Extraction of lithium from Chinese salt-lake brines by membranes: Design and practice

Surface-engineered nanofiltration membranes for sustainable lithium recovery from real brine: Addressing fouling and scaling challenges

Nanofiltration (NF) membranes hold great promise for lithium (Li) recovery from brines, with numerous studies focusing on improving Li/Mg separation performance. However, real brine environments pose significant challenges, as fouling and scaling severely hinder Li recovery efficiency. Despite their critical impact, these challenges have received limited attention. This study addresses these issues through surface engineering of polyamide (PA) NF membranes, achieving a positively charged, ultra-smooth surface. The engineered membrane demonstrated exceptional fouling and scaling resistance during real brine treatment, exhibiting only a 12 % flux decline over 12 h, compared to 28 % and 20 % for the control and commercial NF270 membranes, respectively. This superior antifouling performance enabled sustained high Li flux (>80 mM·m⁻2·h⁻1) while reducing the Mg/Li mass ratio from 4.1 in the feed to 1.4 in the permeate. Additionally, the membrane displayed remarkable resistance to scaling in synthetic brine containing high concentrations of Ca2+ and SO42-. Systematic evaluations in both synthetic and real brines revealed that the enhanced process stability arises from the synergistic effects of reduced surface roughness and optimized surface charge, which together minimize foulant adhesion and mitigate scaling. These findings mark a significant advancement toward the practical implementation of membrane-based Li recovery, underscoring the critical importance of addressing fouling and scaling in real brine environments.

Covalent organic framework membranes for lithium extraction: facilitated ion transport strategies to enhance selectivity

The surging global demand for lithium, driven by the proliferation of electric vehicles and energy storage technologies, has exposed significant limitations in conventional lithium extraction methods, including inefficiency and environmental harm. Covalent organic frameworks (COFs) have emerged as a promising platform to address this challenge and enable more sustainable lithium extraction, owing to their unique advantages such as precisely tunable pore sizes, robust stability, and the ability to incorporate functional binding sites for selective ion transport. This review focuses on structural design and functionalization strategies in COFs to optimize lithium-ion separation, highlighting how pore confinement effects, tailored interlayer stacking arrangements, and strategic functional group modifications can dramatically enhance Li+ selectivity over competing ions present in brine solutions. A particular emphasis is placed on the fundamental energy barriers associated with lithium-ion transport. In particular, we discuss how appropriately designed pore environments and lithium-binding functional groups reduce the dehydration energy required for Li+ to enter and traverse COF nanochannels, thereby facilitating faster and more selective Li+ conduction. We also survey recent advancements in COF-based lithium separation technologies, such as high-performance COF membranes and sorbents for extracting lithium from brines and seawater, evaluating their potential, as well as remaining challenges, for sustainable industrial implementation. This review provides a comprehensive understanding of how advanced COF engineering can enable efficient and selective lithium-ion transport, offering valuable insights for the development of next-generation lithium extraction materials and technologies.

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.

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.

High selectivity, capacity and stability for electrochemical lithium extraction on boron-doped H1.6Mn1.6O4 by tailoring lattice constant and intercalation energy

A sustainable supply of lithium from salt-lake brines is necessary due to the surge in demand of the lithium-battery market. However, the presence of coexisting ions, particularly Na+, poses a significant challenge due to the similarities in charge, electronic structure, and hydrated size. The electrochemical system with manganese (Mn)-based lithium-ion (Li+) sieves electrodes is a promising method for Li+ recovery, but often suffers from geometric configuration distortion, which reduces their selectivity and capacity. In this work, we developed a boron-modified H1.6Mn1.6O4 (HMO-B) material for Li+ extraction through hybrid capacitive deionization (HCDI) intercalation. Characterizations and theoretical calculations verified that the formation of the BO bond reduces the lattice constant, significantly inhibiting the Jahn-Teller distortion of Mn3+, thereby stabilizing the crystal structure. The transformation of Mn3+ to Mn4+ effectively prevents Mn dissolution during the electro-de-intercalation process. B doping narrows the lattice spacing and increases the intercalation energy difference between Li+ and Na+. Consequently, HMO-B exhibits an outstanding Li/Na selectivity of 1211.68. The reduction in interface impedance improves current efficiency, while the increase in specific surface area provides abundant recognition sites for Li+, enhancing Li+ intercalation performance from 14 mg g-1 day-1 for HMO to 34.94 mg g-1 h-1 for HMO-B. Additionally, Mn dissolution reduces from 7 % for HMO to 1.13 % for HMO-B after 10 cycles. This work holds substantial practical value for the selective Li extraction from salt lake brine and is anticipated to provide a stable Li supply for the burgeoning new energy industry.

Artificial Cation-Chloride Co-Transporters for Chloride-Facilitated Lithium/Magnesium Separation

Inspired by nature, many artificial ion sieving materials have been developed, shedding light on the next-generation ion, e.g., Li+, extraction applications. Artificial co-transporters remain difficult to construct since they have a much more complex ion-sieving property. For example, the cation-chloride co-transporters have both alkaline ion and chloride ion selectivity but no alkaline ion/chloride ion selectivity. We here demonstrate a method to construct artificial co-transporters, using a porous organic framework membrane which has a relatively disordered stacking structure and rich quaternary ammonium groups paired with counter-ions. This imparts the membrane with extremely narrow pores (∼0.3 nm) and almost no surface charge, enabling size-based high alkaline ion selectivity against other cations, high Cl- selectivity against other anions, but almost no alkaline ion/Cl- selectivity. Such synchronized sieving property allows us to enhance the extraction of high-value cations (Li+) by simply feeding excessive low-value anions (Cl-). As a demonstration, we realized high-flux (0.44 mol m-2 h-1) and highly selective (selectivity: 185) Li+/Mg2+ separation by reversing the current industrial brine-based lithium extraction process, i.e., sieving Li+ before removing NaCl.

Ultrashort and Vertically Aligned Channels: Boosted Lithium Selective Extraction via Hybrid Capacitive Deionization

Hybrid capacitive deionization (HCDI) is energetically and operationally favorable for Li+ extraction from salt lake brines. The bottlenecks of current LiMn2O4 (LMO)-based electrodes are their limited Li+ adsorption rate and capacity, caused by disordered electron/ion transport channels and insufficient ion-accessible sites. Inspired by selective ion uptake processes in mangroves, we propose the strategy, fabricating ultrashort, vertically aligned channels for Li+ transport in the electrode to enhance the Li+ selective performance of HCDI. The self-supporting graphene/LMO/bacterial cellulose electrode featuring vertically aligned channels (VGLB) possesses sturdy framework, excellent electrical conductivity, fast electron/ion transport channels, and abundant available Li+ adsorption sites, enabling an ultrahigh Li+ adsorption rate of 2.6 mg g-1 min-1 and capacity up to 33.9 mg g-1 with a high retention of 91.62% after 100 cycles. VGLB also manifests superior selectivity in various simulated salt lake brines with Li+ purity in recovered solution of over 85%. Most importantly, VGLB enables selective Li+ extraction in low-grade brine from Jingbian oil and gas-produced water. We conduct finite element simulations to study the Li+ distribution in the electrode and disclose how the electrode microstructure influences the Li+ extraction performance. This approach put forward an avenue for electrode structure design for efficient Li+ extraction from both salt lakes and low-grade brines with HCDI application.

