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 ).