Thursday, 4 June 2020

Memories of our first journey to Cape Town in 1969

Travel is unfortunately on hold at the moment, and our next long-haul journey is likely to be to Cape Town next April for Comminution '21 and the XXX IMPC.
So I thought I might reminisce about our first ever journey to Cape Town, which might stir a few memories for blog readers who also experienced the leisurely manner of slowly eating up the 9700 km of ocean between Europe and South Africa's Mother City.
On a grey September afternoon in September 1969, Barbara and I slowly sailed from the port of Southampton; ahead of us two weeks on the RMS Windsor Castle, the flagship of the Union Castle Line.
RMS Windsor Castle
Launched in 1959, she was then, at 38,000 tons, the largest liner built in England. She was a very fine vessel, and we quickly settled in and made friends with a South African couple, Cath and Nels Jackson, who were returning to their home in Luanshya, Zambia after a long European holiday.
Compared with our usual 12 hours by Boeing 747, this was indeed a leisurely journey, with one stop at Las Palmas de Gran Canaria, days spent swimming and playing deck quoits, evening discos and games and, of course the ‘crossing the line ceremony’ as we entered the southern hemisphere for the first time in our lives.
The Windsor Castle's Commodore Hort welcomes us on board
Youngsters at dinner
Crossing the line: the 'Greasy Pole' competition
Hippy night
The highlight of the journey was to be the approach to Cape Town, our stately entrance to South Africa, with the magnificent Table Mountain dominating the Table Bay skyline. We dragged ourselves on deck as day broke on that final day, only to be met by weather typical of that we had just left behind in Southampton, cold, grey and wet, and no sign of Table Mountain even as we approached our berthing. We did eventually see the mountain in all its glory, but that was 13 years later!
South Africa was in its most intense phase of Apartheid in 1969, and we spent a couple of days with Cath and Nels in a very uninviting Cape Town waiting for our cars to be unloaded, before heading off up the Great North Road (the N1) to an even more uninviting Johannesburg (MEI Blog 25 November 2010). Here Nels persuaded me to purchase short shorts and long socks, essential items in the Southern African uniform. I felt that they looked ridiculous then, and even more so now- at least Barbara was well suited to the fashions of the day!
Johannesburg: 1969 Southern African fashions, VERY short skirts and shorts and VERY long socks
After two days in Johannesburg, we said our goodbyes and headed north again, relieved to leave South Africa and drive through Rhodesia's Matabeleland and on to Victoria Falls, a journey which we did by luxury train only 6 months ago (MEI Blog 9 December 2019). And then across the Zambezi and on to our new life in Zambia.
Wonderful memories of what is now a long-gone era. It would be great to hear from you if you experienced this before the Union Castle line ceased operations in 1977.

Monday, 1 June 2020

May: the first easing of the lockdown

Living through a plague is something very few people experience, so I am hoping to summarise our progress at the end of each month:
At the beginning of the month Prime Minister Boris Johnson announced that the UK was “past the peak” of the coronavirus outbreak and “we are on a downward slope," acknowledging that every mountaineer knows that this is often the most dangerous part of the climb!
As Amanda said in the MEI Online newsletter of May 7th, we at MEI would like to thank you for all your support during this tough time. With over 38,000 Covid-19 deaths in the UK our privations are miniscule compared with the sufferings of many people and businesses, but MEI is a small family business, and the decisions we've had to make in the last few weeks will impact on us for some time to come.  Knowing that we are part of a larger, wonderful community, made up of people from all over the world, helps us to remain positive, and the many messages we've received have made us feel a little less isolated, so thank you.
We are fortunate, however, to live in one of the most beautiful areas of the world and our spirits have been uplifted by long walks on the Falmouth coastal path, all the time observing social distancing. 
There was certainly no social distancing on May 8th 1945, when crowds poured out onto the streets of Britain to celebrate Victory in Europe (VE) day. It was a much more muted celebration 75 years on, and in her second televised address to the nation during the pandemic the Queen praised the nation's lockdown spirit and urged Britain to "never give up, never despair" and to draw inspiration from how those dark days of WW2 were overcome.
Two days after the Queen's broadcast, Boris Johnson addressed the nation and set out his "conditional plan"for a gradual exit from the lockdown, encouraging those who cannot work from home to return to workplaces in order to kick-start the economy of the UK, which is now heading towards its worst recession since 1706 in the reign of Queen Anne. The gradual exit allowed us to spend unlimited time out of doors, and within days the Falmouth beaches began to take on their pre-virus look, as we "held our breaths" hoping that there would not be a consequential increase in infection rate (or the R number, which must be maintained below a value of 1).

