The strategy, which the authors call cascading utilization, treats the lithium-ion sieve as a two-stage asset rather than a single-use consumable. In the first stage, the spinel framework performs its designed job of selectively extracting lithium from aqueous resources. In the second stage, the same powder, now depleted and structurally altered by hundreds of lithium extraction cycles, is converted into a functional electrode for a completely different electrochemical device. This cross-domain repurposing addresses a genuine sustainability problem: lithium-ion sieve powders are expensive to synthesize, requiring high-temperature solid-state reactions and careful acid treatment, and throwing them away after their sieving performance declines wastes both the embedded manganese and the energy invested in their manufacture.

The central challenge in converting a cycled sieve into a battery cathode lies in the chemistry of the spinel itself. Fresh H1.6Mn1.6O4 is essentially a lithium-depleted manganese oxide with a dense spinel lattice, and its suitability for hosting zinc ions, which are divalent and much larger than lithium ions, is far from obvious. Zinc-ion batteries store charge by intercalating Zn2+ into host structures at the cathode, and polyvalent cations like zinc diffuse sluggishly through tight crystal frameworks. The researchers recognized, however, that the repeated lithium extraction process the sieve had already endured might have done some of the activation work for them. Each cycle of Li+ removal and reinsertion subtly reshapes the spinel, and the team hypothesized that these structural changes could create favorable diffusion pathways for zinc.

To prepare the cycled powder for its new role, the team applied a photo-excitation-assisted oxidative delithiation process using sodium persulfate as the oxidant. This step removes any residual lithium left in the framework after the sieving cycles while preserving the spinel structure. Conventional acid-based delithiation methods, such as treatment with hydrochloric acid, are known to cause manganese dissolution, which erodes the spinel lattice and degrades performance. The persulfate approach, assisted by photo-excitation, is gentler: it oxidatively extracts lithium without the harsh acidic conditions that dissolve manganese from the framework. The result is a material that retains high structural integrity while carrying the surface activation and diffusion pathways introduced by its prior life as a sieve.

When the regenerated material was assembled into cathodes and tested in aqueous zinc-ion batteries, the performance confirmed the team’s hypothesis. The directly regenerated lithium-ion sieve delivered a reversible capacity of 101.5 mAh per gram at a current density of 0.03 A per gram, a respectable figure for a spinel manganese oxide cathode operating through zinc intercalation. More striking was the cycling stability: the material exhibited a Coulombic efficiency of approximately 99 percent over 200 cycles, indicating that nearly every unit of charge inserted into the cathode during each cycle was recoverable on discharge. Coulombic efficiency close to 99 percent sustained over hundreds of cycles is a hallmark of an electrode whose intercalation chemistry is well matched to the electrolyte and whose structural framework survives repeated zinc insertion and extraction without collapse.

The mechanism behind this performance is rooted in the dual benefit the cycled sieve carries into the battery. First, the repeated Li+ extraction cycles that the material endured during lithium recovery introduced favorable diffusion pathways within the spinel framework, effectively pre-etching channels through which Zn2+ can travel during charge and discharge. Second, the surface activation that accumulates over many sieving cycles lowers the energetic barrier for zinc intercalation at the particle surface, facilitating Zn2+ storage. In effect, the very process that wears out the sieve as a lithium extractor is the process that primes it as a zinc host. This is what makes the cascading strategy so elegant: the degradation in one application is the activation in another.

The connection between lithium-ion sieves and zinc-ion battery cathodes runs deeper than mere convenience, and the researchers situate their work within an established lineage of spinel manganese oxide research. When LiMn2O4 spinel is delithiated, the product is a metastable form of manganese dioxide known as λ-MnO2, first prepared as a new crystal form of manganese dioxide in 1981. λ-MnO2 and related spinel manganese oxides have long been investigated as intercalation hosts for polyvalent cations including Mg2+ and Zn2+ in aqueous batteries. Spinel zinc manganates, formed when zinc intercalates into these frameworks, are recognized cathode materials for zinc-ion batteries. The cycled H1.6Mn1.6O4 sieve, having already been stripped of most of its lithium, occupies precisely this chemical territory, which explains why it can function as a zinc host without extensive reprocessing.

What distinguishes this study from prior recycling efforts is the directness of the conversion. Previous work has regenerated spent lithium manganate battery materials into doped manganese dioxide cathodes for aqueous zinc batteries, and other teams have selectively recycled spent lithium-ion battery components into zinc-ion battery cathodes. But those approaches typically start from battery materials and involve substantial reprocessing, such as doping with aluminum or other elements to stabilize the framework. The Northeastern University team instead starts from an industrial adsorbent, a material whose primary function was never electrochemical, and uses it directly as a cathode after only a mild delithiation treatment. No doping, no reconstruction, no synthesis of a new compound: the cycled sieve powder is simply delithiated, washed, and made into an electrode.

