Effects of heterogeneous hydrocyclone feed in a magnetite grinding circuit

Hydrocyclones classify particles based on both density and size, with the d50 size becoming finer as the particle density increases. As a result, when the hydrocyclone feed is a heterogenous mixture of particles with different densities, each type of particle follows a different efficiency curve. This can lead to the bulk efficiency curve deviating markedly from the ideal S-shaped efficiency curve that occurs when particles have a uniform density. To evaluate the effect that this has on an operating mineral processing plant, samples from a magnetite grinding circuit which exhibited a non-S-shaped hydrocyclone efficiency curve were analyzed with respect to size distribution and magnetite assay, and individual magnetite and quartz efficiency curves were calculated. The particle density effect was shown to cause significant retention of the fine magnetite in the grinding circuit by the hydrocyclone, resulting in over-grinding of magnetite and a subsequent waste of approximately 7% of the total grinding energy. Suggested sizing improvements either the addition of screens to the grinding circuit to supplement the hydrocyclones, or the complete replacement of hydrocyclones with screens. © 2005 Taylor & Francis Group