Monday, 15 June 2015

Physical Separation '15 Conference Diary

The Physical Separation conferences, of which this was the 4th in the series, have always been held in Falmouth. They always attract a small, but very interesting gathering- an eclectic mix of specialists in gravity concentration, magnetic and electrical separation, and increasingly, electronic sorting. Cornwall is an appropriate place to hold these events, as it was the first place in the world where physical separation methods were practiced on a large scale, and I always look forward to taking delegates on a pilgrimage to the Camborne-Redruth mining district, the 'birthplace of modern mining'.

Physical Separation '15 was held at the St. Michael's Hotel, Falmouth from June 11-12, 2015, immediately following Computational Modelling '15 (posting of June 13th), and was sponsored by TOMRA Sorting Solutions, Steinert Elektromagnetbau, ST Equipment & Technology, with media sponsors AT International and Industrial Minerals.

Thursday June 11th
Jon opened the conference this morning, welcoming the 56 delegates from 13 countries.

It is no surprise that two of the three conference sponsors are leaders in the field of electronic sorting, which represents a future direction for the mining industry as it seeks to reduce costs associated with comminution, waste handling, and mining. Rapid advances in high speed computers and sensors will see more and more plants in the future adopting this technology.

In the first session of the conference, chaired by Kristian Waters, of McGill University, Canada, Rob Morrison of the JKMRC, Australia, set the scene in his keynote lecture, in which he considered opportunities for reducing the use of energy in comminution by doing as little of it as possible by using physical separation over a wide range of sizes. These ideas also lead to strategies which might reduce water use and even to what might constitute a mineral deposit.

TOMRA Sorting GmbH, Germany has recently been named the winner of the European Business of the Year Award, being recognised as one of the best European companies in terms of demonstrating innovation, business ethics and financial success (MEI Online). Jens-Michael Bergmann of TOMRA continued the theme of reducing water usage via electronic sorting. Processing of ores and industrial minerals worldwide is consuming an incredibly large quantity of process water. This water has to be extracted, transported, recovered, and discharged with all its commercial and environmental impacts. Sensor sorting could considerably cut the crushing and milling cost, reduce the water consumption, save costs for water treatment and disposal, and finally improve the overall environmental image of our industry. Machines scan each rock and identify its physical properties by a sensor. The “wanted” material will enter the downstream beneficiation steps and the “unwanted” is waste. No water will be disposed with these, no pond is necessary, no slurries with high leachate potential have to be stored and monitored for years.

I met Joe Lessard of Orchard Material Technology (OMT) at this year's SME Meeting in Denver (posting of 20th February). I had been impressed with a paper that he had co-authored, on the economic impact of ore sorting in a comminution circuit, which had been published in Minerals Engineering (posting of 8 Sept 2014), so I invited him to present a paper at Physical Separation '15. Conference sponsor Steinert, who provides state-of-the-art sorting equipment and sophisticated magnetic separation technology, is now working with OMT to generate a more complete picture of the economic ramifications (i.e. capital, operating, and maintenance costs) associated with bringing sorting to existing processes. Joe took us to the coffee break by showing that a major barrier to widespread implementation of sorting in hard rock mining is a knowledge gap: sorting equipment manufacturers have made modest footholds in the mining industry, while miners and plant operators are largely unaware of recent developments and the state-of-the-art technology. Most importantly, a widespread understanding of how ore sorters can be implemented and their significant economic impacts is lacking. The impacts of ore sorting on the economics and the process flow sheet of an existing semi-autogenous milling circuit of a US copper mine were discussed and the advantages of large scale ore sorting outlined in terms of mine and processing economics.

