Properties evaluation of electric smelting furnace slag: Viscosity and sulfide capacity under different MgO and FeO content

Abstract

This study investigated the viscosity and sulfide capacity of electric smelting furnace (ESF) slag with a fixed CaO/SiO₂ mass ratio of 0.8. The sulfide capacity was determined using a gas-slag equilibrium method under a CO-CO₂-SO₂-Ar mixed atmosphere, while structural variations were analyzed through Fourier transformation infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). These techniques collectively elucidated the mechanisms by which FeO and MgO regulate slag viscosity and sulfide capacity through modifications in depolymerization behavior. The addition of MgO (6 wt.%–10 wt.%) increased the viscosity and critical temperature (T_cr) of slag. The increase in FeO content (5 wt.%–25 wt.%) also reduced slag viscosity. However, due to the phase transformation from spinel to melilite and clinopyroxene, the T_cr initially decreased before subsequently rising. Additionally, the sulfide capacity of slag increases with the addition of FeO and MgO contents. And the increase amplitude of sulfide capacity during FeO increase from 5 wt.% to 15 wt.% exceeds that observed between 15 wt.% and 25 wt.%. Complementary FTIR, Raman, and XPS spectroscopic analyses demonstrated that FeO and MgO increased free oxygen ion content while reducing the average bridging oxygen number from 2.18 to 1.63, indicating reduced polymerization degree of the slag structure. This structural depolymerization consequently enhances slag fluidity and desulfurization performance. Based on those findings, it is recommended to gradually increase the content of basic oxides, which commensurate with the extent of iron oxide reduction to sustain adequate fluidity and sulfide capacity.