Author: Customer
Company: ARO

Abstract
Organoclays produced by replacing the exchangeable inorganic cations on layer silicates
with organic cations are known as effective sorbents for non-ionic compounds in aqueous
solutions, comparably to many minerals and inorganic surfaces in which a hydrophilic
environment prevents effective interactions between organic molecules and a sorbent.
In our experimental studies, the effect of sorbent hydration on sorption of selected
organic compounds, nitrobenzene, phenol and m-nitrophenol, was examined and
compared on original Fisher bentonite and bentonite exchanged by n-hexadecyltrimethylammonium
(HDTMA) by 43% and 89% of the CEC. For that, synthesized
sorbents were freeze-dried to have a low water content (~1%, according to the 105 0C
dehydration test), and sorption of probe organic compounds on these dehydrated sorbents
was measured and compared from water (“wet” sorbent) and from the inert solvent, nhexadecane
(“dry” sorbent).With increasing bentonite exchange by the HDTMA-cation,
aqueous sorption of organic compounds was increased thus indicating an important role
of organic coverage. By comparing different sorbates on one sorbent, both in water and
n-hexadecane, it was shown that, according to ability to undergo the molecular
interactions, studied sorbates followed a series: nitrobenzene<phenol<m-nitrophenol.
Measured sorption isotherms in water are affected by solute-water interactions and by
integral hydration effect on sorbed state interactions involving both organoclay (clay) and
sorbate molecules. Thus, a delineation of the hydration effect on sorbed state interactions
based on a comparison between sorption from water and from n-hexadecane needs
accounting for differences in the solute-solvent interactions between water and nhexadecane.
The present work establishes the sorbent hydration effect on sorption
interactions of selected probe organic compounds with a differently HDTMA (nhexadecyl-
trimethylammonium)-exchanged bentonite based on sorption isotherms
determined in water (i.e. on wet sorbent) and in an inert solvent, n-hexadecane (i.e. on a
"dry" sorbent). The effect of hydration on sorbate interactions in the sorbent phase is
extracted from aqueous and n-hexadecane-based sorption isotherms, using a solute
activity scale. Disappearance (or diminishing) of a hydration-induced suppressive effect
on sorption correlates with an increasing potential of a sorbate to undergo molecular
interactions (and to compete effectively with water for sorption sites).