Coal permeability directly affects the efficiency of gas extraction. Using the multiphase and multifield true triaxial dynamic seepage test system of coal and rock, combined with acoustic emission monitoring, ultrasonic testing and high-resolution image processing, the fracture structure and permeability evolution of in-situ coal subjected to hydraulic fracturing with low-concentration ammonium persulfate were investigated, and the influence mechanism of five groups of different liquid injection rates and pressure injection spaces (the action space between fracturing fluid and coal wall in the open hole section) was quantitatively analyzed. The results show that the larger the liquid injection rate is, the shorter the time required for coal to fracture is, the larger the pressure injection space is, the lower the coal fracture pressure is, and the 4-hole fracturing tube (the largest pressure injection space) has the most acoustic emission positioning points and the widest distribution. After hydraulic fracturing, the ultrasonic velocity of five groups of coal samples decreased. Compared with water fracturing, the coal fractured with ammonium persulfate has fewer acoustic emission positioning points (lower damage), but the oxidation and dissolution of ammonium persulfate can further improve the degree of fracture development, and the effect is better in improving coal permeability. Under the same conditions, the larger the pressure injection space is, the wider the range of coal fracture penetration and ammonium persulfate action is, and the more significant the permeability improvement is. When the pressure injection space is the same, the lower the liquid injection rate, the better the permeability improvement effect. The synergistic effect of oxidation dissolution of ammonium persulfate and hydraulic fracturing can promote the expansion of coal fracture network, and the pressure injection space affects the fracture expansion range and density. The research results can provide theoretical guidance for the modification of seepage characteristics of low permeability coal seams.

In order to study the stage mechanical response characteristics of dry and water-saturated siltstone during splitting process, Brazilian splitting test was carried out, and the stage division method of full stress-strain curve of rock splitting process based on splitting modulus was established. The response law and mechanical mechanism of stress characteristic value and strain characteristic value in each stage were systematically analyzed. The results show that water significantly affects the stress evolution path and strain development path of Brazilian splitting process in siltstone. The average values of compaction stress, yield stress, peak stress and unloading stress of water-saturated samples decrease to 62.65%, 50.21%, 48.93% and 68.11% of dry samples, respectively. The average value of stress ratio in compaction stage increases by 28.50%, and the average values of stress ratio in elastic stage, yield stage and failure stage decrease by 19.60%, 41.35% and 11.99%, respectively. The average values of compaction strain, yield strain, peak strain and unloading strain of water-saturated samples are 4.12%, 19.26%, 20.70% and 17.92% lower than those of dry samples, respectively. The average value of strain ratio in compaction stage increases by 20.38%. The average values of strain ratio in elastic stage and yield stage decrease by 29.64% and 36.93%, respectively, and the average value of strain ratio in failure stage increases by 347.73%. Saturated treatment enhances the plastic characteristics of splitting process. After saturated treatment, the bending energy index of siltstone decrease by 73.77%, and the impact tendency decrease from class Ⅲ to class Ⅱ. The research results can provide theoretical basis for water injection softening and anti-impact technology of deep mine roof.

Aiming at the calculation problem of soil pressure in foundation pit engineering, an analytical method for soil pressure was established, and the influence effects of various factors were analyzed. Based on the basic assumptions of Coulomb's soil pressure theory, and fully considering the friction angle between the wall back and backfill, the soil internal friction angle, foundation pit excavation depth and other factors, a soil pressure calculation model was constructed, and quantitative formulas for soil pressure and its influence range induced by excavation disturbance were proposed. Through the sensitivity analysis of influencing factors, the influence order of each factor on the excavation influence range was clarified under the conditions with or without steel supports. The variation laws of the influence range under different working conditions and excavation stages were studied, and comparative verification was carried out. The results show that the distribution patterns of soil pressure along the foundation pit excavation depth from the two methods are consistent, which verifies the accuracy of the model. Sensitivity analysis shows that the excavation depth of a foundation pit exerts the most significant effect on the excavation influence range without supports, and the excavation depth of the foundation pit remains the main controlling factor after steel supports are installed. The model proposed in this paper can quantitatively analyze the soil pressure distribution and disturbance influence range during the foundation pit excavation of a 110 kV substation as part of a supporting project of an energy development base in Hefei, Anhui Province. The results can provide a theoretical reference for the design and analysis of foundation pit engineering of related energy and mineral resources development infrastructure.

