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This work focuses on the formation of evaporite minerals through a progressive evaporation of water of Sebkha Oum El Khialate. The precipitated salt is variable along the evaporation path. Weights of evaporite before each phase of precipitation indicate a heterogeneous evaporation process with a final cumulative amount of 294 g L−1. With an increasing evaporation of Oum El Khialate brine, the number of precipitated mineral species is increased. The cumulative number of species along the evaporation process reaches eight in the following depositional sequence: calcite (CaCO3) (29%), Vaterite (CaCO3) (10%), Potassium Pentasulphate (K2S5O16) (9%), thenardite (Na2SO4) (33%), beryllium sulfate (BeSO4) (10%), brucite (Mg(OH)2) (4%), gypsum (CaSO4·2H2O) (2%) and mirabilite (Na2SO4·10 H2O) (3%). The sebkha can provide 86 kt of evaporite deposits per year at 100% evaporation. These evaporite minerals have variable industrial, medical and military uses. However, beryllium sulfate may cause a health risk to the population including lung cancer. The study shows that the use of a fractional crystallization may decrease the cost of salt extraction and the environmental risks by localizing the crystallization domains of valuable and hazardous minerals.

For the production of sodium sulfate, a brine is crystallized and crystals of glauber salt are generated by this process. The phase data related to the most common sodium sulfate minerals are as follows: mirabilite (Na2SO4 ⋅ 10H2O), tenardite (Na2SO4), glauberite (Na2SO4 ⋅ CaSO4), astrakanite (Na2SO4 ⋅ MgSO4 ⋅ 4H2O). The units commonly used to express the phases are moles of salt per 1000 moles of water. These latter units simplify the construction of the commonly employed four-sided Janecke phase diagrams. The cooling temperature or the speed with which the solution is cooled has an effect on the size and purity, as well as the amount of crystals produced. We seek to establish, through the population balance equations (PBE), which process variables can be modified to obtain a specific crystal size, as well as to validate the mathematical model that best predicts the amount of crystals precipitated as a function of temperature. The adjustment by least squares, cubic splines, pitzer equations and Lagrange interpolation is tested. The experimental results agree with the characteristics of the proposed models.

High-temperature SiO2-rich springs are one of the most indicative manifestations of deep geothermal activities. Although they often represent the valuable geothermal potentials and significances of the areas, their high SiO2 contents usually bring some non-negligible problems when we exploit the geothermal resources, especially the silica scales. To understand the sedimentation sequences of SiO2-rich hot springs and to expose its potential relationships with natural sinter deposits and silica scales in geothermal plants, this study make a couple of analyses of the water and solid samples collected from a natural SiO2-rich hot spring in Tengchong (i.e. Dagunguo spring) and isothermal evaporation experiments, including water chemistry analyses, X-ray diffraction, thin-section observation, and electron microscopy analyses. The modern sinters in Dagunguo spring are amorphous SiO2 which is largely formed of tight siliceous layers and some amorphous SiO2 spheres. Some silicified microorganisms, elemental sulfur, and clay are also found. The Dagunguo spring water is Na–Cl–HCO3-type SiO2-rich water, with a pH of about 8 and low dissolved concentrations of Al3+, Fe3+ and Mg2+. Isothermal evaporation (T = 84 °C) resulted in a sequence of precipitated minerals: amorphous SiO2 → halite → sodium sesquicarbonate dihydrate (trona) → potassium chloride (sylvine), accompanied by calcite, hydrous sodium sulfate (mirabilite) and sodium bicarbonate (baking soda). The amorphous SiO2 produced in the evaporation experiments exhibited different shapes and structures than the spherical opal-A formed by hot spring water precipitation under natural conditions. The study of precipitation sequence and minerals of hot spring water provides insight into the scaling mechanism of silica-rich geothermal water and anti-scaling measures that can be applied in the process of exploitation and utilization of geothermal resources.

The small stalactites found on the ceiling at level I near the Sutoris shaft in the thirteenth-century historic salt mine in Bochnia, Poland, are mainly composed of mirabilite (Na2SO4·10H2O) followed by blödite (Na2Mg(SO4)2·4H2O). The unique presence of these two minerals in only one location in this old underground mine is attributed to contemporary precipitation from percolating solutions. This can be caused by a combination of at least two factors: a specific and stable microclimate (characterised by a low temperature, high humidity, and relatively strong air circulation which accelerates the processes of evaporation and crystallisation) and the specific chemical composition of the leaking solution (contains a low carbonate and high sulphate content, and characterised by acidic pH (4.8) and intermediate-mineralisation (174,308 mg/L)). The microclimate specified above can be linked to the long distance from the ventilation shaft that pumps the air from the surface to the mine, while the composition of the leaking solution as well as the hydrochemical modelling results obtained with PHREEQC can be directly related to the top anhydrite layer and the overlying secondary cap consisting mainly of claystone, anhydrite, and gypsum. In this study, the challenges underlying the preservation of mirabilite in the underground environment of the salt mine are discussed, in terms of both nature and mining law. Based on the results of detailed geological, mineralogical, and chemical research, appropriate solutions that can be practically applied for the management, preservation, and protection of the mirabilite efflorescence are proposed. The presence of this intriguing mineral, with appropriate protection, can be another geological attraction for tourists visiting this thirteenth-century UNESCO-recognised salt mine.

