Experimental study on phosphorus distribution between CaO–FeO*–SiO₂–P₂O₅(15%)–CaF₂ slag and carbon-saturated hot metal at 1573⋅15 K

Abstract

The traditional slag/metal equilibrium technique cannot be applied to the direct measurement of the distribution of phosphorus between slag and carbon-saturated hot metal for slag with higher iron oxide contents. In this paper, the indirect measurement approach was used, i.e. to measure the distribution ratio of phosphorus between slag and solid iron and then to obtain the ratio between slag and carbon-saturated hot metal through conversion, and the dephosporisation capacity of CaO–FeO*–SiO₂–P₂O₅(15%)–CaF₂ systems at 1573⋅15 K (1300°C) was investigated. In the mean time, the techniques of scanning electronic microscope, energy spectrum analysis and X-ray diffraction were applied to study the form of phosphorus presence in the dephosphorisation slag. The results demonstrated that (i) the phosphorus distribution ratio decreases with an increase in (FeO*) at higher basicity of about 7⋅0, (ii) when the CaO/SiO₂ ratio is bigger than 3⋅76, the phosphorus distribution ratio decreases with an increase in the CaO/SiO₂ ratio, (iii) higher phosphorus absorption capacities can be ensured by reasonably decreasing CaO/SiO₂ at higher (FeO*), (iv) the phosphorus-containing phases are liquid slag and Ca₅(PO₄)₃F and the range of phosphorus content in these two phases are 2⋅45–4⋅25% and 22⋅99–27⋅16%, respectively.

Keywords:

• High phosphorus content hot metal
• Dephosphorisation pretreatment
• Phosphorus distribution
• Phosphorus presence forms

Acknowledgements

This work was in the frame of a research project financed by the Ministry of Science and Technology, China. The authors wish to thank Dr Wu Jie and Mr Wen Zhi-jun of the R&D Institute, Wuhan Iron and Steel Corporation (Group) for their help in providing test materials, conducting microscopic analysis and valuable discussions.