| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
|
| Initial Amendment Date: | March 6, 2012 |
| Latest Amendment Date: | March 6, 2012 |
| Award Number: | 1147728 |
| Award Instrument: | Standard Grant |
| Program Manager: |
hailiang dong
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | March 15, 2012 |
| End Date: | February 29, 2016 (Estimated) |
| Total Intended Award Amount: | $350,349.00 |
| Total Awarded Amount to Date: | $350,349.00 |
| Funds Obligated to Date: |
|
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
201 OLD MAIN UNIVERSITY PARK PA US 16802-1503 (814)865-1372 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
110 Technology Center University Park PA US 16802-7000 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): | Geobiology & Low-Temp Geochem |
| Primary Program Source: |
|
| Program Reference Code(s): | |
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Technical Description. This project will explore the dissolution of iron and manganese oxides by siderophores using real-time, in situ X-ray diffraction to determine mechanisms and rate laws for these important soil reactions. Our preliminary results reveal that the siderophore desferrioxamine-B (DFOB) at concentrations ranging from 0.1 to 10 mM will induce complete dissolution of the layered Mn oxide birnessite within hours. Moreover, Rietveld analysis of our time-resolved synchrotron XRD data have revealed that Mn(III) is selectively removed from the birnessite structure relative to Mn(IV). Removal of 20 mol% Mn(III) induces a critical instability in triclinic birnessite, and the structure collapses when vacancy concentrations increase beyond this value.
These observations lead us to hypothesize that the mechanism by which siderophores dissolve minerals depends on the heterogeneity of metal valence state. In mixed-valence metal (hydr)oxides, siderophore-mediated dissolution occurs by a structural collapse after a critical 3-dimensional vacancy concentration is achieved. In contrast, homovalent metal (hydr)oxides dissolve by the more conventional mode of 2-dimensional surface depletion. We will test these ideas by applying TR-XRD techniques to DFOB-assisted dissolution of a variety of heterovalent oxides (e.g., magnetite [Fe3+ (Fe2+,3+)2O4], hausmannite [Mn3+(Mn2+,3+)2O4], riebeckite [Na2Fe2+3Fe3+2(Si8O22)(OH)2] and homovalent oxides (e.g., hematite [Fe3+2O3], goethite [Fe3+O(OH)]), in the presence and absence of light.
Broader Impacts. Mineral dissolution mechanisms are foundational to a range of societally important issues, including soil fertility and the cycling of metals in the critical zone, contaminant transport, the sequestration of CO2, and the chemistry of Earth?s surface waters. Most prior studies of the rates by which minerals dissolve in aqueous solutions have monitored reaction progress through changes in fluid chemistry. Here we propose a novel and complementary strategy that correlates the chemical evolution of the fluid with structural changes in the reacting solid. By this approach, we can rigorously couple the chemical kinetics of the fluid with structural mineral transitions, greatly expanding our understanding of the underlying reaction mechanisms.
The work described in this proposal will help reveal the factors that control the mechanisms and rates by which siderophores can extract insoluble metals to sustain healthy metabolic activity in soil and marine environments. Siderophores are low-weight, biogenic compounds that occur ubiquitously in micromolar concentrations in soil and marine waters, and they are produced by a wide variety of microbes, fungi, and grasses to gain a selective advantage in severely Fe-limited conditions. Siderophores can extract Fe(III) and Mn(III) from nearly insoluble Fe(III) and Mn(III,IV) oxides with extremely high specificity, transporting the cations to parent organisms to satisfy nutritive or redox metabolic needs. Insights gained from this work may lead to a better understanding of methods to increase metal bioavailability in iron-deficient agricultural regions, and they will improve our understanding of mineral weathering, a major means of atmospheric CO2 drawdown.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
Note:
When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external
site maintained by the publisher. Some full text articles may not yet be available without a
charge during the embargo (administrative interval).
Some links on this page may take you to non-federal websites. Their policies may differ from
this site.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The primary motivation for this project was the measurement of crystallographic changes in Fe and Mn oxides in the presence of siderophores – organic compounds that selectively remove Fe(III) and Mn(III) from minerals. Our previous work revealed that the siderophore called desferrioxamine-B (DFOB) extracts Mn(III) from the layered manganate called birnessite, not merely from the surface of the mineral but throughout the volume. Specifically, we reproducibly demonstrated that bulk occupancy values for Mn in birnessite decreased from 100% to 85% in the presence of DFOB. Beyond a 15% vacancy value, birnessite dissolved.
We hypothesized that siderophore-assisted dissolution of mixed valence Mn(II,III,IV) and Fe(II,III) oxides would generate metastable phases with high concentrations of Mn and Fe vacancies. We proposed that this behavior extends to reductive dissolution via organic acids and transition metals. In contrast, we also expected that homovalent Mn(IV) and Fe(III) oxides would dissolve in a congruent fashion.
Graduate student Florence Ling synthesized nanoparticulate hematite and magnetite, and she acquired natural magnetite from the Smithsonian Institution. Using these powders, she conducted batch dissolution experiments at room temperature using 0.1 M DFOB, and for purposes of comparison, she also investigated the reductive dissolution of Fe oxides by organic acids that are known to extract and complex Fe. In addition, Ms. Ling investigated reductive dissolution of Mn and Fe oxides by transition and heavy metals (Cr, Co, Zn). In these experiments, she collaborated with Dr. Xiang Gao, a visiting professor from the China University of Geosciences who worked with Heaney’s group.
Ms. Ling's experiments with siderophore-assisted batch dissolution of hematite and magnetite revealed that, as we expected, hematite dissolved congruently through surface extraction of Fe(III). Scherer analysis of X-ray diffraction peaks allowed us to quantify the change in particle size. We expected that the experiments with magnetite would display incongruent dissolution, as Fe(III) was selectively removed relative to Fe(II). Instead we observed no obvious change in crystallinity or in Fe occupancies. However, these experiments were troubled by extremely slow dissolution rates. Consequently, we have teamed with Dr. Christopher Gorski, a newly hired assistant professor of civil engineering at Penn State. Dr. Gorski has innovated electrochemical techniques to explore the reductive dissolution of Fe-containing clays and oxides using molecular electron shuttles to mediate the process. Ms. Ling has been working with his group to apply these electrochemical techniques to Fe oxides and, for the first time, to Mn oxides. Ms. Ling will defend her PhD in July 2016.
In close alignment with these studies, another graduate student, Kristina Peterson, monitored the hydrothermal nucleation and growth of beta-FeOOH (akaganéite) and hematite as part of her PhD research (PhD in 2015). Ms. Peterson studied the crystallization, dissolution, and transformation of these phases using in situ, time-resolved X-ray diffraction up to 200 oC followed by Rietveld analysis. She demonstrated that when beta-FeOOH (akaganéite) transforms to hematite in hydrothermal solutions at 160 to 200 oC, the first hematite crystals to nucleate contain 25% vacancies in the Fe sites. The implication is that the first-formed “hematite” structure exhibits an Fe:O ratio of 1:2, identical to that of FeOOH. Thus, the first “hematite” crystal actually has the formula FeOOH. Moreover, the experiments at 200 oC generated crystals with a distorted hematite structure, which we refined in an I2/a ...
Please report errors in award information by writing to: awardsearch@nsf.gov.
