A Thermodynamic Understanding of Clay-Swelling Inhibition by Potassium Ions

X. Liu and X. Lu, Angewandte Chemie International Edition, 45, 6300-6303 (2006).

Smectites are important in geological processes and have industrial and engineering applications.1-3 They consist of negatively charged clay platelets and interlayer counterions. Water can enter the interlayer space and force the clay platelets apart, causing clay swelling.2, 4 Generally, this swelling behavior can be divided into two types: intra-crystalline swelling, with a limited amount of adsorbed water, and osmotic swelling, which involves a much larger amount of water. This unique property has resulted in numerous studies because of its direct applicability in civil and petroleum engineering.3, 5 It has been found, for instance, that K-smectites do not expand to the osmotic regime and form crystalline hydrates even in aqueous suspension.6, 7 Thus, the K+ ion can be used as a swelling inhibitor in drilling mud to prevent the well-bore collapse typically caused by the macroscopic swelling of Na-smectites.7 However, the fundamental mechanisms of the inhibition of clay swelling by K+ ions are not clear,8-10 and the striking stability of the single-layer K-hydrate cannot yet be explained.10, 11

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