Benefit evaluation of geological environment restoration aims to serve the prediction of the benefits of geological environment governance in abandoned mines and the assessment of the effectiveness of restoration, providing reliable decision-making support and effective supervision methods for restoration engineering practices. Through the review of domestic and foreign literatures and the cluster analysis of relevant influencing indicators, combined with the triple bottom line theory and sustainable development theory, a benefit evaluation index system for the geological environment restoration of abandoned mines was constructed from four dimensions, including economy, society, ecology, and sustainable development. The analytic hierarchy process (AHP) and entropy method were used in combination to assign weights to the indicators, and the fuzzy comprehensive evaluation method was used to construct the restoration evaluation model. The model was empirically applied in the geological environment restoration project of historical abandoned mines in Zhangjiakou city. The results show that the evaluation result benefit of geological environment restoration of abandoned mines in the city is 89.85, and the restoration effectiveness level is good. The ecological and social benefit evaluation values are relatively high, indicating that the case project has generally achieved the restoration goals of eliminating hazards, improving the ecology, and enhancing functions. The sustainable development and economic benefit evaluation values are relatively low, and measures still need to be optimized from aspects such as improving maintenance systems and mechanisms, strengthening publicity and education, and implementing dynamic monitoring and supervision to further improve the comprehensive benefits of restoration. The proposed evaluation index system and model are scientific and feasible, and can effectively evaluate the benefits of geological environment restoration in abandoned mines, providing a reference for the benefit evaluation of similar projects.

Aiming at the pain points of heavy assets, high energy consumption and low reliability of equipment in traditional aggregate plants, the Distributed Control System (DCS) has been adopted. Through the implementation of hardware redundancy configuration, Modbus communication protocol integration and advanced control algorithm, the DCS designed and optimized the whole process of crushing, screening, sand making and water circulation control in Zhuzailing Aggregate Factory. The application effect of DCS in material balance, equipment monitoring and energy consumption management were analyzed. The results show that since the system has put into operation, the no-load energy consumption of the equipment is reduced by 15%, and the comprehensive energy consumption is reduced by 18%. The average fault interval time is increased from 1 200 h to 2 100 h, the average repair time is shortened by 47%, the comprehensive efficiency of the equipment is increased from 74% to 89%, and the turnover rate of spare parts is increased by 62%. The whole life cycle of the equipment is extended by 3-5 a, and the annual production capacity is increased by 150 000 tons. At the same time, the technical problems such as signal interference, lightning strike and power fluctuation in high dust environment have been solved. DCS can systematically improve the energy efficiency, reliability and intelligence level of aggregate plants, and provide engineering reference for the green and intelligent transformation of similar enterprises.

Flotation of cassiterite is a critical step for the efficient utilization of complex mineral resources. Based on domestic and international research, a systematic review of the research progress in the development of cassiterite flotation reagents and the mechanisms of interfacial interactions was conducted. Based on the surface anisotropy of cassiterite crystals, the distribution of active sites on the (110) (100) and (101) crystal planes was analyzed in detail. The synergistic adsorption mechanism among multiple crystal planes was elucidated, and the coordination chemistry of metal ions (such as Pb²⁺ and Fe³⁺ ) in surface activation was revealed. In terms of the pharmaceutical system, molecular design strategies for novel hydroxamic acid derivatives, phenylphosphonic acid derivatives, and environmentally friendly amino acid-based collectors were reviewed, noting that targeted functional group modification can effectively enhance chelation selectivity toward Sn sites. In terms of mechanism of action, composite agents significantly enhanced interfacial adsorption density through chelation and synergistic adsorption. For example, the combination of hydroxamic acid and fatty acids formed a multilayer adsorption structure, while cationic-anionic composite collectors reinforced both electrostatic and coordination interactions. Composite inhibitors such as polyacrylic acid-lignosulfonate achieved precise inhibition of calcium and magnesium gangue minerals through steric hindrance and selective adsorption. Future research should focus on establishing a quantitative relationship among "molecular structure, adsorption configuration and flotation performance", and combining with computational chemistry methods to advance the rational design and industrial application of green, high-efficiency reagents.

To address the environmental hazards caused by red mud stockpiling during Bayer process alumina production and achieve efficient utilization of secondary resources, this study takes Bayer process red mud as the research object. It systematically reviews the fundamental characteristics and environmental risks of red mud, focusing on the current research status of recovering valuable metals such as Fe, Al, Ti and Sc. The study provides an in-depth comparison of the operational principles and industrial application effects of different recovery processes, and analyzes the advantages, disadvantages, and applicable scenarios of each process. Research findings indicate that the physical method for Fe recovery features simple operation but achieves a recovery rate of only 55%-60%. The reduction roasting-magnetic separation method can attain a recovery rate of 87%-92.8%, albeit with relatively high energy consumption. Acid leaching methods yield relatively high leaching rates for Al, Ti, and Sc recovery, but suffer from high acid consumption. Combined processes can enhance overall recovery efficiency, though they involve complex flowsheets. Currently, the comprehensive utilization rate of red mud has increased to approximately 12%, yet a gap remains compared with that of developed countries. Front-end phase regulation, the development of green processes, the advancement of combined processes, and the preparation of high-value-added materials from red mud represent the core development directions for future valuable metal recovery from red mud. This review can provide a reference for technological upgrading within the industry.

