[P]+5[FeO]+4[CaO]=4CaO.P2O5+5[Fe]+Q, if the reaction is favorable for the dephosphorization direction, it is necessary to increase the concentration of the reactants and reduce the concentration of the product, that is, 

increase CaO content (ie increase alkalinity R), 

increase the content of (FeO) in the slag,

reduce the concentration of (4CaO.P2O5) - slag discharge or increase the amount of slag, 

then see that the reaction is an exothermic reaction, 

and the reaction to lower the temperature is favorable. 

However, when the temperature is too low, the slag cannot be formed and has no fluidity. Therefore, favorable conditions for removing P are high alkalinity, high (FeO), large slag amount, and appropriate low temperature.