86 research outputs found

    Quantifying the effects of mass transport in the curing and leaching of agglomerated ores using X-ray Microtomography

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    Agglomeration and subsequent curing are widely used as pre-treatments for ore prior to heap leaching as they both improve the permeability of the heap and bring leaching solution into close contact with the ore, initializing the leaching reactions. In this thesis, a low-grade copper sulphide ore was used for the experiments and two different agglomeration/leaching solutions were tested, namely a more standard sulphuric acid solution including ferric/ferrous ions, and a solution which also contained chloride ions. A novel image processing methodology was developed to track grains over both the curing and leaching process, taking into account the anisometric changes experienced by the agglomerates and the formation and depletion of species. A combination of XMT and SEM/EDX was used to characterise the chemical and mineralogical changes occurring over both processes. The formation and depletion of mineral components were quantified and tracked beyond the typical time scales used industrially, highlighting that the presence of chloride ions makes a substantial difference to the chemical and structural evolution of the agglomerates. Over the curing process, at least 20 days are required to perceive a significant degree of dissolution. Reprecipitation of metal containing species was observed, especially near the agglomerate surfaces. These precipitates are water-soluble species, and 50% of the initial sulphides were extracted from the agglomerates containing chloride ions, but only 20% from the other agglomerates after curing and water washing. A model of the agglomerate behaviour over the curing process is proposed based on the results observed from the XMT measurements. This model considers both the metal dissolution extent, as well as the reprecipitation of species due to water evaporation. The mathematical model is explained together with the computational approach used to solve it, and the simulation results are compared with the experimental results. This model is able to successfully predict the trends seen in the experiments, with the relative reaction and evaporation rates being a controlling factor. The leach performance was assessed for agglomerates leached using the same recipes used for the agglomeration stage. The compaction and changes in microporosity in the sample were quantified, showing that these changes do not significantly influence the leaching performance. By taking advantage of the more selective leaching that takes place when chloride ions are added to the leach solution, the leaching variability in the system was assessed. SEM/EDX measurements were then used to calibrate the XMT quantifications, isolating the dissolution of copper-containing grains from the pyrite dissolution. It was, thus, possible to quantify the surface kinetics of the hundreds of thousands of grains in the sample, with these kinetics being represented by a family of bi-modal curves. It was shown that the mass transport and mineralogical changes occurring throughout the curing and leaching processes could be quantified both at the grain-scale and the macro-scale by using the developed methodology for combining SEM/EDX measurements with XMT. By incorporating this data into particle scale and, ultimately, heap scale leach models, improved predictions and optimisation of leach performance can be made.Open Acces

    Acidithiobacillus ferrooxidans metabolism: from genome sequence to industrial applications

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    <p>Abstract</p> <p>Background</p> <p><it>Acidithiobacillus ferrooxidans </it>is a major participant in consortia of microorganisms used for the industrial recovery of copper (bioleaching or biomining). It is a chemolithoautrophic, γ-proteobacterium using energy from the oxidation of iron- and sulfur-containing minerals for growth. It thrives at extremely low pH (pH 1–2) and fixes both carbon and nitrogen from the atmosphere. It solubilizes copper and other metals from rocks and plays an important role in nutrient and metal biogeochemical cycling in acid environments. The lack of a well-developed system for genetic manipulation has prevented thorough exploration of its physiology. Also, confusion has been caused by prior metabolic models constructed based upon the examination of multiple, and sometimes distantly related, strains of the microorganism.</p> <p>Results</p> <p>The genome of the type strain <it>A. ferrooxidans </it>ATCC 23270 was sequenced and annotated to identify general features and provide a framework for <it>in silico </it>metabolic reconstruction. Earlier models of iron and sulfur oxidation, biofilm formation, quorum sensing, inorganic ion uptake, and amino acid metabolism are confirmed and extended. Initial models are presented for central carbon metabolism, anaerobic metabolism (including sulfur reduction, hydrogen metabolism and nitrogen fixation), stress responses, DNA repair, and metal and toxic compound fluxes.</p> <p>Conclusion</p> <p>Bioinformatics analysis provides a valuable platform for gene discovery and functional prediction that helps explain the activity of <it>A. ferrooxidans </it>in industrial bioleaching and its role as a primary producer in acidic environments. An analysis of the genome of the type strain provides a coherent view of its gene content and metabolic potential.</p

