THE RATE OF HOT METAL DESULFURIZATION BY NA2O-CAO FLUX

Study was made on the effect of Na2O content and phosphorus content of hot metal on the desulfurization rate by Na2O-CaO mixed flux at 1623K under argon gas atmosphere. In the case of high phosphorus content of hot metal, the optimum Na2O content was observed. Na2O may act not on ly as a desulfurization material but also as a oxidizer at slag-metal interface by decomposition reaction. The optimum Na2O content appeared as a compromise between oxygen activity and sulfide capacity. Higher degree of desulfurization was obtained when hot metal of higher phosph orus content was treated. This result was ascribed to lowered oxygen a ctivity at slag-metal interface caused by reduction of Na2O activity a nd suppression of Na2O decomposition by P2O5, formed by dephosphorizat ion reaction. The highest degree of desulfurization could be achieved by Na2O-SiO2 flux, and this result support the mechanism described abo ve. Through the experiment, large amount of unknown sulfur was observe d and the rate of unknown sulfur increased with increase in Na2O conte nt in flux. To reveal this reaction mechanism, coupled reaction model calculation was performed. Although no evidence of gas formation at sl ag-metal interface could be obtained directly from this analysis, ther mo-dynamic considerations suggested the possibility of SO2 gas formati on reaction in slag bulk phase.