Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Abatement of Chromium Emissions from Steelmaking Slags - Cr Stabilization by Phase Separation
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Chromium is an important alloying element in stainless steel but also environmentally harmful element. A number of mineralogical phases present in the slag matrix can contain chromium and lead to chromium leaching. Chromium in slag if not stabilized, could oxidize to the cancerogenic hexavalent state, and leach out if exposed to acidic and oxygen rich environment. Other environmental concerns are slag dusting and chromium escape to the atmosphere. Despite the fact that there is a certain risk of Cr-emission from slags at operating conditions, still very little is known regarding the emission of the oxides of chromium during the slag tapping. Spinel phase is known to be important for controlling the leaching properties of chromium from the slag. The objective of the present study was to get an understanding of the phase relationships and chromium partition in the chromium-containing industrial slags and synthetic slags with a view to control the chromium stabilization in spinel phase. The impact of slag basicity, heat treatment, oxygen partial pressure and Al2O3 addition, on the phase relationships and chromium partition has been determined. The experimental results were compared with the phase equilibrium calculations. It was found that the oxygen partial pressure in the gas phase had a strong impact on chromium partition. The experimental results show that the impact of the slag basicity on chromium partition at lower oxygen partial pressures was negligible in contrast to that in air. The amount of spinel phase was found to increase with increased Al2O3 content. Slow cooling of slag and soaking at low oxygen partial pressure would improve the spinel phase precipitation. This treatment will also lead to less Cr dissolved in the unstable matrix phases. Chromium oxide was found to be emitted when chromium containing slags were exposed to oxidizing atmosphere. The results indicate that chromium oxide evaporation increases with increase in temperature and oxygen partial pressure, but decreases with slag basicity and sample thickness.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , xi, 53 p.
Keyword [en]
spinel; slag basicity; oxygen partial pressure; chromium oxide vaporization
Keyword [ru]
шпинель; шлак; парциальное давление кислорода, испарение оксидa хрома
Keyword [zh]
尖晶石;炉渣碱度;氧分压;铬氧化物汽化
Keyword [sv]
spinell, slaggbasicitet, syrepartialtryck, förångning av kromoxid
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-133480ISBN: 978-91-7501-666-5 (print)OAI: oai:DiVA.org:kth-133480DiVA: diva2:661947
Public defence
2013-12-06, B3, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Steel Eco-Cycle
Funder
Mistra - The Swedish Foundation for Strategic Environmental ResearchKnut and Alice Wallenberg Foundation
Note

QC 20131114

Available from: 2013-11-14 Created: 2013-11-05 Last updated: 2013-11-14Bibliographically approved
List of papers
1. Effect of basicity on chromium partition in CaO-MgO-SiO2-Cr 2O3 synthetic slag at 1873 K
Open this publication in new window or tab >>Effect of basicity on chromium partition in CaO-MgO-SiO2-Cr 2O3 synthetic slag at 1873 K
2014 (English)In: Transactions of the Institution of Mining and Metallurgy Section C - Mineral Processing and Extractive Metallurgy, ISSN 0371-9553, E-ISSN 1743-2855, Vol. 123, no 2, 116-122 p.Article in journal (Refereed) Published
Abstract [en]

The objective of the present work is to get an understanding of the phase relationships in the CaO-MgO-SiO2-Cr2O3 system with a view to control the precipitation of Cr-spinel in the slag phase. The equilibrium phases in CaO-MgO-SiO2-Cr2O3 slag system at 1873 K (1600°C) have been investigated experimentally and compared with the results from thermodynamic calculations. The Cr2O 3 and MgO contents in the slag were fixed at 6 and 8 wt-% respectively. The basicity (CaO/SiO2) of slag was varied in the range 1·0-2·0. A gas/slag equilibrium technique was adopted to synthesise the slag at a high temperature in air. The samples were heated to and soaked at 1873 K (1600°C) for 24 h in order to achieve the equilibrium state and subsequently quenched in water. The chromium distribution and phase compositions in the quenched slag were studied using scanning electron microscope wavelength dispersive spectroscopy and X-ray diffraction techniques. FactSage software was used for the phase equilibrium calculations. The experimental results obtained from the present work were compared with the calculation results from FactSage software. It was found that the spinel formation at 1873 K (1600°C) is favoured in the slag basicity range 1·0-1·4.

Keyword
phase equilibrium, chromium partition, slag basicity, spinel, scanning electron microscope (SEM)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-50908 (URN)10.1179/1743285513Y.0000000038 (DOI)2-s2.0-84901700588 (Scopus ID)
Note

QC 20150317. Updated from accepted to published.