    Bioprocess Monitoring and Control

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    Process monitoring and control are fundamental to all processes; this holds especially for bioprocesses, due to their complex nature. Usually, bioprocesses deal with living cells, which have their own regulatory systems. It helps to adjust the cell to its environmental condition. This must not be the optimal condition that the cell needs to produce whatever is desired. Therefore, a close monitoring of the cell and its environment is essential to provide optimal conditions for production. Without measurement, no information of the current process state is obtained. In this book, methods and techniques are provided for the monitoring and control of bioprocesses. From new developments for sensors, the application of spectroscopy and modelling approaches, the estimation and observer implementation for ethanol production and the development and scale-up of various bioprocesses and their closed loop control information are presented. The processes discussed here are very diverse. The major applications are cultivation processes, where microorganisms were grown, but also an incubation process of bird’s eggs, as well as an indoor climate control for humans, will be discussed. Altogether, in 12 chapters, nine original research papers and three reviews are presented

    Predicting the time related generation of acid rock drainage from mine waste: a copper case study

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    Includes bibliographical references.The mining and beneficiation of coal and hard rock ores generates large volumes of sulphidic waste that may oxidise in the presence of oxygen and result in the generation of acid rock drainage (ARD). In order to effectively manage the long term effects of ARD, there is a need to reliably quantify the associated impacts and how these impacts evolve with time. Traditional laboratory-scale tests only provide a partial picture of ARD generation, and their extrapolation to full-scale deposits is highly uncertain and controversial. This has prompted the development of mathematical models which take into account the governing chemical reaction and physical transport mechanisms. Whilst the accurate and reliable quantification of the time-related ARD profiles requires rigorous mechanistic modeling of both the (bio) chemical reaction and physical transport mechanisms under non-ideal flow conditions, advanced models are complex and only suitable for site-specific studies and operational decision-making contexts. However, in the early stage screening of waste for potential environmental impacts, simple geochemical mass transport models such as PHREEQC can be used. PHREEQC V.2 has capabilities to simulate a wide range of processes that include equilibrium controlled reactions, kinetically controlled reactions and 1-D advective-dispersion transport, and has been used in a wide range of geochemical applications. However, despite its capabilities, little has been published on its applications to ARD prediction. This study focused on the development and application of a PHREEQC based predictive modeling tool, suitable for the early or screening evaluation of the potential long-term ARD risks associated with sulphidic waste deposits

    Physical, chemical, and microbiological characterization of Kettara Mine Tailings, Morocco

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    The mining industry is of major importance to Morocco’s economy. However, the abandoned pyritic mines are a source of potentially toxic elements that can cause the disruption of the surrounding ecosystems, constituting a huge threat to wellbeing and human health. The present study aimed to analyze the physical and chemical characteristics of different types of tailings and to investigate the microbial populations of acidophilic bacteria involved in the oxidation of pyrite. Coarse and fine tailings collected from different zones of the mine (dike and pond) at two different depths (oxidized and non-oxidized residues) were analyzed for their pH, electrical conductivity, total organic carbon, total nitrogen, available P, major elements, and pseudo-total metal concentrations. The abundance of acidophilic bacteria was determined, and some acidophilic bacterial strains were isolated and tested for their metal tolerance. Tailings showed a pH ≈ 2, very low nutritional content, and high concentrations of Cu, As, Zn, and Pb, which were higher in the non-oxidized samples. The microbial counts of iron- and sulfur-oxidizing bacteria were higher than heterotrophic bacteria, with the highest numbers detected in the oxidized fine tailings. The five acidophilic bacteria isolated from the tailings were affiliated to genera Alicyclobacillus and Sulfobacillus, commonly found in this kind of environment.info:eu-repo/semantics/publishedVersio

    Causes and consequences of mine waste microbial community structure

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    Acid mine drainage (AMD) is a widely studied environment in microbiology and geochemistry. However, there have been far fewer detailed studies of the microbiology and biogeochemistry of historic sulfidic mine wastes giving rise to AMD. Key questions have yet to be answered about the ecological mechanisms underlying the relationship between microbial communities and mineral substrates, the environmental features imposing selective pressure on such communities compared to nearby soils and the main ecological principles that can be used to explain such complex relationships. The South West of England has been subject to intensive mining activity, resulting in a variety of mine wastes and disused underground tunnels left undisturbed for decades. The microbial consortia inhabiting these environments make an interesting case study, as they derive from the same region and yet their similarity is unknown. Samples of mine waste and nearby soils were collected from twelve sites in Cornwall and West Devon. Geochemistry and microbial ecology were analysed to study the environmental drivers of microbial community composition. Metals from different fractions of the samples were analysed (total, readily extractable and pore water) and their compositions related to the microbial community. The microbial ecology of most sites appeared to be largely associated with pH, and to a lesser extent to the bulk metals composition. and communities were more diverse in waste sites than nearby soils. This suggested the possibility of strong local adaptation or dispersal limitation. Information on local adaptation of consortia is potentially useful for further manipulations as it provides insights into their performance in defined conditions. Therefore, inocula prepared from the twelve mine wastes were assessed for local adaptation to sympatric and allopatric substrates via a reciprocal transplant experiment. Results revealed that, with the exemption of a few sites, microbial communities were not generally locally adapted. Bioleaching performance (pyrite dissolution) was further analysed to understand how this is improved (or not) through community mixing and coalescence. Four inocula were mixed in all possible sixteen combinations to form new coalesced inocula whose performance was tested in pyrite, showing that coalescence potentially increases performance. The results give insights for the use of communities in biotechnologies such as biohydrometallurgy, as well as the microbial ecology of AMD-generating wastes. This study contributes to the knowledge of the microbial ecology of acidophiles in the scenario of whole communities coalescence and transplant

