Isolation of Metals - Major steps involved for isolation of metal from its ore

  • Ores are naturally occurring rocks that contain high concentrations of metal compounds.
  • The process of extracting metals from their ores is called metallurgy.
  • The major steps involved in the isolation of metals from their ores are as follows:

1. Crushing and Grinding

  • The ore is first crushed into small pieces to increase the surface area for better exposure to the chemical reactions.
  • The crushed ore is then ground into a fine powder using a ball mill or stamp mill.
  • This process is called pulverization.

2. Concentration of Ore

  • The process of removing impurities from the ore is called concentration.
  • The purpose of concentration is to increase the percentage of metal in the ore.
  • Various methods like gravity separation, magnetic separation, or flotation are used for concentration.

3. Roasting and Calcination

  • Roasting and calcination are methods used for the conversion of concentrated ore into its oxide form.
  • Roasting involves heating the ore in the presence of excess air, which converts the sulfide ores into oxides.
  • Calcination involves the heating of carbonate ores, which drives off carbon dioxide and leaves behind the metal oxide.

4. Reduction of Metal Oxide

  • Metal oxides obtained from roasting or calcination are reduced to obtain the pure metal.
  • Reduction is the process of removing oxygen from a compound.
  • Commonly used reducing agents include carbon, carbon monoxide, and hydrogen.

5. Purification of Metal

  • The pure metal obtained from reduction may still contain impurities.
  • Purification is done to remove these impurities.
  • Methods like electrolysis, distillation, or fractional crystallization are used for purification.

6. Electrolytic Refining

  • Electrolytic refining is used to purify impure metals which are obtained from the reduction process.
  • The impure metal is made the anode, and a thin strip of pure metal is made the cathode for electrolysis.
  • Impurities settle at the bottom of the electrolytic cell, while pure metal is deposited on the cathode.

7. Extraction of Gold and Silver

  • Gold and silver are noble metals and are usually found in their native form in nature.
  • These metals are extracted by hydraulic washing or gravity separation.
  • They can also be extracted by the process of cyanidation using a dilute solution of sodium cyanide.

8. Refining of Copper

  • Copper is a widely used metal, and its extraction involves a series of steps.
  • The ore is first concentrated by froth flotation.
  • The concentrated ore is then roasted to convert sulfide ores to oxides.
  • Finally, electrolytic refining is done to obtain pure copper.

9. Refining of Aluminium

  • Aluminium is extracted from its ore, bauxite, by the Bayer’s process.
  • The ore is first crushed and then treated with sodium hydroxide solution to form sodium aluminate.
  • Impurities are filtered out, and pure alumina is obtained, which is then electrolyzed to obtain aluminium metal.

10. Refining of Iron

  • Iron is extracted from its ore, hematite, by the process of reduction with carbon monoxide gas.
  • The iron ore is first crushed and then heated in a blast furnace with coke (carbon) and limestone.
  • Molten iron is obtained at the bottom of the furnace, which is then purified using various methods.

11. Refining of Zinc

  • Zinc is extracted from its ore, zinc blende (ZnS), by the process of roasting followed by reduction.
  • The ore is first roasted in the presence of excess air to convert zinc sulfide into zinc oxide and sulfur dioxide gas:
    • 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g)
  • The zinc oxide obtained is then reduced using carbon:
    • ZnO(s) + C(s) → Zn(s) + CO(g)
  • The impure zinc obtained is further purified using electrolytic refining.

12. Refining of Tin

  • Tin is extracted from its ore, cassiterite (SnO2), by the process of smelting followed by refining.
  • The ore is first crushed and then concentrated using gravity separation or magnetic separation.
  • The concentrated ore is then heated in a furnace with carbon to remove the oxygen and obtain crude tin:
    • SnO2(s) + 2C(s) → Sn(s) + 2CO(g)
  • The crude tin obtained is then purified using liquation or electro-refining.

13. Refining of Lead

  • Lead is extracted from its ore, galena (PbS), by the process of smelting followed by refining.
  • The ore is first crushed and then concentrated using gravity separation or froth flotation.
  • The concentrated ore is then heated in a furnace with coke (carbon) to obtain lead:
    • 2PbS(s) + 3O2(g) → 2PbO(s) + 2SO2(g)
    • PbO(s) + C(s) → Pb(l) + CO(g)
  • The impure lead obtained is further purified using electro-refining.

14. Refining of Chromium

  • Chromium is extracted from its ore, chromite (FeCr2O4), by the process of roasting followed by reduction.
  • The ore is first roasted with sodium carbonate or calcium carbonate to convert chromium and iron oxide into their soluble forms:
    • FeCr2O4(s) + 4Na2CO3(s) + 9O2(g) → 2Na2CrO4(aq) + 4CO2(g) + 2Fe2O3(s)
  • The soluble chromium salt is then treated with sodium hydroxide to form sodium chromate:
    • Na2CrO4(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CrO4^2-(aq)
  • The sodium chromate is acidified with sulfuric acid to precipitate chromium hydroxide, which is then reduced to obtain pure chromium.

