Rare earth elements were considered alternative additives beneficial to the TiCN based cermets, but their effect with high content Mo₂C has not been thoroughly investigated. In this study, Ti(C, N)-WC-Mo₂C-Cr₃C₂-Ni-Co cermets containing 12 wt.% Mo₂C doped with different contents of La₂O₃ were prepared by vacuum hot-press sintering at 1500 °C. Parametrical analysis on La₂O₃ addition (0, 0.5 wt.%, 1.0 wt.%, 1.5 wt.%, and 2.0 wt.%) was conducted, in terms of microstructure and mechanical properties of Ti(C, N) based cermets. Experimental results show that when the content of La₂O₃ increases from 0 to 1.0 wt.%, the ratio of core phase increases while the ratio of brittle rim phase decreases. Nanostructure is formed on the grain boundary of ceramic phase, which effectively inhibits the abnormal growth of rim structures. This can thin the brittle shell, coarsen the core phase, and refine the grains, thus improving its mechanical properties, including hardness and fracture toughness. When the addition amount of La₂O₃ increases from 1.5 wt.% to 2.0 wt.%, it will aggregate to form larger particles of about 100 nm, which sharply reduces its mechanical properties. The optimal La₂O₃ addition is 1.0 wt.%, in which Ti(C,N)-based cermets show the optimal comprehensive mechanical properties: the Vickers hardness and fracture toughness are 16.55 GPa and 6.14 MPa·m^1/2, respectively. This work provides further knowledge about the effect of rare earth on the core-rim structure and mechanical properties of Ti(C,N)-based cermets with high Mo₂C contents.

This article is structured around the mathematical analysis of magnetohydrodynamical flow through a stretching/shrinking nonparallel channel containing macromolecules with the ability to move independently. Maxwellian approach establishing the external magnetic field impact on the viscoelastic fluid flow appears as a body force in the classical fluid dynamic momentum equation. The mathematical model is reinforced by angular momentum equation for the complete description of the microstructural phenomena. The resulting nonlinear problem is numerical handled by the finite difference method of Keller box. The mathematical structure in the form of differential equations is solved and results are represented in the form of graphs and table for the values of physical parameters like Hartmann number (1≤Ha≤5), stretching parameter (−4≤C≤4), rotation parameter (3≤K≤9), Weissenberg number (0.3≤Wi≤0.9) and Reynolds number (50≤Re≤150). Of all the cases discussed, it is only the angular velocity in the divergent channel that seems to be increasing with increasing Hartmann number, indicating that microstructural rotations are stimulated by a strong magnetic field.

Substance flow analysis (SFA), an analytical tool, was applied to a high-pressure acid leaching (HPAL) process of laterites. The results show that although the HPAL process has become the mainstream process for the treatment of laterites, a large amount of solid waste discharge has caused great harm to the environment and restricted its large-scale development. The annual treatment capacity of laterites by HPAL process is 321×10⁴ t, and 300×10⁴ t of high-pressure leaching residue, 10×10⁴ t of sulfate residue, 1.6×10⁴ t of iron and aluminum residue, and 0.08×10⁴ t of acid leaching residue are discharged every year. Nickel, cobalt, and manganese are used as the raw materials for the preparation of a precursor, and the masses finally flowing into the precursor preparation process are 2.70×10⁴ t/a, 0.24×10⁴ t/a, and 0.29×10⁴ t/a, respectively, and the proportions are 77.14%, 75.00%, and 13.12%, respectively. Scandium finally flows into the scandium extraction process is 40.00 t/a, and the proportion is 37.70%. A total of 98.11% of iron and 99.86% of aluminum can be selectively removed by the high-pressure acid leaching. Some recommendations for improving emission control and resource recycling for the high-pressure acid leaching process of laterites are put forward in the conclusions of this study.

