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Evaporites were deposited in every saline lake in the western Qaidam Basin (QB) during the late Quaternary, but the role of the Quaternary glacial environment in the formation of evaporite deposits remains to be clarified. In this paper, five upper Quaternary evaporite-bearing profiles in the western QB are studied. Uranium-thorium (U–Th) dating was applied to obtain the depositional ages of these profiles, and X-ray powder diffraction (XRD) analysis was applied to identify the evaporite minerals. The U–Th dating results indicate that halite (NaCl)-dominated profile D08 and mirabilite (Na2SO4·10H2O)-dominated profile MXK were deposited between 146.1 ± 53.4 ka and 171.3 ± 27.2 ka, mainly corresponding to Marine Isotope Stage (MIS) 6; the bloedite (Na2Mg(SO4)2·4H2O)-dominated profiles WMX1 and WMX2 were deposited between 182.1 ± 2.5 ka and 206.7 ± 7.0 ka, mainly corresponding to the late period of MIS7; and the mirabilite and halite-dominated salt layers in profile D30 were deposited between 9.0 ± 0.7 ka and 14.3 ± 1.6 ka, with mirabilite deposit ages corresponding to MIS2 and early MIS1. The minerals in the profiles identified by XRD analyses are mirabilite, thenardite (Na2SO4), bloedite, gypsum (CaSO4·2H2O), starkeyite (MgSO4·4H2O), hexahydrite (MgSO4·6H2O) and halite. This study, combined with those of previously reported evaporite deposits in the western QB, indicates that MIS7, MIS6 and MIS2 were important evaporite deposition periods in the late Quaternary. Evaporite depositions in the QB during MIS6 and MIS2 were attributed to a decrease in temperature and shrinkage of the saline lake hydrosphere. The cold glacial climate during MIS6 and MIS2 was conducive to mirabilite deposition in the western QB, while the relatively warm climate of the late period MIS7 was conducive to bloedite deposition.

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.

The use of ground granulated blast furnace slag (GGBFS) is environmentally sustainable and prevalent in the cement industry, but the original alkali-activated slag binder cannot be used for mine backfilling. Few reports have studied slag binders with high slag proportions (>90%) and low-cost activators (solid waste is used) that have higher performance than cement for backfilling. To increase the utilization of slag in the mining industry, this work presents a new slag binder (SB) comprised of 91% slag powder and 9% activator (3% clinker, 5% desulfurized gypsum, and 1% mirabilite). Its performance was evaluated by testing its strength, yield stress, and viscosity, which are three key properties for backfilling. We also investigated its microstructure using SEM, XRD and thermogravimetric analysis (TG/DTG). The results showed that the SB composites have a slightly lower early-age (28 d). Although the SB backfilling composites had a twofold higher yield stress and nearly the same viscosity as Portland cement, the pressure drop in a pipe was only slightly higher through friction factor modeling. The proposed SB may provide a sustainable binder for the mining industry with better performance and lower cost.

Based on principles of chemical thermodynamics, the relationship between temperature and the Gibbs free energy of erosion products generated during the sulfate attack on cement concrete was deduced. The orientation of chemical reactions of sulfate attack on cement concrete was theoretically determined as well as the critical sulfate ion concentration and the formation conditions of erosion products. The phase composition, microstructure, crystal form, and morphology of erosion products before and after sulfate attack were investigated by environmental scanning electron microscope and energy spectrum analysis (ESEM-EDS) and X-ray diffraction (XRD). The results show that the effects of sulfate ion concentration and temperature on cement concrete sulfate attack are significant, and different influencing factors correlate with each other. The crystal transition temperature between the anhydrite and dihydrate gypsum is 42°C, and the corresponding concentration of sulfate ion is about 2.3 × 10−3 mol/L. Simultaneously, the crystal transition temperature between the thenardite and mirabilite is 32.4°C. Moreover, the theoretical upper limit temperature and sulfate ion lower limit concentration of thaumasite are 44°C and 0.0023 mol/L, respectively. The ESEM-EDS and XRD results imply that the chemical thermodynamics can be used to reveal the erosion mechanism of sulfate attack on cement concrete. The major erosion products of sulfate attack on cement concrete are rod-like ettringite with a larger slenderness ratio, plate-like gypsum, granular sulfate salt, incompletely corroded calcium hydroxide, and residual skeleton of calcium silicate hydrate. The sulfate attack has double effects on mechanical properties of specimens, which can affect the microstructure, phase composition, type, and morphology of erosion products.

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.

Many of the large number of underground works constructed or under construction in recent years are in unfavorable terrains facing unusual situations and construction conditions. This is the case of the subject under study in this paper: a tunnel excavated in evaporitic rocks that experienced significant karstification problems very quickly over time. As a result of this situation, the causes that may underlie this rapid karstification are investigated and a novel methodology is presented in civil engineering where the use of saturation indices for the different mineral specimens present has been crucial. The drainage of the rock massif of El Regajal (Madrid-Toledo, Spain, in the Madrid-Valencia high-speed train line) was studied and permitted the in-situ study of the hydrogeochemical evolution of water flow in the Miocene evaporitic materials of the Tajo Basin as a full-scale testing laboratory, that are conforms as a whole, a single aquifer. The work provides a novel methodology based on the calculation of activities through the hydrogeochemical study of water samples in different piezometers, estimating the saturation index of different saline materials and the dissolution capacity of the brine, which is surprisingly very high despite the high electrical conductivity. The circulating brine appears unsaturated with respect to thenardite, mirabilite, epsomite, glauberite, and halite. The alteration of the underground flow and the consequent renewal of the water of the aquifer by the infiltration water of rain and irrigation is the cause of the hydrogeochemical imbalance and the modification of the characteristics of the massif. These modifications include very important loss of material by dissolution, altering the resistance of the terrain and the increase of the porosity. Simultaneously, different expansive and recrystallization processes that decrease the porosity of the massif were identified in the present work. The hydrogeochemical study allows the evolution of these phenomena to be followed over time, and this, in turn, may facilitate the implementation of preventive works in civil engineering.

