Salt Crystallization Research Articles

Construction of Hydrogels with Highly Salt-Resistant Honeycomb Porous Structures for Solar Desalination and Steam Generation.

Interfacial solar desalination is a method for desalinating seawater using solar energy, and the long-term use of this technology requires a stable evaporation rate and some ability to prevent salt crystallization. To address these issues, carbonized polydopamine-coated bentonite (C@PBT), poly(vinyl alcohol), and cellulose nanofibers were used to construct a three-dimensional oriented hydrogel evaporator with a multilayered honeycomb porous structure for long-term desalination. Carbon nanoparticles transferred between the layers of the bentonite, which increases the spacing of the layers and confers a more effective solar light trapping ability. The evaporation rate was 2.26 kg m-2 h-1 in 20 wt % NaCl solution, and no salt crystals were precipitated from the surface of the evaporator in 12 h of continuous operation. This phenomenon occurs due to the wide distribution of pore sizes and the large size of the pores within the evaporator, which create ample space for salt ions to move freely. Furthermore, after undergoing 300 cycles of compression, its internal pore structure remains intact, and the rate of evaporation remains stable. It ensures the evaporator stability during outdoor cycles. The research work provides an effective method to solve the salt accumulation problem and shows its great potential for application.

Probing Chemical Equilibrium in Frozen Sodium Phosphate Buffer Solution by 31P Solid-State NMR.

Phosphate buffers are crucial for cryopreservative stability in pharmaceuticals, food processing, biomedical sciences, and biology. However, their freeze concentrates lack quantitative characterization, especially regarding the physicochemical properties of phosphate salt species in equilibrium at subzero temperatures. This study employs 31P solid-state NMR (ssNMR) to analyze frozen sodium phosphate (NaP) solutions, providing insights into phase composition, ionic strength, and pH. For the first time, we have directly quantified phosphate species in frozen NaP buffer, including crystallized disodium phosphate dodecahydrate (Na2HPO4·12H2O) content and the concentrations of H2PO4- and HPO42- in the freeze concentrate. This enabled the calculation of the pH as well as the ionic strength in the freeze concentrate. Trehalose effectively mitigated pH shifts in buffer solutions by preventing the selective crystallization of salt, a spectroscopic phenomenon not previously observed experimentally.

State of conservation of an industrial brick masonry chimney: a case-study in Montijo, Portugal

AbstractIndustrial masonry chimneys became widespread in the mid-19th century and were eventually integrated into urban landscapes, gaining significance as symbolic historical remnants of local industries. This poses new challenges, particularly concerning the safety of populations and goods, as well as the preservation of the now-historical structures. In this article, we assess the conservation status of the 45-meter-high chimney of the former cork processing factory Mundet, located in Montijo, Portugal. The study involved a structural survey conducted using height access equipment, along with an investigation to diagnose moisture and salt decay at the base of the chimney. The later included measuring current and hygroscopic moisture distributions, as well as XRD characterization of brick and mortar samples. At the chimney’s base, salt crystallization causes efflorescence and erosion leading to masonry disintegration. This is associated with rising damp and the presence of sodium sulfate in the brick and sodium chloride in the mortar. In the shaft, mortar erosion becomes more pronounced as we ascend. At the crown, extensive mortar erosion and limited compression have caused the NE-facing half to disappear, while the rest is at risk of imminent collapse. Damage mitigation measures to address this situation are proposed.

A laboratory study on the durability of limestone wastes in harsh environments for their suitability as aggregate in concrete

