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Yu, C., Drake, H., Dideriksen, K., Tillberg, M., Song, Z., Mørup, S. & Åström, M. E. (2020). A Combined X-ray Absorption and Mössbauer Spectroscopy Study on Fe Valence and Secondary Mineralogy in Granitoid Fracture Networks: Implications for Geological Disposal of Spent Nuclear Fuels [Letter to the editor]. Environmental Science and Technology, 54(5), 2832-2842
Open this publication in new window or tab >>A Combined X-ray Absorption and Mössbauer Spectroscopy Study on Fe Valence and Secondary Mineralogy in Granitoid Fracture Networks: Implications for Geological Disposal of Spent Nuclear Fuels
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2020 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 54, no 5, p. 2832-2842Article in journal, Letter (Refereed) Published
Abstract [en]

Underground repository in crystalline bedrock is a widely accepted solution for long-term disposal of spent nuclear fuels. During future deglaciations, meltwater will intrude via bedrock fractures to the depths of future repositories where O2 left in the meltwater could corrode metal canisters and enhance the migration of redox-sensitive radionuclides. Since glacial meltwater is poor in reduced phases, the quantity and (bio)accessibility of minerogenic Fe(II) in bedrock fractures determine to what extent O2 in future meltwater can be consumed. Here, we determined Fe valence and mineralogy in secondary mineral assemblages sampled throughout the upper kilometer of fractured crystalline bedrock at two sites on the Baltic Shield, using X-ray absorption and Mössbauer spectroscopic techniques that were found to deliver matching results. The data point to extensive O2-consuming capacity of the bedrock fractures, because Fe(II)-rich phyllosilicates were abundant and secondary pyrite was dispersed deep into the bedrock with no overall increase in Fe(II) concentrations and Fe(II)/Fe(III) proportions with depth. The results imply that repeated Pleistocene deglaciations did not cause a measurable decrease in the Fe(II) pool. In surficial fractures, largely opened during glacial unloading, ferrihydrite and illite have formed abundantly via oxidative transformation of Fe(II)-rich phyllosilicates and recently exposed primary biotite/hornblende.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2020
National Category
Earth and Related Environmental Sciences
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-92512 (URN)10.1021/acs.est.9b07064 (DOI)000518235100029 ()
Available from: 2020-03-03 Created: 2020-03-03 Last updated: 2020-03-26Bibliographically approved
Alakangas, L. J., Mathurin, F. A. & Åström, M. E. (2020). Diverse fractionation patterns of Rare Earth Elements in deep fracture groundwater in the Baltic Shield - Progress from utilisation of Diffusive Gradients in Thin-films (DGT) at the Aspo Hard Rock Laboratory. Geochimica et Cosmochimica Acta, 269, 15-38
Open this publication in new window or tab >>Diverse fractionation patterns of Rare Earth Elements in deep fracture groundwater in the Baltic Shield - Progress from utilisation of Diffusive Gradients in Thin-films (DGT) at the Aspo Hard Rock Laboratory
2020 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 269, p. 15-38Article in journal (Refereed) Published
Abstract [en]

