Immiscibility of Liquid Phases and Liquid–Liquid Critical Phenomena in Aqueous Solutions of Sodium and Potassium Phosphates

Abstract

Phase equilibria were studied in aqueous solutions of sodium and potassium phosphates at elevated temperatures (to 425°C) and pressures (to 63 MPa). Experimental data were obtained on the transformation of gas–liquid equilibria into heterogeneous equilibria of two liquid phases with increasing pressure, which ends in the critical phenomena of immiscibility (L₁ = L₂). Based on the experimental and literature data, it was concluded that the binary water–salt systems containing KH₂PO₄, K₂HPO₄, K₃PO₄, NaH₂PO₄, and Na₂HPO₄ are characterized by phase diagrams of the first type [1, 2], which have two critical invariant end points: N (G–L₁ = L₂) and R (G = L₁–L₂).