Quantification of diffusion of phenolic compounds in virgin GCL and in GCL after contact with a synthetic leachate

Abstract

To quantify the diffusion coefficients of p-cresol, 2,4-dimethylphenol (2,4-DMP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-DCP), 2,3,5,6-tetrachlorophenol (2,3,5,6-TeCP), and pentachlorophenol (PCP), in-laboratory tests were conducted of diffusion through a needle-punched geosynthetic clay liner (GCL) containing natural sodium bentonite. The diffusion coefficient was qualified for the virgin GCL and for GCL that had undergone cation exchange after being exposed to a synthetic leachate. The goal of the experiment was to see if an increase in the hydraulic conductivity generated by cation exchange in a GCL would lead to significant increases in the diffusion coefficients of phenolic compounds. For all pollutants studied at a given bulk-GCL void ratio close to 3.0, the results reveal an increase in the diffusion coefficient for transit through the GCL exposed to the synthetic leachate. The increase in the diffusion coefficient due to synthetic-leachate permeation ranged from a maximum factor of 5.0 for 4-CP to a minimum factor of 1.3 for 2,3,5,6-TeCP and PCP. For virgin GCL specimens, the chemical properties of the compounds studied did not influence the diffusion coefficient. However, for the GCL specimens exposed to the synthetic leachate, the diffusion coefficient increased with the aqueous solubility and decreased with log Kow and the molecular weight.