The sandstone fissure aquifer of the Permian main mining coal seam is the direct water-filled aquifer of the coal mine in northern Anhui Province, China. Hydro-chemistry is important for solving the issue related to water disasters of coal mines, as it can be used for the determination of source of inrush water, and understanding the water-rock interaction process. In this paper, major ion concentrations of groundwater from the in the roof (RW) and floor (FW) in Haizi coal mine have been processed by statistical analysis and water-rock interaction analysis in order to study the differences of hydro-chemical characteristics and genesis. The results show that sandstone fissure water ion contents in RW and FW are obviously different; the chemistry type of FW is Ca-Mg-SO4, followed by HCO3-Cl and HCO3-Cl-SO4, and that of RW is HCO3-Cl, followed by SO4-HCO3-Cl. Compared with the fourth aquifer, Taiyuan group limestone water, goaf water, the proportion of Ca2+, Mg2+, SO42- in the FW and Cl-, HCO3- in the RW are significantly different. Factor analysis and water-rock interaction research show that the FW of 10th coal seam aquifer controlled by “removing sulfate,” silicate mineral dissolution and impact of groundwater runoff. However, the RW is mainly related with the dissolution of minerals, for example, salt minerals (e.g., mirabilite), bitter salt minerals (e.g., salt), silicate minerals, and the dissolution of gypsum.

Serpentinite tailings from La Nationale chrysotile mine in Thetford Mines (Quebec, Canada) were studied to extract the Mg contained therein. The study began with an initial chemical characterization of the residue to determine the Mg concentration in the different grain size fractions. The resulting Mg-containing fractions were leached under a variety of parameters such as type of acid, acid concentration, treatment time, and temperature, and the obtained solution was neutralized with NaOH for the selective recovery of the metals. The results of this study were used to design a process to obtain Mg as a marketable chemical. The tested process consists of a leaching step using an H2SO4 solution followed by the purification of the leachates using NaOH at pH 8 and Mg recovery with NaOH at pH 10. A final product composed of mirabilite (Na2SO4) and brucite (Mg(OH)2) was obtained. The procedure was tested, and its economic viability was discussed. The approach proved to be technically feasible, promoting clean production.

The Biyang Depression, lying in the eastern Nanxiang Basin, has a dustpan-shape with faults developed to the southwest and southeast. The Paleogene Hetaoyuan Formation in this depression hosts one of the oldest soda-deposits, the Anpeng deposit. These sodium carbonate-bearing strata consist of lutites, muddy dolomites, and bedded soda-deposits, which are dominated by nahcolite with little trona, mirabilite, and halite. In the top Unit 3 and lower Unit 2 of Hetaoyuan Formation where the sodium carbonates are concentrated, dolomitic shale, muddy carbonate, and sodium carbonate can be separated based on their distinct Al2O3, TiO2, Na2O, MgO+CaO, and LOI (loss on ignition) contents. By using Na2O/(MgO+CaO) ratio as an indicator for the relative concentration of Na carbonates to Mg-Ca carbonates, the muddy dolomites can be classified into two groups. One group with Na2O/(MgO+CaO) 0.6 presents a negative correlation. As the clastic proportion decreases, the former indicates that it tends to form pure Mg-Ca carbonates reflecting evaporation less than or equal to replenishment for the lake water in a relative humid climate, and the latter reveals a trend to form sodium carbonates with lake water’s evaporation more than replenishment in a relatively dry climate. From muddy dolomite to sodium carbonate samples, with Na2O/(MgO+CaO) ratio increasing, the Al normalized Zr, Ti, La, K, Rb, and Ba tend to be enriched and the post-Archean Average Shale (PAAS) normalized positive Eu anomaly becomes more obvious. Integrated with the high B contents and the report of searlesite in the bedded sodium carbonates and the regional extensional tectonic regime, the above geochemical characteristics were interpreted to signify hydrothermal contribution to forming these soda-deposits through the deep fault systems of basin margins.

Sodium sulfates are well known to be the most damaging salts in building materials and rocks. Unfortunately, the crystallization processes of sodium sulfates are not completely understood. In addition, the metastable heptahydrate has long been neglected in scientific works on salt damage until recently. In this study, we use temperature monitoring and differential scanning calorimetry to detect and identify the crystallization of sodium sulfate hydrates (i.e., mirabilite and heptahydrate) upon cooling/heating a bulk solution. The presence of impurities seems to play a major role in the crystallization sequence and can explain the crystallization of mirabilite and ice close to −10 °C. The crystallization of heptahydrate does not seem to be sensitive to the presence of impurities and does not always occur prior to the crystallization of mirabilite as commonly observed. The heptahydrate and mirabilite show different and characteristic thermal signatures that enable to distinguish each other. The shape, the intensity and the duration of the peak of temperature due to the crystallization depict these differences. Therefore, the thermal signatures can be used in further experimental studies to estimate the role of the different sodium sulfate hydrates involved in the salt weathering of rocks.