Current and Future Impacts of Lithium Carbonate from Brines: A Global Regionalized Life Cycle Assessment Model

Lithium (Li) is essential for decarbonization strategies, such as electric vehicles and renewable energy storage, which experiences the largest growth rates among metals required for low-carbon technologies. To meet this demand, the raw materials sector must increase current capacities and develop new capacities at untapped deposits. Understanding life cycle impacts is crucial to avoid severe environmental burden shifts in the future. Although site-specific life cycle inventories exist, they do not allow for a comprehensive global assessment of the Li sector, particularly in capturing technological developments. To address this, our study presents a life cycle inventory model for brines that maintains essential site-specific parameters while providing a global perspective. We define core parameters for site-specific modeling of Li carbonate (Li2CO3) production and develop a systematic approach to addressing data gaps. Our model employs a class-based structure for 30 mapped processes from the literature and quantifies environmental and technical flows. Overall, we cover 25 sites, representing 300 kilotonnes (90%) of current Li2CO3 production from brines and an additional 315 kilotonnes of potential future production. One key finding is that sites using direct Li extraction have 7-fold higher climate change impacts than sites using conventional technologies on average, while water scarcity impacts are doubled on average. The difference is a result of the larger brine mass required to be treated due to lower Li grades. Furthermore, our model allows the implications for Li-ion battery production to be analyzed.

Pillared Laminar Vermiculite Membranes with Tunable Monovalent and Multivalent Ion Selectivity

Effective membrane separation of Li+ from Na+ and Mg2+ is crucial for lithium extraction from water yet challenging for conventional polymeric membranes. Two dimensional (2D) membranes with ordered laminar structures and tunable physicochemical properties offer distinctive ion-sieving capabilities promising for lithium extraction. Recently, phyllosilicates are introduced as abundant and cost-effective source materials for such membranes. However, their water instability and low inherent ion transport selectivity hinder practical applications. Herein, a new class of laminar membranes with excellent stability and tunable ion sieving is reported by incorporating inorganic alumina pillars into vermiculite interlayers. Crosslinking vermiculite flakes with alumina pillars significantly strengthens interlamellar interactions, resulting in robust water stability. Doping of Na+ before the pillaring process reverses the membrane's surface charge, substantially boosting Li+ separation from multivalent cations via electrostatic interactions. Lithium extraction is often complicated by the presence of co-existing monovalent cations (e.g., Na+) at higher concentrations. Here, by introducing excess Na+ into the membrane after the pillaring process, the separation of Li+ from monovalent cations is enhanced through steric effects. This work realizes both monovalent/multivalent and monovalent/monovalent selective ion sieving with the same membrane platform. A separation mechanism is proposed based on Donnan exclusion and size exclusion, providing new insights for membrane design for resource recovery applications.

Specific capture of magnesium ions by phosphorus atomic sites on self-floating nuclei advances Mg/Li separation in salt lakes brine

Efficient magnesium-lithium separation is a critical step in extracting lithium ions from salt lakes brine. Precipitation of Mg2+ from liquid to solid is the simplest separation method, but a side reaction of Li+ adsorption by precipitated floc leads to incomplete Mg/Li separation and lithium loss. In this study, we grafted phosphorus atomic sites onto silica-based nuclei with self-floating separation capability to prepare adsorbents with specific capture ability for Mg2+, achieving efficient Mg/Li separation from brine. Surface composition analysis shows that the content of P element is 0.99 %, which contributed 82.20 mg g⁻1 of Mg2+ adsorption capacity of at room temperature. During this process, the content of Na and Ca elements in the material decreased by 1.47 % and 0.85 %, respectively, due to ion exchange and surface coverage. In samples of the same water quality as Smackover brine, the Li content in the Mg2+-captured material was only 3.20 % of that in directly precipitated Mg(OH)2, due to the adsorption selectivity coefficient of the material for Mg²⁺ to Li⁺ reaching 62.26. The outcomes of this research enlighten the selective capture ability and mechanism of phosphorus atomic sites for Mg2+, providing new insights for efficient Mg/Li separation from salt lakes to improve raw brain grade.

Enhancing Membrane Materials for Efficient Li Recycling and Recovery

Rapid uptake of lithium-centric technology, e.g., electric vehicles and large-scale energy storage, is increasing the demand for efficient technologies for lithium extraction from aqueous sources. Among various lithium-extraction technologies, membrane processes hold great promise due to energy efficiency and flexible operation in a continuous process with potential commercial viability. However, membrane separators face challenges such as the extraction efficiency due to the limited selectivity toward lithium relative to other species. Low selectivity can be ascribed to the uncontrollable selective channels and inefficient exclusion functions. However, recent selectivity enhancements for other membrane applications, such as in gas separation and energy storage, suggest that this may also be possible for lithium extraction. This review article focuses on the innovations in the membrane chemistries based on rational design following separation principles and unveiling the theories behind enhanced selectivity. Furthermore, recent progress in membrane-based lithium extraction technologies is summarized with the emphasis on inorganic, organic, and composite materials. The challenges and opportunities for developing the next generation of selective membranes for lithium recovery are also pointed out.

Study on the application of brine mixing method in lithium extraction from Zabuye salt lake, Tibet

With the rapid development of new energy industry, the demand for lithium resources continues to rise. The salinity-gradient solar pond (SGSP) technology is used to extract the lithium carbonate from Zabuye salt lake brine in the Tibet Plateau of China. Years of production practice proved that due to the unsatisfactory quality and insufficient amount of lithium-rich brine used to make the SGSP, the yield and grade of lithium concentrate in the solar pond has been seriously affected. In this paper, it has been investigated that the change rule of brine composition with different brine mixing ratios through the same/cross-year brine mixing laboratory experiments and the cross-year brine mixing production test. The optimal brine mixing ratio of winter concentrated brine and summer brine, the relevant operation parameters and the yield increase effect of lithium concentrate in the solar pond are obtained. The results show that the cross-year brine mixing method can not only significantly improve the yield and grade of lithium carbonate, but also alleviate the pressure of brine production in salt field. It is suggested that the SGSP technology coupled with the cross-year brine mixing method should be given priority in the production of lithium carbonate in Zabuye mining area.

