邯邢磁铁矿精粉用作球团矿原料的试验研究

邯郸和邢台地区的磁铁矿含有部分CaO和MgO,为缓解该地区球团矿原料紧缺问题,我们在试验室模拟球团矿生产条件,以辽宁地区磁铁矿精粉为基准,探讨了邯邢地区磁铁矿精粉用于球团矿原料的可行性.     

MgO对生球质量和球团矿抗压强度的影响

通过采用A精粉、B精粉和轻烧白云石改变球团矿中MgO含量来研究MgO对生球质量和酸性球团矿抗压强度的影响。研究发现:生球的抗压强度和落下强度随着MgO含量的增大先降低后升高,热爆裂温度先升高后降低,生球质量的变化主要与矿粉的比表面积等基础性能相关;经过焙烧的球团矿抗压强度随着MgO含量的增加而降低,一分部Mg原子进入到赤铁矿晶体中并替代了Fe原子,Mg-O键键强低于Fe-O键键强,同时一少部分MgO进入到渣相中破坏了硅酸盐网络结构,改善了渣相的流动性,其中一部分渣相分散到赤铁矿晶粒之间,其它渣相互聚集一起,冷却后渣相和赤铁矿晶粒间空隙增大,导致球团矿抗压强度降低。     

球团矿化学成分控制现状及展望

 综述了近年来国内外高炉球团矿使用比例的现状,分析了球团矿化学成分控制以及不同化学成分对球团矿冶金性能的影响。分析表明,多数国内钢铁企业球团矿TFe的质量分数较低,SiO₂质量分数较高且差异较大。不同企业球团矿Al₂O₃和FeO的质量分数不同。应控制球团矿中SiO₂、Al₂O₃和FeO的质量分数。随着CaO和MgO质量分数的提高,球团矿抗压强度均降低。适宜质量分数的CaO有利于改善球团矿的还原膨胀性能。随着MgO质量分数的提高,球团矿的还原膨胀性和软熔滴落性能均变好。高炉炉料结构采用低MgO烧结矿、酸性球团矿和镁质球团相结合,可以充分发挥球团矿的冶炼优势,实现球团矿入炉比例的提高。MgO和CaO在球团矿焙烧过程中的作用机理,以及如何控制镁质球团中的液相含量以提高球团矿的抗压强度等需要进一步深入研究。     

MgO添加方式对改善球团矿冶金性能的影响

 为改善球团矿的冶金性能,进行了含MgO球团矿的冶金性能试验研究,分析了不同MgO添加方式造球工艺的效果。结果表明,在合理的MgO添加方式下,对含MgO球团矿,氧化镁含量由0.6%提高到1.8%后,球团矿RDI+3.15由62.2%增加到约75%,还原度RI由34%增加到45%～53%（900℃还原1h）,还原膨胀指数RSI（还原度40%）由23%降低到约20%,且软熔温度明显提高,冶金性能改善。认为提高氧化镁含量的方式应当是菱镁石或含MgO精矿粉,避免添加白云石。     

通钢球团配加硼镁铁精粉的工业试验

硼镁铁精矿是硼铁精矿磁选分离的副产品，其中TFe含量在54％以上，并含有一定量的氧化镁和三氧化二硼等有用成分，经加工磨细后，可以作为含铁原料用于球团生产。从成本上，硼镁铁精矿价格低于杂精粉，可降低部分原料费用；从球团质量上，硼镁铁精矿中含MgO比较高，MgO可以改善球团矿冶金性能，同时少量的硼对改善钢的性能有利。     

脉石含量对球团矿性能的影响

应用微型烧结法，通过添加化学纯Al2O3,MgO,SiO2,CaO改变球团中Al2O3,MgO,SiO2,CaO的含量，研究了不同脉石成分对球团矿质量的影响，结果表明，SiO2含量为6.5%时，球团矿抗压强度高，Al2O3,MgO含量高对球团强度不利，应尽量降低他们的含量；在低碱度范围内，提高碱度对改善球团抗压强度有利，但FeO含量将升高。     

