**1.2.1 The stable phase equilibria of salt-water systems**

The research method for the stable phase equilibria of salt-water system is isothermal dissolution method. It is worthy of pointing out that the status of the stable phase equilibrium of salt-water system is the in a sealed condition under stirring sufficiently, and the speed of dissolution and crystallization of equilibrium solid phase is completely equal with the marker of no change for the liquid phase composition. As to the thermodynamic stable equilibrium studies aiming at sea water system (Na – K – Mg – Cl – SO4 – H2O), J.H. Vant'hollf (1912) was in the earliest to report the stable phase diagram at 293.15 K with isothermal dissolution method.

In order to accelerate the exploiting of Qaidam Basin, China, a number of the stable phase equilibria of salt-water systems were published at recent decades (Li et al., 2006; Song, 1998, 2000; Song & Du, 1986; Song & Yao, 2001, 2003).
