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  • 1.
    Kaasalainen, Hanna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Institute of Earth Sciences, Science Institute, University of Iceland, Reykjavik.
    Stefansson, Andri
    Institute of Earth Sciences, Science Institute, University of Iceland, Reykjavik.
    Druschel, Gregory K.
    bDepartment of Earth Sciences, Indiana University-Purdue University Indianapolis.
    Determination of Fe(II), Fe(III) and Fetotal in thermal water byion chromatography spectrophotometry (IC-Vis)2016In: International Journal of Environmental Analytical Chemistry, ISSN 0306-7319, E-ISSN 1029-0397, Vol. 96, no 11, p. 1074-1090Article in journal (Refereed)
    Abstract [en]

    Determination of iron speciation in water is one of the major challenges in environmental analytical chemistry. Here, we present and discuss a method for sampling and analysis of dissolved Fe(II), Fe(III), and Fetotal concentrations in natural thermal water covering a wide range of temperature, pH, chemical composition, and redox conditions. Various methods were tried in the collection, preservation, and storage of natural thermal water samples for the Fe(II) and Fe(III) determinations, yet the resultant Fe speciation determined was often found to be significantly affected by the methodology applied. Due to difficulties in preserving accurate Fe speciation in natural samples for later laboratory analysis, a field-deployed on-site method using ion-chromatography and spectrophotometry was developed and tested. The IC-Vis method takes advantage of ion chromatographic separation of Fe(II) and Fe(III), followed by post-column colour reaction and spectrophotometric detection, thus allowing analysis of Fe(II) and Fe(III) in a single 15-minute run. Additionally, Fetotal can be determined after sample oxidation. The analytical detection limits are ~2 µg L−1 (LOD) using 200–1000 µL injection volumes and depend on the blank and reagent quality. The power of this method relies on the capability to directly determine a wide range of absolute and relative concentrations of Fe(II) and Fe(III) in the field. The field-deployed IC-Vis method was applied for the determination of Fe(II) and Fe(III) concentrations in natural thermal water with discharge temperatures ranging from 12°C to 95°C, pH between 2.46 and 9.75, and Fetotal concentrations ranging from a few μg L−c up to 8.3 mg L−1.

  • 2.
    Kaasalainen, Hanna
    et al.
    Nordic Volcanological Center, University of Iceland, Institute of Earth Sciences.
    Stefánsson, Andri
    Institute of Earth Sciences, University of Iceland.
    Chemical analysis of sulfur species in geothermal waters2011In: Talanta: The International Journal of Pure and Applied Analytical Chemistry, ISSN 0039-9140, E-ISSN 1873-3573, Vol. 85, no 4, p. 1897-1903Article in journal (Refereed)
    Abstract [en]

    Analytical methods have been developed to determine sulfur species concentrations in natural geothermal waters using Reagent-Free™ Ion Chromatography (RF™-IC), titrations and spectrophotometry. The sulfur species include SO 4 2-, S 2O 3 2-, and ∑S 2- with additional determination of SO 3 2- and S xO 6 2- that remains somewhat semiquantitative. The observed workable limits of detections were ≤0.5 μM depending on sample matrix and the analytical detection limits were 0.1 μM. Due to changes in sulfur species concentrations upon storage, on-site analyses of natural water samples were preferred. Alternatively, the samples may be stabilized on resin for later elution and analysis in the laboratory. The analytical method further allowed simultaneous determination of other anions including F -, Cl -, dissolved inorganic carbon (DIC) and NO 3 - without sample preservation or stabilization. The power of the newly developed methods relies in routine analysis of sulfur speciation of importance in natural waters using techniques and facilities available in most laboratories doing water sample analysis. The new methods were successfully applied for the determination of sulfur species concentrations in samples of natural and synthetic waters. © 2011 Elsevier B.V. All rights reserved.

