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

DOI: 10.1002/2015JC011032 DOI Help

Authors: Ben Butler (Bangor University) , Hilary Kennedy (University of Bangor)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Geophysical Research: Oceans , VOL 120 (8) , PAGES 5686-5697

State: Published (Approved)
Published: July 2015
Diamond Proposal Number(s): 12301

Open Access Open Access

Abstract: Frozen seawater is a composite material with a sponge-like structure. The framework of the structure is comprised of pure ice, and within the pores exists a concentrated seawater brine. When the temperature is reduced, the volume of this residual brine decreases, whilst 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 sub-zero 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 towards an equilibrium crystallisation 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.

Journal Keywords: Sea Ice; Hydrohalite; Mirabilite

Subject Areas: Environment, Chemistry, Biology and Bio-materials

Instruments: I11-High Resolution Powder Diffraction

Added On: 07/08/2015 14:18

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