Phase Equilibria in the KNO3-KH2PO4-K2SO4-H2O System at 298.2 K

Data regarding the solubility of salts in the KNO3-KH2PO4-K2SO4-H2O system can be used to optimize the composition of liquid complex fertilizers. This research considers phase equilibria in the quaternary system KNO3-KH2PO4-K2SO4-H2O at 298.2 K for the first time. A phase diagram with a plotted grid of isohydric lines was constructed based on the results of the experiment. The phase diagram displays a single quaternary invariant point, three ternary invariant points, three univariant curves, and three crystallization regions that correspond to KH2PO4, K2SO4, and KNO3. Among these, the crystallization region of K2SO4 is the largest, while that of KNO3 is the smallest. The order of decreasing solubility for the salts is KNO3 > KH2PO4 > K2SO4. No crystalline hydrates, double salts, or solid solutions were found in the system. The solution that is maximally saturated with salts corresponds to the quaternary invariant point.