Tin is indispensable for the development of advanced technology and cassiterite is the only mineral of commercial importance, from which tin can be extracted economically. In the past two decades, tin reserves in China have experienced a rapid decline because of active mining activities; simultaneously, cassiterite beneficiation has been facing with the many dilemmas like lower tin-grade, finer grain size, and more complicated mineralogy. Therefore, a review has been made here to summarize the development and progress on the recovery of tin from natural resources and secondary resources in China by demonstrating a series of breakthroughs made in process flowsheet, gravity separation equipment, innovative flotation theories, fine particles flotation, new cassiterite collectors, and tin recycling technologies in recent years, which will doubtlessly contribute to increasing tin resource utilization rate and promoting sustainable development of tin industry whether in China or the world. As for the future, the research and development of fine or ultra-fine cassiterite gravity separation equipment, green and low lost cassiterite flotation reagent, as well as the reusing and recycling of tin from tin-containing secondary resources deserve more attention, which will encourage researchers to move forward.

Microstructure and corrosion properties of micro-beam plasma remelted (MPRMed) Mg-12Dy-1.1Ni (wt%) alloy were investigated. The as-cast alloy was mainly composed of α-Mg, lamellar Mg₁₂DyNi phase with a 18R-long period stacking order (LPSO) structure, and Mg₂₄Dy₅ phase. After micro-beam plasma remelting (MPR), the grain size of the as-cast alloy was remarkably refined to 11 µm, and the amounts of 18R-LPSO phase increased from 18.3% to 26.0% and distributed as continuous network. The electrochemical and immersion tests indicated that the MPRMed alloy exhibited a lower mass loss rate 0.31 g/(cm²·d) and corrosion current density (605.3 µA/cm², and ∼38.5% reduction after MPR) than the as-cast alloy in 0.1 mol/L NaCl solution. The improved corrosion resistance of the MPRMed alloy was primarily ascribed to the uniform microstructure, denser corrosion products and continuous distribution of 18R-LPSO phase.

In recent years, nitrogenous metallic-complex catalysts for oxygen reduction reaction (ORR) have been extensively reported, but the exact role of Fe₃C in the catalytic process is not clear due to the interference of reactive sites such as Fe_xN, N_xC and Fe nanoparticles. In this work, a new type of pyrolysis catalyst Fe₃C-core/C-shell (Fe₃C/C) was designed using Fe₂O₃ nanospheres and bacterial cellulose (BC) as raw materials. The encased nitrogen-free carbide isolated from the electrolyte, promoting the graphitic layers to form after BC carbonization toward high ORR catalytic activity, and the graphitic layers protected the internal carbide which exhibited excellent ORR activity and stability in both acidic and alkaline media. The catalyst was a model system for understanding the ORR active site of such encapsulated catalysts without other element doping. The carbide-based catalyst and mechanism proposed in this work provided a new idea for the development of ORR catalyst.

The hot compression deformation behavior of a nickel-based superalloy was characterized by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) techniques. The main microstructure characteristics of the studied superalloy after hot compression deformation featured the development of subgrains, dynamic recrystallization (DRX) nuclei, DRX grain growth, and annealing twins. Considering the approximate orientation between deformed grains and the dynamic recrystallization results, we concluded that the continuous dynamic recrystallization (CDRX) nucleation mechanism characterized by subgrain bonding and rotation played a major role at low temperatures and high strain rate in addition to twinning-assisted recrystallization nucleation. The presence of MC and γ′ phase precipitated phases at low temperatures (900 and 1000 °C) facilitated the nucleation of DRX but hindered the growth of recrystallization. Grain growth at high deformation temperatures depended on the mutual annexation of grains induced by high-angle grain boundary migration, which consumed part of the annealing twins, and only a few annealing twins remained stable after orientation deflection.