The El Ghine-Oum El Khialate sebkha extends in southeast Tunisia on over than 75 km2. This depression is filled by recent Quaternary deposits containing a brines aquifer situated at a depth varying from 1 to 10 m. This aquifer is highly rich in sodium sulphate. At the surface, noticeable is the deposition of mirabilite and thenardite encrusting. To quantify the salt reserves for a rational exploitation, thirty dry cores (approximately 160 m of core) were carried out in the sebkha. They underwent integrated geological, geochemical and hydrogeological studies. The estimated reserves are in the range of 8.106 t: Na2SO4, 2.106 t NaCl and 1.106 t MgCl2. The extraction of these salts is restricted by the relatively poor hydrodynamic characteristics of the reservoir evaluated during pumping tests.

The Turpan Basin is located in the arid zone of northwestern China and is a typical closed inland basin surrounded by high mountains. It is one of the most arid regions in the world and, as a result, the groundwater in this area is very important for both domestic and agricultural uses. In the present study, the relationships of major elements (K+, Na+, Ca2+, Mg2+, HCO3−, SO42− and Cl−) and environmental isotopes (δ18O, δ2H and T) in groundwater were analyzed to investigate the evolution of the regional hydrochemistry within the Turpan Basin. The hydrochemistry results demonstrate that groundwater with high total dissolved solids (TDS) concentration is dominated by sodium chloride (Na-Cl) and sodium sulfate (Na-SO4) type water, whereas that with low TDS concentration (typically from near mountain areas) is dominated by calcium bicarbonate (Ca-HCO3) type water. The evolution of groundwater hydrochemistry within the Turpan Basin is a result of calcium carbonate precipitation, evaporation concentration, cation exchange and dissolution of evaporites (i.e. halite, mirabilite and gypsum). Furthermore, evaporite dissolution associated with irrigation practice plays a key role in the groundwater salinization, especially in the central part of the basin. Environmental isotopes reveal that the groundwater is recharged by precipitation in the mountain areas and fast vertical infiltration of irrigation return flow. In the southern sub-basin the shallow groundwater and the deep groundwater is separated at a depth of about 40 m, with substantial differences in terms of hydrochemical and isotopic characteristics. The results are useful for decision making related to sustainable water resource utilization in the Turpan Basin and other regions in northwestern China.

The chemical composition of groundwater within the multilayer Jeffara aquifer and the detailed analysis of saturation indices enables identification of the origin of mineralization and hydrogeochemical processes occurring in groundwater. It has been demonstrated that groundwater is mainly characterized by a Ca–Mg–SO4–Cl water type. Geochemical pattern is controlled by the dissolution of evaporites, largely abundant in the study area and incongruent dissolution of dolomite. Gypsum, anhydrite, mirabilite and thenardite have been examined as potential sources of sulphate dissolved in groundwater. Since Jeffara groundwater is recharged by the Continental Intercalaire (CI) geothermal water, water temperature decreases from the CI to the Jeffara aquifer. Solubility of the majority of minerals is modified by this change in temperature and thus a mixing process of thermal and non-thermal waters was examined.

Groundwater is the only water source of the shelterbelt along the Taklimakan Desert Highway in northwestern China. Understanding the hydrochemical zoning characteristics, material source, and hydrochemical processes of this desert groundwater is important for rational groundwater exploitation. Meanwhile, determining the location of the dividing boundary, which divides the influence ranges of the Tarim river and the Kunlun mountain river system on the desert groundwater, is meaningful for the local desert hydrogeological study. For these objectives, 105 groundwater samples were investigated to obtain analytical data of groundwater chemistry, and ionic relations methods including ratio graphs and Gibbs plots were applied in the chemical analysis for these data. Chemical analysis shows that desert groundwater is characterized by Cl·SO4–Na·Mg and Cl−·SO4–Na types with total dissolved solid (TDS) of 2.80–29.77 g/L. Spatial variation patterns of major ions, TDS, and SO4 2−/Cl− molar ratio reveal clear four hydrochemical zones along the groundwater flow direction on one hand; on the other hand, these variation patterns also indicate that the boundary dividing the influence ranges of the Tarim river and the Kunlun mountain river system is the approximate location of Well 030. Ratio graphs show that the average molar ratios (Na+ + K+)/Cl− (1.05) and (Ca2+ + Mg2+)/SO4 2− (0.93) are approximately equal to 1, and there is an approximately linear correlation between (Na+ + K+) and SO4 2−. These results reveal that the groundwater composition is mainly influenced by dissolution of evaporate (halite, gypsum, and mirabilite). Moreover, ionic relations demonstrate that the dominating hydrochemical processes in the groundwater evolution are evaporation and cations exchange.

