Abstract: Paste technology can effectively solve the environmental and safety issues caused by mining and is a key technology toward realizing green mining. In the recent years, scientific progress has accelerated the pace of intelligent control and the precise preparation and personalized filling of paste technology. Thereby, the research level of paste technology in China has risen. In this paper, the basic concepts and characteristics of paste technology were introduced and the development process of paste technology in China was statistically analyzed. Additionally, the latest research progress in thickening dewatering technology with applications to unclassified tailings, pipeline transportation technology of structure flow, multi-field influence mechanism in stopes, development of new materials, and the construction of a paste engineering laboratory, was systematically analyzed. Furthermore, the practical effects of paste technology in underground backfill and surface deposition were introduced. In the future, paste technology will break through via digitization and intelligence, and realize the adaptive control of the concentration, precision, and preparation of paste, in addition to personalized stope fillings, and the 3D and modular design and assembly of a system, and will thereby lead the mining industry in China toward green development.
Abstract: Tailings dam failure accidents with limited emergency response time and substantial potential threats often lead to heavy casualties and severe financial losses. In recent years, the decreasing trend of tailings dam failure accidents shows the development of modern technology and safety management. However, the frequency of major tailings dam failure accidents has increased, rather than decreased. The 2015 Samarco Accident in Brazil and the 2014 Mount Polley Accident in Canada, along with their disastrous consequences, once again sounded the alarm to improve the safety of tailings ponds. China is now facing a complicated safety situation because there are 8869 tailings ponds throughout the country, including 1425 overhead tailings ponds that represent the tailings ponds located within 1 km upstream of residential areas, workshops, schools, or other important facilities. Based on a large number of relevant research studies, focusing on three main aspects of accident prevention and management that include safety monitoring, early-warning and emergency preparation, safety management codes and standards, the status and frontier progress are reviewed in this paper. Furthermore, the relevant problems in China are discussed, and several improvement recommendations are presented that can provide a reference for theoretical research and technological innovation for preventing tailings pond accidents. The results are as follows:(1) The safety monitoring standards in China are relatively strict. However, the monitoring instruments lack stability, reliability, and practicability. Thus, specific devices and new technologies need to be developed. (2) The current early-warning method lacks diversity and reliability, and using information technology in interdisciplinary applications is becoming the developing trend. (3) The emergency management and decision-making should be based on sufficient scientific proof. However, the relevant research is limited by test methods and simulating algorithms. (4) Lastly, China has established a complete system of safety management codes and standards, but with the current problems of safety level classification, life-cycle management, change management process, and accident investigation, greater progress is needed.
Abstract: The separation of Cu-Zn polymetallic sulfide by flotation has been a difficult and well-researched topic in the field of mineral processing. One of the important reasons why it is difficult to separate Cu and Zn is the presence of a large amount of copper ions in the pulp, which results in the unavoidable activation of sphalerite. The key to solving this difficulty is the development of a high-selectivity depressor for sphalerite. Sodium dimethyl dithiocarbamate (SDD, C3H6NS2Na) is the lowest homologue of dialkyldithiocarbamate salts, and it has the shortest hydrophobic group (-CH3) in its molecular structure with weak hydrophobicity. In preliminary exploration experiments, it was found that SDD has good selectivity for Cu-Zn sulfide flotation and can achieve better separation performance than conventional depressors. However, the depression mechanism is not very clear. In this work, the depression effect of SDD on copper-activated sphalerite was revealed by conducting a monomineral flotation test. Based on the results of this test, the competitive adsorption mechanism of SDD and BX on the surface of copper-activated sphalerite was further studied by conducting the Zeta potential test, LEIS (local AC impedance) test of Versa STAT electrochemical workstation, and frontal orbital theory calculation. The flotation results show that the SDD can effectively act as a depressant in copper-zinc separation. Sphalerite is depressed effectively in the presence of SDD, while chalcopyrite is not depressed. In addition, SDD has the characteristics of small dosage and high sensitivity. Under the optimum conditions with pH of 10 and SDD dosage of 4.0×10-5 mol·L-1, the recovery of copper-activated sphalerite can be reduced to 16.59%, while the recovery of chalcopyrite is 81.64%. Analysis of the results of the Zeta potential test and LEIS show that SDD can not only occupy the activation site of copper-activated sphalerite surface but also afford better adsorption capacity than BX, which greatly reduces the adsorption of BX on the surface of sphalerite. As a result, SDD shows a good depression effect for copper-activated sphalerite. The frontier orbital calculations further confirm that SDD is superior to BX in its ability to interact with minerals.
