Monday, 9 December 2019

A nostalgic journey through Matabeleland on the Rovos train

Just over fifty years ago, in September 1969, Barbara and I said farewell to South African friends who had travelled with us from Cape Town to Johannesburg, and we set off for our new life in Zambia, our first time alone in this vast continent!
The Great North Road took us on a 485 km journey to the Limpopo River, the border between South Africa and Rhodesia, now Zimbabwe. After an overnight stop in the small town of Gwanda, we passed through the heart of Matabeleland and the anachronistic town of Bulawayo, with its 1950s cars, and roads, wide enough to turn a full span of 16 oxen, lined with jacaranda and bougainvillea. Then on to Victoria Falls along the straight 450km road through unchanging dense bush. At last we came to the mighty Zambezi river and crossed the Victoria Falls Bridge and into Zambia and the start of my now half century in the mining industry.
On the Victoria Falls bridge overlooking the Zambezi
So impressed were we with Rhodesia that a year later we spent a couple of weeks touring this beautiful country (YouTube), the 'bread basket of Africa'. The roads were immaculate, hotels and restaurants of a very high standard and the local people were friendly and accommodating. Rhodesia, like South Africa, was also under white minority rule, Ian Smith’s Government having declared unilateral independence from Britain four years earlier and there was a pervading air of optimism and confidence in the future of this small country, which had everything to sustain it, agriculture, minerals and enormous potential for tourism. Who could have envisaged that South Africa would enjoy peaceful transition to majority black rule under Nelson Mandela, whereas Rhodesia would be plunged into a bloody civil war, leading to the horrors of Robert Mugabe’s Zimbabwe?
Just over 50 years later Barbara and I travelled the same route last month after Flotation '19 in Cape Town, but this time by rail, rather than road, and through a very different Zimbabwe, economically ruined by the despotic Mugabe and his successor Emmerson Mnangagwa, known as 'the crocodile' because of his political cunning. The people of Matabeleland suffered the most under Mugabe, particularly in the early 1980s when he sent in troops to put down opposition supporters in this region.
We travelled to Victoria Falls by the Rovos train, South Africa's rival to the more famous but equally luxurious Blue Train, from Pretoria, the Great North Road running parallel to the train track for much of the route, and we entered Matabeleland as in 1969 at Beitbridge. 
Crossing the Tropic of Capricorn near Mokopane

The first of our three fine dinners, prior to crossing the Limpopo
The following morning we passed slowly through baobab country and almost 30 hours after leaving Pretoria we arrived at Gwanda, our first overnight stop half a century ago.
Baobab country
A short stop at Gwanda
The third day was particularly interesting as we travelled between Matabeleland's capital, Bulawayo, and Victoria Falls, passing through the vast Hwangwe National Park, where passengers could spot game from the train.

A late  afternoon game drive provided many with their first really close encounters with African wildlife, always a very special experience.

And what better way to end a memorable day than a sundowner in the bush before returning to the train to dress for the final dinner.


The following morning, exactly three days after leaving Pretoria, we pulled into Victoria Falls station and said our goodbyes to our fellow travellers and the exemplary Rovos staff and the end of a truly memorable journey. 
Victoria Falls would be the highlight of any itinerary to Southern Africa and can be reached via direct flights from Cape Town, so would I recommend the Rovos experience, a 3 night excursion from Pretoria?
For many of the international travellers on the train, this was their first experience of Africa and without exception they enthused about this mode of travel, a luxurious reminder of a bygone era. The service and food on Rovos were first class, and the journey delivered everything that was promised and more,  unlike the Blue Train from Pretoria to Cape Town, which promised a visit to the diamond museum and Big Hole at Kimberley, something which did not happen, and apparently rarely does.
But don't expect to glide smoothly through the endless and ever-changing African landscape. For most of the route, particularly in Limpopo, and much of Zimbabwe, the train bucks and rolls along the poorly maintained undulating track. However, if you enjoy train travel, meeting people of all nationalities and being transported back to a time of elegance where dressing for dinner was expected, then this is a great option for experiencing this most wonderful of continents, providing you can manage without those modern necessities internet and mobile phones for three whole days. Without hesitation we would recommend Rovos to anyone wishing to experience the magic of Africa in a relaxed and leisurely way.
And a final recommendation: Victoria Falls is not only a magnificent spectacle viewed from Zimbabwe and across the river in Zambia (see The Smoke that Thunders).
The Devil's Cataract, Zimbabwe
The Eastern Cataract, Zambia
The region teems with wildlife (see also posting of 26th November), so an evening sundowner on the Zambezi is highly recommended, as is a day excursion into Botswana to Chobe, perhaps Africa's most impressive National Park (see Nature's Paradise: Chobe, Botswana).

Evening sundowner cruise on the Zambezi
Elusive black rhinos near Victoria Falls
Some of Chobe's resident 120,000 elephants, the highest concentration in the world
If you would like to experience this 'taste of Africa' trip after a Cape Town conference, I would suggest that you contact MEI's excellent agent Rene Simpson (simpsontours@gmail.com) who will arrange a seamless, custom-made itinerary for you.

@barrywills

Friday, 6 December 2019

Exciting times ahead for the extraction of lithium in Cornwall

2019 has been another momentous year for Cornish Lithium, an innovative mineral extraction company using cutting-edge digital technology to evaluate the potential of extracting lithium from geothermal waters that circulate deep beneath the surface of Cornwall.
The company has commenced drilling two research holes in the Gwennap area, close to the United Downs Deep Geothermal Power Project. This year included a successful crowdfunding campaign, which raised over £1.4m, and the award of funding from the Faraday Battery Challenge. These funds have enabled Cornish Lithium to continue their work to identify deposits of lithium and other battery metals in Cornwall which they hope will enable the UK to develop its own supply chain of critical raw materials for a modern battery industry.
To celebrate all this the company hosted a Christmas party earlier this week at the Royal Cornwall Museum in Truro, where invited guests had the opportunity of meeting the CEO, Jeremy Wrathall and his impressive team, particularly the young geoscientists who have determined the precise location of the boreholes following three years of extensive research and digital modelling of the subsurface.
It was a particular pleasure to congratulate senior geologist Lucy Crane on her recent award of Young Rising Star in Mining at last month's Outstanding Achievement Awards and Gala Dinner, hosted by Mines & Money in London. All the more pleasing as both Jeremy and Lucy are Camborne School of Mines graduates, Jeremy with a BSc in Mining Engineering and Lucy an MSc in Mining Geology.
Jeremy and Lucy
Drilling will be to between 800m and 1000m, adjacent to the former Wheal Clifford mine, this being particularly significant as the original discovery of lithium in brine was made at Wheal Clifford in 1864 by Professor Miller of Kings College, London, who noted that the occurrence of “so large an amount of lithium” in hot springs could be commercially significant.
Drilling commences in the old mining region
Extensive mining for tin and copper that took place in Gwennap Parish in centuries past has yielded a wealth of information that indicates that lithium is present in geothermal waters deep beneath historic mine workings at United Downs, and Cornish Lithium is drilling to intercept these natural features well below the depths reached during historic mining operations and is not targeting water in the old mines themselves.
The team are hoping to intersect two to three permeable structures in each hole, and will be isolating and sampling the geothermal waters circulating within each of them. These ‘geothermal’ waters are now understood to circulate through natural permeable structures which act as pathways through the otherwise impermeable rock. Currently they are just over halfway through the first hole so should finish that before Christmas, and the second one in the New Year.
Expect to hear much more of Cornish Lithium in 2020, and a great deal on lithium processing, both from brines and hard rock ores, at Hi-Tech Metals '20 in October.

