Sustainable Minerals '18 Conference Diary

Sustainable Minerals ’18 immediately followed Biohydromet ’18 at the Windhoek Country Club, Namibia, and was MEI’s 5th in the series. The conference was organised in collaboration with the Namibia University of Science & Technology, and was sponsored by Zeiss and Outotec, with International Mining as a media partner, and CEEC as the Industry Advocate. As always, our consultant for the event was Prof. Markus Reuter, the Director of the Helmholtz Institute Freiberg for Resource Technology.

Windhoek Country Club

Thursday 14th June

This morning I welcomed the 55 delegates from 13 countries to the conference, although we had met many of them last night at the conference dinner which was held at the end of the Biohydromet conference (posting of 14th June).

Prior to getting the conference underway we observed a minute's silence in remembrance of Prof. Dee Bradshaw (posting of June 8th), a former MEI Conferences consultant, who was a great advocate of sustainable minerals and green mining, and who would surely have been at this event.

Rob Dunne

After I highlighted the crucial role that mineral processing has in sustainability (posting of June 15th) the conference got under way with a very appropriate keynote lecture from Rob Dunne, who is an Adjunct Professor at Curtin University, and the University Of Queensland, Australia. Rob’s lecture “Water- crisis, conflict, resolution (?)”, is detailed in the posting of 24th April 2017, and set the scene for two more important presentations on water which took us up to the coffee break.

Bruno Michaux, of Helmholtz Institute Freiberg for Resource Technology, Germany, discussed the potential of mineral processing simulators as a tool for water-saving strategies in the mining industry. As the mining industry is facing an increasing number of issues related to its fresh water consumption, water-saving strategies are progressively being implemented in the mineral processing plants, often leading to variations in the process water chemistry. However, the impact of water chemistry variations on the process performance is rarely known beforehand, thus creating an obstacle to the implementation of those water-saving strategies. To tackle this problem, a simulation-based approach was suggested, which relies on the modification of the flotation kinetics under varying water chemistries. This approach was illustrated with the case of a fluorite ore and compared to the more traditional approach, which consists in determining the shift in the grade – recovery curve when the process water is subject to change.

Bruno Michaux (left) with Edison Charikinya, Nicole Uys, and Jochen Petersen

Päivi Kinnunen, of VTT, Finland, introduced the European Union-funded ITERAMS project (Integrated mineral technologies for more sustainable raw material supply), which delivers new solutions to enable closed water loops in the mining operations. The isolation of process waters completely from the adjacent water systems requires development of new methods for optimising and controlling water qualities at each process step. As a bonus, this will also facilitate the recovery of additional valuable constituents. The tightly closed water cycles can be realised only if the tailings can be filtered and stacked dry. Tailings streams are modified for their easier geopolymerisation. Geopolymerisation is used to create water and oxygen tight covers on the deposited tailings. The main objective is to obtain a new paradigm proof of concept at mine sites to recycle water and valorise tailings for an improved environmental and economic result.

Päivi Kinnunen with Jennifer Broadhurst



Poster viewing during the long coffee break

Amanda with some of the excellent Country Club staff

Groundwater quality reflects the various bio- and geo-chemical interactions between the organic and inorganic matter within aqueous sediments and associated secondary water sources, impacting on the quality and speciation of the concomitant aquifer. In the case of pyrite (FeS2)-rich sediment and acid mine drainage, the oxidation in the oxic zone and the resulting acidic leachate affect the water quality. Heavy or toxic metals bearing minerals undergo leaching and redox reactions which may lead to the release of the toxic species into the porewater, with adverse consequence of chemical pollution of the environment. Jonas Addai-Mensah, of the Namibia University of Science & Technology, described a study which examined the impact of pyrite-rite sediment redox process on the quality of porewater along the sediment depth column, and on the water quality transformation of external water bodies that are in association with the pyrite-rich sediment. The implications of the findings in relationship to environmental remediation principles and sustainable development and use of land were discussed.

With Jonas Addai-Mensah and his NUST colleague Harmony Musiyarira

Sue Harrison

The co-disposal of waste rock with fine desulfurised tailings can potentially aid in the prevention of acid rock drainage (ARD) by restricting the access of oxidants to sulfide bearing rock surfaces. However, in prevention studies, optimising the packing density of waste rock dumps remains a challenge. Large void spaces between particles are prevalent. This low degree of interlocking between particles reduces the packing strength and amplifies seepage. High seepage rates contribute to oxidative weathering of the sulfide bearing rocks. A standard protocol for material placement, to enhance the packing density of these beds, is therefore paramount for the success of these co-disposal prevention methods. Conference consultant Sue Harrison, of the University of Cape Town, showed how particle packing models are exploited to obtain optimum packed beds. These packing models are evaluated by applying incremental loads to the ore beds. The pack strength of these beds is then assessed at various loads using stress-strain correlations. This study forms the basis for the development of optimised packing models for the prevention of ARD at both bench-scale and field application.

ARD mobilises deleterious elements, increasing environmental burden for mining sector and local communities. In a further presentation by Sue Harrison, she discussed why characterisation of ARD potential of waste rock is necessary to inform their appropriate disposal in order to minimize the pollution risks. This characterisation has been typically limited to static tests using strong acid and oxidative leaching to give worst case net acid forming potential scenarios. Where ARD is considered important, long-term kinetic tests determine the rate of the net acid generation under field conditions. However, the relative kinetics of acid neutralisation and generation are not taken into account. More recently, approaches to refine ARD characterisation and prediction are being sought. The UCT biokinetic test is one of a suite of tests informing this characterisation.

