The research, led by K. Li and J. E. Dykstra of Wageningen University & Research together with A. N. Shocron of Ben-Gurion University of the Negev, P. Śledzik and S. Porada of Wroclaw University of Science and Technology, and H. H. M. Rijnaarts, tackles a deceptively simple question: when two competing technologies claim to be selective, how do you know which one actually performs better? The authors’ answer is that, until now, you often could not tell, because conventional selectivity metrics provide limited practical value when applied across different systems.

Selectivity matters far beyond the laboratory. In agriculture, irrigation water must be upgraded so that sodium and chloride are stripped away while nutrients remain. In industry, recovering valuable metals such as silver from streams contaminated with copper requires membranes and electrodes that discriminate between ions differing by only a single charge or a fraction of a nanometre in size. In environmental protection, the targeted removal of nitrate, fluoride or heavy metals from drinking water depends on the same underlying physics. The new paper situates itself squarely in this landscape of water treatment and resource circularity, where the difference between a good separator and a mediocre one is measured in energy, cost and sustainability.

To make their case, the researchers performed a rigorous comparative analysis of two leading electrochemical technologies: electrodialysis, or ED, and membrane capacitive deionization, known as MCDI. Electrodialysis drives ions through a stack of ion-exchange membranes using an electric field, with charged membranes acting as gates that admit some ions and block others. Membrane capacitive deionization works differently: ions are stored electrically in porous carbon electrodes, with ion-exchange membranes shielding each electrode from counter-charged species. Both technologies can be made selective, but they achieve selectivity through fundamentally different mechanisms, and the study reveals that their selective separation behaviour is not directly comparable under the traditional metrics.

The heart of the problem is representation. A typical selectivity number, such as a separation factor between two ions, compresses an entire separation process into a single value, discarding information about purity, water recovery and the degree of removal. A technology might achieve impressive selectivity while recovering only a trickle of usable water, or deliver high recovery while quietly failing to remove the target ion. Because each subfield reports its results in its own format, cross-technology comparison becomes an exercise in apples-to-oranges reasoning. The authors demonstrate this by mapping electrodialysis and MCDI results side by side, showing how the same underlying performance looks misleadingly different depending on the metric chosen.

Their proposed solution is an integrative framework in which selectivity, purity and water recovery can be visualized together on a single plot. Instead of collapsing performance into one number, the framework preserves the trade-offs that engineers actually face: how much of the target ion is removed, how much of the competing ion is left untouched, and how much water comes out the other end. By plotting separation results in this unified space, the researchers show that the advantages of different removal regimes become visible at a glance, allowing a flexible and concise analysis that single metrics cannot provide.

Perhaps the most striking findings concern two advantages that the analysis identifies as unique to membrane capacitive deionization. The first is electrode-enhanced selectivity: in MCDI, the carbon electrodes themselves contribute to discrimination between ions, beyond what the ion-exchange membranes provide. The second is more remarkable still. Because MCDI operates cyclically, adsorbing ions during charging and releasing them during discharge, the timing of the cycle can be tuned to exploit differences in how quickly different ions are absorbed and desorbed. The study shows that this cyclic operation enables what the authors call infinite selectivity, a regime in which target ions are completely removed while competing ions achieve zero removal, based purely on the distinct absorption and desorption dynamics of each ion species.

This time-dependent selectivity builds on a body of theory showing that in porous electrodes, ions do not all arrive at the same rate. Smaller, more mobile ions race ahead during the early stages of charging, while others catch up later. By cutting the adsorption phase at precisely the right moment, an operator can harvest a stream enriched almost exclusively in the target ion. The paper’s simulations, developed with COMSOL for the electrodialysis model and Maple for the MCDI model, trace these dynamics in detail, and the authors have made both codebases openly available through Code Ocean, a move that supports reproducibility and invites the community to build on their framework.

The implications reach across the water technology sector. For designers of electrodialysis stacks, the framework offers a way to quantify honestly how monovalent-selective membranes perform under realistic multi-ionic conditions. For the capacitive deionization community, it provides a common language for reporting the gains from modified electrodes, coating chemistries and cycle-timing strategies. And for decision-makers choosing between technologies for a specific application, whether softening hard groundwater, recovering nutrients from greenhouse drainage water or removing micropollutants, the single-plot visualization promises a more transparent basis for comparison than the fragmented metrics of the past.

