Biohydromet ’16 was the eighth International Symposium on Biohydrometallurgy organised by MEI with consultants Prof Sue Harrison, Dr Patrick d’Hugues and Dr Chris Bryan and it was sponsored by Outotec, with International Mining as media partner. There were 65 delegates from 19 countries at the St. Michael’s Hotel, Falmouth, UK.The technical sessions got underway with a keynote presentation from Frank Roberto of Newmont Mining, who discussed the commercial heap bio-oxidation of refractory gold ores, revisiting Newmont’s successful deployment at Carlin, the parameters that influenced performance of the on-off heap bio-oxidation process, and factors that led to the discontinuation of the operation. The potential for in-situ bioleaching to extract metals from deep-buried sulphide ores via the BioMORE concept is interesting and in the second paper of the day Eva Pakostova, of Bangor University, UK, described the BioMOre design concept, and presented data from experiments in which a polymetallic ore (Talvivaara, Finland) and copper-rich kupferschiefer (Rudna mine, Poland) have been subjected to indirect bioleaching under laboratory conditions. Results confirm the possibility of using such an approach for deep in situ biomining of base metal ores. Jarno Mäkinen of VTT Technical Research Centre of Finland explained that uranium ores occasionally contain remarkable concentrations of phosphorus minerals. and although phosphorus is a valuable element, it is easily lost in traditional uranium processes; moreover it can disrupt the uranium recovery. He showed how bioleaching was used to recover uranium and phosphorus separately from an artificial uranite-fluorapatite ore and the potential for winning both uranium and phosphorus from complex, impure ores, increasing their value and utilization possibilities.Sarah Smith gave the second Bangor University paper of the morning. She explained how the world-wide demand for cobalt is increasing significantly as a result of its use in electronics, chemicals and super-alloys for example, and lack of suitable alternatives necessitates the development of novel cobalt extraction and recovery technologies. She discussed the oxidative and reductive bioprocessing of cobalt bearing ores, and the recovery of cobalt minerals via biosulphidogenesis.Bioleaching of metal sulfides in a presence of chloride is still very problematic but Marek Kaszuba, of TU Bergakademie Freiberg, Germany, showed how leaching is possible with Ferrimicrobium acidiphilum.High voltage breakage (HVB) has the ability to pre-weaken ore by inducing micro-fractures along grain boundaries. It has been suggested that there may be beneficial effects on mineral leaching via improved grain accessibility using HVB over mechanical comminution alone. Conference consultant Chris Bryan, of the University of Exeter, reported on the first ever investigation of the effect of HVB on bioleaching, discussing the work, carried out in collaboration with Swiss company Selfrag AG, in the context of energy input, breakage mechanism, ore permeability and potential disruption of galvanic interactions.The University of Cape Town (UCT) had five presentations this week, all co-authored by MEI Consultant Sue Harrison. In the first of these papers, Elaine Govender-Opitz showed how recent studies of microbial growth within heap leaching systems have found higher microbial populations associated with the mineral (interstitial liquid and ore phases) than in the bulk flowing pregnant leach solution. However, little information on microbial growth rates on low-grade whole ore during the start-up phase of heap and column leaching is available. Recent work at UCT has extended the knowledge base of growth and activity of mesophiles on low-grade ore in a simulated heap bioleaching environment.Micro-organisms with importance to mineral biotechnology are commonly maintained through subculturing, which can be labour intensive and expensive. Subculturing can also result in contamination, genetic drift and loss of traits or whole strains. Naomi Boxall, of CSIRO, Australia, presented results of a study aimed at determining the best method for the preservation of mixed microbial cultures capable of bioleaching chalcopyrite under salt stress.A second paper from the University of Cape Town discussed how microbial colonization of mineral ore is critical in efficient mineral solubilisation for metal recovery via biohydrometallurgy. Didi Makaula described the use of isothermal microcalorimetry to measure the metabolic activity of the mineral-associated microbial community in bioleaching. This was followed by three papers from Germany. Simone Schopf of TU Bergakademie Freiberg discussed comparative genomics on Acidithiobacillus ferrooxidans, and Sabrina Hedrich of Federal Institute for Geosciences and Natural Resources discussed the development of molecular assays to efficiently monitor and quantify microbial species during bioleaching of copper-rich ores. In the final paper of the day Fabian Giebner, of TU Freiberg, discussed the toxicity of leaching additives on the respiration activity of Acidithiobacillus ferrooxidans.The merger of the BIOX, ASTER and HiTeCC technologies with