EGU2020-5982
https://doi.org/10.5194/egusphere-egu2020-5982
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Interfacial processes at dissimilarly charged mineral surfaces in contact – a surface forces apparatus study

Joanna Dziadkowiec1,2, Hsiu-Wei Cheng2, Anja Røyne1, and Markus Valtiner2
Joanna Dziadkowiec et al.
  • 1University of Oslo, NJORD Centre, Department of Physics, Norway (joanna.dziadkowiec@fys.uio.no)
  • 2Vienna University of Technology, Applied Interface Physics, Austria

When two mineral surfaces are in close contact, nanometers to microns apart, the proximity of another surface can significantly influence the pathways of chemical reactions happening in the interfacial region. Apart from affecting the kinetics of dissolution and nucleation reactions in spatial confinement, the proximity of charged surfaces can lead to electrochemically induced recrystallization processes. The latter may happen in an asymmetric system, in which two surfaces have a dissimilar surface charge. The charge and mass transferred during electrochemical reactions can induce dissolution or growth of solids and can significantly affect the local topography of surfaces, causing them to smooth out or to roughen. In this work, we present the experimental study of reactive mineral interfaces, immersed in geologically relevant electrolyte solutions, obtained with the electrochemical surface forces apparatus (EC-SFA). EC-SFA setup consists of one mineral surface and one gold surface (working electrode), the surface charge of which is controlled by applying an electrical potential. EC-SFA can, therefore, monitor electrochemically induced surface recrystallization processes. As the SFA technique is based on white light interferometry measurements, the changes in mineral thickness during recrystallization can be determined with an accuracy better than a nanometer over micrometer-large contact regions. Moreover, SFA allows in situ measurement of surface forces acting between mineral surfaces, which can provide additional information about how the surface reactivity influences the cohesion between mineral surfaces by modifying adhesive and repulsive forces acting between them at small separations.

How to cite: Dziadkowiec, J., Cheng, H.-W., Røyne, A., and Valtiner, M.: Interfacial processes at dissimilarly charged mineral surfaces in contact – a surface forces apparatus study , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5982, https://doi.org/10.5194/egusphere-egu2020-5982, 2020

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Presentation version 2 – uploaded on 23 Apr 2020
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  • CC1: Comment on EGU2020-5982, Davide Geremia, 26 Apr 2020

    Dear authors,

    I am Davide Geremia, currently undertaking a PhD at Cergy-Paris university. I am working on water-weakening effects on mechanical properties of carbonate rocks.

    Firstly, very interesting work and methodology. It is crucial to investigate the reactions taking place in grains contact region.

    I would have a question about the phase before the precipitation but first I would need a confirmation (related also to the paper "Nucleation in confinement generates long-range repulsion between rough calcite surfaces").

    If I understood well, before the precipitation front takes place there is a phase of dissolution of the confining surfaces (i.e. the at the contact area between the grains) which lead to a supersaturation inducing precipitation. Is it right?

    Then, with a MgCl2 solution this process is delayed, would this mean a higher degree of dissolution before precipitation? When finally precipitation occurs, does this induce the same magnitude of repulsive force?

    Thank you very much in advance,

    Kind regards,

    Davide

  • AC1: Comment on EGU2020-5982, Joanna Dziadkowiec, 27 Apr 2020

    Dear Davide,

    thank you for your interest in this work and for your comment :) 

    Yes, you are right: the precipitation fronts followed the dissolution of the confining calcite surfaces. In MgCl2, the precipitation events were significantly postponed (observed after 10 to 15 h after solution injection for two experiments but not detected for the rest of the experiments within this time). This is in part because MgCl2 solutions require a higher amount of dissolved Ca2+ to become supersaturated in comparison with NaCl and CaCl2 so that the whole process takes longer (you can refer to Figure 5b in the publication). Other effects are also possible as Mg2+ also modifies the growth rate of CaCO3.

    To answer your other question: the repulsive forces due to nucleation of CaCO3 in confinement observed in the presence of Mg2+ were weaker than for the other salts (this is expressed by the exponential decay of repulsive forces plotted in Figure 6, bottom panel, in the publication; the higher λ the stronger repulsion). This could be simply related to the smaller amount of recrystallized material in the precipitation fronts in MgCl2 solutions as the dissolution of calcite surfaces was generally the smallest in comparison with other salts (this could be deduced from the calcite thickness change in our setup). However, other Mg2+-specific effects are also possible. 

    Please let me know if you have any other questions :)

    Best, Joanna

Presentation version 1 – uploaded on 23 Apr 2020 , no comments