Behaviors of vanadium and chromium in coal-based direct reduction of high-chromium vanadium-bearing titanomagnetite concentrates followed by magnetic separation

The reduction behaviors of FeO·V2O3 and FeO·Cr2O3 during coal-based direct reduction have a decisive impact on the efficient utilization of high-chromium vanadium-bearing titanomagnetite concentrates. The effects of molar ratio of C to Fe n(C)/n(Fe) and temperature on the behaviors of vanadium and chromium during direct reduction and magnetic separation were investigated. The reduced samples were characterized by X-ray diffraction(XRD), scanning election microscopy(SEM) and energy dispersive spectrometry(EDS) techniques. Experimental results indicate that the recoveries of vanadium and chromium rapidly increase from 10.0% and 9.6% to 45.3% and 74.3%, respectively, as the n(C)/n(Fe) increases from 0.8 to 1.4. At n(C)/n(Fe) of 0.8, the recoveries of vanadium and chromium are always lower than 10.0% in the whole temperature range of 1100-1250 °C. However, at n(C)/n(Fe) of 1.2, the recoveries of vanadium and chromium considerably increase from 17.8% and 33.8% to 42.4% and 76.0%, respectively, as the temperature increases from 1100 °C to 1250 °C. At n(C)/n(Fe) lower than 0.8, most of the FeO·V2O3 and FeO·Cr2O3 are not reduced to carbides because of the lack of carbonaceous reductants, and the temperature has little effect on the reduction behaviors of FeO·V2O3 and FeO·Cr2O3, resulting in very low recoveries of vanadium and chromium during magnetic separation. However, at higher n(C)/n(Fe), the reduction rates of FeO·V2O3 and FeO·Cr2O3 increase significatly because of the excess amount of carbonaceous reductants. Moreover, higher temperatures largely induce the reduction of FeO·V2O3 and FeO·Cr2O3 to carbides. The newly formed carbides are then dissolved in the γ(FCC) phase, and recovered accompanied with the metallic iron during magnetic separation.

Comparison of reduction behavior of Fe_2O_3, ZnO and ZnFe_2O_4 by TPR technique

Advanced integrated gasification combined cycle （IGCC） power generation systems require the development of high-temperature, regenerable, desulfurization sorbents capable of removing hydrogen sulfide from coal gasifier gas to very low levels. As a sort of effective desufurizer, such as Fe2O3, ZnO and ZnFe2O4, it will endure strong reducing atmosphere in desulfurization process. The reduced degree of desufurizer can have an effect on its desulfurization reactivity. In this paper, Fe2O3, ZnO and ZnFe2O4 were synthesized by precipitation or co-precipitation at constant pH. After aging, washing and drying, the solids were calcined at 800℃. The reduction behaviors of sample were characterized by temperature-programmed reduction （TPR）. It is found that there are two reduction peaks for Fe2O3 in TPR, and whereas no reduction peaks for ZnO are found. The reduction process of ZnFe2O4 prepared by co-precipitation is different from that of Fe2O3. ZnFe2O4 is easier to be reduced than Fe2O3. The activation energy of reduction process for Fe2O3 and ZnFe2O4 is obtained at different reduction periods.

Gas-based reduction of vanadium titano-magnetite concentrate:behavior and mechanisms

The reduction of vanadium titano-magnetite pellets by H_2-CO at temperatures from 850 to 1050°C was investigated in this paper. The influences of pre-oxidation treatment, reduction temperature, and V_（H_2）/（V_（H_2） ＋ VCO） on the metallization degree were studied. The results showed that pre-oxidation played a substantial role in the reduction of vanadium titano-magnetite pellets. During the reduction process, the metallization degree increased with increasing temperature and increasing V_（H_2） /（V_（H_2） ＋ VCO）. The phase transformation of pre-oxidized vanadium titano-magnetite pellets during the reduction process under an H_2 atmosphere and a CO atmosphere was discussed, and the reduced samples were analyzed by scanning electron microscopy（SEM） in conjunction with back scatter electron（BSE） imaging. The results show that the difference in thermodynamic reducing ability between H_2 and CO is not the only factor that leads to differences in the reduction results obtained using different atmospheres. Some of Fe_（3-x）Ti_xO_4 cannot be reduced under a CO atmosphere because of the densification of particles＇ structure and because of the enrichment of Mg in unreacted cores. By contrast, a loose structure of particles was obtained when the pellets were reduced under an H_2 atmosphere and this structure decreased the resistance to gas diffusion. Moreover, the phenomenon of Mg enrichment in unreacted cores disappeared during H_2 reduction. Both the lower resistance to gas diffusion and the lack of Mg enrichment facilitated the reduction of vanadium titano-magnetite.

