2009 Volume 49 Issue 12 Pages 1838-1844
Hot metal dephosphorization slags in the BOF can be considered to be within the CaO–SiO2–FeO–P2O5 system, and are usually in the dicalcium silicate (C2S) saturated composition range. It is well known that C2S forms a pseudo-binary solid solution with tricalcium phosphate (C3P) over a wide composition range at the dephosphorization treatment temperature. To increase the reaction efficiency of dephosphorization, it is important to increase the mass transfer rate of P2O5 from the liquid slag to the solid solution.
In order to clarify the mechanism of mass transfer of P2O5 between the solid solution and liquid slag, an artificially made C2S–C3P solid solution rod was dipped into the C2S–C3P saturated slag and the interface was observed.
When the activity of P2O5 in liquid slag was higher than that in solid solution, a reaction layer was formed at the interface, and its width increased with immersion time. A concentration gradient of P2O5 was observed in the solid solution.
When the activity of P2O5 in liquid slag was lower than that in solid solution, no reaction layer was formed, and P2O5 did not transfer to the liquid slag. In this case, P2O5 in the solid solution was quite stable.
The reason for these phenomena was discussed. The mass transfer of CaO and SiO2 must occur simultaneously with the mass transfer of P2O5 in order to maintain the pseudo-binary relation of the solid solution.