Decreasing Iron Content in Phosphoric Acid Produced from New Valley Phosphates by Novel Precipitation Technique

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.