Joe Lessard, Jens-Michael Bergmann, Rob Morrison and Jon
Following the coffee break, chaired by Claude Bazin, of Laval University, Canada, Cristian Carrasco, of the Cooperative Research Centre for Optimising Resource Extraction, Australia described the development of a novel tool to rapidly assess metal preconcentration by size potential. This methodology identifies samples that are economically amenable for screening, providing a dynamic rock “recipe”. This changes depending on cut-off, proportion of the accepted (high grade, fine material) and rejected stream (low grade, coarse material) produced by screening. It is claimed that this methodology can eventually be used to support short term operational decision when grade by size variability is exploited by screening.

Lewis Baker, of conference sponsor ST Equipment & Technology LLC, USA, then described how the company's tribo-electrostatic belt separator provides the mineral processing industry with a means to beneficiate fine materials with an entirely dry technology. He discussed how the high efficiency multi-stage separation through internal charging/recharging and recycle results in far superior separations than can be achieved with other conventional single-stage electrostatic systems. The triboelectric belt separator technology has been used to separate a wide range of materials including mixtures of glassy aluminosilicates/carbon, calcite/quartz, talc/magnesite, and barite/quartz. He claims that the enhanced separation capabilities of the STET system may be a very effective alternative to flotation processes, as the dry process results in a simpler process flow sheet with less equipment than flotation with both capital and operating expenses reduced by around 30%.

Lewis Baker with Roy Dobson of Fairport Engineering, UK
 We are pleased to have seven representatives of the China University of Mining & Technology at the conference, and Yaqun He described the triboelectrostatic separation of pulverized coal based on combined mineralogical characterization analyses. Multi-analytical techniques were utilised for raw coal and pulverized coal, respectively, to evaluate the potential for beneficiation of coal after grinding.

With China University of Mining & Technology's Wiening Xie, Cheng Sheng, Yaqun He,
Yuemin Zhao, Chenglong Duan and Bo Zhang
In many parts of the world, important reserves of Microscopic Biogenous Sediments are found in which an intimate association of Diatomaceous Earth (DE) and CaCO3 is experienced. DE is a hydrous form of opaline silica with many industrial applications, for instance, as filter aids to produce a clear filtrate from a broad range of fluids. The presence of CaCO3 can have a negative influence on the pH and taste of food products filtrated. Therefore, this impurity in the DE products should be removed down to the level suitable for the industrial food. In a study described by Saeid Moradi, of Imerys Minerals, UK, the separation of CaCO3 from a DE product using a conventional corona electrostatic separator and an advanced tribo-electrostatic separator was investigated. Important controllable variables were incorporated into mathematical models which predicted the performance of a single stage of separation for each separator and showed the merits of using the advanced tribo-electrostatic separator.

The final paper of the morning, presented by Philipp Hartlieb, of Montanuniversitaet Leoben, Austria, dealt with experimental studies measuring the microwave absorption properties of granite, sandstone and basalt in the temperature range of 0 - 800°C and the thermo-physical rock properties in the same temperature range. Numerical analyses were used to demonstrate the influence of varying parameters. The results of these measurements and analyses were linked to microwave irradiation tests at 25 kW output power demonstrating the strong variation of effects depending on the parameter rock / mineralogy showing possible applications in a mineral processing environment.

The afternoon session, chaired by Kathryn Hadler, of Grinding Solutions, UK, commenced with a very topical paper from my old CSM student Charlie Northfield. Charlie is processing plant manager with Wolf Minerals, whose Drakelands tungsten-tin mine, Britain's first new metal mine in over 40 years, is due to commence operations on June 16th. This must be a very busy time for Charlie so we appreciate his taking time to cross the border into Cornwall to give us an update on the operations, an interesting flowsheet incorporating DMS, spirals, tables, low and high intensity magnetic separation, and flotation.

