The study of the sorption properties of materials using physico-chemical method of adsorption sites distribution
Abstract
Adsorption of a large set of indicators demonstrates the way adsorption sites are distributed on a solid
surface according to their acid-base (donor-acceptor) properties. The adsorption sites distribution method
(ASD method) allows for prediction of the selective adsorption of various substances on specific active sites.
The aim of this paper is to determine the sorption properties of certain solid materials with respect to heavy metal cations (HMC), using the surface characteristics as determined by the ASD method and the nature of the contaminants.
The ASD method was used to study foam concrete of various initial densities and ground granulated
blast-furnace slag. The distribution of the adsorption sites on the surface of the samples was analysed before and after the saturation of the ground samples with solutions containing Fe(III) and Mn(II).
The analysis demonstrates that there are two types of adsorption sites on the surface of the initial
sample of foam concrete with the density of 300 kg/m3 . According to the proposed classification, these types correspond to Brønsted bases (pKa=6-10.5). The adsorption occurs precisely in this area, which is experimentally confirmed by a dramatic decrease in the number of such sites after the interaction of the sample with the solution containing the HMC. A large number of Brønsted acid and base adsorption sites were observed on the surface of the initial foam concrete sample with the density of 500 kg/m3 . The concentration of the active sites in the area of Brønsted bases decreased after the interaction of the sample with a solution containing iron ions, which means that the adsorption of iron ions occurred. At the same time, the number of Brønsted acids remained practically constant, which demonstrates the adsorption selectivity. The analysis of the nature of the ASD on the surface of ground granulated blast-furnace slag (initial and processed) showed that the intensity of the adsorption zones in the pKa=7.3 site of the initial slag sample decreases sharply after the interaction with the solution. This proves that the HMC are adsorbed on the Brønsted core centres. The large quantity of active sites on the surface of the material is accounted for by high dispersion (fraction <0.08 mm).
Thus, the analysis of the distribution of active sites on the examined samples surface according to
their acid-base properties demonstrated that the ASD method, as a physico-chemical method of studying solid surfaces, can be used to predict the sorption properties of solid materials and expand their application field.
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