As a type of industrial solid waste with huge emission and heap stock, high-aluminum pulverized coal ash has a significant negative impact on resources and the environment. At the same time, as a secondary resource, its aluminum content can reach 50%, which is close to that of medium-grade bauxite; thus, it can be used as a substitute for bauxite resources. We propose a new method for extracting aluminum from fly ash via leaching. By designing the thermal reaction system of the molten brine, high-purity hydroxyl sodalite (90.2%) was prepared from fly ash. In this study, aluminum and other valuable elements were extracted using a hydrochloric acid leaching method from prepared high-purity hydroxyl sodalite in the form of ions by converting fly ash into a fixed hydroxyl sodalite solid product system. The major factors affecting the leaching rate are the hydrochloric acid concentration, liquid–solid product quality ratio, reaction temperature, and reaction time. Through analysis and calculation, within the scope of study, the leaching rate of aluminum reached more than 90%. The optimal experimental conditions are a leaching concentration of 1.5 mol/L, a liquid–solid volume–mass ratio of 20, a leaching time of 120 min, and a leaching temperature of 85 °C. Aluminum exists in the leaching solution in the form of Al³⁺, while the silica is partly dissolved in the hydrochloric acid solution; the other part remains in the solid phase as the main part of the hydrochloric acid leaching residue in the form of silica gel. In addition, this method not only can treat high-alumina fly ash, but also can be applied to other types of fly ash.

In this study, SiO₂–Al₂O₃–CaO–MgO steel slag ceramics containing 5 wt % MgO were used for the preparation of ceramic bodies, with the replacement of 5–20 wt % quartz and feldspar by fly ash. The effect of the addition of fly ash on the sintering shrinkage, water absorption, sintering range, and flexural strength of the steel slag ceramic was studied. Furthermore, the crystalline phase transitions and microstructures of the sintered samples were investigated by XRD, Fourier transform infrared (FTIR), and SEM. The results showed that the addition of fly ash affected the crystalline phases of the sintered ceramic samples. The main crystal phases of the base steel slag ceramic sample without fly ash were quartz, diopside, and augite. With increasing fly ash content, the quartz diffraction peak decreased gradually, while the diffraction peak intensity of anorthite became stronger. The mechanical properties of the samples decreased with the increasing amount of fly ash. The addition of fly ash (0–20 wt %) affected the optimum sintering temperature (1130–1160 °C) and widened the sintering range. The maximum addition amount of fly ash should be 15 wt %, for which the optimum sintering temperature was 1145 °C, water absorption was 0.03%, and flexural strength was 43.37 MPa higher than the Chinese national standard GBT 4100-2015 requirements.