Multipass Nanofiltration for Lithium Separation with High Selectivity and Recovery

Breaking the trade-off between lithium purity and lithium recovery: A comprehensive mathematical modeling based on membrane structure-property-performance relationships

The application of nanofiltration (NF) membranes for resource recovery, particularly lithium (Li) extraction from high magnesium (Mg) brines, is a rapidly growing research area. However, the trade-off between high Li+ purity and recovery remains challenging. In our study, we extend the widely adopted Donnan Steric Pore Model with Dielectric Exclusion (DSPM-DE) to analyze membrane structure-property-performance relationships at the process scale. For the first time, we quantify how membrane intrinsic parameters (e.g., pore size, effective thickness, and charge density) affect Li+ purity and recovery under module-scale processes. Under this framework, we demonstrate that electrically neutral and positively charged membranes outperform negatively charged membranes, albeit at the cost of slightly higher required hydraulic pressure. Notably, positively charged membranes with smaller pore size yet high water permeance (40-80 L m-2 h-1 bar-1) are preferred, which could simultaneously achieve excellent Li+ purity (∼98 %) and high Li+ recovery (∼93 %) in the single-pass process, effectively overcoming the purity-recovery trade-off correlation. We further demonstrate that negative Li+ rejection plays a crucial role in overcoming the trade-off correlation by significantly increasing Li+ recovery. Nevertheless, poor system flux distribution is inadvertently observed in the regions where strong negative rejection occurs, highlighting the need for careful consideration of the balance between system stability and lithium extraction performances. Our study identifies critical membrane parameters for achieving optimal lithium extraction performance at the process scale, offering fundamental insights for designing high-performance membranes for resource recovery.

Randomly oriented covalent organic framework membrane for selective Li+ sieving from other ions

Certain biological channels exhibit remarkable selectivity, effectively distinguishing between competing cations. If artificial membranes could achieve similar precision in differentiating competing ions from Li+, it could advance sustainable technologies in lithium extraction. In this study, we present a covalent organic framework (COF) membrane featuring a randomly oriented structure that enables selective separation of major competing ions from Li+. The random orientation results in narrow pores, which impart size-based selectivity among alkaline ions. Additionally, the COF incorporates sulfonic groups that preferentially bind to Na+ and K+, facilitating their transport while retaining Li+. These synergistic mechanisms endow the membrane with a selectivity beyond detection limit for K+ and Na+ over Li+. When driven by an electrical potential, the ion flux through the membrane is enhanced by over an order of magnitude. Notably, the membrane also permits the transport of Mg2+ and Ca2+ while still rejecting Li+, leveraging differences in their ion mobility. This work should advance the design and construction of biomimetic materials for the extraction of valuable species from seawater and other aqueous sources.

Nanomorphogenesis of interlayered polyamide membranes for precise ion sieving in lithium extraction

Nanofiltration (NF) offers a scalable and energy-efficient method for lithium extraction from salt lakes. However, the selective separation of lithium from magnesium, particularly in brines with high magnesium concentrations, remains a significant challenge due to the close similarity in their hydrated ionic radii. The limited Li+/Mg2+selectivity of current NF membranes is primarily attributed to insufficient control over pore size and surface charge. In this study, we report the development of an interlayered thin-film composite (iTFC) membrane incorporating functionalized sulfonated carrageenan to regulate the interfacial polymerization process. This integrated interlayer plays a crucial role in controlling the diffusion and spatial distribution of amine monomers, leading to the formation of dense, nano-striped polyamide networks. These structural improvements including refined pore size and reduced negative charge significantly enhanced Li+/Mg2+selectivity (133.5) and increased permeance by 2.5 times compared to conventional TFC membranes. Additionally, the nano-striped structure optimized the membrane filtration area while minimizing ion transport resistance, effectively overcoming the traditional trade-off between ion selectivity and permeability. This study highlights the potential of iTFC membranes for achieving both high lithium purity and recovery, offering a promising avenue for large-scale lithium extraction from brines.

