Seawater utilization is crucial for the sustainable human development. Despite growing interest in forward osmosis (FO) due to its unique properties, conventional FO membranes with salt-water selectivity have limitations in applying to specific salt-salt separation processes, which hinders their application in resource utilization. In this work, a new concept, “selective forward osmosis (SFO)”, was proposed, which ingeniously employed an SFO membrane consisting of an ion-selective layer on a denser substrate. The denser substrate is designed to control water flux so as to alleviate the solution dilution and improve the salt-salt separation. Moreover, the sucrose and pure water were used separately as feed solution to provide different water flux to influence the various salt fluxes, showing that pure water feed could enhance the salt-salt separation efficiency, although it could dilute the draw solution to some extent. Therefore, pure water was selected as feed in the subsequent experiments. The optimized SFO membrane achieved high NaSO/NaCl selectivity (∼54.8) and MgCl/NaCl selectivity (∼9.2) in single-salt draw solutions. With mixed-salt and heavy-metal-mixed-salt draw solutions, the Mg/Na selectivity was enhanced to ∼14.5, and further to 29.3. In real seawater tests, the SFO system effectively permeated monovalent elements (such as Na flux of ∼68.6 g m h) while maintaining a higher rejection for bivalent elements (such as Mg flux of ∼0.08 g m h), showing high selectivities for Mg/Na, U/Na, Sr/Na, Ni/Na, and Ca/Na. These results demonstrate the potential of SFO for resource utilization, especially in complex saline environments. This work contributes a new route for salt-salt separation in the pretreatment of seawater resources.

中文翻译：

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用于盐盐分离的选择性正向渗透（SFO）作为海水预处理以实现资源利用的概念和研究

海水利用对于人类可持续发展至关重要。尽管正向渗透（FO）因其独特的性能而受到越来越多的关注，但传统的具有盐水选择性的FO膜在应用于特定的盐-盐分离过程中存在局限性，这阻碍了其在资源利用中的应用。在这项工作中，提出了一个新概念“选择性正向渗透（SFO）”，它巧妙地采用了由致密基底上的离子选择性层组成的SFO膜。较致密的基质旨在控制水通量，从而减轻溶液稀释并改善盐盐分离。此外，分别使用蔗糖和纯水作为进料溶液，提供不同的水通量来影响各种盐通量，表明纯水进料可以提高盐盐分离效率，尽管它会在一定程度上稀释汲取溶液。因此，后续实验均选择纯净水作为进料。优化的 SFO 膜在单盐汲取溶液中实现了高 NaSO/NaCl 选择性 (∼54.8) 和 MgCl/NaCl 选择性 (∼9.2)。使用混合盐和重金属混合盐驱动溶液，Mg/Na 选择性提高至~14.5，并进一步提高至 29.3。在实际海水测试中，SFO系统有效渗透一价元素（例如Na通量~68.6 gmh），同时保持对二价元素较高的截留率（例如Mg通量~0.08 gmh），表现出对Mg/Na、U的高选择性/Na、Sr/Na、Ni/Na 和 Ca/Na。这些结果证明了 SFO 在资源利用方面的潜力，特别是在复杂的盐环境中。该工作为海水资源预处理中的盐盐分离提供了一条新途径。