Reduction and Swelling of Fired Hematite Iron Ore Pellets by Non-coking Coal Fines for Application in Sponge Ironmaking

In the present investigation, the reduction and swelling behaviors (in low grade coal) of fired iron ore pellets, prepared by blending hematite iron ore fines of ?100, ?18 + 25, and ?10 + 16 mesh sizes in different proportions, have been studied in the temperature range of 850–1000°C with an objective to promote massive utilization of fines in sponge ironmaking. An increase in temperature up to the range studied (850–1000°C) substantially enhanced the reduction rate and the rate was found to be highest in the first 15–30 min at all these temperatures. All the fired pellets, made by mixing iron ore particles of ± 100 mesh size, have shown approximately the same reduction rates and slightly higher swelling indices than those made from fines of ?100 mesh size only. In all the fired pellets reduced at temperatures of 850°C and 900°C, the results indicated an increase in the extent of swelling with reduction time. Reduction of fired pellets at temperatures of 950°C and 1000°C exhibited shrinkage in their reduced products, and the extent of this shrinkage increased with increase in exposure time.     

Brazilian Iron Ore and Production of Pellets

Brazil is the second-largest producer of iron ore in the world. Brazilian richer superficial deposits are composed of brittle material with fine texture and significant amounts of fines are generated during mining and transport. Another type of ore found in this country is the itabirites that have lower iron contents. Beneficiation and concentration steps are required to prepare these materials for the pelletizing process. A general view of Brazilian types of iron ores, mines, and mining companies is given in this work. Special attention is given to pelletizing and the influence of mineralogical characteristics of different ores on the production and final properties of iron ore pellets.     

铁矿粉和煤粉复合等温还原

通过铁矿粉和煤粉复合圆柱试样在1100~1250℃等温还原,研究了还原温度、还原时间和W_煤粉/W_矿粉比对还原度的影响,确定了适宜配煤量。用积分法计算了不同还原阶段的表现活化能。通过化学分析和电镜观察,检查了试样沿直径方向的还原均匀程度。     

含碳球团冷固结成形的正交回归试验研究

 通过正交试验研究了用铁矿石和煤粉制造冷固结含碳球团的影响因素。考察了粘结剂的加入量、水含量、压球机的压力、压球机进料速度、压球速度、烘干温度和烘干时间对球团抗压强度的影响。结果表明：粘结剂加入量、烘干时间与水含量对球团的抗压强度影响最大,并进一步通过回归试验获得了这3个影响因素与球团抗压强度之间的回归方程。经验证,方程在一定范围内与试验结果符合较好。试验过程中获得的铁矿石冷固结含碳球团的最大抗压强度为25167N。     

铁矿球团复合粘结剂技术经济评价

基于国内外球团矿复合粘结剂研究情况,介绍了球团矿粘结剂的理想模型及复合作用机理,详细论述了复合粘结剂种类、化学成分、基本物性,重点阐述了复合粘结剂对生球质量、成品球团质量、显微组织及其经济性的影响。目前,生产中广泛应用的是由膨润土和有机粘结剂制备的复合粘结剂,而添加镁质复合粘结剂、SF碱性粘结剂和含铁复合粘结剂是改善球团矿品质的重要途径,但其在生产中推广应用还有待进一步研究。     

高铝铁矿石球团气基还原物相状态研究

在温度为950℃、还原气氛为纯CO条件下,对高铝铁矿石球团进行气基还原,还原时间分别为0、5、10、 20、40、60、80 min以及110 min,以明确各时间段内物相的变化情况。研究结果表明,还原5 min时即出现金属铁、 FeAl 2 O 4 和Fe 2 SiO 4 3种物相,10 min以至更长时间时金属铁峰强度有所增强,而其他2相变化并不明显;另外,该 种铁矿石中氧化铁的逐级还原规律并不明显,当金属铁相过早出现时,Fe 3 O 4 相以及独立存在的浮士体相未检测到。     

Effects of Binder on the Properties of Iron Ore-Coal Composite Pellets

Large amounts of fines and superfines are generated in Indian iron ore and coal mines due to mechanized mining and mineral dressing operations. Utilization of these fines for extracting metal is of vital concern for resource utilization and pollution control. For agglomeration of these fines, a suitable binder is required. Iron ore-coal composite pellets were prepared by cold bonding. Various binders such as lime, Ca(OH)₂, slaked lime, dextrose, molasses, and sodium polyacrylate (SPA), alone or in combination, were employed for making composite briquettes. The slaked lime–dextrose combination produced the highest strength among the various binders employed for producing composite briquettes and was therefore selected for producing composite pellets for the smelting reduction. In cold bonding, the composite pellets attain the requisite properties due to physico-chemical changes of the binder in ambient conditions. It was possible to obtain a dry strength of more than 300 N per pellet in some cases and more than 200 N per pellet in many trials. Drop strength and shatter index values of composite pellets were also measured. In the present paper an attempt has been made to evaluate the mechanical properties of cold-bonded composite pellets so as to throw some light on the capacity of these pellets to withstand stresses during handling and transportation.     

