Electrokinetic barrier to contaminant transport through compacted clay.

摘要

The industrial commitment required to support the needs of our ever-increasing population and ever-improving living standard is producing more and more waste products and by-products. Despite intense efforts at waste minimization, recycling, and alternative forms of waste disposal, landfills and surface impoundments will continue to play a major role in isolating these wastes from human contacts.; Double liner systems with leachate collection systems above and between liners are required for landfills and surface impoundments in compliance with the law. These liners may be synthetic membranes, compacted clay layers or a composite of both components. However, there is always uncertainty about the long term integrity of synthetic membranes in landfills. The compacted clay liner may release some seepage under a sustained hydraulic head. Moreover, chemical diffusion through the clay liner under a concentration gradient may increase the rate of contaminant migration into the environment. An electro-kinetic barrier created by the continuous or periodic application of an electrical gradient across a compacted clay liner may inhibit migration of hazardous constituents into the environment. The research described in this dissertation has been done to investigate this possibility.; The coupled simultaneous flow equations of water, electricity, cations and anions under hydraulic, electrical and chemical gradients were formulated by the formalism of thermodynamics of irreversible processes. The phenomenological coefficients were then related to measurable soil parameters. An explicit integrated finite difference numerical model was developed to simulate the migrations of cations and anions under these imposed gradients. An experimental program was developed to evaluate the validity of the developed theory.; The existence of electro-osmotic flow in partially or fully saturated compacted clay was experimentally demonstrated. The measured coefficients of electro-osmotic permeability of compacted clay are in the range of values for most other soils. The developed theory reasonably predicted the migration of contaminants under combined hydraulic, electrical and chemical gradients. An electrical gradient may move some inorganic species in soils much more effectively than a hydraulic gradient. An electro-kinetic barrier halted the migration of the cation but accelerated that of the anion under laboratory testing conditions.