Effect of temperature on magnetizing reduction of agbaja iron ore

Agbaja oolitic iron ore, which has not been responsive to such beneficiation processes as froth flotation, gravity concentration, magnetic separation, and electrostatic separation, has been concentrated to 60 pct Fe grade and 87.3 pet Fe recovery (starting from a crude assaying 45.6 pct Fe) by the magnetizing reduction technique. The main parameter investigated was the effect of temperature on the magnetizing reduction process, and 600 °C was established as the optimum temperature for the reduction step. X-ray diffraction studies of the reduction products showed that the iron oxides were converted to magnetite, to wustite, or to metallic iron, depending on the temperature of reduction. The results from the subsequent magnetic concentration step were, in the main, dependent on the observed reduction products.     

Effect of temperature and reaction path interaction on fluidization reduction kinetics of iron ore powder

Due to the instability of FeO at temperatures below 843 K,the fluidization reduction pathway of iron ore powder changes with the reduction temperature.Thus,the effect of temperature and reaction pathway interaction on the kinetics of fluidization reduction of iron ore powder under low-temperature conditions ranging from 783 to 903 K was investigated to describe the fluidization reduction rate of iron ore powder from three aspects:microstructure change,reaction limiting link,and apparent activation energy of the reaction,exploring their internal correlation.The experimental results revealed that in a temperature range of 783-813 K,the formation of a dense iron layer hindered the internal diffusion of reducing gas,resulting in relatively high gas diffusion resistance.In addition,due to the differences in limiting links and reaction pathways in the intermediate stage of reduction,the apparent activation energy of the reaction varied.The apparent activation energy of the reaction ranged from 23.36 to 89.13 kJ/mol at temperature ranging from 783 to 813 K,while it ranged from 14.30 to 68.34 kJ/mol at temperature ranging from 873 to 903 K.     

Smelting reduction of iron ore

On the basis of MIP development several process concepts for primary ironmaking technology were investigated. In the smelting reduction process described the reduction of iron ore occurs in three stages: in the first step the ore is preheated and prereduced in a cyclon-heat exchanger system. In the second step it is melted. The final reduction of the partially reduced and melted ore to metallic iron takes place in the MIP reactor.     

Effect of Ca-Fe oxides additives on NO_x reduction in iron ore sintering

As the emission control regulations get stricter,the NO_x reduction in the sintering process becomes an important environmental concern owing to its role in the formation of photochemical smog and acid rain.The NOxemissions from the sintering machine account for 48% of total amount from the iron and steel industry.Thus,it is essential to reduce NO_x emissions from the sintering machine,for the achievement of clean production of sinter.Ca-Fe oxides,serving as the main binding phase in the sinter,are therefore used as additives into the sintering mixture to reduce NOxemissions.The results show that the NO_x reduction ratio achieves 27.76% with 8% Ca-Fe oxides additives since the Ca-Fe oxides can advance the ignition and inhibit the nitrogen oxidation compared with the conventional condition.Meanwhile,the existence of Ca-Fe oxides was beneficial to the sinter quality since they were typical low melting point compounds.The optimal mass fraction of Ca-Fe oxides additives should be less than 8%since the permeability of sintering bed was significantly decreased with a further increase of the Ca-Fe oxides fines,inhibiting the mineralization reaction of sintering mixture.Additionally,the appropriate particle size can be obtained when mixing an equal amount of Ca-Fe oxides additives of-0.5 mm and 0.5-3.0 mm in size.     

Mechanism of improved magnetizing roasting of siderite–hematite iron ore using a synergistic CO–H2 mixture

A fluidized-bed magnetizing roasting-magnetic separation process was selected to treat this type of material.Phase transformations and microstructural changes in the product resulting from magnetizing roasting under different reducing gases(CO,H2,CO+H2)were clarified by vibrating sample magnetometry,X-ray diffraction,scanning electron microscopy,and energy-dispersive X-ray spectroscopy.The results indicated that the conversion ratio and saturation magnetization of samples roasted in a mixed gas of CO and H2 were higher than those of samples produced under CO or H2 alone.This indicated that synergy of the combined CO and H2 gas had a positive effect on the fluidized-bed magnetizing roasting process.The mechanism and kinetics of the improved magnetizing roasting of a siderite-hematite iron ore mixture under this synergistic CO-H2 system were investigated under isothermal conditions.The results indicated that the apparent activation energies of the reactions of the iron oxides decreased from 37.7 and 17.9 to 15.9 kJ/moI when the roasting atmosphere was changed from pure H2 or CO to a gas mixture of CO and H2,respectively.The mixed CO-H2 gas promoted the conversion ratio of hematite and siderite to magnetite,thereby improving the conversion ratio in the fluidized-bed magnetizing roasting process.     