Influence of hydrogen-enriched atmosphere under coke oven gas injection on reduction swelling behaviors of oxidized pellet

It is of great importance to elucidate reduction swelling behaviors and reaction mechanism of oxidized pellet in hydrogen-enriched atmosphere under coke oven gas injection. In this work, the effects of hydrogen concentration in N_2-CO-H_2 atmosphere with unchanged CO content on reduction swelling behaviors of oxidized pellet at 1173 K were studied, to clarify the mechanism of hydrogen-enriched reduction and exclude the influences of CO. Then, the reduction swelling behaviors of oxidized pellet at 1173 K in actual atmosphere under coke oven gas(COG) injection, got from the simulation results of multi-fluid blast furnace model, were investigated. The results show that with the concentration of hydrogen increasing in N_2-CO-H_2 gas from 2% to 18%, the reduction swelling index of pellet decreases from 10.12% to 5.57% while the reduction ratio of pellet increases obviously from 39.85% to 69.58%. In addition, with COG injection rate increasing from 0 to 152.34 m^3/t, the reduction swelling index of pellet decreases slightly from 10.71% to 9.54% while the reduction ratio of pellet is increased from 31.57% to 36.39%. The microstructures of pellet are transformed from the platy structure to the flocculent structure.

Reduction behaviors of iron ore lump and pellets with H_2 -CO gas

The differences of reduction behaviors between iron ore lump and pellets were studied by conducting low temperature reduction degradation, static load reduction and droplet tests. These tests simulated the conditions of reduction temperature and hydrogen-containing gas in COREX. Due to its dense structure and low porosity compared with pellets, lump ore possesses poor reduction degradation index （RDI） and slower reduction rate in early and medium reaction stages ,showing signs of lower strength, lower softening and melting temperatures, as well as a wider melting zone and higher AP. That provides some basis to explain the phenomena of differential pressure rise,metallization decline and more sticking after the usage of lump ore in COREX plant.

Fluidization behavior and reduction kinetics of pre-oxidized magnetite-based iron ore in a hydrogen-induced fluidized bed

The influence of different pre-oxidation temperatures and pre-oxidation degrees on the reduction and fluidization behaviors of magnetite-based iron ore was investigated in a hydrogen-induced fluidized bed.The raw magnetite-based iron ore was pre-oxidized at 800 and1000℃ for a certain time to reach a partly oxidation and deeply oxidation state.The structure and morphology of the reduced particles were analyzed via optical microscope and scanning electron microscopy(SEM).The reaction kinetic mechanism was determined based on the double-logarithm analysis.The results indicate that the materials with higher oxidation temperature and wider particle size range show better fluidization behaviors.The lower oxidation temperature is more beneficial for the reduction rate,especially in the later reduction stage.The pre-oxidation degree shows no obvious influence on the fluidization and reduction behaviors.Based on the kinetic analysis,the reduction progress can be divided into three stages.The reduction mechanism was discussed combing the surface morphology and phase structure.

Effects of basicity and temperature on mineralogy and reduction behaviors of high-chromium vanadium-titanium magnetite sinters

The effects of basicity and temperature on the reduction process of Hongge high-chromium vanadium-titanium magnetite(HCVTM)sinter were investigated in this work.The main characterization methods of X-ray fluorescence(XRF),X-ray diffraction(XRD),scanning electron microscope(SEM),and metallographic microscope were employed in this study.In this work,the reduction of HCVTM sinter with different temperature and basicity were experimented.The Fe,FeO,and TiO in reductive samples increase with increasing basicity and temperatures.The increase of basicity and temperature is favorable to the reduction of HCVTM sinter.The Fe phase has out-migration tendency to the surface of sinter while the perovskite and silicate phases have in-migration tendency to the inside of sinter.The reduction degradation index(RDI)decreases while the reduction index(RI)increases with increasing basicity.The RI increases from 67.14%to 82.09%with increasing temperature from 1073 K to 1373 K.

