Preparation of feed-grade monocalcium phosphate by crystallization in aqueous medium: Calculation and experiments

Abstract

Monocalcium phosphate is one of the most commonly used forms of inorganic feed phosphates for certain types of animals. It can be prepared by the reaction between phosphoric acid and a calcium source, the resulting slurry is then dried. In this paper, we use the graphical calculation method to quantify the formation of monocalcium phosphate in acidic solution as a guide for the experiments. The calculation and experimental results show that monocalcium phosphate can be formed in the solid phase when the reactants are added to the mother liquor at 10 °C, then this system is cooled down to 25°C. The mother liquor plays the role of medium for the precipitation and crystallization of monocalcium phosphate. The weight ratio of the fresh phosphoric acid to the mother liquor can vary in a fairly wide range from 1:1 to 1:4.The results show that the solid yield reaches 92.4%, the final product is a single phase with a structure similar to the one of Ca(H2PO4)2.H2O and contains parallelogram-like crystals with a length of about 20 -50 μm, a width of 20 -30 μm, and a thickness of a few microns. The formation of monocalcium phosphate has been confirmed by the XRD data and chemical analysis.