Cosorption of aromatic n heterocycles and pyrene by smectites in aqueous solutions

Traina, S. J.; Onken, B. M.

The simultaneous sorption of the polycyclic aromatic hydrocarbon, pyrene, and the aromatic N-heterocycles, quinoline and acridine, by aqueous suspensions of either Na-montmorillonite or Na-hectorite was examined. In all cases, pyrene sorption in the absence of sorbed N-heterocycles was not detected. In the presence of sorbed N-heterocycles, pyrene sorption increased with increased surface concentrations of quinoline or acridine. The pH-dependent sorption of quinoline and acridine caused an apparent pH dependence in pyrene sorption. Fluorescence emission spectra indicated that the acridinium ion was the dominant form of sorbed acridine on hectorite. Fluorescence emission spectra of pyrene, cosorbed with quinoline by hectorite, indicated that the surface-bound pyrene resided in an environment of lower polarity than bulk H2O. A linear isotherm for pyrene sorption on Na-montmorillonite was obtained at a quinoline surface concentration of 27.19 cmol kg-1, while the pyrene sorption isotherm was curvilinear when there was only 4.67 cmol kg-1 quinoline present on the clay surface. In all experiments, the value of Koc for pyrene sorption decreased with increased surface concentrations of N-heterocycles. We postulate that pyrene sorption at low concentrations of quinoline or acridine is due to the adsorption of pyrene by sorbed N-heterocycles. Increased concentrations of quinoline or acridine promote sorption of pyrene through a partition reaction with sorbed N-heterocycles.