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  • 1.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Rosenkranz, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Hällström, Lina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Project: Improve Resource Efficiency and Minimize Environmental Footprint2016Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The REMinE project is organized in five work packages that comprise: detailedcharacterization and risk assessment of the mine wastes selected (WP2), identification of new processing methods for mine waste (WP3), characterization and risk assessment of the remaining residuals (WP4), outlining business opportunities and environmental impact in a conceptual model for sustainable mining (WP5). The project comprises case studies of historical mine wastes from three different European countries, namely Portugal, Romania and Sweden. The interdisciplinary research collaboration in this project is innovative in the sense that separation of minerals and extraction of metals not only are basedon technical and economic gain but also considers the environmental perspective.

  • 2. Awe, Samuel Ayowole
    et al.
    Khoshkhoo, Mohammad
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kruger, Paul
    Boliden Mineral AB.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Modelling and process optimisation of antimony removal from a complex copper concentrate2012In: Transactions of Nonferrous Metals Society of China, ISSN 1003-6326, E-ISSN 2210-3384, Vol. 22, no 3, p. 675-685Article in journal (Refereed)
    Abstract [en]

    The modelling and optimization for the alkaline sulphide leaching of a complex copper concentrate containing 1.69% Sb and 0.14% Sn were studied. Response surface methodology, in combination with central composite face-centred design (RSM-CCF), was used to optimise the operating parameters. The leaching temperature, sulphide ion concentration and solid concentration werechosen as the variables, and the response parameters were antimony and tin recovery, and the time required to achieve 90% Sb dissolution. It was confirmed that the leaching process was strongly dependent on the reaction temperature as well as the sulphide ion concentration without any significant dependence on the solid concentration. Furthermore, a mathematical model was constructed tocharacterise the leaching behaviour. The results from the model allow identification of the most favourable leaching conditions. The model was validated experimentally, and the results show that the model is reliable and accurate in predicting the leaching process.

  • 3.
    Awe, Samuel Ayowole
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Lennartsson, Andreas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mostaghel, Sina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Samuelsson, Caisa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Wise process routes for varying feedstock in base metal extraction2011In: Proceedings, European Metallurgical Conference EMC 2011: Process Metallurgy, Recycling/Waste Treatment and Prevention, Germany: GDMB , 2011, Vol. 4, p. 1315-1322Conference paper (Refereed)
    Abstract [en]

    In Sweden, there are several large but low-grade ore deposits that have not been extracted so far. The main reason is presence of impurities such as arsenic and antimony that increase the overall cost of the process and make the extraction uneconomical. In-depth experimental studies, plant data and theoretical modelling and innovations are needed to develop new techniques for an efficient use of the resources. Besides, recycling of metals from end of life scrap and metal containing waste, e.g. waste electric and electronic equipment (WEEE), is an important part of a metal production plant. Most of these secondary raw materials contain mixtures of different metals together with various plastics and ceramics that may adversely affect products and by-products of the metallurgical opera-tion. Therefore, a thorough study on how to control possible changes of properties is required. The aim of the research is to develop an optimum combination of hydro- and pyro- metallurgical path-ways to bleed out impurities from the metal extraction chain and/or convert them into valuable by-products. The first part of the current paper focuses on impurity removal from a complex copper concentrate as an upgrading stage. It is shown that by selective dissolution of tetrahedrite in alkaline sulphide solution, antimony and arsenic would be eliminated and the concentrate can be treated in pyro-metallurgical processes. In the second part of the paper, influences of one of the most common and significant compounds that is included in most of the secondary raw materials, alumina Al2O3, on properties of a copper production slag are explained. Results show that increased alumina content of the slag will cause formation of a new phase and rises the liquidus temperature, while its leaching properties are not adversely affected.

  • 4. Awe, Samuel Ayowole
    et al.
    Samuelsson, Caisa
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Dissolution kinetics of tetrahedrite mineral in alkaline sulphide media2010In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 103, no 1-4, p. 167-172Article in journal (Refereed)
    Abstract [en]

    The present study investigates the dissolution kinetics of tetrahedrite in aqueous alkaline sodium sulphide solutions. Effect of reaction temperature, mineral particle size, sodium sulphide and sodium hydroxide concentrations on antimony and arsenic dissolution rate from tetrahedrite were studied. It was found that the rate of reaction increases with increase in reaction temperature, sodium sulphide concentration, and sodium hydroxide concentration and with decrease in mineral particle size. The kinetic study indicates that the rate of tetrahedrite leaching in the lixiviant under selected conditions is chemically controlled through the particle surface reaction. The estimated activation energies were found to be 81 kJ/mol and 75 kJ/mol, respectively, for antimony and arsenic dissolution from tetrahedrite, which are in agreement with the values of activation energies reported for the chemically controlled reaction process

  • 5.
    Awe, Samuel Ayowole
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Samuelsson, Caisa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Elimination and recovery of antimony from copper resources2013Conference paper (Refereed)
    Abstract [en]

    In a response to the recent growth in the global demand for copper products, mining industries have intensified in their mining operations. Unfortunately, the grade of copper ore concentrates mined today is declining due to the intensive mining of the relatively high grade copper resources. Therefore, future copper ore deposits to be mined are likely to be richer in impurity elements like antimony and arsenic which attract smelter’s penalty if the content of these impurities is too high. It is however imperative to selectively eliminate and recover the antimony impurity of the copper concentrates in an environmentally friendly process with a view of upgrading the concentrates for a pyrometallurgical processing.This paper discusses the alkaline sulphide hydrometallurgical technology to selectively solubilize antimony impurity from a copper concentrate. The effect of sodium sulphide and sodium hydroxide concentrations, leaching time and leaching temperature on antimony dissolution will be examined. Furthermore, antimony recovery as a marketable product from simulated pregnant leach liquor through electrodeposition will be discussed. Various experimental factors that influence antimony deposition from alkaline sulphide electrolyte are reported.

  • 6.
    Awe, Samuel Ayowole
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Electrowinning of antimony from model sulphide alkaline solutions2013In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 137, p. 60-67Article in journal (Refereed)
    Abstract [en]

    The influence of initial antimony concentration, cathode current density, the concentrations of Na2S and NaOH, gas sparging and electrolyte temperature on average cell voltage, specific energy and current efficiency of antimony deposition has been studied. The experiments were conducted in a nondiaphragm electrolytic cell. Results revealed that increase in initial antimony concentration, temperature of the electrolyte and NaOH concentration enhanced the current efficiency. Excessive sodium sulphide concentration in the electrolyte promotes the formation of unwanted polysulphide and thiosulphate ions which can significantly decrease the current efficiency of the process. Sparging of the electrolyte facilitates a smooth and adherent antimony deposit with an improved purity. About 99.6% antimony purity was achieved when the electrolyte was sparged at 10 mL/min. The result showed that increase in NaOH concentration considerably promotes the formation of sulphate ions as the main anodic product. Anodic current efficiencies of 98% and 99% based on the amount of sulphate formed were obtained at sodium hydroxide concentrations of 8.75 M and 10 M, respectively. Average cell potential increased with increasing NaOH concentration and cathode current density. The preferred crystallographic orientations of the antimony deposit obtained at 2.5 M NaOH concentration are in the orders (012) (202) (110) (104), but the order becomes (012) (110) (104) (202) when NaOH concentration is increased further. The order of crystal orientations for antimony electrodeposition at 50 A/m2 cathodic current density is (012) (110) (104) (202), which does not change with increasing cathode current density but the peaks at (110) (104) (202) crystal planes become more broadened and suppressed as current density increased.

  • 7. Awe, Samuel Ayowole
    et al.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Leaching mechanism of tetrahedrite in alkaline sulfide solution2010In: Conference in Minerals Engineering: Luleå, 2 -3 februari 2010, Luleå tekniska universitet, 2010, p. 13-24Conference paper (Other academic)
    Abstract [en]

    The dissolution kinetics of tetrahedrite in aqueous alkaline sodium sulfide solutions was investigated in this present study. The effect of mineral particle size, reaction temperature, sodium sulfide and sodium hydroxide concentrations on the rate of dissolving antimony from tetrahedrite were studied. The result reveals that the rate of reaction increases with increasing reaction temperature, sodium sulfide concentration, sodium hydroxide concentration and with decreasing mineral particle size. The kinetics study indicates that tetrahedrite leaching rate by the lixiviant under the selected conditions is chemically controlled through the particle surface reaction. Therefore, the activation energy of antimony dissolution from tetrahedrite was estimated to be 81 kJ/ mol, which is in agreement with the value reported for the chemically controlled reactions process.

