Could comminution be eliminated from the mining process?

This provocative question will be posed at next year’s Comminution ’14 in a keynote lecture, The Next Stage in Evolution in Comminution, by Alan Muir, Vice President Metallurgy at AngloGold Ashanti, South Africa.

Alan Muir

In the current mining environment, the need to reduce cost whilst maintaining throughput and recovery, places existing technology in a precarious position. Having evolved over time to adapt to the new environment, Alan feels that current comminution activities are rapidly becoming unsustainable. Whilst there is still value to be had in reducing the unit cost efficiency of existing processing methods by applying “known science” in different ways, this is ultimately an evolutionary dead end. Tumbling mills are inherently incapable of making the jump to a new evolutionary curve and will become extinct sometime in the not too distant future, as has been discussed at previous comminution conferences (posting of 14th March 2013).

Alan will show that it is important that the industry begins to focus on the next “species” of comminution devices and indeed on a new paradigm where the actual comminution step is eliminated from the mining process. Whilst this will require significant investment to conduct fundamental research work, the potential benefits are expected to be considerably greater. The solutions which survive will probably be those that address more than one step in the mining value chain.

How this will be achieved? We will have to wait for Alan’s keynote, which will outline some thinking on a roadmap aimed at facilitating this fundamental evolutionary change.

Falmouth conferences only 4 weeks away

The Falmouth coastal path, with the conference venue centre right

MEI's Falmouth conferences are now only 4 weeks away. Its is not too late to register!

Computational Modelling '13 commences four weeks on Tuesday, followed by Physical Separation '13 on the Thursday. Full details, including programme, registration and accommodation, can be found on the respective web sites.

Adaptation of mineral processing techniques for recycling of lithium-ion and nickel metal hydride batteries

Production of lithium-ion (LiBs) and nickel metal hydride (NiMH) batteries is expected to increase rapidly due to the soaring price of oil and gas, which increases interest in renewable energy, as well as the introduction of hybrid vehicles and electric vehicles which use such batteries as an effective energy storage device (see also the posting of 20 June 2011).

Development of an efficient recycling scheme to recover the valuable parts and safely dispose the harmful ones at the end life of the batteries is a necessity. The challenge, however, is how to recover all the valuable metals without sacrificing the economics of the recycling process.

Several LiBs and NiMH battery recycling processes have been developed in recent years. A review of these processes and their development has been presented in a recently published paper in Minerals Engineering, which has become the 3rd highest downloaded paper over the past 3 months, highlighting the intense interest in recycling.

It was found that the major drawback of these recycling processes is the loss of some of the valuable battery parts, as the techniques were not originally developed for these types of batteries. Also, some of these processes are expensive and designed for specific types of batteries which ignore contamination of the recycling stream with impurities and other battery types.

Using mineral processing operations such as grinding, screening, magnetic, electrostatic, and gravity separations to liberate the electrodal materials and to concentrate valuable metals is a critical step in any recycling process. The review showed that applying these processes reduces the volume of LiBs and NiMH scrap, liberates their valuables, reduces the need for leachate purification in hydrometallurgical processes, and facilitates decomposition of the battery electrolyte. Based on these results a flowsheet to recycle mixed stream LiBs and NiMH battery scrap has been proposed.

Energy recovery potential in comminution processes

My posting of 23rd April discussed Tim Napier-Munn’s forthcoming keynote lecture, which will be presented at next year’s Comminution ’14. Tim asked the question “Is progress in energy efficient comminution doomed?”

Comminution processes are cited as having an efficiency of less than 1%. Even if the efficiency of these processes could be increased to 5%, as is suggested to be possible, the conclusion would remain that comminution processes are very inefficient, with some 95% of the input energy lost to the environment as heat. This is an interesting observation as one could suggest that, although comminution systems are very inefficient in producing new surface energy, they should be very efficient in producing heat. On the other hand, high efficiency in generating heat might be off-set by a limit on the energy that can be recovered.

This is the theme of a very interesting and thought-provoking paper by Peter Radziszewski of McGill University, Canada, which has recently been published in Minerals Engineering. Four issues are addressed in the paper: heat generated in comminution, potential energy recovery, different means to increase energy recovery in comminution processes and avenues to possible implementation.

