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As the steel industry expands worldwide, slag dumps with transition metals (especially chromium and vanadium) are becoming more common, posing a serious environmental threat. Understanding the properties of slags containing transition metal oxides, as well as how to use the slags to recover and recycle metal values, is critical. Toward this end, the University of Science and Technology Beijing (USTB) and Royal Institute of Technology (KTH) have been collaborating on slags containing transition metals for decades. The research was carried out from a fundamental viewpoint to get a better understanding of the structure of these slags and their properties, as well as industrial practices. The research focused on the three “R”s, viz. retention, recovery, and recycling. The present paper attempts to highlight some of the important achievements in these joint studies., QC 20230116Correction in: International Journal of Minerals, Metallurgy and Materials, Volume 29, Issue 6, Pages 1304, June 2022. DOI:10.1007/s12613-022-2495-3, WOS: 000782346900001, Scopus: 2-s2.0-85128041953

Process modelling of smelting in submerged arc furnaces has been carried out since the 1980s, both in 2D and 3D. While these models have improved production technology and give a better understanding of the process for ferroalloy production, many of the models lack verification from industry. Modelling of electrodes, lining, and off gases are helpful for better understanding conditions inside the furnace and for decreasing the breaking of electrodes, prolonging the lifetime of the lining, and decreasing power consumption in the SAF. There has only been limited modelling of ferroalloy refining converters, but some studies of Creusot-Loire-Uddeholm (CLU) type reactors using physical cold models and CFD simulations show interesting results in terms of mass transfer coefficients, mixing times, and plum characteristics., Process modelling of smelting in submerged arc furnaces has been carried out since the 1980s, both in 2D and 3D. While these models have improved production technology and give a better understanding of the process for ferroalloy production, many of the models lack verification from industry. Modelling of electrodes, lining, and off gases are helpful for better understanding conditions inside the furnace and for decreasing the breaking of electrodes, prolonging the lifetime of the lining, and decreasing power consumption in the SAF. There has only been limited modelling of ferroalloy refining converters, but some studies of Creusot-Loire-Uddeholm (CLU) type reactors using physical cold models and CFD simulations show interesting results in terms of mass transfer coefficients, mixing times, and plum characteristics.

The oxidation states of vanadium in the CaO-MgO-Al2O3-SiO2-VOx slag system are investigated with the initial V2O5 concentration in the range of 1-10 mole fraction, in the temperature range, 1823-1923K, partial pressures of oxygen from 10(-5) to 10(3)Pa, and with the basicities in the range of 0.85-2.20. The valance states of vanadium are determined by the X-Ray Absorption Near-Edge Structure (XANES) method. The results indicates that, for the oxide VOx, at a given temperature, and basicity, x is found to increase slightly with increase of initial V2O5 concentration. With the increase of slag basicity, x is increased. It is also found that x in VOx decreases with the increase of temperature, whereas, at constant basicity, the value of x increases with the increased oxygen partial pressure. The present results are useful in the quantification of V3+/V4+ and V4+/V5+ ratios for a given slag as functions of basicity, temperature, and oxygen partial pressure., QC 20160309

In the current work, oxidation kinetics of Fe-Cr and Fe-Cr-C melts by gas mixtures containing CO2 was investigated by Thermogravimetric Analysis (TGA). The experiments were conducted keeping the melt in alumina crucibles, allowing the alloy melt to get oxidized by an oxidant gas. The oxidation rate was followed by the weight changes as a function of time. The oxidation experiments were conducted using various mixtures of O-2 and CO2 with = 10(-2) to 10(4) Pa. In order to understand the mechanism of oxidation, the wetting properties between the alumina container and the alloys used in the thermogravimetric analysis (TGA) experiments and the change of the alloy drop shape during the course of the oxidation were investigated by X-ray radiography.The experiments demonstrated that the oxidation rate of Fe-Cr melt increased slightly with temperature under the current experimental conditions, but it is strongly related to the Cr-content of the alloy as well as the oxygen partial pressure in the oxidant gas mixture, both of which caused an increase in the rate. For the Fe-Cr-C system, the oxidation rate has a negative relationship with carbon content, viz. with increasing carbon, the oxidation rate of the alloy melt slightly decreased. The chemical reaction was found to be the rate determining step during the initial stages, whereas as the reaction progressed, the diffusion of oxygen ions through slag phase to the slag-melt interface was found to have a strong impact on the oxidation rate. The overall impact of different factors on the chemical reaction rate for the oxidation process derived from the current experimental results can be expressed by the relationship: A model for describing the kinetics of oxidation of Fe-Cr and Fe-Cr-C alloys under pure CO2 was developed. Simulation of the oxidation kinetics using this model showed good agreement with the experimental results., Updated from "Submitted" to "Published". QC 20140127

