Influence mechanism of direct current electric field on the sulfur removal of fluorine-containing spent refining slag

Abstract

To promote the recycling of spent refining slag effectively, the effect of direct current (DC) voltage (0–4 V) on sulfur migration, structure and properties of CaO-SiO2-Al2O3-MgO-F-S slag with 4–7 wt% F was investigated at in present study. It was concluded that with the increase of voltage, the slag network structure depolymerized, the melting temperature decreased, and the sulfur removal rate increased. Thereinto, the highest mobility of sulfur removal, which was up to 85%, was achieved when the voltage was 4 V with the slag containing 5 wt% F. The coupled electrochemical mechanism of sulfur migration was reflected by the comprehensive effect of cathodic and anodic reactions. In the slag, Ca2+ and Mg2+ undergone cathode reaction, some of which generated gas overflow and some migrated to molten steel, while the [SiO4]4- cathodic reaction had less influence on electrochemical balance. To maintain electrical neutrality, S2- in the slag underwent anodic reaction and migrated to the molten steel, while CO generated by the anodic reaction at slag-metal interface led to large size gas holes. However, the loss of electrons of Fe2+ and Fe3+ caused negative electrons to accumulate at the slag-metal interface, which formed the charge resistance of sulfur migration. Collectively, as voltage increased in the range of 0–4 V, the electric field force enhanced, diffusion resistance depleted and charge resistance aggregated, resulting in an overall increase in sulfur migration from spent refining slag to molten steel.