Electrodialysis of Merchant

Electrodialysis of Merchant-Grade Phosphoric Acid
J. J Machorroa, J. C. Olverab, R. Garciaa, G. Orozcob*
a
Universidad Tecnológica de San Juan del Río
Av. La Palma No. 125, Col. Vista Hermosa, San Juan del Río.Querétaro, México.
b
Centro de Investigación y Desarrollo Tecnológico en Electroquímica S.C.
Parque Tecnológico Querétaro, Sanfandila Pedro Escobedo,
Querétaro, México
*e-mail: [email protected]
Abstract
The goal of this research was to study the purification of merchant-grade phosphoric
acid by electrodialysis. A three-compartment cell with anion and cation membranes
was used. The acid was introduced into the central compartment, see Fig 1. The
composition of cations and phosphates were reduced in the central compartment.
However, the ratios cation-concentration-/ phosphates-concentrarion- were unchanged
by the process. Thus, electrodialysis cannot purify the acid in the central compartment;
simultaneously the migration of phosphate ions to the anolite produced a highly
concentrated phosphoric acid. However, the migration of the phosphate ions consumed
a large amount of energy. Detailed speciation diagrams were constructed in this study.
These diagrams showed that metal-phosphate complexes are predominant in the
phosphoric acid solution. The speciation diagrams explained the experimental results
adequately.
Figure 1. Schematic of phosphoric acid demineralization process