A Knudsen effusion mass spectrometric method was used to study the vaporization processes and thermodynamic properties of pure V2O3 and 14 samples of vanadium-containing slags in the CaO-MgO-Al2O3-SiO2 system in the temperature range 1875-2625 K. The system was calibrated using gold in the liquid state as the standard. Vaporization was carried out from double tungsten effusion cells. First it was shown that, in vapor over V2O3 and the vanadium-containing slags in the temperature range 1875-2100 K, the following vapor species were present: VO2, VO, O, WO3 and WO2, with the latter two species being formed as a result of interaction with the tungsten crucibles. The temperature dependencies of the partial pressures of these vapor species were obtained over V2O3 and the slags. The ion current comparison method was used for the determination of the V2O3 activities in slags as a function of temperature with solid V2O3 as a reference state. The V2O3 activity coefficients in the slags under investigation indicated positive deviations from ideality at 1900 K and a tendency to ideal behavior at 2100K. It was shown that the V2O3 activity as a function of the slag basicity decreased at 1900 K and 2000 K and was practically constant in the slag melts at 2100K. The results are expected to be valuable in the optimization of slag composition in high-alloy steelmaking processes as well as for their environmental implications. Copyright (C) 2010 John Wiley & Sons, Ltd., QC 20101201

The oxidation mechanism of liquid Fe-V alloys with V content from 5 to 20 mass pct under different oxygen partial pressures using CO2-O-2 mixtures with CO2 varying from 80 pct to 100 pct was investigated by thermogravimetric analysis between 1823 K and 1923 K (1550 degrees C and 1650 degrees C). The products after oxidation were identified by scanning electron microscopy energy-dispersive spectrograph and X-ray diffraction. The results indicate that the oxidation process can be divided into the following steps: an apparent incubation period, followed by a chemical reaction step with a transition step before the reaction, and diffusion as the last stage. At the initial stage, a period of slow mass increase was observed that could be attributed to possible oxygen dissolution in the liquid iron-vanadium coupled with the vaporization of V2O. The length of this period increased with increasing temperature as well as vanadium content in the melt and decreased with increasing oxygen partial pressure of the oxidant gas. This analysis was followed by a region of chemical oxidation. The oxidation rate increased with the increase of the O-2 ratio in the CO2-O-2 gas mixtures. During the final stage, the oxidation seemed to proceed with the diffusion of oxygen through the product layer to the reaction front. The Arrhenius activation energies for chemical reaction and diffusion were calculated, and kinetic equations for various steps were setup to describe the experimental results. The transition from one reaction mechanism to the next was described mathematically as mixed-control equations. Thus, uniform kinetic equations have been setup that could simulate the experimental results with good precision., QC 20110104

Gas liquid reactors are extensively used in many metallurgical processes involving the refining of liquid metals. In these processes, reactions leading to the oxidation of various solutes in liquid metal often compete with each other, which ultimately determine the liquid metal composition. In the present paper, a model has been proposed to simulate the evolution of solute contents in a metallic melt considering mass transfer of solutes in the melt in the vicinity of the bubble, equilibrium at the gas-metal interface and gas composition evolution in the bubble during its ascent through the melt. The composition of solutes at the metal-gas interface in principle can be altered by changing the injected gas composition. The model was applied to the case of oxygen injection through a lance into liquid steel-containing C and Cr, aiming sufficient decarburization without much oxidation of Cr to the slag. The Cr loss to the slag by oxidation is generally much more than that expected based on equilibrium thermodynamics applied to the bulk metal and gas. The actual Cr loss, as shown by the present model, is determined by the composition of solutes at the metal-gas interface rather than in the bulk. The effect of change of the partial pressure of oxygen in the bubble by replacing oxygen by carbon dioxide in the injected gas and the corresponding evolution of C and Cr contents in the melt was simulated. Some preliminary experiments were conducted to validate the model predictions. The frame work of the model is generic and can be extended to many gas-liquid metal reactors in liquid metal processing., QC 20110131

