Metastable Equilibrium of the Salt Lake Brine System Na~+ + K~+ + CO_3~(3-) + SO_4~(2-) + B4O_7~(2-) + H2O at 273.15 K

摘要

The metastable phase equilibrium of the quinary system Na~+ + K~+ + CO_3~(2-) + SO_4~(2-) + B4O_7~(2-) + H2O was studied at 273.15 K using an isothermal evaporation method. The solubilities and densities of the equilibrated solution were measured. On the basis of the experimental data, the stereo metastable phase diagram and the projected phase diagram saturated with salt Na2B4O7 of the quinary system at 273.15 K were constructed. The projected phase diagram of this system consists of six invariant points, 12 univariant curves, and seven crystallization fields corresponding to the single salts Na2SO4·10H2O, K2SO4, K2B4O7·4H2O, Na2CO3·10H2O, and K2CO3·3/2H2O and double salts 2Na2SO4·Na2CO3 and K2CO3·Na2CO3· 12H2O. The double salts 2Na2SO4·Na2CO3 and K2CO3·Na2CO3· 12H2O are formed in the quinary system and also exist in the other quinary or quaternary systems containing the Na2CO3-Na2SO4-H2O and K2CO3-Na2CO3-H2O ternary subsystems at 273.15 K. The forms of sodium and potassium borate are Na2B4O5(OH)4·8H2O and K2B4O5(OH)4·2H2O, respectively. In contrast to the phase diagrams of its subsystems, the crystallization area of K2CO3·3/2H2O increases clearly in the quinary system.