Abstract: The isothermal oxidation kinetics and mineralogical characteristics of Hongge chromium containing vanadium and titanium magnetite (HCVTM) pellets were investigated. The experiments related to the isothermal oxidation kinetics were performed over a temperature range of 1073 to 1373 K and a time range of 10 to 60 min. First, the microstructure and variations in the mineral composition of the pellets were analyzed. Further, the oxidation rate and its change regulation were calculated and analyzed by combining the defined oxidation rate function, and the effects of the mineral phase structures on the rate of oxidation were determined. Finally, the modified oxidation rate function, Arrhenius equation, reaction rate constant, correction factor, and reaction activation energy were calculated by combining the shrinking core model, and the restrictive step in the oxidation reaction was determined. The results depict that an increase in temperature causes an increase in the low melting point liquid phase; formation, growth, and recrystallization of hematite grains; and formation of a bonding phase. Additionally, it causes a decrease in the number of interspaces. With an increase in time, the bonding and growth of hematite grains are promoted due to the generation of a liquid phase. However, the structure of pellets is observed to deteriorate due to the formation of silicate and perovskite phases. Meanwhile, perovskite, and pseudobrookite phases are also generated. Oxidation rate decreased with increasing time due to the decrease in the number of interspaces and bonding phases. In HCVTM pellets, the oxidation reaction is controlled by diffusion. The activation energy of the initial reaction is 13.74 kJ·mol-1 while that of the latter reaction is 3.58 kJ·mol-1. Further, the corrected parameter for the oxidation rate function is observed to be 0.03.
Abstract: As the largest iron and steel producing country, China creates a large amount of steel and blast furnace slag each year. If these metallurgical slags are not properly handled, not only do they occupy land and damage the environment, but they also result in a waste of resources. Using steel slag as a building material usually leads to poor stability due to the high free lime (f-CaO) content. To improve its stability and gelation performance, steel slag usually needs to be modified. In this study, based on the chemical and mineral compositions of steel and blast furnace slags, a thermodynamic calculation of the modification process was performed. The results show that SiO2 in blast furnace slag reacts with f-CaO in steel slag to generate a gelatinous phase and f-CaO in the modified steelmaking slag decreases simultaneously. Here, the properties of steelmaking slags modified with hot blast furnace slag, including the mineral composition, f-CaO content, and viscosity, was studied using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy spectrum analysis. The results show that viscosity increases with increasing blast furnace slag content and the f-CaO and RO contents decrease. The gelation performance of the modified steelmaking slags is improved, especially in steelmaking slags modified with 10% blast furnace slag at 1550℃. When the content of 2CaO·SiO2 and 3CaO·SiO2 increase significantly and the f-CaO content decreases to 1.64%, the modified slags meet the requirements for building materials. Additionally, the study also attempted to use coke to reduce the iron in the modified slag. As a result, the facile separation of slag and iron is realized, and the grindability of the modified slag has been improved.
Abstract: The tensile and compressive stresses of demagnetized specimens made of Q235 steel were tested, and magnetic signal variation characteristics under different tensile and compressive stresses were continuously recorded using a magnetic memory on-line monitoring system. The results demonstrate that the resultant magnetic field first decreases and then increases induced by tensile load and becomes stable when approaching and exceeding 0.3 times the yielding strength of the material, while the resultant magnetic field induced by compressive stress rapidly decreases in the initial stage and then fluctuates. The model for J-A magnetomechanical effect was improved by introducing different stress demagnetization terms caused by tensile and compressive stresses, and the simulation results are consistent with the experimental data, which can be used for theoretically explaining different mechanisms induced by tensile and compressive stresses.
