Quaternary reciprocal salt pairs

The square-prism space model Figure 4.30b) illustrates another way in which a quaternary system of the reciprocal salt pair type may be represented. The vertical axis stands for the water content, and the points on the diagram are the same as those marked on Figure 4.30a. In both diagrams all surfaces formed between the internal curves represent solutions of three salts in water saturated with one salt, all internal curves solutions of three salts in water saturated with two salts, and the two points P and Q solutions of three salts in water saturated with the three salts. The section above the internal curved surfaces denotes unsaturated solutions, the section below them mixtures of liquid and solid. 

A special case of great industrial relevance is the examination of reciprocal salt pairs representing a quaternary system of two salts that do not share a common ion... 

Figure 3.6 Representation of a quaternary system in the phase diagram, (a) Three-dimensional representation of a quaternary system A, B, C, and D in the quadrangular prism (square prism base). The four vertical faces of the prism correspond to the four binary systems, A/B, B/C, C/D, and A/D. (b) Square diagram representing the reciprocal salt pairs...

As already introduced in Section 3.1.4, the reciprocal salt pairs represent industrially relevant examples of quaternary systems. They play an important role in the production of inorganic salts via the so-called redprocal conversion in water. Industrial apphcations are the manufacture of K2SO4 and Na2C03 on the basis of mined potash ores according to the following readions ... 

---