RAS-DOE project #RUC2-20006-MO-04, 2004-2007, PI: Perminova I.V.
Investigation and Modeling of the Fundamental Interactions of Actinides with Customized Humic Substances at both the Molecular and Colloidal Levels
This proposal addresses the fundamental interactions between actinides and materials genetically classified as humic substances. The latter may be encountered naturally as solids, soluble or colloidal forms, and are accepted as playing critical roles in the migration of actinides in several different environmental conditions. We propose to investigate and model the basic chemistry and chemical reactions between actinides and to design and prepare special humic substances, which will afford important controls not available with the widely varying properties of their naturally occurring counterparts. The major objective will be to establish relationships between specific molecular features of humic substances and their reactions with the oxidation states of different actinides of particular interest (i.e., U through Am, with special focus on Np and Pu).
The research will probe the interactions between these actinides and a comprehensive group of well-characterized, "designer" humic substances. The latter will include insoluble, soluble and colloidal forms, and cover a wide range of genetic modifications of materials from numerous sources and types. Extensive modifications shall be used for producing these customized materials, which will involve hydroxylation processes, cross-linking, and implanting soluble forms onto colloidal kaolin particles to modify the surface sites of the humic substances. Essentially, innovative treatments will be performed to specifically modify the humic substances to address remediation needs. Modifications will incorporate specific moieties to address the oxidation/reduction, complexation and sorption of actinides. Attaching these modified humic substances to non-mobile substrates (i.e., clays, sand, etc.) can also provide "adhesive" sites for non-reversible immobilization of the actinides. The humic colloids produced will be used to probe for interfacial reactions between the sites and actinides.
This proposed quantitative structure-property approach would define key aspects of structure and property relationships of interactions of humic substances with actinides. A mechanistic understanding of these molecular reactions governing the parameters of the interactions will also be undertaken. Kinetic and steady state studies will be conducted using "batch"-type, "flow-through" approaches and solvent extraction for redox speciation. Important complexation constants, partition coefficients and other data sets will be acquired in this effort. These approaches will advance both our basic understanding of the complex chemistries and our capabilities for modeling and simulating the involved geochemical systems encountered regarding migration of actinides in humic-rich environments. While the proposed work is focused on fundamental science of these systems, the information generated will promote the advancement of technological applications of humic materials and suggest efficient approaches for controlling and understanding actinide migration in the environment.