CHARACTERIZATION OF SILICON AND ALUMINUM SPECIES IN IRON ORES USING SOLID STATE NMR

摘要

Silicon and aluminum in iron ores, usually simplified as SiO2 and AI2O3, actuallybelong to more complicated gangue minerals such as silicates and aiuminosilicates.These minerals consist of not only well-crystallized minerals, but also disorderedones such as clay minerals. In granulation of iron ore particles, hydration anddispersion behavior of clays might play an important role. Therefore, analysis ofsilicates and aiuminosilicates is one of the important themes in iron orecharacterization. In this study, solid state NMR techniques were applied for thispurpose. This technique, a nuclide specific method, allows us to investigate the localchemical environments around targeted nuclei. (27)~AI and (29)~Si NMR spectra of fivebrands of iron ores are successfully acquired although NMR has been believed to beunsuitable to the analysis of materials containing a lot of paramagnetic ions. As theresult of comparison, these iron ores are categorized in two groups, group 1 and 2,according to the type of minerals characterized by (27)~AI and (29)~Si NMR spectra. In summary, alumina (α-AI_2O_5), 4-coodinated Al, and 5-coodinated Al are commonly observed in (27)~AI MAS NMR spectra of both groups. Another main Al species in group 1 is assigned to kaolinite (Al_2Si_2O_5(OH)_4), while that in group 2 is assigned to fluorine-bearing aiuminosilicates. From the (29)~Si MAS NMR spectra, it is found thatmain Si in group 1 mainly occurs as phyllosilicates with Q3 linkage, which is almostconsistent with the result of (27)~AI MAS NMR experiments. In group 2, the ratio of Sibelonging to tectosilicates with Q~4 tetrahedral linkage is higher than in group 1.Characterization by using other analytical methods should be also required to assign main Si components to specific minerals. Despite of the difficulties, the solid state NMR method is found to be useful to characterize Si and Al species in bulk ore samples, and to understand the feature of ores based on the gangue minerals phases.