One of the critical environmental issues in the Chegeni area (Lorestan Province, western Iran) is the production of a large volume of limestone wastes during the quarrying operations. Releasing limestone wastes in the areas neighboring the quarries has caused visual damage to the environment, and adverse effects on the quality of the soil, running water, and groundwater used for agricultural and drinking water purposes. One solution to this issue can be recycling limestone wastes to produce building materials. In the present study, a comprehensive laboratory program is planned for the durability evaluation of the limestone wastes under harsh environments for their suitability as aggregate in concrete. For this purpose, five aging tests, including freeze-thawing (F-T), salt crystallization (SC), acid attack (AA), wetting-drying (WD), and heating-cooling (HC), were conducted on the limestone sample up to 60 cycles. After every 10 cycles, the physico-mechanical characteristics of the sample, including porosity (n), Brazilian tensile strength (BTS), point load index (PLI), and P-wave velocity (Vp) were determined. Moreover, the pores structure modification of the sample subjected to aging tests was examined through scanning electron microscopy (SEM). Data analyses revealed that the sample is highly vulnerable to the AA and SC processes but is durable against FT, WD, and HC actions. These results were in good agreement with the SEM data such that the sample exposed to AA and SC underwent more changes in their pore structure compared to FT, WD, and HC. Among the physico-mechanical characteristics, the Vp and PLI had the highest and the lowest accuracy, respectively, in the durability evaluation of the sample exposed to aging tests. Based on the data analysis, limestone wastes can be used as aggregate in concrete in environments with the possibility of FT, WD, and HC. However, this type of concrete is not suitable for conditions with occurrences of the AA and SC. Finally, in addition to reducing the environmentally harmful impacts of the study area, using limestone wastes as aggregate in the construction of concrete can also be a practical solution for sustainable development from an economic viewpoint. The results of the present study can be used for assessing limestone wastes produced in other areas of Iran and the world.

Migration of Water and Salt in Confined Archaeological Complexes: Comprehensive Investigation Below the Third Courtyard of the Prague Castle

ABSTRACT Archaeological complexes and open-air museums must navigate the delicate balance between their societal role and preserving the displayed heritage. Sheltering from atmospheric hazards is a common preservation strategy, yet it introduces new degradation challenges. This study focuses on the persistent material deterioration, heightened moisture content, and salt efflorescence observed in protected excavations beneath Prague Castle’s third courtyard. The objective is to identify and analyse primary sources and pathways of water infiltration, comprehend complex interactions with masonry, and propose conservation strategies to mitigate the degradation. Through detailed field observations, using various moisture sensors, hydrochemical and salt analyses, rainwater emerges as the primary source of damp masonry and the transporting agent of salt-forming ions. Two penetration mechanisms were observed: ingress through perimeter walls and capillary rise where groundwater is present. Evaluation of moisture measurement methods underscores the superiority of the microwave method for historic masonry and the uranine-probe method’s efficacy for capillary water detection. Addressing water infiltration and salt accumulation challenges, we recommend preventive measures: (i) prevent water infiltration, seepage, and ingress; (ii) reduce salt concentrations; and (iii) stabilise site climate to mitigate salt crystallisation transitions. These recommendations extend beyond the study site, offering valuable insights for similar confined archaeological complexes.

Driving mechanisms and hydro‐chemical variation for assessing salt‐induced weathering of sandstone in grotto relics

AbstractSalt weathering is considered as one of the most damaging processes acting on cultural heritage sites and salt crystallization significantly contributes to the deterioration of natural sandstone in grotto relics. A laboratory partial immersion experiment was carried out to elucidate how humidity influences the salt‐induced weathering in grotto relics. Field environmental observations at the Yungang Grottoes were conducted to evaluate the differences between experimental endeavours and field observations. Superficial salt accumulation was characterized by hydro‐chemical and quantitative atomistic analysis. It revealed the co‐existence of calcium sulphate and magnesium sulphate, with a Ca/Mg molar ratio of 0.27 at RHam and 4.13–18.15 at a constant RH. An average increase of 165 mg/L in Na+ concentration and 120.7 mg/L in Mg2+ concentration in the groundwater was detected after immersion, which was attributed to the dissolution of the sandstone rock. The reduction of 322.5 mg/L in the SO42− concentration in the groundwater after partial immersion shows that capillary forces influence the migration of SO42− from the immersion solution. Calcium sulphate and magnesium sulphate accumulation with a Ca/Mg molar ratio of 0.03–0.17 in the field environment is strongly correlated with the occurrence of salt efflorescence. The upward transport of soluble salt was driven by capillary forces after partial immersion in the groundwater collected from the Yungang Grottoes. It then migrated from the interior to the exterior of the sandstone specimen due to evaporation. Salt efflorescence formed on the upper exposed stone close to the capillary fringe owing to the combined effects of condensation, hygroscopicity and evaporation. These processes were driven by wetting–drying and dissolution–crystallization cycles in response to fluctuating environmental conditions. These results contribute to a better understanding the mechanism of salt‐induced weathering and provide a basis for future conservation to mitigate the harmful impact of salts in heritage sites.

Unraveling the intricate fouling behaviors of landfill leachate components during membrane distillation concentration toward zero liquid discharge

Membrane distillation (MD) holds promise for cost-effectively concentrating wastewater toward zero liquid discharge (ZLD), while membrane fouling problems still hinder its practical application, especially for high-strength wastewater containing complex constituents. This study investigated the effects of different foulant components in actual landfill leachate (LFL) on MD deep concentration performances. The fouling behaviors of LFL components were revealed by comprehensively characterizing and analyzing the physicochemical properties of the fouling layers and membrane-foulant interactions. Results illustrated that suspended solids (SS) and macromolecular organics (MO) played significant yet distinct roles in fouling layer formation. SS (>0.45 μm, ∼24 % TOC) possessed strong adhesion energies with membrane surfaces and constructed the main skeleton of the fouling layer at the preliminary concentration stage; while MO (>20 kDa, 0.36 % TOC) deposition resulted in a densely packed fouling layer, influencing the salt crystallization potential and interfering with water and ammonia transport. In contrast, the low-molecular organics with the highest content (<20 kDa, ∼75 % TOC) were mainly electron-donor monopolar substances weakly adsorbed on the nonpolar membrane surface. Removing SS and MO from LFL notably prevented fouling layer formation and maintained high membrane efficacies (water flux decline mitigated from ∼50 % to ∼15 % and ammonia rejection increased from 71 % to 88 %), even as water recovery increased to 95 %. The findings of this work imply conventional anti-fouling strategies (e.g., complete removal or degradation of organic components) may have gone beyond what is necessary, and will inspire the development of simpler and greener methods to maintain membrane efficacy during high-strength wastewater treatment toward ZLD.

In situ visualization of salt crystallization in sub-/supercritical water environments

Elevated temperature and pressure conditions in sub-/supercritical water environments hinder the direct observation of salt crystallization phenomena, resulting in indeterminate salt crystal morphologies. In this study, an innovative experimental apparatus has been developed to conduct in situ investigations into the crystal morphology of various types of inorganic salts. The results indicate that the critical temperature of the water-salt system is higher than that of pure water systems, with phase transition thresholds for saturated NaCl-H2O and KCl-H2O systems 671.4 K and 728.1 K, respectively. A distinct “flash crystallization” phenomenon is observed during the crystallization of inorganic salts, accompanied by different crystal morphologies. KCl crystals exhibit a dispersed particle form, NaCl crystals manifest in a finely fragmented accumulation form, and Na2SO4 crystals present transparent feather-like structures. The size of NaCl crystals formed on the surface of a Ni wire at 622.8 K through heterogeneous nucleation ranges from 200.4 μm to 450.9 μm. The crystallization characteristics of salt in sub-/supercritical water are influenced by various factors, including electric dipole moment interactions, common ion effect, the effect of type I salts on type II salts, and homo/heterogeneous nucleation.

Optimizing solar evaporation efficiency: integrating controllable water supply and efficient salt collection methods

Solar desalination presents a promising solution for providing high-purity fresh water in regions lacking sophisticated energy infrastructure. Specifically, the efficiency of solar-energy-driven interfacial evaporation relies on achieving a balance between supplied solar energy and the energy demand for evaporation through water supply management. Another significant challenge for practical application is salt crystallization on the photoabsorber surface. To address these issues, two strategies are proposed: I) Construction of a three-dimensional (3D) solar evaporator that achieves a balance between supplied energy and the heat energy required for interfacial evaporation (demand energy) by optimizing the height of the support structure and II) implementation of a tunable two-dimensional water supply path made of cotton. This not only facilitates optimal water supply for interfacial evaporation but also functions as a salt collection layer, enabling efficient salt collection post desalination. With the specific design of the proposed 3D solar evaporator, our device achieves a remarkable efficiency, approaching its performance limit (94%) with an evaporation rate of 2.30 kg/m/2/h, along with efficient salt collection and scalability. This work presents a novel approach for fabricating a cost-effective solar evaporator capable of consistently delivering affordable fresh water in remote areas.

