Конденсированные среды и межфазные границы (Dec 2017)

TOTAL AND PARTIAL CURRENT-VOLTAGE CHARACTERISTICS OF ANION-EXCHANGE MEMBRANES IN NaCl AND NaH2PO4 SOLUTIONS

  • Tsygurina Ksenia A.,
  • Rybalkina Olesya A.,
  • Melnikova Ekaterina D.,
  • Pismenskaya Natalia D.

DOI
https://doi.org/10.17308/kcmf.2017.19/241
Journal volume & issue
Vol. 19, no. 4
pp. 585 – 595

Abstract

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Anions of phosphoric acid are nutrients. They are necessary for people, animals or plants to ensure normal life. The combination of biochemical and various membrane methods with electrodialysis as a fi nishing step for selective extraction and concentration of nutrients has already proved its economic and environmental feasibility. The complexity of experimental and theoretical studies of the phosphate transfer mechanisms in systems with ion-exchange membranes is because the amphoteric properties of this substance. This work is aimed to investigate the transfer mechanisms in the desalting channels of electrodialyzers containing NaH2PO4 solution. The object of the study is the homogeneous anion exchange membrane AX in a 0.02 M NaH2PO4 solution. Due to the protonation-deprotonation reactions of the dihydrogen phosphate anion, the last can be transformed into hydrogen phosphate and phosphate anions with the formation of protons and hydroxyl ions, which can participate in the charge transfer in the AX/NaH2PO4 system. As a result, the transport of phosphates in systems with ion-exchange membranes is characterized by anomalous (in comparison with NaCl solutions) concentration dependences of electrical conductivity, diffusion permeability, and current-voltage characteristics, which have two plateaus. In this paper, we propose a simple method that allows us to determine the partial currents and transport numbers of counter ions through the anion exchange membrane, and to estimate the number of protons coming from the membrane boundary into the desalting channel of the electrodialyzer in the under-limiting and over-limiting current modes. Using this method, it was found that the transformation of single-charged anions H PO 2 4- in the membrane fi rst into double-charged HPO4 2- and then into triple-charged PO4 3- ions causes differences in the shape of the total current-voltage characteristics in comparison with obtained in NaCl solutions.

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