Ultrafine desliming using a REFLUX™ classifier subjected to centrifugal G forces

Ultrafine desliming of a silica feed, covering the particle size range of 0-100 µm, was investigated using a pair of 171 mm × 178 mm cross-section REFLUX™ Classifier modules subjected to 55 G force in a spinning centrifuge. The modules consisted of a system of inclined channels, with perpendicular spacing of 1 mm, formed through 3D printing, attached to a fluidized bed housing. This centrifugal system is termed the REFLUX™ Graviton. The feed was varied from 36 to 115 L/min with concentrations from 2 to 30 wt% solids. Continuous steady state separations at cut sizes from 20 µm down to 5 µm and Ep values of 3-6 µm were routinely achieved. The hydrodynamic benefits of the so-called inclined settling effect multiplied with the hydrodynamic benefits of centrifugal forces, resulting in better than 1000-fold throughput advantage over conventional settling. The partition curves exhibited a strong "fish-hook" effect influenced by both the fluidisation velocity and the underflow-exit tube diameter. The diameter of the tube also had a significant effect on the sharpness of the separation. When the tube was undersized, the excess solids partitioned into the overflow resulting in poorer sharpness of separation. Conversely, when the tube was oversized, some material that should have exited in the overflow instead bypassed to the underflow. Experiments also found an optimum fluidisation velocity, below which inadequate fluidisation resulted in excessive fine particles exiting in the underflow and above which the sharpness of separation deteriorated due to excessive mixing.