2019 Volume 105 Issue 6 Pages 610-618
In order to clarify the effect of the lime dissolution rate in slag on hot metal dephosphorization, a 150 kg scale hot metal dephosphorization experiment was carried out. The rate of decrease of free CaO and the dephosphorization rate were measured while varying the ratio of the CaO and SiO2 which was denoted as basicity.
The dephosphorization rate showed its maximum value at basicity of around 1.0. At basicity higher than 1.0, the dephosphorization rate decreased due to poor dissolution of CaO in the flux.
A thermodynamic calculation revealed that crystallization of 2CaO·SiO2 (-3CaO·P2O5) in the liquid slag deteriorated lime dissolution when basicity was higher than 1.5.
The mass transfer coefficient of CaO in slag was calculated assuming that the interface between the lime and liquid slag is saturated with CaO. High basicity showed a low mass transfer coefficient.
The apparent slag viscosity was calculated in terms of the solid phase, and correlated with the CaO diffusion rate. The CaO diffusion rate in slag decreased with higher values of not only liquid slag viscosity, but also solid-liquid coexistent slag viscosity. These results suggest the existence of an optimum basicity exists for effective CaO dissolution.