In this paper, the friction stir welding (FSW) of ultrafine-grained Al-Sc alloy sheets, obtained by accumulative roll bonding (ARB) method, has been simulated in order to indicate the impact of the FSW on the microstructure, thermal and mechanical properties. In addition, the effectiveness of the FSW parameters, i. e, tool rotational speed, welding speed, and tool tilt angle was investigated to achieve the optimized parameters. The numerical modelling was implemented in SYSWELD and Visual-Environment software and was validated by experimental results. The findings indicated that FSW is a beneficial process to maintain the ultrafine-grained (UFG) microstructure, having high mechanical properties in the accumulative roll bonded material. Tool rotational speed had the highest impact on thermal and mechanical properties. The highest values of the hardness and the yield strength of the Al-Sc sheets were achieved under the optimal parameters of the tool rotational speed, welding speed, and tool tilt angle of 700 r/min, 80 mm/min, and 3°, respectively.

In this work, ovalbumin-stabilized gold nanoclusters (OVA-Au NCs) fluorescent nanoprobes were synthesized by microwave heating and applied to detect picric acid (PA). The nanoprobes emitted red fluorescence with the maximum fluorescence peak of 680 nm under the excitation wavelength of 350 nm, and the Stokes shifts could be up to 330 nm which could effectively eliminate the interference of resonance scattering light. Compared with hydrothermal method, the synthesis method was simple and fast, and only took 50 s. Due to the absorption peak of PA overlapped with the emission peak of OVA-Au NCs in a large range, PA could selectively quench the fluorescence of OVA-Au NCs based on the inner filter effect (IFE) and a quick response time (1 min). Therefore, a new and sensitive method for PA monitoring was established. Under the optimal conditions, the concentration of PA demonstrated a satisfactory linear correlation with the fluorescence quenching degree ΔF/F₀ of the sensing system in the range of 20–240 µmol/L with the detection limit of 6.4 µmol/L. The proposed method is simple, fast, accurate, and easy to realize real-time monitoring.

Preparation of high purity platinum nitrate using spent Pt-Rh catalyst from the production of nitric acid was studied, including separation of rhodium from aqua regia leaching solution, precipitation with ammonium chloride to obtain ammonium chloroplatinate precipitate, calcination of precipitate to obtain sponge platinum, dissolving with aqua regia and removing nitric acid to obtain chloroplatinic acid, precipitation with potassium chloride and reduction with potassium oxalate to obtain potassium chloroplatinite, hydrolysis with potassium hydroxide, removal of potassium and chloride, and neutralization with nitric acid. Effects of temperature, concentration, time and pH on the purity and yield of intermediate and final products were investigated and the suitable operating conditions were obtained. The yield of platinum nitrate is 94%, the mass fraction of Pt²⁺ in platinum nitrate is greater than 15%, and the mass fractions of Cl⁻ and K⁺ are far less than 0.005%. The reaction kinetics and thermodynamics of potassium chloroplatinate to potassium chloroplatinite was studied, and the reaction order is 1.39 for PtCl₆²⁻ and 1.55 for C₂O₄²⁻, and the activation energy is 35.13 kJ/mol.

Microbial-mineral interface is the main biochemical reaction place of bioleaching, and the mechanism of interface interaction is the key to elucidating the behavior of microbial leaching. In this paper, bioleaching experiments and biofilm colonization experiments of pyrite grains and pyrite slices were conducted by three moderately thermophilic mixed bacteria, Acidithiobacillus caldus, Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans, respectively. The distribution and content changes of interfacial extracellular polymeric substance (EPS) and iron ions during bioleaching were evaluated based on a highly selective and sensitive metal fluorescence probe combined with confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) and physical extraction methods. The results show that EPS was laid flat on the surface of pyrite slices to form sheet biofilms, mainly in the early and middle stages of bioleaching, reaching 17.21 mg/g on the 15th day, and the main component was extracellular protein. At the early stage of bioleaching, the surface of pyrite was mainly dominated by Fe²⁺ of 0.75 mg/g, while Fe³⁺ was only 0.08 mg/g. With the increase of leaching time, a large amount of Fe³⁺ (11.97 mg/g) was enriched at the microbe-mineral interface.

