FLUX : PYROMETALLURGY:

The substance used in metallurgical process to decrease melting point of an ore or a substance used to react gangue (impurities present in ore) to form Slag.

Type of flux: Fluxes are of two types’ viz., acidic flux and basic flux.

(A) Acidic flux: It is an acidic oxide (oxide of a non-metal) like SiO₂, P₂O₅, and B₂O₃ (from borax).

It is used to remove the basic impurity like CaO, FeO, MgO etc. The acidic flux combines with the basic impurity and forms a slag. 

(B) Basic flux: It is a basic oxide (i.e., oxide of a metal) like CaO (obtained from lime stone, CaCO₃), MgO (from magnesite, MgCO₃), haematite (Fe₂O₃) etc. It is used to remove the acidic impurity like SiO₂, P₂O₅ etc. The basic flux combines with the acidic impurity and forms a slag. 

Thus, slag can be defined as a fusible mass, which is obtained when a flux reacts with an infusible acidic or basic impurity present in the oxide ore.