Effect of Ce2O3 on the sulfide capacity and structure of MnO-SiO2-Al2O3 system

Abstract

Sulfide capacity of the MnO-SiO2-Al2O3-Ce2O3 system was measured at 1873 K and the structural analysis was also carried out using micro-Raman spectroscopy to understand the role of Ce2O3 in the sulfur dissolution behavior in the present system. Not only from the predominance diagram of the Ce-O-S system but also from the XPS analysis of the glass samples, it was confirmed that Ce3+ is more stable than Ce4+. The sulfide capacity of the melts with basic composition, i.e. MnO/SiO2 (mole ratio)=2.54, decreases with increasing content of Ce2O3 to approx. 4mol%, beyond which it increases. The sulfide capacity continuously decreases as the Ce2O3 is added in the less basic system (MnO/SiO2=0.85), whereas it is hardly affected by Ce2O3 in the relatively acidic composition (MnO/SiO2=0.28). There was a significant increase in the intensity of Raman band at 600 cm-1 by Ce2O3 addition in the high MnO/SiO2 (=2.54) 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 the Mn-aluminosilicate melts can be explained by the following factors. 1) the activity of MnO in the melts decreased by addition of Ce2O3; 2) the free oxygen was consumed in the structure modification from [(Al,Mn0.5)O4] to [(Al,Ce)O6]-unit by addition of Ce2O3; 3) when the Ce3+ content was greater than critical value (~4mol%) in the high MnO/SiO2(=2.54) melts, excess Ce3+ and Mn2+ ions competitively reacted with S2- ions, resulting in an increase of sulfide capacity.