(i) Calcination is the process in which the concentrated ore is strongly heated in the absence of air. During this process, the water of crystallisation present in the hydrated oxide escapes as moisture.
(ii) Example: \(\mathrm{CaCO}_{3} \rightarrow \mathrm{CaO}+\mathrm{CO}_{2} \uparrow\)

(i) Roasting is the method, usually applied for the conversion of sulphide ores into their oxides. In this method, the concentrated ore is oxidised by heating it with excess of oxygen in a suitable furnace below the melting point of the metal.
(ii) Example: \(2 \mathrm{PbS}+3 \mathrm{O}_{2} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{PbO}+2 \mathrm{SO}_{2} \uparrow\)

Ellingham diagram for the formation of ZnO and CO₂ intersects around 1200 K. Above this temperature ZnO lies above Carbon which indicates Carbon is the better reducing agent CO is more effective reducing agent only below 983 K.

(i) Copper is extracted form copper matte which contains iron as impurity.
(ii) Silica is added to remove this impurity as iron silicate in the form of Fusible slag.
\(\underset { Impurity }{ FeO } +{ SiO }_{ 2 }\longrightarrow \underset { Ironsilicate(slag) }{ { FeSiO }_{ 3 } } \)

1. This process is called as Hall-Heroult process.
Cathode: In this method, electrolysis is carried out in an iron tank lined with carbon which acts as the cathode.
Anode: The carbon blocks immersed in the electrolyte acts as a anode.
Eletrolyte: A 20% solution of alumina, obtained from the bauxite ore is mixed with molten Cryolite and is taken in the electrolysis chamber.
2. About 10% calcium chloride is also added to the solution.
3. Here Calcium chloride helps to lower the melting point of the mixture.
Temperature: The fused mixture is maintained at a temperature of above 1270 K.
4. The chemical reactions involved in this process as follows
(a) Ionisaiton of alumina: \({ A }l_{ 2 }{ O }_{ 3 }\longrightarrow { 2Al }^{ 3+ }+{ 3O }^{ 2- }\)
(b) Reaction at cathode: \(2{ Al }^{ 3+ }_{(melt)}+{ 6e }^{ - }\longrightarrow { Al }_{ (l) }\)
(c) Reaction at anode: \(6{ O }^{2-}_{(melt)}\longrightarrow { 3O }_{ 2 }+{ 12e }^{ - }\)
5. Since carbon acts as anode the following reaction also takes place
(a) \({ C }_{ (s) }+{ O }^{ 2- }_{(melt)}\longrightarrow CO+{ 2e }^{ - }\)
(b) \({ C }_{ (s) }+{ 2O }^{ 2- }_{(melt)}\longrightarrow { CO }_{ 2 }+{ 4e }^{ - }\)
6. Due to the above two reactions, anodes are slowly consumed during the electrolysis.
7. The pure aluminium is formed at the cathode. The net electrolysis reaction can be written as
\({ 4Al }^{ 3+ }_{(melt)}+{ 6O }^{ 2- }_{(melt)}+{ 3C }_{ (s) }\longrightarrow { 4Al }_{ (l) }+{ 3CO }_{ 2(g) }\)

This method is commonly used to concentrate sulphide ores such as galena (PbS), zinc blende (ZnS) etc.
In this method, the metallic ore particles which are preferentially wetted by oil can be separated from gangue.

