NO_x reduction in the sintering process

A new process, NOx reduction with recycling flue gas and modifying coke breeze, was proposed. The effects of modified coke breeze and recycled flue gas on NOx reduction were investigated by sinter pot tests. The results show that the NOx reduction rate is over 10wt% in the sintering of modified coke breeze, the effects of the additives on NOx reduction are： CeO2〉CaO〉K2CO3. The NOx reduction rate increases with the amount of recycled flue gas, and is 22.35wt% in the sintering with recycling 30vol% of the flue gas. When 30vol% of the flue gas is recycled into the sintering of CeO2, CaO, and K2CO3 modified coke breeze, the NOx reduction rates are 36.10wt%, 32.56wt%, and 32.17wt%, respectively.

NO_x reduction by coupling combustion with recycling flue gas in iron ore sintering process

A new process called＇NOx reduction by coupling combustion with recycling flue gas（RCCRF）＇was proposed to decrease NOx emission during the iron ore sintering process.The simulation test of NOx reduction was performed over sintered ore and in the process of coke combustion.Experimentally,NOx reduction was also carried out by sintering pot test.For sintered ore,the amount of NOx emission is reduced by 15wt%-25wt% at 400-550oC using 2.0vol% H2 or 2.0vol% CO,or reduced by 10wt%-30wt% at 560-720oC using 0.15vol% NH3.NOx reduction is around 10wt% by coupling combustion of pyrolysis gas and coke,or around 16wt% by recycling flue gas into coke combustion.By RCCRF,the maximum NOx reduction ratio is about 23wt% in coke combustion experiment and over 40wt% in sintering pot test.

Influence of hydrogen concentration on Fe_2O_3 particle reduction in fluidized beds under constant drag force

The fixed-gas drag force from a model calculation method that stabilizes the agitation capabilities of different gas ratios was used to explore the influence of temperature and hydrogen concentration on fluidizing duration, metallization ratio, utilization rate of reduction gas, and sticking behavior. Different hydrogen concentrations from 5vol%to 100vol%at 1073 and 1273 K were used while the drag force with the flow of N2 and H2 （N2：2 L·min^-1;H2：2 L·min^-1） at 1073 K was chosen as the standard drag force. The metallization ratio, mean reduc-tion rate, and utilization rate of reduction gas were observed to generally increase with increasing hydrogen concentration. Faster reduction rates and higher metallization ratios were obtained when the reduction temperature decreased from 1273 to 1073 K. A numerical relation among particle diameter, particle drag force, and fluidization state was plotted in a diagram by this model.

Effects of gravity on the electrodeposition and characterization of nickel foils

The effects of gravity on nickel electrodeposition,the morphology and mechanical properties of deposits were studied in a super gravity field.Predictions in a microgravity field were also presented based on the obtained experimental tendency.Linear sweep voltammetry reveals that the nickel electrodeposition process is enhanced by increasing the gravity coefficient（G）.The limiting current density changes from 10.2 to 293.0 mA·cm-2 with the increase of the G value from 10-4 to 354.The morphology of deposits was analyzed by scanning electron microscopy（SEM） and atomic force microscopy（AFM）.The images show that the morphology deposited in the super gravity field has finer grain sizes and denser and smoother surfaces.The roughness reduces from 48.3 to 4.9 nm with the increase of the G value from 10-4 to 354.Meanwhile,mechanical tests indicate that the mechanical properties of nickel foils are greatly improved due to introducing a super gravity field during electrodeposition.

Supergravity separation of Pb and Sn from waste printed circuit boards at different temperatures

Printed circuit boards（PCBs） contain many toxic substances as well as valuable metals, e.g., lead（Pb） and tin（Sn）. In this study, a novel technology, named supergravity, was used to separate different mass ratios of Pb and Sn from Pb–Sn alloys in PCBs. In a supergravity field, the liquid metal phase can permeate from solid particles. Hence, temperatures of 200, 280, and 400°C were chosen to separate Pb and Sn from PCBs. The results depicted that gravity coefficient only affected the recovery rates of Pb and Sn, whereas it had little effect on the mass ratios of Pb and Sn in the obtained alloys. With an increase in gravity coefficient, the recovery values of Pb and Sn in each step of the separation process increased. In the single-step separation process, the mass ratios of Pb and Sn in Pb–Sn alloys were 0.55, 0.40, and 0.64 at 200, 280, and 400°C, respectively. In the two-step separation process, the mass ratios were 0.12 and 0.55 at 280 and 400°C, respectively. Further, the mass ratio was observed to be 0.76 at 400°C in the three-step separation process. This process provides an innovative approach to the recycling mechanism of Pb and Sn from PCBs.

