Sorpcioni procesi na graničnoj površini koloidnog silicijumdioksida

Abstract

Colloidal silica, the production of which has been patented all over the world, has a remarkable application in over a hundred different industrial branches. Laboratory process, which can serve as a basis for an industrial production of this important material, has been developed in this work, solely on the basis of available literature data and personal contacts. A complete characterization of initial, intermediate and final product has been made. Experimental data unambiguously suggest that the quality of the colloidal silica obtained, fully corresponds to the quality of the products commercially available from the leading world companies. This work is devoted to a better understanding of the sorption properties of colloidal silica and solids obtained from it. Accordingly, we intended to fulfill the following goals: to examine the sorption of alkali metals from aqueous solutions, sorption of a numerous organic compounds on the solid materials obtained by coagulation from the colloidal silica, to study the stability of the colloidal silica in the presence of alkali metal ions and, finally, to determine the heat of immersion of powders obtained from colloidal silica. The sorption of alkali metal ions from aqueous solutions on colloidal silica, has been studied at 298 K using the potentiometric titration method. Due to the considerable solubility of the colloidal silica, at the elevated pH values, the limit of the method used had to be determined. The application of the potentiometric titration method has been critically reconsidered with special regard to the literature data concerning the region in which dissolution process is a dominant one. The obtained hysteresis on the sorption-desorption curves, is explained in view of significant solubility of the colloidal silica at the particular pH region. Alkali metal ion selectivity sequence corresponds to the Hofmeister series, i.e. for the cations of the same charge the sorption affinity decreases with the increased hydrated radii, and this is valid for the lower electrolyte concentrations and low pH values. A change in alkali metal ion sorption sequence has been found at the given pH values as a consequence of both ion concentration and pH values of the solution. Such a behaviour was successfully explained taking into account activities of the cations studied. On the basis of these date, it is possible to predict the sorption sequence of alkali metal ions on the colloidal silica surface, and to our opinion on other Si02 forms as well, taking into consideration the electrolyte concentration and pH of the solution. We do think that the solution composition is of great importance for the sorption properties of other inorganic oxides and should be accepted as a suggestion for further investigations...