| 1. |
- Das, A., et al.
(författare)
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Surface chemical and adsorption studies using Thiobacillus ferrooxidans with reference to bacterial adhesion to sulfide minerals
- 1999
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Ingår i: Biohydrometallurgy and the Environment toward the Mining of the 21st century. - : Elsevier. - 0444501932 ; , s. 697-707
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Konferensbidrag (refereegranskat)abstract
- Adhesion of Thiobacillus ferrooxidans to pyrite and chalcopyrite in relation to its importance in bioleaching and bioflotation has been studied. Electrokinetic studies as well as FT-IR spectra suggest that the surface chemistry of Thiobacillus ferrooxidans depends on bacterial growth conditions. Sulfur-,Pyrite- and chalcopyrite-grown Thiobacillus ferrooxidans were found to be relatively more hydrophobic. The altered surface chemistry of Thiobacillus ferrooxidans was due to secretion of newer and specific proteinaceous compounds. The adsorption density corresponds to a monolayer coverage in a horizontal orientation of the cells. The xanthate flotation of pyrite in presence of Thiobacillus ferrooxidans is strongly depressed where as the cells have insignificant effect on chalcopyrite flotation. This study demonstrate that:(a)Thiobacillus ferrooxidans cells can be used for selective flotation of chalcopyrite from pyrite and importantly at natural pH values.(b)Sulfur-grown cells exhibits higher leaching kinetics than ferrous ion-grown cells.
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| 2. |
- Dahlberg, D, et al.
(författare)
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Measurements of the ferromagnetic/antiferromagnetic interfacial exchange energy in CO/CoO and Fe/FeF2 layers
- 1998
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 83:11, s. 6893-6895
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Tidskriftsartikel (refereegranskat)abstract
- Two measurement techniques, both relying on reversible rotations of the magnetization, have been used to determine the magnitude of the interfacial exchange energy (IEE) between ferromagnetic and antiferromagnetic (F/AF) layers. One technique is to use the anisotropic magnetoresistance to determine rotations of the magnetization away from the unidirectional easy axis, where the rotation is accomplished by applying external magnetic fields less than the effective F/AF exchange field. The second technique uses measurements of the ac susceptibility as a function of the angle between the ac field and the unidirectional exchange field. Both of the reversible process techniques result in values of the IEE larger (by as much as a factor of 10 in Co/CoO bilayers) than the traditional irreversible technique of measuring a shift in the hysteresis loop. The ac susceptibility technique was also used to measure one Fe/FeF2 bilayer. For this sample, the IEE values obtained by reversible and irreversible methods are equivalent.
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| 3. |
- Deo, N., et al.
(författare)
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Biodegradation of some organic reagents from mineral process effluents
- 1999
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Ingår i: Biohydrometallurgy and the Environment toward the Mining of the 21st century. - : Elsevier. - 0444501932 ; , s. 687-696
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Konferensbidrag (refereegranskat)abstract
- The utility of a soil microbe, namely Bacillus polymyxa, in the removal of organic reagents such as dodecylamine, ether diamine, isopropyl xanthate and sodium oleate from aqueous solutions is demonstrated. Time-bound removal of the above organic reagents from an alkaline solution was investigated under different experimental conditions during bacterial growth and in the presence of metabolites by frequent monitoring of residual concentrations as a function of time, reagent concentration and cell density. The stages and mechanisms in the biodegradation process were monitored through UV-visible and FTIR spectroscopy. Surface chemistry of the bacterial cells as well as the biosorption tendency for various organics were also established through electrokinetic and adsorption density measurements. Both the cationic amines were found to be biosorbed followed by their degradation through bacterial metabolism. The presence of the organic reagents promoted bacterial growth through effective bacterial utilization of nitrogen and carbon from the organics. Under optimal conditions, complete degradation and bioremoval of all the organics could be achieved
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| 4. |
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| 5. |
- Sharma, P.K., et al.
(författare)
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Role of a heterotrophic Paenibacillus polymyxa bacteria in the bioflotation of some sulfide minerals
- 1999
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Ingår i: Minerals & metallurgical processing. - 0747-9182. ; 16:4, s. 35-41
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Tidskriftsartikel (refereegranskat)abstract
- A pure strain of Paenibacillus polymyxa and mineral-adapted strains are used to bring about surface chemical changes on pyrite and chalcopyrite and, thus, their flotation. Paenibacillus polymyxa was adapted by repeated subculturing in the presence of pyrite and chalcopyrite. The surface chemical changes of bacteria due to adaptation and of minerals after their interaction with bacterial cultures are evaluated by electrokinetic and infrared spectroscopy and are discussed with reference to their flotation responses. Interaction of bacterial cells, bacterial metabolites and whole bacterial cultures affected the Hallimond flotation behavior of the sulfide minerals. The Xanthate flotation results show that pyrite, but not chalcopyrite, is depressed when the tests are carried out after interaction with chalcopyrite-adapted Paenibacillus polymyxa. This investigation demonstrated that the surface chemical properties of bacteria can be manipulated successfully to achieve the desired effects in the flotation process.
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| 6. |
- Sharma, P.K., et al.