Peter shows that at the discharge of the comminution circuit, the working fluid mineral slurry has captured a certain amount of energy that can be defined by its heat capacity and temperature. The greatest potential for energy recovery is therefore found at the discharge of the grinding circuit, which of course coincides with the input to the flotation circuit. It is at this location that one would find the highest slurry temperature. Also, at this location one could either divert the energy carrying slurry into a separate heat conversion system or find a heat conversion system that has the potential to be integrated or retrofitted directly with the flotation circuit. In the literature a number of workers indicate that increased temperatures might be advantageous to flotation. It is suggested that more focused research should be initiated to explore in more detail the effect of increased slurry temperatures on flotation performance.

However, the paper recognises the challenges of insulating and sealing a comminution circuit, the implementation of a capture and energy conversion system, and effects that the application of an energy recovery system might have on other dimensions to mineral processing such as flotation, wear and water recovery.

Insulating and sealing an existing comminution circuit is in itself a non-trivial challenge. The minimal requirement of an insulating system for a rotating mill such as a SAG or ball mill would be that it does not increase the downtime for liner change-outs. Further, it would be unrealistic to completely seal an existing comminution circuit. However, measures can be made to reduce such loss by covering mill trunnions and sumps. In this analysis, only SAG and ball mills were considered. However, higher intensity stirred mills, and in general higher intensity grinding, may provide higher slurry discharge temperatures and therefore higher energy recovery potentials. This observation may justify the development of new, yet higher intensity, grinding systems that may provide both increased throughput and higher energy recovery potentials, resulting in higher overall comminution efficiencies.

Therefore, it might be time to propose that the desired goal of comminution processes is not only to grind a given ore to a target granulometry, but also to capture and recover the heat generated in comminution, but despite the promise of increased comminution circuit efficiency and potentially substantial annual energy savings, there remain a number of challenges before such energy harvesting technologies can be brought successfully to the mining industry.

Food for thought though? Let’s have your opinions.

Cornwall's King Edward Mine mill wins major Engineering Heritage Award

Delegates at next month's Physical Separation ’13 will have the opportunity of taking a fascinating tour of the Camborne-Redruth mining area, the ‘birthplace of modern mining’ (see posting of 25th March). The tour will start at the King Edward Mine (KEM) museum, which I rate as the world’s best mineral processing museum, the working mill simulating a 19th Century tin dressing circuit.


KEM Mill

So it was good to hear that the Institute of Mechanical Engineers (IMechE) has awarded KEM an Engineering Heritage Award, the mill at KEM being the first to be recognised in Devon and Cornwall. The nearest other recipients of the award are the Hindley Steam engine in Sherborne, Dorset and the SS Great Britain in Bristol.

Other recipients include Tower Bridge, the Channel Tunnel, the Ffestiniog Railway and the Battle of Britain Memorial Flight, so KEM is privileged to be listed alongside such world famous names. KEM’s award is the 83rd IMechE Award, the 82nd Award beings for the 'Mallard' - fastest steam locomotive, putting KEM with the best of British engineering.

If you are registering for Physical Separation ’13, don’t forget to book your free ticket for the mine visit!!

Nchanga Metallurgists, 1970s

This is really an update on previous Zambia postings and my quest to get in touch with long lost colleagues from those days.

Just over a week ago, Don Maxwell, who was an engineer at Nchanga in the 70s, commented on my posting Return to Chingola. Don had also returned to Chingola in 2010, accompanied by Peter Bulloch (Section Engineer, Concentrator) and Roger and Janet Thomas. Although I only vaguely remembered Peter Bulloch, it was great to see Roger and Janet in the mine photo, and to be able to contact them after all these years.


Peter Bulloch, Janet Thomas, Don Maxwell and Roger Thomas at Nchanga, 2010

Roger was acting plant metallurgist on the concentrator when I arrived in Zambia. He remembers me as a “slim, slightly nervous metallurgist, accompanied by a fair young damsel”. I’m not sure who that was, but I will ask Barbara, maybe she will remember! He also remembers supervising my first duty on the concentrator- looking after the daily and monthly metallurgical accounts. I also have vivid memories of Roger praising me for how quickly I produced the first monthly account, and then the next date berating me, as I had completely cocked it up – never mind, it’s a bit like washing-up, break a few pots and you are not asked again!

