Laboratory studies on smelting reduction – a contribution to reaction mechanisms in the production of liquid iron from iron oxide melts

Iron oxide slags are subjected to reduction at 1550 °C with the use of various reducing agents. The experiments with carbon monoxide are subdivided into series of top-blowing, injection or bottom-blowing experiments. Moreover, solid carbon is employed for further experiments. As a result of the necessary addition of Al₂O₃ – because of the corrosivity of FeO_n towards the crucible material during experiments – reaction-inhibiting barrier layers precipitate in the form of spinels during reduction. Foams containing CO_n exert the same effect. From the experimental results, it can be concluded that the reduction of liquid oxides by carbon monoxide or by solid carbon does not consistently obey any law of reaction during the entire process sequence. The essential, decisive parameter for the carbon monoxide blowing experiments is the blowing rate. The experiments performed with the use of solid carbon exhibit the highest reduction rates, on the whole. For the purpose of elucidating the reaction mechanisms, only the experiments conducted by blowing carbon monoxide onto the melt yield clearcut results. After a possible initial steep rise, a reaction of first order is then established, as a first approximation. The further course of the experiment is characterized by covering of the blowing trough. Mass transfer can then proceed only through the spinel layer near the surface, or through the channels between the spinels.     

Fundamental research on phosphorus behaviour in the smelting reduction process

The behaviour of phosphorus in the smelting reduction process was investigated in this paper. Experiments were carried out under the conditions of smelting reduction: the phosphate reduction in molten slag by solid carbon, liquid iron saturated with carbon and CO gas, respectively. Furthermore, experiments on the phosphate reduction in pre-reduced iron ore by liquid iron saturated with carbon were carried out respectively when liquid iron was in permanent contact with molten pre-reduced iron ore, and when powders of the pre-reduced iron ore were injected into the iron bath from the bottom. The results showed that there was considerable unreduced P₂O₅ in the slag. Part of the reduction product of phosphorus escaped from the bath, while the other part was absorbed by liquid iron. The pig iron with low content of phosphorus can be obtained by smelting reduction in comparison with blast furnace. In the process of liquid iron bath with coal-oxygen-ore injection, the phosphorus content in liquid iron could be kept constant in 100 kg scale tests.     

Conclusions on the development of smelting reduction

The present paper summarizes the results of the US-German Symposium on “Innovative Iron and Steel Making Processes”. A survey is given on the state-of-the-art technology as well as the state and further needs of research.     

熔融还原技术的发展

文章概述了近20年来熔融还原技术的发展及其前景。并根据其在国际上的发展趋势,对我国熔融还原技术的发展与应用提出了一些建议。     

关于发展熔融还原炼铁技术的思考

近年来,不断遇到有关发展熔融还原炼铁技术的问题。为此,本文就这个问题发表个人观点,供大家研究分析。一、世界发展熔融还原炼铁技术的背景1．几十年来,为减少对炼焦煤的依赖和环境保护的需要,有不少国家的研究机构和钢铁企业开展了熔融还原炼铁技术的研究,研发了多种熔融还原炼铁工艺。如,Dios工艺、Corex工艺、Hismelt工艺等。     

On the smelting reduction of iron ores with hydrogen-argon plasma

Investigations of the plasma smelting reduction of iron ore have been carried out on a laboratory scale using a transferred argon-hydrogen plasma arc. Pyrometric measurements show that the surface temperature near the arc foot is about 2600 K when the hydrogen is mixed with the plasma-gas in front of the cathode, about 2250 K when the hydrogen is introduced laterally into the arc and ca. 2150 K when a pure argon plasma is used. With the help of thermodynamic plasma data the corresponding arc temperatures have been estimated to be 13 000 K, 11000 K and 9500 K. It has been shown that the reduction rate after the smelting phase remains constant and is practically independent of the manner of addition of the hydrogen. The measured efficiencies of utilization of hydrogen were 43% and 50% and thus correspond closely to the equilibrium FeO + H₂ = Fe + H₂O. A combination of the rate constants obtained for the plasma smelting reduction with those found in literature for lower temperatures leads to an activation energy of approximately 67 kJ/mol. This value lies in the range of energies reported for the reduction of wustite after precipitation of the iron phase. It is therefore not unlikely, that in the case of plasma smelting reduction also, the rate determining step is the reaction H^ad+OH^ad → H₂O^ad.     

熔融还原炼铁技术发展情况和未来的思考

由于全球钢铁冶炼资源的变化和环保要求的提升,非高炉炼铁技术越来越受到业界人士的高度关注。近年来,在非高炉炼铁领域,新工艺、新技术层出不穷,结合这些新的前沿技术,特别是重点介绍几种有产业化前景的熔融还原技术（COREX、FINEX、HIsmelt）,并结合宝钢集团在COREX-3000的生产操作实践、探索与创新,较客观地指出了熔融还原炼铁技术目前存在的不足和缺陷,并结合宝钢在这些方面的实践,提出未来发展熔融还原炼铁技术需要关注的内容。     

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.     

