Physical Separation ‘13 - conference diary

Physical Separation ‘13 was held at the St. Michael’s Hotel, Falmouth, UK, from June 20-21, 2013 and was sponsored by FLSmidth, TOMRA Sorting Solutions, Limn The Flowsheet Processor, International Mining, Industrial Minerals and AT International. 

As always, this is my diary of events, which I hope will be supplemented by comments from delegates.

Thursday June 20th

I opened the conference this morning and welcomed our 58 delegates, representing 15 countries: Australia, Brazil, Canada, Chile, France, Germany, India, Israel, Japan, Poland, Russia, Spain, Sweden, UK and USA. Thirteen of the delegates from Computational Modelling ‘13 had stayed on for this conference, including 6 from the University of New South Wales.

Before the start of the technical sessions I had the great pleasure of presenting Randall Zahn, of FLSmidth, USA with the MEI Young Persons Award for 2012 (see MEI Online for the citation).

David Wiseman and MEI's Amanda

Conference sponsor David Wiseman of Limn: The Flowsheet Processor, Australia, presented the first paper in the technical sessions, showing how physical separation processes can often be modelled and simulated to a useful degree of accuracy using relatively simple techniques. By selection of appropriate component species sets and limiting model complexity to the simplest required to answer the problem posed, many of the pitfalls normally associated with mathematical modelling and simulation can be avoided.The mining and processing industry relies on macro scale avoidance of waste at the front end of the operation, followed by the progressive removal of waste and contaminants via comminution and separation.  Unfortunately the low grade of valuable content in most metalliferous operations, dictates that vast quantities of associated host rock and gangue accompanies the valuable material to the processing plant.

David Bowman, of Bear Rock Solutions, Australia described how, in association with Newcrest Mining Ltd, a robust scientific plan has been devised which examines the fundamental nature of waste rejection, the possibilities for exploitation and how it could be employed across their various operating sites and in future operations.  The total project examines a range of waste rejection techniques capable of deployment at coarser size ranges and these include systems based on, size, gravity, physical and chemical properties.  The results of this study show that some process streams offer significant potential for waste rejection, but in most cases there is no “one pass” waste rejection option. Rather the rejection process becomes a series of liberate-separate cycles. At each stage the altered physical characteristics of the material open different possibilities for rejection techniques.

Suresh Srinivasan of the Indian Institute of Technology reviewed the recent developments in microwave applications in metallurgical processes including mineral processing, microwave assisted grinding, microwave enhanced magnetic separation, microwave treatment of coal, and also in the field of extractive metallurgy such as roasting and calcination, leaching, and reduction. This was followed by a presentation from the University of Queensland on the FDTD simulation of microwave heating of a variable feed inside two microwave applicators, with different uniformity parameters.

There was an interesting array of papers after the morning coffee break. Martin Brandaeur of the Karlsruhe Institute of Technology, Germany, presented a paper on the physical separation of secondary waste from the decommissioning of nuclear facilities and Vladimir Rizmanoski of the University of Queensland showed how micro-cone beam tomography offers a non-destructive way of identifying coarse and fine mineral grain dissemination on a particle by particle basis. There is substantial potential benefit for separate treatment if a practical means of coarse separation based on texture existed.

Martin Brandaeur and John Clout prepare for their presentations

John Clout of Australia discussed recent advances in iron ore beneficiation, particularly for low grade hematite-goethite ores containing clay and quartz gangue, which have proved difficult to upgrade and capital intensive to process when using existing beneficiation technology. A number of wet plants have recently been constructed in the Pilbara region of Western Australia using a new flowsheet, consisting of wet screens, hydrocyclones, upcurrent classifiers, spirals and dewatering screens. The process overcomes many of the disadvantages of more traditional iron ore processing flowsheets.

The average grades of many mineral ores are in long term decline while the demand for minerals and metals continues to increase. The overall effect is to increase the consumption of energy per tonne of metal produced. For many ores, most energy is consumed in communition, and for many low grade ores much of the communition energy is expended on barren rock.

One way to moderate this dilemma is to sort ore at coarse sizes to reject very low grade or barren gangue. Rejecting waste at coarse sizes reduces the energy required for communition and per unit of metal produced. Such dry ore beneficiation is an objective in many mines nowadays. Water withdrawal and disposal and all related environmental aspects became key issues, even more in arid areas. Sensor based sorting technology using X-Ray-Transmission (XRT) has proven its ability in recent years in industrial scale applications. High efficiencies and recovery rates can be achieved using the latest technologies. Powerful computers and increasingly sensitive X-ray scintillation counters have allowed the development of high-performance units. The machines have reached a status of rigid and reliable field stability and can be operated at grain sizes of 8 mm up to 70 mm, depending on the individual ore.

