Hot metal dephosphorisation by low basicity slag in the early stage of converting process

The suitable process parameters and mechanism on dephosphorisation by low basicity slag become the key problem of the return-slag and double-slag operation (RDO) in the early stage of converting steelmaking process. The experimental results of 80 t converter steelmaking show that the dephosphorisation ratio of hot metal is high in condition that the slag basicity is 1.2–2 and the temperature of slag tapping is 1600–1700 K in the early stage. The observations on the mineralogical phase of the dephosphorisation slag suggest that C2S precipitation accompanying with phosphorous enrichment in the slag is key to increase phosphorus distribution ratio. The results of X-ray photoelectron spectroscopy show that the dephosphorisation slag contains C2S and C3P, which suggest that Ca2+ reacts with SiO44− and PO43− originated from the oxidation of hot metal to form C2S and C3P in the early stage. Furthermore, C2S and C3P could form a solid solution of C2S + C3P (R) and R + C2S in low basicity slag.