Title

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

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

Authorship

Takahashi, Takafumi; Kanehashi, Koji; Fujioka., Yuji

Takahashi, Takafumi

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Kanehashi, Koji

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Fujioka., Yuji

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DOI

10.5151/2594-357X-22213

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Abstract

Silicon and aluminum in iron ores, usually simplified as SiO2 and Al2O3, actually belong to more complicated gangue minerals such as silicates and aluminosilicates. These minerals consist of not only well-crystallized minerals, but also disordered ones such as clay minerals. In granulation of iron ore particles, hydration and dispersion behavior of clays might play an important role. Therefore, analysis of silicates and aluminosilicates is one of the important themes in iron ore characterization. In this study, solid state NMR techniques were applied for this purpose. This technique, a nuclide specific method, allows us to investigate the local chemical environments around targeted nuclei. 27Al and 29Si NMR spectra of five brands of iron ores are successfully acquired although NMR has been believed to be unsuitable to the analysis of materials containing a lot of paramagnetic ions. As the result of comparison, these iron ores are categorized in two groups, group 1 and 2, according to the type of minerals characterized by 27Al and 29Si NMR spectra. In summary, alumina (α-Al2O3), 4-coodinated Al, and 5-coodinated Al are commonly observed in 27Al MAS NMR spectra of both groups. Another main Al species in group 1 is assigned to kaolinite (Al2Si2O5(OH)4), while that in group 2 is assigned to fluorine-bearing aluminosilicates. From the 29Si MAS NMR spectra, it is found that main Si in group 1 mainly occurs as phyllosilicates with Q3 linkage, which is almost consistent with the result of 27Al MAS NMR experiments. In group 2, the ratio of Si belonging to tectosilicates with Q4 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.

Silicon and aluminum in iron ores, usually simplified as SiO2 and Al2O3, actually belong to more complicated gangue minerals such as silicates and aluminosilicates. These minerals consist of not only well-crystallized minerals, but also disordered ones such as clay minerals. In granulation of iron ore particles, hydration and dispersion behavior of clays might play an important role. Therefore, analysis of silicates and aluminosilicates is one of the important themes in iron ore characterization. In this study, solid state NMR techniques were applied for this purpose. This technique, a nuclide specific method, allows us to investigate the local chemical environments around targeted nuclei. 27Al and 29Si NMR spectra of five brands of iron ores are successfully acquired although NMR has been believed to be unsuitable to the analysis of materials containing a lot of paramagnetic ions. As the result of comparison, these iron ores are categorized in two groups, group 1 and 2, according to the type of minerals characterized by 27Al and 29Si NMR spectra. In summary, alumina (α-Al2O3), 4-coodinated Al, and 5-coodinated Al are commonly observed in 27Al MAS NMR spectra of both groups. Another main Al species in group 1 is assigned to kaolinite (Al2Si2O5(OH)4), while that in group 2 is assigned to fluorine-bearing aluminosilicates. From the 29Si MAS NMR spectra, it is found that main Si in group 1 mainly occurs as phyllosilicates with Q3 linkage, which is almost consistent with the result of 27Al MAS NMR experiments. In group 2, the ratio of Si belonging to tectosilicates with Q4 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.

Keywords

Aluminum; Silicon; Solid state NMR.

Aluminum; Silicon; Solid state NMR.