Monday, 21 August 2017

Comminution '18- final call for abstracts

With mining companies having to tighten their belts in these hard times, the importance of optimising comminution, the most energy intensive operation in mineral processing, becomes ever more important.

"Comminution must be the key mineral processing technology during the next 50 years." - Prof. Alban Lynch (August 2013)
Comminution '18, which will be held in Cape Town in April, is the 11th in MEI's conference series. Comminution '16 attracted 177 delegates from 23 countries to Cape Town  (see full report and pictures, and comments from delegates, in posting of 25 April 2016).
Reflecting the need to reduce energy and increase the efficiency of comminution, the conference once more has the backing of the Coalition for Eco-Efficient Comminution (CEEC) as Industry Advocate, and already 13 companies are providing major corporate support to what we are sure will be another opportunity for experts from around the world to discuss new ideas and common problems.
Current sponsors
There is now a final call for abstracts. All accepted papers will be published in draft form in the conference Proceedings, and after the conference all authors will be invited to submit final papers for peer-review for a special comminution issue of Minerals Engineering. The deadline for abstract submission is the end of September.
Highlights of the technical sessions will be two keynote lectures from world renowned experts in comminution.  "Comminution in 2068 - will SAG mills still be relevant?" will be presented by Prof. Holger Lieberwirth of TU Bergakademie Freiberg, Germany. "Superior comminution circuit performance: integrating classification during design is the key" will be given by Prof. Aubrey Mainza, of the University of Cape Town, South Africa.
As always the conference will be held in Cape Town's Vineyard Hotel, its superb gardens under Table Mountain providing the perfect setting for the extended coffee breaks, lunches and happy hours, intended to give delegates the opportunity of relaxing and networking in the best of conditions.

Networking at Comminution '16
Registration is already open, and if you would like to exhibit, the exhibition layout is available, showing those companies who have already reserved booths.
At the Comminution '16 exhibition
We look forward to seeing you in Cape Town next April.

Congratulations on a great conference (Comminution '16). Good papers, made more powerful by a single stream which meant high attendance at each session, and good long breaks for informal discussions throughout the day, and meals in a spacious vendors area to encourage circulation. A great formula for a conference - quality over quantity, and time for discussion and networking and to keep the energy levels high. I wish all conferences could manage this balance so well.
Joe Pease, Mineralis Consulting, Chairman CEEC

Friday, 18 August 2017

Talk of Cornish lithium and hot rocks

Last night's monthly Cornish Mining Sundowner was held, for the first time, at The 'Front pub, by Falmouth's inner harbour. There were many familiar old faces, mainly past CSM students, who had travelled down to Cornwall for the funeral on Wednesday of former CSM Director Prof Keith Atkinson (posting of 6th August) in the tiny village of St. Mawgan. There was also a welcome guest, Paul Moore, editor of International Mining, a media partner for MEI Conferences, who is on holiday in Falmouth with his family.
With Paul Moore of International Mining
Amongst the chat last night was the news that Cornish Lithium has secured 1 million pounds ($1.30 million) to explore for lithium in Cornwall, taking the UK a step closer to a domestic source of the strategic mineral, which will play a huge part in the electric car revolution. There was much talk of this at the sundowner in January (posting of 20 January 2017), when Cornish Lithium said it had reached a mineral rights agreement with Canada's Strongbow Exploration, who are looking at the reopening of the South Crofty tin mine, leading to a hoped for revival in metal mining in Cornwall, once the world's largest producer of tin and copper.
Evaporation plays a major part in treatment of lithium brines, but new technology  is helping to make other options more viable. However the development of geothermal energy in Cornwall might also contribute to an evaporation option. The United Downs Deep Geothermal Project, operated by Geothermal Energy Ltd, close to the proposed lithium deposits, is seeking to produce energy by drilling deep into Cornish granite, which naturally produces heat. The pioneering project to produce power from hot rocks several kilometres under the ground in Cornwall will begin drilling early next year, if a multimillion-pound fundraising drive succeeds. Cornwall’s extensive granite means it has long been seen as the most promising part of the UK for the technology, which one study found could provide a fifth of the country’s power, which would be a welcome addition to the extra electrical energy needed when the electric car revolution really takes off. If all goes as planned, the Cornish operation could be operational in 2020. The amount of power the wells are expected to produce will be small, at a capacity of 1-3 megawatts (enough to power 1,500-4,500 homes), similar to a single onshore wind turbine, but geothermal has one big advantage: unlike wind and solar, it can provide constant power if needed.
Geothermal Engineering Ltd is in partnership with Geoscience Ltd, founded in 1985 by my old Camborne School of Mines colleague Dr. Tony Batchelor, as a spin-off from the Hot Dry Rock geothermal research project run by Camborne School of Mines. That project, based at Rosemanowes Quarry near Penryn, developed techniques for the creation of artificial geothermal reservoirs that have been applied around the world.  Iceland is the world leader in geothermal power (posting of 22 January 2015), where deep holes are drilled to reach hot rocks, water is pumped down, heated and returned to the surface to generate electricity or provide heating.
Tony Batchelor (centre) with CSM mining graduates
Stuart Daveridge (1992) and Stephen Lovelock (2017)
There was also talk last night of an exciting new collaborative initiative between Camborne School of Mines and Canada's University of British Columbia, whereby CSM undergraduate students will spend time in Canada studying mineral processing, and UBC students at Camborne studying mining. I look forward to hearing more on this.

