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    Development of highly selective composite polymeric membranes for Li+/Mg2+ separation

    Year: 2021

    Journal: J. Membr. Sci., Volume 620, FEB 15

    Authors: Saif, H. M.; Huertas, R. M.; Pawlowski, S.; Crespo, J. G.; Velizarov, S.

    Organizations: European Union's Horizon 2020 research and innovation programme [869467]; Associate Laboratory for Green Chemistry-LAQV - Portuguese national funds from FCT/MCTES [UID/QUI/50006/2019]; Programa Operacional Regional de Lisboa, na componente FEDER; Fundacao para a Ciencia e Tecnologia, I.P. [PTDC/EQU-EPQ/29579/2017, CEECIND/01617/2017, CEECIND/00340/2018]; Fundacao para a Ciencia e Tecnologia [iNOVA4Health UIDB/Multi/04462/2020]; INTERFACE Programme, through the Innovation, Technology and Circular Economy Fund (FITEC)

    Keywords: Lithium recovery; Composite membranes; Lithium ion sieves (LIS); Sea mining; Diffusion dialysis

    To meet the exponentially rising demand for lithium, it becomes vital to develop environmentally friendly processes for its recovery from brines, salt lakes and/or seawater. In this work, novel composite lithium transport selective polymeric membranes were developed to separate lithium and magnesium ions. Hydrogen manganese oxide (HMO) (at weight percentage from 0 to 25%), polystyrene sulfonate sodium salt (PSS-Na) and lithium triflate (LiCF3SO3) were added into the sulfonated polyethersulfone (SPES) matrix to prepare composite membranes. The developed membranes showed high mechanical stability and a homogeneous distribution of HMO. The most promising membrane, containing 20% (w/w) of HMO, showed an almost 13 times higher Li+ ionic conductivity (8.28 mS/cm) compared to the control composite membrane (without HMO) and an average ideal selectivity of 11.75 for the Li+/Mg2+ pair. The composite-20% membrane had the lowest intermolecular distance between the polymer chains (according to X-ray diffraction (XRD) analysis), the most flexible structure (lowest T-g) and showed the homogeneous dispersion of HMO (SEM images), which explains its highest Li+ /Mg2+ selectivity among the tested membranes. The lithium ion transport performance and separation efficiency were investigated through diffusion dialysis experiments, under different operating conditions. A binary separation factor of 9.10 for Li+/Mg2+ and Li+ molar flux of 0.026 mol/(m(2).h) was achieved without applying any external potential difference. When an external potential difference of 0.2 V was applied, the binary separation factor of Li+/Mg2+ pair was 5, while the Li+ molar flux increased almost 5 times. The obtained results provide the basis to design and develop composite lithium transport selective polymeric membranes, thus representing a promising step for future implementation of such membranes to recover lithium from saline streams.
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