Dephosphorization and desulfurization of hot metal by CaO based fluxes containing Fe-oxide and Mn-oxide as oxidant.

Abstract

Experiments on hot metal dephosphorization by using the mixtures of Fe-oxide and Mn-oxide as oxidant were achieved by the use of Tammann furnace. The results were analyzed by the coupled reaction model which consisted of mass transfer equations of each component. Among many unknown parameters in the model, the effective equilibrium constants of P, Mn and S and the mass transfer coefficient in slag phase were changed by the experimental condition and determined by fitting to the experimental result. The observed distribution ratio of P, S and Mn was consistent with the calculated value for each experiment and the applicability of the coupled reaction model was proved.(1) When a mixture of Fe-oxide and Mn-oxide was used as oxidant, as the ratio of FeO to the total content of Fe-oxide and Mn-oxide in flux decreased, the effective equilibrium constants of P and S and the mass transfer coefficient in slag decreased and the effective equilibrium constant of Mn increased. This result indicated that the degree of dephosphorization, desulfurization, Mn recovery and the reaction rate of these reactions increased as the increase of Fe-oxide ratio in flux.(2) The addition of CaF2 and CaCl2 did not significantly change the effective equilibrium constants but modified the mass transfer coefficient in slag. Together with the result of temperature dependence, the necessary amount of CaF2 to obtain the equivalent reaction rate for each temperature was clarified.(3) The activity coefficients of FeO, P2O5 and MnO converted from the effective equilibrium constants were compared with those values calculated by the thermodynamic models. However satisfactory agreements were not obtained especially for γMnO.