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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