  • 3.
    Kaasalainen, Hanna
    et al.
    Nordic Volcanological Center, University of Iceland, Institute of Earth Sciences.
    Stefánsson, Andri
    Institute of Earth Sciences, University of Iceland.
    Sulfur speciation in natural hydrothermal waters, Iceland2011In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 75, no 10, p. 2777-2791Article in journal (Refereed)
    Abstract [en]

    The speciation of aqueous dissolved sulfur was determined in hydrothermal waters in Iceland. The waters sampled included hot springs, acid-sulfate pools and mud pots, sub-boiling well discharges and two-phase wells. The water temperatures ranged from 4 to 210°C, the pHT was between 2.20 and 9.30 at the discharge temperature and the SO4 and Cl concentrations were 0.020-52.7 and <0.01-10.0mmolkg-1, respectively. The analyses were carried out on-site within ~10min of sampling using ion chromatography (IC) for sulfate (SO42-), thiosulfate (S2O32-) and polythionates (SxO62-) and titration and/or colorimetry for total dissolved sulfide (S2-). Sulfite (SO32-) could also be determined in a few cases using IC. Alternatively, for few samples in remote locations the sulfur oxyanions were stabilized on a resin on site following elution and analysis by IC in the laboratory. Dissolved sulfate and with few exceptions also S2- were detected in all samples with concentrations of 0.02-52.7mmolkg-1 and <1-4100μmolkg-1, respectively. Thiosulfate was detected in 49 samples of the 73 analyzed with concentrations in the range of <1-394μmolkg-1 (S-equivalents). Sulfite was detected in few samples with concentrations in the range of <1-3μmolkg-1. Thiosulfate and SO32- were not detected in <100°C well waters and S2O32- was observed only at low concentrations (<1-8μmolkg-1) in ~200°C well waters. In alkaline and neutral pH hot springs, S2O32- was present in significant concentrations sometimes corresponding to up to 23% of total dissolved sulfur (STOT). In steam-heated acid-sulfate waters, S2O32- was not a significant sulfur species. The results demonstrate that S2O32- and SO32- do not occur in the deeper parts of <150°C hydrothermal systems and only in trace concentrations in ~200-300°C systems. Upon ascent to the surface and mixing with oxygenated ground and surface waters and/or dissolution of atmospheric O2, S2- is degassed and oxidized to SO32- and S2O32- and eventually to SO42- at pH >8. In near-neutral hydrothermal waters the oxidation of S2- and the interaction of S2- and S0 resulting in the formation of Sx2- are considered important. At lower pH values the reactions seemed to proceed relatively rapidly to SO42- and the sulfur chemistry of acid-sulfate pools was dominated by SO42-, which corresponded to >99% of STOT. The results suggest that the aqueous speciation of sulfur in natural hydrothermal waters is dynamic and both kinetically and source-controlled and cannot be estimated from thermodynamic speciation calculations. © 2011 Elsevier Ltd.

  • 4.
    Kaasalainen, Hanna
    et al.
    Nordic Volcanological Center, University of Iceland, Institute of Earth Sciences.
    Stefánsson, Andri
    Institute of Earth Sciences, University of Iceland.
    The chemistry of trace elements in surface geothermal waters and steam, Iceland2012In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 330-331, p. 60-85Article in journal (Refereed)
    Abstract [en]

