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Formation of potassium slag in olivine fluxed blast furnace pellets
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2007 (English)In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 34, no 5, 422-430 p.Article in journal (Refereed) Published
Abstract [en]

Mineralogical evaluation of olivine pellets coated with kaolinite, taken from the LKAB experimental blast furnace, shows significant reactions with potassium. Sampling has revealed strong potassium deposition in pellets in the lower shaft close to the wall, but much less deposition towards the furnace centre. Iron reduction and the deformation of the pellets were enhanced in the zone of high alkali deposition. Thin sections of pellet samples were prepared to distinguish amorphous and crystalline slag phases for a better understanding of the formation of the potassium rich slag. Olivine breaks down to various extents to form a SiO2-FeO-MgO-K2O glass. The kaolinite coating shows strong reaction throughout the cross-section of the lower shaft to form kalsilite (KAlSiO4) and K2O rich glassy slag. Studies of thin sections of the slag products were shown to be very useful in separating amorphous phases such as the K2O rich glass from the crystalline olivine rim.

Place, publisher, year, edition, pages
2007. Vol. 34, no 5, 422-430 p.
Keyword [en]
blast furnace, kaolinite coated pellets, alkali, thin section
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97779DOI: 10.1179/174328106X149833ISI: 000252522500009OAI: oai:DiVA.org:uu-97779DiVA: diva2:172847
Available from: 2008-10-30 Created: 2008-10-30 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Mineral Reactions and Slag Formation During Reduction of Olivine Blast Furnace Pellets
Open this publication in new window or tab >>Mineral Reactions and Slag Formation During Reduction of Olivine Blast Furnace Pellets
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present work focuses on mineral reactions and slag formation of LKAB olivine iron ore pellets (MPBO) subjected to reducing conditions in the LKAB experimental blast furnace (EBF). The emphasis is on olivine reactions with surrounding iron oxides. Many factors influence the olivine behaviour. The study was performed by use of micro methods; optical microscopy, micro probe analysis, micro Raman and Mössbuer spectroscopy and thremodynamic modeling. During manufacturing, in oxidising atmosphere at high temperature (1350°C), olivine alterations occur through slag formation and rim reactions with iron oxides and other additives. To be able to describe olivine behaviour in the rather complex blast furnace reduction process one has to consider factors such as reactions kinetics, reduction degree of iron oxides, vertical and horizontal position in the furnace and reactions with alkali. Samples were collected from the EBF both from in shaft probing during operation and from excavation following quenching of the EBF.

The initial slag forming olivine consist of primary forsterite – (Mg1.9Fe0.1)SiO4 – with inclusions of hematite and an amorphous silica rich phase, a first corona with lamellae of magnesioferrite, olivine and orthopyroxene, a second corona of amorphous silica and magnesioferrite. During reduction in the upper shaft in the EBF (700-900°C) Fe3+ reduces to Fe2+. The amorphous silica in the second corona absorbs alkali, Al, Fe2+, Mg, and Ca and form glasses of varying compositions. The lamellae in the first corona will merge into a single phase olivine rim. With further reduction the glasses in the second corona will merge with the olivine rim forming an iron rich olivine rim and leaving the elements that do not fit into the olivine crystal lattice as small silicate glass inclusions. Diffusion of magnesium and iron between olivines and iron oxides increase with increasing temperature in the lower shaft of the EBF (750-1100°C). In the cohesive zone of the EBF (1100-1200°C) Fe2+ is not stable any longer and Fe2+ will be expelled from the olivine as metallic iron blebs, and the olivine will form a complex melt with a typical composition of alkali-Al2O3-MgO-SiO2. Alkali plays an important role in this final olivine consumption.

The quench time for samples collected with probes and excavation are minutes respectively hours. A study of the quench rate’s effect on the phases showed no differences in the upper shaft. However, in the lower shaft wüstite separates into wüstite and magnetite when wüstite grows out of its stability field during slow cooling of excavated samples. There is also a higher alkali and aluminium deposition in the glass phases surrounding olivines in excavated pellets as a result of alkali and aluminium gas condensing on the burden in the EBF during cooling.

Coating applied to olivine pellets was studied in the EBF with the aim to investigate its behaviour, particularly its ability to capture alkali. The coating materials were kaolinite, bauxite, olivine and limestone. No significant reactions were observed in the upper shaft. In the lower shaft a majority of the phases were amorphous and reflecting the original coating compositions. Deposition from the EBF gas phase occurs and kalsilite (KAlSiO4) is found in all samples; coating used for binding alkali is redundant from a quality perspective.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 45 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 575
Keyword
olivine, iron ore pellets, blast furnace, reduction, alkali, coating, slag formation
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-9389 (URN)978-91-554-7340-2 (ISBN)
Public defence
2008-11-20, Axel Hambergsalen, Geocentrum, Villavägen 16, 752 36 Uppsala, 10:00
Opponent
Supervisors
Available from: 2008-10-30 Created: 2008-10-30Bibliographically approved

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