Polyelectrolyte nanofiltration membranes for base separation and recovery

Nanofiltration (NF) membranes have the potential to significantly advance resource recovery efforts where monovalent/divalent ion separation is critical, but their utilization is limited by inadequate stability under extreme conditions. "Base separation"-i.e., separating hydroxide from other ions-has emerged as an essential approach in resource recovery, enabling the extraction of multivalent anions (e.g., carbonates and phosphates) from hydroxide-rich streams. There is a particularly high demand for membranes capable of separating carbonates from hydroxide-rich CO2 capture solvents and phosphates from hydroxide-rich adsorbent regeneration solvents. However, conventional polyamide NF membranes degrade during long-term exposure to alkaline conditions, limiting their application in extreme conditions. In this study, alkaline-resistant polyelectrolyte membranes are fabricated by depositing alternating layers of polycation, poly(diallyl dimethylammonium chloride) (PDADMAC), and polyanion, poly(sodium 4-styrenesulfonate) (PSS) to a polyethersulfone substrate. The membranes are tested for hydroxide/carbonate and hydroxide/phosphate separation performance, as well as performance stability during prolonged exposure to highly alkaline conditions. Results indicate that higher feed solution pH improves carbonate and phosphate rejection by promoting ion deprotonation and strengthening electrostatic repulsion from the negatively charged membrane. In contrast, increasing carbonate and phosphate concentrations in the feed solution reduces the rejection due to charge screening. The six-bilayer PDADMAC/PSS membrane removes more than 99 % of carbonates and phosphates while allowing extensive passage of hydroxide at pH 13. Stability tests confirm that PDADMAC/PSS membranes maintain excellent ion selectivity over four weeks of exposure to pH 13 KOH, whereas commercial polyamide NF membranes degrade within one week. These findings highlight the potential for PDADMAC/PSS membranes to advance critical resource recovery efforts, providing a durable and effective solution for applications under extreme conditions.

Mix-Charged Nanofiltration Membrane for Efficient Organic Removal from High-Salinity Wastewater: The Role of Charge Spatial Distribution

The efficient removal of organic contaminants from high-salinity wastewater is crucial for resource recovery and achieving zero discharge. Nanofiltration (NF) membranes are effective in separating organic compounds and monovalent salts, but they typically exhibit an excessive rejection of divalent salts. Modifying the charge characteristics of NF membranes can improve salt permeation; however, the role of charge spatial distribution in governing salt transport behavior is not fully understood. In this study, we developed a mix-charged NF membrane with a horizontal charge distribution by employing interfacial polymerization combined with a polyester template etching and solvent-induced polyamine intercalation strategy. The ratio of positive to negative charge domains in the membrane can be precisely controlled by adjusting the aqueous monomer ratio and polyamine modifier type. X-ray photoelectron spectroscopy (XPS) depth profiling and separation layer thickness analysis confirmed the complete penetration of polyamines into the separation layer, providing direct evidence of the formation of horizontally distributed charge domains. This unique charge distribution results in a high charge density and a near-electroneutral surface, which facilitates the permeation of the divalent salts. The size-dependent "plug-in" modification and covalent cross-linking further reduce pore size, enhancing rejection of small organic molecules. Additionally, the membrane demonstrated exceptional antifouling performance against both negatively and positively charged pollutants, attributed to its unique charge distribution and smooth surface. Molecular dynamics (MD) simulations further revealed that weak electrostatic interactions and a tightly bound hydration layer contribute to the membrane's superior antifouling properties. This work provides valuable insights into the design of NF membranes with tailored microstructures and charge distributions for improved water treatment performance.

