Growing Process of Crystal Precipitated in the Dephosphorization Slag and Phosphorous Partition between Crystal and Liquid

Abstract

To reduce the amount of steelmaking slag and the free CaO, it is necessary to increase the reaction efficiency of CaO. Several investigations have been carried out to clarify the reaction of solid CaO in a molten slag. The process of dissolving CaO is quite complicated, because the melting point changes in accordance with the CaO content.
In the previous study, using the Hot Thermocouple Technique (HTT), the twelve kinds of artificial dephosphorization (de-P) slag have been melted and quenched. The effects of basicity and Fe_tO content on the crystallization behavior of the de-P slag have been investigated at the initial stage of solidification.
In the present study, the growing process of the precipitated crystal until 10000 s was investigated and the change of the phosphorous distribution between the crystal and the liquid in slag was clarified. The growth of a crystal can be expressed by Johnson–Mehl type equation, while the number of crystal decreases through a coalescence of each crystal and the equation of half-life for atomic disintegration was applied to the coalescence of crystals in the initial stage of crystal growth process. Total volume of the precipitated crystal increased within the initial stage of crystal growth, on the other hand, the total volume of crystal was a constant within the later stage of crystal growth.
The Lp (5(P₂O₅)cry/(P₂O₅)liq) was obtained at different temperatures (1550°C and 1350°C). The maximum value of Lp at 1550°C was 6.5 to 9.5 in the time range from 5 s to 15 s, while the equilibrium value was 2.0 to 2.2. On the other hand, at 1350°C, the maximum Lp was 4.0 to 4.5 around 5 s and the equilibrium value was 2.6 to 3.0 which is higher than that at 1550°C.