The study also joins a growing conversation about measurement itself in separation science. Recent work in the literature has questioned how selectivity is reported in membrane-based separations generally, and this paper extends that critique into electrochemistry with a concrete alternative. By demonstrating that electrodialysis and MCDI behave in fundamentally different ways under equivalent conditions, the authors make a compelling argument that the field needs not just better materials but better ways of seeing what those materials do. As water scarcity intensifies and resource recovery becomes an industrial imperative, the ability to compare separation technologies on shared, meaningful terms may prove as important as the technologies themselves.

Subject of Research: Selective ion removal and selectivity metrics in electrochemical water separation technologies

Article Title: Comparative analysis of selective ion removal in electrochemical technologies reveals the need for a new data representation framework

Article References: Li, K., Shocron, A. N., Śledzik, P., Rijnaarts, H. H. M., Porada, S., & Dykstra, J. E. (2026). Comparative analysis of selective ion removal in electrochemical technologies reveals the need for a new data representation framework. Nature Water. https://doi.org/10.1038/s44221-026-00715-9

Image Credits: AI Generated

DOI: 10.1038/s44221-026-00715-9

Keywords: ion selectivity, electrodialysis, membrane capacitive deionization, water treatment, desalination, resource recovery, ion-exchange membranes, porous carbon electrodes, separation metrics, water recovery, electrochemistry, Nature Water

The scale of the challenge is staggering. China alone consumes roughly half of the world’s lithium, driven largely by its dominant position in the electric vehicle market, and has pledged to cut greenhouse gas emissions by 60 to 65 percent by 2030. Meanwhile, mining these metals generates vast quantities of tailings laden with heavy metals and chemicals. When improperly disposed of, these wastes contaminate water supplies, destroy biodiversity, and degrade soil — with acid mine drainage, in which sulfide minerals oxidize to produce extremely acidic runoff, posing the single greatest threat to water quality across large regions. Conventional recycling routes offer little relief: pyrometallurgical smelting is energy-hungry, while hydrometallurgical leaching demands aggressive acids and generates sludge and saline effluents of its own.

Membranes work on an entirely different principle. Instead of burning or dissolving entire waste streams, they act as molecular gatekeepers — semi-permeable barriers that allow some ions to pass while blocking others based on size, electrical charge, or specific chemical interactions. Pressure-driven systems such as ultrafiltration, nanofiltration, and reverse osmosis push liquid through these barriers, while electro-driven systems like electrodialysis use an applied voltage to steer ions toward oppositely charged electrodes. The review categorizes four main feed streams — battery leachates, acid mine drainage, salt-lake brines, and industrial effluents — each with distinct chemistries that demand tailored membrane approaches rather than one-size-fits-all solutions.

The most striking results come from lithium recovery. In acidic sulfate leachates from spent batteries, lithium exists largely as free Li+ ions while cobalt, nickel, and manganese form sulfate complexes. Negatively charged nanofiltration membranes exploit this difference: they repel the multivalent transition metal cations through electrostatic repulsion and size exclusion while allowing the smaller, singly charged lithium ions to permeate. One study cited in the review achieved 99.5 percent pure lithium carbonate after just two nanofiltration passes — approaching battery-grade material without harmful chemical additives. Another research group using polymer inclusion membrane electrodialysis, where selective carriers embedded in a PVDF-HFP polymer matrix bind lithium and cobalt ions, reported recoveries of 99.1 percent for lithium and 99.9 percent for cobalt, with a carbon footprint of just 3.1 kilograms of CO2-equivalent per kilogram of lithium recovered.

Separating lithium from magnesium in brines presents an even tougher puzzle because the two ions have similar ionic radii. Here, the review explains that the key lies in hydration energy: magnesium ions hold water molecules far more tightly than lithium does, giving Mg2+ a bulkier, more strongly bound hydration shell. Negatively charged nanofiltration membranes exploit this by electrostatically repelling the divalent magnesium while the monovalent lithium slips through more easily. Separating cobalt from nickel is harder still — both are divalent with nearly identical hydrated radii — so simple charge exclusion fails. Supported liquid membranes, which impregnate a porous support with a tailored organic extractant that reversibly binds one metal preferentially, offer a way forward, achieving extraction and stripping efficiencies of 85.7 and 83.2 percent for nickel in one reported case.

