Chemistry and Physics at Interfaces
Mechanisms and Rates of Reaction at Mineral-Water Interfaces from Atomic to Pore Scales: Blending Simulation, Theory and ExperimentMarch 08, 2013
Quantitative prediction of mineral reaction rates in natural systems remains a daunting task, partly because the atomic-level reaction mechanisms that ultimately determine the net rates are poorly understood. Porous subsurface environments such as aquifers, rocks and soils also affect these reactions through interfacial phenomena and transport of reactants within a porous media; these effects are similarly not well constrained. Here I report on our recent efforts to identify reaction mechanisms for mineral growth and use these to build a predictive model for the growth of sparingly-soluble, ionically-bonded minerals (CaCO3, BaSO4). We use molecular dynamics simulations, validated by comparison to neutron scattering measurements, and rare event theories to discover atomic-level reaction mechanisms and their rates. In situ atomic force microscopy is used to measure mesoscale rates of growth for individual crystal surfaces and X-ray scattering allows us to determine how precipitation reactions are affected by porous media. Lastly, in theory development, we generate expressions that are consistent with atomic-level reaction mechanisms but can describe macroscopic rates. The results have implications for the sequestration of carbon and toxic metals by mineral trapping, scale formation in industrial environments and the rational design of mineral morphology and other properties.