International Journal of Mining Science and Technology最新文献

Fracture propagation in shale under in situ conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments were conducted on hollow double-wing crack specimens of the Longmaxi shale under conditions simulating the ground surface (confining pressure σ_cp=0, room temperature (T_r)) and at depths of 1600 m (σ_cp=40 MPa, T_i=70 °C) and 3300 m (σ_cp=80 MPa, high temperature T_i=110 °C) in the study area. High in situ stress was found to significantly increase fracture toughness through constrained microcracking and particle frictional bridging mechanisms. Increasing the temperature enhances rather than weakens the fracture resistance because it increases the grain debonding length, which dissipates more plastic energy and enlarges grains to close microdefects and generate compressive stress to inhibit microcracking. Interestingly, the fracture toughness anisotropy in the shale was found to be nearly constant across burial depths, despite reported variations with increasing confining pressure. Heated water was not found to be as important as the in situ environment in influencing shale fracture. These findings emphasize the need to test the fracture toughness of deep shales under coupled in situ stress and temperature conditions rather than focusing on either in situ stress or temperature alone.

In order to alleviate the pressure on the supply of lithium resources, this research proposes the use of binary/ternary collectors with high selectivity and collecting ability to enhance the flotation purification of low-grade zinnwaldite ore. The binary collector is a mixture of dodecylamine polyoxyethylene ether and DL-2-octanol. A binary collector is added first, followed by sodium oleate, known as a ternary collector. Under acidic conditions, the recovery of Li₂O in the concentrate was increased by 8.26% with the binary collector and 13.70% with the ternary collector, compared to the dodecylamine polyoxyethylene ether. The binary collector enhanced the dispersibility of the single collector, while co-adsorption strengthened the hydrophobic nature of the zinnwaldite surface. Consequently, zinnwaldite particles, after the application of binary collector, displayed inter-particle flocculation and attachment to bubbles within 60×10⁻⁹ m compared to other particles. Ternary collector exhibited the capacity to lower critical micelle concentration and surface tension, subsequently inducing a denser and thicker hydrophobic layer through electrostatic forces, hydrophobic interactions, and chemical reactions. The objective of this research is to facilitate the recovery of lithium resources from low-grade ores in order to meet the needs of sustainable development.

Understanding the effects of microwave irradiation and thermal treatment on the dynamic compression and fragmentation properties of rocks is essential to quantify energy consumption in rock engineering. In this study, Fangshan granite (FG) specimens were exposed to microwave irradiation and heat treatment. The damage of FG specimens induced by these two methods was compared using X-ray CT scanning and ultrasonic wave method. The temperatures of FG after microwave irradiation and thermal treatment were effectively evaluated using a newly proposed technique. A novelty method for precisely determining the geometric features of fragments is developed to estimate the fragmentation energy. Thus, the dynamic uniaxial compressive strength (UCS), the dynamic fragmentation characteristics, and the fragmentation energy of FG after these two pretreatment methods can be reasonably compared. The noticeable distinction of loading rate effect on the dynamic UCS of FG between these two pretreatment methods is first observed. A relationship is established between the dynamic UCS and the damage induced by microwave irradiation and heat treatment. Moreover, fragmentation energy fan analysis is introduced to accurately compare the fragmentation properties of FG after two pretreatment methods in dynamic compression tests.

