New challenges for gravity concentration and classification of fine particles

Abstract

“The net zero emission” mantra may prove to become the new “mother of invention” for minerals processing. The need for change is locked in, and rising, creating new opportunities, especially in gravity concentration and classification. The challenge is to identify and deliver what is required.This paper is concerned with the gravity concentration and classification of particles in a medium of water, involving particles typically finer than 1.0 mm. One of the greatest challenges is in delivering large scale, highly efficient, desliming at ∼10 μm to overcome the effects of viscosity, and in turn maximize the value of the resource. This need is most apparent in one of the world’s most significant commodities, iron ore.There should also be a much greater role for gravity concentration across this full-size range, increasingly in the range below 0.1 mm, the historical preserve of flotation. If the particle density can deliver sufficient selectivity, then in principle gravity concentration should be considered. This is especially true where reverse flotation is deployed, which requires a multi-stage flowsheet, very large footprint, and chemicals, to deliver what could be achieved in a single physical stage of gravity concentration. Mechanisms for amplifying segregation forces, including G forces and inclined settling, need to be exploited to deliver the necessary solids throughput.Classification will be challenged by the emerging requirements for gravity concentration, comminution, and coarse/fine particle flotation circuits to ensure beneficiation can straddle two decades in size ranges from 1.0 to 0.1 mm down to 0.1 to 0.01 mm, via classification at an intermediate size, nominally 0.1 mm. While in principle mechanical screens offer ideal classification, the hydrodynamic approach may ultimately deliver the optimum robustness, control, throughput, and efficiency, despite the variation in separation size with particle density, provided synergy can be realised by integrating it correctly within the overall circuit.