Towards better understanding of the phosphorus removal from hot metal with low-basicity slags, electrochemical technique incorporating MgO-stabilized zirconia was conducted to measure simultaneously the activities of FeO and P 2 O 5 within heterogeneous CaO-SiO 2 -P 2 O 5 -FeO slags. The FeO activity was fairly insensitive to the variation of Ca 3 P 2 O 8 content in solid solutions between Ca 2 SiO 4 -Ca 3 P 2 O 8 , while the P 2 O 5 activity increased with an increase in Ca 3 P 2 O 8 content. By using the present values for activities, phosphorus distribution ratios were estimated between molten slag and carbon-saturated iron. The relationship between phosphorus distribution ratio and FeO content in molten slag was consistent with the phase diagram of the pseudo-ternary CaO-(SiO 2 + P 2 O 5 )-FeO system.

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In steelmaking processes, there are incentives to reduce slag volume and CaO consumption. The key to meet these requirements is the better understanding of CaO dissolution mechanism into molten slag, which relies on the knowledge of the thermochemical properties of slags and fluxes used for dephosphorization. In this study, the liquidus compositions coexisted with solid CaO and Ca 2 SiO 4-Ca 3 P 2 O 8 solid solution simultaneously were determined in the quaternary system CaO-SiO 2-P 2 O 5-Fe x O at 1573 K. Measurements were also conducted on the Fe x O activities at temperatures between 1542 K and 1604 K by virtue of an electrochemical technique. By using the present experimental results, phosphorus distribution ratios were estimated.