But the review is refreshingly honest about where membranes struggle. Real battery leachates are not clean laboratory solutions: they are acidic (often below pH 2), highly saline, loaded with organic residues from binders and electrolytes, and contain a shifting cast of competing ions. Under these conditions, membranes fail in chemistry-specific ways. Precipitation is the most common culprit — as pH, temperature, or ionic strength shifts, salts like calcium carbonate, magnesium hydroxide, and gypsum (calcium sulfate dihydrate) become supersaturated and crystallize on membrane surfaces, blocking pores and causing irreversible flux decline. Iron and aluminum hydrolyze into gelatinous hydroxides that clog membranes, while oxidants such as hydrogen peroxide and hypochlorite — often added during leaching — attack polyamide membranes chemically, degrading the polymer itself.

Long-term durability emerges as the review’s central concern. In one particularly revealing study, commercial NF270 and DK nanofiltration membranes were exposed to hydrochloric acid at pH 1 for up to 30 days. Both initially retained divalent ions at 96.5 percent or better, but NF270’s rejection dropped from 99.1 to 84.3 percent over the exposure period — a systematic decline the authors attribute to acid hydrolysis of the polyamide active layer. Another group incorporated sulfonated covalent organic framework nanosheets into a nanofiltration membrane to boost acid resistance; initial lithium rejection was moderate at 43.7 percent while divalent metals exceeded 90 percent, but even this engineered membrane lost significant performance after 7 to 14 days in acid. The lesson, the review argues, is that short-term laboratory tests cannot predict months-long industrial performance.

On economics, the numbers are encouraging but conditional. Membrane processes like electrodialysis and nanofiltration typically consume 0.5 to 5 kWh per cubic meter of treated water — substantially less than conventional thermal or precipitation-based routes, which can exceed 10 kWh per cubic meter when the full water-intensive mining chain is accounted for. Membrane-hybrid systems have demonstrated 50 to 84 percent reductions in total energy demand compared to conventional solvent extraction. Lithium recovered from salt-lake brines costs roughly USD 2 to 3 per kilogram, compared with around USD 80 per kilogram from seawater, while lithium carbonate commands a market price near USD 24 per kilogram — making brine-based membrane recovery economically attractive. Polymeric membranes last 5 to 8 years and ceramic membranes 15 to 20, offering long-term savings through reduced replacement frequency.

Yet the review is careful to position membranes as complementary rather than replacement technology. Nanofiltration achieves lithium selectivity in the 70 to 90 percent range with transition metal rejections typically above 90 percent, but separating chemically similar divalent cations like nickel from cobalt remains limited. Fluxes in concentrated leachates are often constrained to below 10 liters per square meter per hour due to osmotic pressure and fouling. Membranes excel at lithium concentration and acid recovery, but solvent extraction or precipitation is still needed for full transition metal separation. The realistic industrial pathway, the authors suggest, is a hybrid flowsheet: membranes as selective concentration and acid-recycling steps, followed by conventional precipitation to deliver battery-grade products.

The review’s conclusion is both a warning and a roadmap. The principal bottleneck in membrane-based critical material recovery is not initial separation performance — many studies already report 90 to 99 percent recovery — but sustained stability, fouling control, and honest accounting of energy per kilogram of product, membrane lifetime, and cleaning frequency under realistic leachate conditions. Few studies report these parameters, and most rely on simulated rather than real battery-derived streams. Future progress, the authors argue, depends on targeted material innovations such as acid-resistant thin-film composites and crown ether-functionalized ion-exchange membranes, thorough long-term stability testing, and integration into holistic pretreatment and recovery trains. If those gaps close, membranes could shift from promising laboratory curiosities to indispensable components of a circular economy that treats yesterday’s batteries and mine waste as tomorrow’s ore bodies.

Subject of Research: Membrane-based separation technologies for recovering critical metals from spent batteries and mineral wastes

Article Title: Membrane-based extraction of critical materials from spent batteries and other mineral wastes

Article References: Matebese, F., Raseala, M. J., & Moutloali, R. M. (2026). Membrane-based extraction of critical materials from spent batteries and other mineral wastes. Frontiers in Membrane Science and Technology, 5, Article 1766669. https://doi.org/10.3389/frmst.2026.1766669

Image Credits: AI Generated

DOI: 10.3389/frmst.2026.1766669

Keywords: membrane technology, lithium recovery, battery recycling, nanofiltration, electrodialysis, acid mine drainage, critical materials, circular economy, cobalt, nickel, fouling, hydrometallurgy

The review, published on 2 September 2026, addresses a gap the authors identify in the existing literature: most previous summaries of acid mine drainage remediation have focused on pollutant removal, treating the dissolved metals as a problem to be disposed of rather than a resource to be recovered. Li and colleagues instead organize the field around the dual remediation-recovery potential of electrochemical technologies, systematically categorizing four core approaches: electrocoagulation, membrane-assisted systems, electrodeposition, and capacitive deionization. Each of these uses electrical energy to drive chemical separations, and each offers a different balance between water cleanup and metal harvesting.

