In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite,the reaction control mechanism and the migration regularity of valuable components in the process of direct melting r...In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite,the reaction control mechanism and the migration regularity of valuable components in the process of direct melting reduction were investigated using kinetic empirical equation by fitting and combining with X-ray diffraction,X-ray fluorescence,scanning electron microscopy,energy-dispersive spectrometry,and optical microscopy.The results show that iron reduction is controlled by the mass transfer process of(FeOx)in the slag,while vanadium reduction is controlled by both the mass transfer of(VOx)in the slag and the mass transfer of[V]in the molten iron,and the slag–metal interfacial reaction is the only pathway for vanadium reduction.The reduction of iron and vanadium is an obvious first-order reaction,with activation energy of 101.6051 and 197.416 kJ mol^(−1),respectively.Increasing the vortex rate and reaction temperature is beneficial to improving the reaction rate and reduction efficiency.The mineral phase variation of iron and vanadium in the slag during the reduction process is Fe_(2)O_(3)→Fe_(3)O_(4)/FeV_(2)O_(4)→FeTiO_(3) and FeV_(2)O_(4)→MgV_(2)O_(5);titanium in slag is mainly in the form of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and CaTiO_(3).As the reaction time went on,the molar ratio(nTi/nMg)in Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and the Ti2O_(3) content in the slag gradually went up,while the area proportion of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)went up and then down,and the porosity of the slag and the grain size of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)got smaller.展开更多
A low-grade nickel laterite ore was reduced at different reduction temperatures. The morphology of metallic particles was investigated by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS）...A low-grade nickel laterite ore was reduced at different reduction temperatures. The morphology of metallic particles was investigated by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS）. Experimental results indicate that the metallic nickel and iron gradually assemble and grow into larger spherical particles with increasing temperature and prolonging time. After reduction, the nickel laterite ore obviously changes into two parts of Fe-Ni metallic particles and slag matrix. An obvious relationship is found between the reduction of iron magnesium olivine and its crystal chemical properties. The nickel and iron oxides are reduced to metallic by reductant, and the lattice of olivine is destroyed. The entire reduction process is comprised of oxide reduction and metallic phase growth.展开更多
Bionic non-smooth surfaces （BNSS） can reduce drag. Much attention has been paid to the mechanism of shear stress reduction by riblets. The mechanism of pressure force reduction by bionic non-smooth surfaces on bodie...Bionic non-smooth surfaces （BNSS） can reduce drag. Much attention has been paid to the mechanism of shear stress reduction by riblets. The mechanism of pressure force reduction by bionic non-smooth surfaces on bodies of revolution has not been well investigated. In this work CFD simulation has revealed the mechanism of drag reduction by BNSS, which may work in three ways. First, BNSS on bodies of revolution may lower the surface velocity of the medium, which prevents the sudden speed up of air on the cross section. So the bottom pressure of the model would not be disturbed sharply, resulting in less energy loss and drag reduction. Second, the magnitude of vorticity induced by the bionic model becomes smaller because, due to the sculpturing, the growth of tiny air bubbles is avoided. Thus the large moment of inertia induced by large air bubble is reduced. The reduction of the vorticity could reduce the dissipation of the eddy. So the pressure force could also be reduced. Third, the thickness of the momentum layer on the model becomes less which, according to the relationship between the drag coefficient and the momentum thickness, reduces drag.展开更多
The reduction of the nitrobenzene compounds （NBCs） by the catalyzed Fe-Cu process and the relationship between the electrochemical reduction characteristics of NBCs at copper electrode and reduction rate were studie...The reduction of the nitrobenzene compounds （NBCs） by the catalyzed Fe-Cu process and the relationship between the electrochemical reduction characteristics of NBCs at copper electrode and reduction rate were studied in alkaline medium（pH=11）. The catalyzed Fe-Cu process was found more effective on degradation of NBCs compared to Master Builder＇s iron. The reduction rate by the catalyzed Fe-Cu process decreased in the following order： nitrobenzene 〉4-chloro-nitrobenzene ≥m-dinitrobenzene ：〉 4-nitrophenol ≥2,4-dinitrotoluene 〉2-nitrophenol. The reduction rate by Master Builder＇s iron decreased in the following order： m-dinitrobenzene ≥4-chloro-nitrobenzene 〉4-nitrophenol 〉2,4-dinitrotoluene ≈nitrobenzene 〉2-nitrophenol. NBCs were reduced directly on the surface of copper rather than by the hydrogen produced at cathode in the catalyzed Fe-Cu process. The reduction was realized by the hydrogen produced at cathode and Fe（OH）2 in Master Builder＇s iron, It is an essential difference in reaction mechanisms between these two technologies. For this reason, the reduction by the catalyzed Fe-Cu depended greatly on NBC＇s electron withdrawing ability.展开更多
To achieve the high-efficiency utilization of vanadium-titanium magnetite（ VTM）,reduction experiments were conducted to determine the carbothermic reduction mechanism of VTM. Effects of volatile matter,temperature,t...To achieve the high-efficiency utilization of vanadium-titanium magnetite（ VTM）,reduction experiments were conducted to determine the carbothermic reduction mechanism of VTM. Effects of volatile matter,temperature,time,and carbon ratio（ molar ratio of fixed carbon in coal to oxygen in iron oxides of VTM） on reduction degree were investigated.Results show that reduction degree increases with increasing volatile matter in coal,temperature,time,and carbon ratio.Phase transformation,microstructure,and reduction path were analyzed by X-ray diffraction,scanning electron microscopy,energy-dispersive X-ray spectroscopy,and Fact Sage 6. 0. The thermoravimetry-differential scanning calorimetry-quadrupole mass spectrometer method was used for kinetic analysis of the main reduction process. Results indicate that the kinetic mechanism follows the principle of random nucleation and growth（ n = 4）,and the activation energy values at 600-900 and 900-1 350 ℃ are 88. 7 and 295. 5 kJ / mol,respectively.展开更多