Salt weathering is one of the most damaging processes affecting stone conservation and represents an extensively debated topic in heritage science. The main subject of previous research is the built heritage, whereas other types of assets are often neglected, such as underground cultural heritage. This paper introduces an investigation of stone decay in the subterranean environment focused on salt weathering, its patterns, compositional features, and variability in time and space, aiming at finding its driving forces in the rock properties and environmental setting. Field explorations and the mineralogical analysis of salt efflorescences and crusts were integrated by the petrographic, geochemical, and petrophysical characterization of the rock substrates, a microclimate monitoring, and the chemical analysis of groundwater and rainwater. The subject of study is the underground archaeological-historical site of Yoshimi Hyaku Ana in Japan, a complex of Kofun tombs of the 6th–7th century and galleries of the WWII era. The site is affected by intense salt weathering, involving efflorescences and crusts composed of mixed soluble sulfates, mostly hydrated: gypsum, alunogen, alum-(Na), halotrichite, epsomite, polyhalite, tamarugite, thenardite, and mirabilite. They derive principally from the dissolution of rock-forming minerals and components (pyrite, glass, feldspars, etc.) from the Miocene volcanic tuffs into which the site is excavated. The tuffs show a certain lithological diversity (e.g., glass amount and chemico-mineralogical composition) that controls the space variability of salt composition. Another major influencing factor is the underground microclimate, which also affects the time variability and seasonality of salt weathering. The innermost underground areas have an extremely high relative humidity (~100%) and are essentially salt-free, whereas, nearby the site entrances, the wider fluctuations of air temperature and humidity create conditions for salt crystallization in the dry winter season and deliquescence in summer. Depending on the solubility of each salt phase, cycles of crystallization/dissolution and hydration/dehydration can occur both seasonally and in the short-term, causing severe stresses to the stone and damage.

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.

Groundwater origin, flow and geochemical evolution in the Golmud River watershed of the Qaidam Basin was assessed using hydrogeochemical, isotopic and numerical approaches. The stable isotopic results show groundwater in the basin originates from precipitation and meltwater in the mountainous areas of the Tibetan Plateau. Modern water was found in the alluvial fan and shallow aquifers of the loess plain. Deep confined groundwater was recharged by paleowater during the late Pleistocene and Holocene under a cold climate. Groundwater in the low-lying depression of the central basin is composed of paleobrines migrated from the western part of the basin due to tectonic uplift in the geological past. Groundwater chemistry is controlled by mineral dissolution (halite, gypsum, anhydrite, mirabilite), silicate weathering, cation exchange, evaporation and mineral precipitation (halite, gypsum, anhydrite, aragonite, calcite, dolomite) and varies from fresh to brine with the water types evolving from HCO3 ⋅ Cl-Ca ⋅ Mg ⋅ Na to Cl-Na, Cl-K-Na and Cl-Mg type along the flow path. Groundwater flow patterns are closely related to stratigraphic control and lithological distribution. Three hierarchical groundwater flow systems, namely local, intermediate and regional, were identified using numerical modeling. The quantity of water discharge from these three systems accounts for approximately 83 %, 14 % and 3 %, respectively, of the total groundwater quantity of the watershed. This study can enhance the understanding of groundwater origin, circulation and evolution in the Qaidam Basin as well as other arid endorheic watersheds in northwestern China and elsewhere worldwide.

Seasonal desiccation of Mg2+–(Na+)–(Ca2+)–SO42−–(Cl−) saline lakes in La Mancha (Central Spain) that host microbial mats led to the precipitation of hydrated Na-Mg sulphates and gypsum. Sulphates precipitated in the submerged conditions form extensive biolaminites, whilst in marginal areas they produce thin crusts. Sedimentological, mineralogical, petrographic and high resolution textural studies reveal that the crusts were formed within the benthic microbial mats that thrive at salinities ranging from 160 to 340 g·L−1. The minerals of the crusts are primary bloedite (Na2Mg(SO4)2·4H2O), epsomite (MgSO4·7H2O), gypsum (CaSO4·2H2O) and mirabilite (Na2SO4·10H2O), as well as secondary hexahydrite (MgSO4·6H2O) and thenardite (Na2SO4). Primary bloedite crystals, which form the framework of surficial and submerged crusts are seen to nucleate subaqueously and grow incorporatively within the matgrounds. Displacive and incorporative epsomite grows on previous bloedite crystals and also on the ground. Mirabilite is precipitated rapidly at the brine-air interface over bloedite and epsomite. Hexahydrite and thenardite are formed due to dehydration of epsomite and mirabilite, respectively.

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.

Groundwater quality degradation has raised widespread concerns about water supplies and ecological crises in China. In this study, hydrogeochemistry, environmental stable isotopes (&delta, 18O, &delta, D), and principal component analysis were conducted together to reveal the mechanism&rsquo, s response to the hydrogeochemical and quality degradation of groundwater in Yuncheng Basin, Northern China, so that reasonable water resource management strategies can be developed. The study reveals that groundwater faces a tremendous risk of quality decrease during the past decade: (1) the hydrochemical facies of groundwater shows that the bicarbonate and chloride type water was replaced with sulfate type water and the occupying area of SO4&middot, Cl-Na, SO4&middot, HCO3-Na type water expanded dramatically in shallow and intermediate-deep aquifers. (2) Major ion chemistry and hydrogen and oxygen isotope compositions indicate that the major hydrogeochemical processes responsible for groundwater quality deterioration include the dissolution of evaporates (i.e., halite, gypsum, and mirabilite), ion exchange, and evaporation process. Additionally, (3) anthropogenic activities (overutilization of fertilizer) have resulted in nitrate contamination, and have thereby led to groundwater quality degradation.

The study was aimed at mineralogical and geochemical characteristics of secondary phases related to deterioration of historic building materials. The investigations, carried out in the Holy Trinity Basilica in Krakow, Poland, focused on the southern facade of the 17th-century Myszkowskis Chapel, built of the Miocene Pinczow limestone. Lower part of the facade is covered with a cement render, and the exposed foundations are made of Jurassic limestone and Cretaceous sandstone, both of local origin from the Krakow region and neighbouring Carpathians, in the form of irregular blocks bound with a cement mortar. The wall surface exhibits clear signs of damage; from dark grey soiling and scaling to efflorescences. Sampled materials, deteriorated, altered crusts and efflorescences were analysed with optical and scanning electron microscopy, X-ray diffraction, and Raman microspectroscopy methods. The secondary minerals distinguished include abundant gypsum CaSO 4 ·2H 2 O, less common thenardite Na 2 SO 4 (and/or mirabilite Na 2 SO 4 ·10H 2 O), aphthitalite (K, Na) 3 Na(SO 4 ) 2 , darapskite Na 3 (SO 4 )(NO 3 )·H 2 O, ettringite Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ·26H 2 O, monosulphite Ca 4 Al 2 O 6 SO 3 ·11H 2 O, as well as scarce nitre KNO 3 , nitratine NaNO3 and halite NaCl. Gypsum usually forms surface crusts and fills the pores inside some materials. The efflorescences, sampled from the exposed foundations, consisted of thenardite and/or mirabilite, aphthitalite and darapskite, whereas ettringite and monosulphite were connected with cement renders. Traces of nitre, nitratine and halite were detected at various elements of the chapel facade and foundations. The origin of the salts is related to composition and physicochemical properties of the building materials, as well as to anthropogenic factors.

Many irrigated plains in arid and semi-arid regions have groundwater quality issues due to both intensive human activity and natural processes. Comprehensive studies are urgently needed to explore hydrogeochemical evolutions, investigate possible pollution sources, and understand the controls on groundwater compositions in such regions. Here, we combine geostatistical techniques and hydrogeochemical assessments to characterize groundwater quality over time in the Yinchuan Plain (a typical irrigated plain in China), using 12 physicochemical variables derived from sampling in 600 and 602 wells in 2004 and 2014, respectively. Our results show that groundwater-rock interactions and evaporation are the key natural factors controlling groundwater compositions. Hydrogeochemical water types in both 2004 and 2014 were Ca-HCO3, Na-Cl, and mixed Ca&middot, Mg-Cl. Along with the hydrogeochemical compositions, we used ionic ratios and the saturation index to delineate mineral solution reactions and weathering processes. Dissolution of gypsum, halite, fluorite, and mirabilite, along with silicate weathering and cation exchange, were identified in the study area. Our results indicated rising ion concentrations in groundwater, which could be the result of anthropogenic influences. Increasing total hardness and nitrates over the study period were most likely caused by agricultural activity and the discharge of waste water from human residential areas.

The rapid development of urbanization and agriculture poses serious impacts on groundwater in arid and semi-arid areas, which typically have high groundwater depletion rates. In this study, chemical and isotopic analyses combined with different data interpretation methods (diagrams, bivariate analyses, principal component analysis (PCA), and hierarchical cluster analysis (HCA)) were used to identify the major factors controlling groundwater chemistry in an arid and semi-arid region of North China. Sixty-four groundwater samples (35 from unconfined aquifer, 29 from confined aquifer) were collected in Baotou City, North China, and 17 chemical variables were detected for each sample. The complex hydrochemical types in unconfined groundwater (e.g., HCO3-Ca·Mg, HCO3·Cl-Na·Mg, SO4-Na·Mg, and Cl·SO4-Na types) may be related to anthropogenic activities, while the main hydrochemical types in confined groundwater are HCO3-Ca·Mg, HCO3-Na·Mg, HCO3·Cl-Na·Ca, SO4·HCO3-Na·Mg, and Cl·SO4-Na types. Three component models for unconfined and confined groundwater were revealed using PCA, which explained approximately 79.69% and 80.68% of the data variance, respectively, providing a deeper insight into groundwater composition controlled by geochemistry and anthropogenic activities. Three clusters were yielded from HCA. The factors and identified clusters were verified with hydrochemical investigations. Among the natural factors, the main hydrochemical processes involve the dissolution of various minerals (halite, gypsum, feldspar, fluorite, mirabilite, biotite, dolomite, and calcite), cation exchange, evaporation, and mixing. The anthropogenic factors include domestic sewage intrusion and agricultural activities, which are most likely to lead to further declines in groundwater quality. These findings may be useful for improving groundwater resource management for sustainable development in arid and semi-arid areas.

Tafoni are one of the most interesting weathering features developed in many areas of the world from tropical areas to polar ones such as Antarctica. Here, we present the results on 4 tafoni in similar conditions (aspect, slope, distance from the sea, elevation) and in the same granite close to the Italian Antarctic station at Mario Zucchelli Station (74°42′S). These tafoni were thermally monitored through infrared thermography and in situ thermistors for an austral summer (2018/19). They were also mineralogically characterized through the image analyses in each tafone sectors (Top, Ceiling, Side and Floor). Salts concentration on the weathered material removed through the scratching was also detected through chemical analyses. Moreover, the weathering rate was calculated through periodic sample weightings of the scratched material from the different tafone sectors. Our results confirmed the importance of the fractures inclination that seem to favor the vertical development of the cavities where basal fractures occurred and the backward development where fractures are vertical. The weathering rates shown that vertical development was always faster than the backward (except for O4) and that the former is statistically linked with the size of the tafone. At mineralogical scale, the higher weathered removal of the quartz concentration could be more closely related to the higher cryogenic weathering of intra-crystal fractures that occur at very low temperatures (−20 °C) in winter than to the thermal stress, thermal shock, or potential freeze-thaw cycles during the summer. Among the different salts, the strong relationship between weathering removals and chlorides suggests that chlorides in this climate are more effective than sulphates. The seasonal trend of weathering matches well with the breaking up of sea ice towards the Tethys Bay and can provide a supply of sea spray that is richer in chlorides (halite) than in sulphates (thenardite, mirabilite). From the analyses of the spatial thermal variability, we could argue that the thermal stress during the summer is not relevant except for the tafone O4. The fact that higher weathering removal were recorded in the innermost (C and S) of the tafoni where thermal variability and AMP were lower suggests that higher moisture content is the crucial factor for a high evaporation flux that can enhance the salt action.

