Sorption of organic cations onto silica surfaces over a wide concentration range of competing electrolytes.
The fundamental understanding of organic cation-solid phase interactions is essential for improved predictions of the transport and ultimate environmental fates of widely used substances (e.g., pharmaceutical compounds) in the aquatic environment. We report sorption experiments of two cationic model compounds using two silica gels and a natural aquifer sediment. The sorbents were extensively characterized and the results of surface titrations under various background electrolyte concentrations were discussed. The salt dependency of sorption was systematically studied in batch experiments over a wide concentration range (five orders of magnitude) of inorganic ions in order to examine the influence of increasing competition on the sorption of organic cations. The organic cation uptake followed the Freundlich isotherm model and the sorption capacity decreases with an increase in the electrolyte concentration due to the underlying cation exchange processes. However, the sorption recovers considerably at high ionic strength (I>1M). To our knowledge, this effect has not been observed before and appears to be independent from the sorbent characteristics and sorbate structure. Furthermore, the recovery of sorption was attributed to specific, non-ionic interactions and a connection between the sorption coefficient and activity coefficient of the medium is presumed. Eventually, the reasons for the differing sorption affinities of both sorbates are discussed.
Institute of Water Chemistry, Technische Universität Dresden, 01062 Dresden, Germany(1). Electronic address: Susann.Kutzner@mailbox.tu-dresden.de.
Susann
S
Kutzner
Geoscience Centre, Department of Applied Geology, Hydrochemistry Group, University of Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany(2).
Mario
M
Schaffer
Geoscience Centre, Department of Applied Geology, Hydrochemistry Group, University of Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany(2).
Tobias
T
Licha
Institute of Water Chemistry, Technische Universität Dresden, 01062 Dresden, Germany(1).
Eckhard
E
Worch
Institute of Water Chemistry, Technische Universität Dresden, 01062 Dresden, Germany(1).
Hilmar
H
Börnick
Activity coefficient; Cation exchange; Competitive sorption; Freundlich isotherm; Organic cation; Silica gel