滨海地区饮水型氟中毒和海水入侵十分普遍。 海水入侵引起地下水性质的改变对岩(土)氟迁移具有潜在影响, 但尚未有直接模拟实验证实, 其氟迁移机理也不明确。 用淡水和海(卤)水混合及配制溶液模拟海水入侵过程, 对含水砂层沉积物进行静态水-岩(土)氟迁移模拟实验, 对比分析沉积物FTIR特征, 探讨海水入侵对岩(土)氟迁移影响规律及机理。 结果表明, 含水砂层沉积物氟迁移量大小顺序为: 海水>1∶1淡海>淡水; 卤水>1∶1淡卤>淡水, 随海(卤)水混入程度增加, 含水砂层沉积物岩(土)氟迁移能力增强。 氟迁移能力随NaCl和NaHCO₃浓度增加而增加, 随CaCl₂浓度增加而降低。 对含水砂层沉积物傅里叶红外吸收光谱(FTIR)分析表明, 随NaCl和NaHCO₃浓度增加, NaCl溶液中沉积物Si—O—Si键伸缩振动峰强度明显增强, 氟磷灰石弯曲振动峰减弱, O—H键特征峰变化不明显, 而NaHCO₃溶液中沉积物羟基磷灰石弯曲振动峰和Si—O—Si键伸缩振动峰强度变化不明显, O—H键特征峰强度变化明显, 表明NaHCO₃溶液主要通过OH^-与F^-离子交换, 而NaCl溶液是通过Si—O—Si键中Si—O置换来影响岩(土)氟迁移。 随CaCl₂浓度增加, Si—O—Si键伸缩振动峰强度明显减弱, 氟磷灰石弯曲振动峰强度增强, 表明Ca²⁺强烈地抑制岩(土)氟析出。 同时, 随NaCl和NaHCO₃浓度增加和CaCl₂浓度减少, Si—F特征峰强度减弱, Si—O—Si键弯曲振动峰向低波数偏移。 由于大气CO₂混入, 1 mol·L^-1 CaCl₂作用沉积物出现1 460和1 420 cm^-1碳酸根特征峰。 由于碳酸根沉积作用, 1 mol·L^-1的NaHCO₃作用的沉积物在1 460 cm^-1处峰强度增强, 且在875 cm^-1出现新峰, 但是在淡海卤水和NaCl溶液作用的沉积物中无碳酸根特征峰, 表明含水砂层中无萤石(CaF₂)溶解作用。 海水入侵引起的偏碱性、 高钠低钙的环境促进岩(土)氟迁移释放, 是滨海地区高氟地下水重要动力。

Drinking-water fluorosis and seawater intrusion are common phenomena along coastal zones. The groundwater property variation evoked by seawater intrusion has the potential effect on fluorine transformation of rock (soil), but it lacks the direct simulation experiments, and the mechanism of fluorine transformation is still unclear. The static simulation experiments of fluorine transformation of sediments in the aquifers were performed by simulating the seawater intrusion process with the mixture of fresh water, seawater, brine water and laboratory solutions, and the FTIR spectrum of sediments was compared. By this way, the laws and mechanism of the effect of seawater intrusion on rock (soil) fluorine transformation are expected to be detected. The results are gained as follows: the orders of the fluorine transformation ability are: seawater>1∶1 fresh water and seawater>fresh water, and brine water>1∶1 fresh water and brine water>fresh water. The more fluorine in rock(soil) transforms with the more mixture of seawater or brine water. The sediments show higher ability of fluorine transformation with the higher levels of NaCl and NaHCO₃, and with the lower levels of CaCl₂. The intensity of Si—O—Si stretching vibration peak increases, that of bending vibration of fluorapatite decreases, and that of O—H adsorption peak doesn’t change with the higher levels of NaCl, but the opposite case occurs with the higher levels of NaHCO₃, which indicates the fluorine migration mainly by the OH^--F^- exchange in NaHCO₃ solution and instead by Si substitution of Si—O—Si bond in NaCl solution. The intensity of Si—O—Si stretching vibration peaks is weakened and that of fluorapatite bending vibration increases with the higher levels of CaCl₂, indicating that Ca²⁺ can restrain the rock(soil) fluorine transformation. Meanwhile, the intensity of Si-F bending variation peak decreases and Si—O bending variation peak moves towards the low wavenumber with the increase of NaCl and NaHCO₃ concentrations and the decrease of CaCl₂ concentration. The 1 460 and 1 420 cm^-1 CO32- absorption peaks occur when the sediment interacts with 1 mol·L^-1 CaCl₂ because of the CO₂ mixture. The sediment has the higher intensity of 1 460 cm^-1 absorption peak and the new 875 cm^-1 absorption peak when interacting with 1 mol·L^-1 NaHCO₃. But the sediment has no CO32- absorption peaks when interacting with seawater, brine water and NaCl solution. These facts indicates no fluorite (CaF₂) dissolution. Thus, the alkaline, high Na⁺ and low Ca²⁺ conditions due to seawater intrusion lead to the high fluorine-leaching ability of rock(soil), which should be the important dynamics of high-fluorine groundwater along coastal zones.