CSM Association Secretary Claire Yelland, former secretary Linda Shimmield, and Barbara Wills
Twitter @barrywills

Monday, 14 August 2017

In Conversation with Roe-Hoan Yoon

Prof. Roe-Hoan Yoon is one of the world’s most distinguished flotation scientists, and the holder of many coveted awards, including the IMPC’s Lifetime Achievement Award. We are privileged to have him give a keynote lecture at this year’s Flotation ’17 in Cape Town, and I was honoured when he accepted my invitation to take part in one of the MEI Interviews. In the event he made my task very easy: I asked him many questions and he did not merely reply, but put together a fascinating mini-autobiography of his life from humble origins in South Korea to his position now as one of the world’s top scientists in his field, and his story should be an inspiration to all young scientists embarking on their careers. I publish it below as received.
Prof. Yoon with the Lifetime Achievement Award at IMPC 2014
 "I recall a high school chemistry class, in which a teacher drew a micelle on a blackboard to explain how detergency works. It fascinated a young mind. As is well known, micellization is a hydrophobic interaction in molecular scale. In college, I was fascinated again to learn how air bubbles selectively collect hydrophobic particles from water, which I now teach students as a hydrophobic interaction in macroscopic scale. Despite the large difference length scales, both are driven by the water molecules striving to maximize H-bonding in the vicinity of hydrophobic surfaces.  
Prof. Yunshik Kim of Seoul National University was my first flotation teacher. After completing his Master’s degree program under Iwao Iwasaki at the University of Minnesota, he returned to his alma mater to teach. Upon graduation in 1967, I worked briefly at the Korea Institute of Science and Technology (KIST), where I learned how to measure ζ-potentials to determine the points of zero charge (pzc) of minerals. Drs. Jae-Hyun Oh and Hyung-Sup Choi were my supervisors. After I left Korea for my graduate training at McGll University, the latter became the Minister of Science and Technology, who is credited for laying the foundation for R&D and economic development.
With Tal Salman in a flotation laboratory
at McGill in 1968
At McGill, I studied under Prof. Talat Salman to recover copper and cobalt ions from solution by ion and precipitate flotation. He earned his Ph.D. in gas-phase adsorption and was an expert in gold extraction and mineral flotation. After receiving my MS degree, I continued to work essentially on the same project for my dissertation. With a fellowship from the National Research Council (NRC) of Canada, I had a degree of freedom to do more fundamental research. One aspect of my work was to study the thermodynamics of adsorption, which included building a micro-calorimeter to measure enthalpy changes. It was a frustrating experience to build a major piece of equipment; however, it gave me an opportunity to learn instrumentation and thermodynamics, which was helpful later when I studied hydrophobic interactions. Both my Master’s and Ph.D. theses work were rated ‘excellent,’ for which I graduated with Dean’s Honor. Tal Salman was a nice person, and I got along with him well. His wife Alba occasionally visited our home in Ottawa, Ontario, when I was working at CANMET as a Research Scientist.

