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. 1. Introduction The annual global phosphorus consumption is approximately 20,764 million metric tons [1]. Phosphoric acid and phosphate salts have several applications. For example, phosphoric acid fuel cells use liquid phosphoric acid as an electrolyte [2, 3]. Industrial-grade phosphoric acid is produced from phosphate rock and consequently has a high content of mineral impurities, which lower the acid quality for commercial use. This industrial-grade phosphoric acid (52–54% P2O5) is also named as merchant-grade acid. Phosphoric acid purification is a major challenge, and a variety of methods have been used to eliminate the impurities in the industrial-grade phosphoric acid [4–18]. These methods which are described in the literature are enumerated in Table 1. In addition, Table 2 shows electrodialysis process for concentrating industrial-grade phosphoric acid [19–27]. These studies in Table 2 provided more comprehensive and consistent information on the energy requirements for the process. Comparing these methods is very difficult for the following reasons: (a) there is a wide variation in the types of the impurities in industrial-grade acid because
References
[1]
G. Villalba, Y. Liu, H. Schroder, and R. U. Ayres, “Global phosphorus flows in the industrial economy from a production perspective,” Journal of Industrial Ecology, vol. 12, no. 4, pp. 557–569, 2008.
[2]
M. Ghouse and H. Abaoud, “Materials used in the development of a 1？kW phospshoric acid fuel cell stack,” Journal of New Materials for Electrochemical Systems, vol. 2, no. 3, pp. 201–206, 1999.
[3]
H.-Y. Kwak, H.-S. Lee, J.-Y. Jung, J.-S. Jeon, and D.-R. Park, “Exergetic and thermoeconomic analysis of a 200？kW phosphoric acid fuel cell plant,” Fuel, vol. 83, no. 14-15, pp. 2087–2094, 2004.
[4]
R. J. Kepfer and W. R. Devor, “Phosphoric acid purification,” U.S. Patent 2,174,158, 1939.
[5]
D. Goldstein, “Phosphoric acid purification,” U.S. Patent 3,819,810, 1974.
[6]
D. H. Michalski and V. Srinivasan, “Process of removing cationic impurities from wet process phosphoric acid,” U.S. Patent 4,639,359, 1987.
[7]
L. W. Bierman, M. L. Lopez, and J. E. Perkins, “Purification of phosphoric acid,” U.S. Patent: 4,877,594, 1989.
[8]
A. I. Alonso, A. M. Urtiaga, S. Zamacona, A. Irabien, and I. Ortiz, “Kinetic modelling of cadmium removal from phosphoric acid by non-dispersive solvent extraction,” Journal of Membrane Science, vol. 130, no. 1-2, pp. 193–203, 1997.
[9]
H. F. T. Haraldsen, “Method for removal of heavy metals from phosphoric acid containing solutions,” U.S. Patent 4,986,970, 1991.
[10]
H. J. Skidmore and K. J. Hutter, “Methods of purifying phosphoric acid,” U.S. Patent 5,945,000, 1999.
[11]
L. H. Reyes, I. S. Medina, R. N. Mendoza, J. R. Vázquez, M. A. Rodríguez, and E. Guibal, “Extraction of cadmium from phosphoric acid using resins impregnated with organophosphorus extractants,” Industrial and Engineering Chemistry Research, vol. 40, no. 5, pp. 1422–1433, 2001.
[12]
M. P. González, R. Navarro, I. Saucedo, M. Avila, J. Revilla, and C. Bouchard, “Purification of phosphoric acid solutions by reverse osmosis and nanofiltration,” Desalination, vol. 147, no. 1–3, pp. 315–320, 2002.
[13]
K. Hotta and F. Kubota, “Method for purification of phosphoric acid high purity polyphosphoric acid,” U.S. Patent: 6,861,039, 2005.