    The geochemistry of trace elements in surface geothermal fluids in Iceland was studied. The sampled fluids included hot springs, mud pots, steam vents and soil solutions with temperatures ranging from 4 to 100. °C, pH between 2.01 and 9.10 and total dissolved solids between 86 and 4375. ppm. The surface geothermal waters may be categorized into three groups based on their chemical composition, namely NaCl waters, steam-heated acid-sulfate waters and mixed waters. NaCl waters with pH >. 8 are considered to represent aquifer geothermal fluids that have undergone boiling in the upflow. They contained only low concentrations of most metals, <. 0.1. ppb of Cd and Co, <. 1. ppb of Ni, Pb, Cr and Cu and <. 10. ppb of Zr, V and Zn, whereas somewhat higher concentrations of Ba (0.06-15. ppb), Sr (1.2-107. ppb), Cs (0.08-19. ppb), Rb (7.1-163. ppb), Li (18-380. ppb), As (<. 0.2-252. ppb), Sb (0.05-40. ppb), Mo (0.16-50. ppb), W (2.4-88. ppb), Mn (0.1-163. ppb), Fe (1.8-157. ppb) and Al (21-1510. ppb) were found. Steam-heated acid-sulfate waters typically had a pH <. 4. They form by condensation and mixing of steam in shallow non-thermal water. Compared to NaCl waters, steam-heated acid-sulfate waters typically had high concentrations of Al (0.02-267. ppm), Fe (0.66-360. ppm), Mn (44-4231. ppb), V (1.1-1120. ppb), Cr (0.15-660. ppb), Zn (3.1-633. ppb), Ni (0.20-192. ppb), Cu (0.09-121. ppb), Co (0.02-90. ppb), Ba (1.0-60. ppb) and Sr (2.8-316. ppb), whereas concentrations of Li (<. 0.03-57. ppb), Cs (<. 0.01-0.77. ppb), Rb (0.12-24. ppb), As (<. 0.1-61. ppb), Mo (<. 0.01-14. ppb), Sb (<. 0.01-25. ppb) and W (<. 0.01-6.9. ppb) were lower. Mixed waters are mixtures between NaCl waters, steam-heated acid-sulfate waters and non-thermal water, and showed chemical characteristics of these end-member waters. The steam discharged by the steam vents was found to carry trace elements including B, As, Cu and Cd in the ppt to ppb concentration range. The geochemistry of Li, Cs, Rb, As, Mo, Sb and W in surface geothermal waters was dominated by rock leaching, together with mixing of condensed steam and non-thermal surface waters at a low pH and with incorporation into secondary minerals including aluminum silicates and sulfides under alkaline conditions. In contrast, aqueous Ba and Sr concentrations were largely influenced by the formation of secondary minerals including sulfates, carbonates and Ca-minerals in all water types. At a low pH, the behavior of Al, Fe, Mn, Co, Ni, Zn, Cd, Cu, Pb, Cr and V was generally dominated by rock leaching, though occasionally by mineral precipitation in the case of Fe, Al, Cu, Co and Zr. With increasing pH, these metals became immobile due to their incorporation into secondary sulfide (Fe, Co, Ni, Zn, Cd, Cu, Pb), (hydr)oxide (Al, Fe, Cr, V, Zr) and aluminum- silicate (Al) minerals limiting their aqueous concentrations. © 2012 Elsevier B.V.

  • 5.
    Kaasalainen, Hanna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Institute of Earth Sciences, Science Institute, University of Iceland.
    Stefánsson, Andri
    Institute of Earth Sciences, Science Institute, University of Iceland.
    Druschel, Gregory K.
    Department of Earth Sciences, Indiana University-Purdue University Indianapolis.
    Geochemistry and speciation of Fe(II) and Fe(III) in natural geothermal water, Iceland2017In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 87, p. 146-157Article in journal (Refereed)
    Abstract [en]

