Monday, 10 December 2018

Is CO2 the most maligned gas in history?

The mining industry is one of the world's greatest emitters of carbon dioxide, and legislation to reduce emissions has a severe impact not only on existing operations but on the potential start up of new ventures. And all at a time when the demand for metals is growing, particularly with the electric vehicle revolution.
It is not surprising, therefore, that talk at major mineral processing conferences often drifts towards climate change and its causes. Mineral processors are not climate change scientists but they are entitled to their views. As is the veteran broadcaster Sir David Attenborough, who last week was the keynote speaker at the opening ceremony of the United Nations-sponsored climate talks in Katowice, Poland, the most critical meeting on climate change since the 2015 Paris agreement.
Sir David painted a truly apocalyptic vision of the future with the collapse of civilisations and the extinction of "much of the natural world".  "Right now," he said "we are facing a man-made disaster of global scale. Our greatest threat in thousands of years. Climate change". He urged everyone to change their habits, in particular avoiding air travel- a little hypocritical maybe, as he spends half his life in the air travelling to remote locations for his excellent natural history series.
Sir David's comments were the lead story on the BBC national news that evening. Not surprising as his views reflect the BBC's hard-line policy, an article in The Times (BBC freezes out climate change sceptics, September 8th 2018) reporting that science staff have been told that they need no longer invite those who deny anthropogenic global warming on its programmes, suggesting that allowing them to speak was "like letting someone deny last week's football scores". It is very noticeable that the BBC's references to climate change are almost always preceded by 'man-made', but what really angers me is the repeated assertion that "all scientists agree that climate change is due to the activities of man".
This is just not true. When I discuss the topic at conferences there are, of course, many who back anthropogenic warming, but there are many who are sceptics who question some, or much, of the science. Many, however, are outright deniers of man-made climate change and feel that it is more likely that the temperature rise is due to natural cycles. Geologists in particular tend to support this, claiming that they have seen it all before, although not literally, and some astrophysicists argue that the temperature rise is due to solar activity.
There was much intense debate on the blog a few years ago, and a very eminent geologist, Prof. Ian Plimer, Emeritus Professor of the University of Melbourne, presented some very convincing arguments against anthropogenic global warming, which led to some interesting comments, and a long response against his arguments by the University of Exeter's Dr. Stephan Harrison. Many geologists that I speak to support Plimer's views.
So where do I stand on this extremely complex topic? I have spent almost 40% of my life as an editor of a peer-reviewed journal and have developed a nose for sniffing out bad science and I have to admit that I have been very sceptical about some of the science advocating anthropogenic global warming. I am a great believer in the motto of the Royal Society, nullius in verba (take nobody's word for it) and believe that all scientists should question the work of others even though they may not be directly involved in that field.
If pushed I would take the view that climate change is mainly a natural phenomenon, to which we humans contribute but by how much nobody knows. The suggestion that a small increase in concentration of a trace gas in the atmosphere can have such a profound effect on climate, and on the acidification of the oceans, leading to the disappearance of coral reefs, is not easy for me to accept. The media regularly report that CO2 levels have increased by around 40% since pre-industrial times, and the temperature has risen by 0.8 C. A question that I have asked before, but have not really got a satisfactory answer to, is 'how do we know this'? How can we compare temperatures and CO2 levels now to those of pre-industrial times when there was then no real interest in these levels?
An increase in 40% seems a lot, but in absolute terms this is an increase in concentration from just under 0.03% to the present level of just over 0.04%. Can this small increase have such a profound effect? Many scientists are convinced that it can, as the Danish electrochemist Arrhenius showed in the early 20th century that without the greenhouse gases H2O, CO2, CH4, O3 and N2O, the surface of the earth would be about -20C , like the moon. In this complex mix CO2 is the gas which has the second largest impact on reducing the amount of long wavelength radiation emitted by the earth, warmed by the Sun, back to space. The most potent green-house gas is water vapour and rising temperatures increase the amount of this gas in the atmosphere. Other major green-house gases are hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride. These are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. They are typically emitted in smaller quantities than CO2, but because they are powerful greenhouse gases, they are sometimes referred to as High Global Warming Potential gases.
But suppose Plimer is right, and temperature rise is part of a natural cycle. The oceans contain trillions of tonnes of CO2 and a rise in temperature must, according to Henry's Law, release CO2 into the atmosphere, explaining the correlation between temperature and CO2 levels, the argument behind the climate change debate. The CO2 level would then be expected to lag behind the temperature rise, and there have been many articles in reputable journals over the past decade saying just this, although there have not been many reports of this in the media. So, does temperature drive CO2 levels, and not the other way round? Or maybe it is a combination of both?
What I find really hard to swallow, however, is that an increase in CO2 concentration from 0.03% to 0.04% can acidify the oceans to such an extent that Sir David Attenborough predicted in his superb series, The Blue Planet, that the coral reefs would disappear by the end of the century. The programme even had a ludicrous demonstration of this, showing that when acid was poured onto a piece of coral it bubbled and fizzed- of course it would.
Carbonic acid is one of the weakest of acids, but even so, an increase in ocean temperature must release CO2, so if indeed the rate of attack on the coral reefs is increasing, what is causing it? Well every hydrometallurgist knows that the rate of leaching increases not only with acid concentration, but also with temperature.
So back to my eponymous question. Is CO2 the most maligned gas in history? It is present in trace amounts in the atmosphere, it is not a pollutant and is essential for plant growth and the production of oxygen.
Is the emphasis on CO2 taking the pressure off the real killer in the atmosphere? Air pollution is one of the world's major causes of death, and one of the main culprits is NO2 in internal combustion engine emissions. Electric vehicles will play a major role in the reduction of such emissions, and the mining industry will be vital in producing the materials for these vehicles. Let's hope that it is not hamstrung by the need to spend billions on controlling its own CO2 emissions. Mining is the primary industry, which feeds all other industries, and without a thriving mining industry civilisations would indeed collapse. So if draconian cuts in emissions are imposed, maybe it could be considered as a special case? Very unlikely I would suspect.
I am expecting a bit of flak by publishing this post, but it is basically to solicit your views on this controversial subject. Do you believe that climate change is solely down to human activity, is it a purely natural phenomenon, or do you feel that it is probably a combination of both?
Twitter @barrywills

Thursday, 6 December 2018

Hi-Tech Metals '18: conference diary

Hi-Tech Metals '18, the first in the planned series, got off to a very quiet start at Cape Town's Vineyard Hotel, with 31 delegates from 10 countries, 15 of the delegates having attended Process Mineralogy '18 earlier in the week. 
Vineyard Hotel, Cape Town
Processing of the Hi-Tech Metals is an area of crucial importance to society as a whole, and mineral processing will play a vital role, so we expect this conference series to evolve and grow in future years.
Thursday November 22nd
In recent years a number of expressions have been applied to describe a group of commodities that are considered essential ingredients for technology development and economic prosperity. In some publications, these are referred to as “high technology metals”, in others they are named “strategic” or even “critical raw materials“. To add confusion the actual composition of this this large and disjointed group of commodities is subject to ongoing change – depending largely on perspective, technology and material development, geostrategic positioning and market status.
Jens Gutzmer
In his opening keynote lecture, Jens Gutzmer, of Helmholtz Institute Freiberg for Resource Technology, Germany, attending his first MEI Conference, set the scene for the conference by addressing the reasons for the apparent confusion – and the inherent weakness of processes to identify “critical raw materials”. Furthermore, results of current efforts to quantify global resource potentials especially of by-product metals – many of which are regarded as “critical” - were discussed, as well as considering the role of recycling vs. primary production in the near- to mid-term supply of high technology metals.
 There is no doubt that recycling will be one of the great future challenges of minerals processing. With increasing trends in the production and consumption of technology devices and materials, the demand for metals including lithium, cobalt and rare earth elements are increasing exponentially.