[14]
M. P. González Mu？oz, R. Navarro, I. Saucedo et al., “Hydrofluoric acid treatment for improved performance of a nanofiltration membrane,” Desalination, vol. 191, no. 1–3, pp. 273–278, 2006.
[15]
A. Hannachi, D. Habaili, C. Chtara, and A. Ratel, “Purification of wet process phosphoric acid by solvent extraction with TBP and MIBK mixtures,” Separation and Purification Technology, vol. 55, no. 2, pp. 212–216, 2007.
[16]
A. A. El-Asmy, H. M. Serag, M. A. Mahdy, and M. I. Amin, “Purification of phosphoric acid by minimizing iron, copper, cadmium and fluoride,” Separation and Purification Technology, vol. 61, no. 3, pp. 287–292, 2008.
[17]
K. Ishikawa, K. Yokoi, K. Takeuchi, Y. Kurita, and H. Uchiyama, “High purity phosphoric acid and process of producing the same,” U.S. Patent: 7,470,414,B2, 2008.
[18]
M. I. Amin, M. M. Ali, H. M. Kamal, A. M. Youssef, and M. A. Akl, “Recovery of high grade phosphoric acid from wet process acid by solvent extraction with aliphatic alcohols,” Hydrometallurgy, vol. 105, no. 1-2, pp. 115–119, 2010.
[19]
K. W. Loest and J. T. Schaefer, “Production of monobasic potassium phosphate by electrodialysis,” US Patent: 4,033,842, 1977.
[20]
T. R. Hanley, H.-K. Chiu, and R. J. Urban, “Phosphoric acid concentration by electrodialysis,” AIChE Symposium Series, vol. 82, pp. 121–132, 1986.
[21]
D. Touaibia, H. Kerdjoudj, and A. T. Cherif, “Concentration and purification of wet industrial phosphoric acid by electro-electrodialysis,” Journal of Applied Electrochemistry, vol. 26, no. 10, pp. 1071–1073, 1996.
[22]
S. A. Ueda, “Method for purifying phosphoric acid,” Japanese Patent Kokai No. Sho 48 [1973]-10312, 1973.
[23]
M. B. C. Elleuch, M. B. Amor, and G. Pourcelly, “Phosphoric acid purification by a membrane process: electrodeionization on ion-exchange textiles,” Separation and Purification Technology, vol. 51, no. 3, pp. 285–290, 2006.
[24]
Y. K. Litsis and B. A. Popov, “Method of extraction of phosphoric acid,” Russian Inventor's Certification No.443839, 1974.
[25]
T. Yamabe, “Method for the manufacture of phosphoric acid,” Japanese Patent Kokai No. Sho 48 [1976]-106696, 1976.
[26]
T. Yoshihara, “A method for refining phosphoric acid,” Japanese Patent Kokai No. Sho 53 [1978]-96994, 1978.
[27]
K. Moeglich, “Electrochemical processes utilizing layered membrane electrochemical processes utilizing layered membrane,” U.S. Patent 4,326,935, 1982.
[28]
P. D？ugo？ecki, K. Nymeijer, S. Metz, and M. Wessling, “Current status of ion exchange membranes for power generation from salinity gradients,” Journal of Membrane Science, vol. 319, no. 1-2, pp. 214–222, 2008.
[29]
E. H？gfeldt, Stability Constants of Metal-Ion Complexes. Part A: Inorganic Ligands, vol. 21 of IUPAC Chemical Data Series, Pergamon Press, 1982.
[30]
D. D. Perrin, Dissociation Constants of Inorganic Acids and Bases in Aqueous Solution, IUPAC, Butterworths, London, UK, 1969.
[31]
A. E. Martell and R. M. Smith, Critical Stability Constants, vol. 4 of Inorganic Complexes, Plenum Press, New York, NY, USA, 1976.
[32]
J. N. Butler, Ionic Equilibrium: Solubility and PH Calculations, John Wiley & Sons, Toronto, Canada, 1998.
[33]
T. S. Sorensen, Interfacial Electrodynamics of Membranes and Polymer Films, in Surface Chemistry and Electrochemistry of Membranes, CRC Press, New York, NY, USA, 1999.
