Recyclable composite nanofiber adsorbent for Li+ recovery from seawater desalination retentate

Abstract

Composite poly(acrylonitrile) (PAN) nanofibers with H1.6Mn1.6O4 (HMO) lithium ion-sieves were prepared, characterized and tested for lithium ion (Li+) recovery. Nanofibers were prepared by electrospinning 10 wt% HMO/PAN dope solutions in dimethylformamide with varied HMO loadings. Characterizations performed via XRD, SEM-EDS, capillary flow porometry and mechanical testing revealed highly porous, mechanically and chemically stable composite nanofibers with high water absorption capacity. The similar nanofiber diameters (<300 nm) and HMO particle sizes (<100 nm) rendered PAN as a binder to have minimal hindrance to the HMOs. Exposure of HMOs on the fiber surface provided good accessibility to the Li+ source, as indicated by the minimal loss of Li+ adsorption capacity of HMOs in PAN as compared to the support-free powdered HMO. All tested adsorbents followed Langmuir-type Li+ adsorption (qm). Increased HMO loadings resulted in improved adsorption performance as more HMOs were exposed on fiber surface and became less affected by the binder; the highest qm = 10.3 mg/g obtained from 60 wt% HMO/PAN was only 4% lower than the support-free HMO. Adsorption loss after ten reuses was minor (<4%), which suggests the long-term stability of HMO/PAN. In seawater desalination retentate, HMO/PAN (60 wt%) preferentially adsorbed Li+ over other cations, achieving 99–5312 Li+ separation factors and high Li+ distribution coefficient (KD = 770). Li+ was concentrated up to 486 times while interfering cations were enriched only up to <7 times. Overall results demonstrate the potential use and recyclability of the developed HMO/PAN composite nanofiber for Li+ recovery from seawater or other prospective sources.