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  • 1.
    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.

  • 2.
    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.

  • 3.
    Gahan, Chandra Sekhar
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Comparative study on different industrial oxidic by-products as neutralising agent in bioleaching2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A comparative study on bioleaching of a pyrite concentrate using ten different industrial oxidic by-products as neutralising agent has been performed with a commercial grade slaked lime chemical serving as reference material. The acid produced during oxidation of pyrite was neutralised by regular additions of neutralising agent whenever needed to maintain a pH of 1.5. Bioleaching was conducted as batch experiments in 1-L scale reactors, with a mixed mesophilic culture at a temperature of 35º C. The different industrial oxidic by-products used were steel slag, ashes, dust and lime sludge. The aim of the study was to investigate the possibility to replace normally used lime or limestone with oxidic by-products, considering their neutralising capacities and possible negative impact on the bacterial activity. The bioleaching efficiency was found to be equally good or better, when by-products were used for neutralisation instead of slaked lime, and the bioleaching yields of pyrite were in the range 69-80%, except the Waste ash, which had a leaching yield of 59%. Some of the by-products 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. The Waste ash contained a large number potentially toxic elements and a high chloride concentration of 11%, which had a negative effect as observed on the lower redox potential and leaching yield. Slags originating from stainless steel production should be avoided for environmental reasons, due to the presence of chromium. The electric arc furnace (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 all the steel slags, EAF dust, Bioash and Mesalime with a range of 16-37 g 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. Hence, it is concluded that considerable savings in operational costs can be obtained by replacement of lime or limestone with steel slag, ash, dust or sludge without negative impact on bioleaching efficiency. Use of industrial oxidic by-products would provide opportunities to recycle elements present in them as for example zinc rendering an eco-friendly process and a means for sustainable use of natural resources.

  • 4.
    Gahan, Chandra Sekhar
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Possibilities to use industrial oxidic by-products as neutralising agent in bioleaching and the effect of chloride on biooxidation2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The cost for neutralisation is the second largest cost in a bioleaching operation for which, possibilities to replace generally used lime/limestone was tested. Industrial oxidic by-products generated form Swedish industries were investigated for neutralising capacities by chemical leaching with sulphuric acid at pH 1.5, which is the optimum pH for bioleaching operations. The by-products used for the study comprised of five different steel slags from ore and scrap based steel making, electric arc furnace (EAF) dust from scrap based steel plant, Mesalime from paper and pulp industry and three different types of ashes from combustion for energy production. All the by-products showed a good neutralising capacity, while some of them had higher capacities than the reference Ca(OH)2. Due to the good neutralising potential of the by-products obtained from the chemical leaching, attempts were made to use them as neutralising agent in batch bioleaching of pyrite in stirred tank reactor to determine their neutralising potential, eventual toxic effects on the microorganisms and pyrite oxidation. Pyrite oxidation in all the batch bioleaching was in the range of 69-80%, except the Waste ash experiment which was 59%. Neutralising capacity was high for all the by-products except Waste ash and Coal & Tyres ash compared to slaked lime. No remarkable toxic effects due to the by-products were observed except in the Waste ash experiment, which was probably due to the high content of chloride. To confirm if the chloride in the Waste ash caused any toxic effect on the bioxidation activity, batch bioleaching studies were conducted with Ca(OH)2 + NaCl as neutralizing agent with a similar chloride concentration profile obtained in the Waste ash experiment. Effect of the chloride on the biooxidation of pyrite by sudden exposure of 2 g/L, 3 g/L, and 4 g/L of chloride in the log phase of the biooxidation of pyrite was investigated. Addition of 2 g/L chloride resulted jarosite precipitation with a lower pyrite recovery than the reference experiment, 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 showed the variation in the microbial species at different stages of the biooxidation of pyrite. The study with sudden exposure of 4 g/L of chloride was found to be lethal to the microbes. Out of all the by-products used in batch bioleaching studies, Mesalime and Electric Arc Furnace (EAF) dust were used as a neutralising agent in continuous biooxidation of refractory gold concentrate. The neutralising capacity of EAF dust was lower, while the Mesalime was similar to the Ca(OH)2 reference. The arsenopyrite oxidation in the experiments ranged from 85-90%, whereas the pyrite oxidation was 63-74%. In subsequent cyanidation 90% of the gold was achieved in the bioresidues from Mesalime and Ca(OH)2, while 85% of gold was recovered in bioresidue from EAF dust. A probable explanation for the low recovery of gold from the EAF dust experiment could be due to the encapsulation of the part of the gold by high elemental sulphur content present in the EAF dust. Cyanide consumption was relatively high and ranged from 8.1-9.2 kg/tonne feed after 24 hours of cyanidation. Both Mesalime and EAF dust proved to be feasible options as neutralising agents in bioleaching operations. Studies on the modelling of ferrous iron oxidation by a Leptospirillum ferriphilum-dominated culture was conducted with 9 g/L or 18 g/L ferrous iron in a chemostat. Modelling data suggested that the kinetics and yield parameters changed with the overall solution composition. The apparent Fe3+ inhibition on specific Fe2+ utilisation rate was a direct consequence of the declining biomass yield on the Fe2+ oxidation, when dilution rate was decreased. The maintenance activity contributed up to 90% of the maximum specific Fe2+ utilisation rate, which appears close to the critical dilution rate. Determination of the toxic limit of chloride were studied both in batch and chemostat conditions. Batch studies showed a toxic limit at 12 g/L chloride, while chemostat studies showed a toxic limit of 4 g/L. Modelling of the ferrous iron oxidation in chloride environment showed a decrease in maximum specific growth rate and increase in the substrate constant. The biomass concentration decreased with the increase in chloride concentration due to the toxic effect on the microorganisms. The maintenance coefficient decreased by 70% in the chloride environment.

