Salt Harvesting Research Articles

Surface patterned polyvinyl alcohol/CNT hydrogels for sustained solar powered high concentration brine desalination and salt harvesting

Solar-driven interfacial evaporation is an attractive way to achieve water purification. However, high water evaporation rates often result in the precipitation of salt crystals on the surface of the evaporator leading to decay of the evaporation efficiency over time, which makes it difficult to balance high water evaporation rates with salt resistance. Herein, an anisotropic polyvinyl alcohol/CNT hydrogel is constructed by directional freezing and surface patterning. The polymer backbone formed by the polyvinyl alcohol chains interacts with the water clusters to reduce the evaporation enthalpy of water and the absorbed water can be released by squeezing the hydrogels due to the micron-sized vertically aligned pores. More importantly, by designing the structure of the hydrogels surface, the gas–liquid interface of the evaporators can be increased while the growth direction of the salt crystals can be controlled. As a result, the water evaporation rate can be increased from 3.26 kg m-2h−1 to 3.69 kg m-2h−1 under one sun irradiation through surface patterning. After 50 h of continuous operation in 10 wt% NaCl solution under one sun irradiation, the water evaporation rate gradually increases and a large amount of salt collection is collected, which proves its satisfactory salt resistance.

Superhydrophobic pancake-like graphene oxide for zero liquid discharge solar desalination of real brines

Solar interfacial desalination offers a promising solution to meet the demand for portable water, especially in arid regions. Although various materials have demonstrated high solar-to-steam conversion efficiencies in concentrated solutions, most studies have utilized simulated solutions rather than real seawater. Herein, we developed a pancake-like graphene oxide photothermal membrane with superhydrophobic properties optimized for interfacial heating to desalinate real seawater and brine. Under 1 sun, the membrane efficiently achieves a sustained high evaporation rate of 1.23 kg.m−2.h−1 with a photothermal conversion efficiency of 80 %, while remarkably facilitating salt harvesting. Notably, the membrane maintained stable performance and exhibited no salt accumulation on its surface when tested outdoors with real seawater, demonstrating its practical scalability. The membrane exhibited long-term stability in desalination processes, with full performance restoration through an energy-free cleaning method. These results highlight a potential pathway toward zero-liquid discharge desalination.

Cost-Effective Salt Harvesting: Efficient and Sustainable Production through Technological Innovation

Maximizing the quantity, quality, and cost-efficiency of salt production requires innovative approaches. This study presents a novel geo-membrane (GM)-based salt production technique that significantly improves salt yield and quality for Indian salt producers. The GM method is simple to implement across various salt production facilities, requiring only basic equipment. Compared to traditional methods, statistical analyses demonstrate substantial improvements in both the quantity and quality of salt produced with the GM method. The process enhances salt purity by 12–15%, reduces production costs by 15-20%, and prevents brine leakage, optimizing solar energy utilization in crystallization ponds. Keywords: salt production, geo-membrane, salt crystallization pond, cost-efficiency,sustainability

Novel mushroom-like cotton-based evaporator for simultaneous freshwater production and salt harvesting via edge-preferential crystallization

Solar-driven interfacial evaporation (SDIE) has emerged as a promising technology to alleviate the global freshwater scarcity. However, the simultaneous collection of water and salt as resources while maintaining stable evaporation rate without salt contamination at the evaporation interface remains a huge challenge. Herein, we report a novel mushroom-like cotton-based evaporator, inspired by the vertical stem and inclined caps of mushrooms, for simultaneous freshwater production and salt harvesting. By depositing polyaniline (PANI) and carbon nanotubes (CNTs) onto the cotton fabric (CF), an evaporation rate of 1.88 kg m−2h−1 and a high solar evaporation efficiency of 99.4 % can be achieved in 3.5 wt% NaCl solution under one solar irradiation. Furthermore, a significant water collection efficiency of 70.2 % and a high salt harvesting rate of 42.1 g m−2h−1 can be derived. Even exposed to high-concentration (15 wt%) brine, our design still effectively prevents salt contamination. The distinctive edge-preferential crystallization not only avoids the salt contamination but also promotes the salt harvesting, due to the capillary force, the criss-cross water channels from the nature of cotton cloth, as well as the gravity-assisted water transport of the “mushroom cap” during evaporation. In addition, the low thermal conductivity (0.163 W m−1 K−1) of the photothermal layer with the integration of PANI and CNTs, as well as the vertical water upward transport via the “mushroom stem” effectively reduce the heat loss. This research holds great potential for seawater desalination applications with the comprehensive utilization of seawater resources.