The presence of multiple pollutants such as fluoride, SO₂, and CO₂ in aluminum electrolysis flue gas is harmful to the environment and human beings. The current research on aluminum electrolysis flue gas purification does not involve recovering carbon resources. We propose a one-step purification technology for aluminum electrolysis flue gas purification to address this problem. It is a resource conversion technology that integrates the purification of fluoride, SO₂, and CO₂ and converts the exhaust pollutants into cryolite and compound ammonia fertilizer. This paper studies an ammonium fluoride-containing absorption solution after one-step ammonia purification of aluminum electrolysis flue gas. It generates cryolites by adding NaOH and Al(OH)₃ for chemical precipitation. The optimal operating parameters were obtained by using a fluoride ion electrode, XRD and SEM analysis and detection, under the condition of temperature of 70 °C, stirring speed of 400 r/min, reactant concentration of 0.5 mol/L, and α_k (molecular ratio of NaOH to Al(OH)₃) of 3.1.

The present researches and developments for ammonium paratungstate tetrahydrate production always suffer from at least one of the following problems: long production process, high-energy consumption, low tungsten crystallization ratio and serious environmental pollutions. The objective of this work is to develop a sustainable technology to directly produce ammonium paratungstate tetrahydrate. The results show that the starting material, tungsten trioxide monohydrate, can stoichiometrically react with ammonium bicarbonate or ammonium carbonate by direct transformation reaction in an airtight container under different experimental conditions. The dense-surface ammonium paratungstate tetrahydrate with the average particle size of 61.7 µm was prepared by adding solid tungsten trioxide monohydrate and 80×10⁻⁶ g/L PEG2000 into the ammonium bicarbonate solution with the liquid-to-solid mass ratio of 2 at 80 °C for 3 h. The chemical purity of the transformed ammonium paratungstate tetrahydrate meets the standards of APT·4H₂O-0 grade.

In this work, a two-step vacuum metallurgy method was proposed to produce Sb₂S₃ from complex lead-antimony sulfide ore. As revealed from the experimental results, jamesonite (Pb₄FeSb₆S₁₄) is overall decomposed into PbS, Sb₂S₃ and FeS at 750 °C. The first step vacuum distillation was performed at 650 °C for 80 min, by which the purity of Sb₂S₃ collected was 99.07 wt%. The second step vacuum distillation was to carry out the residue after the first-step distillation at 800 ° C for 40 min, by which the purity of Sb₂S₃ obtained after fractional condensation was 99.41 wt%. Then the total direct recovery of Sb in the two-step vacuum metallurgy method was 95.84%. The proposed method could be used to effectively exploit antimony resources from the source of complex lead antimony sulfide ore, produce high-purity Sb₂S₃ and achieve clean smelting as compared with conventional technology.

Tailings pastes are high-concentration mixtures and exhibit complex thixotropy. This study is to investigate the equilibrium and transient thixotropic behaviours of tailings pastes via a series of constant shear rate tests. The thixotropic model proposed by ZHANG et al is utilized to analyze the effect of solids concentration on thixotropy of tailings pastes. The empirical functions that represent the relationship between equilibrium rheological parameters and solids concentrations is proposed. Meanwhile, a time-dependent model is established to characterize the effect of solids content on the transient shear stress. These functions enable the quantitative analysis of concentration-dependent equilibrium and transient stress evolution for tailings pastes.

Squeezing, slabbing, and strainburst are typical failure modes of overstressed rock masses in deep rock excavation engineering. This study considered intact rock properties to evaluate squeezing, slabbing, and strainburst, owing to the effectiveness and availability of these parameters. Hybrid models combining the Jaya algorithm and support vector machine (JA-SVM) were proposed to predict the failure modes of overstressed rock masses based on the collected database. JA-SVM model achieved a training accuracy of 0.970 and a testing accuracy of 0.875. Ranking system and Taylor diagrams showed that the developed hybrid model was superior to other machine learning (ML) models, including SVM, artificial neural network, etc. Receiver operator characteristic curves suggested that JA-SVM had a more powerful ability to predict strainburst and slabbing compared to other widely applied ML techniques. Performed sensitive analysis revealed that the brittleness index and elastic modulus were vital factors in estimating failure modes. The developed model can be applied to identify failure modes of overstressed rock masses in the initial phases of a deep underground project, and appropriate support measures can be prepared beforehand based on estimation results.

