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Gahan, Chandra Sekhar
Publications (10 of 15) Show all publications
Gahan, C. S., Sundkvist, J.-E., Engström, F. & Sandström, Å. (2011). Comparative assesment of Industrial oxidic by-products as neutralising agents in biooxidation and their influence on gold recovery in subsequent cyanidation (ed.). In: (Ed.), R. Ringh; A. Das; P.K. Banerjee; K.K. Bhattacharyya; N.G. Goswami (Ed.), Proceedings of the XI International Seminar onMineral Processing Technology (MPT-2010): . Paper presented at International Seminar on Mineral Processing Technology : 15/12/2010 - 17/12/2010 (pp. 1293-1302).
Open this publication in new window or tab >>Comparative assesment of Industrial oxidic by-products as neutralising agents in biooxidation and their influence on gold recovery in subsequent cyanidation
2011 (English)In: 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, Published 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.

National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-31442 (URN)59d2ab70-c3e5-11df-a707-000ea68e967b (Local ID)59d2ab70-c3e5-11df-a707-000ea68e967b (Archive number)59d2ab70-c3e5-11df-a707-000ea68e967b (OAI)
Conference
International Seminar on Mineral Processing Technology : 15/12/2010 - 17/12/2010
Note
Godkänd; 2010; 20110412 (andbra)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-28Bibliographically approved
Gahan, C. S., Sundkvist, J.-E., Engström, F. & Sandström, Å. (2011). Utilisation of steel slags as neutralising agents in biooxidation of a refractory gold concentrate and their influence on the subsequent cyanidation (ed.). Paper presented at . Resources, Conservation and Recycling, 55(5), 541-547
Open this publication in new window or tab >>Utilisation of steel slags as neutralising agents in biooxidation of a refractory gold concentrate and their influence on the subsequent cyanidation
2011 (English)In: Resources, Conservation and Recycling, ISSN 0921-3449, E-ISSN 1879-0658, Vol. 55, no 5, p. 541-547Article in journal (Refereed) Published
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.

National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-9285 (URN)10.1016/j.resconrec.2011.01.005 (DOI)000289327800006 ()2-s2.0-79952536755 (Scopus ID)7dfd50b0-c3e3-11df-a707-000ea68e967b (Local ID)7dfd50b0-c3e3-11df-a707-000ea68e967b (Archive number)7dfd50b0-c3e3-11df-a707-000ea68e967b (OAI)
Note
Validerad; 2011; 20100919 (sekgah)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Gahan, C. S., Cunha, M. L., Sundkvist, J.-E. & Sandström, Å. (2010). Application of industrial oxidic by-products as neutralising agent in bioleaching (ed.). In: (Ed.), B.B. Mishra; H.N. Thatoi (Ed.), Microbial Biotechnology: (pp. 254-297). Paper presented at . New Delhi, India: A.P.H. Publishing Corp.
Open this publication in new window or tab >>Application of industrial oxidic by-products as neutralising agent in bioleaching
2010 (English)In: Microbial Biotechnology, New Delhi, India: A.P.H. Publishing Corp. , 2010, p. 254-297Chapter in book (Other academic)
Place, publisher, year, edition, pages
New Delhi, India: A.P.H. Publishing Corp., 2010
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-20115 (URN)210b0430-8bf6-11df-8806-000ea68e967b (Local ID)9788131308493 (ISBN)210b0430-8bf6-11df-8806-000ea68e967b (Archive number)210b0430-8bf6-11df-8806-000ea68e967b (OAI)
Note
Godkänd; 2010; 20100710 (sekgah)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Gahan, C. S., Sundkvist, J.-E., Dopson, M. & Sandström, Å. (2010). Effect of chloride on ferrous iron oxidation by a Leptospirillum ferriphilum-dominated chemostat culture (ed.). Biotechnology and Bioengineering, 106(3), 422-431
Open this publication in new window or tab >>Effect of chloride on ferrous iron oxidation by a Leptospirillum ferriphilum-dominated chemostat culture
2010 (English)In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 106, no 3, p. 422-431Article in journal (Refereed) Published
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.

Keywords
ferrous iron oxidation, chloride, modeling, chemostat, Leptospirillum ferriphilum
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-3533 (URN)10.1002/bit.22709 (DOI)000277817300009 ()20198654 (PubMedID)2-s2.0-77953547607 (Scopus ID)15ccf040-1c09-11df-be83-000ea68e967b (Local ID)15ccf040-1c09-11df-be83-000ea68e967b (Archive number)15ccf040-1c09-11df-be83-000ea68e967b (OAI)
Note

Validerad; 2010; 20100217 (sekgah)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2019-09-25Bibliographically approved
Gahan, C. S., Sundkvist, J.-E. & Sandström, Å. (2010). Use of mesalime and electric arc furnace (EAF) dust as neutralising agents in biooxidation and their effects on gold recovery in subsequent cyanidation (ed.). Paper presented at . Minerals Engineering, 23(9), 731-738
Open this publication in new window or tab >>Use of mesalime and electric arc furnace (EAF) dust as neutralising agents in biooxidation and their effects on gold recovery in subsequent cyanidation
2010 (English)In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 23, no 9, p. 731-738Article in journal (Refereed) Published
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.

