Sunday, 23 June 2019

Report on Physical Separation '19

Physical Separation '19 was the 6th in the physical separation series of MEI Conferences, and was held for the first time at the National Maritime Museum in Falmouth, Cornwall. The 2-day event, from June 13-14 2019, was sponsored by Holman-Wilfley, Steinert, TOMRA Sorting Solutions, Outotec, Master Magnets, Hudbay Minerals and CRC ORE. Media partners were International Mining and Imformed and industry advocate was CEEC. The conference was attended by 83 delegates from 18 countries.

This posting will summarise the papers presented at the event, social events and people being highlighted in the postings of 14th June and 15th June.
Thursday June 13th

For almost 40 years engineers have explored opportunities for using microwave energy to improve the efficiency of mineral and metallurgical processes.  Given the vast energy consumption of such processes this is not a surprise  as microwave heating has long been assumed to reduce energy consumption in process engineering unit operations.  Selective heating of microwave-absorbent sulphides and metal oxides deported in a microwave-transparent gangue matrix results in differential thermal expansion of the heated phase, yielding micro-fracture around grain margins. Subsequent downstream processing may then yield higher recovery of valuable mineral sulphides and/or lower specific comminution energy, compared to non-microwave treated ore.
But while the mechanistic principles are well established, the scientific and engineering challenges of developing a commercial scale system have been immense. Typical throughputs of a large copper mine can be in excess of 5000 tph of milled ore and a microwave based treatment system would need to handle equivalent throughputs. This is at least an order of magnitude higher than any other microwave process ever built.
However, recent work has shown for the first time that microwave technology can be used in commercial mineral processing plants and that it can be used at significant scale with several of the largest microwave processing plants ever built being applied.  A multidisciplinary team of engineers from the University of Nottingham and Teledyne e2v have developed a revolutionary process for extracting copper from its ore by exposing rocks to powerful microwave energy for a fraction of a second. The team combined their skills in microwave technology and engineering to develop the largest microwave processing system ever constructed, capable of processing up to 3000 tonnes of ore per hour.
We were fortunate to have the team leader, Prof. Sam Kingman, deliver a keynote lecture "What's cooking in mining?" which examined the steps required to scale up such processes, and to draw conclusions as to the steps required to see this technology in daily use across our industry - a time which he feels may be sooner than some workers may have previously thought.

Sam Kingman (right) with Dan Alexander

Canada's University of Toronto is also very much involved with the commercialisation of microwave technology and three papers were presented this morning on the subject. One of the barriers to scale-up has, according to Erin Bobicki, been a lack of understanding of how microwaves interact with minerals and ores. Key parameters include the real and imaginary permittivities, which influence both the heating rate and microwave penetration depth. Over the past years, the University of Toronto and Queen's University have conducted high-temperature permittivity measurements on various materials using the cavity perturbation technique. Erin presented permittivity data as a function of temperature across a range of frequencies for a variety of minerals and ores. On the basis of this data, recommendations were made for how microwave technology can be best utilised for sustainable metallurgical processing. 
In the second paper from the University of Toronto, Darryel Boucher showed why, although the mining of ultramafic ores is required to meet society’s continued demand for nickel, these deposits are difficult to process due to their serpentine content. Serpentine increases slurry viscosity, slimes-coats the valuable Ni-bearing mineral pentlandite, and reports to and dilutes the froth during flotation via the formation of bubble-fibre aggregates and entrainment. Darryel showed how microwave pre-treatment can be used to convert the serpentine gangue to olivine, which should improve ore processing. 

Erin Bobicki and Darryel Boucher with Kai Bartram of Steinert

Also on the subject of nickel, Toronto's Matthew Goldbaum discussed why, due to its low concentration of nickel and high sulphur content, the current practice is for pyrrhotite to be rejected from conventional nickel sulphide processing circuits. However, the nickel content of pyrrhotite tailings (up to 1 wt.% Ni) represents a significant resource, and a new flowsheet, based on the microwave heating of the pyrrhotite tailings to produce FeNi and FeS phases is under development. 

Matthew Goldbaum with Carolina Vargas of TOMRA
Improvements in grindability and energy consumption using microwave pre-treatment have been reported extensively in the literature. However, as argued by Ahmad Hassanzadeh, of the Helmholtz-Institute Freiberg for Resource Technology, Germany, the impact of the location of the microwave irradiation in a communition circuit has not yet been addressed. Collaborative work between Germany and Iran has assessed the influence of microwave location, exposure time and grinding time on particle size distribution, particle liberation degree and energy consumption for a porphyry copper complex deposit, showing that the correct location of the irradiation can significantly improve the grindability of materials.
There are a number of potential technology opportunities to effect up-front gangue rejection in the minerals sector. Australia's CRC ORE, one of the conference sponsors, has been working with several of its mining participants to assess the efficacy of a range of such technologies, across a variety of operations and commodities. CRC ORE's “Grade Engineering®” approach references a suite of integrated technologies across several separation “levers” – dependent on the textural amenability of the ore domains concerned.
Ben Adair, CEO and Managing Director of CRC ORE, detailed recent implementation trials of Grade Engineering® at the Sumitomo-owned Minera San Cristobal operation in Bolivia. This Pb/Zn/Ag mine operates with some of the lowest head grades in the industry – yet ranks as one of the most profitable. The implementation strategies at the site trials were presented, the upgrading of “mineralised waste halos” to ores detailed, and the textural attributes that facilitates gangue rejection at scale. This success has implications for unlocking “hidden value” across the sector. 

Ben Adair with Dan Alexander

Following on from this, Raoni Lage, of the JKMRC, Australia showed that mineralisation is not evenly distributed across the whole particle size distribution after blasting and crushing. For some ores, valuable minerals can concentrate in the finer size fractions. This grade by size deportment has been utilised by the Grade Engineering™ (GE) approach, which results in coarse gangue rejection. Raoni described a study in which the effect on coarse gangue rejection by using precisely controlled impact breakage energy applied to single and multiple ore particles was investigated. The JKMRC Rotary Breakage Tester (JKRBT) and a lab-scale Vertical Shaft Impactor (VSI) were used for breaking individual particles (particle by particle) and high feed throughputs (multiple particles) respectively. The amount of target metal in the coarse progenies was compared to investigate the benefit of particle interaction within a lab-scale VSI for coarse gangue rejection. 

