Thermodynamics calculation on the oxidation and sulfur removal abilities of slag in EAF dust pellet reduction process

ＥＡＦｄｕｓｔｈａｓｂｅｅｎｃｌａｓｓｉｆｉｅｄａｓｈａｚａｒｄｏｕｓｗａｓｔｅ ,ａｎｄｉｔｉｓｈａｒｍｆｕｌｉｎｔｈｅｃｏｎｖｅｎｔｉｏｎａｌｌａｎｄ ｆａｌｌｄｕｅｔｏｃｏｎｔａｉｎｉｎｇｈｅａｖｙｍｅｔａｌｓ[1] .Ｍｏｓｔｒｅｃｙ ｃｌｉｎｇｍｅｔｈｏｄｓ[2 8] ｄｅｖｅｌｏｐｅｄｆｏｒｔｈｅｄｕｓｔｓａｒｅｏｎｌｙｆｏｒｔｈｅｒｅｃｏｖｅｒｙｏｆｌｅａｄ ,ｚｉｎｃａｎｄｃａｄｍｉｕｍ .ＴｈｅＥＡＦｄｕｓｔｆｒｏｍｓｔａｉｎｌｅｓｓｓｔｅｅｌｍａｋｉｎｇｍａｉｎｌｙｃｏｎ ｔａｉｎｓｎｉｃｋｅ…     

Oxidation performance of Fe-Al/WC composite coatings produced by high velocity arc spraying

Fe-Al intermetallics with remarkable high-temperature intensity and excellent erosion, high-temperature oxidation and sulfuration resistance are potential low cost high-temperature structural materials. But the room temperature brittleness induces shape difficult and limits its industrial application. The Fe-Al intermetallic coatings were prepared by high velocity arc spraying technology with cored wire on 20G steel, which will not only obviate the problems faced in fabrication of these alloys into useful shapes, but also allow the effective use of their outstanding high-temperature performance. The Fe-Al/WC intermetallic composite coatings were prepared by high velocity arc spraying technology on 20G steel and the oxidation performance of Fe-Al/WC composite coatings was studied by means of thermogrativmetic analyzer at 450, 650 and 800°C. The results demonstrate that the kinetics curve of oxidation at three temperatures approximately follows the logarithmic law. The composition of the oxidized coating is mainly composed of Al₂O₃, Fe₂O₃, Fe₃O₄ and FeO. These phases distribute unevenly. The protective Al₂O₃ film firstly forms and preserves the coatings from further oxidation. Foundation item: Project(50235030) supported by the National Natural Science Foundation of China; Project(98BK014) supported by the Foundation of State Economy Trade Committee of China     

Pressureless sintered 3Y-TZP/20%Al2O3 composite ceramic

Nanometer 3Y-TZP/20%Al₂O₃ (mass fraction) composite powders prepared by the chemical coprecipitation method were pressureless sintered at 1550 °C for 2 h. Effects of calcining temperatures at 800 °C, 1 000 °C, and 1 200 °C on phase structure, relative density, and Vicker’s hardness of the sintered bodies were studied. The results show that 1 000 °C was the optimal calcining temperature, and the powder calcined was composed of tetragonal zirconia with the Scherrer crystalline size of 6.3nm. The relative density was up to 98.5% under pressureless sintering, and the sintered body was t-ZrO₂ (without m-ZrO₂)+α-Al₂O₃ with the average size of 0.4 μm. Foundation item: State Key Laboratory for Powder Metallurgy(No.9706-36) Biography of the first author: YIN Bang-yao, born in 1966, majoring in advanced ceramic materials.     

Preparation of LiFePO4 for lithium ion battery using Fe2P2O7 as precursor

In order to obtain a new precursor for LiFePO4, Fe2P2O7 with high purity was prepared through solid phase reaction at 650 ℃ using starting materials of FeC2O4 and NH4H2PO4 in an argon atmosphere. Using the as-prepared Fe2P2O7, Li2CO3 and glucose as raw materials, pure LiFePO4 and LiFePO4/C composite materials were respectively synthesized by solid state reaction at 700 ℃ in an argon atmosphere. X-ray diffractometry and scanning electron microscopy（SEM） were employed to characterize the as-prepared Fe2P2O7, LiFePO4 and LiFePO4/C. The as-prepared Fe2P2O7 crystallizes in the Cl space group and belongs to β-Fe2P2O7 for crystal phase. The particle size distribution of Fe2P2O7 observed by SEM is 0.4-3.0 μm. During the Li^＋ ion chemical intercalation, radical P2O7^4- is disrupted into two PO4^3- ions in the presence of O^2-, thus providing a feasible technique to dispose this poor dissolvable pyrophosphate. LiFePO4/C composite exhibits initial charge and discharge capacities of 154 and 132 mA·h/g, respectively.     

