for Journals by Title or ISSN
for Articles by Keywords
help
  Subjects -> MATHEMATICS (Total: 791 journals)
    - APPLIED MATHEMATICS (33 journals)
    - GEOMETRY AND TOPOLOGY (19 journals)
    - MATHEMATICS (626 journals)
    - MATHEMATICS (GENERAL) (39 journals)
    - NUMERICAL ANALYSIS (15 journals)
    - PROBABILITIES. MATHEMATICAL STATISTICS (59 journals)

MATHEMATICS (626 journals)            First | 1 2 3 4 5 6 7 | Last

Journal of Uncertainty Analysis and Applications     Open Access  
Journal of Urban Regeneration and Renewal     Full-text available via subscription   (Followers: 9)
Journal of Water and Land Development     Open Access   (Followers: 1)
Journal on Chain and Network Science     Full-text available via subscription   (Followers: 2)
Jurnal Penelitian Sains (JPS)     Open Access  
Le Matematiche     Open Access  
Learning and Teaching Mathematics     Full-text available via subscription   (Followers: 1)
Linear and Multilinear Algebra     Hybrid Journal   (Followers: 1)
Lithuanian Mathematical Journal     Hybrid Journal  
LMS Journal of Computation and Mathematics     Free  
Lobachevskii Journal of Mathematics     Open Access  
Logic and Analysis     Hybrid Journal  
Logic Journal of the IGPL     Hybrid Journal  
Logica Universalis     Hybrid Journal  
manuscripta mathematica     Hybrid Journal  
Marine Genomics     Hybrid Journal   (Followers: 1)
Matemáticas: Enseñanza Universitaria     Open Access  
Matematychni Studii     Open Access  
Math Horizons     Full-text available via subscription   (Followers: 2)
Mathematica Scandinavica     Open Access   (Followers: 1)
Mathematica Slovaca     Hybrid Journal   (Followers: 1)
Mathematical and Computational Forestry & Natural-Resource Sciences     Free  
Mathematical Computation     Open Access   (Followers: 1)
Mathematical Geosciences     Hybrid Journal   (Followers: 2)
Mathematical Medicine and Biology: A Journal of the IMA     Hybrid Journal   (Followers: 2)
Mathematical Methods in the Applied Sciences     Hybrid Journal  
Mathematical Methods of Statistics     Hybrid Journal   (Followers: 1)
Mathematical Modelling and Analysis     Hybrid Journal   (Followers: 1)
Mathematical Modelling of Natural Phenomena     Full-text available via subscription   (Followers: 1)
Mathematical Models and Methods in Applied Sciences     Hybrid Journal   (Followers: 2)
Mathematical Notes     Hybrid Journal  
Mathematical Proceedings of the Cambridge Philosophical Society     Full-text available via subscription   (Followers: 1)
Mathematical Proceedings of the Royal Irish Academy     Full-text available via subscription   (Followers: 1)
Mathematical Programming Computation     Hybrid Journal   (Followers: 2)
Mathematical Sciences     Open Access  
Mathematical Social Sciences     Hybrid Journal  
Mathematical Theory and Modeling     Open Access   (Followers: 6)
Mathematical Thinking and Learning     Hybrid Journal   (Followers: 2)
Mathematics and Statistics     Open Access  
Mathematics Education Research Journal     Partially Free   (Followers: 8)
Mathematics in Science and Engineering     Full-text available via subscription  
Mathematics Magazine     Full-text available via subscription   (Followers: 3)
Mathematics of Control, Signals, and Systems (MCSS)     Hybrid Journal   (Followers: 5)
Mathematics Teacher     Full-text available via subscription   (Followers: 12)
Mathematics Teacher Educator     Full-text available via subscription   (Followers: 5)
Mathematics Teaching in the Middle School     Full-text available via subscription   (Followers: 9)
Mathématiques et sciences humaines     Open Access   (Followers: 1)
Mathematische Annalen     Hybrid Journal   (Followers: 1)
Mathematische Nachrichten     Hybrid Journal   (Followers: 1)
Mathematische Semesterberichte     Hybrid Journal  
Mathematische Zeitschrift     Hybrid Journal   (Followers: 1)
Measurement Science Review     Open Access   (Followers: 1)
Mediterranean Journal of Mathematics     Hybrid Journal   (Followers: 1)
Memetic Computing     Hybrid Journal  
Metals and Materials International     Hybrid Journal   (Followers: 1)
Metascience     Hybrid Journal   (Followers: 1)
Methods in Next Generation Sequencing     Full-text available via subscription  
Milan Journal of Mathematics     Hybrid Journal  
Mitteilungen der DMV     Full-text available via subscription  
MLQ- Mathematical Logic Quarterly     Hybrid Journal  
Monatshefte fur Mathematik     Hybrid Journal  
Moscow University Mathematics Bulletin     Hybrid Journal  
MSOR Connections     Open Access  
Multiagent and Grid Systems     Hybrid Journal  
Multiscale Modeling and Simulation     Full-text available via subscription   (Followers: 2)
Nano Research     Hybrid Journal   (Followers: 4)
Nanoscale Systems : Mathematical Modeling, Theory and Applications     Open Access  
Nanotechnologies in Russia     Hybrid Journal   (Followers: 1)
Natural Resource Modeling     Hybrid Journal  
New Mathematics and Natural Computation     Hybrid Journal  
Nonlinear Analysis: Hybrid Systems     Hybrid Journal  
Nonlinear Analysis: Real World Applications     Hybrid Journal   (Followers: 1)
Nonlinear Differential Equations and Applications NoDEA     Hybrid Journal  
Nonlinear Engineering : Modeling and Application     Full-text available via subscription   (Followers: 1)
Nonlinear Oscillations     Hybrid Journal   (Followers: 1)
North-Holland Mathematical Library     Full-text available via subscription   (Followers: 2)
North-Holland Mathematics Studies     Full-text available via subscription  
North-Holland Series in Applied Mathematics and Mechanics     Full-text available via subscription   (Followers: 1)
Note di Matematica     Open Access  
NTM Zeitschrift für Geschichte der Wissenschaften, Technik und Medizin     Hybrid Journal   (Followers: 4)
Numeracy : Advancing Education in Quantitative Literacy     Open Access  
Numerical Analysis and Applications     Hybrid Journal  
Numerical Functional Analysis and Optimization     Hybrid Journal   (Followers: 1)
Numerical Linear Algebra with Applications     Hybrid Journal   (Followers: 1)
Numerische Mathematik     Hybrid Journal  
Online Journal of Analytic Combinatorics     Open Access  
Open Journal of Discrete Mathematics     Open Access   (Followers: 3)
Open Mathematics     Open Access  
Operations Research Letters     Hybrid Journal   (Followers: 5)
Optimization Letters     Hybrid Journal   (Followers: 1)
Optimization Methods and Software     Hybrid Journal   (Followers: 4)
Order     Hybrid Journal  
ORiON     Open Access  
P-Adic Numbers, Ultrametric Analysis, and Applications     Hybrid Journal  
PAMM : Proceedings in Applied Mathematics and Mechanics     Free  
Parallel Processing Letters     Hybrid Journal   (Followers: 1)
Periodica Mathematica Hungarica     Full-text available via subscription   (Followers: 1)
Petroleum Science     Full-text available via subscription   (Followers: 2)
Philosophia Mathematica     Hybrid Journal   (Followers: 1)
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences     Full-text available via subscription   (Followers: 5)

