Abstract: Cemented paste backfill (CPB) technology is a significant approach for the development of green mining in metal mines and can provide safe, environmentally friendly, and efficient technical support for deep underground mining. As the theoretical basis of paste backfill, the rheological concepts, characteristics, and models of paste had been systematically reviewed, and the rheological measurement methods were analyzed herein. Rheological measurement enables the quantitative characterization of the rheological behavior of paste, and on this basis, a series of studies, such as the rheological constitutive equations of paste, evaluation of the influence of both internal and external factors on paste rheology, and quality control of CPB, was conducted. Generally, the rheology of paste is influenced by certain constituents, including solids concentration, particle size distribution, density, and cement hydration, and various external conditions, such as shear stress and temperature. The rheological properties of paste differ significantly, and currently, a unified method is not yet available for the rheological measurement of paste. Hence, comprehensive knowledge of rheological measurement is essential to achieve a better combination of rheology and CPB engineering, particularly in consideration of the specific physical and chemical properties of tailings and the common practice in the mining field. Therefore, the principles and applications of commonly used approaches, including the vane rheometer, slump cone, L-shaped tube, inclined pipe, and loop facility, were summarized, with emphasis on the measurement of yield stress because of its influence on the paste, that is, a non-Newtonian fluid. Furthermore, the applicability of the aforementioned measurement methods was comprehensively discussed. Given that rheological measurement has a profound effect on the development of paste rheology theory and paste backfill technology, the key problems were discussed by emphasizing the importance of the establishment of rheological measurement standards and the application of rheological measurement to paste backfill processes in real time. The development trend of research on paste rheology was also explored.
Abstract: China is one of the major antibiotic producing and consuming countries in the world and demand for and output of antibiotics are increasing year by year. The wastewater produced during the production of antibiotics is of complex composition, high chemical oxygen demand, high concentrations of toxic and harmful substances and strong resistance to biodegradation. This is problematic for the process of pharmaceutical wastewater treatment. Additionally, due to the extensive use of antibiotics, a variety of antibiotics are constantly released into the environment, with adverse effects on aquatic organisms. Although antibiotic concentrations in wastewater are low, the accumulation of low-dose, long-duration antibiotics can lead to the development of drug-resistant strains that threaten human health and the entire ecosystem. Therefore, how to effectively remove antibiotic residues in water is an important challenge toward ensuring the safety of water quality, the environment, and ecology. Advanced oxidation technology (AOP), which has an extremely high oxidation potential, can generate hydroxyl radicals in the reaction process, and can degrade organic compounds rapidly without secondary pollution. Therefore, it exhibits clear advantages in the treatment of antibiotics in water. As a kind of AOP, homogeneous Fenton oxidation technology (Fe2+/H2O2 system) has attracted considerable attention owing to its rapid reaction, simplicity, and high degradation efficiency. Heterogeneous Fenton-like oxidation technology using an iron-based solid catalyst instead of Fe2+ ions can effectively reduce the formation of iron-containing sludge and broaden the pH reaction range to overcome the shortcomings of Homogeneous Fenton. Moreover, recycling of the catalyst has been developed rapidly in recent years and has achieved ideal results when applied to the degradation of antibiotics. In this paper, research progress in heterogeneous Fenton-like catalysts for degradation of antibiotics was reviewed. Based on the core issues of heterogeneous Fenton-like catalysts, the methods, measures, and new viewpoints for improving catalytic performance were expounded upon. Aiming at the problems of heterogeneous Fenton-like technology in degrading antibiotics, future development directions were presented.
