TY - JOUR

T1 - An investigation of mineral dynamics in frozen seawater brines by direct measurement with synchrotron X-ray powder diffraction

AU - Butler, B.M.

AU - Kennedy, H.A.

PY - 2015/8/14

Y1 - 2015/8/14

N2 - 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.

AB - 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.

U2 - 10.1002/2015JC011032

DO - 10.1002/2015JC011032

M3 - Article

SP - 5686

EP - 5697

JO - Journal of Geophysical Research

JF - Journal of Geophysical Research

SN - 0148-0227

IS - 8

ER -