  First | 1 2 3 4 5 6 7 | Last

Journal Cover Process Metallurgy
   Journal TOC RSS feeds Export to Zotero Follow    
   Full-text available via subscription Subscription journal
     ISSN (Print) 1572-4409
     Published by Elsevier Homepage  [2570 journals]
  • Bioleaching behaviour of chalcopyrite in the presence of silver at
           35° and 68°C
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Chalcopyrite bioleaching kinetics has been improved by using catalytic ions able to modify the mechanism of electrochemical dissolution of chalcopyrite through its fixation on the sulphide surfaces. Among these cations, silver has been proven to be the most effective ion for chalcopyrite dissolution with mesophilic microorganisms (35°C). In this way, bioleaching kinetics has been accelerated by means of thermophilic microorganisms (68°C). However, different studies with these bacteria and in the presence of silver have shown no improvement in the copper recovery. This scattered behaviour of the silver-catalysed chalcopyrite bioleaching at 35° and 68°C leads to several questions, such us: is there a different mechanism of the silver attack at each temperature', is there any problem associated with the toxic effect of the catalytic ion on the thermophilic microorganisms' or simply, the surface film formed by the interaction between Ag+ ions and chalcopyrite is different' In an attempt to answer these questions, the influence of the catalyst concentration on chalcopyrite bioleaching at 35° and 68°C has been examined at first place. Furthermore, the composition of the different phases formed on the mineral surface during the attack has been analysed by EDX and electron microprobe. Finally, the bacterial attack on the chalcopyrite has been simulated in an electrochemical cell. The results show that the chalcopyrite attack at 35° and 68°C takes place through different mechanisms, as a consequence of the formation of different compounds during the interactions between silver ions and chalcopyrite. At 35°C a thin layer of silver sulphide was formed, whereas at 68°C a thicker film, mainly formed by metallic silver, was detected. Evidence of a high silver penetration through chalcopyrite cracks at 35°C compared to a silver deposition only on the surface at 68°C was obtained.


      PubDate: 2012-12-15T09:50:33Z
       
  • Acid-bacterial leaching of pyrite single crystal
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      To clarify the role of crystallographic orientation of the ore on the reaction mechanism of bacterial oxidation, single crystals of pyrite were oxidized by using Thiobacillus ferrooxidans and representative plane orientations of (100) and (111) of pyrite were adopted for this purpose. According to SEM and AFM characterization, the surface corrosion associated with microbial oxidation seems different between (100) and (111) planes.


      PubDate: 2012-12-15T09:50:33Z
       
  • Adsorption of Bacillus subtilis to minerals: effect on the flotation of
           dolomite and apatite
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Many strains of bacteria are able to adsorb Ca(II) and Mg(II) ions from aqueous solution and, in some cases, the adsorption can be very specific. For example, Bacillus subtilis typically binds Mg(II) much more readily than Ca(II). Bacteria can also adhere to the surfaces of minerals containing calcium and magnesium, either enhancing or depressing the flotation of these minerals. Since B. subtilis binds Mg(II) preferentially, it was reasoned that adhesion to a mineral containing magnesium and calcium (dolomite) might be quite different from adhesion to a mineral containing only calcium (apatite) and this difference could possibly be utilized in minerals processing. Experiments investigating the binding of Ca(II) and Mg(II) to B. subtilis cells were initiated and anionic collector microflotation of pure dolomite and apatite mineral samples in the presence and absence of these bacteria was performed. Since Ca(II) and Mg(II) also bind to dolomite and apatite, zeta potential measurements as a function of pH in the presence and absence of these ions were performed in order to better elucidate the effect this binding may have on the attachment of B. subtilis to the two minerals.


      PubDate: 2012-12-15T09:50:33Z
       
  • Mineralogical factors affecting arsenopyrite oxidation rate during acid
           ferric sulphate and bacterial leaching of refractory gold ores
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      The acid ferric sulphate and bacterial leach behaviour of compositionally distinct gold-bearing arsenopyrite concentrates from four different ore deposits were compared. The changes during leaching were monitored microscopically, and post-leach samples were examined by means of electron microprobe analysis and Auger Electron Spectroscopy. Results show that the oxidation rate of arsenopyrite is determined by its major and trace element content. Arsenopyrite types which show strong zoning into As-rich and S-rich zones leach rapidly under both ferric sulphate and bacterial leach conditions. Arsenopyrite crystals with finely-interspaced zones leach more quickly than those with a coarse zone distribution. The presence of a cobalt content of as little as 0.1 mass per cent increases the arsenopyrite oxidation rate. During both bacterial and acid ferric sulphate oxidation, arsenic appears to be removed first from the surface of the arsenopyrite crystals, followed by iron, and eventually a thin, non-passivating sulphur layer forms, which persists until the crystal is leached out. The relative leach behaviour of the four arsenopyrite types does not differ between bacterial and non-bacterial leaching. The major difference observed is the strong dependence on crystal orientation during ferric sulphate leaching, and the stronger galvanic effects present during bacterial leaching. The leach rate is also accelerated by the mere presence of the catalytic bacteria. Since the orientation effect would be minimal during fine powder leaching, it is clear that cheaper and more controllable ferric sulphate leach amenability tests can safely be used to predict relative leach behaviour of an ore under bacterial conditions. A prior mineralogical examination of the ore could provide a great deal of information on its subsequent leach behaviour.