    Recovering resources from abandoned metal mine waters : an assessment of the potential options at passive treatment systems

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    PhD Thesis Appendices can be consulted at the Philip Robinson Library.Remediation of metal-rich discharges from abandoned mines entails capture of metals within a treatment system and, typically, disposal of the waste. A preferable option would be to recover the metals for reuse. For many long-abandoned mines metal loads are often relatively small, albeit they often cause significant environmental pollution. Low-cost passive treatment systems, in which metals are retained in some form of treatment substrate, such as compost, are often preferred. This thesis investigates the amenability of such treatment systems to resource recovery. Two down-flow compost bioreactors, treating zinc-rich discharges, were the focus of the research: a pilot-scale unit at Nenthead, and a full-scale system at Force Crag, both in Cumbria, England. Laboratory investigations of the Nenthead substrate identified 7,900mg/kg zinc in the upper horizons of the substrate, and 2,400mg/kg in the lower horizons, after two years of operation. Acid leaching tests effectively de-contaminated the substrate with respect to zinc and cadmium. Complete recovery of zinc was observed after ≤30 hours across a range of acid leach tests, although 23-37 days were required before equivalent recovery was achieved by biological leaching. The Force Crag system removed >95% zinc over the first year of operation and, removal rates suggest that after 10 years of operation >20,000mg/kg zinc will have accumulated in the substrate. Substrate de-contamination could offer substantial life-cycle cost savings at passive treatment sites, especially by limiting volumes of material for disposal to landfill. Furthermore, recovery of metals has important implications for resource sustainability and circular economics. Other resource recovery options may exist at abandoned mine sites. At Force Crag 1.6kW of kinetic energy exists in flowing mine water, in addition to thermal energy which could be recovered for space heating applications. Recovering this energy would convert this site into a net-generator of power. Because of their often remote locations, renewable energy may be of particular value to off-grid facilities at some mine sites.partially funded by The Coal Authorit

    Desulphurisation flotation for the selective removal of pyrite from coal discards using microorganisms

