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

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Ünal, H. İ., Turgut, E., Atapek, Ş. H.and Alkan, A.
The iron also can be produced from its ore by the direct reduction of iron ore by a reducing agent which is coal
based or may be a gaseous reducing agent, which is called direct reduced iron (DRI) or sponge iron. Direct
reduced iron (DRI) is a good substitute of scrap for making steel in electric arc furnace, basic oxygen furnace etc.
and there has been a rapid worldwide growth in its production. DRI is a solid state product of direct reduction
processes which is produced either in the form of lump or pellet. Availability of huge amounts of non-coking coal,
scarcity of coking coal deposits and industrial significance of DRI led to many efforts for the development of many
direct reduction processes [6, 11].
In this study, two different techniques were applied for the reduction of ferrous oxide materials. In the first stage,
the reduction of mill scale was carried out in a rotating furnace using solid and gas reductants to produce sponge
iron. The coal is used as solid reductant and its features have been given in Section 2.1. The source of hydrogen
used as gas reductant is liquefied natural gas (LNG). The mixture of gas formed after the decomposition by
combustion of LNG has 95 % H2. The flow of reduction in the rotating furnace is summarized in Table 4. The
reduction in the rotating furnace were carried out in two media : (i) solid coal and (ii) solid coal and hydrogen gas.
After reduction, produced sponge irons are smelted and the decomposition of metal-slag was done. In the second
stage, the reduction of hematite ore formed as pellets was carried out using solid carbon in a furnace. The
furnace is heated up to 1100 ºC step by step with 10 °C/min. The pellets having different Cfix / Fetotal were
reduced at 1100 ºC for 60 and 120 minutes. Table 5 shows the reduction conditions for ore as pellet form. In order
to reduce all iron oxides, carbon ratio was selected as 1.5 and 2 times of the theoretical amount. The amount of
binder in pellet was neglected.
Table 4. The flow of reduction in the rotating furnace used.
Process
Charging of materials (mill scale + coal + slag formers) to furnace
1 st reduction (entrance to furnace) : ~ 850 – 900 °C
2 nd reduction (middle of furnace) : ~ 950 – 1000 °C
3 rd reduction (close to nozzle) : ~ 1200 °C
Table 5. The reduction conditions for pellet material.
Carbon ratio Cfix / Fetotal Temperature, °C Time, min.
2.3. Calculation of ore reduction
1.5 0.48
60
1100
2 0.64 120
The stoichiometric amount of carbon was determined using the reaction given in equation 7. All reduced products
were cooled from selected reaction temperature to room temperature in the furnace and scaled to determine %reduction
(R). This value was calculated using equation 8.
Fe2O3 + 3C = 2Fe + 3CO (equation 7)
% R = (removed oxygen/total oxygen) x 100 (equation 8)
2.4. Microscopic examinations
Solidified sponge iron and its slag were prepared by metallographic methods. Grinding was carried out with 320,
600 and 1000 mesh size SiC abrasives, respectively and then ground surfaces were polished with 3 μm diamond
solution. Etching was done with nital (% 3 HNO3) to characterize the microstructure. Zeiss Axiotech 100 light
microscope and Jeol JSM 6060 and JSM 840A scanning electron microscopes (SEM) were used for
metallographic examinations. Energy dispersive x-ray spectrometer (EDS) was used for elemental analysis of the
phases observed in the electron microscope.