Microstructures and mechanism of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al composites fabricated by the reaction between SiO<Subscript>2</Subscript> and molten aluminum

Al₂ O₃/Al composite was fabricated by the reaction between SiO₂ and molten aluminum. The microstructures of the composite obtained under different reaction conditions were analyzed. The formation mechanism of the composite microstructure was discussed. Results show that the reaction kinetics is influenced remarkably by the reaction temperature, reaction time and the quantity of SiO₂. The morphologies of Al₂O₃ have different features, depending on the reaction temperature. The composite has equaxed Al₂O₃ grains when materials reacted below 1200°C, and the composite is composed of a large number of fine Al₂O₃ grains and aluninum. The composite has a frame-shaped Al₂O₃ microstructure at the reaction temperature of above 1250°C. CHENG Xiao-min: Born in 1964 Funded by the National Natural Science Foundation of China (No. 91522)     

Selective leaching of vanadium from V-Ti magnetite concentrates by pellet calcification roasting-H_2SO_4 leaching process

A novel method of pellet calcification roasting-H_2 SO_4 leaching was proposed to efficiently separate and extract vanadium(V) from vanadium-titanium(V-Ti) magnetite concentrates.The leaching rate of V is as high as 88.98%,while the leaching rate of impurity iron is only 1.79%.Moreover,the leached pellets can be used as raw materials for blast furnace ironmaking after secondary roasting.X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy with energy dispersive X-ray spectrometry(SEMEDS) analyses showed that V~(3+) was oxidized to V~(5+) after roasting at 1200℃,and V~(5+) was then leached by H_2 SO_4.X-ray diffraction(XRD) analyses and single factor experiment revealed a minimal amount of dissolved Fe_2 O_3 during H_2 SO_4 leaching.Therefore,a high separation degree of V and iron(Fe) from V-Ti magnetite concentrate was achieved through H_2 SO_4 leaching.Compared with the traditional roastingleaching process,this process can achieve a high selectivity of V and Fe,and has excellent prospects for industrial production.     

Kinetics of Fe3O4 formation by air oxidation

The kinetics of Fe₃O₄ formation by air oxidation of slightly acidic suspension of Fe(OH)₂ was studied. The effects of initial concentration of Fe(II), temperature, partial pressure of oxygen, air flow rate and stirring rate on the oxidation rate were investigated. The results show that Fe₃O₄ formation is composed of two-step reaction, the first step is the formation of Fe(OH) ₂ ⁺ by oxidation of Fe(OH)⁺ complex ions, the second step is the formation of magnetite by dehydration and deprotonation of Fe(OH)⁺ and Fe(OH) ₂ ⁺ . The oxidation reaction is zero-order with respect to the concentration of Fe(II) and around 0.5-order with respect to partial pressure of oxygen, and oxygen transfer process is rate-limiting step of oxidation reaction with apparent activation energy of 2.74 kJ · mol⁻¹.     

Thermal Instability and Microstructure of Strontium M-type Hexaferrite Nanoparticles Synthesized by Citrate Approach

The dried gel of SrFe12O19, prepared by citrate approach, was investigated by means of infrared spectroscopy （ IR ）, thermogravimetric analysis （ TG ）, differential scanning calorimetry （ DSC ）, X- ray diffraction（ XRD ） techniques, energy dispersive spectroscopy（ EDS ）, and transmission electron microscopy（ TEM ）. The thermal instability and the thermal decomposition of low-temperature strontium M-type hexaferrite crystallized at about 600℃ were confirmed for the first time by XRD method. The decomposition of the low-temperature strontium M-type hexaferrite took place at about 688.6℃ determined by DSC investigation. The low-temperature strontium M-type hexaferrite nanopartieles were decomposed into SrFeO2.5 with an orthorthombic cell and Fe2O3 with a tetragonal cell as well as possibl α-Fe2O3 . The agglomerated particles with sizes less than 200 nm obtained at 800℃ were plesiomorphous to strontium M-type hexaferrite. The thermally stable strontium M-type hexaferrite nanopartieles with sizes less than 100um cotdd take place at 900 ℃ . Up to 1000 ℃ , the phose transformotion to form strontium M-type hexaferrite was ended, the calcinations with the sizes more than 1μm were composed of α-Fe2O3 and strontium M-type hexaferrite. The method of distinguishing γ-Fe2O3 with a spinel structure from Fe2O3 with tetragonal cells by using powder XRD method was proposed. Fe2O3 with tetragonal cells to be crystallized before the crystallization of thermally stable strontium M-type hexaferrite was confirmed for the first time. The reason why α- Fe2O3 as an additional phase appears in the calcinations is the cationic vacancy of stroutium M-type hexaferrite , SrFe12-x□O19 （0≤x ≤0.5）.     

