Application of lubrication theory to modeling stack geometry of high density mine tailings

Abstract

Consideration of non-Newtonian flow behavior has been important in the management of mineral resource wastes for some time, chiefly in regards to dewatering and pumping of concentrated suspensions of mill tailings. These dewatered tailings, often referred to as “thickened” or “high-density” tailings, may be deposited on surface, and if they are sufficiently dewatered to exhibit a yield stress, they will form gently sloped stacks. The geometry of these stacks is in part influenced by the rheology of the tailings, as well as by depositional parameters such as flow rate and the overall slope of the stack. Predicting or managing the evolution of the geometry of such deposits or stacks of high density tailings, is an important issue in mine waste management – mine tailings impoundments can cover several square kilometers, therefore the average slope strongly affects the capacity of the tailings storage impoundment and therefore cost and environmental footprint. Controlling layer thickness is also important for operations where evaporation is relied up to further dewater the tailings. The use of non-Newtonian flow theory may be useful in anticipating the geometric evolution of such impoundments. This paper describes three-dimensional bench scale physical simulations of the deposition of high density tailings from a gold mine. The experimental results are modeled using lubrication theory based equations for equilibrium profiles of simple geometries. Using the yield stress interpreted from slump tests, the lubrication theory equations provide good estimates of the evolving stack, despite the sometimes asymmetric nature of the three-dimensional flows. Limited comparisons are made to a small-set of field data. The behavior of the laboratory stack shows good qualitative agreement with early deposition in the field. Two important issues are discussed, one, the tendency of the stack to evolve a convex profile characterized by high slopes near the deposition point and lower slopes in the later stages of deposition, and two, the influence of settling and capillary action on the rheological behavior of tailings while they are flowing.