Rare earth elements (REEs) were studied in groundwater in fractures at depths between 144 m and 450 m in Proterozoic granitoids on the Baltic Shield at a coastal site in south eastern Sweden (Aspo Hard Rock Laboratory). A specially designed device was used to sample the groundwater under in situ high pressure and low redox conditions. The REEs were measured via both diffusive gradients in thin-films (DGT) samplers after approximately three-week deployment times, and after conventional filtration (0.45 mu m membrane filters). The concentrations of REEDGT were lower than the REE0.45 mu m concentrations in all 14 studied groundwaters. This is explained by development of a diffuse boundary layer (DBL) in the solution at the DGTs caused by the low flow, and in some of the groundwaters additionally by the presence of organically complexed REE that diffuse slowly in the diffusive gel of the DGT. Among the 14 studied groundwaters there was a huge range in REEDGT-fractionation patterns, ranging from enrichment to a nearly three-order-of-magnitude depletion of the heavy REEs (HREEs), despite a relatively homogenous bedrock (granitoids). The HREE enrichment is explained by preservation of the fractionation signature as HREE enriched sea water intruded and flowed through the fractures, supported by the high proportion of modelled REE fulvic-acid complexes in these waters. The strong HREE depletion, which occurred in saline groundwater, was ascribed to an advanced REE equilibrium between the groundwater and primary and/or secondary minerals and the pore water in the bedrock. Yet other groundwaters had flat or moderately HREE depleted patterns, which in some cases may have been caused by mixing of small portions of surficial waters with saline groundwater. (C) 2019 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Rare earth elements, REE, Diffusive gradients in thin-films, DGT, Aspo Hard Rock Laboratory, Aspo HRL, Deep groundwater
National Category
Earth and Related Environmental Sciences
Research subject
Natural Science
Identifiers
urn:nbn:se:lnu:diva-90916 (URN)10.1016/j.gca.2019.10.026 (DOI)000502332400002 ()
Available from: 2020-01-15 Created: 2020-01-15 Last updated: 2020-01-15Bibliographically approved
Tillberg, M., Drake, H., Zack, T., Kooijman, E., Whitehouse, M. & Åström, M. E. (2020). In situ Rb-Sr dating of slickenfibres in deep crystalline basement faults. Scientific Reports, 10, 1-12, Article ID 562.
Open this publication in new window or tab >>In situ Rb-Sr dating of slickenfibres in deep crystalline basement faults
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2020 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 10, p. 1-12, article id 562Article in journal (Refereed) Published
Abstract [en]

Establishing temporal constraints of faulting is of importance for tectonic and seismicity reconstructions and predictions. Conventional fault dating techniques commonly use bulk samples of syn-kinematic illite and other K-bearing minerals in fault gouges, which results in mixed ages of repeatedly reactivated faults as well as grain-size dependent age variations. Here we present a new approach to resolve fault reactivation histories by applying high-spatial resolution Rb-Sr dating to fine-grained mineral slickenfibres in faults occurring in Paleoproterozoic crystalline rocks. Slickenfibre illite and/or K-feldspar together with co-genetic calcite and/or albite were targeted with 50 µm laser ablation triple quadrupole inductively coupled plasma mass spectrometry analyses (LA-ICP-MS/MS). The ages obtained disclose slickenfibre growth at several occasions spanning over 1 billion years, from at least 1527 Ma to 349 ± 9 Ma. The timing of these growth phases and the associated structural orientation information of the kinematic indicators on the fracture surfaces are linked to far-field tectonic events, including the Caledonian orogeny. Our approach links faulting to individual regional deformation events by minimizing age mixing through micro-scale analysis of individual grains and narrow crystal zones in common fault mineral assemblages.

Place, publisher, year, edition, pages
Nature Publishing Group, 2020
National Category
Earth and Related Environmental Sciences
Research subject
Natural Science
Identifiers
urn:nbn:se:lnu:diva-91835 (URN)10.1038/s41598-019-57262-5 (DOI)
Funder
Swedish Research Council Formas, 2017-00766Swedish Research Council, 2017-05186
Available from: 2020-02-04 Created: 2020-02-04 Last updated: 2020-02-21Bibliographically approved
Christel, S., Yu, C., Wu, X., Josefsson, S., Lillhonga, T., Högfors-Rönnholm, E., . . . Dopson, M. (2019). Comparison of Boreal Acid Sulfate Soil Microbial Communities in Oxidative and Reductive Environments [Letter to the editor]. Research in Microbiology, 170(6-7), 288-295
Open this publication in new window or tab >>Comparison of Boreal Acid Sulfate Soil Microbial Communities in Oxidative and Reductive Environments
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2019 (English)In: Research in Microbiology, ISSN 0923-2508, E-ISSN 1769-7123, Vol. 170, no 6-7, p. 288-295Article in journal, Letter (Refereed) Published
Abstract [en]