It is now widely accepted that technology and metal-rich industrial waste represent significant secondary resources that must be harnessed to sustain the development of new technology materials. However, the recovery and re-use of the metals from these strategic wastes are still challenging. In particular, the solubilisation, separation and recovery in forms that are useful for manufacturing remain key areas that warrant further research.

Naomi Boxall, of CSIRO Land and Water, Australia, reviewed the recycling of technology-relevant metals from electronic, mining and industrial wastes, and opportunities and challenges associated with their re-use in the manufacture of new technology materials were identified. Naomi also discussed the extent to which the recovery and recycling of value from these wastes minimises the environmental impact associated with their production and disposal. Clearly, effective recycling of metals can help sustain the future of technology manufacturing.
However, as highlighted by Rudolf Stauber, of Fraunhofer ISC, Germany, the complexity of devices is high making recycling for technology metals complicated. Therefore the generation of concentrated fractions is an important step in the process chain of treating secondary raw materials. In addition there is an increasing demand for intelligent sorting solutions to meet the growing complexity and heterogeneity of material flows.

Rudolf focused on innovative recycling technologies for the recovery of critical raw materials from secondary resources by gas phase transport reactions, hydrogen processes and bioleaching. These recycling technologies can be adapted amongst others for rare earth based permanent magnets (REPM) and lithium-ion batteries. Hence in the field of magnets he highlighted the performance of recycled REPM produced out of scrap material for the application in electric motors. 
Rudolf Stauber and Naomi Boxall
Following the coffee break Philippe Giaro of Université de Liège, Belgium stressed that the characterization of e-waste is critical in ensuring an optimized recovery of “hi-tech” and critical elements. While this is a new problem that is focused on e-waste, it is an old problem relatively well understood in mining through process mineralogy. Characterization of metallic alloys and their associated textures (i.e. liberation, association) are all key metrics, which help provide a better understanding on the distribution and location of economical valuable element/metals, and thus opening opportunities for recovery process optimization.

Philippe presented a study on the first use of the Zeiss Mineralogic (and possibly Automated Quantitative Mineralogy) being deployed in e-waste characterization. This study outlines a new application area for automated mineralogy in e-waste characterization and how for effective recycling, there is a need for careful and robust material characterization.
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. In the first of four presentations by Chris Marion, of McGill University, Canada, he showed how recent studies investigating the use of a Knelson Concentrator and a Multi Gravity Separator (MGS) have demonstrated that both centrifugal gravity techniques have the potential to produce a high-grade pre-concentrate. However, both techniques resulted in low recoveries. This study investigates multiple stages of centrifugal gravity separation, operating at more ideal conditions, to evaluate and compare the effectiveness of a Knelson Concentrator and a MGS for the beneficiation of the Nechalacho Deposit.  
Philippe Giaro and Chris Marion
Rare Earths were also the subject of the papers in the afternoon session. Nebeal Faris, of RMIT University, Australia) described how the beneficiation of ferruginous rare earth bearing ores, derived from lateritic deposits, by conventional mineral dressing processes is made difficult by the characteristics of the ore such as fine grain size, complex texture and similar physical characteristics between rare earth minerals and iron oxide gangue.

Nebeal showed how the removal of iron oxides would offer significant advantages with respect to downstream rare earth mineral processing. The purpose of the work presented was to demonstrate at bench scale the feasibility of magnetically separating iron oxides from a lateritic rare earth ore after the ore had been subjected to reduction roasting to convert weakly magnetic iron (III) oxides to magnetite. The target products from the test work were an upgraded rare earth feed and an iron concentrate suitable for further processing.  
The rare-earth elements are strategic metals and their growing economic and strategic importance, coupled with uncertainty in the global supply of REE from China, have led to concerns about the future supply of many of these metals. Due to these supply concerns and the increasing demand of REE, many new rare earth mineral deposits with novel mineralogy are being investigated. These deposits are often complex and contain multiple REMs for which there is limited processing knowledge.

Chris Marion of McGill University looked at expansion of the flotation knowledge base of various REMs through an improved understanding of their physico-chemical properties. The minerals investigated were bastnäsite, parasite, monazite, eudialyte, fergusonite and allanite. The study included zeta potential and microflotation studies using common rare-earth collectors (fatty acids and hydroximates), in the presence and absence of activating ions (cobalt and lead) and depressants (citric acid and biopolymers). 
Anthony Geneyton, of Université de Lorraine, France, discussed a study to develop a new approach using a lanthanum chloride and carboxylate collector combination with the aim of improving the selective and effective collector adsorption onto the rare-earth phosphate minerals. Bubble/particle adhesion tests with sodium oleate collector were performed indicating a higher mineral surface hydrophobicity when using lanthanum chloride. Flotation experiments were performed with sodium oleate showing enhanced monazite recovery and flotation rate in presence of lanthanum chloride. The best flotation performance was obtained when the lanthanum chloride was added prior to the collector.

With regards to the performed XPS study and the literature data, Anthony suggested that lanthanum ions or lanthanum species strongly interact with the under-coordinated phosphate groups on the monazite surface playing a role of a bridge between the monazite surface and the carboxylate group of the collector. The workers observed that the lanthanum chloride dosage and mode of addition must be strictly controlled to avoid a decrease of the availability of the collector and thus a decrease of the monazite recovery and flotation rate. It was shown that the addition of non-ionic reagents significantly enhanced the adsorption of the collector and thus the rare earth recovery under conditions where the presence of cations limit the natural collector adsorption. 
Nebeal Faris and Anthony Geneyton
According to Levie Bumhira, of Stellenbosch University, South Africa, recovery of rare earth elements from secondary resources such as end-of-life fluorescent lamps will play an increasingly important role in the REEs market. Recycling of REEs from fluorescent powders often focuses on the recovery of Y and Eu, which have high value and are easily recovered. However, the recovery of other REEs present in more stable phosphor powders (e.g. Ce and Tb) should also be considered.

