長野県中房温泉産のケイ華中のヒ素 [in Japanese] Arsenic in siliceous sinters from Nakabusa Hog Springs, Nagano Prefecture [in Japanese]
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Up to 100 ppm of As was found in siliceous sinters from Nakabusa Hot Springs, despite a low As concentration (0.16 mg/l) in sinter-depositing thermal waters. In the sinters, As is strongly correlated with Ca, but not with Al, which is considered as being capable of adsorbing As. Evidently As-adsorbing sites on Al were blocked by Na and Ca ions. Excess Ca in the sinters may be present as CaCO<sub>3</sub>, as the waters are supersaturated with aragonite. CaCO<sub>3</sub> behaves as an effective collector of finely dispersed As precipitates, thus leading to the formation of As-enriched sinters. This conclusion is supported by the fact that Ca and As were dissolved simultaneously by mild acid leaching of powdered sinter samples.
Chikyukagaku 22(2), 157-161, 1988
The Geochemical Society of Japan