Mineralogy and Morphology of Iraqi Sea Salt and Sabkhas

A few studies have investigated the morphology and mineralogy of the salt deposits in Iraq. These deposits have amassed in substantial amounts as a result of the rise in temperature, specifically during the summer season. This study aims to analyze and characterize the mineral composition, morphology, and salt crystallization of the sabkhas and sea salt. The physicochemical tests (X-ray Diffraction, X-ray fluorescence, Field Emission Scanning Electron Microscopy, and energy dispersive spectroscopy) were used in this study. Samples were collected from sabkha salts in Diyala, Al-Emara, and the sea salt in Al-Basra. These locations exhibit an important and unique distribution of precipitated salt. The study showed that a semi-arid to arid climate in small pools located in specific locations led to the generation of Sabkhas and sea salt through saltwater evaporation. After processing the samples, the half-and-quarter method was used to obtain a 20-gram sample from the investigated bulk substance. According to the XRD analysis, halite is the main evaporite mineral present in the samples, with calcite, anhydrate, gypsum, and bischofite following it in decreasing order of abundance. The predominant trace elements include sulfur (S), magnesium (Mg), calcium (Ca), aluminum (Al), silicon (Si), iron (Fe), and molybdenum (Mo). Sea salt from the Al-Fao in Al-Basra exhibits exceptional mineral concentration and forms cubic-shaped crystals due to excellent evaporation of seawater. The most common crystallization patterns found in sabkhas and sea salt consist of hopper shapes, cubic crystals, rhombic crystals, cryptocrystals, and tabular shapes. Each of these forms of crystallization occurs at ambient temperatures.

Characterization of Anisotropic Salt Weathering through Nondestructive Techniques Mapping Using a GIS Environment.

Doctrinal texts on architectural heritage conservation emphasize the importance of fully understanding the structural and material characteristics and utilizing information systems. Photogrammetry allows for the generation of detailed, geo-referenced Digital Elevation Models of architectural elements at a low cost, while GIS software enables the addition of layers of material characteristic data to these models, creating different property maps that can be combined through map algebra. This paper presents the results of the mechanical characterization of materials and salt-related decay forms of the polygonal apse of the 13th-century monastery of Santa María de Bonaval (Guadalajara, Spain), which is primarily affected by salt crystallization. Rock strength is estimated using on-site nondestructive testing (ultrasound pulse velocity and Leeb hardness). They are mapped and combined through map algebra to derive a single mechanical soundness index (MSI) to determine whether the decay of the walls could be dependent on the orientation. The presented results show that salt decay in the building is anisotropic, with the south-facing side of the apse displaying an overall lower MSI than the others. The relative overheating of the south-facing side of the apse enhances the effect of salt crystallization, thereby promoting phase transitions between epsomite and hexahydrite.

Resistance of consolidated lime mortars to freeze–thaw and salt crystallization cycles by different accelerated durability tests

The present study aimed at evaluating the performance of untreated and consolidated lime mortars, in terms of durability and possible “delayed incompatibility” of the consolidants. Lime mortars samples were treated by an aqueous solution of diammonium hydrogen phosphate (DAP treatment) and a dispersion of nanolimes (NL treatment). The samples were then subjected to accelerated ageing by different methods: (1) freeze–thaw cycles; (2) salt crystallization cycles based on the European standard EN 12370 (often considered as highly aggressive); (3) salt crystallization cycles according to a new recommendation proposed by the RILEM TC 271-ASC (designed to provide less aggressive and more reliable ageing). The results of the study showed that the DAP-based treatment was able to significantly reduce damage caused by freeze–thaw cycles and salt weathering cycles by the RILEM procedure. In the case of salt weathering by the EN procedure, some risk of “delayed incompatibility” was highlighted for DAP, which can be considered an outcome of the combination between the salt weathering procedure itself and the consolidating treatment. For both freeze–thaw and salt weathering by either procedure, the residual mechanical properties of DAP samples at the end of the cycles were significantly higher than those of the untreated references and of the NL samples, for which the effects of the NL treatment were very modest.

An assessment of the durability of untreated and water repellent-treated cultural heritage stone (Döğer tuff-Turkey) by salt mist and salt crystallization tests

Salt mist and salt crystallization tests were conducted to determine the resistance of the untreated and water-repellent-treated Döğer tuff samples to salt damage. The Döğer tuffs are of volcanic origin and consist of porous pyroclastic rocks. A series of characterization studies were performed to determine the physicochemical and chemical properties (XRF), mineralogical-petrographic characteristics (polarizing optical microscopy, XRD, and SEM), and pore-size distribution (MIP) of the Döğer tuff prior to the aging tests. Following the aging experiments, the changes in weight, ultrasound pulse velocity, uniaxial compressive strength, and variations in pore size distribution were examined in the tested tuffs. In addition, SEM studies were conducted to analyze the microstructures. The untreated tuff samples were more severely affected by salt crystallization. The increases in dry weight for untreated and water-repellent-treated Döğer tuff samples were 0.27% and 0.13% after 60 cycles of salt mist exposure and 7.2% and 3.76% after salt crystallization cycles using a sodium chloride solution, respectively. Both conditions resulted from the accumulation of NaCl crystals on the tuff surface and within the pores. Salt crystal formation in a sodium sulfate solution led to dry weight change of 2.02% and 0.29% in the untreated and water-repellent-treated samples, respectively. The uniaxial compressive strength of the untreated tuff samples decreased by 36.71% in the presence of sodium chloride solution and by 72.58% in the presence of sodium sulfate solution. The ultrasound pulse velocity values decreased in all tuff samples after the salt crystallization test. However, the Döğer tuff samples were still distinguishable after both tests and their physical integrity remained intact.

Capillary Imbibition Laws of Fresh–Brackish Waters in Sandstone

Understanding the capillary imbibition laws of brackish water in rocks is necessary to reveal the mechanism of fluid, salt, and ion transport. In this study, we investigated the capillary imbibition laws of a Na2SO4 solution of different concentrations in sandstone by measuring the parameters of water absorption mass, water migration front height, nuclear magnetic resonance (NMR) T2 spectra, and stratified moisture distribution. The results indicate the following: (1) With an increase in the salt solution concentration, the water absorption rate of samples increases, specifically manifested in an increase in the rate of absorption mass and a rising rate of the absorption front. (2) With an increase in the salt solution concentration, the total NMR signals in samples measured at the end of water absorption decreases; that is, the total amount of water absorption decreases. (3) When the solution concentration exceeds 0.50 g/L, variations in the NMR signal of samples and the absorbed water mass over time are not synchronic and are even opposite at some stages. Based on the capillary dynamic theories of liquid, the influence of salts on solution properties and the modification of the pore structure by crystallization are considered when discussing the underlying mechanism of capillary imbibition in sandstone. By calculating the physical properties such as the density, viscosity, surface tension, and contact angle of solutions with different concentrations, the imbibition process does not exhibit any significant variation with the difference in the properties of the liquid. The equivalent capillary radii of the samples at varying salt concentrations are obtained by fitting the capillary dynamics curves with the theoretically calculated values. The equivalent capillary radii of samples in higher salt concentrations are larger, i.e., the difference in capillary imbibition laws introduced by the salt concentration should be attributed to modifications to the pore structure caused by salt crystallization.

Study on the Damage of Fiber-Reinforced Seawater Sea Sand Concrete by Freezing and Thawing of Seawater.

