Influence of Magnesia on Iron Ore Sinter Properties and Productivity – Use of Dolomite and Dunite

For production of fluxed sinter the use of dolomite and other MgO bearing materials has increased in the recent past. Flux materials influence the microstructure and chemical properties of the resultant sinter. Improvement in raw material quality and use of alternative raw materials play an important role for improving the sinter quality and overall economics of iron and steel making. The physical and metallurgical properties of sinter mainly depend on the mineralogy of the sinter. Dolomite is composed of calcium magnesium carbonate and dunite consists of magnesium silicate. In the present work laboratory sintering experiments have been carried out with different MgO level (1.40 to 2.60 mass%) to know the influence of MgO on the mineralogy, productivity, physical and metallurgical properties of sinter prepared by using dolomite and dunite. Microstructural examinations of the produced sinter revealed that dunite sinter is bounded with higher amounts of hematite and less calcium ferrites when compared to dolomite sinter. Hematite and calcium ferrite phases decreased whereas magnetite phase increased with increase of magnetite content in sinter using both dolomite and dunite. From the test results it was found that dunite sinter showed better metallurgical properties whereas dolomite sinter showed better physical properties.     

白云石和蛇纹石对烧结矿质量及显微结构的影响

白云石和蛇纹石对烧结矿质量及显微结构影响的研究结果表明:配加白云石提高烧结矿的MgO含量,烧结矿转鼓强度降低,而配加蛇纹石提高烧结矿的MgO含量时,转鼓强度提高.配加白云石后,烧结矿矿物组成主要为铁酸钙与骸晶状赤铁矿,骸晶状赤铁矿周围有大量以玻璃质物相存在的硅酸盐矿物,且有大量微细裂纹;烧结矿孔隙率大,气孔为大孔薄壁结构,所以烧结矿强度低.配加蛇纹石后,烧结矿矿物组成主要为磁铁矿和铁酸钙,钙铁橄榄石矿物增多变大,气孔为中孔厚壁结构,所以烧结矿的质量得以改善.     

烧结矿中MgO作用机理

研究了烧结矿中MgO对烧结液相生成、固结成矿的影响机理,以及不同镁质熔剂对固结强度的影响规律,并在此基础上进行了烧结杯实验研究.结果表明:随着烧结矿中MgO含量的增加,烧结液相开始形成温度上升,液相流动性和黏结相强度均降低;使用不同种类的镁质熔剂时,烧结黏结相强度有差异,在1 280℃和1 320℃下,使用蛇纹石时黏结相强度相对最高,其次是使用轻烧白云石的情况,而使用白云石时黏结相强度相对最低;在兼顾烧结矿产量、质量指标及冶金性能的前提下,烧结矿中适宜的MgO质量分数在1.2%左右,镁质熔剂则适宜选用白云石和蛇纹石组合或者单独使用轻烧白云石.     

Influence of MgO addition on mineralogy of iron ore sinter

The influence of MgO addition on sinter mineralogy was studied on sinters produced in a laboratory installation, with a wide range of MgO/CaO ratios at several basicity indices [B = (CaO + MgO)/ (SiO₂ + A1₂O₃)] between 0.7 to 1.9. The most striking influence of MgO is the suppression of hematite and Ca-ferrite phases and the increase in magnetite phase. In general, MgO favors the formation of glass and suppresses the precipitation of dicalcium silicates in favor of Ca-Fe-Mg olivines and pyroxenes. Microprobe studies revealed that most of the Mg was picked up by the magnetite phase to form mixed spinels of type (Fe, Mg)O · Fe₂O₃. At a constant basicity index, increased replacement of CaO by MgO also led to increased participation of FeO in the slag formation process, thus increasing the overall FeO content of sinter. A mechanism for the formation of mixed spinels has been proposed. The effect on various sinter properties resulting due to change in sinter mineralogy has been outlined. S. C. PANIGRAHY, with Department of Metallurgy and Metallography, State University of Ghent, Ghent, Belgium at the time the experiments were carried out     

The effect of dolomite addition on the properties of sinters produced from a high aluminous iron ore

This study provides a systematic approach to an evaluation of the sinter properties with increased MgO addition for superfluxed sinters produced from a high aluminous ore. The investigation revealed that part or full replacement of limestone by dolomite in the sinter mix leads to a drop in sinter cold strength, reducibility and production rate, but has a favourable influence on low-temperature reduction strength and probably better softening and meltdown properties. The change in sinter mineralogy due to the MgO addition has a paramount influence on the sinter properties. The Gua iron ore having a high alumina content, is easily amenable to sintering and the sinters produced can constitute a good burden material because of their high reducibility, good cold and hot-strength characteristics. Improved production rates can be expected by choosing dolomites having a smaller crystal size or choosing other suitable MgO-bearing materials. A high circulating load should be expected while producing MgO-bearing sinters.     