Abstract: Path tracking control is a key technology in the hierarchical unmanned driving system. Its function is to control the vehicle so that it drives along the reference path given by the path planning system. The information such as the position and posture of the vehicle required for path tracking control is provided by the perception and positioning system. In recent years, the development of path tracking control has been very rapid, and researchers have published considerable research. As there are some common technical problems and solutions in path tracking control under the same or similar scenarios, recent research results are reviewed from the perspective of both low-speed and high-speed path tracking control. In the research of low-speed path tracking control, researchers pay more attention to the influence of system constraints on the accuracy of path tracking such as front-wheel angle speed. At present, methods to reduce the influence of system constraints include: (1) taking the system constraints into consideration when planning a reference path; (2) using preview control to make the controller respond early; and (3) using model predictive control methods, such as linear model predictive control (LMPC) or non-linear model predictive control (NMPC), as path tracking control methods. NMPC can reduce the impact of system constraints and does not need manual setting of preview distance. It has strong resistance to disturbance factors such as positioning errors. Since low-speed path tracking control has low real-time requirements, it can be considered that NMPC can meet most needs of low-speed path tracking control. High-speed path tracking control, in addition to being affected by system constraints, is also challenged by insufficient driving stability caused by higher vehicle speeds. Therefore, LMPC, which can take the dynamics-level complex system constraints into account, has a lower computational cost. It is often used as the path tracking control method. However, due to high-speed path tracking control, there is a coupling relationship between path tracking accuracy and vehicle driving stability. The use of dynamics-level LMPC or other dynamics-level control methods cannot completely solve the problem caused by this coupling relationship. The current common solution is to add an extra speed adjustment module or weight distribution module to path tracking control. Additionally, in high-speed path tracking control, the influence of environmental parameters, such as ground adhesion coefficient, is also greater. Hence, the estimation of environmental parameters, such as ground adhesion coefficient, has also become an important research direction in the field of high-speed path tracking control.
Abstract: Mine tailings, the byproducts of mineral processing, are special solid wastes generally classified as loose sandy silts or silty sands that are vulnerable to wind erosion, especially in arid and semiarid regions. Mine tailings also contain potentially toxic elements such as Cd, Cr, Mn, Ni, Zn, Pb, and As. Thus, fugitive dust from mine tailings is associated with a number of environmental and safety concerns. In recent years, dust control has become a hot topic in the environmental management of tailings storage facilities. Using the response variables of wind erosion resistance and penetration resistance, the experimental variables of the solution concentration, spray amount, and external air speed, laboratory tests were conducted to investigate the effects of conventional halides and polymer materials on dust control. The results indicate that the wind erosion resistance and penetration resistance of the crust can be improved with increase in the concentration of the dust-depressor and the amount of spray used. In the halide solution, CaCl2 exhibited the best dust control effect. When the wind speed is 7.5 m·s?1 and the spraying amount of CaCl2 is 4.5 L·m?2 at a concentration of 50 g·L?1, the loss quantity of tailings is 0.75 g·m?2·min?1 and the penetration resistance is 466 kPa. Among the polymer materials, polyacrylamide exhibits the best dust control effect. The loss quantity of tailings is 0.30 g·m?2·min?1 and the penetration resistance is 248 kPa when the wind speed is 7.5 m·s?1 and the spraying amount of polyacrylamide is 4.5 L·m?2 at a concentration of 0.5 g·L?1. This paper emphasizes that the selection of dust-depressor can be determined based on the local annual mean wind speed, whereby polyacrylamide should be selected as the dust suppressant for a tailings pond when the annual mean wind speed is high. Otherwise, CaCl2 should be selected as the dust-depressor for a tailings pond.
Abstract: Bioleaching technology, a method used in mining, utilizes organisms or microorganisms to dissolve and leach useful components from ore. This technology is applied widely in many countries in mining and production of various metals. Although considerable economic benefits have been obtained with the help of bioleaching technology, this technology faces many challenges. For example, as the leaching process progresses, the permeability of the ore heap is worsened from the presence of fine particles and muddy ore. As such, improving heap permeability is a key focus in the field of leaching mining technology. Agglomeration technology, an effective method for improving the permeability of ore heaps, involves crushing the ore and agglomerating it with binders before leaching, which alters the structure of the ore, especially ore powder. The resulting granular structure provides space for the flow of the solution and greatly improves the permeability of the leaching system. The pore structure is constantly changing as the leaching process progresses, which affects the seepage of the solution and even the effect of leaching the ore. In this study, leaching tests were conducted using single-ore granulation of secondary copper sulfide ore powder, binders, and NaCl. Changes in the pore structure during leaching were investigated using X-ray computerized tomography, digital image processing, and three-dimensional reconstruction methods. In addition, COMSOL Multiphysics simulation software was used to construct a simulation model of the flow of the solution in the pore channels. The results reveal that the number, average volume, average surface area, and average equivalent diameter of pores inside the granulated ore increase respectively by 99%, 151%, 223%, and 90%. In addition, the porosity increases fourfold and the pore connectivity nearly triples. The flow velocity and pressure of the solution was found to increase sharply as the solution flows through the narrow and bottom areas of the pore channels, which has a great impact on the stability of the ore granulation structure.