Raoni Lage (centre) with Bernard Agbenuvor and Kevin Galvin

Particle breakage by impact was also the subject of the next two papers.  Gregor Borg, of PMS GmbH, Germany and Martin Luther University Halle-Wittenberg, Germany, showed how the innovative VeRo Liberator® applies a mechanical high-velocity comminution principle, where numerous hammer tools rotate clockwise and anti-clockwise on three levels around a vertical shaft-in-shaft (hollow shaft) system. The resulting high-frequency, high-velocity impacts cause a highly turbulent particle flow and trigger fracture nucleation and fracture propagation preferentially at and along mineral boundaries. Breakage of coarser particles occurs from the high-velocity stimulation of bulk ore particles, where the elasticity and compressibility modules control differential particle behaviour. The improved breakage behaviour results in reduced energy consumption and very high degrees of particle liberation in the relatively coarse fraction of the product.
On an industrial scale, Anglo American applies already two VeRo Liberators® in their South African operations and Penoles and Fresnillo, Mexico, have carried out advanced test-comminution of ores from several of their gold-silver-zinc-lead mines in Mexico. Gregor described results from test-comminution by VeRo Liberator® of ores from Cienega Mine, Durango Province, Mexico, in comparison to Cienega’s conventional comminution by SAG milling and ball milling. The results show that the VeRo Liberator® achieves a similarly high degree of particle liberation compared to the SAG mill, but at a drastically coarser particle size. 

Gregor Borg (right) with Oscar Scharfe
In a further JKMRC paper, Bernard Agbenuvor showed how precise impact breakage has been identified to have the potential to enhance early coarse gangue rejection. This form of breakage targets to concentrate valuable minerals into finer fractions, which allow utilising a simple screening for rejection of coarse economically barren material.  Bernard described how the effect on coarse gangue rejection by using single and multi-stage precise impact breakage techniques was investigated. It was found that subsequent stages of precise breakage reduce the amount of valuable minerals in coarse particles and has the potential to improve the outcome of early coarse gangue rejection. 
In the final paper of the morning Daniel Parvaz, of SELFRAG AG, Switzerland, described how a continuous electric pulse fragmentation system has been used by the SAIDEF incinerator in Switzerland since 2016. This system is the first of its kind and has led to many additional developments in the processing of incinerator bottom ash (IBA). Disposal of IBA, the solid residues of municipal waste incineration is a challenge, as the metal content can be up to 12%, classing it as a ‘reactive’ waste, increasing landfill costs. Metal recovery decontaminates and reduces the volume to landfill and generates additional revenue.

The afternoon session was dominated by eight papers on ore sorting. With the depletion of global ore deposits, there has been an increasing industry trend towards mining of lower average grade deposits in order to meet global demand, resulting in increased processing cost, energy usage and water usage. Consequently, there is significant interest in pre-concentration technologies, and bulk ore sorting is one approach that is gaining increasing attention.
As pre-concentration at crushing sizes is dependent on the ore texture and consequently relies on the mineral liberation degree at those sizes, a straightforward methodology to assess mineralogical quantitative data of the ore macro texture has been developed, and was discussed by Rui Sousa, of the National Laboratory of Energy & Geology, and the University of Porto, Portugal.

Daniel Parvaz and Rui Sousa

Nick Cutmore, of CSIRO, Australia, described the development of a large scale magnetic resonance based technology for the rapid quantitative detection of selected copper, iron and arsenic minerals in bulk ore. The technology is suited to measurement on large primary conveyors for enabling “pod” based bulk ore sorting, where barren ore pods, at the 1-10 tonne scale, are diverted from conventional processing. The technology has been demonstrated for a wide range of copper, arsenic and iron minerals and full scale ore sensing and sorting systems are under trial.
All round the world the processing of coal, ores and industrial minerals is combined with the use of a huge quantity of water. This water must be obtained and - after use - recycled, discharged, or it leaves the process with the product or the tailings. This generates quite large environmental challenges. To overcome this, Jens-Michael Bergmann, of conference sponsor TOMRA Sorting, Germany, described how TOMRA developed its own, unique X-ray transmission (XRT) sorting technology back in 2003, using the patented Dual Energy XRT approach. The TOMRA XRT-technology enables materials to be recognized and separated based on their average atomic density in a water-free way. The technology can create an extremely high purity level in the sorted materials irrespectively of size, moisture or contamination. In recent years TOMRA has gained much experience applying this technology in the recycling industry and on various minerals and ores. The sorting performance and the feed capacity have increased considerably; nowadays one modern sorting machine can (depending on grain size) handle up to 750 tph feed capacity and accurately remove the unwanted contaminants.

Jens-Michael Bergmann (2nd left) with Carolina Vargas, Jeff Gurtler and John Williams

James McFarlane, of Mining Plus UK Ltd, also acknowledged that ore sorting technology has proven and well understood downstream benefits on a mining and processing operation. However, the upstream impacts are often less well appreciated and offer opportunities to maximise the economic impact on an operation. James presented a study on work undertaken by Mining Plus at the Hemerdon tungsten/tin deposit, which was exploited briefly by the ill-fated Drakelands Mine, utilising the results of an on-site Steinert XRT ore sorter pilot plant to maximise the economic impact across the mining operation. The approach capitalised on the geo-metallurgical block model developed for the project and results showed improved project economics in all ore sorting scenarios, which were used to develop a revised grade control system with impacts on mining method, fleet size, ROM pad design and layout, mill feed strategy and production forecasting.
The performance of a sensor-based sorting operation is affected by mechanical and physical factors along with the correct identification of the materials. Hence, it is necessary to ensure and monitor that all the accurately identified particles are reported to the correct product stream, either “accept” or “reject”. Ergin Gülcan, of Hacettepe University, Turkey, presented a novel approach for sensor based sorting performance determination and compared the results with previous approaches.
Jacek Kolacz, of Comex Polska, Poland, introduced a new sorting system which has been developed by Comex to achieve efficient separation at low mineral content levels. The system employs high sensitivity X-ray sensors providing multi-energy analysis, thus giving maximal information about processed materials. This allows analysis of the internal structure of the particles and to directly detect intrusions of minerals and metals like copper or gold, while allowing high efficiency analysis, quantification and removal of rock particles representing a waste fraction with very low metal content.