    The geochemistry of Fe(II) and Fe(III) was studied in natural geothermal waters in Iceland. Samples of surface and spring water and sub-boiling geothermal well water were collected and analyzed for Fe(II), Fe(III) and Fetotal concentrations. The samples had discharge temperatures in the range 27–99 °C, pH between 2.46 and 9.77 and total dissolved solids 155–1090 mg/L. The concentrations of Fe(II) and Fe(III) were determined in the <0.2 μm filtered and acidified fraction using a field-deployed ion chromatography spectrophotometry (IC-Vis) method within minutes to a few hours of sampling in order to prevent post-sampling changes. The concentrations of Fe(II) and Fe(III) were <0.1–130 μmoL/L and <0.2–42 μmoL/L, respectively. In-situ dialysis coupled with Fe(II) and Fe(III) determinations suggest that in some cases a significant fraction of Fe passing the standard <0.2 μm filtration method may be present in colloidal/particulate form. Therefore, such filter size may not truly represent the dissolved fraction of Fe but also nano-sized particles. The Fe(II) and Fe(III) speciation and Fetotal concentrations are largely influenced by the water pH, which in turn reflects the water type formed through various processes. In water having pH of ∼7–9, the total Fe concentrations were <2 μmoL/L with Fe(III) predominating. With decreasing pH, the total Fe concentrations increased with Fe(II) becoming increasingly important and predominating at pH < 3. In particular in waters having pH ∼6 and above, iron redox equilibrium may be approached with Fe(II) and Fe(III) possibly being controlled by equilibrium with respect to Fe minerals. In many acid waters, the Fe(II) and Fe(III) distribution may not have reached equilibrium and be controlled by the source(s), reaction kinetics or microbial reactions

  • 6.
    Kaasalainen, Hanna
    et al.
    University of Iceland.
    Stefánsson, Andri
    University of Iceland, Institute of Earth Sciences.
    Druschel, Gregory K
    Indiana University-Purdue University Indianapolis.
    Nuzzio, Don
    Analytical Instrument Systems Inc.
    Keller, Nicole
    University of Iceland, Institute of Earth Sciences.
    Speciation matters – views on iron and sulfur chemistry in geothermal water, Iceland2016Conference paper (Other academic)
  • 7.
    Kaasalainen, Hanna
    et al.
    Nordic Volcanological Center, University of Iceland, Institute of Earth Sciences.
    Stefánsson, Andri
    Institute of Earth Sciences, University of Iceland.
    Giroud, Niels
    Nagra.
    Arnórsson, Stefán
    Institute of Earth Sciences, University of Iceland.
    The geochemistry of trace elements in geothermal fluids, Iceland2015In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 62, p. 207-223Article in journal (Refereed)
    Abstract [en]

    Trace element geochemistry was studied in geothermal fluids in Iceland. The major and trace element compositions of hot springs, sub-boiling, and two-phase (liquid and vapor) wells from 10 geothermal areas were used to reconstruct the fluid composition in the aquifers at depth. Aquifer fluid temperatures ranged from 4 to 300 °C, pH values between 4.5 and 9.3, and fluids typically contained total dissolved solids <1000 ppm, except in geothermal areas that have seawater and seawater-meteoric water mixtures. Trace alkali elements Li, Rb and Cs are among the most mobile elements in aquifer fluids, with concentrations in the range of <1. ppb to 3.49 ppm Li, <0.01 to 57 ppb Cs, and <1 ppb to 3.77 ppm Rb. Their chemistry is thought to be dominated by rock leaching and partitioning into Na- and K-containing major alteration minerals. Arsenic, Sb, Mo and W are typically present in concentrations in the range of 1-100. ppb. They are relatively mobile, yet Mo may be limited by molybdenite solubility. The alkaline earth elements Ba and Sr are quite immobile with concentrations in the range of <0.1-10. ppb Ba and <1-100 ppb Sr in the dilute fluids, but up to 5.9 ppm Ba and 8.2 ppm Sr in saline fluids. These elements show a systematic relationship with Ca, possibly due to substitution for Ca in Ca-containing major alteration minerals like calcite, epidote and anhydrite. Incorporation into major Ca-minerals may also be important for Mn. Many metals including Fe, Cr, Ni, Zn, Cu, Co, Pb and Ag have low mobility and concentrations, typically <1. ppb for Ag, Cd, Co, Cr, Cu, Ni, and Pb, <10 ppb for Zn and < 100 ppb for Fe, although for some metals higher concentrations are associated with saline fluids. Based on the metals assessed, saturation is approached with respect to many sulfide minerals and in some cases oxide minerals but Cu, Ni and Pb minerals are slightly but systematically undersaturated, and Ag phases significantly undersaturated. Evaluation of mineral-fluid equilibria for these metals is problematic due to their low concentrations, problems associated with assessing the aqueous species distribution by thermodynamic calculations, and uncertainties concerning the exact minerals possibly involved in such reactions. Reaction path calculations, poor comparison of concentrations measured in the samples collected at the wellhead and published downhole data as well as boiling, cooling and mass precipitation calculations suggest removal of many metals due to changes upon depressurization boiling and conductive cooling of the aquifer fluids as they ascend in wells. These results imply that processes such as mass precipitation upon fluid ascent may be highly important and emphasize the importance of considering mass movement in geothermal systems.