In order to achieve the full utilization of red mud, the unfired lightweight bricks were prepared by compaction molding technology using dealkalized calcium silicate residue, cement and sand, and the effects of raw material formula and molding pressure on the physical properties and phase transition of unfired bricks were investigated by X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) methods. The dealkalized calcium silicate residue presented as irregular honeycomb particles is mainly composed of calcium silicate hydrate (C-S-H) and some CaTiO₃, CaCO₃ and SiO₂. Increasing the content of calcium silicate residue increases the compressive strength of unfired bricks and reduces bulk density, but excessive calcium silicate residue reduces the compressive strength and softening coefficient, and increases water absorption. When the consumption of calcium silicate residue reaches 50%–70%, the compressive strength, bulk density, softening coefficient and water absorption of the unfired bricks are in the range of 15.10–24.16 MPa, 1.3–1.5 g/cm³, 0.77–0.91 and 28.41%–43.52%, respectively. During the curing process, the calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) gels produced by hydration reactions flocculate the raw material particles together to strengthen the strength of the unfired bricks. The leaching results of heavy metals and Na ions show that the unfired lightweight bricks are harmless to the environment.

Aiming at high energy consumption and large Co loss in the pyrometallurgy of low-nickel matte, a process of NH₄Cl roasting-water leaching was proposed to co-extract metals, followed by the separation and utilization of metals. The effect of several factors on metal extractions in NH₄Cl roasting process and the optimized process conditions were investigated by orthogonal experiments. The most influencing factors were roasting temperature and NH₄Cl dosage, and the optimized chlorination conditions were as follows: particle size of low-nickel matte <75 µm, roasting temperature of 500 °C, roasting time of 2.5 h, NH₄Cl dosage of 250% and O₂ flow rate of 20 mL/min. By studying the effect of temperature and time on the extraction efficiency of metals, the appropriate leaching conditions were determined as temperature 90 °C and time 2 h. The extraction efficiency of nickel, copper, cobalt and iron can reach 97.6%, 96.2%, 94.5% and 29.2%, respectively. The (Ni, Cu, Co)Fe₂O₄ photocatalyst was synthesized from leaching solution using α-Fe₂O₃ as a carrier to composite with other metals. The optimum conditions were determined as precipitation temperature 25 °C and molar ratio of Ni-Cu-Co to Fe 1:3. The as-prepared catalysts were spherical nanoparticles of approximate 40–60 nm, and the degradation rate of which to methylene blue solution can reach 99.8% within 120 min.

V-bearing stone coal is an important vanadium resource with huge reserves in China. For stone coal with high carbon content, the decarbonization process improves the vanadium leaching rate and reduces the acid consumption. Study of decarbonization temperature of stone coal is beneficial for avoiding high-temperature sintering and utilizing its heat, which is meaningful for efficient and energy-saving roasting. In this paper, the optimum roasting conditions of 650 °C, 50 min, 500 mL/min, and 20% O₂ were determined. Under the optimal decarbonization and leaching indicators, the entire process of stone coal suspension roasting was systematically analyzed and studied. Within the initial 3.9 min, the sample was rapidly heated to 560.1 °C and continuing to 10.3 min, the sample temperature raised the highest peak of 741.5 °C with the decomposition of dolomite and kaolinite. Finally, the sample was cooled to 622.5 °C at the combustion end. This indicated that the decarbonization mainly occurs in the initial 30 min and the maximum temperature of shale is about 120 °C higher than the final temperature caused by carbon combustion. In addition, intense combustion and local sintering caused by high temperatures and high oxygen content should be seriously avoided.

The carbothermal reduction process of spodumene ore effectively separates Al and Si components from spodumene ore while also extracting lithium (Li). The high value-added sputum heat reduction process of spodumene ore was proposed. Fe₂O₃ was used as an auxiliary agent. Si is combined with Fe to form Si-Fe alloy and Al is enriched in the slag. The experimental results showed that the addition of Fe₂O₃ could significantly promote the carbothermal reduction of spodumene ore, when the mass ratio of Fe/Si is not less than 2. Experiments confirmed that the optimal experimental conditions were 1823 K and heated for 8 h. During the reduction process, the reduction rate of Li was higher than 90%, and the direct yield of Si-Fe alloy was higher than 85%. In addition, the content of Li in dust could reach 29.5%, about 16 times that of the spodumene ore.