Cr(Ⅵ) is a common heavy metal ion, which will seriously harm human body and environment.Therefore, the removal of Cr(Ⅵ) has become an attractive topic.In this work, cinder was used as a raw material to synthesize a ...Cr(Ⅵ) is a common heavy metal ion, which will seriously harm human body and environment.Therefore, the removal of Cr(Ⅵ) has become an attractive topic.In this work, cinder was used as a raw material to synthesize a nanoneedle material: γ-(AlOOH@FeOOH)(γ-Al@Fe).The physicochemical properties of γ-Al@Fe were thoroughly characterized, and its effectiveness as a catalyst for photocatalytic reduction of Cr(Ⅵ) was evaluated.The results showed that Cr(Ⅵ) could be efficiently reduced by γ-Al@Fe in the presence of tartaric acid(TA) under visible light.The variable factors on the reaction were investigated in detail, and the results showed that under optimal conditions(γ-Al@Fe 0.4 g/L, TA 0.6 g/L, pH 2), Cr(Ⅵ)was completely reduced within 7 min.Besides, scavenger experiments and EPR proved that O_(2)^(·-) and CO_(2)^(·-) played a significant role in the photocatalytic reduction of Cr(Ⅵ).TA acts as a sacrificial agent to trap the holes and generate strong reducing free radicals: CO_(2)^(·-).Dissolving O_(2) could react with electrons to generate O_(2)^(·-).This work discussed the performance and mechanism of photocatalytic reduction of Cr(Ⅵ) in detail, which provided a new idea for the resource utilization of solid waste and the treatment of heavy metal sewage.展开更多
The reduction of high-chromium vanadium–titanium magnetite as a typical titanomagnetite containing 0.95wt% V2O5 and 0.61wt% Cr2O3 by H2–CO–CO2 gas mixtures was investigated from 1223 to 1373 K. Both the reduction d...The reduction of high-chromium vanadium–titanium magnetite as a typical titanomagnetite containing 0.95wt% V2O5 and 0.61wt% Cr2O3 by H2–CO–CO2 gas mixtures was investigated from 1223 to 1373 K. Both the reduction degree and reduction rate increase with increasing temperature and increasing hydrogen content. At a temperature of 1373 K, an H2/CO ratio of 5/2 by volume, and a reduction time of 40 min, the degree of reduction reaches 95%. The phase transformation during reduction is hypothesized to proceed as follows： Fe2O3 → Fe3O4 → FeO → Fe; Fe9 TiO 15 ＋ Fe2Ti3O9 → Fe2.75Ti0.25O4 → FeT iO 3 → TiO 2;（Cr0.15V0.85）2O3 → Fe2VO4; and Cr1.3Fe0.7O3 → FeC r2O4. The reduction is controlled by the mixed internal diffusion and interfacial reaction at the initial stage; however, the interfacial reaction is dominant. As the reduction proceeds, the internal diffusion becomes the controlling step.展开更多
The electrochemical behavior of Sc^(3+) in LiF-NaF system was investigated. The cyclic voltammetry and chronopotentiometry were used to investigate the reduction mechanism of the electrochemical deposition of Sc^(3+) ...The electrochemical behavior of Sc^(3+) in LiF-NaF system was investigated. The cyclic voltammetry and chronopotentiometry were used to investigate the reduction mechanism of the electrochemical deposition of Sc^(3+) to Sc on Ag electrode in LiF-NaF system at 1043 K. Experimental results indicate that the electroreduction of Sc^(3+) to Sc is a reversible process with simple 3-electron transfer in one step controlled by diffusion.展开更多
High-quality upgraded titanium slag obtained through semi-molten reduction with the addition of Na_(2)CO_(3)is important for the fluidizing chlorination process to produce TiO_(2)pigments.The key is the effect of Na_(...High-quality upgraded titanium slag obtained through semi-molten reduction with the addition of Na_(2)CO_(3)is important for the fluidizing chlorination process to produce TiO_(2)pigments.The key is the effect of Na_(2)CO_(3)on the reduction behavior of iron.Therefore,the effects of Na_(2)CO_(3)on reduction mechanism and kinetics of iron during deep reduction of ilmenite concentrate were studied.The results indicated that the metallization ratio of the reduced sample increased with increasing temperature,time,and dose of Na_(2)CO_(3).The addition of Na_(2)CO_(3)significantly accelerated the reduction of iron in the ilmenite concentrate and promoted the growth of iron particles.However,the addition of Na_(2)CO_(3)produced sodium iron titanates;thus,the metallization ratio of the sample decreased with an increase in the temperature and time when the temperature was above 1200℃and the time was more than 30 min.When the doses of Na_(2)CO_(3)were 0,3,and 6 wt.%,the reduction of iron was controlled by the interfacial chemical reaction,both the interfacial chemical reaction and diffusion,and diffusion,respectively,and the apparent activation energies were 134.91,64.89,and 120.82 kJ/mol,respectively.展开更多
The issue of low-frequency structural noise radiated from high-speed railway(HSR) box-girder bridges(BGBs) is a significant challenge worldwide. Although it is known that vibrations in BGBs caused by moving trains can...The issue of low-frequency structural noise radiated from high-speed railway(HSR) box-girder bridges(BGBs) is a significant challenge worldwide. Although it is known that vibrations in BGBs caused by moving trains can be reduced by installing multiple tuned mass dampers(MTMDs) on the top plate, there is limited research on the noise reduction achieved by this method. This study aims to investigate the noise reduction mechanism of BGBs installed with MTMDs on the top plate. A sound radiation prediction model for the BGB installed with MTMDs is developed, based on the vehicle–track–bridge coupled dynamics and acoustics boundary element method. After being verified by field tested results, the prediction model is employed to study the reduction of vibration and noise of BGBs caused by the MTMDs. It is found that installing MTMDs on top plate can significantly affect the vibration distribution and sound radiation law of BGBs. However, its impact on the sound radiation caused by vibrations dominated by the global modes of BGBs is minimal. The noise reduction achieved by MTMDs is mainly through changing the acoustic radiation contributions of each plate of the bridge. In the lower frequency range, the noise reduction of BGB caused by MTMDs can be more effective if the installation of MTMDs can modify the vibration frequency and distribution of the BGB to avoid the influence of small vibrations and disperse the sound radiation from each plate.展开更多