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.

Enhancing Ion Selectivity of Nanofiltration Membranes via Heterogeneous Charge Distribution

Nanofiltration technology holds significant potential for precisely separating monovalent and multivalent ions, such as lithium (Li) and magnesium (Mg) ions, during lithium extraction from salt lakes. This study bridges a crucial gap in understanding the impact of the membrane spatial charge distribution on ion-selective separation. We developed two types of mixed-charge membranes with similar pore sizes but distinct longitudinal and horizontal distributions of oppositely charged domains. The charge-mosaic membrane, synthesized and utilized for ion fractionation for the first time, achieved an exceptional water permeance of 15.4 LMH/bar and a Li/Mg selectivity of 108, outperforming the majority of published reports. Through comprehensive characterization, mathematical modeling, and machine learning methods, we provide evidence that the spatial charge distribution dominantly determines ion selectivity. The charge-mosaic structure excels by substantially promoting ion selectivity through locally enhanced Donnan effects while remaining unaffected by variations in feedwater concentration. Our findings not only demonstrate the applicability of charge-mosaic membranes to precise nanofiltration but also have profound implications for technologies demanding advanced ion selectivity, including those in the sustainable water treatment and energy storage industries.

Lithium-Ion-Sieve-Embedded Hybrid Membranes for Anion-Exchange- and Cation-Concentration-Driven Li/Mg Separation

There is an urgent need to develop efficient and environmentally friendly technologies for separating Li+ from brines containing abundant Mg2+ to meet the growing demand for lithium resources. In this work, we prepared hybrid membranes by integrating hydrogen manganese oxide (HMO), a lithium-ion sieve, as a filler into anion-exchange membranes (AEMs), the quaternary ammonium-functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) and poly(m-terphenyl piperidinium) (m-PTP). Cations are transported by electrostatic attraction originating from anions and the concentration difference across membranes. Because of the effects of electrostatic repulsion of the fixed cationic groups and steric resistance in AEMs, Li+ with less charge and smaller radius will preferentially pass through the membrane. In addition, the presence of HMO provides an additional fast transport channel for Li+, resulting in an enhanced Li+/Mg2+ separation performance. The results show that 20%HMO@m-PTP exhibits high Li+ flux (0.48 mol/m2·h) and Li+/Mg2+ selectivity (βLi+/Mg2+ = 14.1). Molecular dynamics simulations show that m-PTP has more free volume than QPPO, which is beneficial for rapid cation transport. Spectral analysis confirms the insertion and sieving of Li+ in HMO. This work illustrates the great potential of anion-exchange- and cation-concentration-driven hybrid membranes based on lithium-ion sieves for low-energy and efficient Li+ extraction processes.

A novel trimesoyl chloride/hyper branched polyethyleneimine/MOF (MIL-303)/P84 co-polyimide nanocomposite mixed matrix membranes with an ultra-thin surface cross linking layer for removing toxic heavy metal ions from wastewater

In this study, a positively charged nanofiltration (NF) nanocomposite mixed matrix membrane (MMM) was developed by incorporating metal-organic frameworks (MOFs) (MIL-303) into P84 co-polyimide and cross-linking with hyperbranched polyethyleneimine (HPEI). A very thin selective layer was subsequently formed on the cross-linked membrane surface using trimesoyl chloride (TMC). The incorporation of MIL-303 introduced specific water channels, enhancing the permeance of the nanocomposite MMMs. Additionally, it improved hydrophilicity and influenced the diffusion of the TMC monomer through the channels. The cross-linker HPEI resulted in NF membranes with increased electro-positivity and a reduced mean pore diameter. The very thin crosslinked TMC layer further improved permeance and heavy metal ions rejection of the membrane. This optimized membrane exhibited excellent rejection for both bivalent and monovalent ions, as well as heavy metal ions, effectively overcoming the common trade-off between permeance and rejection in NF membranes. The membrane demonstrated a remarkable permeance of 13.0 LMH/bar, coupled with exceptional rejection for heavy metal ions (96.8 % for Zn²⁺, 95.2 % for Ni²⁺, 95.7 % for Cu²⁺, 93.2 % for Pb²⁺, and 92.9 % for Cd²⁺). The TMC/HPEI/MIL-303/P84 system presented in this study holds significant promise for customizing high-performance positively charged NF membranes for the removal of heavy metal ions from wastewater.

Lithium extraction from low-quality brines

In the quest for environmental sustainability, the rising demand for electric vehicles and renewable energy technologies has substantially increased the need for efficient lithium extraction methods. Traditional lithium production, relying on geographically concentrated hard-rock ores and salar brines, is associated with considerable energy consumption, greenhouse gas emissions, groundwater depletion and land disturbance, thereby posing notable environmental and supply chain challenges. On the other hand, low-quality brines-such as those found in sedimentary waters, geothermal fluids, oilfield-produced waters, seawater and some salar brines and salt lakes-hold large potential owing to their extensive reserves and widespread geographical distribution. However, extracting lithium from these sources presents technical challenges owing to low lithium concentrations and high magnesium-to-lithium ratios. This Review explores the latest advances and continuing challenges in lithium extraction from these demanding yet promising sources, covering a variety of methods, including precipitation, solvent extraction, sorption, membrane-based separation and electrochemical-based separation. Furthermore, we share perspectives on the future development of lithium extraction technologies, framed within the basic principles of separation processes. The aim is to encourage the development of innovative extraction methods capable of making use of the substantial potential of low-quality brines.

