Basic Research Needs for Geosciences - Energetics Meetings and ...

PRIORITY RESEARCH DIRECTION:NANOPARTICULATE AND COLLOID CHEMISTRY AND PHYSICSSUMMARY OF RESEARCH DIRECTIONThe overall goal is to develop new approaches for the characterization of colloids and predictionof their behavior in natural environments. This will involve:• Improving techniques to reliably sample the distribution of colloids in natural systems• Developing new experimental and analytical methods to measure and characterize thestructure, stability, and reactivity of synthesized and natural colloids• Constructing new conceptual models and simulation methodologies across the range oftemporal and spatial scales relevant to the chemical interactions and physical transport ofcolloidsCompletion of these objectives will require access to national user facilities including lightsources, neutron sources, mass spectrometers, NMR spectrometers, nanoscience and technologycenters, and high-performance computers.SCIENTIFIC CHALLENGESTo address the above issues, the following advances in basic science must be achieved:• Formulate a fundamental theory for the formation, structure, and stability of colloids derivedfrom organic, inorganic and microbial sources• Develop new methods to measure and predict the interaction and reactivity of colloids withradionuclides, and inorganic and organic ligands• Develop novel approaches to characterize and predict the mobilization and transport ofcolloids in heterogeneous natural systemsColloids (see sidebar on What is a colloid?) are ubiquitous, occurring even in distilled water(Bundschuh et al. 2001) due to leaching from container walls and introduction during processing.Colloids can either be intrinsic or pseudocolloids, inorganic or organic, crystalline or amorphous.Inorganic colloids of interest include metal oxides and clays. Recent studies of intrinsic actinidecolloids have shown that the distribution of the radionuclide (Pu) among dissolved, colloidal, andsolid phases and among various oxidation states can be described using equilibriumthermodynamics; however, thermodynamics alone may be inadequate to describe the colloidalbehavior of other contaminants.Organic colloids are composed of biopolymers or geopolymers. Biopolymeric colloids includeexopolymeric substances (EPS) excreted by microorganisms (MW = 10–1000s kDa). EPS helpmicroorganisms attach to surfaces within biofilms or aggregates, but it is not known howmicrobial communities regulate the attachment properties of their EPS, nor how fast differentEPS molecules are degraded and/or transformed by exoenzymes. Geopolymers include humicand fulvic acids, which are residues of biogenic organic matter (MW = 1–10 kDa) (Trumbore2000; Backau et al. 2004). In general, fulvic acids have high mobility, and humics and EPS havelower mobility. Both bio- and geopolymers have good complexing properties for trace metalsand radionuclides, as well as amphiphilic properties, i.e., hydrophilic and hydrophobic regions ormoieties, which give them special surface-active (e.g., surfactant, emulsifying) properties.Hydrophobic regions of aquatic colloids are often “hidden” from the water by conformationalBasic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 115