SORPTION AND AVAILABILITY OF METALS AND RADIONUCLIDES IN SOILS

Project Information

Principal Investigator	J. B.; Flury, M. Harsh
Institution	WASHINGTON STATE UNIVERSITY
Project URL	View
Relevance to Implications	High
Class of Nanomaterial	Generic
Impact Sector	Environment
Broad Research Categories	Generation, Dispersion, Transformation etc. Characterization
NNI identifier	c4-22

Funding Information

Country	USA
Anticipated Total Funding	n/a
Annual Funding	n/a
Funding Source	USDA
Funding Mechanism
Funding Sector
Start Year	2006
Anticipated End Year	2009

Abstract/Summary

NON-TECHNICAL SUMMARY: Metals in soils provide nutrients for plants and microorganisms and their sequestration and release by soil minerals often governs their availability to these organisms. Many metals are also toxic to soil organisms and constitute a threat to consumers of crops and drinking water. These metals include radionuclides that have been added to soil as a result of disposal or accidental release of nuclear waste from weapons production or nuclear power production. The first part of this project investigates the types of colloidal particles that can carry radionclides to groundwater. The project seeks also to determine how the nature of the particle—its charge and morphological characteristics—can be used to make predictions of its susceptibility to transport through soils and sediments. The second part of the project seeks to determine how the mineral illite is transformed around the root of a plant by the organic compounds that are produced by plants and microorganisms in this rhizosphere environment. We know that these compounds weaken the association between cesium and illite. In this study, we look for the cause of this change in the interaction. OBJECTIVES: The first objective of this project is to quantify colloidal stability and chemistry of radionuclide colloids in Hanford pore water. We will determine how radionuclide sorption by colliodal- and/or nano-particles or the formation of such particles by nucleation of new solid phases enhances or inhibits the transport of radionuclides through soils and sediments. Secondly, we will determine the mechanism of illite weathering by organic anions. Using oxalate as a surrogate for Al-complexing ligands in the rhizosphere, we will follow the changes in structure and chemistry of illite when subjected to solutions similar to what is found near plant roots. APPROACH: Radionuclides or their surrogates (e.g. europium as a surrogate for americium) will be adsorbed on particles less than 1 um in diameter (such as smectite clays), co-precipitated with other metals or metalloids (e.g., feldspathoids or silica), and precipitated as intrinsic colloids. We will characterize the relevant surface and structural properties of the particles that determine colloidal stability and transport (e.g. electrophoretic mobility, solid/air/liquid interaction energy, morphology, and size). The colloidal stability will be determined in solutions similar to those found in the Hanford environment. Column studies will be used to determine transport parameters. Organic colloids and inorganic colloids with organic coating will be included. For the illite weathering study, illite reacted with organic anion solutions will be characterized by x-ray diffraction, atomic force microscopy, electron microscopy, and NMR and IR spectroscopy to determine the weathering mechanism. Diffraction and microscopy will allow us to distinguish between reduction in the number of layers in a fundamental particle from an increase in the fraying of layer edges as mechanisms for altering illite chemistry. Spectroscopy will test the hypothesis that weathering proceeds by the selective loss of tetrahedrally-coordinated Al from the illite structure. PROGRESS: 2006/01 TO 2006/12 We have characterized the particle size of illite particles by analyzing the coherent scattering domains with the Bertaut-Warren-Averbach xrd technique (BWA). We used the MudMaster computer program to obtain fundamental particle sizes for three illites. We are now working to characterize one of these illites by atomic force microscopy (AFM). Using nanometer resolution, we have been able to determine the distribution of particle thicknesses. We are experimenting with different dispersion techniques to maximize separation of fundamental particles by ultrasound after pretreatment. Successful dispersion will be determined by observation with AFM and good correspondence with the x-ray diffraction analysis. Once we are confident we have a good dispersion of fundamental particles, we will compare untreated illite with illite weathered with organic acids. One undergraduate researcher is employed on this project through an undergraduate student research award by Washington State University’s College of Agricultural, Human, and Natural Resource Sciences.IMPACT: 2006/01 TO 2006/12 Illite weathering is a process that governs both nutrient and contaminant availability to plants. Potassium, an essential plant nutrient, can be present in high concentration in illitic soils, but relatively unavailable because of its strong association with the mineral. Weathering of illite in the rhizosphere directly affects its uptake by plants. Cesium-137, a radioactive element that contaminates former DOE weapons production sites such as Hanford and INEL, also associates strongly with illite. Its mobility in the vadose zone and its availability to plants used for phytoremediation, will be determined, in large part, by its interaction with illite. Determining the mechanisms of its sorption and release is essential to predicting its behavior in such systems.