Dr Dariusz Lelinski, FLSmidth, USA, outlines how new approaches to flotation and froth recovery can cut coarse particle loss and increase efficiency.
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lotation systems are a vital technology in minerals processing and extraction. But, despite their overall effectiveness, particles of valuable ore still get disposed of along with waste material. These can add up, accounting for a significant loss in potential revenue. Additionally, the energy consumption that flotation systems require to function effectively is high. So, while flotation systems are necessary when recovering ore, making them more sustainable and energy-efficient has been a challenge. One recent approach to optimising flotation has been to divide the flotation process into its two constituent stages: the first part is the formation of the bubble-particle aggregates in the slurry; and the second is the recovery of these aggregates in the froth. Historically, most attention – both from the theoretical and practical point of view – has been given to the first part of this process. However, due to a newly developed instrumentation package, optimising froth recovery rates is now set to deliver real dividends. It is probably no exaggeration to say that the potential from augmenting froth recovery rates – in terms of what more efficient control of the level, residence time in froth, and pulling rates could deliver – was only truly recognised a few years ago by the industry.
48 MAy/June 2021 // global mining review
This is because it was incorrectly assumed that there are no losses during transport from slurry to the launder. It was only a few years ago that it was measured fully, and the results showed that the loses are typically 50% – reaching as high as 90% for coarse particles. What it means is that 50% of particles, averaging across all sizes, must be re-captured after becoming detached in the froth phase.
Simplifying a complex solution What if it were possible to increase the probability of recovery of particles in the froth phase, especially coarse ones? A good idea, but there is no simple way to put it into practice. It would require a combination of instruments and devices, more or less a froth-recovery instrumentation package, flexible enough to achieve this goal in the majority of flotation applications. A new and practical solution comes from the recognition that the combination of exact slurry level measurement and accurate control of flow using redesigned dart valves and new Festo actuators allows for better control of the froth phase. This in turn results in quicker reactions to flow and slurry density changes, which dramatically improves the performance of flotation machines.