Sunday, 1 December 2019

Flotation '19 Final Report

MEI's 9th International Flotation Conference was held at the Vineyard Hotel, Cape Town, and as always featured two discrete symposia, Fundamentals, followed by Applications and Plant Practice. We are indebted to Jim Finch, Emeritus Professor at McGill University, Canada, for his continued support as consultant to this series of events.
Due to the record number of abstracts received this year, oral presentations were limited to a maximum of 15 minutes. Because of this high number of presentations, my report this year only summarises the technical sessions, and all the abstracts, both for oral and poster presentation, are available online.  The full draft papers are available from MEI Online. All the postings on the conference have been grouped together and can be seen by clicking here, and an album of photos is available for free downloads.
 Monday November 11th
In opening the conference this morning, welcoming the first of the 293 delegates from 33 countries, and thanking our sponsors for their valued support, I paid tribute to the late Prof. Dee Bradshaw, who will be sadly missed this year, having attended all previous flotation conferences. Dee was a great ambassador for women in mining, and as a mentor for many young people in this field.
I then had the great pleasure of presenting the 2018 MEI Young Person's Award to an outstanding mineral processor, Dr. Zhiyong Gao, of Central South University China.
One of Zhiyong's nominators was Prof. John Ralston, of the University of South Australia, and the first Director of the Ian Wark Research Institute. John presented the keynote lecture this morning tracing the legacy of Dr. Joseph Kitchener, one of the 20th century's foremost flotation and colloid scientists, who died 10 years ago. Throughout his impeccable career at Imperial College, London, he influenced, guided and educated many international scientists and engineers, as well as inspiring his colleagues. John Ralston worked under Dr. Kitchener for a research fellowship at Imperial College and he discussed how Kitchener's work underpins a significant amount of modern research in mineral flotation and colloid science.
The importance of flotation to the mining industry cannot be overemphasised. In his 1979 article on the evolution of mineral processing, Prof. Alban Lynch, the first director of the JKMRC, felt that it was depressing that that there had been up to that time only three major advances in mineral processing during the century, one occurring in each quarter of the century. However he stressed that "our reputation as engineers" was somewhat restored by the fact that the first of these developments was froth flotation, "one of the greatest technological advances of our age and this will be realised if an attempt is made to conceive of a world without ample and cheap supplies of copper, lead, zinc and nickel".
Flotation continues to evolve, 115 years since its patent, and its importance increases with the need to treat increasingly complex ores, including the treatment of secondary deposits, and all the 'new' metals which are essential as we move into the 4th Industrial revolution. I doubt if Prof. Lynch could have envisaged fifty years ago the huge developments in flotation machines, reagents, control and simulation which will be discussed at this conference and future flotation conferences.
By 1908, 4 years after its patent, flotation was working well for bulk flotation of zinc tailings, but the search was then on for means of treating primary sulphides, which led to the development of xanthate collectors, selective activators and depressants, and still the search goes on for more efficient and environmentally friendly reagents. Appropriately the first presentation after the keynote came from one of the major reagent manufacturers, Solvay, who with other chemical companies at the conference, are developing novel reagent systems, tailored to enable processing of difficult ore systems.
Tarun Bhambhani, of Solvay felt that research and development in mineral processing chemicals have reached a plateau in contrast to mounting industry challenges related to decline in the ore grade and quality, and to health, safety and environmental aspects, water and energy consumption, economic uncertainty, and rapidly eroding chemistry knowledge and expertise in the industry.  This predicament can be attributed largely to a fading recognition of the critical role of chemicals in minerals extraction and their true value. Success in developing novel technologies and understanding the true value of chemicals will be greatly improved when we can confront the chemical complexity in mineral processing systems, in both the process and valuation sense, and he believes that this in itself is one of the grand challenges facing the industry.
Although we have had representation from the Korea Institute of Geoscience and Mineral Resources at a number of MEI Conferences in Falmouth, Kwanho Kim and Kwangsuk You were the first at a flotation conference, and their paper on the direct measurement of the interaction force between a solid surface and an air bubble took us to a long coffee break, giving everyone the chance to get to know the exhibitors (see YouTube video), and to view the poster presentations.
Back in the conference room, surface chemistry and particle-bubble interactions were the subject of the four papers from Australia, Finland and Germany, taking us to the first of the Vineyard's excellent lunches.
After a fine lunch, an interesting afternoon began with two more papers on surface chemistry and particle-bubble attachment, both from China, the first a study on the surface characteristics and flotation mechanism of pitchblende and uraninite, and the second on the attachment and detachment interactions between bubbles and hematite/quartz particles.
Positron emission particle tracking (PEPT) was initially used in the medical imaging industry, and was adapted for engineering by the University of Birmingham, UK. It is increasingly used in flotation research to produce detailed and quantitative measurements of different particle classes inside flotation vessels, with the goal to improve fundamentally based computational models of physics phenomena. It has become a very important tool in large cell design and three papers were presented this afternoon from three of the key institutes involved with PEPT, the University of Cape Town (UCT), Imperial College London, and the Institute of Fluid Dynamics, Germany.
Juan Yianatos of the University of Santa Maria, Chile, has attended every one of the flotation series of conferences, and his presentation on a new approach for flotation circuit modelling and simulation, addressing the challenges for improving the froth behaviour by varying the cell design as well as the potential for circuit optimization took us to the afternoon coffee break.


 In his 1979 paper, Prof. Alban Lynch predicted that the solution of the problem of concentrating fine particles less than about 10 microns in size could be the fourth achievement of the 20th century. Twenty years into the 21st century, this is an area that is still intensively researched and the final three papers of the day were concerned with the flotation of ultrafines.
It is known that ultrafine particles are difficult to float mainly due to the low bubble-particle collision efficiency. Workers from the University of Lorraine, France and TurboflotServices, Ukraine, discussed the effect of microbubble carriers on flotation of fine quartz particles (below 50 µm and with 44% less than 20 µm).  The advantages of microbubbles may be attributed to the more efficient bubble-particle collision/attachment rate and to the preferential adsorption of collector on the bubble surface rather than fine particles.
Bringing the day's sessions to an end a contribution from the University of Santa Maria, Chile, presented a new technology to improve fine particles flotation (less than 20 µm) performance based on the addition of hydrophobized hollow glass microspheres. The conclusion was that the new technology shows a feasible approach to recover fine particles. 
A fine ending to a fine first day at the conference, after which we spent a couple of hours relaxing in the hotel gardens, for the first of the evening sundowners.