In the final paper of the morning Chris Bryan, formerly with Camborne School of Mines, UK, and now with BRGM, France, and also a conference consultant, discussed the analysis of sulfidic coal production wastes using biokinetic tests combined with QEMSCAN. 

Chris Bryan (centre), with Megan Barnett and Simon Gregory of the British Geological Survey

Our two representatives from Rossing Uranium, Ignatius Shaduka and Jacklyn Mwenze

It is good to have the Dundee Precious Metals (DPM) smelter so well represented at the conference. The smelter is located near the town of Tsumeb, north-east Namibia, and has been in operation since 1963. It has been designed and build specifically to treat complex polymetallic concentrates from Tsumeb Mine, which contains high levels of copper, lead, zinc, arsenic and cadmium. An Ausmelt furnace was commissioned to treat lead concentrates in 1996 and then conversed to treat copper concentrate in 2008, when Namibian copper mines closed. Tsumeb smelter was acquired by DPM in 2010 and feed from DPM’s Chelopech mine was provided. Since the acquisition, significant investments have been made to transform the smelter to a sustainable toll-treatment facility with specific focus on improving occupational, health, safety and environmental aspects of the operation. This includes new off-gas and emissions management, new dust management system, new oxygen plant, new hazardous waste deposition facility, two new Peirce-Smith converters and new sulphuric acid plant. Barcelona Tsauses discussed how DPM is focused on empowering local people wherever it operates. Community investment in Tsumeb include small and medium enterprise development projects, education, social services and culture. Commitment to meaningful stakeholder dialogue and engagement has been the approach followed by the company. 

Barcelona Tsauses (right) with her DPM colleagues, Lawrence Tjatindi,
Zebra Kasete and Buks Kruger

The mining and minerals industry faces some of the most difficult sustainability challenges of any industrial sector. To secure its continued ‘social licence’ to operate, the industry must respond to these challenges by engaging its many different stakeholders and addressing their sustainability concerns. Many mining companies, particularly multi-nationals, are reporting the outcomes of their sustainability performance in publicly available annual reports, using integrated frameworks developed under the auspices of the responsible mining initiatives. However, the proliferation of standards and the voluntary nature of the reporting results in reporting inconsistencies both in terms of data presented (quantity and quality) and terminologies used. David Viljoen, of the University of Cape Town, discussed the application and applicability of existing sustainable performance assessment frameworks and metrics in the context of the South African gold mining industry. He reviewed and evaluated current sustainable performance reporting practices in the industry, assessing their effectiveness in promoting the sharing of information, critical to strengthening transparency and accountability.

David Viljoen (right) with Rodrigo de Almeida Silva

Low concentrated heavy metal ions are causing diverse problems for conventional metal processing, and Robert Braun, of Helmholtz Institute Freiberg for Resource Technology, Germany, discussed new biosorbents for metal recovery. Artificial peptides with metal binding affinities combine high specificity and sensitivity and being biodegradable, they do not add additional environmental pressure, therefore they are of high potential for geobiotechnology. Robert described the development of novel peptidic bio-materials for the recovery of cobalt and nickel.  

Robert Braun (left) with Guillermo Luque Consuegra, Megan Barnett and Simon Gregory

In a further paper from the Helmholtz Institute Freiberg for Resource Technology, Rohan Jain discussed the cost-competitiveness of siderophores in recovering of critical metals from waste streams. Siderophores are known for their specificity and sensitivity towards the critical metals whose supply is at risk in the future. Thus, the use of these siderophores for the recovery of these critical metals from their low concentrated wastewater is a very attractive option. However, there is no detailed cost estimation for their application in wastewater. This study detailed the economic feasibility of application of desferrioxamines for the recovery of gallium from industrial wastewater, factors such as regeneration recycles, downstream processing, cost of gallium, operational cost of the technology and cost and grade of desferrioxamine production being taken into account.

Rohan Jain (centre) with Pankaj Kumar Choubey and Rodrigo de Almeida Silva

Refractory gold ores have been the subject of numerous investigations in order to improve the leaching kinetics. This is because the cyanidation process cycle, although well established and well researched, remains very long.  Faster kinetics would help lower the production cost which is very necessary especially during lean and tough industry times. Jean Jacques Mabayo, of University of the Witwatersrand, South Africa, introduced the development and application of a new and promising reactor “Jetleach reactor” in improving the leaching kinetics of refractory ores. The Jetleach reactor is designed to create and propagate micro-cavitation by impacting two pulp streams against one another at a high velocity. The impact is expected to lead to some comminution of the solid particle in the pulp which further results in exposure of the ore to the lixiviant, permitting an enhanced attack on the ore in the pulp and thus improving the reaction kinetics.

Mauricio Torem

Excess boron in drinking and irrigation water is a serious environment and health problem because it can be toxic to many crops and lead to various human and animal diseases with long-term consumption. Mauricio Torem, of PUC-Rio, Brazil, showed how the removal of boron from aqueous solution was carried out by electrocoagulation using aluminum electrodes as anode and cathode.

