FeO In Slag Research Articles

Thermodynamic studies of slags containing FeO and their impact on ladle refining process

In the ladle refining process, the FeO content of the ladle slag is of great importance in the chemistry as well as the energetics of the process. Optimisation of the process requires an accurate knowledge of the thermodynamic activities of FeO in the ladle slags. Due to the discrepancies in existing data, renewed attempts are being made at the Royal Institute of Technology to generate reliable data for binary, ternary and multicomponent slags containing FeO at steelmaking temperatures. In order to measure the activities of FeO in the slags, a gas equilibration technique was employed in the present work. The slags, kept in Pt crucibles were equilibrated with a CO–CO2–Ar gas mixture and quenched after equilibration. The chemical composition of the slag was analysed. From knowledge of the thermodynamics of the Fe–Pt system, the 'FeO' activities in the slag were evaluated. The results of the present studies, together with other literature values, were optimised in the slag software THERMOSLAG developed at the Royal Institute of Technology, Sweden. The results of the optimisation are presented. Model calculations were performed with the KTH slag software THERMOSLAG using plant data from Ovako Steel, Hofors, Sweden. It was found that oxygen estimations in the metal from the FeO analyses of slags, obtained by a conventional sampling and analysis method were less reliable. Estimation of the oxygen levels utilising the sulphur partition between the slag and the metal were carried out using the THERMOSLAG software. Reasonable estimations of the oxygen content in the metal confirmed that this could be a very useful tool for the plant operator.

The role of slag modifiers on the selective recovery of cobalt and copper from waste smelter slag

Slag cleaning is important from both an economical and environmental perspective. Dump slags from copper smelting prove to be a valuable source of base metals, but the abundance of iron in the slag leads to significant amounts of iron reporting to the alloy phase during carbothermic reduction, which poses a significant cost to remove in subsequent hydrometallurgical processes. A carbothermic reduction of nonferrous smelter slag was conducted under the influence of three different slag modifiers to investigate the recovery of cobalt (and copper) versus iron recovery. The test work was performed in two campaigns; one campaign was performed under a constant oxygen potential of 4.33×10 −9 atm, while the other set of test work was performed using graphite under a pure argon atmosphere. It is shown in both cases that, out of these slag modifiers used, TiO 2 had a more selective recovery of cobalt compared to CaO and CaF 2. It appears that TiO 2 reduces the activity coefficient of the FeO in slag due to its strong affinity for FeO in the slag phase.

Kinetics of iron oxide reduction in molten slag

Experiments on reduction of FeO in molten slag have been carried out using a graphite crucible in a 50 kW capacity plasma reactor. The crucible surface serves as reductant which implies that reduction of FeO takes place by solid carbon. Influence of amount of FeO in slag, crucible surface area, initial slag height and CaF 2 addition on reduction rate has been investigated. It is shown that the kinetics follows a 1 st order reaction which implies that FeO diffusion in the slag phase controlls the rate. Linear variation of the rate constant with respect to FeO variation confirms this.

Recent advances in the fundamentals of the kinetics of steelmaking reactions

G.R. Belton was the leader in developing our understanding of the kinetics of metallurgical reactions. Selected recent kinetic studies, based on this understanding and the application of the results to actual processes, are presented in this article. In particular, the rates of reaction of carbon and carbon in iron with CO2 and H2O gases and FeO in slag are reviewed and applied to the iron smelting process. In addition, our basic understanding of the kinetics of the nitrogen reaction with iron is reviewed, and the results are used in comprehensive models, which can predict the nitrogen content in steel as a function of operating variables in the basic oxygen furnace, electric arc furnace (EAF), and vacuum degassing.

Reduction of FeO in Slag with Coal Char.

Recently, many blast furnaces have increased pulverized coal injection. Unburnt coal char is generated from pulverized coal injection and a portion of it remains in the slag. This interferes with tapping by increasing slag viscosity, and can make blast furnace operation unstable. Reduction of FeO with different types of coal was measured in simulated blast furnace slags at 1450°C, using a constant volume pressure increase (CVPI). The reaction rate of FeO was observed to be independent of the type of coal used regardless of different components such as volatile matter and ash. The measured rates at 1.0% and 3.0% of FeO in the slag were 2.77 × 10 -7 and 1.58 × 10 -8 mol/cm 2 s respectively. The overall rate is controlled by a series of processes such as the reaction of CO 2 with C, CO with FeO in slag, liquid phase mass transfer of FeO in the slag, and gas phase mass transfer. For low FeO contents, when the gas evolution rate is low, liquid phase mass transfer is the primarily controlling mechanism. A model to predict the amount of char in the slag at tap based on these results is presented.