Measurements of chemical composition and environmental isotopes were conducted to investigate the main geochemical processes controlling the salinization of shallow groundwater adjacent to an inland salt lake in the Yuncheng Basin. Hydrogeochemical and isotopic studies were carried out by collecting thirty shallow groundwater, two rainfalls, and one salt lake water samples from the study area. About 80 % of the shallow groundwater samples had total dissolved solids more than 500 mg/L, implying significant water-quality deterioration in the study area. Shallow groundwater showed a clear increased salinity along regional flow paths toward the center of the basin where a salt lake is located. Results of environmental isotopes, ionic ratio, and saturation indices’ calculation indicated that the major geochemical processes responsible for groundwater salinization included dissolution of evaporites (halite, gypsum, and mirabilite), cation exchange, and evapotranspiration. Groundwater salinization as a result of salt lake intrusion from the salt lake was limited to the northern shore of the lake.

The behaviour of two types of limestones having a different porosity, Maastricht and Euville limestone, laden with aqueous solutions of equimolar mixtures of sodium sulphate/sodium nitrate or sodium sulphate/potassium sulphate was investigated. At 50 % RH, the efflorescences on Maastricht samples during the first 30 h of drying consisted of similar amounts of thenardite and darapskite in case of an equimolar mixture of sodium sulphate/sodium nitrate while those on Euville samples under the same conditions contained mainly darapskite. After drying at 20 °C and 85 % RH, thenardite, formed through the precipitation and dehydration of mirabilite, was mostly detected in the efflorescences on both Maastricht and Euville samples. Re-wetting by increasing the RH from 50 to 85 % resulted in substantial damage on Maastricht stone laden with an equimolar mixture of sodium sulphate/sodium nitrate as a consequence of high supersaturation of mirabilite. In case of a contamination with equimolar amounts of sodium sulphate and potassium sulphate, the efflorescence on both limestones during drying at 50 % RH contained predominantly aphthitalite. The observed crystallisation behaviour is compared to the theoretical behaviour. The results indicate a strong influence of stone properties on the crystallisation behaviour of salt mixtures.

The Zhabei Salt Lake is located in the hinterland of the northern Qinghai-Tibet Plateau, China. The salt lake is of the sodium sulfate subtype and rich in lithium. In order to exploit lithium in the brine of the salt lake, a 273.15 K-isothermal evaporation experiment of the brine from the Zhabei Salt Lake was carried out for the first time. Based on the 273.15 K-isothermal phase diagram of the quaternary system Na+, Mg2+//Cl−, SO4 2−–H2O, the evaporation-crystallization path of the brine was drawn and the sequence of salt precipitation was confirmed. The experimental results show that due to the large amount of SO4 2− precipitated as mirabilite, the concentration of SO4 2− in the brine was stabilized at about 0.25 mol L−1, thus avoiding formation of Li2SO4·3Na2SO4·12H2O in the early stages of the low-temperature evaporation process. Lithium was effectively concentrated to 1.09 mol L−1 in residual mother liquor as the evaporation rate reached 96.76 %, and the molar ratio of Mg/Li decreased from 1.25 to 0.23. The enrichment behavior of lithium is described as a power function of Y = k(1 − X)−1, where Y = the concentration of lithium in the residual brine, X = the extent of evaporation, and k = the initial value of lithium concentration of the brine. In addition, the experiment suggests that the salts precipitated from the brine of the Zhabai Salt Lake contain not only the mineral assemblage with the characteristics of carbonate-type salt lakes, such as borax and lansfordite, but also the mineral assemblage with the characteristics of sulfate-type salt lakes, such as carnallite and lithium sulfate monohydrate. This finding, the data from the Zhabei Salt Lake’s brine in 1978, and the distribution characteristics of the hydrochemical zones of salt lakes on the Qinghai-Tibet Plateau, indicate that this salt lake is in a special stage of transition from a sulfate-type salt lake to a carbonate-type.

The shallow Plio-Quaternary (PQ) water table, present over almost the whole Djerid and Chott El Gharsa basins (southern Tunisia), is used as a complement of oases irrigation, especially in summer season. The simplicity of the Plio-Quaternary lithology is confronted to the complexity of the mineralisation mechanisms and the water origin in this aquifer. An approach combining the use of water-dissolved chemical species and isotopic contents has been used to better understand the PQ behaviour under severe increasing exploitation and to determinate the origin of its different water bodies. In southern Tunisia, the aquifer system is composed of the upper unconfined PQ aquifer, the intermediate semi-confined/confined Complexe Terminal (CT) and the deeper confined Continental Intercalaire (CI). Chemical analyses highlighted an origin of mineralisation in close relationship to the dissolution of both sulphated salts (MgSO4 and Na2SO4) and chlorinated salts (NaCl and MgCl) abundant in the surface and subsurface gypsum crust. Positive correlations between gypsum anhydrite, mirabilite, thenardite and halite saturation indexes with respective mineral species, confirm evaporites dissolutions. Isotopic data showed that in addition of sporadic rainfall events, there is a contribution from the CI and the CT Saharan groundwaters, recharging the PQ aquifer in the study area. Return flow irrigation is partly affected by evaporation, before recharging the shallow aquifer, in oases limits.

