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  • 1. Fredriksson, Andreas
    Adsorption of heptyl xanthate at the metal sulphide/aqueousinterface2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In sulphide mineral flotation a sufficient hydrophobicity of the mineral surfaces is obtained by the adsorption of collector chemicals at the metal sulphide/aqueous interface. This surface alteration is of fundamental and applied interest. In this thesis, attenuated total reflection infrared spectroscopy has been used to monitor the adsorption kinetics and the orientation of heptyl xanthate when adsorbed onto three solid surfaces - germanium, zinc sulphide and lead sulphide in-situ. The choice of using the ATR technique is because it is very suitable when working with water as solvent, and the choice of germanium as internal reflection element is because of its small penetration depth due to a high refraction index. The Chemical Bath Deposition method has been used to deposit metal sulphides onto germanium internal reflection elements. For determining the adsorption of heptyl xanthate onto lead sulphide a novel method has been tested, and verified as capable in recovering information about surface reactions at a lead sulphide/aqueous interface. In the study of surface reactions the substrate is of vast importance, implying that the chemistry of the surface has to be well characterised. This work has utilized X-ray Photoelectron spectroscopy, and ATR spectroscopy, in the characterisation of the different surfaces. The adsorption kinetics has been followed to adsorption equilibrium at different concentrations. In the case of heptyl xanthate adsorbed at the zinc sulphide/aqueous interface, an adsorption isotherm has been calculated from the equilibrium data. On the assumption that the adsorption step was rate controlling a second order rate equation was derived and adsorption rate data tested according to this equation. In addition, an orientation study of the heptyl xanthate molecule at the different interfaces was performed, which requires polarised infrared light. In the case of heptyl xanthate adorbed onto germanium, both surface excess and a degree of alignment of the alkyl chain from the surface normal has been calculated.

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  • 2.
    Fredriksson, Andreas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kinetics of collector in-situ adsorption on metal sulphide surfaces studied by ATR-FTIR spectroscopy2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In sulphide mineral flotation, a sufficient hydrophobicity of the mineral surfaces is obtained by the adsorption of collector chemicals at the metal sulphide/aqueous interface. This surface alteration is of fundamental and applied interest. In this thesis, attenuated total reflection infrared spectroscopy has been used to monitor the adsorption kinetics and the orientation of heptyl xanthate when adsorbed onto three solid surfaces - germanium, zinc sulphide and lead sulphide in-situ. The Chemical Bath Deposition method has been used to deposit metal sulphides onto germanium internal reflection elements, and verified as capable in synthesizing metal sulphide surfaces for adsorption studies recovering information about surface reactions at metal sulphide/solution interfaces. In the study of surface reactions the substrate is of great importance, implying that the chemistry of the surface has to be well characterised. This work has utilized X-ray photoelectron spectroscopy in the characterisation of the different surfaces. The adsorption kinetics has been followed to monitor the adsorption equilibria at different concentrations. In the case of heptyl xanthate adsorbed at the zinc sulphide/aqueous interface, an adsorption isotherm has been calculated from the equilibrium data. On the assumption that the adsorption step was rate controlling a pseudo-first order equation was derived and adsorption rate data, in all the three studied systems, tested according to this equation. In addition, an orientation study of the heptyl xanthate molecule at the different interfaces was performed, which requires polarised infrared light. Density Functional calculations of a free heptyl xanthate molecule, and a heptyl xanthate molecule adsorbed on a pure Ge(111) were utilized to get more information about the in-situ adsorption of heptyl xanthate on a germanium surface. The important vibration bands were assigned to different vibrations, and the theoretical infrared spectra were compared with the experimentally analyzed spectra. This study shows the strengths of using advanced first-principle Density Functional Theory in the interpretation of real surface adsorption systems.