The effect of carbon content on the rate of reduction of FeO in slag relevant to iron smelting

In the iron smelting, or bath smelting, process the tapped metal contains high amounts of sulfur and the slag contains high amounts of FeO, relative to blast furnace slag. After tapping, the FeO can be further reduced by carbon in the metal, which will also lead to better desulfurization. Although there have been many studies of the reaction of carbon in iron with FeO in slag, discrepancies exist with regards to the effect of carbon in iron on the rate of FeO reduction in slag, which is the subject of this study. Experiments were conducted at 1723 K, using a slag with basicity close to one with an FeO mass content of 5 %. The rate of reduction was measured using a pressure increase technique. For moderate and high sulfur contents, as in the case of iron smelting, the rate is primarily controlled by the dissociation of CO2 on the surface of the molten iron. Furthermore, if the effect of carbon on sulfur is taken into account, for the range of carbon mass contents of 2 to 4.5 %, there is no effect of the carbon level on the rate of FeO reduction. At low sulfur contents it was found that there is considerable slag foaming, which inhibits mass transfer of FeO in the slag, and significantly reduces the rate. Even when there is no slag foaming at low sulfur contents, mass transfer of FeO in the slag can influence the rate of FeO reduction.

A study of the reduction rate of FeO in slag by solid carbon

The reduction reaction of FeO in slag by carbon plays an important role in bath smelting reduction processes. In this study, the rate of this reaction was measured to understand the kinetic behavior of FeO reduction in slag by using the mass spectrometer technique. The present experimental results implied that the rate-determining step would change from the mass transfer of FeO at a low FeO content ( 30 wt pct), while the total reduction rate would increase with an increasing FeO content in the slag. Based on the results of this study and comparisons with thermodynamical data for FeO in slag, the reduction rate of FeO can be expressed by the following equation: $$r = 4.4 \times 10^{ - 5} (a_{FeO} )^{1.34} or r = 1.67 \times 10^{ - 7} (wt pct Feo)^{1.26} $$ The activation energy of the present reaction was measured to be 60.0 kcal/mol for 10 wt pct FeO. The large value of the activation energy suggested that the chemical reactions at the gas/carbon interface would be the rate-limiting step for FeO contents higher than 30 wt pct. In the meantime, the reduction mechanism would change from a chemical reaction at the carbon surface to a mixed controlling step of chemical reactions and mass transfer of FeO in slag for FeO contents lower than 5 wt pct.

Reaction mechanism of FeO reduction by solid and dissolved carbon

The reduction reactions of FeO by carbon have been studied in order to be able to understand the fundamental phenomena occurring in smelting reduction process. The reduction of pure FeO by solid carbon proceeds mostly according to the same reaction mechanism as that by dissolved carbon in iron, the rate of which was experimentally determined to be controlled by the interfacial chemical reaction between Fe‐C melt and intermediate CO2 gas. Hence, the reduction rate of pure FeO by solid carbon is also chemically controlled by the Boudouard reaction between the dissolved carbon and CO2 at the interface of by‐product Fe droplet/gas phase, the activation energy of which was found to be about 193.2 kJ/mol. In addition, the reduction reaction of FeO in CaO‐SiO2‐Al2O3‐FeO slags by the dissolved carbon in Fe melt was also investigated over the FeO mass content less than 20 %. The reduction rate shows first order dependence with respect to FeO concentration. The surface active sulphur content in iron does not affect the reduction rate, and the temperature dependence of reduction rate gives the activation energy of 24.78 kJ/mol. Therefore, the reduction rate of FeO in slags by the dissolved carbon can be safely mentioned to be controlled by the liquid phase mass transfer of FeO through the slag phase diffusion‐resistant boundary layer over the limited FeO concentration range. The empirical expression for the mass transfer controlled reactioe, deren Aktivierungsenergie ca. 193.2 kJ/mol beträgt. Außerdem wurde die Reduktion von FeO in CaO‐SiO2‐Al2O3‐FeO‐Schlacken mit dem in der Eisenschmelze gelöstem Kohlenstoff fär FeO‐Massengehalte von weniger als 20% untersucht. Die Reduktionsgeschwindigkeit weist hinsichtlich der FeO‐Konzentration eine Abhängigkeit 1. Ordnung auf. Der Anteil an oberflächenaktivemn rate was determined as r = 5.94(±0.07).10−6.exp(‐24780/RT).(%FeOP)0.96 over the reaction conditions employed.