Although Drakelands is in neighbouring Devon, and Cornwall's era of metal mining is long past, Cornwall still has a very dynamic mining network, which will be of great use to the new mine. Also much involved with the Cornish mining network is Salter Cyclones, and it was good to see Ian Daniels representing the company at the conference. Salter Cyclones manufacture and sell the hydrocyclones and Multi-Gravity Concentrators (MGS) originally developed by Richard Mozley (posting of 4th June). Although Ian never worked for Richard Mozley Ltd, he was working with Axsia when they bought out RM Ltd in 2000. This is Ian's 6th MEI Conference. In 2006 he represented Axsia-Mozley at Gravity '06 and Hydrocyclones '06, and at Physical Separation '09 with the Mozley Group, which quickly became Salter Cyclones, who he represented at Physical Separation '11 and Physical Separation '13. Although based in Cheltenham, Salter Cyclones still retains the old Richard Mozley premises in Redruth for testwork and is much involved with local companies SGS and Grinding Solutions. When SGS has samples that need cycloning, or use of the MGS, they send the samples to Salter Cyclones, and when SC has samples that need analysing this is done by SGS at the Wheal Jane site. Ultrafine size analyses are handled by Grinding Solutions in Truro, so samples bounce between Salter, SGS, and Grinding Solutions, all helping each other in promoting the knowledge and skills available within the Cornish mining network. Also based in Cornwall, and feeding into the network is the UK base for the USA's Deister Concentrator, and Petrolab, which provides advanced mineralogical facilities, as does the Camborne School of Mines. Representatives from the network are photographed below with Charlie.

Ian Daniels (2nd left) and Charlie Northfield (3rd left) with Cornish mining network representatives
Luke Rogers (Deister Concentrator), James Strongman (Petrolab),
Dave Goldburn (SGS) and Kathryn Hadler (Grinding Solutions)
I met Bill Weldon, of Mineral Technologies Inc, USA, at the SME Meeting in Denver and invited him to Falmouth to present a paper on a new mineral sands operation which is being developed in Georgia by Southern Ionics, Inc. (SII). The process uses traditional physical separation equipment; however a new MT spiral, the MG12, was selected for use on board the floating wet concentrator plant for roughing duty. The MG12 spiral is a two-stage, twelve-turn spiral that has been proven to achieve very high recoveries of heavy minerals. The floating plant includes feed desliming operations, a central MT surge bin for optimum spiral circuit feed control and ancillary operations for concentrate and tailings handling. Scrubbed heavy mineral concentrate (HMC) is then transported to the MSP for concentration of the titanium and zirconium bearing mineral fractions. 

Bill Weldon with Luke Rogers
Another interesting operations paper was presented by Adam Jordens of McGill University, Canada. The Nechalacho rare earth deposit in Canada's Northwest Territories contains multiple low specific gravity, diamagnetic silicate gangue minerals (predominantly feldspars and quartz) as well as high specific gravity, iron oxide minerals (magnetite and hematite). The valuable REE minerals in the deposit consist of a variety of relatively high specific gravity, paramagnetic minerals. A process has been proposed to concentrate the value RE minerals through a combination of gravity (rejecting silicate gangue) and magnetic (rejecting Fe-oxide gangue) separation steps prior to froth flotation.

Rare Earth Elements (REE) are common in Waste from Electronic and Electric Equipment (WEEE), but the average REE grades are low, and current recycling rates are close to nil. Bertil Pålsson, of Luleå University of Technology, Sweden, presented results from a European research project where different ways of upgrading waste containing REE have been tried. One of the ways is to identify recycling streams with higher grades and volumes of REE. Samples from the streams are then processed to liberate as much as possible of the contained REE. It was found that especially Nd emanating from strongly magnetic and brittle materials can be separated by a simple process of thermal demagnetisation, pre-screening, cryo-grinding and fine sieving.

Bertil Pålsson and Adam Jordens
Gregor Borg, of PMS Hamburg, Germany, described the VeRo-Liberator®, a new impact crusher suitable for the comminution of ores, smelter slags, waste incinerator slags, concrete and numerous other complexly intergrown materials (MEI Online). The technical advantages are very low energy consumption, very high degree of particle liberation, and particle size reduction from 100-120 mm to typically >90% less than 500 micron in a single pass.

