The fusible compound formed by the combination of flux and gangue is called
Flux + Gangue \(\longrightarrow \) Slag
Eg: In the extraction of copper from copper pyrites, the ore is mixed with coke and heated in blast furnace.
Infusible FeO is converted to FeSiO₃ (slag) and is removed.
\(\underset { Gangue }{ FeO } +\underset { Flux }{ { SiO }_{ 2 } } \longrightarrow \underset { slag }{ { FeSiO }_{ 3 } } \)

(i) Depressant are used to prevent one type of sulphide ore particles from forming the froth with air bubbles.
(ii) Eg: In the process of separation of lead sulphide (Pbs) ore from zinc sulphide (ZnS) ore, sodium cyanide is used as depressant.

In Ellingham diagram, the graph of \(CO\rightarrow { CO }_{ 2 }\) conversion remains below \(Fe\rightarrow { Fe }_{ 2 }{ O }_{ 3 }\)  upto 1073 K
(for Fe\(\longrightarrow \) FeO). SO, CO (g) act as reducing agent upto this temperature.
\(3{ Fe }_{ 2 }{ O }_{ 3 }+CO\longrightarrow 2{ Fe }_{ 3 }{ O }_{ 4 }\) (i.e. FeO.Fe₂O₃) + CO₂
\({ Fe }_{ 3 }{ O }_{ 4 }+CO\longrightarrow 3Feo+{ CO }_{ 2 }\)
FeO + CO \(\longrightarrow \) Fe + CO₂
Also, graph of C\(\longrightarrow \) CO is below the graph of
Fe \(\longrightarrow \)Fe₂O₃ after 1123 K. So, carbon acts as reducing agent above this temperature.
Fe₂O₃ + C\(\longrightarrow \) 3 CO + 2 Fe.

(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) Calcination is the process in which the concentrated ore is strongly heated in the absence of air.
(ii)  During this process, the water of crystallisation present in the hydrated oxide escapes as moisture.
(iii) Any organic matter (if present) also get expelled leaving behind a porous ore.
(iv) This method can also be carried out with 4 limited supply of air.
(v) During calcination of carbonate ore carbon dioxide is expelled.
\(Pb{ CO }_{ 2 }\overset { \Delta }{ \longrightarrow } PbO+{ CO }_{ 2 }\uparrow \)

(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) In the concentrated ore, the metal exists in positive oxidation state and hence it is to be reduced to its elemental state.
(ii) From the principles of thermodynamics; that the reduction of oxide is easier when compared to reduction of other compounds of metal and hence, before reduction, the are is first converted into the oxide of metal of interest.

(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.

(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
\({ 4Au }_{ (s) }+{ 8CN }_{ (aq) }^{ - }+{ O }_{ 2(g) }+2{ H }_{ 2 }{ O }_{ (l) }\longrightarrow 4\left[ Au(CN)_{ 2 } \right] +_{ (aq) }^{ - }+{ 4OH }_{ (aq) }^{ - }\)