Ma Xiong-Ying, Xia Zhao, Su Chen-Xi, Cheng Yin, Yu Hao, Kang Xin
Research Center for Advanced Underground Space Technologies of Hunan University, Changsha 410082, China.
Key Laboratory of Building Safety and Energy Efficiency of the Ministry of Education, Hunan University, Changsha 410082, China.
Langmuir. 2023 Oct 17;39(41):14500-14510. doi: 10.1021/acs.langmuir.3c01394. Epub 2023 Oct 4.
Diffusion of pollutants in the earth's strata threatens both the environment and human health. The clay soil microstructure that plays a crucial role in the diffusion of pollutants is significantly influenced by the pore water chemistry. However, there is still a lack of quantitative evaluation of pore water chemistry on clay fabric evolution. To bring new insights, we systematically examined the impact of water chemistry (mainly refers to salt ion concentration and pH) on the self-assembly form (fabric) of kaolin platelets and evaluated the fabric quantitatively. The results show that as the salt ion concentration increases, the "kaolin book" structure is formed, which can be captured by the (001) and (020) pole figures. Under acidic conditions, kaolin platelets turn randomly arranged; however, with the increase of pH, the edge-to-face (EF) microstructure of kaolin platelets gradually changes to a face-to-face (FF) structure. Under alkali-eq conditions, kaolin platelets form a dispersion assembly dominated by FF repulsion. However, the strong alkaline condition triggers the decomposition of kaolin, leading to a notable decrease in the maximum pole density. The conclusions were substantiated through insightful AFM tests. Moreover, we addressed the advantages and limitations of 1DXRD and 2DXRD by analyzing the trend between the OI and pole density, with 2DXRD being favored for its accuracy. Overall, this study provides insights into clay platelets and the self-assembly of kaolin under different water chemistry conditions, which have significant implications for predicting and modeling the physical properties of clay under special environmental conditions.
污染物在地球地层中的扩散威胁着环境和人类健康。在污染物扩散中起关键作用的黏土土壤微观结构受孔隙水化学性质的显著影响。然而，目前仍缺乏对孔隙水化学性质对黏土结构演化的定量评估。为了提供新的见解，我们系统地研究了水化学性质（主要指盐离子浓度和pH值）对高岭土片层自组装形式（结构）的影响，并对结构进行了定量评估。结果表明，随着盐离子浓度的增加，会形成“高岭土书”结构，这可以通过（001）和（020）极图来捕捉。在酸性条件下，高岭土片层呈随机排列；然而，随着pH值的升高，高岭土片层的边对面（EF）微观结构逐渐转变为面对面（FF）结构。在碱当量条件下，高岭土片层形成以FF排斥为主导的分散组装。然而，强碱性条件会引发高岭土的分解，导致最大极密度显著降低。这些结论通过有见地的原子力显微镜测试得到了证实。此外，我们通过分析取向指数（OI）和极密度之间的趋势，阐述了一维X射线衍射（1DXRD）和二维X射线衍射（2DXRD）的优缺点，二维X射线衍射因其准确性而更受青睐。总体而言，本研究深入了解了不同水化学条件下黏土片层和高岭土的自组装，这对于预测和模拟特殊环境条件下黏土的物理性质具有重要意义。