Tuesday November 12th
Flotation is a physico-chemical process, and there is often much debate as to which is more important, physics or chemistry, but it is undoubtedly reagent chemistry and the right choice of reagents which promotes selectivity in the flotation process and the 13 papers presented in this morning's session all dealt with chemical reagents, both old and new.
The seven papers up to the first coffee break covered developments in well known reagents, such as thiol collectors, cationic collectors, the interaction between collectors and frothers and mixed frother systems. Two new collectors were introduced, a paper from Central South University, China describing the development of a new collector for sulfide mineral flotation, 5-(butylthio)-1,3,4-thiadiazole-2-thiol, which has been used as the selective collector for improved flotation separation of galena and sphalerite from pyrite.
Tecflote is a new group of nitrile-based collectors for sulphide flotation, developed by conference sponsor Nouryon Surface Chemistry, Sweden, and its mechanisms were proposed in a paper by Edgar Schach of the Helmholtz Institute Freiberg for Resource Technology in Germany.
I spent some time at the Nouryon booth during the coffee break. Nouryon was formerly Akzo Nobel Specialty Chemicals and the company is well known as a sponsor of the flotation series of conferences.  Apart from Edgar's paper, Odair Lima from Nouryon will present a paper in the Applications Symposium describing results from a full scale operation with Tecflote S11 at Boliden Aitik in Sweden. 
Another new reagent was introduced in one of the six presentations leading up to lunch. Orfom® D8 is a low carbon-chain trithiocarbonate with anionic functional groups at both ends.  It was tested as an organic depressant in the differential flotation of molybdenite from chalcopyrite in the presence of either sodium isopropyl xanthate or potassium ethyl xanthate, the results showing that it depresses chalcopyrite while molybdenite remains floatable. Courtney Young, of Montana Technical University, USA, discussed results of successful trial runs of a large pilot plant facility along with the economics comparing Orfom® D8 to traditional inorganic NaSH depressant.
Coutrney Young with Barbara Wills
Sulphidisation and flotation of oxidised copper minerals has always been a subject of research, and workers at the University of Queensland have sought to further improve this process, while research at the BGRIMM Technology Group, China, has investigated the flotation behaviour of malachite from calcite and quartz with a chelating collector.
A paper from Japan described the effect of hydrogen peroxide on the separation of copper sulfide minerals and arsenic-bearing copper minerals and there were papers from Germany and China describing the potential role of colloidal silica as a calcite depressant in scheelite flotation, and the adsorption mechanism of gallic acid/ pyrogallic acid/tannic acid on calcium-bearing mineral surfaces. 
Water conservation is now a critical aspect of mineral processing operations, and the first four papers after lunch dealt with this all important topic. Water quality within flotation will impact the bubble particle attachment and as more operations recycle their water on site, an understanding of this process becomes vital, and in the first paper from University of Cape Town and Aalto University, Finland, workers described fundamental and flotation techniques for assessing the effect of water quality on bubble-particle attachment of chalcopyrite and galena.
Flotation using sea water has been intensively studied over the years, and two papers, from China and Japan looked at the flotation of copper, and chalcopyrite-molybdenum separation in sea water. A third paper, from Chile, described how the bacterium Acidithiobacillus ferrooxidans has shown to be a good depressant of pyrite in seawater flotation.
Workers from Turkey's Hacettepe University then showed how they have developed a highly sensitive electrochemical electrode, fabricated by plating gold on the surface of a stainless steel electrode for detection and measurement of thiosulfate ion in flotation process water.
The final paper of the day, from Aalto University, Finland described the employment of hexyl amine cellulose nanocrystals as renewable reagents for the replacement of molecular amines in the flotation of quartz as well as a novel in-house engineered automated contact timer apparatus to analyse the mineral's floatability.
And so an excellent Fundamentals Symposium ended with discussions over coffee in preparation for the evening's entertainment, a chance to slip into another world and relax at the conference dinner at the beautiful Kirstenbosch Botanical Gardens.