Rapid removal of copper impurity from bismuth-copper alloy melts via super-gravity separation

A green method of super-gravity separation,which can enhance the filtration process of bismuth and copper phases,was investigated and discussed for the rapid removal of copper impurity from bismuth-copper alloy melts.After separation by the super-gravity field,the bismuth-rich liquid phases were mainly filtered from the alloy melt along the super-gravity direction,whereas most of the fine copper phases were retained in the opposite direction.With optimized conditions of separation temperature at 280℃,gravity coefficient at 450,and separation time at 200 s,the mass proportion of the separated bismuth from the Bi-2 wt%Cu and Bi-10 wt%Cu alloys respectively reached 96%and 85%,which indicated the minimal loss of bismuth in the residual.Simultaneously,the removal ratio of impurity copper from the Bi-2 wt%Cu and Bi-10 wt%Cu alloys reached 88%and 98%,respectively.Furthermore,the separation process could be completed rapidly and is environmentally friendly and efficient.

Removal of phosphorus-rich phase from high-phosphorous iron ore by melt separation at 1573 K in a super-gravity field

A new approach of removing the phosphorus-rich phase from high-phosphorous iron ore by melt separation at 1573 K in a super-gravity field was investigated. The iron？slag separation by super-gravity resulted in phosphorus being effectively removed from the iron-rich phase and concentrated as a phosphorus-rich phase at a temperature below the melting point of iron. The samples obtained by super-gravity exhibited obvious layered structures. All the iron grains concentrated at the bottom of the sample along the super-gravity direction, whereas the molten slag concentrated in the upper part of the sample along the opposite direction. Meanwhile, fine apatite crystals collided and grew into larger crystals and concentrated at the slag–iron interface. Consequently, in the case of centrifugation with a gravity coefficient of G = 900, the mass fractions of the slag phase and iron-rich phase were similar to their respective theoretical values. The mass fraction of MFe in the iron-rich phase was as high as 97.77wt% and that of P was decreased to 0.092wt%.

Synthesis and characterization of Co_3O_4 prepared from atmospheric pressure acid leach liquors of nickel laterite ores

A chemical precipitation-thermal decomposition method was developed to synthesize Co3O4 nanoparticles using cobalt liquor obtained from the atmospheric pressure acid leaching process of nickel laterite ores. The effects of the precursor reaction temperature, the concentration of Co2＋, and the calcination temperature on the specific surface area, morphology, and the electrochemical behavior of the ob- tained Co304 particles were investigated. The precursor basic cobaltous carbonate and cobaltosic oxide products were characterized and ana- lyzed by Fourier transform infrared spectroscopy, thermogravimetric differential thermal analysis, X-ray diffraction, field-emission scanning electron microscopy, specific surface area analysis, and electrochemical analysis. The results indicate that the specific surface area of the Co3O4particles with a diameter of 30 rim, which were obtained under the optimum conditions of a precursor reaction temperature of 30℃, 0.25 mol/L Co2＋, and a calcination temperature of 350℃, was 48.89 m2/g. Electrodes fabricated using Co3O4 nanoparticles exhibited good electrochemical properties, with a specific capacitance of 216.3 F/g at a scan rate of 100 mV/s.

Oxide coating mechanism during fluidized bed reduction: solid-state reaction characteristics between iron ore particles and MgO

Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles＇ surface during fluidized bed reduction. MgO powders and iron ore particles were mixed and compressed into briquettes and, subsequently, roasted at different temperatures and for different time periods. A Mg-containing layer was observed on the outer edge of the iron ore particles when the roasting temperature was greater than 1173 K. The concentration of Fe in the Mg-containing layer was evenly distributed and was approximately 10wt%, regardless of the temperature change. Boundary layers of Mg and Fe were observed outside of the iron ore particles. The change in concentration of Fe in the boundary layers was simulated using a gas–solid diffusion model, and the diffusion coefficients of Fe and Mg in these layers at different temperatures were calculated. The diffusion activation energies of Fe and Mg in the boundary layers in these experiments were evaluated to be approximately 176 and 172 k J/mol, respectively.