With Maurice Fuerstenau after my Richard Award lecture
at the 2007 SME meeting
McGill used to offer short courses annually for industry personnel, which created opportunities for students like me to visit with famous speakers such as George Pauling, who used infrared spectroscopy to identify the xanthate species adsorbing on surfaces; Vern Plitt who developed an excellent hydrocyclone model; and Maurie Fuerstenau, who was one of the most productive researchers at the time. I particularly enjoyed a seminar by Vern on the first bitumen extraction plant built in Alberta. I also discussed with Maurice my fractional charge model, which served as a basis for my points of zero charge (pzc) model. I got to know him better when I took a job at Virginia Tech. I also visited his department at University of Nevada to give a seminar on hydrophobic interactions. Shortly after my visit, he nominated me for some major national awards, for which I am grateful to this date. One day, he confided to me about him becoming 80 years old in the next year. Not long after that conversation, I heard the sad news that he died of pneumonia, which started as a common cold. I was saddened by his loss and continue to miss him a great deal.
From McGill, I went to work for CANMET, Ottawa, in 1976. I took this job over another in the U.S. in order to gain a working experience in sulfide flotation. Having studied the chemistry of oxide flotation at McGill, I was anxious to learn something different. CANMET had a long history of base metals flotation research, including extensive pilot-scale testing and field trips. I thought that sulfide flotation was both dynamic, in the sense that its chemistry changes continuously due to oxidation, and complex, as the collector adsorption mechanisms are controlled by multiple variables, e.g., Eh, pH, galvanic contacts, semiconducting properties, etc. My first project there was to construct mass-balanced Eh-pH diagrams for common sulfide minerals in the presence of xanthate collectors so that I could predict flotation from thermodynamic data readily available in literature.
I had planned to validate my thermodynamic predictions against a set of micro-flotation data conducted on pure minerals, but I immediately ran into a problem. The pure mineral samples I prepared were hydrophobic before any xanthate treatment. I had treated the samples using sodium sulfide and pyridine to remove surface oxidation products. I observed the same phenomenon with actual ore samples in a flotation cell. As soon as I reported these observations under the heading ‘collectorless flotation,’ it attracted a lot of attention and the subject matter became a controversy. Another project I started at CANMET was fine particle flotation, which was probably the most popular research topic at the time. I recall reading a paper written by Graeme Jameson on the hydrodynamics of bubble-particle collision, which inspired me to do something on it.
With Prof. Graeme Jameson at Flotation '11 in Cape Town
I took-up a faculty position at Virginia Tech in 1979, so that I could do more fundamental research. During the first year, I submitted four research proposals, all of which were funded – a feat I have since never repeated. So, I had a good start, which I would attribute to Dick Lucas and Paul Torgersen, who hired me and nurtured my career. I am thankful to them to this date. Knowing that I came from a minerals school, Dick suggested I develop a coal project to serve the local mining industry and introduced me to some of his friends in industry. One day, a U.S. Congressman, Rick Boucher, walked into to my lab without warning with a TV crew following behind him. I saw myself on a local evening news that night.
One day the Congressman invited me to a dinner meeting with coal company executives. After the meal, he stood at a corner of the room and gave a speech on what he did in Washington, D.C., and asked what he should be doing for the next three months. For a young oriental man who grew up under dictatorships all his life, it was a revelation. For the first time I witnessed at close range how democracy works for the first time. In later years, Rep. Boucher gave me opportunities to testify at Congressional hearings in a panel of experts whom I had seen only on TV. It was a humbling experience indeed. I do not think I did a good job, as I was nervous.  
Following Dick’s advice, I soon developed two coal projects: one was on the salt flotation of coal and the other was on fine coal flotation using small air bubbles (or microbubbles). Although I did not realize its significance at the time, the Kitchener’s group at Imperial College, London, invoked the term hydrophobic force for the first time in 1972 to explain the salt flotation phenomenon, which may be referred to as collectorless flotation of naturally hydrophobic materials. The graduate student who worked on the project (John Sabey) went on to work for Vern Degner of Wemco – a well-known flotation expert.
Bbuilding a pilot-scale microbubble flotation column
with Jerry Luttrell
