Green liquor dregs (GLD), a residual product from sulfate paper mills, was blended with tailings, fly ash, and bark sludge with the aim of improving the material’s physical properties so that it could function as a sealing layer in dry covers on sulfidic mine waste. Geotechnical and geochemical investigations, including weathering cell tests, were carried out on GLD with admixtures to assess their effectiveness. Due to its alkaline character, GLD was shown to have the potential to improve leachate quality by decreasing metal mobility when blended with tailings. The admixtures showed favorable sealing layer properties such as high water retention capacity and low hydraulic conductivity. However, caution must be exercised when the dregs are blended with tailings containing large amounts of As and Mo, since increased leaching of these elements may be expected.