With the progress of high alloy steelmaking processes, it is essential to minimize the loss of valuable metals, like chromium and vanadium during the decarburization process, from both economic as well as environmental view points. One unique technique to realize this aim, used in the present work, is the decarburization of high alloy steel grades using oxygen with CO2 in order to reduce the partial pressure of oxygen. In the present work, the investigation on the oxidation of iron-chromium and iron-vanadium molten alloys under CO2-O2 mixtures was carried out and presented in this dissertation. For oxidation study on Fe-Cr molten alloy with CO2-O2 mixtures, on the basis of thermodynamic analysis, energy balance calculation and modeling results, experimental validation in laboratory was carried out, and later on, the oxidation kinetics of Fe-Cr and Fe-Cr-C melts under controlled partial pressure of oxygen was investigated. Thermodynamics calculation and energy balance estimation demonstrated that, it is possible to use CO2 or CO2-O2 mixtures as decarburizers during EAF process and high initial carbon contents in the steel can be adopted at the beginning in order to reduce the cost. A generic model has been developed to describe the overall process kinetics prevailing in metallurgical reactors containing liquid metal and gas bubbles. This model is general and can be extended further to consider any gas liquid reactions in any chemical engineering reactor, and especially the metallurgical ones, like AOD. In the present dissertation, the model is applied in predicting the evolution of Cr and C contents in a Fe-C-Cr melt during injection of different O2-CO2 mixtures. The related simulation results illustrated that CO2 is efficient in Cr retention. In order to verify the modeling results, 1kg induction furnace experiments were carried out in the present laboratory. The results indicated that the predictions of the model are in good agreement with the experimental results., QC20100628

The work was carried out in four parallel directions. The thermodynamic activities of oxides of Cr in steel slags were determined by slag-gas equilibration technique. The ratio of Cr2+/Cr3+ in CaO-MgO(-FeO)-AlO3-SiO2-CrO(x)system slags was measured by X-ray absorption near edge spectra (XANES). High-temperature mass spectrometry method was also used to obtain the distribution of chromium oxides. A mathematical correlation was established for estimating the ratio of Cr2+/Cr3+ as a function of temperature, partial pressure of oxygen and slag basicity. Laboratory investigations of the decarburization of high alloy steels under controlled oxygen potentials have been carried out to retain Cr in the steel phase. A mathematical model has been developed for the decarburization process with controlled oxygen partial pressure. Experimental and theoretical investigations have been carried out in optimizing the Mo-additions to steel in the EAF practice in Uddeholm Tooling AB. Substantial saving of Mo as well as less emissions of Mo-bearing dust are indicated in the study. A salt extraction process was developed to extract the metal values from steel slags. Successful extractions, followed by electrolysis indicate that this could be a viable route towards recovery of metals from metallurgical slags., QC 20110329

In order to make the stainless steel making process efficient and environment friendly, it is essential to minimize the loss of chromium to the slag phase. With a view to investigate the advantages of using CO2 to attain moderate oxygen partial pressures in the oxidant gas during the decarbirization of stainless steel, the present experiments were carried out to understand the oxidation kinetics of Fe-Cr alloy and Fe-Cr-C alloy with gas mixtures containing CO2. In the present work, the oxidation behavior of Fe-Cr was examined by thermogravimetric analysis (TGA). Various mixtures of O2 and CO2 were used as the oxidant gas and the oxidation rate was followed by the weight changes as a function of time. One trial was made on the oxidation of Fe-Cr-C alloy with CO2 as the oxidant. The experiments demonstrated that the oxidation rate is independent of temperature at present experimental situation, but has strongly related to the Cr-content of the alloy as well as the oxygen partial pressure in the oxidant gas mixture. The wetting of alumina by the iron drop and the change of the drop shape during the course of the oxidation were investigated by X-ray radiography., QC 20140815