Sylvi Schrader

Siderophores are biomolecules, which can form strong complexes with different metals. They are produced by microorganisms and a biotechnological production of these chelators offers an application in different processing methods. Particularly amphiphilic siderophores are very interesting for the froth flotation process, as discussed by Sylvi Schrader, of Helmholtz Institute Freiberg for Resource Technology, Germany in the final paper of the day. The hydrophilic part, carrying hydroxamate groups, is responsible for the binding of the metals. Flotation agents produced by the chemical industry with the same functional groups have already been applied successfully and Sylvi suggested that siderophores carrying the same functional groups also work well as collectors. The fatty acid tail, that is representing the hydrophobic part, contacts the bubbles and avoids additional chemicals and further working steps for making the target mineral particles hydrophobic.

The Windhoek Country Club Golf Club provided the setting for the evening sundowner:

Friday 15th June

Yiannis Pontikes

The second day began with a keynote lecture from Yiannis Pontikes, of KU Leuven, Belgium) who discussed the conversion of iron-rich residues from metallurgical processes into novel materials. A number of hydro- and pyro-metallurgical processes lead also to Fe-rich residues that find limited applications; notable uses are in the raw meal for cement production, as aggregate in concrete, as abrasive blasting grit, and as media in geotechnical and road pavement applications. Yiannis described an alternative process, where the Fe-rich residue is used as raw material in the synthesis of inorganic polymers. These materials show properties comparable to Portland cement while having a smaller environmental footprint. 

The progressive development of new technologies increases the demand for raw materials. But primary resources are finite and mining has to be constantly optimized in order to extract raw materials from larger depths, costs rise and recycling becomes attractive. Recycling of metal-containing waste is currently performed only to a limited extent and huge amounts of potential recyclables fall into oblivion. Conventional recycling strategies based on pyrometallurgical or hydrometallurgical processes are often costly due to high energy requirements and usage of chemicals. As discussed by Rudolf Stauber, of Fraunhofer ISC, Germany, bioleaching offers a green recycling strategy, where leaching of waste material is performed by microorganisms. In this study the recycling potential of end-of life magnets was investigated by means of bioleaching with various bacteria. The highest leaching efficiencies were achieved with bacteria of the ferrooxidans species.  

Rudolf Stauber (right) with Markus Reuter



Zaynab Sadan , of the University of Cape Town, also highlighted that electronic waste is one of the fastest growing waste streams in the world and Africa is no exception. Although generally classified as hazardous waste, e-waste streams contain a diversity of materials which include metals, plastics, glass among other chemical substances. With the appropriate technology, these materials can be gainfully recovered while minimising the otherwise adverse damage that irresponsible disposal or recycling would have on humans and the environment. In the African context, recycling of e-waste presents an opportunity to develop an industry that can allow for the upskilling of the otherwise largely unskilled labour force currently employed in this industry, minimise the diverting to landfills of resource-rich waste streams and promotes the development of a secondary resource economy which is a driving force for sustainable resource management. Jochen presented a review of the current status of the e-waste recycling industry in Africa and how it aligns with sustainable resource management practices. 



Naomi Boxall

Naomi Boxall, of CSIRO Land and Water, Australia, described how Australia is at a crossroads in the management of lithium ion battery (LIB) wastes. In Australia, LIB are not classified as hazardous, despite having significant human and environmental health risks if handled and disposed of incorrectly. Unlike in Europe and Asia, there are no regulations or polices to enforce or encourage product stewardship in Australia, with the majority of small recycling schemes targeting the behaviour of the consumer, and voluntary actions of manufacturers and distributors. Although the manual sorting and dismantling of LIB waste occurs onshore, the valuable components are sent overseas for further processing, because of the limited capacity to recover the inherent metal values. Naomi reviewed the state of play for LIB recycling, considering the projections of LIB waste generation, identification of future trends, opportunities and potential for innovation for LIB recycling in Australia.

While the many definitions of a circular economy (CE) elegantly highlight its many dimensions, ultimately to fully understand the economic viability of the CE, as would be the case for any economically viable processing system, a deep understanding of all the losses, environmental impact and associated risks from the system must be understood and quantified economically, said Markus Reuter, of Helmholtz Institute for Resource Technology, Germany.  A meaningful analysis of the CE can only be made if a detailed understanding is available of the distribution of all metals and materials through the system. Above all, all required fundamental thermodynamic data and physical properties must be available for this analysis so that a simulation basis can be applied to perform this analysis and economic optimization of the complete system – from product design through recycling to final metal, material and energy recovery. This provides a more realistic process engineering analysis of the performance of the significant actors in the CE system. With the objective to improve material recovery and resource efficiency in the electronics sector, it will require brands, manufacturers and recyclers to take a product-centred approach to understand the complete lifecycle, where the inefficiencies occur in the system and which frameworks can offer solutions. To take the first step in this direction, Fairphone is starting by examining the end-of-life phase of its latest smartphone (Fairphone 2) by applying HSC Sim simulation software from Outotec to understand the phone’s recyclability, system environmental footprint, energy recovery as well as exergetic efficiency. Markus discussed these aspects, and there is more on the posting of 19th February.

