Chemistry
(a) Give the chemical names and formulae of the main ores of
(i) aluminium,
(ii) iron and
(iii) zinc.
(b) Which impurities are present in bauxite?
(c) What is red mud, how is it removed?
Metallurgy
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Answer
(i) Ores of aluminium :
| Name | Chemical name | Formula |
|---|---|---|
| Bauxite | Hydrated aluminium oxide | Al2O3.2H2O |
| Cryolite | Sodium aluminium flouride | Na3AlF6 |
(ii) Ores of iron:
| Name | Chemical name | Formula |
|---|---|---|
| Red haematite | Anhydrous ferric oxide | Fe2O3 |
| Brown haematite | Hydrated ferric oxide | 2Fe2O3.3H2O |
(iii) zinc
| Name | Chemical name | Formula |
|---|---|---|
| Zinc Blende | Zinc sulphide | ZnS |
| Calamine | Zinc Carbonate | ZnCO3 |
(b) Bauxite contains 60% aluminium oxide, the rest being sand, ferric oxide and titanium oxide.
(c) Finely grinded Bauxite is heated under pressure with caustic soda. Bauxite dissolves and forms sodium meta aluminate, leaving behind insoluble impurities called red mud. It consists of ferric oxide, sand etc. which are removed by filtration.
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