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) The standard free energy for the formation of CuFeS₂ (copper pyrites) is greater than those of CS₂ and H₂S.
(ii) Hence, CuFeS₂ cannot be reduced carbon or hydrogen.
(iii) However, the free energy of copper oxide less than that of CO₂,
(iv) That is the reason, extraction of copper easier from its oxide through reduction.

(i) Gold is usually found in native state
(ii) The leaching process is intended to concentrate the gold metal
\(4Au_{ (s) }+8Na{ CN }_{ (aq) }^{ - }+2{ H }_{ 2 }O_{ (aq) }+{ O }_{ 2(g) }\longrightarrow 4Na[Au\left( CN \right) _{ 2 }]^{ - }_{ (aq) }+4NaO{ H }^{ -1 }_{ (aq) }\)
\(2Na\left[ Au(CN)_{ 2 } \right] +Zn\longrightarrow { Na }_{ 2 }\left[ Zn\left( CN \right) \right] +2Au\downarrow \)
(iii) In this reaction, Zn acts as a reducing agent.

(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) The end product of both the processes is oxide of metal.
(ii) Volatile impurities are removed from the ore and surface area for the further reaction increases.

Sulphide ores are generally roasted in reverberatory furnace in free supply of air below its melting point. Ore changes to oxide with larger surface area and volatile impurities are removed.
\(2ZnS+{ 3O }_{ 2 }\overset { \Delta }{ \longrightarrow } 2ZnO+{ 2SO }_{ 2 }\)
\(2PbS+{ 3O }_{ 2 }\overset { \Delta }{ \longrightarrow } pbO+{ 2SO }_{ 2 }\)

Iron, Lead and Copper

Metal oxides to metal : Carbon, carbon monoxide, hydrogen, aluminum and metals like sodium.

The preliminary step in metallurgical process is removal of the impurities. This removal process is known as concentration of ore.

Metallurgy relates to the science and technology of metals. The various steps involved in the extraction of metals form their ores as well as refining of crude metals are collectively know as metallurgy.

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.

(i) Concentration of the ore
(ii) Extraction of crude metal
(iii) Refining of crude metal

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.
\(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]_{(g)} \stackrel{460 \mathrm{~K}}{\longrightarrow} \mathrm{Ni}_{(s)(\text { pure })}+4 \mathrm{CO}_{(\mathrm{g})}\)