Continuous gravity separation of concentrated bidisperse suspensions in an inclined plate settler

Abstract

An experimental study for the continuous separation of concentrated bidisperse suspensions in an inclined plate settler has been conducted. The bidisperse suspension examined consisted of light polystyrene and heavy polyvinyl chloride beads in a salt solution. The effects of the feed total solids concentration, feed flow rate, angle of inclination and split ratio (defined as the ratio of either the underflow or the overflow to the feed flow rate) on the performance of the settler were examined. For a feed having high total solids volume fraction lateral non-homogeneities in the form of instabilities (fingers) were observed in the settler. The recovery of the heavy particles in the underflow stream significantly increased as the concentration of the light particles in the feed was increased. However, this had an adverse effect on the recovery of the light particles in the overflow stream at low feed flow rate and an angle of inclination of 30°. The enhancement in the recovery of the particles due to the presence of local instabilities for the vertical settler was much greater than that at an angle of inclination of 30°. A previous model due to Masliyah et al. was found to predict the experimental measurements for the dilute bidisperse suspensions. For high feed total solids volume fractions where strong instabilities were present, the model was used to assess the improvement in the settler performance as a result of these instabilities.