Wednesday November 13th
Jon Wills welcomed the 30 new delegates to the conference for the first of the two days at the Applications Symposium.
Jan Nesset and Jon Wills
More than a century after its adoption and adaptation as a major mineral separation technology within the mining industry, significant new developments in flotation continue to appear. A number of important contributions have come from Canadians and a selection of these were highlighted by Jan Nesset, of NesseTech Consulting Services Inc, Canada, in his keynote lecture this morning. These contributions include the developments that led to the successful milling of the highly complex Sullivan ore by Cominco starting in the early 1920’s, to column flotation developed in the 1960’s, to the staged flotation reactor (SFR) technology recently introduced by Woodgrove Technologies. The development of industrially-robust sensors at McGill University, where Jan is an Adjunct Professor, has permitted new insights into the process, including the key relationships between bubble size and frothers. The joint development of the continuous mini pilot plant by Canadian laboratories and equipment suppliers is also seen as a significant contribution to flotation technology as evidenced by its adoption by testing laboratories worldwide.
The next presentation from Outotec's Australian and South African Divisions, highlighted that it is very common for operators to be treating ore material that is significantly different to the plant design conditions. The paper discussed the optimisation of flotation cells at various mine sites, showing that flotation cell components are rarely reviewed to determine whether these are still suitable for the new feed conditions. For example, customising the launder configuration will improve froth mobility whilst optimising the rotor type and speed will improve the float cell hydrodynamics.
Following this, collaboration between Outotec, Finland, and Santa Maria University, Chile, has developed a new approach for flotation circuit design which addressed the challenges for improving the cell design and operation, as well as the potential for circuit optimization in terms of selecting the best compromise of cell size and number of cells per bank. For this purpose, a flotation simulator USM-FLOTMOD, built on industrial data from modern and large mechanical flotation cells, was developed. 
There are many mining activities in extremely cold climates worldwide, including mining operations in Scandinavian countries such as Northern Sweden, and joint research by Sweden's Luleå University of Technology and Boliden Mineral AB examined the current knowledge on the effect of low temperature on flotation performance in order to identify suitable flotation reagents/reagent regimes and hydrodynamic concepts adapted to mineral processing and tailings treatment in cold climates.
The final paper before the coffee break was from the Beijing General Research Institute for Mining & Metallurgy (BGRIMM) Technology Group, China, and their business partner Roytec Global, South Africa, the two companies sharing an exhibition booth at the conference. As Robin Melville, of Roytec, noted, stepwise arrangement of flotation cells is the most common layout for flotation circuits in the mineral processing industry. In such design, slurry flows from upstream to downstream by gravity and the middling products are returned to previous stages by pumps. The presentation introduced an alternative solution in which slurry-suction flotation cells are adopted so that all the flotation cells can be placed on a same horizontal platform and no pumps are needed for middling product transfer.
During the long break for exhibition and poster viewing I called in at the BGRIMM/Roytec booth. BGRIMM and Roytec Global have combined forces to offer African clients access to BGRIMM's flotation technology backed up by Roytec local support, service and spares. BGRIMM is China’s leading mineral institute, established in 1956 and employing +3500 technical staff. Roytec Global was established in 2001 and is a privately owned and managed company. Over the past 50 years BGRIMM has developed world-leading flotation technology, with over 20,000 cells in the field. Many cells with capacities up to 320m³ have been put into successful operation and BGRIMM has cell designs up to 680m³. 
Robin Melville (2nd left), of Roytec, shares a joke in the BGRIMM/Roytec booth