In this study, the preparation of tungsten slag-bentonite particle adsorbent was studied using orthogonal and static adsorption tests. The adsorbent was characterized, and its adsorption performance for heavy metal lead ions was clarified. The results indicate that the optimum conditions are as follows: mass ratio of tungsten slag to bentonite of 5:1, particle size of 2 mm, and sintering at 800 °C for 2 h. The adsorbent primarily consisted of granular Fe-Mn oxides with a large number of holes on its surface. When the pH value of the solution is 6, adsorbent dosage is 15 g/L, initial lead concentration is 300 mg/L and adsorption time is 200 min, the removal rate of lead in wastewater by adsorbent reaches 99.95%. The adsorption process conforms to the pseudo-second-order kinetic equation, and its adsorption isotherm conforms to the langmuir equation. The adsorption of lead belongs to the specific chemical adsorption of single molecular layer.

Efficient extraction of scheelite using a NaOH-SiO₂ roasting and water leaching system was assessed. Initially, the NaOH-SiO₂ roasting process was thermodynamically analyzed using Δ G^Θ − T diagrams of the possible reactions, which indicated that the CaWO₄ transforming to Na₂WO₄ and Na₂CaSiO₄ under roasting conditions was feasible. Subsequently, the effect of the thermal decomposition and leaching parameters was investigated. The results showed that the optimal extraction conditions were achieved with a Na₂O-to-WO₃ molar ratio of 2.2, a SiO₂-to-WO₃ molar ratio of 1.0, a roasting temperature of 700 °C, a roasting time of 2 h, a leaching temperature of 80 °C, a liquid-to-solid ratio of 3.2:1 and a leaching time of 4 h. Under those conditions, the leaching rate of tungsten was 99.33% and WO₃ mass content in residue was 0.71%. Further mineralogical analysis showed that the CaWO₄ of scheelite was effectively transformed to Na₂CaSiO₄ and Na₂WO₄ under NaOH-SiO₂ roasting process. Broadly, the results of this paper provided a reference for the efficient extraction of scheelite using a pyrometallurgy process.

This study proposed a method of dense drilling that could induce the formation of a discontinuous surface to weaken the roof. According to the geological conditions of the Chahasu coal mine, a PFC^2D numerical model was established to explore the stress response mechanism and crack expansion law around dense drilling. The study found that, after the dense drilling excavation, progressive damage occurred around the boreholes, and then an elliptical pressure relief zone was created concentric with the direction of the minimum horizontal principal stress as the long-axis and the direction of the maximum horizontal principal stress as the short-axis. Meanwhile, the cumulative area ratio of pixels (λ) increased from 0 to 6.42% and the pressure relief zone width ratio (μ) increased from 11.55% to 54.6% when the drilling diameter increased from 30 mm to 133 mm. When the spacing of drilling was increased from 300 mm and 700 mm, λ decreased from 30.86% to 9.74%; μ decreased from 63.9% to 33.2%, which means that larger diameters and smaller spacing are beneficial for pressure relief. Field tests found that the discontinuous weak surface induced by dense drilling effectively improves the roadway stress environment. This study can provide reference and experience for hard roof control in coal mines.

In deep mining, the rock mass is characterized by high in-situ stress, which makes the traditional drilling and blasting methods difficult, inefficient, and costly. To overcome this difficulty, LS-DYNA software was used to simulate the process of fan-hole blasting under in-situ stress. The blasting design was carried out for a 932.5 m depth of rock mass in combination with the actual mining conditions. The results show that the damage extent has an obvious correlation with in-situ stress level. The peak particle velocity, effective stress, and kinetic energy for rock mass were reduced under in-situ stress and the ore fragmentation was more heterogeneous. The effect of hole-bottom spacing and minimum burden on the mechanical response obtained from the simulation was analyzed by the response surface method, and the best blasting cost and effect were obtained with a hole bottom spacing of 2.48 m and a minimum burden of 1.6 m using the desirability function. This study can provide solutions to the fan-holes blasting difficulties that are encountered with deep mining.

To improve discipline systems and address shortcomings of traditional mining theory, this work defines the safe and intelligent mining using the advanced theory and technology in the era of big data. It gives some explorations and challenges for the mining discipline theory and the basic construction of the course content system. Firstly, according to the development process of mining science and the situation of intelligent mining around the world, it presents the concept of safe and intelligent mining, and analyzes the connotations and attributes of the discipline. Secondly, it gives the discipline basis and tasks of safe and intelligent mining from the construction of discipline, and structures the discipline content system. Finally, the work introduces the challenges and discusses the research tasks and application prospects of safe and intelligent mining in terms of mining technology, equipment, methods, data and information platforms, and environment in the future. The construction of safe and intelligent mining is a trend that is unavoidable as the field of information-based mining engineering develops in the age of big data. This trend injects vitality and vigor into the field’s development while enhancing the environmental protection of mines.

