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An in Situ Potential-Enhanced Ion Transport System Based on FeHCF–PPy/PSS Membrane for the Removal of Ca2+ and Mg2+ from Dilute Aqueous Solution

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journal contribution
posted on 09.05.2016, 00:00 by Pengle Zhang, Junlan Zheng, Zhongde Wang, Xiao Du, Fengfeng Gao, Xiaogang Hao, Guoqing Guan, Chuncheng Li, Shibin Liu
An in situ potential-enhanced ion transport system based on the electrochemically switched ion permselectivity (ESIP) membrane was developed for the effective removal of Ca2+ and Mg2+ from dilute aqueous solution. In this system, uptake/release of the target ions can be realized by modulating the redox states of the ESIP membrane, and continuously permselective separation of the target ions through the ESIP membrane can be achieved by tactfully applying a pulse potential on the membrane and combining with an external electric field. In this study, iron hexacyanoferrate (FeHCF)–polypyrrole/polystyrenesulfonate (PPy/PSS) ESIP membrane with high conductivity and high flux was prepared by using stainless steel wire mesh (SSWM) as conductive substrate. The driving force for the ion transport was analyzed in detail by the equivalent circuit of the system. It is found that the FeHCF interlayer between the SSWM substrate and the PPy/PSS membrane played an important role in removing Ca2+ and Mg2+ from aqueous solutions, and markedly enhanced the separation performance of the membrane due to the improvement of the electroactivity as well as the change of the surface morphology. Influences of the applied cell voltage of the external electric field and the pulse (constant) potential across the membrane on the separation of Ca2+ and Mg2+ were investigated. It is demonstrated that the pulse potential was more beneficial for improving the removal efficiency than the constant potential applied on the membrane. The hardness of the treated water was reduced to 50 ppm (CaCO3) by applying a pulse potential of ±2.0 V and an cell voltage of 5.0 V when the initial concentration of Ca2+ was 10 mM (1000 ppm (CaCO3)). It is expected that the in situ potential-enhanced ion transport system based on the FeHCF–PPy/PSS membrane could be used as a novel water softening technology.

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