Developments in the use of deinking residues in cover systems for acid generating mine tailings

Pulp and Paper industries produce deinking residues in great quantities. Most of it is presently landfilled at great costs. Due to its particular hydraulic characteristics, including a high retention capacity, this material can be recycled and used in different geoenvironmental applications, such as capillary barriers in cover systems for mine tailings. A capillary barrier constituted of deinking residues was placed over two tailings sites near Sherbrooke, Quebec, Canada. Oxygen, CO 2 and methane profiles showed that the O 2 concentration 20 cm below the surface was virtually nil and that the concentrations of CO 2 and CH 4 increased with time. Water content, temperature and organic percentage profiles were determined in the field. Oxygen diffusion tests performed in the laboratory confirmed the field data in showing that deinking residues placed at high degrees of saturation work as an effective barrier to oxygen migration; diffusion coefficients in the range of 3.5 m 2 /yr to 110 m 2 /yr were obtained. The lower values are associated with degrees of saturation in the range of 85%, whereas the higher values are associated with degrees of saturation in the range of 76%. During these tests, oxygen consumption and CO 2 generation were observed, meaning that the deinking residues may also work as an oxygen consuming barrier. Suction tests under different conditions yielded air entry values (ψ a ) in the range of 30–65 kPa. Part of the physico-chemical characterization of the material is presented.