Use of Amended Tailings as Mine Waste Cover

Abstract

The present study addresses the effectiveness of green liquor dregs (GLD, a residue from paper pulp-making) as a paste additive with different proportions in tailings for stabilizing mine waste by testing of uniaxial compressive strength and hydraulic conductivity. Selected samples were also investigated for freeze–thaw effect on hydraulic conductivity, and the water retention capacity was discussed based on previous results. Fly ash was also added to the paste to study the auxiliary functions such as solidification in the sealing material. GLD have the potential for use as a barrier layer material for stabilizing mine tailings by decreasing water percolation and improving water retention properties. However, the solidified paste of GLD-amended tailings possesses low uniaxial compressive strength, but the addition of fly ash to the paste increased the uniaxial compressive strength by up to 2–3 times 1 month after it was solidified, with a further two- to threefold strength increase after 3-months curing time. Although the hydraulic conductivity of the tailings paste decreased as a consequence of mixing with both GLD and FA, the difference was within one order of magnitude. The hydraulic conductivity was also reduced as the water/solid ratio of pure GLD decreased. The climatic freeze–thaw cyclic process led to 20 % increase in hydraulic conductivity. A proportion of 7:2:1 for tailings:GLD:FA was found to be a geotechnical satisfactory recipe to seal the mine waste. If porosity is reduced, improved water retention capacity and no cracking in the tailings can be assured, oxygen diffusion is limited, and oxidation of the mine waste is decelerated, thus mitigating acid rock drainage.