Three-year investigation was conducted to demonstrate the mechanism of reduction of soybean yield aroused by continuous and every second year cropping. Compared to normal cropping, there are many unfavorable changes i...Three-year investigation was conducted to demonstrate the mechanism of reduction of soybean yield aroused by continuous and every second year cropping. Compared to normal cropping, there are many unfavorable changes in some major elements of soybean plant and soil environment. Chloropyll content was lower. Phosphorous content of soybean plant was decreased seriously. Potassium content was lower while calcium content was higher. Magnesium content was wot affected and decreased in susceptive varieties. Some deseases and insects of soybean under continuous and wery second year cropping conditions became serious as continuous years prolonged. Organic matter content tended to go down from normal rotation to continuous cropping. Amount of bacteria and antinomyces decreased while amount of fungi increased. The development of symbiotic nitrogen fixation system wsa deteriorated.展开更多
The radon control mechanism of Na_(2)O·nSiO_(2)−CaCl_(2)modified soil was studied through the laboratory simulation experiment of tailing covering radon control.The radon exhalation rate(J)is negatively correlate...The radon control mechanism of Na_(2)O·nSiO_(2)−CaCl_(2)modified soil was studied through the laboratory simulation experiment of tailing covering radon control.The radon exhalation rate(J)is negatively correlated with the coverage thickness(H),and it has a non-linear relationship with the temperature.The moisture content variation rate of the covering soil significantly decreases,which helps to reduce soil damage and enhance the resistance of the covering soil to ambient temperature interference.The formation of silicic gel and C−S−H gel effectively optimizes the pore structure and permeability,reduces the diffusion and migration of radon gas in the covering soil,and the average radon exhalation rate is decreased by 1.01×10^(−2)Bq/(m^(3)·s).The research results show that the Na_(2)O·nSiO_(2)−CaCl_(2)modified covering soil can effectively improve the radon control performance of the covering soil and reduce the cost of cover treatment.展开更多
In order to analyze the complex chemical kinetic mechanism systematically and find out the redundant species and reactions, a numerical platform for mechanism analysis and simplification is established basing on Path ...In order to analyze the complex chemical kinetic mechanism systematically and find out the redundant species and reactions, a numerical platform for mechanism analysis and simplification is established basing on Path Flux Analysis （PFA）. It is used to reduce a detailed mechanism for flame inhibited by phosphorus containing compounds, a reduced mechanism with 65 species and 335 reactions is obtained. The detailed and reduced mechanism are both used to calculate the freely-propagating premix C3H8/air flame with different dimethyl methylphosphonate doped over a wide range of equivalence ratios. The concentration distributions of free radicals and major species are compared, and the results under two different mechanisms agree well. The laminar flame speed obtained by the two mechanisms also matches well, with the maximum relative error introduces as a small value of 1.7%. On the basis of the reduced mechanism validation, the correlativity analysis is conducted between flame speed and flee radical concentrations, which can provide information for target species selection in the further mechanism reduction. By analyzing the species and reactions fluxes, the species and reaction paths which contribute the flame inhibition significantly are determined.展开更多
The process of deep reduction and magnetic separation was proposed to enrich nickel and iron from laterite nickel ores.Results show that nickel-iron concentrates with nickel grade of 6.96%,nickel recovery of 94.06%,ir...The process of deep reduction and magnetic separation was proposed to enrich nickel and iron from laterite nickel ores.Results show that nickel-iron concentrates with nickel grade of 6.96%,nickel recovery of 94.06%,iron grade of 34.74%,and iron recovery of 80.44% could be obtained after magnetic separation under the conditions of reduction temperature of 1275℃,reduction time of 50 min,slag basicity of 1.0,carbon-containing coefficient of 2.5,and magnetic field strength of 72 kA/m.Reduction temperature and time affected the possibility of deep reduction and reaction progress.Slag basicity affected the composition of slag in burden and the spilling and enriching rate of nickel-iron from a matrix to form nickel-iron particles.Nickel-iron particles were generated,aggregated,and grew gradually in the reduction process.Nickel-iron particles can be effectively separated from gangue minerals by magnetic separation.展开更多
The polarization behavior of the couple Fe/Cu in 100 mg/L nitrobenzene aqueous solution was studied using Evans coupling diagrams.The results indicated that the iron corrosion was limited by both anodic and cathodic h...The polarization behavior of the couple Fe/Cu in 100 mg/L nitrobenzene aqueous solution was studied using Evans coupling diagrams.The results indicated that the iron corrosion was limited by both anodic and cathodic half-cell reactions under the neutral conditions,and cathodically controlled under the alkaline conditions.Batch experiments were performed to study the effect of solution pH,reaction duration,concentration,type of electrolyte,and dissolved oxygen(DO)on the reduction of nitrobenzene by the catal...展开更多
Large Eddy Simulation（LES） is performed to investigate the airfoil broadband noise reduction with wavy leading edge under anisotropic incoming turbulence. The anisotropic incoming turbulence is generated by a rod wi...Large Eddy Simulation（LES） is performed to investigate the airfoil broadband noise reduction with wavy leading edge under anisotropic incoming turbulence. The anisotropic incoming turbulence is generated by a rod with a diameter of 10 mm. The incoming flow velocity is 40 m/s and the corresponding Reynolds numbers based on airfoil chord and rod diameter are about 397000 and 26000, respectively. The far-field acoustic field is predicted using an acoustic analogy method which has been validated by the experiment. A straight leading edge airfoil and a wavy leading edge airfoil are simulated. The results show that wavy leading edge increases the airfoil lift and drag whereas the lift and drag fluctuations are substantially reduced. In addition, wavy leading edge can significantly change the flow pattern around the leading edge and a pair of counter-rotating streamwise vortices stemming from each wavy leading edge peak are observed.An averaged noise reduction of 9.5 dB is observed with the wavy leading edge at the azimuthal angle of 90°. Moreover, the wavy leading edge can mitigate noise radiation at all the azimuthal angles without significantly changing the noise directivity. The underlying noise reduction mechanisms are then analyzed in detail.展开更多
