Sink-Hole fluidization for dry separation of mineral particles

Abstract: A novel Sink-Hole fluidization method was investigated for dry separation of mineral particles (1 to 10 mm in size) using a combination of dense medium fluidization and vibration. The device referred to as a Sink-Hole fluidizer consisted of a 200 mm diameter fluidized bed, a 1 mm aperture mesh mounted on top of the fluidized bed with a centrally-located large hole (compared to the mesh aperture) referred to as a Sink-Hole, and a 1 mm aperture mesh underneath to capture the denser particles. The unit was mounted on top of a Kason vibrating device. Experiments were conducted using 2.0-8.0 mm tracer particles of density varying from 2400 to 4800 kg/m³. The fluidized sand medium, subjected to vibration, expanded towards the upper screen, permeating strongly through the large Sink-Hole, and to a lesser extent through the finer apertures. In fact, the excess sand on the upper screen then returned back to the lower fluidized bed via the fine screen apertures. The upward movement of the suspension through the Sink-Hole produced a strong density based separation of the larger tracer particles. It was possible to achieve sharp separation at different separation densities under batch conditions. This paper reports the effect of varying air rate and bed mass on the separation performance. Density cut points in the range 2500 to 3200 kg/m³ were obtained, which are significantly higher than the density of fluidised media, at separation efficiency (Ep) values of around 0.15.