Functionalized Li/NH2/MIL-101(Cr) and Li/NH2/MIL-100(Fe) for Lithium Adsorption and Separation from Aqueous Solutions

MIL-101(Cr) and MIL-100(Fe) are both representative MIL-type Metal-Organic-Frameworks (MOFs) materials, renowned for their large specific surface areas and size-tunable characteristics, making them suitable candidates for Li+ extraction from lithium-containing solvent. By introducing -NH2 functional groups and using LiNO3 as both a template and mineralizer, the functionalized MOF materials Li/NH2/MIL-101(Cr) and Li/NH2/MIL-100(Fe) were synthesized. Following modification, their Li+ adsorption capacities were increased, reaching 43.58 and 38.22 mg/g, respectively. The dosage of mineralizer, initial Li+ concentration, adsorbent dosage, solution pH value, and temperature all have an impact on the adsorption capacity of adsorbents. In addition, through the establishment of the pseudo-first-order kinetic model, pseudo-second-order kinetic model, as well as Langmuir and Freundlich thermodynamic models, it can be known that the adsorption of the materials belonged to monolayer chemisorption, and the adsorption process was exothermic. Furthermore, both adsorbents showed good reusability, retaining over 85% of their initial adsorption capacity after four adsorption-desorption cycles, highlighting their practical applicability in lithium recovery processes. In Mg-Li mixed solution systems, both materials exhibited exceptional Li+ selectivity. At a low Mg2+/Li+ ratio of 3, the separation factor (α) exceeded 80; even at a high Mg2+/Li+ ratio of 10, α remained near 50. Additionally, in systems with coexistence of multiple interfering ions, the distribution coefficient (Kd) followed the order: Li+ ≫ Mg2+ > Ca2+ > Na+ > K+. In the mixed systems, Li/NH2/MIL-101(Cr) and Li/NH2/MIL-100(Fe) exhibited certain separation effect for Li+ against competing cations.