Keywords
Mesalime, EAF dust, Neutralisation, Biooxidation, Cyanidation, Other technology - Environmental engineering, Övriga teknikvetenskaper - Miljöteknik
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-12196 (URN)10.1016/j.mineng.2010.04.012 (DOI)000280614700010 ()2-s2.0-77955307018 (Scopus ID)b4a61e90-5529-11df-a0f4-000ea68e967b (Local ID)b4a61e90-5529-11df-a0f4-000ea68e967b (Archive number)b4a61e90-5529-11df-a0f4-000ea68e967b (OAI)
Note
Validerad; 2010; 20100501 (sekgah)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Gahan, C. S., Sundkvist, J.-E. & Sandström, Å. (2009). A study on the toxic effects of chloride on the biooxidation efficiency of pyrite (ed.). Paper presented at . Journal of Hazardous Materials, 172(2-3), 1273-1281
Open this publication in new window or tab >>A study on the toxic effects of chloride on the biooxidation efficiency of pyrite
2009 (English)In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 172, no 2-3, p. 1273-1281Article in journal (Refereed) Published
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.

National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-11369 (URN)10.1016/j.jhazmat.2009.07.133 (DOI)000271980800101 ()19720455 (PubMedID)2-s2.0-71749112371 (Scopus ID)a51f0780-7d0b-11de-8da0-000ea68e967b (Local ID)a51f0780-7d0b-11de-8da0-000ea68e967b (Archive number)a51f0780-7d0b-11de-8da0-000ea68e967b (OAI)
Note
Validerad; 2009; 20090730 (sekgah)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Gahan, C. S., Cunha, M. L. & Sandström, Å. (2009). Comparative study on different steel slags as neutralising agent in bioleaching (ed.). Paper presented at . Hydrometallurgy, 95(3-4), 190-197
Open this publication in new window or tab >>Comparative study on different steel slags as neutralising agent in bioleaching
2009 (English)In: Hydrometallurgy, ISSN 0304-386X, E-ISSN 1879-1158, Vol. 95, no 3-4, p. 190-197Article in journal (Refereed) Published
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.

Keywords
Technology - Chemical engineering, Teknikvetenskap - Kemiteknik
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-7811 (URN)10.1016/j.hydromet.2008.05.042 (DOI)000262593400003 ()2-s2.0-57049164217 (Scopus ID)63a9da20-3fb1-11dd-8634-000ea68e967b (Local ID)63a9da20-3fb1-11dd-8634-000ea68e967b (Archive number)63a9da20-3fb1-11dd-8634-000ea68e967b (OAI)
Note
Validerad; 2009; 20080621 (sekgah)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Gahan, C. S., Cunha, M. L. & Sandström, Å. (2009). Possibilities to use industrial oxidic by-products as neutralising agent in bioleaching (ed.). In: (Ed.), Edgardo R. Donati; Marisa R. Viera; Eduardo L. Tavani; Maria A. Giaveno; Teresa L. Lavalle; Patricia A. Chiacchiarini (Ed.), IBS 2009 Abstract Book: . Paper presented at International Biohydrometallurgy Symposium : 13/09/2009 - 17/09/2009 (pp. 139).
Open this publication in new window or tab >>Possibilities to use industrial oxidic by-products as neutralising agent in bioleaching
2009 (English)In: 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, Meeting abstract (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.

National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-29457 (URN)2f229d20-c3ec-11df-a707-000ea68e967b (Local ID)2f229d20-c3ec-11df-a707-000ea68e967b (Archive number)2f229d20-c3ec-11df-a707-000ea68e967b (OAI)
Conference
International Biohydrometallurgy Symposium : 13/09/2009 - 17/09/2009
Note
Godkänd; 2009; 20100919 (sekgah)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-25Bibliographically approved
Gahan, C. S. (2009). Possibilities to use industrial oxidic by-products as neutralising agent in bioleaching and the effect of chloride on biooxidation (ed.). (Doctoral dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Possibilities to use industrial oxidic by-products as neutralising agent in bioleaching and the effect of chloride on biooxidation
2009 (English)Doctoral 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.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2009. p. 81
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-26279 (URN)d7b3b240-cf68-11de-b769-000ea68e967b (Local ID)978-91-7439-049-0 (ISBN)d7b3b240-cf68-11de-b769-000ea68e967b (Archive number)d7b3b240-cf68-11de-b769-000ea68e967b (OAI)
Note
Godkänd; 2009; 20091112 (sekgah); DISPUTATION Ämnesområde: Processmetallurgi/Process Metallurgy Opponent: Professor S. Subramanian, Indian Institute of Science, Indien Ordförande: Professor Åke Sandström, Luleå tekniska universitet Tid: Måndag den 21 december 2009, kl 10.00 Plats: F 531, Luleå tekniska universitetAvailable from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-24Bibliographically approved
Gahan, C. S. (2008). Comparative study on different industrial oxidic by-products as neutralising agent in bioleaching (ed.). (Licentiate dissertation). Paper presented at . Luleå: Luleå tekniska universitet
Open this publication in new window or tab >>Comparative study on different industrial oxidic by-products as neutralising agent in bioleaching
2008 (English)Licentiate 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.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2008. p. 46
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757 ; 2008:19
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
urn:nbn:se:ltu:diva-26739 (URN)fdf1af30-257c-11dd-9e62-000ea68e967b (Local ID)fdf1af30-257c-11dd-9e62-000ea68e967b (Archive number)fdf1af30-257c-11dd-9e62-000ea68e967b (OAI)
Note
Godkänd; 2008; 20080519 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-11-24Bibliographically approved
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