Adsorption of hydrolyzable ions

In view of the fact that no hafnium is present in the unhydrolyzed form under any of the conditions given in Table II, the ion exchange mechanism of adsorption by glass may be disregarded. This is substantiated by the fact that a different treatment of the glass had no effect upon its adsorption capacity for hafnium. This is similar to the results of Starik and Rozovskaya who found small effects upon the adsorptivity of hydrolyzed ions caused by glass modification even when drastic treatment... 

Properties of a° (pH) curves are basic elements in the Interpretation of more complicated systems involving oxides. One of these is the adsorption of hydrolyzable ions (Cd, Al, etc.) or anions that themselves can be titrated (HPO, etc.). In sec. 3.14 some of the relevant applications will be discussed. Another application is that of mixed oxides. The systems include mechanically mixed pure oxides and mixed crystals (such as spinels and ferrites). A number of authors have studied such mixed oxides, thereby reporting the variation of the pH° as a function of the mole fraction of the solid. Sometimes linearity was found, sometimes not. No genered rules can be given. The surface composition is not necessarily identical to that of the bulk, molecules of one oxide may leach and adsorb onto the other and lateral interactions of surface groups of the two constituents affect their pK s and pK s. Mixed oxides are important for a number of technical applications (heterogeneous catalysts with special properties, components of batteries) and also occur in clay minerals, the topic of the following subsection. 

The adsorption of hydrolyzing ions Cr and Co on siUca gel was investigated [78], and speciation of mononucleus hydroxy species in the equiUbrium aqueous phase was also considered to calculate the equilibrium distribution between the soUd phase and bulk solution over the broad range of pH s. Although the different surface complexes of chromium and cobaltic assumed to form on surface sites of silica were not proved by any independent method, the fitting procedure was executed successfully, if only all the possible equilibria were accounted for in the SCMs. 

Adsorption of hydrolyzable ions takes places through various mechanisms in which hydrolysis by surface nucleophilic groups and hydrolysis by the solution itself (OH , water molecules) compete. Therefore, as long as the hydrolysis and precipitation pH is not reached, the surface is likely to behave as a ligand, leading to chemisorption through a true substitution reaction ... 

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