The dissolution rate of superphosphate

Abstract

The dissolution rate of commercial superphosphate fertiliser was studied at 25°, 35° and 45°c using a rotating disc of the solid material. The kinetics were followed by means of a calcium ion-selective electrode and spectrophotometric analyses. The initial dissolution was observed to consist predominately of monocalcium phosphate and was transport controlled with an apparent activation energy of 3.2 ± 0.7 kcal./mole. Thereafter diffusion of dissolved monocalcium phosphate through a porous layer, of increasing thickness, determined the rate of dissolution.