Falmouth beaches 25th May
Relaxing the rules regarding distances that can be travelled to beauty spots has led to worries that the virus will be brought into remote and attractive areas such as Cornwall and the "normal" beach scenes have contributed to a feeling among many that the crisis is over and that social distancing can be relaxed. The Government's messages have unfortunately not been particularly clear, highlighted by the PM's ludicrous equation for the virus threat, which he proudly revealed in his address to the nation:
Even a 10-year old would see that this is nonsense, as C is between 1 and 5, R should be below 1, and N is hundreds of thousands!
In truth the Government has shown remarkable ineptitude in dealing with all aspects of the pandemic, culminating last week with many Conservative MPs calling for the resignation of the PM's chief advisor, Dominic Cummings, after it emerged that he had travelled to Durham from London with his family during the lockdown when his wife had coronavirus symptoms. As Cummings was a major force behind the "stay at home" message, his actions were met with almost universal condemnation, an insult to many people, including those who have not been allowed to leave home to be with dying loved-ones or to attend their funerals. However, not surprisingly, many cabinet ministers flocked to his defence and in a dismal press conference that totally failed to allay concerns the PM insisted that Cummings had acted "reasonably, legally and with integrity." The following day's hour long grilling of Cummings from an angry press did little to calm the general feeling, but it did lead to senior ministers digging enough holes to fill the Albert Hall while pathetically attempting to justify his actions. At the time of writing Cummings remains in his post, and for once Boris has unfortunately not performed one of his famous U-turns.
(Peter Brookes The Times, 22nd May)
MEI's major decision this month was the cancellation of our October conferences in Cape Town.  Most international events for this year are now either postponed or cancelled, including the International Mineral Processing Congress (IMPC) scheduled for October in Cape Town, the first time in the 68 year history of IMPC that a congress has had to be rescheduled. The XXX IMPC will now be held in Cape Town in April next year, an unfortunate and surprising clash with MEI's Comminution conference, which was postponed eight weeks earlier. However, we are working with the IMPC to bring these two events together successfully over a single week in Cape Town, knowing that when air travel becomes viable again it is likely to be more expensive than in pre-Coronavirus days.
Cape Town and South Africa in general had a very severe lockdown imposed, with even a ban on the sale of tobacco and alcohol. Now the lockdown is being eased, and concerned about the possibility of multiple mine closures, and inactive mines becoming potential safety risks, the South African government had already permitted all mines to operate at 50% capacity as of April 16, and by 1 May open cast mines were able to operate at 100% capacity, while underground mines remained at 50%. The decision was not easy, however, as work on a mine poses inherent challenges to social distancing, especially underground where it is near impossible, and towards the end of the month some operations were forced to close again due to an increase in infection rate.
And finally some good news. Captain Tom Moore, the war veteran who raised more than £32m for NHS charities by walking 100 laps of his garden before his 100th birthday this month, was "overawed" to find that he was being awarded a knighthood for his fundraising efforts. He will be formally known as Captain Sir Thomas Moore, and PM Boris Johnson said the veteran had provided the country with "a beacon of light through the fog of coronavirus".
Let's hope that easing of lockdown, which will be relaxed further from today, has not been premature and that there will be more good news in June to light up our lives.

