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  • 1.
    Jolsterå, Rickard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Reactions at the water-mineral interface of olivine and silicate modified maghemite2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main objectives for this licentiate thesis have been to study and model the reactions at the water-mineral interface of two subsystems: maghemite-H+-silicate and olivine-H+. An increased knowledge of these systems will make it possible to further extend the complexity of the aqueous phase in future experiments. This will make it possible to further approach a composition that resembles the flotation and agglomeration process water in the production of iron ore pellets. To be able to characterise and predict the influence of different species from the process water on the different mineral particle surfaces, is an important step towards optimisation of the pellet production process and increased recirculation of the process water. Both synthetic and natural minerals were used in the experiments, in which the protolytic surface exchange reactions of the subsystems were analysed by high precision potentiometric titrations. The minerals and their surfaces were characterised using XRD, XPS, SEM-EDS and BET, both before and after the experiments. The zeta potential of olivine and silicate modified maghemite particles were also determined as a function of pH. Surface complexation models were derived to describe the reactions in the systems. The Constant Capacitance Model (CCM) was used to model the experimental results.The evaluation of the potentiometric data from the studies of the maghemite-H+-silicate system indicates that soluble silicates will mainly adsorb to maghemite as monodentate surface species at the defined experimental conditions. Models including polymerisation of adsorbed silicates and/or bidentate silicate ligands were tested, but could not well be fitted to titration data. The adsorption maximum of silicates was found to be within the range pH 9.0 to 9.5. At the experimental conditions used, approximately 82 % of the added silicate was adsorbed. At higher pH, the silicate started to desorb from the maghemite surface and at pH 11.1 only 60 % was still adsorbed. Olivine ((Mg,Fe)2SiO4), one of the major rock forming silicate minerals in nature, is added in the agglomeration process to improve the performance of the iron ore pellets in the blast furnace. The results from the studies of the olivine - H+ system shows that the dissolution of olivine is essentially incongruent, with an excess of magnesium ions released in to the aqueous suspension. Studies of olivine samples equilibrated in electrolytes with magnesium ions added using XPS, SEM and zeta potential measurements have also shown that the magnesium ion release and adsorption at the surface layers is reversible, no support for surface precipitation of new phases as Mg(OH)2 could be found. Experimental potentiometric data of olivine-H+ at alkaline conditions was successfully fitted to a two pKa electrostatically corrected model. The importance of steady state conditions when acquiring titration data was illustrated by comparing the amount of active surface sites detected by steady state titrations and considerably faster titrations.

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  • 2.
    Jolsterå, Rickard
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Surface reactions of magnetite and maghemite with dissolved and added ions in process water2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Reactions between mineral surfaces and dissolved species in process water, both inorganic and organic play an important role in mineral processing. Reverse flotation of finely comminuted iron ore is sometimes employed in order to remove the phosphorous mineral apatite. An anionic collector, designed to specifically adsorb at the calcium specific surface sites of apatite is added, rendering the apatite particles hydrophobic properties. However, some of the collector adsorbs also at the magnetite surfaces, thereby introducing undesired characteristics to the upgraded iron ore concentrate.Of this reason, magnetite and maghemite surfaces and their interactions with the most abundant and important ions in the process water during flotation, and their potential influence on collector adsorption at magnetite was studied. Maghemite was included in the experiments, since previous work had shown that oxidation of the magnetite surface into maghemite may occur during the processing of the iron ore concentrate. The complex system that the dissolved ions in the process water and the iron oxide particles constitute at flotation and agglomeration was divided into smaller subsystems.The protolytic characteristics for the magnetite-H+ and maghemite-H+ systems proved to be similar when their modelled intrinsic surface complexation constants were compared. However, the surface site density of magnetite was found to be 50 % greater than for maghemite. Both potentiometric titrations and ATR-FTIR spectroscopy were used to study and characterize the adsorption of silicate. The results from the surface complexation modelling suggested that the silicate adsorbed as monodentate surface complexes at the maghemite surfaces. The results showed a silicate adsorption maximum at pH 8.5 to 9.5 for both iron oxides. Within this range pH, the surface complex ΞFeOSiO(OH)2 - was proposed as the dominating surface specie in the maghemite-silicate system.The iron ore pellet additive olivine proved to release substantial amounts of Mg2+ when immersed in water, indicating that olivine probably is the main source of Mg2+ to the process water. Thus, the surface characteristic of olivine particles in water suspensions was studied. Since olivine proved to be a significant source of magnesium ions, adsorption of Mg2+ at maghemite and magnetite was studied and modelled. The results suggested that magnesium ions adsorbed as a mix of mono- and bidentate surface complexes when the number of surface sites was in excess. Increased amounts of Mg2+ i.e., ≥1 Mg2+ site-1, resulted in a model including only monodentate surface complexes.Experiments involving competitive adsorption of carbonate and silicate showed that added silicate replaced adsorbed carbonate. Other competitive experiments, with Mg2+ and Ca2+, showed that Mg2+ had a stronger affinity for the magnetite surface than Ca2+. The preferential adsorption of Mg2+ at the iron oxide surface may then have protective properties, by preventing adsorption of the calcium specific collector. Results from both in-situ ATR-FTIR spectroscopy and contact angle measurements indicated also that added Mg2+ reduced the adsorption of collector and thereby increased the wettability of the magnetite surfaces.