Levie discussed a project aimed at evaluating a multiple stage leaching process for REE recovery from phosphor powders by investigating the effects of temperature, acid concentration and material pre-treatment on leaching behaviour. First stage leaching with H2SO4 resulted in 98 % yttrium and 91 % europium dissolution, but insignificant terbium and cerium leaching. Following alkali fusion of the first stage residue, Tb and Ce recoveries exceeding 95 % were achieved in the second HCl leaching stage. The precipitation of Ca species impacted REE leaching efficiency.    
Levie Bumhira with Stellenbosch colleague Bruce Musariri
and University of Coventry's John Graves

A very good first day ended with a sundowner in the hotel gardens.

More on day 1 on the posting of November 22nd.
Friday November 23rd
Lithium was the focus of the 6 papers presented in the morning session. Lithium is a strategic metal due to its high-tech usages, mostly for batteries in electrical vehicles, but it also has a high supply risk. Due to high market prices, several resources are under (re)evaluation.

Reiner Neumann, of CETEM, Brazil, presented a case study on a pre-concentrate from the Argemela deposit in northern Portugal, which has an overall grade of 4.1% Li2O, the carrier being montebrasite. The ore grades around 40% of the mineral, and the main gangue phases are quartz (also around 40%) and muscovite. Several other phosphates are associated with montebrasite, planerite and childrenite predominating. This challenges the hydrometallurgical extraction of lithium from the concentrate.

Reiner showed how an initial sulphuric roasting step was optimized by TGA at 800°C, above the dehydroxilation of planerite (340°C) and decomposition of montebrasite (740°C) temperatures. Over 95% of the lithium was extracted with water at room temperature, and the residue, dominated by quartz and berlinite, has less than 0.5% Li2O. Al and Fe are then precipitated as hydroxides by lowering the pH, and after filtering them out any Mg is precipitated by raising the pH to 12. The final lithium carbonate is precipitated by reacting with Na2CO3, at neutral pH. 
Lev Filippov, of Université de Lorraine, France, also presented a case study on a Portugese ore, the Gonçalo lithium bearing mica rich pegmatite ore, on which mineralogical analysis indicated that lepidolite occurs in coarse grained textures, which allows a noticeable liberation of gangue minerals from the fine grained lepidolite intergrowths with quartz, K feldspar and albite, making full liberation difficult to attain.

Taking advantage of the coarser gangue liberation, image analysis was used to predict grade histograms of different size fractions, simulated by a developed random comminution algorithm. These histograms were used to simulate different pre-concentration scenarios at crushing sizes using optical sorting, allowing a Li pre-concentrate to be produced. A scaled approach of grinding and sieving produced a lepidolite rich fraction >210 µm which was processed using a Corona electrostatic separator to obtain a Li pre-concentrate assaying 3.5 % Li2O from a feed grade containing 1.8 % Li2O. Flotation testwork performed with the fine size fraction (-210+63 µm),  showed that lepidolite flotation is optimized between pH 3 and 5, where concentrates assaying 4.2-4.5 % Li2O corresponding to 87-95% Li recovery were attained at the rougher stage.  
Reiner Neumann and Lev Filippov
Traditionally, lithium has been obtained from brines, however, the expected increase in demand will require new hard rock deposits to be found and exploited. The main mineral containing lithium in pegmatite hard rock deposits is spodumene. There is relatively little recent work that has been published on the flotation of spodumene, which is an issue at a time where lithium supply security has become a top priority for technology companies. To develop an improved fundamental understanding of spodumene flotation, its zeta potential and microflotation behaviour in the presence and absence of different flotation reagents were studied at McGill University, Canada, and presented by Chris Marion. The reagents tested were sodium oleate, octyl hydroxamate and dodecylamine. Chris compared the results obtained for spodumene with that of common gangue minerals.
Keliber Ltd. is a Finnish SME aiming at production of battery-grade lithium carbonate using a novel leaching process and utilizing the company’s own spodumene ores as the raw material. The process chain, starting with mining and ending with the production of high-quality lithium carbonate is multi-staged and complicated. Pekka Tanskanen, of Keliber,  presented the main process stages and underlined certain points critical for lithium recovery and the quality of the final product. 
As the lithium ion battery (LiB) market is growing rapidly, LiB wastes will increase in the future and LiB components such as Co, Li, but also graphite, are forecast to be critical materials. These critical materials are contained in the black mass produced by LiBs recycling.

Anna Vanderbruggen, of Helmholtz Institute Freiberg for Resource Technology, Germany, presented original research focused on graphite beneficiation from cathode lithium metal oxides by flotation. Detailed characterization of the pyrolyzed black mass (inculding MLA, XRF and XRD) showed that the graphite particles are fully liberated from the copper foils. Batch flotation showed that pretreatment, such as attritioning, improves process efficiency while preserving the shape of spheriodized graphite. Concentrate impurities mainly comprise fine particles from cathode active materials, which can be removed with desliming and flotation cleaner stages. Anna felt that this research is expected to bring about an innovative and useful process for the recycling industry. 
Pekka Tanskanen and Anna Vanderbruggen
Bruce Musariri, of Stellenbosch University, South Africa, also discussed the importance of recycling LiBs. Current hydrometallurgical metal recycling processes involve dismantling and size reduction followed by leaching with mineral acids; these lixiviants present environmental challenges of their own.

Bruce described a project to evaluate the technical feasibility of using organic acids, which potentially have a smaller environmental impact than mineral acids, as lixiviants to recover lithium, cobalt and nickel from LiBs. Batch atmospheric leaching tests were performed with citric acid and DL-malic acid to investigate the effect of acid concentration, leaching temperature and H2O2 addition on metal leaching. Leaching with 1-1.5 M citric acid and 2 volume % H2O2 at 95°C achieved more than 95 % Co and Li dissolution; these results suggest that organic acids can possibly substitute inorganic acids as environmentally friendly lixiviants.
Significant cobalt mineralization associated with known Paleoproterozoic gold has recently been discovered at the Palokas Prospect in Northern Finland. This discovery has the potential to contribute significantly to the supply of cobalt for current battery technologies. The rocks are petrologically challenging because of their complex metamorphic and structural history, and in the first paper of the afternoon session, Pieter Botha, of Hippo Geoscience, Australia, described the development of analytical workflows based on the integration of multi-scale, multi-modal, and multi-dimensional technologies.

