(423f) On the Just Suspended Speed in Widely Graded Slurries

Typical correlations to calculate an impeller’s just suspended speed are based upon experiments with slurries with narrow particle size distributions and concentrations smaller than 20-30%v/v in which suspension is due to turbulent eddies in the inertial subrange. In the minerals processing industry, however, particles are often widely graded with a significant portion of them (≈>50%) being smaller than 75 µm. While at elevated concentrations (>20-30% v/v), these types of slurries can become viscous and even non-Newtonian, we do not have an applicable correlation. New suspension experiments are presented for three model widely graded slurries over concentrations of 1 < x_v < 50%v/v. As the concentration increases, the suspension mechanism changes from inertial subrange turbulence to the viscous regime. We present a preliminary correlation for the viscous suspension regime, for which one is not currently available. This correlation exploits a suspension viscosity due to the presence of the fines.