Like me and the fair damsel, Roger and Janet were adventurous, and they certainly made the most of their time in Zambia, travelling to East Africa (as we did), and climbing Kilimanjaro (which we did not do). They also made an overland trip to UK, driving through India and Afghanistan, something which no sane person would attempt today.

Janet and Roger Thomas

Roger and Janet left Chingola in early 1971 to study for MBAs at the University of Cape Town. He then left the metallurgical profession to develop his entrepreneurial skills, first in boat building and truck hire and then in engineering supply, where he became Managing Director and then Chairman of a company supplying anticorrosive and low friction products. After retirement seven years ago Roger and Janet, and their three children, settled in Cape Town. They live in Constantia, and a nearby neighbour is Jack Holmes, who I believe was metallurgical manager at Nchanga in the 70s. Roger is also in regular contact with Les Stewart, Paul Smithson, Roger Kelley, Willem Duyvesteyn, Ken Severs, Dave Parker, John Duckworth and Dave Deuchar, familiar names to any metallurgist who worked at Nchanga in the 70s.
 

In early 1972 I was transferred from the Concentrator to the commisioning team for stage 1 of the Tailings Leach Plant (TLP) Project, where I had the pleasure of working with metallurgist Tom Whitehouse. I totally lost track of Tom after leaving Zambia, but he traced me a couple of months ago, via my posting on my days at TLP. He left Zambia in 1978 after spending some time at Broken Hill in Kabwe, and Nampundwe Mine near Lusaka. On returning to UK he retrained as a secondary school teacher, and he and his wife Fran now live in Rochdale in the north of England.

Tom and Fran Whitehouse

I left Zambia in 1973, too late to see the giant TLP come into operation, so it was great to see this during my visit to the mine last year. I have made contact with many old friends from the past recently, but none so far back as that of Roy Jeffrey. He and I were friends in the very early 1960s, at the local Youth Club, where I also first met Barbara! Roy and I lost touch when I went to Leeds University in 1963 and then on to Zambia.



Pam and Roy Jeffrey, 1987

Roy also studied metallurgy, at Swansea University, and then also left for Zambia as a metallurgist on the High Grade Leach Plant (HGLP) (which no longer exists). He became assistant superintendent of the HGLP and then moved on to the TLP as assistant superintendent/acting superintendent. On leaving Zambia in 1990, Roy, like Tom, retrained as a teacher, and he and his wife Pam now live in Stalybridge, not too far away from the old Youth Club!

It must be around 50 years since we last saw Roy and Pam, so it was great to see them again today. They are on a Bank Holiday weekend holiday in Cornwall and dropped into Falmouth for lunch with us at the lovely Cove restaurant.

More and more people are visiting the blog (the page views have doubled over the last 5 months to over 18000 per month) so I am sure that many other old colleagues from the past will read this posting. If you do, please get in touch.

Flotation ’13 only 6 months away!

MEI’s premier event, Flotation ’13, will be held at its usual venue, the Vineyard Hotel, Cape Town in November. Interest in this has been unprecedented, with 15 companies providing corporate support, and all exhibit booths already sold.

The 4-day conference features two discrete symposia, Fundamentals (Physics and Chemistry) and Applications/Plant Practice. Prof. Kari Heiskanen, of Aalto University, Finland, will present a keynote lecture at the former symposium, and Dr. Dariusz Lelinski, of FLSmidth, USA, at the latter.

There is good reason to present a paper at the conference, as all papers will be peer-reviewed after the event for possible inclusion in the special Froth Flotation issue of Minerals Engineering, now regarded as the state-of-the-art volume for flotation innovation and research. Short abstracts should be submitted no later than the end of next month, and if accepted draft papers will be needed prior to the conference, for inclusion in the unrefereed Proceedings.

Apart from the technical presentations, there will be much to enjoy in Cape Town, including an informal conference dinner at the Waterfront, a guided hike up Table Mountain, and a number of pre-conference workshops and courses- more details will be in a blog posting later this month.

The latest updates can be viewed on Twitter (#Flotation13).