Rheology for deposition control of polymer-amended oil sands tailings

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.