地熱熱水から生成したシリカスケール中の希土類元素

概要

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As an investigation about behaviors of minor elements in geothermal system, rare earth elements (REE) in a geothermal water sample and nine siliceous deposit (silica scale) samples in Kyushu, Japan were determined by ICP-AES after the specific separation/concentration of REE. The total REE concentration in the silica scales was 7-18 ppm. The concentration factor for REE from geothermal water to silica scale was estimated to be 105-106, indicating that REE can be considerably concentrated during the formation of silica scales. From the correlation analyses between contents of major elements and REE, the uptake of REE into silica scales possibly results from cation exchange by smectite and by surface complexation with surface hydroxyl groups on hydrous iron(III) oxide (adsorption due to the formation of REE-O-Fe bond). The chondrite-normalized REE pattern for silica scale showed the light REE enrichment, suggesting that the light REE can be enriched into silica scales from geothermal water during the formation of silica scales but heavy REE have tendency to remain in geothermal water. The results of this study may be useful to elucidate the formation mechanism of ion exchange adsorption type REE deposits which is expected as a REE source in the near future.
日本地熱学会の論文