Understanding Sulfur Transfer Reaction between Molten Iron and Molten Slag under Electric Field

Abstract

The steelmaking industry should refine sulfur from iron since the demand for high-quality products is growing. That’s why many researchers have investigated a possibility that applying electric field could improve the desulfurization on the basis of its electrochemical character. Even though it was confirmed that supplying electricity enhanced the desulfurization by increasing its rate or lowering final S content, it was unclear to understand the actual mechanism of S transfer and the effectiveness of the desulfurization under electric field. Therefore, in the present study, S transfer between molten iron and molten slag was investigated in terms of electrochemical nature of S transfer. C saturated molten iron including S was allowed to react with CaO-SiO2-Al2O3-MgO based slag at 1400 ℃ until the two phases arrived at chemical equilibrium. Then, by applying electric current on the phases, S content in the molten iron decreased and reached at a new equilibrium level. However, after the electricity was off, S content did not recover its chemical equilibrium. Meanwhile, applying reversed current or injecting CO gas proceeded substantial reversion of S. During the whole reaction, there were side reactions which might be coupled to the S transfer. Based on the experimental observation, the electrochemical character of the S transfer was verified and the possible reaction mechanism was presented in the present study. In order to confirm the effectiveness of desulfurization under electricity, a wide array of experiments were conducted in given conditions. Using designed kinetic interpretation, it was found that the higher electric current was flowed to the phases, the more the additional desulfurization could proceed since the S distribution was increased by the current applied. However, current efficiency for the desulfurization was low, when the current intensity was high, due to the change of the remaining S content in the molten iron. The rest of the current efficiency is thought to be consumed by other reactions or resistive heating. The S transfer seemed not to be advantageous at high experimental temperature since the slag resistance and the electric potential across the slag might decrease. High basicity slag including many free oxygen (O2-) could react with C electrode under electricity and supply electrons further to desulfurize S from the iron.