物理化学学报 >> 2006, Vol. 22 >> Issue (09): 1137-1142.doi: 10.1016/S1872-1508(06)60053-3

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水化Na-蒙脱石和Na/Mg-蒙脱石的分子动力学模拟

那平;张帆;李艳妮   

  1. 天津大学化工学院, 天津 300072
  • 收稿日期:2006-05-08 修回日期:2005-05-30 发布日期:2006-09-04
  • 通讯作者: 那平 E-mail:naping@tju.edu.cn

Molecular Dynamics Simulation of Na-montmorillonite and Na/Mg-montmorillonite Hydrates

NA Ping;ZHANG Fan;LI Yan-Ni   

  1. School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P. R. China
  • Received:2006-05-08 Revised:2005-05-30 Published:2006-09-04
  • Contact: NA Ping E-mail:naping@tju.edu.cn

摘要: 利用分子动力学方法(MD)研究了Na-蒙脱石和Na/Mg-蒙脱石层间的补偿阳离子和水分子的结构及扩散性质. 模拟结果表明, 在一定水含量范围内Na-蒙脱石和Na/Mg-蒙脱石表现出不同的膨胀形式, 特别是层间水分子数目在48~72之间时, Na/Mg-蒙脱石的层间距比Na-蒙脱石有较为明显的增大. Na/Mg-蒙脱石两层水化物的层间水分子与Mg2+形成了明显的两层水合壳; 而与Na+只形成了一层平面的水合壳. 在Na/Mg-蒙脱石中, Na+和 Mg2+的扩散方式不同, Na+的扩散范围相对更广, 自扩散系数更大. Na/Mg-蒙脱石比相同水含量下的Na-蒙脱石层间水的自扩散系数小. 由于Mg2+和Na+对层间结构的强烈影响, 从而使有少量Mg2+取代Na+的Na/Mg-蒙脱石与Na-蒙脱石表现出不同的膨胀性质和层间物质的扩散性质.

关键词: Na-蒙脱石, Na/Mg-蒙脱石, 分子动力学, 水合性质, 自扩散

Abstract: Molecular dynamics (MD) is used to investigate the structural and diffusive properties of interlayer species, namely water and counterion speciations of Na-montmorillonite and Na/Mg-montmorillonite. It is found that Na/Mg-montmorillonite exhibits a higher swellability compored with that of Na-montmorillonite for given water content, especially with 48~72 water molecules of interlayer, the expansion of layer spacings of Na/Mg-montmorillonite is greater than those of Na-montmmorillonite. Interlayer water molecules have a stronger tendency to solvate Mg2+ compared to that of Na+. Inner-sphere complexes and outer-sphere complexes of Mg2+ with water are observed, whereas only planar inner-sphere complexes of Na+ with water are found for two-layer Na/Mg-montmorillonite hydrates. The results also indicate the different diffusion modes of Na+ and Mg2+ for Na/Mg montmorillonite: Na+ remains close to the surfaces of the sheets, whereas Mg2+ is easily hydrated and is located in the middle of the interlayer. Comparatively, Na+ has a wider diffusion range and higher self-diffusion coefficient than Mg2+. Moreover, self-diffusion coefficient of interlayer water is higher for Na-montmorillonite than that for Na/Mg-montmorillonite at the same water content. Most of the results obtained in this study can be understood in terms of the strong solvation of Mg2+ with water molecules, and Mg2+ and Na+ have different influences on the structure of interlayer. It can therefore be assumed that the replacement of a relatively small amount of interlayer Na+ cations by Mg2+ in Na-montmorillonite during the initial stage can substantially change the swelling and diffusion properties of interlayer species.

Key words: Na-montmorillonite, Na/Mg-montmorillonite, Molecular dynamics, Hydration, Self-diffusion