| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | February 24, 2015 |
| Latest Amendment Date: | February 24, 2015 |
| Award Number: | 1451996 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Enriqueta Barrera
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | August 1, 2015 |
| End Date: | July 31, 2018 (Estimated) |
| Total Intended Award Amount: | $271,687.00 |
| Total Awarded Amount to Date: | $271,687.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
300 TURNER ST NW BLACKSBURG VA US 24060-3359 (540)231-5281 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
4044 Derring Hall Blacksburg VA US 24061-0001 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Geobiology & Low-Temp Geochem |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Our ability to understand crystallization processes is a key to interpreting the past, present, and future evolution of our planet. Yet our scientific understanding of crystallization - the transformation of dissolved species into solids - is incomplete. Recent research is revealing a diversity of new "nonclassical" pathways and mechanisms by which crystals, particularly nanocrystals, form and grow through attachment of intermediate and precursor particles. However, immense gaps remain in our understanding of these processes. This project will investigate the assembly of clusters to form the ferric oxyhydroxide mineral schwertmannite in order to understand how it forms via nonclassical route. Schwertmannite is pervasive and of broad interest in acidic environments because it exhibits high surface area and an affinity for a variety of potential pollutants. Additionally, because schwertmannite and other poorly crystalline minerals are so abundant and important at and near Earth's surface, understanding their formation is the key to interpreting the geologic record and the interaction between organisms and geologic media.
The overarching objective of this research is to document the nature of schwertmannite precursor clusters as a function of solution composition and growth conditions, and then to use that information to construct a general model that shows how dissolved iron and sulfate react in solution forming schwertmannite. Preliminary in situ synchrotron scattering data show the formation of clusters (~1.5 nm) having schwertmannite-like structural characteristics. These clusters are stable in solution as long as the solution remains turbulent (for up to 40 hours), but quickly aggregate and transform to schwertmannite under static fluid conditions. Based on preliminary data, the investigators hypothesize that schwertmannite forms via a nonclassical pathway involving self-assembly of schwertmannite-like precursor particles. They also hypothesize that the composition and properties of schwertmannite should reflect the structure and composition of the particles that aggregate. The investigators will apply a suite of in situ laboratory and synchrotron mineral characterization techniques to study the real-time formation of synthetic schwertmannite precursor clusters in solution and their aggregation into schwertmannite solids. The investigators will also collect and characterize water samples and sediments from an active AMD system and evaluate schwertmannite formation in nature. The structural, chemical, and physical data from these experiments will be used to develop a general crystallization model for schwertmannite that is consistent with thermodynamic and chemical principles, and with observations in the literature and this project of schwertmannite formation in nature.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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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.
Iron minerals are abundant in the environment and important in controlling water and soil quality. Yet our scientific understanding of how and when iron minerals form is drastically incomplete. This is in part because their crystallization – the transformation of dissolved species into solids (think of salt water into salt) – often happens quickly and in stages, making it difficult to observe. In addition, there are few experimental approaches that allow researchers to control and measure crystallization processes as they occur in real time. The research supported by this award developed new devices to study crystallization processes and applied them in a model system involving schwertmannite, a ferric iron sulfate mineral. The results of our experiments showed that schwertmannite crystallization happens in several stages involving the formation, aggregation, and assembly of extremely small precursor solids, known as nanoparticles. Interestingly, some of the behaviors we observed suggest that crystallization of iron minerals may be controlled by a combination of chemical and physical (i.e., solution turbulence) effects. The effects of solution turbulence remains largely unexplored in most crystallization systems.
Our schwertmannite crystallization experiments were made possible by the development of some new experimental devices. We used 3D design software along with desktop additive manufacturing (also known as 3D printing) to make custom experimental equipment. One such device was a mixed flow reactor that was used for controlled schwertmannite synthesis. This approach is rapid, low-cost, and more adaptable than traditional machining methods. In a related study, we showed that the 3D printed plastic used for fabrication is stable over a wide range of chemical conditions. This is important because it means that devices fabricated by 3D printing can be used for many kinds of geochemical studies and engineering tests. We also developed a simple and inexpensive method to test the stability of 3D printed plastics. This will be important for future studies that rely on this fabrication method because the materials used for 3D printing technology continue to evolve with time. The reactor designs developed under this award were disseminated through journal publications that make the models and fabrication details available for use by other groups. This award also supported a related invention disclosed as intellectual property. Overall, we expect the results generated through this award will improve our understanding of schwertmannite formation processes. In addition, the technical developments made will help to expand the use of desktop 3D printed apparatus in geosciences and related fields.
Last Modified: 11/27/2018
Modified by: Frederick Marc Michel
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