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Decreasing Iron Content In Fertilizer-Grade Phosphoric Acid Using Ion Exchange Method

E.A.Abdel-Aal, S.A.Dardeer, N.M.Rageh, H.M.Rageh

In Egypt, concentrated wet-process phosphoric acid is produced from phosphate concentrate by the conventional dihydrate process in which phosphate concentrate leached with sulfuric and weak phosphoric acids. It is an important intermediate product for production of phosphatic fertilizers. The produced acid contains iron ranging from 2.0 % to 4.0 % Fe2O3 as inorganic impurity and 48% P2O5. Ion-exchange method is used to reduce the concentration of ferric ions content. Ferric ions affect the quality of produced fertilizers as they combine with P2O5 and form insoluble compounds. Decreasing Fe2O3 content to less than 1.0% was achieved by reaction of fertilizer-grade phosphoric acid with strong acid cation exchanger (Dowex-50). The following optimum reaction conditions were determined: 30°C reaction temperature, 30 min. raction time, 1.25 weight ratio of cation-exchange resin to acid and 28 % P2O5 from acid concentration. These conditions lead to removal of 80.3 % from Fe2O3 in the treated acid. Reduction of ferric ions to ferrous ions is a must for higher Fe2O3 removal efficiency. Also, regeneration conditions of loaded resin were systematically studied.