Water vapor adsorption on the mixtures of swelling and non-swelling clays

Comprehending water molecules adsorption mechanism on clays is crucial to hydraulic fracturing technology application in clay-rich shale formation. In this research, the adsorption of water vapor on non-swelling of kaolinite (Kaol), swelling clay of montmorillonite (Mt), and their three different mixtures (75:25/Mt:Kaol, 50:50/Mt:Kaol and 25:75/Mt:Kaol) was studied. The effect of mixing ratio of Mt and Kaol on the adsorption process of water vapor was discussed. The obtained findings display that the swelling clay of Mt possesses the greater water vapor adsorption ability than the non-swelling clay of Kaol. Enhancing the mass ratio of Mt in the mixture can obviously improve the uptake for water vapor. For Mt, primary adsorption exhibits a more apparent effect on the adsorption of water vapor adsorption. For Kaol, the effect of secondary adsorption on water vapor adsorption is more significant. With increasing mass ratio of Kaol in the mixture, the difference between secondary adsorption and primary adsorption gradually decreases. The affinity of water vapor adsorption on Mt is the biggest, followed by 75:25/Mt:Kaol, 50:50/Mt:Kaol, 25:75/Mt:Kaol, and Kaol, in sequence. Mt has the highest surface potential, and surface potential for Kaol is the lowest. There is a positive relationship between surface potential and the mass ratio of Mt in the mixture. As the pressure increases, Gibbs free energy change quickly enhances and then decreases. The reduction of adsorption spontaneity on Kaol under high pressure is more manifest. Water vapor adsorption spontaneity on clay mixture is improved by enlarging mass ratio of Mt in the mixture.