Electrocoagulation is perhaps the most industrially mature of the four. In this process, sacrificial electrodes, typically made of iron or aluminum, dissolve under an applied current, releasing metal ions that hydrolyze into positively charged hydroxide flocs. These flocs sweep up dissolved metals, arsenic species, and sulfate as they settle, effectively neutralizing the acidity while concentrating contaminants into a manageable solid. Recent studies highlighted in the review demonstrate simultaneous removal of copper and arsenic from acid mine drainage, and comparative work has shown electrocoagulation can outperform conventional chemical precipitation for coal mine drainage. The technique’s appeal lies in its simplicity and reduced chemical dosing, though the review notes that electrode consumption and sludge management remain practical constraints.

Electrodeposition takes a more direct route to recovery. By carefully controlling the cathode potential, dissolved metal ions can be reduced and plated onto an electrode surface as elemental metal, essentially electroplating copper, zinc, or other valuable metals straight out of mine water. The review emphasizes that selectivity is the central challenge here: acid mine drainage is a chemical soup in which competing ions, particularly magnesium hardness, interfere with the recovery of zinc and copper. Recent work on electrodeposition has quantified exactly how magnesium affects the purity and efficiency of recovered metals, and staged electrochemical treatment guided by process modeling has been shown to enable targeted recovery of metals and even rare earth elements from the same waste stream.

Membrane-assisted systems, including electrodialysis, use ion-exchange membranes and electric fields to separate charged species. Water recovery from acid mine drainage by electrodialysis has been demonstrated since the early 2010s, and more recent modeling studies have extended the approach to recovering low-concentration waste acid, effectively regenerating the sulfuric acid that makes the drainage so corrosive. The review also covers bioelectrochemical hybrids, in which microbial fuel cells oxidize residual organic matter or ferrous iron to generate current while metals are recovered at the cathode. Studies cited in the review report simultaneous energy and copper recovery from acid mine drainage using carbon felt anodes, and even membranes synthesized from agar and eggshell waste, pointing toward low-cost, circular-economy-compatible designs.

Capacitive deionization represents the newest frontier. Instead of driving chemical reactions, CDI stores ions electrostatically in the electric double layers of porous carbon electrodes, pulling salt and metal ions out of solution when a voltage is applied and releasing them when the voltage is removed. The review describes how flow-electrode and membrane-assisted variants have expanded CDI’s reach, and how electrode materials, from activated carbon derived from agricultural by-products to MXene-reduced graphene oxide composites, are being engineered for selectivity. A striking recent advance highlighted in the review is the electroextraction of low-concentration, redox-active heavy metals with standard potentials below zero volts from acid mine drainage, published in PNAS, which demonstrates that even trace metals once considered unrecoverable can be captured electrochemically.

The authors devote considerable attention to hybrid processes designed to overcome the two great weaknesses of any single electrochemical approach: matrix interference and low concentration limitations. Acid mine drainage is chemically aggressive, with pH values that can fall below 3, high sulfate loads, and fluctuating metal compositions that vary from site to site and season to season. Coupled systems, such as a process that recovers schwertmannite, an iron oxyhydroxysulfate mineral with adsorption value, by exploiting anodic reactive oxygen species and cathodic alkalinity, or visible light-assisted photo-electrochemical systems that overcome iron precipitation barriers, show how pairing reactions can turn interference into functionality. An electrochemically activated limestone system reported in Nature Communications exemplifies the trend of integrating electrochemistry with cheap, abundant materials to extract valuable metals.

None of this is without cost. The review is candid about the technical bottlenecks that stand between laboratory promise and industrial deployment: electrode fouling, in which deposits and biofilms degrade performance over time; high energy consumption, particularly for treating dilute streams where the electrical cost per kilogram of recovered metal can exceed its market value; membrane fouling and replacement costs; and the sheer variability of acid mine drainage chemistry, which complicates process control. The authors also assess industrial scaling barriers, noting that most demonstrations remain at bench or pilot scale, and that techno-economic analyses, including assessments of associated carbon dioxide emissions, must be integrated into process design if electrochemical recovery is to compete with conventional lime neutralization, which simply buries the metals in sludge.