Abstract: In recent years, the development of next-generation nuclear reactors with enhanced requirements for the safe and reliable production of nuclear energy has been attracting increasing attention. The thorium molten salt reactor (TMSR) has been regarded as the most promising prospective next-generation nuclear reactor because of its high security, desirable online refueling properties, minimization of nuclear waste, nuclear non-proliferation, etc. The structural materials for molten salt reactors should exhibit high temperature resistance and good corrosion and neutron irradiation resistance. The Ni-Cr-Mo-based superalloy GH3535 is the preferred material for TMSR applications because of its superior corrosion resistance and good mechanical properties. The Mo content of GH3535 is 15%~18% (mass fraction), which leads to the precipitation of a large amount of Mo-enriched M6C carbides in the matrix. Numerous studies have shown that the precipitation of these carbides directly affects the grain size and mechanical properties of GH3535 alloy. In this study, the effects of heat treatment on the grain size, carbide distribution, and mechanical properties of GH3535 alloy were investigated by cold-rolled-pipe tests. To provide the experimental and theoretical basis for applying heat treatment to control the properties of GH3535 alloy, the thermodynamic and kinetics characteristics of GH3535 were calculated using the JMatPro simulation software. The influence of heat treatments on the size and homogeneity of grains, the precipitation character of carbides, and the mechanical properties of the alloy were investigated. The results show that the equilibrium precipitate of the GH3535 at temperatures between 900℃ and 1500℃ is a Mo-rich carbide of M6C type and that the initial precipitation temperature of this M6C-type carbide is in the liquid-solid phase range. The grains grow slowly when the solution temperature is less than 1200℃. When the solution temperature is increased to 1230℃, the grains grow quickly to an average size of 160 μm; the grains are homogeneous when the temperature is maintained at 1180℃ for 10 min. Tensile tests show that a higher solution temperature decreases the strength and increases the elongation. The tensile fracture mechanism of GH3535 alloy is microporous aggregation.
Abstract: Non-quenched and tempered steels offer many advantages such as energy saving, emission reduction, simple processing, short production time, and low cost. Demand for energy saving and emission reduction is increasing with the rapid increase of car production and ownership. As a result, the usage of non-quenched and tempered steel in automotive parts has attracted increasing attention. The main problem with non-quenched and tempered steel in actual production is the lack of a hot deformation process and a cooling process that can be used to precisely control the microstructure and properties of the material. The material 1538MV is a type of pearlite+ferrite non-quenched and tempered steel, and its use for building crankshafts has not been studied sufficiently thus far. The main factors affecting the structure of a crankshaft are deformation, final forging temperature, and metal flow and cooling after forging. In this paper, the forging process of 1538MV non-quenched and tempered steel for building a crankshaft was studied by means of numerical simulation, microstructures of the rolled material and finished crankshaft were analyzed, and influence of deformation on the microstructure of the crankshaft was discussed. The results show that the microstructure of a crankshaft forged at a higher temperature and with smaller deformation is coarser than that of a crankshaft made of rolled material. The inhomogeneity of the microstructure is caused by unevenness of temperature and strain distribution during crankshaft deformation. The ferrite content of the crankshaft and the pitch of the pearlite were lower than those of the rolled material, and the bainite structure appeared in a few parts, which indicated that the cooling rate was too fast during phase transformation. Therefore, the cooling process should be optimized further. In addition, the metal flow in the segregation zone during the crankshaft forging process significantly influences the forged microstructure of the crankshaft, which is another cause of the formation of bainite. Therefore, the quality of the rolled material should be strictly controlled. The above results provide directions for improving the quality of the rolled material, optimization of the crankshaft forging process, and optimization of the cooling process after forging.
Abstract: The corrosion behavior of 2507 duplex stainless steel in simulated seawater containing different concentrations of NaHSO3 solution was investigated using open circuit potential, electrochemical impedance spectroscopy (EIS), Mott-Schottky curves, and an immersion corrosion test. The results depict that the open circuit potential shifts negatively with an increase in the concentration of NaHSO3, whereas the corrosion tendency of the steel increases. The charge transfer resistance (Rt) decreases with the increased concentration of NaHSO3, which suggests that the corrosion resistance is reduced. The corroded stainless steel exhibits localized pitting corrosion. Further, the degree of corrosion as well as the corrosion rate increases with an increase in the concentration of NaHSO3. The results that are obtained using the Mott-Schottky curves and EIS test depict that the addition of NaHSO3 increases the concentration of point defects on the passive surface film of 2507 stainless steel, reducing its stability and decreasing its charge transfer resistance, resulting in an increased probability of corrosion. This may be caused due to the fact that the addition of NaHSO3 increases the acidity of the solution, which accelerates the damage that is caused to the passive film on the stainless steel.
