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The hydraulic conductivity and adsorptivity of clay barrier materials containing organoclay Denham, William T.

Abstract

This study investigated the hydraulic conductivity (k) and adsorptivity of simulated clay barrier material which contained organoclay, for the purpose of discovering if the inclusion of organoclay in clay barrier material could effectively immobilize inorganic contaminants. The organoclay was produced using sodium bentonite and the cationic surfactant hexadecyltrimethylammonium (HDTMA) . The test chemicals used to investigate k and adsorptivity were pentachlorophenol (PCP), naphthalene (NP), toluene (TL), and methyl ethyl ketone (MEK). Batch adsorption tests using the test chemicals in dilute concentrations were performed on bentonite and organoclay. Clay barrier materials were produced with bentonite, organoclay, and sand. These clay barrier materials were compacted, placed in a rigid-wall permeameter, and permeated with 0.01 M CaSO4 or 0.01 M CaCl2, and also with dilute solutions of the test chemicals. Air pressure was used to create hydraulic head through the permeameter, and k of the clay barrier materials with and without organoclay was determined. The effluent from the permeameter was collected and analyzed for the test chemicals. Results from the batch adsorption tests indicated that organoclay was much more effective than bentonite in adsorbing PCP, NP and TL from a dilute aqueous solution. These three chemicals are sparing soluble in water. Neither organoclay nor bentonite effectively adsorbed MEK, the only test chemical in the study that was highly soluble in water. However, organoclay did adsorb more MEK than bentonite. Organoclay was shown to have a significant effect on k in the clay barrier materials, always increasing k as compared to clay barrier material which did not contain organoclay. There was also a considerable interaction between k, organoclay, and the test chemicals. NP and TL caused a large increase in k in the clay barrier materials containing organoclay, and MEK caused a decrease. This interaction, though present, was not as pronounced in the clay barrier materials which did not contain organoclay. Testing of the effluent in the permeameter tests showed that clay barrier materials containing organoclay retained PCP much better than clay barrier materials without organoclay. However, the retention of PCP was not as great as would be predicted using the results of the batch adsorption tests. [Scientific formulae used in this abstract could not be reproduced.]

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