Available from: 2011-12-08 Created: 2011-12-08 Last updated: 2017-12-08Bibliographically approved
2. Effect of the heat treatment on the chromium partition in CaO-MgO-SiO2-Cr2O3 synthetic slags
Open this publication in new window or tab >>Effect of the heat treatment on the chromium partition in CaO-MgO-SiO2-Cr2O3 synthetic slags
2013 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 44, no 6, 1586-1597 p.Article in journal (Refereed) Published
Abstract [en]

Mg-spinel phase is known to be important for control of Cr leaching from Cr-containing slags. The objective of the present study is to get an understanding of the phase relationships in the CaO-MgO-SiO2-Cr2O3 system with a view to control the precipitation of Cr-spinel in the slag phase. The equilibrium phases in CaO-MgO-SiO2-Cr2O3 slag system in the range of 1673 K to 1873 K (1400 A degrees C to 1600 A degrees C) have been investigated experimentally and compared with the results from thermodynamic calculations. The slag compositions close to the industrial slag systems were chosen. The Cr2O3 and MgO contents in the slag were fixed to be 6 and 8 wt pct, respectively. The basicity (CaO/SiO2) of the slag was varied in the range of 1.0 to 2.0. The slags were synthesized at a pre-determined oxygen partial pressure (10(-4)) or air (2.13 x 10(4) Pa) at a temperature above the liquidus temperature. The samples were then soaked at targeted temperatures for 24 hours in controlled atmosphere in order to achieve the equilibrium state before quenching in water. Four different heat-treatment regimes (defined as Ia, Ib, II.a and II.b) in Section II-D) were used in the present experiments. The lower oxygen partial pressure was maintained by a suitable mixture of CO and CO2 gases. Phases present and their compositions in the quenched slags were studied using scanning electron microscopy coupled with energy-dispersive spectroscopy and X-ray diffraction techniques. The chromium content in the phases present was analyzed using wavelength-dispersive spectrometer. The experimental results obtained are compared with the calculation results from Factsage software. The size of spinel crystals increased drastically after slow-cooling from 1873 K (1600 A degrees C) followed by annealing at 1673 K (1400 A degrees C) for 24 hours (heating regimes II) compared to samples being quenched directly after soaking at 1873 K (1600 A degrees C) (heating regime I.a). It was found that the amount of foreign elements in the spinel phase, and other phases decreased after soaking at oxygen partial pressure of 10(-4) Pa resulting in phases with less defects and foreign oxide contents compared to those treated in air. The size of spinel crystals was found to be larger in samples with lower basicity.

Keyword
phase equilibrium, chromium partition, slag basicity, spinel, scanning electron microscope (SEM)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-50928 (URN)10.1007/s11663-013-9939-0 (DOI)000327383100029 ()2-s2.0-84890559757 (Scopus ID)
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research, MISTRA-88035
Note

Updated from "Manuscript" to "Articles" QC 20131105

Available from: 2011-12-08 Created: 2011-12-08 Last updated: 2017-12-08Bibliographically approved
3. Effect of Low Oxygen Partial Pressure on the Chromium Partition in CaO-MgO-SiO2-Cr2O3-Al2O3 Synthetic Slag at Elevated Temperatures
Open this publication in new window or tab >>Effect of Low Oxygen Partial Pressure on the Chromium Partition in CaO-MgO-SiO2-Cr2O3-Al2O3 Synthetic Slag at Elevated Temperatures
Show others...
2013 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, no 7, 670-679 p.Article in journal (Refereed) Published
Abstract [en]

The objective of the present work is to get an understanding of the impact of Al2O3 addition on the phase relationships in the CaO-MgO-Al2O3-SiO2-Cr2O3 slags at low oxygen partial pressures (P-O2 = 10(-4) Pa), with a view to control the precipitation of Cr-spinel in the slag. The equilibrium phases in CaO-MgO-Al2O3-SiO2-Cr2O3 slag system in the range on 1673-1873 K have been investigated. The compositions close to the industrial slag systems were chosen. The Cr2O3 content was fixed at 6 wt% and MgO at 8 wt%. Al2O3 contents in the slag were varied in the range of 3-12 wt%. The basicity (CaO/SiO2) of slag was set to 1.6. Gas/slag equilibrium technique was adopted. The samples were heated to 1873 K and soaked at this temperature for 24 h. The samples were then slow cooled to 1673 K and equilibrated for an additional 24 h. The oxygen partial pressure was kept at 10(-4) Pa. A gas mixture of CO/CO2 was used to control the oxygen partial pressure. After the equilibration, the samples were quenched in water. The chromium distribution and phase compositions in the quenched slags were studied using SEM-WDS and XRD techniques. The results were compared with the phase equilibrium calculations obtained from FACTSAGE software and the samples equilibrated in air. The size of spinel crystals increased drastically after slow cooling followed by annealing compared to samples being quenched after soaking at 1873 K. It was also found that low oxygen partial pressure had a strong impact on chromium partition. The amount of spinel phase increases with increased Al2O3 content.

