Phase partition of organic pollutants between coal tar and water under variable experimental conditions

Abstract

On some abandoned manufactured-gas plant sites the presence of a particular non-aqueous phase liquid (NAPL), namely coal tar, represents a potential source of groundwater pollution. The aim of this study was to characterise the phase partition of aromatic pollutants between coal tar and water. Batch trials have been carried out in order to evaluate the state of phase partition equilibrium of pollutants between coal tar and water, under variable experimental conditions (temperature, pH, ionic strength, coal tar composition). The experimental results clearly show that coal tar cannot be considered as an ideal solution with regards to phase partition of pollutants with water. The main identified mechanisms of phase partition are the quasi instantaneous solubilization of pollutants near the coal tar/water interphase, and the diffusion of pollutants within the organic phase or at the interphase which controls the transfer kinetics of pollutants towards the aqueous phase. The dissolution kinetics experimentally observed were therefore correlated to a diffusional model of mass transfer. The formation of a film which increased resistance to mass transfer was also observed at the coal tar/water interphase. This ageing phenomenon of the coal tar/water interphase was found to be an important aspect which can have a significant influence on the long term fate of coal tar in soils or subsoils, as well as on soil remediation techniques.