<p>This study performed a systematic thermodynamic analysis of FeAsS oxidation roasting by calculating the standard Gibbs free energy changes (Δ_r<i>G</i>_m^θ) for 56 possible reactions at 300–1200&#xa0;K and simulating equilibrium compositions via the Reaction and Equilib modules in FactSage software. The results indicate that the pyrolysis of FeAsS is thermodynamically spontaneous. Oxidation reactions are thermodynamically more favorable than pyrolysis, with direct oxidation to Fe₃O₄/Fe₂O₃ being preferred, whereas inappropriate conditions promote the formation of arsenates and sulfates that hinder de-arsenification. Equilibrium simulations further reveal that the de-arsenification ratio initially increases and then decreases with rising oxygen content, roasting temperature, and carbon addition. Under carbon-free conditions, the optimal de-arsenification efficiency of 80% is achieved at 700&#xa0;K with an O₂/FeAsS molar ratio of 2.7. The addition of carbon at a C/O₂/FeAsS molar ratio of 13:150:50 significantly improves the de-arsenification ratio to 94.38%, as carbon facilitates the reduction of arsenates and sulfates to iron oxides and promotes the volatilization of As₄O₆(g). However, excessive carbon addition is detrimental due to competitive oxygen consumption. These findings provide a theoretical foundation for optimizing the oxidation roasting parameters of arsenopyrite, enabling efficient de-arsenification and improving gold recovery in industrial practice.</p>