Rock masses with filled flaws play the main bearing role after excavation of pre-grouting roadway. In this study, the excavation stress path was obtained by numerical simulation, and rocks with filled flaws were loaded under the conventional compression and excavation stress path respectively. The failure process was simultaneously monitored by digital image correlation method and acoustic emission equipment. The results showed that the three simultaneous changes were caused by the excavation stress path: 1) compaction; 2) non-uniform change in strength near the flaws; 3) pre-cracking occurs at the flaw tip. Compaction decreased the crack initiation angle of resin-filled specimens. Variations in strength near the flaw resulted in the alternate appearance of tensile and compressive deformation in unfilled specimens near the long side of the flaw. The deformation in cement-filled specimens changed from sudden to progressive, whereas that in resin-filled specimens was the opposite. Pre-cracking weakened the unfilled specimens and changed the propagation direction of shear cracks in cement-filled specimens.

The coal-backfilling composite structure jointly bears the overburden stress. The interface between the coal pillar and backfilling body can easily induce splitting failure of composite system. The failure pattern and load-acoustic emission (AE)-digital image correlation (DIC) response of coal-backfilling (CB) composite structures were investigated through Brazilian splitting tests. The mesoscopic force-fracture distribution, azimuth angle of contact force and displacement vector were then obtained from particle flow code (PFC) numerical simulations. The results show that three types of failure patterns are observed for different CB composite specimens during the Brazilian loading process; with an increase of interface angle, the failure shifts firstly from Type I to Type I-II pattern, then turns into Type III, and finally becomes Type II pattern; For the CB composite specimens with different interface angles, the load — AE — DIC response characteristics correspond to the failure patterns; tensile fracture is dominant when the fracture is distributed on coal or backfilling elements. The fracture may be tensile, shear, or combined tensile-shear fracture when the fracture occurs at the interface.

Aiming at the practical problem of toxic gases generated in the process of cemented backfill with phosphorus waste (phosphogypsum as aggregate and yellow phosphorus slag as the binder), sources and dynamics of gas generation and the method of gas inhibition were investigated by monitoring the gas generated in the aggregate, the binder and the cemented slurry stirring process. The main findings proved that the gases were mainly generated from the binder in an acidic circumstance, and the gas generation sequence is PCl₃, PH₃, NO, H₂S, NH₃, and CO. Furthermore, lowering the pH value of the cemented slurry would increase the gas yield. The original gas yield of the slurry without acid addition was only 6.3% of the maximum gas yield after acid addition. By analyzing the circumstances of gas generation, a method of directly adding alkaline CaO to the slurry to control the gas generation was proposed. The addition of 12 wt% CaO was noted to reduce the gas yield by 99%. When the pH of the backfill slurry reached 10, the gas generation could be controlled. The results have implications for ensuring the health of mining workers and decreasing environmental pollution.

Efficient breaking of hard rock and prevention and control of rock burst disasters are two key concerns for construction in deep areas with high in-situ stresses and are two of the most important ways to ensure the safe and efficient construction of deep engineering. Therefore, this study considers microwave weakening and fracturing of hard rock, taking the duration of a single microwave irradiation treatment as a variable, and synchronously combines mechanical testing and acoustic emission monitoring methods to demonstrate the possibility of rock burst disaster prevention and the control with this treatment method. The result shows that under microwave irradiation, the proportion of crack damage stress decreased from 77% to 62%; the proportion of dissipated energy increased from 6% to 20%, and the energy-based brittleness index also decreased from 0.94 to 0.72; acoustic emission monitoring found that after microwave irradiation, the quiet stage of the rock was greatly reduced from 56.2% and 59.6% to 11.5% and 8.6% with the monitoring time. In this test, the threshold of the duration of 1 kW microwave irradiation is 2 min; beyond this threshold, the rock is irreversibly damaged. The research results can provide necessary theoretical support and technical guidance for efficient and safe rock breaking in deep areas with high in situ stresses.

The whole process of tunnel structure from deformation to instability under earthquake motion is closely related to the input, transformation and dissipation of seismic energy. Based on the energy response of tunnel structure, this paper establishes an energy balanced equation under the seismic wave excitation. According to the relationship between input energy and inherent energy of structure, the instability criterion is proposed based on failure of overall structure. Firstly, the energy response characteristics of tunnels across different fault widths are analyzed under seismic excitation, and the relationship between energy-based structural instability and deformation is verified through combining the energy stability functions and structural deformation. Secondly, on the basis of releasable elastic strain energy, the longitudinal affected sections of cross-fault tunnel are divided under strong ground motion. Thus, the self-adaptability deformation characteristic of tunnel structure is studied inside the fault fracture zones during earthquake motion, and then the segmental lining is designed to adapt deformation of surrounding rock at the main influenced areas of fault belt. Lastly, the dynamic stability functions are compared and analyzed at different positions of the fault, and the optimal anti-seismic measure is proposed to improve aseismic performance of tunnel structure based on energy criterion.