Currently, fluidization techniques have been widely applied to separate and recover coarse particles (>74 μm) in mineral processing. Studies show that the main parameters affecting this regard are hydrodynamic conditions and interphase interactions. The main objective is to investigate the influences of collision coefficient and drag models on the hydrodynamic behavior of liquid-solid fluid beds. Eulerian-Eulerian method was used and spherical and irregular coarse particles were considered in calculations. In this regard, Gibilaro, Gidaspow, Huilin-Gidaspow, and Syamlal-O’ Brien equations were used to obtain the drag force. Moreover, experimental data of particle volume fraction and fluid bed expansion ratio were employed to evaluate the proposed models. The effects of three restitution coefficients (0.85, 0.90 and 0.99) and four specularity coefficients (0.01, 0.10, 0.50 and 0.99) on fluidization characteristics were studied. The results indicate that for spherical and irregular particles, Gidaspow and Hulin-Gidaspow models have good agreement with experimental data in predicting fluid bed expansion ratio and particle volume fraction. Meanwhile, high prediction accuracy can be achieved when the restitution coefficient is 0.9 and the specularity coefficient is 0.1. The results improve the understanding of coarse particle behavior in liquid-solid fluidization and provide useful information for further investigation of three-phase flotation processes.

In order to study the influence of concrete shrinkage and creep effect and temperature change on the extra-wide concrete self-anchored suspension bridge under vehicle load, the Hunan Road Bridge, which is the widest concrete self-anchored suspension bridge in China, was chosen as background. Firstly, the refined finite element model (FEM) was established, which was validated by the measured data of field load test. Secondly, the structural states at different ages were predicted. Finally, the evolution laws of component responses were analyzed. The research results show that the bearing type of girder has significant influence on the response change trends. The shear lag effect of girder and local effect of wheel are significant. Under the temperature rise of 20 °C and standard vehicle load, the maximum tower displacement is 0.033 m after 30 years. In addition, the longitudinal tensile stress in most area of bottom plate at middle section exceeds 5 MPa. Moreover, the difference of girder deflection between road centerline and edge reaches 0.07 m under eccentric load after 10 years. The research results can provide an important basis for the health monitoring and safety evaluation of similar extra-wide concrete self-anchored suspension bridges.

To avoid engineering diseases induced by negative geotechnical properties of red clay and to positively reduce adverse impacts on ecological environments caused by employing lots of inorganic solidified material for treating the clays, it is essential to explore low-environmental impact material to improve engineering mechanical performances of the red clay. To date, xanthan gum (XG) biopolymer is regarded as a potentially eco-friendly material with excellent pseudo-plasticity, safety, and stability. Hence, unconfined compressive strength, unconsolidated undrained shear, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction tests were performed to study the solidification effects and strengthening mechanism of XG for red clay under varied additive contents and curing period. The results indicated the optimal XG content and curing ages to increase the macro-mechanics of red clay are 1.5% and 28 d, in which the compressive strength and cohesion are increased by 93.31% and 79.47%, respectively. Further, the mathematical model is established by modifying the Duncan-Chang constitutive model and used to describe the stress–strain relationship of XG-solidified red clay, presenting preferable consistency in the calculated and trial results. The strengthening mechanism is derived from the ionic bondings between XG and red clay, producing significant effects of cementing and filling to form compact composite matrices during the microstructural evolution process.

