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Diffusion Coefficients of Organics in High Density Polyethylene (HDPE)

Texas A&M University, Soil and Crop Science Department, College Station, TX 77843-2474, U.S.A.

K.W. Brown

Texas A&M University, Soil and Crop Science Department, College Station, TX 77843-2474, U.S.A.

J.C. Thomas

Texas A&M University, Soil and Crop Science Department, College Station, TX 77843-2474, U.S.A.

Only limited data are available on the diffusion of volatile organic solvents through flexible membrane liners (FMLS) used for lining impoundments and landfills. To expand this database, a rapid, inexpensive method is needed to measure the diffusion coefficients of volatile organic solvents through FML materials. An absorption method has been developed to determine the diffusion coefficients of volatile organic solvents through FML materials. The method is based on the depletion of an organic compound from an aqueous solution due to absorption by a submerged sample of FML. A numerical solution of Fick's second law of diffusion was used to develop a graph which can be used to determine the diffusion coefficient from the time dependent concentration data. The diffusion coefficients obtained from the absorption tests were validated by comparing them with coefficients determined using a two chamber diffusion cell. The diffusion coefficients determined for toluene and xylene in high density polyethylene (HDPE) were 5.1 x 10^-9 cm²s^-1 and 1.0 x 10^-9 cm²s^-1 by the two methods, respectively. The data indicate that the coefficient of distribution (K_d) between the FML and the organic solution, a value which is needed to calculate the diffusion coefficient from the data, can be estimated from the log of the octanol-water partition coefficient (K_ow), a commonly measured and reported value for many chemicals.

Key Words: Landfill • liner • solvents • leachate • leakage • mechanism • Fick's law • partitioning.

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