      PubDate: 2012-12-15T09:50:33Z
       
  • Semi-continuous bioleaching of heavy metals and trace elements from coal
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      The micro-organisms used in the processes of sulphur elimination from coal by bioleaching are currently considered to play an important part in the dissolving of other elements (Cu, V, Ni, Pb, Cr, Se, As, etc.). In this study an analysis is carried out a process of biodesulphurization of coal and the elimination of certain heavy and trace elements. An 8.4-1itre reactor was used, comprising three columns connected in series with a volume of 2.8 litres each. Twenty elements were studied, in three groups according to the criteria of the National Research Council of the USA, major components found in most coals in large quantities, elements hamafial to the environment and dements of medium and low environmental impact. Of the major components, only iron, calcium and phosphorous are leached throughout the process. Of the harmful dements, it can be said that almost all the cadmiun released is due to bioleaching. Arsenic and boron are also bioleached in the process. Of the elements of medium and low environmental impact, it is our opinion that only copper is dissolved, at least to any great extent, by bioleaching


      PubDate: 2012-12-15T09:50:33Z
       
  • Bacterial succession in bioheap leaching
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Bioheap leaching of secondary copper ores is applied commercially at operations in Chile and Australia. Bioheap leaching of sulfidic refractory gold ores has been demonstrated at large scale. There is limited comprehension of what actually occurs microbiologically in full-scale bioheap operations, despite the commercial achievement of copper ore bioheap leaching and the anticipated technical and commercial success of gold ore bioheap leaching. Copper bioheaps are typically inoculated with the bacteria contained in the raffinate, whereas, sulfidic refractory gold ore bioheaps can be inoculated with bacteria developed in a separate reactor. Chemical and physical conditions within bioheaps change radically from the time the bioheap is stacked and inoculated until bioleaching is completed. Redox, acidity, temperature, oxygen and solution chemistry conditions can vary widely during the oxidation period. Such conditions likely select for microorganisms or may, in fact, effect a succession of organisms in portions of the bioheap. Bioheap solutions are recycled and constituent build-up over time also affects the microbiology. Heterotrophic microorganisms may also play some role in bioheap leaching. Understanding the microbiology of bioheaps is key to advancing commercial bioheap applications. Such knowledge will increase the ore types as well as the diversity of mineral deposits that can be processed by bioheap technology. It will also enable better control of conditions to improve leach rates, metal recoveries and costs. This paper briefly explains commercial practices, describes chemical, physical and microbiological monitoring of bioheap, considers conditions that control microbial populations in bioheaps, and examines the types of ore deposits that could be bioleached, if the microbiology was elucidated.


      PubDate: 2012-12-15T09:50:33Z
       
  • Present and future commercial applications of biohydrometallurgy
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Modem commercial application of biohydrometallurgy for processing ores became reality in the 1950s with the advent of copper bioleaching by what was Kennecott Copper Corporation. Early application entailed dump leaching of low-grade, low-value, run-of-mine material. Dump bioleaching has evolved into a commercially accepted option for copper bioheap leaching of higher-grade, higher value ores. This commercial practice is exemplified at the Quebrada Blanca Mine operation and others. Paradoxically, application of biohydrometallurgy in the pretreatment of refractory gold ores began with processing high value concentrates, using biooxidation-tank processes and was followed by extension to processing low-grade, lower value ores in heaps.Even with the current success of biohydrometallurgical applications in the mining industry, the real potential of biotechnology in mining remains to be realized. As confidence in commercial bioprocessing grows and experience extends the application's knowledge base, innovations and new commercial practices will emerge. Near term future commercial applications will likely remain focused on recoveries of copper and gold.Recent technical advances show that very refractory chalcopyrite can be successfully bioleached. Processes for copper recovery from this mineral will include both heap and stirred-tank reactor systems. Next generation technologies for pretreatment of refractory gold ores will be based on use of thermophilic bacteria for sulfide oxidation. For biohydrometallurgy to commercially advance, the microbiologist must work cooperatively with the practitioners of the technology for mutual understanding of operational limitations and practical constraints affecting the microbiological component.


      PubDate: 2012-12-15T09:50:33Z
       
  • Direct versus indirect bioleaching
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      The dissolution of metal sulfides is controlled by their solubility product and thus the [H+] concentration of the solution and further enhanced by several chemical mechanisms which lead to a disruption of sulfide chemical bonds. They include extraction of electrons and bond breaking by [Fe3+] extraction of sulfur by polysulfide and iron complexes forming reactants [Y+] and electrochemical dissolution by polarization of the sulfide [high Fe3+ concentration]. All these mechanisms have been exploited by sulfide and iron oxidizing bacteria. Basically, the bacterial action is a catalytic one during which [H+], [Fe3+] and [Y+] are breaking chemical bonds and are recycled by the bacterial metabolism. While the cyclic bacterial oxidative action via [H+] and [Fe3+] can be called indirect, bacteria had difficulties harvesting chemical energy from an abundant sulfide such as FeS2, the electron exchange properties of which are governed by coordination chemical mechanisms (extraction of electrons does not lead to a disruption of chemical bonds but to an increase of the oxidation state of interfacial iron). Here bacteria have evolved alternative strategies which require an extra cellular polymeric layer for appropriately conditioned contact with the sulfide. Thiobacillus ferrooxidans cycles [Y+] across such a layer to disrupt FeS2 and Leptospyrillum ferrooxidans accumulates [Fe3+] in it to depolarize FeS2 to a potential where electrochemical oxidation to sulfate occurs. Corrosion pits and high resolution electron microscopy leave no doubt that these mechanisms are strictly localized and depend on specific conditions which bacteria create. Nevertheless they can not be called ‘direct because the definition would require an enzymatic interaction between the bacterial membrane and the cell. Therefore, the term 'contact' leaching is proposed for this situation. In practice, multiple patterns of bacterial leaching coexist, including indirect leaching, contact leaching and a recently discovered cooperative (symbiotic) leaching where ‘contact leaching bacteria are feeding so wastefully that soluble and particulate sulfide species are supplied to bacteria in the surrounding electrolyte.


