盐离子对蒙脱石水化膨胀特性的影响

采用热失重法与经离心法、直接烘干法、冷冻干燥法结合对蒙脱石样品水含量进行测量，分析了NaCl浓度对蒙脱石中结合水与自由水含量的影响，探讨了蒙脱石中总含水量及结合水含量随NaCl溶液浓度变化的规律，研究了NaCl溶液中蒙脱石的水化膨胀特性及盐离子的抑制作用。结果表明，蒙脱石的水化膨胀受盐离子的抑制，盐离子的存在减小了渗透水化力，影响了水分子间的范德华力及水分子和蒙脱石表面间的氢键力和静电引力，总含水量随盐离子浓度增加而降低，盐离子浓度为0.2 mol/L时趋近最低值，样品膨胀程度由6.6缩小至1.6，盐离子对蒙脱石水化膨胀的抑制作用达峰值。盐离子浓度大于0.2 mol/L时，随盐离子浓度增加，自由水与结合水含量变化不明显。

Effects of salt ions on the hydration and expansion characteristics of montmorillonite

As an important component of natural gas hydrate reservoir, montmorillonite is of great research significance to the exploitation and application of natural gas hydrate. The inhibition of salt ions in seawater on the hydration expansion of montmorillonite has important effects on the distribution of free water and bound water in hydrate reservoirs. Water content in montmorillonite with NaCl solution was measured by thermogravimetric method combined with several pretreatment methods (the centrifugal method, the direct drying method and the freeze-dried method). The effects of salt concentration on bound water and free water content of montmorillonite were analyzed. The variations of total water content and bound water content in montmorillonite with different NaCl solution concentration were discussed. The hydration and expansion characteristics of montmorillonite and the inhibition of salt ions were studied. The results indicated that the hydration expansion of montmorillonite was inhibited by salt ions. The existence of salt ions reduced osmotic hydration force. Meanwhile, it affected the van der Waals force between water molecules, the hydrogen bonding force and the electrostatic attraction force between water molecules and the surface of montmorillonite. The total water content of montmorillonite decreased with the increase of salt ions concentration. In the same time, bound water content of montmorillonite was inverse related to the salt ions concentration, and approached the minimum when the salt ions concentration was 0.2 mol/L, as the inhibition effect of salt ions on the hydration expansion of montmorillonite reached the peak. When the ion concentration was greater than 0.2 mol/L, the content of free water and bound water did not change significantly with the increase of salt ion concentration. Therefore, the study on the influence of salt ions on hydration and expansion characteristics of montmorillonite, so as to further explore the influence of salt ions on the formation of hydrate in montmorillonite, has important guiding significance for the study of hydrate distribution characteristics in deep-sea sediments.