It is a matter of observational experience that slurry flow confines itself into a self-formed channel to find its way down the beach, Williams (2001). It is believed that the channel flow characteristics determine the overall beach slope. The present research project was undertaken to understand the flow characteristics of the channelized tailings. All tests were carried out in controlled conditions in a full-scale experimental flume installed at a mine site, using the flow of fresh mine tailings from the discharge pipeline. For each test, a limiting equilibrium bed slope was obtained. Velocity and density fluctuations and also the average profile with depth were recorded. It is thought that this is the first time that profile measurements on a full scale slurry flow of this type have been carried out. Results from the tests cover many issues and aspects of the on-going work. The mechanisms involved in beach formation and development as well as the occurrence of laminar and turbulent slurry flow regimes on a real stack and the affecting parameters on beach slope, have been investigated in detail. A summary of the key data and the preliminary conclusions that can be drawn have been presented.
Modelling of a tailings beach using a time series of thickener output (flow rate and solids concentration) was first reported by Fitton et al. (2007). Seddon and Fitton (2011) presented statistical data on the performance of thickeners, and showed that the observed concave shape in tailings beaches could be adequately explained by this variability. They then proposed a stochastic method for the generalised modelling of tailings beaches. The aim of this paper is to demonstrate the application and results obtained by the use of this method. This paper shows how thickener performance statistics in the form of frequency functions for variations in (a) underflow solids concentration; and (b) mass flow rate, can be combined with a set of rheology results to develop a predictive beach slope distribution. Data developed from this distribution are then used as an input to a deposition modelling program. The developed beach profile is presented for a typical case.
A series of tilting (variable slope) flume tests were undertaken at the pilot plant facility at Chuquicamata copper mine in northern Chile to study the achievable tailings beach slope for different tailings solids concentrations and flowrates. The pilot plant facility was part of a prefeasibility study into upgrading the existing conventional tailings disposal facility, to a thickened tailings disposal scheme. The tilting flume facility was included into the pilot plant trial to produce reliable data for verification of theoretical beach slope prediction models. The tests were conducted on existing tailings from the Chuquicamata plant. A pilot size (2.5 m diameter) thickener was used to thicken the slurry to higher solids concentration before feeding the tilting flume. A range of different slurry flowrates (ranging from 5.5 to 18 L/s) and solids concentrations (ranging from 56.5 to 72.5%) were tested. The testing methodology, the test results and analysis, are discussed in this paper. The actual measured beach slope (based on hydrodynamics of channel flow theory) for each flowrate and slurry solids concentration are also presented.
The operational fluctuations of tailings thickeners have the potential to cause significant impacts on the tailings transport system and the tailings deposition at a tailings storage facility (TSF). The statistical analysis of actual recorded data of underflow solids concentration and flowrate of different thickeners is presented in this paper. The collected data are from the operation of four different mines; one Zinc-lead, two Copper and one Gold mine. The variability in these two important parameters can be related to process fluctuations, design or construction defects including instrumentation and controls, the variability in mine orebody during the life of the project or operation of the thickener. The analysis of the data shows that the actual performance of the thickener can be significantly different from what is usually considered at the design stage. An example is presented to show the impacts of thickener performance variability on tailings transport system and thickened tailings beach slope quantitatively.
Sheared and un-sheared segregation and settling behavior of fine sand particles in hyperconcentrated homogeneous sand-water mixture flows Ségrégation cisaillée ou non et comportement du dépôt des particules fines dans les écoulements hyperconcentrés homogènes de mélange eau-sable ABSTRACT Segregation and settling of fine solids particles in hyperconcentrated homogeneous sand-water mixtures were studied for un-sheared and sheared conditions in settling columns in the laboratory. Specific solids percent values were able to be determined as the segregation threshold limit for un-sheared static settling conditions as well as for sheared settling with different rates of shear. Full-scale flume tests were also performed in the field with mine tailings slurry to study the settling and segregation behavior of fine sand particles in the flow of a hyperconcentrated sand-water mixture under equilibrium slope conditions. The solids contents of slurry mixtures were within the range 44 to 58% (by weight). The solids particles in the slurries had D 50 = 10 µm. Experimental results showed that increasing the shear rate in the settling column up to a certain level had the effect of increasing the segregation threshold limit value. Slurry density in hyperconcentrated flow remained constant with depth. Although the flow of the hyperconcentrated mixture under equilibrium slope condition was shown to be total transport flow, further detailed grain size analysis revealed that there was always a slightly higher portion of coarse solids particles that tended to accumulate towards the bottom of the flow. RÉSUMÉLa ségrégation et le dépôt des particules solides fines dans les mélanges homogènes hyperconcentrés eau-sable ont été étudiés en laboratoire dans des colonnes de décantation avec ou sans cisaillement. Les valeurs spécifiques de poucentage solide pouvaient être déterminées comme limite du seuil de ségrégation aussi bien pour des conditions de dépôt statique non cisaillé que pour le dépôt cisaillé avec différents taux de cisaillement. Des essais à échelle 1 ont également été réalisés en nature avec des rejets de boues de mine pour étudier le dépôt et le comportement de ségrégation des particules fines de sable dans l'écoulement hyperconcentré du mélange eau-sable sous des conditions de pente d'équilibre. Les teneurs en solides des mélanges de boue étaient dans une gamme de 44 à 58% (en poids). Les particules solides dans les boues avaient un D 50 = 10 µm. Les résultats expérimentaux ont montré que l'augmentation du taux de cisaillement dans la colonne de dépôt jusqu'à un certain niveau a pour effet d'augmenter la valeur limite du seuil de ségrégation. La densité de boue hyperconcentrée dans l'écoulement est restée constante avec la profondeur. Bien qu'il s'avère que l'écoulement du mélange hyperconcentré dans la condition de pente d'équilibre soit un transport total, une analyse granulométrique détaillée indique qu'il y a toujours une part légèrement plus importante de grosses particules qui tendent à s'accumuler vers le fond de l'éc...
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