Efficient Lithium Recovery from Water Using Polyamide Thin-Film Nanocomposite (TFN) Membrane Modified with Positively Charged Silica Nanoparticles

The separation of Li+ from Mg2+ in salt-lake brines using nanofiltration (NF) has become the most popular solution to meet the rising demand for lithium, particularly driven by the extensive use of lithium-ion batteries. This study presents the fabrication of a uniquely designed polyamide (PA) thin-film nanocomposite (TFN) membranes with ultrahigh Li+/Mg2+ selectivity and enhanced water flux by covalently incorporating mixed ligands functionalized silica nanoparticles (F-SiO2NPs) into the selective PA layer and covalently bonding them to the membrane surface. In this strategy, bare silica nanoparticles (SiO2NPs) were functionalized with mixed superhydrophilic ligands, including primary amine and quaternary ammonium groups, resulting in a highly positive surface charge primarily from the quaternary ammonium groups and enabling covalent conjugation via amine groups. Among the F-SiO2NP-incorporated membranes, M500 containing 500 ppm of F-SiO2NPs exhibited the best performance. In a solution with 2000 ppm salt concentration (Li+/Mg2+ ratio of 1:20), the M500 membrane showed an improved Li+/Mg2+ selectivity of 7.41 compared to the nonmodified TFC membrane, which had a selectivity of 5.05. Further surface conjugation of the M500 sample with 1500 ppm of F-SiO2NPs resulted in the C1500 membrane, demonstrating the best performance among all of the surface-modified membranes. C1500 showed an outstanding Li+/Mg2+ selectivity of 37.95, with a Mg2+ rejection of 95.7% and a Li+ rejection of -63.2%, and a water flux of 56.0 L m-2 h-1 at 70 psi. Notably, a 7.5-fold improvement in Li+/Mg2+ selectivity over the TFC membrane was achieved without compromising the water flux. This is evident from the nearly identical water flux values of the TFC, M500, and C1500 membranes, which were 57.1, 54.8, and 56.0 L m-2 h-1, respectively. Considering key factors for large-scale applications, such as cost-effectiveness, environmental impact, the abundance of synthetic precursors, and the maturity of synthesis and tailoring technologies, SiO2NP-based modifications outperform all other reported approaches to date.

Supramolecular-coordinated nanofiltration membranes with quaternary-ammonium Cyclen for efficient lithium extraction from high magnesium/lithium ratio brine

Ion-selective membranes (ISM) with sub-nanosized pore channels hold significant potential for applications in saline wastewater treatment and resource recovery. Herein, novel synergistic ion channels featuring bi-periodic structures were constructed through the coordination of functional Cyclen (quaternary_1,4,7,10-tetraazacyclododecane, Q_Cyclen) and Cu2+-m-Phenylenediamine (Cu2+-MPD) to develop supramolecular membranes for lithium extraction. The exterior quaternary ammonium-rich sites exhibit a significant Donnan exclusion effect, resulting in tremendous mono/divalent (Li+/Mg2+) ion selectivity; while the interior regular-confined channels of Cyclen yield a fast vehicular pathway, facilitating water molecules and Li+ ion-selective transport. The optimized membrane exhibited an increased water permeance of 19.2 L·m-2·h-1·bar-1 and simultaneously promoted Li+/Mg2+ selectivity (achieving a selectivity of 18.5 under a Mg2+/Li+ mass ratio of 30), surpassing the trade-off limit of conventional nanofiltration membranes. Due to the acquired excellent Li+/Mg2+ selectivity, lithium extraction from simulated salt-lake brines was successfully achieved through a two-stage nanofiltration process, reducing the Mg2+/Li+ mass ratio from 40 to 1.1. This work validates the applicability of macrocyclic with intrinsic sub-nanosized channels and desired multifunctionality for developing high-performance ISM for efficient lithium separation and beyond.

Eliminating the effect of pH: Dual-matrix modulation adsorbent enables efficient lithium extraction from concentrated seawater

Lithium ion sieve adsorbents frequently extract liquid lithium resources due to their adsorption effect and cost advantages. However, the adsorption effect is significantly influenced by the ambient pH. The pH effects on the adsorption process can be categorized into two main areas: the competition adsorption of impurity ions and the difference in surface zeta potential. A dual-matrix modulation adsorbent was prepared, comprising a carrier matrix modified with zwitterionic quaternary ammonium bases and an adsorption matrix modified with carboxylation. The zwitterionic quaternary ammonium base groups were employed to mitigate the competitive adsorption of impurity ions by acid-base neutralization. Furthermore, the negative charge of carboxyl groups was employed to diminish the discrepancy in surface zeta potential. The adsorption effect of the ion sieve adsorbent under natural conditions appeared to be significantly enhanced by the dual-matrix modulation, with the saturated adsorption capacity (28 mg/g) and adsorption selectivity (α(Li+/Mg2+)=24.23) being 6.3 and 7.8 times higher than that of the manganese-based adsorbent (HMO) under the same conditions, respectively. Moreover, the adsorption effect was found to be consistent with HMO under alkaline conditions. The results demonstrate that by optimizing the adsorption conditions of the adsorbent, the detrimental impact of pH on the adsorption process of lithium ion sieves can be eliminated.

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.

Polyethyleneimine Modified Two-Dimensional GO/MXene Composite Membranes with Enhanced Mg2+/Li+ Separation Performance for Salt Lake Brine

As global demand for renewable energy and electric vehicles increases, the need for lithium has surged significantly. Extracting lithium from salt lake brine has become a cutting-edge technology in lithium resource production. In this study, two-dimensional (2D) GO/MXene composite membranes were fabricated using pressure-assisted filtration with a polyethyleneimine (PEI) coating, resulting in positively charged PEI-GO/MXene membranes. These innovative membranes, taking advantage of the synergistic effects of interlayer channel sieving and the Donnan effect, demonstrated excellent performance in Mg2+/Li+ separation with a mass ratio of 20 (Mg2+ rejection = 85.3%, Li+ rejection = 16.7%, SLi,Mg = 5.7) in simulated saline lake brine. Testing on actual salt lake brine in Tibet, China, confirmed the composite membrane's potential for effective Mg2+/Li+ separation. In the actual brine test with high concentration, Mg2+/Li+ after membrane separation is 2.2, which indicates that the membrane can significantly reduce the concentration of Mg2+ in the brine. Additionally, the PEI-GO/MXene composite membrane demonstrated strong anti-swelling properties and effective divalent ion rejection. This research presents an innovative approach to advance the development of 2D membranes for the selective removal of Mg2+ and Li+ from salt lake brine.

Photoelectrochemical Lithium Extraction from Waste Batteries

The amount of global hybrid-electric and all electric vehicle has increased dramatically in just five years and reached an all-time high of over 10 million units in 2022. A good deal of waste lithium (Li)-containing batteries from dead vehicles are invaluable unconventional resources with high usage of Li. However, the recycle of Li by green approaches is extremely inefficient and rare from waste batteries, giving rise to severe environmental pollutions and huge squandering of resources. Thus, in this mini review, we briefly summarized a green and promising route-photoelectrochemical (PEC) technology for extracting the Li from the waste lithium-containing batteries. This review first focuses on the critical factors of PEC performance, including light harvesting, charge-carrier dynamics, and surface chemical reactions. Subsequently, the conventional and PEC technologies applying in the area of Li recovery processes are analyzed and discussed in depth, and the potential challenges and future perspective for rational and healthy development of PEC Li extraction are provided positively.

Ion-Concentration-Hopping Heterolayer Gel for Ultrahigh Gradient Energy Conversion

Conventional solid ion channel systems relying on single one- or two-dimensional confined nanochannels enabled selective and ultrafast convective ion transport. However, due to intrinsic solid channel stacking, these systems often face pore-pore polarization and ion concentration blockage, thereby restricting their efficiency in macroscale ion transport. Here, we constructed a soft heterolayer-gel system that integrated an ion-selective hydrogel layer with a water-barrier organogel layer, achieving ultrahigh cation selectivity and flux and effectively providing high-efficiency gradient energy conversion on a macroscale order of magnitude. Specifically, the hydrogel layer featured an unconfined 3D network, where the fluctuations of highly hydrated polyelectrolyte chains driven by thermal dynamics enhanced cation selectivity and mitigated transfer energy barriers. Such chain fluctuation mechanisms facilitated ion-cluster internal transmission, thereby enhancing ion concentration hopping for more efficient ion-selective transport. Compared to the existing rigid nanochannel-based gradient energy conversion systems, such a heterogel-based power generator exhibited a record power density of 192.90 and 1.07 W/m2 at the square micrometer scale and square centimeter scale, respectively (under a 500-fold artificial solution). We anticipate that such heterolayer gels would be a promising candidate for energy separation and storage applications.

Precision ion separation via self-assembled channels

Selective nanofiltration membranes with accurate molecular sieving offer a solution to recover rare metals and other valuable elements from brines. However, the development of membranes with precise sub-nanometer pores is challenging. Here, we report a scalable approach for membrane fabrication in which functionalized macrocycles are seamlessly oriented via supramolecular interactions during the interfacial polycondensation on a polyacrylonitrile support layer. The rational incorporation of macrocycles enables the formation of nanofilms with self-assembled channels holding precise molecular sieving capabilities and a threshold of 6.6 ångström, which corresponds to the macrocycle cavity size. The resulting membranes provide a 100-fold increase in selectivity for Li+/Mg2+ separation, outperforming commercially available and state-of-the-art nanocomposite membranes for lithium recovery. Their performance is further assessed in high-recovery tests under realistic nanofiltration conditions using simulated brines or concentrated seawater with various Li+ levels and demonstrates their remarkable potential in ion separation and Li+ recovery applications.

Ion-imprinted membranes for lithium recovery: A review

This review critically examines the effectiveness of ion-imprinted membranes (IIMs) in selectively recovering lithium (Li) from challenging sources such as seawater and brine. These membranes feature customized binding sites that specifically target Li ions, enabling selective separation from other ions, thanks to cavities shaped with crown ether or calixarene for improved selectivity. The review thoroughly investigates the application of IIMs in Li extraction, covering extensive sections on 12-crown-4 ether (a fundamental crown ether for Li), its modifications, calixarenes, and other materials for creating imprinting sites. It evaluates these systems against several criteria, including the source solution's complexity, Li+ concentration, operational pH, selectivity, and membrane's ability for regeneration and repeated use. This evaluation places IIMs as a leading-edge technology for Li extraction, surpassing traditional methods like ion-sieves, particularly in high Mg2+/Li+ ratio brines. It also highlights the developmental challenges of IIMs, focusing on optimizing adsorption, maintaining selectivity across varied ionic solutions, and enhancing permselectivity. The review reveals that while the bulk of research is still exploratory, only a limited portion has progressed to detailed lab verification, indicating that the application of IIMs in Li+ recovery is still at an embryonic stage, with no instances of pilot-scale trials reported. This thorough review elucidates the potential of IIMs in Li recovery, cataloging advancements, pinpointing challenges, and suggesting directions for forthcoming research endeavors. This informative synthesis serves as a valuable resource for both the scientific community and industry professionals navigating this evolving field.

Microenvironment-Modulating Adsorption Enables Highly Efficient Lithium Extraction under Natural pH Conditions

Ion-sieve adsorbents are effective materials in practical applications for extracting liquid lithium. However, it is greatly suppressed in adsorption capacity and selectivity (Li/Mg) under natural near-neutral conditions of seawater or salt lakes, due to the interference of in situ released H+ and Mg2+ impurity. This paper proposes an adsorbent with a microenvironment-modulating function as a solution. The introduction of quaternary ammonium groups into the carrier accelerates the migration of H+, while preventing the diffusion of Mg2+ by electrostatic repulsion. Besides, it can also prestore OH-, effectively consuming the generated hydrogen ions in situ. Based on the rational design, the alkali consumption of the microenvironment-modulating strategy is dramatically reduced to 1/144 of the traditional alkali-adding method. Additionally, adsorption performance is significantly promoted under natural pH conditions, with a maximum 33 times higher separation factor (selectivity) and 4 times higher adsorption capacity than commercial ion-sieve adsorbents. This development indicates the feasibility of using microenvironment modulation for effective lithium extraction and inspires the development of next-generation high-performance adsorbents.

Extreme Li-Mg selectivity via precise ion size differentiation of polyamide membrane

Achieving high selectivity of Li+ and Mg2+ is of paramount importance for effective lithium extraction from brines, and nanofiltration (NF) membrane plays a critical role in this process. The key to achieving high selectivity lies in the on-demand design of NF membrane pores in accordance with the size difference between Li+ and Mg2+ ions, but this poses a huge challenge for traditional NF membranes and difficult to be realized. In this work, we report the fabrication of polyamide (PA) NF membranes with ultra-high Li+/Mg2+ selectivity by modifying the interfacial polymerization (IP) process between piperazine (PIP) and trimesoyl chloride (TMC) with an oil-soluble surfactant that forms a monolayer at oil/water interface, referred to as OSARIP. The OSARIP benefits to regulate the membrane pores so that all of them are smaller than Mg2+ ions. Under the solely size sieving effect, an exceptional Mg2+ rejection rate of over 99.9% is achieved. This results in an exceptionally high Li+/Mg2+ selectivity, which is one to two orders of magnitude higher than all the currently reported pressure-driven membranes, and even higher than the microporous framework materials, including COFs, MOFs, and POPs. The large enhancement of ion separation performance of NF membranes may innovate the current lithium extraction process and greatly improve the lithium extraction efficiency.

