High resolution solid-state NMR studies on dissolution and alteration of Na-montmorillonite under highly alkaline conditions
High resolution solid-state NMR studies on dissolution and alteration of Na-montmorillonite under highly alkaline conditions
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DOI：
10.1016/j.micromeso.2007.03.008
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发表时间：
2007-11
影响因子：
5.2
通讯作者：
Takafumi Takahashi;T. Ohkubo;Kensuke Suzuki;Y. Ikeda
中科院分区：
文献类型：
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作者：
Takafumi Takahashi;T. Ohkubo;Kensuke Suzuki;Y. Ikeda
用高分辨固体27 Al/29 Si MAS和27 Al 3Q MAS NMR研究了钠基蒙脱石在强碱性条件下的溶解和蚀变。通过在高碱性Ca（OH）2溶液（0.01M：M=moldm-3）中处理Na-mon 1周至3个月，制备了6个改变的样品。未蚀变和蚀变样品的3Q MAS NMR谱表明存在一个八面体Al位（AlVI）和两个四面体Al位（AlaIV，AlbIV）。AlaIV和AlbIV位分别归属于Q3（3Si）和Q4（4Si）单元。根据X射线粉末衍射图和27 Al MAS NMR谱，将蚀变样品中的AlbIV矿归属于方沸石的形成。平均各向同性化学位移和四极产物在碱处理前后保持不变。AlaIV/AlVI的比值表明四面体Al比八面体Al更容易溶解。29 Si MAS NMR谱表明，Na-mon的四面体结构主要由Q3（0Al）和Q3（1Al）单元组成，碱蚀不影响Na-mon的键角（Si-O-Si）和键长（Si-Si）.此外，高碱处理前后，Q3（0Al）和Q3（1Al）位的29 Si NMR峰的半高宽（FWHMs）基本不变。这些结果表明，四面体硅周围的配位结构没有很大的改变，由碱处理。
Dissolution and alteration of Na-montmorillonite (Na-mon) under highly alkaline conditions have been studied by high resolution solid state27Al/29Si MAS and27Al 3Q MAS NMR. Six altered samples were prepared by treating Na-mon in a highly alkaline Ca(OH)2solution (0.01M: M=moldm−3) from 1week to 3months. The 3Q MAS NMR spectra of non-altered and altered samples indicated the existence of one octahedral Al site (AlVI) and two tetrahedral Al sites (AlaIV,AlbIV). The AlaIVand AlbIVsites were assigned to Q3(3Si) and Q4(4Si) units, respectively. The AlbIVsite of altered samples was ascribed to formation of analcime on the basis of powder X-ray diffraction patterns and27Al MAS NMR spectra. The average isotropic chemical shifts and the quadrupolar products remained constant before and after the alkaline treatment. The ratio of AlaIV/AlVIindicated that the tetrahedral Al is more easily dissolved than the octahedral one. Therefore, we proposed a model that octahedral sites of Na-mon are exposed due to partial removal of external tetrahedral sites.29Si MAS NMR spectra showed that tetrahedral sheets of the Na-mon mainly consist of Q3(0Al) and Q3(1Al) units, and that the estimated bond angles (Si–O–Si) and bond lengths (Si–Si) are not affected by alkaline alteration. Furthermore, the full widths at half-maximum (FWHMs) of29Si NMR peaks corresponding to Q3(0Al) and Q3(1Al) sites were constant before and after the highly alkaline treatment. These results suggest that the coordination structure around tetrahedral Si is not largely changed by the alkaline treatment.