High-phosphorus iron ore resource is considered a refractory iron ore because of its high-phosphorus content and complex ore phase structure. Therefore, the development of innovative technology to realize the efficien...High-phosphorus iron ore resource is considered a refractory iron ore because of its high-phosphorus content and complex ore phase structure. Therefore, the development of innovative technology to realize the efficient utilization of high-phosphorus iron ore resources is of theoretical and practical significance. Thus, a method for phosphorus removal by gasification in the hydrogen-rich sintering process was proposed. In this study, the reduction mechanism of phosphorus in hydrogen-rich sintering, as well as the reduction kinetics of apatite based on the non-isothermal kinetic method, was investigated. Results showed that, by increasing the reduction time from 20 to 60 min, the dephosphorization rate increased from 10.93%to 29.51%. With apatite reduction, the metal iron accumulates, and part of the reduced phosphorus gas is absorbed by the metal iron to form stable iron-phosphorus compounds, resulting in a significant reduction of the dephosphorization rate. Apatite reduction is mainly concentrated in the sintering and burning zones, and the reduced phosphorus gas moves downward along with flue gas under suction pressure and is condensed and adsorbed partly by the sintering bed when passing through the drying zone and over the wet zone. As a result, the dephosphorization rate is considerably reduced. Based on the Ozawa formula of the iso-conversion rate, the activation energy of apatite reduction is 80.42 kJ/mol. The mechanism function of apatite reduction is determined by a differential method (i.e., the Freeman-Carroll method) and an integral method (i.e., the Coats-Redfern method). The differential form of the equation is f(α)=2(1-α)^(1/2), and the integral form of the equation is G(α)=1-(1-α)^(1/2).展开更多
Transition metal iron and persistent free radicals(PFRs)both affect the redox properties of biochar,but the electron transfer relationship between them and the coupling reduction mechanism of Cr(Ⅵ)requires further in...Transition metal iron and persistent free radicals(PFRs)both affect the redox properties of biochar,but the electron transfer relationship between them and the coupling reduction mechanism of Cr(Ⅵ)requires further investigation.To untangle the interplay between iron and PFRs in biochar and the infuences on redox properties,FeCl_(3)-modified rice husk biochar(FBCs)was prepared and its reduction mechanism for Cr(Ⅵ)without light was evaluated.The FBCs had higher surface positive charges,oxygen-containing functional groups,and PFRs compared with pristine rice husk biochar(BC).Phenoxyl PFRs with high electrondonating capability formed in biochar.The pronounced electron paramagnetic resonance signals showed that the PFRs preferred to form at lower Fe(Ⅲ)concentrations.While a high concentration of Fe(Ⅲ)would be reduced to Fe(Ⅱ)and consumed the formed PFRs.Adsorption kinetics and X-ray photoelectron spectroscopy analysis indicated that the FBCs effectively enhanced the Cr(Ⅵ)removal efficiency by 1.54-8.20 fold and the Cr(Ⅵ)reduction efficiency by 1.88-9.29 fold compared to those of BC.PFRs quenching and competitive reductant addition experiments revealed that the higher Cr(Ⅵ)reduction performance of FBCs was mainly attributed to the formed PFRs,which could contribute to~74.0%of Cr(Ⅵ)reduction by direct or indirect electron transfer.The PFRs on FBCs surfaces could promote the Fe(Ⅲ)/Fe(Ⅱ)cycle through single electron transfer and synergistically accelerate~52.3%of Cr(Ⅵ)reduction.This study provides an improved understanding of the reduction mechanism of iron-modified biochar PFRs on Cr(Ⅵ)in environments.展开更多
The enhanced reduction mechanism and kinetics of different Na_(2)CO_(3) additions in the carbothermic reduction of ilmenite concentrate were investigated.The reduction process was carried out at different heating rate...The enhanced reduction mechanism and kinetics of different Na_(2)CO_(3) additions in the carbothermic reduction of ilmenite concentrate were investigated.The reduction process was carried out at different heating rates in a thermogravimetry facility,and the kinetics was studied using the Starink method.The results indicate that Na_(2)CO_(3) addition enhanced the reduction effect as well as reduced the initial temperature of the reaction and the activation energy by increasing reactant activity in reactant form;however,it deteriorated the late-stage kinetic conditions by generating a molten phase,thereby reducing the reaction rate in the late stages of reduction.The average apparent activation energies of ilmenite concentrate with 0%,3%,and 6%Na_(2)CO_(3) are 447,289,and 430 kJ/mol,respectively.The results from kinetics parameters confirm that Na_(2)CO_(3) addition accelerated the reduction kinetics;however,excessive addition worsened the reduction kinetics.展开更多
The reduction kinetics and mechanisms of hematite ore with various particle sizes with hydrogen at low temperature were studied using the thermogravimetric analysis. At the same temperature, after the particle size of...The reduction kinetics and mechanisms of hematite ore with various particle sizes with hydrogen at low temperature were studied using the thermogravimetric analysis. At the same temperature, after the particle size of powder decreases from 107. 5μm to 2. 0 μm, the surface area of the powder and the contact area between the powder and gas increase, which makes the reduction process of hematite accelerate by about 8 times, and the apparent activation energy of the reduction reaction drops to 36.9 kJ/mol from 78. 3 kJ/mol because the activity of ore powder is improved by refining gradually. With the same reaction rate, the reaction temperature of 6.5 μm powder decreases by about 80 ℃ compared with that of 107. 5 μm powder. Thinner diffusion layer can also accelerate the reaction owing to powder refining. The higher the temperature, the greater is the peak of the reduction rate; at the same temperature, the greater the particle size, the smaller is the peak value of the reduction rate; both inner diffusion and interface chemical reaction play an important role in the whole reaction process.展开更多
基金supported by the National Natural Science Foundation of China(U1908225)the Fundamental Research Funds for Central Universities(N2225012 and N232405-06).
