Membrane technologies for Li+/Mg2+ separation from salt-lake brines and seawater: A comprehensive review

Tailored design of nanofiltration membranes for water treatment based on synthesis-property-performance relationships

Tailored design of high-performance nanofiltration (NF) membranes is desirable because the requirements for membrane performance, particularly ion/salt rejection and selectivity, differ among the various applications of NF technology ranging from drinking water production to resource mining. However, this customization greatly relies on a comprehensive understanding of the influence of membrane fabrication methods and conditions on membrane properties and the relationships between the membrane structural and physicochemical properties and membrane performance. Since the inception of NF, much progress has been made in forming the foundation of tailored design of NF membranes and the underlying governing principles. This progress includes theories regarding NF mass transfer and solute rejection, further exploitation of the classical interfacial polymerization technique, and development of novel materials and membrane fabrication methods. In this critical review, we first summarize the progress made in controllable design of NF membrane properties in recent years from the perspective of optimizing interfacial polymerization techniques and adopting new manufacturing processes and materials. We then discuss the property-performance relationships based on solvent/solute mass transfer theories and mathematical models, and draw conclusions on membrane structural and physicochemical parameter regulation by modifying the fabrication process to improve membrane separation performance. Next, existing and potential applications of these NF membranes in water treatment processes are systematically discussed according to the different separation requirements. Finally, we point out the prospects and challenges of tailored design of NF membranes for water treatment applications. This review bridges the long-existing gaps between the pressing demand for suitable NF membranes from the industrial community and the surge of publications by the scientific community in recent years.

Technology for the Recovery of Lithium from Geothermal Brines

Lithium is the principal component of high-energy-density batteries and is a critical material necessary for the economy and security of the United States. Brines from geothermal power production have been identified as a potential domestic source of lithium; however, lithium-rich geothermal brines are characterized by complex chemistry, high salinity, and high temperatures, which pose unique challenges for economic lithium extraction. The purpose of this paper is to examine and analyze direct lithium extraction technology in the context of developing sustainable lithium production from geothermal brines. In this paper, we are focused on the challenges of applying direct lithium extraction technology to geothermal brines; however, applications to other brines (such as coproduced brines from oil wells) are considered. The most technologically advanced approach for direct lithium extraction from geothermal brines is adsorption of lithium using inorganic sorbents. Other separation processes include extraction using solvents, sorption on organic resin and polymer materials, chemical precipitation, and membrane-dependent processes. The Salton Sea geothermal field in California has been identified as the most significant lithium brine resource in the US and past and present efforts to extract lithium and other minerals from Salton Sea brines were evaluated. Extraction of lithium with inorganic molecular sieve ion-exchange sorbents appears to offer the most immediate pathway for the development of economic lithium extraction and recovery from Salton Sea brines. Other promising technologies are still in early development, but may one day offer a second generation of methods for direct, selective lithium extraction. Initial studies have demonstrated that lithium extraction and recovery from geothermal brines are technically feasible, but challenges still remain in developing an economically and environmentally sustainable process at scale.

Origins of Lithium/Sodium Reverse Permeability Selectivity in 12-Crown-4-Functionalized Polymer Membranes

Direct lithium extraction via membrane separations has been fundamentally limited by lack of monovalent ion selectivity exhibited by conventional polymeric membranes, particularly between sodium and lithium ions. Recently, a 12-Crown-4-functionalized polynorbornene membrane was shown to have the largest lithium/sodium permeability selectivity observed in a fully aqueous system to date. Using atomistic molecular dynamics simulations, we reveal that this selectivity is due to strong interactions between sodium ions and 12-Crown-4 moieties, which reduce sodium ion diffusivity while leaving lithium ion mobility relatively unaffected. Moreover, the ion diffusivities in the membrane, when scaled by their respective solution diffusivities and free ion fractions, can be collapsed to an almost universal relationship depending on solvent volume fraction.

