DIFFUSION OF 1-NAPHTHOL AND NAPHTHALENE THROUGH CLAY MATERIALS - MEASUREMENT OF APPARENT EXCLUSION OF SOLUTE FROM THE PORE-SPACE

Diffusion is fundamental in controlling movement of organic contaminan ts in clay textured materials. Diffusion coefficients for 1-napthol an d naphthalene were measured for a weathered shale based on the breakth rough time and on the steady state flux of solute through the clay bar rier. Steady state solute flux through the clay barrier was 9 to 35 ti mes lower than that predicted based on breakthrough diffusion coeffici ents within the clay barrier. Analysis of napthalene concentration in the pore solution of a non-sorbing medium (montmorillonite clay) showe d that the solute concentration in the clay pores was only 40% of that in the free solution suggesting that the clay barrier was restricting the entry of the solute into the clay pore space. Results suggest tha t the clay can act to exclude the diffusing species from the pore spac e, reducing the effective solute concentration gradient within the cla y cell. This will act to further enhance the ability of clay materials to limit contaminant flux. (C) 1997 Elsevier Science B.V.