Meleshyn Artur, Bunnenberg Claus
Center for Radiation Protection and Radioecology (ZSR), University of Hannover, Herrenhäuser Strasse 2, 30419 Hannover, Germany.
J Chem Phys. 2005 Aug 15;123(7):074706. doi: 10.1063/1.2011392.
While the swelling behavior of laboratory-prepared homoionic montmorillonites has been studied extensively in numerous experimental and simulation works, far less attention has been given to much more abundant natural montmorillonites, containing a mix of monovalent and/or bivalent cations in interlayer spaces. We carried out a series of Monte Carlo simulations in order to investigate the reasons for the remarkable difference of experimental swelling patterns of a natural Na-rich/Mg-poor montmorillonite and a homoionic Na-montmorillonite. The simulations reproduced the swelling pattern of a natural montmorillonite, suggesting a mechanism of its hydration different from that of the homoionic montmorillonite. We also found that the differences in size and hydration energy of Mg2+ and Na+ ions have strong implications for the structure and the internal energy of interlayer water. This leads to a difference in the layer spacings of the simulated Mg- and Na-montmorillonites as large as approximately 2.1 A at lower water contents.
虽然在众多实验和模拟研究中已对实验室制备的纯离子蒙脱石的膨胀行为进行了广泛研究，但对于层间含有一价和/或二价阳离子混合物的更为丰富的天然蒙脱石，关注却少得多。我们进行了一系列蒙特卡洛模拟，以探究天然富钠/贫镁蒙脱石和纯离子钠蒙脱石实验膨胀模式存在显著差异的原因。模拟结果再现了天然蒙脱石的膨胀模式，表明其水化机制与纯离子蒙脱石不同。我们还发现，Mg2+和Na+离子在大小和水化能方面的差异对层间水的结构和内能有很大影响。这导致在较低含水量下，模拟的镁蒙脱石和钠蒙脱石的层间距差异高达约2.1埃。