Edson Charikinya

South Africa is one of the world’s major suppliers of Platinum Group Metals (PGMs). The PGMs are hosted in the Bushveld Complex, which includes three distinct mineral-bearing reefs: the Merensky Reef, the UG2 Reef and Platreef. The ores from the different reefs are processed through a number of stages that include concentration, smelting and refining to produce PGMs and base metal byproducts.  Edson Charikinya, of the University of Cape Town, described the work undertaken to develop Life Cycle Inventory (LCI) datasets, related to the production of PGMs in South Africa. A new modelling approach which aims to provide LCI metal datasets that have the highest possible degree of modularity was used. In this approach the primary production of PGMs was modelled by linking together datasets that represent different processing stages. Challenges encountered in implementing this new modelling approach were described, along with results of LCI datasets as built primarily from published company reports complemented by mass balance modelling.

Markus Reuter presented a simulation-based methodology to calculate the cost of recycling and waste treatment. Unlike conventional analysis, this methodology uses the Second Law of Thermodynamics to introduce the entropy concept to the analysis, so the quality of the flows of the system is also considered. The methodology was tested in a copper production process. The simulated process starts with a copper ore and a concentration plant through flotation. Then, copper cathodes are produced through the pyrometallurgical route of copper. As several residues are produced, i.e. dust, slags or off-gas, a sulfur capture plant and a gold refining stage is linked to the flowsheet. Once the process has been simulated with HSC Chemistry, a thermoeconomic analysis is conducted. Therefore, the cost of the copper production itself and including the sulfur capture and gold recovery is obtained.

Corby Anderson, of the Colorado School of Mines, USA, was scheduled to present the final paper of the morning, but unfortunately United Airlines had left him stranded in Washington. His paper, describing a novel process that has been developed for the dezincing of galvanized steel, can be found in the conference Proceedings.

Corby's absence allowed us to take a very long leisurely lunch and enjoy the fine food in the hotel restaurant.

As discussed by UCT’s Sue Harrison, appropriate handling and disposal of coal waste is key to maximize the sustainability performance in coal processing activities. Fine particulate material comprising the desulfurized fraction of fine coal ‘waste’ streams from a two-stage flotation process was considered as the substratum for manufacture of fabricated soils, with potential for use as top soil in the rehabilitation of mine sites.  Coal waste and native soil from the Middelburg area in South Africa were used as the main substratum. Compost, anaerobic digested sludge and microalgae were added as organic matter and nutrient source. Malt residue from a micro brewing process were used as physical ameliorant. In order to validate the potential of the fabricated soils, germination and growth of the grass Eragrotis Teff indigenous to the Mpumalanga region was investigated. The germination and growth experiments showed the soil mixtures amended with malt residue gave a better response in terms of final biomass production. According this study, the use of these soil substitutes could reduce the amount of top soil used in land restoration by up to 75%. This use would significantly reduce the land-use footprint and the social and environmental impact of mining activities, thus promoting the circular economy zero-waste strategy. 

Desulphurization must be considered as an interesting approach to reclaim abandoned mines along with the recovery of valuable elements. Indeed, desulphurization produces sulfide-lean tailings, used as a mine cover, and sulfide-rich concentrate, which can contain gold associated with sulfides. Because of the weathering of old tailings, layers of oxidation products are formed on the surface of these minerals. This surface oxidation reduces sulfide hydrophobicity and consequently flotation efficiency. Ahlem Skandrani, of Université du Québec en Abitibi-Témiscamingue, Canada, described a study whose main goal was the establishment of mechanical pre-treatments of old tailings that will facilitate flotation, to ultimately produce a final desulphurized tailings and a sulfide concentrate with gold recovery. Results show that it is possible to produce a concentrate rich in sulphide and gold. Mineralogical characterization also confirms mechanical pre-treatment selection and efficiency by removing oxidation products at the particles surfaces.

Ahlem Skandrani with Zaynab Sadan

Cristina Vila

Cristina Vila, of University of Porto, Portugal, described work aimed at the recovery of valuable metals through reprocessing of abandoned mine waste deposits. Cabeço do Pião site, an old tailings dam whose property was transferred from Panasqueira Mine to the Municipality of Fundão in Portugal was used as a case study. The material deposited in the dam constitutes an imminent risk to the environment, in particular to Zézere’s river that flows close to the bottom of the tailings pile and is the main contributor for drinking water supply to the city of Lisbon. Multivariate analysis of chemical data allowed the establishment of mineralogical associations, proving to be a useful planning tool in a future selective re-mining of the tailings pile.

Aino-Maija Lakaniemi

Aino-Maija Lakaniemi, of Tampere University of Technology, Finland, showed how removal and recovery of uranium(VI) from synthetic wastewaters was studied using waste digested activated sludge (WDAS) in its native form i.e. without drying/dewatering. Batch adsorption experiments showed that WDAS can adsorb 200 (± 9.0) mg of uranium per g of WDAS. Desorption of more than 95% of uranium from WDAS was successful with both acidic (0.5 M HCl) and alkaline (1.0 M Na2CO3) eluents, such that the desorbed uranium solution could, in principle, be fed to the uranium ore processing infrastructure.

 To fully understand the limits of the Circular Economy (CE), a comprehensive model taking into account its different stages (product design, mechanical pre-processing, metallurgy, etc.) is required. A crucial aspect is to understand the inevitable losses at different stages of recycling. The complexity of the material streams in mechanical separation processes requires a detailed description of particles and their properties to successfully simulate unit processes. In the final paper of the conference, Juho Hannula, of Helmholtz Institute Freiberg for Resource Technology, Germany, presented a new approach that connects measurement-based particle properties to statistical modelling and simulation of mechanical separation processes. The proposed approach combines particle tracking with the generalization ability of neural networks. In order to demonstrate the new approach, Juho showed how Mineral Liberation Analysis data from magnetic and gravity separation processes of a complex ore was used. The applicability of the proposed approach to modelling and simulation of mechanical recycling processes was also discussed.

