Phosphorus Separation from Steelmaking Slag by High Temperature Reduction with Mechanical Stirring

Abstract

The effects of temperature (1473–1873K) and slag composition (CaO/SiO₂=1.2–4.0) on reduction of (Fe_xO) and (P₂O₅) in steelmaking slag by carbon with mechanical stirring were investigated in laboratory-scale experiments. The results were summarized as follows.
1) The reduction ratios of (Fe_xO) and (P₂O₅) in steelmaking slag obtained in this research were 0–98% and 3–98%, respectively. These values were highly dependent on both slag basicity and the reduction temperature.
2) (P₂O₅) was reduced by carbon and concentrated in iron, which was obtained by reduction of (Fe_xO). Higher reduction ratios of (P₂O₅) exceeding 50% were obtained under the condition that the activity of (Fe_xO) in the slag was less than 0.01. The (P₂O₅) reduction ratio decreased as the equilibrium phosphorus partition ratio between slag and metal calculated by slag composition and temperature increased.
3) From the phosphorus mass balance before and after experiments, 1–29 mass% of unidentified phosphorus was confirmed. The ratio of unidentified phosphorus increased as the equilibrium P₂ gas partial pressure calculated with an equation for the gaseous dephosphorization reaction increased. The mechanism of (P₂O₅) reduction in steelmaking slag was discussed based on the results of phosphorus distribution and observation of the reduced slag by EPMA analysis.