Derivation of Phase Diagrams from Solubility Data

There are two types of quinary salt-water systems (Fig. 2. 1). One of them comprises three different cations (A+, B+, C+) and two different anions (X-,.Y-). These yield the salts AX, BX, CX, AY, BY, and CY. The other one comprises two different cations (A+, B+) and three different anions (X-, Y-, Z-) which yield the salts AX, AY, AZ, BX, BY, and BZ. The quinary seawater system Na₂2+-K₂2+-Mg2+-Cl₂2--SO₄2--H₂0 which yields Na₂Cl₂, K₂C1₂, MgCl₂, Na₂SO₄, K₂SO₄ and MgSO₄ belongs to the first type. In the following sections it will be explained how this type originates from its subsystems, in which way the subsystems are related to each other and to the quinary system, and how projections of the various subsystems and the quinary system are obtained. As a matter of fact, all explanations apply likewise to the second type of the quinary systems, in principle.