Wednesday, March 17, 2010

How to Reduce Metal Oxides

To reduce metal oxide from metal means to remove oxygen from oxides. If a metal is to be extracted from its ore – the metal oxide – the oxygen must be removed from the ore. The ore is reduced with the help of reducing agents, i.e. elements with a greater affinity for oxygen. The metal oxide may be either in the molten or the solid state.

Experiment: if copper oxide is mixed with powdered charcoal (carbon) in a least tube and heated strongly, the black oxide gradually becomes reddish – if is reduced to copper. The carbon combine with the oxygen in the copper oxide to form carbon dioxide.

Other reducing agents are hydrogen and carbon monoxide.

Experiment: if a stream of hydrogen is passed over black copper oxide heated strongly in a refractory glass tube, red copper is produced.

Conclusion: reducing agents remove oxygen from iron metal oxides.

Reducing of Iron Oxide

Oxide ore are reduced to metal by coke and carbon monoxide in the blast furnace.

1. Preliminary heating zone

Fe2O3. n H2O → Fe2O3 + n H2O water vapour escape

2. Reduction zone:

3 Fe2O3 + CO → 3 Fe3O4 + CO2

Fe3O4 + CO → 3 FeO + CO2

3. 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 ores gives up sulphur 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, sulphur and phosphorus.
  4. The ore melts completely in the melting zone. Impurities combine with lime to form slag. The molten pig iron collects at the bottom of the furnace, with the lighter slag floating above it. These are drawn oil at regular interval (through a common opening in modern blast furnace).

In the direct reduction process, the iron ore gradually sinks downwards in a shaft furnace under the influence of gravity. The reduction gas (H2, CO), heated to 800oC flows upwards, against the direction of movement of the ore and remove the oxygen from it. Sponge iron is produced which is processed to make steel. The metallization takes place directly without a molten phase.

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