Sorption of humic substances on a weakly basic anion-exchange resin: Relationship with the adsorbate structure
Sorption of humic substances on a weakly basic anion-exchange resin: Relationship with the adsorbate structure. Pankratov D.A., Anuchina M.M., Borisova E.M., Volikov A.B., Konstantinov A.I., Perminova I.V. //Russian Journal of Physical Chemistry A. 2017. V.91. №6. P.1109-1115.
Adsorption of a broad range of humic substances (HS) of different origins and fractional compositions on a macroporous weakly basic anion-exchange resin is studied. It is found that the nature of the humic substances has a substantial effect on both the efficiency of sorption and the mechanism of interaction with the adsorbent. The dependence of the determined thermodynamic parameters of sorption on the humic substances origin, composition, and structure is shown for a broad range of humic substances. It is concluded that the results can be used to predict the sorption properties of weakly basic anion-exchange resins with respect to humic substances of known origin and structural group composition.
Humic substances (HS) are natural hyperbranched polyelectrolytes in which the aromatic skeleton is replaced with both oxygen-containing functional groups—mostly carboxyl (–СООН) and hydroxyl groups (–ОН) —and nitrogen-containing groups. In addition to a hydrophobic aromatic skeleton, humic substances consist of hydrophilic polysaccharide and peptide moieties. Owing to this composition, humic substances are capable of participating in ionic, donor–acceptor, and hydrophobic interactions, and are therefore highly active in sorption processes. These properties are responsible for the key role of humic substances in the surface modification of clay minerals, which is fundamental to the formation of soil structure because humic films form hydrophobic regions on the surfaces of hydrophilic clay minerals. It was shown in that the surface morphology of the adsorbed layers of silanized humic substances at a water–glass interface is largely determined by the molecular structure of the adsorbate, i.e., the presence or absence of bulk polysaccharide moieties in the adsorbate’s structure. This relationship allows us to predict the properties of silanized humic substances films. At the same time, it is important to determine the relationship between the structure and sorption properties of native humic preparations without preliminarily modifying them with organosilanes in order to substantially deepen our understanding of the driving forces that determine humic substances adsorption on different solid substrates.
The aim of this work was to examine the sorption properties of humic substances of different origins on a weakly basic anion-exchange resin and determine a relationship between these properties and the adsorbate’s structure. A weakly basic anion-exchange resin was selected as a model substrate to study the sorption of humic substances not preliminarily modified.
Our study of the adsorption of humic substances of different origins and fractional compositions on an ANS macroporous weakly basic anion-exchange resin shows that the highest degree of sorption is observed for potassium humate produced from lignite. Analysis of the determined thermodynamic parameters of sorption for a broad range of humic substances showed that the parameters depend on the origin, composition, and structure of an humic substances. Equations to relate the adsorption of humic substances on an anion-exchange resin and the relative content of aromatic to aliphatic carbon were proposed.