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eMinerals project outline
What is the project about?
The eminerals project is primarily concerned with the challenge of using computer simulations performed on molecular length and time scales to address important environmental issues.
Who are the participants?
We are a team of simulation scientists, simulation code developers and computer experts from the universities of Bath, Birkbeck College, Cambridge, Reading and UCL, the Royal Institution and the CCLRC Daresbury. This team is genuinely interdisciplinary, containing a mix of environmental scientists, physicists, chemists and computer scientists.
How is the project structured?
We are organised around three main areas of work:
1. The science that drives the whole research effort.
2. The development of the codes to serve the science.
3. The development of the grid infrastructure upon which to build the research.
What is our challenge?
The development of emerging capabilities is leading to the development of Grand Challenge computational projects in environmental studies. The near future will see the development of projects that are larger by orders-of-magnitude than simulations that are the norm. They will focus on building highly-realistic models, taking account of all physical and chemical variabilities in the systems (e.g. chemical composition, fluid pH, temperature). These simulations will generate massive quantities of data, which cannot be analysed by conventional means. Tackling Grand Challenge simulations will require new methods of collaborative cross-laboratory working patterns.
It is convenient to collate the science drivers into two main areas, namely modelling of surfaces and interfaces, and modelling of bulk behaviour. Each case will require the use of a wide range of simulation methods. Here we sketch brief summaries of the issues; more details are given in the Science section (link above).
1 Surfaces and surface-fluid interactions: adsorption of pollutants, crystal growth and dissolution
- Adsorption of heavy metal contaminants. The sorption of heavy metals and radionucleides to minerals limits the solubility and bioavailability of such contaminants. Metals may sorb by forming inner-sphere or outer sphere adsorption complexes on mineral surfaces, surface precipitates and solid solutions with cations in soil minerals. The mechanisms by which contaminants are incorporated into mineral structures or adsorbed onto mineral surfaces must be understood at the atomic and molecular levels before we can reliably extrapolate laboratory sorption isotherms and solubility measurements to field models. An atomistic understanding is especially urgent in light of increasing use of “natural attenuation” approaches to contaminated soil remediation. The focus will be on constituents of soil materials (clays, sands, iron hydroxides) and iron sulphides.
- Adsorption of organic pollutants. The processes by which organic molecules adsorb onto mineral surfaces, including soil minerals, is a related challenge. This is important because of the wide range of industrial organic pollutants (e.g. DDTs, PCBs, dioxins) found in soils and increasingly being detected in the human food chain, together with the known problems for health and reproduction. An atomistic approach must account for realistic mineral surfaces in contact with fluids containing ionic components with variable pH, and the role of natural organic matter at mineral surfaces. Progress in this area will give critical guidance to soil remediation strategies. The focus will be on soil minerals.
- Crystal growth and scale inhibition. Crystal growth by precipitation depends on the aqueous conditions, and proceeds at defects such as steps and dislocations. Scale is a major problem in oil extraction and other hot-fluid industrial processes, and descaling agents in current use pose environmental problems. Growth rates are significantly affected by the organic molecules or cations adsorbed on the growing surfaces. Large-scale simulations with realistic fluid interfaces are required to study growth process and to explore potential environment-friendly inhibition additives. The initial focus will be on carbonates, barytes and apatites.
- Crystal dissolution and weathering. Dissolution and weathering processes proceed by leaching of ions from surfaces and cracks. The challenge is to simulate dissolution processes within a range of fluid environments, which will give understanding of the atomic processes, quantitative estimates of weathering rates, and pointers towards dissolution retardation strategies. The focus will be on carbonates, silicates and sulphides.
2 Atomic processes in bulk minerals: radiation damage and diffusion of pollutant atoms
- Radiation damage and encapsulation of high-level radioactive waste material. Permanent encapsulation of radioactive waste has been based on the use of glasses, but research is now focussing also on crystalline ceramics because these have much lower leach rates. Natural materials, such as zircon, are known to have encapsulated natural radioactive atoms for geological times. Research is needed to understand localised structural damage of ceramics due to radioactive decay, with effects from both recoil nuclei and alpha particles. The challenge is to scale up to realistic recoil energies (current limitations are an order of magnitude too small), to have sufficiently large samples, and to be able to run for long enough to establish equilibrium after radioactive decay events. Results will guide development of national and international strategies for long-term storage of radioactive waste.
- Leaching processes. The transport mechanisms of pollutant atoms, whether in rocks or in solid-state encapsulation, needs to be tackled by atomistic simulations. Processes include grain boundaries, phase interfaces, and domain walls. The presence of water will increase leaching rates. However, unsaturated fluid flow is poorly understood yet it controls the migration of cations along mineral grain boundaries. Realistic large-scale simulations, which include interfaces and several phases, will provide important insights and quantitative leaching rates.
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