[34]
U. López-García, R. Anta？o-López, G. Orozco, T. Chapman, and F. Castaneda, “Characterization of electrodialysis membranes by electrochemical impedance spectroscopy at low polarization and by Raman spectroscopy,” Separation and Purification Technology, vol. 68, no. 3, pp. 375–381, 2009.
[35]
D. R. Migneault and R. K. Forcé, “Dissociation constants of phosphoric acid at 25°C and the ion pairing of sodium with orthophosphate ligands at 25°C,” Journal of Solution Chemistry, vol. 17, no. 10, pp. 987–997, 1988.
[36]
A. D. Pethybridge, J. D. R. Talbot, and W. A. House, “Precise conductance measurements on dilute aqueous solutions of sodium and potassium hydrogenphosphate and dihydrogenphosphate,” Journal of Solution Chemistry, vol. 35, no. 3, pp. 381–393, 2006.
[37]
I. Puigdomenech, Make Equilibrium Diagrams Using Sophisticated Algorithms (MEDUSA), Inorganic Chemistry, Royal Institute of Technology, Stockholm, Sweden, 2004.
[38]
M. Azaroual, C. Kervevan, A. Lassin et al., “Thermo-kinetic and physico-chemical modeling of processes generating scaling problems in phosphoric acid and fertilizers production industries,” Procedia Engineering, vol. 46, pp. 68–675, 2012.
[39]
V. M. M. Lobo, Handbook of Electrolyte Solutions, Part A. Physical, vol. 41 of Sciences Data, Elsevier Science, New York, NY, USA, 1989.
[40]
F. A. Cotton and G. Wilkinson, Química Inorgánica Avanzada, Limusa, Cancun, Mexico, 1st edition, 1993.
[41]
M. Cherif, A. Mgaidi, N. Ammar, G. Vallée, and W. Fürst, “A new investigation of aqueous orthophosphoric acid speciation using Raman spectroscopy,” Journal of Solution Chemistry, vol. 29, no. 3, pp. 255–269, 2000.
[42]
W. W. Rudolph, “Raman-spectroscopic measurements of the first dissociation constant of aqueous phosphoric acid solution from 5 to 301°C,” Journal of Solution Chemistry, vol. 41, no. 4, pp. 630–645, 2012.
[43]
H. Diallo, M. Rabiller-Baudry, K. Khaless, and B. Chaufer, “On the electrostatic interactions in the transfer mechanisms of iron during nanofiltration in high concentrated phosphoric acid,” Journal of Membrane Science, vol. 427, pp. 37–47, 2013.
[44]
N. Pismenskaya, E. Laktionov, V. Nikonenko, A. El Attar, B. Auclair, and G. Pourcelly, “Dependence of composition of anion-exchange membranes and their electrical conductivity on concentration of sodium salts of carbonic and phosphoric acids,” Journal of Membrane Science, vol. 181, no. 2, pp. 185–197, 2001.
[45]
N. Pismenskaya, V. Nikonenko, B. Auclair, and G. Pourcelly, “Transport of weak-electrolyte anions through anion exchange membranes: Current-voltage characteristics,” Journal of Membrane Science, vol. 189, no. 1, pp. 129–140, 2001.
[46]
S. Koter and M. Kultys, “Modeling the electric transport of sulfuric and phosphoric acids through anion-exchange membranes,” Separation and Purification Technology, vol. 73, no. 2, pp. 219–229, 2010.
[47]
V. Koleva and V. Stefov, “Phosphate ion vibrations in dihydrogen phosphate salts of the type M(H2PO4)2·2H2O (M = Mg, Mn, Co, Ni, Zn, Cd): Spectra-structure correlate,” Vibrational Spectroscopy, vol. 64, pp. 89–100, 2013.