Reduction and melting behavior of carbon composite lateritic bauxite pellets

Direct reduction of low-grade lateritic bauxite was studied at high temperature to recover Fe and beneficiate AlzO3 slag. The re- sults show that a metallization rate of 97.9% and a nugget recovery rate of 85.1% can be achieved when the reducing and melting tempera- tures are 1350 and 1480℃, respectively. Moreover, a higher-grade calcium aluminate slag （A1203 = 50.52wt%） can also be obtained, which is mainly composed of ct-A1203, hercynite （FeAI：O4）, and gehlenite （Ca2A12SiO7）. In addition, high-quality iron nuggets have been produced from low-grade lateritic bauxite. The nugget is mainly composed of iron （93.82wt%） and carbon （3.86wt%）, with almost no gangue （slag）.

REDUCTION BEHAVIOR OF IRON ORE PELLETS CONTAININGCARBON UNDER NON-ISOTHERMAL CONDITION

The reduction behavior of iron ore pellets containing carbon under non-isothermal condition in the temperature range from 573 to 1373 K was investigated in a laboratory scale setup. The test results show that carbon content has no obvious effect on reduction degree of composite pellets (C/O mole ratio=1.0) by CO in the temperature range from 573 to 1373 K under linear temperature-rising program; reduction degree of iron ore pellets containing carbon is large in 90%CO-10%CO2 mixture than that of in 100%CO atmosphere or in 80%CO-20%CO2 mixture; the s type temperature-rising program has a better effect than that of linear one in increasing the reduction degree; and reduction degree of slower linear temperature-rising program is greater than that of faster one, but the final reduction degrees, i.e., those at the highest temperature are about the same for various CO partial pressures or temperature-rising programs. The kinetic analysis also shows that the reduction of iron ore-carbon composite pellets by CO or CO-CO2 mixture under non-isothermal condition should be controlled by surface reaction, and the apparent reduction activation energy changes with the reduction progress under various test conditions.

An empirical study of the effects of a speaking anxiety reduction model developed from the rational emotive behavioral therapy

Thirty-two Chinese EFL learners took part in a true experiment on the effects of a Speaking Anxiety Reduction Model （SARM） developed from the Rational Emotive Behavioral Therapy （REBT）. The participants were randomly assigned to the treatment and the control group. Both groups received a pre- and post- test of their Speaking Anxiety （SA）, Speaking State Anxiety （SAstate） as well as speaking performance. Those involved in the treatment group also received a treatment with the SARM between the tests. The results showed that, with the effects of Language Achievement （LA） being controlled： （1） the SARM could significantly reduce the SA, SAstate, and increase the total number of words in Communication Units （CUs）; and （2） the effects of the SARM did not differ significantly in terms of gender.

S^(2-) behaviors analysis in leaching SrS and precipitating high purity SrCO_3 by reduction-decomposition process

A new preparation method （reduction-decomposition process） for high purity SrCO3 was investigated, which mainly includes four processes: reduction, leaching, purification and precipitation. The affecting factors about S2- behaviors in leaching process and the effects of variables on purity and particle sizes distribution of SrCO3 were analyzed theoretically and practically. It is concluded that with the increase of temperature or decrease of pH value in leaching process, the strontium recovery increases, but SrS decomposes and hydrogen sulphide （H2S） gas discharges. The purity of SrCO3 is dependent on dissolution-recrystallization times, for example, the purity of （SrCO3） is as high as 99.97% when it is recrystallized three times. Besides, the solution concentration of Sr（OH）2 and flow rate of CO2 have important effects on particle size distribution of SrCO3 particles, especially, the particle sizes of （SrCO3） meanly distribute in 0.11.0 μm when the flow rate of CO2 is about 2 000 mL/min and other parameters are invariable.

Electrochemical reduction mechanism of Zn^(2+)in molten NaCl-KCl eutectic

A process comprising selective chlorination and molten salt electrolysis was proposed to develop an efficient and environmental-friendly technology for zinc recovery from metallurgical dusts.The theoretical feasibility of this technology was firstly estimated based on thermodynamic fundamentals.Subsequently,the electrochemical behavior of Zn^(2+)on tungsten electrode was investigated in molten NaCl-KCl eutectic at 973 K by many electrochemical transient methods.The results showed that the reduction of Zn^(2+)on tungsten electrode was found to be a one-step process exchanging two electrons with the initial reduction potential of-0.74 V(vs Ag/AgCl),and the electrode process was considered as quasi-reversible and controlled by diffusion.The diffusion coefficient of Zn^(2+)ions in the melts was determined in the order of 10^(-5)cm^(2)/s.Finally,the electrolytic preparation of zinc was carried out by potentiostatic electrolysis in molten NaCl-KCl-ZnCl_(2)eutectic at-1.6 V(vs Ag/AgCl).Spheroidic granular metal with silver-white luster was attained after electrolysis for 9.5 h,and identified as pure Zn.The present study confirms that it is practically feasible to extract pure zinc metal by direct electrolysis of ZnCl_(2)in molten NaCl-KCl eutectic,and provides a valuable theoretical reference for the efficient recovery of zinc from metallurgical dusts.

