How Chemical Nature of Fixed Groups of Anion-Exchange Membranes Affects the Performance of Electrodialysis of Phosphate-Containing Solutions?

Author:

Pismenskaya Natalia1,Rybalkina Olesya1,Solonchenko Ksenia1,Pasechnaya Evgeniia1,Sarapulova Veronika1ORCID,Wang Yaoming2,Jiang Chenxiao2,Xu Tongwen2,Nikonenko Victor1ORCID

Affiliation:

1. Russian Federation, Kuban State University, 149, Stavropolskaya Str., 350040 Krasnodar, Russia

2. Anhui Provincial Engineering Laboratory of Functional Membrane Science and Technology, Department of Applied Chemistry, School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China

Abstract

Innovative ion exchange membranes have become commercially available in recent years. However, information about their structural and transport characteristics is often extremely insufficient. To address this issue, homogeneous anion exchange membranes with the trade names ASE, CJMA-3 and CJMA-6 have been investigated in NaxH(3−x)PO4 solutions with pH 4.4 ± 0.1, 6.6 and 10.0 ± 0.2, as well as NaCl solutions with pH 5.5 ± 0.1. Using IR spectroscopy and processing the concentration dependences of the electrical conductivity of these membranes in NaCl solutions, it was shown that ASE has a highly cross-linked aromatic matrix and mainly contains quaternary ammonium groups. Other membranes have a less cross-linked aliphatic matrix based on polyvinylidene fluoride (CJMA-3) or polyolefin (CJMA-6) and contain quaternary amines (CJMA-3) or a mixture of strongly basic (quaternary) and weakly basic (secondary) amines (CJMA-6). As expected, in dilute solutions of NaCl, the conductivity of membranes increases with an increase in their ion-exchange capacity: CJMA-6 < CJMA-3 << ASE. Weakly basic amines appear to form bound species with proton-containing phosphoric acid anions. This phenomenon causes a decrease in the electrical conductivity of CJMA-6 membranes compared to other studied membranes in phosphate-containing solutions. In addition, the formation of the neutral and negatively charged bound species suppresses the generation of protons by the “acid dissociation” mechanism. Moreover, when the membrane is operated in overlimiting current modes and/or in alkaline solutions, a bipolar junction is formed at the CJMA- 6/depleted solution interface. The CJMA-6 current-voltage curve becomes similar to the well-known curves for bipolar membranes, and water splitting intensifies in underlimiting and overlimiting modes. As a result, energy consumption for electrodialysis recovery of phosphates from aqueous solutions almost doubles when using the CJMA-6 membrane compared to the CJMA-3 membrane.

Funder

Russian Science Foundation

Publisher

MDPI AG

Subject

Polymers and Plastics,General Chemistry

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