Engineering Li/Na selectivity in 12-Crown-4-functionalized polymer membranes

Lithium is widely used in contemporary energy applications, but its isolation from natural reserves is plagued by time-consuming and costly processes. While polymer membranes could, in principle, circumvent these challenges by efficiently extracting lithium from aqueous solutions, they usually exhibit poor ion-specific selectivity. Toward this end, we have incorporated host-guest interactions into a tunable polynorbornene network by copolymerizing 1) 12-crown-4 ligands to impart ion selectivity, 2) poly(ethylene oxide) side chains to control water content, and 3) a crosslinker to form robust solids at room temperature. Single salt transport measurements indicate these materials exhibit unprecedented reverse permeability selectivity (∼2.3) for LiCl over NaCl-the highest documented to date for a dense, water-swollen polymer. As demonstrated by molecular dynamics simulations, this behavior originates from the ability of 12-crown-4 to bind Na+ ions more strongly than Li+ in an aqueous environment, which reduces Na+ mobility (relative to Li+) and offsets the increase in Na+ solubility due to binding with crown ethers. Under mixed salt conditions, 12-crown-4 functionalized membranes showed identical solubility selectivity relative to single salt conditions; however, the permeability and diffusivity selectivity of LiCl over NaCl decreased, presumably due to flux coupling. These results reveal insights for designing advanced membranes with solute-specific selectivity by utilizing host-guest interactions.

Novel Positively Charged Metal-Coordinated Nanofiltration Membrane for Lithium Recovery

Nanofiltration (NF) with high water flux and precise separation performance with high Li⁺/Mg²⁺ selectivity is ideal for lithium brine recovery. However, conventional polyamide-based commercial NF membranes are ineffective in lithium recovery processes due to their undesired Li⁺/Mg²⁺ selectivity. In addition, they are constrained by the water permeance selectivity trade-off, which means that a highly permeable membrane often has lower selectivity. In this study, we developed a novel nonpolyamide NF membrane based on metal-coordinated structure, which exhibits simultaneously improved water permeance and Li⁺/Mg²⁺ selectivity. Specifically, the optimized Cu-m-phenylenediamine (MPD) membrane demonstrated a high water permeance of 16.2 ± 2.7 LMH/bar and a high Li⁺/Mg²⁺ selectivity of 8.0 ± 1.0, which surpassed the trade-off of permeance selectivity. Meanwhile, the existence of copper in the Cu-MPD membrane further enhanced anti-biofouling property and the metal-coordinated nanofiltration membrane possesses a pH-responsive property. Finally, a transport model based on the Nernst-Planck equations has been developed to fit the water flux and rejection of uncharged solutes to the experiments conducted. The model had a deviation below 2% for all experiments performed and suggested an average pore radius of 1.25 nm with a porosity of 21% for the Cu-MPD membrane. Overall, our study provides an exciting approach for fabricating a nonpolyamide high-performance nanofiltration membrane in the context of lithium recovery.

Ionic Mobility in Ion-Exchange Membranes

Membrane technologies are widely demanded in a number of modern industries. Ion-exchange membranes are one of the most widespread and demanded types of membranes. Their main task is the selective transfer of certain ions and prevention of transfer of other ions or molecules, and the most important characteristics are ionic conductivity and selectivity of transfer processes. Both parameters are determined by ionic and molecular mobility in membranes. To study this mobility, the main techniques used are nuclear magnetic resonance and impedance spectroscopy. In this comprehensive review, mechanisms of transfer processes in various ion-exchange membranes, including homogeneous, heterogeneous, and hybrid ones, are discussed. Correlations of structures of ion-exchange membranes and their hydration with ion transport mechanisms are also reviewed. The features of proton transfer, which plays a decisive role in the membrane used in fuel cells and electrolyzers, are highlighted. These devices largely determine development of hydrogen energy in the modern world. The features of ion transfer in heterogeneous and hybrid membranes with inorganic nanoparticles are also discussed.