Breakdown of porous materials by salts occurs when growing crystals exert pressure on the pore walls, inducing stress in the material that exceeds its tensile strength. In this work, we quantify the mechanical stresses caused by a particularly destructive mechanism: the dissolution of an anhydrate (thenardite, Na2SO4) followed by precipitation of a hydrated salt (mirabilite, Na2SO4·10H2O). Stresses are measured using a composite specimen consisting of a plate of glass bonded to a plate of limestone (CaCO3) whose pores are impregnated with thenardite. As water wicks into the limestone, thenardite dissolves and mirabilite precipitates. The limestone expands from the pressure exerted by the salt resulting in deflection of the composite, and the stresses can be obtained from an elastic analysis. Synchrotron x-ray diffraction reveals the dissolution–crystallization rate. Numerical modeling shows that the stresses are affected by the kinetics of crystallization and dissolution, permeability, and mechanical properties of the stone, allowing us to determine the amount of salt that causes material fracture.

Lake Kitagata, Uganda, is a hypersaline crater lake with Na–SO4–Cl–HCO3–CO3 chemistry, high pH and relatively small amounts of SiO2. EQL/EVP, a brine evaporation equilibrium model (Risacher and Clement 2001), was used to model the major ion chemistry of the evolving brine and the order and masses of chemically precipitated sediments. Chemical sediments in a 1.6-m-long sediment core from Lake Kitagata occur as primary chemical mud (calcite, magadiite [NaSi7O13(OH)3·3H2O], burkeite [Na6(CO3)(SO4)2]) and as diagenetic intrasediment growths (mirabilite (Na2SO4·10H2O)). Predicted mineral assemblages formed by evaporative concentration were compared with those observed in salt crusts along the shoreline and in the core from the lake center. Most simulations match closely with observed natural assemblages. The dominant inflow water, groundwater, plays a significant role in driving the chemical evolution of Lake Kitagata water and mineral precipitation sequences. Simulated evaporation of Lake Kitagata waters cannot, however, explain the large masses of magadiite found in cores and the formation of burkeite earlier in the evaporation sequence than predicted. The masses and timing of formation of magadiite and burkeite may be explained by past groundwater inflow with higher alkalinity and SiO2 concentrations than exist today.

A rare lacustrine rhythmite from the Qiulinanmu Playa Lake in Tibet is presented, which was composed of distinct layers of mirabilite, borax, and clay with thickness measuring 1.5–75 cm, 0.5–20 mm, and 0.5–30 mm, respectively. The thickness of each layer was measured in the field and dating was performed using 14C and U data. The lake was previously supplied by river water, groundwater, and hot springs enriched in sodium, sulfur, and boron. Control factors on the rhythmite were climate oscillations and compositional differences of water. The adsorption of boron by clay minerals could be attributed to the alternation between clay and borax layers. Low temperature, high pH, and high evaporation exerted significant influences on the precipitation of original borax and mirabilite. In the evaporative lake, the precipitation of mirabilite (a mineral indicative of a cold-dry environment) was dominant and produced the asymmetric couplets. The lake water was poor in chloride and rich in sodium sulfate, and an abrupt change was observed at 11.4 cal. kyr bp. According to the laminated sediment and the thickness of the minerals, the climate was dry-cold with four sub-warm phases before 11.4 kyr bp (after 20.6–11.4 kyr bp), and wet-warm with four sub-cold pulses after 11.4 kyr bp (11.4–5.2 kyr bp). The two thickest mirabilite layers suggested extremely hard conditions after 20.6 kyr bp, and before 11.4 kyr bp, respectively.

The authors have carried out scientific investigations of salt lakes on the Qinghai-Tibet Plateau since 1956 and collected 550 hydrochemical data from various types of salt lakes. On that basis, combined with the tectonic characteristics of the plateau, the hydrochemical characteristics of the salt lakes of the plateau are discussed. The salinity of the lakes of the plateau is closely related to the natural environment of lake evolution, especially the climatic conditions. According to the available data and interpretation of satellite images, the salinity of the lakes of the plateau has a general trend of decreasing from north and northwest to south and southeast, broadly showing synchronous variations with the annual precipitation and aridity (annual evaporation/annual precipitation) of the modern plateau. The pH values of the plateau salt lakes are related to both hydrochemical types and salinities of the lake waters, i.e., the pH values tend to decrease from the carbonate type → sodium sulfate subtype → magnesium sulfate subtype → chloride type; on the other hand, a negative correlation is observed between the pH and salinities of the lakes. Geoscientists and biological limnologists generally use main ions in salt lakes as the basis for the hydrochemical classification of salt lakes. The common ions in salt lakes are Ca2+, Mg2+, Na+, K+, Cl− SO4 2−, CO3 2−, and HCO3 −. In this paper, the Kurnakov-Valyashko classification is used to divide the salt lakes into the chloride type, magnesium sulfate subtype, sodium sulfate subtype and carbonate type, and then according to different total alkalinities (K C = Na2CO3 + NaHCO3/total salt × 100%) and different saline mineral assemblages, the carbonate type is further divided into three subtypes, namely, strong carbonate subtype, moderate carbonate subtype and weak carbonate subtypes. According to the aforesaid hydrochemical classifications, a complete and meticulous hydrochemical classification of the salt lakes of the plateau has been made and then a clear understanding of the characteristics of N–S hydrochemical zoning and E-W hydrochemical differentiation has been obtained. The plateau is divided into four zones and one area. There is a genetic association between certain saline minerals and specific salt lake hydrochemical types: the representative mineral assemblages of the carbonate type of salt lake is borax (tincalconite) and borax-zabuyelite (L2CO3) and alkali carbonate-mirabilite; the representative mineral assemblages of the sodium sulfate subtype are mirabilite (thenardite)-halite and magnesium borate (kurnakovite, inderite etc.)-ulexite-mirabilite; the representative mineral assemblages of the magnesium sulfate subtype are magnesium sulfate (epsomite, bloedite)-halite, magnesium borate-mirabilite, and mirabilite-schoenite-halite, as well as large amount of gypsum; The representative mineral assemblages of the chloride type are carnallite-bischofite-halite and carnallite-halite, with antarcticite in a few individual salt lakes. The above-mentioned salt lake mineral assemblages of various types on the plateau have features of cold-phase assemblages. Mirabilite and its associated cold-phase saline minerals are important indicators for the study of paleoclimate changes of the plateau. A total of 59 elements have been detected in lake waters of the plateau now, of which the concentrations of Na, K, Mg, Ca, and Cl, and SO4 2−, CO3 2−, and HCO3 − ions are highest, but, compared with the hydrochemical compositions of other salt lake regions, the plateau salt lakes, especially those in the southern Qiangtang carbonate type subzone (I2), contain high concentrations of Li, B, K, Cs, and Rb, and there are also As, U, Th, Br, Sr, and Nd positive anomalies in some lakes. In the plateau lake waters, B is intimately associated with Li, Cs, K and Rb and its concentration shows a general positive correlation with increasing salinity of the lake waters. The highest positive anomalies of B, Li, Cs, and K center on the Ngangla Ringco Lake area in the western segment of the southern Qiangtang carbonate type subzone (I2) and coincide with Miocene volcanic-sedimentary rocks and high-value areas of B, Li, and Cs of the plateau. This strongly demonstrates that special elements such as B, Li, and Cs on the plateau were related to deep sources. Based on recent voluminous geophysical study and geochemical study of volcanic rocks, their origin had close genetic relation to anatectic magmatism resulting from India–Eurasia continent–continent collision, and B–Li (-Ce) salt lakes in the Cordillera Plateau of South America just originated on active continental margins, both of which indicate that global specific tectonically active belts are the main cause for the high abundances of B, Li, and Cs (K and Rb) in natural water and mineralization of these elements.

Starting from 1961, the Aral Sea, a major saline lake in Central Asia, has been continuously shrinking because of deficiency in its water budget. Accordingly, the salinity of the once brackish lake increased by a factor of magnitude. During the desiccation, the salt composition of the Aral Sea has been subject to continuous changes because of chemical precipitation accompanying the salinity buildup. This paper provides a summary of these changes based on water samples collected from the so-called Large Aral Sea during the field surveys of 2002–2007. Once fully ventilated, the lake developed anoxic conditions and H2S contamination is frequently observed in the bottom layers. However, hydrogen sulfide is a variable rather than a permanent feature of the present Aral Sea. Because of the precipitation of calcium carbonate, gypsum, and, possibly, mirabilite, which successively occurred as the salinity increased, the relative content of SO4− and Ca2+ ions decreased. Accordingly, compared with the pre-desiccation period before 1960, the sulfate-to-chloride mass ratio decreased by 10–30%, while the relative content of calcium decreased almost 7-fold. The depletion in calcium is more pronounced in the shallow eastern part of the lake, where salinity is much higher. However, the reduction of the sulfate-to-chloride ratio in the eastern basin is smaller than that for the western basin of the Aral Sea. Hypothetically, this could be explained through precipitation of halite already taking place in the eastern basin, but not yet in the western basin. Vertical profiles of the ionic content in the relatively deep western part of the lake reveal a decrease of calcium content and relative increase of sulfate ion content toward the bottom, which is consistent with the previously published concept that the bottom layers of the western trench contain a significant admixture of the water advected from the eastern basin.

The Great Salt Lake (GSL) of Utah, USA, is the largest saline lake in North America, and its brines are some of the most concentrated anywhere in the world. The lake occupies a closed basin system whose chemistry reflects solute inputs from the weathering of a diverse suite of rocks in its drainage basin. GSL is the remnant of a much larger lacustrine body, Lake Bonneville, and it has a long history of carbonate deposition. Inflow to the lake is from three major rivers that drain mountain ranges to the east and empty into the southern arm of the lake, from precipitation directly on the lake, and from minor groundwater inflow. Outflow is by evaporation. The greatest solute inputs are from calcium bicarbonate river waters mixed with sodium chloride-type springs and groundwaters. Prior to 1930 the lake concentration inversely tracked lake volume, which reflected climatic variation in the drainage, but since then salt precipitation and re-solution, primarily halite and mirabilite, have periodically modified lake-brine chemistry through density stratification and compositional differentiation. In addition, construction of a railway causeway has restricted circulation, nearly isolating the northern from the southern part of the lake, leading to halite precipitation in the north. These and other conditions have created brine differentiation, mixing, and fractional precipitation of salts as major factors in solute evolution. Pore fluids and diagenetic reactions have been identified as important sources and especially sinks for CaCO3, Mg, and K in the lake, depending on the concentration gradient and clays.

