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Mineral slurries may be dewatered to the point that they manifest non-Newtonian behavior. Many such slurries exhibit both thixotropic and hysteric behavior in their rheology, which has important implications for managing their deposition in tailings impoundments. This paper characterizes the rheology of a mineral slurry with relatively high clay content, which is treated with a high molecular weight anionic polymer to induce flocculation. The rheology exhibits viscosity bifurcation behavior similar to pure clay, including shear history-dependent apparent yield stress values. Rheometry results are presented including stress growth, controlled stress tests, and oscillatory rheometry, all using a vane fixture. The measured rheology is modeled using a previously published viscosity bifurcation model that accounts for hysteresis in the apparent yield stress. The rheology results are used semi-quantitatively to explain deposition rate-dependent behavior seen in flume tests. The geometry of tailings in flume tests with relatively slow deposition is affected by the presence of deposited tailings that have come to rest sufficiently to manifest the yield stress of initially fully structured material, rather than the lower value yield stress that characterizes when the material first comes to a stop. This full recovery of the yield stress seems to be particularly important to managing surface deposition, as zones of tailings that have stopped moving substantially steepen the slope of deposits near the deposition point. [ABSTRACT FROM AUTHOR]

Tailings are a slurry of silt-sized residual material derived from the milling of rock. High density (HD) tailings are tailings that have been sufficiently dewatered to a point where they exhibit a yield stress upon deposition. They form gently sloped stacks on the surface when deposited; this eliminates or minimizes the need for dams or embankments for containment. Understanding the flow behaviour of high density tailings is essential for estimating the final stack geometry and overall slope angle. This paper focuses on modelling the flow behaviour of HD tailings using smoothed particle hydrodynamics (SPH) method incorporating a 'bi-viscosity' model to simulate the non-Newtonian behaviour. The model is validated by comparing the numerical results with bench scale experiments simulating single or multi-layer deposits in two-dimensions. The results indicate that the model agreed fairly well with the experimental work, excepting some repulsion of particles away from the bottom boundary closer to the toe of the deposits. Novel aspects of the work, compared to other simulation of Bingham fluids by SPH, are the simulation of multilayer deposits and the use of a stopping criteria to characterize the rest state. [ABSTRACT FROM AUTHOR]

The authors (Lloret-Cabot et al. in Acta Geotech 1-23, 2017) applied the glasgow coupled model (GCM), originally proposed by Wheeler et al. (Géotechnique 53(1):41-54, 2003), to the simulation of several experimental tests that involve transition between saturated and unsaturated states. The authors show qualitatively, but not quantitatively, predictions of GCM for shrinkage during air drying of normally consolidated samples (Fig. 13) under low mechanical stress conditions, without presenting the material parameters. The discussers, who have worked with GCM to model multilayer deposition of tailings/soft soils (Qi in Numerical investigation for slope stability of expansive soils and large strain consolidation of soft soils. Doctoral dissertation, University of Ottawa, 2017; Qi et al. in J Geotech Geoenviron Eng 143(7):04017018, 2017, Qi et al. J Geotech Geoenviron Eng 143(7):04017019, 2017), have made quantitative predictions of similar cases. Satisfactory simulations of such cases using GCM are sensitive to the selection of the coupling parameters k1 and k2. By considering an alternative analytical form of GCM, an analytical procedure can be derived for calibrating the coupling parameters for problems involving virgin drying. [ABSTRACT FROM AUTHOR]

A problem in implementing water covers over existing tailing impoundments is the dissolution of minerals produced through oxidation and the subsequent flux of metals into the water cover. One possible solution is to place a protective layer of non-reactive soil at the tailings/water interface to inhibit metal transport. A laboratory evaluation of different water cover systems was performed employing columns packed with tailings submerged beneath 1 m of water. A ten-centimeter layer of sand or peat was placed at the tailings/water interface. The experiments were kept stagnant for 183 days, and then flushed with water at a steady rate for 468 days. Both protective covers prevented degradation of water cover quality for the duration of the experiments, as pH exceeded 5.5; however, the quality of the tailings pore water remained poor and even declined slightly from pH > 4 to pH < 3. Leaching of iron and sulphate from the tailings with a sand protective layer ceased during the experiments. Conversely, in the columns with a peat layer, substantial leaching of metals and sulphate from the tailings continued to the end of the experiments. It is postulated that the peat is a source of chelating agents, such as organic acids, which are known to accelerate the dissolution of certain minerals formed through weathering. The sensitivity of metal transfer rates to the thickness and type of protective cover above the tailings were modelled. A 10-cm peat layer was predicted to prevent substantial degradation of the water cover for at least ten years. [ABSTRACT FROM AUTHOR]

To evaluate the effectiveness of soil covers, column experiments were conducted on tailings protected by a three-layer soil cover and tailings directly exposed in the open laboratory for a period of 760 days. Periodic rain application was performed to simulate field conditions, and at four times during the experiments the pore water was completely flushed out of each column for analysis. Profiles of oxygen, temperature, and volumetric water content were measured throughout the experiment, and the post-testing pore water quality was also characterized. A one-dimensional semi-analytic diffusion model was used to simulate oxygen profiles in the uncovered tailings. Modelling performedusing the geochemical code MINTEQ showed that in the laboratory, aluminium concentrations in the tailings pore water were controlled by Al(OH)SO4, sulphate by gypsum and Al(OH)SO4 and iron by lepidocrocite in the upper half and by ferrihydrite in the lower half. In the field, however, the iron oxyhydroxide minerals formed in the oxidized zone appear to be dissolving. It was found that thecover was effective in preventing significant desaturation of the clay, even over a 150-day drying period. The covered tailings did not oxidize much during the experiments. In the uncovered tailings, oxygenmodelling and examination of the geochemistry show that the rate of gross oxidation and the advancement of the oxidation front decreases with time. However, pore water quality is controlled by geochemical processes other than oxidation, as reported in the field. [ABSTRACT FROM AUTHOR]