Dephosphorization of Hot Metal with Injection of Lime Bearing Fluxes in a Ladle

Abstract

Experiments have been made in a 270 t transfer ladle. The reaction of dephosphorization proceeds coupled with the oxidation of manganese; the lower the manganese content in the hot metal, the higher the rate of dephosphorization. Gaseous oxygen accelerates the removal rate of manganese and retards that of phosphorus. Although from the industrial point of view, some amounts of gaseous oxygen are required to suppress the temperature drop of hot metal, it should be kept at minimum during treatment. The preferential oxidation of manganese over phosphorus is interpreted in terms of the difference of free energy change of oxidation between the two. To suppress the manganese oxidation the basicity of the slag is a key factor and should be kept higher than 3.0. In comparison with gaseous oxygen, oxide source such as ore, mill scale, etc. provides a better dephosphorization. The rates of dephosphorization and demanganization are approximated as the first order reaction and the apparent rate constants have been experimentally obtained.
The apparent rate constants for dephosphorization were compared between Q-BOP, LD, K-BOP and the present ladle injection. A comprehensive understanding has been made in terms of modified feeding rate of total oxygen.