Quantifying the Reactive Surface Area of Environmental Materials
EMSL Project ID
44743
Abstract
A large number of natural and anthropogenic processes in our environment are dominated by chemical reactions at the interface between solid and aqueous phases. These reactions include the adsorption of organic and inorganic species, the release of elements into the environment from the dissolution of solids, and the removal of dissolved constituents by precipitation. Interfacial processes control the concentration and distribution of contaminants, nutrients, and salts in all of Earth's aqueous environments. To quantify sorption capacity or the rates of dissolution/precipitation processes, chemists and geochemists typically normalize the sorbed concentration or rate of chemical change by the surface area available for reaction. While conventional specific surface area measurements (e.g., BET) depend on the area available for adsorption of an inert gas, or the calculation of geometric surface area based on known particle sizes, it has long been recognized that environmental surface reactions are determined by the reactive surface area, a measure of the surface species that actually participate in the chemical process. This research program will investigate new probes of environmental chemical reactivity through laboratory and computational studies of the reactive surface area of model substrates that are important sources or sinks for chemical species in the environment. This proposal will specifically address the question of surface site reactivity with respect to the sorption of metal ions and their competition for surface hydroxyl sites on oxide and clay minerals and the sorption of organic ligands and ligand-promoted dissolution of a clay mineral. The proposed research will further develop and apply the technique of using a site-specific probe molecule with high-sensitivity, solid-state nuclear magnetic resonance (NMR) detection to quantify active sites. This method, combined with complementary bulk (BET, TGA) and spectroscopic characterizations (XAS, DR-FTIR) and with computational chemistry calculations will be used to elucidate the structures, energetics, and spectroscopic properties of reactive surface sites and complexes in model laboratory systems. Capturing the scale dependence of environmental chemical reactions has been indentified as the most difficult challenge associated with the application of field-scale reactive transport models to natural systems. The ability to accurately scale mineral surface reactivity is essential for assessing risks associated with environmental contaminants (e.g., surface and subsurface migration of radionuclides within the DOE nuclear complex; mobilization of organic and inorganic contaminants at Superfund and other contaminated sites; capacity of aquifers for natural attenuation of subsurface contaminants), as well as for quantifying processes such as nutrient input of P, N, and Fe sorbed on mineral particles to lakes or the oceans, or for estimating the extent of carbon dioxide reaction and sequestration by minerals in subsurface injection.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2011-10-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
Kubicki JD, HD Watts, KT Mueller, PA O'Day, M Small, and N Govind. 2014. "Experimental and computational study of Cd(II) and Pb(II) on gibbsite and kaolinite." Abstract submitted to American Chemical Society Fall Meeting 2014, San Francisco, CA. PNNL-SA-101002.
Watts HD, M Small, ET Poweleit, PA O'Day, KT Mueller, N Govind, and JD Kubicki. 2014. "Applying quantum chemistry to interpret XAS and NMR of Cd(II) adsorbed onto gibbsite and kaolinite ." Abstract submitted to Goldschmidt 2014, Sacramento, CA. PNNL-SA-101424.