Modeling of Data Reduction in Wireless Sensor Networks

In this paper, we present a stochastic model for data in a Wireless Sensor Network (WSN) using random field theory. The model captures the space-time behavior of the underlying phenomenon being observed by the network. We present results regarding the size and spatial distribution of the regions of the network that sense statistically extreme values of the underlying phenomenon using the theory of extreme excursion regions. These results compliment many existing works in the literature that describe algorithms to reduce the data load, but lack an analytical approach to evaluate the size and spatial distribution of this load. We show that if only the statistically extreme data is transmitted in the network, then the data load can be significantly reduced. Finally, a simple performance model of a WSN is developed based on a collection of asynchronous M/M/1 servers that work in parallel. We derive several performance measures from this performance model. The presented results will be useful in the design of large scale sensor networks.

Physical modeling of gas induced bath flow in drained aluminum reduction cell

A room temperature physical model was used to study the bubble behavior and gas induced bath circulation in a drained aluminum reduction cell. By passing compressed argon through the penetrated Plexiglas box bottom plate immersed in water, gas evolution at the anode bottom surface was simulated. Bubble behavior and liquid flow field were studied and analysis was presented. Bath secondary recirculation was observed in the interpolar gap not the net rising flow as expected. Liquid driven by the bubbles forms small vortices along the interpolar gap with small mean and turbulent velocities and accordingly poor mass transfer. Secondary recirculation also exists between the slot and interpolar gap, part of the flow in the interpolar gap go to the slot with the bubbles and fluid at the bottom of the slot enters the interpolar gap directly without going to the center channel. The existence of the fluid secondary recirculation is very unfavorable to the alumina dissolution and dispersion. Increasing the anode tilt or gas flow rate, or decreasing the anode-cathode distance can make the secondary recirculation in the interpolar gap weak, however, will intensify the secondary recirculation between the slot and interpolar gap.

Effect of structural characteristics distribution on strength demand and ductility reduction factor of MDOF systems considering soil-structure interaction

It is known that structural stiffness and strength distributions have an important role in the seismic response of buildings. The effect of using different code-specified lateral load patterns on the seismic performance of fixed-base buildings has been investigated by researchers during the past two decades. However, no investigation has yet been carried out for the case of soil-structure systems. In the present study, through intensive parametric analyses of 21,600 linear and nonlinear MDOF systems and considering five different shear strength and stiffness distribution patterns, including three code-specified patterns as well as uniform and concentric patterns subjected to a group of earthquakes recorded on alluvium and soft soils, the effect of structural characteristics distribution on the strength demand and ductility reduction factor of MDOF fixed-base and soil-structure systems are parametrically investigated. The results of this study show that depending on the level of inelasticity, soil flexibility and number of degrees-of-freedoms (DOFs), structural characteristics distribution can significantly affect the strength demand and ductility reduction factor of MDOF systems. It is also found that at high levels of inelasticity, the ductility reduction factor of low-rise MDOF soil-structure systems could be significantly less than that of fixed-base structures and the reduction is less pronounced as the number of stories increases.

Effect of temperature on suspension magnetization roasting of hematite using biomass waste as reductant:A perspective of gas evolution

The magnetization reduction of hematite using biomass waste can effectively utilize waste and reduce CO_(2) emission to achieve the goals of carbon peaking and carbon neutrality.The effects of temperatures on suspension magnetization roasting of hematite using biomass waste for evolved gases have been investigated using TG-FTIR,Py-GC/MS and gas composition analyzer.The mixture reduction process is divided into four stages.In the temperature range of 200-450℃ for mixture,the release of CO_(2),acids,and ketones is dominated in gases products.The yield and concentration of small molecules reducing gases increase when the temperature increases from 450 to 900℃.At 700℃,the volume concentrations of CO,H_(2) and CH_(4) peak at 8.91%,8.90% and 4.91%,respectively.During the suspension magnetization roasting process,an optimal iron concentrate with an iron grade of 70.86%,a recovery of 98.66% and a magnetic conversion of 45.70% is obtained at 700℃.Therefore,the magnetization reduction could react greatly in the temperature range of 600 to 700℃ owing to the suitable reducing gases.This study shows a detail gaseous evolution of roasting temperature and provides a new insight for studying the reduction process of hematite using biomass waste.

