الفهرس 
LITERATURE REVIEWOnly 14 pages are availabe for public view
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Abstract
Pure phosphoric acid is widely used as a feedstock for the production of fertilizers, food products, detergents and pharmaceutical products. In Egypt, Abu-Tartur phosphate deposit has iron content of 3-4 % as Fe2O3. This work aims to develop a novel and cost effective method for purification of commercial grade phosphoric acid for fertilizers, food and other industries. The phosphoric acid used is prepared from run of mine rocks of Abu-Tartur mine. Oxalic acid is used for precipitation of iron in the freshly prepared dilute phosphoric acid (26% P2O5). The process developed in this study could apply to filter phosphoric acid with high iron content. Herein, we focused on Abu-Tartur Egyptian phosphate ores because it’s one of the highest iron content in the world.
A method has been developed to reduce the iron content in phosphoric acid produced by the dihydrate wet process from open cast phosphate rock of Abu-Tartur mine in Egypt. In this method, oxalic acid was used to precipitate iron as ferrous oxalate dihydrate (FeC2O4.2H2O). The achieved removal efficiency of iron was about 91% due to the low solubility of the precipitated salt in dilute phosphoric acid medium. The maximum P2O5 losses were less than 1.0 %. The optimum conditions of oxalate precipitation method were obtained using synthetic dilute phosphoric acid (28 % P2O5) with iron content amounting 2.8 % Fe2O3. It was found that, the clarification time, reaction temperature, P2O5 concentration and oxalic acid dose were 2 hours, 60 oC, 28% P2O5 and 7.5 g oxalic/100 g 28% P2O5 acid, respectively. These conditions were applied using wet-process phosphoric acid (28% P2O5). Firstly, ferric ions in the acid were reduced to ferrous ions using iron scrap, followed by oxalic acid addition.
Mostly all iron ions in the solution are in the divalent state at Electro Motive Force (EMF) values less than 275 mV. The solubility of ferrous oxalate dihydrate was measured at different temperatures and phosphoric acid concentrations. A recovery study for oxalic acid from the precipitated FeC2O4.2H2O has performed.
In addition, fundamentals and basic study of ferrous oxalate dihydrate (FeC2O4.2H2O) crystallization including supersaturation, nucleation and crystal growth in simulated dihydrate phosphoric acid product with and without Cetyl Pyridinium Chloride (CPC) additive were studied. Oxalic acid and ferrous sulfate heptahydrate crystals were mixed with dilute phosphoric acid (28% P2O5) at 60 oC and the turbidity of the reaction mixture was measured at different time intervals. Induction time of ferrous oxalate dihydrate crystals was calculated at different supersaturation ratios ranging from 2.5 to 6.7. With increasing the supersaturation ratio, the induction time decreased. The nucleation rates are 46.4 × 1028 nuclei/cm3.s and 50.2 × 1028
nuclei/cm3.s at supersaturation ratio 6.7 with and without CPC addition, respectively.
The surface energy increases with CPC addition compared to the baseline. In addition, the formed crystals are modified from cubic shape to rod-like shape with increasing CPC dose.
Also, nucleation fundamentals and morphologies of iron II oxalate dihydrate crystals, FeC2O4.2H2O, in deionized water and diluted phosphoric acid (28% P2O5) media were studied. Oxalic acid and iron II sulfate heptahydrate crystals were mixed with deionized water and diluted phosphoric acid (28% P2O5) media at 25 oC with concentration range of 2.7 - 7.2 g/100 mL. The turbidity of the reaction mixture was measured at different time intervals and the induction time of iron II oxalate dihydrate
crystals was calculated. It was found that, the increase of induction time in phosphoric
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acid medium is more than that in deionized water at the same concentration of iron II
oxalate dihydrate crystals. The nucleation rates are 30.5 × 1028 nuclei/cm3.s and 70.2
× 1028 nuclei/cm3.s at 7.2 % concentration of iron II oxalate dihydrate in deionized water and phosphoric acid media, respectively. The surface energy increases in water medium compared to phosphoric acid medium. In addition, the formed crystals are converted from cubic to rectangular shape with increasing concentration of iron II oxalate dihydrate in water medium. On the other hand, the crystals are converted from cubic to octahedral while changing the medium from water to phosphoric acid at 2.7
% Iron II oxalate concentration.