Knowing that smaller air bubbles can give higher collision frequencies and hence higher flotation rates, I approached Al Deurbrouck, Director of Coal Preparation, DOE, who gave me an Oakridge Summer Faculty fellowship. I worked with Ken Miller, in-house flotation specialist, to demonstrate that the concept of microbubble flotation works well for fine coal. In fact, it worked so well with usual flotation feeds finer than 100 mesh that Ken and I ball mill-ground coal samples to obtain micron-size feeds. We then found that the product coal became much cleaner with finer coal, which was of course due to improved liberation. After my return to Virginia Tech, I wrote a proposal to DOE and received a small grant from the University Coal Research Program, which continues to this day.
This project led us to successive research projects involving scale-up, pilot-plant testing, and eventual commercialization under the trade name Microcel. During the course of this successful project, eight graduate students were trained on flotation, many becoming leaders in industry and academia.
Some years later, I competed for a large ($16 million) DOE project and lost. Its objective was to produce premium fuels, defined as the coal-water slurries prepared from super-clean coals with < 2-3% ash. Despite the loss, we received a subcontract for fine coal dewatering, which led us to the development of a series of advanced technologies such as dewatering aids, hyperbaric centrifuge, and dewatering by displacement (DbD). The first two have been commercialized, with the third one being in the process of commercialization. The DbD process has been developed further to a new process known as hydrophobic-hydrophilic separation (HHS), which is capable of recovering and simultaneously dewatering ultrafine particles. Both of these processes appear to be independent of particle size.
When I first arrived in Blacksburg from Canada, I was unsure if I could survive as a tenure-track faculty without a single degree received in the U.S. One phone call helped me overcome this fear. It was probably during the  first quarter of my teaching job at Virginia Tech, when Prof. Doug Fuerstenau of Berkeley called to inform me that Prof. George Parks of Stanford University was coming to give a departmental seminar on my work just published. It was my model for predicting pzc’s of minerals from crystallographic information, and was an improved version of George Park’s original model. I simply incorporated the charge neutrality principle of Linus Pauling into Park’s model and achieved a better fit between model predictions and experimental data.
Doug helped me in many other ways during my career at Virginia Tech. He came to visit with us in Blacksburg a couple of times. His first visit was in June, 1982, when I organized a flotation symposium as part of the 56th Colloid and Surface Science Symposium. It was very nice of Prof. Jim Wightman, Conference Chair, to ask me to organize the symposium. It gave me an opportunity to bring many famous flotation scientists to Blacksburg and show my laboratories and ongoing research.
Attendees for the flotation symposium in Blacksburg:
Fuerstenau, Yen, Wakamatsu, name unknown, Yoon, Mukerjie of NSF, Iwasaki
Of the many flotation scientists who attended the flotation symposium in Blacksburg were Bill Trahar and Ron Woods both from CSIRO. Bill was famous for identifying the upper and lower particle limits of flotation. He took much of his data from operating plants, which made his work particularly meaningful. Based on his basic training in electrochemistry, Ron consolidated the mixed potential theory for xanthate adsorption, for which he received the 2016 A.M. Gaudin Award and the 2017 Victoria Order. Bill had received the Gaudin award earlier in 1989. I was happy to see them attending the symposium I had organized. On the other hand, I was scared to see them as two of the world’s foremost leaders in sulfide flotation opposed my view on the origin of the collectorless flotation. I thought that sulfide minerals become hydrophobic when the sulfoxy oxidation products are removed, while both Bill and Ron suggested that it was the elemental sulfur formed during the initial stages of oxidation. I contended that elemental sulfur is unstable in alkaline media where I did all of my experiments, and that we could not detect the elemental sulfur by mass spectroscopy. For these reasons, we proposed that the hydrophobic species responsible for the collectorless flotation may be polysilfides rather than the elemental sulfur. The debate went on for more than a decade involving many other scientists, which I enjoyed. Despite the opposing views, we kept our friendships unspoiled for a long time.
With Ron Woods