The use of seawater and sea sand as replacements for fresh water and river sand in the preparation of seawater and sea sand concrete can effectively address issues such as high transportation costs, extended construction periods, and resource wastage. Nevertheless, in northern coastal areas, the problem of concrete durability in the complex and changing marine environment is more prominent. Research on the durability of seawater sea sand concrete is beneficial to the widening of its application range. To investigate the impact of glass fiber (GF) and polyvinyl alcohol fiber (PVA) with different blending methods on the seawater freeze-thaw resistance of seawater sea sand concrete (SSC), corresponding specimens were prepared, and seawater freeze-thaw cycling tests were conducted. By adopting the slow-freezing method and combining macro-structure and micro-morphology, the damage mechanism and the deterioration law of fiber-reinforced SSC under seawater freezing and thawing were investigated. The results indicate that, macroscopically, the incorporation of GF and PVA can effectively mitigate the damage to the matrix and reduce the effects of external erosive substances on the rate of strength loss, the rate of mass loss, and the relative dynamic elastic modulus. After 75 cycles, the SSC with a total volume doping of 0.3% and a blending ratio of 1:1 showed a 41.23% and 27.55% reduction in mass loss and strength loss, respectively, and a 29.9% improvement in relative dynamic elastic modulus compared with the basic group. Microscopic analysis reveals that the combined effect of freezing and expansion forces, the expansive substances generated by seawater intrusion into the interior of the matrix, and salt crystallization all weaken the bond between aggregate and mortar, leading to accelerated deterioration of the concrete. The incorporation of fibers enables the matrix to become denser and improves its crack-resistant properties, resulting in a better durability than that of the basic group. The damage prediction model established by the NSGM(1,N) model of gray system theory exhibits high accuracy and is suitable for long-term prediction, accurately predicting the damage of seawater sea sand concrete under seawater freeze-thaw coupling.

Experimental Study on Salt-Bearing Sandstone Samples Under the Change of Temperature and Humidity Cycle

ABSTRACT Salt crystallization is a common type of disease in grottoes. Due to the change in temperature and humidity, the soluble salt originally existing in sandstone will have a negative impact on the protection of rock relics. In this study, sandstone samples containing Na2SO4 solution and distilled water were used to study the difference in sample damage under the condition of temperature and humidity cycle changes. It was found that the damage degree of samples containing soluble salts was much higher than that of salt-free samples, especially under the influence of freeze-thaw cycles. With the increase of freeze-thaw cycles, the internal friction angle and wave velocity of sandstone decrease linearly, while the surface hardness, tensile strength, and cohesion decrease exponentially. In addition, the damage caused by freeze-thaw cycles and dry-wet cycles develops from the inside to the outside of the rock sample, which is manifested by the increase in the number of macropores and the emergence of new pores. The different combinations of several effects lead to different changes in pore structure and mineral composition of the samples under the four conditions. The research results are helpful in providing a scientific basis for the disease control of stone cultural relics.

Elastic, Janus 3D evaporator with arch-shaped design for low-footprint and high-performance solar-driven zero-liquid discharge

Solar-driven zero-liquid discharge (ZLD) is a promising wastewater management strategy for freshwater recovery and solid waste harvesting. However, practical application of the solar-driven ZLD is severely constrained due to its low evaporation efficiency, large footprint, and rapid salt accumulation. Here, we present a Janus arch-shaped solar-driven evaporator (▪) comprising a hydrophobic top photothermal layer for effective light absorption, solar-thermal conversion, and vapor evaporation, which exhibits an evaporation rate of 2.82 kg∙m−2∙h−1 in pure water. The design also includes shapable delignified longitudinal wood (D-L-wood) serving as the hydrophilic bottom water transport layer, which enables dual-directional saltwater transportation and salt crystallization. D-L-wood, with numerous aligned channels, exhibits a low thermal conductivity of 0.04 W·m−1·K−1 along perpendicular direction and can effectively localize heat on the photothermal layer of the evaporator. D-L-wood has excellent hydrophilicity, and the salty water can be transferred quickly along both ends of the wood, providing sufficient salty water for rapid evaporation. The anisotropy of the wood makes the heat transfer quickly along the channel, improving the thermal management ability of the evaporator. Moreover, during vapor evaporation on the hydrophilic-hydrophobic interface, salt is crystallized at the hydrophilic layer, resulting in an enhanced anti-salt performance, a 1.5 folds evaporation rate compared with non-Janus evaporator after 15 h test. Under the conditions of a salt concentration of 3.5 %, a high salt harvest performance of 62.4 g∙m−2∙h−1 can be obtained under AM 1.5 solar irradiation. The arch-shaped design fully utilizes the upper space and effectively reduces evaporator footprint, resulting in an evaporation area to footprint ratio of 1.57:1. The designed evaporator can also be utilized for ZLD treatment of other heavy metal polluted water including Cu2+, CrO42−, Co2+, and so on. Therefore, the Janus-arch-shaped, solar-driven evaporator enables a potentially low-footprint, low-cost, scalable, and practical ZLD strategy for sustainable wastewater treatment.

