Cationic Effect of Ferrous Ions on Sulfide Capacity of CaO-Fe_tO-Al₂O₃-SiO₂ Slag System

The cationic effect of ferrous ions on the sulfide capacity of CaO-Fe_tO-Al₂O₃-SiO₂ slags was studied from the viewpoint of the ionic structure in the slag using micro-Raman spectroscopy. In the cation-excess region (M²⁺/2(Fe³⁺ + Al³⁺) > 1.0), the sulfide capacity was directly proportional to the basicity of the slags, owing to the S²⁻ stabilizing effect of excess cations. However, in the cation-deficient region (M²⁺/2(Fe³⁺ + Al³⁺) < 1.0), the sulfide capacity was independent of the basicity of the slags owing to the deficiency of cations required for charge compensation with Al³⁺ and Fe³⁺. The cation-substitution effect on the sulfide capacity of the CaO-rich slags (Fe_tO/(Fe_tO + CaO < 0.5) exhibited a linear relationship with the Fe²⁺ content because Fe²⁺ had a stronger affinity with S²⁻ compared to that with Ca²⁺. However, in the Fe_tO-rich slags (Fe_tO/(Fe_tO + CaO > 0.5), the sulfide capacity decreased with the increase of the Fe²⁺ content owing to the Qⁿ unit affinity of the Fe²⁺ ion. The sulfide capacity was determined by the competition between the Qⁿ unit affinity and stability of the S²⁻ ion, depending on the type of cation. Therefore, the partial covalent bonding between the M²⁺ cations (M: Ca, Fe) and aluminosilicate affected the ionic interactions with the S²⁻ ions.