Jens-Michael Bergmann with
Industrial Minerals' Laura Syrett

Jens-Michael Bergmann, of conference sponsor TOMRA Sorting, Germany, described the basics of XRT-sorting technology followed by a case study of a chromite processing plant in South Africa where a state-of-the-art XRT sorting machine is operating together with spiral concentrators. The sorter is pre-concentrating the ROM chromite ore by removing barren waste and low grade rocks, while after comminution the spirals are concentrating the ore to a market grade of above 46% Cr₂O₃.
Rob Morrison of the University of Queensland described how to measure the potential of ore for sorting and the development of a range of indices which can be used to describe their intrinsic sortability and their actual sortability for any sorting process. He also showed how many mineral deposits do not have sharp, well defined boundaries. They grade away to very low grades through a non-economic halo which may contain as much metal as the economic part of the deposit. If some of the halo ore can be upgraded by sorting, the size of the deposit is increased. If marginal ore can be upgraded, the effective capacity of the concentrator can be increased “making space” for the upgraded ore from the low grade halo. These opportunities do not fit into the conventional cut off grade model for ore selection, and the paper considered alternative strategies for the definition of “ore” which may also lead to enhanced value of the deposit with a lowered requirement of environmental remediation.

Three papers on hydrocyclones started the afternoon session. Johann Dueck of the Friedrich-Alexander-Universitat, Germany, described an approximate analytical method for calculating and explaining the non-monotonic partition curve (fish-hook effect) of a hydrocyclone.

Positron Emission Particle Tracking (PEPT) was developed at Birmingham University in the late 1980s, and has proven to be a powerful visualization tool for industrial engineering applications. Many attempts have been made to capture the key relationships between hydrocyclone operating and geometrical variables in models, but hydrocyclone characterization is still heavily empirical and on a case-by-case basis. Jen Radman, of McGill University, Canada showed how hydrocyclone flow patterns can be quantified under realistic industrial conditions using PEPT.

Maryam Ghodrat, of the University of NSW, Australia, showed that hydrocyclones usually follow conventional cone design and may have some limitations on separation performances. A continuum-based multiphase flow model showed that cyclone performance is sensitive to cone section length as well as cone shape. Robert Johansson, of Chalmers University, Sweden, then showed how modelling was being used by Chalmers University, Sweden, to predict the performance of a two-step air classifier, using data from a Swedish crushing plant.

Chris Rehmann with Suresh Srinivasan

Modern mining processes require the use of large quantities of water, yet clean water is a finite and ever-scarcer resource. Chris Rehmann of AESSEAL Inc., USA described, in the final paper of the day, a proven sealing technology which enhances physical separation and filtration processes, and improves filter-press cycle times. This is accomplished by replacing traditional flushed gland packing on pumps with a double mechanical seal that recirculates clean water from a novel seal support system which has no moving parts. It was claimed that improvements in pump and filtration systems using this system are now saving over 25 billion gallons of water worldwide each year.

Talking of water, the weather has been atrocious today, but despite the conditions, around 20 hardy souls braved the elements for the evening coastal path walk. The 17th century Chain Locker pub provided a warm and dry destination, and good Cornish ale in the company of the Cornish Mining Sundowner whose monthly meeting happily coincided with the walk.

Drying out at the Chain Locker

Friday June 21st
This morning’s papers were an eclectic mix, starting with a presentation from Daniel Amariei of COREM, Canada on the reflux classifier, one of COREM’s research projects dealing with the introduction of new potential technologies for the recovery of fine particles. The reflux classifier is mainly used in the coal and minerals industries, but the paper summarised the experimental work undertaken for the assessment of concentration capacity of the reflux classifier for iron fines beneficiation, where the recovery of fines has become a high priority.

Jian Cheng, of the University of New South Wales showed how Computational Fluid Dynamics and DEM modelling can optimise the design and operation of dense medium cyclones in coal preparation, and then Darryel Boucher, of McGill University, showed how PEPT is a powerful method to visualise the behaviour of particles during the concentration process, providing data that will be used for the validation of new models of spiral concentrator performance.

Gravity concentration modelling was also the subject of a paper by Jean-Sebastien Kroll-Rabotin, of the University of Alberta, who described the validation of a predictive model for industrial scale Falcon concentrators, enhanced gravity devices which are commonly used in the mining industry.

Eduardo Crespo, of Daytal Resources, Spain described the development of a new DEM mathematical model for the description of segregation and dispersion in jigging beds, which also gives important insights into the jigging mechanism. Agnieszka Surowiak of AGH University of Science and Technology, Poland then provided a comparative assessment of separation efficiency in jigging.

