Prediction Model of Sulfide Capacity for CaO-FeO-Fe₂O₃-Al₂O₃-P₂O₅ Slags in a Large Variation Range of Oxygen Potential Based on the Ion and Molecule Coexistence Theory

A thermodynamic model for predicting sulfide capacity \( C_{{{\text{S}}^{2 -}}} \) of CaO-FeO-Fe₂O₃-Al₂O₃-P₂O₅ slags in a large variation range of oxygen potential \( p_{{{\text{O}}_{ 2}}} \) corresponding to mass percentage of Fe _t O from 1.88 to 55.50 pct, i.e., IMCT-\( C_{{{\text{S}}^{2 -}}} \) model, has been developed by coupling with the deduced desulfurization mechanism of the slags based on the ion and molecule coexistence theory (IMCT). The developed IMCT-\( C_{{{\text{S}}^{2 -}}} \) model has been verified through comparing the determined sulfide capacity \( C_{{{\text{S}}^{ 2-} , {\text{ determined}}}} \) after Ban-ya et al.[20] with the calculated \( C_{{{\text{S}}^{ 2-} , {\text{ calculated}}}}^{\text{IMCT}} \) by the developed IMCT-\( C_{{{\text{S}}^{2 -}}} \) model and the calculated \( C_{{{\text{S}}^{ 2-} , {\text{ calculated}}}}^{i} \) by the reported sulfide capacity \( C_{{{\text{S}}^{2 -}}} \) models such as the KTH model. Mass percentage of Fe _t O as 6.75 pct corresponding to the mass action concentration \( N_{{{\text{Fe}}_{t} {\text{O}}}} \) of Fe _t O as 0.0637 or oxygen partial \( p_{{{\text{O}}_{2} }} \) as 2.27 × 10⁻⁶ Pa is the criterion for distinguishing reducing and oxidizing zones for the slags. Sulfide capacity \( C_{{{\text{S}}^{2 - } }} \) of the slags in reducing zone is controlled by reaction ability of CaO regardless of slag oxidization ability. However, sulfide capacity \( C_{{{\text{S}}^{2 - } }} \) of the slags in oxidizing zone shows an obvious increase tendency with the increasing of slag oxidization ability. Sulfide capacity \( C_{{{\text{S}}^{2 - } }} \) of the slags in reducing zone keeps almost constant with variation of the simplified complex basicity (pct CaO)/((pct Al₂O₃) + (pct P₂O₅)), or optical basicity, or the mass action concentration ratios of N _FeO/N _CaO, \( N_{{{\text{Fe}}_{ 2} {\text{O}}_{ 3} }} /N_{\text{CaO}} \), \( N_{{{\text{FeO}} \cdot {\text{Fe}}_{2} {\text{O}}_{3} }} /N_{\text{CaO}} \), and \( N_{{{\text{Fe}}_{t} {\text{O}}}} /N_{\text{CaO}} \). Sulfide capacity \( C_{{{\text{S}}^{2 - } }} \) of the slags in oxidizing zone shows an obvious increase with the increasing of the simplified complex basicity (pct CaO)/((pct Al₂O₃) + (pct P₂O₅)) or optical basicity, or the aforementioned mass action concentration ratios. Thus, the aforementioned mass action concentration ratios and the corresponding mass percentage ratios of various iron oxides to basic oxide CaO are recommended to represent the comprehensive effect of various iron oxides and basic oxide CaO on sulfide capacity \( C_{{{\text{S}}^{2 - } }} \) of the slags.