Abstract: The preparation of high-quality iron concentrate from pyrite cinder by means of desulphurization has potential industrial applications. On one hand, the comprehensive utilization of pyrite cinder can be achieved, while on the other hand, the environmental problems that it causes can be solved effectively. In this study, the desulfurization technology and its process flowsheet, as well as recent advances, were summarized in detail. There are mainly three desulfurization methods, namely, chemical leaching, combined process, and bioleaching method. Chemical leaching mainly involves the acid leaching and alkali leaching processes. The combined process contains the alkali-acid leaching process, flotation-magnetic separation, gravity separation-flotation, magnetic roasting-magnetic separation, etc. The technical features of these methods were introduced, and it is concluded that bioleaching has a potential application value. The research areas of bioleaching method in a future will be included as:the breeding of effective desulfurization bacteria, cyclic utilization of desulfurization water, synergistic recovery of valuable metals, and basic investigation and engineering technology research in the bioleaching desulfurization process.
Abstract: The cemented backfill body with sulphide-containing tailings exhibits a swelling phenomenon with an extension of curing age. The test results from the uniaxial compressive strength test of the backfill specimen with an obvious fracture are very discrete, and the mechanical parameters of the filling body will not be obtained effectively. The fractured surface image of the backfill were binarized by the digital image processing technology. Additionally, its fractal dimension was calculated and analyzed. Then, the relationship between fractal dimension and uniaxial compressive strength was established. The results indicate that the cracks on the surface of the backfill specimen exhibite self-similarity. The fractal dimension increases with the development of surface cracks. There is a negative correlation between fractal dimension and uniaxial compressive strength for the sulphide-containing backfill. It is of practical significance to determine the research value of the compression test using the fractal dimension. When the fractal dimension of the surface cracks is less than a certain threshold, the results of the specimen strength tests would be reliable.
Abstract: Horizontal spray tower technology is a new flue gas desulfurization system technology that was developed at the University of Science and Technology Beijing, Center for the Environment, overcoming the shortcomings of the vertical spray tower with regard to high desulfurization efficiency, small pressure loss, low operation cost, and easy maintenance, among others. However, the actual project still requires further improvement. In order to study the influence of the layout pattern of different spray on the internal flow field of the horizontal spray tower, the physical model of the horizontal spray tower was built, the grid was divided by Icem software, the Fluent software was used to simulate the numerical simulation. K-epsilon turbulence and stochastic models were selected for numerical simulation. The simulation results, obtained by the SIMPLE algorithm, show that the double spray sets the spray cone angle at 90°, the upper spray height is at 0.9 m from the top, the lower part of the spraying height is at 2.4 m from the top layer, the spray distance is 1.5 m, the desulfurization tower effectively reduces the pressure loss and energy consumption, the absorption area of the flue gas flow rate is uniform, and the gas-liquid contact frequency increases. The gas temperature is suitable for a gas-liquid reaction. The overall increase in the efficiency of flue gas desulphurization provides guidance for the design of practical engineering applications.
Abstract: Thus far, a lot of concrete structures have been aging owing to the rapid development of highways, railways, and the construction industry in China. Concrete structure diseases, such as concrete surface cracks and erosion, require serious consideration due to the effect of long-term use and environmental impact. Some man-made factors have exacerbated these problems, such as insufficient operating level and corners, among others. This has obscured safety risks associated with these concrete structures. However, not all of these structures could not be decommissioned to reduce the negative social and economic impact and to ensure the safety of buildings; therefore, a reasonable approach was to repair and reinforce the old concrete structures. Additionally, in the process of maintenance and reinforcement, planting bars between the new and old concrete must be considered, and especially the corroded planting bar from an aged project that has been terminated. Many studies for the bonding performance of new and old concrete have been conducted by the experts and scholars at home and abroad; thereby, some results have been achieved. Only a few scholars have investigated the bonding performance between new and old concrete with planting bars and especially corroded planting bars from old reconstruction projects that have been terminated. Therefore, investigating the shear performance of new and old concrete with corroded planting bars was of utmost importance. To study the mechanical properties of the interface between new and old concrete with corroded planting bars, the new and old concrete specimens with different planting bar ratios (0%, 0.223%, 0.446%, 0.502%, 0.893%, 1.004%, 1.396%,1.786%, and 2.792%) were prepared based on the corroded planting bars. These corroded planting bars came from the tunnel lining structure of a project that had been terminated for over five years. Shear tests were conducted for new and old concrete under different initial static pressures (0-4 MPa) in an RYL-600 microcomputer control servo rock shear rheometer. The evolution law of the deformation and destruction of new and old concrete specimens under the action of external forces was obtained through summarizing the shear stresses and displacement curves of the specimens. The law of shear strength along with the variation of the steel planting ratio, as well as the initial pressure, were acquired by analyzing the shear strength of the new and old concrete interface with corroded planting bars. Moreover, the influence of different planting bar ratios and the initial pressure on the failure mode of concrete specimens was analyzed emphatically based on specimen failure results. The test results provided the theoretical basis for investigating the mechanical performance of new and old concrete.