The implications for resource efficiency are considerable. Lithium-ion sieves are deployed in some of the most demanding environments in the chemical industry, from salt-lake brines to shale gas wastewater, and the field has invested heavily in improving their selectivity, capacity, and stability. Researchers have tailored lattice constants and intercalation energies to boost performance, doped sieves with titanium, tungsten, lanthanum, and other high-valence elements to suppress manganese dissolution, and engineered porous and granular structures to improve kinetics. All of this engineering makes the sieves more valuable, and all of it is lost when the cycled powder is discarded. The cascading utilization strategy recovers that value by routing the spent adsorbent into energy storage, where its structural framework, its embedded manganese, and even its cycling-induced defects all contribute to function.

For zinc-ion batteries themselves, the study offers a new avenue toward low-cost and sustainable cathode materials. Aqueous zinc-ion batteries are attractive because they use water-based electrolytes, inexpensive zinc metal anodes, and ambient-air assembly, making them inherently safer than lithium-ion systems and well suited to stationary storage. Their main bottleneck has been the cathode: manganese dioxide and vanadium oxide hosts suffer from dissolution, structural instability, and sluggish zinc diffusion. A cathode derived from a recycled industrial adsorbent, with pre-existing diffusion pathways and a spinel framework proven stable over hundreds of lithium extraction cycles, addresses several of these issues at once. The team confirmed the feasibility of cross-domain application of cycled lithium-ion sieve powder, and in doing so opened a path where the waste stream of one clean technology, lithium recovery from brine, feeds directly into the supply chain of another, grid-scale zinc battery storage. As demand for both lithium and stationary energy storage accelerates worldwide, strategies that link the two, turning one technology’s spent materials into another’s functional components, may prove to be among the most resource-efficient ideas in the battery field.

Subject of Research: Materials Science

Article Title: Direct cascading utilization of cycled H1.6Mn1.6O4 lithium-ion sieves as cathodes for zinc-ion batteries

Article References: Liu, X., Li, Y., Yang, H., & Li, F. (2026). Direct cascading utilization of cycled H1.6Mn1.6O4 lithium-ion sieves as cathodes for zinc-ion batteries. Ionics. https://doi.org/10.1007/s11581-026-07575-z

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07575-z

Keywords: lithium-ion sieve, zinc-ion batteries, H1.6Mn1.6O4, cathode recycling, spinel manganese oxide, sustainable energy storage, lithium recovery, cascading utilization, Direct, cascading, utilization, cycled

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

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

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

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

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

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

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

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

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

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

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

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

Image Credits: AI Generated

DOI: 10.3389/frmst.2026.1766669

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

Quinizarin, chemically known as 1,4-dihydroxyanthraquinone, is a planar aromatic molecule built around an anthraquinone backbone decorated with two hydroxyl groups. Its oxygen-rich framework gives it a natural affinity for metal ions with high charge density, and lithium — the smallest and most charge-dense metal ion in common use — is exactly the kind of target it should embrace. But while quinizarin’s coordination chemistry with heavier metals such as aluminum has been documented, its interaction with lithium had received little theoretical attention. A study published in the journal Ionics by Állefe Barbosa Cruz, Douglas Henrique Pereira and colleagues at the Instituto Tecnológico de Aeronáutica, the Universidade Federal dos Vales do Jequitinhonha e Mucuri and the Universidade Federal de Ouro Preto set out to fill that gap using quantum chemical simulation.

The team employed density functional theory, or DFT, the workhorse method of modern computational chemistry, to model quinizarin and its complexes with one and two lithium ions. Geometry optimizations and vibrational frequency calculations were carried out with the ωB97X-D functional, a long-range corrected hybrid functional that includes damped atom–atom dispersion corrections, combined with the 6–31+G(d,p) basis set. To mimic realistic conditions, the researchers used the SMD implicit solvation model to represent an aqueous environment — a sensible compromise, since explicit solvent molecules would have multiplied the computational cost without dramatically changing the dominant electrostatic effects. The absence of negative vibrational frequencies confirmed that every optimized structure sat at a true energy minimum.

The first striking result came from the frontier molecular orbital analysis. In the free quinizarin molecule, the highest occupied molecular orbital and its unoccupied counterpart are separated by a gap of just 1.63 electronvolts, a signature of a relatively reactive electronic structure. When a single lithium ion coordinates to the oxygen centers, that gap balloons to 6.50 electronvolts, and with two lithium ions it remains nearly as wide at 6.41 electronvolts. A large HOMO–LUMO gap generally signals chemical stability and reduced reactivity in the ground state. In other words, donating electron density to lithium stabilizes the dye so profoundly that its electronic personality changes almost completely — a transformation that could also be exploited optically, since frontier orbital energies govern the ultraviolet-visible absorption behavior that underpins cheap spectroscopic detection.

