Change search
Refine search result
1 - 10 of 10
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Roonasi, Payman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Adsorption and surface reaction properties of synthesized magnetite nano-particles2007Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The surface chemistry of inorganic materials is of great significance in a number of industrially important processes such as separation of ore by flotation, catalysis, water purification, paper coating and pharmaceutical industry. The purpose of this study has been firsly to develop a method for optimal synthesis of magnetite nanoparticles and secondly to utilize these particles as adsorbent in order to investigate their adsorption/desorption properties. The magnetite nanoparticles were synthesized by coprecipitation of FeCl2 and FeCl3 in alkaline media. The precipitated magnetite was analysed with XRD, TEM and FTIR spectroscopy. For evaluation of the mechanism of magnetite formation via coprecipitation method, iron isotopic measurement was applied and compared with magnetite produced from oxidation of ferrous hydroxide (paper 1). No fractionation of iron isotopes was observed for the magnetite synthesized by coprecipitation, whilst the magnetite formed from ferrous hydroxide showed higher abundance of 54Fe compared to 56Fe in the beginning of the reaction. The synthesized magnetite was coated with a primary layer of oleate and subjected to high temperature in air and argon atmosphere (paper 2).Oleate was selected as a model for Atrac which is a collector used for separation of apatite from magnetite. A combination of thermal analysis and infrared spectroscopy method were used in this study. It was found that calcination of the magnetite-oleate system in air involves oxidation of the double bond of oleate and formation of intermediate oxygen-rich molecules. Thermal decomposition of magnetite coated with a primary layer of oleate under argon atmosphere exhibits two steps weight loss. The first step at ~330oC is associated with oleate desorption/decomposition and an enthalpy change of ÄH = 49.86 J/g. Another weight loss occurs at elevated temperature (740oC) leading to partial reduction of magnetite to wustite and iron. In another work, the synthesized magnetite was deposited over an ATR internal reflection element to study adsorption of carbonate and sulphate anions in-situ. It was concluded from the IR spectra that there are two carbonate species on the surface at pH=8, one tightly bond carbonate as inner sphere complex with monodentate binuclear geometry and the other one is a loosely bond outer-sphere hydrogen bonded carbonate. Adsorption of sulphate was also studied using in-situ ATR spectroscopy (paper 3). Three maxima at 1115, 1044 and 979 cm-1 were observed, based on second derivative spectral method analysis. From the adsorption isotherm, the Langmuir affinity constant, K, was estimated to be 1.2344 x 104 M-1 at pH=4, implying a ∆G0ads= - 33.3 KJ/mol at T= 298oK. The kinetic of adsorption showed an initial fast adsorption especially at higher concentrations, eventually reaching an equilibrium plateau value. The calculated pseudo first order rate constant was (0.09± 0.01) min-1.