微波预热新型有机粘结剂球团

 针对有机粘结剂铁矿球团预热球强度低的问题,进行了微波预热球团的试验研究,并与常规管炉预热球团进行了比较,通过光学显微镜和SEM等测试手段,分析了微波预热铁矿球团的成矿机理。试验结果表明,当预热温度为750 ℃时,微波预热球抗压强度为448 N/个,而常规管炉预热球的强度仅为129 N/个。测试分析表明,微波预热球团内部磁铁矿大部分已氧化成赤铁矿,赤铁矿连接成片,并产生了赤铁矿晶粒相互连接,球团矿预热强度得以提高。     

不同巴润精矿配比球团矿的还原膨胀试验研究

对不同巴润精矿配比球团矿的还原膨胀进行了试验研究,结果表明,球团矿的还原膨胀率与巴润精矿的配比呈显著的正相关。球团生产配加巴润精矿时,其配比应控制在30%以内。巴润精矿球团矿的还原膨胀率高主要是由于巴润精矿中含有较高的挥发组分所致,挥发组分还原膨胀的观点,可以圆满地解释白云鄂博铁精矿引起的球团矿的恶性膨胀,是对球团矿还原膨胀理论的完善和创新。     

球团矿高温还原过程中抗压强度变化及机理

 运用自行设计制造的固态物料高温抗压强度与蠕变在线测试仪,分别测试球团矿在不同温度及还原度状态下的抗压强度及蠕变量,用以表征球团矿在高炉内不同位置的抗压能力。研究发现：未发生还原反应球团矿在中性气氛中,当温度达到1 000 ℃时,球团矿的抗压强度为2 750 N以上,继续升温,球团矿抗压强度下降迅速;球团矿在还原气氛下,还原初期球团矿抗压强度比同温度下中性气氛球团矿抗压强度有较大下降,当温度高于900 ℃时,球团矿抗压强度只有1 250 N,且在抗压试验中形变明显。微观结构分析表明：还原过程中高价铁氧化物到低价铁氧化物变化过程中晶格增大、新生铁相基体孔隙增加、裂纹产生以及颗粒间固相固结减弱是导致强度下降的主要原因。     

Cold Bonding of Iron Ore Concentrate Pellets

Iron ore concentrate pellets are traditionally hardened at high temperatures in horizontal grates and grate-kiln furnaces. However, heat induration requires tremendous quantities of energy to produce high-quality pellets, and is consequently expensive. Cold bonding is a low-temperature alternative to heat induration. Pellets can be cold bonded using lime, cement, sponge iron powder, and organic materials such as starch and flour. Cold bonding consumes less energy than heat induration, and has found favor for bonding self-reducing pellets and for refractory ores that are difficult to heat-treat. Herein, we review the principal cold bonding methods and their fundamentals.     

含碳球团的还原熔分行为

通过高温电阻炉对含碳球团还原熔分的行为进行热态模拟研究,考察温度、配碳比、化学成分等因素对球团还原熔分的影响程度.结果表明,温度、配碳比和球团传热方向上的尺寸是控制球团还原熔分的关键;化学成分对还原速率影响不明显,但是通过改变渣的组成可对渣铁熔分起促进或抑制作用.     

Mass Loss and Direct Reduction Characteristics of Iron Ore-coal Composite Pellets

Mass loss and direct reduction characteristics of iron ore-coal composite pellets under different technological parameters were investigated. Meanwhile, changes of iron phase at different temperatures were analyzed by using X-ray diffraction （XRD）, and characteristics of crushed products were studied by using a scanning electron microscope （SEM）. The results showed that heating rate had little influence on the reduction, but the temperature played an important role in the reduction process. The mass loss rate increased rapidly from 800 to 1 100 ℃. The reduction process can be divided into three steps which correspond to different temperature ranges. Fe2 03 began to transform into Fe304 below 500 ℃, and FeO was reduced into Fe from 900 ℃. At 900 ℃, the reduction product showed a clear porous structure, which promoted the reduction progress. At 1000 ℃, the metallic Fe dominated the sample, and the reduction reached a very high degree.     

Swelling Behavior of Iron Ore Pellets during Reduction in H2 and N2/H2 Atmospheres at Different Temperatures

The need to develop green steelmaking techniques has led to the replacement of reducing agents such as CO with H₂. H₂ and N₂/H₂ mixtures can be used for the carbothermal reduction of iron ore. Herein, the reduction swelling index (RSI) of iron ore pellets in a forming gas (N₂/H₂) atmosphere at temperatures of 700–1000 °C is investigated and it is compared with that in pure H₂. It is showed in the experimental results that the RSI increases with increasing temperature for both the H₂ and N₂/H₂ atmospheres. The maximum swelling is reached approximately 5 min into the H₂ reduction process, while in the N₂/H₂ atmosphere, it is reached after 25–45 min of reduction, depending on the temperature. When the reduction temperature exceeds 900 °C, the RSI is greater than 20%. Scanning electron microscopy/energy-dispersive X-ray spectroscopy is performed to detect the changes in the microstructure and chemical composition of the samples. The nonreduced areas in the reduced pellets during the N₂/H₂ reduction process are analyzed using light optical microscopy.     

铁矿球团生球的固结机理及强化途径

通过生球强度破坏机理分析,得出通过对造球原料进行润磨可以有效的增大晶粒间的范德华力,增加生球的机械强度,添加能够通过范德华力、静电力、氢键、化学键、配位键等与铁矿颗粒表面发生作用的粘结剂也可以有效地提高生球的机械强度;提高球团的爆裂温度的有效方法是均衡球团表面气化和内部扩散作用,均衡球团表面气化和内部扩散作用的主要措施是降低球团表面气化的速度,使表面扩散速度减小,添加具有亲水基的有机粘结剂和膨润土可以降低自由水或毛细水的扩散速度,提高球团的爆裂温度;通过对造球原料的改性对生球的强度的提高是有限的,添加有机粘结剂或复合粘结剂强化生球强度仍然是今后发展的一个重要方向。     

含中等程度结晶水的铁矿粉烧结试验研究

根据鞍钢原料条件采用最优试验设计方法,在实验室条件下进行了烧结配加含中等程度结晶水的铁矿粉烧结实验,研究了该粉矿配比对烧结主要技术经济指标的影响.实验结果表明,含中等程度结晶水的进口铁矿粉配比为10%～30%时,通过调整配碳量,可以得到满足高炉要求的烧结矿.经过优化,该进口粉矿的最佳配比为15%,燃料配比为5.4%～5.5%.     

Iron Ore Pellet Dustiness Part II: Effects of Firing Route and Abrasion Resistance on Fines and Dust Generation

Iron ore pellets abrade during their production and handling, which lowers product quality and leads to dustiness issues. Pellets were collected from a variety of plants (operating either Straight-Grate (SG) or Grate-Kiln (GK) furnaces) to understand whether furnace type affects fines and dust formation. Results showed that pellets fired in SG furnaces were less abrasion-resistant (3.5 × lower) than pellets fired in GK furnaces. Concurrently, laboratory pellets were prepared using various ores, binders, and firing temperatures. These were tested to understand the relationship between abrasion index and dustiness. AI was observed to range from 1 to 14%. Dustiness, determined via AI and size distributions of abrasion progeny, ranged from 0.2 to 1.6%. For AI greater than 5%, AI can be used to indicate potentially high levels of dust. For AI less than 5%, there was a poor correlation between AI and dustiness. This was explained by the observation that as AI decreased, the abrasion product fineness increased. The results from parts I and II of this investigation suggest that material loss and levels of pellet dustiness may be significantly affected by pellet quality up to a certain point. Poorly fired pellets will be dusty during handling and transportation, while well-fired pellets will generate less – but finer – material as their quality improves. This could lead to little observed changes in dust generation over a wide range of pellet quality. Dust generation at each site would then depend on the quantity of material produced and their extent of handling.     

基于铁水成本的铁矿粉烧结经济价值评价方法

传统的铁矿粉烧结评价方法存在未考虑MgO、Al2O3脉石和酸性炉料的影响等缺点,本文提出了一种新的基于铁水成本的铁矿粉烧结经济价值评价方法,即在一定的炉渣二元碱度和镁铝比下,以单烧矿的铁水成本(元/t)作为铁矿粉烧结经济价值评价指标。其结果比以往的评价方法更准确可靠,能够反映铁矿粉烧结的经济效益。     

Utilization of High Sulfur Raw Materials in Iron Ore Pellets

Pyrite cinder and high sulfur magnetite were used as raw materials to produce iron ore pellets. Good qualities of green balls and fired pellets were obtained from the feed comprising 50% pyrite cinder and 50% high sulfur magnetite concentrate at a small scale. Small-scale tests were proven by pilot-scale tests. The high grade fired pellets, assaying 63.22% Fe, were analyzed, and the compressive strength of fired pellets was over 2500 N/pellet. The fired pellets possessed excellent metallurgical performances, such as reducibility index higher than 67%, reduction swelling index lower than 15% and low temperature reduction degradation index (+ 3.15 mm) higher than 1%, which can be used as the burden for blast furnace.