Electrodialysis of Phosphates in Industrial-Grade Phosphoric Acid

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.

Selectivity and competitive mechanism of cation exchange resin for Fe, Mg, and Al ions in phosphoric acid

“…[24] This may be due to the formation of complexes between Fe 2+ and phosphoric acid, which reduces the removal of Fe 2+ from solution. [1,25] Mg-Al binary system In accordance with the Fe-Mg binary system, the kinetics of aluminum and magnesium displacement adsorption were shown in Figure 9. The experimental and analytical methods are consistent with the above and will not be repeated here.…”

“…This may be due to the formation of AlH 2 PO 4 2+ complexes between aluminum and phosphoric acid, which can decrease the concentration of free Al 3+ and consequently reduce the replacement capacity of aluminum ions. [1,25] Fe-Al binary system Similarly, the iron and aluminum displacement adsorption kinetics are shown in Figure 10. Iron can almost completely replace the aluminum loaded in the resin, which indicates the replacement capacity: Fe > Al.…”

Overview on the removal of iron from phosphoric acid: A Comparative study

“…Machorro et al, [29] investigated the purification of industrial-grade phosphoric acid [P 2 O 5 = 54%] by conventional electrodialysis using a three-compartment cell with anion and cation membranes, where the acid was introduced into the central compartment. The results show that Na + , Mg 2+ and PO 4 3were reduced and the ratios of the concentration of the above mentioned ions were unchanged, also the anions as sulfates and chlorides would also migrate, i.e, electrodialysis could not purify the acid.…”

“…The concentration of iron should be <1.5% Fe 2 O 3 as standard for fertilizer grade phosphoric acid of 50% P 2 O 5 [16][17][18][19]. Many trials were performed by various techniques in order to purify the WPA via precipitation [4], adsorption, , ion exchange [20][21][22], reverse osmosis, ultrafiltration [23][24][25][26][27][28], electrodeposition [29], solvent extraction [30][31][32] and magnetic separation [33] The concentration of iron in phosphate rocks varies from 0.1% -4.0 % as Fe 2 O 3 depend on their origin [34,35].The present overview discusses some of the techniques used for iron removal from WPA mainly, precipitation, adsorption and solvent extraction, magnetic separation, crystallization, reverse osmosis, nanofilteration as well as electrodialysis.…”

The use of Alizarin modified bentonite for removal of some heavy metals ions from the wet process phosphoric acid

“…The choice of an economically suitable technique depends upon many parameters such as the concentration of wet process phosphoric acid, the amount and the concentration of the co-dissolved impurities. These techniques are precipitation (Abdennebi et al, 2017), floatation (Haraldsen, 1991), membrane extraction (Al-Harahsheh et al, 2017;Machorro et al, 2013), crystallization ((Aaltonen et al, 2004;Chen et al, 2012), ion exchange (Marcus et al, 2004;Cheira, 2015), liquid-liquid extraction (Singh et al, 2009;Chen et al, 2016;Assuncao et al, 2017;Li et al, 2017), and solid phase extraction (Awwad et al, 2013 ).…”