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  • 3.
    Jolsterå, Rickard
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Gunneriusson, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsling, Willis
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Adsorption and surface complex modeling of silicates on maghemite in aqueous suspensions2010In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 342, no 2, p. 493-498Article in journal (Refereed)
    Abstract [en]

    Adsorption of soluble silicate species, (Si(OH)4) on maghemite, (γ-Fe2O3) has been studied by high precision potentiometric titrations, spectroscopic analyses and zeta potential determinations. Titrations were performed at 25.0 °C within the range 2.8 < pH < 11.1 and at a constant ionic strength of 0.100 mol dm-3. The experimental data were evaluated using the constant capacitance model. For the maghemite - H+ system, the following values for the surface complexation constants and capacitance were found: ≡FeOH + H+ ↔ ≡FeOH2+; log βs11(int) = 5.39 ± 0.01 ≡FeOH ↔ ≡FeO- + H+; log βs-11(int) = -7.51 ± 0.01; C = 2.40 Fm-2.Three different concentration ratios of the determined concentration of active surface sites and added total silicate concentration, [≡FeOH]:[Si(OH)4], were examined (1:1, 2:1 and 3:1). A model comprising of three surface complexes, ≡FeOSi(OH)3, log βs011(int) = 3.61 ± 0.02; ≡FeOSiO(OH)2-, log βs-111(int) = -3.00 ± 0.01; and ≡FeOSiO2(OH)2-, log βs-211(int) = -11.35 ± 0.02; was found to best describe the experimental observations. Attempts to model the adsorption of silicates on maghemite as bidentate or polynuclear silicate complexes were not successful. The maximum silicate adsorption for the 1:1 ratio, approximately 80%, was obtained at pH 9 - 9.5. The IEP of maghemite in the presence of silicates (1:1 ratio) was determined from ζ-potential measurements, giving pHIEP ≈ 6.6.

  • 4.
    Jolsterå, Rickard
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Gunneriusson, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsling, Willis
    Surface characterisation and modelling of olivine at alkaline conditions2010In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, no 12/Suppl 1, p. A477-Article in journal (Other academic)
  • 5.
    Jolsterå, Rickard
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Gunneriusson, Lars
    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.
    Surface complexation modeling of Fe3O4-H+ and Mg(II) sorption onto maghemite and magnetite2012In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 386, no 1, p. 260-267Article in journal (Refereed)
    Abstract [en]

    The surface acid/base properties of magnetite (Fe3O4) particles and the sorption of Mg2+ onto magnetite and maghemite (γ-Fe2O3), have been studied using high precision potentiometric titrations, batch experiments and zeta potential measurements. The acid/base properties of magnetite were found to be very similar to maghemite except for the difference in surface site density, Ns (sites nm-2), 1.50±0.08 for magnetite and 0.99±0.05 for maghemite. The experimental proton exchange of the magnetite surface increased from pH 10 and above, indicating dissolution/transformation reactions of magnetite at alkaline conditions. Thus, magnetite with its Fe(II) content proved to be less stable towards dissolution in comparison with pure Fe(III) oxides also at high pH values.Three different ratios between surface sites and added Mg2+ were used in the sorption experiments viz. 0.5, 1 and 2 Mg2+ site-1. Surface complexation modeling of the Mg2+ sorption onto maghemite and magnetite, was restricted to pH conditions where the interference from Mg(OH)2(s) precipitation could be ruled out. The model calculations showed that Mg2+ sorb onto the magnetite and maghemite surfaces as a mixture of mono- or bidentate surface complexes at 0.5 Mg2+ site-1 and as monodentate complexes at 1 and 2 Mg2+ site-1 conditions. Mg2+ was also found to adsorb more readily at the maghemite surfaces in comparison with magnetite surfaces. For experiments with excess Mg2+ relative to the number of surface sites, the calculations suggested the formation of polynuclear surface complexes on maghemite.