This study aims to investigate the damage mechanism and predict the failure time of concrete subjected to wetting and drying (WD) cycles in a sodium sulfate solution. To explore the growth rules and the growth rates of gypsum, the reaction-rate constant calculation formula of gypsum is proposed based on theories of chemical reaction kinetics. Subsequently, the formulae of the volume fractions of mirabilite and gypsum in the pore under each WD cycle are proposed and used to calculate the macroscopical tensile stress to determine the WD cycle number that the concrete can sustain. Finally, the reliability of the proposed model is verified by an indoor experiment. In addition, a new damage type of concrete, induced by filling-damaging cycles, is also found during the experiment. These findings can be used for evaluating the damage of concrete that is subjected to cyclic WD in sodium sulfate solution.

The Pliocene-Quaternary aridification of the Asian interior is key to understanding the impacts of global cooling and Tibetan Plateau uplift and the potential linkage to North Pacific Ocean biochemical processes and global changes. However, there is a lack of detailed continuous Pliocene-Quaternary paleoclimatic records from the Asian interior because most climatic records have been obtained from discontinuous coarse sediment outcrops around the rims of inland basins. Here, we provide a continuous, high-resolution 3.1 Myr record of grain size from the well-dated SG-3 borehole in the western Qaidam Basin on the northeastern Tibetan Plateau, NW China. The results reveal a long-term upward coarsening trend in grain-size that can be divided into three phases: (i) 3.1–1.1 Ma, laminated fine sediments (fine to medium silts) containing scattered gypsum crystals and interbedded by thin beds of marl; (ii) 1.1–0.15 Ma, massive medium to coarse silts interbedded by beds of mirabilite; (iii) 0.15–0 Ma, coarse silts containing thin layers of mirabilite, halite, bloedite, and polyhalite. This pattern reflects the upward shallowing and shrinking of the lake from a brackish lake to a salt lake, and then to a playa, suggesting a long-term stepwise drying of the Asian interior since the Late Pliocene, probably forced by global cooling and uplift of the Tibetan Plateau.

We present a profitable pathway from desalination waste brines to negative CO2 emissions. The method, termed ‘brine to bricks’ (BtB), mineralizes CO2 as nesquehonite (MgCO3･3H2O) using the Mg content of brines. Fresh water, gypsum (CaSO4･2H2O), halite (NaCl), mirabilite (Na2SO4･10H2O), sylvite (KCl), and hydrochloric acid are concurrently produced. To prevent ‘carbon leakage’, BtB does not rely on external chemicals, fossil fuel-derived heat and power, or captured CO2. BtB selectively precipitates CaSO4･2H2O, NaCl, and Na2SO4･10H2O by evaporative concentration and temperature-control. The remaining Na+ and K+ ions are separated as NaCl and KCl from the magnesium chloride slurry by hydrochloric acid-based precipitation. Super-azeotropic hydrochloric acid is regenerated from the slurry using a novel method: low hydration magnesium chloride addition. Purified magnesium chloride is decomposed to amorphous MgO prior to reaction with ambient CO2. The current NET potential of BtB, including the CO2 emissions from desalination, is 136 MtCO2/y. In the current market, BtB can operate at a profitability up to $266/t-CO2, dependent primarily on the availability of waste heat and the local performance of renewable energy. Based on current desalination adoption projections, BtB could remove 0.350-1.784 GtCO2/y by 2050 while providing substantial increases in fresh water, construction materials, and chemicals that are of use to other negative emission technologies.

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.

The behavior of soil solutions in seasonally freezing solonchaks of Mongolia is discussed on the basis of the results of simulation experiments with the use of the FREEZBRINE model of physicochemical equilibria. Data on the chemical composition of soil solutions in solonchaks of the Ekhiin-Gol oasis have been used for modeling. The freezing temperatures; the character of the changes in the composition of the unfrozen brine; and the temperatures and intensities of the precipitation of hydrohalite, mirabilite, calcite, gypsum, and other salts have been calculated. The results obtained in this study allow us to estimate the contribution of the winter period of the soil functioning to the development of the salt profile in the solonchaks. One of the consequences of the cryogenic transformation of soil solutions in these solonchaks is a predominance of the sulfate type of salinization.

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.

In recent years evidence for spring deposits on Mars has been mounting. It seems increasingly likely that groundwater upwelling and surfacing as springs may be responsible for some mineral deposits on Mars’ surface. In order to more easily detect and better understand potential spring deposits on Mars, it is pertinent that we gain a better understanding of the distribution of minerals at cold spring systems on Earth. Here, we report on the detailed mineralogy and distribution of precipitates in crusts and sediments of three non-volcanic perennial saline cold spring systems associated with gypsum/anhydrite diapirs on Axel Heiberg Island, Canada: Wolf spring (WS; also known as Lost Hammer), Colour Peak springs (CP), and Gypsum Hill springs (GH). At these sites permafrost, frigid winter temperatures, and arid atmospheric conditions approximate conditions of present-day, as well as past, Mars. Mineralogy of the three springs is dominated by halite (NaCl), calcite (CaCO 3 ), gypsum (CaSO 4 ·2H 2 O), thenardite (Na 2 SO 4 ), mirabilite (Na 2 SO 4 ·10H 2 O), and elemental sulfur (S°). Minerals at WS are more sodium-rich than at the other two sites, and water salinity is much higher, suggesting water flows through halite in the subsurface. Mirabilite is likely deposit at WS during winter months and dehydrates to thenardite during summer months. Elemental sulfur is typically associated with gypsum, and may be related to microbial metabolism. Spring sediments are home to thriving microbial communities in winter and summer months, and presumably year round. If spring systems did exist on the surface of Mars, they may represent environments capable of supporting microbial life. It is not known to what extent mineral crusts in cold saline spring systems on Earth preserve evidence of microbial life, or if they ever did on Mars. Therefore, studying terrestrial saline spring mineral deposits such as those on Axel Heiberg Island may help us to better understand cold spring precipitation on Mars and guide us in the search for minerals that may have been precipitated in spring systems and that may contain evidence of life. Additionally, spectral data from Europa indicates the presence of mirabilite. While the depositional environment on Europa differs from Axel Heiberg Island, the springs may still be a good mineralogical analogue, given the precipitation of mirabilite by the upwelling of cold, salty subsurface water, in a cold, semi-arid desert environment.

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.

Mammoth Cave displays a wide variety of depositional environments that permit the deposition of some unusual minerals, although the cave overall is rather devoid of speleothems. Calcite in the form of stalactites, stalagmites, and flowstone is the common carbonate mineral and occurs where passages extend beyond the protective caprock. Aragonite also occurs but more rarely. Gypsum is the common sulfate minerals and occurs widely in dry passages beneath the caprock. Gypsum takes the form of crusts and curving crystals known as gypsum flowers. In the exceptionally dry portions of the cave are found other sulfate minerals including mirabilite, Na2SO4·10H2O, epsomite, MgSO4·7H2O, hexahydrite, MgSO4·6H2O, celestine, SrSO4, and blodite, Na2SO4·MgSO4·4H2O. In addition, there is evidence for the rare sulfate minerals eugsterite, 2Na2SO4·CaSO4·2H2O, and wattevilleite, Na2SO4·CaSO4·4H2O. The source of sulfate is likely the oxidation of pyrite, FeS2 that occurs in the limestone and overlying sediments. Saltpetre of uncertain mineralogy occurs in the cave sediments and was mined in the nineteenth Century. Other minerals include black manganese oxides that occur on stream cobbles and on chert ledges.

Acigol Lake is the second largest alkaline lake in the world and is in a region that is one of the most important sodium sulphate production fields in Turkey. The present study focuses on determination of sources of the Na2SO4 deposits with main-trace element contents based on hydro-geochemical studies in the lake basin. The geological and hydrogeological properties of the study area were primarily determined. To identify the hydrogeochemical characteristics of spring/groundwater and lake water, chemical analyses results were evaluated with graphical plots such as Piper, Gibbs and Chadha diagrams and the conceptual hydrogeological model was prepared for the area. Mineral paragenesis of the lake sediments mainly consist of gypsum, aragonite, halite, calcite, dolomite, quartz, muscovite, smectite and illite besides tenardite, mirabilite and bloedite minerals. The dominant hydro geochemical fades are Na-SO4, NaCl, Ca-Mg-HCO3 and Ca-Mg-SO4 which are due to water-rock interaction. The mean Na, Ca, SO4, Cl and Mg concentrations in the spring waters are 221.27, 152.62, 374.81, 185.46 and 58.50 ppm respectively; whereas mean concentrations in the lake waters for Na, Ca, SO4, Cl and Mg ions are 22 507, 646, 16 186, 35 691 and 2399 ppm respectively. These major elements have very high concentrations in the lake waters due to the evaporation leading to enrichment. The main mechanism controlling water chemistry in the Acigol Lake basin is the process of water rock interaction. The enrichment of these elements in the springs waters originate from lithological units such as sedimentary, ophiolitic and young magmatic rocks. (C) 2017 Elsevier Ltd. All rights reserved.

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 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.

Qaidam Basin is a tectonically controlled depression on the northern margin of the Tibetan Plateau. In 2008, a long core was drilled in the Qahansilatu sub-basin in the western Qaidam basin. The sediment layers in the upper 400 m alternate between evaporite mineral layers and carbonaceous clay layers. The detailed mineralogical investigation focused on evaporite minerals including halite, gypsum, mirabilite, thenardite, glauberite, eugsterite, and bloedite. Gypsum and halite make up the majority of the evaporate minerals. Environmentally induced variations in the mineralogy and crystal habit of the sulfates have been extensively investigated. Gypsum has prismatic and pyramid habits, such as disc pyramid, stubby prismatic, slender prismatic. Visible isolated gypsum and aggregates (rosette/radial and twins) are mostly scattered in carbonaceous clay layers, suggesting that secondary gypsum is well developed. Gypsum may be a precursor mineral of glauberite, and thenardite is the precursor of bloedite. As a metastable and rare mineral, eugsterite does not appear in other Tibetan areas. It forms at the expense of pre-existing gypsum or thenardite in the core at an experimental temperature of higher than room temperature. The presence of eugsterite indicates a warm and/or hot climate at its deposition time.

Short crystallisation and deliquescence cycles of mirabilite, epsomite and gypsum are identified by using an automated monitoring system on-site. It consists of digital cameras and RH/T sensors which are computer-controlled and connected to the Internet. Digital images are processed to form a time-lapse movie, so that surface alterations are easily recognised. High resolution imaging (6 mega pixels) in combination with various lenses (12–24 mm zoom, 28–105 mm zoom, 20 mm inversed) results in a wide range of precise observation from 7 to 500 mm width of image. That is essential for discriminating phase transitions of single crystals at the same time as monitoring the evolution of the efflorescence as a whole. Crystallisation-deliquescence cycles are induced by small temperature and humidity variations. Mirabilite and epsomite undergo phase changes from crystallisation to deliquescence and vice versa at about 83% RH (15–20 °C). These equilibrium relative humidities are considerably reduced compared to the pure salt systems as a consequence of mixed salt solutions. Observations confirm predictions by ECOS simulation based on chemical analyses of water extracts from the site. Dehydration of mirabilite is observed when the relative humidity drops below 65% RH. Mirabilite exhibits the most pronounced and rapid phase changes in response to indoor climate variations. As an example, whisker crystals of 1–3 mm length grow within one up to some days. Epsomite responds fainter and slower. Crystallisation of gypsum is distinguished by the growth of new crystals on the stone surface. They have a size of about 10 μ – which is close to the image resolution – when they appear on the image. Crystallisation is associated with an increased granular disaggregation of the stone surface. Rhythmical crystallisation of gypsum appears to correlate with small relative humidity variations of ±2–5% within a band from 65 to 75% RH in the room. However, this needs to be clarified in detail.

