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Iron(III) precipitates formed by iron(II) oxidation in natural waters: Structure, reactivity and impact on arsenic

English title Iron(III) precipitates formed by iron(II) oxidation in natural waters: Structure, reactivity and impact on arsenic
Applicant Voegelin Andreas
Number 152993
Funding scheme Project funding (Div. I-III)
Research institution Swiss Federal Institute of Aquatic Science and Technology (EAWAG)
Institution of higher education Swiss Federal Institute of Aquatic Science and Technology - EAWAG
Main discipline Other disciplines of Environmental Sciences
Start/End 01.04.2014 - 31.07.2016
Approved amount 133'090.00
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All Disciplines (4)

Discipline
Other disciplines of Environmental Sciences
Pedology
Geochemistry
Hydrology, Limnology, Glaciology

Keywords (9)

calcium; phosphate; arsenic; precipitation; kinetics ; iron; dissolution; structure; oxidation

Lay Summary (German)

Lead
Die Oxidation von gelöstem Eisen(II) in Wasser führt zur Bildung schwerlöslicher Eisen(III)-Präzipitate welche auch andere Haupt- und Spurenelemente aufnehmen können. Dieser Prozess spielt eine zentrale Rolle im biogeochemischen Kreislauf des Eisens und beeinflusst auch das Verhalten kotransformierter Nähr- und Schadstoffe in der Umwelt stark, zum Beispiel in Böden und Seen. Zudem spielen Eisen-Präzipitate auch in technischen Systemen eine wichtige Rolle, wie zum Beispiel bei der Arsen-Entfernung aus Trinkwasser oder bei der Sanierung kontaminierter Grundwasserleiter. Die Struktur und die Eigenschaften solcher Eisen-Präzipitate hängen stark von der chemischen Zusammensetzung des Wassers ab in dem sie sich bilden. Trotz der zentralen Bedeutung von Eisen-Präzipitaten in aquatischen und terrestrischen Systemen ist bis anhin jedoch nicht ausreichend bekannt, wie verschiedene gelöste Stoffe die Struktur und die Eigenschaften von Eisen-Präzipitaten beeinflussen.
Lay summary

Ziel dieser Arbeit ist es zu bestimmen (i) wie Phosphat, Silikat und Kalzium die Zusammensetzung und Struktur durch Oxidation entstandener Eisen(III)-Präzipitate beeinflussen und (ii) wie sich strukturelle Unterschiede auf die Reaktivität von Eisen-Präzipitaten und die Kotransformation von Arsen auswirken.

In kürzlich abgeschlossenen Laborexperimenten haben wir Eisen-Präzipitate in künstlichen Grundwässern unterschiedlichster Zusammensetzung synthetisiert und mit modernen spektroskopischen und mikroskopischen Methoden charakterisiert. Zudem haben wir untersucht wie effizient Arsen durch verschiedene Eisen-Präzipitate aus dem Wasser entfernt werden kann. Ziel weiterführender Experimente ist nun, die Kinetik und zeitliche Sequenz der Oxidation und Ausfällung des Eisens und die Kotransformation von Arsen quantitativ und mechanistisch besser zu verstehen. Des Weiteren ist vorgesehen, die Raten der reduktiven Auflösung verschiedener Eisen-Präzipitate zu bestimmen um deren Wichtigkeit für die Retention von Spurenelementen unter anoxischen Bedingungen besser abschätzen zu können, zum Beispiel in kontaminierten Grundwasserleitern oder überfluteten Auenböden.

Mit den Erkenntnissen aus diesem Projekt wollen wir zu einem besseren Verständnis der Umwandlung des Eisens und anderer kotransformierter Elemente in der Umwelt beitragen. Zudem soll dieses Projekt Grundlagen liefern, welche zur Optimierung Eisen-basierter Methoden in der Wasserbehandlung benutzt werden können.