Keyword
phase equilibrium, chromium partition, spinel, scanning electron microscope (SEM), low oxygen partial pressure
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-127508 (URN)10.1002/srin.201200214 (DOI)000322366700006 ()2-s2.0-84879877117 (Scopus ID)
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research, MISTRA-88035
Note

QC 20130830

Available from: 2013-08-30 Created: 2013-08-30 Last updated: 2017-12-06Bibliographically approved
4. Effect of the Heat Treatment on the Chromium Partition in Cr-Containing Industrial and Synthetic Slags
Open this publication in new window or tab >>Effect of the Heat Treatment on the Chromium Partition in Cr-Containing Industrial and Synthetic Slags
2014 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 85, no 10, 1418-1431 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, the effects of the slag composition and heat-treatment conditions on the phase relationships in a number of Cr-containing industrial and synthetic slags were investigated with a view to control the precipitation of Cr-spinel in the slag phase. Gas/slag equilibrium technique was used for the chromium partition and the phase relationship study. The phase relationships in synthetic slags and industrial EAF slags supplied by Swedish steelmaking plants have been investigated experimentally in the temperature range of 1473-1873 K. The slags were re-melted, slow-cooled to, and soaked at targeted temperatures in controlled atmosphere. Two different heat-treatment sequences were used in the present experiments. The oxygen partial pressure (p(O2) = 10(-3) Pa) was maintained by a suitable mixture of CO and CO2 gases. Phases present and their compositions in the quenched slags were studied using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The chromium content in the phases present was analyzed using wavelength-dispersive spectrometer (WDS). Chromium partition was found to depend on the heat-treatment temperature.

Keyword
chromium partition, industrial slags, spinel, slag stability, scanning electron microscope (SEM)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-133486 (URN)10.1002/srin.201300231 (DOI)000342808000002 ()2-s2.0-84908109336 (Scopus ID)
Note

Updated from "Accepted" to "Published". QC 20141112

Available from: 2013-11-05 Created: 2013-11-05 Last updated: 2017-12-06Bibliographically approved
5. Studies of Vaporization of Chromium from Thin Slag Films at Steelmaking Temperatures in Oxidizing Atmosphere
Open this publication in new window or tab >>Studies of Vaporization of Chromium from Thin Slag Films at Steelmaking Temperatures in Oxidizing Atmosphere
2013 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 44, no 5, 1280-1286 p.Article in journal (Refereed) Published
Abstract [en]

In the present work, the volatilization of chromium from thin chromium-containing slag film surfaces was studied in oxidizing atmosphere in the temperature range 1673 K to 1873 K (1400 A degrees C to 1600 A degrees C). The slag films on alumina rings were exposed to air or pure oxygen and the loss of Cr from the post-experiment sample films was examined by SEM/WDS analysis. The mass loss of the samples was also monitored during the heat-treatment. The results indicate that chromium loss increased with increase in temperature and oxygen partial pressure was found also to be relatively less as the sample thickness increased. The implications of chromium escape from slags during the tapping of stainless steel slags are discussed.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-133485 (URN)10.1007/s11663-013-9904-y (DOI)000325431900026 ()2-s2.0-84886095339 (Scopus ID)
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research
Note

QC 20131105

Available from: 2013-11-05 Created: 2013-11-05 Last updated: 2017-12-06Bibliographically approved

Open Access in DiVA

Abatement of Chromium Emissions(2532 kB)593 downloads
File information
File name FULLTEXT01.pdfFile size 2532 kBChecksum SHA-512
b325d9eb5e61c9c76115a604b8c0a00b78dc42e3c2c0d3e2ca14f9cb24198a6de6acd14f5c5671a2ef1aa6ab3ed38639e452c8371b3e091751276f36e4a87ddf
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Albertsson, Galina
By organisation
Materials Process Science
Metallurgy and Metallic Materials

Search outside of DiVA

GoogleGoogle Scholar
Total: 593 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 399 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf