Efficient lithium extraction from aqueous solutions by MIL-100(Fe): A study on adsorption kinetics, thermodynamics and mechanism

MIL-100(Fe) is a kind of metal–organic frameworks (MOFs) with robust water and chemical stability. The adsorption kinetics, isotherms, thermodynamics and regeneration of MIL-100(Fe) were investigated to illustrate the process of efficient lithium adsorption. The adsorption kinetics of MIL-100(Fe) followed Pseudo-second-order model, and the lithium adsorption equilibrium was reached rapidly in 2 h. Langmuir model fit best with the adsorption isotherms, indicating chemisorption of lithium ions on MIL-100(Fe) and possibly a monolayer adsorption process. By calculating thermodynamic parameters (ΔGθ, ΔHθ and ΔS θ), the adsorption of lithium on MIL-100(Fe) can be illustrated by a spontaneous endothermic process. The adsorption mechanism involved electrostatic interaction, impact of crystal defect sites and coordinative interactions between metal active sites and lithium ions (Fe—F‧‧‧Li). MIL-100(Fe) was regenerated for four cycles, and there was only a slightly decrease in adsorption capacity and the morphology remained stable. Combined with extremely short equilibrium time and high stability, MIL-100(Fe) can be a promising adsorbent for lithium extraction.