(i) Vapour phase method, the metal is treated with a suitable reagent which can form a volatile compound with the metal.
(ii) Then the volatile compound is decomposed to give the pure metal.
(iii) Vapour phase method is used for refining nickel.

(i) Roasting is the method, usually applied for the conversion of sulphide ores into their oxides.
(ii) 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.
(iii) \(2PbS+{ 3O }_{ 2 }\overset { \Delta }{ \longrightarrow } 2PbO+{ 2SO }_{ 2 }\uparrow \)
\(2ZnS+{ 3O }_{ 2 }\overset { \Delta }{ \longrightarrow } 2ZnO+2{ SO }_{ 2 }\uparrow \)
\(2Cu_{ 2 }S+{ 3O }_{ 2 }\overset { \Delta }{ \longrightarrow } 2Cu_2O + 2SO_2\uparrow \)
(iii) Roasting also removes impurities such as arsenic, sulphur, phosphorous by converting them into their volatile oxides
(v) Ex.\(4As+{ { 3O }_{ 2 } }\longrightarrow { 2As }_{ 2 }{ O }_{ 3 }\uparrow \)
\( \mathrm{S}_{8}+8 \mathrm{O}_{2} \longrightarrow 8 \mathrm{SO}_{2} \uparrow \)
\(\mathrm{P}_{4}+5 \mathrm{O}_{2} \longrightarrow \mathrm{P}_{4} \mathrm{O}_{10} \uparrow\)

(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

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.

(i) The crushed ore of gold is leached with aerated dilute solution of sodium cyanide.
(ii) Gold is converted into a soluble cyanide complex.
(iii) The gangue, aluminosilicate remains insoluble
\({ 4Au }_{ (s) }+{ 8CN }_{ (aq) }^{ - }+{ O }_{ 2(g) }+2{ H }_{ 2 }{ O }_{ (l) }\longrightarrow 4\left[ Au(CN)_{ 2 } \right] +_{ (aq) }^{ - }+{ 4OH }_{ (aq) }^{ - }\)