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.     

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.     

包头含铌铁精矿选择性还原试验

 采用兰炭为还原剂,利用罐式选择性还原的方法处理铌铁精矿,研究不同还原条件时金属化率的变化规律,利用扫描电镜观察铌的赋存形式,利用电炉熔分脱铁的方法处理还原后的铌铁精矿,考察铌氧化物的富集程度。研究结果表明,当温度为940～970 ℃时,还原2.5 h时铌铁精矿中铁氧化物金属化率可达85%以上,在还原过程中,铌氧化物不被还原成金属铌;铌主要以含钛、铁硅酸盐形式存在于还原后团块中;熔分获得金属铁和富铌渣,富铌渣中铌氧化物是原矿的1.55倍。     

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。     

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%。     

不同铁矿粉替代澳洲低铝矿粉对烧结黏结相高温行为的影响

澳洲某低铝矿粉具有低Al₂O₃、粗粒度、强同化性等优点,是国内钢铁企业进口矿石的主要来源之一,而该低铝矿粉已濒临枯竭,故寻求其他铁矿粉进行替代现已成为迫切需求。采用微型烧结等方法,考察不同铁矿粉替代该低铝矿粉后黏结相高温行为的变化。研究表明,当配加南美矿粉OA后,黏结相同化性减弱,液相流动性增强,铁酸钙含量降低;当配加北非铁矿OB粉后,黏结相同化性和液相流动性均增强,但硅酸钙含量有所增加;当配加2种澳洲铁矿粉OC和OD后,黏结相的同化性减弱,高铝脆性矿物含量增加。基于此,通过澳洲铁矿粉OC搭配北非铁矿粉OB共同替代该低铝矿粉的方式,增强黏结相同化性和流动性,提高铁酸钙含量,抑制了劣质矿物的生成。     

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.     

高磷铁矿石含碳球团等温还原动力学

为了研究高磷铁矿石含碳球团等温还原动力学在温度为1 173、1 273、1 323、1 373、1 423和1 473K时,采用界面化学反应模型、Jander方程、Ginstling-Broushtein方程、G Valensi-R E Carter方程等固-固/气反应机理函数对反应过程进行拟合,并采用XRD、SEM、EDX等对样品的物相组成、微观形貌和元素分布进行表征分析。研究结果表明,随着还原程度提高,反应速率由0迅速增至最大值,随后逐渐减小并趋于平缓;当温度为1 173～1 373K时,反应过程符合界面化学反应,表观活化能为70.02kJ/mol,线性相关系数为0.948 1;当温度为1 373～1 473K时,反应过程符合Jander方程,限制步骤为铁离子固相扩散,表观活化能为215.36kJ/mol,线性相关系数为0.991 2。     

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.     

铁矿粉气基直接还原过程中铁晶须生长观察

采用五段式卧式加热炉装置, 对5种粒度范围的巴西CVRD矿粉进行了不同温度、不同气氛条件下的气基直接还原实验, 还原后得到各个条件下具有不同表面颗粒形貌的矿粉样.对还原后的矿粉样进行金属化率检测和扫描电镜下微观形貌观察, 发现不同的还原条件对铁矿粉还原过程中矿粉颗粒形貌及颗粒表面铁晶须的生长状况具有重要影响, 研究发现可以从还原条件来控制矿粉颗粒的还原状况及颗粒表面形貌, 从而改善气基直接还原中的颗粒粘结状况.