  • 6.
    Potapova, Elisaveta
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical 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.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    In-situ spectroscopic study of surfactants adsorption onto hematite from binary mixtures and the effect of inorganic ions2014In: Surface and Interface Analysis, ISSN 0142-2421, E-ISSN 1096-9918, Vol. 46, no 10-11, p. 1110-1114Article in journal (Refereed)
    Abstract [en]

    Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy has proven to be a powerful tool for surfactant adsorption studies. In many practical applications, surfactant mixtures and waters with different chemistry are employed, which significantly complicates adsorption studies. In this work, we investigate the effect of calcium and carbonate ions, frequently found in natural waters, on the co-adsorption of sodium dodecylbenzenesulfonate (SDBS) and a non-ionic primary alcohol ethoxylate (NEODOL 25–7) onto hematite at pH 8 and 10.5 using ATR-FTIR spectroscopy. Adsorption of SDBS was affected by pH and the presence of inorganic ions to a greater extent than the adsorption of NEODOL 25–7. A larger amount of SDBS was adsorbed at pH 8 than at pH 10.5 in all the experiments. The effect of co-adsorbing ions on the amount of SDBS adsorbed was significant only at pH 10.5 and not at pH 8. Calcium ions promoted adsorption of SBDS onto hematite, whereas addition of carbonate decreased the amount of SDBS adsorbed. In the presence of both calcium and carbonate ions, calcium carbonate precipitate was formed on the hematite surface, promoting accumulation of NEODOL 25–7 at the surface. NEODOL 25–7 was found to have a strong effect on the hydrophilicity of the hematite film when adsorbed in combination with SDBS. A more hydrophilic surface was obtained upon adsorption of the surfactants in the presence of sodium chloride, film dispersion occurred in the presence of calcium chloride, and a less hydrophilic surface was obtained in the presence of both calcium chloride and sodium carbonate

  • 7.
    Potapova, Elisaveta
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Jolsterå, Rickard
    Luossavaara-Kiirunavaara AB, 983 81 Malmberget, Sweden.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    The effect of inorganic ions on dodecylbenzenesulfonate adsorption onto hematite: an ATR-FTIR study2014In: Journal of Surfactants and Detergents (JSD), ISSN 1097-3958, E-ISSN 1558-9293, Vol. 17, no 5, p. 1027-1034Article in journal (Refereed)
    Abstract [en]

    Linear alkylbenzenesulfonates (LAS) are an important group of anionic surfactants within the detergent industry and have also been suggested for use in mineral flotation and enhanced oil recovery. Because of its great industrial importance, there are a number of publications on the adsorption of LAS on metal oxides; however, the effect of co-adsorbing inorganic species on LAS adsorption has rarely been addressed. In this study we investigated the effect of calcium and carbonate ions on the adsorption of sodium dodecylbenzenesulfonate (DBS) onto hematite at pH 8 and 10.5 using in-situ ATR-FTIR spectroscopy. DBS adsorption on hematite was found to increase as pH was decreased from 10.5 to 8. Calcium ions promoted accumulation of DBS on hematite, with a larger amount of DBS on the surface at pH 10.5. Carbonate ions did not have any major effect on DBS adsorption on hematite. In the presence of both calcium and carbonate, the amount of DBS on the hematite surface was higher than without the two co-adsorbing ions but lower than with calcium ions alone. Likely, precipitation of calcite reduced the total concentration of calcium ions available for the interaction with DBS on the hematite surface. The results presented in this work clearly indicate the importance of water chemistry for DBS adsorption and allow predicting adsorption behavior of DBS on iron oxides from natural and process waters of different chemistry, which is important for the industrial applications of DBS and the fate of DBS in the environment.

  • 8.
    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)
  • 9. 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.

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