Thursday, 28 May 2020

Recent comments

There have been comments on the following postings since the last update:

Memories of Egypt and CMRDI
Prof. Doug Rawlings, 1952-2020
2019 MEI Young Person's Award to Nikhil Dhawan
Hi-Tech Metals '20 and Process Mineralogy '20 are cancelled
Cape Town IMPC postponed until April 2021
An exciting new polymetallic mineral deposit found in West Cornwall
Return to Chingola
Major honours to Sue Harrison and Frank Roberto
AusIMM Honorary Fellowships to Tim Napier-Munn and John Ralston
Comminution: developments and thought over the last decade
Is the reopening of mines creating boundless joy?
Why good technical English is essential for journal papers
Malaysia: memories of Penang and the Kinta Valley

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Monday, 25 May 2020

Malaysia: memories of Penang and the Kinta Valley

In the 1980s I had four memorable visits to Malaysia and I hope that this blog posting might put me in touch with some of the many people that I met in that fascinating country, in the same way that my recent blog on Egypt brought me, and Antonio Peres, back in touch with our host in Cairo, Prof. Refaat Boulos.
In 1981 I spent 9 weeks in January-February and 4 weeks in July as a visiting lecturer at the Universiti Sains Malaysia on the beautiful island of Penang.
I wonder what became of the 4 students that I tought during my first visit:
Nine weeks was more than enough to present a short course on mineral processing, so I had plenty of time to explore the island, and to spend a couple of weeks back-packing in Bangkok, Singapore and Bali, but the highlight of both trips was the time that I spent on the mainland in Ipoh in the Kinta Valley. Here for the first time I saw the contrast between the mining and processing of tin in Cornwall, from hard rock ores, and the processing of alluvial deposits on a very large scale.
The tin mining industry was at the time of my visit the major pillar of the Malaysian economy.  The country was producing almost 63,000 tons of tin annually, accounting for 31% of world output. It was the world's leading producer and employed more than 41,000 people, the most important area being the Kinta Valley, the world's most productive tin field. Perak was the wealthiest state in Malaysia, its capital Ipoh being fondly known as “The City of Millionaires”. During my time in Ipoh I was hosted by Mike Joll of Osborne and Chappel, co-author of a book on Malaysian tin mining. The last time I saw Mike he was living in Helston, Cornwall, so I would love to know what became of him.
Dinner with local miners in Ipoh (Mike Joll is 4th from left)
Dinner at SEATRAD (South-East Asia Tin Research and Development)
By the end of the 19th Century, Malaya (now Malaysia) was the world’s largest tin producer and the Cornish industry, once the world's largest producer fell into rapid decline. The mines in Cornwall were very deep, and mining and processing were expensive, comminution of the hard rock being followed by gravity separation on shaking tables, calcining to burn off arsenic, and, in the 20th century, removal of sulphides by froth flotation. Due to large amounts of fines, and poor liberation, recoveries were low and concentrate grades typically lower than 40-60%. Although the alluvial ores were of much lower grade (as low as 0.02% tin) compared with the hard rock ores of Cornwall (around 1% tin), mining could be carried out at a relatively vast scale, no comminution was necessary, the minerals were coarse and fully liberated and very simple, cheap gravity methods effective in producing concentrate grades of 70-75% tin.
Chinese miners were the main producer of Malayan tin ores before the British came. The British brought in dredges, which increased tin production tremendously but the smaller gravel pump mining operations were most commonly used in the Kinta Valley. In these mines the ore-bearing ground is broken down by high pressure water jets known as monitors, the resultant slurry being pumped to a huge wooden sluice box, or palong, down which slurry flows over a series of baffles, behind which the cassiterite and other heavy minerals settle out. Periodically the flow is stopped, the baffles are lifted and the heavy mineral concentrate is sluiced out. Primary tin concentrate is further processed in a secondary concentrator or ‘‘tin shed’’ involving wet and dry gravity methods, magnetic and electrostatic separation, by-products including ilmenite, rutile, zircon, monazite, xenotime, and struverite.
Gravel pump mine
Palong concentrators
It was also interesting to see women toiling in the +30C heat to further recover cassiterite by panning, using wooden pans called dulangs. By 1900 the dulang had become widely used by groups of independent women (dulang-washers) to undertake freelance mining operations. During the 19th and 20th centuries it is estimated that dulang-washers recovered almost 150,000 tonnes of tin in concentrates, or over 2% of the country's total production.
Dredges are very expensive and were operated by large multinational companies, but they are highly efficient machines which can operate practically non-stop and lower grade deposits can be profitable because of the high tonnage of material treated. The dredge is essentially a floating mine where mining and ore dressing are done on board. The ore bearing earth, in flooded paddocks, is dug by chain buckets and broken down by monitors, jigs being used to concentrate the ore. The main disadvantage of dredges is that they cannot recover heavy minerals lying between limestone pinnacles, which are often very rich in tin.
In July 1985 I was back for four weeks at the University in Penang but this time accompanied by Barbara, Amanda and Jon.  
Amanda, Barbara and Jon exploring the Penang capital, Georgetown
With local children on our favourite beach at Batu Ferringhi
In the photo below I am with USM staff Radzali Othman, Tuan Basar, Abdul Latiff and Kok Keong Cheang. Where are they now I wonder?
During our 4 weeks in Penang I made only a very brief trip across the water to the Butterworth tin smelter but the tin operations on the mainland were blissfully unaware of the crisis that would befall on them 3 months later.
At the Butterworth tin smelter
Apart from a fairly recent stop-over in Kuala Lumpur for a couple of days my last visit to Malaysia was in 1988, to give a presentation at the International Symposium on Research and Development in the Extractive Metallurgy of Tin and Related Metals, a very low-key affair as the Malaysian tin industry had suffered very rapid decline since my last visit.
Malaysia had been the world's largest tin producer until October 1985 when prices dropped by 50% and more than 300 tin mines stopped their operations. By 1994, the country's production had fallen to 6,500 tons, with only 3,000 people employed in the industry. The only tin dredge remaining was not producing tin, but was open as a tourist attraction.
Visiting the remaining tin dredge with ISRADEMT delegates
By 2016 Malaysian tin output was only 3,500 tonnes, and by then the country was ranked 9th in the world for production. It seems unlikely that the Kinta Valley will ever be a major producer again, as no new deposits have been found, whereas Cornwall, whose tin mining days were eclipsed by the Malaysia finds, is set for a possible revival.
Whatever happens, we have very fond memories of our time in Malaysia and of its very friendly people.

