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Coprecipitates of hydrous ferric oxide and natural organic matter: properties and biogeochemical reactivity

English title Coprecipitates of hydrous ferric oxide and natural organic matter: properties and biogeochemical reactivity
Applicant Kretzschmar Ruben
Number 127157
Funding scheme Project funding (Div. I-III)
Research institution Institut für Biogeochemie und Schadstoffdynamik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geochemistry
Start/End 01.08.2010 - 31.07.2015
Approved amount 391'308.00
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All Disciplines (3)

Discipline
Geochemistry
Pedology
Other disciplines of Earth Sciences

Keywords (6)

iron biogeochemistry; ferrihydrite; humic substances; arsenic; speciation; EXAFS

Lay Summary (German)

Lead
Eisen in Umweltsystemen bildet häufig schwach kristalline Oxide mit extrem grossen Oberflächen. Diese mineralischen Ausfällungen enthalten auch natürliche organische Substanzen, wodurch ihre Eigenschaften und Reaktivität stark verändert werden. Sie spielen eine wichtige Rolle in Stoffkreisläufen anderer Elemente wie C, P, und As. Die Struktur und Reaktivität dieser Eisenphasen wurde bislang kaum untersucht und ist Gegenstand dieses Projektes.
Lay summary

In diesem Projekt charakterisieren wir schwach kristalline Ausfällungen von Eisen, welche in Anwesenheit von Huminstoffen (aus Torf) im Labor hergestellt werden. Zum Vergleich charakterisieren wir auch natürliche organisch-mineralische Ausfällungen aus einem Moor (Gola di Lago), welches natürlicherweise mit Arsen angereichert ist. Dazu kommen Methoden zum Einsatz, für die man hoch-brilliante Röntgenstrahlung eines Synchrotrons (ein ringförmiger Elektronenbeschleuniger) benötigt. Im zweiten Schritt untersuchen wir die biogeochemische Reaktivität dieser Festphasen. Im Fokus stehen die Reaktionen mit gelöstem Eisen (Fe2+) und Sulfid (S2-). Dabei werden reduktive Umwandlungen der Festphasen sowie gelöste Konzentrationen von Eisen, Arsen, und Schwefel gemessen, sowie die Bindungsformen von Arsen in den Festphasen bestimmt. Wir erhoffen uns ein besseres Verständnis der biogeochemischen Reaktivität solcher Eisenausfällungen in Abhängigkeit des Gehaltes an natürlichen organischen Substanzen.

Direct link to Lay Summary Last update: 10.09.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Sulfidization of Organic Freshwater Flocs from a Minerotrophic Peatland: Speciation Changes of Iron, Sulfur, and Arsenic
ThomasArrigo Laurel K., Mikutta C., Lohmayer R., Planer-Friedrich B., Kretzschmar R. (2016), Sulfidization of Organic Freshwater Flocs from a Minerotrophic Peatland: Speciation Changes of Iron, Sulfur, and Arsenic, in Environmental Science & Technology, 50(7), 3607-3616.
Iron and arsenic speciation and distribution in organic flocs from streambeds of an arsenic-enriched peatland
ThomasArrigo Laurel K., Mikutta Christian, Byrne James, Barmettler Kurt, Kappler Andreas, Kretzschmar Ruben (2014), Iron and arsenic speciation and distribution in organic flocs from streambeds of an arsenic-enriched peatland, in Environmental Science and Technology, 48(22), 13218-13228.
Spectroscopic evidence for ternary complex formation between arsenate and ferric iron complexes of humic substances
Mikutta Christian, Kretzschmar Ruben (2014), Spectroscopic evidence for ternary complex formation between arsenate and ferric iron complexes of humic substances, in Environmental Science and Technology, 45(22), 9550-9557.
X-ray absorption spectroscopy study on the effect of hydroxybenzoic acids on the formation and structure of ferrihydrite
Mikutta Christian (2011), X-ray absorption spectroscopy study on the effect of hydroxybenzoic acids on the formation and structure of ferrihydrite, in GEOCHIMICA ET COSMOCHIMICA ACTA, 75(18), 5122-5139.