Synthesis and characterization of Fe3O4 magnetic nanoparticles and their heating effects under radiofrequency capacitive field

Fe₃O₄ magnetic nanoparticles with diameters varying from 10 to 426 nm were synthesized and characterized. Heating effects of Fe₃O₄ magnetic nanoparticles under radiofrequency capacitive field (RCF) with frequency of 27.12 MHz and power of 60–150 W were investigated. When the power of RCF is lower than 90 W, temperatures of Fe₃O₄ magnetic nanoparticles (75–150 mg/mL) can be raised and maximal temperatures are all lower than 50 °C. When the power of RCF is 90–150 W, temperatures of Fe₃O₄ magnetic nanoparticles can be quickly raised and are all obviously higher than those of normal saline and distilled water under the same conditions. Temperature of Fe₃O₄ magnetic nanoparticles can even reach 70.2 °C under 150 W RCF. Heating effects of Fe₃O₄ magnetic nanoparticles are related to RCF power, particle size and particle concentration.     

Synthesis of Ni-Zn ferrite and its microstructure and magnetic properties

1 INTRODUCTION Ni-Zn ferrite with spinel structure is a versatile technological material due to their high-resistivity and low-eddy current losses, particularly suitable for high-frequency applications. Ni-Zn ferrites have been commercially used in recording heads, antennas rods, loading coils, microwave devices and telecommunication applications fields, and so on[1?2]. Ni-Zn ferrites are usually prepared by the conventional ceramic method[3] and the wet-chemical method[4?16]. The cerami…     

Effect of Mg/Al ratios on hydration mechanism of tabular alumina carbon composites reinforced by Al<Subscript>4</Subscript>C<Subscript>3</Subscript> in situ reaction

Hydration mechanism of tabular alumina carbon composites reinforced by Al₄C₃ in situ reaction with Mg and Al was researched in water steam using super automatic thermostatic water bath from 25 °C to 85 °C. It is shown that hydration mechanism of the composites is chemical reaction control at 44.3 °C-84 °C in H₂O(g). The hydration was controlled by diffusion from 24.7 °C to 33 °C. The ratio of added Mg/Al influences the HMOR of the composites.The mechanism of HMOR of the composites with different ratios of Mg/Al can be discovered by means of SEM analysis. The active Mg/Al powder and flake graphite inside give the composites outstanding hot strength resulting from the interlocking structure of Al₄C₃ crystals at high temperature. Besides, the matrix changes into the Al₄C₃ with high refractoriness. The method of preventing the hydration of tabular alumina carbon composites reinforced by Al₄C₃ in situ reaction was immersed in the wax at suitable temperature or storing them below 33 °C in a dry place or storing them with paraffin-coating.     

Thermodynamics and kinetics of calcium sulphoaluminate

The formation process of calcium suphoaluminate(C4A3S) was investigated by the X-ray diffraction technique and then the thermodynamics was analyzed, finally the kinetics of which was studied by SC-132. XRD results show that the formation of C4A3S is accomplished in three different kinds of ways: one is by solid reaction of Ca (OH)2/ CaO, Al2O3 and CaSO4, other two ways are through such interstitial products as CaO·Al2O3 and CaO·2Al2O3. The formation thermodynamics shows that C4A3S begins to form at 900 ℃-1 000 ℃ and increases as temperature rising; the quantity of reaches the highest at 1 300 ℃-1 350 ℃ and then falls at >1350℃. Kinetics study shows that the formation rate of C4A3S can be described as first-order kinetics at high temperature, and it belongs to the random nucleation growth mechanism. The apparent activation energy is 456.37 kJ·mol-1 and pre-exponential factor is 1.545×1012.     

