The Hydraulic Conductivity and Adsorptivity of Organoclay in a Sand-Bentonite Barrier to Hydrophobic Organic Chemicals

Abstract

This study investigates the hydraulic conductivity and adsorptivity of simulated clay barrier material containing organoclay, for the purpose of discovering whether the inclusion of organoclay in a clay barrier can effectively immobilize hydrophobic organic chemicals. The surface of a commercial Na-bentonite was modified by replacing the original inorganic cations with hexadecyltrimethylammonium, a cationic surfactant. Batch adsorption tests using dilute concentrations of the hydrophobic organic chemicals — pentachlorophenol, naphthalene and toluene — were performed on the bentonite samples and the resulting organoclay. Hydraulic conductivity tests using permeants containing dilute concentrations of pentachlorophenol, naphthalene and toluene were performed on the bentonite samples with and without organoclay. The batch adsorption tests showed that the organoclay adsorbed hydrophobic organic chemicals from 10 to 40 times more effectively than did untreated bentonite. The hydraulic conductivity tests indicated that the presence of organoclay in a clay barrier material significantly increased the hydraulic conductivity whether or not hydrophobic organic chemicals were present in the permeant. Naphthalene or toluene in the permeant increased the hydraulic conductivity of the bentonite samples containing organoclay, while pentachlorophenol in the permeant had no apparent effect on the hydraulic conductivity.