 

Direct link to Lay Summary Last update: 02.04.2014

Lay Summary (English)

Lead
The oxidation of dissolved iron(II) in water leads to the formation of iron(III)-precipitates that also incorporate other major and trace elements. This process affects the cycling of Fe and co-transformed nutrients and contaminants in environments like soils or lakes and also plays a major role in technical applications such as removal of toxic arsenic from drinking water or remediation of contaminated groundwater. The formation, structure and properties of iron oxidation products depend on the composition of the water in which they form. Despite the importance of iron(III)-precipitates in a wide range of systems, however, the interdependent effects of major dissolved species on Fe precipitate structure and properties are still not fully understood.
Lay summary

In this project, we aim to determine how phosphate, silicate and calcium (Ca) affect the structure of Fe oxidation products and how these variations impact the reactivity of the formed solids and arsenic co-transformation. We recently completed laboratory experiments in which we formed Fe oxidation products in synthetic groundwater over a wide range of compositions and characterized the resulting Fe(III)-phases by advanced spectroscopic and microscopic techniques. Furthermore, we also investigated the extent of As removal by different types of precipitates. In continuing experiments, we aim to gain more detailed insight into the kinetics and temporal sequence of Fe oxidation and precipitation and its consequences for As co-transformation. We also plan to quantify the rates of reductive dissolution of different types of Fe(III)-precipitates to gain a better understanding of their role for trace element retention under anoxic conditions, for example in contaminated aquifers or flooded soils.

Direct link to Lay Summary Last update: 02.04.2014

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Reductive dissolution of As(V)-bearing Fe(III)-precipitates formed by Fe(II) oxidation in aqueous solutions
Voegelin Andreas, Senn Anna-Caterina, Kaegi Ralf, Hug Stephan J. (2019), Reductive dissolution of As(V)-bearing Fe(III)-precipitates formed by Fe(II) oxidation in aqueous solutions, in Geochemical Transactions, 20, 2.
Arsenate co-precipitation with Fe(II) oxidation products and retention or release during precipitate aging
Senn Anna-Caterina, Hug Stephan J., Kaegi Ralf, Hering Janet G., Voegelin Andreas (2018), Arsenate co-precipitation with Fe(II) oxidation products and retention or release during precipitate aging, in Water Research, 131, 334-345.
Effect of aging on the structure and phosphate retention of Fe(III)-precipitates formed by Fe(II) oxidation in water
Senn Anna-Caterina, Kaegi Ralf, Hug Stephan J., Hering Janet G., Mangold S., Voegelin A. (2017), Effect of aging on the structure and phosphate retention of Fe(III)-precipitates formed by Fe(II) oxidation in water, in Geochimica et Cosmochimica Acta, 202, 341-360.
Composition and structure of Fe(III)-precipitates formed by Fe(II) oxidation in water at near-neutral pH: Interdependent effects of phosphate, silicate and Ca
Senn Anna-Caterina, Kaegi Ralf, Hug Stephan J., Hering Janet G., Mangold Stefan, Voegelin Andreas (2015), Composition and structure of Fe(III)-precipitates formed by Fe(II) oxidation in water at near-neutral pH: Interdependent effects of phosphate, silicate and Ca, in GEOCHIMICA ET COSMOCHIMICA ACTA, 220-246.

Collaboration

Group / person Country
Types of collaboration
Electron Microscopy Centres at ETH Zurich and EMPA Switzerland (Europe)
- Research Infrastructure
Synchrotrons ESRF France (Europe)
- Research Infrastructure
Synchrotron ANKA Germany (Europe)
- Publication
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Interfaces Against Pollution 2018 Talk given at a conference Arsenate uptake by fresh and aged Fe oxidation products 10.06.2018 La Grande Motte, France Voegelin Andreas;
International Conference on the Biogeochemistry of Trace Elements (ICOBTE) 2017 Talk given at a conference Diversity of iron oxidation productsand their impact on trace elements 17.07.2017 Zürich, Switzerland Voegelin Andreas;
16th Swiss Geoscience Meeting Poster Composition, structure and arsenate sequestration of iron oxidation products 19.11.2016 Genf, Switzerland Senn Anna-Caterina;
XAFS16 - 16th International Conference on X-ray Absorption Fine Structure Talk given at a conference Exploring the formation and structural diversity of Fe(III)-precipitates in aquatic systems using XAS 23.08.2015 Karlsruhe, Germany Voegelin Andreas;
Goldschmidt Conference 2015 Talk given at a conference Amorphous Ca-Fe(III)-phosphates formed by Fe(II) oxidation in water 16.08.2015 Prag, Czech Republic Senn Anna-Caterina;
Goldschmidt Conference 2015 Talk given at a conference Structural diversity and heterogeneity of Fe(III)- precipitates formed by Fe(II) oxidation in water 16.08.2015 Prag, Czech Republic Voegelin Andreas;
SNBL - Planning for the next Decade Talk given at a conference Formation of natural nanoparticles and their impact on trace elements 28.05.2015 Grenoble, France Voegelin Andreas;
Mid-European Clay Conference 2014 Talk given at a conference Fe(III)-precipitates formed by Fe(II) oxidation in water: Structure, reactivity and impact on As 16.09.2014 Dresden, Germany Voegelin Andreas;
Goldschmidt Conference 2014 Talk given at a conference Natural nanoparticles: Formation and impact on trace elements 08.06.2014 Sacramento, United States of America Voegelin Andreas;
Goldschmidt Conference 2014 Poster Structure an arsenate uptake of Fe(III)-Al-precipitates 08.06.2014 Sacramento, United States of America Voegelin Andreas;
Goldschmidt Conference 2014 Talk given at a conference Structure, composition and arsenate uptake of Fe oxidation products 08.06.2014 Sacramento, United States of America Senn Anna-Caterina;
Environment @ Soleil - Results and New Challenges Talk given at a conference Biogeochemistry of trace elements in aquatic and terrestrial systems: Insights gained from X-ray absorption spectroscopy 13.05.2014 Saint Aubin, France Voegelin Andreas;


