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ISRN Electrochemistry
Volume 2013 (2013), Article ID 865727, 12 pages
http://dx.doi.org/10.1155/2013/865727
Research Article

Electrodialysis of Phosphates in Industrial-Grade Phosphoric Acid

1Centro de Investigación y Desarrollo Tecnológico en Electroquímica S.C. Parque, Tecnológico Querétaro, 76703 Sanfandila Pedro Escobedo, QRO, Mexico
2Universidad Tecnológica de Querétaro, 76148 Querétaro, QRO, Mexico
3Universidad del Mar, Ciudad Universitaria, Puerto Ángel, 70902 Distrito de San Pedro Pochutla, OAX, Mexico

Received 27 August 2013; Accepted 31 October 2013

Academic Editors: M. Barragán and H. Zhao

Copyright © 2013 J. J. Machorro et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The objective of this research was to study the purification of industrial-grade phosphoric acid (P2O5) by conventional electrodialysis. The experiments were conducted using a three-compartment cell with anion and cation membranes, and industrial acid solution was introduced into the central compartment. The elemental analysis of the diluted solution indicated that the composition of magnesium, phosphates, and sodium was reduced in the central compartment. The ratios of the concentration of the ions and the phosphates were essentially unchanged by the process. Consequently, electrodialysis could not purify the acid in the central compartment, and the migration of phosphate ions to the anolyte produced a highly concentrated phosphoric acid solution containing sulfates and chlorides as impurities. However, the migration of the phosphate ions across the membrane consumed a large amount of energy. Detailed speciation diagrams were constructed in this study. These diagrams showed that metal-phosphate complexes were predominant in the industrial phosphoric acid solution. This result explains why the ratios of the concentrations of the ion metals and the phosphates did not change in the purification process. The energy consumed in the electrodialysis indicated that the metal-phosphate complexes were less mobile than the free-phosphate ions. The speciation diagrams explained the experimental results satisfactorily.