  • 8. Awe, Samuel Ayowole
    et al.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Selective leaching of arsenic and antimony from a tetrahedrite rich complex sulphide concentrate using alkaline sulphide solution2010In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 23, no 15, p. 1227-1236Article in journal (Refereed)
    Abstract [en]

    Removal of impurity elements in copper metallurgy is one of the major problems encountered today since pure copper ore reserves are becoming exhausted, and the resources of unexploited ores often contain relatively high amounts of impurity elements like antimony, arsenic, mercury and bismuth, which need to be eliminated. The present work is aimed at pre-treating a tetrahedrite rich complex sulphide concentrate by selective dissolution of the impurities, therefore, upgrading it for pyrometallurgical processing. To accomplish this, dissolution of antimony and arsenic by an alkaline sulphide lixiviant from the concentrate were investigated. The lixiviant proved selective and effective to dissolve these impurity elements from the concentrate with good recoveries. Further investigations on the factors influencing the leaching efficiency of the lixiviant were studied. The parameters considered were sulphide ion and hydroxide ion concentrations, mineral particle size, reaction temperature and leaching time. Analysis of the leach residue indicates that copper content of tetrahedrite has transformed into copper sulphides with the average chemical formula Cu1.64S. The grade and economic value of the concentrate were improved greatly after sulphide treatment, and therefore, suitable as a feedstock for smelting. The impurities have been reduced to low levels which are tolerable in the smelting furnace and consequently reduce both the treatment and environmental problem encountered when such concentrate is processed pyrometallurgically.

  • 9.
    Awe, Samuel Ayowole
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Tratamiento hidro-electrometalúrgicos de un concentrado de cobre con contenido de tetraedrita2014In: Mineria, ISSN 0026-4679, Vol. 439, p. 46-52Article in journal (Refereed)
    Abstract [en]

    Elimination of antimony and arsenic impurities is one of the major difficulties encountered in copper metallurgy. This is because the pure copper ore reserves are becoming exhausted and the resources of unexploited ores often contain relatively high amounts of antimony and arsenic. During smelting of copper concentrates, arsenic is easily removed into the offgas while antimony is not readily removed due to its lower partial pressure and high affinity for liquid copper. It is however imperative to selectively eliminate and recover the antimony impurity of the copper concentrates in an environmentally friendly process with a view of upgrading the concentrates for pyrometallurgical processing.This communication discusses (i) alkaline sulphide hydrometallurgy of antimony removal from a complex copper concentrate; and (ii) antimony recovery as a marketable product from synthetic alkaline sulphide pregnant leach liquors by electrowinning in a nondiaphragm cell. Also, the various experimental parameters that influence these processes are discussed.

  • 10.
    Awe, Samuel Ayowole
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Upgrading of an impure copper concentrate for pyrometallurgical processing2011In: Proceedings, European Metallurgical Conference EMC 2011: Copper/ General Pyrometallurgy/ Vessel Integrity/ Process Gas Treatment, Dusseldorf, Germany: GDMB , 2011, Vol. 1, p. 15-31Conference paper (Refereed)
    Abstract [en]

    Copper ore grades are diminishing worldwide as the higher grade reserves are exploited and pro-gressively depleted. Simultaneously, the global demand for copper is increasing continuously. Con-sequently, processing of future copper ores and concentrates will most likely involve the treatment of more complex, fine-grained minerals containing increased levels of impurity elements (e.g. Sb, As and Hg), which are detrimental to the smelting process as well as affecting the physical and me-chanical properties of the copper product. Unfortunately, the prevalence of antimony containing minerals among the copper-bearing ores will reduce their economic value, and therefore, need to be eliminated. However, it is beneficial if antimony can be removed at the early stage of the process as a saleable product instead of ending-up as a waste material in copper metallurgy. This article aims at pre-treating a tetrahedrite-rich copper concentrate by selective dissolution of antimony in alkaline sulphide media, thereby, upgrading the concentrate for smelting operation. Furthermore, the kinetic mechanisms of the leach process as well as the factors affecting it were investigated. The selectivity of the lixiviant towards antimony is also discussed. The results show that the extraction of antimony from the concentrate depends strongly on the concentration of sul-phide and hydroxide ions, reaction temperature, particle size and the leaching time. Kinetic data from the study indicates that tetrahedrite dissolution from the concentrate under selected conditions is chemically controlled through the particle surface reaction with an estimated activation energy of 81 kJ/mol. Analysis of the leach residue proves that the lixiviant is selective and effective to solubi-lize this impurity element from the concentrate with high recovery. The impurity content of the concentrate was found to have reduced to low levels acceptable for smelting operation, and there-fore, lessen the processing problems faced during pyrometallurgical treatment of such impure copper concentrate.

  • 11.
    Awe, Samuel Ayowole
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Bolin, Nils-Johan
    Boliden Mineral AB.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Process flowsheet development for recovering antimony from Sb-bearing copper concentrates2013In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 49, p. 45-53Article in journal (Refereed)
    Abstract [en]

    The technical feasibility, on laboratory scale, of hydro- and electrometallurgical processes of recovering metallic antimony from an antimony-bearing copper sulphide concentrate has been investigated. The influence of Na2S concentration, temperature and solid concentration was studied during the leaching test while the effect of current density, Na2S concentration, electrolyte temperature and NaOH concentration on antimony electrowinning from alkaline sulphide solutions was investigated. The leaching results showed that antimony dissolution is strongly dependent on the concentration of the leaching reagent as well as the leaching temperature. The antimony content in the concentrate was reduced from 1.7% to less than 0.1% Sb which is desirable for copper metallurgy. Cathode current efficiency is one of the important parameters to evaluate the performance of an electrolytic process. It is revealed in this study that current efficiency of antimony deposition from sulphide electrolytes is highly dependent on the concentration of sodium hydroxide and the current density used. The results illustrate that the combined effect of increasing anode current density (which was 10 times higher than the cathode current density) and NaOH concentration enhanced the current efficiency of the electrolytic process. It was demonstrated that excess free sulphide ions impacts the current efficiency of the process detrimentally. An integrated hydro-/electrometallurgical process flowsheet for antimony removal and recovery from a sulphide copper concentrate was developed.

  • 12.
    Awe, Samuel Ayowole
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Formation of sulphur oxyanions and their influence on antimony electrowinning from sulphide electrolytes2013In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 53, p. 39-47Article in journal (Refereed)
    Abstract [en]

    Antimony electrowinning from synthetic alkaline sulphide electrolytes has been studied in a nondiaphragm electrolytic cell. The electrodes were constructed in such a way that the anode produces ten times higher current density than the cathodic current density to promote sulphide oxidation to sulphate at the anode; and simultaneously decreasing the tendency of hydrogen evolution at the cathode. The result revealed that at an anodic current density lower than 1500 A/m2, minute amounts of sulphate ions were formed but when the anode current density increased beyond 1500 A/m2, sulphate formation was promoted. The initial molar concentration ratio between hydroxide and free sulphide ions should be ≥ 10.3 to avoid thiosulphate formation at 2000 A/m2 anodic current density under the conditions used in these experiments. The highest anodic current efficiency obtained based on the amount of sulphate formed was 89%. An increase in the anode current density as well as NaOH concentration enhances the cathodic and anodic current efficiencies with respect to the antimony metal deposited and sulphate ions produced, respectively. Despite the high anodic current densities used, the specific energy of this process ranges from 0.6 to 2.3 kWh/kg which is significantly lower than values reported previously due to the prevention of undesirable sulphur species from being formed. The tests revealed that the concentration of thiosulphate formed during the electrolysis decreased with increasing anode current density and NaOH concentration. Addition of polysulphide from 0 to 30 g/L to the electrolyte decreases the current efficiency from 83% to 32% and correspondingly increases the specific energy from 1.7 to 4.8 kWh/kg. Results showed that a build-up of sulphite and sulphate ions in the solution does not have any detrimental effect on the current efficiency of antimony deposition.

  • 13.
    Aycik, G.A.
    et al.
    Turkish Atomic Energy Authority, Ankara Nuclear Research and Training Center.
    Paul, M.
    Turkish Atomic Energy Authority, Ankara Nuclear Research and Training Center.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Paul, Jan
    Leaching of radioactive isotopes from ash2003Conference paper (Other academic)
    Abstract [en]

    The aim of the study is to reduce the environmental impact of ash deposits. Ash from coal and biomass combustion, containing uranium and thorium from Yatagan-Silopi and Tuncbilek coal; cesium-137 from forests in northeastern Turkey and central Sweden. Turkey is dependent on coal for power generation and huge volumes of ash (>15 Mton/yr) are produced every year. Because of that certain coals, in particular Yatagan, with known problems from Mo and U leaching to the ground water, and Silopi oil shales/asphaltites were studied. Biomass ash comes from branches, bark and other unused parts of the trees and plants. This ash has low concentration of environmentally hazardous metals, but {sup 137}Cs is a problem in certain regions and it is of interest to investigate the possibilities to leach this metal from the ash. Washing ash through rapid chemical leaching at low pH reduces the slow release of metals from ash due to precipitation and besides it may lead to metal recovery from the ash. Initial experiments were done in batch form, in which the neutralizing capacity at pH 1-1.5 was measured by adding sulfuric acid to maintain pH for mixtures of ash and water. Subsequent experiments were done in bench scale. The process also reduced the metal content of the ash, due to chemical leaching of metal oxides and ion exchange at the surfaces of stable oxides. This means that treated ash will not release further metals and, eventually, relaxes the requirements on depositories and allows the ash from coal to be used as an admixture in cement, and to be used as a fertilizer following after treatment of ash from biomass

