Phase equilibrium, structural properties and separation process studies of potassium-ammonium-based solid solution in aqueous-solid solution (AQ-SS)

Abstract

In order to solve the problem that potassium salt product is impure in industrial production. Phase equilibrium, structural properties and separation process of potassium ammonium sulfate in aqueous-solid solution (AQ-SS) was studied. First, we study solid-liquid equilibrium of K2SO4-(NH4)2SO4-H2O ternary system, which revealed complete miscibility in the solid phase. The type of solid solutions was determined by analysis of XRD further confirmed-it is infinite substitutional solid solution. Then, from the analysis of FT-IR, TG-DSC and mapping of [(NH4)0.104K1.896]SO4 and [(NH4)1.79K0.203]SO4 solid solution, we can conclude that two solid solutions are similar, but the absorption position have slight shift to low wave number direction as the increasing of K2SO4 content; the weightlessness decreases with the decrease of NH4+ content; the homogeneous distribution of K+ and NH4+ elements. Finally, based on the phase diagrams and the relevant mass balancing, multistage fractional crystallization experiment to obtain the purity of the K2SO4 is 95.28% after three times cycle operation and we can get about 99.04% K2SO4 in the fourth operation by theoretical analysis, which not only demonstrates the potential application of multistage crystallization to separate K2SO4 from AQ-SS, but also provides guidance and methods for the separation of AQ-SS systems.