Juho Hannula (centre) with Rob Dunne and Rudolf Stauber

Our consultant, Markus Reuter, presented a short summary of the conference, after which MEI's Amanda Wills invited everyone to the next in the series, which will be held in Falmouth, UK, in June 2020.

One of our regular contributors described the series as unmissable events, due not only to the very topical presentations, but also to the 'family atmosphere' engendered by the long breaks, the lack of parallel sessions, and informal social events, such as the final farewell sundowner held by the side of the hotel pool (posting of 16th June).

The draft papers are available on USB from MEI, and authors have been invited to submit final papers for peer review for the virtual special issue of Minerals Engineering.
Twitter @barrywills

Biohydromet '18 Conference Diary

Biohydromet ’18 was MEI’s 9th biohydrometallurgy symposium and was sponsored by Outotec, with International Mining as media partner.

 

Tuesday 12th June

MEI’s Jon Wills opened the conference this morning, welcoming the 50 delegates from 12 countries to the Windhoek Country Club. This is MEI’s first outing in Namibia and we are pleased to be associated with the relatively newly formed Namibia University of Science & Technology. Following Jon’s opening remarks, the Vice-Chancellor of the University Prof. Tjama Tjivikua gave his own words of welcome.

Prof. Tjivikua of NUST, with his colleagues Foibe Uahengo, Godfrey Dzinomwa,
Dick Groot, Jonas Addai-Mensah and Harmony Musiyarira

Sue Harrison

Of the 50 delegates, 32 will be staying on for Sustainable Minerals ’18 which begins on Thursday, the two conferences having a common informal dinner tomorrow evening, so appropriately the first presentation of the day was a keynote lecture by Sue Harrison, of the University of Cape Town, who talked about the role of biohydrometallurgy in the sustainable development of mineral resources (more details on posting of June 12th).

 Outotec's BIOX® process was developed for the pre-treatment of refractory concentrates ahead of conventional cyanide leaching for gold recovery. As the gold is encapsulated in sulfide minerals such as pyrite and arsenopyrite, the gold is prevented from being leached by cyanide. The BIOX process destroys sulfide minerals and exposes the gold for subsequent cyanidation, thereby increasing the achievable gold recovery. Traditionally, cyanide consumption represents a significant operating cost in most gold leach circuits with BIOX® plants included.  Craig van Buuren, of Outotec Biomin, South Africa, discussed how, with an ever increasing environmental and commercial emphasis on cyanide utilisation, expanding its BIOX® technology to meet this challenge saw Outotec continue to develop its MesoTherm technology.  This is a hybrid two-stage process using mesophiles to realise the initial primary stage oxidation and thereafter, using a thermophilic culture to complete the sulphide oxidation.

Craig van Buuren with Jonathan Dean and Mahdi Ghadiri

Craig's paper was followed by an intensive day of papers on bioleaching of complex and refractory ores.

The Horizon2020 funded INTMET Project is composed of twelve partners from seven European Union countries as well as South Africa and Serbia.  The focus of the project is on the beneficiation of low-grade polymetallic and complex ores. Currently there is no economically viable process for on-site metal extraction from these resources and the main objective of the INTMET project is applying on-site and integrated treatment of the resources, combining innovative hydrometallurgical processes and novel more effective metals extraction techniques. The treatment of complex polymetallic concentrates is a niche application for bioleaching processes and Marieke Gericke, of Mintek, South Africa, described the results of test work treating four different polymetallic materials using bioleaching technology.

Marieke Gericke with Rohan Jain, Robert Braun and Guillermo Luque Consuegra

Marieke’s paper took us to an extended coffee break to allow everyone to chat and view the 14 posters on display.

Wallies Olivier, Rosemarie Khoun and Alexsandr Belyi

Amanda Wills, Dick Groot and Mauricio Torem

After the break Mahdi Ghadiri, of the University of Cape Town, discussed the effect of adding surfactant in the leaching solution on the bacterial ferrous iron oxidation and chalcopyrite bioleaching.

The BGR project RoStraMet aims to explore raw material potentials of metals of strategic economic importance worldwide. Bioleaching as a technology for the extraction of trace metals is part of the work plan, and Axel Schippers of Federal Institute for Geosciences and Natural Resources, Germany, showed how bioleaching experiments with a mixed Acidithiobacillus-culture were carried out in shake flasks as well as in percolators with crushed and sieved sphalerite-rich ore with elevated gallium content from a former mine in the German Harz Mountains. An efficient sphalerite dissolution in the bioleaching assays was observed in contrast to the pure chemical leaching experiments and up to 6 g/L zinc and 1 mg/L gallium were measured in the pregnant solution. First data from the simultaneous extraction of major metals and trace metals of strategic importance from this ore type look promising.