Synthesis of MnZn Ferrite Nanoscale Particles by Hydrothermal Method

ＭｎＺｎｆｅｒｒｉｔｅｓａｒｅｗｉｄｅｌｙｕｓｅｄｉｎｅｌｅｃｔｒｏｎｉｃａｐｐｌｉｃａ ｔｉｏｎｓｓｕｃｈａｓｔｒａｎｓｆｏｒｍｓｃｈｏｋｅｃｏｉｌｓａｎｄｎｏｉｓｅｆｉｌｔｅｒｓｂｅ ｃａｕｓｅｏｆｔｈｅｉｒｈｉｇｈｅｒｐｅｒｍｅａｂｉｌｉｔｉｅｓａｎｄｌｏｗｍａｇｎｅｔｉｃｌｏｓｓ ｅｓａｔｈｉｇｈｆｒｅｑｕｅｎｃｉｅｓ .Ｔｈｅｉｒｐｒｏｐｅｒｔｉｅｓｌａｒｇｅｌｙｄｅｐｅｎｄｓｏｎｔｈｅｉｒｍｉｃｒｏｓｔｒｕｃｔｕｒｅ .[1]Ｓｏｔｈｅｎａｎｏ ｔｅｃｈｎｉｑｕｅｗｅｒｅｉｎ ｔｒｏｄｕｃｅｄｔ…     

Preparation and characterization of nanocomposite MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

Nanocomposites MgFe₂O₄/SiO₂ were successfully synthesized by the sol-gel method in the presence of N, N-dimethylformamide (DMF). The formation of pure MgFe₂O₄ was confirmed by powder X-ray diffraction (XRD) and electron diffraction. The structural evolution of MgFe₂O₄ nanocrystals was followed by powder X-ray diffraction and IR absorption spectroscopy. The formation of spinel structure of MgFe₂O₄ started at 800 °C, and completed at 900 °C. The transmission electron microscopy (TEM) measurements suggest that the particle sizes increase with the increasing annealing temperature, and the mean particle sizes of the spherical samples annealed at 800 °C, 900 °C and 1 050 °C are ca. 3 nm, 8 nm and 11 nm, respectively. Magnetization measurements at room temperature and 78 K indicate superparamagnetic nature of these MgFe₂O₄ nanocrystals. Funded by the National Natural Science Foundation of China(No. 30771676), the Natural Science Foundation of Jiangsu Province (No. BK20081842), and the Foundation of Nanjing Bureau of Personal for the Returned Overseas Chinese Excellent Scholars     

Synthesis and characterization of biomimetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/coke magnetic nanoparticles composite material

A composite material (Fe₃O₄/Coke) using coke supported Fe₃O₄ magnetic nanoparticles was successfully prepared via an in-situ chemical oxidation precipitation method and characterized by SEM, XRD, Raman, and FTIR. The results showed that the Fe₃O₄ nanoparticles existed steadily on the surface of coke, with better dispersing and smaller particle size. The catalytic ability of Fe₃O₄/Coke were investigatied by degrading p-nitrophenol (P-NP). The results showed that the apparent rate constant for the P-NP at 1.0 g·L^?1 catalyst, 30 mmol·L^?1 H₂O₂, pH=3.0, 30 °C and the best ratio of Coke/Fe₃O₄ 0.6, was evaluated to be 0.027 min^–1, the removal rate of COD_Cr was 75.47%, and the dissolubility of Fe was 2.42 mg·L^–1. Compared with pure Fe₃O₄, the catalytic ability of Fe₃O₄/Coke in the presence of H₂O₂ was greatly enhanced. And Fe₃O₄/Coke was a green and environmental catalyst with high catalytic activity, showing a good chemical stability and reusability.     

Temperature dependence on reaction of CaCO3 and SO2 in O2/CO2 coal combustion

The temperature dependence on the reaction of desulfurization reagent CaCO₃ and SO₂ in O₂/CO₂ coal combustion was investigated by thermogravimetric analysis, X-ray diffraction measurement and pore structure analysis. The results show that the conversion of the reaction of CaCO₃ and SO₂ in air is higher at 500–1 100 °C and lower at 1 200 °C compared with that in O₂/CO₂ atmosphere. The conversion can be increased by increasing the concentration of SO₂, which causes the inhibition of CaSO₄ decomposition and shifting of the reaction equilibrium toward the products. XRD analysis of the product shows that the reaction mechanism of CaCO₃ and SO₂ differs with temperature in O₂/CO₂ atmosphere, i.e. CaCO₃ directly reacts with SO₂ at 500 °C and CaO from CaCO₃ decomposition reacts with SO₂ at 1 000 °C. The pore analysis of the products indicates that the maximum specific surface area of the products accounts for the highest conversion at 1 100 °C in O₂/CO₂ atmosphere. The results reveal that the effect of the atmosphere on the conversion is temperature dependence.     

