X-RAY METHOD SPEEDS STUDY OF MINERAL-WATER INTERFACES

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X-RAY METHOD SPEEDS STUDY OF MINERAL-WATER INTERFACES
25 March 2007 - DOE/Argonne National Laboratory

Researchers at the U.S. Department of Energy's Argonne National Laboratory have taken the guesswork out of interfacial structure determination. Their work is published in the April 10 issue of Surface Science Letters.

Argonne researchers have directly visualized, in three-dimensions, ion site distributions at the mineral-water interface using a technique called X-ray standing wave imaging. Their finding demonstrates a new capability for revealing complex reactions at mineral-water interfaces that previously could be understood only through more indirect approaches.

XSW, in contrast to X-ray crystallography, measures both the amplitude and phase information that completely describes the molecular-scale structure of interest. In standard crystallography only the amplitudes can be measured, and consequently, an elaborate approach is needed to determine the structure.

“We are the first to show that images of the atom site distributions can be directly obtained with XSW,” said Paul Fenter of Argonne 's Environmental Research Division. “In this case of adsorption at the mineral-water interface, we were able to fully resolve ion-specific sorption sites and distinguish different coordination environments for each ion.”

The XSW imaging approach allows scientists to streamline the tedious process of structure determination. “With XSW imaging,” said Fenter, “data acquisition and analysis can be completed in less than 24 hours. Previously, surface structure determination would take weeks or months to complete.”

Authors on the report, in addition to Fenter, are Zhan Zhang of Northwestern University, Likwan Cheng of Argonne, Neil Sturchio of the University of Illinois at Chicago and Argonne, Michael Bedzyk of Northwestern University and Argonne, Michael Machesky of the Illinois Water Survey, and David Wesolowski of Oak Ridge National Laboratory.

Solid-liquid interface structure is essential to many natural and technological processes. The interaction of mineral surfaces with fluids controls rock weathering, evolution of petroleum reservoirs and ore deposits, and the transport and remediation of contaminants in groundwater aquifers. “Our long term goal is to learn how to use X-rays to ‘see' geochemical processes in action at the molecular level,” said Fenter.

The research was conducted at the Basic Energy Sciences Synchrotron Radiation Center at the Advanced Photon Source at Argonne . The APS, which produces the most brilliant X-rays for research in the Western Hemisphere , is ideal for this type of research. “The APS brilliance allows us to illuminate a small, nearly-perfect region of a larger imperfect crystal and still be able to do the measurement,” said Fenter.

This project was supported by the Department of Energy's Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.

The nation’s first national laboratory, Argonne National Laboratory conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. Since 1990, Argonne has worked with more than 600 companies and numerous federal agencies and other organizations to help advance America's scientific leadership and prepare the nation for the future. Argonne is operated by the University of Chicago for the U.S. Department of Energy's Office of Science.

http://www.anl.gov

About: DOE/Argonne National Laboratory
Argonne National Laboratory is one of the US Department of Energy's largest research centres. It is also the nation's first national laboratory, chartered in 1946.

Argonne is a direct descendant of the University of Chicago's Metallurgical Laboratory, part of the World War Two Manhattan Project. After the war, Argonne was given the mission of developing nuclear reactors for peaceful purposes. Over the years, Argonne's research expanded to include many other areas of science, engineering and technology.

Today, the laboratory has about 4000 employees, including about 1200 scientists and engineers, of whom about 700 hold doctorate degrees.

Argonne occupies two sites. The Illinois site is surrounded by forest preserve about 25 miles southwest of Chicago's Loop. About 3200 of Argonne's 4000 employees work on the site's 1500 wooded acres. The site also houses the US Department of Energy's Chicago Operations Office.

Argonne-West occupies about 900 acres about 50 miles west of Idaho Falls in the Snake River Valley. It is the home of most of Argonne's major nuclear reactor research facilities. About 800 of Argonne's employees work there.

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