Abstract: The turnover time for transporting a hot metal from a blast furnace to a basic oxygen furnace is long and therefore the heat preservation effects are not ideal. These factors affect the temperature and thermal state of the ladle refractories, which leads to the heat loss of the hot metal. Reducing the temperature drop of the hot metal can effectively prevent the hot metal nodules and decrease the frequency of offline baking; moreover, it indirectly increases the turnover rate of the hot metal ladle. At the same time, a hot metal with low temperature seriously affects the addition amount of scrap steel and oxygen blowing operations during the smelting process in the converter. Therefore, it can be observed that controlling the hot metal temperature is one of the key factors for energy saving and efficient production in a steel plant. To reduce the temperature drop of a hot metal, a variety of computation models of ladles with several insulation measures were established. In addition, the Ansys fluent software was used to simulate the temperature fields after the end of the charging. The influence of thermal states of ladles with different insulation measures and unloaded time on the temperature drop of the hot metal was investigated. The analysis shows that reducing the unloaded time from 5 h to 3 h can decrease the temperature loss of the hot metal by 2.2 K·h-1. Using a ladle with an insulation layer of about 6 mm and an insulation cap is the most sensible measure to realize insulation. It can increase the average temperature of a working layer by almost 155 K, and this improvement can reduce the temperature loss of hot metal by 3.4-3.7 K·h-1 during the 3 to 5 h unloaded time. The conclusions provide some academic bases and references for the reasonable insulation measures and control of the unloaded time of a multifunctional hot metal ladle.
Abstract: Iron is one of the major impurity elements in industrially produced crude tin, and it is always removed first during the refining process. In this study, the super gravity field was introduced in the crude tin refining process in order to investigate the directional enriching and separating laws of iron impurity from Sn-3% Fe melt, and thereby purify the crude tin. The experimental results showed that with the gravity coefficient G=500 at a cooling rate of ν=10℃·min-1, all of the iron-rich phase gathered at the bottom area of the sample; it was hard to find any iron-rich phase particles at the upper area of the sample since super gravity greatly increased the sedimentation of the iron-rich phase in the crude tin melt. The mass percentage of iron in the tailing tin was up to 4.817%, while that in the refined tin was only 0.036%. Consequently, the removal rate of iron was up to 98.78%. The iron-rich phase impurity could be separated effectively from the Sn-3% Fe melt using filtration method in the super gravity field, and the recovery rate of the refined tin increased with increase in gravity coefficient in the range of G > 30. After filtration at 240℃ by gravity coefficient G=100 for 1 min, the refined tin was separated to the bottom of the crucible, and the iron-rich dross was intercepted by the carbon fiber felt. The mass percentage of iron in the refined tin was only 0.253%, while that in the iron-rich dross reached 11.528%. As a result, the removal rate of iron was up to 91.44%, while the recovery rate of the refined tin was as high as 82.69%.
Abstract: Sodium oxalate has negative effects on alumina produced by the Bayer process. The behavior of sodium oxalate in the seeded precipitation process of a sodium aluminate solution was investigated. The particle size and morphology of crystallization, as well as the crystal habit of sodium oxalate, and the interaction between sodium oxalate and gibbsite in synthetic or industrial sodium aluminate solutions were also investigated. The results show that sodium oxalate precipitates on the surface or gibbsite clearance, such that the secondary nucleation of gibbsite increases, and the agglomeration of gibbsite is seriously hindered. This is considered as the main cause of gibbsite refinement.
