Extraction and Uses of Metals

Metals in the Earth's crust

• Almost all metals are found in the Earth's crust combined with other elements as ores
• An ore is a rock that contains enough of a wanted metal compound to make extraction economically worthwhile
• Many metal ores are metal oxides; some are sulfides or carbonates
  • Iron is found mainly as haematite, an iron(III) oxide (Fe₂O₃)
  • Aluminium is found mainly as bauxite, a hydrated aluminium oxide ore that is purified to give Al₂O₃ before extraction
  • Copper is found as the sulfide ore chalcopyrite (CuFeS₂) and as carbonate ores such as malachite

Native metals

• A few very unreactive metals are found as the free element in the Earth's crust, not as compounds
• These native metals include gold, platinum and (to a lesser extent) silver
• They occur uncombined because they react so slowly with air, water and acids that they survive in their pure form on geological timescales

Extraction is a reduction

• For an oxide ore, extracting the metal means removing oxygen from the metal compound — by definition, a reduction reaction
• The reactivity series decides how that reduction is carried out (see section 2)