Binder-Free LiMn2 O4 Nanosheets on Carbon Cloth for Selective Lithium Extraction from Brine via Capacitive Deionization

In this study, a three-step strategy including electrochemical cathode deposition, self-oxidation, and hydrothermal reaction is applied to prepare the LiMn2 O4 nanosheets on carbon cloth (LMOns@CC) as a binder-free cathode in a hybrid capacitive deionization (CDI) cell for selectively extracting lithium from salt-lake brine. The binder-free LMOns@CC electrodes are constructed from dozens of 2D LiMn2 O4 nanosheets on carbon cloth substrates, resulting in a uniform 2D array of highly ordered nanosheets with hierarchical nanostructure. The charge/discharge process of the LMOns@CC electrode demonstrates that visible redox peaks and high pseudocapacitive contribution rates endow the LMOns@CC cathode with a maximum Li+ ion electrosorption capacity of 4.71 mmol g-1 at 1.2 V. Moreover, the LMOns@CC electrode performs outstanding cycling stability with a high-capacity retention rate of 97.4% and a manganese mass dissolution rate of 0.35% over ten absorption-desorption cycles. The density functional theory (DFT) theoretical calculations verify that the Li+ selectivity of the LMOns@CC electrode is attributed to the greater adsorption energy of Li+ ions than other ions. Finally, the selective extraction performance of Li+ ions in natural Tibet salt lake brine reveals that the LMOns@CC has selectivity (α Mg 2 + Li + $\alpha _{{\mathrm{Mg}}^{2 + }}^{{\mathrm{Li}}^ + }$ = 7.48) and excellent cycling stability (100 cycles), which would make it a candidate electrode for lithium extraction from salt lakes.

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.

Shearing Liquid-Crystalline MXene into Lamellar Membranes with Super-Aligned Nanochannels for Ion Sieving

Ion-selective membranes are crucial in various chemical and physiological processes. Numerous studies have demonstrated progress in separating monovalent/multivalent ions, but efficient monovalent/monovalent ion sieving remains a great challenge due to their same valence and similar radii. Here, this work reports a two-dimensional (2D) MXene membrane with super-aligned slit-shaped nanochannels with ultrahigh monovalent ion selectivity. The MXene membrane is prepared by applying shear forces to a liquid-crystalline (LC) MXene dispersion, which is conducive to the highly-ordered stacking of the MXene nanosheets. The obtained LC MXene membrane (LCMM) exhibits ultrahigh selectivities toward Li+ /Na+ , Li+ /K+ , and Li+ /Rb+ separation (≈45, ≈49, and ≈59), combined with a fast Li+ transport with a permeation rate of ≈0.35 mol m-2  h-1 , outperforming the state-of-the-art membranes. Theoretical calculations indicate that in MXene nanochannels, the hydrated Li+ with a tetrahedral shape has the smallest diameter among the monovalent ions, contributing to the highest mobility. Besides, the weakest interaction is found between hydrated Li+ and MXene channels which also contributes to the ultrafast permeation of Li+ through the super-aligned MXene channels. This work demonstrates the capability of MXene membranes in monovalent ion separation, which also provides a facile and general strategy to fabricate lamellar membranes in a large scale.

Membrane-based technology in water and resources recovery from the perspective of water social circulation: A review

In this review, the application of membrane-based technology in water social circulation was summarized. Water social circulation encompassed the entire process from the acquirement to discharge of water from natural environment for human living and development. The focus of this review was primarily on the membrane-based technology in recovery of water and other valuable resources such as mineral ions, nitrogen and phosphorus. The main text was divided into four main sections according to water flow in the social circulation: drinking water treatment, agricultural utilization, industrial waste recycling, and urban wastewater reuse. In drinking water treatment, the acquirement of water resources was of the most importance. Pressure-driven membranes, such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) were considered suitable in natural surface water treatment. Additionally, electrodialysis (ED) and membrane capacitive deionization (MCDI) were also effective in brackish water desalination. Agriculture required abundant water with relative low quality for irrigation. Therefore, the recovery of water from other stages of the social circulation has become a reasonable solution. Membrane bioreactor (MBR) was a typical technique attributed to low-toxicity effluent. In industrial waste reuse, the osmosis membranes (FO and PRO) were utilized due to the complex physical and chemical properties of industrial wastewater. Especially, membrane distillation (MD) might be promising when the wastewater was preheated. Resources recovery in urban wastewater was mainly divided into recovery of bioenergy (via anaerobic membrane bioreactors, AnMBR), nitrogen (utilizing MD and gas-permeable membrane), and phosphorus (through MBR with chemical precipitation). Furthermore, hybrid/integrated systems with membranes as the core component enhanced their performance and long-term working ability in utilization. Generally, concentrate management and energy consumption control might be the key areas for future advancements of membrane-based technology.

Self-assembled dendrimer polyamide nanofilms with enhanced effective pore area for ion separation

Membrane technology using well-defined pore structure can achieve high ion purity and recovery. However, fine-tuning the inner pore structure of the separation nanofilm to be uniform and enhance the effective pore area is still challenging. Here, we report dendrimers with different peripheral groups that preferentially self-assemble in aqueous-phase amine solution to facilitate the formation of polyamide nanofilms with a well-defined effective pore range and uniform pore structure. The high permeabilities are maintained by forming asymmetric hollow nanostripe nanofilms, and their well-designed ion effective separation pore ranges show an enhancement, rationalized by molecular simulation. The self-assembled dendrimer polyamide membrane provides Cl-/SO42- selectivity more than 17 times that of its pristine polyamide counterparts, increasing from 167.9 to 2883.0. Furthermore, the designed membranes achieve higher Li purity and Li recovery compared to current state-of-the-art membranes. Such an approach provides a scalable strategy to fine-tune subnanometre structures in ion separation nanofilms.

Solar-driven membrane separation for direct lithium extraction from artificial salt-lake brine

The demand for lithium extraction from salt-lake brines is increasing to address the lithium supply shortage. Nanofiltration separation technology with high Mg2+/Li+ separation efficiency has shown great potential for lithium extraction. However, it usually requires diluting the brine with a large quantity of freshwater and only yields Li+-enriched solution. Inspired by the process of selective ion uptake and salt secretion in mangroves, we report here the direct extraction of lithium from salt-lake brines by utilizing the synergistic effect of ion separation membrane and solar-driven evaporator. The ion separation membrane-based solar evaporator is a multilayer structure consisting of an upper photothermal layer to evaporate water, a hydrophilic porous membrane in the middle to generate capillary pressure as the driving force for water transport, and an ultrathin ion separation membrane at the bottom to allow Li+ to pass through and block other multivalent ions. This process exhibits excellent lithium extraction capability. When treating artificial salt-lake brine with salt concentration as high as 348.4 g L-1, the Mg2+/Li+ ratio is reduced by 66 times (from 19.8 to 0.3). This research combines ion separation with solar-driven evaporation to directly obtain LiCl powder, providing an efficient and sustainable approach for lithium extraction.