15. Refining of Nickel

  • Nickel is extracted from its ore, pentlandite [(Ni,Fe)9S8], by the process of smelting followed by refining.
  • The ore is first crushed and then concentrated using magnetic separation or froth flotation.
  • The concentrated ore is then roasted in the presence of excess air to convert nickel sulfide into nickel oxide and sulfur dioxide gas:
    • (Ni,Fe)9S8(s) + 15O2(g) → (Ni,Fe)O(s) + 8SO2(g)
  • The nickel oxide obtained is reduced using carbon monoxide:
    • NiO(s) + CO(g) → Ni(s) + CO2(g)
  • The impure nickel obtained is further purified using electrolytic refining.

16. Refining of Magnesium

  • Magnesium is extracted from its ore, magnesite (MgCO3), by the process of calcination followed by electrolysis.
  • The ore is first heated in a furnace to drive off carbon dioxide and obtain magnesium oxide:
    • MgCO3(s) → MgO(s) + CO2(g)
  • The magnesium oxide is then converted into magnesium chloride by treating it with hydrochloric acid:
    • MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)
  • The magnesium chloride is then electrolyzed to obtain pure magnesium metal.

17. Refining of Mercury

  • Mercury is extracted from its ore, cinnabar (HgS), by the process of roasting followed by condensation.
  • The ore is first heated in a furnace to convert mercury sulfide into mercury vapor and sulfur dioxide gas:
    • HgS(s) + O2(g) → Hg(l) + SO2(g)
  • The mercury vapor obtained is then condensed and collected.

18. Refining of Platinum

  • Platinum is extracted from its ore, platinum ores, by the process of smelting followed by refining.
  • The ore is first crushed and then concentrated using gravity separation or froth flotation.
  • The concentrated ore is then mixed with a flux and heated in a furnace to remove impurities:
    • PtO2(s) + 2SiO2(s) → Pt(s) + 2SiO(g)
  • The impure platinum obtained is further purified using various methods like solvent extraction or selective precipitation.

19. Refining of Silver

  • Silver is extracted from its ore, argentite (Ag2S), by the process of smelting followed by refining.
  • The ore is first crushed and then concentrated using gravity separation or froth flotation.
  • The concentrated ore is then roasted in the presence of excess air to obtain silver oxide and sulfur dioxide gas:
    • 2Ag2S(s) + 3O2(g) → 2Ag2O(s) + 2SO2(g)
  • The silver oxide obtained is reduced using charcoal or a reducing agent to obtain pure silver metal.

20. Refining of Gold

  • Gold is extracted from its ore, gold ores, by various methods like gravity separation, cyanidation, or smelting followed by refining.
  • Gravity separation involves the use of water and a shaking table to separate gold particles from other impurities.
  • Cyanidation is a chemical process in which a dilute solution of sodium cyanide is used to dissolve gold from its ore:
    • 4Au(s) + 8NaCN(aq) + O2(g) + 2H2O(l) → 4NaAu(CN)2 + 4NaOH(aq)
  • The dissolved gold is then precipitated using zinc:
  • Smelting involves heating the gold ore in a furnace with fluxes and a reducing agent to obtain crude gold:
    • 2Au2S(s) + 3O2(g) → 2Au2O3(s) + 2SO2(g)
    • Au2O3(s) + 2H2(g) → 2Au(s) + 3H2O(g)
  • The crude gold obtained is further purified using various methods like acid treatment or electrolysis.

Summary

  • The isolation of metals from their ores involves several steps, including crushing, grinding, concentration, roasting, reduction, purification, and electrolytic refining.
  • Different methods are used depending on the type of ore and the metal being extracted.
  • Each metal has its own specific process for refining and purification.
  • Overall, the process of isolating metals from their ores is essential for obtaining pure metals that can be used in various industries and applications.

21. Extraction of Copper from Copper Pyrites

  • Copper pyrites (CuFeS2) is the most common ore of copper.
  • Steps involved in the extraction of copper from copper pyrites are as follows:

    • Crushing and grinding of the ore to obtain a fine powder.

    • Concentration of the ore by froth flotation method.

    • Roasting of the concentrated ore in the presence of excess air to convert copper pyrites into copper oxide and sulfur dioxide gas:

      • 2CuFeS2(s) + 4O2(g) → 2Cu2O(s) + 2FeO(s) + 4SO2(g)

    • Reduction of copper oxide to obtain pure copper using carbon monoxide or by electrolysis:

      • 2Cu2O(s) + C(s) → 4Cu(s) + CO2(g)

    • Electrolytic refining of impure copper to obtain pure copper.

