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

CROSSCUTTING ISSUE:HIGHLY REACTIVE SUBSURFACE MATERIALS AND ENVIRONMENTSHIGHLY REACTIVE SUBSURFACE MATERIALS AND ENVIRONMENTSSUMMARYThe emplacement of energy system byproducts into geological repositories perturbs the existinggeochemical environment and causes reactions that alter the minerals, pore fluids, and emplacedmaterials. Perturbations include changes in temperature and pressure, imposition of chemicalgradients, and creation of intense radiation fields. Effects of perturbations may be short induration or last thousands to millions of years. The effects may be dominant near theemplacement site or most significant at great distances. Strong interactions between thegeochemical environment and emplaced materials are expected. The thermodynamic propertiesof complex geological fluids and solids, and the reaction rates among phases and species must beknown to define the critical environmental parameters that control migration or immobilizationof wastes.New insight is needed on equilibria in compositionally complex systems, reaction kinetics inconcentrated aqueous and other solutions, reaction kinetics under near-equilibriumundersaturated and supersaturated conditions, and transient reaction kinetics. Equally important,unifying theories linking kinetics and thermodynamic equilibrium for real-world solids andfluids are virtually nonexistent. Experimental, analytical, and computational approachesavailable to the geochemical community today are merging at the atomic and microscopic scales,and are poised to allow significant advances that will lead directly to quantitative macroscopicmodels of fluid/solid interactions with a high degree of confidence in the ability to accuratelypredict risks associated with contaminant migration.SCIENTIFIC CHALLENGESGeologic fluids (gases, liquids, and supercritical solutions) act as reaction media, reactants, andcarriers of energy and matter in the natural environment. Among the many different types ofgeologic fluids, those containing volatile C-O-H-N-S species and those enriched in chloride salts(brines) are of particular interest. They occur widely and commonly contain significant quantitiesof dissolved and suspended compounds. The relative strengths of complex molecular-scaleinteractions in geologic fluids, and the changes in those interactions with temperature, pressure,and fluid composition, are the fundamental basis for observed fluid properties. Complexation andbinding of organic molecules (e.g., humic acids) in aqueous solutions with or without CO 2 , andthe thermal stabilities of organic acids at high CO 2 loadings in the presence and absence of metalor surface binding will also be important. Although we have gained important quantitativeinsight into the speciation, stability, and kinetics of many organic-based systems of geologicalrelevance, we still lack a fundamental understanding of the effects of mixed-salt composition,elevated pCO 2 and temperature, and Eh/pH conditions on the equilibrium and kinetic propertiesof key organics and biomolecules. Moreover, we are just beginning to understand how moleculespecificinteractions among solutes and solvents eventually lead to homogeneous nucleation,crystallization, and aggregation of colloidal nanoparticles which could participate in andinfluence transport behavior. Understanding these solvent-mediated interactions for broad classesof solutes and suspensions in natural systems over the range of conditions typical of geologicfluids will greatly improve our capability to model and predict fluid behavior, reactivity, and theBasic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 159