Jacek Kolacz (right) with Erik Larsen
Aaron Young, of the University of Utah, USA, described collaborative work between Brazil, Spain, Poland and USA on the affinity of Dual Energy X-ray Transmission (DE-XRT) sensors on minerals bearing heavy rare earth elements. DE-XRT sensor affinity was evaluated for forty-two xenotime heavy rare earth element (HREE) grab samples from the Madeira/AM deposit. In a paper from the Helmholtz Institute Freiberg for Resource Technology, Germany, Laura Tusa then showed how the potential of hyperspectral short-wave infrared (SWIR) sensors combined with machine-learning (ML) routines have been exploited to improve sorting performance. The approach adopted can be adjusted to optimize sorting for a variety of ore types and thus could increase the attraction of sensor sorting in the minerals industry.
 In the final paper of the day Bertil Pålsson, of Luleå University of Technology, Sweden, described the use of electrically heated screen decks for producing narrow sub-millimetre fractions. He showed how the probalistic screen may be evaluated in the same way as a classifier with a cut point and sharpness of separation for each screen deck, and as a total for combinations of screen decks.
It was a great first day at the conference but nice to get some fresh air and in the late afternoon we met up on the seafront for a rather damp 3 mile walk around the Fal estuary to the inner harbour and drinks at the very crowded but atmospheric 17th century Chain Locker pub.

A wet walk by the Fal estuary
Welcome drinks in the Chain Locker
Friday June 14th

Hydrocyclones, the devices most commonly used for classification in the mining industry, were the subject of the first four papers of the morning.
Even though they are in very common use, hydrocyclones don’t get as much attention as more expensive comminution units, and their technological progress has been incremental, according to Vladimir Jokovic, of the JKMRC, Australia. The SMI-JKMRC has conducted a classification study using semi-inverted hydrocyclones. The results from the study were encouraging with lower water split to underflow (WS) and much coarser cut sizes. A hydrocyclone with lower water split to underflow (WS) will improve classification of fines which would otherwise be sent back to the grinding circuit. The ability of hydrocyclones to cut coarser would potentially expand their application in the areas where fine screens are currently in use. Therefore, the very low WS and coarser cut are of paramount importance for a step change in future industrial operation. Vladimir presented the classification performances of semi-inverted hydrocyclones in his paper.
Mini-hydrocyclones have been applied successfully to micron-size particle separation since their diameter is directly proportional to the cutsize that can be achieved. Their use for the processing of fine (less than 20 µm) ore requires a better understanding of how design and operating parameters affect separation performance. In particular, the length of the mini-hydrocyclone’s conical sections has not received much attention, arguably due to the lack of commercially available units of different heights. Pablo Brito-Parada, of Imperial College, UK, showed how this limitation has been overcome by using 3D printing to manufacture specific designs and assessing conical heights along with feed flowrate and solids concentration in a CCRD experimental design. Good particle classification was achieved, which was not affected by design or operating conditions. A linear effect of conical height and feed flowrate on recovery was observed. Interestingly, conical height exhibited a quadratic effect on concentration ratio, thus making this a critical variable to consider for clarification/thickening applications.  

Pablo Brito-Parada (right) with Christian Ihle

Alireza Eslamian, of ESS Engineering Software Steyr GmbH, Austria, presented work on a novel coupled DEM-SPH method for simulation of complex fluid flows inside hydrocyclones. The simulation of slurry flows that carry multidisperse particles is a vital issue for optimal design of hydrocyclones which are used in different mineral material processing lines, especially in dense media separation technology. Although various CFD-DEM methods for simulations of the two-way coupled interaction of particles with slurry flows inside hydrocyclones have already been proposed, almost all of them suffer from high computational cost problems. 

Alireza Eslamian (right) during the coffee break
Process modelling packages used for purposes such as process design and control of mill circuits generally use empirical and semi-empirical correlations to determine the performance of each of the unit operations in the circuit.  It is well known that each of these correlations is subject to uncertainty. Phil Schwarz, of BGRIMM, Australia,  focused on correlations that are presently used for hydrocyclones. Computational Fluid Dynamics (CFD) modelling holds promise for predicting performance of hydrocyclones, but such modelling is also subject to uncertainties, particularly when the solids concentration is significant; however, though the predicted values may not be accurate, the dependence of predictions on operating conditions should be more reliable. Phil showed how the results of CFD simulations are used to determine the dependence of the primary performance measures on geometry and operating conditions.  Performance measures analysed were cut-size, pressure drop, water split and sharpness of cut, and the dependencies compared with those given by the Nageswararao model and the Flintoff-Plitt model. The results point the way to a methodology in which the best aspects of experiment, CFD simulation and process modelling can be combined.
Phil Schwarz with Yann Foucaud
Gravity separation then dominated the rest of the morning, with Patrick Zhang, of the Florida Industrial and Phosphate Research Institute, USA, showing how recent technological breakthroughs have paved the way for commercializing an innovative gravity separation device, the packed column jig (PCJ). Partick presented three case studies of PCJ use for processing tailings/byproducts from the phosphate industry. The world’s phosphate industry generates over 150 million tons of phosphogypsum (PG) annually. The phosphate companies are under great pressure to find uses for PG quickly and the use of PG as construction material could reduce PG accumulation dramatically. A combination of gravity separation using PCJ with flotation produced an upgraded PG acceptable for many construction uses, with soluble P reduced from 0.89% to 0.04% and whiteness increased from 39 to 87.

