Phosphorus and Manganese Distribution between Carbon-saturated Iron and Na₂O-SiO₂ Melts and Nitrogen Solubility in the Melts

Abstract

The phosphorus and manganese distribution between Na₂O-SiO₂ melts and carbon-saturated iron and the solubility of nitrogen in these melts were measured at hot metal temperatures by chemical equilibration. Phosphorus distribution increases and manganese distribution decreases with increasing Na₂O content in the slag. The Na₂O-SiO₂-PO_2.5 system was found to have very large phosphate capacities ranging from 10^26.7 to 10²⁹ at 1200°C. The activity coefficient of FeO in the Na₂O-SiO₂ system ranged from 0.2 to 1.0. The partial pressure of oxygen at the slag-metal interface was estimated to be 10^-17.2 atm at 1200°C from the equilibration test of soda-slag used in the commercial hot metal treatment. Temperature dependences of phosphorus and manganese distribution are expressed as follows:
log(%P)/[%P]=20200/T-10.9, log(%Mn)/[%Mn]=6070/T-2.74.
Nitrogen was found to dissolve into Na₂O-SiO₂ melts as CN^- from the dependence of solubility on the nitrogen partial pressure when graphite coexists, as expressed by the following reaction:
1/2N₂+3/2C+1/2O^2-=CN^-+1/2CO.
The solubility of nitrogen increased with raising temperature and the Na₂O content in melts.