Ion Transfer by Diffusion Through Clayey Barriersby Robert M. Quigley, Univ of Western Ontario, London, Ont, Canada,
Ernest K. Yanful, Univ of Western Ontario, London, Ont, Canada,
Federico Fernandez, Univ of Western Ontario, London, Ont, Canada,
Abstract: The practical aspects of pollutant migration by diffusion through clayey barriers is presented. The discussion is generally restricted to soils of pH approximately equals 8 which contain carbonate. A short review of the theoretical aspects of the nature of diffusion is incorporated with descriptions of methods for measuring or calculating diffusion coefficients. The importance of retardation and the use of distribution coefficients is emphasized. Field diffusion below a domestic waste site is described. Chemical migration has proceeded to a depth of 1. 5 m in 15 years for essentially non-retarded species such as chloride and sodium. Heavy metals (lead, copper, zinc and iron) have migrated only 0. 1 m, the retardation due primarily to precipitation. Profiles for calcium, magnesium and potassium are also presented. Diffusion into soil peds adjacent to compaction-induced fractures and voids produces 'tailed' breakthrough curves of effluent concentration. This phenomenon accompanied by potassium fixation greatly extends the time required for clay/leachate compatibility testing at high gradients.
Subject Headings: Diffusion (porous media) | Diffusion (chemical) | Soil pollution | Clays | Permeability (soil) | Waste sites | Chemical elements
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