Effect of cementitious amendment on the hydrogeological behavior of a surface paste tailings’ disposal

Abstract Surface paste disposal (SPD) can be considered as an effective alternative technique for mine waste management. The technique consists of first removing upstream water (by thickening and/or filtration) from tailings, then depositing them at the surface in a paste-like state. These techniques allow for the recycling of water, limit risks related to the failure of dikes, and favor progressive mine site rehabilitation. However, there are, thus far, only a few studies on the environmental behavior of tailings deposited using the SPD technique. To evaluate the hydrogeological and geochemical behaviors of a sulphidic tailings’ deposit simulating the SPD method, a laboratory study was performed using a physical model. Paste tailings were prepared and deposited inside the physical model in nine layers. In the first stage, only the first two bottom layers were amended with cement (2 % w/w of PC10 Portland cement). The physical model was then subjected to wetting and drying cycles, and the water collected after each flush was analysed for chemistry and its volume was measured. At the end of the 27th cycle, a tenth layer of cemented tailings was deposited on the top of the tailings’ stack. Testing was performed for 34 cycles, and then, the model was dismantled and the collected samples were analysed through a multidisciplinary fine characterisation. The results of this investigation showed that the volume of collected water at the bottom of the physical model varied over the test’s duration. This could be due to seasonal variations in the temperature and moisture of the laboratory. The cemented layer deposited on the top of the physical model appears to play the role of protecting against underlying layers from evaporation. Finally, diffuse oxidation that progressed along the preferential pathway was observed.