In this way it was possible to establish: 1) the general nature of the mineralogy and rock microstructure; 2) specific details on the texture of the ore mineralisation, including its relationship to structural deformation events; and 3) the deportment of commercially important elements. The benefits of this workflow include the ability to upscale micro-scale observations for informing further exploration work, and early-stage predictive geometallurgical models.
Pieter Botha (right) with his co-author Alan Butcher
“Theisenschlamm”, a flue dust of former copper shale processing in Germany, was deposited between 1978 and 1990. Its complex composition comprises high amounts of zinc and lead as well as a variety of low concentrated high-tech metals, such as rhenium, molybdenum, cobalt and germanium, which brought processing of this material back into focus. Since the Theisenschlamm is very fine-grained, it is well suited for hydrometallurgical processing. However, the concentrations of the high-tech metals in the pregnant leach solution are very low (1-10 mg/L). Toni Helbig, of Helmholtz Institute Freiberg for Resource Technology, Germany, described the development of a process route which includes an innovative combination of membrane filtration and solvent extraction in order to achieve selective recovery as well as enrichment of the target elements.
Rhenium is a valuable and extremely rare chemical element with unique chemical properties.  It is extracted commercially as a by-product from the processing of molybdenite associated with porphyry copper ores.  There is a present interest in recovering rhenium from copper pregnant leach solutions (PLS) produced by copper heap and stockpile leaching.  These solutions contain rhenium at very dilute concentrations, typically in the 1 mg/L concentration range.  Brent Hiskey, of the University of Arizona, USA, described laboratory column ion exchange experiments to extract rhenium from these solutions using weakly basic anion exchange resins and actual plant PLS from two operating mines.  The dynamic loading and elution behaviour of Re on Purolite® A170 and A172 was discussed. 
Brent Hiskey and Toni Helbig
Niobium, an important alloying element in steels, is primarily produced from three mines in the world: the Catalão and Araxá mines in Brazil and the Niobec mine in Canada. While current production rates are sufficient to meet global demand, concerns in the supply of niobium exist due to the geographic concentration of production. This has led to the development of many new deposits around the world, however, there is little information regarding niobium mineral beneficiation processes. While flotation is generally accepted as the most promising technique for the recovery of niobium-bearing minerals, such as pyrochlore and columbite, there is limited research detailing fundamental aspects of the process.

In the last of his four presentations, and the final paper of the conference, Chris Marion, of McGill University, described a study examinings the physico-chemical properties of pyrochlore and columbite through zeta potential and microflotation experiments. Common collectors used in niobium mineral flotation (hydroximates, fatty acids, and amines) were studied in the presence and absence of activating ions (cobalt and lead) and depressants (oxalic acid and citric acid). The results were compared to those from dolomite (a common gangue mineral). 
After summarising the conference, Amanda invited everyone for a final sundowner in the Vineyard gardens. 

We look forward to running this conference again in two years time. Although having a slow start we are confident that the series will evolve and grow, as we believe strongly that this is an area where mineral processing will contribute a crucial role in our hi-tech future.
The Proceedings of the conference are available on USB, and all authors have been invited to submit their final papers for peer-review, with a view to publication in a Virtual Special Issue of Minerals Engineering.

Photos taken at the conference can be accessed here.

Twitter @barrywills

Prof. Doug Fuerstenau: 90 years old today

On behalf of us all I would like to wish Prof. Douglas Fuerstenau all the very best wishes on the occasion of his 90th birthday today.
Prof. Fuerstenau is one of the 20th and early 21st century 'greats' of mineral processing, and three years ago I had the honour of interviewing him for the MEI Blog (posting of 20 July 2015).
In his long life as a mineral processor he has received numerous prestigious awards, his latest being the IMPC's Distinguished Service Award (posting of 19 September). Unfortunately he was unable to travel to Moscow to receive the award, but it will be presented in Denver in February, during the International Symposium in his honour (posting of 26 July). I expect many mineral processors to be in Denver for this event, which is part of the SME Annual Meeting. I will certainly be there to report for MEI.
Twitter @barrywills

Monday, 3 December 2018

Process Mineralogy '18: conference diary

Process Mineralogy '18 was MEI's 5th conference in this series, all of which have been held at Cape Town's Vineyard Hotel. The 3 day event was held between 19th and 21st November 2018.

Vineyard Hotel Conference Centre
Monday 19th November
A beautiful day in Cape Town, and this morning MEI's Jon Wills opened the conference, and welcomed the 85 delegates from 16 countries to the Vineyard Hotel,  thanking our sponsors Zeiss, ThermoFisher Scientific, Bruker, Petrolab and our media partners International Mining and Mining Review Journal Zambia.

Following Jon's introduction, our consultant, Megan Becker, of the University of Cape Town, spoke movingly of her great friend and mentor, Prof Dee Bradshaw, who was well known to all in the process mineralogy field, and who died in June after a long battle with cancer.

Our first keynote speaker was Alan Butcher, of the Geological Survey of Finland, who presented "When Scientists and Engineers Talk – Lessons from the Oil Industry and Applications to Mining".

The mineralogy of a rock (the individual constituents defined by their unique combinations of chemistry and crystallography) and the texture of a rock (the way in which the minerals are arranged geospatially, particularly with respect to each other, voids, pores and fractures), together largely control, or influence in some way, every major geological, petrophysical and engineering attribute relevant to the petroleum industry, whether it be density (sonic), hardness and brittleness (frackability), electrical conductivity (resistivity), radioactivity (gamma ray), rock type and lithotype (sedimentary, igneous or metamorphic components).

Can the same be said for mining? Almost certainly yes, according to Alan, who showed how the application of mineral and petrographic information is often quite different, as unlike the oil industry - where the commodities (oil and/or gas) are not measured directly, only the areas in the rock where they reside (mostly pores) - in mining, we investigate the nature of the commodity directly (ore-forming minerals).

This leads us to tackle similar challenges but from completely different perspectives. In mineral processing, we are typically concerned with predicting, measuring, monitoring and improving the behaviour of the (mostly valuable) components as they pass through the drilling, blasting, comminution and separation stages of the mining cycle. There is no question that an ore’s performance is strongly controlled and influenced by its original starting mineralogy and texture.

Alan reviewed which minerals are most likely to cause significant production problems in both worlds. He compared the analytical work flows used to characterize the so-called menace minerals, and suggested what learnings can be made. For example, knowing that one has the right type of pore-lining clay in a reservoir rock is critical to a petroleum engineer; likewise, being made aware that clay is present in an ore before it is processed (rather than after) is very helpful to a minerals engineer. The two industries typically approach characterizing clays from completely different angles, partly because the applications are different, but also the budgets and risk factors are not on the same scale.

But that aside, given that the minerals in each case may be similar (or virtually identical), and that it is applied mineralogists (scientists) who document and deliver the information to the engineers, it is important that all professionals involved in the greater natural resources community share their best practices across what are traditionally separate industrial segments, and that innovations are openly discussed so they can be adopted, if found to be useful and Alan's presentation was a major contribution to popularizing such a cross-disciplinary approach between the oil and gas and mining industries.

Alan Butcher (right), with Willem Swart of Advanced Laboratory Solutions,
a leading supplier of laboratory and scientific instrumentation in South Africa

After this fine introduction to the conference, Keith Taylor, of Oxford Instruments NanoAnalysis, UK, showed how, in order to understand the efficacy and efficiency of a mineral processing operation, it is of great importance that accurate, reliable data is acquired on the particle/grain morphologies and the compositions of the phases which are found.  This data must be acquired in a timely manner in order to enable quick feedback to be provided on the processing operation.

Advances in Energy Dispersive X-ray Spectrometry (EDS) Detectors used on Scanning Electron Microscopes (SEMs) mean that it is now possible to perform this analysis at the highest speeds whilst gathering a sufficiently high level of counts to confidently characterise both major and minor elements during the automated mineralogy process.  Matt reviewed the latest generation of hardware and how it can be applied to best meet the rigorous demands of automated mineralogy, using industrial and academic examples.