Abstract: It is a global fact that the mineral ores degrade to the poor grade status and the various properties of ores are adversely altered such as fine dissemination and complex composition due to the continuous exploitation and utilization of phosphate rock resources. Consequently, separation of minerals has become a difficult and daunting task. The automatic mineral identification and characterization system (AMICS) is mostly used only for mineral characterization. There is no much research and literature on process mineralogy that integrates research parameters with flotation test results to quantitatively explore the mechanism of difficulties or problems faced during mineral separation. In this paper, to further explore and analyze the specific reasons for difficult problems faced while separating collophanite, a systematic in-depth mineralogical analysis based on the chemical analyses, X-ray diffraction, and AMICS has been performed on a refractory collophane flotation feed sample from Yunnan, China. The results show that the phosphorus in the sample mainly exists in the form of fluorapatite and also present in the gangue minerals, which are primarily dolomite and quartz. Fluorapatite has a fine dissemination particle size, which is in the range of 10–75 μm with a degree of mineral liberation 59.17%. Apart from existing in the form of liberated particles, fluorapatite is also present in dolomite and quartz as a composite particle and the mass fraction of composition in dolomite and quartz is found to be 26.23% and 9.92%, respectively. Further, dolomite and quartz relatively have a low degree of mineral liberation with the liberation degree of 46.82% and 39.10%, respectively. The closed-circuit flotation test was carried out with a rougher flotation to remove magnesium. Further a roughing and two stages of scavenging is performed which obtained the flotation performance of concentrate P2O5 grade of 29.75%, P2O5 recovery of 81.95%, and SiO2 grade of 12.63%. When the results were studied together with the mineralogical analysis results, it is found that the fine dissemination particle size of collophanite, the poor degree of mineral liberation, and the serious slime generation are the main causes for not able to achieving a better performance in separation of minerals.
Abstract: To study the corrosion law and life distribution of reinforced concrete in a coupled salt environment, the reinforced concrete specimens were placed in 0.32 mol·L?1 NaCl and 0.4 mol·L?1 MgSO4 salt solutions. The performance of reinforced concrete was tested regularly using an electrochemical workstation. The durability was analyzed through a polarization curve, an AC impedance spectrum, and electrochemical parameters. A three-parameter Weibull distribution was selected for reliability modeling, and a prior false test was performed by the Anderson-Darling (A-D) method. The parameters were estimated by the correlation coefficient optimization method (CCOM), maximum likelihood method (MLM), and moment estimation method (MEM). The reliability curve, density curve, and failure rate curve were each used to analyze the life of reinforced concrete in chloride, sulfate, and magnesium-based corrosion environments. Results show that under the combined action of corrosion ions, the polarization curve gradually moves toward increasing corrosion current density and negative potential, and the AC impedance spectrum moves to the left and shrinks to the real part of the impedance. The resistance of steel bar corrosion gradually decreases whereas the probability gradually increases. The reliability curve is unchanged at the initial stage and rapidly decreases at the later stage. The density curve is symmetric with a single peak, and the failure rate curve remains unchanged at the initial stage and increases linearly at the later stage. Among the three-parameter estimation methods, CCOM and MLM parameter estimation values are similar, stable, and accurate, and the obtained reliability curves are similar. It is suggested that CCOM and MLM should be used for parameter estimation and reliability analysis of small sample failure data that is obtained from an accelerated test of reinforced concrete. The reliability life of C35 reinforced concrete in magnesium sulfate and sodium chloride corrosion environments is about 760 d.