      PubDate: 2012-12-15T09:50:33Z
       
  • The design of bioreactors
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      A survey of the literature on biohydrometallurgical topics revealed that the papers devoted to bioreactors amount to less than 5 % of the total and refers mainly to the analysis of the performance and m design guidelines of stirred tank and of bubble column machines, the so-called Pachuca tanks. These machines can be defined conventional in the sense that they have been borrowed from chemical engineering and hydrometallurgy and adapted to the requirements of biohydrometallurgical processes. However, past experience has shown that these types of reactors do not fully match the very particular conditions that exist in biohydrometallurgical systems that, quite correctly have been qualified as “hybrid, owingto their specificity since they are characterized by many of the features of hydrometallurgical operations and of biological conversions. Literature data and the author's personal experience demonstrate that one of the present major drawbacks of these reactors is the power requirement, that seriously affects the competitivity of biohydrometallurgy with pyrometallurgy. The factors affecting the performance of biohydrometallurgical reactors are discussed with special reference to the process parameters and an analysis of the conditions to be satisfied by an ideal bioreactor is carried out. In the light of these considerations, the reactors currently operating in commercial plants are examined. The new prospects opened up by recent developments are finally discussed and, also on the grounds of experience recently gained on a laboratory scale, the potentials of machines tailor-designed for the conditions reigning in biohydrometallurgical systems are outlined.


      PubDate: 2012-12-15T09:50:33Z
       
  • Direct versus indirect bioleaching
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Bioleaching of metal sulfides isdis effected by bacteria like Thiobacillus ferrooxidans, Leptospirillum ferrooxidans, Sulfolobus/Acidianus etc. via the (re)generation of iron(III) ions and sulfuric acid. According to the new integral model for bioleaching presented here, metal sulfides are degraded by a chemical attack of iron(III) ions and/or protons on the crystal lattice. The primary iron(III) ions are supplied by the EPS, where they are complexed to glucuronic acid residues. The mechanism of degradation is determined by the mineral structure. The disulfides pyrite (FeS2), molybdenite (MoS2), and tungstenite (WS2) are degraded via the main intermediate thiosulfate. Iron(III) ions are exclusively the oxidizing agents for dissolution. Thiosulfate is consequently degraded in a cyclic process to sulfate, with elemental sulfur being a side product. This explains, why only iron(II) ion-oxidizing bacteria are able to oxidize these metal sulfides. The metal sulfides galena (PbS), sphalerite (ZnS), chalcopyrite (CuFeS2), hauerite (MnS2), orpiment (As2S3), and realgar (As4S4) are degradable by iron(III) ion and proton attack. Consequently, the main intermediates are polysulfides and elemental sulfur (thiosulfate is only a by-product of further degradation steps). The dissolution proceeds via a H2S*+-radical and polysulfides to elemental sulfur. Thus, these metal sulfides are degradable by all bacteria able to oxidize sulfur compotmds (like Thiobacillus thiooxidans etc.). The two mechanisms, based on the mineral structure of a metal sulfide, are summarized in the following Figure 1.


      PubDate: 2012-12-15T09:50:33Z
       
  • Summary
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10




      PubDate: 2012-12-15T09:50:33Z
       
  • Author index
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10




      PubDate: 2012-12-15T09:50:33Z
       
  • Foreword
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9




      PubDate: 2012-12-15T09:50:33Z
       
  • Past, present and future of biohydrometallurgy
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      The history of bioleaching and its microbiololgical basis are summarized. A possible future developmental direction is indicated.


      PubDate: 2012-12-15T09:50:33Z
       
  • Chemical and electrochemical basis of bioleaching processes
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      The bioleaching of sulfide minerals involves electrochemical and chemical reactions of the mineral with the leach liquor and the extra-cellular polysaccharide layers on the microorganisms.The microorganisms derive energy by oxidising the sulfur moiety and ferrous iron, which can be interpreted using electrochemistry and chemiosmotic theory. Recently significant advances have been made in understanding the mechanism by which the bioleaching of sulfide minerals occurs. Kinetic models based on the proposed mechanism are being used successfully to predict the performance of continuous bioleach reactors. The measurement of oxygen and carbon dioxide consumption rates together with the measurement of redox potentials, has led to this further elucidation of the mechanism of bioleaching of sulfide minerals and enabled the kinetics of the sub-processes involved to be determined separately. It has been shown that bioleaching involves at least three important sub-processes, viz., attack of the sulfide mineral, microbial oxidation of ferrous iron and some sulfur moiety. The overall process occurs via one of two pathways depending on the nature of the sulfide mineral, a pathway via thiosulfate resulting in sulfate being formed or a polythionate pathway resulting in the formation of elemental sulfur. For the case of pyrite, the primary attack of the sulfide mineral is a chemical ferric leach producing ferrous iron. The role of the bacteria is to re-oxidise the ferrous iron back to the ferric form and maintain a high redox potential as well as oxidising the elemental sulfur that is formed in some cases. The first two sub-processes of chemical ferric reaction with the mineral and bacterial oxidation of the ferrous iron are linked by the redox potential. The sub-processes are in equilibrium when the rate of iron turnover between the mineral and the bacteria is balanced. Rate equations based on redox potential or ferric/ferrous-iron ratio have been used to describe the kinetics of these sub-processes. The kinetics have been described as functions of the ferric/ferrous-iron ratio or redox potential which enables the interactions of the two sub-processes to be linked at a particular redox potential through the rate of ferrous iron turn-over. The use of these models in predicting bioleach behaviour for pyrite presented and discussed. The model is able to predict which bacterial species will predominate at a particular redox potential in the presence of a particular mineral, and which mineral will be preferentially leached. The leach rate and steady state redox potential can be predicted from the bacterial to mineral ratio. The implications of this model on bioleach reactor design and operation are discussed. Research on the chemistry and electrochemistry of the ferric leaching of sulfide minerals and an electrochemical mechanism for ferrous iron oxidation based on chemiosmotic theory will be presented and reviewed.


