Bauxite/dross addition is sometimes done in steel making units. Limitations presented by bauxite shall be kept in mind while looking for the advantages.
There’s no question that alumina keeps secondary slag fluidic. But….the question is where it comes FROM !?
Endogenous or exogenous!? That makes a very very big difference.
To understand this, lets consider the reactions involved in secondary steel making conditions.
Al + CaO => Ca+ + Al2O3
When this alumina is introduced from outside in the form of bauxite, simply it slows down the reaction in the FORWARD direction by establishing equilibirium. New/ fresh alumina formation rate will be reduced.
Then what will happen?! Ca+ generation will also be reduced as alumina (product of this reaction) is made already present. Since Ca-ions generation is reduced, de-S rate will also get reduced.
Instead, if aluminium is added into the heat, that will reduce CaO, FeO, MnO, free-O, to form alumina on the slag. This is ENDOGENOUS alumina, unlike the alumina (EXOGENOUS) introduced from outside into the slag. This alumina indeed keeps the slag fluidic, while creates conditions suitable for de-S too.
Further, bauxite may introduce some FeO also, thereby reducing de-O rate a little. When deO is incomplete, de-S efforts will become incomplete/ inefficient.
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