Extraction of Metals

Reduction of Metal Oxides with Carbon

Reduction of Metal Oxides with Carbon

Metals found lower then carbon in the reactivity series are usually extracted from their ores through a reaction with carbon and carbon monoxide. This method is both cheap and effective. A major example is iron.

Extraction of iron

Carbon monoxide is the cheapest reducing agent for reducing iron from its main ore, haematite (Fe2O3). The reaction takes place in a blast furnace. At the top of the furnace coke and haematite are continuously added while at the base hot air is blown in.

The main chemical processes take place within the furnace are as follows:

  • Heating the furnace: the furnace is kept hot by the exothermic reaction of the coke reacting with the oxygen to produce carbon dioxide at the base:

? C(s) + O2(g) ? CO2(g)

  • Making the reducing agent: as the carbon dioxide rises it reacts with more coke, an endothermic reaction which produces carbon monoxide:

? C(s) + CO2(g) ? 2CO(g)

  • Reducing the iron oxide: the reducing agent, carbon monoxide, reduces the haematite to liquid iron which sinks and is tapped off at the base of the furnace:

? Fe2O3(s) + 3CO(g) ? 2Fe(l) + 3CO2(g)

Some of the haematite, however, is reduced into carbon directly:

? Fe2O3(s) + 3C(s) ? 2Fe(s) + 3CO(g)

Usually there are other oxides in the furnace too which are also reduced by the carbon:

? Fe3O4(s) + 4C(s) ? 3Fe(s) + 4CO(g)

? FeO(s) + C(s) ? Fe(s) + CO(g)

Extraction of manganese and copper

It is also possible to use a blast furnace in a similar way to extract manganese and copper from their oxides:

  • Manganese:

? MnO2(s) + 2CO ? Mn(l) + 2CO2(g)

? MnO2(s) + 2C(s) ? Mn(l) + 2CO(g)

  • Copper:

? CuO(s) + CO(g) ? Cu(l) + CO2(g)

? CuO(s) + C(g) ? Cu(l) + CO(g)

Process advantages and disadvantages

Advantages Disadvantages
  • The raw materials used are cheap
  • Less energy is needed to maintain heat in the furnace as the reaction is exothermic
  • The purity of the iron produced is sufficient for the majority of steel-making requirements
  • The iron can be made efficiently as the process is continuous
  • Carbon dioxide, a greenhouse gas, is produced
  • Metals higher than carbon in the reactivity series, like aluminium, cannot use this extraction method
  • Metals that form carbides with carbon when they react, like tungsten and titanium, cannot use this extraction method
  • Metals that need to be pure cannot use this extraction method as the metal produced always contains a large amount of carbon