In the flotation of sulfide ores, non-sulfide gangue is purported to report to the concentrate by entrainment. While it is long known that particle size affects entrainment, plant practice suggests that certain gangue minerals (e.g. mica) entrain more than others resulting in lower concentrate grades.  Given the platey shape of mica, the first paper after the break, a joint effort between Solvay and Columbia University, USA, investigated the effect of particle size and shape in ore flotation.
Nonlinearity of flotation effects (and their interactions) coupled with non-observability of many flotation variables results in typical control systems being unable to ameliorate inefficient operation. However, visual cues can be obtained from flotation froths and, in conjunction with other measured process variables, provide means with which froth phenomena can be characterized for control and monitoring. In a study carried out by South Africa's Stone Three Digital and Anglo American Platinum, a framework for froth state classification was prepared using readily available online measurements of cell operation (pulp level, aeration rate, etc.) together with variables inferred from flotation froths e.g. froth height, bubble size, and froth velocity.
New technology was also featured by Thomas Bertsch of conference sponsor Festo who discussed the next level towards increased productivity by applying digitalization and artificial intelligence concepts in minerals processing.
Thomas Bertsch (right) at the Festo booth
Timegate Instruments Ltd, from Finland, presented a novel real-time process monitoring method based on time-gated Raman spectroscopy. Timegate was established in 2014 and develops, manufactures and commercialises time-gated Raman spectrometers based on patented Raman technology. The innovation is based on years of research at the VTT Technical Research Centre of Finland and Oulu University, from which Timegate has continued the development to create an instrument for fast and easy material analysis for various industries. 
Amanda Wills with Miia Mikkonen and Mari Tenhunen of Timegate
Mark Ferra, of REXA Inc, USA discussed rougher flotation cell pulp level control to increase recovery, with the example of a copper mine near Globe, Arizona, which improved its rougher cells productivity using technically advanced electro-hydraulic actuators in the flotation process by enabling tank pulp level process stability. 
Flotation cells have increased in size at a near exponential rate for a number of decades, driven by a need to keep operating and capital costs down while simultaneously meeting the coupled challenges of an ever-increasing demand and falling grades, and progress has been made in optimising the performance of existing flotation cells. However, according to a presentation from Luleå University of Technology, Sweden, there is still lack of understanding of the relationship between the cell dimensioning and flotation performance, and the effect of mechanical cell height on flotation efficiency was explored.
The final morning paper from Imperial College, UK, demonstrated that as cells get larger they become more carrying capacity constrained, which implies a transition from typical first order kinetics towards zero order behaviour. A theoretical model for this transition has been developed, and the question was asked is there a maximum size for an efficient flotation cell?
And very large cells were the subject of two papers after lunch. The first two Outotec e630 TankCells®, with 630 m³ of effective flotation volume were commissioned at Buenavista del Cobre (BVC) Cu-Mo concentrator plant in Northern Mexico as the first cells in two existing rougher lines. Commissioning was finished in March 2018. Since start-up, the plant has reported increased copper recoveries while maintaining the final grade. A joint paper from Outotec's Finland and Canada Divisions, and BVC provided a review of the cell operation at BVC.
The KYF-680 Machine, a new generation forced-air flotation cell, has been developed by BGRIMM, China, in recent years and the capacity of 680m3 makes it the largest cell in the world at present. The first unit has been installed, tested and is currently operating at the DeXing Copper Mine in China to reprocess the tailing. The design principles and hydrodynamic characteristics were presented by the BGRIMM group, with the emphasis on flow control technology and the effects on metallurgical performance.
Novel flotation devices such as the Eriez HydroFloat™ achieve improved coarse particle recovery through a fluidised bed region that acts as a barrier to sparger-induced turbulence in the upper part of the cell. Flotation recovery of coarse particles has many benefits for the mining industry, most notably a cost benefit in terms of grinding and throughput. A joint paper from Australia's JKMRC, and Eriez Manufacturing Company, USA, described the development of a semi-empirical hindered settling classification model of the Cell.
A further paper, from JKMRC, University of Cape Town and Anglo American South Africa, described the use of positron emission particle tracking to compare the behaviour of solid particles inside an aerated and non-aerated laboratory-scale fluidised bed flotation device under a range of different operating conditions.
At Flotation '17 Graeme Jameson and Cagri Emer, of the University of Newcastle, Australia, presented a paper describing the development of a new froth flotation machine, known as the NovaCell. This innovative paper was awarded the CEEC Medal for Technical Research and it was good to have a further paper from the authors today, presented by Prof. Jameson. The phenomenon of drop back has been proposed by various workers to explain why the discharge of hydrophobic particles in the froth from a flotation cell is less than expected. It is assumed that some particles detach from bubbles in the froth and drop back into the flotation cell. Graeme presented an alternative explanation, in which particles don’t necessarily drop out of the froth. Instead, they never enter the froth in the first place!
A presentation by South Africa's Mintek and conference sponsor GoldOre showed that the use of hydrodynamic cavitation devices to improve the recovery of valuable mineral from fine and oxidised feed material has been clearly demonstrated by research studies and plant application.  In these reactors, the nucleation of ultrafine (nano) bubbles on the surfaces of fine valuable particles during contacting in a venturi aids their agglomeration and subsequent recovery by micro- and macro-bubbles during flotation.  This, together with enhanced cleaning of particle surfaces, leads to increased kinetics and concentrate grades.
Activity at the Mintek booth

