Solid-Liquid Phase Equilibria in the Quaternary System (KCl + MgCl2 + K2B4O7 + MgB4O7 + H2O) at 308.15 K

Solubility data for the quaternary system (KCl + MgCl 2 + K 2 B 4 O 7 + MgB 4 O 7 + H 2 O) is very important for the separation of potassium and boron from the salt lake brines in Qaidam Basin. The solubility of the quaternary system (KCl + MgCl 2 + K 2 B 4 O 7 + MgB 4 O 7 + H 2 O) at T = 308.15 K and p = 0.1 MPa has been investigated experimentally with the method of isothermal dissolution equilibrium, and meanwhile physicochemical properties including density, refractive index, and pH value have been determined. In the phase diagrams of the quaternary system at 308.15 K, there are three invariant points, seven univariant isothermal dissolution curves, and five crystallization regions corresponding to KCl, MgCl 2 ·6H 2 O, K 2 B 4 O 7 · 4H 2 O, Mg 2 B 6 O 11 ·15H 2 O, and double salt KCl·MgCl 2 ·6H 2 O, respectively. The density, refractive index and pH value of the quaternary system at 308.15 K present a regular variation with the increasing of Mg 2+ concentration.