  • 14.
    Cunha, Maria Lucelinda
    et al.
    Departamento de Ciência dos Materiais, FCT/UNL, Caparica.
    Gahan, Chandra Sekhar
    Menad, Nourreddine
    BRGM-EPI, ECO, 3, Avenue Claude Guillemin, Orléans.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Leaching behaviour of industrial oxidic by-products: possibilities to use as neutralisation agent in bioleaching2008In: Advanced Materials Forum IV: selected, peer reviewed papers from the IV International Materials Symposium Materiais 2007 and XIII Encontro da Sociedade Portuguesa de Materiais - SPM, Faculdade de Engenharia da Universidade do Porto, April 1 - 4, Porto, Portugal, 2007 / [ed] António Torres Marques; António Fernando Silva, Stafa-Zurich: Trans Tech Publications Inc., 2008, p. 748-752Conference paper (Refereed)
    Abstract [en]

    In this study chemical leaching with sulphuric acid has been performed on 10 selected oxidic by-products in order to determine their neutralising capacity. The ultimate aim with this work is to replace the lime or limestone normally used in bioleaching operations to maintain pH at 1.5, the optimum pH-level for bioleaching microorganisms, with oxidic by-products. The investigated by-products includes three ashes from combustion for energy production, five slag samples from ore and scrap based steelmaking, an EAF dust and mesa lime from a paper and pulp industry, slaked lime (Ca(OH)2) was used as reference material. The neutralising potential of the by-products were evaluated by leaching them with sulphuric acid and comparing the amount of acid needed to that of the reference. Most of the by-products examined had good neutralisation potential and some had even higher capacities than Ca(OH)2. Neutralisation kinetics were lower for some slag products due to slow dissolution of some of the silicates present, but kinetics are considered good enough since stirred tank bioleaching is a relatively slow process. Zinc recoveries from the zinc containing materials were high, which thus is an additional benefit if these materials were to be used for neutralisation in a bioleaching process for zinc recovery.

  • 15.
    Cunha, Maria Lucelinda
    et al.
    Departamento de Ciência dos Materiais, FCT/UNL, Caparica.
    Gahan, Chandra Sekhar
    Menad, Nourreddine
    BRGM-EPI, ECO, 3, Avenue Claude Guillemin, Orléans.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Possibilities to use oxidic by-products for precipitation of Fe/As from leaching solutions for subsequent base metal recovery2008In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 21, no 1, p. 38-47Article in journal (Refereed)
    Abstract [en]

    In acidic biological and chemical leaching processes for base metal recovery, iron is dissolved in addition to the desired metal values. Prior to valuable metal extraction iron has to be removed. This is usually achieved through hydroxide precipitation of ferric iron by the addition of lime or limestone to a pH of approximately 3 whereby ferric hydroxide is formed. The aim of this work has been to investigate the possibility to substitute lime or limestone with oxidic industrial by-products for neutralisation and precipitation of iron from leaching solutions. The neutralisation potential for 10 selected oxidic by-products like slags, ashes and dusts were examined and compared with slaked lime.Experiments were performed by decreasing pH to 3 by additions of H2SO4 to slurry of respective by-product at an S/L ratio of 1/10 at 25 °C and continued till no changes in pH were observed during 10 days. Original samples, residues and solutions were analysed by ICP-MS and XRD in order to identify potential harmful elements for the subsequent metal recovery steps.Characterisation of the by-products revealed high concentrations of oxides such as lime, calcite and metal oxides as well as different forms of silicates in the materials which all dissolved at pH 3. The neutralising potential was found to be high for most of the by-products investigated and in the case of Ladle slag it was even higher than for slaked lime. Slags generally had higher neutralisation potential and long-term effects while the ashes had high initial reactivity which is important for continuous neutralisation in stirred tanks with limited retention times. The most reactive materials were Bioash and Mesa lime which both contained considerable amounts of calcite. Replacement of the conventional lime and limestone with oxidic by-products for neutralisation of acidic leaching solutions has the potential to save costs, environmental resources, reduce CO2 emissions and to recycle metal values like zinc contained in the by-products.

  • 16. Cunha, M.L.
    et al.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Characterisation of by-products for use as neutralizing agent in bioleaching2006In: Proceedings of the XXIII International Mineral Processing Congress: Istanbul, Turkey 3 - 8 September 2006 / [ed] Güven Önal, Istanbul: IMPC , 2006, Vol. 2, p. 1392-1397Conference paper (Refereed)
  • 17.
    Dinkla, Inez J.T.
    et al.
    Bioclear BV.
    Gonzalez-Contreras, Paula
    Sub-department of Environmental Technology, Wageningen University.
    Gahan, Chandra Sekhar
    SRM Research Institute, SRM University, Kattankulathur, Chennai.
    Weijma, Jan
    Sub-department of Environmental Technology, Wageningen University.
    Buisman, Cees J.N.
    Sub-department of Environmental Technology, Wageningen University.
    Henssen, Maurice J.C.
    Bioclear BV.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Quantifying microorganisms during biooxidation of arsenite and bioleaching of zinc sulfide2013In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 48, p. 25-30Article in journal (Refereed)
    Abstract [en]

    The development of molecular tools for the detection and quantification of both species as well as functional traits, aids in a better understanding and control of microbial processes. Presently, these methods can also be used to assess the activity of these organisms or functions, even in complex ecosystems and difficult matrices such as ores and low pH samples. In this paper we present the versatility of one of these tools, Q-PCR, to allow accurate and fast insight in changes in two types of microbial processes representing two ways in which microbes can interact with metals, bioleaching and bioprecipitation. Using the Q-PCR technique it was possible to identify and quantify the thermoacidophilic archaeon Acidianus sp. to be the main microbial strain responsible for biooxidation of arsenite in a low pH reactor. The method was also used to study the dynamics between the iron oxidizing and sulfur oxidizing acidophiles during bioleaching of a zinc concentrate in a batch reactor system and showed that the iron oxidizer Leptospirillum ferriphilum that dominated the starting culture disappeared upon addition of the concentrate. Gradually, bacterial activity was regained starting with growth of sulfur oxidizers and at later stage iron oxidizers started to grow. Molecular analysis can be used to direct research to the relevant organisms involved and concentrate on improving their application (in the arsenite case Acidianus sp.) or in understanding appearances and disappearances of microorganisms (during leaching of zinc concentrate the disappearance of Leptospirillum after high inoculation levels) in order to allow optimization of leaching efficiencies at the lowest (oxygen) costs.

  • 18.
    Edelbro, R.
    et al.
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Paul, Jan
    Full potential calculations on the electron band structures of Sphalerite, Pyrite and Chalcopyrite2003In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 206, no 1-4, p. 300-313Article in journal (Refereed)
    Abstract [en]

    The metal contents of ore can be as low as 0.4%m This means sophisticated methods of enrichment have to be applied. Better understanding of the processes of flotation and leaching may lead to higher yields and less damage to the environment. The bulk electronic structures of Sphalerite, Pyrite and Chalcopyrite have been calculated within an ab initio, full potential, density functional approach. The exchange term was approximated with the Dirac exchange functional, the Vosko-Wilk-Nusair parameterization of the Cepler-Alder free electron gas was used for correlation and linear combinations of Gaussian type orbitals were used as basis functions. The Sphalerite (zinc blend) band gap was calculated to be direct with a width of 2.23 eV. The Sphalerite valence band was 5.2 eV wide and composed of a mixture of sulfur and zinc orbitals. The band below the valence band located around -6.2 eV was mainly composed of Zn 3d orbitals. The S 3s orbitals gave rise to a band located around -12.3 eV. Pyrite was calculated to be a semiconductor with an indirect band gap of 0.51 eV, and a direct gap of 0.55 eV. The valence band was 1.25 eV wide and mainly composed of non-bonding Fe 3d orbitals. The band below the valence band was 4.9 eV wide and composed of a mixture of sulfur and iron orbitals. Due to the short inter-atomic distance between the sulfur dumbbells, the S 3s orbitals in Pyrite were split into a bonding and an anti-bonding range. Chalcopyrite was predicted to be a conductor, with no band-crossings at the Fermi level. The bands at -13.2 eV originate from the sulfur 3s orbitals and were quite similar to the sulfur 3s bands in Sphalerite, though somewhat shifted to lower energy. The top of the valence band consisted of a mixture of orbitals from all the atoms. The lower part of the same band showed metal character. Computational modeling as a tool for illuminating the flotation and leaching processes of Pyrite and Chalcopyrite, in connection with surface science experiments, is discussed.