Evaluating Critical Influencing Factors of Desalination by Membrane Distillation Process-Using Multi-Criteria Decision-Making

Water desalination by membrane distillation (MD) can be affected by a wide range of operating parameters. The present work uses combinational approach of Analytical Hierarch process (AHP) and Fuzzy Analytical Hierarchy process (Fuzzy-AHP) to identify the most important parameters in the MD desalination. Five process parameters and key-performance indicators, named derivable outputs (DOs), are considered, along with the critical factors affecting these DOs in the current study. The DOs and the critical influencing factors (CIFs) are selected based on their experimental feasibility. The investigation involves five DOs, which are liquid entry pressure, thermal power consumption, permeate quality, permeate flux, and pumping (feed circulation) power. A total of twenty-five critical influencing factor were associated with the DOs. The identification of the DOs and CIFs was based on the literature review, and further analyses were performed. Both methods, AHP and Fuzzy-AHP, determined six extremely important CIFs in the desalination MD, which are feed temperature, feed concentration, or feed salinity; feed flow rate; membrane hydrophobicity; pore size; and membrane material. Moderately important CIFs are found to be four by both methods. These common CIFs are feed solution properties, membrane thickness, feed channel geometry, and pressure difference along the feed channel. Finally, the least preferred CIFs are four common in both methods that are MD configuration, duration of test, specific heat of feed solution, and viscosity.

Effect of salinity on preconcentration of contaminants of emerging concern by nanofiltration: Application of solar photo-Fenton as a tertiary treatment

This study focused on the effect of salinity on the performance of a pilot-scale nanofiltration (NF) for preconcentration of microcontaminants (MCs) in combination with solar photo-Fenton or photo-Fenton-like treatment for their elimination from NF permeate and concentrate streams. Photo-Fenton was carried out in a solar simulator at pH of 3 and at natural pH using Ethylenediamine-N, N'-disuccinic acid (EDDS) as an iron complexing agent. Degradation efficacy was tested with MCs commonly found in urban wastewater treatment plant effluents (caffeine, imidacloprid, thiacloprid, carbamazepine and diclofenac). Hydrogen peroxide and persulfate were compared in solar processes. Increase in salinity and pressure had a negligible influence on MC permeability order and NF selectivity. Solar photo-Fenton was able to degrade MCs present in the concentrated stream, and rapidly eliminate any residual MCs that might finally be present in permeate streams. Persulfate used instead of hydrogen peroxide was shown to be inefficient for the selected MCs. Fe(III):EDDS at circumneutral pH was able to remove MCs as quickly as classical photo-Fenton at acid pH, or even faster. This effect supports use of Fe(III):EDDS at natural pH for treating NF concentrates or polishing NF permeates when NF membranes are operated under extreme conditions of salinity.

Lithium recovery from salt-lake brine: Impact of competing cations, pretreatment and preconcentration

The global demand of lithium is rising steadily, and many industrially advanced countries may find it hard to secure an uninterrupted supply of lithium for meeting their manufacturing demands. Thus, innovative processes for lithium recovery from a wide range of natural reserves should be explored for meeting the future demands. In this study, a novel integrated approach was investigated by combining nanofiltration (NF), membrane distillation (MD) and precipitation processes for lithium recovery from salt-lake brines. Initially, the brine was filtered with an NF membrane for the separation of lithium ions (Li⁺) from competing ions such as Na⁺, K⁺, Ca²⁺ and Mg²⁺. The extent of permeation of metal ions by the NF membrane was governed by their hydrated ionic radii. Rejection by NF membrane was 42% for Li, 48% for Na and 61% for K, while both the divalent cations were effectively rejected (above 90%). Importantly, in the NF-permeate, Mg²⁺/Li⁺ mass ratio reduced to less than 6 (suggested for lithium recovery). The result showed that MD can enrich lithium with a concentration of 2.5 for raw brine and 5 for NF-treated brine. Following the enrichment of NF-permeate by the MD membrane, a two-stage precipitation method was used for the recovery of lithium. X-ray diffraction confirmed the precipitation of lithium as well as the formation of lithium carbonate crystals.

