An Attempt to Correlate Electrochemical Desulfurization of Molten Iron Using CaO–Al2O3–MgOsat. Molten Slag and Applied Electricity at 1673 K (1400 °C)

Abstract

Desulfurization of molten iron by molten slag is an electrochemical reaction. Previous investigations confirmed that applying electricity could enhance the desulfurization of molten iron, but a quantitative relation between the electricity and the desulfurization was not fully elucidated. The present study attempted to correlate the extent of the electrochemical desulfurization with the applied electricity via a series of high-temperature desulfurization experiments and thermodynamic analyses. A molten iron containing C and S was allowed to react with CaO-Al2O3-MgOsat: slag at 1673 K (1400 degrees C), with and without the electricity of constant current. S distribution coefficients (L-S =(pct S)/[pct S]) were obtained after the normal and the electrochemical equilibria, respectively. The obtained results were interpreted by employing the Nernst equation in order to extract the potential difference (Delta phi(S)) for the electrochemical desulfurization. It was found that applying electric current (I) increased the L-S after the electrochemical desulfurization, which resulted in the increase of Delta phi(S). A resistance, R-DeS = Delta phi(S)/I, or a specific resistivity, rho(DeS) = Delta phi(S)(I/A), where A is the cathodic area, for the electrochemical desulfurization was defined, which can be used to characterize the susceptibility to the electrochemical desulfurization. It was found that R-DeS was independent of the I within the range of this investigation, decreased as (pct CaO)/(pct Al2O3) increased and was proportional to the resistance of the slag (R-slag). A favorable condition for the electrochemical desulfurization is not the same as that for the normal desulfurization condition. The Delta phi(S), which is an indicator of the extent of electrochemical desulfurization, was independently predicted by employing a thermodynamic model for the oxysulfide slag. The model prediction was in a good agreement with the experimental data. The model was used to predict necessary current level for a desired electrochemical desulfurization.