Diffusion of heterocyclic compounds from a complex mixture of coal–tar compounds in natural clayey till

Abstract

The diffusion of coal–tar compounds in natural clayey till was studied experimentally. Cores were exposed to a solution with near constant concentration of coal–tar compounds in a multi-component mixture for 5 months, the cores were subsequently sub-sampled and analyzed. Diffusion profile data strongly indicates highly non-linear sorption isotherms. For dibenzofuran, dibenzothiophene, 2-methylquinoline, carbazole, phenanthrene, and fluorene, the profiles indicated significantly stronger sorption at high solute concentrations than at low solute concentrations, and than expected based on linear sorption isotherms. This corresponds with observed dramatic increase in sorption of these compounds at high surface density. For benzofuran, benzothiophene, quinoline, phenols, naphthalenes, and BTEXs the profiles indicated significantly weaker sorption at high solute concentrations than at low solute concentrations and than expected based on linear or Freundlich isotherms. The observed diffusion profiles have important implications with respect to transport of dissolved coal–tar compounds in multi-component mixtures of high concentrations as expected near immiscible phase coal–tar sources. Breakthrough times and concentration levels are affected significantly.