      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 8 Mechanical activation in technology
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10

      The efficiency of both mineral processing and extractive metallurgy of minerals depends on the separation of individual mineral components and on the exposure of their surface [8.1]. The production of flotation concentrates, with particle sizes of tens of microns, is not sufficient for many hydrometallurgical processes to operate at their optimum. As a consequence, metallurgical plants require for the effective processing high temperatures and pressures and some sort of concentrate pretreatment. Mechanical activation is an innovative procedure where an improvement in hydrometallurgical processes can be attained via a combination of new surface area and formation of crystalline defects in minerals. The lowering of reaction temperatures, the increase of rate and amount of solubility, preparation of water soluble compounds, the necessity for simpler and less expensive reactors and shorter reaction times are some of the advantages of mechanical activation. The environmental aspects of these processes are particularly attractive [8.2 - 8.4]. This Chapter is devoted to the examples of application of mechanical activation in the treatment of sulfidic concentrates by different technological operations like flotation, leaching and sorption.


      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 7 Influence of mechanical activation on bacterial leaching of
           minerals
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10

      Bacterial leaching is based on processes which occur at atmospheric pressure and low temperatures and are a part of the group of processes called biohydrometallurgy [7.1]. The leaching medium is primarily composed of diluted H2SO4 and iron in both ferric and ferrous forms. There are also a range of organic compounds, such as organic acids, proteins and polysacharides which may be products of bacterial metabolism [7.2 – 7.3]. The microorganism, Thiobacillus ferrooxidans (TF), the most frequently studied with respect to biohydrometallurgical treatment of sulfide-bearing minerals is a motile, non- sporeforming, gram-negative, rod-shaped bacterium [7.4]. TF is a chemolithotropic bacterium and oxidizes virtually all know metal sulfides to sulfate and elemental sulfur to sulfuric acid M e S + 2 O 2 → T F M e S O 4 ( 7.1 ) Furthermore, it oxidizes ferrous ion to ferric ion 2 F e S O 4 + H 2 S O 4 + 0.5 O 2 → T F F e 2 ( S O 4 ) 3 + H 2 O ( 7.2 ) Eight electrons need to be removed from the sulfide species to form sulfate, and it has been suggested that the ferric ion reduction system of the bacteria is involved in this process [7.4]. The energy available (in form of electrons) from the above oxidation reactions is captured by TF in form of adenosine triphosphate, a high energy yield compound and used to supply its energy needs. One of the drawbacks of the application of bacteria is the time of leaching which is typically days as opposed to minutes or hours for chemical leaching. Mechanical activation may give an increase in the rate of leaching due to an increase in the surface area where the attachment of bacteria can occur and by disordering the mineral structure resulting in an overall increase in reactivity. The pioneer work in this field was published by Kulebakin et al. [7.5] who pointed out that the oxidizability of iron, antimony, copper, bismuth, molybdenum, zinc, nickel and lead sulfides in acid solutions with thione bacteria present is increased after grinding of these minerals.


      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 6 Chemical leaching of mechanically activated minerals
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10

      The traditional scheme of metals extraction from minerals involves some processes of mechanical character ameliorating the accesibility of the valuable component by the leaching agent. Leaching represents the key stage in the extraction scheme and its course may be affected by selection and choice of the method leaching and/or by convenient pretreatment of the solid phase. Thermal and mechanical activation belongs among the most important pretreatment methods which influence solid phase leachability. The thermal activation of sulfidic ores aims at transforming the poorly soluble minerals into more soluble forms. That enables better selectivity in transfer of usable metal into solution, nevertheless it appears that some new problems concerning exploitation of the sulfur emissions arise. In the past three decades enhanced public awareness and governmental pressure have focussed on the problem of sulfur oxide pollution. Sulfidic minerals account for a large fraction of the sulfur oxides. The special problem of the minerals is the presence of small amounts of As, Hg, Te, Se which may be emitted together with sulfur in form of oxides by the thermal activation. The mechanical activation of minerals makes it possible to reduce their decomposition temperature or causes such a degree of disordering that the thermal activation may be omitted entirely. In this process, the complex influence of surface and bulk properties occurs. The mineral activation leads to a positive influence on the leaching reaction kinetics, to an increase in the measured surface area and to further phenomena, especially the potential mitigation of environmental pollutants which is becoming increasingly important with time. At present, it is not known whether the kinetics of heterogeneous reactions are determined by the contact area, the structure of the mineral, or both. The required modification of the structure can be achieved by mechanical activation of the mineral, typically by intensive grinding. The breaking of bonds in the crystalline lattice of the mineral brings about a decrease (ΔE*) in activation energy and an increase in the rate of leaching [6.1] Δ E * = E − E * ( 6.1 ) where E is the apparent activation energy of the non-disordered mineral and E* is the apparent activation energy of the disordered mineral. The relationship between the rate of leaching and temperature is usually described by the Arrhenius equation k = Z exp ⁡ ( − E / R T ) ( 6.2 ) where k, Z, R and T stand for the rate constant of leaching for the non-disordered mineral, pre-exponential factor, gas constant and reaction temperature, respectively. For the disordered mineral we can write k = Z exp ⁡ ( − E * / R T ) ( 6.3 ) and after substituting for E* from (6.1) we obtain k * = k exp ⁡ ( Δ E * / R T ) ( 6.4 ) From (6.1) it is clear that exp (ΔE*/RT) > 1 and thus it follows from eq. (6.4) that k* > k, i.e., the rate of leaching of a disordered mineral is greater than that of an ordered mineral. It was Senna who analysed the effect of surface area and the structural disordering on the leachability of mechanically activated minerals [6.2]. In order to solve the problem — whether surface area or structural parameters are predominant for the reactivity, the rate constant is divided by the proper surface area and plot against the applied energy by activation (Fig. 6.1). If the rate constant of leaching divided by the surface area remains constant with respect to the applied energy, as shown in Figure 6.1a, then the measured surface area may be the effective surface area and at the same time, the reaction rate is insensitive to structural changes. If, on the other hand, the value k/Si decreases wi...
      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 5 Thermal decomposition of mechanically activated minerals
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10

      Sulfides exhibit a great variety of chemical and physical properties. They display similar structural defects as oxides with cation vacancies, interstitial cations or anionic defects all possible. However, the concentration, structure and mobility of these defects are much more varied in the case of sulfides [5.1]. The cationic vacancies change their properties according to conditions. For instance, their influence on electric properties and character of the chemical bond of sulfides is dependent on temperature [5.2]. The formation of interstitial defects, in which metal ions are displaced from a normal lattice position to an intermediate position, depends on strength of the metal-sulfur bond. The Me-S and S-S bond in sulfides are similar to each other and the difference between them decreases with increasing temperature. However, if sulfur is released, the metal present in the normal crystallographic position remains without a partner and the defectiveness of sulfide increases. The influence of defects on solid phase reactions is frequently more significant than the influence of the sulfide structure [5.3]. The defectiveness of the structure of solid substance can be affected by different treatments prior to thermal decomposition. The potentials for forming different defects by pretreatment of the solid phase are presented in Table 5.1. Mechanical activation belongs among the effective processes enabling us to control and regulate the course of thermal decomposition of sulfides via formation of different defects.


