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

Abstract

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.