Abstract: The corrosion behavior of X65 steel in the CO2/oil/water environment of gathering pipeline was investigated by mass loss, X-ray powder diffraction (XRD), scanning electron microscopy with X-ray microanalysis (SEM-EDS), and electrochemical analysis through dynamic reactor tests. The results indicate that the corrosion rate increases and the corrosion morphology changes with an increase in the water cut. When the water cut of crude oil is within the range 40%-50%, uniform corrosion occurs along with a lower corrosion rate due to the protection of crude oil, but pitting corrosion appears due to the inhomogeneous adsorption of crude oil. When the water cut is between 70%-80%, the barrier effect of crude oil on the steel surface is weakened, the corrosion scales become thick and loose, and the partial loss of corrosion scales cause mesa corrosion. When the water cut is 90%, the damage area of platform corrosion is enlarged. Consequently, the corrosion rate dramatically increases. Crude oil can hinder the corrosion scales from being dissolved in a corrosive medium and change the dimension and accumulation pattern of the crystal grain, thickness and structure of corrosion scales, thus influencing the corrosion rate. Under the corrosion inhibition effect of crude oil, the temperature-sensitive point of X65 steel corrosion moves to a low temperature at -50℃, lower corrosion rate interval is broadened, and the corrosion resistance of X65 steel is enhanced.
Abstract: Due to its specific strength, superior electromagnetic shielding and excellent processing capabilities, the magnesium-lithium (Mg-Li) alloy is regarded as one of the most promising structural metal materials and has been extensively applied in various fields such as aerospace, offshore engineering, and the communication industry. Unfortunately, inferior tribological behavior, caused by low hardness, a fluctuating friction coefficient, and serious adhesive wear, has severely inhibited large-scale application of Mg-Li alloys in industrial engineering. Therefore, in this study, to enhance the tribological performance of a micro-arc oxidation (MAO)-produced ceramic coating on an Mg-Li alloy, a variety of inorganic particles were tentatively added to MAO electrolytes to prepare composite ceramic coatings with pronounced friction and wear resistance properties. MAO in Na2SiO3-KOH electrolytes with graphene additives was used to produce self-lubricating C-containing ceramic coatings on an Mg-Li alloy. The surface morphologies, roughness, hardness, and phase compositions were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), a Vickers hardness test, and X-ray power diffraction (XRD). At room temperature, the tribological properties of the ceramic coatings were evaluated by friction and wear tests. The results indicate that the micro-pores in the C-containing coatings distribute uniformly on the alloy surfaces and a significant decrease in micro-pore size and surface roughness is observed. The surface hardness of the coatings show significant enhancement compared with that of the Mg-Li alloy. The coatings mainly consist of SiO2, Mg2SiO4, and MgO phases; graphene is dispersed throughout via mechanical effects and displayed an antifriction effect. The C-containing coating produced when the volume fraction of graphene in the electrolyte is 1% show good wear resistance and its surface hardness and friction coefficient are 1317.6 HV0.1 kg and 0.09, respectively. Meanwhile, compared with the Mg-Li alloy the wear traces on the coating appears narrower and shallow, and the worn area seems relatively smooth, which indicates that slight adhesive wear occurs on the C-containing coating surface.
Abstract: In the single-spark electrical discharge machining (EDM) process under the action of an orthogonal magnetic field, the plasma from the electric discharge is deflected and extends to the direction of the Lorenz force, which leads to a change in the discharge craters compared with traditional EDM. In this paper, the morphology and characteristics of craters created during the process of magnetic field assisted electrical discharge machining (MF-EDM) were studied. The results of this study may be applied to production practice, and it is expected that the machining of tapered holes can be realized using magnetic field assisted EDM. Based on single-pulse MF-EDM in gas, the crater morphology was observed using a surface topography instrument. During the experiment the voltage waveform was obtained using an oscilloscope and the current waveform was calculated using the simulation software SABER. After measuring the distribution of the orthogonal magnetic field, the ampere force of the electrode at the moment of discharge was calculated. The deformation of the end of the electrode was obtained using simulation software ANSYS15.0. The offset of the starting point of the discharge under the influence of the orthogonal magnetic field was proven. Then, rules for the effects of the magnetic field and discharge parameters on the craters were obtained. The results indicate that crater length increases with an increase in magnetic field intensity and open circuit voltage, but the influence of the electrode overhang length shows the opposite. There is no obvious change rule for crater depth with an increase in magnetic field intensity, open circuit voltage, or electrode overhang length. To obtain the maximum length or minimum depth of the crater, an optimum combination of the capacitance and magnetic field intensity can be used. With an increase in magnetic induction intensity and discharge energy, the offset of the discharge point increases.