  • 2.
    Roonasi, Payman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Sorption reactions between ionic species and magnetite in aqueous solution2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The surface chemistry of inorganic materials is of great significance in a number of industrially important processes such as separation of ore by flotation, catalysis, water purification, leaching, as well as in the formulation of some pharmaceutical preparations. This thesis deals with magnetite and its sorption properties. Especially it was focused on the sorption of ions present in the process water and possibly affecting the balling properties of the magnetite concentrate in the pelletizing process. It is well-known that these properties become deteriorated if the magnetite surface becomes less hydrophilic, which motivated the use of an amphiphilic adsorbate (sodium oleate) in this study.The magnetite nano-particles were synthesized and subsequently characterized by X-ray, electron microscopy, and infrared spectroscopy. The mechanisms of magnetite formation from co-precipitation of Fe (II) and Fe (III) as well as oxidation of ferrous hydroxide were evaluated using iron isotope fractionation measurements (Paper I).Since magnetite pellets are heated during the sintering process and also may contain small amounts of the hydrophobic collector used in the flotation process, it was interesting to follow what happened with a model collector such as sodium oleate upon heating the magnetite/oleate system. This was studied using a combination of thermal analysis and FTIR spectroscopy. It was found that the oleate molecules were bonded to iron atoms by predominantly a bidentate mononuclear complex and formed essentially a single layer with a distance between the oleate molecules of ~36 Å2. Thermogravimetric analysis showed indicated double bond cleavage that yielded products enriched in oxygen and also capable of forming hydrogen bonds (Paper II).To study how the magnetite surface might be modified caused by process water, the magnetite nano-particles were evenly distributed over an internal reflection element and this combination was used to study the adsorption of ions present in the process water in-situ. The ionic system included the model collector (oleate) in stead of the collector used in practise (Atrac) to separate apatite from magnetite. Among ions in the process water, the adsorption properties of sulphate, silicate, and carbonate were studied as well as the effect of calcium ions on the adsorption properties and the competition between silicate and oleate for the magnetite surface. Paper III focused on the effect of Ca (II) on the adsorption of sulphate and it could be concluded that this effect was of minor importance. On the other hand, calcium ions in solution had a large effect on the adsorption of carbonate ions onto magnetite (Paper VII). During the flotation process, silicate is added to the pulp in order to disperse the magnetite particles and make the reverse flotation of apatite from magnetite more efficient. Accordingly, the adsorption of silicate onto magnetite as well as maghemite was investigated as a function of pH (Papers IV and V). Finally, the kinetics of oleate adsorption onto magnetite and competition between sodium oleate and sodium silicate for the magnetite surface was studied. Of particular interest was to which extent oleate could possibly be substituted for silicate and vice versa. These studies are elaborated in Paper VI.

  • 3. Roonasi, Payman
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) study of oleate adsorbed on magnetite nano-particle surface2009In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 255, no 11, p. 5891-5895Article in journal (Refereed)
    Abstract [en]

    Magnetite nano-particles were coated with sodium oleate and the spectral behaviour of the coating layer was studied by FTIR spectroscopy after the particles had been heated in air and argon. Magnetite was synthesized by controlled co-precipitation and subsequently coated with sodium oleate. Thermal analysis in combination with mass spectroscopy was carried out to support the FTIR spectroscopic interpretations, but also to monitor the decomposition and surface reaction of oleate adsorbed on the magnetite surface. It was deduced from FTIR and TGA results that the oleate molecules are bonded to iron atoms by a bidentate mononuclear complex and form essentially a single layer with a distance between oleate molecules of ∼36 Å2. It was shown by IR as well as Raman spectroscopy that oleic acid, when heated in air, undergoes decomposition implying that new carbon-oxygen bonds are formed. Heating the iron oxide-oleate system in air also implies oxidation of the double bond at the C:9 position of the alkyl chain and formation of intermediate oxygen-rich molecules. An enthalpy change of ΔH = 49.86 J/g was obtained for oleate desorption/decomposition at ∼350 °C under argon atmosphere and a carbonaceous graphitic species resulted from this decomposition.

  • 4. Roonasi, Payman
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A study on the mechanism of magnetite formation based on iron isotope fractionation2009In: EPD Congress 2009: proceedings of sessions and symposia sponsored by the Extraction and Processing Division (EPD) of The Minerals, Metals & Materials Society (TMS) / [ed] Stanley M. Howard, Warrendale, Pa.: Minerals, Metals & Materials Society, 2009, p. 829-836Conference paper (Refereed)
    Abstract [en]

    Having knowledge of mechanism of magnetite formation is essential in a number of industrial processes including magnetite synthesis and corrosion of iron. In this study, magnetite nano-particle was synthesized via two different ways; coprecipitation of iron (II) and (III) and oxidation of ferrous hydroxide. The samples were characterized using X-ray diffraction (XRD), Mid-Far IR spectroscopy, scanning electron microscopy (SEM), chemical analysis for determination of Fe II/Fe III ratio and ICP-MS for iron isotopic ratio (56Fe/54Fe) measurement. Since fractionation of iron isotopes depends on reaction rate and bonding strength, interpretation of the isotopic data with respect to the possible mechanisms is discussed. No fractionation of iron isotopes was observed for the magnetite synthesized by coprecipitation, whilst magnetite formed from ferrous hydroxide showed higher abundance of '4Fe compared to 56Fe in the beginning of reaction, implying the significance of the following reaction: Fe (OH)2 (solid) < -- > [Fe (OH)]+(aq) + OH-.

