Carbon Reduction Method for Extracting Metals from their Oxides
- An activity series for metals places the metals in order of their activity (or reactivity) from most active (or reactive) to least active (or reactive).
- The more active (or reactive) a metal is, the more stable the compound it forms and the greater the energy required to produce the metal from its ore.
Very active metals (Group 1, Group 2 and aluminium) require electrolysis to extract the metal while very inactive metals like gold and silver can occur in nature as the element so require no energy to extract the metal.
- Transition metals can often be extracted from their ores by heating the ore with a suitable reducing agent in a process known as thermal reduction.
most reactive elements
(Group 1, Group 2, aluminium)
→ → → → → → → → → → → → → →
least reactive elements
potassium > calcium > sodium > magnesium > aluminium > zinc > iron > nickel > tin > lead > copper > silver > gold electrolysis thermal reduction of oxide native elements
- Carbon can be used as reducing agent for transition metal oxides because carbon is more active than the transition metals in the ores:
most reactive elements → → → → → → → → → → → → → → → → → → → → → → least reactive elements potassium > calcium > sodium > magnesium > aluminium carbon > zinc > iron > nickel > tin > lead > copper > silver > gold
- The general equation for the reactions in which metal oxides are reduced by heating with carbon:
metal oxide + carbon → metal + carbon dioxide*
metal oxide + carbon → metal + carbon monoxide**
- Metal is reduced from a positive oxidation state in the metal oxide to the metallic element.
Carbon is oxidized from elemental carbon to an oxide of carbon in which carbon is in a positive oxidation state (has a positive oxidation number).