Wednesday, 10 August 2011

Innovations in Flotation Machine Design



Following the closing of Metplant '11, I attended an excellent lecture yesterday evening given by Prof. Michael Nelson, department chair in mining engineering at the University of Utah, USA.

This was the inaugural lecture in what will become a series of G.D. Delprat Memorial Flotation Lectures, instigated by Prof. Alban Lynch, the first Director of Australia's JKMRC.

Profs. Nelson and Lynch are co-authors of the AusIMM book The History of Flotation, along with Dr. Greg Harbort of AMEC Minpro. The royalties from the book partially funded the lecture, which was also sponsored by FLSmidth and Outotec.

Although entitled 'Innovations in Flotation', Prof. Nelson focused on mechanical flotation cells, and the trend to ever larger machines. This caused some concern with some members of the large audience, who were expecting opinions on column and Jameson Cells, and a representative from CSIRO questioned whether this focus on mechanical cell size, an area driven by operators and equipment manufacturers, undermined the huge role that research institutions and academia have played in the development of reagents and our understanding of the science of flotation.

Accepting this, and explaining that a short lecture such as this must concentrate on a specific area, Michael presented a fascinating history of how cells have developed since their first use on zinc tailings at Broken Hill in 1905, pioneered by G.D. Delprat, one of the most unrecognised, yet important figures in flotation.

The first Minerals Separation cells were pneumatic, and prone to blinding, and were later superceded by Denver Sub-A, Wemco Fagergren and Galigher Agitair cells, the Denver Equipment Company dominating the market by the middle of the century, with over 50% of world sales. A feature of flotation plants in those days was a multitude of parallel banks of many small cells in series, something I remember from my days at Nchanga in the early 70s where many rows of tiny 1.2 m3 Denver Sub-A cells, 20 in series, were gradually being replaced by the then massive 8.6 m3 Fagergrens.

The quantum change in cell design was the move to very large cells, with the development of large cylindrical cells by Outokumpu in the early 80s, with corresponding reductions in overall capital and operating costs, as well as ease of control. With developments in rotor and stator design, cells of up to 300 m3 are now standard, with plans for 500 m3 cells at full pilot scale.

In concluding Prof. Nelson mused on where the next innovations might be made and suggested that we should be looking outside the narrow confines of the minerals industry, and evaluate the methodologies used in related fields, such as dissolved air flotation in water treatment, and techniques used in oil and tar sands processing, as well as the new field of nanotechnology.

Overall I found this a very interesting and informative lecture, which was very well presented. Prof. Nelson has presented this before in various cities, so if it comes to an area near you, I would definitely advise that you make the effort to attend.

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