Keith Taylor and Matt Hiscock, of Oxford Instruments, talking to MEI's Jon Wills

Marcelene Voigt, of the University of Cape Town, South Africa presented an investigation into the the robustness of using the X-ray computed tomography (XCT) and the grey level co-occurrence matrices (GLCM) method for the quantification of mineral texture in 3D.

This can be achieved by testing the quality of the data that the GLCM outputs (statistics and heat maps) provides in response to changes in XCT conditions (e.g. artefacts, resolution, dual energy, calibration), as well as its response to different mineral texture types (e.g. anisotropic features). She showed how these findings will lead to a better understanding of how the GLCM captures the mineral texture information and assess the best conditions for the XCT analysis. It will further establish the versatility of the method to other mineral texture types and the factors affecting the underlying generic elements (e.g. grain size and mineralogy).

Marcelene's paper is part of the on-going research to develop a 3D mineral texture quantification method to be used in geometallurgy.

During the first poster session
After an extended coffee break, giving everyone time to view the posters and mix with the exhibitors, Lunga Bam, of Stellenbosch University, South Africa showed how X-ray computed tomography (XCT) is increasingly used to visualize and quantify ore characteristics in 3D for a variety of minerals processing applications.

The success of the technique relies on effective X-ray penetration which is most easily obtained for small, low density samples. However, it has been highlighted that sample size not only determines image quality but also whether the volume is an accurate representation of the ore characteristics.

Linked to this, is the challenge of differentiating minerals with insufficient density differences, e.g. chalcopyrite and pyrite. These issues are magnified in high density ore samples. Lunga described recent work that has developed protocols for XCT scanning of such samples.

Measurements of liberation are typically undertaken on materials at sizes where, in most instances, the inherent textural features of the ore have been destroyed. Understanding the contribution of textural characteristics to the evolution of mineral liberation can therefore be challenging.

Elaine Wightman, of Australia's JKMRC showed how, in previous work a method had been developed to measure and interpret the textural features of HQ core that contained both vein structures and disseminated grains.  Using random masking to simulate breakage at different sizes, it was shown that the presence of vein structures lead to liberation of sulphide minerals at coarser particle sizes.  An experimental program was then undertaken to break the core sections and measure the progeny particles created using a combination of areal (2D) and volumetric (3D) measurements.

Elaine described how data from these measurements show evidence of non-random breakage occurring and provides insights into which meso-scale features of the ore are the contributing factors.

Elaine Wightman (left) with Gaynor Yorath, Desh Chetty, Megan Becker, Solly Theron and Pieter Botha

Comminution indices are used to represent the grindability of a certain minerals combination in a specific process. An analogous behavior for the same comminution process is expected from two rocks that have similar index values. However, as shown by Leandro Voisin, of the University of Chile, indices are obtained assuming the breakage of homogeneous and constant materials without considering mineralogical and textural properties at any scale, so eventual differences in the process may not be explained by comminution indices.

Leando described how two different copper ore samples with similar Bond Work index were used to evaluate the influence of mineralogy and texture at meso and micro-scale at laboratory scale using the Magotteaux Ball Mill®, controlling physical and chemical grinding parameters. The effect on grinding was assessed through kinetic experiments and the results confirmed that rock properties at minor scales may affect grinding performance.

Humidity cell tests (HCTs) are a routine analytical tool for assessing the long-term variation in sulfide oxidation kinetics within potential mine waste. The need to understand the role that mineral texture plays in controlling HCT behaviour is integral, and analytical protocols for this are the subject of research by conference sponsor Petrolab Ltd, UK.

James Strongman presented a general protocol, from sample preparation, through to analysis methods and interpretation that has been developed from the analysis of HCT feed samples from Savage River, Australia and an IOCG deposit in Scandinavia.

From this study, and using process mineralogy tools, quantified textural parameters are calculated for the balance of acid-generating minerals and acid-consuming minerals along with the implications this carries for true acid-generation potential. Quantifying the textural controls in this manner are a powerful tool for understanding mineral textures and provide the overseeing geochemist with sufficient information and confidence to interpret current and likely future HCT behaviour.

James Strongman, of Petrolab, with Tata Steel's Sunil Tripathy and Gajanan Kapure

Image analysis aiming at process design or control might be based on several types of microscopy, each providing advantages and limitations. Automated mineralogy systems based on SEM are dominant for ore characterization, but, as discussed by Reiner Neumann, of CETEM, Brazil, in the final paper of the morning, there are relevant cases where such systems cannot perform the required characterization, such as with iron ores and complex multi-metallic rare-earth ores.

The characterization of iron ores is typically performed using reflected light microscopy. Optical image analysis systems can recognize most common iron-bearing minerals, but the discrimination between quartz, other transparent gangue minerals and the embedding resin is very tough.

Reiner presented a correlative microscopy setup that combines reflected light and cathodoluminescence. The correlated use of these signals provides contrast to discriminate resin from quartz and allows the identification of several transparent minerals, besides classifying iron minerals by mineralogy and texture.

Reiner Neumann (left) with Zeiss's Shaun Graham, Allister McBride and Ben Tordoff,
and XPS-Glencore's Michelle Kelvin and Elizabeth Whiteman

A long break for lunch

The classification of phases measured by SEM-EDS automated mineralogy often relies on user-defined mineral chemical criteria. The design of such classification rules can be complicated and time-consuming in addition to being prone to errors due to lack of user experience or knowledge of complex mineral occurrences.

Pieter Botha, of Hippo Geoscience, Australia, described the development of a set of analysis tools that would augment the design of phase classification criteria for SEM-EDS automated mineralogy data. Mathematical methods were applied to a set of raw energy dispersive x-ray spectra to identify the main chemical clusters. These clusters were then used to define initial classification rules and input spectra for phase chemical quantification. Some challenging aspects in automated mineralogy, for example, mixed spectra deconvolution, polished surface imperfections, and grain size limitations were also addressed.

Micro-XRF technology in automated mineralogy has created new opportunities to analyse large samples of rock and drill core with minimal sample preparation, as well as gaining insights from traditional polished sections or briquettes.  The strength of micro-XRF above other techniques is in identifying trace elements.

However, micro-XRF has had shortcomings, for example detecting super light elements (SLE) with low atomic values below sodium (Z < Na).  Consequently, minerals such as calcite and fluorite that can be differentiated only by the fluorine (F) and oxygen (O) content cannot be discriminated from each other.

Samuel Scheller, of Bruker Nano GmbH, Germany, introduced the new M4 TORANDOPLUS, which uses SLE windows and x-ray tube, providing the capability to detect light elements and therefore distinguish carbonates from fluorites.  Samuel discussed these technological advancements and new capabilities using real-world applications in mineralogy in combination with the automated mineralogy software AMICS.

Samuel Scheller (2nd left) with Andrew Menzies, Mark Pownceby, Frances Wall and Joerg Blieffert

Automated mineralogy at its core is a computerised point-counting technique that removes operator bias when determining bulk mineralogy and derived information. However, vendor implementation details can introduce unintended bias unless operators spend significant time to detect and resolve identification artefacts.