Following his first visit, Ron Woods came to Blacksburg to do cooperative research for 14 consecutive years. He always came with his wife Elspeth. We had a great time together including my wife Myungshin. In the laboratory, we went beyond the controversies on collectorless flotation and worked together to better understand the mechanisms of xanthate adsorption on sulfide minerals and precious metals. Courtney Young and Mark Pritzker constructed mass-balanced Eh-pH diagrams in the presence of xanthate, while Ron helped us validate the thermodynamic predictions. Cesar Basilio and Dongsoo Kim carried out electrochemical experiments, while Jersey Mielczarski and Jaakko Leppinen conducted spectroscopic analyses using XPS and in-situ FTIR spectroscopic methods. In general, we were pleased to see the results obtained from the electrochemistry, spectroscopy, thermodynamics corroborate well with each other. We were using mainframe computers to handle the overflow and underflow problems associated with solving high-order polynomial equations. Nowadays, the same job can be done using laptop computers. Looking back, it was probably the most productive period of my career, and all of us in my group appreciated the teachings from Ron on electrochemistry.
Ron’s regular visit to our group attracted some of the best-known sulfide flotation chemists such as Paul Richardson and Norm Finkelstein to Blacksburg. We also attracted significant funding from industry (Cytec, Cominco, Inco, Phosphate Research Center, etc.) and government agencies (USBM and DOE). Companies came to us for help with problems concerning poor selectivity and the difficulties with fine particle recoveries. We helped the former by minimizing the inadvertent activation of sphalerite by potential control and using complexing agents. I was intrigued with the role of DETA as a pyrrhotite depressant. We suggested that the reagent desorbs heavy metal cations by forming water-soluble complexes. The problem of fines recovery was solved by installing better bubble generators.
With some of the best names in one place, I used to joke amongst ourselves that we ought to come up with a major new discovery. In retrospect, it is difficult to say what it was. If nothing at all, we trained many young talents, who became leaders in industry and academia.
In flotation, particles collide with air bubbles and form wetting films in between the two macroscopic surfaces. The thin liquid films (TLF) of water formed on hydrophobic surfaces drain and thin fast and eventually rupture, forming contact angles. The TLFs formed on hydrophilic particles, on the other hand, thin more slowly and never rupture. These differences serve as the basis for flotation separation.
In 1969, Janus Laskowski and Joseph Kitchener analyzed the process of contact angle formation using the Frumkin-Derjaguin isotherm and concluded that one must consider the role of “hydrophobic influence” to explain the contact angle formation. Three years later, Blake and Kitchener used the term “hydrophobic force” instead to explain the phenomenon of film rupture on a methylated silica surface at a high concentration of inorganic electrolyte solution. They thought that the hydrophobic force, which was considered a short-range attractive force, was masked under the influence of the long-range repulsive double-layer force. When the double-layer was compressed at a high concentration of inorganic salt, however, the hydrophobic force emerged as a surface force not considered previously in the classical DLVO theory. The authors thought that this mechanism had a bearing on the salt flotation of inherently hydrophobic materials such as bituminous coal.
With Janus and Barbara Laskowski, and Myungshin at a dinner
I read Janus’s paper when I was a graduate student at McGill and was fascinated. However, I did not quite comprehend its significance until I dug into it recently when we started measuring the hydrophobic forces in wetting films. I was also intrigued by Janus’ other work showing that the ζ-potentials of silica particles do not diminish significantly by methylation. I attributed this observation as a supporting evidence for my fractional charge model discussed above.
 In 1982, Jacob Israelachvili and William Pashley of Australian National University reported the first direct measurement of the hydrophobic force, confirming the suggestion made by Kitchener’s group during late 1960s and early 70s. The measurement was conducted using the surface force apparatus (SFA) by approaching curved mica surfaces to each other in a cationic surfactant solution. Many follow-up papers confirmed Jacob and Bill’s measurement; however, many others were skeptical. The controversy went on for more than a generation. My research group at Virginia Tech has been actively involved in the debate for over 25 years, which I enjoyed immensely. My background in flotation helped me a great deal in the debate. 
Some years ago, I met Jan Christer Eriksson, a thermodynamicist retired from the Royal Institute of Technology, at a surface force symposium in Stockholm. We hit it off with each other instantly as both of us believed in hydrophobic force and thought that it had something to do with water structure. Since the DLVO theory was derived by treating water as a continuum, it cannot address the structural changes associated with film thinning. Derjaguin wrote several papers addressing this issue and called the hydrophobic force a ‘structural force.’

