(i) The process in which no external reducing. When ore is heated in air, a part of the ore gets oxidised which combines with remaining sulphide to give metal.
Eg: Reduction copper glance (Cu₂S)
\({ 2Cu }_{ 2 }S+{ 3O }_{ 2 }\longrightarrow { 2Cu }_{ 2 }O+2{ SO }_{ 2 }\uparrow \)
\({ 2Cu }_{ 2 }O+{ Cu }_{ 2 }S\longrightarrow 6Cu+{ SO }_{ 2 }\uparrow \)
(ii) Electrolytic reduction is used for highly electro positive metals. In this method, fused metal ore is electrolysed and pure metal is deposited at cathode.
Eg: Al is obtained by electrolysis of Al₂O_{3
\({ 2Al }_{ 2 }{ O }_{ 3 }+3C\longrightarrow \underset { Cathode\quad Anode }{ 4Al+{ 3CO }_{ 2 } } \)}
(iii) \({ Cr }_{ 2 }{ O }_{ 3 }+2Al\longrightarrow {Al }_{ 2 }{ O }_{ 3 }+2Cr\)
\(3 \mathrm{Mn} _3 O_{4}+8 \mathrm{Al} \longrightarrow 4 \mathrm{Al}_{2} \mathrm{O}_{3}+9 \mathrm{Mn}\)

(i) Alumina is separated from silica in a bauxite ore through Baeyer's process, in which bauxite ore is concentrated by the method of leaching or chemical separation.
(ii) Chemical method is employed in case where the ore is to be in a very pure form, e.g., aluminium extraction. Bauxite (Al₂O₃), an ore of aluminium, contains SiO₂ and Fe₂O₃ as impurities. When bauxite ore is treated with NaOH, the Al₂O₃ goes into solution as sodium meta aluminate leaving behind the undissolved impurities [Fe₂O₃, SiO₂, Fe(OH)_3' etc.], which are then filtered off.
\({ Al }_{ 2 }{ O }_{ 3 }+{ 2NaOH }\longrightarrow \underset { Sod.meta.aliminate\\ (In \ solution \ form) }{ { 2NaAlO }_{ 2 }+{ H }_{ 2 }O } \)
(iii) The filtrate (containing sodium meta aluminate) on dilution, and stirring gives a precipitate of aluminium hydroxide, which is filtered, and ignited to get pure alumina.
\({ NaAlO }_{ 2 }+2{ H }_{ 2 }O\longrightarrow \underset { Ppt }{ { Al(OH) }_{ 3 } } +NaOH\)
\(2Al\left( OH \right) _{ 3 }\overset { \Delta }{ \longrightarrow } \underset { Pure }{ { Al }_{ 2 }{ O }_{ 3 } } +3{ H }_{ 2 }O\)

(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.
\({ Til }_{ 4 }(vapour)\longrightarrow { { Ti }_{ (s) } }+{ 2I }_{ 2(s) }\)

(i) Magnetic separation is applicable to ferromagnetic ores and it is based on the difference in the magnetic properties of the ore and the impurities.
(ii) For example tin stone can be separated from the wolframite impurities which is magnetic.
(iii) Similarly, ores such as chromite, pyrolusite having magnetic property can be removed from the non magnetic siliceous impurities.
(iv) The crushed ore is poured on to an electromagnetic separator consisting of a belt moving over two rollers of which one is magnetic.
(v) The magnetic part of the ore is attracted towards the magnet and falls as a heap close to the magnetic region while the nonmagnetic part falls away from it as shown in the figure.

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.

a) i) Ellingham diagram for the formation of Al₂O₃ and MgO intersects around 1500^oC. Above this temp Mg lies above the Aluminium line. Hence only above 1500^oC Aluminium might be excepted to reduce magnesia.
ii) Ellingham diagram for the formation of MgO lies below the formation of Al₂O₃. Hence MgO is more stable than Al₂O₃. Hence Magnesium could reduce Alumina.
1. Below 983K, formation of CO line lies below many of the metal oxide formation in Ellingham diagram, hence CO is more effective reducing agent than Carbon.
2. But above this temperature Carbon lies below other metal oxides.
b) Around 1200K Carbon lies below the formation of Fe₂O₃. Hence it is possible to reduce Fe₂O₃ by coke at 1200K.

