Formation Mechanism of 2CaO·SiO₂ and 3CaO·P₂O₅ Solid Solution in CaO-SiO₂-Fe_tO-P₂O₅ Slags

Abstract

In this study, the formation of 2CaO·SiO₂ and 3CaO·P₂O₅ solid solution (nC₂S-C₃P) in hot metal dephosphorization process is discussed. The variations of CaO and SiO₂ mass, both in nC₂S-C₃P solid solution phase and liquid slag phase with increasing P₂O₅ mass in CaO-SiO₂-Fe_tO-P₂O₅ slags were calculated using Factsage software. CaO-SiO₂-FeO_t-P₂O₅ slag containing up to 18 % P₂O₅ was melted at 1823 K then cooled to 1673 K. The contents of CaO and SiO₂ 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 SiO₂ in the solid solution phase decreased, just opposite in the liquid slag phase, with increasing P₂O₅ content in the slags. Formation mechanism of nC₂S-C₃P solid solution in the slags was derived based on the ionic structure theory of molten slag. The SiO₄⁴⁻ in the nC₂S-C₃P solid solution can be replaced by PO₄³⁻ in the liquid phase resulting in the increasing of free Ca²⁺ and SiO₄⁴⁻ in liquid phase.