DIRECT REDUCTION OF FERROUS OXIDES TO FORM AN IRON ...

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Ünal, H. İ., Turgut, E., Atapek, Ş. H.and Alkan, A.
magnetite (Fe3O4). The iron content is normally around 70 %, with traces of non-ferrous metals and alkaline
compounds. Mill scale is formed by flaky particles of a size of generally less than 5.0 mm. The size distribution
depends on the stage in the process where the mill scale is generated [9]. In this study, the particle size of the mill
scale is between 400-500 μm. Table 1 shows the contents of raw materials for 1 ton. The slag formers having a
particle size of ~ 200 μm include bentonite, dolomite, limestone and are added to charge as 20 kg. Table 2 shows
the contents (%) of slag formers used in the study. The content of coal used in mill scale processing is 67.25 %
and its particle size is ~ 150 μm.
Table 1. The contents of raw materials (%).
Raw materials %
Mill scale 76.39
Coal 22.06
Slag formers 1.550
Table 2. The contents of slag formers used in the study (%).
Slag formers %
Bentonite 10
Dolomite 40
Limestone 50
Hematite ores in pellet form was supplied from ERDEMİR A.Ş. and its reduction by solid carbon having a purity of
99 % was investigated as a function of of reduction time and the ratio of Cfix / Fetotal. Cfix / Fetotal ratio can be
described as the amount of carbon necessary to reduce completely the iron oxide that exists in the system [10].
Table 3 shows x-ray fluorescence (XRF) analysis of both mill scale and ore materials.
Table 3. XRF anaylsis of mill scale and ore material used in the experimental study.
Materials Fe Mn Si Al Ca Cr K O
Mill scale 69.10 0.66 0.11 - 0.21 0.10 - 29.82
Hematite
ore
62.40 - 1.20 0.30 0.50 - 0.10 35.50
2.2. Reduction procedure
Industrially iron is produced from iron ores, principally hematite (Fe2O3), magnetite (Fe3O4) by a carbothermic
reaction that is reduction with carbon, in a blast furnace at temperatures about 800-1600 °C. In the blast furnace,
iron ore, carbon in the form of coke, and a flux such as limestone are fed into the top of the furnace, while blast of
heated air is forced into the furnace at the bottom. Reduction of iron oxides occurs either by carbon or by carbon
monoxide, formed by the gasification of carbon. The reduction process carried out by the carbon is called as
direct reduction and the reaction can be defined in equation 1.
FexOy + yC = xFe + yCO (equation 1)
On the other hand, the reduction process conducted with CO is called as indirect reduction and its reaction is
given in equation 2 and 3. The reduction of ferrous materials can be indirectly achieved by hydrogen and
equations 4-6 indicate the stages of reactions. The reduction of iron ores by hydrogen is a gas-solid reaction
which occurs in two or three stages. For temperatures higher than 570°C, hematite (Fe2O3) is first transformed
into magnetite (Fe3O4), then into wustite (Fe1-yO), and finally into metallic iron whereas at temperatures below
570°C, magnetite is directly transformed into iron since wustite is not thermodynamically stable.
FexOy + yCO = xFe + yCO2 (equation 2)
yCO2 + yC = 2yCO (Boudouard Reaction) (equation 3)
3Fe2O3 + H2 → 2Fe3O4 + H2O (equation 4)
Fe3O4 + H2 → 3FeO + H2O (equation 5)
FeO + H2 → Fe + H2O (equation 6)