IMPORTANCE OF TRANSPORT PARAMETERS OF IONS IN THE DESIGN OF SOIL LINERS

摘要

Design of the thickness of soil liners for any waste disposal facilities depends on the rates of migration of ions in the leachates generated within the waste disposal facility. But the migration rates of ions within the leachate vary considerable depending on several factors such as diffusion coefficients of ions and retardation factors and in-situ properties of liner material. Generally the diffusion coefficients of any given ions may not significantly vary and are range bound. But the retardation factor of ions can vary considerably depending on clay liner and contaminant ions present in the leachate. The variation in the retardation factor of potassium ion, in the commonly used montmorillonitic clay as liner material, has been studied in this paper. The transport rates of sodium, which is considered as conservative ions also have been studied. The transport rates of ions are determined through soil column tests. The diffusion coefficient and the retardation factors are determined by comparing the experiments column break through curves with a theoretical curve. The transport parameters are varied so that the theoretical curve matches with experimental curve. The set of values with which the theoretical curves closely match with the experimental curves are taken as the transport parameters of the concerned ion. It was shown in this paper that specific interaction that takes place between potassium ion and montmorillionite clay, which increases the retardation factor considerably for potassium unlike sodium in the same clay. Consequently the breakthrough times for any given thickness of the liner increases if potassium is the critical contaminating ion.