秦皇岛牛心山高氟地下水分布特征及成因

Distribution characteristics and genesis of high-fluoride groundwater in the Niuxin Mountain,Qinhuangdao

柳江盆地北部牛心山地区存在高氟地下水,严重影响居民身体健康。本文选取牛心山地区为研究区,对其浅层地下水运用Piper三线图、Gibbs图、氯碱指数图和离子比例图等方法进行水化学特征及其形成作用分析研究,从矿物溶解与沉淀、离子交换作用角度探讨了地下水中氟的来源和富集机理。结果显示:研究区地下水离子以Ca^(2+)、Na^+和HCO_3^-为主,水体偏碱性,F-浓度超标点位于火成岩侵入边缘地带,水化学类型为Ca-(Na)-HCO_3、Ca-(SO_4)-HCO_3和Ca-(Cl)-SO_4型,高浓度的F-赋存在Ca-(Na)-HCO_3型水中,地下水水化学组分主要受岩石风化作用的影响;水文地球化学过程和地质因素控制地下水化学特征和氟化物的来源、分布;方解石、石膏溶解于地下水作为Ca^(2+)来源影响萤石的溶解与沉淀,阳离子交换作用改变地下水中指定阳离子浓度间接影响F-浓度,同时碱性环境中吸附在黏土矿物上F-被OH-取代,溶解平衡和离子交换是地下水径流中F-浓度变化的主要控制因素。

High-fluoride groundwater has been found in the Niuxin Mountain in the north Liujiang basin.The Piper,Gibbs,Alkali indices and Ion ratio diagrams were used in this study to analyze the chemical characteristics and forming mechanism of shallow groundwater in the area,and the source and enrichment of fluoride in groundwater were discussed from the perspective of mineral dissolution,precipitation and ion exchange.The results showed that the major ions include slightly alkaline Ca2＋,Na＋and HCO3-,with the hydrochemical types of Ca-（Na）-HCO3,Ca-（SO4）-HCO3 and Ca-（Cl）-SO4;high concentration of F-is present in Ca-（Na）-HCO3 type water,and the chemical composition of groundwater is mainly affected by weathering.Moreover,the chemical characteristics of groundwater and the origin and distribution of fluoride are controlled by hydrogeochemical and geological factors.Calcite and gypsum are dissolved into groundwater as Ca2＋source,affecting fluorite dissolution and precipitation.The cation exchange indirectly affects the concentration of F-by changing cations concentration in groundwater,and F-adsorbed on clay minerals is replaced by OH-in the alkaline environment.Based on the new findings,we suggest that dissolution equilibrium and ion-exchange are the major factors controlling fluoride concentration in groundwater runoff.