Effect of Oxygen Potential on Simultaneous Dephosphorization and Desulfurization of Hot Metal by Injecting CaO Base Flux

Abstract

Plant scale experiments have been carried out to dephosphorize and desulfurize hot metal with injecting pulverized CaO base flux in a charging ladle (100t). It has been reveraled from oxygen potential, PO₂, measured by oxygen probes that dephosphorization takes place near lance nozzles where P>O₂ is kept high (=10^-1410^-13 atm), whereas desulfurization at the top slag/hot metal boundary where PO₂ is made lower (_??_10^-15 atm).
The injection treatment which forms the above distribution of PO₂>in hot metal can provide the separation of reaction sites for dephosphorization and desulfurization. Thus, the simultaneous removal of phosphorus and sulfur is possible in one step operation.
Phosphate capacity of the CaO base slag with CaO/SiO₂ of 2.5 has been evaluated as 10^26.5 at 1 200-1 300°C. Since the value of PO₂near the lance nozzles has been measured as 10^-1410^-13 atm, the calculated phosphorus destribution ratio between ascending slag particles and hot metal increases up to ca. 10⁴. This high value is sufficient to dephosphorize hot metal.
Rate of dephosphorization by the slag particles has been studied. The rate-determining step has been shown to be phosphorus transfer in the slag particles at the early stage and halfway of the treatment and in the hot metal boundary layer at the last stage. Observed decrease of phosphorus content in hot metal has agreed well with calculated one.