Effective separation of residual carbon and ash is the basis for the resource utilization of coal gasification fine slag (CGFS). The conventional flotation process of CGFS has the bottlenecks of low carbon recovery and high collector dosage. In order to address these issues, CGFS sample taken from Shaanxi, China was used as the study object in this paper. A new process of size classification − fine grain ultrasonic pretreatment flotation (SC-FGUF) was proposed and its separation effect was compared with that of whole-grain flotation (WGF) as well as size classification − fine grain flotation (SC-FGF). The mechanism of its enhanced separation effect was revealed through flotation kinetic fitting, flotation flow foam layer stability, particle size composition, surface morphology, pore structure, and surface chemical property analysis. The results showed that compared with WGF, pre-classification could reduce the collector dosage by 84.09% and the combination of pre-classification and ultrasonic pretreatment could increase the combustible recovery by 17.29% and up to 93.46%. The SC-FGUF process allows the ineffective adsorption of coarse residual carbon to collector during flotation stage to be reduced by pre-classification, and the tightly embedded state of fine CGFS particles is disrupted and surface oxidizing functional group occupancy was reduced by ultrasonic pretreatment, thus carbon and ash is easier to be separated in the flotation process. In addition, some of the residual carbon particles were broken down to smaller sizes in the ultrasonic pretreatment, which led to an increase in the stability of flotation flow foam layer and a decrease in the probability of detachment of residual carbon particles from the bubbles. Therefore, SC-FGUF could increase the residual carbon recovery and reduce the flotation collector dosage, which is an innovative method for carbon-ash separation of CGFS with good application prospect.

Deep coalbed methane (DCBM), an unconventional gas reservoir, has undergone significant advancements in recent years, sparking a growing interest in assessing pore pressure dynamics within these reservoirs. While some production data analysis techniques have been adapted from conventional oil and gas wells, there remains a gap in the understanding of pore pressure generation and evolution, particularly in wells subjected to large-scale hydraulic fracturing. To address this gap, a novel technique called excess pore pressure analysis (EPPA) has been introduced to the coal seam gas industry for the first time to our knowledge, which employs dual-phase flow principles based on consolidation theory. This technique focuses on the generation and dissipation for excess pore-water pressure (EPWP) and excess pore-gas pressure (EPGP) in stimulated deep coal reservoirs. Equations have been developed respectively and numerical solutions have been provided using the finite element method (FEM). Application of this model to a representative field example reveals that excess pore pressure arises from rapid loading, with overburden weight transferred under undrained condition due to intense hydraulic fracturing, which significantly redistributes the weight-bearing role from the solid coal structure to the injected fluid and liberated gas within artificial pores over a brief timespan. Furthermore, field application indicates that the dissipation of EPWP and EPGP can be actually considered as the process of well production, where methane and water are extracted from deep coalbed methane wells, leading to consolidation for the artificial reservoirs. Moreover, history matching results demonstrate that the excess-pressure model established in this study provides a better explanation for the declining trends observed in both gas and water production curves, compared to conventional practices in coalbed methane reservoir engineering and petroleum engineering. This research not only enhances the understanding of DCBM reservoir behavior but also offers insights applicable to production analysis in other unconventional resources reliant on hydraulic fracturing.

This study delves into the intricate relationship between iron (Fe) content in kaolinite and its impact on the adsorption behavior of sodium oleate. The effects of different iron concentrations on adsorption energy, hydrogen bond kinetics and adsorption efficiency were studied through simulation and experimental verification. The results show that the presence of iron in the kaolinite structure significantly improves the adsorption capacity of sodium oleate. Kaolinite samples with high iron content have better adsorption properties, lower adsorption energy levels and shorter and stronger hydrogen bonds than pure kaolinite. The optimal concentration of oleic acid ions for achieving maximum adsorption efficiency was identified as 1.2 mmol/L across different kaolinite samples. At this concentration, the adsorption rates and capacities reach their peak, with Fe-enriched kaolinite samples exhibiting notably higher flotation recovery rates. This optimal concentration represents a balance between sufficient oleic acid ion availability for surface interactions and the prevention of self-aggregation phenomena that could hinder adsorption. This study offers promising avenues for optimizing the flotation process in mineral processing applications.