The GoldOre booth
The Reflux Flotation Cell (RFC), developed at the University of Newcastle, Australia decouples the relationship between water recovery and gas flux, addressing the need for improvement in feed throughput, recovery, and product grade. Through collaboration between the University of Newcastle and FLSmidth, a portable skid consisting of two RFC units supported by a program logic controller, was established for piloting site trials for the very first time, and site trial were reported.
In a further paper from conference sponsor FLSmidth, the final presentation of the day, the patented newWEMCO™ flotation mechanism was introduced, the newest philosophy for flotation technology designed to retrofit into existing WEMCO® flotation machines. The increased performance of the newWEMCO™ design is due to a change in the rotor profile and a complimentary profile for the disperser.
There was a lot of activity around the exhibition area at the end of the day, for the 2nd sundowner of the week.
At the FLSmidth booth with paper presenter Dariusz Lelinski (2nd left)
 

Thursday November 14th
Innovative flotation cells were the subject of this morning's first three papers. While the Jameson Cell technology has been around for 30 years, it has been applied mainly to coal or base metals. Glencore Technology has now accumulated significant plant data over the years, including now published gold recovery results, which have shown that the Jameson Cell can achieve up to 15%-20% improvement in fine gold recovery over conventional circuits.
Glencore presenter Virginia Lawson (right) in the Glencore Jameson Cell booth
Yesterday we had updates on the world's largest flotation machines but a presentation from Eriez, USA, this morning suggested that this approach, to exploit economies of scale and to build increasingly larger unit operations, is flawed as there is a significant reduction in energy efficiency as the conventional tank designs become larger.  The paper described the industrial application of the high-intensity StackCell flotation technology, which utilises a separate, high-energy bubble-particle contacting zone coupled with a larger chamber for froth/pulp phase separation. This staged method is said to ensure that the energy is focused only on contacting and not wasted on pumping or creating turbulence need for suspending particles.
MEI's Jon Wills talking to Eriez representatives
Victor Ross, of Mintek, then described improved PGM flotation in a pneumo-mechanical cell, the indicating an improved PGM kinetics and recovery, accompanied by a significant improvement in the selectivity between PGMs and chromite.
Flotation in mechanical cells was the subject of the next two papers, the first, from Imperial College, UK discussing the effect of impeller design modifications on froth stability and flotation performance and the second paper, a joint offering from the University of Cape Town, the University of Technology, Iran, the University of São Paulo and the Institute of Technology Vale, Brazil, investigated the effect of particle physical properties on the reverse flotation of iron ore.
Water is of prime importance to the mining industry, therefore, the recycling of process water is good practice in mine sites to minimise the use of fresh water. Sometimes this affects the recovery of valuable minerals since the recycled water contains reagent remnants and undesired ions. Additionally, if the water has hard water type properties and a problematic mineral specie is present, such as pyrrhotite, the selective separation of the valuable minerals from the gangue becomes challenging. A collaboration between CIDT Peñoles and Minera Sabinas, Mexico, and Metso Minerals, Canada, investigated the selective recovery of copper and zinc sulphides in the presence of pyrrhotite and hard process water.
The Metso Minerals booth
There were a number of interesting case studies after the coffee break. A presentation from Magotteaux Australia and South Africa, and ZCCM Investment Holdings, Zambia, investigated the impact of grinding chemistry on sulphide and oxide copper mineral flotation at Lubumbe Mine, Zambia.
Presenter Chris Greet at the Magotteaux booth
Clariant Southern Africa have investigated the reduction of the negative effects of aluminosilicate minerals on copper and gold flotation by a process route involving a new range of Clariant reagents which are able to improve the copper and gold recoveries and concentrate grade of sulfide ores with high aluminosilicate content issues.
Clariant presenter Shani Engelbrecht talking to delegates from Finland, Sweden, Turkey and Iran
Work at the University of Queensland  has compared native starch, oxidized starch and CMC as copper-activated pyrite depressants. The non-toxicity of these naturally sourced biopolymers makes them attractive reagents for improving the sustainability of mineral processing operations.
Recent developments in electromobility are increasing the demand for raw materials such as cobalt, graphite and lithium. The Chilean mining industry, that historically focussed on copper only, is responding to this change-of-scenario with an increased interest in recovering cobalt as by-product in the copper production process and a paper from Chile's Sustainable Minerals Institute, and the Universidad de Chile looked at the challenges and opportunities for cobalt recovery at copper plants.
