Lithium recovery from aqueous sources has gained significant attention due to the growing demand for lithium-ion batteries in electric vehicles and renewable energy storage. Among the various techniques available, adsorption using lithium-selective sorbents stands out for its high selectivity, cost-effectiveness, and scalability. Key sorbents such as manganese oxide (MnOx) and aluminum hydroxide (Al(OH)3) have demonstrated strong affinity for lithium ions, making them suitable for extraction from brines, seawater, and recycled battery leachates.
The adsorption process relies on the interaction between lithium ions and the sorbent material, often governed by ion exchange or surface complexation mechanisms. Manganese oxide-based sorbents, particularly spinel-type λ-MnO2, exhibit high selectivity for lithium due to their unique tunnel structure, which allows for preferential insertion of Li+ ions. Aluminum hydroxide, on the other hand, operates through a layered double hydroxide (LDH) structure, where lithium ions are adsorbed onto the interlayer spaces. The performance of these materials is typically evaluated using adsorption isotherms, with Langmuir and Freundlich models commonly applied to describe equilibrium behavior. Studies indicate that λ-MnO2 can achieve lithium adsorption capacities ranging from 20 to 40 mg/g, depending on solution conditions.
Regeneration of lithium-loaded sorbents is critical for economic feasibility. Acid elution, often using hydrochloric acid (HCl) at concentrations of 0.5 to 1.0 M, is the most widely applied method. The process effectively desorbs lithium ions while maintaining the structural integrity of the sorbent for reuse. Cyclic stability tests show that manganese oxide sorbents retain over 90% of their initial capacity after multiple adsorption-desorption cycles. However, aluminum hydroxide may experience gradual degradation under acidic conditions, necessitating optimization of elution parameters.
Column and fluidized-bed systems are the primary configurations for industrial-scale lithium adsorption. Fixed-bed columns offer simplicity and high recovery rates but may face challenges with clogging and pressure drop. Fluidized-bed reactors, while more complex, provide better mass transfer and reduced fouling, making them suitable for processing large volumes of low-concentration lithium sources. Pilot-scale implementations, such as those tested in South American brine operations, have demonstrated lithium recovery efficiencies exceeding 80% with minimal energy input.
Composite adsorbents represent a recent innovation, combining the advantages of multiple materials to enhance performance. For example, manganese oxide embedded in porous polymer matrices improves mechanical stability and reduces particle loss during fluidized-bed operation. Similarly, graphene oxide-supported aluminum hydroxide composites exhibit faster kinetics and higher capacity compared to pure Al(OH)3. These advancements address key limitations in traditional sorbents, paving the way for broader industrial adoption.
When compared to alternative lithium recovery methods, adsorption offers distinct advantages. Solvent extraction, though effective, involves toxic organic reagents and complex phase separation steps. Precipitation methods, such as those using sodium carbonate, suffer from low selectivity and high chemical consumption. Membrane-based techniques, including nanofiltration and electrodialysis, require significant energy input and are sensitive to feed composition. In contrast, adsorption stands out for its operational simplicity, lower environmental impact, and adaptability to diverse lithium sources.
Scalability remains a critical consideration. While laboratory studies have validated the technical feasibility of lithium-selective adsorption, commercial deployment requires optimization of sorbent synthesis, system design, and process integration. Pilot projects in Chile and China have successfully demonstrated continuous lithium recovery from brines, with some facilities achieving production capacities of several hundred tons per year. Further material innovations, such as the development of nanostructured sorbents with tailored surface properties, could enhance both selectivity and throughput.
In summary, adsorption using lithium-selective sorbents presents a promising pathway for sustainable lithium recovery. Advances in material science, coupled with successful pilot-scale validations, underscore its potential to meet the escalating demand for lithium in a cost-effective and environmentally responsible manner. Continued research into composite adsorbents and system engineering will be essential to fully realize this technology on an industrial scale.