Improvement of P2O5 Content in Tahoua Rock Phosphate Using Synthetic Diammonium Phosphate

Abstract

The rock phosphate Tahoua (TNP) is a nodular sedimentary phosphate, the vast majority of which is fluoroapatite, with an average P2O5 content of around 30%. But it has a range of impurities that prevent its solubility. However, this rock can be used by certain unconventional techniques to prepare a better-quality fertilizer to meet plant nutrient requirements. The aim of this study is to prepare improved rock phosphate at three different particle sizes (63, 100 µm, 160 µm) in order to assess its solubility in perchloric acid solution and distilled water. Diammonium phosphate (DAP) was synthesized at a NH3:H3PO4 molar ratio of 2:1. DAP was produced by reacting two moles of ammonia and one mole of phosphoric acid at laboratory room temperature for 30 minutes with stirring. The resulting product was characterized by X-ray diffraction and infrared spectrophotometry. These analyses confirmed no change in the structural properties of DAP. Next, the percentage mixtures of TNP particle sizes with the synthesized DAP were carried out.  Finally, a dissolution study was carried out. The results obtained from the dissolution of improved rock phosphate in perchloric acid solution and in water are respectively at 5% (50.55%; 43.85%; 45.33%); at 10% (48.90%; 46.88%; 43.70%); 15% (52.70%; 54.9%; 54.83%); 20% (60.67%; 63.95%; 60.44%) and 5% (18.88%; 26.20%; 26.20%); 10% (26.66%; 27.30%; 34.92%); 15% (43.18%; 45.86%; 59.68%); 20% (56.72%; 57.66%; 60.88%) respectively. The improvement in rock phosphate increased the level of P2O5 dissolved in the solutions.  These dissolved P2O5 levels in refined rock phosphate are interesting in water, even at 5%.