Negative Adsorption in Clay-Water Systems with Interacting Double Layers

Abstract

Abstract--A relation was derived which describes negative adsorption (salt exclusion) in systems in which double layer interaction takes place but where the surface potential remains finite, such as in clay pastes and sediments. Exclusion volumes calculated for montmorillonite pastes in equilibrium with 1:1 type electrolytes were found to compare favorably with data obtained by F. A. M. de Haan in an earlier study.

Transfer Processes in Cohesive Sediment Systems

“…There is no absolute definition of a dry clay and a wide variety of drying temperatures has been used, ego 350°C for 16 hrs (Posner and Quirk, 1964), 100°C over a water bath (Helmy et al, 1980), air temperature (Bower and Goertzen, 1955). Our dry clays were dried by heating them to constant weight at 60°C.…”

Extended Version of Gouy-Chapman Electrostatic Theory as Applied to the Exchange Behavior of Clay in Natural Waters

“…Despite much progress (e.g., Bolt, 1955aBolt, , 1979Bolt and Warkentin, 1958;de Haan, 1965, 1979;Edwards and Quirk, 1962;Helmy et al, 1980;Schofield, 1949), electrostatic models are not yet either sufficiently well developed or tested to describe clay-elecCopyright 9 1983, The Clay Minerals Society trolyte solutions. For example, homovalent selectivity coefficients are not close to unity for many clays in a wide variety of mixed electrolyte solutions (Bruggenweft and Kamphorst, 1979) in contradiction to GouyChapman theory where ions are described as point charges (Joshi and Parsons, 1961;Bolt, 1979;Sposito, 1981).…”

Negative adsorption of phosphate by plant roots

“…Both these ion distribution models assume that there is a uniform distribution of indiffusable anions. Donnan's model assumes that charge is uniformly distributed throughout the micellar volume, and GouyChapman's model assumes that charge is uniformly distributed over a plane, or interacting planes (Helmy et al 1980), or spheres (Van Den HuI1982). Neither Received 15 November 1982;revision 18 July 1983 of these conditions are likely to be met in charged surfaces of plant root cell walls, but the gross effects of anion exclusion and the valence and salt effects common to both models should be expressed in cell wall-external solution systems at equilibrium.…”

“…These measurements involve the accurate determinations of concentrations of the external medium unaffected by the surface charge, and of the solution adjacent to the surface exhibiting anion exclusion. In studies on clay minerals this has been done by using homo-ionic preparations (Bolt & Warkentin 1958;Helmy et al 1980), although this may cause some disruption of the mineral (Bolt & Warkentin 1956).…”