Determination of the diffusion coefficient of oxygen for a cover system including a pulp and paper by-product

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Publication date
2004Author(s)
Cabral, Alexandre; Lefebvre, Guy; Tremblay, P.
Subject
Acid rock drainageAbstract
ABSTRACT: 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.