Zhou Jinhong, Boek Edo S, Zhu Jianxi, Lu Xiancai, Sprik Michiel, He Hongping
State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University , Nanjing 210023, China.
Langmuir. 2015 Feb 17;31(6):2008-13. doi: 10.1021/la503900h. Epub 2015 Feb 4.
The swelling behavior of clay minerals is an important issue in industrial processes and environmental applications. Mixed-layer clay minerals containing a smectite fraction, such as rectorite, are neglected even though they could swell and exist in nature widely. The hydration of rectorite has not been well comprehended even though they are meaningful to mineralogy and industry. This study combines molecular dynamics (MD) and Monte Carlo (MC) simulations to disclose the swelling behavior of rectorite and compare with montmorillonite. From grand canonical Monte Carlo (GCMC) and MD simulations, we obtain swelling curves and swelling free-energy curves of rectorite with a relative humidity of 100%. With the comparisons of swelling free-energy minima, we find that the bilayer hydrate of Na-rectorite is more thermodynamically stable than the monolayer hydrate, which is similar to Na-montmorillonite. However, the interlayer sodium ions in rectorite show an asymmetrical distribution quite different from the symmetrical distribution in montmorillonite. Because of unequal layer charges between the smectite part and illite part of retorite, sodium ions prefer to distribute close to the illite part surface.
粘土矿物的膨胀行为在工业过程和环境应用中是一个重要问题。含有蒙脱石组分的混合层粘土矿物，如累托石，尽管它们能够膨胀且在自然界广泛存在，但却被忽视了。尽管累托石的水化作用对矿物学和工业都具有重要意义，但其水化过程尚未得到很好的理解。本研究结合分子动力学（MD）和蒙特卡罗（MC）模拟来揭示累托石的膨胀行为，并与蒙脱石进行比较。通过巨正则蒙特卡罗（GCMC）和MD模拟，我们得到了相对湿度为100%时累托石的膨胀曲线和膨胀自由能曲线。通过比较膨胀自由能最小值，我们发现钠基累托石的双层水合物比单层水合物在热力学上更稳定，这与钠基蒙脱石类似。然而，累托石层间的钠离子呈现出不对称分布，这与蒙脱石中的对称分布有很大不同。由于累托石中蒙脱石部分和伊利石部分的层电荷不相等，钠离子更倾向于分布在靠近伊利石部分的表面。
