Transformation of halloysite and kaolinite into beidellite under hydrothermal condition
Transformation of halloysite and kaolinite into beidellite under hydrothermal condition
复制标题
水热条件下埃洛石和高岭石向贝得石的转化
DOI：
10.2138/am-2017-5935
复制
发表时间：
2017-05-01
影响因子：
3.1
通讯作者：
Dong, Hailiang
中科院分区：
文献类型：
--
作者：
He, Hongping;Ji, Shichao;Dong, Hailiang
摘要了解粘土矿物的转化过程，对于揭示地质和环境过程，以及更好地理解层状硅酸盐的独特结构和性质具有重要意义。到目前为止，已经确定了两种途径，即，2：1型粘土矿物之间的转化（例如，蒙脱石的伊利石化）和从2：1型到1：1型（例如，蒙脱石的高岭土化）。然而，1：1至2：1型转化不常见。在这项研究中，进行了水热实验，以探讨1：1型粘土矿物（即，埃洛石和高岭石）成2：1的（即，贝得石）。采用XRD、TG、FTIR、27 Al和29 Si MAS NMR、HRTEM等手段对产物进行了表征。热液产物的XRD图谱显示蒙脱石族矿物的特征基间距在1.2-1.3 nm，埃洛石和高岭石的（001）反射显著减少/消失。这与HRTEM观察结果一致，其中在所有热液产物中观察到厚度为1.2-1.4 nm的粘土层，并且通过EDS分析测定的Si/Al比接近贝得石的Si/Al比。在乙二醇化后，基底间距增加到约1.70 nm，显示出所得矿物的溶胀能力。在转化过程中，前体矿物中表面OH的消耗导致脱羟基的质量损失急剧减少，并且前体矿物中良好分辨的OH伸缩振动合并为约1。3667 cm−1，这是贝得石的指示。结果表明，在水热条件下，埃洛石和高岭石都可以转化为2：1的贝得石，且埃洛石比高岭石更容易转化。这种1：1粘土矿物向2：1粘土矿物的转化可能是自然界中粘土矿物转化的一种新途径。同时，在新形成的贝得石中发现了Al 3+对Si 4+的替代，表明新形成的Si-O四面体片的化学组成不同于从前体粘土矿物继承的化学组成。这很好地解释了混层层状硅酸盐中“极性层”的形成。这些发现对于更好地理解粘土矿物之间的转化和混层层状硅酸盐的独特结构具有重要意义。
Abstract Understanding clay mineral transformation is of fundamental importance to unraveling geological and environmental processes and to better understanding the unique structure and property of phyllosilicates. To date, two pathways have been identified, i.e., the transformation among 2:1 type clay minerals (e.g., illitization of smectite) and from 2:1 type to 1:1 type (e.g., kaolinization of smectite). However, the transformation of 1:1 to 2:1 type is less commonly observed. In this study, hydrothermal experiments were conducted to investigate the possibility of the transformation of 1:1 type clay minerals (i.e., halloysite and kaolinite) into 2:1 ones (i.e., beidellite). The obtained products were characterized by XRD, TG, FTIR, 27Al and 29Si MAS NMR, and HRTEM. XRD patterns of the hydrothermal products display characteristic basal spacing of smectite group minerals at 1.2–1.3 nm with dramatic decrease/disappearance of the (001) reflection of halloysite and kaolinite. This is consistent with HRTEM observations, in which clay layers with a thickness of 1.2–1.4 nm are observed in all hydrothermal products and the Si/Al ratio determined by EDS analysis is close to that of beidellite. The basal spacing increases to ∼1.70 nm upon ethylene glycolation, displaying swelling ability of the resultant minerals. The consumption of surface OH in precursor minerals during the transformation leads to a dramatic decrease of mass loss of dehydroxylation and merging of the well resolved OH stretching vibrations in precursor minerals into one at ca. 3667 cm−1, which is indicative of beidellite. These results demonstrate that both halloysite and kaolinite can be converted to 2:1 beidellite under hydrothermal condition, and the transformation of halloysite is easier than that of kaolinite. Such transformation of 1:1 clay minerals to 2:1 ones could be a new pathway for the transformation of clay minerals in nature. Meanwhile, the substitution of Al3+ for Si4+ is found in all newly formed beidellite, suggesting the chemical composition of the newly formed Si-O tetrahedral sheet is different from the one inherited from the precursor clay minerals. This can well explain the formation of “polar layer” in mixed-layer phyllosilicates. These findings are of high importance for better understanding the transformation among clay minerals and unique structure of mixed-layer phyllosilicates.