This paper investigates the strength and critical state (CS) behaviours of sand under axisymmetric stress paths with different shearing modes using discrete element method (DEM). The stress paths include axial compression (AC) and axial extension (AE), and the shearing modes include conventional triaxial (CT) mode and constant mean pressure (CP) mode. A series of dense and loose sand samples are generated for this purpose with confining pressures ranging from 100 kPa to 900 kPa. The CS is achieved for all samples after an axial strain (absolute value) of about 45%. The CS value of deviator stress is unique and independent of the initial packing densities for the samples with a given confining pressure, but the unique deviator stress under AC is generally larger than that under AE. The CS values of the stress ratio are independent of the shearing modes and the confining pressures, but are dependent on the stress paths. The CS friction angle for a given confining pressure is found to be unique and independent of the shearing modes, stress paths and initial packing densities, indicating that Mohr-Coulomb criterion (for axisymmetric conditions, equivalent to Matsuoka criterion) is an appropriate CS strength criterion. The CS value of void ratio is independent of the initial packing densities for a given confining pressure and shearing mode under a given stress path. The differences among the CS values of the mechanical coordination number are found to be attributed to changes in the effective mean pressures.

In order to study spalling failure characteristics of rock under oblique incidence of stress wave, a split Hopkinson pressure bar (SHPB) spalling test with a special shaped striker was simulated by Particle Flow Code (PFC). The oblique section angles selected in this study were 30°, 45° and 60°, respectively. The spalling failure characteristics of rock with oblique incidence of stress waves at 5.2 m/s, 5.6 m/s and 6.2 m/s impact levels were analyzed and compared with those for 90° section incidence. The results show that when the angle of the oblique section greater than 45°, the stress wave will be directly reflected into a tensile wave when it encounters the oblique section, and then the reflected tensile waves and compressive waves will alternately appear. When the angle of the oblique section is less than 45°, the reflected stress wave is superimposed multiple times with the incident stress wave in the oblique section, and induces the spalling of the oblique section. Based on the longitudinal wave propagation theory, the function of stress in the 30° oblique section has been derived. The possible fracture position of the oblique section is obtained, which is consistent with the simulation results.

The existence of a quiet period in acoustic emission monitoring brings challenges to early warning of time-dependent rock failure. In order to understand the effect of rock loading paths and water content on acoustic emission (AE) quiet periods and the corresponding electrical resistivity (ER) changes, uniaxial loading, step loading, and incremental cyclic loading-unloading tests were carried out on dry and water-bearing sandstone samples with saturation of 40%, 70% and 100%, respectively. The results show that increasing the water content of sandstone can significantly reduce not only the strength but also the activity of AE signals. With the increase of water content, the quiet periods of AE signals increase, especially in the loading-unloading conditions. Under incremental cyclic loading-unloading conditions, the Felicity effect occurs in water-bearing sandstones. The ER variation is well consistent with stress-induced rock damage and can effectively reflect time-dependent subcritical crack propagation in both dry and water-bearing rocks. ER monitor can be used to compensate for the disadvantages of AE monitor in quiet signal periods.

In recent years, granite fractures have been considered an effective research object to improve the permeability of enhanced geothermal system (EGS). Granite fractures are always in a high-temperature environment, and their shear behavior treated by real-time high temperature is the key to promoting EGS permeability. Hence, the granite fractures shear tests under real-time high temperature were conducted with MTS 816 rock testing machine with a high-temperature sealed shear box. The results indicate that fracture peak shear strength and shear stiffness show a continuous deterioration trend as the temperature increases, which can be classified into a slowly declining stage (30–200 °C) and a rapidly declining stage (200–400 °C). High temperature deteriorates the asperity shear failure on granite fracture surface, which leads to the reduction of the dilatancy deformation of fracture surface with increasing temperature, and its decreasing amplitude becomes larger with increasing normal stress. Coupling synergy between temperature and normal stress can exacerbate shear damage on granite fracture surfaces, and the percentage of shear damage area increases by 21.41% on granite fracture surface as temperature and normal stress increases from 10 MPa and 30 °C to 30 MPa and 400 °C. High temperature aggravates the damage of asperities, which is the principal cause of the degradation of fracture surface roughness with increasing temperature. The research results can provide a theoretical guide for enhancing reservoir permeability and connectivity in geothermal energy development engineering.

