2:45 PM - 3:00 PM
[MIS18-04] Calcium Carbonate Scale Production and its Formation Factors in Tsubakiyama Hot Spring, Aomori Prefecture
Keywords:Hot springs, Calcium carbonate scale, Formation mechanism, Saturation index, Interfacial tension, Dissolved magnesium
Scale, a precipitated substance from dissolved constituents in geothermal water, causes clogged pipes and reduced heat exchange efficiency. In a hot spring heat extraction test in Fukaura town, Aomori Prefecture, the heat extraction efficiency decreased due to scale adhering during the use of the heat of the hot spring. Among the various scale types, calcium carbonate is a representative scale, precipitating in many places in Japan. Due to their rapid growth compared with the others, there is a strong demand for clarification of the formation factors.
Generally, the main trigger of the calcium carbonate precipitation is the degassing of carbon dioxide. Both calcite and aragonite appeared as the calcium carbonate scale. A various factors determine the quantity ratio, including the temperature and supersaturation of the hydrothermal water, as well as the major and minor constituents. This study aimed to analyze the water quality of a specific hot spring in Fukaura-machi, Aomori Prefecture, and quantify scale production, focusing on the factors influencing calcium carbonate scale formation.
The study area was an abandoned hot spring facility in Fukaura-machi, Aomori Prefecture. The source is a self-gushing hot spring near the coast, which is pumped up to 30 m above the cliff and then discharged. Carbon dioxide concentrations were measured at the source and in the drainage channel. For comparison, measurements taken at about 20 m from the drainage channel were taken as atmospheric values. The results showed that the carbon dioxide concentration at the source was clearly higher than the atmospheric value, and the fact that the source was actually firing seriously suggests that carbon dioxide was rapidly degassing. The dissolved components in the source were dominated by Cl- (15,040.0 mg/kg) and Na+ (7,898.0 mg/kg), with Mg2+ (976.0 mg/kg) Ca2+ (732.2 mg/kg) and HCO3- (971.5 mg/kg). On the other hand, scale samples were taken at a point immediately after the hot spring was pumped and discharged. Crystals were identified and their quantity ratios were quantified (X-ray diffraction: XRD). Elemental analysis (energy dispersive X-ray spectroscopy: EDS) was also carried out at arbitrary points, and the columnar crystals were confirmed to be aragonite.
Despite the saturation index indicating that calcite was highly saturated compared to aragonite, aragonite predominantly grew from the hot spring. This result suggests that the nucleation rate, governed by interfacial tension, determines the calcite/aragonite ratio of the crystals.
Generally, the main trigger of the calcium carbonate precipitation is the degassing of carbon dioxide. Both calcite and aragonite appeared as the calcium carbonate scale. A various factors determine the quantity ratio, including the temperature and supersaturation of the hydrothermal water, as well as the major and minor constituents. This study aimed to analyze the water quality of a specific hot spring in Fukaura-machi, Aomori Prefecture, and quantify scale production, focusing on the factors influencing calcium carbonate scale formation.
The study area was an abandoned hot spring facility in Fukaura-machi, Aomori Prefecture. The source is a self-gushing hot spring near the coast, which is pumped up to 30 m above the cliff and then discharged. Carbon dioxide concentrations were measured at the source and in the drainage channel. For comparison, measurements taken at about 20 m from the drainage channel were taken as atmospheric values. The results showed that the carbon dioxide concentration at the source was clearly higher than the atmospheric value, and the fact that the source was actually firing seriously suggests that carbon dioxide was rapidly degassing. The dissolved components in the source were dominated by Cl- (15,040.0 mg/kg) and Na+ (7,898.0 mg/kg), with Mg2+ (976.0 mg/kg) Ca2+ (732.2 mg/kg) and HCO3- (971.5 mg/kg). On the other hand, scale samples were taken at a point immediately after the hot spring was pumped and discharged. Crystals were identified and their quantity ratios were quantified (X-ray diffraction: XRD). Elemental analysis (energy dispersive X-ray spectroscopy: EDS) was also carried out at arbitrary points, and the columnar crystals were confirmed to be aragonite.
Despite the saturation index indicating that calcite was highly saturated compared to aragonite, aragonite predominantly grew from the hot spring. This result suggests that the nucleation rate, governed by interfacial tension, determines the calcite/aragonite ratio of the crystals.