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  • 3. Fredriksson, Andreas
    et al.
    Hellström, Pär
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Comparison between in situ total internal reflection vibrational spectroscopy of an adsorbed collector and spectra calculated by ab initio density functional theory methods2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 26, p. 9299-9304Article in journal (Refereed)
    Abstract [en]

    In this investigation, adsorbed heptyl xanthate on a Ge(111) surface was studied, as well as the free heptyl xanthate molecule, by means of first-principle density functional theory calculations. The modeled results were compared with the in situ total internal reflection vibrational spectroscopy spectra of heptyl xanthate adsorbed on a germanium internal reflection element and the transmission infrared spectrum of a heptyl xanthate ion in aqueous solution. The assignments of the vibrational frequencies were done for the adsorbed xanthate. The region between 1150 and 1000 cm(-1) seems suitable for discussing differences between an adsorbed xanthate and its corresponding ion. The modeled spectra for both the adsorbed xanthate and the xanthate ion are in good agreement with the experimentally retrieved spectra. This investigation shows the strength of using DFT calculations in the interpretation of absorption bands from molecules adsorbed at surfaces in situ.

  • 4. Fredriksson, Andreas
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    An in situ ATR-FTIR investigation of adsorption and orientation of heptyl xanthate at the lead sulphide/aqueous solution interface2007In: Proceedings of Flotation 07: Cape Town, South Africa, Nov. 6-9, 2007 / [ed] Barry Wills, Minerals Engineering International , 2007Conference paper (Refereed)
  • 5. Fredriksson, Andreas
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    An in situ ATR-FTIR investigation of adsorption and orientation of heptyl xanthate at the lead sulphide/aqueous solution interface2008In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 21, no 12-14, p. 1000-1004Article in journal (Refereed)
    Abstract [en]

    A lead sulphide film precipitated on a zinc sulphide layer of an ATR crystal has been used to study in situ surface reactions of heptyl xanthate adsorption. The lead sulphide film was made by the chemical bath deposition method and was analyzed by X-ray photoelectron spectroscopy. In turn deposited layers make it possible to study the PbS/aqueous solution interface in situ and open up interesting areas for attenuated total reflection spectroscopy. Monitoring the adsorption of heptyl xanthate from a 0.1 mM aqueous solution using the vibration band at 1200 cm-1 has shown the existence of adsorbed molecules on the lead sulphide surface as well as precipitated lead xanthate on the surface at bulk concentrations higher than 1 mM. At lower concentrations, the adsorbed species are dominant as is the precipitate at higher concentrations. The rate of adsorption is in accordance with pseudo first-order kinetics with a rate constant of 0.21 s-1. The Dichroic ratio for heptyl xanthate adsorbed on PbS indicates the hydrocarbon chain of the heptyl xanthate to be preferentially orientated perpendicular to the surface normal of the internal reflection element.

  • 6. Fredriksson, Andreas
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    An in situ ATR-FTIR study of the adsorption kinetics of xanthate on germanium2007In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 302, no 1-3, p. 96-101Article in journal (Refereed)
    Abstract [en]

    The in situ adsorption of n-heptyl xanthate on a germanium multiple internal reflection element was studied at constant ionic strength and X-ray photoelectron spectroscopy was used in the investigation of the germanium surface. The kinetics of heptyl xanthate adsorption was evaluated using the integrated absorbance of a sub-band under the vibration at 1200 cm−1. This vibration was assigned to the adsorbed xanthate molecule. It was shown that the adsorption of heptyl xanthate can be represented by a pseudo-first-order rate law and a monodentate binding of the xanthate to the germanium surface is proposed. During the adsorption of xanthate, the dimeric form of xanthate was simultaneously formed.

  • 7. Fredriksson, Andreas
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsling, Willis
    Kinetics of collector adsorption on mineral surfaces2005In: Centenary of flotation symposium / [ed] Graeme J. Jameson, The Australian Institute of Mining and Metallurgy , 2005, p. 433-437Conference paper (Refereed)
    Abstract [en]