Challenging the Conventional Advent of Agriculture with a Salt Harvesting Industry of Early Neolithic Hunters

Early Neolithic Sapiens “Hunters” developed a sophisticated combination of processing their animal carcasses, tanning hides and skins and enabling salts and osmosis dehydration to sanctify their protein victuals. Primitive abattoir industry was enabled by the discovered use of critical quantities of common salt produced in open brine irrigated “fields” and accelerated by the corralling of funnel driven wild animal herds in the early Stone Age. Undissolved salts form where high temperatures and low rainfall create conditions of evaporation and transpiration exceed precipitation. Through capillary action, water containing salts deep in the soil is pulled up to the dry topsoil. As this water evaporates from the soil, the once leached salts are left behind. With no water to dissolve the salts or carry them away, they begin to accumulate in the topsoil. The growth and “gathering” or farming of salt crystals in fields it is hypothesized, has possibly been misinterpreted as evidence of a much later advanced plant cereal and crop spatial agriculture. This paper suggests that an earlier Hesiod metallic Sodium Age, cut short the Paleolithic Stone Age, pre-empting Hesiod’s, Copper, Bronze and Iron ages, and arable food cultivation, to first enable the sanctity and purity of sustaining protein meat.

Multiphase solar evaporator for localized salt harvesting and in-depth water purification

Solar-driven interfacial evaporation (SIE) has been receiving more and more attention on the stage called “Sustainable Development”. However, pursuing a rational coexistence of steady-state evaporation, endogenous resource recovery, and water decontamination in solar evaporators is still a great challenge. To address this problem, a one-dimensional water transport pathway chitosan-based multiphase evaporator (OCHE) was fabricated for simultaneous Marangoni-driven salt mitigation and dye adsorption while solar vapor generation. Due to the efficient energy utilization and water supply, OCHE achieves a water evaporation rate of 1.767 kg m−2 h−1 with an energy efficiency of 96.87% under one sun illumination. More importantly, the 1D water pathway induces directional solute capillary convection and thermocapillary convection in evaporator when OCHE is working in high-salinity brine, leading to localized salt harvesting driven by Marangoni-driven liquid transport. Moreover, OCHE exhibits the good adsorption capacity for methylene blue (MB) and methyl orange (MO). This versatile multiphase evaporator provides a new insight into the design of next-generation eco-friendly, salt-resistant, and in-depth water purification solar evaporators.

Pyramid-shaped solar evaporator with high-efficient interfacial evaporation and salt harvesting capability

Solar-driven interfacial evaporation shows significant potential for addressing challenges associated with freshwater shortages and environmental pollution. In this study, a series of pyramid-shaped solar evaporators were fabricated to achieve highly efficient solar interfacial evaporation. The optimized triangular pyramid evaporator exhibits exceptional adaptability and stability in seawater desalination and wastewater purification, thanks to its excellent light capture and photothermal conversion capacity, controlled water supply, effective thermal management, and energy input from the environment. It maintains a high evaporation rate and energy efficiency even in highly concentrated saltwater and strongly acidic or alkaline solutions. The 3D conical evaporation structure promotes top-preferential crystallization, directing the crystallization process towards the apex and facilitating efficient spatial salt harvesting. The collected condensate meets the drinking water requirements set by the World Health Organization (WHO) and the US Environmental Protection Agency (EPA). Under outdoor evaporation conditions, the evaporator achieves a daily freshwater production of 24.93 and a salt production of 2.09 kg m−2 d−1, fully satisfying the needs of a typical three-person household. Our microstructure control strategy for enhancing solar interfacial evaporation offers valuable insights and inspiration to researchers aiming to improve the performance of 3D solar evaporators.

