Formation Mechanism of 2CaO·SiO_2 and 3CaO·P_2O_5 Solid Solution in CaO-SiO_2-Fe_tO-P_2O_5 Slags

摘要

In this study, the formation of 2CaO·SiO_2 and 3CaO·P_2O_5 solid solution (nC_2S-C_3P) in hot metal dephosphorization process is discussed. The variations of CaO and SiO_2 mass, both in nC_2S-C_3P solid solution phase and liquid slag phase with increasing P_2O_5 mass in CaO-SiO_2-Fe_tO-P_2O_5 slags were calculated using Factsage software. CaO-SiO_2-FeO_t-P_2O_5 slag containing up to 18% P_2O_5 was melted at 1823 K then cooled to 1673 K. The contents of CaO and SiO_2 both in the solid solution phase and liquid slag phase of quenched samples were observed and analyzed by SEM/EDS. Both the calculated and experimental results show that the contents of CaO and SiO_2 in the solid solution phase decreased, just opposite in the liquid slag phase, with increasing P_2O_5 content in the slags. Formation mechanism of nC_2S-C_3P solid solution in the slags was derived based on the ionic structure theory of molten slag. The SiO_4~(4-) in the nC_2S-C_3P solid solution can be replaced by PO_4~(3-) in the liquid phase resulting in the increasing of free Ca~(2+) and SiO_4~(4-) in liquid phase.