Thursday, 21 May 2020

Is the reopening of mines creating boundless joy?

Just about now the May Cornish Mining Sundowner should have been starting at Falmouth's Chain Locker. But, of course, it lies deserted, although I did call by earlier on my afternoon exercise.
What would we have been discussing today? Probably that a number of mines which temporarily closed at the start of the Coronavirus outbreak are now cautiously reopening, but it is difficult to see how underground mines can transport men up and down the mine shaft while observing social-distancing rules. Ironically a century ago, some of the Cornish tin mines had a means of transportation which allowed a constant stream of workers to ascend and descend into the bowels of the mine- this was the formidable and fearsome Man-Engine! (MEI Blog 20 October 2019).
Man-engine at Dolcoath tin mine in the 1890s
(Photo: JC Burrow)
But it is doubtful if everyone is happy with the reopening of mines. The mining industry supplies nearly every product and service in the world, and is fundamental to the development of technologies needed for the transition to clean energy.  A new World Bank Group report suggests that the production of minerals, such as graphite, lithium and cobalt, could increase by nearly 500% by 2050, to meet the growing demand for clean energy technologies. It estimates that over 3 billion tons of minerals and metals will be needed to deploy wind, solar and geothermal power, as well as energy storage, required for achieving a below 2°C future.
Yet mining companies are often faced with intense criticism from society, particularly as younger generations are increasingly aware and conscious of the industry’s social and environmental impact. If the mining industry has to continue to supply the world as we know it, it is essential that it repositions itself by changing the way it communicates to the external world while, at the same time, move to more sustainable practices and processes.
The Social License to Operate plays a key role in this context, being the acceptance of a mine or mining company by its employees, by its community stakeholders and by the general public. The extended stakeholder network that adjudicates on social licence also includes ethical investment funds, international human rights activists, international financial institutions and local and national governments. These key stakeholders are demanding stronger engagement and transparency, so much so that social licence will soon be akin to a mining licence, without which mining companies will find it impossible to operate (click here for more on Social Licensing).
We have discussed on the blog many times how crucial mining is to society, but really we are talking to the converted. How do we reach out to society in general? I would be asking sundowner regulars this today, but maybe blog readers might have suggestions? Maybe we could put together a survey for our non-mining friends to see what they think of the industry, and, just as important, what they know about it?