Characterization of Slag-Metal Droplet-Gas Emulsion in Oxygen Steelmaking Converters.

Metal droplets of various sizes are ejected from the jet impact zone in oxygen steel making converters. The residence time of these droplets in the surrounding gas-slag mixture is calculated for different operating conditions in top blown converters. A new dimensionless emulsion number, En, based on the ratio of the residence time of the metal droplets to the residence time of gas bubbles in liquid slag is proposed. This emulsion number is found to be strongly dependent on the ratio of lance height to the throat diameter of De Laval nozzle. The blowing regimes followed in three plants are analyzed in terms of emulsion number. The reduction of FeO in slag by dissolved carbon in metal droplets also depends upon emulsion number and, in turn, decides the lance height chosen at various stages of the blow as well as lime dissolution, slag formation and slopping. The emulsion number can be used as an effective tool to control slag formation behaviour.

Kinetic model for reduction of iron oxide in molten slags by iron‐carbon melt

Rate of reduction of iron oxide in iron and steelmaking slags by mass contents of dissolved carbon (>3%) in molten iron depends upon activity of FeO, temperature, mixing of bulk slag and other experimental conditions. A general kinetic model is developed by considering mass transfer of FeO in slag, chemical reaction at gas‐metal interface and chemical reaction at gas‐slag interface, respectively, as the three rate controlling steps. A critical analysis of the experimental data reported in literature has been done. It is shown that in the case of slags containing mass contents of less than 5% FeO, the reduction of FeO is controlled by mass transfer of FeO in slag plus chemical reaction at gas‐metal interface; when slags contain more than 40% FeO, the reduction of FeO is controlled by chemical reaction at gas‐metal interface plus chemical reaction at gas‐slag interface; at intermediate FeO mass contents (between ∼ 5 and 40% FeO), the reduction of FeO is controlled by all three steps, namely, mass transfer of FeO in slag, chemical reaction at gas‐metal interface and chemical reaction at gas‐slag interface. The temperature dependence of rate constant for the gas‐slag reaction is obtained as:In k2 = –32345.4(&6128)/ T + 19.0(&3.42); σlnk2,1/T = &0.3.where k2 is expressed in mol m‐2 s‐1 bar‐1. The mass transfer coefficient of iron oxide in bulk slag is found to vary in the range 1.5 × 10‐5 to 5.0 × 10‐5 m/s, depending upon the slag composition as well as experimental conditions.

Rate of reduction of FeO in slag by Fe-C drops

The rate of reduction of FeO in slags by Fe-C drops plays an important role in several metallurgical processes, including iron bath smelting. In this study, the rate of this reaction was determined by measuring the volume of CO generated as a function of time, and the reaction was observed by X-ray fluoroscopy. The drops entered the slag in a nearly spherical shape, remained as single particles, and for the major portion of the reaction remained suspended in the slag surrounded by a gas halo. The rate was found to decrease with carbon content for alloys with low sulfur contents. The rate decreased significantly with increasing the sulfur content. Based on the results and a comparison of the calculated rates, for the possible rate-controlling mechanisms, a kinetic model was developed. The model is a mixed control model including mass transfer in the slag, mass transfer in the gas halo, and chemical kinetics at the metal interface. At high sulfur contents (>0.01 pct), the rate is primarily controlled by the dissociation of CO2 on the surface of the iron drop. At very low sulfur, the rate is controlled by the two mass-transfer steps and increases as the gas evolution from the particle increases.

小型燃焼炉におけるレースウェイ領域での吹込み鉱石粉の伝熱と反応

Influence of injected ore fines on the chemical and physical phenomena in and around the raceway was examined and the mechanism of silicon decrease in iron melt was experimentally investigated by using a small-scale hot furnace.(1) The temperature in the raceway decreases with increasing the amount of injected ore fines mainly due to the endothermic reaction(2) A part of injected ore fines remains inside of the raceway and shows high fractions of melting and reduction. Both fractions of sample increase with the increase of the injection rate, as the proportion of remaining ore also increases.(3) SiO content in the gas and Si content in the metal in the dripping region above the raceway decrease with increasing the injection rate, since SiO gas generated in the raceway can be absorbed by injected iron ore at the molten state.(4) Decrease of Si content in the metal by the reaction with FeO in slag formed by injected ore is negligibly small in the dripping region below the raceway.