  • 5. Roonasi, Payman
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    An ATR-FTIR study of carbonate sorption onto magnetite2010In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 42, no 6-7, p. 1118-1121Article in journal (Refereed)
    Abstract [en]

    Carbonate is one of the most abundant anions in ground water. It also appears as saturated concentration in the process water at LKAB, a mining company in the northern part of Sweden. Sorption of carbonate on magnetite (the major source of iron ore in this company) may affect the surface chemistry of the iron oxide by forming a carbonate surface instead of an oxide surface. This would affect the interactions between magnetite particles and other species dissolved in the process water. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) has proved to be a useful technique in the study of adsorption/desorption properties of ions in mineral processing and environmental science. Magnetite was synthesized by coprecipitation of Fe II and Fe III in alkaline solution and deposited on a ZnS internal reflection element. Adsorption of carbonate on magnetite, and the effect of pH, Na, Ca, and silicate ions on the amount and speciation of adsorbed carbonate was monitored in situ. Adsorption of carbonate onto magnetite was found to increase with the acidity of the solution from pH 8. 5 to pH 6. 5 and also increased with increasing calcium concentration from 0 to 1. 0 mM. The spectroscopy results were discussed and compared with previous findings in the literature

  • 6. Roonasi, Payman
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    An ATR-FTIR study of sulphate sorption on magnetite: rate of adsorption, surface speciation, and effect of calcium ions2009In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 333, no 1, p. 27-32Article in journal (Refereed)
    Abstract [en]

    The adsorption of sulphate on magnetite was studied in-situ using ATR-FTIR spectroscopy. Synthetic magnetite particles were deposited on a ZnSe internal reflection element and the spectra of sulphate adsorbed at pH 4-8.5 were recorded. Two different ionic strengths were used viz. 0.01 M and 0.1 M NaCl. The spectra of adsorbed sulphate on magnetite coated ZnSe were compared with the spectra of sulphate solutions at the same pH values and in contact with uncoated ZnSe. The spectrum of adsorbed sulphate at pH 4 showed three maxima at 979, 1044, and 1115 cm-1 indicating a monodentate adsorption in which the Td symmetry of SO42 - is lowered to C3v. At pH 6.5, sulphate adsorbed as an outer-sphere complex with two weak bands appearing at 1102 and 980 cm-1. Moreover, spectra of the adsorbed sulphate at pH 4 were recorded as a function of time and sulphate concentration. The equilibrium absorbance at different concentrations fitted a Langmuir type adsorption isotherm. The Langmuir affinity constant K at pH 4 was determined from the slope and intercept of the Langmuir plot to be K = 1.2344 × 104 M- 1 and the Gibbs free energy of adsorption Δ Gads0 was estimated from this value to be -33.3 kJ/mol. Kinetic analysis indicated that adsorption at pH 4 is fast, whilst the desorption kinetic at the same pH is very slow. In addition, the effect of Ca ions on sulphate adsorption was also studied. It was shown that Ca ions increased the sulphate adsorption on magnetite at pH 8.5.

  • 7. Roonasi, Payman
    et al.
    Yang, Xiaofang
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Competition between sodium oleate and sodium silicate for a silicate/oleate modified magnetite surface studied by in-situ ATR-FTIR Spectroscopy2010In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 343, no 2, p. 546-552Article in journal (Refereed)
    Abstract [en]

    Attenuated Total Reflection (ATR) IR spectroscopy was utilized to monitor adsorption of sodium oleate and sodium silicate onto synthetic magnetite at pH=8.5, both individually and in a competitive manner. Oleate was adsorbed within a concentration range of 0.01 mM-0.5 mM. It was observed that adsorption of oleate increased linearly with increasing concentration of oleate in solution up to a concentration of 0.1 mM. The infrared spectrum of oleate showed a broad single band at 1535 cm-1 assigned to the asymmetric stretching vibration of carboxylate, implying chemisorption of oleate to the magnetite surface. The kinetics of oleate adsorption followed a pseudo first-order reaction with an apparent rate constant of k1= 0.030 ± 0.002 min-1. Competitve adsorption of silicate and oleate was performed either by adding silicate solution to a magnetite film initially equilibrated with 0.1 mM oleate or adding oleate solution to magnetite treated with silicate solutions in the concentration range 0.1 mM - 5mM. It was shown that silicate, within reasonable time, had only minor effect on the amount of oleate already adsorbed on magnetite. On the other hand, oleate did not efficiently compete with silicate if the latter substance was already adsorbed on the iron oxide.

