Extraction of Metals
Mercury and copper, which belong to the least reactivity series, are often found in the form of their sulphide ores. Cinnabar (HgS) is the ore of mercury. Copper glance (Cu2S) is the ore of copper.
Extraction of Mercury: Cinnabar (HgS) is first heated in plenty of air, so that it can undergo roasting. This turns HgS [mercury sulphide or cinnabar] into HgO (mercury oxide), by liberation of sulphur dioxide.
2HgS + 3O2 ⇨ 2HgO + 2SO2
Mercury oxide so obtained is again heated strongly in limited supply of air, so that it can undergo calcination. This reduces mercury oxide to mercury metal.
2HgO ⇨ 2Hg + O2
Extraction of Copper: Copper glance (Cu2S) is roasted in the presence of air. This results in oxidation of copper sulphide to give copper oxide. Roasting turns copper glance (ore of copper) into copper (I) oxide.
2Cu2S + 3O2 ⇨ 2Cu2O + 2SO2
After that, copper oxide is then heated in the absence of air, so that it can undergo calcination. This reduces copper (I) oxide into copper metal.
2Cu2O + Cu2S ⇨ 6Cu + SO2
Extraction of Metals of middle reactivity:
Iron, zinc, lead, etc. are the metals of middle reactivity. These metals are found in the form of carbonate or sulphide ores. Sulphide ores of metals are first converted into respective oxides through the process of roasting. After that, oxides are subjected to calcination so that they can be reduced to respective metals. Carbonate orese are subjectred to calcination to get oxide of metals.
Extraction of zinc: Zinc blende (ZnS: zinc sulphide) and smithsonite or zinc spar or calamine (ZnCO3: zinc carbonate) are ores of zinc. Zinc blende is roasted, so that it can undergo oxidation to give zinc oxide. Zinc spar is also subjected to calcination to be converted into zinc oxide.
2ZnS + 3O2 ⇨ 2ZnO + 2SO2
ZnCO3 ⇨ ZnO + CO2
Zinc oxide so obtained is reduced to zinc metal by heating with carbon (a reducing agent).
ZnO + C ⇨ Zn + CO
Extraction of Iron: Hematite ore (Fe2O3) is heated with carbon to be reduced to iron metal.
Fe2O3 + 3C ⇨ 4Fe + 3CO2
Extraction of lead from lead oxide: Lead oxide is heated with carbon to be reduced to lead metal.
2PbO + C ⇨ 2Pb + CO2
Reduction of metal oxide by heating with aluminium: Metal oxides are heated with aluminium (a reducing agent) to be reduced to metal. You have read that aluminium oxide is an amphoteric oxide, which means it shows dual nature, i.e. both acidic and basic nature. Following is an example:
Manganese dioxide and copper oxide are reduced to respective metals when heated with aluminium.
3MnO2 + 4Al ⇨ 3Mn + 2Al2O3
3CuO + 2Al ⇨ 3Cu + Al2O3 + heat
Thermite Reaction: Ferric oxide (when heated with aluminium) is reduced to iron metal. In this reaction, lot of heat is produced. This reaction is also known as Thermite Reaction. Thermite reaction is used in welding of electric conductors, iron joints, etc. such as joints in railway tracks. This is also known as Thermite Welding (TW).
Fe2O3 + 2Al ⇨ 2Fe + Al2O3 + heat