Intriguing unanswered questions about reactions between mineral surfaces and solutions exist in many subfields of geology. At low temperatures near Earth's surface, reactions between dissolved and particulate constituents of natural waters and mineral surfaces control global and local-scale processes such as weathering, diagenesis, and mobility of environmental contaminants. A fundamental understanding of processes and reactions at mineral surfaces is highly relevant to other disciplines such as materials science and medical science.

Construction of double-shelled tanks at U.S. Department of Energy site in Hanford, Washington (left); salt-cake remaining in single-shelled tank (right)

We focus our research on developing new insights into and quantifying mechanisms and rates of surface-mediated processes such as dissolution, growth, and sorption, and then applying our results to a wide variety of geological and real-world problems. We also work on the chemistry of systems that occur at extreme limits of the natural world or are ephemeral on a geologic time-scale but important at the human time-scale.

Currently, we are quantifying reactions pertinent to the interaction of radioactive solutions leaked from waste tanks with subsurface sediments at Hanford, Washington; reactions between natural organic matter and mercury or clay minerals; and reactions specific to the mica-water and quartz-water interfaces. We use experimental and surface analytical approaches such as atomic force microscopy and synchrotron X-ray reflectivity to quantify reaction kinetics and theoretical approaches such as solution modeling and molecular modeling to guide and interpret experimental results.

Scanning electron microscopy image of the feldspathoid mineral cancrinite precipitated on quartz reacted with simulated Hanford tank solutions (Bickmore et al., 2001)

The Hanford studies are addressing how radioactive and toxic contaminants released during failure of underground storage tanks may be transported or immobilized in the subsurface. We have focused on understanding rates and mechanisms of quartz and biotite dissolution and secondary mineral formation in the high pH, high aluminum, and high nitrate solutions characteristic of the tank waste. Release of silicon from quartz contributes to precipitation of secondary aluminosilicates that can incorporate radioactive contaminants such as cesium. Release of iron(II) from biotite is considered to be the primary source of reductant species for conversion of chromate to chromium(III), a relatively immobile form of this toxic element.

Mercury interactions with natural organic matter control mercury's bioavailability in the environment. In collaboration with George Aiken of the U.S. Geological Survey and Joseph Ryan of the University of Colorado, we study reactions among humic substances, aqueous mercury, and cinnabar to determine how much mercury is unavailable for uptake by organisms. We are also investigating how natural organic matter plays a role in the nucleation of clay minerals.

Atomic force microscopy image of iron-oxyhydroxide lepidocrocite particles; particle size and shape is related to sorption of cadmium (Manceau et al., 2000)

The structure of an aqueous solution near a mineral surface is central to understanding empirical observations and theoretical models of reactions such as sorption, dissolution, or growth. We are investigating the molecular-scale structure of water and salt solutions at their interface with mica, an analogue for clay minerals, and quartz. The work is being performed using X-ray reflectivity at the Advanced Photon Source , Argonne National Laboratory in collaboration with Paul Fenter and Neil Sturchio. We also quantify the size and shape of environmental mineral particles from the nano- to micron-scales using atomic force microscopy (AFM) and relate surface areas measured by AFM to reactivity.

Personal Information
Mineral-Water Interface Laboratory

Selected recent publications:

Drexel, R.T., Haitzer, M., Ryan, J.N., Aiken, G.R. and Nagy, K.L. , 2002. Mercury(II) binding to two Florida Everglades peats: Evidence for strong binding and competition with dissolved organic matter released from the peat. Environmental Science & Technology , 36: 4058-4064.

Schlegel, M.L., Nagy, K.L. , Fenter, P. and Sturchio, N.C., 2002. Structures of quartz (10-11)- and (101-1)-water interfaces determined by X-ray reflectivity and atomic force microscopy of natural growth surfaces. Geochimica et Cosmochimica Acta , 66: 3037-3054.

Bickmore, B.R., Nagy, K.L. , Sandlin, P.E. and Crater, T.S., 2002. Quantifying surface areas of clays by atomic force microscopy. American Mineralogist , 87: 780-783.

Bickmore, B.R., Nagy, K.L. , Young, J.S. and Drexler, J.W., 2001. Nitrate-cancrinite precipitation on quartz sand in simulated Hanford tank solutions. Environmental Science & Technology , 35: 4481-4486.

Manceau, A., Nagy, K.L. , Spadini, L. and Ragnarsdottir, K.V., 2000. Mechanism of cadmium adsorption on lepidocrocite. Journal of Colloid and Interface Science , 228: 306-316.