Collaboration

Group / person Country
Types of collaboration
Prof. Andreas Kappler Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Stanford Synchrotron Radiation Laboratory United States of America (North America)
- Research Infrastructure
Prof. Britta Planer-Friedrich Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Advanced Photon Source (APS) United States of America (North America)
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Geomicrobiology meets Soil Chemistry - Part IV Talk given at a conference Structural and compositional properties of natural Fe-NOM coprecipitates 15.05.2014 Tübingen, Germany ThomasArrigo Laurel; Mikutta Christian; Kretzschmar Ruben;


Self-organised

Title Date Place
Iron Biogeochemistry - From Molecular Processes to Global Cycles 03.03.2013 Monte Verità, Ascona, Switzerland, Switzerland

Associated projects

Number Title Start Funding scheme
117933 Dynamics of Trace Metal Speciation in Periodically Reduced Soils 01.03.2008 Project funding (Div. I-III)
141562 Structure analysis of nanocrystalline iron arsenates and phosphates 01.02.2012 International short research visits
113737 Geochemical mechanisms of copper acquisition by methanotrophic microorganisms 01.04.2007 Project funding (Div. I-III)

Abstract

Poorly crystalline, nanometer-sized Fe(III)-(hydr)oxides, hereafter referred to as hydrous ferric oxides (HFO), are important sorbents for nutrients and pollutants in soils and sediments. In environmental systems, HFO is commonly formed in the presence of solutions containing dissolved organic C (OC) up to millimolar concentrations, leading to precipitates with significant contents of organic matter (OM). In the context of this proposal, HFO formed in the presence of OM is termed a coprecipitate. The HFO in these mineral-organic associations may significantly differ in its physicochemical properties from pure HFO. Moreover, the effect of natural OM in such coprecipitates on mineral phase transformations and the associated change in the biogeochemical reactivity of such sorbents has yet received only limited attention. Preliminary data indicate that natural OM can have a profound effect on the crystallinity of HFO within coprecipitates, thus affecting the minerals’ reactivity. But there is also evidence that even when the crystallinity of HFO is hardly affected by coprecipitated OM, its biogeochemical reactivity can exceed that of the pure mineral by far. Owing to an increased geochemical reactivity of such organo-mineral sorbents, they may be extremely influential in natural geochemical processes, but quantitative effects are largely unknown. Because we face an almost complete lack of knowledge on the biogeochemical reactivity of HFO coprecipited with macromolecular OM (MW >3.5 kDa), we propose to study (i) their physicochemical and mineralogical properties, (ii) the change of these properties with time, and (iii) the associated reactivity in terms of trace metal sequestration. In the first part of our research, we propose to synthesize HFO in the absence and presence of different types of natural OM ‘representatives’ at varying OC/Fe ratios relevant for environmental systems. For this, we will use well defined terrestrial and aquatic fulvic and humic acids and vary their redox state. In addition, we will humic substances and particulate organic matter isolated from peat. Coprecipitates will subsequently be analyzed by state-of-the-art analytical techniques such as Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, powder X-ray diffraction analysis, 57Fe Mössbauer spectroscopy, small angle X-ray scattering (SAXS), gas adsorption (CO2, N2, H2O), and electrophoretic mobility measurements. The substantial characterization of these coprecipitates and their OM-free counterparts will ultimately aid in establishing the link between the mineralogical/physicochemical properties (e.g., crystallinity of HFO, state of aggregation, charge behavior) and the macroscopic reactivity of these phases. After synthesis and characterization of the solids, we will elucidate the time-dependent cycling of sorbed trace elements between the aqueous and sorbing phase and between the organic and inorganic phase of the composite sorbents. Analogous experiments will be conducted with pure HFO, which serves as a reference. The interaction of trace metals with coprecipitates and pure HFO will be studied by means of macroscopic sorption and release experiments which will be complemented by detailed synchrotron-based spectroscopy analysis of the metals’ speciation. In a second step, we will investigate the reactivity of such coprecipitates with ferrous iron and sulfide. Combined, the results of our research will provide the first comprehensive quantitative and mechanistic data on the effect of natural macromolecular OM on mineralogy, mineral transformations, and reactivity of poorly crystalline Fe(III)-(hydr)oxides formed in its presence. These data will greatly improve our capability to understand the role of dissolved macromolecular OM on the biogeochemistry of Fe in OM-rich environments and its role in the dynamics of pollutants like heavy metals.
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