Study On Migration Law Of Fluorine In The Aquitard In Zhaoyuan Country

In the North of China, fluorine is one common ion in the material of soil and rock. Fluorine can be slowly dissolved in groundwater, and this caused fluorine pollution in groundwater. Fluorine concentration has greatly exceeded the standard of drinking water in phreatic aquifer in partial areas of the Zhaoyuan country. The middle and lower Quaternary aquifers are used as objective layer for drinking to control fluorosis in the Zhaoyuan country. The continuous pumping of confined aquifer could increase the hydraulic head pressure difference between unconfined aquifer and confined aquifer and cause the leakage from the unconfined aquifer to the confined aquifer. The continuous aquitard distributed act an important role for the fluoride ion’s migration from the unconfined aquifer to the confined aquifer.This paper took the Zhaoyuan country as research area, and supported by the National Sci-Tech Support Plan "Drinking water resources protection, innovative treatment technology and demonstration in the Northeast rural area of China".By the analysis of fluorine’s vertical distribution characteristics, the basis of fluorine migration law was provided in the aquitard aquifer. By the adsorption experiments and indoor simulation experiments, the fluorine migration law in the aquitard was studied, and provides a scientific basis for the reasonable exploitation of deep confined water in the study area.The occurrence form of fluoride of vadose zone-unconfined aquifer-aquitard aquifer section indicated that the serious fluorine pollution in vadose zone in the study area. The average total fluorine content is 132 mg/kg and water soluble fluorine content is 11.8mg/kg. The concentration of water soluble fluorine in silty clay is 1.24 times higher than that of silty sand in section of vadose zone-unconfined aquifer-aquitard aquifer.The results of indoor static adsorption experiments were shown as below: the adsorption equilibrium time of silty clay is 24 hours. The adsorption amount and the concentration of fluorine affect the adsorption ability of silty clay. The maximum static absorption amount of fluorine of the silty clay in this area is 73.94mg/kg.The results of fluorine migration experiment indicated that the higher the pressure, the shorter the time of fluorine through the aquitard aquifer in the dynamic adsorption experiments. When the pressure is increasing, the interception function of aquitard aquifer is weaker. And more and more fluorine went into confined aquifer through the aquitard aquifer. The dynamic adsorption of fluorine ion is about 6mg/kg of the aquitard aquifer in the area. In the dynamic desorption experiments, the concentration of fluorine ion at the bottom of the pillar is gradually increasing, the experiment time is shorter and contact time of ultrapure water and silty clay is shorter with the increasing pressure. After the dynamic experiment, the water soluble fluorine of the silty clay in the pillar was 16.9mg/kg. The higher pressure also caused that adsorption amount in migration experiment was lower than that of the dynamic experiment.