KH2PO4 crystallisation from potassium chloride and ammonium dihydrogen phosphate

Abstract

Seeking to obtain bulk (NPK - nitrogen, phosphorus, potassium), chlorine-free fertilizers, the influence of interaction between potassium chloride and ammonium dihydrogen phosphate in aqueous solutions at temperature of 20, 40, 60 and 80°C has been investigated. Components of the solid phase have been identified by methods of chemical and instrumental analysis: radiography (X - ray), infra - red molecular absorption spectroscopy (IR) and scanning electron microscopy (SEM). It has been observed that the largest amount of solid state potassium dihydrogen phosphate was obtained at 60-80°C, when the potassium chloride and ammonium dihydrogen phosphate molar ratio is equal 0.8:0.2. Changing the molar ratio of 0.5:0.5 to 0.8:0.2, and with increasing temperature, various shaped crystals have developed in the remaining aqueous solutions with a morphology shifting from sharp needles to tetragonal prism.