Abstract: During tensile and temperature tests, the latent heat of hot-rolled TRIP steel was dynamically investigated by observing the stress-strain and thermal curves. The results indicated that during the tensile test, the hot-rolled TRIP steel increased the thermal energy, which originated from the partial transformation of plastic work and martensitic transformation. Therefore, the actual heat of the measured sample was higher than that converted by plastic work. During the low speed tensile test, the thermal energy of the TRIP steel was supplemented by the average integrated heat loss coefficient. Through calculation and deduction, it was confirmed that a certain amount of the unstable residual austenite first became martensite, when the plastic deformation had just begun. As the strain increased further, the amount of the remaining, stable, retained austenite that would become martensite, decreased gradually according to its stability. Most of the retained austenite had almost become martensite before the end of the uniform elongation. During the deformation process of the hot rolled TRIP steel, the martensitic transformation could be dynamically described by the change of latent heat.
Abstract: With the increasing speed of high-speed trains, the brake disc heat load has also been increasing, particularly during emergency braking. Therefore, to address such issues, strict requirements for brake disc materials are suggested. Thus, the addition of V was implemented to improve the mechanical properties and thermal fatigue performance of brake disc steel. The effect of V on the microstructure and mechanical properties of Cr-Mo-V steel for brake discs at different quenching temperatures was investigated. The precipitation behavior of carbides at different V levels was also investigated through thermodynamics calculation using the Thermo-Calc software, carbon replica, transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The results indicate that the amount of V(C, N), which precipitates at high temperatures, increases; therefore, the austenite grains and martensite packets are refined. The precipitates in the tested steels after being quenched and tempered are mainly V(C, N),(Mo,V) C, M7C3, and M23C6. With an increase in V content, the precipitation of large size carbides, such as M23C6 and M7C3, is suppressed; therefore, its negative effect on toughness is reduced. With the increase in the amount of small-size (Mo,V) C, the precipitation strengthening effect is enhanced. When the quenching temperature is in the range of 880-900℃, the increments of vanadium content could refine martensite and reduce the content of large size carbides, which negatively affect toughness. Therefore, the impact energy changes little. When the quenching temperature is in the range of 920-940℃, increasing the vanadium content results in a significant increase in the (Mo, V) C content; therefore, the impact energy drops rapidly. Thus, it is concluded that the quenching temperature of tested steel should not exceed 900℃.
Abstract: In-phase (IP) and out-of-phase (OP) thermal-mechanical fatigue (TMF) tests of 4Cr5MoSiV1 hot work die steel were conducted in full reverse mechanical strain control in the temperature range of 400-700℃ by a TMF servo-hydraulic testing system (MTS®). The results indicate that, when the strain amplitude is ±0.50%, the OP TMF life of 4Cr5MoSiV1 steel is~60% of the IP TMF life. The stress-strain hysteresis loops show asymmetries for both IP and OP loading. IP loading leads to comprehensive mean stress, while OP loading gives rise to tensile mean stress in the temperature range of 400-700℃. The changes of maximum strain and peak temperature with maximum stress are inconsistent, and the stress relaxation phenomenon could be observed under IP and OP loading. Moreover, two kinds of TMF cycling exhibite continuous cyclic softening in the high temperature half stage, while in the low temperature half stage, cyclic hardening occurs initially and is then followed by continuous cyclic softening. The fractured surfaces under IP TMF loading display striation and tear ridge, and exhibits quasi-cleavage characteristics. In addition, the cracks are less but longer. However, fractured surfaces under OP TMF loading mainly display striation and dimple characteristics, and the cracks are shorter and more abundant.
Abstract: The oxidation mass increasing method was adopted to explore the oxidation behavior of high-vanadium wear-resistant alloy at 950℃. The oxidation mechanism and cracks behavior were studied with different cooling types (furnace cooling and air cooling). The results indicated that the weight increment per unit area was obviously large at the beginning of the oxidation due to the matrix being in direct contact with the air. Additionally, the oxidation increase gains of furnace and air cooling were 82.7 mg·cm-2 and 39.1 mg·cm-2, respectively, after 8 h of oxidation. At the same time, the preferential formation of Cr2O3 was observed with 50-200 nm at the matrix and oxidation layer interface. Remarkable thermal stress was produced in the oxidation layer due to the larger cooling rate. The warped phenomenon appeared at the oxidation layer due to the production of growth stress. However, the shedding phenomenon rarely occurred in the oxide layer.
