Metal Ores and Method of Extraction

Metals are found in the ground in metal ores.

Definition

Metal ore is a mixture of compound of metal (such as oxides, sulfides, chloride, carbonates) and a large amount of earth and rock.

• Metal ores are sources of metal compounds (such as metal oxides) → from which metals can be extracted.
• Metal ores also contain impurities → which are removed during or before extraction process

Name of Ore	Name and formulae of compound present in ore	Metal to be extracted
Bauxite	Aluminium Oxide ($A{l}_2{O}_3$)	Aluminium
Haematite	Iron (III) oxide ($F{e}_2{O}_3$)	Iron
Copper Pyrite	Copper iron sulfide ($CuFe{S}_2$)	Copper
Zinc Blende	Zinc sulfide (ZnS)	Zinc
Extraction involves reduction of the metal compound to become the metal

• We learnt before → compounds of reactive metals are more stable compared to compounds of less reactive metals.
• Hence more reactive metals are more difficult to extract and less reactive metals are easier to extract from their ores

Electrolysis ElectroChemistry Main Noteof molten compound/ores → used to extract more reactive metals.

Metal	Method of Extraction
Potassium Sodium Calcium Magnesium Aluminium	Electrolysis of molten compound/ore
Zinc Iron Lead Copper	Heating ore with carbon to reduce metal oxide in ore
Silver	heating the ore alone
Gold Platinum	usually found naturally uncombined

Note

1. More reactive metals are extracted by the electrolysis of the molten ore/compound is used to extract them. Electrolysis decomposes the metal compound
2. Moderately reactive metals (zinc to copper) → extracted by reduction of their compounds (metal oxides) with carbon. Heating is required
3. For the least reactive metals, like silver → heating the ore alone (without need of carbon) is sufficient

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Optional Case study: Extraction of iron from Haematite in Blast Furnace

Raw materials:

1. Haematite - an iron ore → containing mainly iron (III) oxide
2. Coke (a form of carbon)
3. Limestone

Hot air is blasted into the blast furnace at the bottom These processes occur inside the 1000 - 1500 degree Celsius blast furnace

Stage 1: Coke reacts with oxygen to form carbon dioxide $C(s)+O_2(g)->C{O}_2(g)$

Stage 2: Carbon dioxide reacts with more coke to form carbon monoxide $C{O}_2(g)+C(s)->2CO(g)$

Stage 3: Carbon monoxide reacts with iron (III) oxide to form iron and carbon dioxide gas $3CO(g)+F{e}_2{O}_3(s)->2Fe(l)+3C{O}_2(g)$

• Molten iron is removed at the bottom of the blast furnace

Removal of Impurities(mainly silicon dioxide, an acidic oxide) Using limestone

• Limestone decomposes to form lime (calcium oxide) and carbon dioxide $CaC{O}_3(s)->CaO(s)+C{O}_2(g)$
• Calcium reacts with the silicon dioxide (sand) to form calcium silicate, which is the molten slag $CaO(s)+Si{O}_2(s)->CaSi{O}_3(l)$
• Molten slag is hot and is removed near the bottom of the blast furnace

Waste gasses of carbon monoxide and carbon dioxide → given off. Unreacted nitrogen and sulfur dioxide (from sulfur impurities in coke) are also released\

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