      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 4 Polymorphous transformations induced in minerals by mechanical
           activation
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10

      It is known that the action of mechanical forces on solid substances frequently leads to polymorphism, i.e. transformation of one crystal structure into another one without chemical change. In this process, the more ordered phases come into existence [4.1]. According to thermodynamics a system at constant pressure and temperature shows a tendency to reach the minimum value of its free energy. If it holds GaGb for two phases, then phase A is liable to turn into phase B. The relationship between pressure p or temperature T and the volumes of both phases is described by the Clausius-Clapeyron equation d p d T = S A − S B V A − V B ( 4.1 ) where Sa and Va are the entropy and molar volume of phase A. Provided VA > Vb, then it holds dp/dT > 0 (the pressure increases with temperature) and the equilibrium shifts to formation of the phase with smaller volume. If VaVB then dp/dT 0 and formation of the phase with larger volume is favoured. The laws of polymorphous transformations of solid substances were described by Buerger in context with coordination of the structure of these substances [4.2]. Later on the description was founded on the transformation mechanism [4.3]. The course of mechanically stimulated phase transformations of some minerals was analyzed by Avvakumov [4.1]. He has alleged that the high local pressures and temperatures at contact surface of the mechanically activated particles as well as the presence of volume defects are responsible for the phase transformations. A pecularity of mechanically stimulated phase transformations is the formation of phases with higher density, unlike thermal transformations where a phase with lower density usually arises.


      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 3 Physico-chemical properties of mechanically activated minerals
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 1 Mechanochemistry and mechanical activation of solids
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 2 Selected methods for the identification of changes in
           mechanically activated solids
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10

      During the history of development of mechanochemistry the number of applied identification methods gradually increased. At the beginning, these methods were directed to at obtaining the characteristics of mechanically activated solid substances, mostly in integral form. This activity encompassed for example, the measurement of specific surface area by sorption methods and the determination of the content of crystalline phase by the methods of X-ray diffraction, etc. At present, the number of methods applied in investigation of mechanically activated substances comprises a few tens. These methods are thoroughly analyzed in special monographs [2.1 -2.5]. This chapter is concerned with principles of five representative identification methods which have been used for characterizing the mechanically activated minerals described in subsequent chapters.


      PubDate: 2012-12-15T09:50:33Z
       
  • Index
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Appendix: Data files
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Introduction
    • Abstract: 2000
      Publication year: 2000
      Source:Process Metallurgy, Volume 10




      PubDate: 2012-12-15T09:50:33Z
       
  • References
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 11 From exploratory data analysis to decision support and process
           control
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 10 Embedding of multivariate dynamic process systems
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 9 Case studies: Dynamic systems analysis and modelling
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 8 Introduction to the modelling of dynamic systems
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 7 Extraction of rules from data with neural networks
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 6 Cluster analysis
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 5 Topographical mappings with neural networks
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 4 Regression Models
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 3 Latent variable methods
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 2 Training of neural networks
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Chapter 1 Introduction to neural networks
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Preface
    • Abstract: 2002
      Publication year: 2002
      Source:Process Metallurgy, Volume 12




      PubDate: 2012-12-15T09:50:33Z
       
  • Bioleaching of a copper sulphide flotation concentrate using mesophilic
           and thermophilic microorganisms
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Pyrometallurgical treatment of sulphide concentrates generates SO2 and, hence, atmospheric pollution. An attractive alternative for metal recovery could be the use of microorganisms due to its low cost and relatively fewer pollution problems compared with conventional hydrometallurgical and pyrometallurgical processes. Bacterial leaching is being commercially well exploited for the copper recovery from low-grade ores. In the present investigation the possibility of copper recovery from a copper sulphide flotation concentrate containing: 29.1% Cu. 21.9% Fe, 1.54% Zn and 23.2% S has been evaluated using both mesophilic and thermophilic microorganisms. Bacterial leaching of copper sulphide flotation concentrates is a complex process, which occurs at a sequential way: chalcocite and digenite are the first minerals to be dissolved, followed by chalcopyfite. Optimal copper recovery was achieved using a moderate thermophilic culture at 45°C. Copper dissolution reached 85% with a copper concentration of 13.8 g/L in solution.


      PubDate: 2012-12-15T09:50:33Z
       
  • Influence of thermophilic microorganisms on the electrochemical behavior
           of pyrite
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      The electrochemical behavior of massive pyrite (FeS2) electrodes has been studied in the absence and in the presence of thermophilic (moderate and extreme) microorganisms using potentiometry, anodic and cathodic polarization and cyclic voltammetry as analytical techniques. The cultures used were moderate and extreme thermophilic microorganosm. First of all, the bacteria cultures were adapted to pyrite. Next, the influence of some physical and chemical factors such as agitation, temperature, scan rate, pH and different nutrient media (9K, Norris and sulfuric acid) was studied in the absence of bacteria. Temperature, scan rate and pH were significant variables influencing the sulfide oxidation. The results showed that in the presence of bacteria the rest potential of the bioleached mineral increased with the leaching time which was related to the electrochemical transformation of the pyrite surface. The pyrite bioleached showed three new signals in the voltammetric scan, one of them corresponding to an oxidation and the other two to reductions. These signals were more important when the attack time increased.


      PubDate: 2012-12-15T09:50:33Z
       
  • Bioleaching of a cobaltiferous pyrite at 20% solids: a continuous
           laboratory-scale study
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      The continuous bioleaching of a cobaltiferous pyrite was carried out at 20% solids in laboratory-scale stirred reactors. Various potentially limiting factors, such as agitation, aeration, dissolved oxygen concentration and nature of the nitrogen source were investigated. Direct measurement of 02 and CO2 consumptions was performed using on-line gas analysers in order to study the physiological behaviour of the micro-organisms during oxidation and to improve the evaluation of oxygen requirements for pyrite oxidation. The study was also used to propose a mathematical model of the bioleaching process, which was calibrated with experimental data.


