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

This paper reports on an experimental and theoretical study of the com bined solvent and steam stripping of contaminated soil. First, feasibi lity experiments on the bench scale are reported concerning the stripp ing 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 rev ealed removal levels to below the detection limits of the contaminants and removal efficiencies of 99.7% for HCH and 97.2% for mercury. Subs equently, a one-dimensional nonequilibrium model is proposed which des cribes the unsteady mass transfer between vapors, condensate and solid phases in a column. A perturbation method is employed to obtain an ap proximate 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). Applicat ion of the model to the experiments performed results in values for th e overall mass transfer coefficients, which can be used for future eng ineering computations. Furthermore, the model enables the prediction o f the initial contaminant level in the soil solely from the measured e xit contaminant concentrations in the flushing fluid. A thorough compa rison of this prediction with the measured soil concentration (prior t o the experiment) yields excellent agreement. The presented model is a pplicable to any other soil flushing experiment for which Me much less than 1.