| 1. |
- Seetharaman, Seshadri, et al.
(författare)
-
Slags containing transition metal (chromium and vanadium) oxides—Conversion from ticking bombs to valuable resources : Collaborative studies between KTH and USTB
- 2022
-
Ingår i: International Journal of Minerals, Metallurgy and Materials. - : Springer Nature. - 1674-4799 .- 1869-103X. ; 29:4, s. 750-757
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 2. |
- Teng, Lidong, et al.
(författare)
-
RETENTION, RECOVERY AND RECYCLING OF METAL VALUES FROM HIGH ALLOYED STEEL SLAGS
- 2010
-
Ingår i: ARCH METALL MATER. - : Polish Academy of Sciences Chancellery. - 1733-3490. ; 55:4, s. 1097-1104
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 3. |
- Wang, Haijuan, et al.
(författare)
-
Determination of Vanadium Oxidation States in CaO-MgO-Al2O3-SiO2-VOx System by K Edge XANES Method
- 2016
-
Ingår i: Steel Research International. - : Wiley-VCH Verlag. - 1611-3683 .- 1869-344X. ; 87:2, s. 199-209
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Wang, Haijuan, et al.
(författare)
-
High-temperature mass spectrometric study of the vaporization processes of V2O3 and vanadium-containing slags
- 2010
-
Ingår i: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 24:16, s. 2420-2430
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 7. |
- Wang, Haijuan, et al.
(författare)
-
Investigation of the oxidation kinetics of Fe-Cr and Fe-Cr-C melts undercontrolled oxygen partial pressures
- 2012
-
Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer Science and Business Media LLC. - 1073-5615 .- 1543-1916. ; 43:6, s. 1476-1487
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
| 8. |
- Wang, Haijuan, 1982-
(författare)
-
Investigations on the Oxidation of Iron-chromium and Iron-vanadium Molten Alloys
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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. Meanwhile, the experimental results indicated that the Cr-losses can be significantly lowered by replacing the oxygen with CO2 in the injected gas, specifically for Fe-Cr-C melts with carbon levels higher than about 0.8 mass%. Subsequently, the oxidation kinetics of Fe-Cr and Fe-Cr-C melts was investigated under different CO2-O2 mixtures. It is indicated that, the oxidation rate is controlled by the chemical reaction at the initial stage and the reaction rate can be expressed as at the Cr range of 11-21 mass% in the Fe-Cr melt.For oxidation study on Fe-V liquid alloy, the investigation of the oxidation kinetics was carried out under CO2-O2 mixtures, which is followed by the study on thermodynamic properties of vanadium containing slags. During oxidation of Fe-V melt, in the case of alloys with vanadium contents exceeding 10 mass%, there exists an incubation period before the chemical reactions prevail the process. In addition, the ‘incubation time’ increased with the increase of temperature and the vanadium content, whereas it decreased with the increase of oxygen partial pressure in the oxidant gas.High-temperature mass spectrometric method was used to determine the activity of the vanadium oxide in CaO-MgO-Al2O3-SiO2-V2O3 slags, whereas, the oxidation states of vanadium in the CaO-MgO-Al2O3-SiO2-VOxslag system was studied by XANES method. The results indicated that, higher basicities stabilize higher vanadium oxidation state, whereas, higher temperature stabilizes lower vanadium oxidation state.The present work, which was carried out within the ECO-STEELMAKING project funded by MISTRA via Jernkontoret is expected to lead to implementation of some modifications in high alloy steel production based on fundamental concepts towards more environment-friendly steel processing.
|
|
| 9. |
- Wang, Haijuan, et al.
(författare)
-
Modeling of Reactions between Gas Bubble and Molten Metal Bath-Experimental Validation in the Case of Decarburization of Fe-Cr-C melts
- 2009
-
Ingår i: High Temperature Materials and Processes. - 0334-6455 .- 2191-0324. ; 28:6, s. 407-419
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 10. |
- Wang, Haijuan, et al.
(författare)
-
Modelling of Physico-Chemical Phenomena between Gas inside a Bubble and Liquid Metal during Injection of Oxidant Gas
- 2010
-
Ingår i: International Journal of Chemical Reactor Engineering. - : Walter de Gruyter GmbH. - 1542-6580. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