Cognitive Behavioral Therapy:A Strategy for Depressive Moods Reduction of in Patients Experiencing Chronic Obstructive Pulmonary Emphysema Disease

Patients with Chronic Obstructive Pulmonary Disease(COPD)often experience difficulty breathing,decreased exercise tolerance and respiratory function as the disease progresses.Pulmonary rehabilitation training can improve respiratory symptoms,increase exercise tolerance and quality of life through exercise stimulation.However,after the end of pulmonary rehabilitation training,the patient's movement behavior is not easy to maintain.Cognitive behavioral therapy(CBT)can effectively enhance cognition,strengthen the motivation of"regular motor behavior",and maintain motor behavior,which can be used as a maintenance strategy for pulmonary rehabilitation training.Objective:To study the effect of cognitive behavioral therapy on the rehabilitation effect and the changing stage of"regular motor behavior"in COPD patients.Methods:30 patients consulted in the Rehabilitation Department of the Third Veterans Hospital of Sichuan Province were interviewed by telephone,and the exercise status and rehabilitation status were recorded and analyzed.From 30 patients,severe and extremely severe(GOLD grade III-IV)in motivation period of"regular exercise behavior"(not starting regular exercise but had exercise thoughts)were randomly divided into two groups.Pulmonary rehabilitation group(CBT-PR group,n=15)conducted one-to-one CBT intervention for 30-40 minutes to discuss the reasons for regular exercise and teach exercise precautions and principles using exercise education form;conventional pulmonary rehabilitation group(conventional PR group,n=15)conducted intensive pulmonary rehabilitation education without consultation and discussion.Both groups underwent 4 weeks of outpatient rehabilitation training,And the regular exercise ability was detected in the first and third months after training(6-Minutes Walking Distance,6-WMD;Short Physical Performance Battery,SPPB),(International Physical Activity Questionnaire,IPAQ),(St.George's Respiratory Scale,St.George's Respiratory Questionnaire,SGRQ),change.

Hot ductility behavior of a Fe-0.3C-9Mn-2Al medium Mn steel

The hot ductility of a Fe-0.3C-9Mn-2Al medium Mn steel was investigated using a Gleeble3800 thermo-mechanical simulator.Hot tensile tests were conducted at different temperatures(600-1300℃)under a constant strain rate of 4×10^(−3)s^(−1).The fracture behavior and mechanism of hot ductility evolution were discussed.Results showed that the hot ductility decreased as the temperature was decreased from 1000℃.The reduction of area(RA)decreased rapidly in the specimens tested below 700℃,whereas that in the specimen tested at 650℃was lower than 65%.Mixed brittle-ductile fracture feature is reflected by the coexistence of cleavage step,intergranular facet,and dimple at the surface.The fracture belonged to ductile failure in the specimens tested between 720-1000℃.Large and deep dimples could delay crack propagation.The change in average width of the dimples was in positive proportion with the change in RA.The wide austenite-ferrite intercritical temperature range was crucial for the hot ductility of medium Mn steel.The formation of ferrite film on austenite grain boundaries led to strain concentration.Yield point elongation occurred at the austenite-ferrite intercritical temperature range during the hot tensile test.

Electrochemical behavior and electrolytic preparation of lead in eutectic NaCl−KCl melts

A novel molten salt extraction process consisting of chlorination roasting and molten salt electrolysis was proposed to develop a more efficient and environmental friendly technology for recovering lead from spent lead acid batteries(LABs).The feasibility of this process was firstly assessed based on thermodynamics fundamentals.The electrochemical behavior of Pb(II)on a tungsten electrode in the eutectic NaCl−KCl melts at 700℃ was then investigated in detail by transient electrochemical techniques.The results indicated that the reduction reaction of Pb(II)in NaCl−KCl melts was a one-step process exchanging two electrons,and it was determined to be a quasi-reversible diffusion-controlled process.Finally,potentiostatic electrolysis was carried out at−0.6 V(vs Ag/AgCl)in the NaCl−KCl−PbCl2 melts,and the obtained cathodic product was identified as pure Pb by X-ray diffraction analysis.This investigation demonstrated that it is practically feasible to produce pure Pb metal by electrochemical reduction of PbCl2 in eutectic NaCl−KCl melts,and has provided important fundamental for the further study on lead recovery from spent LABs via molten salt extraction process.

Effects of microrolling parameters on the microstructure and deformation behavior of pure copper

Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.