Phosphorous Partition in Dephosphorization Slag Occurring with Crystallization at Initial Stage of Solidification

Abstract

Basicity and the amount of Fe_tO were investigated for their effects on the crystallization behavior of the simulated dephosphorizing slags. Twelve kinds of slags were prepared (C/S=1.0–2.5, Fe_tO=10–20%, P₂O₅=5%). In the present experiment, the Hot Thermocouple Technique was used to melt and quench the samples. After quenching, the microstructure of the slag and the distributions of elements were examined by SEM and EDS analysis.
The diameter of the crystal which precipitated in the sample increased with increasing basicity (C/S) and decreasing Fe_tO content. In addition, glassy regions were observed in the two samples whose Fe_tO content was 20% and whose basicity was 1.0 or 1.5. The samples (10% Fe_tO, 5% P₂O₅), whose basicity was 1.0 (sample-1) precipitated as a monocalcium silicate (CaO·SiO₂); the sample (10% Fe_tO, 5% P₂O₅) whose basicity was 1.5 (sample-4) precipitated as a dicalcium silicate (2CaO·SiO₂). In higher Fe_tO (15–20%) slags, the crystals of the solid solution between 3CaO·P₂O₅ and 2CaO·SiO₂ ((C₃P–C₂S)ss) were observed. When the amount of CaO increased from C/S=1.5 to C/S=2.5, 2CaO·SiO₂ appeared with phosphorous content, but phosphorous was not found in CaO·SiO₂.