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,Mn0.5)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,Mn0.5)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.