With the progress of high alloy steelmaking processes, it is essential to minimize the loss of valuable metals, like chromium and vanadium during the decarburization process, from both economic as well as environmental view points. One unique technique to realize this aim, used in the present work, is the decarburization of high alloy steel grades using oxygen with CO2 in order to reduce the partial pressure of oxygen. In the present work, the investigation on the oxidation of iron-chromium and iron-vanadium molten alloys under CO2-O2 mixtures was carried out and presented in this dissertation. For oxidation study on Fe-Cr molten alloy with CO2-O2 mixtures, on the basis of thermodynamic analysis, energy balance calculation and modeling results, experimental validation in laboratory was carried out, and later on, the oxidation kinetics of Fe-Cr and Fe-Cr-C melts under controlled partial pressure of oxygen was investigated. Thermodynamics calculation and energy balance estimation demonstrated that, it is possible to use CO2 or CO2-O2 mixtures as decarburizers during EAF process and high initial carbon contents in the steel can be adopted at the beginning in order to reduce the cost. A generic model has been developed to describe the overall process kinetics prevailing in metallurgical reactors containing liquid metal and gas bubbles. This model is general and can be extended further to consider any gas liquid reactions in any chemical engineering reactor, and especially the metallurgical ones, like AOD. In the present dissertation, the model is applied in predicting the evolution of Cr and C contents in a Fe-C-Cr melt during injection of different O2-CO2 mixtures. The related simulation results illustrated that CO2 is efficient in Cr retention. In order to verify the modeling results, 1kg induction furnace experiments were carried out in the present laboratory. The results indicated that the predictions of the model are in good agreement with the experimental results., QC20100628

In order to make the stainless steel making process efficient and environment friendly, it is essential to minimize the loss of chromium to the slag phase. With a view to investigate the advantages of using CO2 to attain moderate oxygen partial pressures in the oxidant gas during the decarburizations of stainless steel, the present experiments were carried out to understand the oxidation kinetics of Fe-Cr alloys and Fe-V alloy with gas mixtures containing CO2 In the present work, the oxidation behavior of Fe-Cr and Fe-V was examined by thermogravimetric analysis (TGA). Various mixtures of O2 and CO2 were used as the oxidant gas and the oxidation rate was followed by the weight changes as a function of time. The experiments demonstrated that the oxidation rate is independent of temperature at present experimental situation, but has strongly related to the Cr-content of the alloy as well as the oxygen partial pressure in the oxidant gas mixture. The wetting of alumina by the iron drop and the change of the drop shape during the course of the oxidation were investigated by X-ray radiography., QC 20140821

With the progress of high alloy steelmaking processes, it is essential to minimize the loss of valuable metals, like chromium and vanadium during the decarburization process, from both economic as well as environmental view points. One unique technique to realize this aim, used in the present work, is the decarburization of high alloy steel grades using oxygen with CO2 in order to reduce the partial pressure of oxygen. In the present work, the investigation on the oxidation of iron-chromium and iron-vanadium molten alloys under CO2-O2 mixtures was carried out and presented in this dissertation. For oxidation study on Fe-Cr molten alloy with CO2-O2 mixtures, on the basis of thermodynamic analysis, energy balance calculation and modeling results, experimental validation in laboratory was carried out, and later on, the oxidation kinetics of Fe-Cr and Fe-Cr-C melts under controlled partial pressure of oxygen was investigated. Thermodynamics calculation and energy balance estimation demonstrated that, it is possible to use CO2 or CO2-O2 mixtures as decarburizers during EAF process and high initial carbon contents in the steel can be adopted at the beginning in order to reduce the cost. A generic model has been developed to describe the overall process kinetics prevailing in metallurgical reactors containing liquid metal and gas bubbles. This model is general and can be extended further to consider any gas liquid reactions in any chemical engineering reactor, and especially the metallurgical ones, like AOD. In the present dissertation, the model is applied in predicting the evolution of Cr and C contents in a Fe-C-Cr melt during injection of different O2-CO2 mixtures. The related simulation results illustrated that CO2 is efficient in Cr retention. In order to verify the modeling results, 1kg induction furnace experiments were carried out in the present laboratory. The results indicated that the predictions of the model are in good agreement with the experimental results., QC20100628