A Robust Capillary Electrophoresis with Laser-Induced Fluorescence Detection (CE-LIF) Method for Quantitative Compositional Analysis of Trace Amino Acids in Hypersaline Samples.

The search for life in our solar system can be enabled by the characterization of extreme environments representing conditions expected on other planets within our solar system. Molecular abundances observed in these environments help establish instrument design requirements, including limits of detection and pH/salt tolerance, and may be used for validation of proposed planetary science instrumentation. Here, we optimize capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) separations for low limit of detection quantitative compositional analysis of amino acids in hypersaline samples using carboxyfluorescein succinimidyl ester (CFSE) as the amine-reactive fluorescent probe. Two methods were optimized for identification and quantification of proteinogenic amino acids, those with and those without acidic side chains, with limits of detection as low as 250 pM, improving on previous CFSE-amino acid CE-LIF methods by an order of magnitude. The resilience of the method to samples with high concentrations of Mg2+ (>4 M diluted to >0.4 M for analysis) is demonstrated on a sample collected from the salt harvesting facility South Bay Salt Works in San Diego, CA, demonstrating the highest Mg2+ tolerance for CE-LIF methods used in amino acid analyses to date. This advancement enables the rapid and robust analysis of trace amino acids and the search for biosignatures in hypersaline systems.

Salt Production and the Geoheritage of the Huesca Province (Spain): Context, History, and Potential as an Educational Resource

Salt harvesting through natural solar evaporation of salt brines is a practice notably abundant in the Iberian Peninsula. Such activity has been relevant for human consumption, food preservation, livestock feed, and various industries throughout history. The objective of this research is to analyze the productive history and conservation state of the salt evaporation ponds located in Naval and Peralta de la Sal (Huesca, Spain), as well as their didactic potential. These saltworks are associated with clay and gypsum levels from the Upper Triassic (Keuper). The earliest written records of salt production in the area date back to the 10th century, but they were exploited as early as the Bronze Age. Remains of most of the ponds and some buildings are still preserved and are easily accessed, which makes them very interesting from an educational perspective. Both on-site and off-site activities can be carried out to analyze their historical and current significance through modeling and argumentation practices. This can lead to a better understanding of how geology relates to everyday life and facilitate the development of positive attitudes among students towards geoheritage while raising awareness about its preservation and preventing its degradation.

Tourism and work environment in sea salt pans

ABSTRACT The present study focuses on the perceptions of workers in traditional salt pans that receive visits from tourists in the south of Portugal. Methodologically, an ethnographic approach is taken. It is found that, on the one hand, for sea salt workers, the main incentive in their labour is the freedom to work outdoors. On the other hand, for tourists, their main motivations to visit the salt pans are related to the benefit of being outdoors in natural spaces, observe the telluric process of salt harvesting and participate in leisure activities related to this type of space. These findings also suggest that tourism in traditional salt pans enhances cultural heritage values and brings more economic sustainability to the activity.

Polyoxometalates‐Modulated Hydrophilic‐Hydrophobic Composite Interfacial Material for Efficient Solar Water Evaporation and Salt Harvesting in High‐Salinity Brine

