Mixed matrix nanofiber as a flow-through membrane adsorber for continuous Li+ recovery from seawater

A polysulfone (PSf)-based mixed matrix nanofiber (MMN) dispersed with particulate lithium ion sieves (LIS) was developed as a flow-through membrane Li+ adsorber. The MMN was prepared via electrospinning, thermal annealing, and acid pickling (i.e. activated LIS: Li0.67H0.96Mn1.58O4 or MO). The unique dimensional property of the macroporous MMN promoted high MO exposure and distribution on the nanofiber surface. Minimal losses in Li+ adsorption capacity and kinetics, elicited by the PSf matrix, were observed. Moreover, the PSf matrix effectively improved the Li+ selectivity of MO as it alleviated the sorption of interfering cations. As membranes, the MMNs were highly permeable to water under minimal trans-membrane pressure. The convective flow of seawater through the highly accessible MMN facilitated the fast Li+ transport to the MO surface. Breakthrough studies revealed that a balance between kinetics and dynamic Li+ adsorption capacity could be obtained at optimal seawater/MMN contact time, which was easily achieved by adjusting the feed flow-rate or MMN thickness. Continuous flow-through operations were successfully controlled at a very short adsorption-desorption cycle time (one day) while maintaining the dynamic Li+ adsorption capacity of the MMN. Cycled operations confirmed the regenerability of the MMN and its adsorption performance consistency. Enrichment of Li+ was successfully done by repeated Li+ desorption in a small volume of acid solution. Overall results demonstrated the strong potential of the flow-through MMN membrane adsorber for continuous Li+ recovery from alternative resources like seawater.