Obtaining a complex mineral fertilizer from raw materials of varying degrees of purification from impurities

Abstract

The article is devoted to the synthesis of a complex fertilizer magnesium-ammonium phosphate (MAP) from raw materials of varying degrees of purification, the effect of certain impurities on the MAP yield, as well as the choice of optimal conditions for obtaining this fertilizer. Phosphorus, as is known, is an irreplaceable element of plant nutrition, therefore the introduction of compounds containing phosphorus in one form or another is necessary for the normal development of plants during the growing season. Phosphoric acid, obtained by opening natural phosphates with mineral acids, in particular, sulfuric acid, is often used to obtain phosphoric fertilizers. One of the ways to purify the phosphoric acid obtained in this case is purification using various organic solvents. At the output, phosphoric acid is purified from most impurities, containing a small amount of impurity cations and anions, the main of which are fluorides and sulfates. We carried out the MAP synthesis on the basis of chemically pure phosphoric acid and using an acid purified with an organic solvent tributyl phosphate. It has been shown that the presence of sulfates and fluorides in purified phosphoric acid increases the MAP solubility in an aqueous solution by increasing the ionic strength of the solution and leads to a slight decrease in the yield of the synthesis product from 81% to 78%. The interfering effect of impurity anions can be reduced by conducting the process in an alkaline medium, pH 9-10, with the addition of an excess relative to the stoichiometric amount of an aqueous ammonia solution.