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.

The high salt content in saline–alkali soil has a significant impact on plant nutrient absorption and water transport, severely inhibiting crop growth. Through esterification reactions, silicic acid is grafted onto humic acid to form an organic silicon fertilizer (OSiF). The unique Si-O-C bond in the material endows this new type of organic silicon-based fertilizer with the ability to effectively alleviate the harm of high-salt soil to plants. In this study, a soil column experiment was designed to systematically evaluate and compare the effects of organic silicon fertilizers with different organic silicon contents (0%, 5%, and 10%) and traditional compound fertilizers on soil water characteristics, salt ion concentration, pH value, and electrical conductivity. The results showed that the addition of an appropriate amount of organic silicon fertilizer could significantly reduce the activity of salt ions in the soil solution. Experimental data indicated that the 5% and 10% organic silicon fertilizers had the most significant effect on the consumption of major salt ions such as sodium and chloride ions. X-ray photoelectron spectroscopy (XPS) analysis revealed that the reaction of Si-O-C bonds in the soil with Lewis bases led to a shift in the valence state of the 1S electrons of silicon atoms, providing a theoretical basis for the mechanism by which silicon fertilizers alleviate high-salt stress.