      PubDate: 2012-12-15T09:50:33Z
       
  • Superficial compounds produced by Fe(III) mineral oxidation as essential
           reactants for bio-oxidation of pyrite by Thiobacillus ferrooxidans
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      In experiment of pyrite bioleaching by Thiobacillus ferrooxidans (DSM 583), the use of a K+ sulfonic resin to exchange ferrous and ferric ions of the medium in order to eliminate soluble bacterial substrate and mineral oxidizing agent, showed that the bacterial population does not grow efficiently if any substrate, except FeS2, is available. On the other hand, if the medium is free of any chemical oxidizing agent, the sulfide mineral is not oxidized and the leaching does not occur. Moreover, a physico-chemical approach showed that elemental sulfur and ferrous sulfate chemically produced at mineral surface by the action of free ferric ions, are effective substrates for the bacteria. These, non fully oxidized superficial phases ($8, FeSO4) are essential reactants because Thiobacillus ferrooxidans is unable to perform the direct oxidation of the mineral. Their nature, amount and spatial distribution control the kinetics of leaching and the corrosion of pyrite grains.


      PubDate: 2012-12-15T09:50:33Z
       
  • Comparison of chemical leaching and bioleaching of nickel from nickel
           hydroxide sludge
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Nickel hydroxide sludge samples used in this research were obtained from a sand drying bed of a chemical wastewater treatment plant for a nickel electroplating process containing 43% nickel. Its pH was around 8. This research consists of two parts both in a shake flask and a column. The first part of this research is to study the leaching efficiency of nickel hydroxide sludge by sulfuric acid. The experiment in the shake flask was carried out using nickel hydroxide sludge which containing nickel ion at 10 g/L by varying the concentration of sulfuric acid at 0.01, 0.05, 0.1, 0.15, 0.5, 1 and 5N. The result indicated that the concentration of sulfuric acid at 5, 1 and 0.5N can achieve 100% leaching efficiency within 24, 48 and 84 hours respectively. The concentration of sulfuric acid at 0.5 N can consume 1.06g.H2SO4 per g sludge. The experiment in the column was carried out using 500 g of nickel hydroxide sludge in a column 5 cm in diameter with 50 cm height by using 1N H2SO4 at a flow rate of 15 ml/cm2-hr. It can leach nickel at 13.56% within 3.5 hours. The other part of this research is bacterial leaching of nickel from nickel hydroxide sludge by Thiobacillus ferrooxidans and Thiobacillus thiooxidans. The experiment in the shake flask was carried out using nickel hydroxide sludge which containing 10 g/L of nickel ion in a different culture with bacteria. The adapted strain of both types of Thiobacillus spp. has 47% efficiency in leaching nickel which corresponds to the sulfuric acid concentration of 0.15N and is higher than for non-adapted bacteria and the sterile control, respectively. The experiment in a column was carried out using nickel hydroxide sludge in the same size of column as in the first experiment using an adapted strain of T. ferrooxidans and T. thiooxidans in 9K medium and thiomedium, respectively. The optimum condition for T. ferrooxidans was obtained by varying flow rate at 5, 10, 15 and 20 ml/cm2/hr, the inoculum amount of T. ferrooxidans at 10% and 20%(v/v), ferrous ions in 9K medium at 4, 10, 20, 30, 40 and 50 g/L, and quantity of sludge at 250 and 500 g per column. The results indicated that the optimum conditions were at a flow rate of 15 ml/cm2-hr, with 20% inoculum and the concentration of ferrous iron at 30 g/L, under which T. ferrooxidans can leach 250 g of nickel from nickel hydroxide sludge per column at 32% within 90 days. The controlled pH of the aforementioned step is between 2.5–3.0.


      PubDate: 2012-12-15T09:50:33Z
       
  • A comparison of the bacterial and chemical leaching of sphalerite at the
           same solution conditions
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      In this work we describe the use of a novel experiment to study the bacterial leaching of sphalerite (ZnS). We have constructed an experiment in which the conditions in a leaching reactor without bacteria are forced by a control system to follow the conditions in a leaching reactor with bacteria. The leaching with bacteria takes place in a batch reactor where the redox potential is measured continuously.These measurements serve as the setpoint value for a leaching experiment without bacteria in which the solution redox potential is controlled by the application of an electrolytic current.In this manner, the solution conditions of the chemical leaching experiment emulate the conditions found in the bacterial leaching experiment. The results obtained for sphalerite show that the amount of zinc dissolved is initially the same for both chemical and bacterial leaching. After approximately 10 hours, the conversion obtained in the bacterial leaching experiment is higher than that obtained in the chemical leaching experiment. This may be due to the formation a product layer of sulphur that is formed on the unreacted sphalerite in the chemical leaching reaction. Although this sulphur is porous, it limits the rate of leaching under certain conditions. In the bacterial leaching experiments, this product layer is not present, since sulphur is oxidised by the bacteria. The rate of leaching of sphalerite is therefore higher in the bacterial leaching experiment because the product layer has been removed.


      PubDate: 2012-12-15T09:50:33Z
       
  • A kinetic study of the leaching of chalcopyrite with Sulfolobus metallicus
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Batch chalcopyrite leaching experiments have been performed in the presence and absence of Sulfolobus metallicus. The effect of varying the initial concentration of ferric ions and the effect of the presence of medium in the leaching solution was investigated. The range of concentrations of ferric ions investigated in the absence of microorganisms was between 0.001 and 0.50 M. Leaching experiments with Sulfolobus metallicus were performed over the range of initial concentrations of ferric ions of 0.01 to 0.50 M. The rate of leaching of chalcopyrite was found to increase as the initial concentration of ferric ions was increased over the range of 0.001 to 0.05 M. However, the rate decreases with increasing concentration of ferric ions in the range of 0.05 to 0.50 M. This is due to the precipitation of basic ferric sulphates on the surface of the chalcopyrite particles at higher concentrations of ferric ions, which resulted in an increasing diffusional constraint. The maximum initial leaching rate of chalcopyrite in the absence of Sulfolobus metallicus was 1.76 mg/L.hr and the order of the surface reaction with respect to the concentration of ferric ions was found to be 0.34. The maximum conversion of approximately 4 percent was achieved after approximately 45 hours. The batch leach experiments performed in the presence of Sulfolobus metallicus showed similar trends as experiments performed in the absence of organisms. Complete conversion of the chalcopyrite was achieved after approximately 300 hours when an initial concentration of ferric ions of 0.05 M was used. The maximum rate of chalcopyrite leaching attained at an initial ferric ion concentration of 0.05 M was 24.6 mg/L.hr. The calculated initial rates were similar to those for the leaching experiments in the absence of microorganisms. The maximum initial rate of leaching of chalcopyrite was 2.30 mg~.hr in the presence of Sulfolobus metalficus with an initial concentration of ferric ions of 0.10 M. The calculated order of the reaction with respect to the concentration of ferric ions was 0.21.


