Relationship Between Sulfide Capacity and Structure of MnO-SiO₂-Al₂O₃-Ce₂O₃ System

Sulfide capacity of the MnO-SiO₂-Al₂O₃-Ce₂O₃ system was measured at 1873 K (1600 °C), and the structural analysis was carried out using micro-Raman spectroscopy to understand the role of Ce₂O₃ in the sulfur dissolution behavior. Sulfide capacity of the basic melts (MnO/SiO₂ = 2.2(±0.14)) decreased with increasing content of Ce₂O₃ to approx. 4 mol pct, beyond which it increased. Sulfide capacity continuously decreased in the less basic system (MnO/SiO₂ = 1.0(±0.15)), whereas it was hardly affected by Ce₂O₃ in the relatively acidic composition (MnO/SiO₂ = 0.3(±0.05)). There was a significant increase in the intensity of Raman band at 600 cm⁻¹ by Ce₂O₃ addition in high MnO/SiO₂ (=2.2) system, which originated from the transition from [(Al,Mn_0.5)O₄]-tetrahedron to [(Al,Ce)O₆]-octahedron due to strong attraction between Al₂O₃ and Ce₂O₃. Combining thermodynamic and structural information, the effect of Ce₂O₃ on the sulfide capacity of Mn-aluminosilicate melts can be explained by the following factors: (1) Activity of MnO in the melts decreased by addition of Ce₂O₃; (2) Free oxygen was consumed in the structure modification from [(Al,Mn_0.5)O₄] to [(Al,Ce)O₆] unit by addition of Ce₂O₃; and 3) When the Ce³⁺ content was greater than critical value (approx. 4 mol pct) in high MnO/SiO₂ (=2.54) melts, excess Ce³⁺ and Mn²⁺ ions competitively reacted with S²⁻ ions, resulting in an increase of sulfide capacity.