Abstract: Currently in China, the waste acid generated from large-scale smelting plants is treated as “wastewater with high concentration of heavy metals”, which leads to high cost and many wastewater treatment residues (hazardous wastes). In this paper, based on the main components of waste acid and zinc oxide dust, the adoption of a cyclic leaching process was proposed, in which zinc oxide dust is leached by waste acid, thus enabling the recovery of copper (Cu) and zinc (Zn) from the circulating leaching solution and the central treatment of arsenic (As). The main factors affecting the first and second cyclic leaching processes were investigated, including the final pH, leaching temperature, and leaching time. After leaching was completed, several factors in the first and second As removal processes were investigated, including the H2O2 dosage, Na2S dosage, removal temperature, and removal time. The following optimal conditions were identified: the optimal final pH, leaching temperature, and leaching time for the first leaching are 1.5, 85 ℃, and 5 h, respectively. The optimal final pH and leaching temperature for the second leaching are 4 and 85 ℃, respectively. The optimal H2O2 dosage, removal temperature, and removal time for the first As removal are 0.067 mL per 1 mL of the secondary circulation leaching solution, 40 ℃, and 1.5 h, respectively. The optimal Na2S dosage for the second arsenic removal is 0.02 mL per 1 mL of the second circulation leaching solution, and the removal temperature and removal time were determined to be 35 ℃ and 2 h, respectively. Under these conditions, the concentrations of As, Cu, and Zn can be reduced to 3.26, 2.63, and 50.63 mg·L?1, respectively. The pH of the wastewater after processing was neutral, which meets the integrated wastewater discharge standard with minor treatment. In this way, valuable components in the waste acid can be comprehensively recovered, and the harmful element As centrally treated, thus reducing the production of hazardous wastes, saving energy, and reducing emissions.
Abstract: Mold flux plays a significant role in the continuous casting of steel. Especially, the viscosity (or its inverse, fluidity) of mold flux is a key parameter for industrial applications to aid in product quality. In this paper, viscosities of different types of fluorine-containing continuous casting mold fluxes were first measured by the rotating cylinder method, and then a new viscosity estimation model was established based on the Arrhenius equation combined with nonlinear regression analysis to analyze the influence of component changes on the viscosity. Combining model calculation and experimental measurement, an iso-viscosity diagram of the CaF2–Na2O–Al2O3–CaO–SiO2–MgO slag system was also created. It is found that deviation within 10% is calculated using the model in this study compared with the traditional viscosity estimation models of different types of fluorine-containing continuous casting mold fluxes but gradually increases when the w(CaF2) of slag exceeds 20%, mainly due to the change of slag composition caused by fluoride volatilization. Finally, the measured value cannot correspond to the composition of the initial slag, and the model cannot give an accurate estimated value. It is also found that an increase of CaF2 can significantly reduce viscosity, whereas, the effect of Al2O3 and Na2O on viscosity is restricted by CaF2 content. When w(CaF2) > 17%, the viscosity of slag decreases with increasing w(Al2O3), and when w(CaF2) < 17%, the viscosity of slag increases significantly with increasing w(Al2O3). When w(CaF2) > 11.5%, the viscosity of the slag system decreases significantly with increasing w(Na2O) mass. When w(CaF2) < 11.5%, the effect of Na2O on viscosity is not obvious. In addition, the diagram shows that the mass fraction of CaF2 in the low viscosity area is nearly 14%. This shows that the viscosity and fluidity of mold flux can be improved by adjusting the component ratio in this iso-viscosity diagram for applications in the steel industry.
Abstract: It is an important symbol of the metallurgical quality level of special steel for inclusion controlling, which can improve the service performance of special steel to a greater extent. As a typical steel grade, gear steel, in the special steel field, is also required strictly in controlling of inclusions. It is known that total oxygen content can reflect the level of inclusions to some extent. Since the 1980s, ultralow oxygen has become a direction for the development of special steel. To guarantee controlling of nonmetallic inclusions and determine a reasonable control target of total oxygen content in the gear steel, the effect of total oxygen content on nonmetallic inclusions in gear steel was studied. In this study, three kinds of Mn–Cr-system gear steels with different oxygen content were selected as research objects. The number, distribution, and size of nonmetallic inclusions in these gear steels were studied using an Aspex scanning electron microscope (Aspex SEM), the extreme value method, and fatigue test. The relationship between inclusions and the total oxygen content of gear steel was obtained. Under the experimental condition, with the decrease in total oxygen content, the density of the number of oxide inclusions decreases continuously, among which 5–10 μm small inclusions decrease most obviously. In contrast, the number density of large inclusions above 10 μm does not change obviously. Moreover, the results of the extreme value method and fatigue test show that when total oxygen mass fraction is high (0.0013%), the size of maximum oxide inclusion in the steel is relatively large, which is more than 10 μm higher than the inclusion in 0.0010% or 0.0005% total oxygen steel. Simultaneously, when total oxygen mass fraction is low (≤0.0010%), the change of total oxygen mass fraction (0.0010% and 0.0005%) has little effect on the maximum inclusion size in steel.
