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Dissolution mechanism of dolomite in converter slag at 1873K
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.ORCID iD: 0000-0002-3548-8638
2014 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 41, no 1, 75-80 p.Article in journal (Refereed) Published
Abstract [en]

The mechanism of dolomite dissolution in converter slag was studied and found to proceed by two steps: decomposition of dolomite into CaO and MgO and dissolution of the product into the slag. The first step was found to be controlled by heat transfer, which was confirmed by theoretical calculation. The decomposed dolomite had many pores, which allowed easy slag penetration. A discontinuous 2CaO.SiO2 layer along with MgO.Fe2O3 particles was found on the surface of the samples. Some 2CaO.SiO2 islands were found in the vicinity of the samples in the slag, revealing that the dissolution was dominated by peeling-off of the layer of 2CaO.SiO2- MgO.Fe2O3 mixture. 2CaO.SiO2, (Mg, Fe)Oss along with super cooled liquid phases were found inside dolomite samples close to the surface. 2CaO.SiO2 phase was replaced gradually by 3CaO.SiO2 towards the centre of the decomposed sample. While addition of small amounts of dolomite directly into the slag could be considered in steelmaking converter, too much would result in slow dissolution and waste of the raw materials.

Place, publisher, year, edition, pages
2014. Vol. 41, no 1, 75-80 p.
Keyword [en]
Converter slag, Decomposition, Dissolution, Dolomite
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-101416DOI: 10.1179/1743281212Y.0000000101ISI: 000334114700012Scopus ID: 2-s2.0-84893223301OAI: oai:DiVA.org:kth-101416DiVA: diva2:547546
Note

QC 20140317. Updated from submitted to published.

Available from: 2012-08-29 Created: 2012-08-28 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Study on the dissolution of lime and dolomite in converter slag
Open this publication in new window or tab >>Study on the dissolution of lime and dolomite in converter slag
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the present study, the dissolution mechanism and rate of lime, limestone and dolomite in converter slag was studied. Lime dissolution in stagnant slag was studied first and dissolution of lime, limestone and dolomite under forced convection were carried out by new experimental setup.

Dissolution of different CaO samples into stagnant converter slags was carried out in a closed tube furnace at 1873K. In the case of CaO-‘FeO’-SiO2 slag, the dissolution of CaO rod in the stagnant slag was retarded after the initial period (2 minutes). A dense layer of 2CaO∙SiO2 was found to be responsible for the total stop of the dissolution. It could be concluded that constant removal of the 2CaO∙SiO2 layer would be of essence to obtain high dissolution rate of lime. In this connection, it was found necessary to study the dissolution of lime in moving slag.

In order to obtain reliable information of lime dissolution under forced convection, the commonly used rotating rod method was examined. Both CFD calculation and cold model experiments showed evidently that the mass transfer due to radial velocity introduced by forced convection was zero if the rod was centrally placed in a cylindrical container. A new experimental design was therefore developed. A cube was placed in the crucible and stirred by Mo rod along with slag. The whole system could be quenched in order to maintain the state of the system at high temperature. A linear relationship between normalized length and time was obtained for lime dissolution. Different lime samples showed big difference in dissolution rate. It was found that the main mechanism of CaO dissolution in slag was due to the removal of 2CaO∙SiO2 layer.

Decomposition and dissolution of limestone and dolomite in slag at 1873 K were studied. The decomposition was carried out both in argon and in slag under argon atmosphere. The decomposition process was simulated using Comsol. The results showed evidently that the decomposition of limestone and dolomite was controlled mostly by heat transfer.

It was also found that the decomposition of limestone product: CaO had very dense structure, no matter the sample was decomposed in slag or in argon. The slow decomposition and the dense CaO layer would greatly hinder the dissolution of lime in the slag. The present results clearly indicate that addition of limestone instead of lime would not be beneficial in converter process.

Discontinuous 2CaO∙SiO2 layer along with MgO∙Fe2O3 particles was found on the surface of the dolomite sample. Some 2CaO∙SiO2 islands were found in the vicinity of the sample in the slag, which revealed therefore that the dissolution was dominated by the peeling-off of the layer of 2CaO∙SiO2-MgO∙Fe2O3 mixture. 2CaO∙SiO2, (Mg, Fe)Oss along with super cooled liquid phases were found inside dolomite sample close to the surface. 2CaO∙SiO2 phase was replaced gradually by 3CaO∙SiO2 towards the centre of the decomposed sample.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 45 p.
Keyword
dissolution, lime, limestone, dolomite, converter slag
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-101461 (URN)978-91-7501-454-8 (ISBN)
Public defence
2012-09-28, B1, Brinellvägen 23, Kungliga Tekniska Högskolan, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20120829

Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2013-03-20Bibliographically approved

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