Monday, 18 May 2020

Comminution: developments and thoughts over the last decade

Comminution '20 was the first of the MEI Conferences to be postponed until 2021. We were expecting a record turnout, with news of all the recent developments taking place in comminution.
As a substitute I have thrown together edited highlights of some of the developments and thoughts on comminution which took place during the past decade. This is by no means a comprehensive review, it is intended to illicit discussion from comminution specialists from around the world, many of whom would have been in Cape Town last month.

Grinding is evolving and changing fast, with innovations in high pressure grinding rolls and stirred mills threatening to make the tumbling mill, which has been a stalwart for well over a century, obsolete. At the final panel discussion at Comminution '14 (posting of 5 May 2014), Tim Napier-Munn said that in terms of the future of comminution "we really have to get rid of tumbling mills". Are rod mills now finally obsolete? Ball mills would have dominated comminution conferences little over a decade ago, but they are mentioned only rarely now.
SAG mills are still of major importance, but I asked the question at Comminution ’12 whether ball mills would play a significant role in comminution circuits, or would they be superseded by SAG mills. Chris Rule, of Anglo Platinum, felt that rod mills would play an insignificant role, as they are severely limited in terms of size, and ball mills may play a diminishing role as the upper feed size range of stirred mills increases. Stirred mills, unheard of in mineral processing a few decades ago, are now increasingly used for ultrafine grinding applications.  At the SAG '15 conference in Vancouver, Chris showed how ISAMill™ technology has progressed from the original Mount Isa Mines ultrafine grinding applications. Larger ceramic media is now pushing the boundaries of feed size and can offer advantages in grinding efficiencies, product size distribution and internal wear.
At the 2012 SME Meeting in Seattle I was discussing SAG mills with someone who had heard that many operations were having to increase the proportion of steel balls in their SAG mills in order to improve performance, effectively converting them slowly back to ball mills! There was a lot of debate on the blog posting of 25 August 2014 which asked "Where are SAG mills going?".  An article from Weir Minerals suggested that there was an increase in demand for larger cone crushers that are matched with large high pressure grinding rolls for customers who want to replace SAG mills in order to increase efficiency. Utilising cone crushers and HPGRs allows ore to be processed from 250mm to 50mm in cone crushers, then down to less than 6mm from HPGRs.
In his keynote lecture at Comminution '18, Holger Lieberwirth asked whether SAG mills will still be relevant in 50 years’ time. Maybe they will be replaced by circuits containing only High Pressure Grinding Mills, which are crushing ever finer, and stirred mills, adopted for untrafine grinding, but whose upper particle size limit is being pushed towards coarser sizes. At SAG '15 in Vancouver, Paul Staples of Ausenco, Australia, asked whether SAG mills are losing market confidence. Although a mature technology, he said that a number of recent projects were not achieving nameplate capacity, but at Comminution '18 John Starkey, of Starkey & Associates, Canada, a company well known in SAG mill design, showed how single stage AG/SAG milling has the potential to reduce operating costs and increase profitability significantly when properly designed, installed, operated and maintained.
Mining is energy intensive, and grinding is responsible for consuming about 40% of the energy in the whole mining chain. Inefficiency in grinding has long been an outstanding problem, in particular when production of fines and ultra-fines are considered. Unlike milling, crushers are much more energy efficient, therefore it is logical to push the comminution process towards the crushing stage for energy efficiency, said Hamid Manouchehri of Sandwik, Sweden, at Comminution '18. Furthermore, crushing is done dry which reduces water consumption and related potential water contamination. Hamid said that finer crushing could be achieved through design of new crushing chambers, introducing more energy and higher rotation speeds in the crushing chamber, etc.  At the same conference Hakan Benzer, of Hacettepe University, Turkey, explained how novel energy efficient comminution circuit flowsheets incorporating energy efficient dry comminution technologies such as HPGR, Vertimill etc. have the potential to result in significant energy savings.