In Situ Growth of MOF-303 Membranes onto Porous Anodic Aluminum Oxide Substrates for Harvesting Salinity-Gradient Energy

As an emerging metal-organic framework (MOF) material in recent years, the MOF-303 membrane has shown great potential applications in seawater desalination, dehydration, and atmospheric water harvesting. Herein, we report on a dense and uniform MOF-303 membrane fabricated by a facile in situ hydrothermal synthesis approach in the presence of an anodized aluminum oxide (AAO) channel membrane acting as the only Al source and substrate. Interestingly, the MOF-303 isomer can be obtained due to an insufficient amount of organic ligand caused by the less hydrophilic and larger pore size of the AAO substrate. The MOF-based composite membranes possessed surface-charge-governed ionic transport behavior. Moreover, the MOF-303/AAO membrane yielded an output power density of 1.87 W/m2 under a 50-fold KCl concentration gradient. Under a 50-fold gradient of artificial seawater and river water, a maximum power density of 1.46 W/m2 can be obtained. After 30 days of stability testing, the composite membrane still maintained the power output, and the power density was higher than 1.20 W/m2. This work provides a facile and effective strategy for constructing Al-based MOF composite membranes and boosts their applications in harvesting salinity-gradient energy.

A review on artificial water channels incorporated polyamide membranes for water purification: Transport mechanisms and performance

While thin-film composite (TFC) polyamide (PA) membranes are advanced for removing salts and trace organic contaminants (TrOCs) from water, TFC PA membranes encounter a water permeance-selectivity trade-off due to PA layer structural characteristics. Drawing inspiration from the excellent water permeance and solute rejection of natural biological channels, the development of analogous artificial water channels (AWCs) in TFC PA membranes (abbreviated as AWCM) promises to achieve superior mass transfer efficiency, enabling breaking the upper bound of water permeance and selectivity. Herein, we first discussed the types and structural characteristics of AWCs, followed by summarizing the methods for constructing AWCM. We discussed whether the AWCs acted as the primary mass transfer channels in AWCM and emphasized the important role of the AWCs in water transport and ion/TrOCs rejection. We thoroughly summarized the molecular-level mechanisms and structure-performance relationship of water molecules, ions, and TrOCs transport in the confined nanospace of AWCs, which laid the foundation for illustrating the enhanced water permeance and salt/TrOCs selectivity of AWCM. Finally, we discussed the challenges encountered in the field of AWCM and proposed future perspectives for practical applications. This review is expected to offer guidance for understanding the transport mechanisms of AWCM and developing next-generation membrane for effective water treatment.

Ternary Heterostructure Membranes with Two-Dimensional Tunable Channels for Highly Selective Ion Separation

Selective ion separation from brines is pivotal for attaining high-purity lithium, a critical nonrenewable resource. Conventional methods encounter substantial challenges, driving the quest for streamlined, efficient, and swift approaches. Here, we present a graphene oxide (GO)-based ternary heterostructure membrane with a unique design. By utilizing Zn2+-induced confinement synthesis in a two-dimensional (2D) space, we incorporated two-dimensional zeolitic imidazolate framework-8 (ZIF-8) and zinc alginate (ZA) polymers precisely within layers of the GO membrane, creating tunable interlayer channels with a ternary heterostructure. The pivotal design lies in ion insertion into the two-dimensional (2D) membrane layers, achieving meticulous modulation of layer spacing based on ion hydration radius. Notably, the ensuing layer spacing within the hybrid ionic intercalation membrane occupies an intermediary realm, positioned astutely between small-sized hydrated ionic intercalation membrane spacing and their more extensive counterparts. This deliberate configuration accelerates the swift passage of diminutive hydrated ions while simultaneously impeding the movement of bulkier ions within the brine medium. The outcome is remarkable selectivity, demonstrated by the partitioning of K+/Li+ = 20.9, Na+/K+ = 31.2, and Li+/Mg2+ = 9.5 ion pairs. The ZIF-8/GO heterostructure significantly contributes to the selectivity, while the mechanical robustness and stability, improved by the ZA/GO heterostructure, further support its practical applicability. This report reports an advanced membrane design, offering promising prospects for lithium extraction and various ion separation processes.

Tailoring Monovalent Ion Sieving in Graphene-Oxide Membranes with High Flux by Rationally Intercalating Crown Ethers

Two-dimensional membranes have shown promising potential for ion-selective separation due to their well-defined interlayer channels. However, the typical "trade-off" effect of throughput and selectivity limits their developments. Herein, we report a precise tailoring of monovalent cation sieving technology with enhanced water throughput via the intercalation of graphene-oxide membranes with selective crown ethers. By tuning the lamellar spacing of graphene oxide, a critical interlayer distance (∼11.04 Å) is revealed to maximize water flux (53.4 mol m-2 h-2 bar-1) without sacrificing ion selectivity. As a result, the elaborately enlarged interlayer distance offers improved water permeance. Meanwhile, various specific cations with remarkably high selectivity can be separated in mixed solutions because of the strong chelation with crown ethers. This work opens up a new avenue for high-throughput and precise regulation of ion separations for various application scenarios.

Sustainable Lithium Recovery from Hypersaline Salt-Lakes by Selective Electrodialysis: Transport and Thermodynamics

Evaporative technology for lithium mining from salt-lakes exacerbates freshwater scarcity and wetland destruction, and suffers from protracted production cycles. Electrodialysis (ED) offers an environmentally benign alternative for continuous lithium extraction and is amenable to renewable energy usage. Salt-lake brines, however, are hypersaline multicomponent mixtures, and the impact of the complex brine-membrane interactions remains poorly understood. Here, we quantify the influence of the solution composition, salinity, and acidity on the counterion selectivity and thermodynamic efficiency of electrodialysis, leveraging 1250 original measurements with salt-lake brines that span four feed salinities, three pH levels, and five current densities. Our experiments reveal that commonly used binary cation solutions, which neglect Na+ and K+ transport, may overestimate the Li+/Mg2+ selectivity by 250% and underpredict the specific energy consumption (SEC) by a factor of 54.8. As a result of the hypersaline conditions, exposure to salt-lake brine weakens the efficacy of Donnan exclusion, amplifying Mg2+ leakage. Higher current densities enhance the Donnan potential across the solution-membrane interface and ameliorate the selectivity degradation with hypersaline brines. However, a steep trade-off between counterion selectivity and thermodynamic efficiency governs ED's performance: a 6.25 times enhancement in Li+/Mg2+ selectivity is accompanied by a 71.6% increase in the SEC. Lastly, our analysis suggests that an industrial-scale ED module can meet existing salt-lake production capacities, while being powered by a photovoltaic farm that utilizes <1% of the salt-flat area.

