The interaction between bentonite and water vapor

  • Die Interaktion zwischen Bentonit und Wasserdampf

Heuser, Michel; Stanjek, Helge (Thesis advisor); Diedel, Ralf (Thesis advisor)

Aachen (2018)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2018

Abstract

The influence of water vapor on bentonites or smectites, respectively, is of interest in many different fields of applied mineralogy like nuclear waste sealing or casting in foundry industry. The water vapor affects the smectite surface and perhaps its structure, which leads probably to achange of its properties in a mostly unfavorable way. Therefore, the influence of hot water vapor (200 ℃) on the physico-chemical, mineralogical, and electrokinetic parameters and properties of smectite-group minerals has been studied. After the steam treatment, turbidity measurements, methylene blue sorption, water adsorption, and cation exchange capacity were measured on both untreated and treated samples. Mineralogical changes were checked by X-ray diffraction (XRD), X-ray photon spectroscopy (XPS) was done on O, Al, and Si, respectively. Only few parameters showed differences between vapor-treated and raw samples. The measurement of sedimentation volumes (SV) resulted in a decreased SV after the treatment. As shown by XRD and XPS, the crystalline structure of smectite remained unaffected by the steam treatment. Equivalent sphere diameters (ESD) were not systematically affected by the steam treatment. Differences in cation exchange capacity (CEC) between unprocessed and treated samples were observed, but only for smectites with monovalent interlayer cations. From the variety of different measurements and its results, the conclusion is that due to thesteam treatment the charge properties at or near the particle surface of smectite change. While most of physico-chemical and mineralogical properties remained unaffected by watervapor, electrokinetic, rheological, and surface properties react due to exposure of smectite to hotwater vapor. The first physico-chemical and mineralogical experiments suggested that monovalent smectitesoffered changes after steaming, whereas the divalent smectites remained unaffected. This statement is partially true in terms of the experiments of this work. As well the magnitude of the dynamic mobility and isoconductive point, as viscosity and shearstress, derived from electrokinetics and conductometric titrations, potentiometric titrations andrheological measurements react due to the exposure of smectite to water vapor. However, not only the sodium smectites how edchanges comparing unprocessed and vapor treated samples - also the calcium smectite offered almost differences. The comparison of dynamic mobility of this work with electrokinetic potentials of sulfated polystyrene particles, obtained from streaming potentials in plugs (Lyklema & Minor, 1998), indicates a modification of the surface conductance of the smectite particles due to the steam treatment. The idea of a surface charge modification of the smectite due to the exposure to hot watervapor was confirmed by the experiments and its results of this work. Furthermore, the author speculates about a dissolution process of amorphous silica from the rough smectite surface, which was indicated by the determination of fractal dimension and the measurement of silicon. This process would influence the diffuse double layer and hence, electrokinetic parameters, like dynamic mobility and surface conductance. After all performed experiments and calculated parameters a clear statement about the interaction of bentonite or smectite with water vapor is finally only conditionally available. However, a lot of ideas and potential declarations were given, resulting in the assumption, that water vapor or steam affects the surface structure and its charge conditions of the smectite particles.

Institutions

  • Division of Earth Sciences and Geography [530000]
  • Petrology and Fluid Processes Teaching and Research Unit [541320]

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