Lithium Extraction by Metal Organic Framework-Based Adsorbent (MnO2@Co/Zn ZIF) from Aqueous Solutions

Lithium is one of the critical elements in the development of industries, and its amount in seawater and brines (2.5×10^11 tonnes) is estimated to be about 16,000 times more than land-based resources. However, the low lithium concentration in seawater (0.17 ppm) requires an efficient and selective method of lithium extraction. Although metal-organic frameworks (MOFs) are widely utilized for removing or extracting heavy metals from seawater, they have not been extensively employed for lithium extraction from such sources. This research used a bimetallic MOF-based adsorbent (MnO2@Co/Zn ZIF) to extract lithium ions from the solution. The effects of Li+ concentration and contact time on adsorption were investigated. Based on kinetic studies, the pseudo-second-order model adequately represents the kinetic behavior of lithium adsorption. The thermodynamic study demonstrated lithium adsorption with MnO2@Co/Zn ZIF is endothermic, spontaneous, and physisorption. The adsorption process fitted well with the Freundlich isotherm (R2=0.994), and this isotherm showed the maximum adsorption capacity at room temperature to be 71.43 mg/g. The desorption process was carried out with an HCl solution and showed that MnO2@Co/Zn ZIF has excellent desorption ability. In addition, it was demonstrated that the adsorbent could be used for lithium adsorption after three cycles of regeneration. Moreover, MnO2@Co/Zn ZIF is a viable candidate for recovering large amounts of lithium ions from solutions, based on the results.