Solar vapor generation (SVG) represents a promising technique for seawater desalination to alleviate the global water crisis and energy shortage. One of its main bottleneck problems is that the evaporation efficiency and stability are limited by salt crystallization under high‐salinity brines. Herein, we demonstrate that the 3D porous melamine‐foam (MF) wrapped by a type of self‐assembling composite materials based on reduced polyoxometalates (i.e. heteropoly blue, HPB), oleic acid (OA), and polypyrrole (PPy) (labeled with MF@HPB‐PPyn‐OA) can serve as efficient and stable SVG material at high salinity. Structural characterizations of MF@HPB‐PPyn‐OA indicate that both hydrophilic region of HPBs and hydrophobic region of OA co‐exist on the surface of composite materials, optimizing the hydrophilic and hydrophobic interfaces of the SVG materials, and fully exerting its functionality for ultrahigh water‐evaporation and anti‐salt fouling. The optimal MF@HPB‐PPy10‐OA operates continuously and stably for over 100 h in 10 wt% brine. Furthermore, MF@HPB‐PPy10‐OA accomplishes complete salt‐water separation of 10 wt% brine with 3.3 kg m−2 h−1 under 1‐sun irradiation, yielding salt harvesting efficiency of 96.5%, which belongs to the record high of high‐salinity systems reported so far and is close to achieving zero liquid discharge. Moreover, the low cost of MF@HPB‐PPy10‐OA (2.56 $ m−2) suggests its potential application in the practical SVG technique.

Dual-hydrophilic Janus evaporator for Long-term and efficient Bimode solar evaporation

Solar steam generation has emerged as a promising and sustainable technology to solve the global water scarcity. However, the fabrication of low-cost and high-efficiency evaporator with long-term stability remains a great challenge. Herein, a dual-hydrophilic Janus evaporator coupled with inclined isolating structure is fabricated to realize long-term efficient solar evaporation and flexible salt manipulating, where the upper electrospun Mo2C-C@PAN membrane serves as the evaporation layer and the bottom nonwoven fabric functions is used as mass transporting layer. The encapsulating feature of the Mo2C-C@PAN enables better energy confinement and reduces the usage of solar absorber by ∼50 % without deteriorating the evaporation performance. The hydraulic conductivity difference prevents the Marangoni effect inner the Janus evaporator, while the inclined isolating structure enables unidirectional ions transporting. With features of adequate water transport, enhancement of energy confinement, and salt manipulation, the constructed inclined Janus evaporators can not only work stably for 200 h in 10 wt% NaCl solution without salt accumulation, but also achieve efficient salt harvesting with rate of ∼260 g m−2 d−1 under one sun. This study provides new possibilities for a dual-hydrophilic Janus evaporator for a long-term, efficient, and synergistic extraction of fresh water and mineral salt resources.

Solar-thermo-radiative evaporator for continuous steam generation and salt harvesting

Solar-driven interfacial evaporation attracts great attention in desalination and wastewater treatment. However, the gradual decline of evaporation rate caused by salt accumulation restricts its long-term operation. Here, we developed a new solar-thermo-radiative evaporator that uses infrared photons as heating source to promote the interfacial evaporation with edge-preferential crystallization and gravity-assisted salt harvesting. The solar absorber exhibits broadband light-harvesting and converts the sunlight into mid-infrared radiation, localizing the radiative heat at the neighboring water-film for directly phase-change evaporation. Benefiting from the self-manipulated salt water transport, this evaporator spatially isolates the crystallized salts from the evaporative surface, achieving an evaporation rate (0.71 kg∙m−2∙h−1) with high steam temperature (＞80 °C) under 1 sun. As the salt is continuously expelled at the edge of the evaporator, the salt-harvesting performance (36.25 g∙m−2∙h−1) is achieved during 40 h of non-stop solar desalination without affecting water evaporation. Such non-contact design thus circumvents the salt-blocking and/or contamination issue on the solar absorber, making it uniquely suitable for applications in desalination or water purification, with an added benefit of resources recovery.

3D-printed solar evaporator with seashell ornamentation-inspired structure for zero liquid discharge desalination

Solar-driven interfacial evaporation has enormous promise for fresh water recovery and salt harvesting, but salt accumulation-related challenges stand in its way. Herein, we report a spined groove-ridge pairs inspired by the shell ornamentation of the Vasticardium vertebratum, which addresses salt accumulation by artfully integrating salt reflux into localized salt crystallization. The seashell-mimetic radial V-groove array enables the 3D evaporator to transport water rapidly and directionally, resulting in high-performance water evaporation (∼95% efficiency) and localized crystallization. The periodic spines enlightened by the spine-bearing ridge on the seashell provide considerable micro-unit salt reflux. The 2-in-1 integration design endows the three-dimensional evaporator with superior solar-driven zero liquid discharge and excellent long-term salt resistance even when dealing with high-salinity brine (20 wt% NaCl) and a series of heavy metallic salt solutions. Our design offers a new alternative solution to avoiding salt scaling and could advance locally crystallized solar evaporators towards practical applications.