  • 19.
    Engström, Fredrik
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Adolfsson, Daniel
    SSAB EMEA, Luleå.
    Samuelsson, Caisa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A study of the solubility of pure slag minerals2013In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 41, p. 46-52Article in journal (Refereed)
    Abstract [en]

    Large amounts of oxidic by-product are annually produced by the steel industry worldwide. By far the largest in volume is slag, generated from different stages of steel production. In order to avoid landfilling, steelmakers usually try to process the slag into useful resources that can be used externally. However, leaching of different metals can sometimes be a problem. Since steel slags are a mixture of numerous types of minerals, the solubility of each mineral will affect the outcome of the leachability. The aim of this study was to investigate how six common slag minerals behave during dissolution. Mayenite (Ca12Al14O33), merwinite (Ca3MgSi2O8), akermanite (Ca2MgSi2O7), gehlenite (Ca2Al2SiO7), γ-dicalcium silicate (γ-Ca2SiO4) and tricalcium aluminate (Ca3Al2O6) were synthesized and their dissolution was evaluated through titration using HNO3 at constant pH. Acidic to alkaline pHs (4, 7 and 10) were selected to investigate the solubility of the minerals under conditions comparable to those prevailing in newly produced slags, and one pH value, representing acid conditions. It can be concluded that all six minerals behave differently when dissolving and that the rate of dissolution is generally slower at higher pH values, which are normal in the case of steelmaking slags. At pH 10, the solubility of merwinite, akermanite and gehlenite is considered low. The dissolution of γ-Ca2SiO4 is not affected in the same way as the other minerals when the pH is changed.

  • 20.
    Engström, Fredrik
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Lidström-Larsson, Margareta
    Samuelsson, Caisa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Robinson, Ryan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Leaching Behavior of Aged Steel Slags2014In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 85, no 4, p. 607-615Article in journal (Refereed)
    Abstract [en]

    Large amounts of slag are generated by the Swedish Steel Industry each year. The Electric Arc Furnace process generates about 200 000 ton of slag per annum, from which approximately 40% is deposited. An alternative to deposit is to use slag as road construction material. However, leaching of metals from the slag can be a reason to limit slag use in road construction. The aim of this work was to investigate how stable these materials are when aged, in an environment open to seasonable weather conditions, with respect to leaching and mineralogy. Three different EAF-slags from domestic steel plants were used in this study. The materials were characterized after 0, 6, 12, 18, and 24 months to evaluate the ageing process. The analytical techniques that were used to evaluate the effect of ageing are scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and a standard test for leaching. The changes in ageing behavior differ between the three materials. The conductivity and the pH decreases with time for all samples. The leaching of calcium, chromium as well as aluminum decreases with time while the leaching of magnesium increases. CaCO3 was formed on slag surfaces as CaO reacts with moisture and CO2 from the air.

  • 21. Gahan, Chandra Sekhar
    et al.
    Cunha, Maria Lucelinda
    Departamento de Ciência dos Materiais, FCT/UNL, Caparica.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Comparative study on different steel slags as neutralising agent in bioleaching2009In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 95, no 3-4, p. 190-197Article in journal (Refereed)
    Abstract [en]

    A comparative study on bioleaching of a pyrite concentrate using five different steel slags as neutralising agent has been performed with reference to a commercial grade slaked lime. The acid produced during oxidation of pyrite was neutralised by regular additions of neutralising agent to maintain a pH of 1.5. Bioleaching was conducted as batch in 1-L reactors with a mixed mesophilic culture at a temperature of 35 °C. The different steel slags used were Argon Oxygen Decarbonisation (AOD) slag, Basic Oxygen Furnace (BOF) slag, Electric Arc Furnace (EAF) slag, Composition Adjustment by Sealed Argon Bubbling-Oxygen Blowing (CAS-OB) slag and Ladle slag, representing slags produced in both integrated steel plants and scrap based steel plants. The aim of the study was to investigate the possibility to replace normally used lime or limestone with steel slags, considering their neutralising capacity and eventual toxic effects on the bacterial activity.The bioleaching efficiency was found to be equally good or better, when steel slags were used for neutralisation instead of slaked lime and the extent of pyrite oxidation of pyrite was in the range 75-80%. Some of the slags used contained potentially toxic elements for the bacteria, like fluoride, chromium and vanadium, but no negative effect of these elements could be observed on the bacterial activity. However, slags originating from stainless steel production are less environmentally friendly due to the presence of chromium. The neutralising potential of the slags was high, as determined by the amount needed for neutralisation during bioleaching. The range of additions of neutralising agents required to control the pH at 1.5 for all the experiments ranged from 16-27 g, while 22 g was needed in the experiment with slaked lime.Hence, it was concluded that considerable savings in operational costs could be obtained by replacement of lime or limestone with steel slag, without negative impact on bioleaching efficiency. Recycling of steel slags would render an eco-friendly process and provide a means for sustainable use of natural resources.

  • 22. Gahan, Chandra Sekhar
    et al.
    Cunha, Maria Lucelinda
    Departamento de Ciência dos Materiais, FCT/UNL, Caparica.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Possibilities to use industrial oxidic by-products as neutralising agent in bioleaching2009In: IBS 2009 Abstract Book / [ed] Edgardo R. Donati; Marisa R. Viera; Eduardo L. Tavani; Maria A. Giaveno; Teresa L. Lavalle; Patricia A. Chiacchiarini, 2009, p. 139-Conference paper (Other academic)
    Abstract [en]

    The present study aims for the possibilities to use industrial oxidic by-products as neutralising agent in biooxidation. Neutralising agent is required to neutralise the acid produced during the biooxidation. Possibilities to replace conventionally used limestone with by-products based on their neutralising capacities and possible harmful effects were investigated. Ten different by-products were used with reference to slaked lime. Batch bioleaching of a pyrite concentrate were conducted in 1-L reactor using mesophilic microorganisms at 35º C. The by-products used were different types of steel slags, ashes, dust and mesalime. The neutralising capacities of the by-products were determined by the amount of by-products needed for neutralisation during biooxidation. The amount of steel slags, EAF dust, Mesalime and Bioash needed for neutralisation ranged from 16-37 g, Waste ash and Coal & Tyres ash needed 81 g and 57 g, respectively, while the slaked lime reference needed 22 g. The experiment with Waste ash gave the lowest pyrite oxidation of 59 %, while the other by-products had similar or better pyrite oxidation compared to slaked lime, ranging from 69-80%. Fluoride, chromium and vanadium were potentially toxic elements present in some of the by-products, but had no negative impact on the bacterial activity. A chloride concentration of 11%, eventually together with other potentially toxic elements, in the Waste ash caused a negative effect, observed by low redox potential and pyrite oxidation. Stainless steel slags should be avoided for environmental reasons due to the presence of chromium. High content of zinc in EAF dust would enrich the zinc tenor, if used as neutralising agent in bioleaching of zinc sulphides, but chloride should be removed before its use. Replacement of limestone with by-products in biooxidation processes could save operating costs without negative impact on the biooxidation efficiency and conserve virgin limestone deposits.

  • 23. Gahan, Chandra Sekhar
    et al.
    Cunha, Maria Lucelinda
    Departamento de Ciência dos Materiais, FCT/UNL, Caparica.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Study on the possibilities to use ashes, EAF dust and lime sludge as neutralising agent in bioleaching2008In: Open Mineral Processing Journal, ISSN 1874-8414, E-ISSN 1874-8414, Vol. 1, p. 26-36Article in journal (Refereed)
    Abstract [en]

    Studies were conducted to investigate the possibilities to use combustion ashes, electric arc furnace (EAF) dust and lime sludge as neutralising agent with reference to a commercial grade slaked lime. To maintain optimum pH during biooxidation of pyrite the acid produced has to be neutralised. Batch bioleaching was performed on a pyrite concentrate in 1-L reactors, using a mixed mesophilic culture at a temperature of 35ºC. Neutralising agents were added regularly to adjust pH to the desired level of 1.5. The ashes used were Bioash, Waste ash and Coal & Tyres ash, representing ashes generated from combustion of biomass, a mixture of wood chips and municipal waste, and a mixture of coal and tyres. The dust used was an EAF dust produced in a scrap-based steel plant, while the sludge used was Mesalime produced in a paper and pulp plant.The study aimed to investigate the possibility to replace the conventionally used lime or limestone with by-products, based on their neutralising capacity and to observe eventual toxic effects on the bacterial activity. The bioleaching efficiency was similar for all the neutralising agents used except Waste ash, when compared with slaked lime. The extent of pyrite oxidation was in the range 69-75% for all neutralising agents, except Waste ash, which had a pyrite oxidation of 59%. The Waste ash contained a large number of potentially toxic elements and the chloride concentration of 11% probably had a negative effect as observed on the lower redox potential and pyrite oxidation. The EAF dust has a good potential to be used as neutralising agent in bioleaching processes for zinc recovery from zinc sulphides, due to the high content of zinc, however the chlorides present should be removed prior to its use. The neutralising capacity, as determined by the amount needed for neutralisation during bioleaching, were rather high for EAF dust, Bioash and Mesalime with 37 g, 33 g and 29 g, respectively as compared with 22 g needed for slaked lime. However, Waste ash and Coal & Tyres ash had lower neutralising capacities with 81 g and 57 g needed, respectively. It is concluded that the replacement of lime or limestone with ash, dust or lime sludge can render considerable cost savings to the bioleaching operation. In addition, it is a means for sustainable use of natural resources, which would provide opportunities to recycle elements present in them like for example zinc.

