Membrane capacitive deionization (MCDI) is a promising technology for the removal of charged species from aqueous feed streams. In this study, the effects of initial pH on the removal of phosphate (P) species by MCDI were investigated. Two operational modes (constant voltage (CV) and constant current (CC)) were adopted with both the efficacy of P removal and the energy consumption between CV and CC modes compared at different initial pH values. Results indicated that, for feed water only containing phosphate species, the optimized P removal performance was achieved at pH 5.0–6.0 where the monovalent P species (i.e., H₂PO₄⁻) dominated in CC mode more energy-efficiently in terms of P removal than in CV mode. The competitive electrosorption between Cl⁻ and P over a range of initial pH values was examined in CC mode with results indicating that at pH 5.0 and 6.0, where the monovalent P species (i.e., H₂PO₄⁻) dominated, Cl⁻ was preferentially electrosorbed, presumably because of its smaller hydrated radius, while under more alkaline conditions (pH 8.0 and 9.0), divalent P species (i.e., HPO₄²⁻) were more selectively removed due to their charge. A Nernst–Planck equation, in which the ion flux ratio was expressed as a function of diffusion coefficient and charge, provides a good description of the ion selectivity between Cl⁻ and P when the initial concentration of these two ions are equal.

中文翻译：

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通过膜电容去离子（MCDI）研究废水中pH依赖性磷酸盐的去除

膜电容去离子（MCDI）是一种从含水进料流中去除带电物质的有前途的技术。在这项研究中，研究了初始pH对MCDI去除磷酸盐（P）物质的影响。采用两种操作模式（恒定电压（CV）和恒定电流（CC）），在不同的初始pH值下，P去除的效率以及CV和CC模式之间的能耗均得到了比较。结果表明，对于给水只含磷酸盐物质，优化的P移除性能在pH 5.0-6.0实现，其中一价P物质（即，H ₂ PO ₄ ^-）在CC模式下，以P去除方式比在CV模式下更节能。氯之间的竞争电吸附^-在一定范围的初始pH值和P在CC模式，检查与指示的结果，在pH为5.0和6.0，其中所述一价P物质（即，H ₂ PO ₄ ^- ）为主，氯^-是优先电吸附，大概是因为它的水合半径较小，而在更多的碱性条件下（pH 8.0和9.0），二价P物质（即HPO ₄ ^2-）由于其电荷而更具选择性地被移除。能斯特-普朗克方程，其中，所述离子通量比率表示为扩散系数和电荷的功能，提供氯之间的离子选择性的良好描述^-和P当这两个离子的初始浓度是相等的。