Abstract Selective ion removal has been a point of focus in capacitive deionization because of its industrial applications such as water purification, water softening, heavy metal separation and resource recovery. Conventionally, carbon is used as electrode material for selectivity. However, recent developments focus on intercalation materials such as Prussian Blue Analogues, due to their size-based preference towards cations. Selectivity of nickel hexacyanoferrate electrodes from a mixture of Na+, Mg2+, and Ca2+ ions was studied in this work. Here, a CDI cell with two identical NiHCF electrodes was operated in two desalination modes: (a) cyclic, in which ions are removed from and released into the same water reservoir and thus, the ion concentration remains the same after one cycle, and (b) continuous, in which ions are removed from one water reservoir and released back in a different reservoir. An average separation factor of ≈15 and 25, reflecting the selectivity of the electrodes, was obtained for Na+ over Ca2+ and Mg2+ from an equimolar solution of Na+, Ca2+ and Mg2+ in both, cyclic and continuous desalination. It was concluded that NiHCF, used in a symmetric CDI cell, is a promising material for highly selective removal of Na+ from a multivalent ion mixture.

中文翻译：

---

六氰基铁酸镍电极在电容去离子中具有高单价/二价离子选择性

摘要 选择性离子去除因其在水净化、水软化、重金属分离和资源回收等工业应用中的应用而成为电容去离子技术的一个重点。通常，为了选择性，碳被用作电极材料。然而，最近的发展集中在插层材料，如普鲁士蓝类似物，因为它们对阳离子的基于尺寸的偏好。本工作研究了 Na+、Mg2+ 和 Ca2+ 离子混合物对六氰基铁酸镍电极的选择性。在这里，具有两个相同 NiHCF 电极的 CDI 电池在两种脱盐模式下运行：（a）循环，其中离子从同一水库中去除并释放到同一水库中，因此，一个循环后离子浓度保持不变，以及（ b) 连续的，其中离子从一个水库中去除并释放回另一个水库。在循环和连续脱盐过程中，从 Na+、Ca2+ 和 Mg2+ 的等摩尔溶液中获得了 Na+ 相对于 Ca2+ 和 Mg2+ 的平均分离因子 ≈15 和 25，反映了电极的选择性。结论是，用于对称 CDI 电池的 NiHCF 是一种很有前途的材料，可用于从多价离子混合物中高度选择性地去除 Na+。