0.001 mol kg1 NaCl
Liquid Solution Specific Volume (m3 Mg1)
Figure 14. Relationships between unfrozen-solution specific volumes and
ice-solution capillary pressures for sand pastes warmed from 66.6C to
0C. The equilibrating solutions of the pastes were initially 0.1, 0.01, and
0.001 mol kg1 NaCl.
The minerals analyzed in this study may be thought to represent the range of ap-
plicability of capillary theory to explain the freezing behavior of porous solids. The
kaolinite samples were not composed of an expanding-lattice clay with intermedi-
ate particle size, and the experimental results from this material supported the theory
well. Sand and montmorillonite did not support it as well: sand because its particle
size (and, therefore, pore radii) was too large, and montmorillonite because it has a
much smaller particle size and because relatively large volumes of water can be
held in its interlamellar spaces for which capillary forces are less important. Our
study did indicate that capillarity theory coupled with the Pitzer model describes
acceptably the effect of an electrolyte on the freezing curves of minerals of interme-
diate size between sand and montmorillonite.
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