Evaluation of highly thickened tailings technologies requires that during early design stages an understanding is developed for the range of feasible beach slopes to be achieved during deposition. A comprehensive evaluation of the whole range of factors that influence the beach formation process is paramount to ensure that expected performance during design stages is met throughout operations. This paper presents an integral approach for beach slope estimation, considering a broader range of aspects affecting the beach formation process than those commonly used in current models (rheology and discharge rate of the deposited tailings). The additional aspects considered by this approach are site conditions (site morphology and climate), the rate of rise of the tailings impounded (the relationship between the tailings production rate and the available area for tailings spreading) and the deposition sequence (the configuration of the deposition system and its operation, e.g. thin layer deposition with drying cycles). The approach is supported by a beach slope model based on a dimensionless parameter for non-Newtonian flows, associated with sheet flows on an inclined plane, which directly relates to the tailings beach slope expected to be formed due to sub-aerial disposal. This dimensionless parameter provides a closed expression for estimating tailings beach slopes based on rheological properties and discharge rates, but with the integration of site conditions, rate of rise and deposition sequence. High thickened tailings management facility (TMF) design is well supported by this approach, providing key input as the configuration of the distribution system and the minimum area required to achieve expected performance with respect to desired beach slope, density, degree of saturation and strength.
The objective during TSF beach development is to still maintain a slurry that is pumpable and self-distributing at the tailings storage facility (TSF), rather than having to rely on trucks or on conveyors and stacking systems to manage a cake, but one that will deposit at a steeper beach slope than can be achieved by thickening alone. The use of ultra paste has the potential to broaden the range of topographic conditions that will suit thickened tailings discharge. This paper presents a case study for a large copper mine in which underflow from a series of paste thickeners with a nominal tonnage of 3,660 tph at 59% solids concentration would be mixed with 1,363 tph of filter cake at 80% solids concentration. The combined tailings (ultra paste) would be discharged equally into two open channels (flumes) at the combined solids concentration of 63.5%. The ultimate goal of adopting an ultra paste scheme is to produce homogenous consistency tailings, hence proper mixing of the paste and filter cake has to occur. In this study based on a series of tests, the mixing requirement has been assessed. The study also covers a conceptual investigation of natural turbulent mixing (NTM) of the filtered tailings with paste thickened tailings and issues associated with the deposition of the combined tailings, the ultra paste, into the existing TSF. In the conclusion, the study indicates that NTM can possibly occur only for the case in which the total tailings are discharged into one channel, which is not practical due to limitations with regards to tailings management. Hence, mechanical mixing has been recommended in this case.