  • 5. 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.

  • 6. 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.

  • 7. 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.

  • 8. 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)
  • 9. 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.

  • 10. 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.

  • 11. 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.

  • 12. 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.

  • 13. 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.

  • 14.
    Pradhan, Nilotpala
    et al.
    Regional Research Laboratory, CSIR, Bhubaneshwar 751 013, India.
    Das, B.
    Regional Research Laboratory, CSIR, Bhubaneshwar 751 013, India.
    Gahan, Chandra Sekhar
    Kar, Rabi Narayana
    Regional Research Laboratory, CSIR, Bhubaneshwar 751 013, India.
    Sukla, Lala Bihari
    Regional Research Laboratory, CSIR, Bhubaneshwar 751 013, India.
    Beneficiation of iron ore slime using Aspergillus niger and Bacillus circulans2006In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 97, no 15, p. 1876-1879Article in journal (Refereed)
    Abstract [en]

    Studies were carried out on the removal of alumina from iron ore slime containing (%) Fe2O3 75.7, Al2O3 9.95, SiO2 6.1, Fe (total) 52.94 with the help of Bacillus circulans and Aspergillus niger. B. circulans and A. niger showed 39% and 38% alumina removal after six and 15 days of in situ leaching at 10% pulp density, respectively. Culture filtrate leaching with A. niger removed 20% alumina at 2% pulp density with 13 day old culture filtrate. B. circulans was more efficient than A. niger for selective removal of alumina. In case of A. niger in situ leaching rather than culture filtrate leaching was found to be more effective

  • 15.
    Sundkvist, Jan-Eric
    et al.
    Boliden Mineral AB.
    Gahan, Chandra Sekhar
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Modeling of ferrous iron oxidation by a Leptospirillum ferrooxidans-dominated chemostat culture2008In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 99, no 2, p. 378-389Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to evaluate a direct classical bioengineering approach to model data generated from continuous bio-oxidation of Fe2+ by a Leptospirillum ferrooxidans-dominated culture fed with either 9 g or 18 g Fe2+ L-1 under chemostat conditions (dilution rates were between 0.051 and 0.094 h-1). The basic Monod and Pirt equations have successfully been integrated in an overall mass balance procedure, which has not been previously presented in this detail for Fe2+ oxidation. To ensure chemostat conditions, it was found that the range of the dilution rates had to be limited. A too long retention time might cause starvation or non-negligible death rate whereas, a too short retention time may cause a significant alteration in solution chemistry and culture composition. Modeling of the experimental data suggested that the kinetic- and yield parameters changed with the overall solution composition. However, for respective feed solutions only minor changes of ionic strength and chemical speciation can be expected within the studied range of dilution rates, which was confirmed by thermodynamic calculations and conductivity measurements. The presented model also suggests that the apparent Fe3+ inhibition on specific Fe2+ utilization rate was a direct consequence of the declining biomass yield on Fe2+ due to growth uncoupled Fe2+ oxidation when the dilution rate was decreased. The model suggested that the maintenance activities contributed up to 90% of the maximum specific Fe2+ utilization rate, which appears close to the critical dilution rate.

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