Crystallization pressure of salt crystals growing in confined pores is found to be the main cause for damage to stone and masonry. In this work, the crystallization of sodium sulfate salts in Cordova Cream and Indiana limestones is investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The DSC experiments indicate that sodium heptahydrate always precipitates prior to the decahydrate (mirabilite), at a temperature between 15 and 7°C in the selected stones. The threshold supersaturation for the nucleation of heptahydrate is less than 2. In constrast, mirabilite precipitates close to or below 0°C and its crystallization pattern is completely different: precipitation takes place abruptly when the threshold supersaturation is reached, which is greater than 7. Indeed, the DSC and the DMA experiments reveal the rare nature of the nucleation of mirabilite for the investigated stones. The crystallization pressure exerted by heptahydrate does not cause damage under the conditions of the cooling experiments. In contrast, mirabilite exerts a very high crystallization pressure on the pore wall causing damage of the stone; moreover, the transient stress can remain for a long period of time since the relaxation process is slow.

Crystallisation of sodium sulfate solutions by evaporation under controlled climatic conditions has revealed the existence of crystalline hydrated sodium sulfate salts not previously reported. The sodium sulfate phase crystallising and the concentration of the solution at the point of crystallisation depends on the climatic conditions (temperature and evaporation rate). During the rehydration of the anhydrous sodium sulfate phase, thenardite, another previously unreported phase was formed prior to the nucleation of the stable phase, mirabilite Na2SO4 · 10H2O. The addition of organic inhibitors changes both the crystallisation and the rehydration behavior in this system.

The future of Southern Aral Sea water in Kazakhstan, and of the sequence of mineral evaporitic sediments precipitated since the beginning of the present regression from gypsum to bloed-ite (astrakhanite) was studied. A comparison is made with previous regressive deposits discovered earlier in cores by I.V. Rubanov. Absence of mirabilite deposits in sediments of the eastern basin is attributed to deflation processes during the XIVth century AD.

Constructed evaporation ponds are being utilized for disposalof saline subsurface drainage waters in San Joaquin Valley,California. These terminal evaporation ponds are located inhydrologically closed basins and/or regions with no surfacedrainage out of the valley. The saline drainwaters disposedinto the ponds are sodium-sulfate or sodium-sulfate-chloridetype waters and upon desiccation produces mirabilite andhalite. The drainwaters contain excessive levels of traceelements from geochemical origins. The trace element of mostconcern, is selenium because it bioaccumulates in the aquaticfood chain and causes death and deformity of waterbirdsattracted to the pond environment. At the present, the onlyeconomic drainwater disposal option in the southern. portionof the valley is evaporation ponds. The operation of theseponds is heavily regulated by waste discharge requirements toreduce and mitigate wildlife impacts. A case study onevaporation ponds and bird usage from a drainage districtillustrates the extensive monitoring and mitigation required.The prognosis is evaporation basins will be needed for theforeseeable future unless breakthroughs occur in economic andeffective drainwater treatment and drainwater reuseoptions.

Large amounts of halophilic organisms and their fossils that are found in the Barkol mirabilite deposit are identical to those of its modern biological community residing in its surface brines.

The northern Great Plains region of western Canada contains many saline and hypersaline lakes. These lakes exhibit great diversity in geochemical and sedimentological characteristics which results in a wide range of bedding features and lamination types. Because of the high brine salinities and supersaturation with respect to many carbonate and sulfate evaporitic minerals, chemical laminae and beds are the most common stratification types observed. Simple monomineralic carbonate or sulfate layers as well as beds composed of complex mixtures of aragonite, magnesite, hydromagnesite, mirabilite, gypsum, epsomite,and/or bloedite occur frequently in Holocene sequences from these saline lakes. In addition, biolaminae, including microbialite bedding and accretionary tufa and travertine deposits, are present. Due to the dominance of chemical sedimentary processes operating in these lakes, physical laminae are uncommon. Other observed bedding features and sedimentary structures consist of distinctive pedogenic-cryogenic dry zones, salt karst structures, and clastic dykes and diapirs. Although paleoenvironmental investigations of these well-bedded sequences have just recently begun, several basins provide examples of the nature of paleolimnological information that can be derived from the salt lakes of the northern Great Plains. The chemical and biological laminae preserved in the Holocene sequence of Waldsea Lake provide evidence for significant fluctuations in brine chemistry and chemocline depth in this meromictic basin. Freefight Lake, another hypersaline meromictic lake, contains a relatively thick sequence of rapidly deposited, deep-water salts underlain by finely laminated carbonates, sulfates, and microbial mat sediments. These very thin, undisturbed laminae, combined with exceedingly high rates of offshore evaporite mineral accumulation, provide an excellent opportunity for high resolution geochemical and hydrologic reconstructions in a part of the region distinguished by a paucity of other sources of paleoenvironmental information. Chappice Lake, a shallow, hypersaline brine pool, contains a wealth of paleoenvironmental information. Although the basin probably never experienced the deep-water conditions that earmark Waldsea and Freefight lakes, nonetheless, finely laminated and well-bedded sequences abound in the Holocene record of Chappice Lake. The endogenic magnesium and calcium carbonates and sulfates comprising these laminae can be used to interpret the history of brine chemistry fluctuations which may then help to understand past changes in the hydrologic budget and groundwater inflow.

