Adsorption ionic strength dependence

S. Goldberg, Inconsistency in the triple layer model description of ionic strength dependent boron adsorption, J. Colloid Interface Sci. 285, 509-517 (2005). 

Proton adsorption by Na+-H+ exchange is also pH- and ionic-strength dependent. There is a negligible adsorption at relatively high pH, but the adsorption suddenly increases at a given pH. This pH value decreases by increasing the electrolyte concentration. 

These three-layer silicates are characterized by permanent surface charges (due to isomorphic substitutions). Therefore the binding of cations is assumed to be caused by stoichiometric ion exchange of interlayer ions. These concepts hold well for alkaline and earth-alkaline cations their adsorption and their ionic strength dependence can be characterized by distribution coefficients derived from ion exchange theory. It has been known for some time, however, that... 

Zhang Z, Cheng L, Fenter P, Sturchio NC, Bcdzyk M, Machesky ML, Wesolowski DJ (2001) Ionic strength dependence of Zn2+ and Sr21 ion adsorption at the rutile/aqueous interface using X-ray standing waves. Preprints and Extended Abstr ACS Nat Meet, Am Chem Soc, Div Environ Chem... 

Whereas for the adsorption of strong polyelectrolytes there is a distinct salt concentration dependence, the ionic strength is much less important for weak polyelectrolytes, which are characterized by a pH-dependent charge density. The reason is that weak polyelectrolytes can adjust their degree of dissociation in order to compensate the surface charge more effectively. As a result, the substrate-adsorbate complex is virtually neutral, which renders the effect of the salt concentration relatively unimportant. Such small ionic strength dependence for weak polyelectrolytes has indeed been found, both theoretically and experimentally. ... 

Second, most membrane materials adsorb proteins. Worse, the adsorption is membrane-material specific and is dependent on concentration, pH, ionic strength, temperature, and so on. Adsorption has two consequences it changes the membrane pore size because solutes are adsorbed near and in membrane pores and it removes protein from the permeate by adsorption in addition to that removed by sieving. Porter (op. cit., p. 160) gives an illustrative table for adsorption of Cytochrome C on materials used for UF membranes, with values ranging from 1 to 25 percent. Because of the adsorption effects, membranes are characterized only when clean. Fouling has a dramatic effect on membrane retention, as is explained in its own section below. 

Adsorption on Kaolinite. For kaolinite, the polymer adsorption density is strongly dependent on the solid/liquid ratio, S/L, of the clay suspension. As S/L increases, adsorption decreases. This S/L dependence cannot be due totally to autocoagulation of the clay particles since this dependence is observed even in the absence of Ca2+ at pH 7 and at low ionic strength where auto-coagulation as measured by the Bingham yield stress is relatively weak (21). Furthermore, complete dispersion of the particles in solvent by ultra-sonication before addition of... 

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