In this extraction, a basic flux, quick lime (CaO) is used, since the silica gangue present in the ore is acidic in nature. The quick lime combines with it to form calcium silicate (slag).
CaO_(s) + Sio_2(s) ⟶ CaSio_3(s)
Flux       Gangue    Slag

(i) Metallic oxides such as Cr₂O₃ can be reduced by an alumino thermic process. In this process, the metal oxide is mixed with aluminium powder and placed in a fire clay crucible. To initiate the reduction process, an ignition mixture (magnesium and barium peroxide) is used.
\({ BaO }_{ 2 }+Mg\longrightarrow Bao+MgO\)
(ii) During the above reaction a large amount of heat is evolved (Temperature = 2400^oC, reaction enthalpy: 852 kJ mol^-1) which facilitates the reduction of Cr₂O₃ by aluminium powder.
(iii) \({ Cr }_{ 2 }{ O }_{ 3 }+2Al\overset { \Delta }{ \longrightarrow } 2Cr+{ Al }_{ 2 }{ O }_{ 3 }\)

(i) Metallic oxides such as Cr₂O₃ can be reduced by an alumino thermic process. In this process, the metal oxide is mixed with aluminium powder and placed in a fire clay crucible. To initiate the reduction process, an ignition mixture (magnesium and barium peroxide) is used.
\({ BaO }_{ 2 }+Mg\longrightarrow Bao+MgO\)
(ii) During the above reaction a large amount of heat is evolved (Temperature = 2400^oC, reaction enthalpy: 852 kJ mol^-1) which facilitates the reduction of Cr₂O₃ by aluminium powder.
(iii) \({ Cr }_{ 2 }{ O }_{ 3 }+2Al\overset { \Delta }{ \longrightarrow } 2Cr+{ Al }_{ 2 }{ O }_{ 3 }\)

(i) Gangue: The ores are associated with nonmetallic impurities, rocky materials and siliceous matter which are collectively known as gangue.
Eg: SiO₂ is the gangue present in the iron ore (Fe₂O₃)
(ii) Slag: In the smelting process, a flux combines with Silica gangue forming slag.
CaO_(s) + SiO_2(s) → CaSiO_3(s)
Flux     + gangue → Slag

Mond process for refining nickel:
The impure nickel is heated in a stream of carbon monoxide at around 350 K. The nickel reacts with the CO to form a highly volatile nickel tetracarbonyl. The solid impurities are left behind. 
\(\mathrm{Ni}_{(\mathrm{s})}+4 \mathrm{CO}_{(\mathrm{g})}\ \rightarrow \ \left[\mathrm{Ni}(\mathrm{CO})_{4}\right]_{(g)}\)
(ii) When the Nickel Carbonyl Complex is heated at 460 K, it decomposes to give pure nickel.
\(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]_{(g)} \stackrel{460 \mathrm{~K}}{\longrightarrow} \mathrm{Ni}_{(s)(\text { pure })}+4 \mathrm{CO}_{(\mathrm{g})}\)

(i) In the extraction of copper from copper pyrites, the concentrated ore is heated with silica (flux) in the reverberatory furnace.
(ii) The ferrous oxide formed combines with silica forming ferrous silicate (slag).
(iii) The remaining metal sulphides (Cu₂S and FeS) form a copper matte.
\(2 \mathrm{CuFeS}_{2(\mathrm{~s})}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{FeS}_{(1)}+\mathrm{Cu}_{2} \mathrm{~S}_{(1)}+\mathrm{SO}_{2}  \)
\(2 \mathrm{FeS}_{(s)}+3 \mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{FeO}_{(s)}+2 \mathrm{SO}_{2(\mathrm{~g})}  \)
\(\mathrm{FeO}_{(s)}+\mathrm{SiO}_{2(\mathrm{~s})} \rightarrow \mathrm{FeSiO}_{3(\mathrm{~s})} \\ \text { gangue} \quad \text { flux }\quad \quad \text { slag }\)
(iv) The matte is separated from the slag and fed to the converting furnace.
(v) During conversion FeS of matte oxidized to FeO.
(vi) It reacts with silica and removed as slag.
(vii) The remaining copper sulphide is further oxidised to its oxide, which is converted into metallic copper.
\(2 \mathrm{Cu}_{2} \mathrm{~S}_{(\mathrm{l} . \mathrm{s})}+3 \mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{Cu}_{2} \mathrm{O}_{(\mathrm{a}, \mathrm{s})}+2 \mathrm{SO}_{2(\mathrm{~g})}  \)
\(2 \mathrm{Cu}_{2} \mathrm{O}_{(i)}+\mathrm{Cu}_{2} \mathrm{~S}_{(0)} \rightarrow 6 \mathrm{Cu}_{(i)}+\mathrm{SO}_{2(\mathrm{~g})}\)
(viii) The metallic copper is solidified and it has blistered appearance due to the evolution of SO₂.
(ix) This copper is called blistered copper (98 % pure).

