Experimental and theoretical study of combined solvent and steam stripping of 1,2,3,4,5,6-hexachlorocyclohexane (HCH) and mercury from contaminated natural soil

Abstract

This paper reports on an experimental and theoretical study of the combined solvent and steam stripping of contaminated soil. First, feasibility experiments on the bench scale are reported concerning the stripping of soil contaminated with 1,2,3,4,5,6-hexachlorocyclohexane (HCH) and mercury. This natural soil, originating from a contaminated site, was packed and stripped in a glass column. The results of cleaning revealed removal levels to below the detection limits of the contaminants and removal efficiencies of 99.7% for HCH and 97.2% for mercury. Subsequently, a one-dimensional nonequilibrium model is proposed which describes the unsteady mass transfer between vapors, condensate and solid phases in a column. A perturbation method is employed to obtain an approximate solution of the governing equations for small Merkel number Me (this dimensionless number constitutes the column length times the mass transfer coefficient, divided by the flushing velocity). Application of the model to the experiments performed results in values for the overall mass transfer coefficients, which can be used for future engineering computations. Furthermore, the model enables the prediction of the initial contaminant level in the soil solely from the measured exit contaminant concentrations in the flushing fluid. A thorough comparison of this prediction with the measured soil concentration (prior to the experiment) yields excellent agreement. The presented model is applicable to any other soil flushing experiment for which Me ⪡ 1.