The future directions outlined in the review center on adaptive, modular systems aligned with circular economy principles. Rather than one-size-fits-all treatment plants, the authors envision configurable electrochemical trains in which the sequence of electrocoagulation, electrodeposition, membrane separation, and capacitive deionization stages is tuned to the specific metal profile of a given drainage, recovering copper, zinc, rare earth elements, alumina, or even gypsum as value-added products. Performance regulation strategies, including pulsed current operation and real-time potential monitoring, could optimize the trade-off between energy input and recovery efficiency. The review’s framework, supported by funding from the Shenyang Science and Technology Foundation, is intended as a roadmap for researchers and engineers seeking to close the loop on mining’s most notorious waste stream.

The broader significance is hard to overstate. Acid mine drainage affects watersheds on every inhabited continent, and abandoned mines continue to leach acidity long after operations cease. If even a fraction of the dissolved metals in these waters could be economically recovered, remediation could shift from a perpetual financial burden to a self-sustaining enterprise, one in which the pollutant pays for its own cleanup. The review by Li, Zhang, and Yu makes clear that the electrochemical toolbox for achieving this vision already exists in its essentials; what remains is the engineering discipline of making it selective, durable, and cheap enough to run at the scale of a mine site. As demand for critical metals accelerates the global energy transition, the idea of mining our own waste water may be moving from provocative concept to practical necessity.

Subject of Research: Electrochemical technologies for recovering metals from acid mine drainage

Article Title: Electrochemical technologies for sustainable metal recovery from acid mine drainage: recent advances, challenges, and future perspectives

Article References: Li, S., Zhang, L., & Yu, J. (2026). Electrochemical technologies for sustainable metal recovery from acid mine drainage: recent advances, challenges, and future perspectives. Environmental Science and Pollution Research, 33(28), 14116-14139. https://doi.org/10.1007/s11356-026-38201-0

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38201-0

Keywords: acid mine drainage, electrocoagulation, electrodeposition, capacitive deionization, electrodialysis, metal recovery, water remediation, circular economy, heavy metals, mining pollution, bioelectrochemical systems, sustainable mining

To understand the problem, it helps to understand how seaweed gel is actually made. The dominant extraction method is an alkaline process, in which raw seaweed—most importantly the red alga Gracilaria, which contains roughly 30 percent agar and supplies about 53 percent of global agar market demand—is treated with strong alkali. This treatment serves a precise chemical purpose: it converts L-galactose-6-sulfate into 3,6-dehydrated L-galactose, stripping sulfate groups from the polysaccharide chains that would otherwise weaken the gel. The full production line runs from raw seaweed through alkali treatment, neutral cleaning, acidification, bleaching, gel cooking, filtration, cooling, dehydration, and drying. At every stage, chemistry is working to transform a slippery marine plant into a stable, marketable colloid.

That chemistry comes at a cost. During alkali treatment, the alkali attacks the seaweed cell wall, dissolving pigments, polysaccharides, and proteins into the solution, which turns from transparent to a dark liquid known in the trade as black lye. Factories typically reuse industrial lye two or three times, but once the organic concentration climbs too high and the liquid becomes viscous, it can no longer serve. Roughly 30 percent of the alkali remains trapped in the seaweed itself and must be washed out with repeated rinsing and acidification. Producing a single ton of seaweed gel consumes between 8.08 and 10.5 tons of alkali and generates approximately 460 to 600 tons of low-concentration alkali washing wastewater. In Fujian Province, China’s leading seaweed-processing region, nearly 100,000 tons of high-COD waste lye are produced annually; if alkali is reused more than seven times, the chemical oxygen demand can exceed 100,000, making the process unsustainable.

The solid waste stream is equally troubling. Filtration of the gel liquor is hindered by the colloid’s tendency to form a film, so producers add perlite—a porous volcanic glass with a large specific surface area—as a filter aid. The result is a residue that mixes perlite with a substantial load of organic matter. Each ton of seaweed gel generates roughly 2.5 tons of waste residue on a dry basis, and Fujian Province alone produces more than 35,000 dry tons annually. Left to accumulate, this residue decomposes, releasing methane and sulfides and other pollutants. The residue is rich in resources—about 70 percent perlite, along with trehalose, protein, and polyphenols—yet aside from minimal fertilizer recycling and some use as animal feed, most of it ends up as industrial landfill.