    In the present study infrared attenuated total reflection (IR-ATR) was used to monitor the rate of in situ adsorption of heptyl xanthate on a layer of zinc sulfide synthesised on a germanium ATR crystal. The zinc sulfide surface was characterised using x-ray photoelectron spectroscopy (XPS). The absorbance of heptyl xanthate measured increased with increasing bulk concentration of the adsorbate up to an equilibrium plateau value corresponding to a fractional coverage of the surface sites of the substrate. For the adsorption from solutions of concentrations between 10-3 and 10-5 M, the rate of adsorption increased with increasing bulk concentration. At higher concentrations the measured absorbance should be corrected for the absorbance due to the concentration of xanthate in bulk solution. The present work provides a discussion of this correction. Assuming the adsorption stage to be rate-controlling and proportional both to the concentration of the adsorbing species in solution and unreacted surface area, a rate law governing this type of transient adsorption kinetics was derived. By means of absorbance data for the concentrations 0.1 and 0.01 mM, die rate constant of adsorption was calculated. From the initial part of a Langmuir adsorption isotherm, the absorbance at monolayer coverage and the equilibrium constant of adsorption could be estimated.

  • 8. Fredriksson, Andreas
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsling, Willis
    Kinetics of collector adsorption on mineral surfaces2006In: Minerals Engineering, ISSN 0892-6875, E-ISSN 1872-9444, Vol. 19, no 6-8, p. 784-789Article in journal (Refereed)
    Abstract [en]

    In the present study infrared attenuated total reflection (IR-ATR) was used to monitor the rate of in situ adsorption of heptyl xanthate on a layer of zinc sulphide synthesized on a germanium ATR crystal. The zinc sulphide surface was characterized using X-ray photoelectron spectroscopy (XPS). The absorbance of heptyl xanthate measured increased with increasing bulk concentration of the adsorbate up to an equilibrium plateau value corresponding to a fractional coverage of the surface sites of the substrate. For the adsorption from solutions of concentrations between 10−3 and 10−5 M, the rate of adsorption increased with increasing bulk concentration. At higher concentrations the measured absorbance should be corrected for the absorbance due to the concentration of xanthate in bulk solution. The present work provides a discussion of this correction. Assuming the adsorption stage to be rate-controlling and proportional both to the concentration of the adsorbing species in solution and unreacted surface area, a rate law governing this type of transient adsorption kinetics was derived. By means of absorbance data for the concentrations 0.1 and 0.01 mM, the rate constant of adsorption was calculated. From the initial part of a Langmuir adsorption isotherm, the absorbance at monolayer coverage and the equilibrium constant of adsorption could be estimated.

  • 9. Fredriksson, Andreas
    et al.
    Lidström-Larsson, Margareta
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kinetics of xanthate adsorption on metal sulphides2004In: Konferens i mineralteknik / [ed] Marianne Thomaeus; Eric Forssberg, Föreningen Mineralteknisk Forskning / Swedish Mineral Processing Research Association , 2004Conference paper (Other academic)
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  • 10. Fredriksson, Andreas
    et al.
    Lidström-Larsson, Margareta
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    n-Heptyl xanthate adsorption on a ZnS layer synthesized on germanium: an in situ attenuated total reflection IR study2005In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 286, no 1, p. 1-6Article in journal (Refereed)
    Abstract [en]

    Adsorption of n-heptyl xanthate on synthesized zinc sulfide was followed in situ by monitoring the methylene absorption band at 2925 cm-1. The zinc sulfide surface used in the adsorption experiments was synthesized on a germanium internal reflection element using the chemical bath deposition method. Characterization of the adsorbent surface was performed by X-ray photoelectron spectroscopy. The time needed to reach adsorption equilibrium varied with the initial concentration of the aqueous potassium heptyl xanthate solution. The amount of adsorbed xanthate ions increased with the concentration of the solution within the range studied (10 μM-50 mM). The experimental data are reasonably well described by the Langmuir adsorption isotherm. Polarized infrared attenuated total reflection (ATR) was used to determine the average orientation of the heptyl chains by measuring the absorbance of the infrared beam polarized perpendicularly and parallely to the plane of incidence. Measured absorbances were corrected for contribution from heptyl xanthate in bulk solution.