With Kristina and Jan C. Eriksson in Blacksburg
I invited Prof. Eriksson to Blacksburg to work with us to study the thermodynamics of macroscopic hydrophobic interaction. We used an atomic force microscope (AFM) to measure the surface forces between thiol-coated gold surfaces. The measurements were conducted at several different temperatures to determine thermodynamic functions. We were surprised with the results; the interaction was enthalpic, that is, the free energy changes were dominated by enthalpy rather than entropy. This new finding was contrary to what had been known for the hydrophobic interactions at molecular-scale such as self-assembly of hydrocarbon chains.
Our thermodynamic data indicated that the water confined between hydrophobic surfaces becomes increasingly structured with decreasing film thickness. This conclusion was supported by the recent sum frequency generation (SFG) spectroscopic studies showing that the water at the hydrophobic surface/water interfaces forms strongly H-bonded structures, which are often referred to as “ice-like.”
The difference between the macroscopic- and molecular-scale hydrophobic interactions arises from the difference in the curvatures of the hydrophobic surfaces involved, which in turn affect the vicinal water structure. 
We also measured attractive surface forces in ethanol, which we called “solvophobic forces.” Both ethanol and water are H-bonded liquids and hence behave similarly in the TLFs confined between hydrophobic surfaces. In effect, hydrophobic force is a solvophobic force, which arises from the antipathy between the H-bonding molecules in the vicinity of surfaces that cannot support H-bonds.
On a little more practical side, we developed a theoretical model for hydrophobic coagulation by adding a hydrophobic force term to the classical DLVO theory. Gaudin in his textbook on flotation showed that the flotation rate of galena decreased with decreasing particle size but stayed constant below around 5 microns, which may be attributed to the hydrophobic coagulation. Scientists considered this work, which was carried out by Zhenghe Xu as part of his thesis work, provided an indirect evidence for the presence of hydrophobic force in colloid films. After many years of his successful career in Alberta, Zhenghe has accepted the deanship at the Southern University of Science and Technology in China.
With Zhenghe Xu
Encouraged by Zhenghe’s work, I decided to get involved in direct force measurement and bought an SFA from ANU. I was pleased to learn how well the results corroborate with the information available in flotation literature. We found also that hydrophobic force increased with water contact angle, which convinced me of its existence and role in flotation. We also used the SFA to measure the forces between bitumen-coated mica surfaces. At the time, most people thought that the surface chemistry of bitumen droplets in water was controlled by the naturally occurring surfactant, e.g., fatty acids, exposed on the surface. Our SFA data showed for the first time that it was asphaltene, rather than fatty acids, controlling the colloid chemistry of bitumen, which has far-reaching implications in bitumen extraction from oil sands. We then started using the atomic force apparatus (AFM) to measure surface forces, mainly because we were interested in force measurement with opaque minerals such as copper sulfide and precious metals.
We also used the extended DLVO theory that was used to model hydrophobic coagulation to explain the stability of foams and froth. However, our work drew criticisms from some well-known foam specialists in Europe, who had been measuring surface forces in foam films using the thin-film pressure balance (TFPB) technique of Scheludko. If the Hamaker constants are known, one can use the DLVO theory to back-calculate the ζ-potentials at the air/water interface. We found that this approach worked rather well at high surfactant concentrations but not so at lower concentrations. The back-calculated ζ-potentials were substantially lower than calculated using the Gibbs adsorption isotherm or measured experimentally. We suggested that the hydrophobic force not considered in the DLVO theory may account for the discrepancy.
Thus, the idea of air bubbles being hydrophobic was born. If one accepts that air bubbles are hydrophobic, flotation may then be considered a hydrophobic interaction. That air bubbles in water are most hydrophobic in pristine water is consistent with the high interfacial tensions at the air/water interface. When I wrote a book chapter summarizing our work, a letter-to-the-editor apposing our views appeared in Langmuir, to which I responded.
Having spent more than 25 years trying to convince myself of the existence of hydrophobic forces in both colloid and foam films, my next target is the flotation (or wetting) films. I knew that it would be a challenge, as many investigators had troubles coping with bubble deformation, which made it difficult to determine the exact separation distances between the two macroscopic surfaces, i.e., mineral and air bubble. To my surprise, however, it did not take too long for a Master’s degree student (Lei Pan, who now teaches at Michigan Tech) to quickly modify the TFPB that I had for foam film studies, so that it could also be used for studying wetting films. One thing we realized was that wetting films thinned much faster than foam films. Therefore, we used a high-speed camera to capture the fast-evolving optical fringes, which can then be analyzed offline to construct spatiotemporal film profiles. By analyzing the spatiotemporal film profiles, we were able to determine the kinetics of bubble deformation, which in turn could be analyzed to determine the hydrophobic disjoining pressure using the Reynolds lubrication theory and the extended DLVO theory. We found that hydrophobic forces increased with increasing xanthate concentration as reported in Faraday Discussions in 2010.