(författare)
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Thiobacillus ferrooxidans interaction with sulfide minerals and selective chalcopyrite flotation from pyrite
- 1999
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Ingår i: Advances in flotation technology. - : Society for Mining, Metalurgy and Exploration. - 0873351843 ; , s. 147-165
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Konferensbidrag (refereegranskat)abstract
- The acidophilic and chemolithotrophic Thiobacillus ferrooxidans bacteria grown in the presence of soluble ferrous ions and solid substrates (sulfur, pyrite and chalcopyrite) as their energy source have been used in the investigations. The cell surfaces are characterized by zeta-potential, contact angle, FT-IR and FT-Raman studies. The adsorption isotherms of the cells on pyrite and chalcopyrite indicate that the adsorption begins on pyrite at a much lower equilibrium cell population than on chalcopyrite. The isotherms tend to level off at a cell adsorption density corresponding to a horizontal monolayer coverage when the geometrical dimensions of the cells are considered. In the presence of cells, the xanthate flotation of pyrite completely depressed, whereas chalcopyrite flotation is unaffected. The results suggest that chalcopyrite can be selectively floated from pyrite, also at a neutral pH region, in the presence of T. ferrooxidans cells
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| 7. |
- Su, Fenwei, et al.
(författare)
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Dephosphorization of magnetite fines - Part 1: Evaluation of flotation kinetic models
- 1998
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Ingår i: Mineral Processing and Extractive Metallurgy. - 0371-9553 .- 1743-2855. ; 107:SEPT/DEC, s. C95-C102
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Forskningsöversikt (refereegranskat)abstract
- Dephosphorization of magnetite fines by flotation in such a way as to minimize the fatty acid coating left on the magnetite surfaces is the principal technical challenge facing the mineral processing division of LKAB, Sweden. Modelling of flotation kinetics enables the influence of chemical and operational variables on apatite flotation from magnetite fines to be predicted. Five typical first-order flotation kinetic models are evaluated by statistical techniques, after an estimation of model parameters by a nonlinear least-squares fitting program, with use of the authors' own results and results taken from the literature. Evaluation of the models is based on two aspects: goodness of fit to the experimental results and suitability to describe the flotation behaviour. The first-order models with a rectangular distribution of floatabilities and with fast and slow floating components (F-S model) gave an excellent fit to the experimental results of apatite flotation when compared with the other models, the latter being superior not only in the goodness of fit to apatite flotation and other mineral flotation results but also in its description of flotation behaviour. The kinetic parameters (percentage recoveries and rate constants of fast and slow floating particles) in the F-S model have a physical significance and can thus be used for qualitative as well as quantitative interpretation of flotation performance. The influence of collector dose can be effectively included in the F-S model by making realistic simplifications and relating the collector dose to the fraction of slow floating particles. The ratio of fast and slow rate constants can be used to describe the selectivity of apatite flotation from magnetite.
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| 8. |
- Su, Fenwei, et al.
(författare)
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The influence of temperature on the kinetics of apatite flotation from magnetite fines
- 1998
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Ingår i: International Journal of Mineral Processing. - 0301-7516 .- 1879-3525. ; 54:3, s. 131-145
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Tidskriftsartikel (refereegranskat)abstract
- The influence of pulp temperature on the kinetics of apatite flotation from magnetite fines was studied using Atrac (fatty acid type) as collector and sodium silicate as dispersant at pH 8.5–9.0. The batch flotation tests were conducted in a specially designed temperature controlled flotation cell. A modified first-order model, incorporating two rate terms describing fast and slow-floating components, was applied to evaluate the flotation kinetics. The estimation of the model parameters was made by a non-linear least squares fitter program which is based on the Levenberg–Marquardt algorithm. Results indicate that increasing temperature from 10°C to 40°C decreases the phosphorous content in magnetite concentrate but with a simultaneous loss of magnetite recovery. At temperatures below 30°C, an increase in pulp temperature results increasing flotation rate of fast-floating particles and has a marginal effect on slow-floating particles. Above 30°C, the flotation rate of fast-floating particles decreases with increasing pulp temperature. Sodium silicate has a positive effect for increasing the phosphorous recovery and decreasing the phosphorous content in the magnetite concentrate at 20°C for all the levels of collector dosages. In the absence of sodium silicate, collector is active for both apatite and magnetite flotation. The higher selectivity between apatite and magnetite with an acceptable content of phosphorous in the magnetite concentrate is obtained at a moderate dosage of about 400 g/t sodium silicate. The optimum flotation conditions are: 50 g/t collector dosage, 350–400 g/t dispersant dosage, pH 8.5–9 and pulp temperature 25–30°C.
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| 9. |
- Andersson, AM, et al.
(författare)
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Temperature dependence of the passivation layer on graphite
- 1999
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Ingår i: JOURNAL OF POWER SOURCES. - : ELSEVIER SCIENCE SA. - 0378-7753. ; 82, s. 286-290
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The elevated temperature stability of the Solid Electrolyte Interface (SEI) formed on graphite during the first charge/discharge cycle has been investigated. This was done in order to determine its role in the high-temperature degradation process which oc
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| 10. |
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