Dimensionality-Reduced LDH Granules for Rapid Lithium Adsorption from Low-Grade Salt Lakes

Efforts to expand lithium production from continental salt lakes have accelerated in recent years as demand from battery-based energy systems continues to rise. Many of the world’s remaining untapped brines are low-grade resources characterized by modest Li⁺ concentrations and exceptionally high Mg²⁺/Li⁺ ratios, creating a technical bottleneck for most separation technologies. Adsorption–membrane coupling is considered a promising route because it combines the selectivity of solid sorbents with the purification capacity of membrane processes. However, the practical success of this hybrid approach depends strongly on the performance of the adsorbent itself, particularly its ability to capture Li⁺ rapidly from highly saline, viscous feed streams. Aluminum-based lithium adsorbents, specifically Li/Al layered double hydroxides (Li/Al-LDHs), are the most industrially relevant option because they exhibit acid-free desorption and retain chemical stability in harsh brine environments but their deployment at scale remains limited by the longstanding challenge of sluggish intraparticle mass transfer once the powder is converted into mechanically robust granules.

Granulation is unavoidable for fixed-bed operations, yet conventional extrusion or binder-rich molding processes produce millimeter-scale beads with dense interiors that hinder diffusion. Although Li/Al-LDH powders can reach equilibrium within hours, their granulated counterparts often require tens of hours for the same process, and even then a substantial fraction of interior adsorption sites remains inaccessible. The problem is amplified in brines such as Qarhan old brine, where high ionic strength and elevated viscosity slow the penetration of liquid films into compact granules. This mismatch between the sorbent’s intrinsic selectivity and the physical constraints of its granulated form leads to underutilization and ultimately limits throughput in continuous extraction units. To this end, new research paper published in AIChE Journal and conducted by Dr. Jun Chen, Dr. Jianguo Yu, and led by Professor Sen Lin from the East China University of Science, the researchers developed two complementary models to understand and optimize lithium mass transfer in Li/Al-LDH granules: a finite-element diffusion model that quantified how granule diameter controls intraparticle concentration gradients, and an experimentally validated structural model showing how wet-spinning creates a skin–core porous architecture that accelerates Li⁺ transport.

The research team constructed cylindrical geometries in COMSOL, and Li⁺ transport was modeled under salt-lake concentrations. The simulated concentration fields showed that small-diameter cylinders equilibrated rapidly, with the average Li⁺ concentration approaching the bulk value within seconds, whereas cylinders exceeding roughly 1.5 mm remained diffusion-limited for hundreds of seconds. These calculations provided a quantitative basis for selecting a target dimension near 0.6–0.7 mm, where additional diameter reductions yielded diminishing returns. This insight guided the experimental granulation route. Afterward, the team prepared a spinning solution of Li/Al-LDH powder dispersed in polymer binders dissolved in DMF to fabricate granules in this dimensional regime. During wet spinning, the solution was extruded into an aqueous coagulation bath, where rapid solvent exchange induced solidification. The fibers formed in this step exhibited a skin–core architecture: a dense outer sheath that preserved particle integrity and an interior characterized by a loose, porous network capable of hosting nanosheets. Subsequent crushing produced uniformly sized low-dimensional granules (LD-LDHs), each containing embedded Li/Al-LDH domains. The research team conducted microscopy analysis and confirmed that the layered nanosheets remained structurally intact and attached to the porous scaffold. Surface-area analyses further showed a marked increase relative to conventional high-dimensional granules (HD-LDHs), demonstrating that wet spinning not only reduced size but also introduced a favorable pore hierarchy. Moreover, the team performed adsorption tests in Qarhan old brine which showed HD-LDHs required more than a day to reach equilibrium, while LD-LDHs achieved near-complete uptake in about half an hour. Pre-wetting improved initial accessibility by overcoming the hydrophobicity of the binders, allowing Li⁺ to rapidly enter the internal aqueous microenvironment and contact the active nanosheets. The resulting adsorption capacities showed that reducing dimensionality did not degrade the intrinsic performance of the LDH component; instead, it enabled more complete utilization. They also performed kinetic modeling which supported their observation, with LD-LDHs exhibiting larger rate constants and substantially diminished intraparticle diffusion resistance. Desorption was similarly accelerated. Additional experiments at varied Mg²⁺ concentrations showed that LD-LDHs preserved their ionic-strength-driven selectivity, displaying increased uptake at higher Mg²⁺ levels, consistent with electrostatic compression effects. Structural characterization before and after cycling confirmed that the nanosheets remained stable, and the adsorption capacity displayed only narrow fluctuations over ten cycles. The authors’ dynamic fixed-bed experiments also highlighted the practical importance of the design. They noted in breakthrough curves for LD-LDHs remained in the low-concentration trough substantially longer than those of HD-LDHs, regardless of flow rate, and saturation was reached more quickly without sacrificing capacity. Over multiple cycles, LD-LDHs consistently delivered higher working capacities and produced desorption solutions with lower Mg²⁺/Li⁺ ratios, which enables downstream purification.

In conclusion, the new study by Professor Sen Lin and colleagues developed models which established that reducing dimensionality enhances mass-transfer efficiency without compromising structural integrity. This new framework guided the fabrication of low-dimensional LD-LDHs that achieved rapid adsorption and high working capacity in real brines. The implications extend beyond lithium extraction. Many promising adsorbents fail to scale because the granulation step introduces internal diffusion barriers that mask their intrinsic behavior. The approach used here—quantitative modeling followed by dimension-controlled granulation—provides a broadly transferable framework for any system where adsorption sites are abundant yet difficult to access under flow. In the specific context of low-grade salt lakes, the method directly addresses the operational pressures facing lithium producers. Faster adsorption kinetics reduce residence times, allowing smaller equipment footprints and higher throughput. Improved desorption quality, reflected in consistently low Mg²⁺/Li⁺ ratios, eases the downstream burden of producing battery-grade lithium carbonate. The stability demonstrated across repeated cycles suggests that the granules can withstand the hydrodynamic and chemical stresses typical of industrial processes. Additionally, the work highlights the importance of ion-sieve design: the interplay between ionic-strength-driven mechanisms and physical accessibility. Li/Al-LDHs rely on interlayer processes that are favored at high salinity. Yet these same conditions increase solution viscosity and aggravate internal mass-transfer resistance. By engineering a granule that retains nanosheet accessibility even under these conditions, the authors untangle a long-standing contradiction between mechanism and morphology. This resolution is particularly important for brines like Qarhan old brine, which are too low in lithium to tolerate slow kinetics and too viscous to accommodate dense granules. We believe, the study provides a platform for integrating LD-LDHs with membrane-based polishing systems or electrochemical upgrading technologies. Their rapid mass transfer suggests compatibility with high-flux operations, and their stable working capacity points to predictable long-term performance. As demand for lithium continues to outpace conventional sources, methods capable of harvesting lower-grade brines become increasingly valuable and the new dimensionality-reduction strategy presented in the paper strengthens the case for adsorption-based extraction as a viable component of the global lithium supply chain and establishes a general design principle that can be extended to other sorbent families where internal diffusion limits scale-up.