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    Mineral beneficiation processes such as base metal and coal mining produce large amounts of waste rock and coal discards that contain significant quantities of sulphide minerals with Acid Rock Drainage (ARD) generating potential. ARD is caused by the exposure of sulphide minerals, primarily pyrite (FeS2), to both water and oxygen, and microorganisms. This is a naturally occurring process, but the exposure of the sulphide containing mining wastes greatly accelerates ARD formation. Thus, ARD is a major issue associated with inactive mines, waste rock dumps and tailings impoundments, which over time presents a major environmental risk. The desulphurisation of coal discards, mine tailings and finely divided waste rock prior to their disposal has been proposed as a method of preventing ARD formation. This involves the selective separation of residual values from the waste rock, followed by selective separation of sulphide minerals – especially pyrite – from the residual waste material using a two-stage froth flotation to obtain a values stream, a low volume sulphide-rich concentrate that can be easily contained, and a high volume benign tailings fraction that can be safely disposed of. The technical feasibility of this two-stage process has been demonstrated; however, the cost of the flotation reagents used in this process are particularly high in comparison to the other operating costs, contributing as much as 75% of the operating costs for desulphurisation of coal fines. Furthermore, apart from being expensive, many of the inorganic flotation reagents are relatively toxic and could be hazardous to the environment due to their slow degradation rate. Microorganisms and their metabolic products have been identified in literature as potential reagents that can be used in the selective separation of sulphide minerals using froth flotation. Just like conventional chemical flotation reagents, the microorganisms assist separation through surface chemical alterations that modify a mineral’s hydrophobic properties, thus facilitating bioflotation. The aim of this study was to investigate the prevention of ARD formation through the desulphurisation of pyrite-containing coal discards and base metal hard rock samples using microbial cultures as alternative bioflotation reagents. In this study the feasibility of using P. polymyxa, R. palustris, R. opacus, B. subtilis, and B. licheniformis as biocollectors for the removal of pyritic sulphur in the second stage of the two-stage desulphurisation froth flotation process was investigated. Microbial screening tests were performed using a pyrite concentrate to assess each microbial culture’s affinity to pyrite and their ability to float the mineral in a batch flotation cell. Attachment experiments and batch bioflotation tests were carried out to screen for a microbial culture that showed potential. Following attachment experiments at pH 4 and pH 7, all microorganisms except B. licheniformis exhibited attachment to pyrite. The level of attachment was different for each microbial culture. P. polymyxa had the highest percentage attachment of 95.6 ± 1.0 % at pH 4 and 97.1 ± 0.7 % at pH 7 after 20 minutes of interaction. Subsequent results from the pyrite-only bioflotation tests revealed that R. opacus, R. palustris and B. subtilis did not affect the floatability of pyrite. P. polymyxa, however, showed a significant effect on the floatability of pyrite, achieving a cumulative mass recovery of 7.0 ± 0.42 % at pH 4 and 81.3 ± 0.4 % at pH 7. Zeta-potential tests revealed that P. polymyxa had the most neutral net surface charge across the pH range tested, while the other microorganisms had a large net positive or negative charge. Based on this result, it was deduced that the hydrophobicity of P. polymyxa as a consequence of its near neutral surface strongly made it seek out a surface to attach to rather than remaining suspended in water. Hence, P. polymyxa was chosen as the bio-collector candidate for the bioflotation separation of pyritic sulphur from coal discard and base metal hard rock samples. Despite the positive batch pyrite bioflotation tests, P. polymyxa was not successful for the flotation of pyrite from the coal discards nor did it upgrade pyritic sulphur to the concentrate, with the bioflotation results not significantly different from the negative control without collector. P. polymyxa did affect the floatability of the base metal hard rock, achieving cumulative mass recoveries comparable with the chemical control using PAX. However, there was no significant upgrade of pyritic sulphur content, with the biofloat achieving 22.6 % total sulphur in the concentrate which was significantly less than the 66.4 % total sulphur recovered with PAX. The study thus yielded positive results from fundamental studies of P. polymyxa’s ability to enhance the flotability of pyrite. However, tests using actual samples were less successful. Although P. polymyxa enhanced the floatability of the base metal hard rock, it did not achieve the aim of obtaining a low volume sulphide-rich concentrate as the PAX did. Recommendations for the continuation of this work include contact angle measurements and FT-IR spectroscopy to better understand the effects of P. polymyxa attachment, as well as performing a kinetic study on the growth of P. polymyxa alongside adaptation of the microbial culture to a pyrite mineral concentrate in order to test if this can improve selective flotation of the desired mineral owing to modified surface properties

    Desulphurisation flotation for the selective removal of pyrite from coal discards using microorganisms