At Comminution '16 Gerard Van Wyk of ThyssenKrupp Industrial Solutions, Germany, asked if dry final grinding with HPGRs could be the next step ahead in mineral comminution? Historically, HPGRs have been used mainly as tertiary crushers in mineral applications for the production of ball mill feed. In the cement industry, however, HPGR systems have been successfully applied for grinding limestone, clinker and slag to a final product fineness (P80) of between 30 and 90 ┬Ám without the need for downstream ball milling. The total energy consumption of HPGR finish grinding systems in the cement industry has been found to be 30 to 50 % lower than in ball mill systems. This leads to the question of whether the same methodology can be adopted in the mineral industry. Such a step would require the use of dry rather than wet grinding systems.
The comminution circuit is usually made up of comminution devices operated in closed circuit with different types of classifier. The closed circuit arrangement can have separate comminution and classification devices linked through pump-sump arrangements or integrated comminution-classifier systems. It is well documented that the choice and operation of the classifier have a major influence on the performance of the comminution circuit as a whole. An inefficient classifier can increase the energy consumption of the comminution circuit and in most cases also compromise the quality of the product reporting to downstream processes, leading to losses in recovery of the valuable mineral.
Although Prof. Alban Lynch has been involved with hydrocyclones for very many years, in his conversation with me (MEI Blog 11th August 2014)  he said that "the way they are used now is an absolute nonsense, with circulating loads in some cases of well above 200%. The future is high frequency is very clear that these screens are so much better than hydrocyclones."
By classifying by size-only, screens, compared to hydrocyclones, give a sharper separation with multidensity feeds and reduce overgrinding of the dense minerals. Derrick Corporation is the leader in this field and at Comminution '18 Nic Barkhuysen, of Derrick Solutions International, South Africa, said that replacing the ubiquitous cyclone cluster with Stack Sizer screens creates additional capacity, improved mineral recovery and a simultaneous reduction in power consumption.
At Comminution '16 Elizma Ford, of Mintek, South Africa, evaluated the potential throughput benefit of adopting Derrick fine screening technology and  concluded that it is becoming apparent that the ability of these machines to accurately classify by size only at efficiencies in the mid 90% range, as fine as 45 micron, has resulted in a paradigm shift in milling circuits, replacing hydrocyclones in the closing of secondary and tertiary circuits. At Comminution '18 Martyn Hay, of Eurus Mineral Consultants, South Africa, also emphasised that over the past decade there have been a number of success stories where cyclones have been replaced by wet screening resulting in improved grinding efficiency, higher throughput, lower operating work index, better liberation and increased recovery in downstream flotation. He highlighted that inefficiencies in classification efficiency account for the majority of metal loss from the milling/flotation process as well as excessive mill power draw.
The last major comminution conference before the Coronavirus pandemic was the European Symposium on Comminution and Classification, held in Leeds, UK last September. In his plenary lecture, Malcolm Powell, of the University of Queensland's JKMRC, and a regular contributor to MEI's comminution conferences, said that it is high time to dramatically upgrade historic empirical comminution models, that are based on back-fitted breakage rates, to mechanistic models. He presented an approach to embracing the available computational power and the progress in understanding of comminution systems to rewrite models to be predictive and reliable with respect to the range of conditions to be encountered in the current and future devices we use in industry. Underpinning such an approach is the need for appropriate measurement of breakage properties that include mineral association, that respond to the range of conditions encountered in comminution equipment for mineral processing.
Simulating comminution processes is one of the most complex tasks in mineral processing research and the Discrete Element Method (DEM) is one of the most widely used tools. DEM has provided the ability to resolve the complex phenomena experienced by ore within comminution devices such as tumbling mills. The new developments in DEM techniques and the corresponding increase in computational power has made it more feasible to study the movement of individual ore particles as they traverse a tumbling mill. Modelling of energy distribution in tumbling mills is also being increasingly investigated using positron emission particle tracking, a technique now really proving its worth in understanding comminution and flotation processes, as is coupled DEM and SPH (smoothed particle hydrodynamics).
