When I first saw the flotation plant at the Nchanga copper mine in 1969 I was impressed with the sheer scale of the operation, and the multitude of Denver Sub-A flotation machines arranged in parallel banks, each bank containing 20 1-m³ cells. A year later, what were considered to be huge 8.5-m³ Wemco Fagergen cells were introduced into the oxide flotation circuit.
When I made a
return to Nchanga in 2012 all these cells had been replaced by much bigger machines, but even they were not of the size used on many large copper concentrators today.
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| Nchanga's derelict former sulphide flotation plant |
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| Nchanga's current sulphide roughers |
The Applications Symposia of the last few MEI Flotation conferences have highlighted the continued increase in size of machines. The race to increase cell size has become almost a competition between manufacturers, the leading players being Metso and Outotec, who manufacture cells of over 600-m³ capacity, and FLSmidth, with the largest cell in the Western world, the 660-m³ SuperCell.
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| The FLSmidth SuperCell |
At
Flotation '19 Outotec described the commissioning of the first two Outotec e630 TankCells®, with 630-m³ of effective flotation volume, at Buenavista del Cobre Cu-Mo concentrator plant in Northern Mexico as the first cells in two existing rougher lines. Commissioning was finished in March 2018 and since start-up the plant has reported increased copper recoveries while maintaining the final grade.
Leading the race at the moment, however, is Chinese company BGRIMM Technology Group, who described the installation of the 680-m³ KYF-680 Machine, which is currently operating at the DeXing Copper Mine in China to reprocess the tailing.
But is the race ending and have machines now reached a limiting size? This was the question asked by
Stephen Neethling, of Imperial College, UK, at
Flotation '19, who showed that as cells get larger they become more carrying capacity constrained, while a paper from
Eriez Flotation Division, USA, suggested that the approach of exploiting economies of scale and building increasingly larger unit operations is flawed, as there is a significant reduction in energy efficiency as the conventional tank designs become larger.
In
last month's E&MJ,
Carly Leonida conducted an excellent interview on flotation for the 21st century with
Thierry Monredon,
Metso's global manager for flotation. He felt that 600-m³ cells would definitely be the maximum size used in the foreseeable future, suggesting that it is often cheaper to have two banks of 300-m³ cells instead of one bank of 600-m³ cells.
Currently, it is operations with low grades and high throughput, for example, copper mines, that have opted for 600-m³ cells. “Grades have been decreasing, and to maximize efficiency, these operations need to have high throughput,” said Monredon. “In these cases, large diameter flotation cells are compulsory, but again, 600-m³ is really the limit. That’s clear for me, for our company, and I believe that’s what we’ve seen from our competition as well.”
So, what are your views on this? I would be particularly interested in hearing from those of you who have had experience of working with such large machines.