  • 8.
    Nyström, Elsa
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kaasalainen, Hanna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Alakangas, Lena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Prevention of Sulfide Oxidation in Waste Rock using By-products and Industrial Remnants: a Suitability Study2017In: Mine Water & Circular Economy: A Green Congress / [ed] Wolkersdorfer, C.; Sartz, L.; Sillanpää, M. & Häkkinen, A, 2017, Vol. 2, p. 1170-1178Conference paper (Refereed)
    Abstract [en]

    Prevention and mitigation of acid rock drainage from mining are decisive for limiting environmental impact. Five by-products and industrial remnants (lime kiln dust, blast furnace slag, granulated blast furnace slag, cement kiln dust and fly ash) were investigated for their suitability to prevent acidity and metal(loid)s during leaching from highly sulfidic (50wt%, sulfide) waste rock in small scale laboratory test cells. Variations in pH and electrical conductivity in leachate allowed differentiation between the different materials. Lime kiln dust (5wt%) and fly ash (1 and 2.5wt%) were observed to be the most suitable materials to prevent acidity and metal(loid)s leaching.

  • 9.
    Stefánsson, Andri
    et al.
    Institute of Earth Sciences, University of Iceland.
    Arnórsson, Stefán
    Institute of Earth Sciences, University of Iceland.
    Gunnarsson, Ingvi
    Reykjavík Energy.
    Kaasalainen, Hanna
    Institute of Earth Sciences, University of Iceland.
    Gunnlaugsson, Einar
    Reykjavík Energy.
    The geochemistry and sequestration of H2S into the geothermal system at Hellisheidi, Iceland2011In: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 202, no 3-4, p. 179-188Article in journal (Refereed)
    Abstract [en]

    The geochemistry and mineralization of H2S in the geothermal system hosted by basaltic rock formation at Hellisheidi, SW Iceland, was studied. Injection of mixtures of H2S with geothermal waste water and condensed steam into the >230°C geothermal aquifer is planned, where H2S will hopefully be removed in the form of sulphides. The natural H2S concentrations in the aquifer average 130ppm. They are considered to be controlled by close approach to equilibrium with pyrite, pyrrhotite, prehnite and epidote. Injection of H2S will increase significantly the reservoir H2S equilibrium concentrations, resulting in mineralization of pyrite and possibly other sulphides as well as affecting the formation of prehnite and epidote. Based on reaction path modelling, the main factors affecting the H2S mineralization capacity are related to the mobility and oxidation state of iron. At temperatures above 250°C the pyrite mineralization is greatly reduced upon epidote formation leading to the much greater basalt dissolution needed to sequestrate the H2S. Based on these findings, the optimum conditions for H2S injection are aquifers with temperatures below ~250°C where epidote formation is insignificant. Moreover, the results suggest that sequestration of H2S into the geothermal system is feasible. The total flux of H2S from the Hellisheidi power plant is 12,950tonnesyr-1. Injection into 250°C aquifers would result in dissolution of ~1000tonnesyr-1 of basalt for mineralization of H2S as pyrite, corresponding to ~320m3yr-1. © 2011 Elsevier B.V.