Abstract: In recent years, unmanned aerial vehicles (UAVs) have experienced an important growth both in research activities and industrial field. With the abilities to take off, land vertically, and hover along with natural agility and controllability, a hexrotor can extend the potential roles of UAVs. From the view of mechanical structure, hexrotors can be considered simpler than the helicopters because they do not have the swash-plate and do not need to eliminate the gyroscopic torques created by the spinning motors. However, hexrotors are not only extremely sensitive to control inputs and disturbances, they are also complex systems that are nonlinear, highly unstable and with multiple input-multiple output (MIMO) and a high degree of coupling characteristics. This study proposes a hybrid control algorithm combined integral backstepping control with linear active disturbance rejection control to solve the problem of trajectory tracking control for an unmanned hexrotor with lumped disturbance. First, the nonlinear dynamical model of the hexrotor was deduced with the Newton-Euler equation, and the mathematic relation of the input and the output was analyzed. Second, the hexrotor system was divided into the position loop and the attitude loop according to the characteristic of the dynamical model. In the position loop, an integral backstepping control algorithm was applied to design the controller by introducing an integral term to improve the disturbance resistance and eliminate the static error of the trajectory tracking. In the attitude loop, a linear active disturbance rejection control algorithm was used to design the controller by introducing a linear extended state observer to estimate and compensate for the lumped disturbance. Lastly, the effectiveness of the proposed control algorithm was verified through two simulation cases and a flight experiment. The research results show that the proposed algorithm has a strong ability to resist the lumped disturbance and make the hexrotor quickly and steadily track the referenced trajectory. Hence, the algorithm has an important engineering application value.
Abstract: With the rapid development of mobile internet technology and daily increase in wireless user equipment as well as demand of mobile applications, the required quality of service (QoS) by mobile users for wireless communication networks is increasing, and the pressure of backhaul network is also increasing. The emerging cloud radio access network (C-RAN) can effectively improve the network capacity and user service quality. Meanwhile, Passive Optical Network (PON) was used for backhaul network that offers a large bandwidth, high reliability, and low latency backhaul. When the demand of mobile applications is ever-changing and backhaul network resource is limited, an efficient backhaul network resource scheduling strategy is of great importance. This can improve the backhaul network resource utilization and waiting-transmitting delay in C-RAN. To save backhaul network resource, improve the load balance of wavelengths and the utilization of network resource, a downlink resource scheduling strategy was proposed. According to the network demand of wireless users in hot spots, three optimization objectives including the number of used wavelengths, load balance, and well-distribution of real-time traffic were considered in the optimization of adaptive-weighted parallel genetic algorithm. Thus, the wavelength resources were dynamically allocated and resource utilization was improved. The results demonstrate that the proposed downlink resource scheduling strategy can effectively improve the load balance and resource utilization and reduce the waiting-transmitting delay of real-time traffic.
Abstract: In the recent years, an increasing number of loess landslides were triggered due to extreme climate. The initiation of loess landslides was related to water, including surface water and groundwater, landform, geologic structure, and other factors. Both surface water and groundwater significantly affect loess landslides. Rainfall and irrigation provide plenty of water to loess, creating surface water and groundwater. Surface water flows on the surface of a loess, infiltrating into loess at the same time. The infiltration of surface water transforms loess from an unsaturated state to a saturated state in the loess plateau. The weight of slope mass increases due to the increase in water content of loess. Therefore, the loess slope mass bears shear force and seepage stress at the same time, and the deformation of loess gradually increases with time. More attention should be paid to seepage stress during the infiltration. The fabric inside loess is damaged because of shear force and seepage stress. The presence of seepage stress makes the failure mode different from the shear mode in loess. Eventually, a loess landslide forms as the deformation exceeds the bearing capacity. In this study, the 4.29 landslide in Heifangtai was selected for the purpose of research. Based on field investigation, 60 undisturbed samples from the backwall of landslide were used to conduct triaxial tests. To simulate the shear behavior of saturated loess under seepage shear, loading rates of 0.5, 0.1, and 0.05 mm·min-1 were used and the effect of loading rate on shear strength was identified. Moreover, water heads of 0, 1, 2, and 5 m were set to study the effect of water head on shear strength with loading rates of 0.1 mm·min-1. The stress-strain curve shows obvious strain hardening under seepage shear. Loading rate slightly affects the stress-strain relationship of loess during the seepage shear. In contrast, an increasing water head rapidly decreases the shear stress of loess. The cohesion of loess decreases by 5.24%-63.35% due to seepage shear. Further, the strength correction formula for a loess under the seepage shear condition is obtained by fitting the existing strength index. Fitting performance is evaluated following the fitting process. An empirical equation could be used in geotechnical engineering when seepage shear is considered.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
