Interaction of water and organic compounds with clay as determined from heat of immersion and heat of adsorption
Abstract
Four different measurements were made with different homoionic montmorillonites, namely, the heat of immersion of the montmorillonite in water, the amount of each of several organic compounds adsorbed by the montmorillonite, the heat of adsorption of each of these compounds, and the c-axis spacing of the montmorillonite layers at different water contents. It was found that the heat of immersion, Q, decreased monotonously to zero for Li-montmorillonite; whereas, a negative (endothermic) minimum was observed for Na- and K-montmorillonite. After this minimum, it rose to a positive maximum and thereafter fell gradually to zero. When a minimum occurred, its characteristics were related to the nature of the observed jump in the c-axis spacing at the corresponding water content. Hence, the minimum was produced as a result of the energy consumed by this jump. The overall conclusion derived from the respective relations between Q and the initial water content was that the surfaces of the montmorillonite layers influence the adjacent water to a distance at least 7.5 nm. It was found that, in general, the adsorption isotherms for l,4-dioxane, urea, ethanol, and phenol on the montmorillonite were linear. This finding, when used in conjunction with the Gibbs' adsorption theory, established the fact that these compounds were distributed proportionally between an interfacial phase and the bulk phase and were not bonded to the surfaces of the montmorillonite layers. It was observed that acetate ions were negatively adsorbed by Li-, Na-, K- and Ca-montmorillonite. When the adsorption data were used to plot, V$\sb{\rm ex}$ the exclusion volume, for these ions versus b/$\kappa$, where b is a constant depending on the type of electrolyte and $\kappa$ is the Debye-Huckel parameter, a linear relation, identical to that found earlier for chloride ions, was obtained with each homoionic montmorillonite. This coincide indicated that the negative adsorption of anions is nonspecific. Theoretical analysis of the relation between V$\sb{\rm ex}$ and b/$\kappa$ showed that the thickness of the Stern layer is of the order of 0.3 nm.
Degree
Ph.D.
Advisors
Low, Purdue University.
Subject Area
Agronomy
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