Laboratory study of surface paste disposal for sulfidic tailings: Physical model testing

Surface paste disposal (SPD) of tailings is a recent technique for the management of mine tailings. It consists in dewatering (by thickening and filtering) the tailings before deposition to obtain a self-supporting and homogenous tailings stack. Paste tailings could become an advantageous alternative to conventional impoundments used for slurry tailings. However there are only few detailed studies on the environmental behavior of this approach. In this investigation, a sulfidic paste tailings was deposited in a laboratory-scale physical model (area of 2 m × 0.5 m) in nine layers. A proportion of 2 wt.% of binder was added in the two bottom layers; based on a previous study, this configuration should improve the environmental behavior. The paste tailings in the model have been wetted every 4 weeks with 40 L of water. The volumetric water content of the paste was monitored in each layer during the wetting and the drying phases. Two samples were cored in the tailings after 14 wetting/drying cycles to collect paste specimens. The study focuses on the geochemical analyses of the leachate collected during the experiment, the evolution of the water retention in both cemented and uncemented paste layers, and the characterization of the paste samples. Results show that the pH of the leachate remained circum-neutral during the experiment, although some preferential oxidation pathways were observed in the paste samples. The measurements also show that the evolution of the water content during the drying phases was different for cemented and uncemented layers. The desiccations cracks at the surface of the paste stack reopen at the same place after each wetting, but the crack intensity factor (CIF) decreased from 1.48 to approximately 0.2 during the 6th first wetting/drying cycles.