Kaolin surface chemistry

Although kaolin can be regarded as chemically inert it does have a complicated surface chemistry. Hydroxyl ions either from the gibbsite layer or from adsorbed gels readily react with commercial bifunctional silanes [17],titanates or other coupling agents [18]. 

Six surfactants/cosolvents were selected for the evaluation program on the basis of (a) solution chemistry, (b) proven ability to desorb/solubilize PAHs from soil particle surfaces in previous studies, (c) human health and environmental protection, and (d) compatibility with in situ electrochemical remediation technique. The chosen surfactants/cosolvents were (a) 3% Igepal CA-720, (b) 5% Igepal CA-720, (c) 5% Triton X-100, (d) 3% Tween 80, (e) 40% ethanol, and (f) a mixture of 40% ethanol and 5% Igepal CA-720. Two clayey soils, kaolin and glacial till, were selected for the study. Kaolin consists mainly of kaoUnite clay mineral, while glacial till consists of a combination of different soil minerals including quartz, feldspar, carbonates, iUite, chlorite, vermiculite, and trace amounts of smectite. 

Moisture content should be controlled to be as low as possible, bearing in mind the surface area and chemistry of the filler. Low surface area fillers with hydrophobic surfaces will naturally maintain a low moisture content once dried. High surface area fillers with hydrophilic surfaces, such as precipitated silica, will regain moisture from the atmosphere rapidly and relatively high levels of moisture (5-7%) are unavoidable. Other minerals such as kaolin are also sensitive to moisture regain, but to more acceptable levels of moisture (0.5-2.0%). Total absence of moisture, however, should be avoided as water plays a subtle role in many crosslinking reactions. 

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