  • 8. Yang, Xiaofang
    et al.
    Roonasi, Payman
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A study of sodium silicate in aqueous solution and sorbed by synthetic magnetite using in situ ATR-FTIR spectroscopy2008In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 328, no 1, p. 41-47Article in journal (Refereed)
    Abstract [en]

    The sorption of sodium silicate by synthetic magnetite (Fe3O4) at different pH conditions (pH 7-11) and initial silicate concentrations (1×10-3 and 10 x 10-3 mol L-1) was studied using in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The analysis of infrared spectra of sodium silicate in solution as well as adsorbed on magnetite nano-particles clearly showed the evolution of different silicate species depending on pH and silica concentration. The silicate concentration studied (10 x 10-3 mol L-1 ) contained polymeric or condensed silicate species at lower pH as well as monomers at high pH, as evident from infrared spectra. Condensation of monomers resulted in an increased intensity of absorptions in the high frequency part (>1050 cm-1) of the spectral region, which contains information about both silicate in solution and sorbed silicate viz. 1300 cm-1-850 cm-1. In the pH range studied, infrared spectra of sorbed silicate and sorbed silicate during desorption both indicated the presence of different types of surface complexes at the magnetite surface. The sorption mechanism proposed is in accordance with a ligand exchange reaction where both monodentate and bidentate complexes could exist at low surface loading level, the relative proportion of the complexes being due to both pH and concentration in solution. Oligomerization occurred on the magnetite surface at higher surface loading.

  • 9.
    Yang, Xiaofang
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Roonasi, Payman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Jolsterå, Rickard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kinetics of silicate sorption on magnetite and maghemite: an in-situ ATR-FTIR study2008Conference paper (Other academic)
  • 10. Yang, Xiaofang
    et al.
    Roonasi, Payman
    Jolsterå, Rickard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kinetics of silicate sorption on magnetite and maghemite: an in-situ ATR-FTIR study2009In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 343, no 1-3, p. 24-29Article in journal (Refereed)
    Abstract [en]

    Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy was used to monitor the in situ sorption of sodium metasilicate from aqueous solution onto synthesized magnetite and maghemite particles in the pH range 10.8-7.0 using silicate concentrations between 0.1 mM and 5 mM. The spectral data showed that both pH and silicate concentration had great influence on the interfacial reaction between soluble silicate and the iron oxide surfaces, regarding the amount adsorbed per unit mass of iron oxide and the surface species formed. A pH dependent sorption of silicate on iron oxides was observed, implying that a maximum sorption took place in the pH range of 9.5 - 7.0. All experiments showed a fast initial increase in the absorption intensity followed by a slower sorption stage which was strongly dependent on the concentration of silicate in solution and the pH value. The amount of sorption onto magnetite was 3 to 5 times larger than onto maghemite, but there was no significant difference in the line shape of corresponding absorption bands. At pH 8.5 and low concentration (≤ 0.1 mM), the silicate monomers dominate in solution and on the iron oxide surface also monomeric species were dominating as evident from the infrared band at 950 cm-1. However, at higher concentration (0.4-5.0 mM), the dominating absorption band at about 1000 cm-1 shifted to higher frequency during the sorption indicating that oligomeric surface silicate species were formed on the iron oxide surface. Desorption of silicate from the surface of the iron oxides was easier to accomplish at low silicate concentration, whilst the highest concentration showed a comparatively low relative amount of desorbed silicate, suggesting that polymerized species had a stronger affinity for the iron oxide surface as compared to monomeric species.

1 - 10 of 10
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf