Abstract
Contaminant leaching from waste masses usually occurs through a combination of dissolution, diffusion, and dispersion of species from particles or cemented matrix. Under stresses that are induced by external loads or self-weight, important material and hydraulic parameters such as particle shape and size distribution, porosity, permeability and diffusion coefficient (for the specific contaminant) can change significantly. This can lead to marked differences in contaminant leaching rates for loaded and unloaded media. In this paper, various loading scenarios are analyzed with respect to stress patterns and damage of monolith and particulate media from which contaminants can leach. For coal combustion ash subjected to uniaxial compressive stresses of 570, 1425, 2,850 and 5,710 kPa, it is observed that differences in the concentration of copper (Cu) leached by acidified water (pH = 6.0) in column flow-through experiments are significant only during the first 25 h of leaching. The corresponding leachant flow rates are in the range of 0.013–0.9 mL/min. The results show that Cu concentration in the leachate is not necessarily proportional to external load magnitude but may be influenced by factors that are related to particle deformation, change in interparticle porosity, and leachant velocity. A conceptual model for matching material stress and deformation state to leached contaminant concentration is formulated and described.
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