Abstract:

Since a vast amount of lithium-rich coal fly ash (CFA) is produced domestically each year, the extraction of this resource is of great importance for supporting sustainable development of the new energy. However, conventional methods for lithium extraction from CFA are constrained by efficiency and selectivity, owing to the low grade of lithium and its encapsulation within a chemically stable glass phase. To overcome this technical bottleneck, this study proposes a novel multi-stage lithium extraction strategy integrating "activation roasting-mild alkaline leaching-adsorption separation". First, CFA was mixed with sodium sulfate and roasted at 900 ℃ for 2 h. This high-temperature roasting effectively disrupted the Si-O-Al bonds within the glass phase, inducing lattice reconstruction and enabling the thermal activation of lithium and its host minerals. Subsequently, the calcine underwent mild alkaline leaching (1 mol·L^-1 NaOH, 70 ℃, liquid-to-solid ratio of 5 : 1) to achieve the selective release of lithium ions. Finally, a lithium titanate ion sieve, known for its specific memory effect towards lithium, was employed for adsorption, accomplishing the highly efficient and specific separation of lithium from impurities. The new process achieved a total lithium recovery of 73.20% and a lithium/impurity separation factor exceeding 96. The purified solution can be concentrated to directly produce lithium phosphate with a purity of 99.02%, enabling the precise purification of lithium from CFA. This work provides a potential green and efficient approach for the high-value utilization of China’s vast CFA reserves and the development of unconventional lithium resources.

Key words: coal fly ash, activation roasting, mild alkaline leaching, titanium-based adsorption, selective lithium extraction