22. Extraction of Iron from Haematite

  • Haematite (Fe2O3) is the most common ore of iron.
  • Steps involved in the extraction of iron from haematite are as follows:

    • Crushing and grinding of the ore to obtain a fine powder.

    • Concentration of the ore by gravity separation or magnetic separation method.

    • Roasting of the concentrated ore in the presence of excess air to convert haematite into magnetic oxide of iron and gaseous impurities:

      • 2Fe2O3(s) + 3O2(g) → 4Fe3O4(s)

    • Reduction of magnetic oxide of iron to obtain pure iron using carbon monoxide in the presence of limestone as a flux:

      • 4Fe3O4(s) + 8CO(g) → 8Fe(s) + 8CO2(g)
      • Fe(s) + C(s) → Fe(l) + CO(g)

    • Purification of iron by removing impurities using the Bessemer process or the open-hearth process.

23. Extraction of Aluminium from Bauxite

  • Bauxite (Al2O3·2H2O) is the most common ore of aluminium.
  • Steps involved in the extraction of aluminium from bauxite are as follows:

    • Crushing the bauxite ore and mixing it with a solution of sodium hydroxide to form sodium aluminate:

      • Al2O3·2H2O(s) + 2NaOH(aq) + 3H2O(l) → 2NaAl(OH)4(aq)

    • Filtration of the sodium aluminate solution to remove impurities.

    • Precipitation of pure aluminium hydroxide from the filtrate by treating it with carbon dioxide:

      • NaAl(OH)4(aq) + CO2(g) → Al(OH)3(s) + NaHCO3(aq)

    • Calcination of aluminium hydroxide to obtain alumina (Al2O3):

      • 2Al(OH)3(s) → Al2O3(s) + 3H2O(g)

    • Electrolytic reduction of alumina in a molten cryolite (Na3AlF6) bath to obtain pure aluminium.

24. Extraction of Zinc from Zinc Blende

  • Zinc blende (ZnS) is the most common ore of zinc.
  • Steps involved in the extraction of zinc from zinc blende are as follows:

    • Crushing and grinding of the ore to obtain a fine powder.

    • Concentration of the ore by froth flotation method.

    • Roasting of the concentrated ore in the presence of excess air to convert zinc sulfide into zinc oxide and sulfur dioxide gas:

      • ZnS(s) + 3O2(g) → ZnO(s) + 2SO2(g)

    • Reduction of zinc oxide to obtain pure zinc using carbon:

      • ZnO(s) + C(s) → Zn(s) + CO(g)

    • Purification of zinc by distillation or electrolysis.

25. Extraction of Magnesium from Magnesite

  • Magnesite (MgCO3) is the most common ore of magnesium.
  • Steps involved in the extraction of magnesium from magnesite are as follows:

    • Calcination of magnesite to obtain magnesium oxide (MgO):

      • MgCO3(s) → MgO(s) + CO2(g)

    • Preparation of a mixture of magnesium oxide and carbon, and then heating the mixture in an electric furnace to obtain a mixture of magnesium and carbon dioxide:

      • MgO(s) + C(s) → Mg(s) + CO2(g)

    • Purification of magnesium by distillation or electrolysis.

26. Extraction of Silver from Silver Ore

  • Silver ore (Ag2S) is the most common ore of silver.
  • Steps involved in the extraction of silver from silver ore are as follows:

    • Crushing and grinding of the ore to obtain a fine powder.

    • Concentration of the ore by froth flotation method.

    • Roasting of the concentrated ore in the presence of excess air to obtain silver oxide and sulfur dioxide gas:

      • 2Ag2S(s) + 3O2(g) → 2Ag2O(s) + 2SO2(g)

    • Reduction of silver oxide to obtain pure silver using charcoal:

      • Ag2O(s) + C(s) → 2Ag(s) + CO(g)

    • Purification of silver by electrolytic refining.

27. Extraction of Gold from Gold Ore

  • Gold ore is usually found in its native form and does not require extensive extraction processes.
  • Steps involved in the extraction of gold from gold ore are as follows:

    • Crushing and grinding of the ore to obtain a fine powder.

    • Concentration of the ore by gravity separation or cyanidation method.

    • Separation of gold particles from other impurities using water and a shaking table.

    • Treatment of the gold particles with a dilute solution of sodium cyanide to dissolve the gold:

      • 4Au(s) + 8NaCN(aq) + O2(g) + 2H2O(l) → 4NaAu(CN)2 + 4NaOH(aq)

    • Precipitation of pure gold from the solution using zinc:

    • Purification of gold by acid treatment or electrolysis.

28. Extraction of Platinum from Platinum Ore

  • Platinum ore is usually found in association with other metals and requires complex extraction processes.
  • Steps involved in the extraction of platinum from platinum ore are as follows:

    • Crushing and grinding of the ore to obtain a fine powder.

    • Concentration of the ore by gravity separation or froth