  • 11. Hellström, Pär
    et al.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Fredriksson, Andreas
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A theoretical and experimental study of vibrational properties of alkyl xanthates2006In: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy, ISSN 1386-1425, E-ISSN 1873-3557, Vol. 65, no 3-4, p. 887-895Article in journal (Refereed)
    Abstract [en]

    Geometrical structure and vibrational modes of potassium and sodium ethyl/heptyl xanthates were studied, using both theoretical and experimental methods. Both Hartree-Fock and density functional theory were used. The experimental method used was infrared absorption spectroscopy (FTIR). Our work showed that vibrational frequencies calculated with density functional theory, using the local density approximation, are in very good agreement with experiments. The results were not improved by using the more sophisticated and computationally demanding B3LYP functional.

  • 12.
    Karlkvist, Tommy
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Patra, Anuttam
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rao, Hanumantha
    Bordes, Romain
    Chalmers University of Technology, Chalmers University of Technology, Department of Chemical and Biological Engineering.
    Holmberg, Krister
    Chalmers University of Technology, Chalmers University of Technology, Department of Chemical and Biological Engineering.
    Fredriksson, Andreas
    LKAB.
    Molecular recognition in mineral flotation: Selectivity in apatite-calcite system2014Conference paper (Refereed)
    Abstract [en]

    The present investigation aims to develop and distinguish mineral specific reagents with two functional groups for use in flotation of calcium containing minerals. For this purpose, a series of dicarboxylate-based surfactants with varying length between the carboxylate groups (one, two or three methylene groups) were synthesized. As reference, a surfactant with the same alkyl chain length but with only one carboxylate group in the polar part was synthesized. The adsorption behavior of these new reagents on pure apatite and calcite mineral surfaces was studied using Hallimond tube flotation, FTIR and ζ potential measurements. The relation between the adsorption behavior of a given surfactant on a specific mineral surface and its molecular structure over a range of concentration and pH values, as well as the region of maximum recovery were established. It was found that one of the reagents, with a specific distance between the carboxylate groups, was much more selective for a particular mineral surface than the other homologues synthesized. This selective adsorption of a given surfactant to a particular mineral surface relative to other mineral surfaces as evidenced in flotation studies is substantiated by ζ potential and infra-red spectroscopy data.

  • 13.
    Karlkvist, Tommy
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Pålsson, Bertil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Fredriksson, Andreas
    R&D Mineral Processing, LKAB.
    Rao, Hanumantha
    Norwegian University of Science and Technology (NTNU), Trondheim.
    Novel alkyl aminodicarboxylate reagents for mineral specific flotation2016In: 2016 SME Annual Conference and Expo: The Future for Mining in a Data-Driven World, Phoenix, United States, 21 - 24 February 2016, New York: Society for Mining, Metalurgy and Exploration, 2016, p. 807-810Conference paper (Refereed)
    Abstract [en]

    Separation of different calcium minerals have long been an interesting and challenging problem. In this investigation calcium mineral separation is examined by: microflotation, zeta potential measurement and adsorption, using novel collectors having two functional groups instead of one. In theory, by varying the distance between the functional groups, it could be possible to preferentially target one calcium mineral by matching the spatial distance between the sites on the mineral surface. In this investigation two new surfactants have been tested to estimate their ability to float apatite and/or calcite.Preliminary findings show that an increase in distance between the functional groups favors one mineral over the other, and this might be due to differences in the mineral surface structure.

  • 14.
    Larsson, Anna-Carin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Hellström, Pär
    Fredriksson, Andreas
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Study of potassium O,O′-dibutyldithiophosphate combining DFT, 31P CP/MAS NMR and infrared spectroscopy2008In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 112, no 46, p. 11777-11783Article in journal (Refereed)
    Abstract [en]

    Dithiophosphates are used in many different industrial applications. To explain their functions and properties in these applications, a fundamental understanding on a molecular level is needed. Potassium O,O′-Dibutyldithiophosphate and its anion have been investigated by means of a combination of DFT and 31P CP/MAS NMR and infrared spectroscopy. Several low-energy conformations were studied by DFT. Three different conformations with significantly different torsion angles of the O-C bond relative to the O-P-O plane were selected for further studies of infrared frequencies and 31P NMR chemical-shift tensors. A good agreement between theoretical and experimental results was obtained, especially when the IR spectra or 31P chemical shift tensor parameters of all three conformations were added, indicating that, because of the low energy difference between the conformations, the molecules are rapidly fluctuating between them.