The review systematically evaluates the treatment options available for waste lye, and finds most of them wanting. Neutralization followed by activated sludge degradation at sewage plants, the current industrial default, wastes the active substances dissolved in the lye and requires large quantities of acid. Activated carbon adsorption can clean filtered lye, but saturated carbon cannot be reused, creating new disposal problems. Electrochemical oxidation on Ru-iridium titanium electrodes can rapidly strip alkali from seaweed and recover caustic through electrolytic cell reactions—one study reported continuous alkali recovery over 20 days in a bipolar chamber—but it does not recover the organic components. Even green approaches such as using algae to absorb nitrogen and phosphorus from agar wastewater leave the question of concentrated waste lye unresolved.

The most promising lye technology, the authors argue, is electrodialysis combined with membrane concentration. Electrodialysis uses an electric field to drive charged ions selectively across membranes, separating them from the solution; it is already widely used in food processing, salt production, and wastewater treatment. In studies of seaweed-derived waste lye specifically, electrodialysis achieved a cumulative alkali recovery rate of 37 percent while separating alkali from organic matter with low energy consumption and no phase change. The authors’ own group reported a chemical oxygen demand removal rate of 69.97 percent and an alkali recovery rate of 45.31 percent for electrodialysis-treated lye. Membrane concentration adds another layer of capability: multistage membrane systems have recovered tea polyphenols with retention rates of 70 to 83.8 percent, and nanofiltration membranes have cleaned paper-making black lye to reuse standards. New alkali-stable membranes, including quaternized graphene oxide composites that survived 32 days in 2 mol/L sodium hydroxide at 60 degrees Celsius, are making these processes increasingly robust.

For the solid residue, the review champions a hybrid of enzymatic and chemical degradation over calcination, which is costly and can create air pollution, or acid hydrolysis alone, which generates waste acid. Enzymes are gentle catalysts that cleave the glycosidic bonds of polysaccharide macromolecules, producing low-molecular-weight oligosaccharides without generating additional waste. In a key demonstration, the research team enzymatically treated nearly half of the polysaccharides in the residue—excluding the perlite—and recovered specific active oligosaccharides including neoagarobiose, neoagarotetraose, cellobiose, and cellotriose, which initially cleaned the pores of the perlite. Food-grade hydrochloric acid and hydrogen peroxide then degraded the remaining polysaccharides lodged inside the perlite pores, restoring the filter aid’s structure. The recovered perlite achieved a permeability of 2.61 Darcy, meeting reuse standards, and performed comparably to commercial perlite in subsequent gel extraction.

Yet significant scientific puzzles remain, and the review devotes considerable attention to them. During electrodialysis, charges generated in the process are adsorbed by organic substances, which accumulate on the surface of the permeable membrane and reduce the lye recovery rate. Related studies have shown that organic compounds containing benzene rings adsorb especially strongly onto anion exchange membranes, restricting transmembrane ion migration, and that sodium ions alter the internal molecular structure of organic polysaccharides in ways that change how they foul membranes. On the residue side, the structural activity and recovery of organic polysaccharides depend on the specific structure of the enzymes used, and organic material conversion involves energy interactions during solid-liquid separation that are not yet fully understood. These mechanisms, the authors contend, are the critical barriers to industrial-scale recovery of organic active substances from seaweed gel waste.

To crack those mechanisms, the review proposes a concrete analytical toolkit. Trace-charge analysis combined with scanning electron microscopy can quantify how organic active substances aggregate and how charges adsorb and release on membrane surfaces, while charge diffusion models can simulate charge transport during electrodialysis with membrane concentration. For the residue, microcalorimetry and thermodynamic models can track the energy changes that occur as specific enzymes act on organic matter, and Fourier transform infrared spectroscopy, X-ray fluorescence, and X-ray photoelectron spectroscopy can reveal how elemental composition and chemical bonding change during recovery. Analogous work on lignin and sugarcane bagasse has already demonstrated that pyrolysis behavior and potential energy shifts correlate with structural changes during enzymatic hydrolysis, providing a template the seaweed field can follow.