Michael Owen, of Thermofisher Scientific, USA, proposed a new approach that directly models mineral complexity and SEM-EDS interactions. It automates mineral deconvolution quantification for boundary phases and tiny inclusions; allows full mineral solid solutions; and elemental impurity substitutions in mineral definitions. This reduces operator tuning for mineral ID significantly when compared with existing commercial products such as QEMSCAN or MLA.

Michael Owen (centre) with Gaynor Yorath and Philippe Giaro

According to Ivan Fernandes, of Helmholtz Institute Freiberg for Resource Technology, Germany, the minerals industry needs a quick, reliable and powerful predictive tool to perform techno-economic and sustainability evaluation of the raw materials value chain, being able to compare different process flowsheets and adapt to the ever increasing ore variability and complexity.

He described a study demonstrating how the integration of quantitative mineralogical data coupled with simulation tools (HSC Sim) and LCA software (GaBi), are used to truly develop a predictive geometallurgical tool. An MLA-based process simulation takes into account a range of geometallurgical variables, such as sized data, mineral locking, liberation, mineral chemistry and shape to predict metallurgical responses in energy/water/resource efficiency, energy consumption, mass and energy balance, besides the typical grade and recovery.

In addition, this approach creates a direct link from automated mineralogy data to the prediction of environmental footprint of a system, from mineral processing to metallurgy, giving sustainability thinking an important role in the decision-making process.

Ivan Fernandes with Anna Vanderbruggen

The polymetallic Cu-Pb-Zn-Ag Swartberg deposit in South Africa hosts three distinct ‘early stage’ geometallurgical domains across five lithostratigraphic ore types.  Variability within each domain is expressed as noticeable differences and similarities in bulk mineralogy, grain size distribution, gangue mineral association and textural orientation.

Henry Gordon, of Stellenbosch University, South Africa,  assessed the influence of such characteristics on the liberation, recovery, selectivity, throughput and grade of copper minerals within each geometallurgical domain when subjected to flotation in a size by size context. The results have implications for improving the classification of mineralogy-based domains as a function of distinct responses during flotation testing.

Pyrometallurgical processing of polymetallic ores from the Zeehan Field, Western Tasmania, occurred intermittently between 1896 and 1948, primarily focussed on recovering Pb, Ag and Cu. Zinc was not recovered and reported to the slag which was disposed of in two piles (North and South) located near Zeehan.

Anita Parbhakar-Fox, of the University of Tasmania, Australia, described how geometallurgical and geoenvironmental characterisation of slag samples was carried out using XRD, SEM, LA-ICPMS, XRF and static testing.

Samples from the North and South piles contain on average 12% and 18% Zn respectively by bulk analysis. The micro-texture of the slag is highly heterogeneous and includes distinctive dendritic wurtzite and sphalerite, Zn-rich glass phases (containing up to 34 wt.% Zn) and Zn-bearing olivine and pyroxene. Elevated levels of As, Cd, Co, Cu, Pb and Sb within the slag and geoenvironmental assessments indicate these materials are potentially acid forming in their current state. Anita discussed opportunities to reprocess the slag to economically extract Zn by leaching.

Anita Parbhakar-Fox (centre) with Nick Wilshaw, Frances Wall, Nathan Fox and Felicity Wilshaw

Knowledge of the distribution of minerals and elements within a deposit is key to determining the most efficient mineral processing procedure, for example Mn within Au-Ag epithermal deposits.  Cyanide is the primary reagent in gold recovery, and Mn reacts easily, oxidizing the cyanide and transforming it into cyanate, increasing the cyanide comsumption, affecting recovery, and increasing production costs.  In addition, the process solution generates a gel that obstructs plant pipe-lines affecting the process and maintenance.

Andrew Menzies, of Universidad Católica del Norte, Chile, showed how combined automated mineralogy and elemental scanning (µXRF) on two high grade samples from El Peñón in Chile quickly and efficiently identified key information regarding Mn and Au relationships.  Crushed samples identified the Au-Ag mineralogy (QEMSCAN), whilst elemental rock mapping (M4 Tornado) showed Mn does not have a spatial relationship with Au-Ag mineralisation at the micro-scale.  Thus, it was possible to apply geometallurgical processes to remove the Mn phases prior to the application of cyanide without influencing Au-Ag recovery. 

After a good first day, we made use of the warm sunshine for the first of our late afternoon sundowners.

More on day 1 on the posting of 19th November.

Tuesday November 20th
In bio- and acid heap leaching processes, a substantial fraction of the mineral grains are positioned below the surface of the ore particles. Leaching performance of the non-surface mineral grains has potential to be affected by factors including the presence of surfactant, the operating temperature and agglomeration pre-treatment effect.

Mhadi Ghadiri, of the University of Cape Town, showed how non-destructive 3D X-ray micro-computed tomography (µCT), an imaging technique, can be used to quantify the leach performance at the mineral grain scale within the ore particles.

The copper ore deposits found in the north western part of Botswana contain mainly chalcocite.  The plant processing this mineral shut down due to a global fall in copper prices, and decreased grade and recoveries, subsequently leading to high and unsustainable operational costs.

Poloko Nenguba, one of 5 representatives from the Botswana International University of Science and Technology, presented an investigation of how minerals are distributed and associated in the host rock that was processed, analysing the quantitative mineralogical analyses results carried out by XRF, XRD and automated Scanning Electron Microscope technique (QEMSCAN) by Bulk Modal Analysis (BMA) and Specific Mineral Search (SMS).

This analysis consequently identified better methods of processing the minerals of interest. The quantitative analysis of the mineral deportment further provided knowledge on copper speciation, elemental deportment, mineral liberation and their association, as well as the grain size distribution.

Poloko Nenguba with Megan Becker and Elizabeth Whiteman
Knowledge of mineral composition and phase distribution within ilmenite concentrates is important in understanding the inter-granular inclusions of impurities which might have direct effects on the market value and subsequent treatment process.

Mercy Ramakokovhu, of the Tshwane University of Technology, South Africa, described how characterisation of the ilmenite concentrates from Richards Bay, South Africa was investigated along with mineral phase changes associated with the leaching process. A combination of characterisation techniques including the High-resolution Scanning Electron Microscopy and X- Ray diffraction techniques were used.

Mercy Ramakokovhu with her colleague Richard Mbaya
Manganese ores differ extensively in their mineralogical and bulk chemical composition. The result is that these ores follow different mineralogical morphology development paths as the reduction reaction proceeds in the production furnace.

For example the composition and distribution of initial liquid oxide formed at specific temperatures, as well as iron and manganese metallisation patterns due to their distribution in the ore minerals, are significant determining factors in the relative importance of different parallel reduction reaction mechanisms in each ore type. Applied mineralogy is a vital application field to better understand manganese ore reduction reaction mechanisms.

Theresa Coetsee, of the University of Pretoria, South Africa, showed how analysis of reduced ore phase chemistry and phase distribution was used to better explain differences in reduction rate variation with ore type. 

