DEPHOSPHORIZATION AND DESULFURIZATION PRETREATMENT OF MOLTEN IRON WITH CAO-SIO2-CAF2-FEO-NA2O SLAGS

The present work estimated the ability for the removal of phosphorus a nd sulfur from hot metal with CaO-SiO2-CaF2 fluxes which contain 20 ma ss% CaF2 and [mass% CaO/mass%SiO2]=4. Silicon losses were also determi ned along the treatment. Some additions of FeO (4 to 8 mass%) and Na2O (1 to 6 mass%) were used to change the oxygen potential of the molten iron. The experiments were carried out in an open 10 kg induction fur nace using Al2O3 refractory in the temperature range 1350-1 400 degree s C. The oxygen potentials of the melt, continuously measured with a h igh temperature galvanic cell, were between 10(-13.4) atm (before the treatment) and 10(-12.0) atm (after the treatment). FeO and Na2O conte nts in the slag directly affect the oxidation of the alloy elements of the liquid iron. With high silicon contents in the hot metal (0.6%) t he maximum removal of silicon was about 80% whereas the maximum phosph orus and sulfur removal were about 14 and 90%, respectively. By low si licon contents (0.16%) the maximum removal of silicon, phosphorus and sulfur were 80, 40 and 95%, respectively. A thermodynamic analysis was carried out to predict the final composition of the hot metal and the species that were formed in the slag. Both results, calculated and ex perimental, show that sulfur and silicon were diminished in the melt i n a higher extent than phosphorus and manganese. The species in the sl ag predicted by the model are in agreement with the X-ray analysis of the slag.