Effect of Al_(2)O_(3)/SiO_(2) mass ratio and CaO content on viscosity and structure of slag for pyrometallurgical processing of spent automotive catalysts

The effect of Al_(2)O_(3)/SiO_(2) mass ratio and CaO content on the viscosity and structure of the CaO-Al_(2)O_(3)-SiO_(2)-6MgO-1.5ZrO_(2)-1.5CeO_(2) slag was investigated.The results show that with the increase in Al_(2)O_(3)/SiO_(2) mass ratio,the viscous flow units within the slag gradually change from Si-O-Si to Al-O-Al and Al-O-Si.Furthermore,the substitution of Al_(2)O_(3) for SiO_(2) leads to the transformation of Si-O bonds towards weaker Al-O bonds,which weaken the bond strength of the aluminosilicate networks,thus leading to a decrease in the viscosity of slag.The increase in CaO content effectively promotes the depolymerization of the aluminosilicate networks,resulting in a significant decrease in the viscosity of the slag.The slag with Al_(2)O_(3)/SiO_(2) of 0.7-1.5 and CaO of 30 wt.%shows promise as the reference slag system for the Fe-collection smelting of spent automotive catalysts due to its good comprehensive performance.

Fundamental research on recovering metals from hot-dip Zn-Al-Mg dross by supergravity separation

The dross generated in the hot-dip Zn–Al–Mg coating process is a valuable co-product,since it contains high quantities of recyclable alloy.A new method to recover Zn–Al–Mg alloy from the industrial Zn–Al–Mg dross was proposed using supergravity separation.The separation efficiency was analyzed as a function of gravity coefficient(G),separation time,and separation temperature.The separation of Zn–Al–Mg alloy from the dross can be achieved at G>100.The alloy content in the dross decreased gradually with an increase in the gravity coefficient,the separation time,and the separation temperature.The alloy ratio in the enriched dross decreased almost linearly as the gravity coefficient increased,and the recovery of Zn–Al–Mg alloy from the dross exceeded 78%;these results were consistent with the results of the FactSage software calculation.The purified alloy can be in-situ used in the hot-dip Zn–Al–Mg bath for production.The feasibility of supergravity separation as a promising process for efficiently recovering Zn–Al–Mg alloy from Zn–Al–Mg dross was thus demonstrated.

Phosphorus migration mechanism between iron and high phosphorus gangue phase at high temperatures

The phosphorus migration mechanism during melting separation of non-carbon-reduced high phosphorus iron ore was investigated.Firstly,the equilibrium compositions of hydrogen-reduced high phosphorus iron ore at different temperatures were simulated by the use of equilibrium composition module of HSC Chemistry software.Then,thermodynamic calculation was verified by the real heat treatment of simulated hydrogen-reduced high phosphorus iron ore with several pure reagents including self-made pure fluorapatite.The iron particles in the simulated samples gathered and grew up during heat treatment.Meanwhile,the hypoeutectic structure of Fe-P with grid shape of high phosphorus phase and circular shape of low phosphorus phase emerged within those iron particles.With the penetration of phosphorus from the periphery into the iron particles,the grid structure became denser and denser.It proves that the elemenlal phosphorus can be reduced from the gangue phase by metallic iron without solid carbon at high temperatures.

Influence of Coating MgO on Sticking and Functional Mechanism during Fluidized Bed Reduction of Vanadium Titano-magnetite

The vanadium titano-magnetite （VTM） iron ore fines of 110--150/xm in diameter were reduced in a trans- parent quartz fluidized bed by 70 %CO-30 % H2 （volume fraction） mixtures. MgO powders served as coating agent to solve sticking problem. Two coating methods were introduced in this experiment： high temperature injection method and briquetting→oxidizing roast→crushing method. According to the experimental results, the minimum effective coating amount of MgO was 0. 1 mass%. The metallization ratio （MR） of the product rose from around 58% to above 90% with the above treatments. To investigate the sticking mechanism of fine ore, the morphology evolution was in- vestigated. Instead of iron whiskers, an interlaced fibrous porous surface formed. The ulvospinel （2FeO ： TiO2 ） in VTM is more difficult to be reduced than FeO according to thermodynamic calculation. XRD results showed that MgO diffused into Fe203 lattice before forming pleonaste （MgO · Fe2O3 ） during oxidizing roast at 1273 K. The melting point of the pleonaste is 1986 K and that made contribution to prevent the sticking problem.

Slag/metal Separation Process of Gas-reduced Oolitic High-phosphorus Iron Ore Fines

Slag/metal separation process of the highly reduced oolitic high-phosphorus iron ore fines was investigated. Samples were prepared using the reduced ore fines （metallization rate： 88%） and powder additives of CaO and Na2CO3. Slag/metal separation behavior tests were conducted using a quenching method and the obtained metal parts were subjected to direct observation as well as microstructure examination with SEM and EDS; iron recovery and phosphorus distribution tests were conducted using a Si-Mo high temperature furnace and the obtained metal parts were examined by ICP-AES analysis and mass measurement. Thermodynamic calculation using coexistence theory of slag structure was also performed. Results show that temperature for slag/metal separation must be higher than 1823 K and a satisfying slag/metal separation of the highly reduced ore fines needs at least 4 min; phosphorus con- tent of hot metal is mainly determined by thermodynamics; temperature of 1823-1873 K and Na2CO3 mixing ratio of about 3 % are adequate for controlling phosphorus content to be less than 0.3 mass% in hot metal; temperature, time and Na2CO3 mixing ratio do not have significant effect on iron recovery, and iron recovery rate could be higher than 80% as long as a good slag/metal separation result is obtained.

