Sustainable Purification of Wet-Process Phosphoric Acid for High-purity Fertilizer Production

Abstract

In this study, the desulfurization process of Kyzylkum wet-process phosphoric acid (16.51% P2O5; 1.00% F; 1.12% MgO; 0.054% CaO; 0.43% Al2O3; 0.28% Fe2O3; 2.99% SO3;) was carried out using calcium carbonate. At the optimal precipitant norm (125%) the sulfate ion removal efficiency reached 85.66%. For deep purification of the wet-process phosphoric acid from impurities, it was treated with a threefold excess of a mixture containing 99.50% acetone and 99.00% ethanol. The resulting precipitates contained significant amounts of macronutrients - phosphorus, calcium, and magnesium oxides, which can be recommended for use as a phosphorus-calcium-magnesium (PCaMg) fertilizer. Organic solvents were recovered via vacuum evaporation, enabling multiple reuse cycles and reducing operational costs. Subsequently, ammoniation was conducted on the preliminary desulfated, purified, and evaporated phosphoric acid with the following composition (wt. %): 45.65% P2O5, 0.31% F, 0.54% MgO, 0.13% CaO, 0.05% Al2O3, 0.04% Fe2O3, 0.06% SO3 and to a pH of 5.5 and 8.5 in order to obtain monoammonium phosphate (MAP) and diammonium phosphate (DAP), respectively. MAP contains 12.83% N and 61.10% P2O5, and DAP contains 19.26% N and 53.83% P2O5. Their salt composition was determined by X-ray and IR spectroscopic studies.