高吸力段黏土水合机制及微观持水模型研究

Hydration mechanism and microscopic water retention model of clay at high suction range

采用水汽吸附法测定3种蒙脱土在高吸力段的持水特征曲线,基于X射线衍射及BET吸附理论架构,提出了两类水合概化模型并建立了阳离子交换量、比表面积等参数的计算方法。基于极低相对湿度范围段（RH〈0.15）持水能力只受控于层间阳离子水合的机理认识,通过阳离子与水分子相互作用能量方程,推导了极高吸力下（ψ〉250 MPa）持水曲线微观参数模型。研究表明：层间阳离子水合能力的差异会导致蒙脱土吸附起始阶段呈现不同趋势,对于低水合能阳离子交换土,水分子首先吸附于黏土颗粒外表面,之后随相对湿度增加逐渐进入层间吸附,反之,则直接进入层间离子水合阶段;基于BET曲线计算的阳离子交换量、比表面积值与实测值之间吻合较好,构建的持水模型能够对文献报道数据进行有效预测,该模型可量化表征阳离子交换量、化合价、离子半价等微观参数对吸力势的影响程度。

The water retention curves of three montmorillonites are measured using the water vapor adsorption method at the high suction range. Two generalized hydration models and corresponding methods to predict the cation exchange capacity（CEC） and specific surface area（SSA） are proposed based on the XRD results and BET theory. Moreover, the microscopic water retention model at extremely high suction range（ψ〉250 MPa） is derived from interaction energy between cation and water molecule dipole given that the retention capacity is affected merely by the interlayer cation hydration when RH is below 0.15. The results show that the hydration sequence of montmorillonite depends on the hydration energy of interlayer cation. For the cation with low hydration energy, the water absorbs firstly on external surface of clay tactoids followed by absorption into interlayer. Otherwise, the water absorbs directly within interlayer space. The predicted values of CEC and SSA agree well with the measured ones, and the derived microscopic model, taking into account of the effect of CEC, cation valence and radius on the suction potential, can predict the suction value accurately upon comparison with the reported data in literatures.