Sorption of heterocyclic compounds on natural clayey till

Abstract

The sorption of benzofuran, dibenzofuran, benzothiophene, and dibenzothiophene from water on natural clayey till from two locations in Denmark was investigated in single solute systems for a large range of solute concentrations. The variation in sorption of a basic (quinoline) and a neutral (dibenzofuran) heterocyclic compound in samples from different depths in the natural clayey till was also investigated. The sorption isotherms for all four compounds and both clayey tills were highly non-linear, and the overall best fits were obtained with Freundlich isotherms. These observations indicate that sorption is not strictly hydrophobic or that the affinity for organic material is influenced by the sorbed solute, and that multiple components contribute to the sorption. The f oc normalized linear K d-value and Freundlich K f-coefficient were compared with estimated K oc values. Hydrophobic sorption appears to dominate for dibenzofuran, benzothiophene and dibenzothiophene, whereas benzofuran and in particular quinoline sorption is influenced by inorganic sorption sites. This corresponds reasonably well with expectations based on estimates of critical organic carbon content. The sorption of quinoline at the uppermost sample was slightly higher (10%–20%) than for the deeper locations. This is possibly related to a slightly higher clay content at this depth. The sorption of dibenzofuran was higher at the deepest location (approximately 65%) than for the above locations. The only measured geological parameter which was significantly different in the sample from the deep location was the content of fine silt.