Volume 27, Issue 2 (March 2004)
Determination of the Diffusion Coefficient of Oxygen for a Cover System Including a Pulp and Paper By-Product
Among the several solutions that have been proposed to curb the problem posed by the generation of acid rock drainage (ARD), the placement of covers with capillary barrier effect (CCBE) has received particular attention. With the creation of a capillary barrier, oxygen has to migrate through a nearly saturated layer, a much slower process than in air. As a consequence, its availability is drastically reduced, reducing ARD generation. An experimental procedure was developed to obtain the diffusion coefficient of oxygen through compacted deinking residues, an organic matter-rich by-product of paper recycling. With the oxygen concentrations obtained as a function of time, it was possible to deduce the diffusion coefficients based on the best reproductions of laboratory results, using the computer code POLLUTE v.6. As expected, it was found that the diffusion coefficient—and the associated flux—is highly influenced by the degree of saturation of the sample. Beyond a threshold in the vicinity of 85%, a one order of magnitude drop in the diffusion coefficient was observed. A comparison of the results obtained with previously published data shows that deinking residues constitute a very effective oxygen barrier material due both to its ability to maintain a high degree of saturation and to rapidly consume oxygen. Given the latter, special care was needed in defining the most appropriate equipment design, sample preparation method, and testing procedure.