Dr Josh Starrett

In mineral processing, partition curves are used to describe the probability of a particle of a given size or density reporting to the overflow or the underflow stream. One simple descriptor is the Rosin-Rammler (Weibull) functional form, based on a sharpness parameter, a. An alternative descriptor was introduced by Scott and Napier-Munn (1992) based on the simplified Whiten equation expressed in terms of the Ecart probable, Ep. Curiously, this simplified Whiten equation has functional equivalence to the Fermi-Dirac distribution (Fermi, 1926; Dirac, 1926), an exact equation used in quantum mechanics to describe the probability of Fermions residing in either the valency or the conduction band. In this study, the particle size classification data from Starrett and Galvin (2023), produced using the REFLUX¿ Classifier, provided powerful empirical evidence supporting the application of the simplified Whiten equation over the commonly used Rosin-Rammler function. The raw data adhered to the simplified Whiten equation over a range of ± 5Ep, much wider than the Rosin-Rammler function. Hence the simplified Whiten equation, with its equivalence to the fundamental Fermi-Dirac distribution, offers prospects for a stronger theoretical framework for describing the role of a hydrodynamic driving force in particle size classification.

A REFLUX¿ Classifier was used to classify a silica feed (0¿710 µm) based on particle size. Split Fluidisation was used to generate remarkably sharp separations involving solids throughputs of up to 92 t/m2/h. This work builds on the previous study by Starrett and Galvin (2023) but with a focus on coarser separations at higher throughputs. As the separation size increased, there was increasing misplacement of fine particles in excess of 75 µm into the coarse underflow stream. This problem was averted by halving the cross-sectional area of the lower section of the REFLUX¿ Classifier. This change led to a doubling of the superficial fluid velocity in the lower section for a given set of flow rates, ensuring fine particles were unable to settle into the coarse underflow. In general, the separations performed in this study show complete closure of the partition curve at both the coarse and fine ends. It was also found that to deliver sharp separations it is essential to introduce sufficient water to the separator, per unit of solids transport to the overflow, especially for higher solids throughputs with coarser separations. Although the fluidisation rate can be used to control the separation size at finer separations (below 180 µm) and lower throughputs, ultimately the bias flux provides the basis for controlling the separation size at coarser sizes and higher throughputs.