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.

The evolution of pore-water and the composition of solid phases in the vadose zone of pyritic tailings was studied by means of unsaturated column experiments. Several columns of water-saturated mine tailings were dried during 125 days under controlled laboratory conditions. The columns were dismantled at four successive drying stages and the evolution of pore-water, mineralogy, water content and temperature was characterized. Sulfide and aluminosilicate minerals present in the waste dissolved, releasing sulfate and other solutes (mainly Fe, Zn, Cu, Al, Mg and Ca) to the pore-water. Evaporation caused a crust of efflorescent, water-soluble sulfates to develop over the complete top surface of the columns and into the pores of the underlying waste material. This crust, which has also been identified in the field, changed the hydraulic properties of the tailings and produced a decrease in the evaporation rate of the columns. Moreover, these water-soluble precipitates (mainly rozenite, szomolnokite, halotrichite, hexahydrite, mirabilite and gypsum) acted as temporary sinks for Cd, Pb, Co and Ni, which could be released to the surface run-off or the groundwaters during rainfall events under field conditions. Pore-water evolution was determined not only by geochemical processes (dissolution of sulfides and aluminosilicates, precipitation of secondary phases) but also by thermal and hydraulic processes. Progressive dilution was observed in the lower part of the columns. Dilution was caused by the thermally driven vapor flux from the top of the column to its colder bottom and subsequent condensation therein. This process, which may also occur in tailings under sub-arid climate, played a key role on the evolution of pore-water with increasing drying.

This work considers the crystallisation mechanisms of the most common and aggressive salts that generate stress in porous building stones as a result of changing ambient conditions. These mechanisms include the salt crystallisation that result from decreasing relative humidity and changes in temperature and, in hydrated salts, the dissolution of the lower hydrated form and the subsequent precipitation of the hydrated salt. We propose a new methodology for thermodynamic calculations using PHREEQC that includes these crystallisation mechanisms. This approach permits the calculation of the equilibrium relative humidity and the parameterization of the critical relative humidity and crystallisation pressures for the dissolution–precipitation transitions. The influence of other salts on the effectives of salt crystallisation and chemical weathering is also assessed. We review the sodium and magnesium sulphate and sodium chloride systems, in both single and multicomponent solutions, and they are compared to the sodium carbonate and calcium carbonate systems. The variation of crystallisation pressure, the formation of new minerals and the chemical dissolution by the presence of other salts is also evaluated. Results for hydrated salt systems show that high crystallisation pressures are possible as lower hydrated salts dissolve and more hydrated salts precipitate. High stresses may be also produced by decreasing temperature, although it requires that porous materials are wet for long periods of time. The presence of other salts changes the temperature and relative humidity of salt transitions that generates stress rather than reducing the pressure of crystallisation, if any salt has previously precipitated. Several practical conclusions derive from proposed methodology and provide conservators and architects with information on the potential weathering activity of soluble salts. Furthermore, the model calculations might be coupled with projections of future climate to give as improved understanding of the likely changes in the frequency of phase transitions in salts within porous stone. This study was carried out in the framework of the research projects CGL2011-25162 (Spanish Ministry of Science and Innovation) and IJP 2006/R2 (the Royal Society Joint Project).

The geochemistry and vertical stratification of shallow meltwater ponds at 78°S near Bratina Island (McMurdo Ice Shelf) have been determined for late winter (October) and summer (January) conditions as part of the Latitudinal Gradient Project. Of the five frozen ponds investigated in October, all were stratified with respect to conductivity, and three had highly saline basal brines beneath the ice at temperatures of −16 to −20°C. In the ice column, inclusions of saline fluid were observed in channels between ice crystals; the abundance increasing with depth and decreasing ice crystal size. In January, seven of the ten ponds investigated (including ponds sampled in October) retained conductivity stratification, whereas significant thermal stratification was observed in only three ponds (maximum ΔT = 5.5°C). Basal brines, ice and meltwaters were Na-Cl or Na-SO4 dominated. FREZCHEM52 modelling, supported by changes in ion ratios, indicated that the precipitation of mirabilite (Na2SO4.10H2O) and gypsum (CaSO4.2H2O) during progressive freezing is an important determinant in chemical evolution of the basal brine. High pH (8.8–11.2) and over-saturation with respect to dissolved oxygen (> 20 mg L−1) in summer, and the presence of sulphide ions in basal brines in winter, occurred in those ponds which experienced high biological productivity during the summer months.

Las Vegas Wash drains the Las Vegas Basin in Nevada by capturing a series of tributaries and ending in Lake Mead and is being developed into an urban wetland. The soils are part of the Land series and contain high concentrations of pedogenic salts because of local sulfate-rich parent materials and high evapotranspiration rates. These salts cause damage to property, affect plant communities in the wetlands, and contribute to salinity in the Colorado River System. To gain a better understanding of these salts, two soil profiles were described. Whole soil samples were analyzed for ammonium acetate‐extractable and water-soluble elemental analyses, cation exchange capacity (CEC), pH, electrical conductivity, and particle size. Salt minerals were analyzed using scanning electron microscope (SEM)/energy dispersive spectrometer (EDS) and x-ray diffraction (XRD). Results of XRD analyses indicate hexahydrite, bloedite, mirabilite, gypsum, thenardite,halite,vivianite,and sepiolite.SEM/EDS analyses found bloedite, eugsterite, halite, hexahydrite, gypsum, thenardite, and possibly kainite. Gypsum occurs at the surface and in all subsurface horizons. The more soluble salts occur at the surface and in two subsurface horizons. This study documents the third occurrence of eugsterite in the USA and is the first study to document salts other than gypsum forming snowball morphology. We interpret the subsurface zones of soluble salts to represent relict water tables where capillary action, combined with subsurface evaporation, has concentrated Na-Mg sulfates and halite. These relict water tables may represent previous highlevel water tables that were lowered because of increased urbanization resulting in flooding, erosion, and incision of the Las Vegas Wash.

Sodium chloride and the secondary salts, such as sylvite, mirabilite, thenardite, bloedite, carnalite, bischofite, kieserite and polyhalite are not only mined from evaporate deposits, but they have also been produced more economically by solar concentration of brines for centuries. In this study, as an alternative approach, the aim was to create the production of salt co-products together with pure sodium chloride (NaCl) during the NaCl producing period from the Salt Lake water by multiple evaporation-cooling methods, supplemented by mineral and chemical processing. The results of XRD analysis indicated that various types of salts such as pure halite (sodium chloride), sodium sulphate salts, halite + carnalite, halite + langbeinite + sylvite and halite + bischofite + kieserite can be produced as participated materials from the brine of the Salt Lake. © 2005 Elsevier B.V. All rights reserved.

Saline-sodic wetlands along a 200-km stretch of the North Platte River Valley in western Nebraska, USA lie within an important agricultural region, but their processes, salt mineralogy, and geomicrobiology have not previously been investigated. Putative anthropogenic salinization has long been a concern, yet early historical accounts of widespread surface salts in the area have never been applied as comparative standards. Surface salts in the area originate from soil capillarity and surface evaporation. Thenardite (Na 2 SO 4 ) and/or mirabilite (NaSO 4 ·10 H 2 O) dominate, depending on ambient conditions. Bloedite (Na 2 Mg[SO 4 ] 2 ·4[H 2 O]), halite (NaCl), burkeite (Na 6 CO 3 [SO 4 ] 2 ), and calcite (CaCO 3 ) are minor constituents. Historical accounts indicate that salts accumulated naturally long before Euramerican settlement, apparently as a result of rock–water interaction in nearby volcaniclastic sediments of the Brule Formation. Ephemeral to permanent water-holding basins in the wetlands contain Na + -rich waters that vary widely in electrical conductivity (as high as 159 mS/cm) and in ionic composition, but local spring waters are extremely dilute. Basin floors exhibit a unique type of microrelief, which appears to form by the filling of microlows with water and the dispersal of soil material therein by Na + , followed by dewatering and collapse of the soil with drying. Illite dominates basin surface soils, but smectite dominates at depth; high soil pH, available K + , and frequent wetting–drying cycles in the wetlands suggest that in-situ illitization may have occurred. Soil crusts and vesicular surface horizons are common as are upward increases in electrical conductivity. The activity of sulfate-reducing microbes forms prominent near-surface horizons of sulfate reduction in saturated soils, which retract or disappear entirely during dry episodes. Saline-sodic wetland soils in the study area change on daily to seasonal scales. Cycles of surface salt development, microbial activity, and microrelief genesis are all controlled by regular wetting–drying cycles and the interaction of ponded surface waters and shallow groundwaters. Relatively unique aspects of microbial ecology and surface processes make the soils important as “geomicrobial reactors” wherein important parts of hydrological and geochemical cycles occur.

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.

Laboratory driven crystallisation of sodium sulphate and sodium chloride from concentrated solution in unsaturated porous stones has been performed. This contributes to a better understanding of the mechanisms by which salts crystallise and as a consequence limit the durability of porous materials which has an impact on buildings, civil constructions, and historical monuments. The identification of minerals in porous materials has been performed by scanning electron microscopy (SEM), Environmental Scanning Electron Microscopy (ESEM) and sequential profiles of X-ray diffraction (XRD) under temperature control of sample. The study of porous stones has been combined with experiments in capillary tubes. Data from SEM show that halite tends to precipitate on the surface of the stone with a similar distribution in all samples. However, the mirabilite–thenardite precipitation takes place preferably inside the stone and its depth from the surface and its relative concentration depends on the pore size distribution. In addition, mirabilite (Na2SO4·10H2O) crystallises homogeneously, whereas thenardite (Na2SO4) and halite (NaCl) tend to nucleate heterogeneously. To explain the precipitation sequence from concentrated solutions in unsaturated porous materials, a detailed analysis of the thermodynamic equations has been carried out by establishing a simple model. The proposed model shows the influence of the pore structure both on the water activity and saturation degree of involved salts.

MA agurici Cave hosts a diverse assemblage of minerals. The phosphatization of illite and montmorillonite clay rich sediments,located onthecave' sfloor,leadto theformationof taranakiteandfrancoanellite.Mineral assemblagesprecipitatedatthe boundary between limestone bedrock and guano deposits are dominantly hydroxylapatite, brushite, ardealite, and monetite. A number of sulphate minerals (gypsum, bassanite, mirabilite, and cesanite) were precipitated along with the phosphates, strengthen the physico-chemical conditions of the depositional environment. The major parameters controlling the environments under which these mineral assemblages were deposited are: pH, relative humidity, alkali content, and Ca/P ratio. In addition, this study presents the second worldwide reported occurrence of phosphammite discovered in a cave environment. Thisraremineraloccursassmalltransparentcrystalswithin theguanodeposit, precipitatedinanearlystagefromtheliquid fraction of guano.

The hydration of soluble Langbeinite and kieserite was investigated in the presence of potassium chloride and sodium sulfate. The addition of sodium sulfate affects water activity less than in the case of clean water. Therefore, we have conducted a research by adding water instead of schoenite solution. According to the results, hydration of Langbeinite by adding sodium sulfate in the first 240 hours occurs more intensively than without sodium sulfate with formation of a readily soluble schoenite and halite.

We studied the effects of evaporation and groundwater flow on the formation of salt minerals in the Sabkha of Oum El Khialate in South East Tunisia, which contains large amounts of sulfate sodium mineral deposits. Due to the fact that there are no important surface water bodies present in this sabkha, transport of solutes is dominated by advection rather than mixing in lakes. For our study we used both analytical conservative and numerical reactive transport models. Results showed that salinity varies with distance and may reach very high levels near a watershed where the groundwater flux is zero. As a consequence, reactive transport simulations results showed that more minerals precipitate and water activity decreases values near this watershed. Model results also showed that a sequence of precipitating minerals could be deduced after 140,000 years. From the boundary of the sabkha towards the watershed the mineral sequence was dolomite, gypsum, magnesite, bloedite, halite and mirabilite. It was found that the amounts as well as the mineral precipitation distribution strongly depend on salinity and rates of inflowing water. (C) 2014 Elsevier Ltd. All rights reserved.

