The adsorption characteristics and mechanism of montmorillonite with different layer charge density for alkyl ammonium with different carbon chain length

Abstract

The adsorption dynamic and thermodynamic characteristics of Na-Montmorillonite (Na-MT) with two different layer charge density for four types of alkyl ammonium with diverse carbon chain length were systematically studied. The result of adsorption dynamics shows that the adsorption process of Na-MT for alkyl ammonium follows the quasi-second-order dynamics equation; with the increase of layer charge density or carbon chain length of alkyl ammonium, the adsorption reaction rate of Na-MT for alkyl ammonium gradually increases; the adsorption reaction rate of Na-MT for alkyl ammonium at a low amount of added modifier is significantly higher than that at a high amount. The result of adsorption thermodynamics indicates that the adsorption process of Na-MT for alkyl ammonium is an exothermic reaction, and the adsorption efficiency of Na-MT for alkyl ammonium decreases with the decrease of layer charge density or carbon chain length of alkyl ammonium. The change in the entropy of adsorption reaction ΔS showes a decreasing trend after the first increase when the amount of added alkyl ammonium increases; at the same amount of added alkyl ammonium, the increase of temperature contributes to the spontaneous adsorption of Na-MT for alkyl ammonium, and the strength of the spontaneous adsorption process is negatively correlated with the carbon chain length and the amount of added alkyl ammonium. The research result of this study provides a theoretical basis for the application of the adsorption of montmorillonite for alkylammonium in industry.