Mechanical behavior and deformation essence of frozen soft rock under complex environmental conditions is crucial for frozen shaft engineering. The strength and deformation properties of sandstones under different low temperatures were investigated by conducting uniaxial and triaxial compression tests. The energy characteristics of rocks during the deformation were analyzed. The micro-structure features were obtained by scanning electron microscopy (SEM) test. The results show that the sandstones have a noticeable pore compression stage and the medium-grained sandstone is more pronounced. The rock strength decreases and increases non-linearly with the increase of temperature and confining stress, respectively, and the factors affect each other. The elastic modulus increases with the decrease of low temperature, while the changes in Poisson ratio is opposite. In addition, the total strain energy, elastic energy and dissipated energy of sandstones have different evolution laws, revealing the deformation and damage mechanism of rocks. Last, the internal reason of differences in the mechanical properties of sandstones is explained from the microstructural perspective. The above research conclusions could provide a certain theoretical basis for the stability control of shaft engineering in northwest China.

The effect of grain size on the microscopic failure of yellow sandstone was investigated via a series of laboratory experiments. The compressive strength, elastic modulus, tensile strength, internal cohesion, and friction angle of the sandstone are inversely proportional to the grain size. A combination of observation techniques (geological thin sections and scanning electron microscopy) indicated that the quartz and feldspar particles act as the skeleton in yellow sandstone, and the other minerals form the cement that bonds the skeleton particles together. The skeleton particles in fine-grained sandstone are rounder and more compact than those in medium-grained sandstone. Fine-grained sandstone has the highest content of skeleton particles and the densest. In contrast, coarse-grained sandstone exhibits particles that are more angular and loosely packed. As the grain size increases, the percentage of cementing material rises substantially. However, the percentages of SiO₂ and quartz rapidly decrease. The failure process in the yellow sandstone initiates in the cementing materials that have lower strength. Shortly thereafter, the failure extends further to the skeleton grains. X-ray powder diffraction experiments suggest that the strength of yellow sandstone relates to the quartz content of the skeleton grains: the greater the amount of quartz, the greater the strength.

The self-compacting concrete (SCC) filling layer of CRTS III ballastless track is prone to high-cycle fatigue damage under repeated train loads and complex environments. Based on the technology that fully couples damage and finite elements, a fatigue damage analytical method of SCC for the CRTS III ballastless track was established, which discussed how train load change, initial deterioration, and slab end debonding would affect the performance evolution of the filling layer. It is found that the fully-coupled method can reveal the interaction between fatigue damage and the structure’s stress field. As the train load changes, the damage of the filling layer during the service period accumulates pretty much following Miner’s rule in the first place. However, when the initial stress level reaches around 0.33, the fatigue damage of the filling layer presents nonlinear accumulation with the increase of loading times. Therefore, the fully-coupled method at this time can better reflect the time-varying features of the structure. Compared with initial deterioration of the SCC filling layer and the change of train loads, slab end debonding has a more prominent effect on damage accumulation.

As an important source of train aerodynamic drag, the pantograph area is a key region which takes up about 10% contribution of the total. Thus, improving the pressure distribution in the pantograph area becomes a potential and effective method of reducing train aerodynamic drag. Based on the biological pattern of Coleoptera, a novel bionic elytron (i. e., deflector) installed on the pantograph areas of an eight-car grouping high-speed train was proposed to smooth the flow. Four calculation cases were set up, i. e., the original model (Model I), pantograph I with a deflector (Model II), pantograph II with a deflector (Model III), and pantograph I and II with deflectors (Model IV), to explore the mechanism of aerodynamic drag reduction for the train and improve its aerodynamic performance. The results show that after installing the pantograph deflector the aerodynamic drag force of the pantograph area is significantly reduced. The maximum drag reduction in pantograph I region is up to 84.5%, and the maximum drag reduction in pantograph II region is 25.0%. When the deflectors are installed in both pantograph I and pantograph II areas, the total drag reduction in pantographs I and II areas can be achieved by 49.6%. The air flows over the pantograph area in a smoother way with less blockage effect as compared to the base case without deflectors. However, the downstream flow velocity speeds up and impacts the corresponding region, e.g., windshields, leading to an increase of aerodynamic drag. When the deflector is installed in the area of pantograph I or pantograph II alternatively, the total drag of the eight-car group train reduces by up to 4.6% and 1.8%, respectively, while the drag reduction can be up to 6.3% with deflectors installed in both pantograph I and II areas. This paper can provide references for the aerodynamic design of a new generation of highspeed trains.