Mm. Broholm et al., Sorption of heterocyclic compounds from a complex mixture of coal-tar compounds on natural clayey till, J CONTAM HY, 39(3-4), 1999, pp. 201-226
The sorption and desorption of heterocyclic organic compounds in a complex
multisolute system to a natural clayey till was investigated. The compositi
on of the solutes reflect a simplified composition of an aqueous phase in c
ontact with coal tar. Sorption was studied for two ratios (s:1) of clayey t
ill (solid) to aqueous phase (liquid). The effect of the complex mixture of
solutes on sorption of the four heterocyclic compounds: benzofuran, dibenz
ofuran, benzothiophene, and dibenzothiophene is evaluated by comparison wit
h their sorption measured in single-solute systems. Sorption of the four co
mpounds is affected by the complex mixture, with sorption decreases for all
four compounds at high s:1 ratio indicating competitive sorption. The effe
ct on sorption of the individual compounds is not related to solubility or
hydrophobicity of the compounds. Freundlich-type isotherms are observed for
all compounds in the high s:1-ratio experiments, but for the most hydropho
bic compounds isotherms are close to linear. The sorption of N-compounds an
d benzofuran is apparently influenced by cation exchange and dipole-dipole
attraction to clay minerals. At high concentrations a dramatic increase in
the sorption of the most strongly sorbing compounds is observed in the low
s:1-ratio experiment. The dramatic increase in sorption appears to be a res
ult of multimolecular layer sorption or condensation on surfaces in the cla
yey till at high surface density of organic compounds, and the data are fit
ted by BET (Brunauer, Emmet, and Teller) type 2 isotherms. The increase may
or may not be induced by the presence of N-heterocyclic compounds sorbed b
y cation exchange and dipole-dipole attraction. The desorption of the compo
unds was studied for the low s:1 ratio where multimolecular layer formation
apparently had occurred. Partially irreversible sorption, hysteric Langmui
r type desorption with isotherms of very high K-1 coefficient, or behaviour
reflecting dissolution of a condensed phase is observed. (C) 1999 Elsevier
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