Over one half of current global cobalt production is from Cu-Co sediment hosted deposits of the Democratic Republic of Congo (DRC). These deposits are usually composed of the supergene oxide ore blanket grading into a sulphide ore at depth. The transition between the two ore types usually host both Cu-Co oxides and sulphides mineralisation which are extremely difficult to recover through conventional flotation processes. Such ores can be even more complex to process as carbonate minerals such as dolomite and magnesite may represent a significant proportion of the gangue. A study involving the Camborne School of Mines, UK, the Geological Srvey of Finland, and the Université de Lorraine, France, has investigated the flotation behaviour of such a complex carbonate-rich mixed oxide-sulphide ore where copper is hosted in sulphides (bornite, chalcopyrite, chalcocite) and oxides (malachite, chrysocolla) while cobalt is hosted in oxides (heterogenite, kolwezite and Cu-asbolane) and one sulphide (carrollite).
The morning's final paper from Nouryon and Boliden Mines, Sweden, analysed the performance of the rougher-scavenger bank at Boliden Aitik, using the new collector Tecflote™ S11, whose mechanism was described in the Tuesday morning paper.
The impact of water quality on flotation performance was the subject of the first two papers after lunch. Research at Aalto University, Finland, investigated the improvement of the water management system and its affect on flotation, at the Sentinel copper mine, owned by First Quantum and located in the North West province of Zambia.
Solvay Mining Solutions, USA, and Rio Tinto Kennecott, USA presented work on the impact of aqueous species and fine colloidal matter in process water on flotation performance at Rio Tinto Kennecott’s Copperton Concentrator.
Presenter Tarun Bhambhani (2nd right) and his co-author John Moyo, of Rio Tinto Kennecott (2nd left) at the Solvay booth
These two papers were followed by a joint presentation from Australia's University of South Australia, MZ Minerals and the JKMRC, where the question was asked "Pyrite flotation: is it stockpile oxidation or oxidation of fresh particle surfaces during plant processing that has a greater impact?"
The application of flotation hydrodynamics to plants began more than 20 years ago, however there are few applications using this technology to control their performance. A paper from Flottec Canada and Mexico described the initial phase of a project aimed at developing a practical application of hydrodynamic concepts to control metallurgical performance in a plant. This research was executed by Flottec Mexico at Minera Fresnillo, one of the largest silver producers in the world.
Taking us to the coffee break, a joint French-Russian paper described the effect of sonication on the selective flotation and separation contrast between sylvite KCl and halite NaCl in saturated salt solutions. The flotation experiments were performed on the potash ore samples from Verkhnekamskoye deposit in Russia using a primary amine as collector.
Recycling of lithium ion batteries has attracted a lot of attention particularly in regard to metals such as cobalt, nickel and lithium. Despite the growth in graphite consumption and the fact that it is counted as a critical material, there has been little previous work focusing on graphite recycling. A paper from the Helmholtz-Institute Freiberg for Resource Technology, Germany presented original research on graphite recycling using flotation.
Spodumene is the main hard rock lithium bearing mineral. Gravity concentration and flotation are the main methods of concentrating spodumene to a grade suitable for producing lithium hydroxide or carbonate and flotation is mainly carried out using fatty acids as the collector. As fatty acids have slow adsorption nkinetics onto spodumene and are relatively unselective and require very large dosages, BASF Mining Solutions described the development of a novel collector for spodumene flotation that is very selective against iron, silica and alumina-based minerals.
Representatives from BASF
At LKAB’s two main mine sites in northern Sweden, apatite-magnetite ores are mined and beneficiated, the main product being iron ore pellets. Currently the apatite reports to the tailings pond together with the rest of the gangue minerals, the phosphorus grade in the tailings varying typically between 4.1 to 5.7 % P2O5. As part of a larger initiative focusing on recovering valuable materials from tailing streams LKAB is now investigating the possibility of recovering the apatite from the mine tailings by froth flotation.
Rare earth bearing fluoro carbonates (REFK) are one of the most important sources of rare earth elements (REE) globally, with bastnaesite being the most studied mineral of this group in terms of flotation. However, in contrast, the REFK mineral parisite has been little studied with respect to its flotation behavior. A carbonatite REFK ore comprised of mainly parisite and associated Ba-Sr-minerals from Vietnam was investigated by the Helmholtz Institute Freiberg Germany in collaboration with Merker Mineral Processing, Germany, and the Hanoi University of Mining & Geology, Vietnam. It was considered that the work represents a significant advancement in the field, as it is the first time that floatability differences between individual REFK could be proven and numbered by automated mineralogy.
This paper brought an excellent conference to an end. MEI Consultant Prof. Jim Finch summarised the four days, and MEI's Amanda Wills invited everyone back to the Vineyard in two years time for Flotation '21. After the presentation of prizes it was back to the Vineyard Gardens for final chats and goodbyes over a few glasses of Cape wine.
 
More on Day 4

A final thanks to all our sponsors for their continued support:



@barrywills