Mahdi Ghadiri and Axel Schippers

 

Chris Bryan

Mesophile (40-45°C) bioleaching is exploited in the BIOX® process, and for the recovery of nickel from pyrrhotite/pentlandite. While such plants perform well, the process is unable to leach copper from recalcitrant copper sulfides. Thermophile (70-80°C) bioleaching of copper from chalcopyrite concentrates has been developed to commercial pilot scale. While a technical success, the economics of thermophile bioleaching for copper recovery are borderline at best, driven largely by the requirement of pure oxygen and the restricted operating pulp density (~15 %). Chris Bryan, formerly with Camborne School of Mines, UK, now head of the Geomicrobiology and Environmental Monitoring Unit at BRGM, France, detailed the development of a two-stage continuous system for the recovery of nickel and copper from a polymetallic sulfide concentrate. The concentrate is partially leached by a mesophile consortium, solubilising the majority of the nickel, before a thermophile consortium solubilises the copper and remaining nickel.

Anne-Gwénaëlle Guezennec

In bioleaching processes using autotrophic bacteria, CO2 is the carbon source for the growth of the microorganisms and its availability is dependent on gas mass transfer in the bioreactor. Taking us to the first lunch break, Anne-Gwénaëlle Guezennec, of BRGM, presented a study in which the demand in CO2 was investigated during bioleaching of several sulfidic materials (pyritic tailings, Cu concentrate, coal waste) in STR using the “BRGM-KCC” bacterial consortium. The results show (i) that Fe oxidation (and thus microbial activity) is delayed when air is injected without CO2-supplementation, and (ii) that CO2-supplementation improves leaching kinetics. The study proposes also a methodology to determine G/L transfer components and to assess CO2 limitations in the system. It shows that the microorganisms are not only sensitive to the transfer rate of CO2 from the gas to the liquid phase, but also to the availability of CO2 in solution.  

The first of the excellent lunches in the hotel restaurant

Chloride ions are often challenging in biohydrometallurgical operations, but several studies have found that chloride enhances the bacterial leaching of metal sulfides. In the first paper after an excellent lunch, Dieu Huynh, of TU Bergakademie Freiberg, Germany, described a study which was undertaken to compare the effects of chloride on iron oxidation activity and bioleaching performance of iron oxidizers at mesophilic and moderate thermophilic temperatures.

Dieu Huynh (centre) with Nina Ricci Nicomel and Simon Gregory

There are two principal types of nickel deposits: sulfide and laterite ores. Interest in low-grade Ni-laterite ores has increased in recent years as high-grade Ni-sulfide deposits are being quickly depleted. However, processing of Ni-laterite ores has proven technically difficult and costly, and the development of alternative low-cost biotechnologies for Ni solubilization has been encouraged. In this context, Ellen Giese, of CETEM, Brazil, showed how a sample of Brazilian Ni-laterite was analyzed mineralogically and subjected to bioleaching tests using a Bacillus subtilis strain. Application of microwave heating as a Ni-laterite pre-treatment was also tested, this pre-treatment increasing the bioextraction of Ni.  

Ellen Giese (centre) with Pelin Altinkaya and Elaine Govender-Opitz



Jack Carr

Typically, chalcopyrite concentrates are not considered amenable to mesophile (40-45°C) bioleaching, due mainly to uneconomically slow rates of copper dissolution at such temperatures. At the same time, the cost of ultrafine grinding of concentrates has decreased in recent years. Jack Carr, of Grinding Solutions Ltd, UK, presented an integrated comminution and bioleaching concept, whereby ultrafine grinding is used as a pretreatment of a polymetallic concentrate (pyrrhotite, chalcopyrite, pentlandite) prior to bioleaching (at 42°C) of the slurry directly from the mill. 

Sabrina Hedrich

Platinum group elements are used in many high technology applications and have been classified as critical metals by the EU. Increasing demand combined with rising costs prompts the search for potential alternative resources and environmentally friendly processing technologies. Sabrina Hedrich, of Federal Institute for Geosciences and Natural Resources, Germany , presented results of feasibility tests on the oxidative and reductive bioleaching of various South African Platreef ore samples, including oxidized ore, flotation concentrate and drill core sections, with acidophilic cultures in shake flasks and stirred tank bioreactors. Chemical and mineralogical analyses showed, depending on the ore type, the potential of oxidative and reductive bioleaching as promising processing options for PGE ores.

Aino-Maija Lakaniemi

Little is known about the effects of elevated pressure on bioleaching microorganisms as it is not used in existing biomining processes. Aino-Maija Lakaniemi, of Tampere University of Technology, Finland, discussed the effect of elevated pressures of 1, 10 and 20 bar above atmospheric pressure on the biooxidation of a low-grade gold ore in a continuously-stirred reactor. An enrichment culture containing Acidithiobacillus, Ferrimicrobium and Sulfobacillus sp. oxidized the low-grade ore even at +20 bar. Iron oxidation rate was highest at +1 bar and decreased with increasing pressure. This study demonstrates that reactor biooxidation of sulphidic ores is possible under pressurised conditions and warrants further attention.

Megan Barnett

 Megan Barnett, of the British Geological Survey, UK discussed the sequential extraction of Turkish bauxites, showing that between 4 and 17% total REE are acid soluble (acetic acid) and a further 17 to 42% are reducible (hydroxylammonium chloride) and 2 to 24% are oxidisable (hydrogen peroxide).  To target the acid soluble fraction Aspergillus sp. was used to produce organic acids, and to target the reducible and oxidisable fractions Acidithiobacillus ferrooxidans was grown on either sulphur or ferrous iron. Alternative and sustainable sources of rare earth elements (REE) are critical to sustain a green energy future.  Approximately 300 million tonnes of bauxite are processed annually primarily to extract alumina, but can contain moderate concentrations of REE, offering a potential alternative resource.  The REE in bauxites are associated with a range of mineral phases, including iron oxy-hydroxides, fluorocarbonates (bastnäesite) and phosphates (xenotime). These minerals have been bioleaching targets in other deposits, through microbially-mediated organic acid production or redox reactions. 

