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Title: Controls of Microstructure and Chemical Reactivity on the Replacement of Limestone by Fluorite Studied Using Spatially Resolved Small Angle X-ray and Neutron Scattering

Journal Article · · ACS Earth and Space Chemistry
ORCiD logo [1]; ORCiD logo [2];  [3];  [2];  [4];  [5];  [6]; ORCiD logo [7]; ORCiD logo [2]; ORCiD logo [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Alabama, Tucson, AZ (United States). Lunar and Planetary Lab.
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
  4. Argonne National Lab. (ANL), Lemont, IL (United States)
  5. National Inst. for Standards and Technology (NIST), Gaithersburg, MD (United States)
  6. Univ. of Nebraska, Omaha, NE (United States)
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Material Science
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Fluid–mineral interactions can alter the pore structure and mineral composition of earth materials, sometimes leading to complete replacement of one mineral phase by another. A quantitative understanding of these processes is needed for the prediction of contaminant transport in nuclear waste management, oil and gas exploration, geothermal energy production, and in many geological processes. Currently, a detailed understanding of how the original microstructure and chemical reactivity is affecting the replacement rate and porosity development is lacking, which would enable the prediction of contaminant transport. Here, we present a systematic experimental study of limestone replacement in the model system calcite-fluorite varying both the texture and chemical reactivity of the parent rock. By combining X-ray ((U)SAXS) and neutron (ultra) small-angle scattering ((U)SANS) we quantified changes in the porosity as a function of depth within the sample and time. By shielding the samples with a set of annular Cd-masks during neutron scattering, we obtained spatially resolved porosity information. Microstructural changes were investigated using scanning electron microscopy (SEM), and composition changes were assessed using chemical imaging by time-of-flight secondary ion mass spectrometry (ToF–SIMS) and SEM-energy-dispersive X-ray spectroscopy (SEM-EDX). The replacement of limestone via fluorite takes place via advantageous pathways enhancing the available reactive surface area, e.g., fractures, accessible, interconnected porosity, nonconnected porosity grain boundaries and twin boundaries. Our results presented here emphasize the importance of a detailed structural and textural assessment of the starting material both in experimental studies and in modeling studies of natural processes to make accurate predictions about reaction rates.

Research Organization:
Argonne National Lab. (ANL), Argonne, IL (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
AC02-06CH11357; AC05-00OR22725
OSTI ID:
1570224
Alternate ID(s):
OSTI ID: 1607173
Journal Information:
ACS Earth and Space Chemistry, Vol. 3, Issue 9; ISSN 2472-3452
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 7 works
Citation information provided by
Web of Science

Figures / Tables (23)

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
dissolution-reprecipitation
multi-scale analyses
replacement
small angle X-ray scattering porosity analyses
small angle neutron scattering
small angle scattering