Hydraulic fracturing in the exploitation of hot dry rock (HDR) resources could significantly enhance the permeability and heat production of the reservoir. However, the fracturing mechanism of HDR at high temperatures is still not fully understood. In this study, hydraulic fracturing experiments at room temperature and 200 °C were performed respectively on granite under different true triaxial stress to analyze their different fracturing mechanisms. Optical microscope and nuclear magnetic resonance were applied to identify pore and crack characteristics of fractured samples from micro- to macro-scale. The test results show that hydraulic fracturing at 200 °C can significantly reduce the breakdown pressure and fracture initiation pressure under the same stress condition compared to hydraulic fracturing at room temperature. The wellbore pressurization stage at 200 °C deviates distinctly from linearity. The cloud fracture with multi-scale crack, rather than a dominant fracture at room temperature, was formed at 200 °C even under a horizontal stress difference of 20 MPa. Moreover, the nuclear magnetic resonance result shows an increase in fracturing volume caused by the increment of micro-scale crack in the fractured sample at 200 °C. The main reason for the above transition is that the pore pressure diffusion at 200 °C generates more micro-scale cracks.

Coupled support technology for concrete-filled steel tube support (CFSTS) and bolt-cable (BC) used in deep roadways often fails, and increasing the length of BC is a waste of material. Therefore, changing the pre-tightening force of BC to improve the force state in CFSTS is proposed in this paper. Firstly, the damage modes of CFSTS were investigated, and the internal forces in CFSTS contained cable were obtained using the elastic centre method. And the results indicated the cable could reduce the internal force in CFSTS to ensure its high bearing capacity. And then, the numerical calculation models with different lateral pressure coefficients and coupled support conditions were established. Further, the stress and displacement law for the roadway and the support body under different lateral pressures and different support schemes, and increasing the pre-tightening force for bolt-cable in different angle ranges was investigated. And the results show that the best “CFSTS + BC” coupled support effect could be achieved with pre-tightening forces for bolts and cables of 60 and 100 kN, respectively, and the optimal reinforcement angle range is 15°–45°. Finally, “CFSTS + BC” coupled support technology was applied in the field.

The active attenuation method of rockburst stress wave is an important research problem in coal roadway safety control. In this study, the strengths of different propagation media were analyzed and a new type of coal-rock barrier test structure was proposed. The split Hopkinson pressure bar (SHPB) was used to analyze the propagation attenuation law of stress wave, energy dissipation characteristics, and apparent failure degree of coal and rock mass under the influence of barrier layer. The results show that the barrier layer affected the shape of the stress wave peak. The strength of the barrier layer affected the floating oscillation with stronger and weaker barrier layers, resulting in more evident floating oscillation at the reflection and transmission stress wave peaks, respectively. Additionally, an apparent “double peak” was observed for the weaker barrier layers. The barrier layer reduced the frequency of stress wave cycle “stretching and compression”, and ultimately the destructive force of stress wave. Under the influence of the strong barrier layer, the energy absorption capacity of coal and rock mass increased by approximately 10%, while the soft barrier layer accelerated the speed at which the samples reached peak energy absorption.

The frequency and intensity of rockburst in underground engineering have increased with excavation depth. In order to predict rockburst intensity grade, this paper introduces six machine learning algorithms to establish six rockburst prediction models. Based on 289-day microseismic monitoring data and rockburst events of Qinling water conveyance tunnel, the rockburst intensity grade prediction dataset is constructed. In the process of model establishment, the impact of data imbalance on model performance is discussed first, and it is concluded that Borderline-SMOTE1 is the most effective method to eliminate data imbalance. Secondly, the analysis of six models’ performance indicators shows that the rockburst prediction model based on the Adaboost algorithm has the best performance, with the highest accuracy, macro-F₁, and micro-F₁, which are 0.938, 0.937, and 0.938, respectively. Finally, the Borderline-SMOTE1-Adaboost model was applied to the prediction of the rockburst intensity grade of Qinling water conveyance tunnel from June 1, 2020 to June 10, 2020. All ten strong rockbursts are accurately predicted, which verifies the effectiveness of predicting rockburst intensity grade through microseismic parameters. The results show that the Borderline-SMOTE1-Adaboost rockburst prediction model can provide a reference for the early warning of rockburst disasters during the construction of deep-buried tunnels.

