Hydrodynamic classification of a binary density feed with no by-pass

The hydrodynamic classification of two minerals of very different density, silica and hematite, was investigated using a modified REFLUX™ Classifier known as the GradePro™. The primary objective was to achieve efficient classification with no by-pass, meaning no entrainment of relatively fine particles with those that report to the coarse underflow stream. By-pass is a common feature of cyclones in comminution circuits, responsible for overgrinding and hence lower mineral recovery, excessive energy consumption, poor mill utilisation, and increased tailings and water loss. A series of continuous steady state classification experiments was conducted covering a range of separation sizes. The partition curves were produced as a function of the particle size. Pycnometry was used to convert the data into a binary data set composed of the hematite and silica portions. The classification was found to be very sharp, exhibiting closure of the partition curves and no by-pass. The hematite separation size was typically half that of the silica, but calculations indicated the two minerals had the same slip velocity due to the differential levels of hindered settling, governed by the suspension density. This shift in separation size offers a range of benefits which are discussed.