Hysteresis in the Binary Exchange of Cations on 2:1 Clay Minerals: A Critical Review

Abstract

Abstract--The binary exchange of cations on clays and soils is generally regarded as a thermodynamically reversible process. The literature on soil chemistry and geochemistry, however, abounds with reports on cation exchange reactions that appear to have only limited reversibility, i.e., that exhibit hysteresis. A satisfactory explanation of this phenomenon is still lacking, even though a number of mechanisms have been advocated, e.g., charge or site heterogeneity at the surface, differential hydration of cations, dehydration of the exchanger, crystalline swelling hysteresis, and inaccessibility of sites caused by domain or quasi-crystal formation. In the present article, the relevant literature is reviewed and analyzed critically. On the basis of available evidence, it is shown that exchangeable cations can be classified into three groups, defined in such a way that hysteresis has, in the literature, generally not been observed when exchange reactions involved cations belonging to the same group, but has often been found when the reactions involved cations from different groups. Furthermore, it is argued that none of the five mechanisms mentioned can, in and of itself, account fully for the observed exchange hysteresis. A conceptual model is proposed that combines elements of these five mechanisms and is able to describe, at least qualitatively, the effects of factors such as clay type, electrolyte concentration, and extent of dehydration.

Effect of phosphate on the adsorption of Cu and Cd on natural hematite

“…the angle BAC in Fig. 5(a)) were calculated to evaluate the adsorption reversibility (Verburg and Baveye, 1994;Pan and Liss, 1998) and given in Fig. 5.…”

Adsorption of 137Cs on Montmorillonite and Illite: Effect of Charge Compensating Cation, Ionic Strength, Concentration of Cs, K and Fulvic Acid

“…Unless adsorption and desorption isotherms are compared, there is no reason to assume that nondesorbed Cs is fixed. Furthermore, even if hysteresis is detected, it may be a result of experimental techniques, as has been discussed by Verburg and Baveye (1994), and may not reflect the dynamics of Cs in a real clay system.…”

“…Tactoids axe smaller in the presence of monovalent cations and when the electrolyte concentration is low (Schramm and Kwak 1982;Barak 1989;Verburg and Baveye 1994). Therefore, increasing ionic strength increases the proportion of interlayer exchange sites in montmorillonite with the possibility of partial collapse of interlayers.…”

Measurement of Surface Area of Modified Clays by Ethylene Glycol Monoethyl Ether Method

“…The adsorbed cation replaces or exchanges the original negative layer charge balancing cation in solution. This ability of colloidal particles such as clay minerals to retain and exchange positively charged ions is vital as it has a controlling influence on the mobility of positively charged chemical species both in soils and geochemical cycling of cations in general [10]. Cation exchange capacity is normally associated with clay minerals with interlayer exchangeable cations such as smectites.…”