Extracting aluminum from FA is an effective way to improve its utilization rate. Since aluminum oxide is found in high polymerization degree, inert substances such as mullite and sodium aluminosilicate make the reaction process difficult because of their stable chemical properties; within these highly polymerized matrices, the chemical stability of alumina typically persists across a broad temperature range from 1000 °C to over 1600 °C. To address the issue of stable mullite structure that hinders aluminum extraction, a combined acid-base method using sodium carbonate as an activating agent and hydrochloric acid at a temperature of 100 °C as a leaching agent is employed. XRD and SEM were used to analyze the phase characterization and microstructure of fly ash before and after activation and acid leaching, examining the effects of activation parameters and acid leaching parameters on the activation of FA and the aluminum extraction rate. The research results indicate that after calcination activation, mullite is transformed into zeolite, which is easily soluble in acid, and the aluminum within the activated molten material is transferred to the filtrate through acid leaching, achieving the goal of extracting aluminum. Under the activating conditions with sodium carbonate flux, the Al-O bonds in mullite are broken, the crystal structure is transformed, and the aluminum compounds obtained from hydrochloric acid leaching have a stable form of existence, which has a low impact on the error of the experimental results. When the material ratio of fly ash to sodium carbonate is 1:0.7, after reacting at a calcination temperature of 880 °C for 1.5 h, and leaching in 6 mol/L hydrochloric acid at 100 °C with a solid-liquid ratio of 1:6 for 2 h, the extraction rate of aluminum in fly ash is the highest, reaching 97%.

In geotechnical engineering, traditional anchor bolts often have problems such as an insufficient bearing capacity, their ease of loosening, and an unsatisfactory support effect under complex geological conditions (such as soft soil or broken surrounding rock), resulting in it being difficult to guarantee engineering stability. In order to solve these problems, this paper studies the supporting performance of a hollow grouting anchor with an umbrella-shaped expansion head with an expansion pipe. Through theoretical analysis, mechanical performance analysis, and experimental analysis, the supporting mechanisms and mechanical characteristics of a hollow grouting anchor with an umbrella-shaped expansion head are systematically discussed. The calculation formula for the maximum pull-out force of the umbrella-shaped expansion head is clarified, and the fixed range of the expansion body section in relation to the loose ring is quantified. Based on the analysis results, the structural parameters and material properties of the bolt were optimized, and the optimization effect was verified by numerical simulation. The results show that the optimized bolt has significantly improved the pull-out bearing capacity, shear resistance, and reinforcement effect on the soil. The maximum pull-out force of the umbrella-shaped expansion head can be increased by up to 35%, and the fixed range of the expansion body section can be expanded by 45%. The research provides an efficient and reliable support solution for geotechnical engineering fields, such as roadway engineering and tunnel engineering, which significantly improves the stability and safety of engineering under complex geological conditions. At the same time, it provides an important theoretical basis and practical reference for the design and construction of similar projects.

Traditional coal mining methods have led to prominent issues of coal resource waste and large-scale solid waste emissions. The integrated “excavation–backfilling–retention” mining technology for inter-section coal pillars and gate roads is one of the key technologies to solve these problems. However, the excavation and mining process associated with this technology imposes higher requirements on the ventilation system. Aiming at addressing the ventilation challenges existing during the implementation of the “excavation–backfilling–retention” method, research on ventilation safety assurance technology for inter-section coal pillars was carried out. Using COMSOL5.5 software, a full-stage ventilation system design model was constructed, adopting a ventilation mode that combines full-air-pressure ventilation with auxiliary local ventilation. The dynamic variation characteristics of the ventilation system under the “excavation–backfilling–retention” method and its capability to prevent and control the risks of O₂ and CO gas accumulation and coal spontaneous combustion were studied. The results show that during the bypass excavation period, the air supply from the auxiliary fan is sufficient, and during the excavation period for the two gate roads, due to the increased ventilation distance, insufficient airflow occurs near the heading face, accompanied by temperature rise, O₂ concentration decrease, and local CO accumulation, posing risks of coal spontaneous combustion and toxic gas accumulation. During the inter-section coal pillar excavation period and the cyclic operation period, after the full-air-pressure ventilation system is established, the airflow becomes stable, ventilation resistance decreases, and both temperature and gas concentrations are controlled within safe limits. However, in the corner areas, auxiliary local ventilation measures are still required due to insufficient O₂ and CO accumulation. The study verifies the feasibility and safety of the integrated “excavation–backfilling–retention” ventilation system, providing a safe ventilation approach for the integrated mining method and supporting the green mining of coal mines and the synergistic development of coal-based solid waste resource utilization.