Abstract 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 Tg) 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/(m2.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.

中文翻译：

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用于分离 Li+/Mg2+ 的高选择性复合聚合物膜的开发

摘要 为了满足对锂呈指数增长的需求，开发环保工艺从卤水、盐湖和/或海水中回收锂变得至关重要。在这项工作中，开发了新型复合锂传输选择性聚合物膜来分离锂和镁离子。将氧化氢锰 (HMO)（重量百分比为 0% 至 25%）、聚苯乙烯磺酸钠盐 (PSS-Na) 和三氟甲磺酸锂 (LiCF3SO3) 添加到磺化聚醚砜 (SPES) 基质中以制备复合膜。开发的膜显示出高机械稳定性和 HMO 的均匀分布。最有前途的膜含有 20% (w/w) 的 HMO，其 Li+ 离子电导率几乎高出 13 倍 (8. 28 mS/cm）与对照复合膜（不含 HMO）相比，Li+/Mg2+ 对的平均理想选择性为 11.75。20% 复合膜的聚合物链之间的分子间距离最低（根据 X 射线衍射 (XRD) 分析）、最灵活的结构（最低 Tg）并显示出 HMO 的均匀分散（SEM 图像），这解释了在所测试的膜中，它具有最高的 Li+/Mg2+ 选择性。在不同的操作条件下，通过扩散渗析实验研究了锂离子传输性能和分离效率。在不施加任何外部电位差的情况下，Li+/Mg2+ 和 Li+ 摩尔通量的二元分离系数为 9.10，为 0.026 mol/(m2.h)。当施加 0.2 V 的外部电位差时，Li+/Mg2+ 对的二元分离因子为 5，而 Li+ 摩尔通量增加了近 5 倍。所获得的结果为设计和开发复合锂传输选择性聚合物膜提供了基础，因此代表了未来实施此类膜以从盐水流中回收锂的有希望的一步。