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.

(i) Hydraulic washing or gravity separation
(ii) Froth flotation
(iii) Electromagnetic separation
(iv ) Chemical method.

(i) Graphite rods act a anode during electrolytic reduction of alumina.
(ii) At anode, O₂ gas is produced which react with the carbon of anode (rods) to produce CO₂ gas.
(iii) So these graphite rods are consumed slowly and need to be replaced from time to time.

(i) Distillation is employed for low boiling volatile metals like zinc (boiling point 1180 K) and mercury (630 K).
(ii) In this method, the impure metal is heated to evaporate and the vapours are condensed to get pure metal.

(i) Lighter sulphide ore particles are wetted by pine oil and rise to the surface with the from while gangue particles are wetted by water.
(ii) Therefore, the froth flotation method is selected for the concentration of sulphide ores.

Magnetite (Fe₃O₄), haematite (Fe₂O₃) are the ores which can be separated by the magnetic separation method. In these ores, one component is magnetic in nature.

Iron, Lead and Copper

(i) Conversion of ores into oxides.
(ii) Reduction of metal oxides.

i) Silica is an acidic flux which is mixed with Copper pyrites ore and is heated in a reverberatory furnace. The ferrous oxide formed from the ore is basic in nature and it combines with silica to form ferrous silicate. It is removed as slag.
\(\mathrm{FeO}_{(s)}+\mathrm{SiO}_{2(s)} \overset { \Delta }{ \longrightarrow } \mathrm{FeSiO}_{3(s)}\\ gangue \quad flux \quad \quad slag\)
ii) Aluminium oxide does not dissolve in water, but it dissolves in molten cryolite. This is an aluminium compound with a lower melting point than aluminium oxide. The use of cryolite reduces some of the energy costs involved in extracting aluminium.
\(\mathrm{Al}_{2} \mathrm{O}_{3} \overset { \Delta }{ \longrightarrow } 2 \mathrm{Al}^{3+}+3 \mathrm{O}^{2-}\)
iii) Van-Arkel method is based on the thermal decomposition of metal compounds which lead to the formation of pure metals. Zirconium can be purified by using this method. Zirconium metal is heated with iodine at a temperature of 550 K to form zirconium tetraiodide. (ZrI₄). The impurities are left behind
\(\mathrm{Zr}_{(\mathrm{s})}+2 \mathrm{I}_{2(\mathrm{~s})} \frac{550 \mathrm{~K}}{\mathrm{D}} \mathrm{ZrI}_{\text {t(vapour })}\)
The volatile (ZrI₄) on further heating around 1800 K, it gives pure zirconium.
\(\mathrm{ZrI}_{4 \text { (vapour) }} \frac{1800 \mathrm{~K}}{\mathrm{D}} \mathrm{Zr}_{(\mathrm{s})}+2 \mathrm{I}_{2} \)    
iv) In the extraction of lead from galena (PbS) by froth flotation process, if ZnS is present as impurity, Sodium cyanide is added to depresses the flotation property of ZnS. It forms a complex. Na₂[Zn(CN)₄] on the surface of zinc sulphide.

(i) At higher temperature, the reaction between copper and sulphur becomes feasible.
(ii) So they combine together and copper exists as copper sulphides in nature.
(iii) Besides this due to high polarising power of copper and silver ions, their sulphides are more stable.