Rare earth elements are becoming increasingly important for a variety of uses (see posting of 1st February). Rare earth (RE) mineral deposits are typically processed using several different unit operations including gravity, magnetic, electrostatic and flotation separation. Two of the most important beneficiation techniques for RE minerals are gravity and magnetic separation. Many RE minerals are found alongside low specific gravity gangue minerals thereby permitting the use of gravity separations to concentrate the heavy value RE minerals. Magnetic separation is used primarily to remove ferromagnetic gangue minerals as well as to separate individual paramagnetic rare earth minerals. Adam Jordens, of McGill University, described how a series of magnetic separators (wet variable intensity, wet drum permanent magnet, Frantz Isodynamic Separator) in conjunction with gravity pre-concentration steps (Knelson and Falcon centrifugal concentrators) have been used to beneficiate a rare earth ore.

The internal workings of wet Low Intensity Magnetic Separators are poorly understood, and Jan Stener, of Lulea University of Technology, Sweden, showed how ultrasonic velocity profiling could be used to enhance our understanding.

Rob Morrison of the University of Queensland presented work on the investigation of the radiofrequency properties of conductive minerals. Unlike insulating minerals, such as quartz or feldspar, the propensity of conductive minerals to heat using radiofrequency energy has not been particularly well quantified or documented. A detailed knowledge of the RF properties of all minerals is required if RF energy is to be effectively used in many potential applications.

Dave Wiseman with Rob Morrison and Hugh Rice

The final paper of the morning session was presented by Hugh Rice, of Leeds University, who discussed the application of the ultrasonic dual-frequency method, which uses the backscattered signal received by transducers operating in the megahertz range, to determine the concentration profile in suspensions of solid particles in a carrier fluid. The observed trends demonstrate that this technique has great potential for measuring the settling and separation behaviour of real suspensions and slurries in a range of applications, such as the nuclear and minerals processing industries.

Dewatering was the theme of the final session of the conference. Understanding settling and thickening of complex, concentrated sludges and suspensions is a critical requirement in numerous industries. Jaiyana Bux of Leeds University showed how an acoustic backscatter system has demonstrated potential for in situ characterisation with minimal intrusion. A gravity thickener containing a water treatment waste stream was successfully profiled, by correlating the backscatter attenuation in situ with that of homogenous suspensions. Fernando Betancourt, of Universidad de Concepcion, Chile, then described a model to control continuous sedimentation of suspensions in clarifier-thickener units.

In the final presentation, Chris Pickles, of Queen’s University, Canada, showed how microwaves could be used as an alternative energy source for drying a sub-bituminous coal. The results demonstrated that microwave drying had several advantages over conventional drying, such as reduced drying time and increased drying efficiency.

Amanda closed the conference and invited all delegates to Physical Separation ‘15 in two years time.  There were 35 papers presented at the conference, including 7 as posters. These are all available on CD from MEI. Final papers will be peer-reviewed and published in a special Physical Separation issue of Minerals Engineering.

 During the final coffee break I gave a short introduction to the geology of Cornwall, and its copper and tin mineralisation, prior to our late afternoon visit to the Camborne-Redruth mining area, the “birthplace of modern mining”.

During my 22 years at Camborne School of Mines (CSM), I must have made the journey to Camborne and back many thousands of times, but it is always fascinating to see the gradual change in the landscape, from Falmouth's lush greenery to the relatively bleak mining landscape around the famous mining towns of Redruth and Camborne. Our coach passed the South Crofty mine, which closed in 1998, and the site of Dolcoath, which in the late 19th century was the world's greatest and deepest mine. Then on to the village of Troon in the heart of what was once the world's largest producer of copper and tin.

We were privileged to have an exclusive tour of the award winning King Edward Mine (KEM) Museum, once owned by CSM, and where I had my first office! The mill at KEM simulates the flowsheet of an early 20th century tin dressing plant, with now obsolete devices such as Frue vanners, hand jigs, round frames, buddles and rag frames. The Californian stamps were also run for a short period, to give us an impression of the cacophony of sound which must have assaulted the ears in those far-off days when hundreds of mines were operating in this area. On behalf of the group I must thank Tony Clarke, who I worked with all those years at CSM, Frank Kneebone and conference delegate Nigel MacDonald for hosting us, and for their deep knowledge of, and enthusiasm for, Cornish mining.

Shaking Table

Rag Frames

Tony Clarke explains the hand jig

From KEM we drove to the small mining village of Carnkie to explore the ruins of the dressing floors of the Basset Mines, a now peaceful area of what was once a hellish district of danger, smoke-bellowing engine houses, and the ever present ear-splitting pounding of the stamp batteries.

Overlooking Marriott's Shaft, Wheal South Frances

Wheal Basset

West Basset

West Basset with the stamps engine house in the background

Then a leisurely drive back to Falmouth to say our goodbyes after what has been a great week of conferences, with whom Laura Syrett, of sponsor Industrial Minerals, described on Twitter (#PhysicalSeparation13) as mineral processing's elite!