Double-Sided Suspending Evaporator with Top Water Supply for Concurrent Solar Evaporation and Salt Harvesting.

Solar evaporation of seawater is promising to mitigate the fresh water scarcity problem in a green and sustainable way. However, salt accumulation on the photothermal material prevents the system continuous operation, and the water supply driven by capillary force severely limits the scale-up of the evaporators. Here, we demonstrate a double-sided suspending evaporator with top water supply and a surface water distributor for high-efficient concurrent solar evaporation and salt harvesting for large area applications. Both sides of the evaporator can evaporate water with automatic salt harvesting from the edge concurrently. Top water supply gets away from the limitation of capillary force for a larger area application and completely cuts off the heat leak to the bulk water below for higher efficiency. The energy conversion efficiency reaches 95.7% at 1.40 kg·m–2·h–1 with deionized water under 1 sun with a remarkable low surface average temperature (28.2 °C). Based on the simulation and experiment, a novel radial arterial water distribution system is developed to efficiently distribute water on a larger evaporation surface. The water distribution system alters the water transport path in the evaporation surface, leading to salt accumulation on the surface body, where salt is unable to be harvested by gravity automatically. This problem is further resolved by cutting out the salt accumulation area (16.4%) on the surface to create a floriform evaporator, which forcedly exposes the salt at the edge for harvesting. Up to70 h continuous solar evaporation from salt water at a rate of 1.04 kg·m–2·h–1 with concurrent salt collection on this floriform evaporator is achieved. This work resolves water supply and salt accumulation problems in scaling up the solar evaporators and advances the structural design of evaporators for high-efficient large area applications.

From Materials to Devices: Rationally Designing Solar Steam System for Advanced Applications

Solar-driven water vaporization for freshwater production attracts significant interest due to its potential for solving global water scarcity problems. In this review, the recent development of management strategies via diverse rational designs in terms of light, thermal, water, and anti-salt fouling for enhancement of overall vaporization efficiency, is summarized. For device design, a host-guest concept is raised for clearly elaborating the detailed function and interaction between the solar-thermal material and the substrates. In addition, the rising technologies derived from solar vaporization, such as energy generation, photocatalysis, dehumidification, salt harvesting, sterilization, and biofuel production, are also highlighted. This review provides a new horizon toward the development of solar technologies and practical applications.

Microfluidic Salinity Gradient-Induced All-Day Electricity Production in Solar Steam Generation.

Synergistic generation of freshwater and electricity using solar light would be an ideal solution for global freshwater challenges and energy demands. Recently, interface solar steam generation has been considered one of the promising cost-effective alternatives for freshwater generation. Here, we have systematically maintained the salinity gradient within two-legged paper-based microfluidic channels to transport wastewater from the reservoir to the evaporator surface and generate electricity all-day-long. Flowing seawater (3.5 wt % NaCl) on one leg and tap water on the other of the water-conducting channels connected to a conical evaporator, we achieved an average open-circuit voltage (VOC) of 150 mV and a short-circuit current of 6.5 μA across each channel along with a water evaporation efficiency of 88%. As the VOC depends only on the ion concentration gradient within the channel in the direction perpendicular to the water flow, the electricity generation persists throughout the day and can be tuned by varying the salinity. Increasing the salt concentration of the seawater to 20 wt %, the VOC increased to 250 mV in a single channel. In an evaporator connected with four such channels, we achieved a maximum output power density of 9.9 mW m-2 in a series combination without sacrificing the evaporation rate. Furthermore, removing agglomerated salt from the evaporator surface, we harvested salt at a rate of 0.33 kg m-2 h-1. Therefore, our approach provides an alternative way of freshwater generation, salt harvesting, and all-day-long electricity production simultaneously.