Extreme Ion-Transport Inorganic 2D Membranes for Nanofluidic Applications

Inorganic 2D materials offer a new approach to controlling mass diffusion at the nanoscale. Controlling ion transport in nanofluidics is key to energy conversion, energy storage, water purification, and numerous other applications wherein persistent challenges for efficient separation must be addressed. The recent development of 2D membranes in the emerging field of energy harvesting, water desalination, and proton/Li-ion production in the context of green energy and environmental technology is herein discussed. The fundamental mechanisms, 2D membrane fabrication, and challenges toward practical applications are highlighted. Finally, the fundamental issues of thermodynamics and kinetics are outlined along with potential membrane designs that must be resolved to bridge the gap between lab-scale experiments and production levels.

Anisotropic gypsum scaling of corrugated polyvinylidene fluoride hydrophobic membrane in direct contact membrane distillation

Membrane distillation (MD) technology has gained a lot of attention for treatment of geothermal brine, high salinity waste streams. However, mineral scaling remains a major challenge when treating complex high-salt brines. The development of surface-patterned superhydrophobic membranes is one of the core strategies to solve this problem. We prepared flat sheet membranes (F-PVDF) and hydrophobic membranes with micron-scale corrugated pattern (C-PVDF) using a phase separation method. Their scaling behavior was systematically evaluated using calcium sulfate solutions and the impact of the feed flow was innovatively investigated. Although C-PVDF shows higher contact angle and lower sliding angle than F-PVDF, the scaling resistance of C-PVDF in the perpendicular flow direction has worst scaling resistance. Although the nucleation barrier of the corrugated membrane is the same at both parallel and perpendicular flow directions based on the traditional thermodynamic nucleation theory, experimental observations show that the C-PVDF has the best scaling resistance in the parallel flow direction. A 3D computational fluid dynamics (CFD) model was used and the hydrodynamic state of the pattern membranes was assessed as a determinant of the scaling resistance. The corrugated membrane with parallel flow mode (flow direction in parallel to the corrugation ridge) induces higher fluid velocity within the channel, which mitigated the deposition of crystals. While in the perpendicular flow mode (flow direction in perpendicular to the corrugation ridge), the solutions confined in the corrugated grooves due to vortex shielding, which aggravates the scaling. These results shed light on the mechanism of scaling resistance of corrugated membranes from a hydrodynamic perspective and reveal the mechanism of anisotropy exhibited by corrugated membranes in MD.

Multipass Nanofiltration for Lithium Separation with High Selectivity and Recovery

Nanofiltration (NF) is a promising and sustainable process to extract Li+ from brine lakes with high Mg2+/Li+ mass ratios. However, a trade-off between Li/Mg selectivity and Li recovery exists at the process scale, and the Li/Mg selectivity of commercially and lab-made NF membranes in a single-pass NF process is insufficient to achieve the industrially required Li purity. To overcome this challenge, we propose a multipass NF process with brine recirculation to achieve high selectivity without sacrificing Li recovery. We experimentally demonstrate that Li/Mg selectivity of a three-pass NF process with a commercial NF membrane can exceed 1000, despite the compromised Li recovery as a result of co-existing cations. Our theoretical analysis further predicts that a four-pass NF process with brine recirculation can simultaneously achieve an ultrahigh Li/Mg selectivity of over 4500 and a Li recovery of over 95%. This proposed process could potentially facilitate efficient NF-based solute-solute separations of all kinds and contribute to the development of novel membrane-based separation technologies.

Comparison of the Mg2+-Li+ Separation of Different Nanofiltration Membranes

Nanofiltration application for the separation of Mg2+-Li+ from salt-lake brines was attempted in the present work. Four different nanofiltration membranes identified in the manuscript as DL, DK, NF-270, and NF-90 were used to treat salt brine with a magnesium to lithium ratio (MLR) of 61, additionally contaminated by the other ions such as Na+, K+, Ca2+, etc. The effect of the dilution factor, operating pressure, circulation rate, and feed pH were assessed to identify the optimal operating conditions for each membrane based on the retention efficiency of each ion. The results showed an insignificant effect of Ca2+ on the retention performance of Mg2+-Li+. Na+ and K+ had a smaller hydration radius and larger diffusion coefficient, which competed with Li+ and altered the separation of Mg2+-Li+. Under the optimal conditions (dilution factor: 40; operating pressure: 1.2 MPa; circulation flow rate: 500 L/h; pH: 7), the retention efficiency of lithium was as low as 5.17%, separation factor (SF) was as low as 0.074, and the MLR in the permeate reduced to 0.088.

Utilization of Electrodeionization for Lithium Removal

In this work, usage of a hybrid polymeric ion exchange resin and a polymeric ion exchange membrane in the same unit to remove Li⁺ from aqueous solutions was reported. The effects of the applied potential difference to the electrodes, the flow rate of the Li-containing solution, the presence of coexisting ions (Na⁺, K⁺, Ca²⁺, Ba²⁺, and Mg²⁺), and the influence of the electrolyte concentration in the anode and cathode chambers on Li⁺ removal were investigated. At 20 V, 99% of Li⁺ was removed from the Li-containing solution. In addition, a decrease in the flow rate of the Li-containing solution from 2 to 1 L/h resulted in a decrease in the removal rate from 99 to 94%. Similar results were obtained when the concentration of Na₂SO₄ was decreased from 0.01 to 0.005 M. The selectivity test showed that the simultaneous presence of monovalent ions such as Na⁺ and K⁺ did not change the removal rate of Li⁺. However, the presence of divalent ions, Ca²⁺, Mg²⁺, and Ba²⁺, reduced the removal rate of Li⁺. Under optimal conditions, the mass transport coefficient of Li⁺ was found as 5.39 × 10^-4 m/s, and the specific energy consumption was found as 106.2 W h/g LiCl. Electrodeionization provided stable performance in terms of the removal rate and transport of Li⁺ from the central compartment to the cathode compartment.

Selective Ion Transport in Two-Dimensional Lamellar Nanochannel Membranes

Precise and ultrafast ion sieving is highly desirable for many applications in environment-, energy-, and resource-related fields. The development of a permselective lamellar membrane constructed from parallel stacked two-dimensional (2D) nanosheets opened a new avenue for the development of next-generation separation technology because of the unprecedented diversity of the designable interior nanochannels. In this Review, we first discuss the construction of homo- and heterolaminar nanoarchitectures from the starting materials to the emerging preparation strategies. We then explore the property-performance relationships, with a particular emphasis on the effects of physical structural features, chemical properties, and external environment stimuli on ion transport behavior under nanoconfinement. We also present existing and potential applications of 2D membranes in desalination, ion recovery, and energy conversion. Finally, we discuss the challenges and outline research directions in this promising field.