Tracer test is an effective tool for characterizing the complex conduits and exploring the solute transport law for karst aquifers. In this study, three generalized karst conduit models were established, including auxiliary side conduit, cave, and waterfall. A series of tracer tests were conducted to obtain tracer residence time distribution curves. These tracer curves were used for performing temporal moment analysis to estimate fluid flow characteristics and solute transport process of karst conduit models. The results demonstrate that the residence time distribution curves are mainly constrained to the length and path differences of auxiliary side conduits, the lengths and geometries of pools, and the lengths and numbers of waterfalls. Although the multi-peaked residence time distribution curve is the basis for judging the existence of multiple karst conduits with path differences, the number of paths cannot be determined directly. Moreover, it can be presumed that there are some caves or waterfalls when the residence time distribution curve has a long tail. This study provided some useful references for the development of solute transport theory in karst conduits.

Thermal fracture is a typical fracture. Cracks are widely present in brittle solids, and the stress concentration and propagation of cracks under temperature changes have an important effect on thermal fracture. Most of the traditional studies have focused on surface cracks or 2D cracks, while the propagation and the interaction of multiple internal cracks under temperature field are less frequently covered. This paper uses the 3D-internal laser-engraved crack (3D-ILC) method to fabricate 3D double-parallel internal cracks within intact cubic specimens, without causing any damage to the surface. Physical experiments and 3D numerical simulations of crack fracture in different vertical spacing under temperature fields are carried out, and the double crack interaction mode is analyzed and discussed. The results indicate the following: 1) When the double cracks are coplanar, then the temperature field distribution on both sides of the internal crack is symmetrical, the direction of double crack propagation does not shift, and the inner tips of the internal cracks attract each other and eventually coalesce. This is categorized as Mode I crack. In addition, coplanar crack propagation arcs intersect in an “I” shaped fracture morphology. 2) Double cracks attract and coalesce with each other when the ratio of vertical spacing d to crack radius a, i.e., d/a<2, and the interaction degree is maximum when d/a=1. Non-coplanar crack arcs are intersected by “crescent” shaped fracture morphology. 3) After d/a⩾2, the propagation of the inner tip of the double crack is repulsive and this repulsion phenomenon is caused by the boundary effect, not the interaction between multiple cracks, thus categorizing them as Mode I–II mixed cracks. 4) Regardless of the size of the vertical spacing, the stress concentration phenomenon is present on both sides of the tip of the internal crack, while the inner side is much larger than the outer side, so the inner crack propagation length is longer than the outer side. The results of this study provide an experimental and theoretical basis for the study of three-dimensional double-parallel crack interactions under temperature fields.

In seismic analyses of high-speed railway simply-supported bridges, the constraint imposed by the track structure is non-negligible. Despite its great computational efficiency, the bridge model (BM) may produce an unreasonable seismic response, because it does not consider the track structure. The bridge-track model (BTM), which considers the track structure, is very complex, and its computational efficiency for seismic analysis is low. Therefore, developing a simplified calculation model for seismic analysis of high-speed railway bridges has great practical engineering value. In this paper, the simplified bridge-track model (SBTM) for transverse seismic analysis of high-speed railway bridges is established by setting nonlinear springs between girders. These springs can accurately simulate the constraint that the track structure imposes on the bridge. Seismic analysis of a five-span high-speed railway bridge is carried out using the SBTM, and the seismic response is compared to that of BM and BTM. The results show that the seismic responses of both SBTM and BTM match well under different seismic records, which validates the calculation accuracy of SBTM. Compared with the BTM, the calculation time of the SBTM is significantly shorter. The track structure is basically in the elastic stage under frequent earthquakes, while under design earthquakes and rare earthquakes, the stiffness of the track structure will degrade.