Patrick Zhang (centre) in one of the technical sessions
Significant levels of ultrafine particles remain in the feed after desliming in cyclones. These slimes remain a challenge for downstream processing due to the increased viscosity, moisture retention in the product including associated materials handling issues, and entrainment of contaminant with the product. James Carpenter, of the University of Newcastle, Australia, examined the influence of slimes on the recovery of high-grade iron ore fines across a size range of 0 – 0.3 mm using the REFLUX™ Classifier. Experiments were performed using closely spaced inclined plates (3 mm apart and 1000 mm long) over a range of solids throughputs of 3.5 – 28 t/(m2 h). Lower feed solids concentrations led to higher recoveries due to the reduction in the viscosity arising from the slimes. At the higher volumetric flowrates used to increase the solids throughput, the very high shear rates generated in the channels further reduced the viscous effects of the slimes. The results are supported by rheological data, based on the ultrafine solids collected from the overflow stream.
After the coffee break the inventor of the REFLUX™ Classifier, Kevin Galvin, of University of Newcastle, Australia, showed how a Reflux Classifier was used to recover zircon from an ultrafine, low grade mineral sands feed below 300 microns, deslimed to varying degrees below 38 microns. This system consists of a fluidized bed with a set of inclined channels above. The work builds upon previous studies concerned with mineral sands, revealing the benefits of using an inclined channel spacing of 3 mm. 

Kevin Galvin (right) with Stuart Saich
Karlo Leandro Baladad, of the University of the Philippines, presented a study investigating the effect of electrostatic interactions in the separation of magnetite and silica in aqueous media using enhanced gravity concentration. Magnetite and silica suspensions at different coagulation conditions were prepared and subjected to enhanced gravity concentration using a Falcon L40 concentrator. Increased recovery of both magnetite and silica was observed at pH 3 where attractive forces are strongest both for one-component and two-component interactions. However, the increased recovery of both particles caused a decrease in separation efficiency at this condition. At pH 11, where repulsive forces are dominant for both one-component and two-component interactions, recovery of both minerals decreased. The highest separation efficiency of 64.1% was at pH 9. At this condition, two-component interactions were repulsive which led to the increased removal of silica. 

Karlo Baladad (right) with Jane Mulenshi, Amanda Wills and Jon Wills
Scheelite is one of the main minerals for the production of tungsten. It is usually encountered in skarn deposits where it is commonly associated with other calcium minerals as fluorite, apatite and calcium silicates. Worldwide scheelite is beneficiated into chemical grades by direct flotation, but the separation efficiency remains limited due to the similar flotation behaviours of scheelite and gangue minerals with fatty acid. The only solutions used to overcome this issue involve high energy consumption or ecotoxic reagents. Yann Foucaud, of Université de Lorraine, France, described a novel method based on the use of a centrifugal Falcon concentrator to perform an efficient elimination of gangue minerals and fine particles as well as an acceptable scheelite recovery, enabling a decrease in flotation reagent consumption. 
Carl Bergmann, of Mintek, South Africa, showed the value of incorporating mineralogical data into modelling the concentration of chromite ores using gravity spirals. The approach used is based on mapping the deportment of many thousands of individual particles across rougher, cleaner and scavenger spirals at varying product yields. AutoSEM characterisation, using a Mineral Liberation Analyser (MLA), was used to reconcile mineral deportment to measured size and assay data.  Results from 4 different chromite ores from the Bushveld Complex were compared using partition surface models to simulate spiral performance. The benefit of this approach is that the effect of varying head grade, mineral liberation and particle size distribution on circuit performance can be evaluated.
A novel system involving a gas-solid fluidized bed subjected to vibration was described by Deepak Kumar, of the University of Newcastle, Australia. A mesh with an aperture of 1 mm, incorporating a large central hole referred to as a Sink-Hole, was located just below the surface of a fluidized granular media. The fluidized granular media, nominally 0.3 mm sand particles, expanded through the large Sink Hole, spilling onto the top of the mesh, and then sifted back into the lower fluidized zone. The effective density of the medium at the mouth of the Sink Hole was determined by examining the probability of a large tracer particle of a given density floating as opposed to sinking. The effective density was deemed to be the condition denoting a 50 % probability of the tracer particle passing through. Interestingly, this density condition greatly exceeded the density of the medium and invariably the density of the granular media itself. Moreover, the effective density was largely independent of the size of the tracer particles covering the range 2.8 to 8.0 mm, a sign of genuine density-based separation. 
In the final paper of the morning Ozan Kökkiliç, of McGill University, Canada, highlighted how, due to water shortages, developing dry separation methods to replace the commonly used water-based separation has become crucial. One of the candidates for dry gravity processing are gas-solid fluidized beds. The behaviour of bed and solid motion in a fluidized bed have been investigated over the past few decades using various visual and numerical methods, but there are not enough studies focused on the separation behaviour of the fine particles. Ozan detailed the investigation of particle motion through a fluidized bed using the positron emission particle tracking (PEPT) technique. This single particle tracking method is a powerful way to provide knowledge about the separation mechanisms through direct visualisation of the particle trajectory, determined from records of the particle position over time. In this study, by tracking an activated quartz particle, the movements of different sized beds were characterized and then by tracking an activated hematite particle the separation of dense particles in a fluidised bed was observed for different size fractions.