Outotec Finland was completed in November 2015 (covered in IM’s gold recovery article in August). This was a significant step for the three technologies as the technologies are now owned by Outotec. The second morning’s keynote paper was given by Jan van Niekerk, Senior Manager of BIOX, Outotec South Africa. The paper focused on three main points: 1. An update on the status of the current operating BIOX and ASTER plants; 2. Feedback on the progress with the commissioning of BIOX and ASTER plants and the Runruno gold project in the Philippines; and 3. The expanded technology and equipment offering being developed by Outotec.The use of oxygen is a well-known practice in high-temperature bioleaching reactors, whereas air is usually preferred in medium and low-temperature operations due to economic constraints. Under high-sulphide loading conditions, as is the case with high-grade metal sulphide concentrates, the microbial and chemical demand for oxygen is significantly increased during the bioleaching process, which requires the injection of large amounts of air and thus increases the energy costs of the process. Anne-Gwenaelle Guezennec, of BRGM, France, showed how sparging with oxygen enriched gas instead of air may offer an interesting alternative process option to improve gas transfer in the bioleaching reactor and to provide an adequate oxygen supply in order to satisfy the oxygen demand. Stoyan Gaydardzhiev, of the University of Liege, Belgium, discussed the role of solution potential on the reductive leaching of Co(III) from oxide ore in the presence of mesophilic bacteria and added pyrite, suggesting a flowsheet encompassing ferrous/ferric iron cycling supported by bacteria/pyrite interaction as a means to control solution redox potential.The dissolution of mineral sulfide concentrates in bioreactors at 45 to 55°C is more rapid than at lower temperatures. While it is not as rapid or efficient as at higher temperatures, it utilizes moderately thermophilic bacteria that remain active at solids concentrations that inhibit extreme thermophiles. Paul Norris, of the University of Exeter, UK discussed factors that could be used to select the most useful bacteria for copper and nickel concentrate processing at temperatures above 50°C.Finland has several mineral deposits where gold is the main commodity. Finnish gold ores are often refractory, requiring pretreatment prior to cyanide leaching to enhance gold recovery. Sarita Ahoranta, of Tampere University of Technology, Finland showed how bio-oxidation is a commercially viable pretreatment method that improves gold availability to cyanidation, resulting in savings in the overall process.Susan Reichel, of G.E.O.S. Ingenieurgesellschaft mbH, Germany, then discussed how lithium can be recovered from lithium-containing micas using sulfur oxidizing microorganisms. In another paper from Germany, Sophia Kostudis, of the Helmholtz Institute Freiberg for Resource Technology, explained that the European Kupferschiefer deposits constitute a challenging local resource of base metals such as copper. She summarised research results on bioleaching of copper from Kupferschiefer ore in neutral to alkaline environments.Biooxidation is a technology employed for pre-treatment of refractory gold concentrates prior to cyanidation. Biooxidation utilises a microbial community to regenerate pyrite-leaching agents, thereby liberating gold for extraction. Historical process upsets suggest that the microbial community is sensitive to thiocyanate (SCN-) at concentrations as low as 1 mg/litre. Catherine Edward, of the University of Cape Town, described a study focusing on Acidithiobacillus caldus, a predominant sulphur oxidiser within the bio-oxidation community, and its tolerance to elevated concentrations of SCN- (> 1 mg/litre).Chris Bryan, of the University of Exeter, discussed the microbial ecology and solution chemistry of interstitial and flowing liquid phases during the bioleaching of a low-grade sulphide ore.Mingjian Zhang of the General Research Institute for Nonferrous Metals, China, showed how the collaborative bioleaching of chalcopyrite by Alicyclobacillus and acidophiles could increase the efficiency of the acidophiles.The north-central part of Portugal has a promising potential in lithium ores from pegmatites and aplite-pegmatites that have been exploited solely for the production of quartz and feldspar. Bioleaching of lithium ores or concentrates seems to be an interesting process, although little is known about this subject. Cristina Vila, of the University of Porto, described preliminary exploratory studies on the bioleaching of a pegmatite lithium ore from the Gonçalo area.This was followed by two papers from China’s Central South University. Jin-Lan Xia described a study on microbe-mineral interaction and their molecular mechanism based on synchrotron radiation techniques and then presented results on a comparative study of S, Fe and Cu speciation transformation during chalcopyrite bioleaching by mixed mesophiles and mixed thermophiles.In the final paper of the day Cristina Povedano-Priego, of the University of Granada, Spain, presented work on the fungal biomineralization of