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Sulfur and nitrogen in ladle slag
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.ORCID iD: 0000-0001-5080-8401
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present work deals with some aspects of slags related to secondary metallurgy in the steelmaking process. More specifically the focus is given to sulfur and nitrogen in ladle slags. Even though slags have been fairly well-researched in the past, the available data for these elements in typical ladle slag compositions is rather scarce. In some cases the available data is in discordance. There are also inconsistencies between the literature data and what is commonly observed in the industrial processes.

Sulfide capacities were measured at steelmaking temperatures, 1823–1873 K, in ladle slags. The data was found to be in reasonable agreement with the industrial process norms. The sulfide capacity was found to increase with the basic oxides CaO and MgO; and decrease with the acidic components Al2O3 and SiO2. The sulfide capacity was also found to increase with temperature.

The dependence of sulfide capacity on the oxygen partial pressure, for slags containing multivalent elements, was investigated experimentally at 1873 K with a slag containing vanadium oxide. A strong dependence of oxygen partial pressure was observed. The sulfide capacity increase by more than two orders of magnitude when the oxygen partial pressure was increased from 4.6×10-16 atm to 9.7×10-10 atm.

The nitrogen solubility and the effect of carbon was investigated in typical ladle slags and the CaO–MgO–SiO2 system at 1873 K. Carbon increases the nitrogen solubility substantially. In the absence of carbon, the nitrogen solubility is extremely low. Low concentrations of cyanide was detected in the carbon saturated slag. This was much lower than the total nitrogen content and formation of cyanide cannot explain the large increase.

The possibility of removing sulfur with oxidation from used ladle slag was investigated experimentally at 1373–1673 K. The sulfur removal of mostly solid slag was found to be a slow process, and would not suitable for industrial practice. At 1673 K the slag was mostly liquid and more than 85% of the sulfur was removed after 60 min of oxidation in pure oxygen atmosphere.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , vi, 74 p.
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-182981ISBN: 978-91-7595-845-3 (print)OAI: oai:DiVA.org:kth-182981DiVA: diva2:906303
Public defence
2016-04-01, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160229

Available from: 2016-02-26 Created: 2016-02-24 Last updated: 2016-02-29Bibliographically approved
List of papers
1. Sulfide Capacity in Ladle Slag at Steelmaking Temperatures
Open this publication in new window or tab >>Sulfide Capacity in Ladle Slag at Steelmaking Temperatures
2015 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 46, no 6, 2609-2615 p.Article in journal (Refereed) Published
Abstract [en]

Sulfide capacity measurements were conducted at 1823 K and 1873 K (1550 degrees C and 1600 degrees C) for the quaternary Al2O3-CaO-MgO-SiO2 system, for typical compositions used in the ladle in steelmaking. A copper-slag equilibrium was used under controlled oxygen and sulfur potentials. The sulfide capacity is strongly dependent on the composition and it was found to increase with the basic oxides, while it decreases with increase of the acidic components. It was found that CaO is more effective in holding sulfur in the slag compared to MgO when replacing SiO2. For the present slag compositions, Al2O3 and SiO2 behaved similar with respect to sulfur, and no considerable effect could be recorded when replacing one for the other. The sulfide capacity was also found to be strongly dependent on the temperature, increasing with temperature. The present results were compared with industrial data from the ladle, after vacuum treatment, and they were in good agreement.

Place, publisher, year, edition, pages
Springer, 2015
Keyword
SILICATE MELTS, CAO-AL2O3-SIO2 SLAGS
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-180619 (URN)10.1007/s11663-015-0444-5 (DOI)000367067600023 ()2-s2.0-84946489157 (Scopus ID)
Note

QC 20160120

Available from: 2016-01-20 Created: 2016-01-19 Last updated: 2017-11-30Bibliographically approved
2. The Effect of Oxygen Potential on the Sulfide Capacity for Slags Containing Multivalent Species
Open this publication in new window or tab >>The Effect of Oxygen Potential on the Sulfide Capacity for Slags Containing Multivalent Species
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-182948 (URN)
Note

