A novel technique was developed for the recovery of lithium and aluminum from coal fly ash using a combination of pre-desilication and an intensified acid leaching process. The main components of the high-aluminum fly ash were found to be Al₂O₃ and SiO₂, and the Al/Si ratio increased from 1.0 to 1.5 after desiliconization. The lithium content of the coal fly ash met national recycling standards. The optimal acid leaching conditions, under which the leaching efficiencies of lithium and aluminum were 82.23% and 76.72%, respectively, were as follows: 6 mol/L HCl, 1:20 solid to liquid ratio, 120 °C and 4 h. During the hydrochloric acid pressure leaching process, spherical particles of desilicated fly ash were decomposed into flakes. Part of the mullite phase was dissolved, and most of the glass phase leached into the liquor. The generation of the silicates hindered lithium transport, which decreased the leaching rate of lithium. This work suggests that the preprocessing is a promising option for effective recovery of high-aluminum and fly ash-associated lithium.

Experiments were conducted to investigate the process of aluminum and lithium extraction from high-alumina coal fly ash (HCFA) generated from coal-fired power plants located in northern China. The presence of mullite and other aluminosilicates lead to low reactivity of coal fly ash. An activation pretreatment that destroys an inert composition of coal is necessary. The activation roasting of coal fly ash using sodium chloride and a subsequent leaching process were performed in this research. The results showed that almost no aluminum and lithium were dissolved under direct water leaching, while about 7% and 10% of those were leached into the acid solution respectively. Adding NaCl enhanced the atmospheric pressure leaching of aluminum and lithium with a leaching rate around 50%. Phase analysis and equilibrium calculations results showed that the roasting reaction between the HCFA and NaCl occurred, which led to generation of main new phase NaAlSi₃O₈. The pressure extraction efficiencies of aluminum and lithium were increased to about 93% and 98%, respectively. The implications of the findings provide an alternative process for recovering aluminum and lithium from readily available high-alumina coal fly ash.

Rare earth elements are strategic and critical materials for addressing the global energy crisis and advancing sustainable development goals. Coal fly ash, a major byproduct of coal-fired power plants, has emerged as a promising secondary source of REEs. However, conventional extraction methods suffer from low efficiency, high acid consumption, and significant environmental concerns. This study developed a microwave-assisted deep eutectic solvents leaching process for efficient and selective REE recovery from coal fly ash. Three DESs were synthesized using choline chloride as the hydrogen bond acceptor with p-toluenesulfonic acid, lactic acid, or formic acid as hydrogen bond donors. Among these, the ChCl-PTSA DES exhibited superior leaching performance due to its stronger acidity and higher ionization degree. Under optimized conditions, a REEs leaching efficiency of 89.16% was achieved. FT-IR and ¹H NMR analyses confirmed that DES formation is driven by hydrogen-bonding interactions, while the leaching mechanism involves synergistic protonation of the aluminosilicate matrix and coordination of liberated REE³⁺ ions with DES functional groups. This work establishes microwave-assisted DES leaching as a highly efficient, rapid, and sustainable strategy for REEs recovery from coal fly ash, offering a promising alternative to conventional hydrometallurgical processes.