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A study on plasticity and compression strength in wet iron ore green pellets related to real process variations in raw material fineness
LKAB.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
2008 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 181, no 3, p. 321-330Article in journal (Refereed) Published
Abstract [en]

The main binding force in wet iron ore green pellets has been found to be the cohesive force of the viscous binder. The wet compression strength (wet-CS) in green pellets is, however, also influenced by the green pellet plasticity. A certain degree of plasticity is needed to sustain the green pellet growth rate. Too much plasticity results in decreased bed permeability and production problems. As the plasticity increases, wet-CS decreases. The amount of moisture needed to create a given degree of plasticity depends on particle properties and on the particle size distribution. Therefore, it was of interest to study how wet-CS would be influenced by variations in raw material fineness, if the green pellet plasticity was kept constant, i.e. the green pellet properties would be compared under relevant industrial balling conditions. For this purpose, magnetite concentrates of different particle size distributions were balled in a laboratory drum and the moisture content for constant plasticity was determined for each of the materials. No difference in green pellet wet-CS as a function of the raw material fineness was found when the bentonite binder was used and the plasticity was adjusted to a constant level. Green pellets prepared of raw materials with narrow size distributions were just as strong as those with broader ones. This is because the main binding force is the cohesive force of the viscous binder. In green pellets balled without the bentonite binder, wet-CS increased with increasing specific surface area in the raw material, in a similar manner as has been shown in earlier agglomeration literature. In this case, the capillary forces prevail. Comparison of wet-CS at constant moisture, instead of constant plasticity, would lead to erroneous conclusions. Fineness, or rather the slope of the particle size distribution curve, had a major impact on the moisture content needed for constant plasticity. If the slope increases, more water is needed to keep the plasticity on a constant level. Implications of these results in control of industrial iron ore balling circuits are discussed.

Place, publisher, year, edition, pages
2008. Vol. 181, no 3, p. 321-330
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
URN: urn:nbn:se:ltu:diva-6681DOI: 10.1016/j.powtec.2007.05.023ISI: 000253747600012Scopus ID: 2-s2.0-38849148494Local ID: 4f12ae30-a97e-11dc-9057-000ea68e967bOAI: oai:DiVA.org:ltu-6681DiVA, id: diva2:979567
Note
Validerad; 2008; 20071213 (bobj)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved

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Björkman, BoSamskog, Per-Olof

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