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Effect of the Heat Treatment on the Chromium Partition in Cr-Containing Industrial and Synthetic Slags
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
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.

Place, publisher, year, edition, pages
2014. Vol. 85, no 10, 1418-1431 p.
Keyword [en]
chromium partition, industrial slags, spinel, slag stability, scanning electron microscope (SEM)
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-133486DOI: 10.1002/srin.201300231ISI: 000342808000002Scopus ID: 2-s2.0-84908109336OAI: oai:DiVA.org:kth-133486DiVA: diva2:661970
Note

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

Available from: 2013-11-05 Created: 2013-11-05 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Abatement of Chromium Emissions from Steelmaking Slags - Cr Stabilization by Phase Separation
Open this publication in new window or tab >>Abatement of Chromium Emissions from Steelmaking Slags - Cr Stabilization by Phase Separation
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
spinel; slag basicity; oxygen partial pressure; chromium oxide vaporization, шпинель; шлак; парциальное давление кислорода, испарение оксидa хрома, 尖晶石;炉渣碱度;氧分压;铬氧化物汽化, spinell, slaggbasicitet, syrepartialtryck, förångning av kromoxid
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-133480 (URN)978-91-7501-666-5 (ISBN)
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

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