文摘In response to the new mechanism of direct vortex melting reduction of vanadium–titanium magnetite,the reaction control mechanism and the migration regularity of valuable components in the process of direct melting reduction were investigated using kinetic empirical equation by fitting and combining with X-ray diffraction,X-ray fluorescence,scanning electron microscopy,energy-dispersive spectrometry,and optical microscopy.The results show that iron reduction is controlled by the mass transfer process of(FeOx)in the slag,while vanadium reduction is controlled by both the mass transfer of(VOx)in the slag and the mass transfer of[V]in the molten iron,and the slag–metal interfacial reaction is the only pathway for vanadium reduction.The reduction of iron and vanadium is an obvious first-order reaction,with activation energy of 101.6051 and 197.416 kJ mol^(−1),respectively.Increasing the vortex rate and reaction temperature is beneficial to improving the reaction rate and reduction efficiency.The mineral phase variation of iron and vanadium in the slag during the reduction process is Fe_(2)O_(3)→Fe_(3)O_(4)/FeV_(2)O_(4)→FeTiO_(3) and FeV_(2)O_(4)→MgV_(2)O_(5);titanium in slag is mainly in the form of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and CaTiO_(3).As the reaction time went on,the molar ratio(nTi/nMg)in Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)and the Ti2O_(3) content in the slag gradually went up,while the area proportion of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)went up and then down,and the porosity of the slag and the grain size of Mg_(x)Ti_(3−x)O_(5)(0≤x≤1)got smaller.
基金Project(51134002)supported by the National Natural Science Foundation of ChinaProject(2012BAB14B02)supported by the Ministry of Science and Technology of ChinaProject(12120113086600)supported by Ministry of Land and Resources of China
文摘A low-grade nickel laterite ore was reduced at different reduction temperatures. The morphology of metallic particles was investigated by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS）. Experimental results indicate that the metallic nickel and iron gradually assemble and grow into larger spherical particles with increasing temperature and prolonging time. After reduction, the nickel laterite ore obviously changes into two parts of Fe-Ni metallic particles and slag matrix. An obvious relationship is found between the reduction of iron magnesium olivine and its crystal chemical properties. The nickel and iron oxides are reduced to metallic by reductant, and the lattice of olivine is destroyed. The entire reduction process is comprised of oxide reduction and metallic phase growth.
基金National Natural Science Foundation of China （Grant No.50635030） the International Cooperation key Project of Ministry of Science and Technology of China （Grant No. 2005DFA00850）+2 种基金 The key project about ministry of education of science and technology （Grant No. 105059） the international cooperative of Jilin Province （Grant No.20040703-1） Specialized Research fund for the Doctoral Program of higher Education （Grant No. 20050183064）.
文摘Bionic non-smooth surfaces （BNSS） can reduce drag. Much attention has been paid to the mechanism of shear stress reduction by riblets. The mechanism of pressure force reduction by bionic non-smooth surfaces on bodies of revolution has not been well investigated. In this work CFD simulation has revealed the mechanism of drag reduction by BNSS, which may work in three ways. First, BNSS on bodies of revolution may lower the surface velocity of the medium, which prevents the sudden speed up of air on the cross section. So the bottom pressure of the model would not be disturbed sharply, resulting in less energy loss and drag reduction. Second, the magnitude of vorticity induced by the bionic model becomes smaller because, due to the sculpturing, the growth of tiny air bubbles is avoided. Thus the large moment of inertia induced by large air bubble is reduced. The reduction of the vorticity could reduce the dissipation of the eddy. So the pressure force could also be reduced. Third, the thickness of the momentum layer on the model becomes less which, according to the relationship between the drag coefficient and the momentum thickness, reduces drag.
文摘The reduction of the nitrobenzene compounds （NBCs） by the catalyzed Fe-Cu process and the relationship between the electrochemical reduction characteristics of NBCs at copper electrode and reduction rate were studied in alkaline medium（pH=11）. The catalyzed Fe-Cu process was found more effective on degradation of NBCs compared to Master Builder＇s iron. The reduction rate by the catalyzed Fe-Cu process decreased in the following order： nitrobenzene 〉4-chloro-nitrobenzene ≥m-dinitrobenzene ：〉 4-nitrophenol ≥2,4-dinitrotoluene 〉2-nitrophenol. The reduction rate by Master Builder＇s iron decreased in the following order： m-dinitrobenzene ≥4-chloro-nitrobenzene 〉4-nitrophenol 〉2,4-dinitrotoluene ≈nitrobenzene 〉2-nitrophenol. NBCs were reduced directly on the surface of copper rather than by the hydrogen produced at cathode in the catalyzed Fe-Cu process. The reduction was realized by the hydrogen produced at cathode and Fe（OH）2 in Master Builder＇s iron, It is an essential difference in reaction mechanisms between these two technologies. For this reason, the reduction by the catalyzed Fe-Cu depended greatly on NBC＇s electron withdrawing ability.
基金Item Sponsored by National High-tech Research and Development Project of China(2012AA062302)Major Program of National Natural Science Foundation of China(51090384)Fundamental Research Funds for the Central Universities of China(N130602003)
文摘To achieve the high-efficiency utilization of vanadium-titanium magnetite（ VTM）,reduction experiments were conducted to determine the carbothermic reduction mechanism of VTM. Effects of volatile matter,temperature,time,and carbon ratio（ molar ratio of fixed carbon in coal to oxygen in iron oxides of VTM） on reduction degree were investigated.Results show that reduction degree increases with increasing volatile matter in coal,temperature,time,and carbon ratio.Phase transformation,microstructure,and reduction path were analyzed by X-ray diffraction,scanning electron microscopy,energy-dispersive X-ray spectroscopy,and Fact Sage 6. 0. The thermoravimetry-differential scanning calorimetry-quadrupole mass spectrometer method was used for kinetic analysis of the main reduction process. Results indicate that the kinetic mechanism follows the principle of random nucleation and growth（ n = 4）,and the activation energy values at 600-900 and 900-1 350 ℃ are 88. 7 and 295. 5 kJ / mol,respectively.
基金supported by the National Natural Science Foundation of China (Nos.51672077, 51872089)。
文摘Cr(Ⅵ) is a common heavy metal ion, which will seriously harm human body and environment.Therefore, the removal of Cr(Ⅵ) has become an attractive topic.In this work, cinder was used as a raw material to synthesize a nanoneedle material: γ-(AlOOH@FeOOH)(γ-Al@Fe).The physicochemical properties of γ-Al@Fe were thoroughly characterized, and its effectiveness as a catalyst for photocatalytic reduction of Cr(Ⅵ) was evaluated.The results showed that Cr(Ⅵ) could be efficiently reduced by γ-Al@Fe in the presence of tartaric acid(TA) under visible light.The variable factors on the reaction were investigated in detail, and the results showed that under optimal conditions(γ-Al@Fe 0.4 g/L, TA 0.6 g/L, pH 2), Cr(Ⅵ)was completely reduced within 7 min.Besides, scavenger experiments and EPR proved that O_(2)^(·-) and CO_(2)^(·-) played a significant role in the photocatalytic reduction of Cr(Ⅵ).TA acts as a sacrificial agent to trap the holes and generate strong reducing free radicals: CO_(2)^(·-).Dissolving O_(2) could react with electrons to generate O_(2)^(·-).This work discussed the performance and mechanism of photocatalytic reduction of Cr(Ⅵ) in detail, which provided a new idea for the resource utilization of solid waste and the treatment of heavy metal sewage.
基金financially supported by the National Natural Science Foundation of China (No. 51090384)the National High-Tech Research and Development Program of China (No. 2012AA062302)the Fundamental Research Funds for the Central Universities of China (Nos. N110202001 and N130602003)
文摘The reduction of high-chromium vanadium–titanium magnetite as a typical titanomagnetite containing 0.95wt% V2O5 and 0.61wt% Cr2O3 by H2–CO–CO2 gas mixtures was investigated from 1223 to 1373 K. Both the reduction degree and reduction rate increase with increasing temperature and increasing hydrogen content. At a temperature of 1373 K, an H2/CO ratio of 5/2 by volume, and a reduction time of 40 min, the degree of reduction reaches 95%. The phase transformation during reduction is hypothesized to proceed as follows： Fe2O3 → Fe3O4 → FeO → Fe; Fe9 TiO 15 ＋ Fe2Ti3O9 → Fe2.75Ti0.25O4 → FeT iO 3 → TiO 2;（Cr0.15V0.85）2O3 → Fe2VO4; and Cr1.3Fe0.7O3 → FeC r2O4. The reduction is controlled by the mixed internal diffusion and interfacial reaction at the initial stage; however, the interfacial reaction is dominant. As the reduction proceeds, the internal diffusion becomes the controlling step.
文摘The electrochemical behavior of Sc^(3+) in LiF-NaF system was investigated. The cyclic voltammetry and chronopotentiometry were used to investigate the reduction mechanism of the electrochemical deposition of Sc^(3+) to Sc on Ag electrode in LiF-NaF system at 1043 K. Experimental results indicate that the electroreduction of Sc^(3+) to Sc is a reversible process with simple 3-electron transfer in one step controlled by diffusion.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.U1902217 and 52104325).
文摘High-quality upgraded titanium slag obtained through semi-molten reduction with the addition of Na_(2)CO_(3)is important for the fluidizing chlorination process to produce TiO_(2)pigments.The key is the effect of Na_(2)CO_(3)on the reduction behavior of iron.Therefore,the effects of Na_(2)CO_(3)on reduction mechanism and kinetics of iron during deep reduction of ilmenite concentrate were studied.The results indicated that the metallization ratio of the reduced sample increased with increasing temperature,time,and dose of Na_(2)CO_(3).The addition of Na_(2)CO_(3)significantly accelerated the reduction of iron in the ilmenite concentrate and promoted the growth of iron particles.However,the addition of Na_(2)CO_(3)produced sodium iron titanates;thus,the metallization ratio of the sample decreased with an increase in the temperature and time when the temperature was above 1200℃and the time was more than 30 min.When the doses of Na_(2)CO_(3)were 0,3,and 6 wt.%,the reduction of iron was controlled by the interfacial chemical reaction,both the interfacial chemical reaction and diffusion,and diffusion,respectively,and the apparent activation energies were 134.91,64.89,and 120.82 kJ/mol,respectively.
基金supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 52362049 and 52208446)the Natural Science Foundation of Gansu Province (Grant Nos. 22JR5RA344 and 22JR11RA152)+4 种基金the Special Funds for Guiding Local Scientifi c and Technological Development by the Central Government (Grant No. 22ZY1QA005)the Joint Innovation Fund Project of Lanzhou Jiaotong University and Corresponding Supporting University (Grant No. LH2023016)the Fundamental Research Funds for the Central Universities (2682023ZTZ010), the Lanzhou Science and Technology planning Project (Grant No. 2022-ZD-131)the key Research and Development Project of Lanzhou Jiaotong University (Grant No. LZJTU-ZDYF2302)the University Youth Fund Project of Lanzhou Jiaotong University (Grant No. 2021014)。
文摘The issue of low-frequency structural noise radiated from high-speed railway(HSR) box-girder bridges(BGBs) is a significant challenge worldwide. Although it is known that vibrations in BGBs caused by moving trains can be reduced by installing multiple tuned mass dampers(MTMDs) on the top plate, there is limited research on the noise reduction achieved by this method. This study aims to investigate the noise reduction mechanism of BGBs installed with MTMDs on the top plate. A sound radiation prediction model for the BGB installed with MTMDs is developed, based on the vehicle–track–bridge coupled dynamics and acoustics boundary element method. After being verified by field tested results, the prediction model is employed to study the reduction of vibration and noise of BGBs caused by the MTMDs. It is found that installing MTMDs on top plate can significantly affect the vibration distribution and sound radiation law of BGBs. However, its impact on the sound radiation caused by vibrations dominated by the global modes of BGBs is minimal. The noise reduction achieved by MTMDs is mainly through changing the acoustic radiation contributions of each plate of the bridge. In the lower frequency range, the noise reduction of BGB caused by MTMDs can be more effective if the installation of MTMDs can modify the vibration frequency and distribution of the BGB to avoid the influence of small vibrations and disperse the sound radiation from each plate.
文摘Three-year investigation was conducted to demonstrate the mechanism of reduction of soybean yield aroused by continuous and every second year cropping. Compared to normal cropping, there are many unfavorable changes in some major elements of soybean plant and soil environment. Chloropyll content was lower. Phosphorous content of soybean plant was decreased seriously. Potassium content was lower while calcium content was higher. Magnesium content was wot affected and decreased in susceptive varieties. Some deseases and insects of soybean under continuous and wery second year cropping conditions became serious as continuous years prolonged. Organic matter content tended to go down from normal rotation to continuous cropping. Amount of bacteria and antinomyces decreased while amount of fungi increased. The development of symbiotic nitrogen fixation system wsa deteriorated.
基金supported by the National Natural Science Foundation of China(No.51174116)the National Key Research and Development Program of China(No.2023YFC3010903)the Scientific Research Project of Education Department of Hunan Province,China(No.24A0319).
文摘The radon control mechanism of Na_(2)O·nSiO_(2)−CaCl_(2)modified soil was studied through the laboratory simulation experiment of tailing covering radon control.The radon exhalation rate(J)is negatively correlated with the coverage thickness(H),and it has a non-linear relationship with the temperature.The moisture content variation rate of the covering soil significantly decreases,which helps to reduce soil damage and enhance the resistance of the covering soil to ambient temperature interference.The formation of silicic gel and C−S−H gel effectively optimizes the pore structure and permeability,reduces the diffusion and migration of radon gas in the covering soil,and the average radon exhalation rate is decreased by 1.01×10^(−2)Bq/(m^(3)·s).The research results show that the Na_(2)O·nSiO_(2)−CaCl_(2)modified covering soil can effectively improve the radon control performance of the covering soil and reduce the cost of cover treatment.
基金Supported by the National Natural Science Foundation of China （51176181）, the National Basic Research Program of China （2012CB719704）, and the Research Fund for the Doctoral Program of Higher Education （20123402110047）.
文摘In order to analyze the complex chemical kinetic mechanism systematically and find out the redundant species and reactions, a numerical platform for mechanism analysis and simplification is established basing on Path Flux Analysis （PFA）. It is used to reduce a detailed mechanism for flame inhibited by phosphorus containing compounds, a reduced mechanism with 65 species and 335 reactions is obtained. The detailed and reduced mechanism are both used to calculate the freely-propagating premix C3H8/air flame with different dimethyl methylphosphonate doped over a wide range of equivalence ratios. The concentration distributions of free radicals and major species are compared, and the results under two different mechanisms agree well. The laminar flame speed obtained by the two mechanisms also matches well, with the maximum relative error introduces as a small value of 1.7%. On the basis of the reduced mechanism validation, the correlativity analysis is conducted between flame speed and flee radical concentrations, which can provide information for target species selection in the further mechanism reduction. By analyzing the species and reactions fluxes, the species and reaction paths which contribute the flame inhibition significantly are determined.
基金Projects(51904058,51734005)supported by the National Natural Science Foundation of ChinaProject(2018YFC1901901902)supported by the National Key Research and Development Program of China
文摘The process of deep reduction and magnetic separation was proposed to enrich nickel and iron from laterite nickel ores.Results show that nickel-iron concentrates with nickel grade of 6.96%,nickel recovery of 94.06%,iron grade of 34.74%,and iron recovery of 80.44% could be obtained after magnetic separation under the conditions of reduction temperature of 1275℃,reduction time of 50 min,slag basicity of 1.0,carbon-containing coefficient of 2.5,and magnetic field strength of 72 kA/m.Reduction temperature and time affected the possibility of deep reduction and reaction progress.Slag basicity affected the composition of slag in burden and the spilling and enriching rate of nickel-iron from a matrix to form nickel-iron particles.Nickel-iron particles were generated,aggregated,and grew gradually in the reduction process.Nickel-iron particles can be effectively separated from gangue minerals by magnetic separation.
文摘The polarization behavior of the couple Fe/Cu in 100 mg/L nitrobenzene aqueous solution was studied using Evans coupling diagrams.The results indicated that the iron corrosion was limited by both anodic and cathodic half-cell reactions under the neutral conditions,and cathodically controlled under the alkaline conditions.Batch experiments were performed to study the effect of solution pH,reaction duration,concentration,type of electrolyte,and dissolved oxygen(DO)on the reduction of nitrobenzene by the catal...
基金supported by the National Natural Science Foundation of China (Nos.51776174,51476134,51276149 and 11602290)State Key Laboratory of Aerodynamics of China Aerodynamics Research and Development Center (No.SKLA20160201)+1 种基金Key Laboratory of Aerodynamic Noise Control of China Aerodynamics Research and Development Center (No.ANCL20170201)China-Europe IMAGE (Innovative Methodologies and Technologies for Reducing Aircraft Noise Generation and Emission) program (No.688971-IMAGE-H2020MG-20141015)
文摘Large Eddy Simulation（LES） is performed to investigate the airfoil broadband noise reduction with wavy leading edge under anisotropic incoming turbulence. The anisotropic incoming turbulence is generated by a rod with a diameter of 10 mm. The incoming flow velocity is 40 m/s and the corresponding Reynolds numbers based on airfoil chord and rod diameter are about 397000 and 26000, respectively. The far-field acoustic field is predicted using an acoustic analogy method which has been validated by the experiment. A straight leading edge airfoil and a wavy leading edge airfoil are simulated. The results show that wavy leading edge increases the airfoil lift and drag whereas the lift and drag fluctuations are substantially reduced. In addition, wavy leading edge can significantly change the flow pattern around the leading edge and a pair of counter-rotating streamwise vortices stemming from each wavy leading edge peak are observed.An averaged noise reduction of 9.5 dB is observed with the wavy leading edge at the azimuthal angle of 90°. Moreover, the wavy leading edge can mitigate noise radiation at all the azimuthal angles without significantly changing the noise directivity. The underlying noise reduction mechanisms are then analyzed in detail.