  • 24. Gahan, Chandra Sekhar
    et al.
    Cunha, Maria Lucelinda
    Departamento de Ciência dos Materiais, FCT/UNL, Caparica.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Application of industrial oxidic by-products as neutralising agent in bioleaching2010In: Microbial Biotechnology, New Delhi, India: A.P.H. Publishing Corp. , 2010, p. 254-297Chapter in book (Other academic)
  • 25. Gahan, Chandra Sekhar
    et al.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Dopson, Mark
    Department of Molecular Biology, Umeå University.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Effect of chloride on ferrous iron oxidation by a Leptospirillum ferriphilum-dominated chemostat culture2010In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 106, no 3, p. 422-431Article in journal (Refereed)
    Abstract [en]

    Biomining is the use of microorganisms to catalyze metal extraction from sulfide ores. However, the available water in some biomining environments has high chloride concentrations and therefore, chloride toxicity to ferrous oxidizing microorganisms has been investigated. Batch biooxidation of Fe2+ by a Leptospirillum ferriphilum-dominated culture was completely inhibited by 12 g L-1 chloride. In addition, the effects of chloride on oxidation kinetics in a Fe2+ limited chemostat were studied. Results from the chemostat modeling suggest that the chloride toxicity was attributed to affects on the Fe2+ oxidation system, pH homeostasis, and lowering of the proton motive force. Modeling showed a decrease in the maximum specific growth rate (µmax) and an increase in the substrate constant (Ks) with increasing chloride concentrations, indicating an effect on the Fe2+ oxidation system. The model proposes a lowered maintenance activity when the media was fed with 2 to 3 g L-1 chloride with a concomitant drastic decrease in the true yield (Ytrue). This model helps to understand the influence of chloride on Fe2+ biooxidation kinetics.

  • 26. Gahan, Chandra Sekhar
    et al.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Engström, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Comparative assesment of Industrial oxidic by-products as neutralising agents in biooxidation and their influence on gold recovery in subsequent cyanidation2011In: Proceedings of the XI International Seminar onMineral Processing Technology (MPT-2010) / [ed] R. Ringh; A. Das; P.K. Banerjee; K.K. Bhattacharyya; N.G. Goswami, 2011, p. 1293-1302Conference paper (Refereed)
    Abstract [en]

    The neutralisation cost in bioleaching operations is one of the biggest operation costs and therefore the aim of the present study has been to replace the generally used lime/limestone with industrial oxidic by-products. A comparative study on the potential use of some selected industrial by-products as neutralising agents during biooxidation and their influence on subsequent gold recovery was carried out with reference to a commercial grade Ca(OH)2. The by-products used comprised of an electric arc furnace slag (EAF slag), and a slag from ladle refining (Ladle slag) both from scrap based steel production, an EAF dust and a lime sludge from paper and pulp industry (Mesa lime). Continuous biooxidation of a refractory gold concentrate was performed in single stage reactor at a retention time of 56 h with a mixed mesophilic culture. Biooxidation results as well as gold recoveries were good for all by-products investigated and similar to the results obtained with the slaked lime reference. However, cyanide consumption was elevated in the experiments with steel slags and the EAF dust partly because of a higher content of S° in the bioresidues in these experiments. It is however expected, that in a bioleaching operation with several reactors in series, that sulphur oxidation would be more complete, thereby possibly decreasing cyanide consumption.

  • 27.
    Gahan, Chandra Sekhar
    et al.
    SRM Research Institute, SRM University, Chennai.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Engström, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Evaluation of oxidic by-products as neutralizing agents in biooxidation of a refractory gold concentrate and their influence on gold extraction through cyanidation2013In: Research Journal of Recent Sciences, E-ISSN 2277-2502, Vol. 2(10), p. 41-47Article in journal (Refereed)
    Abstract [en]

    The neutralization cost in bioleaching operations is one of the biggest operation costs and therefore the aim of the present study has been to replace the generally used lime/limestone with industrial oxidic by-products. A comparative study on the potential use of some selected industrial by-products as neutralizing agents during biooxidation and their influence on subsequent gold recovery was carried out with reference to a commercial grade Ca(OH)2. The by-products used comprised of an electric arc furnace slag (EAF slag), and a slag from ladle refining (Ladle slag) both from scrap based steel production, an EAF dust and a lime sludge from paper and pulp industry (Mesa lime). Continuous biooxidation of a refractory gold concentrate was performed in single stage reactor at a retention time of 56 h with a mixed mesophilic culture. Biooxidation results as well as gold recoveries were good for all by-products investigated and similar to the results obtained with the slaked lime reference. However, cyanide consumption was elevated in the experiments with steel slags and the EAF dust partly because of a higher content of S in the bioresidues in these experiments. It is however expected, that in a bioleaching operation with several reactors in series, that sulfur oxidation would be more complete, thereby possibly decreasing cyanide consumption.

  • 28. Gahan, Chandra Sekhar
    et al.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Engström, Fredrik
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Utilisation of steel slags as neutralising agents in biooxidation of a refractory gold concentrate and their influence on the subsequent cyanidation2011In: Resources, Conservation and Recycling, ISSN 0921-3449, E-ISSN 1879-0658, Vol. 55, no 5, p. 541-547Article in journal (Refereed)
    Abstract [en]

    A study on the possibilities to utilise steel slag as neutralising agent in biooxidation of a refractory gold concentrate has been done with reference to commercial grade slaked lime. The idea has been to reduce the operating costs for neutralisation in the biooxidation plant, which is known to be the second largest operating cost. Other benefits would be savings in cost for landfilling of slag, possibilities to recycle elements present in the slag and savings of virgin limestone deposits. The slags used were an EAF slag and a slag from ladle refining; both originating from Swedish scrap based steel-making. Continuous biooxidation of the refractory gold concentrate was conducted in a single-stage 5 L reactor at a retention time of 56 h. The neutralisation capacity was determined by comparing the amount needed, per ton of feed concentrate added, to maintain the desired pH of 1.5 during steady state operation. Slaked lime had the highest neutralisation capacity with 110 kg/ton feed followed by ladle slag and EAF slag with values of 152 and 267 kg/ton feed, respectively. Sulphide mineral oxidation was similar and high in all cases although the ladle slag results were slightly better. Gold recoveries after cyanide leaching on the residues obtained were also similar and were in the range of 86–89%. However, the cyanide consumption expressed as kilogram cyanide per ton of concentrate fed to biooxidation, was double in the case of ladle slag and three times as much for the EAF slag compared to the slaked lime experiment. The increased cyanide consumption could not be explained only by the increased amount of elemental sulphur obtained in the slag experiments. The elemental sulphur formed had different reactivities as seen from the thiocyanate formation and cyanide losses due to thiocyanate formation were 16%, 32% and 40% for EAF slag, slaked lime and ladle slag, respectively. It is concluded that the ladle slag could be a possible replacement for limestone if they are mixed in proper proportions so that the microbial carbon dioxide demand is met whereas the EAF slag is less suitable due to the very fine reaction products obtained which gave operational problems with filtration and washing. To come further, experiments with the normal multi-stage biooxidation set-up with total retention time of 120 h should be performed which would increase the sulphur oxidation and eventually also reduce the cyanide consumption.

  • 29. Gahan, Chandra Sekhar
    et al.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A study on the toxic effects of chloride on the biooxidation efficiency of pyrite2009In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 172, no 2-3, p. 1273-1281Article in journal (Refereed)
    Abstract [en]

    Bioleaching operations in areas with limited chloride-free water and use of ashes and dust as neutralizing agents have motivated to study the chloride toxicity and tolerance level of the microorganisms. Biooxidation of pyrite using chloride containing waste ash compared with Ca(OH)2 + NaCl as neutralizing agent was investigated to evaluate the causes of low pyrite oxidation. Both precipitation of jarosite as well as the toxic effect of chloride on the microorganisms were responsible for lower pyrite recoveries. Another study with sudden exposure of chloride during pyrite biooxidation, addition of 4 g/L was lethal for the microorganisms. Addition of 2 g/L chloride resulted in precipitation of jarosite with slightly lower pyrite recovery whereas the addition of 3 g/L chloride temporarily chocked the microorganisms but activity was regained after a short period of adaptation. Population dynamics study conducted on the experiment with 3 g/L chloride surprisingly showed that Leptospirillum ferriphilum, which was dominating in the inoculum, completely disappeared from the culture already before chloride was added. Sulphobacillus sp. was responsible for iron oxidation in the experiment. Both Acidithiobacillus caldus and Sulphobacillus sp. were adaptive and robust in nature and their numbers were slightly affected after chloride addition. Therefore, it was concluded that the microbial species involved in the biooxidation of pyrite vary in population during the different stages of biooxidation.