Theresa Coetsee with Gajanan Kapure and Sunil Tripathy
Phosphorus is one of the most deleterious elements in iron ore as it follows iron in the reduction process forming iron phosphides that make steel brittle. Excess P increases the cost of the steelmaking process and the steel industry has placed an upper limit of 0.07-0.08% P.  Goethite-containing P is abundant in many iron ores and it is difficult to remove without discarding valuable iron-containing units. The goethite forms during supergene metasomatic enrichment of BIF-derived ores with contained P typically associated with other impurity elements (e.g. Si and Al).

Mark Pownceby, of CSIRO Minerals Resources, Australia, discussed a study focussing on determining the distribution and association of P within goethite. Detailed characterisation of goethite-rich high-P iron ores was conducted using XRF, XRD and EPMA to measure their P and other impurity element contents and their distribution. Using this knowledge, the workers speculated on possible P-bearing species that may be present and also possible P substitution mechanisms in goethite.

Igor Tonžetic, of the University of Pretoria showed how the optimization of iron oxide discrimination on a QEMSCAN system was explored through the systematic testing of measurement and analysis parameters. Specifically the influence of backscatter electron (BSE) stabilizers (also known as BSE amplifiers), gun alignment, magnification field sizes and Mg/Ca solid solution in iron oxides were studied. Furthermore, the effect of stage height focus versus beam focus were compared and contrasted. Novel measurement parameters were presented that improve iron oxide distinctions including appropriate 3rd point BSE calibration standards and increased beam dwell times. Finally, a particle characterization mechanism that uses a de-convoluted iron oxide dilation erosion procedure was introduced.

Musarrat Safi, of Council for Geoscience, with Felicity and Nick Wilshaw

Lev Filippov
After the extended lunchbreak, due to a 'no-show' from the University of Johannesburg, Lev Filippov of the Université de Lorraine, France, discussed the Tabuaço tungsten project in Northern Portugal.

The deposit is composed of two skarns layers, namely “Main” and “Lower” skarns, which display significantly different mineralogical and geochemical features. Both skarns contain fine-grained disseminated scheelite but the Lower-skarn gangue is dominated by silicates whereas the Main-skarn gangue contains calcium-bearing minerals as fluorite, apatite and vesuvianite in close association with scheelite.

Preliminary feasibility studies show that direct separation of calcium-bearing minerals by flotation with fatty acids is very difficult due to their similar surface properties. Several routes for each skarn type have been proposed i.e. direct flotation for the Lower skarn and combined gravity/flotation route for the Main skarn. Moreover, the flotation of the Main Skarn has been deeply investigated in terms of depressants reaching a maximum WO3 enrichment ratio of 10 for the optimal conditions. Finally, new collector formulations have been developed to improve the separation contrast, leading to a WO3 enrichment ratio of 27 in the final concentrate.

Middle group (MG) chromitites of the Bushveld Complex are typically processed to recover chromite, with platinum group elements (PGE) derived as a by-product. Oxidised PGE ores, however, have proved problematic for the recovery of PGE by flotation. Desh Chetty, of Mintek, South Africa, showed how oxidised MG chromitites, subjected to flotation to recover PGE after gravity concentration to recover chromite, were characterised in order to understand PGE behaviour during processing. Characterisation was performed using automated scanning electron microscopy, laser ablation ICP-MS and bulk chemical assays.

Glencore's Kidd concentrator and Kidd mine are located in Timmins Ontario Canada and is one of the world’s largest massive sulphide deposits.  Elizabeth Whiteman and co-workers from XPS – Expert Process Solutions, Canada, have worked with Kidd concentrator monitoring performance based on monthly composites during 2015-2017. 

Using automated mineralogy (QEMSCAN, LA-ICP-MS) on sized samples of flotation feed, Cu concentrate, Cu tailings/Zn feed, Zn concentrate and Zn tailings, mineralogical drivers of flotation performance were examined and reported in the presentation.

Björn Lewandowski
Since 2014, fluorite (calcium fluoride) has been one of the 20 most critical materials indexed in the EU Raw Materials Initiative. Currently it is the only fluoride containing raw material to be used for production of fluorine. Barium sulphate, a common gangue of fluorite, behaves in a similar way with collectors as calcium fluoride, making the separation via flotation more complicated. It is of great interest to optimize the productivity of these flotation plants. For quantification of calcium fluoride, X-ray spectroscopy is commonly applied. The main disadvantage of this method is the necessity of a high-energy lamp for detection of fluorine.

Björn Lewandowski, of University of Duisburg-Essen and Niederrhein University of Applied Sciences, Germany), described the application of Raman spectroscopy to a model flotation system containing calcium fluoride and typical gangue particles. Calibration with pure substances showed very good quantification of calcium fluoride and barium sulphate. Application to an industrial flotation system also showed very promising results.

Uwe König, of Malvern Panalytical B.V., The Netherlands, discussed how fast and frequent monitoring of the mineral content and related process parameters brings value to bauxite mining, refining and aluminium production.

X-ray diffraction (XRD) is a critical process tool to efficiently use energy during aluminium production. Traditionally quality control of electrolytic baths, alumina and bauxites have relied on calibration based single peak methods or more advanced full pattern techniques. Recent tests showed that the same XRD measurement used to determinate composition and bath parameters can be used to predict the bath temperature and to calculate liquidus temperature and superheat. This technique saves valuable time and costs for additional temperature monitoring and allows fast counteractions on changing conditions to prevent bath solidification.

Even though today was dull and wet, Kirstenbosch Botanical Gardens was a great venue for the very informal conference dinner, a relaxing respite from the conference atmosphere.

More on the conference dinner on the posting of November 21st.

Wednesday November 21st
The final day of the conference specialised in high-tech metals, as a prelude to the Hi-Tech Metals '18 conference which begins tomorrow.

The day began with a keynote lecture from Frances Wall, of the Camborne School of Mines, UK, who reviewed common problems, and progress towards solutions, in the process mineralogy of rare earths.

The geochemistry and mineralogy of rare earth element (REE) deposits is diverse and ranges from carbonatite-related deposits and alkaline rocks to mineral sands, ion adsorption clays, marine crusts, nodules and clays, by-products of phosphate and bauxite, and re-use of waste materials. Despite the large number of recent exploration projects, very little additional REE production has started. An in-depth understanding of the mineralogy is essential for process design and all of the deposit types have mineralogical advantages and challenges, which Frances reviewed and explained.

Most critical element ore deposits are complex and display a high degree of variability, arising from their inherent geological and mineralogical characteristics, which impact their beneficiation. Process mineralogy for rare and critical elements, including REE, Li, and Nb aim to help with the flowsheet development to avoid extensive and time-consuming bench testing. 

Process mineralogy can provide critical quantitative data i.e., for Li-bearing minerals that may not be recoverable or marketable, the deportment of REE, the type of Nb phases and their liberation.

Tomas Hrstka, of SGS Minerals, Canada, discussed examples of automated mineralogy applied in a geometallurgical framework at an exploration to feasibility level.

Jochen Petersen, of the University of Cape Town, discussed how in-situ leaching of REE from low grade clay deposits formed through subtropical weathering of granites presents a potential alternative due to its low cost and limited infrastructure.

Jochen showed how a REE enriched ion-adsorption clay sample from Madagascar was characterised using a combination of process mineralogy techniques from simple optical microscopy to advanced synchrotron analysis to understand the deportment of the different REE within these clay ores.

Results show the presence of varying morphologies of kaolinite and halloysite, and contribute to further understanding of the movements of Fe, Mn, La and Ce within the weathering cycle. Based on the understanding of the REE deportment, suitable processing routes can be designed and optimised to effectively recover the REEs.

Reiner Neumann, of CETEM, Brazil, showed how recovering REE as by-products of existing mineral operations is a low-investment option to increase supply in the short term. REE-minerals have been reported for the São João del Rei pegmatitic province (southern Minas Gerais State, Brazil) since the late 1940’s, but data is scarce and dubious.

The largest pegmatites in the Province have been mined since 1945 at the Volta Grande Mine, producing Sn (cassiterite) and Nb-Ta (microlite and columbite group minerals) concentrates. The detailed mineralogical and technological characterisation of streams from the beneficiation plants identified apatite with monazite and xenotime microinclusions as the most important REE-bearing mineral. Apatite is well liberated, and reports to the tailings, which contains up to 6.8 (wt.%) that could be reprocessed to generate a product adequate for phosphoric acid production with REE recovery as by-products and would also allow secondary recovery of cassiterite, fluorcalciomicrolite and columbite-(Mn).

Tailings and their disposal have been described as the single most important source of environmental impact from mining operations. Tailings may also provide a potential source for further beneficiation of valuable materials. The fundamentals for any processing or treatment of ore and tailings are initially dictated by the mineralogical and chemical characteristics.

Rita Kallio, of the University of Oulu, Finland, presented two case studies for tailings characterisation. The main objective was to increase mineralogical knowledge of the tailings with an emphasis on liberation analysis. Liberation analyses were conducted with INCAMineral in combination with post-processing the results with GrainAlyzer.

The first case, spodumene flotation tailings from a greenfield lithium mine project, focused on determining the liberation of feldspar and quartz. In the second case, tailings from a closed Fe-Ti-V-mine, the main interest was in the properties of ilmenite in various parts of the old tailings storage facility.

Following the lunch break Pekka Tanskanen, of University of Oulu discussed the on-line monitoring of the spodume heat treatment process using Timegated Raman spectroscopy. Spodumene is the most important hard rock source for lithium. Prior to leaching of lithium from spodumene the natural monoclinic crystal structure must be transformed into tetragonal ß-form by heat treatment. The heat treatment at about 1050 °C is highly energy consuming and can lead to lowered lithium recovery in the leaching stage if the concentrate is over-heated or under-heated. On-line monitoring of the spodumene phase transformation grade gives data for controlling the heat treatment process. 

Timegated® technology is built on the research carried out at VTT Technical Research Centre of Finland and Oulu University since 2009. Timegate Instruments Ltd is based in Oulu, and is exhibiting for the first time at an MEI Conference. The basis of the innovation is novel Timegated®  Raman spectroscopy technology that enables continuous, non-contact, quantitative and qualitative measurements of solids, liquids and slurries.

The sample is illuminated with a laser and the scattered photons provide mineralogical and polymorphic information while minimizing photoluminescence interference which has been a major challenge for conventional Raman spectroscopy. Timegated® Raman technology also minimizes thermal emission interference making high temperature measurements feasible.  

Jussi Soukkamaki, of Timegate Instruments with Rita Kallio and Pekka Tanskanen of University of Oulu

Michelle Kelvin, of XPS Expert Process Solution, Canada, showed how, in the field of process mineralogy, LA-ICP-MS is a valuable tool that can complement other mineralogical techniques used to characterise orebodies and concentrator performance.

Many economic metals are present at ultra-low levels as solid solution within minerals and require complex recovery techniques to separate them from the bulk ore. Understanding metal occurrence is necessary for implementing the proper recovery strategies.

LA-ICP-MS is a cost-effective and versatile method of measuring precious-metals and other economic trace-elements in solid solution in various types of mineral phases while achieving low detection limits. To demonstrate the practical uses of LA-ICP-MS to process mineralogy, Michelle showed how XPS has collected data from a sulphide-rich heavy liquid separation and shaking table concentrate from the Kipushi Cu-Zn deposit, Katanga, DRC.

In addition to Cu and Zn, the Kipushi operation is currently investigating strategies for concentrating Ge and Ga. A combination of gravity separation and recovery of Ge and Ga through flotation of Zn and Cu sulphides is being considered. The objective of the LA-ICP-MS analysis was to determine the proportion of Ge and Ga present in solid solution in sulphides and in discrete mineral phases.

Sphalerite is the most important Zn-bearing ore mineral, however, its flotation response during mineral processing can be complicated by the presence of trace impurities. Previous work has constrained the effects of Fe substitution on sphalerite mineral structure and flotation response, yet minimal work has focussed on the effects of other transition metals such as Cd and Co which readily substitute into the sphalerite mineral structure.

Using electro-kinetic techniques, Lebogang Babedi, of Stellenbosch University, South Africa, discussed the variations in surface charge, Cu-activation and collector adsorption arising from cation substitution in trace-element doped synthetic sphalerite.

These variations include differences in the onset pH during flotation and differences in the reaction products arising during collector adsorption. These differences can be linked to the nucleophilic and electrophilic characteristics of the trace metal substituent. The study highlights the need for fundamental scientific investigation which will enhance predictive capabilities and efficiencies during beneficiation of complex natural ores.

As noted by Andrea Guhl, of Freiberg University of Mining and Technology, Germany, while FEI’s MLA system is a staple in ore characterization and ore process assessment, automated mineralogy systems have been used for a multitude of other materials as well.

When looking at ashes, the high amount of X-Ray amorphous components have prevented a thorough characterization using XRD. Wet chemistry testing has been employed to assess the elemental content of this material, but fails to reflect the nature of ashes. Previous studies of ashes have occasionally highlighted interesting elemental compositions, which encouraged recycling efforts. However, turning waste into a resource requires an intimate knowledge of these materials.

Andrea stressed how evaluating particles – their morphologies and compositions – of ashes is essential in devising treatments for a targeted approach.

Andrea Guhl with Olga Guseva

MEI Consultant Megan Becker briefly summarised the conference, after which MEI's Amanda thanked the sponsors, chairpersons, authors and delegates and invited everyone back to the Vineyard for Process Mineralogy '20, which will be held in October 2020, prior to the IMPC, also in Cape Town.

Farewell drinks in the Vineyard gardens

The Proceedings of the conference are available on USB, and all authors have been invited to submit their final revised papers to Minerals Engineering for peer-review with a view to publication in a virtual special issue of the conference.

All the photos from the event can be viewed here.
Twitter @barrywills