Self-organised

Title Date Place
Session "Effects of Iron Transformations on the Biogeochemistry of Trace Elements" an der "International Conference on the Biogeochemsitry of Trace Elements" (ICOBTE) 2017 16.07.2017 Zürich, Switzerland
Session "Amorphous and Nanocrystalline Materials and their Role in Biogeochemical Element Cycling, Pollutant Remediation and Radioactive Waste Disposal" an Goldschmidt Conference 2015 16.08.2015 Prag, Czech Republic

Associated projects

Number Title Start Funding scheme
149283 Characterization of the redox properties of iron minerals by combined electrochemical and spectroscopic analyses 01.01.2015 Project funding (Div. I-III)
132123 Iron(III) precipitates formed by iron(II) oxidation in natural waters: Structure, reactivity and impact on arsenic 01.02.2011 Project funding (Div. I-III)

Abstract

The oxidation of dissolved Fe(II) in oxygenated water leads to the formation of structurally diverse Fe(III)-precipitates that determine the fate of a wide range of major and trace elements in environmental and technical systems. In an on-going SNF project, we showed for the first time that Fe(II) oxidation in phosphate-containing solution at near-neutral pH leads to initial precipitation of an amorphous Fe(III)-phosphate followed by its transformation into a phosphate-rich hydrous ferric oxide and concomitant precipitation of lepidocrocite during continuing Fe(II) oxidation. Furthermore, we assessed the interdependent effects of phosphate, silicate and Ca in near-neutral solutions on the structure of fresh and aged Fe oxidation products and on the solubility of co-precipitated arsenate. Using Fe K-edge X-ray absorption spectroscopy and electron microscopy for precipitate characterization, we were able to determine in unprecedented detail (i) the structure of fresh Fe(III)-precipitates as a function of the concentrations of dissolved phosphate, silicate and Ca, (ii) structural changes during aging, and (iii) implications for phosphate and arsenate solubility.In this two-year continuation project, we aim to further explore how different types of Fe(III)-precipitates that cover the structural range documented in our current work vary with respect to their reactivity and impact on co-transformed As. Specifically, in a first part, we plan to determine the reductive dissolution kinetics of different Fe(III)-precipitates to assess their susceptibility to reductive dissolution and associated release of co-precipitated phosphate and As under anoxic conditions. In a second part, we aim to determine the kinetics of heterogeneous Fe(II) oxidation and coupled As(III) co-oxidation during the formation of different types of Fe(III)-precipitates in order to quantify the importance of surface-catalyzed Fe(II) oxidation, its dependence on the type of precipitating phase, and implications for coupled As(III) co-oxidation and co-precipitation. This continuation project will enable the PhD student on the current project to continue and complete her PhD studies.Expanding on the findings from the on-going project, the results from this continuation project will allow us achieving a higher level of understanding of (i) how phosphate, silicate and Ca - via their effects on Fe(III)-precipitate formation - affect heterogeneous Fe(II) oxidation and As(III) co-oxidation in oxygenated water and (ii) how different types of amorphous to poorly-crystalline Fe(III)-precipitates vary with respect to reductive dissolution and As release. Such detailed knowledge of the relationships between the formation, structure and reactivity of Fe oxidation products and consequences for co-transformed As is essential for the quantification of nutrient and contaminant behaviour in redox-dynamic terrestrial and aquatic environments and for improved water resource use and water treatment.
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