Effect of Oxygen Potential on Mineral Formation in Lime-fluxed Iron Ore Sinter
Li-Heng Hsieh, J. A. Whiteman
In industrial iron ore sintering, the raw material is heated in a reducing atmosphere and cooled in an oxidizing atmosphere. In order to study the characteristics of mineral formation under different regimes of heating and cooling in industrial sintering, small tablet specimens made from powdered materials were sintered in a tube furnace under controlled gas atmospheres. The results obtained are summarized as follows.
In the heating stage acicular calcium ferrite can be produced from the reaction of hematite and the flux below 1 180°C. With an increase of temperature, the calcium ferrite crystal size increases and at higher temperature the calcium ferrite transforms to magnetite and silicate melt. During the cooling stage, the magnetite tends to react with the silicate melt and oxygen to generate calcium ferrite at a medium oxygen partial pressure (around 1×10-2 atm). Reoxidized hematite is formed from magnetite at a higher oxygen potential (e.g., 5×10-2 atm). The magnetite (produced in the heating stage) is preserved at a low oxygen potential. Acicular calcium ferrite may also be generated from magnetite ore at high oxygen potential (e.g., PO2>5×10-3 atom) during the heating stage of sintering.
Calcium ferrite produced from the reaction of hematite and the flux in heating stage is a form of calcium diferrite (CaO·2Fe2O3) with some substitution of Si and Al. The composition of calcium ferrite generated from magnetite depends on the amounts of SiO2 and CaO from silicate melt reacting with magnetite. The basicity (mole ratio of CaO/SiO2) of silicate melt consumed in the reaction is around 2.
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