The afternoon session was dominated by case studies.
The Nechalacho rare-earth element (REE) deposit is located in the Northwest Territories, Canada. The main rare-earth minerals (REM) in the deposit are zircon, allanite, bastnäsite, synchysite, monazite, columbite (Fe) and fergusonite; with quartz, feldspars and iron oxides accounting for most of the gangue. Recent studies have demonstrated the potential for early gangue rejection, of a relatively coarse feed, using a spiral concentrator, prior to fine particle gravity separation using a Multi Gravity Separator (MGS) to produce a concentrate which comprises primarily REM and iron oxides. These studies were, however, limited in scope, with each technique tested separately and only demonstrated a proof of concept. Ozan Kökkiliç described expansion of this work by investigating a complete flowsheet incorporating early gangue rejection at coarse particle sizes, followed by fine grinding of the pre-concentrate and fine particle gravity separation. The final gravity concentrate is then further upgraded using magnetic separation to separate the valuable REM from the iron oxide gangue.
Currently, about 75% of the EU's chromium is being imported. In the value chain of stainless steel production, significant amounts of chromium are lost in ferrochromium (FeCr) slags and stainless steel (SS) slags. In a slag chromium is mostly present in entrapped metallic particles (Fe-Cr alloys) and/or stable spinels.  To unlock the potential of these low-grade resources, a new approach to metal recovery must be deployed. Fero Kukurugya, of VITO - Flemish Institute for Technological Research, Belgium, described European H2020 project CHROMIC, which aims to develop a process for recovering chromium from SS and FeCr slags based on the smart integration of physical separation and subsequent pyro- or hydrometallurgical treatment. Results of physical separation show significant Cr up-concentration by using magnetic separation techniques and density separation (wet shaking table), where Cr content can be increased almost by a factor of 4.   
Nickel is an important metal with a total global consumption of 2 million tons per year. It is sourced from sulphide and laterite ores, but currently laterites are becoming more attractive for nickel production due to the depletion of high grade nickel sulfide ores. Laterites are generally processed by hydro or pyro-metallurgy and therefore, pre-concentration of nickel before such processes is important. About 60% of land-based nickel reserves are present in laterites with nickel and cobalt grades of 0.8 to 3% and 0.05 to 0.15%, respectively.
Saeed Farrokhpay, of Université de Lorraine, France, discussed the effect of different physical methods on the pre-concentration of nickel in laterite ores. The ores were sourced from different geological zones (saprolite, limonite and intermediate zone) of a laterite mine in South East Asia. Nickel was upgraded using physical methods such as magnetic separation, gravity separation, and sizing. The effect of ore mineralogy on choosing the best strategy to upgrade nickel was highlighted, as was upgrading nickel using a combination of these methods. The findings of this project will help to unlock a substantial volume of nickel with significant value from laterite ores.
An alternative process for laterite treatment, combining pyro-metallurgical pre-treatment followed by mechanical processing to decrease the feed for a subsequent rotary kiln electric furnace (RKEF) process, was described by Klaus Hahn of RWTH Aachen University, Germany. The pre-treatment process consisted of a non-selective segregation of contained metal phases, which changes metal properties and transforms nickel, cobalt and iron to metal alloys with grades around 80% for Ni and Co. Due to its fine grain sizes below 20µm, subsequent processing involving fine grinding and magnetic separation was investigated.
Repositories of historical tailings pose environmental risks but could also become metals and minerals resources, as relatively high mineral and metal contents are due to less efficient extraction methods in the past and/or relatively low metal prices at the time. Jane Mulenshi, of Luleå University of Technology, Sweden, described how the Smaltjärnen tailings repository in Yxsjöberg, Sweden was sampled and the main layers of the longest drill core characterised. Feasible physical separation methods selected were Knelson concentrator, LIMS and HIMS. In the Knelson concentrator, 56 wt.% tungsten was recovered in the 23 wt.% of concentrate produced. In magnetic separation, 82 wt.% tungsten and 91 wt.% copper was recovered in the HIMS magnetic fraction, while sulphur was only 1 wt.% in the HIMS non-magnetic fraction. This study is fundamental in the development of effective methods for separating minerals and extracting metals of interest from these historical tailings so that an inert and environmentally safe residue is left behind.
Niobium is an important element that has been applied in many cutting-edge applications. Currently, its beneficiation is through froth flotation, although the fines are lost as slimes, comprising up to 15 % of the total niobium content. Recent work, described by Mark Lepage, of McGill University, Canada, has shown that gravity and magnetic separation are effective for processing niobium-bearing minerals. However, studies using these techniques in the ultrafine range (below 10 µm) are still limited. The work investigated the feasibility of using enhanced-gravity and magnetic separation techniques to extract niobium-bearing minerals (columbite and pyrochlore) from industrial slimes containing gangue such as dolomite. The results from magnetic separation were then related to the magnetic properties of each individual mineral.
A recent trend in wet processing of incinerator bottom ash is the development of a fine ash treatment module for size fractions - 2 mm. Options for the extraction of the fine size fractions in both wet or conventional dry process plants were presented by Jonas Boehnke, of Sepro Mineral Systems Corp, Canada, and the economical environmental and health and safety aspects of extracting and processing the fines were discussed. Ash samples are exceptionally heterogenous in their composition and this particularly applies for precious metals. Particle shapes also play a significant role in the selection of suitable recycling technology. Comprehensive testwork at laboratory scale has identified a compatible gravimetric separation route and it is explained why only a combination of multiple devices satisfies the diverse requirements to produce a marketable heavy non-ferrous metal product. Experience from laboratory and prototype operations has shaped the process and led to the successful launch of a commercial scale plant at Brantner Oesterreich GmbH‘s operation in Austria.
With the ever increasing need to conserve water, efficient dewatering is a priority. As discussed by Christian Ihle, of Universidad de Chile, this is particularly challenging for dewatering slurries with a large amount of fines. Chilean mining highlights the global trend of decreasing ore grades, with the existence of operations which are located in desert areas, thus having limited access to water close to operations. Christian described numerical simulations of the concurrent impact of Boycott effect and differential heating at the downward facing wall of a lamellar settler operating both at batch and continuous mode. Both types of operation reveal a general enhancement of performance with the amount of heating in the particle accumulation at the bottom for a specific particle size range. However, a trade-off between enhanced settling (and thus system capacity) and re-suspension near the top is observed. Opportunities for scaling up to industrial infrastructure were discussed.
The trend in tailings dewatering has always moved towards a drier product, recovering more water for economic, environmental and social pressure, which are especially important in recent times with tailings disasters being brought to the public eye. This has been achieved through the adoption or application of technology, starting with the implementation of thickeners and the subsequent optimisation which lead to the development of Paste Thickening.
Ten years ago this was very much the "buzz" word of the tailings industry. It seemed that every site, both greenfield and brown, was considering Paste Thickening of their tailings, and vendor pictures of thick toothpaste like tailings removed from the bottom of a pilot plant were a common at conferences. Is this still the case today? Not according to Paul Ainsworth, of Paterson & Cooke Ltd, UK, who said that many mines while operating paste plant above the typical underflows achievable by other thickening technologies do not produce the envisaged thick, stacking tailings that was so prevalent in their advertisements. This is not to say all paste installations failed, on the contrary some are very successful, but not all.
Ten years on while current investigations still consider paste it appears to have taken more of a back seat to the next stage of dewatering, filtration and the tailings storage that comes with it, Dry Stack.  As filtration and dry stack tailings is becoming the new “buzz” phrase of the tailings industry and is under consideration for many projects Paul asked how can it learn from Paste Thickening. He highlighted some of the areas that need to be improved, expanded and better integrated so that dry stack tailings is more successful, avoids the pitfalls and prevent projects from succumbing to the failings that some Paste Thickening operations experienced.