Abstract: Magnesium and its alloys have attracted extensive attention due to their favorable mechanical properties, such as low density and high specific strength. The detwinning process of {$10\bar 12$} tensile twins subjected to periodic loading is one of the microscopic mechanisms of fatigue damage in magnesium and its alloys. Moreover, self-interstitial atoms (SIAs) widely exist as a typical kind of point defects in metals. The migration, aggregation, and interaction with other defects, of SIAs affect the metal mechanical properties. In this work, molecular dynamics simulation was employed to study the detwinning process of {$10\bar 12$} twins under shear loads in magnesium, focusing on the interaction between the twin boundary and SIAs in the detwinning process. A simulation system containing two coherent twin boundaries (CTBs) with periodic boundary conditions applied along the two in-plane directions was adopted. The classic embedded atom method (EAM) interatomic potential developed by Liu et. al was used for simulation accuracy and comparison with other studies. The simulation results show that the SIAs are absorbed by the CTBs and migrate along with them. The absorbed SIAs can be released with the disappearance of the CTBs during the detwinning process. By the SIA adsorption and release, detwinning process will result in a more concentrated SIA distribution. The simulation results reveal that SIAs will be adsorbed by CTB if the distance between the CTB and SIA is less than 0.752 nm at 0 K and 3.59 nm at 273 K. The energy barrier of the adsorption process is also obtained using the nudged elastic band (NEB) method. The SIA spatial distribution changes after the SIA interactions with CTB in detwinning process. Given that the crystal defects such as dislocation loops can be induced by the dense distribution of SIAs at a long timescale, this study clarifies the fatigue mechanical properties of magnesium and magnesium alloys subjected to periodic loading.
Abstract: Pollution from waste plastics has become one of today’s most serious environmental problems, and the recycling of waste plastics is a research hotspot. High-water materials are widely used in mine-filling operations, leak prevention, flame-retardant fire extinguishers, and other related applications due to their advantages of not blocking pipes, ease of pumping, high early strength, and environmental friendliness. These materials are also commonly referred to as high-water quick-setting materials and high-water filling materials. Despite their advantages, high-water materials also have some shortcomings in practical applications such as the need for a large volume of materials and their high engineering costs. Currently, research on waste-doped modified high-water materials has become an important focus in the development of high-water materials. Using this approach, waste can be treated effectively at a reduced cost by the appropriate replacement of materials. The high-water filling material modified with polyethylene plastic (PE) was used as a carrier. The compressive and shear strengths of the modified materials were determined, and the results were compared and analyzed. The results reveal that with increases in the PE powder content, the compressive and shear strengths of the modified high-water material exhibit a decreasing trend. The stress–strain curves of the modified high-water material obviously differ from those of unmodified high-water material. The residual strength of the unmodified material is higher, that of the modified high-water material is generally low, and no shear displacement curve is evident. The addition of PE powder obviously changes the morphology and microstructure of the material. With increasing PE content, the material gradually changes from having a fiber network structure to a flocculated block structure, in which the formation of larger through holes easily occurs between the products. The shear strength of the modified high-water material is significantly lower than the compressive strength, which indicates that the modified high-water filling is not suitable for coal seams with a large inclination.
