| Abstract |
To elucidate the formation mechanism of smectite contained in silica scale formed in the pipeline at geothermal power plants, seven silica scale samples were characterized by chemical analysis, powder X-ray diffraction, and 27Al MAS NMR. Smectite was present in silica scale samples whose magnesium content was higher than 10 % as MgO, and aluminium content was lower than ca. 10 % as Al2O3. The peak assigned to 6-coordinated Al was observed in the 27Al MAS NMR spectra for magnesium-rich samples, while, no peak due to 6-coordinated Al appeared in magnesium-poor samples. From the comparison between the 27Al MAS NMR spectra for synthesized precipitates of Al2O3 and Al2O3-MgO, the half-width of peak for 6-coordinated Al of the Al2O3-MgO was narrower than that of Al2O3, suggesting that magnesium may stabilize the octahedral sheet (AlO6) in smectite. |