Paul Ainsworth (right) with Kathryn Hadler and Tom Naylor
Paul's topical paper ended the many fine presentations over the two days, and after Amanda thanked everyone, particularly the sponsors, for their contributions, I gave an introductory talk, supplemented by a traditional Cornish cream tea, on the geology and mining of Cornwall, a prelude to our short visit to the site of the 19th century Wheal Peevor workings.

By all accounts this has been a fine conference with some very high quality work presented. Once again many thanks to our sponsors, and to the chairmen who kept the conference running on time despite the many short presentations. I would also like to thank the staff of the National Maritime Museum, particularly the tireless Dayna Pope, for making our debut at this magnificent facility so enjoyable. I would very much appreciate feedback from all who attended.

A full set of papers is available from MEI as well as a full set of conference photos.

Physical Separation '21 will be held in Falmouth again in June 2021. Full details will soon be available on MEI Online. Hope to see you there!

Twitter @barrywills

Friday, 21 June 2019

The great outdoors once more at Falmouth's Chain Locker

Falmouth's Chain Locker has been the centre of much mining chatter over the past week or so. Last week delegates from Computational Modelling '19 and Physical Separation '19, who had braved the elements on a 3 mile coastal walk, sought sanctuary in the warm indoors, and this week delegates from Cornish Lithium's Investment in Mining in Cornwall conference, also held at the nearby National Maritime Museum, popped in at regular intervals.
Last night we were back at the Chain Locker for the June Mining Sundowner and thankfully, as we had a large turnout of around 35, we were able to enjoy a little evening sunshine.

Numbers were boosted by a 45 year reunion of some of the Camborne School of Mines class of 1974, the year that I started teaching at CSM.

Some of the CSM class of 1974 with their wives

It was good to see Richard Williams, the President and CEO of Canadian company Strongbow Exploration, responsible for bringing the South Crofty tin mine back to life in the next few years. The license to operate is in place and dewatering of the old workings will be the first stage of operations after completion of the treatment plant which will remove heavy metals before discharge into the local Red River.
Richard is photographed below with Tony Batchelor, chairman of local company GeoScience Ltd, and consultant to the United Downs Deep Geothermal Power Project. Drilling of the two wells is almost complete and the rig will probably be demobilised in July.

Tony and Richard
The next sundowner will be at the Chain Locker again on Thursday 18th July at the usual time of 1730. Drop by if you are in the area.
Twitter @barrywills

Tuesday, 18 June 2019

Report on Computational Modelling '19

Computational Modelling '19 was held at the National Maritime Museum, Falmouth, UK, from June 11-12. The 7th in the series, which began in Cape Town in 2005, this was by far the smallest, with an attendance of 26 delegates representing 12 countries.

This begs the question as to whether this conference series has ran its course. Computational modelling techniques, such as DEM and CFD are now accepted tools in mineral processing, and their use is a feature of all current MEI Conferences, so is there a need for a small specialised conference dealing with developments and uses of these techniques? The argument for is that the conferences do have a multi-disciplinary flavour, the papers this year covering liberation and comminution, flotation, hydrometallurgy, pyrometallurgy, dewatering and materials handling. It is always useful to bring scientists from disparate groups together, as it promotes lateral thinking, but I would like the views of those who attended this year and in previous years.

The following is my report on the papers presented. More detail on people and actvities are in the posting of 12th June.
Tuesday June 11th

Paul Cleary
Particle based modelling is well suited to predicting complex multiphase flows within mineral extraction processes. Applications include comminution with particle breakage and flow in crushers and particle breakage and slurry transport within mills and separation, both wet and dry, by screens. In such models the coarser particulate phases are represented by DEM (Discrete Element Method) and the finer slurry or powder phases by SPH (Smoothed Particle Hydrodynamics). Emerging opportunities also exist in flotation where discrete phases for bubbles and particles can be coupled to continuous free surface liquid phases. These models have become quite sophisticated and continue to increase in the range of scales modelled and the fidelity of the physics represented as computer power continues to rise and computational modelling codes continue to develop. A fine keynote lecture from Paul Cleary, of CSIRO Data61, Australia, showcased a range of leading edge application examples of this modelling and discussed the increasing role of hybrid and multiscale methods.

Process simulators have become increasingly useful for design, optimization and control in mineral processing, evolving from simple models of isolated unit operations to complex integrated simulation environments. There has been an increase in the number of mineral processing simulation platforms available and publications on their application; however, a recent overview of the topic is missing in the literature.

Juliana Segura-Salazar

Juliana Segura-Salazar, of Imperial College, UK,  presented a critical review of the state-of-the-art of process simulators for the minerals industry, discussing and contrasting their capabilities and limitations, as well as identifying some of the challenges that need to be addressed. She discussed recent developments towards the application of these simulators in a more systemic context as a support tool for decision making within the minerals sector. This is particularly relevant if process simulation is to play a key role in overcoming the multiple challenges faced by mineral processing operations in the context of sustainability.

Luis Cisternas
As highlighted by Luis Cisternas, of Universidad de Antofagasta, Chile, mineral processing usually utilizes multi-unit separations because complete separation is seldom achieved in one unit. The analysis and design of these circuits have been an active area of research in the exploration for improvements in mineral processing. Linear circuit analysis (LCA) has been proposed as a simple tool for the analysis of mineral processing circuits. Clearly, LCA is a tool with several advantages, but it does have its limitations and disadvantages. Luis analysed some limitations and disadvantages of LCA. The results show that LCA must be used carefully because its application can introduce errors and incomplete analysis.

Component wear is a key consideration for the minerals industry given the abrasive nature of particle-laden flow such as mineral slurries. Studying wear through experimentation is time-consuming and expensive, thus, an accurate simulator to understand and predict wear is highly desirable. This allows for optimisation of design and operating parameters to improve performance, as well as enhance the service life of these parts. Lily Ip, of Imperial College, UK, described a finite element based CFD wear simulator, which includes the ability to model coupled solid-fluid motion of slurries through representative Lagrangian particles and perform dynamic remeshing of geometry in response to wear and moving components. The capabilities were illustrated through examples ranging from simple geometries to that of complex moving geometries such as centrifugal pumps.

