Fabrication of electrospun adsorptive membranes for lithium extraction from dilute aqueous solutions

• Main Author: Lim, Xin Yi
• Other Authors: Wang Rong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Electrospinning; Lithium adsorption; Membrane
• Online Access: https://hdl.handle.net/10356/177148
• Institution: Nanyang Technological University

The demand for lithium has continued to grow over the years due to its growing use in lithium batteries and electric vehicles, with a 2020 study suggesting that the annual demand for lithium is projected to reach >1,000,000 tonnes by 2030. The precious metal can be found both on land and in the ocean. While lithium on earth has been extensively mined, the ocean is still a relatively untapped but large source of lithium. Consequently, much research has been done into potential methods of seawater lithium extraction — including conventional adsorption, adsorptive membranes, liquid-liquid extraction and electrochemical methods. In this work, we integrated Li2TiO3, an adsorbent, into a nanofibrous membrane scaffold via electrospinning. Four types of nanofibrous membranes were synthesised: a membrane with only polyacrylonitrile (PAN); a direct-blend membrane with both PAN and the adsorbent; a direct-blend membrane with PAN, the adsorbent and pores in the nanofibers; and a core-shell membrane with PAN and pores in the nanofibers. Static adsorption capacity tests in 1 ppm and 10 ppm of both pure lithium and mixed ion (Li+, Na+ and Mg2+) solution were conducted to determine their adsorption capacity. The performance of the porous direct-blend membrane was the highest in both 1 ppm and 10 ppm pure lithium solution. In the mixed ion solution, selectivity of Li+ over other competing ions generally decreased at lower concentrations. Overall adsorption of Li+ was highest for the adsorbent/PAN membrane, while the porous direct-blend membrane was the highest in 10 ppm. The adsorbent/PAN membrane exhibited the highest selectivity for Li over Na ions for both concentrations and the highest Li/Mg selectivity for 10 ppm. However, the porous direct-blend membrane had the highest Li/Mg selectivity at 1 ppm. Considering both adsorption capacity and selectivity for lithium, the adsorbent/PAN membrane has shown the highest potential for lithium recovery so far. However, dynamic adsorption tests and further tweaking will be required to develop an adsorptive membrane that can be used on a large scale, as the adsorption capacities of the membranes are still low at lower concentrations of lithium.