Distribution and genetic mechanism of high arsenic geothermal water in the Batang area, Western Sichuan

Abstract

To determine the main hydrogeochemical processes affecting the migration and enrichment of arsenic in the high arsenic geothermal water in the Batang area of Sichuan Province, the hydrogeochemistry and whole rock geochemistry of groundwater and aquifer sediments were studied. The results show that the groundwater has an arsenic concentration of 3.1 to 80.8 μg L − 1, which is mainly present in the form of arsenate. The arsenic concentration in this groundwater system is correlated with the presence of fluoride ions and the temperature. The thermal storage temperature and cycling depth are significantly correlated with the arsenic concentration. The thermal storage temperature in the Batang area is relatively high (220 °C to 260 °C). When cold water mixing takes place, the temperature falls to 76.56–177.51 °C, the proportion of cold water mixing ranges from 67% to 79%, and the circulation depth reaches 1318.11 to 3443.37 m. The temperature of the groundwater, the competitive adsorption of HCO3−, and the pH level also affect the arsenic concentration. The above results indicate that the alkaline reducing environment in the Batang area of Western Sichuan is beneficial to the enrichment of arsenic in the groundwater. The desorption of the arsenic adsorbed on the surface of Fe oxide/hydroxide minerals is the main route by which arsenic enters the geothermal water. These results provide guidance for the exploitation and utilization of geothermal water in the Batang area.