Due to land uplift after the last ice age, previously stable Baltic Sea sulfidic sediments are becoming dry land. When these sediments are drained, the sulfide minerals are exposed to air and can release large amounts of metals and acid into the environment. This can cause severe ecological damage such as fish kills in rivers feeding the northern Baltic Sea. In this study, five sites were investigated for the occurrence of acid sulfate soils and their geochemistry and microbiology was identified. The pH and soil chemistry identified three of the areas as having classical acid sulfate soil characteristics and culture independent identification of 16S rRNA genes identified populations related to acidophilic bacteria capable of catalyzing sulfidic mineral dissolution, including species likely adapted to low temperature. These results were compared to an acid sulfate soil area that had been flooded for ten years and showed that the previously oxidized sulfidic materials had an increased pH compared to the unremediated oxidizied layers. In addition, the microbiology of the flooded soil had changed such that alkalinity producing ferric and sulfate reducing reactions had likely occurred. This suggested that flooding of acid sulfate soils mitigates their environmental impact.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
sulfide mineral; metal; sulfur; 16S rRNA gene; mitigation; wetland
National Category
Microbiology Earth and Related Environmental Sciences
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-77664 (URN)10.1016/j.resmic.2019.06.002 (DOI)000491121700006 ()
Available from: 2018-09-10 Created: 2018-09-10 Last updated: 2019-10-31Bibliographically approved
Tillberg, M., Maskenskaya, O. M., Drake, H., Hogmalm, J. K., Broman, C., Fallick, A. E. & Åström, M. E. (2019). Fractionation of Rare Earth Elements in Greisen and Hydrothermal Veins Related to A-Type Magmatism. Geofluids, 2019, 1-20, Article ID 4523214.
Open this publication in new window or tab >>Fractionation of Rare Earth Elements in Greisen and Hydrothermal Veins Related to A-Type Magmatism
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2019 (English)In: Geofluids, ISSN 1468-8115, E-ISSN 1468-8123, Vol. 2019, p. 1-20, article id 4523214Article in journal (Refereed) Published
Abstract [en]

This study focuses on concentrations and fractionation of rare earth elements (REE) in a variety of minerals and bulk materials of hydrothermal greisen and vein mineralization in Paleoproterozoic monzodiorite to granodiorite related to the intrusion of Mesoproterozoic alkali- and fluorine-rich granite. The greisen consists of coarse-grained quartz, muscovite, and fluorite, whereas the veins mainly contain quartz, calcite, epidote, chlorite, and fluorite in order of abundance. A temporal and thus genetic link between the granite and the greisen/veins is established via high spatial resolution in situ Rb-Sr dating, supported by several other isotopic signatures (delta S-34, Sr-87/Sr-86, delta O-18, and delta C-13). Fluid-inclusion microthermometry reveals that multiple pulses of moderately to highly saline aqueous to carbonic solutions caused greisenization and vein formation at temperatures above 200-250 degrees C and up to 430 degrees C at the early hydrothermal stage in the veins. Low calculated Sigma REE concentration for bulk vein (15ppm) compared to greisen (75ppm), country rocks (173-224ppm), and the intruding granite (320ppm) points to overall low REE levels in the hydrothermal fluids emanating from the granite. This is explained by efficient REE retention in the granite via incorporation in accessory phosphates, zircon, and fluorite and unfavorable conditions for REE partitioning in fluids at the magmatic and early hydrothermal stages. A noteworthy feature is substantial heavy REE (HREE) enrichment of calcite in the vein system, in contrast to the relatively flat patterns of greisen calcite. The REE fractionation of the vein calcite is explained mainly by fractional crystallization, where the initially precipitated epidote in the veins preferentially incorporates most of the light REE (LREE) pool, leaving a residual fluid enriched in the HREE from which calcite precipitated. Fluorite occurs throughout the system and displays decreasing REE concentrations from granite towards greisen and veins and different fractionation patterns among all these three materials. Taken together, these features confirm efficient REE retention in the early stages of the system and minor control of the REE uptake by mineral-specific partitioning. REE-fractionation patterns and fluid-inclusion data suggest that chloride complexation dominated REE transport during greisenization, whereas carbonate complexation contributed to the HREE enrichment in vein calcite.

Place, publisher, year, edition, pages
Hindawi Publishing Corporation, 2019
National Category
Earth and Related Environmental Sciences
Research subject
Natural Science
Identifiers
urn:nbn:se:lnu:diva-89315 (URN)10.1155/2019/4523214 (DOI)000484731100001 ()
Available from: 2019-09-26 Created: 2019-09-26 Last updated: 2019-09-26Bibliographically approved
Yu, C., Berger, T., Drake, H., Song, Z., Peltola, P. & Åström, M. E. (2019). Geochemical controls on dispersion of U and Th in Quaternary deposits, stream water, and aquatic plants in an area with a granite pluton. Science of the Total Environment, 663, 16-28
Open this publication in new window or tab >>Geochemical controls on dispersion of U and Th in Quaternary deposits, stream water, and aquatic plants in an area with a granite pluton
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2019 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 663, p. 16-28Article in journal (Refereed) Published
Abstract [en]

