Phosphorus Distribution between CaO-containing Slag and Carbon-saturated Iron at Hot Metal Temperatures

Abstract

In order to thermodynamically understand the dephosphorization behavior of hot metals, the equilibrium distribution of phosphorus between a solid iron strip and CaO-bearing slag was measured in the temperature from 1200°C to 1400°C as a function of slag composition, avoiding the possible violent CO evolution if carbon-saturated iron were used. The obtained result was then converted to the value for the hot metal system using available thermodynamic data of phosphorus in solid and liquid irons.
The results are summarized as follows:
1) The CaO-SiO₂-FeO system has very high dephosphorizing capacity when it is saturated with 2CaO·SiO₂.
2) The CaO-CaF₂-FeO system containing a large amount of CaO and CaF₂ has high L_p values, where L_p denotes the distribution ratio of phosphorus between slag and carbon-saturated iron.
3) When FeO content is low, the CaO-SiO₂-CaF₂-FeO system containing a large amount of CaO has very high phosphate capacity.
4) Iron oxide decreases the phosphate capacity of basic slags.
5) From the laboratory equilibration test of the CaO-bearing slags used in the practical hot-metal treatment, the partial pressure of oxygen at the slag-metal interface is estimated at 10^-1410^-15 atm, which is ten it Ines as high as that in the soda-ash treat mem. This lies between the one determined by the reaction Fe+1/2O₂= FeO and the one by C+1/2O₂=CO.