基金financially supported by the National Natu ral Science Foundation of China (No. U1960205)。
文摘High-phosphorus iron ore resource is considered a refractory iron ore because of its high-phosphorus content and complex ore phase structure. Therefore, the development of innovative technology to realize the efficient utilization of high-phosphorus iron ore resources is of theoretical and practical significance. Thus, a method for phosphorus removal by gasification in the hydrogen-rich sintering process was proposed. In this study, the reduction mechanism of phosphorus in hydrogen-rich sintering, as well as the reduction kinetics of apatite based on the non-isothermal kinetic method, was investigated. Results showed that, by increasing the reduction time from 20 to 60 min, the dephosphorization rate increased from 10.93%to 29.51%. With apatite reduction, the metal iron accumulates, and part of the reduced phosphorus gas is absorbed by the metal iron to form stable iron-phosphorus compounds, resulting in a significant reduction of the dephosphorization rate. Apatite reduction is mainly concentrated in the sintering and burning zones, and the reduced phosphorus gas moves downward along with flue gas under suction pressure and is condensed and adsorbed partly by the sintering bed when passing through the drying zone and over the wet zone. As a result, the dephosphorization rate is considerably reduced. Based on the Ozawa formula of the iso-conversion rate, the activation energy of apatite reduction is 80.42 kJ/mol. The mechanism function of apatite reduction is determined by a differential method (i.e., the Freeman-Carroll method) and an integral method (i.e., the Coats-Redfern method). The differential form of the equation is f(α)=2(1-α)^(1/2), and the integral form of the equation is G(α)=1-(1-α)^(1/2).
基金supported by the National Key Research and Development Program of China (No.2020YFC1808500)the National Natural Science Foundation of China (Nos.42107046 and 41907119)+2 种基金the GDAS’Project of Science and Technology Development (Nos.2022GDASZH-2022010105,and 2019GDASYL-0102002-5)the Postdoctoral Science Foundation of China (No.2020M682634)the Guangdong Basic and Applied Basic Research Foundation (No.2021A1515011540)。
文摘Transition metal iron and persistent free radicals(PFRs)both affect the redox properties of biochar,but the electron transfer relationship between them and the coupling reduction mechanism of Cr(Ⅵ)requires further investigation.To untangle the interplay between iron and PFRs in biochar and the infuences on redox properties,FeCl_(3)-modified rice husk biochar(FBCs)was prepared and its reduction mechanism for Cr(Ⅵ)without light was evaluated.The FBCs had higher surface positive charges,oxygen-containing functional groups,and PFRs compared with pristine rice husk biochar(BC).Phenoxyl PFRs with high electrondonating capability formed in biochar.The pronounced electron paramagnetic resonance signals showed that the PFRs preferred to form at lower Fe(Ⅲ)concentrations.While a high concentration of Fe(Ⅲ)would be reduced to Fe(Ⅱ)and consumed the formed PFRs.Adsorption kinetics and X-ray photoelectron spectroscopy analysis indicated that the FBCs effectively enhanced the Cr(Ⅵ)removal efficiency by 1.54-8.20 fold and the Cr(Ⅵ)reduction efficiency by 1.88-9.29 fold compared to those of BC.PFRs quenching and competitive reductant addition experiments revealed that the higher Cr(Ⅵ)reduction performance of FBCs was mainly attributed to the formed PFRs,which could contribute to~74.0%of Cr(Ⅵ)reduction by direct or indirect electron transfer.The PFRs on FBCs surfaces could promote the Fe(Ⅲ)/Fe(Ⅱ)cycle through single electron transfer and synergistically accelerate~52.3%of Cr(Ⅵ)reduction.This study provides an improved understanding of the reduction mechanism of iron-modified biochar PFRs on Cr(Ⅵ)in environments.
基金supported by the National Natural Science Foundation of China (No. U1902217)。
文摘The enhanced reduction mechanism and kinetics of different Na_(2)CO_(3) additions in the carbothermic reduction of ilmenite concentrate were investigated.The reduction process was carried out at different heating rates in a thermogravimetry facility,and the kinetics was studied using the Starink method.The results indicate that Na_(2)CO_(3) addition enhanced the reduction effect as well as reduced the initial temperature of the reaction and the activation energy by increasing reactant activity in reactant form;however,it deteriorated the late-stage kinetic conditions by generating a molten phase,thereby reducing the reaction rate in the late stages of reduction.The average apparent activation energies of ilmenite concentrate with 0%,3%,and 6%Na_(2)CO_(3) are 447,289,and 430 kJ/mol,respectively.The results from kinetics parameters confirm that Na_(2)CO_(3) addition accelerated the reduction kinetics;however,excessive addition worsened the reduction kinetics.
基金Sponsored by National Natural Science Foundation of China(50474006)National Science and Technology Support Program for the 11th Five-Year Plan(2006BAE03A12,2006BAE03A05)
文摘The reduction kinetics and mechanisms of hematite ore with various particle sizes with hydrogen at low temperature were studied using the thermogravimetric analysis. At the same temperature, after the particle size of powder decreases from 107. 5μm to 2. 0 μm, the surface area of the powder and the contact area between the powder and gas increase, which makes the reduction process of hematite accelerate by about 8 times, and the apparent activation energy of the reduction reaction drops to 36.9 kJ/mol from 78. 3 kJ/mol because the activity of ore powder is improved by refining gradually. With the same reaction rate, the reaction temperature of 6.5 μm powder decreases by about 80 ℃ compared with that of 107. 5 μm powder. Thinner diffusion layer can also accelerate the reaction owing to powder refining. The higher the temperature, the greater is the peak of the reduction rate; at the same temperature, the greater the particle size, the smaller is the peak value of the reduction rate; both inner diffusion and interface chemical reaction play an important role in the whole reaction process.
