The hot metal pre-desiliconization technology was developed based on the hot metal pre-dephosphorization technology. 

Since the affinity of oxygen and silicon in molten iron is larger than that of phosphorus, when deoxidizing by adding oxidant, silicon is preferentially oxidized than phosphorus, and the formed SiO2 greatly reduces the alkalinity of the slag. 

For this purpose, the silicon content must be reduced to less than 0.15% before dephosphorization. 

This value is much lower than the silicon content of the blast furnace molten iron. 

That is to say, only when the silicon in the molten iron is mostly oxidized, the phosphorus can be rapidly oxidized and removed. 

Therefore, it is necessary to remove silicon before dephosphorization.