ammonium orthophosphate products are prepared by reacting ammonia and phosphoric acid together at high speed under vigorous mixing conditions by spraying the reactants through a two - phase , dual coaxial mixer / sprayer and separately controlling the supply and axial outflow rate of the phosphoric acid at 1 to 10 m / sec . and the outflow rate of ammonia at 200 to 1000 m / sec . . thorough mixing and a homogeneous product is obtained by directing the outflow spray into a coaxial cylindrical reaction chamber of a specified size with respect to the diameter of the outermost duct of the sprayer / mixer . the product may be granulated on a moving bed of granules and adjusted in respect of the nh 3 to h 3 po 4 content by changing the concentration of the phosphoric acid and / or supplying additional ammonia to the granulation bed .