At the Comminution '14 panel discussion (MEI Blog 5 May 2014) Wolfgang Peukert of University of Erlangen-Nuremberg, Germany, said that much could be gained if the science of comminution and industry could come closer together. It is apparent that modelling now gives us a greater understanding of what is going on in a milling circuit, and there is a lot to be gained from detailed modelling. The models, however, must be checked by reality to give us a reliable toolbox to assess what is happening, particularly with complex multi-phase particles which can be characterised to assess liberation, the balance between strength of grain boundaries and strength of grains.
An interesting debate on liberation was on the blog posting of 16 January 2014, where I asked the question "Is anyone researching liberation enhancement". Prior to this, Frank Shi, of Australia's JKMRC gave an interesting paper at the European Symposium on Comminution and Classification in Germany in 2013. He outlined the programme of work on electrical comminution by high voltage pulses which has led to a number of publications in Minerals Engineering over the last few years. Pre-weakening ore particles and preferential liberation of minerals at coarse sizes are the two major outcomes that may have potential benefits for the mineral industry. He described a novel particle pre-weakening characterisation method by single-particle/single pulse, developed in collaboration with the Swiss company SELFRAG AG.  Dr. Shi discussed the emerging challenges to bring electrical comminution to the mineral industry, including scale-up for industrial application, hybrid circuit design, maximisation of pulse-induced cracks and study of the downstream processing effects.
Gregor Borg, of PMS GmbH, Germany and Martin Luther University Halle-Wittenberg, Germany, showed at Physical Separation '19 how the innovative VeRo Liberator® applies a mechanical high-velocity comminution principle, where numerous hammer tools rotate clockwise and anti-clockwise on three levels around a vertical shaft-in-shaft (hollow shaft) system. The resulting high-frequency, high-velocity impacts cause a highly turbulent particle flow and trigger fracture nucleation and fracture propagation preferentially at and along mineral boundaries. Breakage of coarser particles occurs from the high-velocity stimulation of bulk ore particles, where the elasticity and compressibility modules control differential particle behaviour. The improved breakage behaviour results in reduced energy consumption and very high degrees of particle liberation in the relatively coarse fraction of the product.
Grinding of complex massive sulphide ores consumes vast amounts of energy, and extremely fine mineral dissemination leads to relatively low concentrate grades, and high metal losses, not only in the flotation tailings, but into the ‘wrong’ concentrates, penalties often being imposed for the presence of zinc and lead in copper concentrates. Way back in 2013 (MEI Blog 3rd June 2013) I asked "is there a technique currently available that could eliminate the comminution step in the treatment of these important sources of base metals?" Well, yes there is, and not only could it remove the comminution stage, but also the difficult and inefficient flotation stage! It may seem economically impossible, but it has been proven at pilot stage to be viable. Noel Warner, Emeritus Professor of Minerals Engineering at the University of Birmingham, UK, has often talked passionately of the process that he and his team at Birmingham developed for the treatment of polymetallic massive sulphide deposits. The process was direct ore smelting, but despite its attractions, the process has never been used at full scale, but it was suggested (MEI Blog 3rd June 2013) that it should be looked at more closely.
Alan Muir, Vice President Metallurgy at AngloGold Ashanti, South Africa also asked whether comminution could be eliminated from the mining process in his keynote lecture at Comminution '14, as he felt that current comminution activities were rapidly becoming unsustainable. He suggested that comminution might be removed from the gold mining process completely by moving directly to in-situ liberation and leaching.
I have no doubt that comminution and concentration techniques will continue to evolve, but will there be a time when they lose the battle, when the remaining ores are so finely disseminated and intergrown that they can no longer be treated by physical methods? Is no mineral processing the future of mining, and will the future be direct hydrometallurgical and pyrometallurgical routes?
Hopefully much food for thought here, so let's have your views please.