Probing Adsorption of Divalent Cations on Kaolinite Clay Surfaces by Atomic Force Microscopy

• Author / Creator

  Jing Chang

• Kaolinite is one of the most commonly-used clay minerals in the production of paper, plastics, and ceramics, etc. However, kaolinite is also a hard-to-remove mineral in the processing of valuable minerals or energy resources, such as bauxite, metal sulphide ores, and oil sands. The main problem stems from the stability of the micron-to-nanosized kaolinite particle suspension, which is dominated by the colloidal interactions between the charged kaolinite particles. To provide clear insights into the colloidal behaviour of kaolinite that governs its vast applications in lab research and industry, the surface charging properties of kaolinite particles and interactions of kaolinite with divalent cations were studied using atomic force microscope (AFM).
  The two-layer kaolinite (Al2Si2O54) has three kinds of external surfaces: a siloxane (SiOSi) basal plane, an aluminium oxy-hydroxyl basal plane, and edge surfaces. To obtain different kaolinite basal planes, kaolinite suspensions with particle sizes of 1 ~ 2 μm were prepared and deposited on clean glass and sapphire substrates using a fast heating process. To expose the edge surfaces of kaolinite particles, ultramicrotome cutting technique was applied to cut a resin block with kaolinite particles sandwiched in the middle.
  The interaction forces between AFM tips and different kaolinite surfaces were measured in 10 mM KCl solutions with varying concentrations of Ca2+ and Mg2+ at different pHs. The measured interaction forces were fitted with the classical DLVO theory to derive the Stern potentials of various types of kaolinite surfaces. Distinct responses in the measured Stern potentials of the two basal planes to divalent cations at pH 8 and 11 implied different binding mechanisms of the studied divalent cations at clay-solution interfaces, which were further explored by atomic resolution imaging. The change of the surface patterns of kaolinite basal planes was observed due to the specific adsorption of divalent cations at high pH.
  The three different surfaces of kaolinite were shown to form six possible inter-particle associations in a kaolinite suspension. The interaction energies for these six kinds of associations were calculated using the Stern potentials determined from the AFM force measurements. Based on the calculation, the rheological behaviour and the settling test results of kaolinite suspension were scientifically interpreted.
  The findings in this dissertation provide fundamental understanding on the adsorption of divalent cations at the clay-solution interfaces. The techniques used in this study might open opportunities for more extensive explorations of features on material surfaces at atomic level.

• Subjects / Keywords

  • Kaolinite

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-14g7-6c23

• License

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