As part of his thesis work, Lei Pan carried out more theoretical studies, in which both hydrodynamic and surface forces were determined by analyzing the spatiotemporal film profiles with the help of a fluid mechanist (Dr. Sungwhan Jung) at Virginia Tech. We had no problems detecting the presence of the long-range hydrophobic force on a xanthate-coated gold surface. Analysis of the data using the Frumkin-Derjagiun isotherm suggested, however, that a short-range hydrophobic force must also be present in the film to account for the faster (nearly invisible) film thinning and de-wetting steps during the last stages of a bubble-particle interaction. We, therefore, wrote that the long-range hydrophobic force was responsible for film thinning, while the short-range force was responsible for film rupture in a JCIS paper published in 2011. In effect, we developed a method of using an air bubble as a sensor for the measurement of both the hydrodynamic and surface forces involved in bubble-particle interactions.
Lei Pan with the FADS he designed and constructed
I then challenged Lei Pan to validate the forces calculated by analyzing the spatiotemporal film profiles using direct force measurements. He met the challenge by designing and constructing a new instrument named the “force apparatus for deformable surfaces (FADS).” This new apparatus allows an air bubble to move toward the undersurface of a cantilever spring by means of a piezo crystal, while monitoring spring deflection using a fiber optic sensor. Before the measurement, the spring had been treated by gold and subsequently by xanthate coatings. Detailed methods of determining both the short- and long-range hydrophobic forces and validating them by direct force measurement have been described in our 2016 Minerals Engineering paper.
It seems that we have come full circle since 1969, when my good friend Janus Laskowski suggested that contact angle formation cannot be explained without considering the presence of the hydrophobic force (or influence) in a flotation film. He and Kitchener also wrote: “There is no theory leading to even approximate calculation of negative disjoining pressures on hydrophobic surfaces.” Of course, the negative disjoining pressure arises from the hydrophobic force in wetting films, which in turn arises from a collector coating. By virtue of many researchers’ hard work and vision, we now know how to determine the hydrophobic force using an air bubble as a sensor.
I was given a special honor to present a plenary lecture at the XVII IMPC meeting in Dresden, Germany, in 1991. The title of my lecture was “Hydrodynamic and Surface Forces in Bubble-Particle Interactions.” I was humbled to be at the same plenary panel as Nicolay Churaev, who was the world leader in wetting films. I had been reading his papers, but it was the first time I met him in person. I met him again in the Frumkin Institute in Moscow some years later. At the IMPC, both of us addressed the importance of hydrophobic force in flotation, which was a coincidence but was not surprising. 
At the plenary lecture panel, 1991 XVII IMPC meeting in Dresden:
Schubert, Yoon, Churaev, and Schoenert
It was very nice of Professor Heinrich Schubert, who gave a relatively young unknown investigator an opportunity to present a plenary lecture at the most prestigious meeting in minerals processing. I knew that he liked our work on microbubble flotation, which was intended to improve collision efficiency by reducing bubble size. In my Dresden lecture, I proposed a bubble-particle attachment model, which was in the same form as the Arrhenius equation. In effect, the model suggested that the efficiency of attachment should be a function of both energy barrier, which is determined by the surface forces in wetting films and the kinetic energy of attachment, which should be a function of hydrodynamic forces. As such, the attachment model was the first to link the surface and hydrodynamic forces in one equation, which served as a basis for my flotation model. Since the model has been derived from first principles, it has predictive and diagnostic capabilities, as shown in the special issue of IJMP published to honor Professor Schubert for his 90th birthday. It should be noted here also that of the various surface forces, hydrophobic force is the driving force for bubble-particle attachment and hence flotation.
In retrospect, I advocated the control of bubble size to improve flotation during the early part of my career. During the later stages, I advocated the control of hydrophobic force. I am not certain if I have a proper training to explore the origin of the hydrophobic force. Nevertheless, I will do my best with my graduate students and other colleagues.
I came a long way from a humble origin. I was lucky to have an opportunity to study at McGill, which has grown to become one of the best-known minerals processing schools largely due to the leadership of James Finch – my classmate. I was lucky also that my adviser allowed me to carry out fundamental research while teaching me to do something useful for the industry. I was also lucky that CANMET and Virginia Tech gave me the opportunities to do what I believed was important. This is my 39th year at the university, which is a long time. I was fortunate to have so many good people pass through my laboratory. The most fun part of my job has been to stand around a whiteboard and discuss problems with students, which is a learning experience. I feel that I have not left school because I still have so much to learn. I say to my students that teaching is the best job in the world. And both of our children became teachers like many of my former graduate students".