The structural changes tell the same story at the level of individual bonds. In uncomplexed quinizarin, the two carbonyl bonds measure 1.243 and 1.244 angstroms, in close agreement with experimental crystallographic values — the mean deviation between theory and experiment across the calculated bond lengths was only 0.008 angstroms, a testament to the accuracy of the chosen level of theory. When lithium binds, the interacting carbonyl bond stretches to 1.252 angstroms, a lengthening that reflects the loss of double-bond character as electron density flows toward the metal. Meanwhile, the carbon–carbon bonds adjacent to the new C–O–Li linkage contract, shortening to as little as 1.450 angstroms in the doubly coordinated complex. The newly formed oxygen–lithium bonds themselves measure between 1.870 and 1.879 angstroms. Together, these geometric shifts are the classic fingerprint of genuine chemical coordination rather than a fleeting, superficial contact.

To probe the nature of that bond at a deeper level, the researchers turned to the Quantum Theory of Atoms in Molecules, or QTAIM, a topological framework pioneered by Richard Bader that dissects the electron density distribution into chemically meaningful regions. QTAIM locates bond critical points along the pathways connecting bonded atoms and evaluates properties such as the electron density, its Laplacian, and the local energy densities at those points. For the oxygen–lithium interactions, the electron density at the bond critical points was high, the Laplacian was strongly positive — exceeding 149 kilocalories per mole per cubic bohr — and the total energy density was also positive, above 8 kilocalories per mole. That combination of signs is the textbook signature of a closed-shell, predominantly electrostatic interaction rather than a covalent one.

The energy density ratio -G(r)/V(r) came out at 1.37, comfortably above the threshold of 1.0 that distinguishes purely ionic, non-covalent interactions from partially covalent ones. The bond ellipticity values, ranging from 0.037 to 0.040, were close to zero, meaning the electron density around each bond path is nearly cylindrically symmetric — the hallmark of a well-defined, σ-type electrostatic bond with no significant directional strain. In plain terms, lithium is not sharing electrons with quinizarin so much as being seized by its oxygen atoms through powerful electrostatic attraction. That is precisely the kind of interaction one wants in an adsorbent designed to pluck lithium ions selectively from water.

The thermodynamics sealed the case. The binding energy for the mono-lithium complex came out at −10.74 kilocalories per mole, and for the di-lithium complex it nearly doubled to −20.57 kilocalories per mole, well beyond the −11.95 kilocalories per mole threshold (equivalent to −50 kilojoules per mole) conventionally used to classify an interaction as strong coordination. The Gibbs energy of complexation was negative in both cases — −3.77 and −6.98 kilocalories per mole respectively — confirming that the process occurs spontaneously in the modeled aqueous medium, while the enthalpy changes of −11.20 and −21.45 kilocalories per mole showed that the binding is exothermic, releasing heat as the complexes settle into their stabilized configurations. Doubling the lithium payload roughly doubles the energetic payoff, suggesting that quinizarin’s two oxygen-rich coordination sites can work in concert.

Why does this matter beyond the quantum chemistry? Lithium detection today relies largely on atomic absorption spectroscopy or flame photometry, both of which demand expensive instrumentation and demanding maintenance. Ultraviolet-visible spectroscopy offers a far more accessible alternative, and a ligand whose electronic structure shifts so dramatically upon lithium binding — a four-electronvolt widening of the orbital gap — is exactly the kind of molecular reporter that could translate lithium concentration into an easily measured optical signal. The same strong, spontaneous binding that enables sensing also underpins adsorptive recovery, in which a solid matrix decorated with quinizarin-like sites could capture lithium ions from brines or industrial wastewater for later release and reuse.

The authors are careful to frame the work as a fundamental computational investigation: DFT defines the scope and the limits of what can be claimed, and molecular-level descriptors are meant to guide, not replace, future laboratory experiments. Still, the convergence of evidence is compelling. Structural distortion confirms real coordination, frontier orbital analysis confirms electronic stabilization, QTAIM confirms a strong ionic bond, and thermodynamics confirms spontaneous, heat-releasing capture in water. As the pressure mounts to build sustainable lithium supply chains — from recycling spent batteries to extracting the metal from unconventional sources — simple, cheap organic molecules that grab lithium with both hands may prove to be among the most valuable tools in the chemist’s kit. Quinizarin, a dye that has colored fabrics for generations, may soon help color the lithium economy green.

Subject of Research: Density functional theory study of quinizarin–lithium ion complexation for lithium detection and recovery

Article Title: Computational Investigation of the Structural, Electronic, and Topological Properties of Quinizarin and Quinizarin–Lithium Ion (Li⁺) Complexes

Article References: Cruz, Á. B., Maciel, N. C., Leão, V. A., Sicupira, L. C., Leal, P. V. B., Ferreira, L. F., & Pereira, D. H. (2026). Computational Investigation of the Structural, Electronic, and Topological Properties of Quinizarin and Quinizarin–Lithium Ion (Li⁺) Complexes. Ionics. https://doi.org/10.1007/s11581-026-07568-y

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07568-y

Keywords: quinizarin, lithium, DFT, QTAIM, coordination chemistry, lithium recovery, frontier molecular orbitals, computational chemistry, adsorption, battery materials, spectroscopic detection, sustainable mining