Nanofiltration Membranes for Efficient Lithium Extraction from Salt-Lake Brine: A Critical Review

The global transition to clean energy technologies has escalated the demand for lithium (Li), a critical component in rechargeable Li-ion batteries, highlighting the urgent need for efficient and sustainable Li+ extraction methods. Nanofiltration (NF)-based separations have emerged as a promising solution, offering selective separation capabilities that could advance resource extraction and recovery. However, an NF-based lithium extraction process differs significantly from conventional water treatment, necessitating a paradigm shift in membrane materials design, performance evaluation metrics, and process optimization. In this review, we first explore the state-of-the-art strategies for NF membrane modifications. Machine learning was employed to identify key parameters influencing Li+ extraction efficiency, enabling the rational design of high-performance membranes. We then delve into the evolution of performance evaluation metrics, transitioning from the traditional permeance-selectivity trade-off to a more relevant focus on Li+ purity and recovery balance. A system-scale analysis considering specific energy consumption, flux distribution uniformity, and system-scale Li+ recovery and purity is presented. The review also examines process integration and synergistic combinations of NF with emerging technologies, such as capacitive deionization. Techno-economic and lifecycle assessments are also discussed to provide insights into the economic viability and environmental sustainability of NF-based Li+ extraction. Finally, we highlight future research directions to bridge the gap between fundamental research and practical applications, aiming to accelerate the development of sustainable and cost-effective Li+ extraction methods.

Recycling Lithium-Ion Batteries-Technologies, Environmental, Human Health, and Economic Issues-Mini-Systematic Literature Review

Global concerns about pollution reduction, associated with the continuous technological development of electronic equipment raises challenge for the future regarding lithium-ion batteries exploitation, use, and recovery through recycling of critical metals. Several human and environmental issues are reported, including related diseases caused by lithium waste. Lithium in Li-ion batteries can be recovered through various methods to prevent environmental contamination, and Li can be reused as a recyclable resource. Classical technologies for recovering lithium from batteries are associated with various environmental issues, so lithium recovery remains challenging. However, the emergence of membrane processes has opened new research directions in lithium recovery, offering hope for more efficient and environmentally friendly solutions. These processes can be integrated into current industrial recycling flows, having a high recovery potential and paving the way for a more sustainable future. A second method, biolexivation, is eco-friendly, but this point illustrates significant drawbacks when used on an industrial scale. We discussed toxicity induced by metals associated with Li to iron-oxidizing bacteria, which needs further study since it causes low recycling efficiency. One major environmental problem is the low efficiency of the recovery of Li from the water cycle, which affects global-scale safety. Still, electromembranes can offer promising solutions in the future, but there is needed to update regulations to actual needs for both producing and recycling LIB.

Toward a Circular Lithium Economy with Electrodialysis: Upcycling Spent Battery Leachates with Selective and Bipolar Ion-Exchange Membranes

Recycling spent lithium-ion batteries offers a sustainable solution to reduce ecological degradation from mining and mitigate raw material shortages and price volatility. This study investigates using electrodialysis with selective and bipolar ion-exchange membranes to establish a circular economy for lithium-ion batteries. An experimental data set of over 1700 ion concentration measurements across five current densities, two solution compositions, and three pH levels supports the techno-economic analysis. Selective electrodialysis (SED) isolates lithium ions from battery leachates, yielding a 99% Li-pure retentate with 68.8% lithium retention, achieving relative ionic fluxes up to 2.41 for Li+ over transition metal cations and a selectivity of 5.64 over monovalent cations. Bipolar membrane electrodialysis (BMED) converts LiCl into high-purity LiOH and HCl, essential for battery remanufacturing and reducing acid consumption via acid recycling. High current densities reduce ion leakage, achieving lithium leakage as low as 0.03%, though hydronium and hydroxide leakage in BMED remains high at 11-20%. Our analysis projects LiOH production costs between USD 1.1 and 3.6 per kilogram, significantly lower than current prices. Optimal SED and BMED conditions are identified, emphasizing the need to control proton transport in BMED and improve cobalt-lithium separation in SED to enhance cost efficiency.