Philipp Hartlieb with Gregor Borg and Felix Scharfe of PMS Hamburg
Screens are an important production unit in crushing plants, the performance of the screen being essential to the performance of the plant. In the final paper of the day, Magnus Bengtsson, of Chalmers University of Technology, Sweden, described a mechanistic model of a banana screen and presented a novel model for screen deck configuration. The developed model can be used for optimisation of a screen so that it has the best possible performance with respect to different feeding conditions, in order to obtain a desired separation.

There has been persistent rain during the day, but by late afternoon it had apparently cleared, just in time for our usual walk to the Fal estuary and into old Falmouth. But an hour into the walk we were hit by a deluge, so it was a very wet group that arrived at the 17th century Chain Locker pub to sample the best Cornish ales (see also posting of 11th June). Echoes of Physical Separation '13 where we also had to dry out in the pub!

The lull before the storm!
Drying off in the Chain Locker pub

Friday June 12th
Vibrating screens are widely used, but despite their importance full understanding has often been a major obstacle both in academia and industry. In the first paper of the morning session, chaired by Bertil Palsson, of Lulea University, Sweden, Nicolus Rotich, of Lappeenranta University of Technology, Finland presented new methods for granular-material flow prediction and design of efficient industrial screens.

With Nicolus Rotich
Claude Bazin, of Laval University, Canada, then described an operational model for a spiral classifier, accounting for wash water addition and concentrate cutter openings, two strategic variables for the operation of spiral classifiers which are rarely included in spiral models.

In a further Canadian paper, Darryel Boucher, of McGill University, showed how activated hematite and quartz tracers were tracked along the first two turns of a spiral concentrator to ascertain information on valuable and gangue particle motion. The tracking was made possible in the first and second turns of the spiral by the direct activation of mineral particles, and the use of an adjustable height circular assembly of modular positron emission particle tracking detectors.

The dense medium cyclone (DMC) is recognized as one of the most effective devices to separate run-of-mine coal and in practice the feed material properties in a DMC, such as coal particle density and size distribution, are important variables affecting performance. Although the effects of particle density and size distributions have often been studied separately their interaction has not been well understood. Jian Chen, of Monash University, Australia described a CFD-DEM study of the multiphase flow in a dense medium cyclone, particularly with respect to the interaction of particle density and size distributions.

In the session following the coffee-break, chaired by Gregor Borg, of PMS Hamburg, Germany, Veruska Govender and Carl Bergmann of Mintek, South Africa showed how mineralogical characterisation and process modelling was used to simulate the gravity recovery of ferrochrome fines. Through modelling, it was also possible to evaluate alternative physical separation flowsheets that could be used to recover valuable products using an established mineralogical particle characterisation method.

Mintek's Carla da Corte, Carl Bergmann and Veruska Govender
Centrifugal concentrators have been widely used for recovering fine gold over the past decades. One of the drawbacks of this technique is the large volume of water required during the operation. Recent work at McGill University, Canada, using a laboratory scale Knelson Concentrator, was described by Meng Zhou, who showed that this can be overcome by using air to replace the water as the fluidising medium.

Calcium carbonate may accumulate in Microscopic Biogenous Sediments where Diatomaceous Earth is present. This produces beds of lean-grade DE ores which are found in some parts of the world; these are often exploited ineffectively because they do not meet food contact standards. Selective flocculation is considered a potential technique for DE-CaCO3 separations for materials of fine particle size, as discussed by Saeid Moradi of Imerys Minerals, UK.

During the decommissioning of a nuclear facility, the reactor pressure vessel and its internals have to be cut into small pieces to allow the final disposal in a nuclear repository. One of the cold, and under water, cutting techniques used for this application is the water abrasive suspension cutting, proven to have many advantages compared to mechanical or thermal cutting technologies. The major drawback of this technology, however, is the generation of large amounts of secondary waste, due to the use of the added silicate abrasive. In order to reduce or even eliminate this secondary waste, a new treatment and disposal technique based on physical separation is being developed at the Karlsruhe Institute of Technology, Germany. Martin Brandauer showed how this makes use of the magnetic properties of the steel fraction, as well as the different sedimentation characteristics of the fractions.

