Gravity separation in the REFLUX™ Classifier in the presence of slimes

Significant levels of ultrafine particles remain in the feed after desliming via cyclones. These slimes represent a challenge for downstream processing due to the increased viscosity, moisture retention in the product including associated materials handling issues, and entrainment of contaminant with the product. This paper examines the influence of slimes on the recovery of high-grade iron ore fines across a size range of 0–0.3 mm using the REFLUX™ Classifier. Experiments were performed using closely spaced inclined plates (3 mm apart and 1000 mm long) over a range of solids throughputs of 3.5–28 t/(m ²h). Lower feed solids concentrations led to higher recoveries due to the reduction in the viscosity arising from the slimes. At the higher volumetric flowrates used to increase the solids throughput, the very high shear rates generated in the channels further reduced the viscous effects of the slimes. The results are supported by rheological data, based on the ultrafine solids collected from the overflow stream which show strong shear thinning at the relevant shear rates within the inclined channels.