In the extraction of Cu and Fe, the slag obtained are respectively FeSiO3 and CaSiO3.
The obtained slag is used in road making as well as in the manufacturing of cement and fertilizers.
( ii) Reduction by hydrogen It is done for W or Mo oxide.
iii) Reduction by aluminium It is known as alumino thermic reduction or Gold Schmidt thermite process. Aluminium powder is used for this purpose.
e. g., Cr2O3 + 2Al → Al2O3 + 2Cr
Mixture of the oxide and Al i. n the ratio of 3: 1 is known as thermite and mixture of BaO2 + Mg powder acts as ignition powder.
( iv) Auto reduction This is used for reduction of sulphide ores of Pb, Hg, Cu, etc. The sulphide ore is heated in a supply of air at 770-970 K when the metal sulphide is partially oxidised to form its oxide or sulphate which then reacts with the remaining sulphide to give the metal.
( v) Reduction by Mg
TiCl4 + 2Mg → 2MgCl2 + Ti( Kroll’ s process)
vi) Electrolytic reduction or electrometallurgy It is the process of extracting highly electropositive( active) metals such as Na, K, Ca, Mg, Al, etc by electrolysis of their oxides, hydroxides or chlorides in fused state, e. g., Mg is prepared by the electrolysis of fused salt of MgCl2( Dow’ s process).