  • 15. Lidström-Larsson, Margareta
    et al.
    Fredriksson, Andreas
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Direct observation of a self-assembled monolayer of heptyl xanthate at the germanium/water interface: a polarized FTIR study2004In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 273, no 2, p. 345-349Article in journal (Refereed)
    Abstract [en]

    The adsorption of heptyl xanthate on germanium has been studied by the attenuated total reflection (ATR) technique. Polarized infrared light was used in situ to determine the average orientation of the alkyl chain in heptyl xanthate adsorbed at the germanium/solution interface. Spectra reveal the formation of closely packed xanthate ions with the alkyl chains in the all-trans conformation. The average tilt angle of the alkyl chains of heptyl xanthate was approximately 47° from the surface normal.

  • 16.
    Patra, Anuttam
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Karlkvist, Tommy
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Rao, Hanumantha
    Fredriksson, Andreas
    LKAB.
    Bordes, Romain
    Chalmers University of Technology, Chalmers University of Technology, Department of Chemical and Biological Engineering.
    Holmberg, Krister
    Chalmers University of Technology, Chalmers University of Technology, Department of Chemical and Biological Engineering.
    Design and development of novel mineral-specific collectors for flotation2014Conference paper (Refereed)
    Abstract [en]

    Almost all of the flotation reagents used today were discovered by continued application of empirical methods and/or trial and error experimentation. Moreover, with the metal-ion specific approach used so far, it is difficult to separate the minerals containing the same constituent metal ion. A critical assessment of molecular recognition processes involved in biomineralization suggested the possibility of using reagents which are surface specific. The concept that the molecules consisting of two or more functional groups having appropriate spacing between those so as to achieve structural/stereochemical compatibility during interaction with the mineral surface exhibit structure-specificity is thought to be extended to the design of specific collectors in flotation processes. In the present study, for the first time, a rational design of surface active molecules, and thereby the recognition of crystal faces (of minerals) by these molecules through structural and stereochemical matching is being utilized successfully to selectively float various minerals. For this purpose, carboxylate-based collectors (for mineral specific flotation of calcium minerals) as well as xanthate-based collectors (for mineral specific flotation of sulphide minerals) with a fixed alkyl chain length but having two functional groups with varying geometrical distances (separated by a spacer of one, two and three carbon atoms) between them have been synthesized. In this article, we have discussed the design, synthesis, purification of these novel mineral specific collectors as well as their important solution parameters in relation to flotation processes.

  • 17.
    Pålsson, Bertil
    et al.
    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.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Fredriksson, Andreas
    Mining Technology R and D, LKAB Kiruna Mine.
    Unlocking Rare Earth Elements from European apatite‐iron ores2014In: ERES 2014 - 1st International Conference on European Rare Earth Resources: Book of Proceedings / [ed] Efthymios Balomenos; Dimitrios Panias; Ioannis Paspaliaris, Santorini: Heliotopos Conferences Ltd. , 2014, p. 211-220Conference paper (Refereed)
    Abstract [en]

    Rare Earth Elements are known to occur within apatite‐magnetite ores of the Kiruna type. Previously it was assumed that the REE was associated to the apatite part of the ore. It is now shown that the REE follows the apatite to a much less degree, and that the REE are contained in the minerals monazite, allanite and some unknown REE‐phase still to be identified. Monazite occurs as inclusions in the apatite as well as free particles. Allanite is to some degree in mixed grains with magnetite but also in free particles. Monazite mainly reports to the apatite concentrate while allanite largely goes to the tailings. Laboratory flotation also shows some preferential concentration of heavy REE over light REE to the apatite concentrate. A new EU project, REEcover, will characterise the REE phases in this type of iron ore and among the different process streams within the mineral beneficiation chain.

1 - 17 of 17
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