烧结熔剂活性度及高温液相行为研究

使用指示剂滴定法和"座滴法"研究了烧结熔剂(生石灰、白云石)活性度及高温液相行为。结果表明:生石灰的活性度存在显著差异,生石灰活性度主要取决于"匀速滴定阶段"的活性度;活性度较高的生石灰与Fe_2O_3纯试剂反应的特征温度较低、特征温度区间较窄;石灰石与Fe_2O_3纯试剂反应的特征温度较生石灰低,这主要是由于高温下生成的CaO活性度更高;白云石与Fe_2O_3纯试剂反应的特征温度最高,这主要是由于MgO·Fe_2O_3阻碍了铁酸钙的形成;白云石与Fe_2O_3纯试剂反应后的试样出现了明显的分层现象,内层矿相以MgO形成的高熔点物质为主,外层矿相以低熔点铁酸盐为主。     

MgO对含钛烧结矿矿相结构及软熔滴落性能的影响

为了深入探究MgO对烧结矿矿物组成及冶金性能的影响,采用扫描电子显微镜和荷重软化熔滴设备研究了MgO对含钛烧结矿矿相结构与软熔滴落性能影响.实验结果表明,随着烧结料中MgO质量分数从2.04%增加到3.96%,烧结过程液相生成量逐渐减少,烧结矿中的赤铁矿和铁酸钙等含量都有不同程度的降低,赤铁矿质量分数从13.57%降低到9.99%,铁酸钙的质量分数由38.7%降低到30.17%,磁铁矿、硅酸盐和烧结矿中的孔洞逐步增加.因此,增加烧结矿中MgO会降低烧结矿中液相生成量,不利于烧结矿转鼓强度和还原性的提高.高碱度含钛烧结矿中的镁主要分布于烧结矿中复合铁酸钙相中,进一步提高烧结矿中镁的质量分数,烧结矿的磁铁矿相比例将增加,有一部分镁固溶于磁铁矿中;在高镁烧结矿中,也会形成一定量的橄榄石,其中固溶有少量镁、钛等元素.随着烧结矿中MgO质量分数的增加,开始软化温度逐渐升高,试样软化开始温度均在1120℃以上,软化温度区间Δt_A随着MgO含量的升高而逐渐变宽.     

Influence of magnesia on sintering characteristics of iron ore

Abstract

The MgO in blast furnace slag provides an optimum condition in terms of both good flowability and desulphurisation. The mode of its addition to the blast furnace changed from, initially, as raw flux in the form of dolomite, to via sinter, with the argument that raw flux demands energy for its decomposition inside the blast furnace. Thus, the decomposition reaction was diverted from the blast furnace to the sintering bed, and the energy source for decomposition was changed from costly blast furnace coke to a relatively cheap coke breeze. Now olivine/dunite/serpentine is being used as a source of MgO, where energy for decomposition is not required; this also provides a source of SiO₂, which eliminates need for the addition of quartzite. The effect of MgO on blast furnace slag is fairly well established, but its effect on sintering and sinter quality is unclear. Operating results of the sinter plants show that, with an increase of MgO, the sintering rate, the fuel rate, and sinter strength and reducibility deteriorate; however, high temperature properties such as the reduction degradation index and the softening-melting characteristics of the sinter improve. The present work attempts to establish this influence on the sintermaking process and sinter quality with the help of operating plant data.     

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。      

Influence of limestone particle size on iron ore sinter properties and productivity

Iron ore fluxed sinter is the main ferrous burden of Jindal south west steel limited (JSWSL) blast furnaces. In sinter plant fluxes including limestone and dolomite are added to improve the sinter properties of iron ore and to provide an appropriate slag composition of the blast furnace. The raw material grain size affects the sinter process considerably because the sinter productivity and quality are strongly dependent on the green permeability of the bed, which is determined by the particle size distribution of the raw materials, the granulation effectiveness and by the sintering process itself. It is well‐known that in fluxed sinter, the size of limestone affects productivity and physical and metallurgical properties of the sinter. It is therefore necessary to understand the role of limestone particle size on sinter properties and productivity. In the present work laboratory sintering experiments have been carried out with different levels of limestone mean particle size (from 0.14 to 1.83mm) to understand the influence of limestone particle size on mineralogy, productivity, physical and metallurgical properties of the sinter. Sinter productivity increased with increasing limestone mean particle size due to improved sinter bed permeability. Sinter with limestone mean particle size of 1.25 to 1.52 mm yielded better sinter strength and lower RDI compared to sinter with smaller or larger limestone mean particle size. Higher sinter strength is due to better and uniform distribution of limestone particles, and better bed permeability enabled easy assimilation and effective distribution of calcium ferrite phases. The improvement in sinter RDI is due to change in mineralogy of the sinter compared to coarser and finer limestone mean particle size.     

