of Fe and 99.86 % of Li were leached using 0.75 M citric acid at 80 °C for 90 min. The leaching behavior of the FJH product conforms to the Avrami model. This method demonstrates advantages in energy consumption, processing and cost, offering a new strategy for the FA recovery.