配加赤铁矿竖炉生产含MgO球团的实验研究

酸性球团存在软熔性能差的问题，而加入一定量MgO有助于提高酸性球团矿的高温冶金性能。本论文立足于莱钢条件，进行了配加轻烧白云石粉及巴西精粉的工业条件下的球团试验研究，表明：在磁铁精矿配加25％巴西精粉的条件下生产含MgO球团，适宜的轻烧白云石粉配入量是5．5％，这时球团内含铁约为56．5％，合MgO约为3．64％。     

含菱镁矿球团的高温还原及软化性能

为了提高高炉的生产率,有必要改善球团矿的高温还原性能和降低其软化程度。本文介绍了球团矿中MgO/SiO_2的比值和CaO/SiO_2的比值对高温还原和软化性能的影响。已经证实,MgO/SiO_2比值控制在0.6以上:CaO/SiO_2比值控制在0.05以下的球团矿较之酸性球团矿或自熔性球团矿具有更好的高温性能。即使SiO_2的含量高,亦不会使球团矿性能变差。     

首钢京唐高镁球团工业试验

为了进一步满足大高炉对球团矿质量的要求,京唐球团厂拟采取配加MgO粉的方式来改善球团矿综合冶金性能,并进行了2天的工业生产试验.结果表明:MgO含量从0.94％提高到1.56％的情况下,球团矿强度及各项冶金性能指标均有改善,FeO含量也有所降低,高炉使用后,铁水质量提高,取得了满意的效果.     

w(MgO)对熔剂性球团矿冶金性能的影响

 为了研究添加高镁粉时w(MgO)对熔剂性球团矿冶金性能的影响。考察了w(MgO)为1.6%～2.4%时,其对球团矿抗压强度、RI(还原性指数)、RDI(低温还原粉化指数)和RSI(还原膨胀指数)的影响。采用光学显微镜和X射线衍射仪对球团矿微观结构和矿物组成进行了分析。结果表明,随着MgO质量分数的增加,抗压强度呈先升高后降低的趋势,w(MgO)为2.0%时,抗压强度最大,为3 533 N;随着w(MgO)由1.6%增加到2.4%,球团矿RI、RDI和RSI得到改善;w(MgO)为1.8%～2.0%时,球团矿微观形貌和矿物组成较好,赤铁矿成片结晶,球团矿强度良好。在用高镁粉和研山精粉造球时,w(MgO)控制为1.8%～2.0%,以期得到较低的还原膨胀指数和较好的冶金性能。     

Reduction swelling behaviour of haematite/magnetite agglomerates with addition of MgO and CaO

Abstract

The influence of three kinds of CaO and MgO additives (dolomite, burnt lime and serpentine) on the reduction swelling behaviour of haematite–magnetite (H–M) concentrates pellets was studied. Burnt lime and dolomite increased the reduction swelling index of H–M oxidised pellets, while the reduction swelling index was able to be reduced when serpentine was added. CaO accelerated the formation and growth of metallic iron whiskers and led to abnormal swelling of the magnetite briquettes, while MgO was able to be dissolved in wüstite and reduced the migration rate of Fe²⁺; therefore, there was no catastrophic swelling in either the haematite or magnetite briquettes. As far as H–M concentrate pellets were concerned, because the solubility of CaO in magnetite was greater than that in the primary haematite and the secondary haematite generated from magnetite during the oxidation was easy to be reduced to wüstite, there was abnormal swelling in the reduced H–M pellets with CaO addition.     

MgO含量和来源对球团焙烧特性及冶金性能的影响

分别以5种不同的含镁添加剂（高镁磁铁矿、镁橄榄石、白云石、菱镁石和氧化镁粉）制备镁质球团,阐述MgO含量和来源对磁铁矿球团焙烧特性及冶金性能的影响。研究结果表明:不同的含镁添加剂对于生球的落下强度有着一定影响,其中氧化镁粉与高镁磁铁矿均能够提高球团的落下强度。相同的预热焙烧制度下,提高MgO含量会增加球团孔隙率,降低预热和焙烧球团的抗压强度,其中白云石对焙烧球团强度的不利影响最小。增加预热球团的氧化度有利于促进镁质焙烧球团固结,提高其抗压强度。在MgO来源相同的情况下,MgO含量的增加会导致球团孔隙的增减,降低了球团强度,而配加不同种类的含镁添加剂,均能不同程度改善球团的还原膨胀性、低温还原粉化性和还原性,其中配加高镁磁铁矿的球团的还原膨胀性和低温还原粉化性均优于于其他含镁球团。      

Oxidation and Induration Characteristics of Pellets Made from Western Australian Ultrafine Magnetite Concentrates and Its Utilization Strategy

Western Australian magnetite concentrates normally have ultrafine granularity and much higher specific surface areas than Chinese magnetite concentrates owing to the significant pre-grinding and beneficiation for saleable iron grade.Such characteristics will inevitably affect the subsequent pelletization process.However,very few investigations have been done before.Thus,the oxidation and induration characteristics of pellet made from a Western Australian ultrafine magnetite concentrate were revealed by conducting routine preheating-roasting tests in an electric tube furnace and investigating the microstructure of fired pellets under an optical microscope in comparison with that of pellets made from typical Chinese magnetite concentrate.The liquidus regions of CaO-SiO_2-Fe_2O_3 and CaOSiO_2-Al_2O_3 ternary systems in air at various temperatures were calculated by FactSage software to explain the importance of liquid phase in the consolidation of fired pellets.The results show that pellet made from ultrafine magnetite concentrate possesses better oxidability and preheating performance than that made from Chinese magnetite concentrate.However,it has inferior roasting performance,usually requiring conditions of roasting at 1 280℃ for at least 30 min to acquire sufficiently high compressive strength,which are attributed to higher temperature sensitivity caused by its smaller particle size and less formation of liquid phase because of low impurities like CaO and Al_2O_3 in raw materials.Correspondingly,its roasting performance can be significantly improved by blending with Chinese magnetite concentrates or increasing the pellet basicity(wCaO/wSiO_2).By comprehensive evaluation,blending with Chinese iron ore concentrates is an appropriate way to utilize Western Australia ultrafine magnetite concentrates.     

MgO质量分数对氧化球团性能的影响

 为了改善澳洲某磁铁矿氧化球团的冶金性能,研究了MgO质量分数对其质量的影响。研究结果表明,随着MgO质量分数的提高,生球落下强度和爆裂温度提高,MgO质量分数对生球抗压强度影响较小。随着MgO质量分数提高,预热球团和焙烧球团抗压强度降低,还原度有所改善;提高MgO质量分数可以有效抑制球团的低温还原粉化和球团的还原膨胀,软化开始温度、软化结束温度和滴落温度均有所提高,软熔性能得以改善。这主要是由于提高MgO质量分数,渣相中铁酸镁和钙镁橄榄石质量分数升高,在还原过程中Mg2+与Fe2+发生晶格取代,生成FeO与MgO的固溶体,具有稳定晶格的作用,从而抑制还原膨胀和低温还原粉化。     

Chemistry,microstructure, and reduction characteristics of dolomite-fluxed magnetite pellets

The addition of dolomite to iron ore pellets improves high temperature reduction properties, primarily by increasing their softening point and reducibility. This study was made to ascertain the compositional ranges within which dolomite fluxed magnetite pellets show such an improvement over good acid pellets. A variety of compositions with MgO levels from 1 to 2 wt pct and CaO/SiO₂ ratios of 0.6 to 1.8 were prepared using Hibbing magnetic concentrate. These compositions were balled and then pot-grate fired to various temperatures. Petrographic examination and electron microprobe analyses were used to characterize the phase assemblages. Reduction characteristics were also evaluated. As evidenced by the following petrographically observed relationships, the CaO/SiO₂ ratio (c/S) was found to be the controlling factor for pellet microstructure: a) The low c/S (< 0.8) pellets were predominantly oxide-bonded, b) the intermediate c/S (0.8 to 1.3) pellets were slag- and oxide-bonded, and c) the high C/S (> 1.3) pellets were mostly calcium ferrite-bonded. Intermediate c/S compositions contain more magnesioferrite than do either low or high basicity compositions. Pellets must be fired to a high enough temperature to generate sufficient liquid for ion transport but not so high as to cause pellets to stick together. Well-fired pellets with a c/S of 1.3 or less performed adequately in low temperature degradation tests. Pellets with a c/S of 0.8 or greater displayed satisfactory swelling behavior. Therefore, we determined that pellets within a c/S range of 0.8 to 1.3 are technically acceptable. Pellets containing 1.5 wt pct MgO had the best reduction characteristics, but all fluxed compositions reduced faster and more completely than did acid pellets. Increasing MgO content up to 2.0 pct increased the softening temperature by 165‡C over acid pellets. On the basis of pellet test results and taking into consideration the auxiliary influence of economic and operating considerations, we determined the optimum composition of dolomite fluxed Hibbing pellets to be 1.5 pct MgO and a C/S of 0.8.     

Formation and decomposition of C4F7 type calcium ferrites in superfluxed magnetite based pellets during oxidation and reduction

Abstract

In the current work the reactions of magnetite based pellets with large additions of calcite (3%CaO) during reduction have been investigated. This made it possible to use both X-ray diffraction (XRD) and scanning electron microscopy (SEM) to detect reaction phases that normally occur in very small amounts. The main binding phase in the pellets after oxidation was (CaO,MgO,FeO)₄(Fe₂O₃)₇, whereas the one commonly reported in the literature is (CaO)(Fe₂O₃)₂. During reduction at 500–700°C severe cracking occurred in these pellets, especially in the calcium ferrite phase. However, the decomposition of this phase began at 600°C, and therefore it is believed that the reason for the cracks is low strength of the phase itself, rather than weakness induced by reduction of the phase. Upon reduction of magnetite into wüstite at 800°C, the calcium began dissolving in the wüstite, and at 900°C porous calciowüstite had formed in the entire sample, except for some remaining magnetite left in the pellet cores.     

含硼磁铁矿对超细粒级磁铁矿球团性能的影响

 超细粒级精矿球团化对中国贫矿资源应用有着特殊意义,但存在成球困难、生球质量差、成品球团强度低等问题,硼铁矿中硼和铁嵌布密切,应用难度大,然而其配加对提高球团性能有益。采用气体吸附法(BET法)测量比表面积并用扫描电镜(JSM6490)评价铁精矿粉和焙烧球团矿的微观结构,研究了添加含硼磁铁矿对超细精矿的成球性能、生球质量、预热焙烧强度的影响。结果表明,超细精矿中配加30%硼铁矿后,混合精矿成球性得到改善,达到中等成球性指标,生球落下强度从2.4 次/(0.5 m)升高到4.0 次/(0.5 m)、抗压强度从15.38 N/个增加到19.08 N/个、爆裂温度从340 ℃升高到410 ℃,优化配矿下可提高爆裂温度至460 ℃,球团的预热与焙烧时间缩短、温度降低,在预热时间与温度不变、焙烧时间相同、焙烧温度为1 175 ℃条件下,球团强度(与100%超细精矿相比)提高900 N/个左右,达到了3 500 N/个以上,在相同强度下,可降低焙烧温度近100 ℃。加入含硼磁铁矿可改善球团性能的原因为,含硼磁铁矿颗粒形貌复杂、碱性物质含量多、粒度粗,从而能有效帮助颗粒间嵌合,增加粉料分子水含量,改善成球性,提高生球强度与爆裂温度。MgO和B₂O₃会在球团内部生成低熔点液相,填充孔隙,促进焙烧温度降低,增强颗粒间网格状的均匀连结,提高焙烧球团的强度。     

MgO、F、碱金属对球团矿相组织的影响

因为白云鄂博铁精矿球团含有较多的碱金属和氟,从而产生异常还原膨胀,而添加MgO可以有效抑制其还原膨胀,但是MgO的添加势必影响球团的矿相组成.目前研究多注重MgO、F、碱金属中某一单因素对球团物相的影响,而对3者共同作用于球团物相的影响还缺乏深入研究.采用正交试验的方法研究了(K2O+Na2O)、CaF2和MgO对赤铁...     

提高高硫精矿球团矿强度的途径

以安庆含硫１．６１％的磁铁精矿为对象,研究了用高硫磁铁精矿制备满足高炉冶炼要求的氧化球团矿的可行性。采用含镁工业盐类矿物为添加剂,通过系统地试验研究,获得了抗压强度２５５２Ｎ／个、含硫量０．０１８％、ＦｅＯ含量１．６７％、冶金性能良好的球团矿。探讨了添加剂强化高硫磁铁精矿球团氧化固结的机理。