In mineral processing material transport is commonly monitored between unit operations; flow speed, solids concentration, and particle size distribution of suspension flow in pipes are measured online using standard equipment. In many situations this information would be complemented by measurements inside the process equipment. In work at Luleå University of Technology, Sweden a wet Low-Intensity Magnetic Separator (LIMS), where no means for internal measurements exist today, is used as a proof of concept, as described by Jan Stener. An ultrasound-based method was utilized for carrying out direct measurements of internal material flows in a bench scale unit of the counter-current type. Using this method it was possible to study the effect of slurry feed velocity, slurry solids concentration, magnet assembly angle, and drum rotational speed on the internal particle flow patterns. These direct measurements can aid in both machine design and improved process control.

The final session of the conference was chaired by Philipp Hartlieb of Montanuniversitaet Leoben, Austria, who introduced Richard Pascoe of Camborne School of Mines, UK, who described an investigation of the performance of a low intensity magnetic separator using QEMSCAN analysis.

Richard Pascoe (right) with Bertil Pålsson, Anders Sand and Ian Daniels
Steelmaking slag includes much entrained iron. In order to recover this iron Kyohei Ishida, of JFE Steel Corporation, Japan proposed an efficient approach to dry fine particle separation using mechanical stirring by a fluctuating magnetic field, generated by a magnet roll with multiple poles, the quick change of magnetic field generating strong agitation.

Yuemin Zhao of the China University of Mining & Technology showed that the magnetic separation removal rate of pyrite can be improved effectively by increasing the susceptibility of pyrite. The electromagnetic characteristics and absorption response performance of high-sulfur fine coal were studied in strengthening the susceptibility of pyrite. Microwaves improved the susceptibility in the ultra-high frequency region, which is the most natural resonance.

Waste from acid leaching of low grade copper oxides must be dewatered to reduce the volume of disposed materials and to mitigate potential environmental hazards. The use of electro-osmotic potential to assist in the dewatering of this waste is an attractive option, being more efficient than mechanical filtration alone, and less energy intensive than thermal drying. In a study at McGill University, Canada, described by Mayeli Alvarez-Silva, the influence of voltage, humidity and pressure on the electro-osmotic dewatering of waste from acid leaching was evaluated at laboratory scale.

Mayeli Alvarez-Silva with Patrick Blonde of IMERYS Talc, Canada
and Saeid Moradi of IMERYS Minerals, UK
Thickening is one of the most important unit operations where water is recovered in copper concentrators, and in the final paper Fernando Betancourt of Universidad de Concepción, Chile, showed how flocculation is a critical step in this process where flocs are formed from destabilized particles. In general, flocculator reactors, hydraulic and mechanical, are devices with a large footprint. A new kind of equipment, with small foot print, in the class of ultraflocculator reactors, has been studied at a pilot scale level and by using CFD techniques including population balances.

Fernando Betancourt (centre) with Francisco Rojas and
Luis Felipe Ruiz of Advanced Mineral Processing, Spain
Amanda closed the conference and invited delegates to attend Physical Separation '17 in Falmouth in two years time. She invited all authors to submit their final papers for peer-review to Minerals Engineering, for possible inclusion in the special Physical Separation issue, which will be published early next year. All the conference draft papers are available on USB from MEI.

I then gave a quick briefing, over a Cornish cream tea, of the Cornish copper and tin mining industry, before around 25 of us set off for Camborne by coach.  Unfortunately, however, due to the wet conditions we had to abandon the planned walking tour of the historic Basset Mines, and instead had an excellent extended visit of the award-winning King Edward Mine Museum, for which I would like to thank our knowledgeable guides Tony Clarke and Nigel MacDonald (see posting of 12th June for more photos and information.)


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