A Simplified Model for the Phase Composition Curve of Saline Soils Considering the Second Phase Transition

Abstract

Phase composition curves are the basis for the thermo‐hydraulic analysis of saline soil in cold regions. Two types of phase transition, namely, the water‐ice and solution‐crystal phase transitions, would occur in saline soils due to the variation in temperature and migration of moisture and solute, and the occurrence order of the two types of phase transition is governed by the initial salt and water content. This study proposed a conceptual model for the water phase composition curve in saline soils by simplifying the correlation between pore solution properties and soil grain. This model was subsequently applied to the analysis of phase composition characteristics and explained the occurrence of a second phase transition in saline soil. The model was validated by the experimental data from known soils and showed both good results and ease of use when compared to three previous models. The conceptual model provides a convenient and intuitive way to understand the phase composition characteristics of pore solution in saline soil in cold regions and is also easy to use in the thermo‐hydraulic analysis such as the prediction of unfrozen water content and solute concentration.

Changes in Unfrozen Water Contents in Warming Permafrost Soils

“…However, temperature variations are controlled by the composition of permafrost, as well as the effect of deeply penetrating heat pulses. Our results, as well as published data [21,25,27,34,38,78,82], show that the amount of unfrozen pore water varies as a function of salinity and peat content: it is much greater in saline and peat-rich sediments (Figures 3 and 4) than in non-saline rocks poor in organic matter. This fact must be taken into account in the operation of existing engineering structures and in new projects.…”

Regolith Inhibits Salt and Ice Crystallization in Mg(ClO4)2 Brine, Implying More Persistent and Potentially Habitable Brines on Mars

“…We find that at Mars-relevant wt.% salt, regolith does strongly depress the melting point of Mg(ClO 4 ) 2 brine. These results are also consistent with numerous terrestrial studies, which demonstrate that soils reduce the freezing point of various salt solutions (Banin & Anderson 1974;Bing & Ma 2011;Wang et al 2021). Some relatively dry samples showed no signs of melting or freezing whatsoever, despite being cooled to −150 °C.…”

“…Some relatively dry samples showed no signs of melting or freezing whatsoever, despite being cooled to −150 °C. When wet soils freeze, a layer of unfrozen water can persist as thin, mobile films between soil surfaces and ice (Anderson 1967;Wang et al 2021). In our experiments, the samples that remained entirely unfrozen had very low water content and high salt concentration.…”

“…Despite extensive research on pure perchlorate brines (salt + water) and on adsorbed and unfrozen water in regolith (water + regolith), systems of brines in Martian regolith (salt + regolith + water) are relatively poorly studied. Numerous terrestrial investigations have found that brines freeze at colder temperatures when they exist in the pore space of clays and soils (Banin & Anderson 1974;Bing & Ma 2011;Wang et al 2021). We might expect Martian regolith to similarly depress the freezing point of Mg(ClO 4 ) 2 brine, yet previous studies have treated regolith as inert and neglected any effect it may have on the brine's properties.…”

Predicting the Electrical Conductivity of Partially Saturated Frozen Porous Media, a Fractal Model for Wide Ranges of Temperature and Salinity

“…For an ideal dilute solution (e.g., containing NaCl), as the experimental temperature decreases, liquid water in the pore is converted to bulk ice. As the liquid water content diminishes below freezing temperature, the salts are discharged from the solid ice into the pore water, thus the ionic concentration of the liquid water increases when temperature declines, leading to the freezing temperature of the remaining liquid water in frozen soils that is further depressed (L. Y. Wang et al., 2021; Zhou et al., 2020). The initial saturation condition (i.e., the equivalent water saturation above freezing conditions) is also another considerable factor affecting the hydromechanical issues.…”