The name is absent

Chapter 4

It is not known which sites are responsible. The pH in oil sands operation process
is around 8.5. At this pH, the basal surface of kaolinite is negatively-charged,
while the edge surface of kaolinite is likely positively-charged.

Surface charge is important to kaolinite wettability. Takamura et al. found the
carboxyl groups in bitumen can dissociate and form negatively charged sites on
bitumen/ water interface ^[6]. The positively-charged edges of the kaolinite may
adsorb negatively charged carboxylate components (i.e. naphthenates) of the oil
and make that portion of clay solids partially oil-wet. The partially oil-wet clay
solids can retard water-in-oil emulsion coalescence. They also entrap oil drops
and form aggregates, which results in a rag layer in the middle of the sample.

If negatively charged carboxylate components can be replaced by other
anions or can react with some cations, the surface of the solids can be made
more hydrophilic. In this case, some of the adsorbed oil on the solid surface may
be replaced by water, allowing the solid to settle to the bottom.

In clay wettability study, kaolinite is chosen as the model clay because it is a
major ingredient of the clay solids and has heterogeneous wettability. Sodium
naphthenate is used to modify kaolinite to be partially oil-wet. Different chemicals
are applied to change the wettability of kaolinite from partially oil-wet to more
water-wet.

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