With the progress of high alloy steelmaking processes, it is essential to minimize the loss of valuable metals, like chromium and vanadium during the decarburization process, from both economic as well as environmental view points. One unique technique to realize this aim, used in the present work, is the decarburization of high alloy steel grades using oxygen with CO2 in order to reduce the partial pressure of oxygen. In the present work, the investigation on the oxidation of iron-chromium and iron-vanadium molten alloys under CO2-O2 mixtures was carried out and presented in this dissertation. For oxidation study on Fe-Cr molten alloy with CO2-O2 mixtures, on the basis of thermodynamic analysis, energy balance calculation and modeling results, experimental validation in laboratory was carried out, and later on, the oxidation kinetics of Fe-Cr and Fe-Cr-C melts under controlled partial pressure of oxygen was investigated. Thermodynamics calculation and energy balance estimation demonstrated that, it is possible to use CO2 or CO2-O2 mixtures as decarburizers during EAF process and high initial carbon contents in the steel can be adopted at the beginning in order to reduce the cost. A generic model has been developed to describe the overall process kinetics prevailing in metallurgical reactors containing liquid metal and gas bubbles. This model is general and can be extended further to consider any gas liquid reactions in any chemical engineering reactor, and especially the metallurgical ones, like AOD. In the present dissertation, the model is applied in predicting the evolution of Cr and C contents in a Fe-C-Cr melt during injection of different O2-CO2 mixtures. The related simulation results illustrated that CO2 is efficient in Cr retention. In order to verify the modeling results, 1kg induction furnace experiments were carried out in the present laboratory. The results indicated that the predictions of the model are in good agreement with the experimental results., QC20100628

A theoretical generic model describing the mass transfer phenomena between rising gas bubbles and a metal bath has earlier been developed by the present authors, to predict the composition change in the melt as consequence of blowing different oxidant gases. In order to verify the model predictions, a series of experiments involving reactions between Fe-Cr-C melts and different O(2)-CO(2) gas mixtures were carried out. The results showed that the decarburization deviates significantly from thermodynamic paths predicted on the basis of bulk compositions and that the model was able to make reasonably reliable predictions of the changes of chromium and carbon contents in the melt as a function of time. According to the model, the compositions at the vicinity of injection point as well as at the gas-melt interface in the bubble are likely to be far from that in the bulk. The results of the present set of experiments showed, with CO(2) injection, the utilization of the available oxygen for decarburization was higher as compared to O(2) injection in the case of melts containing higher carbon levels (>1mass%). Reverse is the case in low carbon melts. The results also indicate relatively less Cr-losses from the metal bath when CO(2) is used as the oxidant. As the model predictions are found to be reasonably reliable, the model predictions are extended to predict the impact of the variation of different process parameters., QC 20111107

QS 20120328

The converter process for steelmaking in China developed very rapidly for several decades as the technologies of slag splashing, top and bottom combined blowing, sublance end point control, etc. played an important role. Currently, many BOF steelworks use the Slag-Remaining + Double-Slag steelmaking process, by which the lime consumption and slag volume are greatly decreased. The ‘De-P + De-C’ (dephosphorisation + decarburisation) steelmaking process has been applied on a large scale as well and good results have been obtained on reducing lime consumption and shortening the tap-to-tap time. In the coming 10 to 15 years, more attention will be paid on technologies for sustainable development, such as the technology of even stronger bottom blown combined blowing, application of AI in BOF production, higher scrap consumption, dry de-dusting system, recovery of P and Fe from steelmaking slags, etc. Compared to the steel industry, the development of converter technologies in ferroalloys is slower although there is some progress, like the application of the top and bottom combined blowing technology, AOD (argon oxygen decarburisation) as well as vacuum converter. However, it is still difficult to make LCFeCr (low carbon ferrochrome) through a converter in China and the use of a converter for M-LFeMn production is not yet industrialised., The converter process for steelmaking in China developed very rapidly for several decades as the technologies of slag splashing, top and bottom combined blowing, sublance end point control, etc. played an important role. Currently, many BOF steelworks use the Slag-Remaining + Double-Slag steelmaking process, by which the lime consumption and slag volume are greatly decreased. The ‘De-P + De-C’ (dephosphorisation + decarburisation) steelmaking process has been applied on a large scale as well and good results have been obtained on reducing lime consumption and shortening the tap-to-tap time. In the coming 10 to 15 years, more attention will be paid on technologies for sustainable development, such as the technology of even stronger bottom blown combined blowing, application of AI in BOF production, higher scrap consumption, dry de-dusting system, recovery of P and Fe from steelmaking slags, etc. Compared to the steel industry, the development of converter technologies in ferroalloys is slower although there is some progress, like the application of the top and bottom combined blowing technology, AOD (argon oxygen decarburisation) as well as vacuum converter. However, it is still difficult to make LCFeCr (low carbon ferrochrome) through a converter in China and the use of a converter for M-LFeMn production is not yet industrialised.