Hot metal dephosphorization slags in the BOF can be considered to be within the CaO–SiO
2–FeO–P
2O
5 system, and are usually in the dicalcium silicate (C
2S) saturated composition range. It is well known that C
2S forms a pseudo-binary solid solution with tricalcium phosphate (C
3P) 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 P
2O
5 from the liquid slag to the solid solution.
In order to clarify the mechanism of mass transfer of P
2O
5 between the solid solution and liquid slag, an artificially made C
2S–C
3P solid solution rod was dipped into the C
2S–C
3P saturated slag and the interface was observed.
When the activity of P
2O
5 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 P
2O
5 was observed in the solid solution.
When the activity of P
2O
5 in liquid slag was lower than that in solid solution, no reaction layer was formed, and P
2O
5 did not transfer to the liquid slag. In this case, P
2O
5 in the solid solution was quite stable.
The reason for these phenomena was discussed. The mass transfer of CaO and SiO
2 must occur simultaneously with the mass transfer of P
2O
5 in order to maintain the pseudo-binary relation of the solid solution.
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