Desulphurization reaction is a slag /metal reaction.

	(1)
	(2)

K is equilibrium constant of reaction 1 and  is activity coefficient of sulphur in metal.

 is called partition coefficient of sulphur or index of desulphurization. From equation 2 the best conditions for desulphurization can be derived.

• High  i.e. high activity coefficient of sulphur in metal. Carbon, silicon and phosphorus increases  which means hot metal is better for desulphurization than molten steel.
  
  
• High in slag which means highly basic slag.
  
  
• Low  in metal. Reaction 1 suggests that removal of S from hot metal is accompanied by oxygen transfer  to metal. This oxygen must be removed for efficient desulphurization.
  
  
• High temperature which leads to high K.

Desiliconization and dephosphorization

Silicon can be removed easily by oxygen and is discussed in detail in lecture 6.

Dephosphorization requires low temperature, basic slag and oxidizing conditions. Presence of silicon in hot metal impedes dephosphorization. The best conditions for dephosphroization are discussed in lecture 8.