An Attempt to Correlate Electrochemical Desulfurization of Molten Iron Using CaO–Al₂O₃–MgO_sat. 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–$\hbox {Al}_{{2}}\hbox {O}_{{3}}$–$\hbox {MgO}_{\text {sat.}}$ slag at 1673 K (1400 $^\circ$C), with and without the electricity of constant current. S distribution coefficients ($L_{\text {S}}$ = (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 ($\varDelta \phi _{\text {S}}$) for the electrochemical desulfurization. It was found that applying electric current (I) increased the $L_{\text {S}}$ after the electrochemical desulfurization, which resulted in the increase of $\varDelta \phi _{\text {S}}$. A resistance, $R_{\text {DeS}} = \varDelta \phi _{\text {S}}$/I, or a specific resistivity, $\rho _{\text {DeS}} = \varDelta \phi _{\text {S}}$/(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 $R_{\text {DeS}}$ was independent of the I within the range of this investigation, decreased as (pct CaO)/(pct $\hbox {Al}_{{2}}\hbox {O}_{{3}}$) increased and was proportional to the resistance of the slag ($R_{\text {slag}}$). A favorable condition for the electrochemical desulfurization is not the same as that for the normal desulfurization condition. The $\varDelta \phi _{\text {S}}$, 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.