A review on approaches for hazardous organics removal from Bayer liquors

Alumina is a valuable raw material for the production of adsorbents, abrasives, polishing agents, refractory materials, and aluminum. It is generally produced from bauxites through the Bayer process. Several organic compounds such as humic matters and oxalates are introduced into the Bayer liquor during the digestion process, resulting in significant hazards to precipitation of aluminum hydroxide. Therefore, it is crucial to remove these organic compounds from Bayer liquor to enhance the production of alumina. It is difficult to remove these organic compounds. Various approaches for organics removal from Bayer liquors have been developed in the past few decades, including thermal treatment, chemical precipitation, membrane technology, photocatalytic degradation, biodegradation, and wet oxidation. This paper reviews the technologies for organics removal from Bayer liquor and the relative mechanisms proposed in the literature to identify its essential parameters. Chemicals dosage, temperature, pH value, reaction time, and solution concentration are essential factors in the process. Removal efficiency, green principle, and economic viability of various methods are discussed, and potential technologies are suggested. Wet oxidation appears to be a promising method for removing organic matters in Bayer liquors. Moreover, the combination of wet oxidation and electrooxidation shows excellent potential in organics removal. Various approaches for removing organic compounds and perspectives for further investigation are proposed.

Industrial Recycling of Lithium-Ion Batteries—A Critical Review of Metallurgical Process Routes

Research for the recycling of lithium-ion batteries (LIBs) started about 15 years ago. In recent years, several processes have been realized in small-scale industrial plants in Europe, which can be classified into two major process routes. The first one combines pyrometallurgy with subsequent hydrometallurgy, while the second one combines mechanical processing, often after thermal pre-treatment, with metallurgical processing. Both process routes have a series of advantages and disadvantages with respect to legislative and health, safety and environmental requirements, possible recovery rates of the components, process robustness, and economic factors. This review critically discusses the current status of development, focusing on the metallurgical processing of LIB modules and cells. Although the main metallurgical process routes are defined, some issues remain unsolved. Most process routes achieve high yields for the valuable metals cobalt, copper, and nickel. In comparison, lithium is only recovered in few processes and with a lower yield, albeit a high economic value. The recovery of the low value components graphite, manganese, and electrolyte solvents is technically feasible but economically challenging. The handling of organic and halogenic components causes technical difficulties and high costs in all process routes. Therefore, further improvements need to be achieved to close the LIB loop before high amounts of LIB scrap return.

High-Performance Zwitterionic Nanofiltration Membranes Fabricated via Microwave-Assisted Grafting of Betaine

The thin-film composite (TFC) nanofiltration (NF) membrane is a very important method in solving the water crisis. However, the fabrication and industrialization of high-performance NF membranes still remains challenging. In this work, zwitterionic NF membranes via microwave-assisted grafting of betaine was first proposed. The resulting polyamide layer showed leaflike nanostructures after modification. Because of the enlarged permeation area and enhanced hydrophilicity derived from the unique leaflike structure, the optimal membrane permeability reached 40.8 L m^-1 h^-1 bar^-1. This water permeance was 2.2 times as high as the original polypiperazine-amide membrane, with a Na₂SO₄ rejection maintained at 97.0%. More importantly, the membrane demonstrated excellent selectivity to monovalent and divalent anions. This zwitterionic membrane fabricated by microwave-assisted grafting of betaine provides new insight for industrial scalable NF membranes with great potentials.