The stakes extend well beyond one industry. Seaweed aquaculture reached approximately 36.3 million tons globally in 2021—97 percent of it cultivated—and China alone produced 2.72 million tons in 2022, with Fujian Province accounting for nearly 48 percent of that output and 60.36 percent of national seaweed gel production. As the blue industry expands, the review’s framework offers a way to close the loop: recover the alkali, reclaim the perlite, extract the oligosaccharides, and return cleaner water to coastal ecosystems. If electrodialysis and enzyme chemistry can be scaled from laboratory benchmarks to factory floors, the mountains of black lye and perlite-laden sludge that currently shadow the seaweed gel industry could become feedstocks rather than liabilities—turning one of aquaculture’s messiest byproducts into one of its most elegant success stories.

Subject of Research: Waste reduction and resource recovery technologies in seaweed gel (agar and carrageenan) production

Article Title: Frontier review of key reduction technologies and resource utilization of waste during the seaweed gel production process

Article References: Luo, X., Wu, Y., Wang, S., Xiong, Z., Du, X., Zheng, M., Zhu, Y., Jiang, Z., Li, Q., Ni, H., Li, Z., & Chen, Z. (2024). Frontier review of key reduction technologies and resource utilization of waste during the seaweed gel production process. Blue Biotechnology, 1(1), Article 12. https://doi.org/10.1186/s44315-024-00013-7

Image Credits: AI Generated

DOI: 10.1186/s44315-024-00013-7

Keywords: seaweed gel, agar, carrageenan, waste lye, electrodialysis, membrane concentration, perlite recovery, enzymatic degradation, polysaccharides, oligosaccharides, wastewater treatment, blue biotechnology

The scale of the disposal problem is considerable. Coastal discharge can deliver salinity shocks to marine ecosystems, harming corals, seagrasses and shellfish that cannot tolerate hypersaline conditions. Elevated salinity disrupts the osmotic balance of marine organisms, causing dehydration, impaired reproduction and elevated mortality among juvenile fish and larvae. Chemical residues from antiscalants, coagulants and chlorine-based disinfectants add a toxic dimension, while heavy metals such as lead, mercury and chromium, released through pipeline and equipment corrosion, accumulate in marine sediments and can bioaccumulate through the food chain. Thermal desalination plants, which use multi-stage flash and multi-effect distillation, discharge brine at elevated temperatures that can trigger thermal shock in sensitive species and promote algal blooms, whereas reverse osmosis plants produce cooler brine with fewer temperature-related impacts.

Inland disposal carries its own hazards. Deep-well injection risks aquifer salinization if brine migrates through geological formations into freshwater reserves, and poorly lined evaporation ponds can leak salt and contaminants into surrounding soils and groundwater. Regulators have responded with an increasingly complex patchwork of rules. The United Nations Environment Programme recommends limiting discharge salinity to no more than 5 percent above ambient seawater, while the International Maritime Organization’s MARPOL Convention classifies brine as non-harmful only if pre-treated to remove toxic additives. In the United States, the Environmental Protection Agency enforces limits on total dissolved solids and boron under the Clean Water Act, and California’s Carlsbad plant now recovers 98 percent of its brine for industrial salt production. Saudi Arabia mandates offshore diffuser systems, and the United Arab Emirates caps brine temperature at 3 degrees Celsius above ambient seawater.

Yet the same chemistry that makes brine an environmental liability makes it a potential treasure trove. Sodium chloride constitutes roughly 60 to 70 percent of the dissolved solids in brine and can feed the chlor-alkali, Solvay and Hargreaves industrial processes. Magnesium, present at 1350 to 1660 milligrams per cubic decimeter, can be precipitated as magnesium hydroxide and converted into fertilizers or magnesium oxide. Calcium supports the production of gypsum and calcium carbonate, materials consumed at more than 200 million and 100 million tons per year worldwide respectively. Potassium and sulfate are valuable for fertilizers, and trace elements including strontium, boron, rubidium and cesium serve niche markets in drilling fluids, glass and electronics.

The most coveted target is lithium. Although seawater-derived brine contains only about 0.17 milligrams of lithium per cubic decimeter, surging battery demand has strained terrestrial supply chains and focused attention on unconventional sources. Recent pilot projects have achieved lithium concentrations 43,000 times seawater levels through iterative membrane sieving, and electrochemical intercalation and manganese dioxide-based adsorption offer selective extraction routes. Market analyses project that global demand for lithium will rise by 300 percent by 2030, with magnesium demand growing 50 percent, underscoring the strategic value of securing these elements from an existing industrial waste stream rather than opening new mines.

