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Resolving dissolution-precipitation processes in porous media: Pore-scale lattice Boltzmann modelling combined with synchrotron based X-ray characterization

English title Resolving dissolution-precipitation processes in porous media: Pore-scale lattice Boltzmann modelling combined with synchrotron based X-ray characterization
Applicant Prasianakis Nikolaos
Number 172618
Funding scheme Project funding (Div. I-III)
Research institution Nukleare Energie und Sicherheit Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Geochemistry
Start/End 01.02.2018 - 31.01.2022
Approved amount 253'550.00
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All Disciplines (2)

Discipline
Geochemistry
Mineralogy

Keywords (9)

micropore; dissolution precipitation; X-ray characterization; lattice Boltzmann; porous media; materials; permeability; diffusivity; nucleation theory

Lay Summary (German)

Lead
Auflösung-Ausfällungsreaktionen in porösen Medien bestimmen das Verhalten vieler geochemischer Prozesse und Industrieanwendungen. Dazu zählen z.B. die Gewinnung geothermischer Energie und Erdöl, die Evolution von Tiefenlager für radioaktive Abfälle, sowie die Entwicklung pharmazeutischer Produkte, Batterien, Katalysatoren. Die Auflösung oder Ausfällung von Festphasen kann den Porenraum des Mediums, und somit den Transport gelöster Substanzen (z.B. giftige Metalle), in komplexer Art und Weise verändern. Moderne reaktive Transportmodelle und Simulationen berücksichtigen solche Phänomene und schaffen die Grundlage zu deren Verständnis.
Lay summary

Häufig werden solche Simulationen auf makroskopischer Ebene (Feldskala) durchgeführt. Dabei werden bestimmte Prozesse, welche auf  mikroskopischer Skala stattfinden, vereinfacht durch gemittelte Parameter dargestellt. Zum Beispiel werden die durch chemische Reaktionen verursachten Durchlässigkeits- und Diffusivitätänderungen in einem porösen Medium mit empirischen Gesetzen und justierbaren Parametern beschrieben. Es gibt eindeutige Hinweise, dass makroskopische Eigenschaften des porösen Mediums (Durchlässigkeit und Diffusivität) nicht-linear von chemisch-physikalischen Prozessen abhängen, die auf der Porenskala stattfinden. Dieses Projekt kombiniert fortgeschrittene Lattice-Boltzmann Modelle auf der Porenskala mit klassischer Nukleationstheorie und modernsten Charakterisisrungmethoden  (Synchrotron-basierte Röntgenstrahlenmethoden). Ziel ist es, ein Fenster für ein besseres Verständnis und eine genauere Vorhersehbarkeit solcher Prozesse zu öffnen.

Durch diese Arbeit soll ein verbessertes Verständnis der mikroskopischen Mechanismen geschafft werden, welche Auflösung-/Ausfällungsreaktionen kontrollieren. Dadurch   erhofft man sich Einsicht zu gewinnen, wie solche Mechanismen die hydraulischen Eigenschaften poröser Gesteine, und deren Wirken auf relevante geochemische Prozesse, beeinflussen.


Direct link to Lay Summary Last update: 24.11.2017

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Abstract

Precipitation and dissolution reactions in porous media dominate and control a large number of geochemical processes and industrial applications that span from geothermal energy and oil industry to pharmaceutical products, batteries, catalysts and to long-term nuclear waste containment. The precipitation-dissolution of minerals from aqueous solutions alters the pore space and its connectivity in a way that has a complex feedback to the ion transport in aqueous phase itself. Reactive transport models and simulations are providing the framework to understand and predict such phenomena. Very often, simulations are done at the macroscopic level (field scale) using a simplified description of the processes that actually take place at the microscale. For example, the change in permeability and diffusivity of a porous medium due to reactions is correlated to a global change of the bulk porosity in the medium, using empirical laws with adjustable parameters. There are clear evidences that the macroscopic properties of the medium depend on the physical and chemical processes that occur at the micropore scale in a strongly non-linear way. It is therefore not surprising, that smooth simplified relations, frequently are inadequate to predict accurately the temporal evolution of the system of interest. It is the microscopic physics per se that ultimately control the macroscopic processes. Fundamental in-depth understanding and accurate prediction of the underlying processes can be enhanced by direct pore-scale modeling, supported by experimental investigations.This project aims at:(i)combining a state-of-the-art reactive transport algorithm with classical nucleation theory concept;(ii)modelling competing precipitation mechanisms along with dissolution in realistic systems;(iii)using advanced synchrotron-based X-ray techniques to gain insight of the micro-meter level processes;(iv)validating the resulting numerical modelling framework against reactive transport experiments.The modelling activities will be based on the lattice Boltzmann (LB) numerical method and will be supported with results obtained from reactive transport experiments and advanced instrumental diagnostics with special focus to the celestite-barite system. The selection of the celestite-barite system is primarily motivated by the environmental relevance of barite scale formation in industrial applications related to large scale geochemical systems (oil exploration, geothermal heat extraction, uranium mining) and by the availability of an exceptionally complete set of thermodynamic and kinetic data. Moreover, results and samples of relevant reactive transport experiments have been already produced in-house, in the framework of a recently completed PhD thesis (2016). Therein, a simple system consisting of reactive celestite (SrSO4) intermixed with a comparatively inert matrix (quartz sand) was selected. By saturating the pore space with barium chloride solution (BaCl2), celestite is partially dissolved and replaced by the more insoluble barite (BaSO4) thus modifying the hydraulic properties of the medium (porosity, permeability, connectivity). Further characterization of experimental results will be carried out and analyzed at the Swiss Light Source (SLS) synchrotron, by means of advanced synchrotron-based X-ray techniques, including micro X-ray diffraction/fluorescence and 3D-microtomography. The prospected methodology will be able to describe, as a function of time and at high spatial resolution (micrometer scale), a number of observable processes and mechanisms, such as precipitation via homogeneous (nano-crystalline) and heterogeneous nucleation (epitaxial growth). The obtained results are expected to provide fundamental insights on the microscopic mechanisms governing dissolution-precipitation reactions and on how these mechanisms are affecting bulk hydraulic properties in geochemically relevant porous media.
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