Abstract
Engineered soil covers are being evaluated under Canada's Mine Environment Neutral Drainage (MEND) program for their effectiveness in preventing and controlling acid generation in sulphidic mill tailings. A critical parameter for predicting the performance of these covers is the diffusion coefficient of gaseous oxygen in the cover materials. Laboratory experiments conducted to determine the effective diffusion coefficient of a candidate cover material, a glacial till from an active mine site, are described. The diffusion coefficient is determined by fitting a semianalytic solution of the one‐dimensional, transient diffusion equation to experimental gaseous oxygen concentration versus time graphs. Effective diffusion coefficients determined at high water saturations (85%–95%) were of the order of 8×10-8m2/s. The diffusion coefficients decreased with increase in water saturation as a result of the low diffusivity of gaseous oxygen in water relative to that in air and the low solubility of oxygen in water. Placement of soil covers in high saturation conditions would ensure that the flux of oxygen into tailings underneath such covers is low, resulting in low acid flux. This is confirmed by combined laboratory, field, and modeling studies.
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