Novel strategy for improved sylvite flotation through controlled crystallization

By understanding minerals as crystals, a crystallization-controlled methodology was performed to enhance the floatability of soluble minerals. Here, aimed strategies were applied to modulate the crystallization of KCl salt to grow crystals with various shapes as cubic-, hopper- and needle-like structure. Stereoscope and scanning electronic microscopy (SEM) helped to unveil the morphologies where X ray diffraction (XRD) characterized their high crystallinities. Afterwards, Atomic Force Microscope (AFM) was performed to research the crystallizing behaviors that cubic-like structure was obtained by turbid fast growth, while hopper-like structure formation was due to the constant high supersaturation and needle-like crystal occurred under still fast crystallization. Flotation tests with octadecylamine hydrochloride (ODA) as collector demonstrated the floatability of samples obeyed the order as needle-like (96.19 %) > hopper-like (81.59 %) > cubic-like (80.08 %) KCl samples. The mechanism was studied by surface area and related interaction tests. BET result demonstrated the highest surface area of needle-like structure than that of hopper-like and cubic-like structure. Besides, induction time combined with adhesion & desorption force tests further explained the better interaction of needle-like sample with bubble than cubic-like sample. While the special structure of hopper-like structure with lower weight but inner filled solution resulted in its near equivalent floatability with cubic-like sample. In conclusion, a new strategy for promoting flotation behavior by designing the crystallization of soluble KCl was proposed, shedding some light on further application on other soluble or semi-soluble minerals.

Inclined solar interface evaporation system with downward steam generation for efficient desalination and salt crystallization positioning

Solar-driven Interfacial Vapor Generation (SIVG) has been recognized as a potentially effective method of converting seawater into potable freshwater resources. In this work, we employed a straightforward approach to cultivate CuS and polypyrrole on copper foam as an solar absorber, while sterilized face towels served as water an evaporation interface and water transport sites. An inclined steam blocking evaporator with a salt-out part that attracts salt aggregation was ingeniously designed to improve the salt-resistant performance. Even in 15 wt% brine, the evaporation equipment maintained a stable and high evaporation rate, with an average evaporation rate of about 1.588 kg m−2 h−1 under 1 solar illumination. More particularly, in order to improve the water collection rate, a beveled condensers placed at the bottom of the steam blocking evaporator was customized, so as to shorten the steam condensation path and achieve internal water collection. Therefore, the water collection rate of the evaporator is as high as 2.238 kg m−2 h−1 and water collection efficiency is 85.90 %. Additionally, the evaporation device can effectively purify heavy metal ions and organic matter. This study can provide a new idea for the design and performance improvement of solar interfacial vapor generation and water collection device.

Highly efficient three‐dimensional solar evaporator for zero liquid discharge desalination of high‐salinity brine

AbstractSolar‐driven interfacial evaporation is a promising technology for freshwater production from seawater, but salt accumulation on the evaporator surface hinders its performance and sustainability. In this study, we report a simple and green strategy to fabricate a three‐dimensional porous graphene spiral roll (3GSR) that enables highly efficient solar evaporation, salt collection, and water production from near‐saturated brine with zero liquid discharge (ZLD). The 3GSR design facilitates energy recovery, radial brine transport, and directional salt crystallization, thereby resulting in an ultrahigh evaporation rate of 9.05 kg m−2 h−1 in 25 wt% brine under 1‐sun illumination for 48 h continuously. Remarkably, the directional salt crystallization on its outer surface not only enlarges the evaporation area but also achieves an ultrahigh salt collection rate of 2.92 kg m−2 h−1, thus enabling ZLD desalination. Additionally, 3GSR exhibits a record‐high water production rate of 3.14 kg m−2 h−1 in an outdoor test. This innovative solution offers a highly efficient and continuous solar desalination method for water production and ZLD brine treatment, which has great implications for addressing global water scarcity and environmental issues arising from brine disposal.