Tansport Of Boron In The Aquatic Environment Of The Yangbajing Geothermal Field, Tibet

Geothermal resource is a renewable energy that are rich in resource, wide-distribution, multi-use and low operation cost. Yangbajing geothermal field is the only geothermal power plant in China, the geothermal fluid from Yangbajing contains some harmful chemical constituents with higher concentrations, such as B, As and F. Wastewater discharge of the Yangbajing geothermal power plant has comparatively higher concentrations of B, As and F(up to 3.82,0.27 and 1.85 mg/L, respectively), which have caused contamination in the Zangbo River.In this paper, boron occurance, distribution and transformation in geothermal fluid, geothermal wastewater, surface water and groundwater were studied. Through the analysis of geothermal fluid, boron absorption and extraction experiment, conclusions can be drawn as following:1. The surface waters, cold groundwaters and stream waters are dominantly HCO3-Ca type water, whereas geothermal water and wastewater of the power plant are Cl-Na types. The chemical constituents of thermal groundwater from deep reservoir are different from those from shallow reservoir.2. The water quality of Zngbo River is influenced by thermal power plant and boron content charges regularly from upstream to downstream.3. The boron adsorption of Zngbo Rver sediment samples follows Langmuir isothermal adsorption model.4. The trends along the river flow for the water soluble boron and total boron in the riverbed sediments are basically the same, and the total boron content in the riverbed sediments decrease gradually along the river flow.5. The comprehensive attenuation coefficients of B in the Zangbo River and the adsorption coefficients of the relative sediments have a clear correlation, indicating that the riverbed sediment is a sink for boron from geothermal wastewater.