The weathering of U and/or Th rich granite plutons, which occurs worldwide, may serve as a potentially important, but as yet poorly defined source for U and Th in (sub-)surface environments. Here, we assessed the impact of an outcrop of such granite (5 km in diameter) and its erosional products on the distribution of U and Th in four nemo-boreal catchments. The results showed that (i) the pluton was enriched in both U and Th; and (ii) secondary U and Th phases were accumulated by peat/gyttja and in other Quaternary deposits with high contents of organic matter. Movement of the ice sheet during the latest glaciation led to dispersal of U- and Th-rich materials eroded from the pluton, resulting in a progressive increase in dissolved U and Th concentrations, as well as U concentrations in aquatic plants with increasing proximity to the pluton. The accumulation of U in the aquatic plants growing upon the pluton (100–365 mg kg−1, dry ash weight) shows that this rock represents a long-term risk for adjacent ecosystems. Dissolved pools of U and Th were correlated with those of dissolved organic matter (DOM) and were predicted to largely occur as organic complexes. This demonstrates the importance of DOM in the transport of U and Th in the catchments. Large fractions of Ca2UO2(CO3)30(aq) were modeled to occur in the stream with highest pH and alkalinity and thus, explain the strongly elevated U concentrations and fluxes in this particular stream. In future climate scenarios, boreal catchments will experience intensified runoff and warmer temperature that favor the production of hydrologically accessible DOM and alkalinity. Therefore, the results obtained from this study have implications for predicting the distribution and transport of Th and U in boreal catchments, especially those associated with U and/or Th rich granite plutons.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Uranium, Thorium, Nemo-boreal catchments, Climate change, Weathering
National Category
Environmental Sciences Geochemistry
Research subject
Natural Science, Environmental Science; Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-80032 (URN)10.1016/j.scitotenv.2019.01.293 (DOI)000459858500002 ()30708213 (PubMedID)2-s2.0-85060730596 (Scopus ID)
Available from: 2019-01-30 Created: 2019-01-30 Last updated: 2019-08-29Bibliographically approved
Uddh Söderberg, T., Berggren Kleja, D., Åström, M. E., Jarsjö, J., Fröberg, M., Svensson, P. A. & Augustsson, A. (2019). Metal solubility and transport at a contaminated landfill site – From the source zone into the groundwater. Science of the Total Environment, 668, 1064-1076
Open this publication in new window or tab >>Metal solubility and transport at a contaminated landfill site – From the source zone into the groundwater
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2019 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 668, p. 1064-1076Article in journal (Refereed) Published
Abstract [en]

Risks associated with metal contaminated sites are tightly linked to material leachability and contaminant mobility. In this study, metal solubility and transport were characterized within a glass waste landfill through i) lysimeter-collection of pore water and standardized batch leaching tests, ii) soil profiles extending from the landfill surface, through unsaturated soil underneath, and into the groundwater zone, and iii) groundwater samples upstream, at, and downstream of the landfill. The soil analyzes targeted both pseudo-total and geochemically active concentrations of contaminant metals (As, Cd, Pb, Sb) and basic soil geochemistry (pH, org. C, Fe,Mn). Water samples were analyzed for dissolved, colloid-bound and particulate metals, and speciation modelling of the aqueous phase was conducted. The results revealed a highly contaminated system, with mean metal concentrationsin the waste zone between 90 and 250 times the regional background levels. Despite severe contamination of the waste zone and high geochemically active fractions (80–100%) of all contaminant metals as well as elevated concentrations in landfill pore water, the concentrations of Cd and Pb decrease abruptly at the transition between landfill and underlying natural soil and no indication of groundwater contamination was found. The efficient cation retention is likely due to the high pH. However, the sorption of As and Sb is weaker at such high pH,which explains their higher mobility from the pore water zone into groundwater. The field soil:solution for Pb, ranging from 140 to 2,900,000 l kg−1), despite little variability in basic geochemical variables, which we suggest is due to waste material heterogeneity.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Soil and groundwater metal pollution, Glass waste, Soil:Solution partitioning (Kd), Leachability, Mobility, Colloids
National Category
Environmental Sciences
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-81555 (URN)10.1016/j.scitotenv.2019.03.013 (DOI)000462776800098 ()2-s2.0-85062735396 (Scopus ID)
Funder
The Geological Survey of Sweden (SGU), 36-1778/2014
Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-08-29Bibliographically approved
Yu, C., Drake, H., Lopez-Fernandez, M., Whitehouse, M., Dopson, M. & Åström, M. E. (2019). Micro-scale isotopic variability of low-temperature pyrite in fractured crystalline bedrock ― A large Fe isotope fractionation between Fe(II)aq/pyrite and absence of Fe-S isotope co-variation. Chemical Geology, 522, 192-207
Open this publication in new window or tab >>Micro-scale isotopic variability of low-temperature pyrite in fractured crystalline bedrock ― A large Fe isotope fractionation between Fe(II)aq/pyrite and absence of Fe-S isotope co-variation
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2019 (English)In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 522, p. 192-207Article in journal (Refereed) Published
Abstract [en]