Selectivity of Transport Processes in Ion-Exchange Membranes: Relationship with the Structure and Methods for Its Improvement

Nowadays, ion-exchange membranes have numerous applications in water desalination, electrolysis, chemistry, food, health, energy, environment and other fields. All of these applications require high selectivity of ion transfer, i.e., high membrane permselectivity. The transport properties of ion-exchange membranes are determined by their structure, composition and preparation method. For various applications, the selectivity of transfer processes can be characterized by different parameters, for example, by the transport number of counterions (permselectivity in electrodialysis) or by the ratio of ionic conductivity to the permeability of some gases (crossover in fuel cells). However, in most cases there is a correlation: the higher the flux density of the target component through the membrane, the lower the selectivity of the process. This correlation has two aspects: first, it follows from the membrane material properties, often expressed as the trade-off between membrane permeability and permselectivity; and, second, it is due to the concentration polarization phenomenon, which increases with an increase in the applied driving force. In this review, both aspects are considered. Recent research and progress in the membrane selectivity improvement, mainly including a number of approaches as crosslinking, nanoparticle doping, surface modification, and the use of special synthetic methods (e.g., synthesis of grafted membranes or membranes with a fairly rigid three-dimensional matrix) are summarized. These approaches are promising for the ion-exchange membranes synthesis for electrodialysis, alternative energy, and the valuable component extraction from natural or waste-water. Perspectives on future development in this research field are also discussed.

Rod-like Eutectic Structure in Biodegradable Zn-Al-Sn Alloy Exhibiting Enhanced Mechanical Strength

Zn alloy is recognized as a promising biodegradable metal for bone implant applications because of its good biocompatibility and moderate degradation rate. Nevertheless, the insufficient strength limits its applications. In this study, a rod-like eutectic structure was fabricated in Zn-Al-Sn alloy with the addition of Sn via selective laser melting. It was found that the Al-enriched phase nucleated primarily during cooling and caused the rapid precipitation of Zn. This inevitably consumed the liquid Zn and increased the ratio of Sn to Zn in the liquid phase, resulting in the formation of the eutectic, which was composed of the Sn-enriched phase and the Zn-enriched phase. More importantly, the coupled growth of the Sn-enriched and Zn-enriched phases and their volume differences together led to a rod-like morphology of the eutectic according to the volume fraction theory. Consequently, the yield and ultimate compressive strengths were enhanced to 180 ± 18.8 and 325 ± 29.6 MPa for the Zn-Al-2Sn alloy, respectively. This could be attributed to the pinning effect of the rod-like eutectic, which could block dislocation motion and result in dislocation pile-up, thereby conducing to the mechanical reinforcement. In addition, the Zn-Al-Sn alloy also exhibited good biocompatibility and increased degradation rate because of the enhanced galvanic corrosion. This study showed the potential of rod-like eutectic for the mechanical enhancement of the biodegradable Zn alloy.

The Performance and Adsorption Mechanism of a Novel Collector, Dodecyl Dimethyl Betaine (BS-12), for the Flotation Separation of Ilmenite and Titanaugite

In this paper, a novel collector, dodecyl dimethyl betaine (BS-12), was used in the selective separation of ilmenite from titanaugite. The flotation performance and associated adsorption mechanism were studied by micro-flotation experiments, particle size analysis, Fourier-transform infrared (FT-IR) spectroscopy analysis, and X-ray photoelectron spectroscopy (XPS) analysis. The micro-flotation results indicated that BS-12 exhibited a stronger collecting ability towards ilmenite than titanaugite within an acidic pH range, and that the recovery of ilmenite was about 50% higher than that of titanaugite under the optimum flotation conditions. Particle size analysis demonstrated that BS-12 could selectively agglomerate ilmenite to a certain extent and then contribute to the flotation difference between ilmenite and titanaugite. FT-IR results showed some characteristic bands of BS-12 on treated ilmenite, and on titanaugite with BS-12. The XPS analysis further confirmed that BS-12 chemisorbed onto ilmenite and titanaugite in a similar way, but the limited active sites on titanaugite in comparison with ilmenite accounted for their differences in flotation.