Prediction of an iron oxide concentration in the induction smelting process

Induction smelting process, ISP, is a direct smelting process in which self-fluxed composite pellets (made of iron ore, brown coal and lime) are melted in a single phase induction furnace in conjunction with top blown oxygen. A mass transfer model to predict the concentration of iron oxide, has been developed for this process. Transient mass balance equation with complex boundary conditions has been worked out by adopting a relatively new approach known as the cell model approach. These equations have been solved numerically using finite difference technique to obtain the iron oxide concentration profile in the induction smelting process. Numerical and experimental results obtained for the iron oxide concentration show a reasonable agreement with each other.     

Reaction mechanism on the smelting reduction of iron ore by solid carbon

The kinetics of the smelting reduction of iron ore by a graphite crucible and carbon-saturated molten iron was investigated between 1400 °C and 1550 °C, and its reaction phenomena were continuously observed in situ by X-ray fluoroscopy. In the smelting reduction by graphite, it was shown from the observation results that the smelting reduction reaction proceeded by the following two stages: an initial quiet reduction without foaming (stage I) and a following highly active reduction with severe foaming (stage II). At 1500 °C, by the graphite crucible, the reduction rate of iron ore was found to be 8.88×10⁻⁵ mol/cm² · s, and by the molten iron, 8.25×10⁻⁵ mol/cm²·s. The activation energies for the reduction by the graphite crucible and the molten iron were 24.1 and 22.9 kcal/mol, respectively. Based on the results of kinetic research and X-ray fluoroscopic observations, it can be concluded that these two types of smelting reduction reactions of iron ore by the graphite crucible and by the molten iron are essentially the same.     

贫化铜渣熔融还原提铁试验研究

研究以贫化铜渣为对象,首先对贫化铜渣熔融还原进行理论分析,并进行试验考察炉渣碱度、碳氧比、冶炼时间和冶炼温度四个因素对铜渣中铁元素回收率的影响。试验结果表明,(1)贫化铜渣熔融还原提铁合理的试验参数为:铜渣碱度0.3~0.5,碳氧比为1.15~12,冶炼温度为1 500~1 550℃,冶炼时间为40~45 min;(2)在合理试验参数下,铁元素回收率在90%以上,铜元素全部进入金属相;(3)试验获得了铁含量88%~90%,铜含量4.2%~4.6%的含铜铁,可望用于耐候钢等舍铜钢种的冶炼。尾渣中SiO2含量高达50%以上,可使用制备矿物棉等高附加值产品,从而实现铜渣资源的全部高附加值利用。     

利用湿法炼锌赤铁矿法沉铁渣制备铁红工艺

针对赤铁矿渣中存在杂质,影响其综合回收利用的问题,开展赤铁矿渣高温水热法脱杂,制备铁红的研究。研究了不同酸度、温度、时间和液固比条件,对铁红产品中铁、锌、硫含量以及锌、硫脱除率和铁溶出率的影响。实验结果表明:pH值为1,温度220 ℃,保温时间3 h,液固比6∶1,转速400 r·min?1条件下,铁红产品中铁质量分数由58.66%上升为66.83%;赤褐铁类矿物含铁由占总铁质量分数94.05%,上升为97.79%;硫质量分数由2.96%下降至0.82%;锌质量分数由1.03%下降至0.18%。经X射线衍射检测,与赤铁矿渣相比,铁红产品中氧化铁信号峰值提高,杂峰减少。通过扫描电镜/能量散射X射线分析,铁红产品表面附着的硫酸盐等杂质经高温水热法处理后明显减少;实验前后,赤铁矿渣与铁红产品颗粒形貌与大小没有发生变化。实验处理后的铁红产品经检测,满足国家标准氧化铁红含铁量C级,水溶物和水溶性氯化物及硫酸盐含量III型,筛余物2型,105 ℃挥发物V₂型,来源a型标准。      

两步三段式厚渣层铁浴熔融还原炼铁工艺

针对目前熔融还原设备无法将煤气二次燃烧氧化区与铁氧化物还原区隔离而导致能耗偏高的问题,提出了一种两步三段式厚渣层铁浴熔融还原炼铁工艺,以期利用厚渣层冶炼的方法使得氧化区与还原区的梯度隔离。设计了主反应器铁浴炉尺寸与产能,并建立了工艺的整体静态模型,考察了球团金属化率与铁浴炉炉顶煤气氧化度对工艺煤耗、氧耗以及能耗的影响。在选定的适宜操作参数,即煤气氧化度55%,球团金属化率80%条件下,冶炼1t铁水,消耗球团矿1 869.83kg,煤粉674.07kg,同时得到还原度71%的改质煤气898.44kg。结合反应器的设计产能,反应器可处理球团矿3 793.66kg/(h·m2)。     

