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

Solubility data for the quaternary system (KCl + MgCl2 + K2B4O7 + MgB4O7 + H2O) 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 + MgCl2 + K2B4O7 + MgB4O7 + H2O) 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, MgCl2 center dot 6H(2)O, K2B4O7 center dot 4H(2)O, Mg2B6O11 center dot 15H(2)O, and double salt KCl center dot MgCl2 center dot 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 Mg2+ concentration.