pyromorphite and cerussite on the surface of lead metal, showing that fungi contribute, together with abiotic factors, to the biomineralization of pyromorphite, a very stable form of lead useful for the bioremediation of lead contaminated sites. The final day of the conference dealt with environmental aspects, intending to overlap with the Sustainable Minerals ’16 conference that followed (see tomorrow’s post).In the first paper Ana Santos, of Bangor University, UK, discussed acid mine drainage, one of the most important problems affecting mining companies around the world, and the potential for remediation of acidic metal-rich waste waters using sulphidogenic bioreactor sustained by algal biomass. Acidic waters draining active and abandoned mines are usually rich in sulphate which can complex aluminium to form oxy-hydroxysulfates, which are toxic to many organisms. Carmen Falagan, also of Bangor, presented results on a study aimed at testing the hypothesis that it is possible to remove aluminium from contaminated acid waters via biosulfidogenesis.As discussed by Alex Opitz, of University of Cape Town, the rate of acid rock drainage generation is exacerbated by the regeneration of lixiviates by iron- and sulphur-oxidising micro-organisms. Microbial action is excluded from current ARD characterisation and prediction methods. The recently developed UCT biokinetic test provides initial rate information on acid neutralising and acid generating behaviour of waste samples under microbially-mediated conditions. To date, a mixed mesophilic culture containing iron- and sulphur-oxidising micro-organisms in a non-microbially limited environment has been used to study the ARD generating behaviour of waste samples, the findings indicating potential configuration of waste coal dumps.Shafiq Alam, of the University of Saskatchewan, presented a paper discussing the treatment of mine-site polluted water through biosorption.Waste materials from metal mining, such as mineral tailings, often contain significant amounts of potentially valuable metals, particularly where, as in many historic operations, the efficiency of flotation technologies used to concentrate target minerals was not as great as at present. In a third paper this morning from Bangor University, Carmen Falagan discussed new approaches for recovering metals from such mine wastes.Continuing with this theme, Shreya Ghosh of Siksha O. Anusandhan University, India, showed how manganese recovery from mining waste can be enhanced by using a mixed culture of indigenously isolated bacterial strains.Pyrometallurgical processes for sulphide concentrates produce slag that contains metals as carry-over impurities. Anna Kaksonen, of CSIRO, Australia, showed how varied quantities of the metal content can be solubilized from the slag through chemical or bioleaching. Production of high grade steel also generates vast amounts of slag, which is a potential source of valuable elements such as vanadium, and Viktor Sjöberg of Örebro University, Sweden, discussed work on the bioleaching of steel slag for metal recovery.In the final paper of the morning Axel Schippers of BGR Hannover, Germany showed that there is economic potential for reprocessing copper mine tailings in Chile. Anita Parbhakar-Fox, of the University of Tasmania, presented the first paper of the final session on a study aimed at evaluating if reprocessing is a viable option for managing the historic Old Tailings Dam in Western Tasmania. The dam contains 38 Mt of pyritic material, and is actively generating acid and metalliferous drainage. Consequently, the water quality of the adjacent Savage River has been impacted, with elevated copper relative to international drinking water standards measured downstream. Several processing options have been evaluated including bioleaching.Danilo Borja Padilla is from Equador, and is currently doing an MSc at the Chonbuk National University, Republic of Korea. He presented work on the continuous tank bioleaching of mine tailings, containing high amounts of arsenic, by a mesophilic bacterial culture. As explained by Michael Schlömann of TU Bergakademie Freiberg, Germany , some bacteria are able to live in the presence of arsenic, because they have different mechanisms to deal with the toxicity of this metalloid. She discussed a screening assay on siderophore production and extraction, developed to evaluate the capacity of metabolites formed to bind arsenic.Coal waste generates much acid mine drainage, so reducing coal waste storage by finding new uses for the waste is attractive. Beatriz Firpo, of the Universidade Federal do Rio Grande do Sul, Brazil, showed how coal waste can be used as one of the components of plant growing medium, namely fabricated soils, cultivated with Panicum maximum.Following this final paper of the conference, MEI consultant Sue Harrison, of the University of Cape Town, summarised the event. Biohydromet ’18 is hoped to be held in Windhoek, Namibia, in June 2018.The conference draft papers are available from MEI and authors have been invited to submit their final papers to Minerals Engineering, for a special biohydrometallurgy issue which will be published early next year.