  • 30. Gahan, Chandra Sekhar
    et al.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Use of mesalime and electric arc furnace (EAF) dust as neutralising agents in biooxidation and their effects on gold recovery in subsequent cyanidation2010In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 23, no 9, p. 731-738Article in journal (Refereed)
    Abstract [en]

    The cost of lime/limestone for neutralisation is the second largest operating cost in bioleaching. Therefore, these studies have been conducted with the aim to investigate the possibilities for use of by-products such as mesalime and electric arc furnace (EAF) dust for neutralisation during biooxidation of a refractory gold concentrate. Experiments were carried out using a retention time of 57 h in a one-stage reactor and the influence of two industrial by-products on the biooxidation performance was evaluated. The neutralising capacity of EAF dust was lower, while the mesalime was similar to the Ca(OH)2 reference. The arsenopyrite oxidation in experiments ranged from 85% to 90%, whereas the pyrite oxidation was 63-74%. In subsequent cyanidation, final gold recoveries of 90% were achieved in bioresidues from mesalime and Ca(OH)2, while the EAF dust bioresidue had a recovery of 85%. A comparatively high elemental sulphur content in EAF dust probably encapsulates part of the gold, which explains the lower recovery for the EAF dust bioresidue despite a longer residence time. Cyanide consumption was relatively high and ranged from 8.1 to 9.2 kg/ton feed after 24 h of cyanidation. Overall, the by-products tested here have proved to be feasible options as neutralising agents in bioleaching operations.

  • 31.
    Gunneriusson, Lars
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kuzmann, Ernő
    Laboratory of Nuclear Chemistry, Institute of Chemistry, Eötvös Loránd University.
    Kovacs, Krisztina
    Laboratory of Nuclear Chemistry, Institute of Chemistry, Eötvös Loránd University.
    Vertes, Attila
    Laboratory of Nuclear Chemistry, Institute of Chemistry, Eötvös Loránd University.
    Jarosite inclusion of fluoride and its potential significance to bioleaching of sulphide minerals2009In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 96, no 1-2, p. 108-116Article in journal (Refereed)
    Abstract [en]

    Incorporation of fluoride ions into the structure of jarosite, a common precipitate in bioleaching, was studied. Crystalline jarosite was synthesized in the presence of various concentrations of fluoride ions and characterized by spectroscopic- and chemical analysis.The results showed that substantial amounts of fluoride were sorbed to jarosite, increasing with pH and fluoride concentration. FTIR, XRD and Mössbauer analysis supported a structural incorporation of the fluoride. Due to the size similarity between fluoride and hydroxide ions, a probable mechanism is an exchange of hydroxide ions and fluoride ions within the jarosite, giving the composition KFe3(SO4)2(OH)6 - xFx(s). For the maximum concentration of fluoride used during synthesis, 200 mM, about 25% of the hydroxide ions were exchanged for fluoride ions. The mass of jarosite precipitated shown to be highly dependent on the fluoride concentration, with approximately half the yield using 200 mM potassium fluoride compared to in the absence of fluoride ions.To test the influence on toxicity of the incorporation of fluoride in jarosite, a bioleaching study was performed at 65 °C. A suspension of pyrite concentrate with 4% solid content (w/v) in the modified 9 K medium was bioleached under additions of potassium fluoride. The results indicated a higher tolerance for fluoride ions, as compared to earlier reported studies on fluoride toxicity during bioleaching.

  • 32.
    Johansson, Örjan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Pamidi, Taraka
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Khoshkhoo, Mohammad
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Sustainable and energy efficient leaching of tungsten(W) by ultrasound controlled cavitation2017Report (Other academic)
    Abstract [en]

    The project aims to use ultrasound controlled cavitation to achieve a more energy efficient leaching process. Locally, collapsing cavitation bubbles cause an extremely high pressure, shock waves and high temperature, which provide an opportunity to perform the leaching process at a much lower temperature than in an autoclave (20 bar overpressure and 220 ° C). The results show that the method works, but that a higher static pressure and thus temperatures are necessary to achieve a leaching recovery rate corresponding to today's autoclave technology. Another process parameter of importance is flow control and the initiation of cavitation bubbles that occur through a geometrically optimized nozzle (orifice plate). Numerical and experimental adaptation of the developed reactor with respect to the leaching conditions (Sodium hydroxide and Scheelite concentrate), required more time than expected. Best test results show that an energy supplement with ultrasonic controlled cavitation of 104 kWh / kg increases the leaching recovery by 21%. The leaching reagent temperature 60° C was determined regarding available reference data and was thought to be close to optimum for intensive cavitation in atmospheric pressure. Optimum temperature relates to the leaching reagent, vaporization temperature, density, boiling point, surface tension, and viscosity. Generally, for leaching is that higher temperatures are required to increase the chemical reaction rate (requires overpressure). The modified reactor principle provides stable results and is possible to scale up. Higher cavitation intensity for shorter finishing time and higher recovery rate require advanced flow induction, multiple excitation frequencies adapted to the optimized reactor geometry, as well as optimal process pressure and temperature.

  • 33.
    Khoshkhoo, Mohammad
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Dopson, Mark
    Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University.
    Engström, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    New insights into the influence of redox potential on chalcopyrite leaching behaviour2017In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 100, p. 9-16Article in journal (Refereed)
    Abstract [en]

    Chalcopyrite (CuFeS2) is the most economically important and most refractory copper mineral when treated in conventional sulphate media leaching systems. In this study, the effect of solution redox potential on leaching of a pure and a pyritic chalcopyrite concentrate was investigated using concentrates with fresh and aged surfaces. In experiments using concentrates with fresh surfaces, the response to redox potential depended on the presence of pyrite: fresh pyritic concentrate leached more effectively at low redox potential (in agreement with reductive leaching mechanisms), while the leaching efficiencies from fresh pure concentrate were similar at high and low redox potentials. The data suggested that the reductive leaching mechanism does not necessarily result in higher and faster recoveries in the absence of the galvanic interaction induced by the presence of pyrite. It was also found that exposure of chalcopyrite to atmospheric oxidation prior to leaching (ageing) had an effect on leaching behaviour in response to redox potential: copper recoveries in leaching of aged concentrates were higher at high redox potentials. This behaviour was attributed to the presence of iron–oxyhydroxides on the surface of aged concentrates. Based on the data from this investigation and previous surface studies, it is proposed that iron–oxyhydroxides play an important role in triggering the hindered dissolution of chalcopyrite.

  • 34.
    Khoshkhoo, Mohammad
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Dopson, Mark
    Linnaeus University, Kalmar.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Bioleaching and electrochemical leaching of a pyritic chalcopyrite concentrate2013In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 825, p. 254-257Article in journal (Refereed)
    Abstract [en]

    Moderately thermophilic bioleaching of a pyritic chalcopyrite concentrate was mimicked in an electrochemical vessel. The bioleaching was carried out for 28 days at 45°C with 2.5% (wt/vol) solid content at pH 1.5. Data from the redox potential development was used to program a redox potential controller in an electrochemical vessel to reproduce the same leaching conditions in the absence of microorganisms. Despite precipitation of iron as jarosite and formation of elemental sulphur in the electrochemical experiment, the copper recoveries were almost the same in both experiments.

  • 35.
    Khoshkhoo, Mohammad
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Dopson, Mark
    Linnaeus University, Kalmar, Department of Molecular Biology, Umeå University, Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University.
    Shchukarev, Andrey
    Department of Chemistry, Umeå University.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Chalcopyrite leaching and bioleaching: An X-ray photoelectron spectroscopic (XPS) investigation on the nature of hindered dissolution2014In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 149, p. 220-227Article in journal (Refereed)
    Abstract [en]

    Chalcopyrite (CuFeS2) is both the most economically important and the most difficult copper mineral to (bio)leach. The main reason for the slow rate of chalcopyrite dissolution is the formation of a layer on the surface of the mineral that hinders dissolution, termed “passivation”. The nature of this layer is still under debate. In this work, the role of bacterial activity was examined on the leaching efficiency of chalcopyrite by mimicking the redox potential conditions during moderately thermophilic bioleaching of a pure chalcopyrite concentrate in an abiotic experiment using chemical/electrochemical methods. The results showed that the copper recoveries were equal in the presence and absence of the mixed culture. It was found that the presence of bulk jarosite and elemental sulphur in the abiotic experiment did not hamper the copper dissolution compared to the bioleaching experiment. The leaching curves had no sign of passivation, rather that they indicated a hindered dissolution. XPS measurements carried out on massive chalcopyrite samples leached in the bioleaching and abiotic experiments revealed that common phases on the surface of the samples leached for different durations of time were elemental sulphur and iron-oxyhydroxides. The elemental sulphur on the surface of the samples was rigidly bound in a way that it did not sublimate in the ultra-high vacuum environment of the XPS spectrometer at room temperature. Jarosite was observed in only one sample from the abiotic experiment but no correlation between its presence and the hindered leaching behaviour could be made. In conclusion, a multi-component surface layer consisting of mainly elemental sulphur and iron-oxyhydroxides were considered to be responsible for the hindered dissolution.