New technique of comprehensive utilization of spent Al2O3 -based catalyst

A new technology was developed to recover multiple valuable elements from the spent Al2O3-based catalyst by X-ray phase analysis and exploratory experiments. The experimental results show that in the condition of roasting temperature of 750 ℃ and roasting time of 30 min, molar ratio of Na2O to Al2O3 of 1.2, the leaching rates of alumina, vanadium and molybdenum in the spent catalyst are 97.2%, 95.8% and 98.9%, respectively. Vanadium and molybdenum in sodium aluminate solution can be recovered by precipitators A and B, and the precipitation rates of vanadium and molybdenum are 94. 8% and 92. 6%. Al（OH）3 was prepared from sodium aluminate solution in the carbonation decomposition process, and the purity of Al2O3 is 99. 9% after calcination, the recovery of alumina reaches 90. 6% in the whole process; the Ni-Co concentrate was leached by sulfuric acid, a nickel recovery of 98. 2% and cobalt recovery over 98.5% can be obtained under the experimental condition of 30% H2SO4, 80 ℃, reaction time 4 h, mass ratio of liquid to solid 8, stirring rate 800 r/min.     

Study on solubility of Nb2O5 in KOH solution and alkali leaching of niobite

Solubility of Nb₂O₅ and leaching behaviors of Nb and Ta from niobite in KOH solution have been investigated in order to develop an alkali hydrothermal leaching process of Nb and Ta. The solubility of Nb₂O₅ was measured in the range of 40 °C to 200 °C at various molar ratios of K₂O to Nb₂O₅(n(K₂O)/n(Nb₂O₅)). It has been found that Nb₂O₅ shows the maximum solubility at the solution composition of n(K₂O)/n(Nb₂O₅)=4/3 at a given temperature; the rise of temperature increases the solubility of Nb₂O₅ below 120 °C, but decreases it above 120 °C. The leaching behaviors of Nb and Ta were studied in the range of 150 °C to 250 °C and 0.1 MPa to 5 MPa. With the rise of temperature, the leaching degree increases when the leaching temperature is below 200 °C, but it decreases when the leaching temperature is above 200 °C. The maximum leaching degree is about 90% at 200 °C. It was proved that the alkali hydrothermal leaching process is effective for the recovery of Nb and Ta from niobite concentrate. Foundation item: The Key Project of Science and Technology Agency of Japan, 1994 Biography of the first author: ZHOU Kang-gen, doctor of engineering, professor, born in 1963, majoring in extractive metallurgy of rare metals and application of membrane separation technology.     

Synthesis of γ-Al2O3 nanoparticles by chemical precipitation method

Highly pure active γ-Al₂O₃ nanoparticles were synthesized from aluminum nitrate and ammonium carbonate with a little surfactant by chemical precipitation method. The factors affecting the synthesis process were studied. The properties of γ-Al₂O₃ nanoparticles were characterized by DTA, XRD, BET, TEM, laser granularity analysis and impurity content analysis. The results show that the amorphous precursor Al(OH)₃ sols are produced by using 0.1 mol/L Al(NO₃)₃ · 9H₂O and 0.16 mol/L (NH₄)₂CO₃ · H₂O reaction solutions, according to the volume ratio 1.33, adding 0.024% (volume fraction) surfactant PEG600, and reacting at 40 °C, 1 000 r/min stirring rate for 15 min. Then, after stabilizing for 24 h, the precursors were extracted and filtrated by vacuum, washed thoroughly with deionized water and dehydrated ethanol, dried in vacuum at 80°C for 8 h, final calcined at 800 °C for 1 h in the air, and high purity active γ-Al₂O₃ nanoparticles can be prepared with cubic in crystal system, O _H ⁷ -FD3M in space group, about 9 nm in crystal grain size, about 20 nm in particle size and uniform size distribution, 131. 35 m²/g in BET specific surface area, 7 – 11 nm in pore diameter, and not lower than 99.93% in purity. Foundation item: Project(03JJY3015) supported by the Natural Science Foundation of Hunan Province     

Influence of heat treatment temperature on microstructure and bonding of TiO<Subscript>2</Subscript> film coated on diamond particles surface

TiO₂ films were coated on the surface of diamond particles using a sol-gel method. The effects of heat treatment temperature on the morphology, phase composition and chemical bond of diamond particles coated with TiO₂ films were investigated through SEM, TEM, X-ray diffraction analysis, Raman spectroscopy, FTIR, and XPS. The results showed that when being heat-treated at 600 °C, the amorphous TiO₂ film transfered to the anatase film which bonded well with diamond substrate. Meanwhile, the Ti-O-C bond formed between TiO₂ film and diamond substrate. When being heat-treated at 800 °C, TiO₂ film was still anatase, and partial diamond began to graphitize. The graphitizated carbon could also form the Ti-O-C bond with TiO₂ film, although TiO₂ film would tend to crack in this case.