High‐Performance Integrated Solar Steam Generator for Synergetic Freshwater Production, Salt Harvesting, and Electricity Generation

Photothermal desalination driven by solar energy has emerged as a promising strategy for freshwater and clean energy production. One of the great challenges in interfacial evaporation is simultaneous achievement of superior freshwater production, salt harvesting, and electricity generation in an evaporator. Herein, an all‐inclusive photothermal solar steam generator using high‐performance photothermic converting film is reported, featuring in interconnected fibrous network, broadband absorption, heat insulation, and unidirectional water transfer. The superior characteristics can readily form a constant salinity gradient in system during vaporization, not only realizing the spatial isolation of evaporation and salt crystallization zones to harvesting freshwater and salt separately, but more importantly achieving continuous electricity generation from salinity gradient power without trade‐offs. Such stable solar steam generator integrated with efficient photothermal converting material and rational structural design highlights the practical consideration toward solar distillation by deep desalination, which can not only sustainably achieve the freshwater and salt production, but collaboratively generate the electricity for emergency needs.

Umbrella evaporator for continuous solar vapor generation and salt harvesting from seawater

Solar vapor generation, which uses photothermal materials to desalinate seawater by evaporation, is a promising technology to mitigate the water scarcity problem, but its performance is hindered by large heat leak and salt accumulation problems. Here we report an umbrella evaporator that achieves efficient vapor generation and salt harvesting concurrently via double-sided evaporation and reveal the salt nucleation, growth, and falling mechanism. The evaporator reaches an evaporation rate of 1.25 kg m −2 ·h −1 under ambient conditions, and its continuous operation for vapor and salt production from seawater is demonstrated. The salt mobility on the evaporation surface determines whether the salt could accumulate at the edge, which is influenced by water supply, solar intensity, salinity, and Mg 2+ and Ca 2+ contents.A simple salt creeping test on a glass slide is developed to determine whether and to what extent seawater needs to be pre-treated for continuous operation. • Umbrella evaporator achieves a high efficiency via double-sided evaporation • Central water supply results in salt accumulation at edges • Salt grows from the front by wicking water through its porous structures • Salt creeping behaviors indicate if Ca 2+ and Mg 2+ content is below the lower limit Solar evaporation could mitigate water stress problems, but challenges remain in structural improvement of devices, salt accumulation, and salt harvesting mechanisms. Ma et al. show an umbrella evaporator that achieves efficient vapor generation and salt harvesting concurrently via double-sided evaporation and reveal the salt nucleation, growth, and falling mechanism of salt harvesting.

Brine shrimps adrift: historical species turnover in Western Mediterranean Artemia (Anostraca)

Brine shrimps (Artemia) have undergone geographic range and demographic expansions as a result of their interaction with humans since the beginning of salt harvesting. This interaction has favoured the expansion of some species but compromising the survival of others. Mediterranean native populations of Artemia salina from coastal salterns and lagoons are facing the presence and expansion of the introduced and invasive American species Artemia monica (= A. franciscana). However, this species could not be the only threat. Parthenogenetic populations of the Asian species A. urmiana and A. sinica are widespread along the Mediterranean and other areas of the world. In this work, with the use of large cox1 and mitogenomic datasets, phylogenetic and phylogeographic inferences, and a time calibrated tree, we confirmed the Asian origin and recent arrival of the current Western Mediterranean parthenogenetic populations of Artemia. In addition, the replacement of Iberian populations of A. salina by Asiatic parthenogenetic populations lead us to recognize parthenogens as invasive. Current salterns development and commercial importance of Artemia make human-mediated introduction probable. These results demonstrate again the impact that changing human interests have on population expansion or decline of species adapted to anthropogenic habitats. Artemia salina decline makes urgent the implementation of conservation measures such as its use in fish farming and salt production or its inoculation in inland salterns.