The Qaidam Basin is a tectonically controlled depression at 2700 m altitude on the northern margin of the Tibet Plateau. A succession of Neogene clastic sediments indicates lake depocentre migration from NW to SE. Towards late Pliocene, evaporative conditions developed with formation of gypsum, halite, celestite, mirabilite and bloedite. Continued deformation through Pleistocene developed a series of NW-SE trending domes and troughs. This setting continued to exert a controlling influence on basin and brine evolution and the progressive development of sulfate to chloride brines as dry conditions intensified in late Pleistocene, at the end of which, extensive flat floors were formed in Dalangtan, Qarhan and other playas.

In much of the northern Great Plains, saline and hypersaline lacustrine brines are the only surface waters present. As a group, the lakes of this region are unique: there is no other area in the world that can match the concentration and diversity of saline lake environments exhibited in the prairie region of Canada and northern United States. The immense number of individual salt lakes and saline wetlands in this region of North America is staggering. Estimates vary from about one million to greater than 10 million, with densities in some areas being as high as 120 lakes/km2. Despite over a century of scientific investigation of these salt lakes, we have only in the last twenty years advanced far enough to appreciate the wide spectrum of lake types, water chemistries, and limnological processes that are operating in the modern settings. Hydrochemical data are available for about 800 of the lake brines in the region. Composition, textural, and geochemical information on the modern bottom sediments has been collected for just over 150 of these lakes. Characterization of the biological and ecological features of these lakes is based on even fewer investigations, and the stratigraphic records of only twenty basins have been examined. The lake waters show a considerable range in ionic composition and concentration. Early investigators, concentrating on the most saline brines, emphasized a strong predominance of Na+ and SO4 -2 in the lakes. It is now realized, however, that not only is there a complete spectrum of salinities from less than 1 ppt TDS to nearly 400 ppt, but also virtually every water chemistry type is represented in lakes of the region. With such a vast array of compositions, it is difficult to generalize. Nonetheless, the paucity of Cl-rich lakes makes the northern Great Plains basins somewhat unusual compared with salt lakes in many other areas of the world (e.g., Australia, western United States). Compilations of the lake water chemistries show distinct spatial trends and regional variations controlled by groundwater input, climate, and geomorphology. Short-term temporal variations in the brine composition, which can have significant effects on the composition of the modern sediments, have also been well documented in several individual basins. From a sedimentological and mineralogical perspective, the wide range of water chemistries exhibited by the lakes leads to an unusually large diversity of modern sediment composition. Over 40 species of endogenic precipitates and authigenic minerals have been identified in the lacustrine sediments. The most common non-detrital components of the modern sediments include: calcium and calcium-magnesium carbonates (magnesian calcite, aragonite, dolomite), and sodium, magnesium, and sodium-magnesium sulfates (mirabilite, thenardite, bloedite, epsomite). Many of the basins whose brines have very high Mg/Ca ratios also have hydromagnesite, magnesite, and nesquehonite. Unlike salt lakes in many other areas of the world, halite, gypsum, and calcite are relatively rare endogenic precipitates in the Great Plains lakes. The detrital fraction of the lacustrine sediments is normally dominated by clay minerals, carbonate minerals, quartz, and feldspars. Sediment accumulation in these salt lakes is controlled and modified by a wide variety of physical, chemical, and biological processes. Although the details of these modern sedimentary processes can be exceedingly complex and difficult to discuss in isolation, in broad terms, the processes operating in the salt lakes of the Great Plains are ultimately controlled by three basic factors or conditions of the basin: (a) basin morphology; (b) basin hydrology; and (c) water salinity and composition. Combinations of these parameters interact to control nearly all aspects of modern sedimentation in these salt lakes and give rise to four 'end member' types of modern saline lacustrine settings in the Great Plains: (a) clastics-dominated playas; (b) salt-dominated playas; (c) deep water, non-stratified lakes; and (d) deep water, "permanently" stratified lakes.

The All-Union Research Institute for Halurgy carried out laboratory investigations of a new method for crystallization of mirabilite from connate brine by direct contact with an immiscible dispersed refrigerant. A scale up unit was manufactured, and is schematicized. The process of the unit and the control system are described in detail. The flow rates and temperatures of the continuous and disperse phases at the column inlet and outlet, the chemical composition of the starting solution, the residual kerosene, and the grain size distribution of the crystals were all determined. On the basis of the results of industrial tests, a technical assignment was developed for a pilot model of the unit.