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February 2015

Speeding Up the Epochs

New model quickly shows if minerals form, which could be vital to creating cleaner energy

Carbon dioxide and sequestration
By calculating the thermodynamics from first principles or ab initio, scientists are providing a way to understand why some minerals form and others don’t. This information can be generalized to any material structure with impurities, defects, and a mixed composition.Enlarge/expand Image.
Norway coast The research can answer basic questions about mineral formation in difficult-to-access locations. For example, there is a mineral that only forms in the coldest waters off the coast of Norway and Antarctica. Re-creating these minerals and keeping them around long enough to study requires balancing a very narrow range of pressures, temperatures, and concentrations. Now, scientists can study these minerals in more detail with the framework. [Public Domain: Credit: Gestumblindi]Enlarge/expand Image.

Results: Minerals can require years to form or take mere moments. To reduce emissions from coal-fired power plants, scientists want to quickly transform the carbon dioxide into minerals and have those minerals last for thousands of years. At Pacific Northwest National Laboratory, scientists devised a way around the time constraint. They created a computational model that determines if and when minerals form. The model uses first principles, meaning it includes atomic properties and does not rely on estimates.

"It's difficult for us to create in the laboratory the full range of conditions the carbon dioxide might experience underground in order to measure if carbonate minerals will form or not," said Dr. Anne Chaka, the study's lead author. "And, we certainly can't measure over the time scales we need to ensure it's safely sequestered underground. With the new model, we can determine if the minerals will form and if they are stable enough to persist on geological timescales." 

Why It Matters: Coal-fired power plants release carbon dioxide in the process of converting coal into electricity. Carbon dioxide levels are linked to floods and droughts. Carbon dioxide emissions could be reduced by storing it underground, turning it into carbonate minerals. With the model or framework, scientists can determine how carbonates would form and explore the impact of water and thousands of years. The framework also has uses in determining how toxins spread from nuclear waste and industrial sites.

Methods: For nearly 2 years, Chaka and Dr. Andrew Felmy at PNNL (retired) designed and built the framework to calculate thermodynamics, relationships between heat and other forms of energy. The framework uses first principles, making it extremely accurate and in need of a supercomputer. The team used resources at PNNL Institutional Computing and the U.S. Department of Energy's EMSL, a national scientific user facility.

"It was a real advantage to be able to do bigger calculations on more realistic systems," said Chaka.

Once the framework was done, the team tested it out and settled a decades-old controversy. Worldwide, scientists got different minerals when forming carbonates from brucite. Subtle differences in temperature and carbon dioxide concentration were the culprits. Also, the team resolved another dilemma. They provided accurate energy values for lansfordite, another carbonate, correcting the published thermodynamic values.

What's Next? Chaka is leading research to determine the stability of heavy metals that contaminate areas near certain waste sites. Understanding the conditions that cause mercury, uranium, and other metals to spread could be very important to environmental cleanup efforts.

Acknowledgments

Sponsor: Geosciences Research Program in the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division

Research Area: Subsurface Science

User Facilities: EMSL

Research Team: Anne Chaka and Andrew Felmy, PNNL

Reference:  Chaka AM and AR Felmy. 2014. "Ab Initio Thermodynamic Model for Magnesium Carbonates and Hydrates." Journal of Physical Chemistry A 118(35):7469-7488. DOI: 10.1021/jp500271n


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