A Study on the Formation of Smectite in Silica Scales Precipitated from Geothermal Water: The Effect of Magnesium |
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| Authors: | Yoshinobu Aramaki Takushi Yokoyama Yoshihiro Okaue Akira Imai Koichiro Watanabe |
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| Institution: | Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812–8581, Japan [e-mail: ];Department of Chemistry, Faculty of Science, Kyushu University, Ropponmatsu, Chuo-ku, Fukuoka 810–8560, Japan |
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| Abstract: | Abstract. Silica scales containing large amounts of smectite were recently found in the pipelines for geothermal water at a geothermal power plant. To elucidate the mechanism of smectite formation, seven silica scale samples were characterized by powder X-ray diffraction, chemical analysis and 27A1 MAS NMR. Smectite was present in samples with MgO levels above 10 wt% and Al2O3 levels below 10 wt%. In 27A1 MAS NMR spectra, peaks assigned to both tetrahedrally and octahedrally coordinated aluminum (Al(4) and Al(6)) were observed for Mg-rich samples, whereas a peak due to Al(4) alone appeared in Mg-poor samples. From these observation and comparison between 27A1 MAS NMR spectra for synthesized precipitates of Al2O3-SiO2 containing MgO and not containing MgO, it is concluded that magnesium plays an important role in the stabilization of Al(6), and results in the formation of smectite |
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| Keywords: | silica scale smectite 27A1 MAS NMR |
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