    Get PDF
    Mineral beneficiation processes such as base metal and coal mining produce large amounts of waste rock and coal discards that contain significant quantities of sulphide minerals with Acid Rock Drainage (ARD) generating potential. ARD is caused by the exposure of sulphide minerals, primarily pyrite (FeS2), to both water and oxygen, and microorganisms. This is a naturally occurring process, but the exposure of the sulphide containing mining wastes greatly accelerates ARD formation. Thus, ARD is a major issue associated with inactive mines, waste rock dumps and tailings impoundments, which over time presents a major environmental risk. The desulphurisation of coal discards, mine tailings and finely divided waste rock prior to their disposal has been proposed as a method of preventing ARD formation. This involves the selective separation of residual values from the waste rock, followed by selective separation of sulphide minerals – especially pyrite – from the residual waste material using a two-stage froth flotation to obtain a values stream, a low volume sulphide-rich concentrate that can be easily contained, and a high volume benign tailings fraction that can be safely disposed of. The technical feasibility of this two-stage process has been demonstrated; however, the cost of the flotation reagents used in this process are particularly high in comparison to the other operating costs, contributing as much as 75% of the operating costs for desulphurisation of coal fines. Furthermore, apart from being expensive, many of the inorganic flotation reagents are relatively toxic and could be hazardous to the environment due to their slow degradation rate. Microorganisms and their metabolic products have been identified in literature as potential reagents that can be used in the selective separation of sulphide minerals using froth flotation. Just like conventional chemical flotation reagents, the microorganisms assist separation through surface chemical alterations that modify a mineral’s hydrophobic properties, thus facilitating bioflotation. The aim of this study was to investigate the prevention of ARD formation through the desulphurisation of pyrite-containing coal discards and base metal hard rock samples using microbial cultures as alternative bioflotation reagents. In this study the feasibility of using P. polymyxa, R. palustris, R. opacus, B. subtilis, and B. licheniformis as biocollectors for the removal of pyritic sulphur in the second stage of the two-stage desulphurisation froth flotation process was investigated. Microbial screening tests were performed using a pyrite concentrate to assess each microbial culture’s affinity to pyrite and their ability to float the mineral in a batch flotation cell. Attachment experiments and batch bioflotation tests were carried out to screen for a microbial culture that showed potential. Following attachment experiments at pH 4 and pH 7, all microorganisms except B. licheniformis exhibited attachment to pyrite. The level of attachment was different for each microbial culture. P. polymyxa had the highest percentage attachment of 95.6 ± 1.0 % at pH 4 and 97.1 ± 0.7 % at pH 7 after 20 minutes of interaction. Subsequent results from the pyrite-only bioflotation tests revealed that R. opacus, R. palustris and B. subtilis did not affect the floatability of pyrite. P. polymyxa, however, showed a significant effect on the floatability of pyrite, achieving a cumulative mass recovery of 7.0 ± 0.42 % at pH 4 and 81.3 ± 0.4 % at pH 7. Zeta-potential tests revealed that P. polymyxa had the most neutral net surface charge across the pH range tested, while the other microorganisms had a large net positive or negative charge. Based on this result, it was deduced that the hydrophobicity of P. polymyxa as a consequence of its near neutral surface strongly made it seek out a surface to attach to rather than remaining suspended in water. Hence, P. polymyxa was chosen as the bio-collector candidate for the bioflotation separation of pyritic sulphur from coal discard and base metal hard rock samples. Despite the positive batch pyrite bioflotation tests, P. polymyxa was not successful for the flotation of pyrite from the coal discards nor did it upgrade pyritic sulphur to the concentrate, with the bioflotation results not significantly different from the negative control without collector. P. polymyxa did affect the floatability of the base metal hard rock, achieving cumulative mass recoveries comparable with the chemical control using PAX. However, there was no significant upgrade of pyritic sulphur content, with the biofloat achieving 22.6 % total sulphur in the concentrate which was significantly less than the 66.4 % total sulphur recovered with PAX. The study thus yielded positive results from fundamental studies of P. polymyxa’s ability to enhance the flotability of pyrite. However, tests using actual samples were less successful. Although P. polymyxa enhanced the floatability of the base metal hard rock, it did not achieve the aim of obtaining a low volume sulphide-rich concentrate as the PAX did. Recommendations for the continuation of this work include contact angle measurements and FT-IR spectroscopy to better understand the effects of P. polymyxa attachment, as well as performing a kinetic study on the growth of P. polymyxa alongside adaptation of the microbial culture to a pyrite mineral concentrate in order to test if this can improve selective flotation of the desired mineral owing to modified surface properties

    Recovery of critical and other raw materials from mining waste and landfills

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    The transition to a more circular economy is essential to develop a sustainable, low carbon, resource efficient, and competitive economy in the EU. In this context Critical Raw Materials (CRM) are defined as those which are of particularly great importance to the EU economy and at the same time there is a high risk of supply disruptions. First and foremost, improving the circular use of CRM is a key strategy in improving the security of supply and not surprisingly is an objective of various policy documents. This report delivers on action #39 of the Circular Economy Action Plan: "Sharing of best practice for the recovery of critical raw materials from mining waste and landfills". It builds on discussions held during two 2018 workshops and gathers together six examples of existing practices for the recovery of critical, precious, and other materials from extractive waste and landfills, highlighting technological innovation and contributions that have been made to a more comprehensive knowledge-base on raw materials. The report also provides various estimates of potential recovery of certain materials compared to their current demand. Lessons learnt from the practices include awareness that it is very unlikely that recovery processes can target one or just a few specific materials of great interest and disregard other elements or bulk matrixes. Especially in case of very low concentrations, most of the mineral resources and other bulk materials in which they are embedded must be valorised in order to increase economic viability and minimise waste disposal. As recovery processes can be very energy intensive, environmental and land use related aspects are also particularly relevant even though environmental gains may also occur and, moreover, land space can be liberated and reused for new purposes and services. Finally, availability of data and information on secondary materials as well as a harmonized legislative framework within the EU appear to be crucial for the large-scale deployment of recovery practices.JRC.D.3-Land Resource
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