Understanding the generation and evolution of reaction-induced porosity in the replacement of calcite by gypsum: a combined microscopy, X-ray micro-tomography, and USANS/SANS study
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Date
2021-11-25
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Nuclear Science and Technology Organisation
Abstract
Fluid-mediated mineral replacement reactions are common in natural systems and are essential for geological
and engineering processes. In these reactions, a primary mineral is replaced by a product mineral via a mechanism
called coupled dissolution-reprecipitation. This mechanism leads to the preservation of the shape of the
primary mineral into the product mineral. The product mineral includes reaction-induced porosity contributing
to enhanced permeability, which is crucial for the replacement reaction to progress from the surface to the
core of the primary mineral grain. These reaction-induced pores are complex in size, shape and connectivity,
and can evolve with time. However, the mechanisms of the creation and evolution of such pores are still
poorly understood. Therefore, we investigated the replacement of calcite (CaCO3) by gypsum (CaSO4.2H2O)
to understand porosity creation in the replacement stage and the evolution of such porosity after complete
replacement. This replacement reaction is important for the applications such as groundwater reservoir evaluation,
CO2 sequestration, cultural heritage preservation, and acid mine drainage remediation. Samples collected
at various reaction stages over 18 months were characterised by ultra-small-angle neutron scattering
and small-angle neutron scattering (USANS/SANS), ultra-high-resolution electron microscopy (UHR-SEM),
and X-ray micro-computed tomography (X-μCT). Results show the formation of micro-voids in the core of
the gypsum grain and the generation of nanometre-sized elongated pores in the newly formed gypsum crystals.
Micrometre-sized pores were mostly open, while pores smaller than 30 nm were mainly closed. After
complete replacement, continued porosity coarsening occurred in the 18 months’ time, driven by Ostwald
ripening.
Description
Keywords
Porosity, Calcite, Gypsum, Microscopy, Tomography, Small angle scattering, Minerals, Carbon sequestration, Cultural objects, Preservation
Citation
Kartal, M, Xia, F, Mata, J. Sokolova, A., Adegoke, I., & Putnis. A. (2021). Understanding the generation and evolution of reaction-induced porosity in the replacement of calcite by gypsum: a combined microscopy, X-ray micro-tomography, and USANS/SANS study. Presentation to the ANSTO User Meeting, 24-26 November 2021, Online. Retrieved from: https://events01.synchrotron.org.au/event/146/contributions/4307/contribution.pdf