Mechanism of Oxidation of Si in Molten Cu by FeO in Slag

Etude experimentale du mecanisme de transfert de masse entre l'alliage Cu−Si et les scories a 1523 K. Cinetique du processus d'oxydation

Reduction of FeO in Molten Slags by Solid Carbon in the Electric Arc Furnace Operation

the course of operation of 70 l UHP furnace in Chita Plant, Daido Steel, solid carbon has been injected in order to facilitate the reduction of FeO in slag and to improve the energy saving and heating efficiency. In this paper, the effect of the injection method on the reduction rate of FeO in slag is discussed in relation to the quality and size of carbon powder injected, injection rate and nature of molten slag. Moreover the relation between the fundamental data of waste gas and the degree of slag reduction has been comfirmed. The results obtained are summarized as follows:(1) Volatile matter in solid carbon gives a large influence on the reducing reaction. In the coke of higher content of volatile matter, the reduction is controlled by the chemical reaction, while in the coke o f lower content of volatile matter, the reduction is controlled by the transport of FeO in slag.(2) The reduction rate depends on the basicity of molten slag. The reduction rate increases as the basicity of molten slag increases.(3) Estimation of carbon content of molten steel for a rapid operation is found to be possible by the use of the fundamental data of waste gas.

Reduction of Molten Iron Oxide and FeO Bearing Slags by H2-Ar Plasma

(I) Reduction of molten iron oxide and FeO bearing slag by H2-Ar plasma was studied using water cooled Cu crucible. The sample weights were 25 to 75g, the flow rate of mixture-gas was 20l/mm and DC electric power of plasma was 8.3kW. Results obtained were as follows:(1) The reduction of molten iron oxides proceeds linearly with time and the reaction rate is proportional to the partial pressure of atomic hydrogen. Therefore, it is considered that the rate determining step is the chemical reaction between FeO and the atomic hydrogen formed by thermal dissociation in the plasma.(2) The rate of reduction of FeO bearing slag is lower than that of molten iron oxide and is proportional to the FeO concentration in slag. It is presumed that the reduction rate is controlled by both the chemical reaction rate of FeO with atomic hydrogen at the gas-solid interface and the mass transport rate of FeO across the boundary layer between the interface and the molten slag bulk.(3) The reduction of molten iron oxide and FeO bearing slag by H2-Ar plasma takes place only on the cavity formed at the surface of melt by the momentum of plasma jet gas.(II) Continuous melting of pre-reduced ore powder, obtained by a fluidized bed reduction was examined using MgO crucible and H2-Ar plasma.Following results were obtained:(1) Carry-over loss of the pre-reduced ore powder during the melting in plasma arc furnace was small, when the condition of powder feeding and plasma arc were properly chosen.(2) Reduction of FeO in slag, accompanied in fed material, by H2-Ar plasma, could be described by a simple model of continuous melting and reduction, based on experimental results of the reduction of FeO bearing slag as described (1-2).With this model, the rate of reduction during continuous melting was determined.

The deoxidation of low-alloy steel ingots during ESR.

The mechanisms of deoxidation in the electroslag remelting process have been studied, with particular reference to the reactions involving calcium. ESR ingots made with varying deoxidation rates have been examined with respect to their bulk composition and oxide inclusion composition. We find that at high oxygen potentials (% FeO>0.7 in the slag), reactions between slag FeO and the deoxidant predominate. At low oxygen potentials (% FeO<0.2 in the slag) exchange reactions between deoxidant and the slag components control the inclusion composition. At intermediate oxygen potentials, the inclusion composition is strongly influenced by the SiO2 content of the slag. The manufacture of low-oxygen, low-sulphur steels by ESR will hence require slags with small contents of both SiO2 and Al2O3.

スラッグ及び鉱石等のFeO定量における硫化物の影響による誤差の大きさについて

スラッグ及び鉱石等のFeO定量における硫化物の影響による誤差の大きさについて