QS 2016

Available from: 2016-02-24 Created: 2016-02-24 Last updated: 2016-02-29Bibliographically approved
3. A Study of Nitrogen Pickup from the Slag during Waiting Time of Ladle Treatment
Open this publication in new window or tab >>A Study of Nitrogen Pickup from the Slag during Waiting Time of Ladle Treatment
2014 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 85, no 4, 689-696 p.Article in journal (Refereed) Published
Abstract [en]

An investigation of the nitrogen pickup of liquid steel from ladle slag after vacuum degassing was made. Nitride capacities, C-N, of a number of ladle slags were determined at controlled nitrogen and oxygen potentials at 1873K. The nitride capacities in the composition range studied were found to be very low. In accordance with the literature, the nitride capacity was found to increase with increasing SiO2 content. Industrial trials were performed. The nitrogen content of the steel was determined before and after vacuum degassing as well as after the waiting period. Three different trends of the variation of nitrogen content in the steel were observed. Both the laboratory study and the industrial trials revealed that the transfer of nitrogen from slag to steel was not the reason for nitrogen pickup in the steel subsequent to vacuum degassing.

Keyword
nitrogen pickup, nitride capacity, ladle slag, vacuum degassing
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-146155 (URN)10.1002/srin.201300211 (DOI)000333909700021 ()2-s2.0-84898069553 (Scopus ID)
Note

QC 20140609

Available from: 2014-06-09 Created: 2014-06-09 Last updated: 2017-12-05Bibliographically approved
4. Effect of carbon on the solubility of nitrogen in slag
Open this publication in new window or tab >>Effect of carbon on the solubility of nitrogen in slag
2015 (English)In: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 106, no 8, 822-830 p.Article in journal (Refereed) Published
Abstract [en]

The effect of carbon on nitrogen solubility in slag was investigated for the ternary CaO-MgO-SiO2 and the quaternary Al2O3-CaO-MgO-SiO2 slag systems at 1 873 K under controlled oxygen and nitrogen potentials. Gas-slag equilibration experiments were conducted using molybdenum and graphite crucibles. In the absence of carbon, the nitrogen solubility was very low. The presence of carbon greatly increased the nitrogen solubility in slag. The total nitrogen content was found to increase with SiO2 and MgO concentration for the carbon saturated slags. Low levels of cyanide were found by wet chemistry with considerable uncertainty. The results analyzed by different methods ruled out cyanide formation being the main reason for the large increase in nitrogen solubility in the presence of pure carbon.

Keyword
Nitrogen, Solubility, Slag, Cyanide, Nitride
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-173283 (URN)10.3139/146.111253 (DOI)000359388900001 ()2-s2.0-84981328388 (Scopus ID)
Note

QC 20150909

Available from: 2015-09-09 Created: 2015-09-09 Last updated: 2017-12-04Bibliographically approved
5. Possibility of Sulfur Removal from Ladle Slag by Oxidation in the Temperature Range 1373-1673 K
Open this publication in new window or tab >>Possibility of Sulfur Removal from Ladle Slag by Oxidation in the Temperature Range 1373-1673 K
2015 (English)In: Journal of Sustainable Metallurgy, ISSN 2199-3823, Vol. 1, no 3, 229-239 p.Article in journal (Refereed) Published
Abstract [en]

Experiments were conducted to investigate the possibility of removing sulfur from used ladle slag by oxidation. Slag samples (solid, two-phase mixture, and liquid with a small fraction of solid MgO particles) were subjected to an oxygen-rich atmosphere in the temperature range 1373–1673 K. The sulfur removal from the samples of solid and two-phase mixture was found to be a slow process due to the slow diffusion. The sulfur removal was found to have little dependence on temperature in the range 1373–1573 K. When the slag was mostly liquid (at 1673 K), the sulfur removal was significantly increased. More than 85 % of the sulfur could be removed after 60 min of oxidation in pure oxygen. An increase in oxygen partial pressure was found to increase the desulfurization slightly. Increasing the Al2O3 content in the slag decreased the degree of sulfur removal.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-182833 (URN)10.1007/s40831-015-0018-4 (DOI)
Note

QC 20160229

Available from: 2016-02-23 Created: 2016-02-23 Last updated: 2016-02-29Bibliographically approved

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