Hydrogeochemical and environmental isotope methods were integrated to delineate the spatial distribution and enrichment of fluoride in groundwater at Yuncheng Basin in northern China. One hundred groundwater samples and 10 Quaternary sediment samples were collected from the Basin. Over 69% of the shallow groundwater (with a F− concentration of up to 14.1 mg/L), 44% of groundwater samples from the intermediate and 31% from the deep aquifers had F− concentrations above the WHO provisional drinking water guideline of 1.5 mg/L. Groundwater with high F− concentrations displayed a distinctive major ion chemistry: Na-rich and Ca-poor with a high pH value and high HCO3− content. Hydrochemical diagrams and profiles and hydrogen and oxygen isotope compositions indicate that variations in the major ion chemistry and pH are controlled by mineral dissolution, cation exchange and evaporation in the aquifer systems, which are important for F− mobilization as well. Leakage of shallow groundwater and/or evaporite (gypsum and mirabilite) dissolution may be the major sources for F− in groundwater of the intermediate and deep aquifers.

The Qinling orogen extends 1650 km E-W and has a width of 95-255 km. It has a long evolutionary history of ∼3.02 Ga and a mineralization history of approximately 2.5 Ga. There are more than 400 mineral deposits of Au, Ag, Pb, Zn, Sb, Hg, Mo, W, Fe, Ni, Mn, rare elements, REE, U, V, P, As, Ba, Sr, Ti, Al, pyrite, gypsum, trona, halite, glauberite, mirabilite, blue asbestos, fluorite, rock crystal, mica, vermiculite, graphite, kyanite, andalusite, talc, fireclay, and K-feldspar in the Qinling orogen and adjacent areas. The deposits were formed in six tectono-minerogenic cycles and have been grouped into 21 regional minerogenic series. The metallogeny of the Qinling orogen is closely associated with the tectonic evolution of the orogen, and most of the ore deposits were formed in two important metallogenic periods: (1) Middle Proterozoic to Early Paleozoic, which was characterized by spreading and rifting-related minerogenetic processes; during this period, the minerogenic series are directly associated with...

Seawater is the most abundant aqueous solution on Earth. Nevertheless, controversy exists with respect to the pathway for seawater freezing. The “Ringer–Nelson–Thompson pathway” is the current paradigm for seawater freezing; along this pathway, calcium precipitates as antarcticite (CaCl2·6H2O), and the eutectic temperature is −54°C. Along the “Gitterman pathway” for seawater freezing, calcium precipitates as gypsum (CaSO4·2H2O), and the eutectic temperature is −36°C. Recently, we estimated the solubility product for gypsum at subzero temperatures, which allows us to theoretically examine the alternative pathways for thermodynamic stability. When seawater freezing is simulated, mirabilite (Na2SO4·10H2O) begins precipitating at −6.3°C and is the dominant sink for sulfate. But contrary to some experimental evidence, the model also predicts the precipitation of gypsum, which begins at −22.2°C. The model predictions for soluble calcium and sulfate closely follow the Gitterman pathway and culminates in an eutectic temperature of −36.2°C. Experimental evidence is presented that demonstrates that gypsum can precipitate spontaneously during seawater freezing. Differences in experimental protocols explain the contradictory experimental evidence. The theoretical model and experimental evidence argue in favor of the Gitterman pathway as the thermodynamically stable pathway for seawater freezing. The metastable Ringer–Nelson–Thompson pathway is attributable to slow kinetics and fractional crystallization during the freezing process.

New chemical and isotopic data for deep seated calcium chloride brine from the Miramar Con gold mine, Yellowknife N.W.T., strongly suggest that the brine salinity is of marine origin. Diagnostic marine properties include uniformly elevated Br/Cl ratios typical of seawater concentrated beyond halite saturation, and Li/Br ratios (0.0254–0.0325) and δ 6 Li compositions (−32.1 to −36.3‰) similar to seawater (−32.3‰). The mean δ 6 Li for all mine water samples of −35.1‰ may reflect minor uptake of Li by secondary minerals. This interpretation is supported by analyses of altered metabasalt from fault zones which is enriched in Li but depleted in δ 6 Li (−14.7 to −15.6‰) relative to the unaltered metabasalt (−5.4‰). The mechanism responsible for concentrating the hypersaline brine end member is not unequivocal as evidence exists to support both evaporative and cryogenic processes. On the one hand, the Devonian sedimentary record in the Great Slave Lake region, in conjunction with Yellowknife brine isotopic compositions ( δ 2 H and δ 34 S SO 4 ) that are similar to various Devonian fluids, support an evaporative origin. On the other hand, the Na/Cl–Br/Cl relationship in the brine strongly suggests a cryogenic mechanism. Regardless of the concentrative mechanism, the chemical data indicate that the Yellowknife parent brine was concentrated 28- to 30-fold relative to seawater. The extreme depletion of Mg and enrichment of Ca in the brines, accompanied by Sr/Ca ratios similar to that of seawater, are accounted for by dolomitization of an aragonite-rich marine sediment by the brine before infiltration into the crystalline basement rocks. Subsequent alteration of silicate minerals in the shield added additional Ca and Sr to the brine as indicated by their radiogenic 87 Sr / 86 Sr ratios (up to 0.7147). Based on mineral balance calculations, the major mineral products of the cryogenic and evaporitic concentration and evolution paths are significantly different. The cryogenic evolution results in some 15% mirabilite, 60% hydrohalite, and 18% dolomite whereas the major minerals formed from the evaporitic evolutionary sequence are 36% halite, 8% gypsum, 17% dolomite, and 30% albite. The great similarity between the calcium chloride brine from Yellowknife and other such Canadian Shield brines indicates that they may share a common marine origin.