Thursday, December 8, 2011

Reduction of Iron Oxide

Oxide ores are reduced to metal by coke and carbon monoxide in the blast furnace:

Preliminary heating zone:

Fe2O3.nH2O --> Fe2O3 + nH2O water vapor escape

Reduction zone:

3Fe2O3 + CO --> 2Fe3O4 + CO2
Fe3O4 + CO --> 3 FeO + CO2

Carburizing zone:

3 FeO + 3 CO --> 3 Fe + 3 CO2
3 Fe + C --> Fe3C
A simplified description of the processes within the blast furnace consist of 4 steps:
  1. The ore gives up its sulfur and water in the preliminary heating zone.
  2. The ore is reduced to ferrous oxide (FeO) by an ascending stream of carbon monoxide in the reduction zone.
  3. Further reduction to metallic iron takes place in the carburizing zone. At the same time the iron absorbs carbon, silicon, manganese, sulfur and phosphorous.
  4. The ore melts completely in the melting zone, impurities combine with time to form slag. The molten pig iron collects at the bottom of the furnace, with the lighter slag floating above it. These are drawn off at regular intervals (through a common in modern blast furnace).
In the direct reduction process, the iron ore gradually sinks downward in a shaft furnace under the influence of gravity. The reduction gas (H2, CO2 heated to 800 oC flows upwards against the direction of movement of the ore and removes the oxygen from it. Sponge iron is produced which is processed to make steel. The metallisation take place directly without a molten phase.

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