  • 10.
    Stefánsson, Andri
    et al.
    Institute of Earth Sciences, University of Iceland.
    Gunnarsson, Ingvi
    Reykjavík Energy.
    Kaasalainen, Hanna
    Institute of Earth Sciences, University of Iceland.
    Arnórsson, Stefán
    Institute of Earth Sciences, University of Iceland.
    Chromium geochemistry and speciation in natural waters, Iceland2015In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 62, p. 200-206Article in journal (Refereed)
    Abstract [en]

    Natural waters in Iceland were collected and analyzed for chromium concentration and speciation (CrIII, CrVI and CrTOT). The water sampled included non-thermal surface and spring water, surface geothermal water, and single and two-phase geothermal well discharges with sampling temperatures of 0-178°C, pH of 2.0-9.5, and total dissolved solids (TDS) of 35-4030ppm. The total Cr concentration was between <0.01 and 660ppb with highest concentrations in waters with the lowest pH. At pH>4 the measured CrIII concentration was low, generally <1ppb but with decreasing pH higher CrIII concentrations were observed reaching values of hundreds of ppb. At pH<6 no measurable CrVI was detected whereas in neutral to alkaline waters measured CrVI concentrations were as high as 3ppb, frequently dominating over CrIII. The Cr chemistry in natural waters associated with mafic rocks in Iceland is largely influenced by the water pH. At low pH Cr-containing minerals are unstable and Cr leaches into the waters as CrIII. Possible oxidation of CrIII to CrVI is minimized thermodynamically and the mobility of CrVI is further reduced by surface complexation reactions. At neutral to alkaline pH the primary Cr-containing mineral phases like titanomagnetite and chromite may be stable, limiting Cr-rock leaching. Solubility of secondary CrIII-FeIII-mineral phases may further reduce and/or limit the CrIII availability. In contrast, CrVI mobility is enhanced at a pH>8 associated with decreasing importance of mineral surface complexation. Hence, CrVI becomes an increasingly dominant form of dissolved Cr at pH above 7-8. Many groundwater drinking supplies associated with mafic rocks are characterized by moderately alkaline pH resulting in CrVI concentrations of a few ppb.

  • 11.
    Stefánsson, Andri
    et al.
    University of Iceland.
    Keller, Nicole S.
    University of Iceland.
    Robin, Jóhann Gunnarsson
    University of Iceland.
    Kaasalainen, Hanna
    University of Iceland.
    Björnsdóttir, Snædís
    Faculty of Life and Environmental Sciences, University of Iceland.
    Pétursdóttir, Sólveig
    Jóhannesson, Haukur
    Bardarvogur 44.
    Hreggvidsson, Gudmundur Óli
    Faculty of Life and Environmental Sciences, University of Iceland.
    Quantifying mixing, boiling, degassing, oxidation and reactivity of thermal waters at Vonarskard, Iceland2016In: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 309, p. 53-62Article in journal (Refereed)
    Abstract [en]

    The chemical composition of geothermal fluids may be altered upon ascent from the reservoir to surface by processes including boiling, degassing, mixing, oxidation and water-rock interaction. In an attempt to quantify these processes, a three step model was developed that includes: (1) defining the composition of the end-member fluid types present in the system, (2) quantifying mixing between the end-members using non-reactive elemental concentrations and enthalpy and (3) quantifying the changes of reactive elements including degassing, oxidation and water-rock interaction. The model was applied to geothermal water at Vonarskard, Iceland, for demonstration having temperatures of 3-98°C, pH of 2.15-9.95 and TDS of 323-2250ppm, and was thought to be produced from boiled reservoir water, condensed steam and non-thermal water. Most geothermal water represented mixture of non-thermal water and condensed steam whereas the boiled reservoir water was insignificantly mixed. CO2 and H2S degassing was found to be quantitative in steam-heated water, with oxidation of H2S to SO4 also occurred. In contrast, major rock forming elements are enriched in steam-heated water relative to their mixing ratios, suggesting water-rock interaction in the surface zone. Boiled reservoir water observed in alkaline hot springs have, however, undergone less geochemical changes upon ascent to surface and within the surface zone.

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