轻烧白云石对烧结矿性能的影响

 针对水钢大量轻烧白云石粉末未能有效利用的情况,进行了烧结中添加轻烧白云石的试验。研究了轻烧白云石与白云石的质量比和MgO含量这2种因素对烧结矿性能的影响。结果表明：随着轻烧白云石与白云石质量比的增加,烧结矿质量指标和低温还原粉化性能先增加后降低,轻烧白云石与白云石质量比为0.67时,烧结矿转鼓强度为68.26%,落下强度为73.51%,成品率为76.14%;MgO质量分数在1.9%~2.5%之间变化时,MgO含量对烧结矿质量影响不明显,MgO含量增加有利于提高烧结矿的低温还原粉化性能,但MgO含量增加将导致烧结矿TFe含量的降低,TFe质量分数从54.27%降至53.28%;综合考虑,最佳工艺条件为轻烧白云石与白云石质量比为0.67,MgO质量分数为1.9%。     

不同MgO熔剂添加剂的烧结试验及生产

介绍了白云石、轻烧白云石、高镁粉等分别作烧结矿MgO熔剂添加剂的实验室试验情况和工业生产情况.试验和工业生产结果表明,在安钢原料工艺条件下,和白云石和轻烧白云石相比,高镁粉是一种比较理想的烧结矿MgO熔剂添加剂.     

烧结添加轻烧白云石的试验研究及生产应用

介绍了烧结配加轻烧替代高镁粉作烧结矿MgO熔剂添加剂的实验室试验和工业生产情况.试验和工业生产结果表明,在安钢原料工艺条件下,轻烧白云石和高镁粉相比,轻烧白云石是一种比较理想的烧结矿MgO熔剂添加剂.     

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对铁矿石烧结过程中二次赤铁矿形成的影响

前人研究表明,二次赤铁矿是导致烧结矿低温还原粉化的主要因素,它的生成与烧结原料中MgO含量有关,但其影响机理尚不明确。通过热重法测定不同MgO和Fe_2O_3比例试样在升温-恒温-降温过程中质量变化,定量地了解MgO对Fe_2O_3向Fe_3O_4转变的影响。同时结合XRD分析和光学显微镜观察,揭示了矿物和相结构变化,研究了烧结过程中MgO对二次赤铁矿生成的抑制机理。结果表明,加入MgO后,它与Fe_2O_3反应形成了铁酸镁和含镁磁铁矿,前者促进了升温过程含镁磁铁矿生成,而后者低温下比磁铁矿更稳定,抑制了降温过程磁铁矿氧化,减少了二次赤铁矿的生成。因此,明确了加入少量MgO改善烧结矿低温还原粉化性能的主要原因。     

A study on the physicochemical and thermal characterisation of dolomite and limestone samples for use in ironmaking and steelmaking

Limestone and dolostone are used in industries depending on their physicochemical characteristics. They can be used in construction, agricultural, environmental industries and especially in ironmaking and steelmaking as flux. Dolomite is also used in the production of refractory materials. As the properties of products are significantly affected by physicochemical specifications of limestone or dolomite, the characterisation of those materials is important. This study was initiated to analyse the chemical, decrepitation, and degradation properties of dolomite and limestone samples to determine their suitability as flux. Since the degradation indices were found different for the chemically similar samples, the study was expanded to determine the reason. Complete physicochemical and thermal characterisation was performed via XRF, XRD, TG, FTIR, and thin section microscopic analyses. Although two dolomite samples were mineralogically similar, thermal behaviours were determined different. Microscopic analyses results showed that the crystal structures/sizes affect the thermal behaviour and degradation index of carbonate samples.     

