Structural Understanding of MnO-SiO2-Al2O3-Ce2O3 Slag via Raman, Al-27 NMR and X-ray Photoelectron Spectroscopies

Abstract

In order to understand sulfur solubility in the MnO-SiO2-Al2O3-Ce2O3 slag or inclusion system (mol MnO/mol SiO2=M/S=2.2 or 0.9, Al2O3=14.2[1.8] mol%, Ce2O3=0-5.6 mol%), the effect of Ce3+ ions on the structure of the Mn-aluminosilicate system with different M/S molar ratios has been studied by micro-Raman spectroscopy, solid-state nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Because constant oxygen partial pressure was maintained at p(O-2)=2.8x10(-7) atm, oxidation state of Mn and Ce would be in Mn2+ and Ce3+ in the MnO-SiO2-Al2O3-Ce2O3 system, which were also confirmed by XPS analysis. Although it was difficult to measure the Al-27 solid-state NMR spectra of the quenched MnO-SiO2-Al2O3 system due to the paramagnetic effect, Al-27 NMR spectra did show structural changes in aluminate when cerium was added to the Mn-aluminosilicate melts. Addition of Ce2O3 in the high M/S(=2.2) system caused both an explosive enhancement in the intensity of Raman bands at 600 cm(-1) and a peak shift in Al-27 NMR spectra, indicating the transition from the [AlO4](-):0.5Mn(2+) tetrahedron to a [AlO6](3-):Ce3+ octahedron complex due to a strong attraction between aluminate and the cerium ion. XPS spectra show that the transition of the aluminate structure upon introduction of Ce3+ ions consumes free oxygen in Mn-aluminosilicate melts in high M/S(=2.2) system. However, the same structural changes were not observed when Ce2O3 was added to lower M/S(=0.9) system, because Ce3+ ions primarily interact with the pre-existing [AlO6]-octahedron in low M/S system.