Abstract: Macrosegregation forms due to relative motion between liquid and solid phases on the macro scale during solidification. As macrosegregation is formed during a solidification process, it is difficult to remove it in the subsequent rolling and heat treatment processes, thereby deteriorating the mechanical properties and stability of products. Studies of macrosegregation of billets for industrial trials have become a challenge due to the high temperature of the casting process. To improve macrosegregation of billet, a moving slice model was developed using the ProCAST software based on a continuous casting process of gear steel billet in a domestic steel mill. During the continuous casting process, macrosegregation can be calculated using the above model. The effects of superheat, secondary cooling water flows, and casting speed on macrosegregation were simulated. These results were consistent with the measured outcomes of carbon macrosegregation, validating the moving slice model to calculate the macrosegregation of billet. The solute concentration on the loose side is higher than that on the fixed side due to solute buoyancy. The degree of carbon segregation in the billet center increases from 1.06 to 1.15, with an increase in superheat, which should be controlled below 25 ℃ to ensure the degree of carbon segregation within 1.10. However, the degree of carbon segregation in the billet center decreases from 1.16 to 1.13, with an increase of secondary cooling water flow and a little improvement in central segregation. With an increase in casting speed, the central segregation becomes serious, and the degree of carbon segregation in the billet center increases from 1.14 to 1.21. However, when the casting speed is lower than 1.4 m·min?1, the degree of carbon segregation in the billet center comes lower than 1.15.
Abstract: The hot metal temperature is a key process parameter for blast furnace (BF) ironmaking that reflects the quality of hot metal, the thermal state of BF hearth, the energy utilization efficiency of BF, and many other information. Prediction of the hot metal temperature in the next smelting cycle will be helpful in gaining a better understanding of the change trend of hot metal quality and BF smelting status in time. With this, corresponding operational measures can be conducted to maintain the BF stable and smooth state, high production, and low consumption. Nowadays, big data technology has made considerable progress toward a more accurate and faster collection, storage, transmission, query, analysis, and integration of mass data, providing a good data foundation for data-driven machine learning models. In addition, with the substantial increase in computer calculation speed and the significant development of algorithms, the prediction accuracy of deep machine learning models has noticeably improved. The development of these technologies provides feasibility for the prediction of important indicators under complex industrial conditions. Based on the data produced from a 4000-m3 BF in a large span time range (2014–2019) and daily time dimension, this paper considered hot metal temperature as the objective function. First, the characteristic parameters of hot metal temperature were processed by linear and nonlinear correlation analysis, feature selection, and normalization methods. Then, the positive and negative correlation characteristic parameters that have a significant influence on the temperature of the hot metal were obtained. Finally, prediction models of hot metal temperature were established based on two algorithms of support vector regression and extreme learning machine. Although both the algorithms can achieve effective prediction, results from support vector regression are better at an average absolute error of 4.33 °C and a hit rate of 94.0% (±10 °C).
Abstract: High energy consumption and low energy efficiency are problems that have plagued vessels in operation for many years. Traditional technologies such as thermoelectric generator (TEG) and organic Rankine cycle (ORC) are difficult to take into account the different characteristics to various waste heat of vessels. Simultaneously, the utilization rate of vessel waste heat is relatively low. To achieve the purpose of various types of waste heat from vessels, this study presents a vessel waste heat cascade utilization device system, which is based on the TEG-ORC combined cycle. The effects of the ORC evaporation pressure on the performance of the system were analyzed, which includes the combined cycle system output power, system thermal efficiency, multi-stage waste heat utilization and power generation cost of the system. The results show that the TEG-ORC combined cycle system improves the waste heat utilization performance and the combined cycle enables the optimization of power generation cost and system thermal efficiency. Based on the condition that the TEG-ORC basic cycle ratio of 0.615, the utilization rate of flue gas waste heat generated by the main engine, fluctuates in a small interval with the increase of ORC evaporation pressure. The waste heat utilization power of each unit, output power and thermal efficiency of the system enhance with the increase in the ORC evaporation pressure. At the same time, the unit power generation cost of the system decreases with the increase in the ORC evaporation pressure. When the ORC evaporation pressure reaches 0.9 MPa, the waste heat utilization rate of the flue gas generated by the main engine is 62.15%, the waste heat utilization power of the system is 1919.68 W, the output power of the system is 139.22 W, the thermal efficiency of the system is 7.25%, and the cost of system unit power generation is 3.09 ￥·(kW·h)–1.
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