Sabine Kutschke

Ion adsorption clay deposits (IAC) are the world's main source of heavy rare earth elements. In situ leaching is the most common extraction technology for REE from IAC's but it is responsible for tremendous environmental damages. Sabine Kutschke, of Helmholtz Institute Freiberg for Resource Technology, Germany, described how new biodegradable leaching agents were tested to extract REEs from an IAC from Madagascar. They are culture broths of S. urea, Y. lipolytica, and B. licheniformis. The culture broth of Y. lipolytica, containing tricarboxylic acids, revealed a generally low recovery except for gadolinium. Pr and Dy were selectively leached by the broth of S. urea. The highest recovery of REE was achieved by the B. licheniformis culture.

It has been an intensive day of fine presentations, so the late afternoon sundowner by the pool was a welcome opportunity to relax and unwind over a few glasses of wine (more pictures on the posting of 13th June).

Wednesday 13th June

Mariette Smart

The BIOX® process for microbial assisted leaching of gold-bearing sulphidic refractory ores and concentrates is catalysed by a mixed bacterial and archaeal community. Traditionally, the mixed culture is dominated by bacterial species such as Leptospirillum ferriphilum and Acidithiobacillus caldus with a small proportion (less than 15%) of archaea. Laboratory operated BIOX® reactors appear to retain the traditional community structure, while industrially operated reactors have been reported to be archaeal dominated (greater than 90%) by species such as Acidiplasma cupricumulans, Ferroplasma acidiphilum and a Thermoplasma sp, exhibiting similar bioleaching performance on the same pyrite/arsenopyrite mineral concentrate. Mariette Smart, of the University of Cape Town, reported on the iron and sulphur oxidising potential of the archaeal dominated BIOX® community compared to the bacterial dominated laboratory BIOX® culture subjected to variations in operating conditions such as pH, temperature and dissolved oxygen. 

Critical heavy metal concentrations can be found in environmental and/or industrial systems. Removal of metals for detoxification (bioremediation) and recovery of metals (geobiotechnology) from natural water bodies or waste waters is challenging because of low concentrated metal ions. Artificial peptides, that able to bind metal ions, are of great potential as they combine unique sensitivity and high specificity. Robert Braun, of Helmholtz Institute Freiberg for Resource Technology, Germany, described the development of peptide-based biosorptive materials for heavy metal removal, including identification, adaptation and characterization of specific peptides binding nickel and cobalt. The study provides a system that can be adapted to other materials and knowledge about the nature of metal-peptide interaction, which may lead to the discovery of novel metal-interacting biomolecules, e.g. enzymes and peptides.

Indium is a critical raw material mainly used in liquid crystal display (LCD) panels. Through urban mining, end-of-life LCDs can thus serve as an alternative source of In. However, although metallurgical processes have been demonstrated to be applicable to waste LCDs, methods used to recover In from resulting process solutions are mostly unfavourable to the environment. Nina Ricci Nicomel, of Ghent University, Belgium, showed how adsorption characteristics of In by microalgal biomass were investigated by batch experiments, a maximum adsorption capacity of 23.1 mg In/g of microalgae being obtained, which is higher than chemically-modified sorbents reported in the literature. Selectivity of indium was also observed over other elements commonly present in waste LCD leach solutions such as Sn, Cu, Zn, and Al. From the initial results, microalgae proves to have potential in In biosorption from aqueous solutions.

Hydrometallurgical process waters often contain various contaminants due to the dissolution of gangue minerals during ore processing. Anna Kaksonen, of CSIRO Land and Water, Australia), discussed the fate and impact of contaminants in a biological iron oxidation and jarosite precipitation process operated at room temperature. Päivi Kinnunen, of VTT Technical Research Centre of Finland, then described the development of a treatment method for mine site tailings to simultaneously leach and recover valuable metals, and to remove negative environmental effects and risks related to tailings, and Cristina Vila, of University of Porto, Portugal, discussed the removal of cadmium and arsenic removal from Panasqueira mine tailings by a microbial consortium.  

Anna Kaksonen, Päivi Kinnunen and Cristina Vila 

Angela Murray



The dual / linked challenges of environmental remediation and global scarcity of strategic and critical elements are issues that are forecast to increase as the 21st century progresses and population / industrialisation continues to rise, said Angela Murray, of the University of Birmingham, UK. The project Beyond Biorecovery: Environmental Win-win by Biorefining of Metallic Wastes into New Functional Materials, held jointly by the Universities of Birmingham, Bangor and Exeter, has for the last three years united a cohort of problem holders, researchers, technology providers and end users to translate biotechnologies to (i) conserve primary resources (ii) reduce the environmental impacts of primary resource extraction/refining and  (iii) bypass their commercial refining, making new 'green products' for sustainable energy. Angela presented three case studies from the project (catalysts / electricity production, solar light upgrading and radioactive waste capture) discussing the technology, proposed supply chains and routes to commercialisation.  Each included a life cycle analysis to compare traditional extraction and processing routes for these strategic elements with the comparable biotechnology taking into account environmental as well as techno-economic factors.

