Phosphorous partition in dephosphorization slag occurring with crystallization at initial stage of solidification

Abstract

Basicity and the amount of Fe,O 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,O= 10-20%, P2O 5=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,O content. In addition, glassy regions were observed in the two samples whose Fe,O content was 20% and whose basicity was 1.0 or 1.5. The samples (10% Fe,O, 5%P2O5), whose basicity was 1.0 (sample-1) precipitated as a monocalcium silicate (CaO·SiO2); the sample (10% Fe,O, 5% P2O 5) whose basicity was 1.5 (sample-4) precipitated as a dicalcium silicate (2CaO SiO2). In higher Fe,O (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·SiO 2 appeared with phosphorous content, but phosphorous was not found in CaO·SiO2.