  • 36.
    Khoshkhoo, Mohammad
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Dopson, Mark
    Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University.
    Shchukarev, Andrey
    Department of Chemistry, Umeå University.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Electrochemical Simulation of Redox Potential Development in Bioleaching of a Pyritic Chalcopyrite Concentrate2014In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 144-145, p. 7-14Article in journal (Refereed)
    Abstract [en]

    The majority of the world’s copper reserves are bound in the sulphide mineral chalcopyrite (CuFeS2), but supply of the copper is hindered by the recalcitrance of chalcopyrite to (bio)leaching. The main reason for the slow rate of chalcopyrite dissolution is the formation of a layer on the surface of the mineral that hinders dissolution, termed “passivation”. The nature of this layer and the role of microorganisms in chalcopyrite leaching behaviour are still under debate. Moderately thermophilic bioleaching of a pyritic chalcopyrite concentrate was mimicked in an electrochemical vessel to investigate the effect of absence and presence of microorganisms in copper dissolution efficiency. Data from the redox potential development during bioleaching was used to program a redox potential controller in an electrochemical vessel to accurately reproduce the same leaching conditions in the absence of microorganisms. Two electrochemical experiments were carried out with slightly different methods of redox potential control. Despite massive precipitation of iron as jarosite in one of the electrochemically controlled experiments and formation of elemental sulphur in both electrochemical experiments, the efficiencies of copper dissolution were similar in the electrochemical tests as well as in the bioleaching experiment. No passivation was observed and copper recoveries exhibited a linear behaviour versus the leaching time possibly due to the galvanic effect between chalcopyrite and pyrite. The data suggest that the main role of microorganisms in bioleaching of a pyritic chalcopyrite concentrate was regeneration of ferric iron. It was also shown that the X-Ray photoelectron spectroscopy (XPS) measurements on the residues containing bulk precipitates cannot be employed for a successful surface characterization.

  • 37.
    Koleini, S.M. Javad
    et al.
    Department of Mineral Processing, Faculty of Engineering, Tarbiat Modares University, Tehran.
    Aghazadeh, Valeh
    Department of Mineral Processing, Faculty of Engineering, Tarbiat Modares University, Tehran.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Acidic sulphate leaching of chalcopyrite concentrates in presence of pyrite2011In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 24, no 5, p. 381-386Article in journal (Refereed)
    Abstract [en]

    Copper concentrates with mineralogy dominated by chalcopyrite have slow leaching kinetics at atmospheric pressure in sulphate media because of the formation of passivation layer on its surface during the leaching. To enhance the leaching rate of the copper concentrate, pyrite was added to act as a catalyst. Pyrite and copper sulphide minerals then form a galvanic cell which increases both the copper leaching rate and yield. Effect of parameters such as solution redox potential, temperature, initial acid concentration, solids content, total initial iron concentration and pyrite to copper sulphide minerals mass ratio were investigated. Mineralogical analyses by XRD were performed on selected leach residues and the feed materials. A copper recovery higher than 80% in 24 h was achieved at a redox potential of 410 mV vs Ag, AgCl, a temperature of 85 °C, 15 g/L of initial acid concentration, a solid content of 7.8% (w/v), a total initial iron concentration 5 g/L and pyrite to copper sulphide minerals mass ratio 2:1. XRD patterns on leach residues showed that candidates for surface passivation, i.e. jarosite and elemental sulphur, were formed at high total initial iron concentrations

  • 38.
    Kovács, Krisztina
    et al.
    Eötvös Loránd University.
    Kuzmann, E.
    Hungarian Academy of Sciences.
    Homonnay, Z.
    Hungarian Academy of Sciences.
    Vértes, Attila
    Hungarian Academy of Sciences.
    Gunneriusson, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mössbauer study of synthetic jarosites2008In: Hyperfine Interactions, ISSN 0304-3843, E-ISSN 1572-9540, Vol. 186, no 1-3, p. 69-73Article in journal (Refereed)
    Abstract [en]

    57Fe Mössbauer spectroscopy and PXRD were used to study artificially prepared jarosites with the compositions of KFe3(SO4)2(OH)6 - x F x x = 0 - 1.6 PXRD measurements revealed single phase jarosite samples. All Mössbauer spectra taken at room temperature exhibit a quadrupole doublet corresponding to mineral jarosite. However, at low temperature where the mineral jarosite has a well resolved sextet, the synthetic jarosite even with x = 0 F -  content shows a relaxation transition. The spectra indicate that with increasing F -  concentration, the paramagnetic-antiferromagnetic transition temperature is decreasing. The results can be used in the analysis of artificial jarosites or those formed during biomineralization processes.

  • 39.
    Lindblom, B
    et al.
    Luleå tekniska universitet.
    Samuelsson, Caisa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sandström, Åke
    Ye, Guozhu
    Swerea MEFOS AB.
    Fine-particle characterization an important recycling tool2002In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 54, no 12, p. 35-38Article in journal (Refereed)
    Abstract [en]

    This paper summarizes the results from different research projects on fine-particle characterization of metallurgical residues, such as hydroxide sludge, electric-arc, furnace dust, and copper-converter dust. These studies demonstrated that characterization is essential for developing new recycling strategies. The basic knowledge of the chemical and physical properties of the residues obtained by the characterizations also provides necessary information on potential problems that could be encountered during the processing of such materials.

  • 40.
    Lindblom, B
    et al.
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Menad, Nourreddine
    Thermal decomposition of zinc hydroxo-carbonate obtained after leaching of EAF dust2003In: EPD Congress 2003: proceedings of sessions and symposia sponsored by the Extraction and Processing Division (EPD) of TMS (The Minerals, Metals & Materials Society) held during the 2003 TMS annual meeting in San Diego, California, March 2 - 6, 2003 / [ed] Mark E. Schlesinger, Warrendale, Pa.: Minerals, Metals & Materials Society, 2003, p. 365-376Conference paper (Refereed)
    Abstract [en]

    An EAF dust generated in a Swedish steel mill has been leached in hydrochloric acid at pH = 3. The solution obtained has been subjected to purification by cementation followed by precipitation of zinc with sodium carbonate. The thermal decomposition of the precipitate was studied using thermal analysis and X-ray diffraction. The results show that during the calcination of the precipitate three different reactions occur. The decomposition of the solid phases Zn5(CO3)2(OH)6, CaZn(CO3)2 and CaCO3 occur completely at 370DGC, 560DGC and 940DGC respectively, yielding a final product containing 61.9% ZnO and 38.1% CaO. Methods to minimize calcium and manganese in the final product are discussed.

  • 41.
    Lindström, E. Börje
    et al.
    Umeå universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sundkvist, Jan-Eric
    Boliden Mineral AB.
    A sequential two-step process using moderately and extremely thermophilic cultures for biooxidation of refractory gold concentrates2003In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 71, no 1-2, p. 21-30Article in journal (Refereed)
    Abstract [en]

    In many cases, the use of extreme thermophiles, like the archeon Sulfolobus metallicus, in a continuous bioleaching process of gold concentrates is limited by the arsenic content in the feed. In this work, a sequential two-step bioleaching process for gold-containing refractory pyrite/arsenopyrite concentrates has been investigated for the possibility of lowering the toxicity of arsenic with respect to the extremely thermophilic culture. In the first stage, a moderately thermophilic culture was used followed by the extremely thermophilic S. metallicus in the second stage. It was found that the S. metallicus culture survives higher arsenic concentrations than expected when the concentrate was pre-oxidized at a lower temperature. Thus, with this sequential two-step bioleaching process, it is possible to reduce the toxicity of the released arsenic. Therefore, the use of higher pulp densities of arsenic-containing minerals is enabled. When the leached mineral residues were subjected to cyanidation, cyanide consumption and thiocyanate formation were significantly lower after the second stage. In addition, a somewhat higher gold and silver grade was found in the residue from the concentrate ultimately oxidized by S. metallicus.

  • 42.
    Liu, X.
    et al.
    Luleå tekniska universitet.
    Pettersson, Stig
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mesophilic vs. Moderate Thermophilic Bioleaching1993In: Biohydrometallurgical technologies: proceedings of an International Biohydrometallurgy Symposium held in Jackson Hole, Wyoming, USA, August 22-25, 1993 / [ed] Arpad E. Torma, Warrendale, Pa: Minerals, Metals & Materials Society, 1993, p. 29-38Conference paper (Refereed)
    Abstract [en]

    A comparative study on bioleaching with mesophilic and moderate thermophilic bacteria has been performed. The study was carried out by continuous bioleaching with a series of three reactors with a total volume of 20 l. A refractory gold flotation concentrate consisting mainly of pyrite and with a relatively high arsenopyrite content has been used for the study. The correlation between the pyrite and the arsenopyrite oxidation levels and the gold recoveries after cyanidation has been determined. The leaching rates of pyrite in the different experiments as well as the calculated oxygen uptake rates are presented. Anomalies in the gold recoveries between experiments with different types of bacterial are discussed.

