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Crystallization of sodium sulfate into mirabilite in sulfate saline soil harms the soil potential and intensifies the reparative expenses for subgrade. However, the effects of pore relative humidity (PRH) on the salt swelling behavior have not been thoroughly explored. The multiple-humidity cycles experiments, in this paper, were performed to investigate salt swelling behavior in sulfate saline soil. The effects of different salinity, temperatures, and PRH values on salt swelling displacement (SSD) and salt swelling rate (SSR) of sulfate saline soil were analyzed. The X-ray Diffraction (XRD) technique was employed to investigate the mineral composition of post-experiment soil samples. All test results show that the SSD and SSR of soil samples increase with the increase of PRH and salinity and decreases as the increasing temperature. The enhancement of salt swelling in the presence of PRH was 80-90-80%. Besides, XRD results denote that the existence of mirabilite in the test soil samples verified for the salt swelling to be closely related to PRH in terms of microstructure. All the results further improve the mechanism of salt swelling in sulfate saline soil in the presence of PRH, which is of great significance to analysis and remediation of salt swelling behavior.

Sodium sulfate is generally seen as one of the most destructive salts in the weathering of historical objects. The crystallization which causes the damage can either be induced by drying and/or cooling of a salt solution in a porous material. In this study we have studied the crystallization of sodium sulfate during the drying of various porous materials at different temperatures. The experiments were conducted such that the Peclet number was smaller than one, i.e., the ion transport in the porous material is dominated by diffusion. The results show that at temperatures above 22 °C during the drying the anhydrous crystal phase of sodium sulfate, i.e., thenardite is eventually formed. Below 22 °C heptahydrate crystal phase is formed, which is metastable with respect to the corresponding mirabilite solubility.

Recent satellite inferences of hydrous sulfates as recurrent minerals on the surface of icy planetary bodies link with the potential mineral composition of their interior. Blodite, a mixed Mg-Na sulfate, is here taken as representative mineral of icy satellites surface to investigate its crystal structure and stability at conditions of the interior of icy bodies. To this aim we performed in situ synchrotron angle-dispersive X-ray powder diffraction experiments on natural blodite at pressures up to ∼10.4 GPa and temperatures from ∼118.8 K to ∼490.0 K using diamond anvil cell technique to investigate the compression behavior and establish a low-to-high temperature equation of state that can be used as reference when modeling the interior of sulfate-rich icy satellites such as Ganymede. The experimentally determined volume expansivity, α, varies from 7.6 (7) 10−5 K−1 at 0.0001 GPa (from 118.8 to 413.15 K) to 2.6 (3) 10−5 K−1 at 10 GPa (from 313.0 to 453.0 K) with a δα/δP coefficient = −5.6(9)10−6 GPa−1 K−1. The bulk modulus calculated from the least squares fitting of P-V data on the isotherm at 413 K using a second-order Birch - Murnaghan equation of state is 38(5) GPa, which gives the value of δK/δT equal to 0.01(5) GPa K−1. The thermo-baric behavior of blodite appears strongly anisotropic with c lattice parameter being more deformed with respect to a and b. Thermogravimetric analyses performed at ambient pressure showed three endotherms at 413 K, 533 K and 973 K with weight losses of approximately 11%, 11% and 43% caused by partial dehydration, full dehydration and sulfate decomposition respectively. Interestingly, no clear evidence of dehydration was observed up to ∼453 K and ∼10.4 GPa, suggesting that pressure acts to stabilize the crystalline structure of blodite. The data collected allow to write the following equation of state, V(P, T) = V0[1 + 7.6(7)10 − 5ΔT − 0.026(3)P − 5.6(9)10 − 6PΔT−6.6(9)10 − 6PΔT)] from which the density of blodite can be determined at conditions of the mantle of the large icy satellites of Jupiter. Blodite has higher density, bulk modulus and thermal stability than similar hydrous sulfates (e.g. mirabilite and epsomite) implying, therefore, a different contribution of these minerals to the extent of deep oceans in icy planets and their distribution over the local geotherms.

Gypsum and the related sulfate minerals mirabilite and epsomite crystallize in dry caves in a variety of speleothems. Among these are crusts, stalactites, gypsum flowers, and some very thin fibrous forms known as cave cotton and angel hair. The sulfate minerals can be derived from the bedrock and from the oxidation of sulfide minerals, usually pyrite, and the oxidation of H 2 S. Gypsum flowers are formed of curving, fibrous crystals that radiate outward from a growth center, producing a flower-like speleothem.

This chapter discusses the occurrence of sodium sulfate deposits from the surface of several lakes and playa in the world. One of the world's most unusual occurrences of sodium sulfate is in the scattered large and small deposits and numerous surface crusts of mirabilite(Na 2 S0 4 • 10H 2 O) and thenardite (Na 2 S0 4 ) found in Antarctica. Seawater appears to be the obvious source for most of the sodium sulfate in Antarctica because its δ 34 S values are the same as in seawater, and essentially all of the sodium sulfate in the massive amounts of seawater that freezes each year is crystallized. Also, there are discontinuous mirabilite beds up to 1 m thick in a 1250 X 250 m area on the Ross Ice Shelf, called the Cape Spirit beds. They are underlain by up to 8 cm of marine mud (containing marine diatoms) and have non marine algal mats above them. By far, the most common occurrence of mirabilite and thenardite in the Antarctic is in the form of efflorescences and encrustations on the surface, or accumulations just beneath it, of the area's boulders and rocks.

Publisher Summary This chapter focuses on the physical properties, as well as the phase data that exists for the aqueous solutions of sodium sulfate, both alone and in combination with other salts. However, because most of this data is not important in the processing of natural sodium sulfate ores, it is limited to the phase data involved with the most common sodium sulfate minerals including mirabilite (Na 2 SO 4 .10H 2 O), thenardite (Na 2 S0 4 ), glauberite (Na 2 S0 4 .CaS0 4 ), astrakanite (Na 2 S0 4 .MgS0 4 .4H 2 0), and burkeite (2Na 2 S0 4 *Na 2 C0 3 ), along with the production of potassium sulfate from sodium sulfate. These latter units simplify the construction of the commonly employed four-sided Janecke phase diagrams. The chapter presents a table that presents the smoothed phase data for the solubility of pure sodium sulfate in water. The chapter also provides information on the solubility of sodium sulfate when the solution is also saturated with sodium chloride.