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An investigation of mineral dynamics in frozen seawater brines by direct measurement with synchrotron X-ray powder diffraction

Butler, B.M. and Kennedy, H.A. (2015) An investigation of mineral dynamics in frozen seawater brines by direct measurement with synchrotron X-ray powder diffraction. Journal of Geophysical Research (8). pp. 5686-5697. DOI: 10.1002/2015JC011032

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Abstract

Frozen seawater is a composite material with a sponge-like structure. The framework of the structure is composed of pure ice, and within the pores exists a concentrated seawater brine. When the temperature is reduced, the volume of this residual brine decreases, while its salinity increases. As a result of the paired changes to temperature and salinity, the brine eventually becomes supersaturated with respect to a mineral, resulting in the precipitation of microscopic crystals throughout the ice structure. Due to experimental constraints, the current understanding about the formation of these minerals relies on the analysis of the residual brine, rather than the mineral phase. Here synchrotron X-ray powder diffraction was used to assess the dynamics that occur between ice, brine, and mineral phases within frozen seawater brines that were subjected to cooling and warming at subzero temperatures. The method was able to detect crystalline phases of ice, mirabilite (Na2SO4·10H2O), and hydrohalite (NaCl·2H2O). Results illustrate a highly dynamic geochemical environment where ice-brine-mineral interactions tend toward an equilibrium crystallization process, which supports the process of seawater freezing that is described by the Gitterman Pathway and FREZCHEM model. This study highlights the power of synchrotron techniques in observing the mineralogical dynamics of inaccessible environmental systems.

Item Type: Article
Subjects: Research Publications
Departments: College of Natural Sciences > School of Ocean Sciences
Date Deposited: 07 Oct 2015 02:49
Last Modified: 03 Nov 2015 03:41
ISSN: 2169-9291
URI: http://e.bangor.ac.uk/id/eprint/5553
Identification Number: DOI: 10.1002/2015JC011032
Publisher: Wiley
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