Electrochemical desulfurization of molten steel with molten slag: Reaction rate and current efficiency

It has been known that desulfurization of a molten steel using a molten slag can be enhanced by applying an electric field across the slag. In order to evaluate feasibility of the electrochemical desulfurization, a series of experiments were carried out using a high temperature reaction furnace under controlled electricity (constant current). A C-saturated molten steel including S was allowed to react with CaO-SiO2-Al2O3-MgO slags under various conditions: different currents (0, 0.05, 0.1, and 0.2 A) and reaction temperatures (1400, 1500, and 1600°C). Obtained experimental results were analyzed by employing kinetic rate equations including the Nernst-Planck equation. It was found that applying electric field enhanced the electrochemical desulfurization, both in final S content in the steel and in reaction rate. However, current efficiency for the desulfurization gradually decreased, due to deficient of S remained for the desulfurization in the molten steel. Electrochemical desulfurization under constant current was found to be effective at lower temperature, contrary to the normal desulfurization without the electric field. It is attributed to a fact that increasing temperature lowers resistivity of the slag, subsequently lowering electric potential difference exerted across the slag. Therefore, increasing reaction temperature would decrease the current efficiency for the electrochemical desulfurization, in terms of reaction rate and final extent of desulfurization.