MgO对烧结矿液相形成性能和微观结构特性的影响

为了探究MgO对烧结矿液相形成性能和微观结构特性的影响,采用Factsage 7.1热力学软件模拟分析了MgO对烧结矿液相形成性能的影响,并且开展了不同MgO含量的烧结杯试验研究。研究表明,随着MgO含量增加,烧结矿理论液相生成量减少,液相黏度降低,液相中w(Fe₂O₃)/w(CaO)增加,使得混合料中CaO的活度提高,铁酸钙相形成的热力学条件改善;当MgO质量分数由1.60%提高至1.90%,一方面,烧结矿矿相组成中枝晶状铁酸钙相含量增加,针状及板柱状铁酸钙相发展受到抑制,铁酸钙黏结相总量降低,硅酸盐相含量增加,导致液相黏结包裹矿粉颗粒能力变差,固结强度性能受到不利影响;另一方面,由于MgO是高熔点物质,矿化反应过程中,MgO易固溶进入磁铁矿晶格,并在高温固相反应中形成难熔物相,使得烧结矿磁铁矿相含量增加,赤铁矿相含量减少,从而降低烧结矿低温还原反应过程中产生的晶格结构畸变应力,改善低温还原粉化性能。     

济钢烧结配加复合轻烧镁粉的试验研究与应用

为了优化烧结熔剂结构,寻求最优的烧结镁质熔剂,济钢开展了配加复合轻烧镁粉的烧结试验研究与生产应用,即用复合轻烧镁粉完全取代轻烧白云石粉,增加石灰石粉用量以维持烧结矿碱度稳定。结果表明,配加复合轻烧镁粉比配加轻烧白云石粉能提高烧结矿化学成分的稳定性（尤其是碱度及MgO的稳定性）,改善烧结矿粒级组成及冶金性能,降低烧结矿成本;同时,烧结过程参数得到了优化稳定,烧结机产能水平得到了提高。     

Influence of Alumina on Iron Ore Sinter Properties and Productivity in the Conventional and Selective Granulation Sintering Process

Iron ore sinter constitutes a major proportion of blast furnace burden. Hence, its quality and consistency have a significant impact on blast furnace performance. Iron ore fines are the main source for sinter, and the chemical composition of the iron ore fines, together with the thermal conditions that blends are subjected to, plays an important role in forming the primary melt during the sintering process and accordingly determines the sinter structure and quality. Therefore, considerable importance has been placed on the chemical composition and consistency of iron ore fines, particularly in terms of alumina content. Due to depletion of high grade iron ore resources, alumina content in the iron ore fines is expected to increase gradually. Ore with higher alumina content is usually expected to be detrimental in forming the sinter matrix, if sintered alone, due to the low reactivity of alumina bearing minerals and the high viscosity of primary melts. The selective granulation process is a new sintering process for high alumina iron ore fines, and can eliminate the adverse effects of ‘hard to sinter’ or ‘unsuitable – for ironmaking’ ores. In the present work laboratory sintering experiments have been carried out with iron ore fines of different alumina level (2.00 to 5.46 mass‐%) to know the influence of alumina on mineralogy, productivity, physical and metallurgical properties of sinter prepared by the conventional and the selective granulation process. With increasing alumina content in sinter of both the conventional and selective granulation process, the fractions of hematite and of silico‐ferrites of calcium and alumina (SFCA) as well as the pore phase increased whereas the magnetite and silicate phases decreased. With increase in alumina content sinter productivity and tumbler index (T.I.) decreased, and metallurgical properties like sinter RDI and reducibility improved. However, sinter of the selective granulation process showed better results compared to the conventional process.     

Influence of coke breeze particle size on quality of sinter

Abstract

Iron ore sintering is an extremely complex process involving fuel combustion to generate heat and reducing gases like CO. This heat allows physicochemical, solid and solid–liquid reactions to form liquids of complex components as fuel particles are consumed and cooling processes allow the formation of solid mineral phases. At JSW coke breeze from coke ovens is used as solid fuel in sinter. The properties (size) of the solid fuel play a very important role in determining the sinter microstructural properties and sinter quality. The microstructure of the sinter is a basic necessity and also the first step towards establishing the structural property relationship. Microstructural studies have been carried out to understand the effect of coke breeze particle size on sinter microstructure and sinter properties. The present paper is an attempt to understand and correlate the physical and metallurgical properties of sinter with varying size of the coke breeze particle in sinter mix. It was observed that as the proportion of coke breeze below 3 mm in the sinter mix increased from 53·0 to 90·0% the calcium ferrite phase increased, the number of bigger size pores decreased, and thereby decreased the reduction degradation index (?3·15 mm) of sinter from 39·7 to 23·5%. Superior sinter properties were obtained with the ?3 mm coke breeze size ～90% in the sinter mix.