Lily Ip with Stefan Kirsch
Taking us to the lunch break, Stefan Kirsch, of Robert Bosch Packaging Technology B.V., The Netherlands and Technical University Dresden, Germany, discussed how vertical discharge and filling processes of granular media have been successfully described with the aid of DEM in the past. However, a major challenge is often the identification of accurate interaction parameters (model calibration) such as friction and restitution coefficients. In-situ bulk calibration has been shown to be an efficient approach to generate high fidelity models. However, Stefan showed that in the case of vertical transfer and especially when working with low particle counts, randomness intrinsic to the process, can be detrimental to efficient and reliable implementation. A second constraint is shortcomings in the physical model of DEM and differences between lab scale and industrial equipment. These factors can lead to systematic errors in the calibration process and may restrict model transferability. Stefan described a study where several example media were assessed to deduce suitable calibration and quantitative validation strategies for DEM models.

Grinding and liberation were the topics discussed in the five papers in the afternoon session.

Feed size distribution is one of the important parameters that affect ball milling and can be tailored to optimally produce a desired mill product. To that end, Ngonidzashe Chimwani, of the University of South Africa, described how batch tests were used to investigate the effect of feed tailoring in ball milling using a South African gold ore. Narrow-size feeds of the ore were prepared and milled with sets of single-size balls. From the experimental data obtained, milling parameters of the gold ore were determined, validated and then used to simulate the breakage patterns of different feed size distributions for further analysis, with the purpose of finding the feed size distribution that produces the highest amount of the desired size range for gold leaching.

Ngonidzashe Chimwani with Bertil Palsson and Jarrod Hart
Discrete element methods (DEM) have provided the ability to resolve the complex phenomena experienced by ore within comminution devices such as tumbling mills. The new developments in DEM techniques and the corresponding increase in computational power has made it more feasible to study the movement of individual ore particles as they traverse a tumbling mill. A range of information can be extracted on individual particle impact histories, such as kinetic energy at the time of collision, velocities of individual particles, per-particle stress tensors, impulse and collision energy. DEM codes have been modified to provide the required information that can be analysed in an associated software to investigate the impact of varied operational parameters on the resultant granular dynamics, and we were looking forward to Olumide Ogunmodimu, of JKMRC, Australia, exploring the reaction of individual ore particles to the breakage environment within a tumbling mill using DEM techniques, studying the stressing conditions that would lead to either impact or abrasive breakage. Unfortunately, however, entirely due to no fault of his own, Olumide was unable to attend the conference but his paper is available on the Proceedings USB.

Simon Larsson
Modelling of wet grinding in stirred media mills requires the simultaneous modelling of grinding media, a moving internal stirrer, and the pulp fluid. Simon Larsson of Luleå University of Technology, Sweden, showed how wet grinding in a stirred media mill was simulated using coupled incompressible computational fluid dynamics (ICFD) and discrete element method (DEM) and finite element method (FEM) simulations. The grinding media was modelled with the DEM, the pulp fluid flow using the ICFD and the mill structure using the FEM. The combined model was used to predict the wear rate in the system. The model can be used to study process parameters and their effect on the wear map distribution and power consumption. The two-way fully coupled ICFD-DEM-FEM preserves the robustness and efficiency, and it allows the use of large time steps for the fluid with very low computation times.

The main roles of liners are to protect the mill shell and promote effective ball motion for grinding. For this reason the liner profile is carefully selected to ensure that the productivity is maximized and due liner replacement is made when this objective is no longer met. These issues have been extensively studied on shell liners as mill relining is a significant cost component of ball milling. To date, not much has been written about end-liners and the kind of forces they are subjected to. In his second paper,   Ngonidzashe Chimwani described a DEM simulation scheme which was conducted to look at how ball size distribution, mill filling, end-liner configuration and shape affect the distribution of forces acting on the few liners that were used as a case study to understand end-liner wear and damage.
Mapilane Madiba
In mineral processing plants there is a challenge in turnaround time for issuing results timely to reduce delays in the decision-making process. Mineral liberation is considered as one of the efficiency drivers for downstream processes such as flotation. Thus, delayed decision could be costly. Mapilane Madiba of University of South Africa, described the development of a procedure to quantify and minimise the time analysis for mineral liberation.

After a good first day of presentations, a number of hardy souls braved the cold and windy conditions for a 3 mile walk around the Pendennis Headland and to awaiting drinks in one of Falmouth's oldest pubs, the Chain Locker.

In the 16th century Pendennis Castle moat
Welcome ale in the Chain Locker
Wednesday June 12th

Mapilane Madiba of University of South Africa was back on the podium first thing to further review correction methods to solve limited representativeness in mineralogical analysis of measured liberation data. Although progress is being achieved, there are still challenges facing correction methods. Therefore, the advantages and disadvantages of specific issues, such as point spread function, excitation energies and the monochromatic assumption of X- Ray source, facing the correction methods were discussed.

Flotation then dominated the morning session. Luis Cisternas, of Universidad de Antofagasta, Chile discussed how regrinding of rougher concentrate, scavenger concentrate, and/or cleaner tailing is common practice to liberate valuable mineral attached to gangue particles. However, the methodologies proposed for the design of flotation circuit based on optimization usually do not consider regrinding. Luis analysed the effect of regrinding in the design of flotation circuit structures.
Guichao Wang
Guichao Wang, of Southern University of Science & Technology, China, showed how direct numerical simulations of a particle-bubble collision system composed of monosized spherical solid particles and air bubbles in a quiescent liquid and homogeneous isotropic turbulence have been performed. Particle-bubble collisions in a quiescent liquid were first simulated and compared to the existing experimental work of particle-bubble collisions. A DNS model for studying the effect of turbulence on the collisions between particles and bubbles was then developed. Turbulence was found to first increase particle-bubble collisions to a certain extent, and, with further increase turbulence intensity, the particle-bubble collision rate was reduced.

Phil Schwarz described how the flow field, gas dispersion and solids concentration in a flotation cell fitted with an Outotec flotation mechanism were studied at CSIRO Minerals Resources, Australia, using both experimental and multi-phase CFD modelling. He showed that the complex multi-phase CFD model can be used to predict the major characteristics determining flotation kinetics: namely turbulence, bubble size and distribution, and solids distribution. The CFD flotation model can therefore be used for investigations on the design and operation of the cell, for example, in parametric studies on the effect of stirring speeds and aeration.