Magnetic properties of low-grade hematite ore after magnetizing reduction and reoxidation using a fluidized bed

Magnetizing roasting via a fluidized bed,which was recognized as an efficient method for beneficiation of low-grade iron ores,has attracted much attention in China recently due to the fluctuation of the international iron ore market.In order to examine the effects of magnetic properties on the separability and to optimize the operating parameters,magnetic susceptibility and coercivity of a low-grade hematite after magnetizing reduction and reoxidation under different conditions were investigated.It was found that the magnetic susceptibility of roasted ore increased with reduction degree and particle diameter to different degrees.The magnetite was re-oxidized to maghemite when the temperature was below 400℃,and the magnetic susceptibility decreased slightly.The recovery efficiency decreased notably with the particle size for very fine grains although no significant change was found in magnetic susceptibility.The coercivity and remanence of roasted ores decreased with increasing roasting temperature.The scanning electron microscope(SEM) study showed that more cracks were produced by the reoxidation of reduced ores,which could possibly favor the intergranular fracturing and the liberation for further treatment.     

铁精矿粉粒度对精控还原工艺的影响

本文以河北承德地区的铁精矿粉为原料,选用模拟隧道窑还原工艺制备海绵铁粉,研究了铁精矿粉粒度对精控还原工艺的影响。结果表明:铁精矿粉粒度对其还原工艺影响很大,并直接影响海绵铁粉的产品性能。在既定试验条件下,随着铁精矿粉粒度的增大,其精控还原所需最优还原温度随着增加,最佳配碳量先减少后增大,而最佳还原时间随粒度的增大呈现出先增大后减小的变化趋势。究其原因为粒度过小导致的粉体烧结和粒度过大导致的粉体芯部不易还原均会阻碍还原过程的进行。45~75μm粒度区间铁精矿粉最适合作为制备优质海绵铁粉原料,其在配碳量0.8、还原温度1150℃、还原时间4.5 h的精控还原工艺下可制得的海绵铁粉的铁含量高达97.88%。     

高温还原对水雾化铁粉压缩性的影响

以莱钢集团粉末冶金有限公司LAP100.29水雾化铁粉为原料,在900℃下进行高温氢气还原,研究高温还原处理对水雾化铁粉的显微硬度、化学成分、松装密度、流动性、压缩性等性质的影响,以期对实际生产起到一定的借鉴和指导作用。结果表明:经900℃高温氢气还原处理后的铁粉纯度提高,大部分样品的流动性提高约2 s/50 g,松装密度提高0.1 g/cm3左右,压制密度提高0.1 g/cm3以上,而粉末显微硬度大幅降低至69～89 HV。在600 MPa下铁粉压制密度大部分达到7.15 g/cm3以上。     

生物质焦油还原多孔铁矿粉试验研究

针对生物质碳基还原动力学条件差、还原效率低的问题,将生物质裂解产物焦油作为还原剂,与铁矿粉混合还原炼铁。通过还原试验,对铁矿粉预热温度、还原温度、焦油与铁矿粉当量比等影响因素进行探讨。结果表明:铁产品质量随预热温度升高先上升后下降,在预热温度为450℃时达到最高;增加反应温度和铁矿粉与焦油当量比,能提高铁产品的还原度。当采用最佳工况(450℃预热30min,焦油与铁矿粉质量比1.2∶1,1 000℃下还原45min),可得到还原度为72.6%的还原铁产品。     

铁矿石等温气固还原动力学研究

将未反应核模型拓展应用于烧结矿气相还原,采用四阶龙格库塔法通过编制程序求解混合控制方程.通过数值计算与实验数据的对比,证明烧结矿的气固还原过程和球团矿一样可以用未反应核模型来描述.烧结矿形状不规则,不具有明确的半径,通过与前人研究的比较,本文摒弃了传统处理中的平均半径选取,利用数据分析得到了适用于烧结矿的等效半径,解决了烧结矿应用未反应核模型时的半径选取问题,为铁矿气固还原动力学的研究提供了新的参考.     

Morphology and reduction kinetics of fluxed iron ore pellets

Abstract

The present paper describes studies of the reduction and sintering behaviour, followed by examination of the structural changes taking place, during direct reduction of fluxed composite (ore plus coal) pellets. The kinetics and morphological aspects of the direct reduction of fluxed composite pellets are compared with those for the gaseous reduction of fluxed ore pellets without carbon addition. It is shown that the chemical reaction is the rate limiting factor for fluxed composite pellets, and the mass transport of reactant gas through the reaction product iron layer governs the overall reduction process in the case of fluxed ore pellets. Microscopic analysis of the fluxed composite pellets has indicated no tendency to form a reduction inhibition iron shell towards the end of the reduction, as found in the case of gaseous reduction of fluxed ore pellets under identical reduction process conditions. The effects of basicity, Fe/C, temperature, and other variables on morphological and microstructural changes in the directly reduced fluxed composite pellets have been experimentally investigated in the present work.     