Solar transpiration-powered lithium extraction and storage

Lithium mining is energy intensive and environmentally costly. This is because lithium ions are typically present in brines as a minor component mixed with physiochemically similar cations that are difficult to separate. Inspired by nature's ability to selectively extract species in transpiration, we report a solar transpiration-powered lithium extraction and storage (STLES) device that can extract and store lithium from brines using natural sunlight. Specifically, the device uses a hierarchically structured solar transpirational evaporator to create a pressure gradient, which allows for the extraction of lithium from brines through a membrane and its storage in a vascular storage layer. Long-term experiments, various membrane tests, and different size assessments demonstrate the stability, compatibility, and scalability of STLES. This solar-powered mining technology provides an alternative developing pathway toward the sustainable extraction of critical resources.

Congener-welded crystalline carbon nitride membrane for robust and highly selective Li/Mg separation

Extracting lithium from salt-lake brines critically relies on the separation of Li+ and Mg2+, which could combat the lithium shortage. However, designing robust sieving membrane with high Li+/Mg2+ selectivity in the long-time operation has remained highly challenging. Here, we demonstrate a bioinspired congener-welded crystalline carbon nitride membrane that can accomplish efficient and stable monovalent ion sieving over divalent Mg ion. The crystalline carbon nitrides have uniform and narrow pore size to reject the large hydrated Mg2+ and rich ligating sites to facilitate an almost barrierless Li+ transport as suggested by ab initio simulations. These crystals were then welded by vapor-deposited congeners, i.e., amorphous polymer carbon nitride, which have similar composition and chemistry with the crystals, forming intimate and compatible crystal/polymer interface. As a result, our membrane can sieve out highly dilute Li+ (0.002 M) from concentrated Mg2+ (1.0 M) with a high selectivity of 1708, and can be continuously operated for 10 days.

Granulation of hydrometallurgically synthesized spinel lithium manganese oxide using cross-linked chitosan for lithium adsorption from water

A drastic increase in demand for electric vehicles and energy storage systems increases lithium (Li) need as a critical metal for the 21st century. Lithium manganese oxides stand out among inorganic adsorbents because of their high capacity, chemical stability, selectivity, and affordability for lithium recovery from aqueous media. This study investigates using hydrometallurgically synthesized lithium manganese oxide (Li1.6Mn1.6O4) in granular form coated with cross-linked chitosan for lithium recovery from water. Characterization methods such as SEM, FTIR, XRD, and BET reveal the successful synthesis of the composite adsorbent. Granular cross-linked chitosan-coated and delithiated lithium manganese oxide (CTS/HMO) adsorbent demonstrated optimal removal efficiency of 86 % at pH 12 with 4 g/L of adsorbent dosage. The Langmuir isotherm at 25 °C, which showed monolayer adsorption with a maximum capacity of 4.94 mg/g, a better fit for the adsorption behavior of CTS/HMO. Adsorption was endothermic and thermodynamically spontaneous. Lithium adsorption followed the pseudo-first-order kinetic model.

Membrane Design Principles for Ion-Selective Electrodialysis: An Analysis for Li/Mg Separation

Selective electrodialysis (ED) is a promising membrane-based process to separate Li+ from Mg2+, which is the most critical step for Li extraction from brine lakes. This study theoretically compares the ED-based Li/Mg separation performance of different monovalent selective cation exchange membranes (CEMs) and nanofiltration (NF) membranes at the coupon scale using a unified mass transport model, i.e., a solution-friction model. We demonstrated that monovalent selective CEMs with a dense surface thin film like a polyamide film are more effective in enhancing the Li/Mg separation performance than those with a loose but highly charged thin film. Polyamide film-coated CEMs when used in ED have a performance similar to that of polyamide-based NF membranes when used in NF. NF membranes, when expected to replace monovalent selective CEMs in ED for Li/Mg separation, will require a thin support layer with low tortuosity and high porosity to reduce the internal concentration polarization. The coupon-scale performance analysis and comparison provide new insights into the design of composite membranes used for ED-based selective ion-ion separation.