This study assessed Fe-isotope ratio (56Fe/54Fe, expressed as δ56Fe relative to the IRMM-014 standard) variability and controls in pyrite that has among the largest reported S-isotope variability (maximum δ34S: 140‰). The pyrite occurs as fine-grained secondary crystals in fractures throughout the upper kilometer of granitoids of the Baltic Shield, and was analyzed here for δ56Fe by in situ secondary ion mass spectrometry (SIMS). Part of these pyrite crystals were picked from borehole instrumentation at depths of >400 m below sea level (m.b.s.l.), and thus are modern (known to have formed within 17 years) and can be compared with the δ56Fe of the source dissolved ferrous iron. The δ56Fe values of the modern pyrite crystals (−1.81‰ to +2.29‰) varied to a much greater extent than those of the groundwaters from which they formed (−0.48‰ to +0.13‰), providing strong field evidence for a large Fe isotope fractionation during the conversion of Fe(II)aq to FeS and ultimately to pyrite. Enrichment of 56Fe in pyrite relative to the groundwater was explained by equilibrium Fe(II)aq-FeS isotope fractionation, whereas depletion of 56Fe in pyrite relative to the groundwater was mainly the result of sulfidization of magnetite and kinetic isotopic fractionation during partial transformation of microsized FeS to pyrite. In many pyrite crystals, there is an increase in δ34S from crystal center to rim reflecting Rayleigh distillation processes (reservoir effects) caused by the development of closed-system conditions in the micro-environment near the growing crystals. A corresponding center-to-rim feature was not observed for the δ56Fe values. It is therefore unlikely that the groundwater near the growing pyrite crystals became progressively enriched in the heavy Fe isotope, in contrast to what has been found for the sulfur in sulfate. Other pyrite crystals formed following bacterial sulfate reduction in the time period of mid-Mesozoicum to Quaternary, had an almost identical Fe-isotope variability (total range: −1.50‰ to +2.76‰), frequency-distribution pattern, and relationship with δ34S as the recent pyrite formed on the borehole instrumentation. These features suggest that fundamental processes are operating and governing the Fe-isotope composition of pyrite crystals formed in fractured crystalline bedrock over large time scales.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Pyrite, Iron isotopes, Equilibrium Fe-isotope fractionation, Magnetite sulfidization, Partial pyritization, Fractured crystalline bedrock
National Category
Earth and Related Environmental Sciences
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-84618 (URN)10.1016/j.chemgeo.2019.05.026 (DOI)000480330600016 ()2-s2.0-85066994013 (Scopus ID)
Funder
Swedish Research Council, 2017-05186Swedish Research Council, 2014-4398Swedish Research Council Formas, 2017-00766
Available from: 2019-06-05 Created: 2019-06-05 Last updated: 2019-08-29Bibliographically approved
Drake, H., Roberts, N. M. W., Heim, C., Whitehouse, M. J., Siljeström, S., Kooijman, E., . . . Åström, M. E. (2019). Timing and origin of natural gas accumulation in the Siljan impact structure, Sweden. Nature Communications, 10, 1-14, Article ID 4736.
Open this publication in new window or tab >>Timing and origin of natural gas accumulation in the Siljan impact structure, Sweden
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2019 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, p. 1-14, article id 4736Article in journal (Refereed) Published
Abstract [en]

