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:
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Crushing and grinding of the ore to obtain a fine powder.
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Concentration of the ore by froth flotation method.
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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)
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Reduction of copper oxide to obtain pure copper using carbon monoxide or by electrolysis:
- 2Cu2O(s) + C(s) → 4Cu(s) + CO2(g)
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Electrolytic refining of impure copper to obtain pure copper.
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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:
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Crushing and grinding of the ore to obtain a fine powder.
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Concentration of the ore by gravity separation or magnetic separation method.
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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)
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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)
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Purification of iron by removing impurities using the Bessemer process or the open-hearth process.
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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:
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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)
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Filtration of the sodium aluminate solution to remove impurities.
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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)
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Calcination of aluminium hydroxide to obtain alumina (Al2O3):
- 2Al(OH)3(s) → Al2O3(s) + 3H2O(g)
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Electrolytic reduction of alumina in a molten cryolite (Na3AlF6) bath to obtain pure aluminium.
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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:
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Crushing and grinding of the ore to obtain a fine powder.
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Concentration of the ore by froth flotation method.
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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)
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Reduction of zinc oxide to obtain pure zinc using carbon:
- ZnO(s) + C(s) → Zn(s) + CO(g)
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Purification of zinc by distillation or electrolysis.
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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:
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Calcination of magnesite to obtain magnesium oxide (MgO):
- MgCO3(s) → MgO(s) + CO2(g)
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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)
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Purification of magnesium by distillation or electrolysis.
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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:
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Crushing and grinding of the ore to obtain a fine powder.
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Concentration of the ore by froth flotation method.
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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)
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Reduction of silver oxide to obtain pure silver using charcoal:
- Ag2O(s) + C(s) → 2Ag(s) + CO(g)
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Purification of silver by electrolytic refining.
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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:
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Crushing and grinding of the ore to obtain a fine powder.
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Concentration of the ore by gravity separation or cyanidation method.
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Separation of gold particles from other impurities using water and a shaking table.
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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)
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Precipitation of pure gold from the solution using zinc:
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Purification of gold by acid treatment or electrolysis.
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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:
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Crushing and grinding of the ore to obtain a fine powder.
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Concentration of the ore by gravity separation or froth
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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: