Continuous lithium mining from aqueous resources by an adsorbent filter with a 3D polymeric nanofiber network infused with ion sieves

Abstract

Electrospun composite nanofiber (NF) was fabricated and employed as an adsorbent membrane filter in a continuous Li+ mining process from seawater. The filter was composed of a hydrophilic polyacrylonitrile (PAN) matrix infused with lithium ion sieves (LIS) H1.6Mn1.6O4. Characterization of the LIS/PAN NF confirmed its favorable structural and surface properties for effective Li+ adsorption. The LIS/PAN NF was mechanically suitable as a microfiltration membrane with high water flux and low pressure requirement. Breakthrough experiments at varied feed concentrations (Cf), seawater flowrates (F), and NF thicknesses (Z) revealed the dynamic adsorption behavior of the filter. The seawater residence time was most critical and must be kept ⩾0.12min at any given Cf and Z to maximize the Li+ capacity of the filter. This can be conveniently achieved by adjusting the F of the process. Analogous to a packed bed system, the predictive power of nine breakthrough models were determined through non-linear regression analyses. Results reveal that bed-depth-space-time, Bohart-Adams (BA) and Thomas models adequately predicted the performance of the filter albeit BA exhibited the best agreement. Meanwhile, Wolborska failed to converge with any of the experimental results while Yoon-Nelson, Wang, Clark, dose-response, and modified dose-response were too simple to provide any meaningful information. Cycled Li+ adsorption-desorption runs successfully collected and concentrated Li+ in a mild acid stripping solution. After ten cycles, Li+ was separated 155–1552 times more efficiently than Na+, K+, Mg2+ and Ca2+. Overall results demonstrate the potential of LIS/PAN NF as an adsorbent membrane filter for continuous Li+ mining from aqueous resources.