Abstract
A fundamental understanding of mineral precipitation kinetics relies largely on microscopic observations of the dynamics of mineral surfaces exposed to supersaturated solutions. Deconvolution of tightly bound transport, surface reaction, and crystal nucleation phenomena still remains one of the main challenges. Particularly, the influence of these processes on texture and morphology of mineral precipitate remains unclear. This study presents a coupling of pore-scale reactive transport modeling with the Arbitrary Lagrangian-Eulerian approach for tracking evolution of explicit solid interface during mineral precipitation. It incorporates a heterogeneous nucleation mechanism according to Classical Nucleation Theory which can be turned “on” or “off.” This approach allows us to demonstrate the role of nucleation on precipitate texture with a focus at micrometer scale. In this work precipitate formation is modeled on a 10 micrometer radius particle in reactive flow. The evolution of explicit interface accounts for the surface curvature which is crucial at this scale in the regime of emerging instabilities. The results illustrate how the surface reaction and reactive fluid flow affect the shape of precipitate on a solid particle. It is shown that nucleation promotes the formation of irregularly shaped precipitate and diminishes the effect of the flow on the asymmetry of precipitation around the particle. The observed differences in precipitate structure are expected to be an important benchmark for reaction-driven precipitation in natural environments.
Highlights
Recent advances in studies of natural minerals and chemical processes occurring in the subsurface have significantly improved understanding of reaction kinetics at mineral-water interfaces (Brantley et al, 2008; Putnis and Ruiz-Agudo, 2013; Beckingham et al, 2016; Yuan et al, 2019; Noiriel et al, 2020)
To focus on the implementation of the porescale reactive transport model coupled with heterogeneous reactions and dynamic interface, the simplest surface reaction model has been chosen
The heterogeneous nucleation based on Classical Nucleation Theory (CNT) was integrated into the model
Summary
Recent advances in studies of natural minerals and chemical processes occurring in the subsurface have significantly improved understanding of reaction kinetics at mineral-water interfaces (Brantley et al, 2008; Putnis and Ruiz-Agudo, 2013; Beckingham et al, 2016; Yuan et al, 2019; Noiriel et al, 2020). Different upscaling techniques connect local molecular scale processes obtained from Atomic Force Microscopy data to overall reactivity (Teng et al, 2000; Yoreo et al, 2009; Bracco et al, 2013) In these studies the rate of crystal growth is linked to the surface features and their dynamics such as velocity of step propagation (Bosbach et al, 1996), kink cite. Modern computational techniques and synchrothron-based sources allowed us to investigate mineral reactivity at meso- and pore-scale using reactive transport modeling and X-ray tomography (Godinho et al, 2016; Noiriel et al, 2019) These methods provide an opportunity to incorporate flow in porous media (Molins et al, 2014) and resolve the interface between solid and fluid (Dutka et al, 2020)
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