Once again I thank Prof. Yoon for taking some considerable time out of his very active life to provide for MEI the story of his journey through life, and I look forward to seeing him in Cape Town in November for what will be his second MEI Conference. I am sure that all who read this account will agree that he was a very worthy recipient of the IMPC's Lifetime Achievement Award.

References to all the research projects reported above can be found by contacting Prof. Yoon at

Sunday, 13 August 2017

The Red Arrows, the major attraction during Falmouth's Festival Week

Falmouth was teeming with visitors this week, for Falmouth Week, which ended last night. With its origins in a local sailing regatta dating back at least as far 1837, the Week has evolved into not only a major sailing competition in the south west but also an opportunity for tourists and locals to enjoy the many daytime and evening attractions in the town.
Crowds on Gyllyngvase beach await the Red Arrows
The highlight, as always, was the annual display by the RAF's Aerobatic team, the Red Arrows, which attracted so many people to the local beaches and headland that the narrow roads in the town were completely gridlocked. But it was certainly a display worth waiting for.
The arrival of the Red Arrows

Twitter @barrywills

Friday, 11 August 2017

Minerals and metals to play a significant role in a low-carbon future

The rise of green energy technologies required for a low-carbon future is expected to lead to significant growth in demand for a wide range of minerals and metals, such as aluminium, copper, lead, lithium, manganese, nickel, silver, steel, and zinc and rare earth minerals, according to a new World Bank report, The Growing Role of Minerals and Metals for a Low-Carbon Future.
The mighty Outotec will play a big part in this green future. Last year the international company was ranked for the second time as the world's third most sustainable company (MEI Online) and in 2015 strengthened its portfolio of gold processing technologies by acquiring Biomin's BIOX® bioleaching technology (MEI Online).
So we are delighted to welcome Outotec as a major sponsor of MEI's conferences in Namibia next year. Sustainable Minerals '18 and Biohydromet '18 will run back to back in Windhoek in June, and the role of biohydrometallurgy in the sustainable development of mineral resources will be emphasised by Prof. Sue Harrison in her keynote lecture at Biohydromet '18.

Thursday, 10 August 2017

The beautiful River Dart and an invention which changed the world

During last week's visit to South Devon, we spent a couple of days around the estuary of the River Dart near Kingswear.
Looking down on the coast path just beyond the Dart estuary
Coleton Fishacre, 1920s country retreat of the D'Oyly Carte family
Greenway, holiday home of Agatha Christie and her family

Views of the River Dart from the Greenway Estate
A short ferry ride across the Dart from Kingswear took us to the historic naval town of Dartmouth, where residing in the Visitors' Centre is one of the world's most important inventions.
I have claimed many times that froth flotation is one of the world's most important technological inventions, certainly since the industrial revolution, but without the invention of the steam engine there would have been no industrial revolution.
The inventor of the first practical steam engine was born in Dartmouth in 1664. Thomas Newcomen will be a name unknown to many but his atmospheric engine allowed water to be pumped from deep below ground, allowing miners to go deeper to access coal and minerals to feed the new industrialised world. Hundreds of Newcomen Engines were constructed through the 18th century.
One of the original Newcomen Engines, at Dartmouth
The engine operated by condensing steam drawn into the cylinder, which was mounted directly on top of the boiler. Steam from the boiler filled the cylinder, replacing the air. The steam was then condensed by injecting cold water into the cylinder, the resulting vacuum then allowing the pressure of the surrounding air to force the piston down to complete the working stroke. On completion of the stroke the weight of the pump rods drew the piston back up the cylinder, ready for the next stroke.
Although the thermal efficiency was only around 0.75% the engine was so sound in principle that it laid a solid foundation on which later engines could be built, as well as performing unchanged in basic concept for over 150 years.
James Watt's later engine design in 1776 was an improved version of the Newcomen engine that roughly doubled fuel efficiency. Many atmospheric engines were converted to the Watt design, for a price based on a fraction of the savings in fuel. As a result, Watt is today better known than Newcomen in relation to the origin of the steam engine. He later realised that Newcomen engine designs wasted a great deal of energy by repeatedly cooling and reheating the cylinder and introduced a design enhancement, the separate condenser, which avoided this waste of energy and radically improved the power, efficiency, and cost-effectiveness of steam engines. In the early 19th century Cornishman Richard Trevithick (posting of 25th April 2015) increased thermal efficiency to around 9% with the high pressure steam engine.
So let's salute these great inventors and remember that steam is still used to generate most of the electrical energy that we use today, whether it be from fossil fuel or nuclear power stations.
Twitter @barrywills