Abstract: A 6005A aluminum alloy was produced by an actual surface with less defects, multiple defect samples, and as-ground samples for the purpose of investigating the effect of aluminum alloy surface damage on corrosion resistance and its corrosion electrochemical behavior in seawater. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were employed in order to characterize the surface states of the 6005A aluminum alloy. The results show that the surface defects caused by aluminum alloy products consist mainly of scratches. With the increase of surface defects, an obvious increase in Ra is observed, and Ra could quantitatively describe the severity of surface damage. In simulated seawater, the 6005A aluminum alloy undergoes comprehensive corrosion and pitting; thereby, corrosion resistance deteriorates as the amount of defects increases. Electrochemical test results show that the larger the number of surface defects is, the greater are the roughness and lower corrosion potential. Additionally, the greater the corrosion current density is, the worse is the corrosion resistance. A 6005A aluminum alloy that has suffered surface damage and whose corrosion resistance was affected due to seawater can cause the following:the more surface defects are, the greater is the roughness and surface film damage; thereby, the plastic deformation of the surface becomes more serious. The protective layer of the oxide filmis reduced, and the substrate has a higher corrosion rate. The passive film for the samples with less defects is more compact and uniform and could protect the substrate, while effectively reducing further corrosion.
Abstract: The single-phase free surface lattice Boltzmann model (LBM) was used to investigate the counter-gravity mould filling process of large plate castings. Computational efficiency can be improved by ignoring the variation of the gas lattice. In this paper, a weight coefficient redistribution method was proposed for dealing with the liquid phase discharge problem and distribution in a grid. First, the model was used to calculate the anti-gravity filling process of a large plate cavity with a single gate, with the same parameters, the water filling experiment of high speed camera is taken as a reference, the characteristics of the flow field and the fluid morphology of numerical simulation are in good agreement with the experimental results. Furthermore, the velocity profile of the flow field is used to analyze the characteristics of the flow field, and a criterion called "the altitude difference of free surface" is introduced to evaluate the stability of the fluid. Subsequently, the counter-gravity filling process of a plate with a double gate and the same plate with one gate and a cylindrical obstruction to turbulent flow are investigated. Due to the mutual influence between the two gates, the vortex formed by the double gates is greater than that formed by the single gate. However, the obstacles under the conditions of cylindrical turbulent flow obstruction could reduce the degree of fluid sloshing and improve the stability of the filling.
Abstract: To solve the material supply problem of multiple parallel assembly jobs in aircraft moving assembly line, an integrated material delivery and line-side storage decision making model and corresponding algorithm were proposed. The decisions about the storage of line-side material were introduced on the basis of the material-batching and vehicle scheduling problems. An integrated mathematical model with the objective of minimizing the number of deliveries was established and a heuristic algorithm based on the immune algorithm was proposed. A joint decision of batching, delivery time and storage position for each job's material was proposed considering delivery capability, reusing and sharing of line-side space through backward-dynamic vehicle scheduling and look-ahead storage algorithms while seeking the advantages of the immune algorithm. The results of the numerical experiments proved the validity of the model and algorithms.
Abstract: The thermal control and heat management of lithium-ion (Li-ion) batteries in high-power applications remains a challenge to be addressed before widespread commercialization. To solve the problem, micro heat pipe array (MHPA) is used to design Liion battery packs cooling system. Experiments were conducted utilizing Li-ion battery packs under open conditions with constant current of 18 A(1 C) and 36 A(2 C). The temperatures were measured with and without micro heat pipe arrays during the charge-discharge cycle. At the rates of 1 C and 2 C, the temperature results of the Li-ion battery packs validate the effectiveness of the functional heat conducting material-MHPA in lowering the temperature of the battery packs, as well as the temperature difference inside the packs, the temperature and temperature difference could be controlled within 40℃ and 5℃ respectively. Thus, they preliminarily solve the influence of temperature on battery life and capacity. Based on the experimental data, the heat in one of the 2 C working conditions was calculated, and the convection heat dissipation by MHPA reached 40% of the heat generation in the pack.
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
