Yield stress versus arresting stress for managing high density tailings deposition

S. Mizani, P. Simms

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Mining Geotechnics

ABSTRACT: tress versus arresting stress for managing high density tailings deposition Mizani, S., & Simms, P. Department of Civil and Environmental Engineering, Carleton University, Ottawa, Canada ABSTRACT One of the challenges faced when predicting deposition geometry of high density tailings is to identify appropriate rheological parameters. In fact, uncertainty in the rheology is often cited as a reason for relatively poor accuracy of predictions of beach slope geometry or layer thickness. One reason might be a poor choice for the yield stress used in a prediction. Yield stress is often measured directly as the point of initiation of flow (or failure), starting from zero stress, or is back-calculated from shear stress shear strain data while the tailings are being sheared. While these methods are appropriate for determining the yield for initiating flow in a pipeline, in the first case, or determining friction loss in a pipeline for the second case, these values may not be applicable to deposition. The stress that best quantifies when the tailings stop, or the for two kinds of tailings: gold and polymer amended oil sand tailings. A controlled decreasing shear stress test appears to simulate stress history during deposition, and provides accurate values of the arresting stress. RÉSUMÉ L'une des difficultés rencontrées lorsque prédire géométrie de dépôts de résidus miniers haute densité est d'identifier les paramètres rhéologiques appropriés. En fait, l'incertitude de la rhéologie est souvent cité comme une raison pour relativement faible précision des prédictions de plage pente géométrie ou couche d'épaisseur. Une des raisons directement comme le point d'initiation de flux (ou l'échec), à partir de zéro stress, ou est rétro-calcul du cisaillement stress données de déformation de cisaillement tandis que les résidus sont cisaillé. Bien que ces méthodes ne conviennent pas pour déterminer le rendement d'émission débit dans une canalisation, dans le premier cas, ou la détermination des pertes par frottement dans un pipeline pour le second cas, la valeur de ces peut ne pas être applicable aux dépôts. Le stress que sur les meilleures quantifie lorsque larrêt de résidus, ou l'arrestation « stress » est examiné dans cette étude pour deux types de résidus : or et polymère modifié sables bitumineux. Un test contrôlé de la contrainte de cisaillement décroissante apparaît pour simuler l'histoire des contraintes durant la déposition et fournit des valeurs précises de la contrainte de l'arrestation. 1 INTRODUCTION Successful implementation of high-density tailings disposal requires foreknowledge or control of how the geometry of a stack will evolve over time. Having a good estimate of the beach slope is critical to sizing the tailings impoundment, and will often dictate important costs such as dam construction volume. The thickness of individual lifts, which can be optimized to promote post-deposition dewatering, is another important parameter. Neither of these parameters can be predicted with much certainty at the preliminary design stage. For beach slope, it is fair to say that at least a 1% uncertainty exists, for a parameter that averages about 2% in the field (Simms et al. 2011). Several factors contribute to this uncertainty, such as reliability of thickener operation, effects of how deposition is engineered (type, number and placement of spigots, cyclic, split, or central discharge), and also potentially how the rheology of the tailings varies down the beach until they come to a stop, This last factor is the topic of this paper. We present a number of different rheometry measurements for two types of tailings: i) a gold tailings thickened to 70% solids (38% gravimetric water content, GWC), and ii) a polymer amended oil sand mature fine tailings that is mixed at about 38% solids (180% GWC), which would subsequently dewaters to 45-50% solids within 24 hours. We attempt to identify a rheometry technique that best characterizes the stress history experienced by the tailings as they flow down the beach. 2 MATERIALS 2.1 Gold tailings The gold tailings were transported from a gold mine and arrived as a cake with about 25% water content in 20 litre pails. Bleed water at the top of the pails was used to remix the tailings to GWC of 38%. The specific gravity (solid phase density) was determined to be 2.9 using ASTM D854 (2000). The particle size distribution of tailings was established by the combination of sieve (wet technique) and hydrometer analyses results based on ASTM D 422-63 (2002). The D90, D60, and D50, and D10 are 80, 50, 40, and 5 microns. About 15% of the material passes 2 micorns. Liquid Limit (LL), and Plastic Limit (PL) were 22.5%, and 20% respectively, using a fall cone (ASTM D4318, 2000). The mineralogical analysis of the gold mine tailings

RÉSUMÉ: d stress versus arresting stress for managing high density tailings deposition Mizani, S., & Simms, P. Department of Civil and Environmental Engineering, Carleton University, Ottawa, Canada ABSTRACT One of the challenges faced when predicting deposition geometry of high density tailings is to identify appropriate rheological parameters. In fact, uncertainty in the rheology is often cited as a reason for relatively poor accuracy of predictions of beach slope geometry or layer thickness. One reason might be a poor choice for the yield stress used in a prediction. Yield stress is often measured directly as the point of initiation of flow (or failure), starting from zero stress, or is back-calculated from shear stress

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Cite this article:
S. Mizani; P. Simms (2014) Yield stress versus arresting stress for managing high density tailings deposition in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper460,author = S. Mizani; P. Simms,title = Yield stress versus arresting stress for managing high density tailings deposition ,year = 2014}