College of Resources and Environment & Chongqing Key Laboratory of Soil Multi-scale Interfacial Process, Southwest University, Chongqing 400715, China.
Phys Chem Chem Phys. 2019 Jan 23;21(4):1963-1971. doi: 10.1039/c8cp07567k.
Clay swelling occurs frequently and is closely relevant to a number of engineering and industrial processes, while the underlying mechanisms remain elusive. In this study, K+-bearing clay systems with different charge amounts and charge locations have been simulated by molecular dynamics, showing that swelling is unfavorable for lower charge amounts (1.00 and 1.25 e uc-1) while it relies on charge locations for higher charge amounts (1.50 and 1.75 e uc-1): inhibited when tetrahedrally charged and favored when octahedrally charged. Accordingly, K+ shows dual characteristics and is not always a swelling inhibitor as generally thought. The various influencing factors are inspected and only the hydration effect interprets satisfactorily the swelling behaviors for all K+-bearing clay systems. The critical role of hydration effect during clay swelling is corroborated by the results of residence time, distribution of interlayer water and divergent swelling behaviors from Na+-bearing clay systems. Although water participates in a wide spectrum of physical and chemical processes, hydration is not necessarily among the most important influencing factors. Hydration effect has been evidenced as critical for clay swelling, and the results provide new insights into unraveling the complex swelling processes and resolving the associated engineering and industrial problems.
黏土的膨胀现象时有发生，与许多工程和工业过程密切相关，但其背后的机制仍难以捉摸。本研究通过分子动力学模拟了具有不同荷质比和荷质位置的含钾黏土系统，表明膨胀对于较低的荷质比（1.00 和 1.25 e uc-1）不利，而对于较高的荷质比（1.50 和 1.75 e uc-1）则取决于荷质位置：四面体荷质比时受抑制，八面体荷质比时受促进。因此，钾并不总是像通常认为的那样是膨胀抑制剂，具有双重特性。研究了各种影响因素，只有水合作用能够很好地解释所有含钾黏土系统的膨胀行为。水合作用在黏土膨胀过程中的关键作用得到了居留时间、层间水分布和与含钠黏土系统不同的膨胀行为的结果的证实。尽管水参与了广泛的物理和化学过程，但水合作用不一定是最重要的影响因素之一。水合作用对黏土的膨胀起着至关重要的作用，研究结果为揭示复杂的膨胀过程和解决相关的工程和工业问题提供了新的见解。