Carbon Dioxide Sequestration via Steelmaking Slag Carbonation in Alkali Solutions: Experimental Investigation and Process Evaluation

Carbon dioxide mineral sequestration with steelmaking slag is a promising method for reducing carbon dioxide in a large- scale setting. Existing calcium oxide or calcium hydroxide in steelmaking slag can be easily leached by water, and the formed calcium carbonate can be easily wrapped on the surface of unreacted steelmaking slag particles. Thus, further increase in the carbonation reaction rate can be prevented. Enhanced carbon dioxide mineral sequestration with steel- making slag in dilute alkali solution was analysed in this study through experiments and process evaluation. Operating conditions, namely alkali concentration, reaction temperature and time, and liquid-to-solid ratio, were initially investigated. Then, the material and energy balance of the entire process was calculated, and the net carbon dioxide sequestration efficiency at different reaction times was evaluated. Results showed that dilute alkali solution participated in slowing down the leaching of active calcium in the steelmaking slag and in significantly improving carbonation conversion rate. The highest carbonation conversion rate of approximately 50% can be obtained at the optimal conditions of 20 g/L alkali concentration, 2 mL/L liquid-to-solid ratio, and 70 ℃ reaction temperature. Carbonation reaction time significantly influences the net carbon dioxide sequestration efficiency. According to calculation, carbon dioxide emission of 52.6 kg/t- slag was avoided at a relatively long time of 120 min.

In situ observation of iron ore particle reduction above 1373K by confocal microscopy

The reduction behavior of single iron ore particle was investigated at high temperatures(above 1373 K)with CO/CO2 mixture.A high-temperature laser scanning confocal microscope for in situ observation and a vertical quenching furnace for offline characterization were designed.The reduction process of ore particles at different temperatures and in different atmospheres was videoed using the confocal microscope.In the temperature range studied,the transformation of Fe2O3-FeO firstly occurred in the ore particles,and there was no metallic iron until the ore particles completely converted to FeG phase.During the formation of FeO phase,its crystal lattice transforms along the most close-packed direction of its close-packed plane(111).The gangue-rich area firstly melts during reduction around 1573 K.Above 1673 K,the iron ore particles melt and form spherical liquid drops with metallic iron in the center.The gas-based reduction behavior of iron ore particles above 1373K is deduced and graphically presented.

Recovery of zinc from Zn-Al-Fe alloys by gas pressure filtration

The recovery of zinc from galvanizing dross and the removal of iron contained dross particles by gas pressure filtration were investigated using the model of Zn-Fe-Al alloys.The majority of molten zinc was separated after filtration,and the residue intercepted by the filter consisting mostly of dross particles.The effects of the pressure differential(p),separation temperature(T)and alloy composition on the zinc recovery and iron removal were investigated.At p=0.30 MPa and T=723 K,86.2 wt.%zinc was recovered from the Zn-4Al-2Fe alloy,and up to 99.9 wt.%of the iron was concentrated in the residue.Applying a higher pressure differential led to the improved filtration efficiency,and the desired separation temperature was about 723 K.The aluminum content in the Zn-Al-Fe alloy had little effect on separation efficiency,whereas increasing the iron content led to a decrease in the separation efficiency.Our findings demonstrate the potential of the gas pressure filtration method for the recovery of zinc from galvanizing dross.

Evolution of microstructure,mechanical and magnetic properties of electrodeposited 50% Ni-Fe alloy foil after thermal treatment

In order to expand the application of the electrodeposited Ni-Fe alloy foil,their mechanical and magnetic properties were studied after heat treatment.The development of grain growth during annealing was in-situ online investigated using a heating stage microscope,and the texture was analyzed via X-ray diffraction（XRD）and electron back-scattered diffraction（EBSD）.The results indicated that abnormal grain growth usually occurred during annealing at 1000-1050°C.The{111}oriented grains preferentially grew as the annealing temperature and holding time increased.The plasticities of the electrodeposited Ni-Fe alloy foils after heat treatment were better than those of the original samples.The excellent ductility was obtained without a loss in magnetic properties after annealing at 1100°C for 6h.