      PubDate: 2012-12-15T09:50:33Z
       
  • Comparative copper and zinc bioextraction at various stages of scale up
           using T. ferrooxidans consortium
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Aim of the present study was to compare copper and zinc extraction from GMDC polymetallie concentrate in shake flasks, stirred tanks and large reactors. The concentrate used in the study contained chaleopyrite, sphalerite, galena and pyrite as main constituents. Thiobacillus ferrooxidans consortium used in this study was adapted to a high pulp density upto 20% of the concentrate. Scale up experiments were performed at 0.1 dm3, 3 dm3 and 100 dm3 levels at 30°, 40° and more than 40° C temperatures. During the experiments, 16 to 26 g of sulphuric acid was consumed per kilogram of the concentrate. At the end of experiment, the attained pH was 2.05±0.1. Solubilized Fe2+ and oxidation reduction potential ranged between 0.13 to 1.89 g.1-1 and 337 to 456 mV respectively on fifteenth day of experiment. Long lag phase was observed in all the scale up levels where the temperature was more than 38° C.In 100 dm3 pilot reactors, temperature raised to 46° C during the process. The developed consortium in first cycle of experiment resulted in 66.4, 62.0, 56.3 and 38.6% copper and 94.3, 71.8, 75.7 and 48.0% zinc extraction in shake flasks incubated at 30° and 40° C temperatures, 3 dm3 STR (40° C) and 100 dm3 (40° to 46° C) reactors respectively in 15 days of bioleaching~ time. Once temperature tolerant consortium was selected, both copper and zinc extraction reached to 54±2% irrespective of the level of scale up within 7 days of contact time. The consortium and 100 dm3 pilot reactor developed in this study is a promising step towards large scale economical process for metal extraction from the polymetallic concentrate.


      PubDate: 2012-12-15T09:50:33Z
       
  • Bioleaching of base metal sulphide concentrates: A comparison of mesophile
           and thermophile bacterial cultures
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      Billiton Process Research has carried out extensive research over the past four years to develop new process technology using bioleaching for extraction of copper and nickel from their sulphide concentrates. Continuous pilot scale and laboratory batch testwork has been carried out with adapted mesophile bacterial cultures at 40°C – 45°C, moderate thermophile cultures at 50°C – 55°C and thermophile cultures at 65°C – 85°C. Pilot scale work has demonstrated the commercial viability of mesophile cultures for bioleaching of secondary copper sulphide and nickel sulphide concentrates. Moderate thermophiles offer benefits in terms of reduced cooling requirements for commercial reactors and, in the case of bioleaching of nickel concentrates, some selectivity over bioleaching of pyrite. Continuous pilot scale testwork has shown that thermophiles achieve efficient bioleaching of primary copper sulphide and nickel sulphide concentrates, giving much higher recoveries than achieved by bioleaching with a mesophile or moderate thermophile culture.


      PubDate: 2012-12-15T09:50:33Z
       
  • Gold solubilisation by the cyanide producing bacteria Chromobacterium
           violaceum
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      The cyanogenic bacterium Chromobacterium violaceum was investigated for gold extraction from gold bearing ores, as part of the search for environmentally friendly lixiviants to be used in heap leach situations. The bacteria continuously produce small amounts of cyanide, which reaches a peak at the onset of the stationery phase of growth. It is considered that cyanide volatilises at the pH values most conducive to bacterial growth, and the higher the pH the more cyanide will stay in solution. However, at pH values above 8, growth becomes inhibited. Thus leaching experiments, using the bacteria, were carried out at pH 8. The salts ferrous sulphate and di-sodium hydrogen orthophosphate improve cyanide production(1) but have an inhibitory effect on gold extraction. Also, ores with a high iron content cannot be leached effectively by the bacteria. It was found that 53% of the gold could be extracted from low grade ore containing 3.2 g/t Au after 20 days. On the other hand, 10 days leaching of a high grade ore with 58.5 g/t Au extracted only 16% gold as compared to the 44.5% achieved after 10 days leaching of low grade ore. It was concluded that the bacteria show potential for gold solubilisation from low grade ores under heap leach conditions where much longer leach periods are required.


      PubDate: 2012-12-15T09:50:33Z
       
  • A study of the adaptation of native iron oxidizing bacteria to thiourea
    • Abstract: 1999
      Publication year: 1999
      Source:Process Metallurgy, Volume 9

      To improve gold dissolution from a pyrrhotite - arsenopyrite refractory ore with a combined process of bioleaching and thiourea leaching, three iron oxidizing bacteria cultures isolated from Ecuadorian mines were used. The capability of these bacteria to resist high contents of thiourea in solution was studied. The cultures were inoculated in progressively higher concentrations of thiourea, starting from 10 ppm, up to 400 ppm in the TK nutrient media with 7 g/l Fe2+, at pH 1.8, 30 °C, and 125 rpm in a reciprocating shaking bath. Bacterial population and ferrous ion concentration were controlled by Thoma plate microscope count and by titration with KMnO4, respectively. Results show that the bacteria were insensitive to lowest concentration of thiourea with good rates of growing population and Fe2+ oxidation. Higher concentration of thiourea in the solution created more difficulties for the bacterial development and required more adaptation steps. One of the cultures was also adapted to pH < 1 in order to decrease jarosite precipitation. The test was carried out to 300 ppm of thiourea. The bacteria survived at these extreme conditions, but needed a longer time to grow and to oxidize the ferrous ion.


      PubDate: 2012-12-15T09:50:33Z
       
 
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
 
About JournalTOCs
API
Help
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-2014