热还原法炼镁的技术现状及进展

综述了热还原法炼镁工艺的特点,分析了硅热法存在的问题,介绍了我国皮江法炼镁工艺技术的发展状况,提出了一种内热法炼镁的新思路。     

Investigation of iron oxide reduction by TEM

An “environmental cell” located in a high voltage transmission electron microscope has been used to study the reduction of single crystal iron oxides by hydrogen and hydrogen-argon mixtures. The cell enables a direct observation of the solid during reaction, thus permitting the nucleation and growth of solid reaction products to be observed. Hematite was reduced at temperatures in the range 387 to 610°C with gas pressures up to 5.3 kP. Reduction with pure hydrogen was considerably faster than when argon was present. Lath magnetite which rapidly transforms to porous magnetite and thence (more slowly) to porous iron was observed. The reduction of magnetite and of wustite single crystals was observed in the temperature range 300 to 514°C using both hydrogen and hydrogen-argon mixtures at gas pressures up to 6.6 kP. Incubation periods were found for magnetite reduction; during these periods faceted pits formed in the oxide. Iron formed in the early stages was epitaxial with the host magnetite; at later stages the epitaxy was lost and fissures frequently formed in the metal. The morphology of the iron differed between the gas mixtures. Disproportionation accompanied the reduction of wustite, producing intermediate polycrystalline magnetite despite reducing conditions. The disproportionation appeared to be promoted by the reduction reaction. For both oxides, reduction in the hydrogen-argon mixture was slower than in pure hydrogen.     

碱度对转炉钢渣熔融还原提铁的影响

为了使熔融钢渣的"渣"和"热"得到双利用,采用熔融还原法进行了钢渣提铁实验,探讨了二元碱度对还原提铁的影响.结果显示随着碱度的增大铁的回收率及金属化率呈先升后降的趋势,在碱度1.1时铁的回收率和金属化率达到最大,分别为95.8%和99.2%.与炼钢用生铁国标相比,回收的铁块中C、Si、Mn的含量较低,而S、P含量远远高于炼钢用生铁.     

热还原法炼镁的技术现状及进展

综述了热还原法炼镁工艺的特点，分析了硅热法存在的问题，介绍了我国皮江法炼镁工艺技术的发展状况，提出了一种内热法炼镁的新思路。     

Heat transfer in an iron bath of a two-stage smelting reduction process

Mechanisms of the heat transfer by means of iron and slag drops in smelting reduction are discussed. The quantity of slag on the molten iron exists in two forms depending on the different processes: either a thin slag layer or a voluminous slag layer. In the case of a small amount of slag, iron and slag drops are spattered in the free space above the bath furnace. By smelting reduction with a high post-combustion degree, the spattered iron drops are quickly oxidized in the free space. The spattered slag drops transfer heat from the free space to the molten iron. A definition for the heat transfer efficiency in the iron bath of a two-stage smelting reduction process is presented. Experiments on heat transfer were made in an experimental EOF-furnace with 100 kg iron. The post-combustion degree and the heat transfer efficiency were on a high level, because inleaked air was used.     

On the mechanism of iron oxide reduction by carbon

A theoretical analysis has been made to determine the conditions under which the reduction of iron oxide by carbon takes place according to the 2 step mechanism involving the Boudouard reaction. This is based on the concept of minimum temperature of reduction (T _min) below which the Boudouard reaction does not affect the reduction process. The effect of variables such as carbon reactivity, total pressure and so forth onT _min has been studied. TheT _min can be used to determine if metallization is possible under a given set of conditions.     

Fundamental studies on the continuous electrolytic reduction of uranyl sulfate

With the aim of developing a process for continuous electrolytic reduction of uranyl sulfate, the effects of temperature and HF concentration on the electrolytic reduction were investigated using both a rectangular cell and a bipolar cell. Some tests on the semicontinuous-type elec-trolytic reduction of U(VI) and the continuous monitoring of U(VI) in a catholyte were carried out to examine the feasibility of a process for continuous electrolytic reduction. The reduction rate and current efficiency of the electrolysis were increased with increasing temperature up to 333 K, due to an increase in the diffusion coefficient of uranyl sulfate. The presence of a small amount of HF in the catholyte improved the polarization characteristics of the electrolysis. The precipitation of uranous sulfate occurring in electrolysis above 323 K was eliminated by the addition of HF of 2.3 g dm^-3. However, the addition of the excess amount of HF causes the precipitation of UF₄ on the cathode surface during electrolysis. Increase in electric current was not effective in the semicontinuous electrolytic reduction of U(VI) for catholytes with high reduction ratios, and a catholyte with a composition of around 50 pct reduction ratio is pref-erable for continuous operation. The concentration of U(VI) in a catholyte can be monitored continuously either in the absence or in the presence of HF by using a device consisting of three small electrodes. Formerly Graduate Student in the Department of Metallurgy, Kyoto University Formerly Director, Mining and Ore Processing Division, Ningyo-toge Works, PNC Japan