(i) Simple roasting of some of the ores give the crude metal. In such cases, the use of and hydrogen which does not rust and gives reducing agents is not necessary.
(ii) For example, mercury is obtained by Write the chemical composition of the roasting of its ore cinnabar (HgS)
\(Hg{ S }_{ (s) }+{ O }_{ 2(g) }\longrightarrow { Hg }_{ (I) }+{ SO }_{ 2 }\uparrow \)

(i) Aluminium cannot be extracted by melting process due to the following reasons.
(a) Aluminium (AI) being highly electropositive element has very: strong affinity for oxygen. So, Al₂O₃ is very stable compound and cannot be reduced by C.
(b) On heating Al₂O₃ with C, aluminium carbide is formed 
\({ 2Al }_{ 2 }{ O }_{ 3 }+9C\longrightarrow { Al }_{ 4 }{ C }_{ 3 }+6CO\)
(ii) Below 1073 k, CO is more effective, because the \(\Delta { G }^{ 0 }\) value for the conversion of CO into CO₂ is more negative.

Ore	Molecular composition	Metal
Magnetite	Fe3O4	Iron
Calamine	ZnCO3	Zinc
Bauxite	Al2O3.nH2O	Aluminium

Roasting	Calcination
Roasting is a process which ore is heated in the presence of excess of air.	Calcination is a process in which ore is heated in the absence of air.
As a result of roasting the sulphide ores are converted into their oxides.	As a result of calcination, the carbonal ore is converted into its oxide.
\(2PbS+3O2\overset { \Delta }{ \longrightarrow } PbO+{ 2SO }_{ 2 }\uparrow \)	\(PbCO\overset { \Delta }{ \longrightarrow } PbO+{ CO }_{ 2 }\uparrow \)
Roasting removes impurities such as arsenic, sulphur phosphorous by converting them into their volatile oxides \(4As+{ 3O }_{ 2 }\longrightarrow { 2As }_{ 2 }{ O }_{ 3 }\)	During calcination of hydrated ore, the water of hydration is expelled as vapour.

(i) Leaching of sulphide ores such as ZnS, PbS etc., can be done by treating them with hot aqueous sulphuric acid
\(2Zn{ S }_{ (s) }+{ 2H }_{ 2 }{ SO }_{ 4(aq) }+{ O }_{ 2(g) }\longrightarrow { 2ZnSO }_{ 4(aq) }+2{ S }_{ (s) }+{ H }_{ 2 }O\)
(ii) In this process the insoluble sulphide is converted into soluble sulphate and elemental sulphur

(i) In this method, the ore is treated with aqueous alkali to form a soluble complex.
(ii) Bauxite, an important ore of aluminum is heated with a solution of sodium hydroxide or sodium carbonate in the temperature range 470 - 520 K at 35 atm to form soluble sodium meta-aluminate leaving behind the impurities, iron oxide and titanium oxide.
\({ Al }_{ 2 }{ O }_{ 3(s) }+2NaO{ H }_{ (aq) }+3{ H }_{ 2 }{ O }_{ (l) }\longrightarrow 2Na[Al({ OH })_{ 4 }]_{ (aq) }\)
(iii) The hot solution is decanted, cooled, and diluted. This solution is neutralised by passing CO₂ gas, to the form hydrated Al₂O₃ precipitate
\(2Na\left[ Al\left( OH \right) _{ 4 } \right] _{ (aq) }+{ CO }_{ 2(g) }\longrightarrow { Al }_{ 2 }{ { O }_{ 3 }.x{ H }_{ 2 }O_{ (s) }+2NaHCO_{ 3(aq) } }\)
(iii) The precipitate is filtered off and heated around 1670 K to get pure alumina Al₂O₃

When a crushed ore containing nickel, copper and cobalt is treated with aqueous ammonia under suitable pressure, ammonia selectively leaches these metals by forming their soluble complexes viz. [Ni(NH₃)₆]2+, [Cu(NH₃)₄]²⁺, and [Co(NH₃)₅H₂O]³⁺ respectively from the ore leaving behind the gangue, iron(III) oxides/ hydroxides and aluminosilicate.