Investigating flotation at the bench scale - the effect of design modifications on flotation performance and the link to particle size
Creators: name: Mackay, Isobel
Publisher: name: Imperial College London
Year: 2019

description: There is a huge potential to optimise the froth flotation industry as even small improvements in the extraction of metals from the mineral ores can translate to a substantially higher revenue. Typically, laboratory studies into froth flotation involve batch tests where the system does not operate at steady-state, making it difficult to directly apply results to industrial systems. In this work, a continuously overflowing flotation cell, which does operate at steady state, has been used to investigate the effects of different operating conditions on flotation performance. This work used two experimental systems which are more comparable to industrial systems than previous studies using the same bench scale flotation cell. The first system investigated in this thesis used a copper tailings ore. The effects of varying the particle size distribution on the flotation performance and froth stability were investigated. For the first time, a direct comparison between two measures of stability was made, and both measures showed an optimum in froth stability with an intermediate particle size distribution. This optimal particle size distribution also resulted in an improved copper recovery which has important implications for the reprocessing of tailings material via froth flotation. The second system investigated used a synthetic magnetite-silica ore. This ore allows more control over the system, whilst still providing a good proxy for industrial flotation. This system was used to investigate the effects that inserting two retrofit design modifications (horizontal meshes) into the cell had on flotation performance. These meshes were designed to provide a more quiescent environment at the pulp-froth interface (PFI) and reduce particle detachment. The “basic mesh” shifted the grade-recovery curve to an improved grade, while the “blocked mesh” resulted in a significant improvement in recovery and a reduction in entrained magnetite. Positron emission particle tracking (PEPT), a technique that tracks the movement of radioactive tracer particles, was used to investigate the mechanisms that resulted in the improved flotation performance when using the meshes. PEPT experiments were performed with different tracer types and tracer sizes. It was shown that the presence of the mesh reduced the presence of swirl at the pulp-froth interface, and formed a secondary, more quiescent, pulp zone with a shallower froth. In some cases, a mixing loop formed in this secondary pulp zone which promoted the reattachment of detached valuable mineral. It was also shown that both meshes improved the flotation of the coarsest tracer size indicating that the meshes can be used to improve the recovery of coarse particles. For the first time, a continuous bench scale flotation cell has been used to investigate the relationship between design modifications, particle size and the flotation performance. This was done using two different ores, both more complex than what has previously been investigated in similar equipment. These experiments also utilised PEPT to further the understanding of the effect that design modifications have on the flotation performance of different types of particle. The results of this work have two primary applications to improving the flotation of both fine and coarse particles for improving the sustainability of the minerals processing industry. The first application relates to fine particle flotation by finding an optimal feed particle size distribution. This will enhance the ability to reprocess tailings material by froth flotation and therefore improve the sustainability of the industry. The second application relates to coarse particle flotation by using a simple retrofit design modification to increase the floatability of these particles. This will improve sustainability within minerals processing by reducing the comminution requirements and therefore energy consumption. There is, however, more work needed to investigate these modifications further to ensure they are applicable at an industrial scale.