  • 43.
    Liu, Xiaoyue
    et al.
    Luleå tekniska universitet.
    Pettersson, Stig
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Evaluation of process variables in bench-scale biooxidation of the Olympias concentrate1993In: FEMS Microbiology Reviews, ISSN 0168-6445, E-ISSN 1574-6976, Vol. 11, no 1-3, p. 207-214Article in journal (Refereed)
    Abstract [en]

    A statistically designed set of eight bio-oxidation tests on the Olympias concentrate was conducted in bench-scale equipment to evaluate the effects of important variables on pyrite/arsenopyrite oxidation and gold extraction. The variables studied were total retention time, feed solid concentration and particle size. High degrees of arsenopyrite oxidation were observed in all tests, as the arsenopyrite oxidation was very fast and therefore not dependent on the variables within the studied range. Statistical analysis of the experimental data reveals that the pyrite oxidation and gold extraction are dependent mainly on the retention time and to a lesser extent on the particle size. The feed solid concentration had a small influence only on the gold extraction. Regressed equations of the experimental data can be used to predict proper operating conditions

  • 44.
    Mehtap, Paul
    et al.
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Paul, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Bioleaching of sulphidic concentrates ans pH-control with ashes2007In: World of coal ash: 2007 proceedings ; science, applications and sustainability ; Covington, Kentucky, May 7 - 10, 2007 ; 2007 World of Coal Ash (WOCA) Conference, Lexington, Ky, 2007Conference paper (Refereed)
  • 45.
    Nilsson, L.
    et al.
    Luleå tekniska universitet.
    Pettersson, Stig
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Iron and arsenic removal from bacterial leaching effluents by precipitation with limestone1994In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 23, no 4, p. 184-189Article in journal (Refereed)
    Abstract [en]

    By bacterial leaching of bulk concentrates of complex sulphide ores, acid leachates are produced which besides valuable metals as zinc and copper also contain high concentrations of impurities such as iron and arsenic, In order to evaluate the proper conditions for removal of iron and arsenic by precipitation as ferric arsenate with limestone, a series of batch precipitation experiments was conducted at various pH values in the range 2-6. The results from these tests showed that pentavalent arsenic and ferric iron can be effectively precipitated to low concentrations when the precipitation is carried out at pH 3 without causing losses of zinc; however, the ferrous iron, approximately 1 g/l, remains in solution. When the precipitation is carried out at pH above 3 in order to oxidize ferrous iron, unacceptable high zinc losses were obtained.

  • 46.
    Nilsson, L.
    et al.
    Luleå tekniska universitet.
    Pettersson, Stig
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    New process for zinc recovery from bacterial leach solutions1996In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 25, no 4, p. 161-171Article in journal (Refereed)
    Abstract [en]

    As an alternative to traditional treatment of complex zinc-containing sulphide ores, application of bio-hydrometallurgical routes can be a possible and economical alternative. When the bio-leaching of such ores or concentrates takes place, dilute acidic leachates are produced, which in addition to valuable metals as zinc and copper, also contain high concentrations of impurities such as iron and arsenic. The aim of the present study has been to develop a new process for recovery of zinc and other base metal values from such leachates. In this process, iron and arsenic are precipitated from the leachate with limestone at pH 3. After a solid/liquid separation step the pH is further increased by lime addition whereby zinc, copper and cadmium are precipitated. The hydroxides formed are after a solid/liquid separation step dissolved with sulphuric acid generated by electrowinning of zinc. As a result a solution concentrated in zinc is produced, which after solid/liquid separation and purification, is fed to the tank house for electrolytic production of zinc metal. The results showed that the proposed process is capable of recovering metal values from leachates of variable compositions. Furthermore, the process can handle solutions which contain chloride, thus giving the method an advantage over conventional zinc electrowinning processes. Raw materials and neutralising agents which contain fluoride and to a lesser extent magnesium must, however, be avoided.

  • 47.
    Paul, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Paul, Mehtap
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Aycik, Gul Asiye
    Seferinoglu, Meryem
    Acid leaching of coal and coal-ash: kinetics and dominant ions2004In: American Chemical Society, 228th National Meeting, Washington, DC: American Chemical Society (ACS), 2004Conference paper (Other academic)
    Abstract [en]

    The leaching of ash in sulfuric acid (pH 1.0, 25EC, S/L 1:10) was studied as a function of time. Data for the acid consumption and the extraction of dominant ions are presented. The study embraced 14 coal- ashes, including lignite-ash and ash from the combustion of asphaltites and softwood sawmill residues. The kinetics of acid consumption for ash treatment was compared with the acid consumption of the corresponding ground coals (250-1000 _m fraction). The whole coals consumed acid rapidly during the first few minutes, followed by almost negligible consumption. Coal-ashes consumed acid in two stages, one rapid extending < 30 min and one slow extending ca. 10 days. The rapid phase was dominated by the dissolution of Ca, K and Mg ions for wood-ash, by Ca, Al and Mg ions for lignite-ash and Ca and Mg ions for ash from asphaltites. The slow phase was different for the different fuels, but embraced the leaching of several elements - Fe, Al, K, Na and Mn - with kinetics well described by a diffusion controlled shrinking core model (SCM). The sulfur concentration in solution and the concentration of Ca, Fe, K, Mg, Na, P, Al and Mn in the aqueous phase verified the neutralizing capacity of the untreated ashes as well as the formation of insoluble sulfates in the residues.

  • 48.
    Paul, M.
    et al.
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Paul, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prospects for cleaning ash in the acidic effluent from bioleaching of sulfidic concentrates2004In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 106, no 1, p. 39-54Article in journal (Refereed)
    Abstract [en]

    Leaching of ashes in sulfuric acid (pH 1.0, liquid-to-solid (L/S) ratio 10:1, 25 °C) has been characterized with respect to the neutralizing capacity and the dissolution of dominant ions and trace elements. The conditions mimic the oxidation stage of a biohydrometallurgical process for base metal production from sulfidic mineral concentrates. Direct acid leaching of ash, integrated with this metallurgical process, offers a feasible route to the sustainable handling of metal-rich ashes. The treated ash will be deposited together with the inert mineral residue. Cd, Co, Cu, Ni and Zn are effectively leached and can be recovered utilizing existing hydrometallurgical technology, but the recovery of other readily dissolved metals, notably Mn, U and V, requires that additional steps are implemented. We make two recommendations for industrial processes. The first is to replace limestone with ash from biofuels, except peat, for pH control in biohydrometallurgical processing. This requires a modest increase of fresh alkali compared with limestone. The second is to implement sulfuric acid leaching of fly ash from the combustion of solid waste and other metal-rich fuels (used wood, tires), thereby avoiding costly ash-deposits. There is a significant economic incentive for these changes, since no costly ash-deposits and less limestone will be needed.

  • 49.
    Paul, Mehtap
    et al.
    Turkish Atomic Energy Authority, Ankara Nuclear Research and Training Center.
    Seferinoğlu, Meryem
    MTA, Mineral Research and Exploration Directorate, 06520 Balgat, Ankara.
    Ayçık, Gul Asiye
    Turkish Atomic Energy Authority, Ankara Nuclear Research and Training Center.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Smith, Michael L.
    Anabolic Laboratories, Inc., Tempe, AZ.
    Paul, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Acid leaching of ash and coal: time dependence and trace element occurrences2006In: International Journal of Mineral Processing, ISSN 0301-7516, E-ISSN 1879-3525, Vol. 79, no 1, p. 27-41Article in journal (Refereed)
    Abstract [en]

    The leaching of coal and coal/asphaltite/wood-ashes in sulfuric acid (pH 1.0, 25 °C, S/L, 1:10) was studied as a function of time; acid consumption and extracted metal concentrations are presented. Whole coals consumed acid rapidly during the first few minutes, followed by slow acid consumption. Wood-, lignite-, and asphaltite-ashes consumed acid in two stages, the rapid phase extending < 30 min and the slow phase extended up to 10 days. The rapid phase was dominated by the dissolution of Ca, K and Mg ions for wood-ash, by Ca, Al and Mg ions for lignite-ash and Ca and Mg ions for asphaltite-ash. The sulfur concentration in solution and the concentrations of Ca, Fe, K, Mg, Na, P, Al and Mn in the aqueous phase verified the neutralizing capacity of the untreated ashes as well as the formation of insoluble sulfates in the residues. The slow phase kinetics differed for different fuels and exhibited leaching of several abundant elements-Fe, Al, K, Na and Mn. Trace elements (Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Th, U, V, Zn) sometimes required up to 32 h for maximal extraction from ashes. Suggestions are presented regarding the chemical nature of trace elements in the untreated coals and ashes and suitable residence times for economical industrial processes. We think it possible to combine bacteriological oxidation of sulfidic concentrates of acid leaching from ash of various qualities or even whole coals.

  • 50.
    Petersson, Stig
    et al.
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Bioteknisk metallutvinning ur komplexmalmer1994In: Konferens i mineralteknik: Luleå, 2-4 februari 1993 / [ed] Marianne Thomaeus; Eric Forssberg, MinFo , 1994, p. 127-136Conference paper (Other academic)
12 1 - 50 of 68
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