The precipitation extraction process of rare earths from ionic rare earth ore by ammonium salt leads to eutrophication of receiving water bodies and disruption of aquatic ecological balance. It also triggers cascading ecological issues such as soil acidification and compaction in surrounding areas, as well as threats to human health. To address this ammonia nitrogen pollution problem, the leachate from an ionic rare earth mine in Longnan was taken as the research object. A light-burned, ammonia-free, high-activity magnesium oxide precipitant was prepared, and its influence on the rare earth precipitation behavior was investigated. Meanwhile, XRD, SEM, and TG-DTG characterization techniques were employed to systematically compare and analyze the precipitation products derived from different magnesium oxide systems. The results show that the reactivity of the prepared magnesium oxide is significantly higher than that of industrial magnesium oxide. Using active magnesium oxide slurry as the precipitant under the optimal precipitation condition (molar ratio of 8, reaction temperature of 90 ℃, and reaction time of 4 h), a precipitation product with a purity of 37.45% and a precipitation rate of 96.17% can be obtained. In contrast, when industrial magnesium oxide slurry is used as the precipitant, the product purity is 32.07% and the precipitation rate is 90.17%, both of which are significantly lower than those achieved in the active magnesium oxide system. The mixed rare earth oxides from the active magnesium oxide system exhibit distinct diffraction peaks for Y₂O₃ and Dy₂O₃. Furthermore, the crystallinity of the products is superior to that of the industrial magnesium oxide system, characterized by a dense and smooth surface, clear contours, and uniform particles. The research results can provide new theoretical and technical support for the green chemical extraction of ionic rare earth ores.

Due to the characteristics of low grade and fine disseminated particle size, lean hematite is prone to overgrinding in grinding operations, resulting in a large number of fine-grained minerals. Due to the small particle size and large specific surface area, such fine-grained minerals are prone to coverage and surface adsorption competition effects during the flotation process, which significantly weakens the selective adsorption capacity of flotation reagents. Aiming at the problem of selective inhibition in the separation process of fine-grained hematite, a new K⁺ starch inhibitor was developed. Based on the flotation tests of pure minerals of quartz and hematite, combined with contact angle, Zeta potential, Fourier transform infrared spectroscopy and scanning electron microscopy (SEM)-EDS analysis, the inhibition mechanism of new K⁺ starch on fine-grained hematite was systematically revealed. The results showed that when the dosage of K⁺ starch was 150 mg·L^-1, the dosage of activator CaO was 100 mg·L^-1, and the dosage of collector sodium oleate was 200 mg·L^-1, the recovery rate of quartz was 83.5%, which was 4.00 percentage points higher than that of traditional corn starch, while the recovery rate of hematite decreased to 15.85%. In the flotation of mixed magnetic concentrate, the concentrate grade and recovery rate obtained under the action of new K⁺starch were 7.28 percentage points and 5.30 percentage points higher than those of corn starch, respectively. The mechanism analysis showed that K⁺ starch combined with O^2- to form K—O^- bond when K⁺ starch adsorbed onto hematite surface, which reduced the contact angle of hematite surface to 22.31° and formed a hydrophilic film, thus realizing the selective inhibition of hematite. The research results provided the design concept and theoretical basis of new environmentally friendly inhibitors for the efficient separation of fine-grained hematite.

Ilmenite and titanaugite have similar physicochemical properties, and their flotation separation is difficult to achieve. Through flotation tests, Zeta potential measurements and adsorption capacity tests, the adsorption mode and action mechanism of naphthyl hydroxamic acid on the surfaces of ilmenite and titanaugite were investigated, and the key factors affecting flotation performance were clarified. The results show that the adsorption capacity of naphthyl hydroxamic acid on ilmenite is significantly higher than that on titanaugite, and its influence on the surface potential of ilmenite is greater than that on titanaugite. Such adsorption differences increase the flotation difference between ilmenite and titanaugite. The results of actual ore flotation tests show that when naphthyl hydroxamic acid is used as the collector for ilmenite, a titanium concentrate with TiO₂ grade of 47.26% and recovery rate of 80.60% can be obtained in the closed-circuit flotation test, achieving the flotation separation of ilmenite and titanaugite. The research results can provide theoretical support for the development of novel flotation reagents for ilmenite and the optimization of titanium ore flotation processes.