Fractured rocks of impact craters may be suitable hosts for deep microbial communities on Earth and potentially other terrestrial planets, yet direct evidence remains elusive. Here, we present a study of the largest crater of Europe, the Devonian Siljan structure, showing that impact structures can be important unexplored hosts for long-term deep microbial activity. Secondary carbonate minerals dated to 80 +/- 5 to 22 +/- 3 million years, and thus postdating the impact by more than 300 million years, have isotopic signatures revealing both microbial methanogenesis and anaerobic oxidation of methane in the bedrock. Hydrocarbons mobilized from matured shale source rocks were utilized by subsurface microorganisms, leading to accumulation of microbial methane mixed with a thermogenic and possibly a minor abiotic gas fraction beneath a sedimentary cap rock at the crater rim. These new insights into crater hosted gas accumulation and microbial activity have implications for understanding the astrobiological consequences of impacts.

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Microbiology
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-89969 (URN)10.1038/s41467-019-12728-y (DOI)000490981900005 ()31628335 (PubMedID)
Available from: 2019-11-08 Created: 2019-11-08 Last updated: 2019-11-08Bibliographically approved
Yu, C., Boily, J.-F., Shchukarev, A., Drake, H., Song, Z., Hogmalm, K. J. & Åström, M. E. (2018). A cryogenic XPS study of Ce fixation on nanosized manganite and vernadite: Interfacial reactions and effects of fulvic acid complexation. Chemical Geology, 483, 304-311
Open this publication in new window or tab >>A cryogenic XPS study of Ce fixation on nanosized manganite and vernadite: Interfacial reactions and effects of fulvic acid complexation
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2018 (English)In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 483, p. 304-311Article in journal (Refereed) Published
Abstract [en]

This study investigated interfacial reactions between aqueous Ce(III) and two synthetic nanosized Mn (hydr-) oxides (manganite: γ-MnOOH, and vernadite: δ-MnO2) in the absence and presence of Nordic Lake fulvic acid (NLFA) at circumneutral pH by batch experiments and cryogenic X-ray photoelectron spectroscopy (XPS). The surfaces of manganite and vernadite were negatively charged (XPS-derived loadings of (Na+K)/Cl > 1) and loaded with 0.42–4.33 Ce ions nm−2. Manganite stabilized Ce-oxidation states almost identical to those for vernadite (approximately 75% Ce(IV) and 25% Ce(III)), providing the first experimental evidence that also a Mn (III) phase (manganite) can act as an important scavenger for Ce(IV) and thus, contribute to the decoupling of Ce from its neighboring rare earth elements and the development of Ce anomaly. In contrast, when exposed to Ce (III)-NLFA complexes, the oxidation of Ce by these two Mn (hydr-)oxides was strongly suppressed, suggesting that the formation of Ce(III) complexes with fulvic acid can stabilize Ce(III) even in the presence of oxidative Mn oxide surfaces. The experiments also showed that Ce(III) complexed with excess NLFA was nearly completely removed, pointing to a strong preferential sorption of Ce(III)-complexed NLFA over free NLFA. This finding suggests that the Ce(III)-NLFA complexes were most likely sorbed by their cation side, i.e. Ce(III) bridging between oxide groups on the Mn (hydr-)oxides and negatively-charged functional groups in NLFA. Hence, Ce(III) was in direct contact with the oxidative manganite and vernadite but despite that not oxidized. An implication is that in organic-rich environments there may be an absence of Ce(IV) and Ce anomaly despite otherwise favorable conditions for Ce(III) oxidation.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Cryogenic XPS, Manganite, Vernadite, Oxidative scavenging, Ce anomaly
National Category
Earth and Related Environmental Sciences
Research subject
Natural Science
Identifiers
urn:nbn:se:lnu:diva-72684 (URN)10.1016/j.chemgeo.2018.02.033 (DOI)000429492300027 ()2-s2.0-85042905870 (Scopus ID)
Available from: 2018-04-13 Created: 2018-04-13 Last updated: 2019-08-29Bibliographically approved
Projects
Syntrofi och symbios för överlevnad och tillväxt i den djupa terrestra biosfären [202100-6271]; Linnaeus University
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3585-2209

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