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

GRAND CHALLENGE: COMPUTATIONAL THERMODYNAMICS OF COMPLEX FLUIDS AND SOLIDSFigure 22. The structure of [(UO 2 ) 2 (μ-OH) 2 (OH 2 ) 6 ] 2+ . In a solution this would be solvated with four to fivewaters in the first shell and many in the surrounding region (Richens 1997, The Chemistry of Aqua Ions, copyright ©1997 John Wiley & Sons).poorly understood. Direct simulation of the properties of these mixtures may be the mosteffective way to develop the required data. These simulations usually require free energyproperties and therefore demand very large computational resources. New parallel algorithmdevelopment will be required to exploit the computational power of new classes of computers.Even with the development of first-principles predictive capabilities, it must be kept in mind thatwhile atomic detail is an essential starting point, averaged (i.e., thermodynamic) behavior isrequired for practical long-term prediction. Equations of State summarize the averaged behaviorat the atomic level by providing thermodynamic potentials (here we are including irreversiblethermodynamic properties, e.g., reaction rates, diffusion constants) and other properties (e.g.,chemical rates) as a function of P-T-X that are required in higher-level predictive tools (e.g.,reactive flow simulators). While the development of EOS has been a topic of research for manyyears, adequate EOS for many of the key mixtures encountered in storage applications are notavailable. Obviously these equations must incorporate the yet-to-be-discovered behavior of thecomplex systems that will be encountered in these storage problems. Unfortunately, becausepresent EOS methods are poorly based in theory, they do not provide a very large range ofextrapolation or interpolation, and are highly dependent on the availability of data. A keysynergistic role of theory is to inform the development of EOS. Appropriate equations need to bedeveloped that can more efficiently describe the chemical and physical properties of gaseous,liquid and solid mixtures. Nevertheless, it must be kept in mind that reliable EOS will, for theforeseeable future, have to be heavily based on experimental data.SCIENTIFIC CHALLENGESUnderstanding the chemical properties of aqueous electrolyte and nonaqueous solution phases,their mixtures and their interactions with solid mineral phases is central to the interpretation ofenergy applications, such as safe storage of nuclear waste (Ewing 2006; Bruno and Ewing 2006),sequestration of CO 2 in geologic formations, the transport of ore forming and toxic materials, theexploitation of geothermal energy, and others. For many systems the structure of species insolutions is complex and still very poorly known. For example, the presence of charged ions inaqueous solutions creates local structure (hydration shells) and local changes in the chemistry ofthe solution, such as changes in the acid/base chemistry, which may in turn create new species insolution. Examples of such species are oxyhydroxo polyions (e.g., AlO 4 Al 12 (OH) 24 (H 2 O) 12 andBasic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 69