The nitrogen reaction between carbon saturated Iron and Na2O-SiO2 Slag: Part 1. Thermodynamics

Abstract

The nitrogen partition ratio between Na2O-SiO2 slags and carbon saturated iron was measured for slags containing from 0.4 to 0.55 mole fraction of Na2O and the temperature range 1200° to 1350 °C. The nitrogen is dissolved in the slag as the cyanide ion (CN−) and the partition ratio is proportional to the oxygen pressure to the −1/4 power as predicted for CN− dissolution. The oxygen pressure for carbon saturated iron silicon alloys is controlled by the Si (metal)-SiO2 (slag) equilibrium. The nitrogen partition ratio and the cyanide capacity increase with Na2O content and temperature. Calculations indicate that Na2O-SiO2 slags will absorb three times more nitrogen than CaO-Al2O3 slags at the same basicity and temperature. Based on thermodynamic calculations it is estimated that for a typical Na2CO3 hot metal treatment, half of the nitrogen in the metal could possibly be removed.