Blasting operations, which are crucial to open-pit mine production due to their simplicity and efficiency, require precise control through accurate vibration velocity calculations. The conventional Sadowski formula mainly focuses on blast center distance but neglects the amplification effect of blasting vibration waves by terraced terrain, from which the calculated blasting vibration velocities are smaller than the actual values, affecting the safety of the project. To address this issue, our model introduces the influences of slope and time into Sadowski formula to measure safety through blast vibration displacement. In the northern section of the open-pit quartz mine in Jinchang City, Gansu Province, China, the data of a continuous blasting slope project are referred to. Our findings reveal a noticeable vibration amplification effect during blasting when a multi-stage slope platform undergoes a sudden cross-sectional change near the upper overhanging surface. The amplification vibration coefficient increases with height, while vibration waves within rocks decrease from bottom to top. Conversely, platforms without distinct cross-sectional changes exhibit no pronounced amplification during blasting. In addition, the vibration intensity decreases with distance as the rock height difference change propagates. The results obtained by the proposed blast vibration displacement equation incorporating slope shape influence closely agree with real-world scenarios. According to Pearson correlation coefficient (PPMCC) analysis, the average accuracy rate of our model is 88.84%, which exceeds the conventional Sadowski formula (46.92%).

2D profile lines play a critical role in cost-effectively evaluating rock joint properties and shear strength. However, the interval (ΔI_L) between these lines significantly impacts roughness and shear strength assessments. A detailed study of 45 joint samples using four statistical measures across 500 different ΔI_L values identified a clear line interval effect with two stages: stable and fluctuation-discrete. Further statistical analysis showed a linear relationship between the error bounds of four parameters, shear strength evaluation, and their corresponding maximum ΔI_L values, where the gradient k of this linear relationship was influenced by the basic friction angle and normal stress. Accounting for these factors, lower-limit linear models were employed to determine the optimal ΔI_L values that met error tolerances (1%–10%) for all metrics and shear strength. The study also explored the consistent size effect on joints regardless of ΔI_L changes, revealing three types of size effects based on morphological heterogeneity. Notably, larger joints required generally higher ΔI_L to maintain the predefined error limits, suggesting an increased interval for large joint analyses. Consequently, this research provides a basis for determining the optimal ΔI_L, improving accuracy in 2D profile line assessments of joint characteristics.

Ground hydraulic fracturing plays a crucial role in controlling the far-field hard roof, making it imperative to identify the most suitable target stratum for effective control. Physical experiments are conducted based on engineering properties to simulate the gradual collapse of the roof during longwall top coal caving (LTCC). A numerical model is established using the material point method (MPM) and the strain-softening damage constitutive model according to the structure of the physical model. Numerical simulations are conducted to analyze the LTCC process under different hard roofs for ground hydraulic fracturing. The results show that ground hydraulic fracturing releases the energy and stress of the target stratum, resulting in a substantial lag in the fracturing of the overburden before collapse occurs in the hydraulic fracturing stratum. Ground hydraulic fracturing of a low hard roof reduces the lag effect of hydraulic fractures, dissipates the energy consumed by the fracture of the hard roof, and reduces the abutment stress. Therefore, it is advisable to prioritize the selection of the lower hard roof as the target stratum.

Current practice of underground artificial ground freezing (AGF) typically involves huge refrigeration systems of large economic and environmental costs. In this study, a novel AGF technique is proposed deploying available cold wind in cold regions. This is achieved by a static heat transfer device called thermosyphon equipped with an air insulation layer. A refrigeration unit can be optionally integrated to meet additional cooling requirements. The introduction of air insulation isolates the thermosyphon from ground zones where freezing is not needed, resulting in: (1) steering the cooling resources (cold wind or refrigeration) towards zones of interest; and (2) minimizing refrigeration load. This design is demonstrated using well-validated mathematical models from our previous work based on two-phase enthalpy method of the ground coupled with a thermal resistance network for the thermosyphon. Two Canadian mines are considered: the Cigar Lake Mine and the Giant Mine. The results show that our proposed design can speed the freezing time by 30% at the Giant Mine and by two months at the Cigar Lake Mine. Further, a cooling load of 2.4 GWh can be saved at the Cigar Lake Mine. Overall, this study provides mining practitioners with sustainable solutions of underground AGF.