Brine also offers a surprising climate benefit. Its high magnesium and calcium content makes it a potent medium for carbon dioxide mineralization, in which carbonation reactions convert these ions into stable carbonates such as magnesium carbonate and calcium carbonate. The process can sequester up to 2 tons of carbon dioxide per ton of magnesium while producing marketable materials for cement and soil stabilization. A California brackish water treatment plant already produces calcium carbonate pellets that offset 15 percent of its operational emissions, and electrodialysis-coupled carbonation systems have demonstrated feasibility at pilot scale. Advances in pH control and antiscalant-free precipitation are narrowing the gap between laboratory success and commercial deployment.

The salinity gradient between brine and freshwater represents a third avenue of value: renewable energy. Pressure retarded osmosis and reverse electrodialysis harness the chemical potential difference across semi-permeable membranes, and pilot-scale systems have achieved power densities of 2 to 4 watts per square meter. A 240 cubic meter per day pilot plant combining seawater reverse osmosis with pressure retarded osmosis demonstrated a potential 20 percent energy reduction, while hybrid reverse electrodialysis systems integrated with nanofiltration aim to offset desalination energy costs by 20 to 30 percent. Each approach has trade-offs: pressure retarded osmosis delivers higher power density but is more vulnerable to membrane fouling, whereas reverse electrodialysis offers more stable output with lower pretreatment demands.

The technology portfolio for brine valorization is expanding rapidly. Nanofiltration serves as a pretreatment that separates monovalent from divalent ions, generating enriched streams for targeted extraction, while ultra-high pressure reverse osmosis, osmotically assisted reverse osmosis and high-pressure nanofiltration overcome the extreme osmotic pressures of concentrated brines. Electrodialysis with bipolar membranes produces acid and alkaline solutions, and capacitive deionization achieves unprecedented lithium selectivity through electrochemical adsorption. Eutectic freeze crystallization offers an energy-efficient alternative to thermal evaporation for recovering high-purity sodium and potassium chlorides, and membrane distillation-crystallization enables zero-liquid discharge while recovering gypsum and salt. Even biotechnology is entering the field, with halophilic microbes and algal biosorption providing low-energy pathways for metal recovery.

Real-world deployments are beginning to validate the concept. Saudi Arabia’s Water Authority has developed pilot projects recovering magnesium, calcium and sodium chloride from brine, and the Shoaiba nanofiltration facility generates magnesium-enriched streams of up to 1530 milligrams per cubic decimeter for drinking water supplementation and liquid fertilizers. The UAE’s Masdar Initiative has integrated brine management into its sustainability goals, and the EU-funded SEA4VALUE project has demonstrated a modular multimineral recovery process. In the United States and Europe, brine-to-energy pilots are testing osmotic power generation, though scaling these systems remains technically and economically difficult.

Significant barriers persist. Concentrating hypersaline brine can demand 10 to 15 kilowatt-hours per cubic meter, far above the 3 to 4 kilowatt-hours of standard reverse osmosis, and electrochemical lithium extraction currently requires more than 20 kilowatt-hours per kilogram, exceeding terrestrial mining costs by 50 percent. Adsorption systems that perform well in controlled settings lose efficiency in real brine matrices laden with competing ions, and capacitive deionization electrodes degrade during continuous operation. The review’s authors argue that the path forward lies in modular designs, artificial intelligence-driven process optimization, ion-selective membranes including graphene oxide composites, and emerging photoelectrochemical methods that have demonstrated lithium recovery rates of up to 90 percent at around 5 kilowatt-hours per kilogram. Integrated with renewable energy and circular economy frameworks such as the EU’s ZERO BRINE project, brine mining could transform desalination from a water-security measure into a resource-positive industry aligned with the United Nations Sustainable Development Goals on clean water and climate action.

Subject of Research: Recovery of minerals, carbon dioxide sequestration and energy generation from desalination brine

Article Title: Challenges, opportunities, and technological advances in desalination brine mining: a mini review

Article References: Lee, J., & Lee, S. (2025). Challenges, opportunities, and technological advances in desalination brine mining: a mini review. Advances in Industrial and Engineering Chemistry, 1(1), Article 7. https://doi.org/10.1007/s44405-025-00007-y

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00007-y

Keywords: desalination, brine mining, lithium extraction, magnesium recovery, CO2 sequestration, salinity gradient power, reverse osmosis, nanofiltration, electrodialysis, zero liquid discharge, circular economy, water scarcity