Phil Schwarz (centre) with Guichao Wang and Russia's Dmitrii Maiorov
at the Chain Locker

Asmaa Hadane
Flotation is an important separation process for beneficiation of sedimentary phosphate rocks. In order to evaluate hydrodynamic efficiency, Asmaa Hadane, Mohammed V University in Rabat and Mohammed 6th Polytechnic University, Morocco, showed how a CFD multiphase model of water-phosphate flow was used to investigate the main hydrodynamic criteria namely: the agitator power consumption and the solid distribution in the flotation cell depending on the impeller rotational speed and the phosphate volume fraction.  A second CFD study considered the injection of air bubbles. She described work on the air dispersion and the solid distribution in the complete cell volume, in order to analyse the phosphate-air contacts within the flotation tank, which represent the key elements to establish convenient conditions to maximize the flotation performance.

Several ore deposits are polymetallic with two, three or more base metals. These base metals include copper, lead, zinc, cobalt, nickel, molybdenum, and pyrite among others. Usually, polymetallic ore is separated by sequential flotation circuits for each base metal. In his 3rd paper of the conference, Luis Cisternas argued that the methodologies proposed in the literature for the design of flotation circuits consider only one base metal and there is no literature for the design of integrated flotation circuit for polymetallic ores. Luis proposed a procedure for the design of polymetallic integrated flotation circuits, the methodology considering a superstructure to represent the set of feasible flotation circuits, disjunctive expressions for the selection of operation conditions of flotation stages, and a mixed integer nonlinear programming model. The integrated flotation designs were compared with sequential flotation circuits, and advantages and disadvantages identified. 

A better understanding of controlling factors in mineral flotation will undoubtedly be possible using advanced CFD simulations over entire full-scale industrial cells. Such macro-scale simulations require sub-models to quantitatively describe the rates of bubble-particle attachment and detachment: the huge number of particles and bubbles in an industrial cell mean that macro-scale models cannot resolve the details of bubble-particle interaction. Micro-scale models and experimental investigations can be used to improve sub-model formulas for attachment and detachment rates. In his second paper, Phil Schwarz, of CSIRO, showed how micro-scale models of bubble-particle interaction are extended to account for near-field hydrodynamic effects, ie effects that have influence on particle motion near the bubble interface. These near-field effects include the mobility of the bubble interface (which influences the shear rate near the interface); the so-called lubrication force (which slows the particle approach); lift force; and modification to the drag force on the particle. The micro-scale CFD simulations show that the lubrication force is the most significant of these additional affects, and that the degree of interface mobility has an important influence on the magnitude of the other additional forces. Recommendations for sub-models for use in macro-scale CFD models were discussed.

Yann Foucaud
Continuing with the flotation theme after lunch, Yann Foucaud, of Université de Lorraine, France, stressed that understanding the adsorption mechanisms of reagents is a key step to enhance flotation. New depressants and collectors, which are more efficient, selective, and environmental friendly have been developed, but few experimental methods can currently identify the surface molecular mechanisms with accuracy and confidence. Yann showed that atomistic simulations aid understanding of the mechanisms involved in reagent adsorption.
Derek Machalek

After Yann's presentation, there was a complete change of direction. Derek Machalek, of the University of Utah, USA, showed that rotary kilns require large fans to blow air through them to support processing of minerals and if fan controls can be modified to respond to rapid changes in electric demand, they can become valuable grid assets. Due to their considerable thermal inertia, kilns and the associated fans are traditionally operated continuously in a steady manner to avoid process disruption. However, advanced model predictive control (MPC) can allow for the rigid process to be operated flexibly. Ultimately the flexible process can respond to grid demand requirements by ramping the kiln fan.

In a further paper Derek showed how the evolution of the electrical grid requires flexibility in electricity consumption. Given the tremendous amount of electricity consumed by mineral processing, these facilities could become a grid asset if they can leverage sources of flexibility. While facilities generally try to maximize ore throughput, de-watering represents one source of flexibility due to the holdup capacity of the water table itself and storage tanks to which the water is pumped. A second source of flexibility is intermediate product transportation with storage capabilities at each end. By developing predictive automation algorithms, these holdup capacities can be effectively leveraged. This makes the facility able to respond to grid signals, which can save on demand charges, while also becoming an asset to the grid.

Alireza Eslamian
Alireza Eslamian, of ESS Engineering Software Steyr GmbH, Austria, presented a novel coupled DEM-SPH method that simulates agglomeration and spheronization of powder mixtures to produce pellets. Optimal design of iron ore pelletizers, which allows generation of pellets of uniform size and form, is a common challenge and demands a deep insight into the physics of powder mixture accumulation and agglomeration. Iron ore pellets are spheres ranging between 6 and 16 mm, used as feed for blast furnaces, and usually contain 64-72% Fe, while the residuals consist of limestone, dolomite, and bentonite as binder.  Alireza said that no method for simulating the formation of pellets out of raw material mixtures in pelletizers has yet been proposed. He showed how a coupled DEM-SPH method has been developed by ESS. SPH is used to simulate the raw material mixture as a continuum media, while DEM simulates the formation of pellets in connection with raw material mixture.

It is standard practice to never stop the drive on a thickener, even during a shutdown, unless the bed in the thickener is drawn down to such an extent that the soft bed remaining will not pose a problem during restart. To avoid this, thickeners are typically equipped with an uninterrupted power supply to ensure non-stop raking. In the final paper of the conference Justin Jacobs, of Paterson & Cooke Ltd, USA, described how a client was interested in being able to stop and restart the thickener rake as needed, without drawing down the thickener bed. For this case, hydraulic transport and deposition of the thickener underflow required a specific rheology, eliminating the drawing down option. Justin showed how a complete rheology characterisation, using CFD established the drive size required to make a thickener restart under load possible. The CFD model was validated using an existing thickener rake with a known geometry, fluid rheology, and motor torque measurements.

Justin Jacobs (right) relaxing with delegates at the Chain Locker

Despite the low numbers this has been a productive conference and I will, of course, advise if we intend to continue with this series. All the papers presented are available on USB from MEI.

Twitter @barrywills