高铝铁矿含碳球团直接还原的研究

用高铝铁矿粉配加煤粉造球,在实验室条件下,通过改变还原温度和碳氧比研究了含碳球团的还原,对还原后的球团进行化学分析以及X-射线衍射(XRD)检测。结果表明:试样在石墨坩埚中恒温还原4 h,还原完毕后立即取出通入惰性气体冷却,在还原温度为1 200℃、碳氧比为1.3时金属化率较高,达到88.45%,在此条件下,铁、铝分离效果较好。同时从工业应用角度分析了转底炉处理高铝铁矿石的可行性。     

高铝铁矿焙烧球团非等温还原研究

采用CO、H_2对高铝铁矿焙烧球团在高温同步热分析仪(NETZSCH STA 409C/CD)中进行非等温还原.结果表明:焙烧球团经CO还原后,随着设定温度由1 273 K升高到1 473 K,最终还原度由32.21%仅增加到46.78%;而经H_2还原后,随着设定温度由1 273 K升高到1 573 K,最终还原度由81.93%增加到100%.在纯氢气还原条件下,高铝铁矿焙烧球团中的铁氧化物是可以被彻底还原的.     

温度对氢气还原氧化铁影响及电化学性能研究

采用纯的氧化铁进行直接还原的实验研究,利用H2作为还原气体在高温管式炉中进行焙烧还原.结果表明,随着反应时间的增加,氧化铁块还原率相应的增大.反应温度的不同,氧化铁块还原速率及电导率也相应的不同.600~900℃下经过一定时间的氢还原,还原产物的还原速率随温度的增加而增加,均可达到95%以上.通过交流阻抗法对还原产物的电导率的测试,得到了还原产物的电导率随时间和还原度的变化曲线.随着温度及时间的不同,电导率也相应变化,电导率的不同,可间接反映还原过程中产生了导电性不同的物质.     

Study of solid mushroom formation in direct iron ore smelting reduction process using low temperature water model

Abstract

In the direct iron ore smelting reduction process, molten iron near the bottom blowing gas tuyere is cooled by low temperature/endothermic gas and forms a mushroom shaped solid on top of the tuyere. The formation of an appropriate solid mushroom, which covers the tuyere, can protect the tuyere and the surrounding refractory. In the present study, a water model with a low temperature gas system was established to investigate formation of the solid mushroom and the effects of operating conditions on its shape and dimensions. Transparent acrylic was used to construct the water model, which was 40% of the size of the actual furnace. Water was used to simulate the molten iron. Low temperature air, obtained by passing air through a heat exchanger cooled by liquid nitrogen, was blown into the water bath through a bottom tuyere. The air temperature was able to reach-188±1°C. In the water model experiments, water near the tuyere was cooled, and formed an ice mushroom surrounding the tuyere. The effects of operating conditions, mainly gas flowrate and mould material surrounding the tuyere, on the parameters of the solid mushroom were investigated. The parameters of the solid mushroom included whether it could be formed and duration of the solid mushroom, as well as the shape, dimensions, and weight of the solid mushroom. Attempts were also made to relate the temperature-time and pressure-time relationships of the blown gas to the parameters of the solid mushroom. With copper used as mould material surrounding the tuyere, the water model experiments were conducted with flowrate of the bottom blown gas set in the range 30-90 NL min^-1. The results show that as the gas flowrate was increased, the highest water temperature which allowed the solid mushroom to form in the water model was increased. Three different types of pressure-time curve were obtained under different gas flowrates in the present study. They also corresponded to different forms of solid mushroom. As peaks appeared in the pressure-time curve, they revealed ice capsulation and subsequent bursting to release the pressure. A gas flowrate of 80 NL min^-1 and water temperature of 19·2°C with copper plate as the bottom material are considered to be optimal conditions of the water model for growth of the appropriate ice mushroom. These data are rather consistent with the gas flowrate and superheat for the actual direct iron ore smelting reduction unit, which are 2700 NL min^-1 and 120°C (equivalent to 70 NL min^-1 and 22·7°C in the water model).     

Kinetics of smelting reduction of fluxed composite iron ore pellets

Kinetic studies on smelting reduction of unreduced fluxed composite pellets (FCP) and fluxed composite pre-reduced iron ore pellets (FCRIP) have been carried out in an induction furnace. The pellets are charged into the slag layer floating on the carbon saturated molten iron bath in a graphite crucible. The slag basicity was however varied such that it has the same value as that of the pellets charged. The temperature of the slag is varied within the range of 1623K to 1823K for the pellets of basicity 2.0. Kinetic studies show a mixed kinetic model of both diffusion and chemical reaction controlled. While the smelting of FCRIP follows the model expressed as G(or) = 1-(2/3)(α) -(1-α)^2/3, the unreduced FCP pellets initially follow the diffusion controlled model of G(α) = α² followed by a chemical reaction controlled first order model of -ln(1-α) at the latter stages of smelting reduction, where α denotes the degree of reduction. The basicity dependence on the kinetics is not very significant. Comparison of the activation energy values explains that the smelting reduction with pre-reduced pellets seems to be a rather less energy intensive process.