Gravity separation or Hydraulic wash
In this method, the ore having high specific gravity is separated from the gangue that has low specific gravity by simply washing with running water. Ore is crushed to a finely powdered form and treated with rapidly flowing current of water. During this process the lighter gangue particles are washed away by the running water. This method is generally applied to concentrate the native ore such as gold and oxide ores such as haematite (Fe₂O₃), tin stone (SnO₂) etc.

(i) Van-Arkel method is based on the thermal decomposition of metal compounds which lead to the formation of pure metals.
(ii) Titanium and zirconium can be purified, using this method.
(iii) For example, the impure titanium metal is heated in an evacuated vessel with iodine at a temperature of 550 K to form the volatile titanium tetra-iodide(Til₄)
(iv) The impurities are left behind, as they do not react with iodine
\({ Ti }_{ (s) }+{ 2I }_{ 2(s) }\longrightarrow { Til }_{ 4 }(vapour)\)
(v) The volatile titanium tetraiodide vapour is passed over a tungsten filament at a temperature around 1800 K.
(vi) The titanium tetraiodide is decomposed and pure titanium is deposited on the filament
(vii) The iodine is reused.
\({ Til }_{ 4 }(vapour)\longrightarrow { { Ti }_{ (s) } }+{ 2I }_{ 2(s) }\)

1. The crude metal is refined by electrolysis. It is carried out in an electrolytic cell
Anode : Impure metal to be refined with dilute acid.
Cathode : Thin strips of pure metal
Electrolyte : Aqueous solution of the salts of the metal with dilute acid.
2. The metal dissolves from the anode, pass into the solution.
3. At the same amount of metal ions from the solution will be deposited at the cathode.
4. During electrolysis, the less electropositive impurities in the anode, settle down at the bottom and are removed as anode mud.
Example: Electrolytic refining of silver.
Cathode: Pure silver
Anode: lmpure silver rods
Electrolyte: Acidified aqueous solution of silver nitrate
5. When a current is passed through the electrodes the following reactions will take place
(a) Reaction at anode: \({ Ag }_{ (s) }\longrightarrow { Ag }^{ + }_{ (aq) }+{ 1e }^{ - }\)
(b) Reaction at cathode: \({ Ag }^{ + }_{ (aq) }+{ 1e }^{ - }\longrightarrow { Ag }_{ (s) }\)
6. During electrolysis, at anode silver loses electrons and form silver ions and the silver ions migrate towards the cathode and get discharged and deposited on the cathode.
7. Copper, Zinc etc can also be refined by this process.

Zone refining :
1. Zone refining method is based on the principles of fractional crystallisation.
2. When an impure metal is melted and allowed to solidify, the impurities will prefer to be in the molten region. In this process the impure metal is taken in the form of a rod.
3. One end of the rod is heated using a mobile induction heater which results in melting of the metal on that portion of the rod.
4. When the heater is slowly moved to the other end the pure metal crystallises while the impurities will move on to the adjacent molten zone.
5. As the heater moves further away, the molten zone containing impurities also moves along with it.
6. The process is repeated several times by moving the heater in the same direction again and again to get pure metal.
7. This process is carried out in an inert gas atmosphere to prevent the oxidation of metals.
8. Elements such as germanium (Ge), silicon (Si) and galium (Ga) that are used as semiconductor are refined using this process.