Both coal and hard rock mining operations result in a large amount of waste rock and discards. These wastes are an environmental concern. Exposure of sulfide minerals present in these discards to natural oxidants cause acidic runoff referred to acid rock drainage (ARD). Typically used as a means to extract base metals from low grade ores, Sue Harrison, of the University of Cape Town, showed how heap leaching presents an opportunity in long-term ARD prevention. It has potential as an easily implementable and cost-effective approach to biodesulfurisation. Upon the controlled initiation of the bioleaching reactions, the acid generated within these systems can be used to sustain the desulfurization process by utilising the acidic leachate as an ARD mitigating asset. The iron solubilized is microbially oxidized to ferric iron, facilitating further leaching. Consequently, leaching reactions are accelerated to produce environmentally benign waste with economic prospects.

Pelin Altinkaya

In the final paper of the morning Pelin Altinkaya, of Outotec Research Centre, Finland discussed the effect of biological pretreatment on metal extraction from flotation tailings for chloride leaching. She showed that the combination of biological pretreatment and chloride leaching can improve the extraction of valuable metals from low-grade tailings as non-toxic processes.

 Characterisation of ARD generation potential of mine wastes, through static and (bio)kinetic tests, is critical for its effective prediction and thus mitigation through treatment and disposal. The current batch biokinetic test developed at the University of Cape Town (UCT) accounts for microbial activity, not considered in the static tests and provides kinetic data, collected over a 30-90 day period. It does not, however, represent the typical contacting mechanism for waste rock well nor does it account for washout of neutralising capacity typical of a flow-through system. Didi Makaula, of UCT, showed how refinement of the batch biokinetic test into a flow-through test will remove these limitations.

Didi Makaula, with Jonathan Dean, Mahdi Ghadiri and Svitlana Lyubchyk

The last three papers focussed on bioleaching methods for metal recovery from printed circuit boards.  The metal constituents of PCBs primarily include copper, lead, aluminium, tin and iron alongside other heavy metals such as nickel, zinc and cadmium.  The ongoing generation of electronic waste (eWaste), driven by rapid electronic and technological innovation, has provided a metal-rich waste stream with potential to form a key resource from which metals may be recovered and recycled in line with the desire for an increasingly circular economy.  Bioleaching has demonstrated promise as a processing option for the recovery of valuable base metals from eWaste and pretreatment of the PCB for further recovery of precious metals. The microbes generate the leach agent (ferric iron) that facilitates solubilisation of the metals embedded within PCBs. 

Stoyan Gaydaedzhiev, of University of Liege, Belgium, discussed the effects of operational parameters on the bio-assisted leaching of copper from PCBs, which form an integral part of numerous electronic devices and contain 28 - 30% metal. The boards were initially subjected to proprietary pyrolysis resulting in a copper-rich char.

Stoyan Gaydaedzhiev and Agathe Hubau

Catherine Edward

However, as discussed by Catherine Edward, of University of Cape Town, numerous metals are known to elicit inhibitory effects on microbial leaching performance.  Catherine and her co-authors quantified the effect of key metals associated with eWaste on microbial oxidation of ferrous iron and the subsequent generation of the ferric lixiviant. Using the ratio of metals present on typical PCBs, copper has been demonstrated to be most inhibitory to microbial biooxidation.  Further, in mixed metal solutions, the inhibitory effects are cumulative. The data collected in this study were used to provide insight into the mode of microbial inhibition incurred on exposure to PCB-associated metals.  Adaptation of the microbial culture to the presence of copper improved performance in both copper-containing solutions and in mixed metal solutions. 

Agathe Hubau, of BRGM, France, argued that the efficiency of bioleaching of WEEE is strongly dependent not only on the microorganisms but also on the design of the reactor, since solid-liquid-gas mass transfer plays an important role. She described how comminuted spent PCBs were bioleached into a double-stage continuous bioreactor. The first stage of the bioreactor is a bubble column used to oxidize iron(II) into iron(III) which was inoculated with an acidophilic consortium (BRGM-KCC) mainly composed of Leptospirillum ferriphilum and Sulfobacillus benefaciens. The resulting lixiviant solution was sent to the second stage where bioleaching of PCB occurred under mechanical stirring. The bubble column, in the first stage, favors the growth of microorganisms, which may be limited in the second stage due to the presence of inhibitory metals in solution. Such a double-stage reactor is particularly performant to achieve high bioleaching efficiency.

Conference consultant Chris Bryan summarised the conference, after which MEI's Amanda Wills invited everyone to the next event in two years' time, which will have the new title of Biomining, to reflect the increasingly important role of biohydrometallurgy not only in primary mining, but in the treatment of wastes, bioremediation, and the use of biological reagents in flotation. During the final farewell coffee session, prior to leaving for the conference dinner (posting of 14th June), Akexandr Belyi, of JSC "Polyus Krasnoyarsk", Russia's largest gold mining company, and one of the top 10 gold mining companies globally, gave an informal presentation on its unique biohydrometallurgical operations, which I hope we will hear more of at Biomine '20.

The general consensus was that this has been an excellent event showing how biohydrometallurgy is moving on within the industry. The draft papers are available on USB from MEI, and authors have been invited to submit their final papers for review for a virtual special issue of Minerals Engineering.

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