Predicting particle settling rate in a sheared mining slurry
Many tailings slurries are comprised of fine particles suspended in a carrier fluid. For high enough concentrations, the fines and water combine to form a non Newtonian slurry. In a number of important applications, these slurries also contain larger, denser particles that are able to settle under shear. This results in inhomogeneity in the flow and can potentially significantly increase the pressure gradient required to drive it. A key unanswered question is how the settling rate of large particles is related to the rheology of the fluid and the local shear in the particle vicinity. In this paper, a numerical investigation of large particle settling in un sheared and sheared mining slurries is presented. For power law rheology, the ratio of sheared to un sheared particle settling rate increases with increasing imposed shear and with increasing shear thinning. We propose a criterion for estimating the settling velocity under shear that can be used to provide estimates of particle settling during transport and the likely distance before complete stratification in laminar flow.