关键词: phase diagram, non-equilibrium state, evaporation, salt-forming, bittern

Abstract: Salt-forming regions for a complex salt-water system in non-equilibrium state of evaporation process are usually different from those in solubility diagrams.To understand the solid-forming region of NaCl and improve the utilization of bittern resources,experiments were carried out to evaporate 20 representative mixture solution samples of Na⁺,Mg²⁺//Cl^-,SO₄^2--H₂O system with an average evaporation intensity of (1.4±0.4) g·L^-1 ·min^-1 (water) at boiling temperature 348 K,and determine the NaCl solid-forming regions in non-equilibrium state.Because of the complexity of salt-forming region,a maximal region and a minimal region were proposed to express the non-equilibrium state salt-forming region with different crystal seed,and a conditional salt-forming region was proposed to present the characteristic region of non-equilibrium salt-forming phase diagram.The areas of the maximal and minimal regions are 2.00 and 1.56 times those in solubility diagram,so it is possible to utilize bittern resources in high efficiency.The recovery rates of NaCl were 99.65%,93.14%,88.57%,72.76%,and 83.68%for six typical bittern sources from Tulantai Salt Lake (China),Dongtai Salt Lake (China),Jilantai Salt Lake (China),Qarun Salt Lake (Egypt) and seawater,respectively.It is testified that the non-equilibrium state salt-forming phase diagram can be used in industrial processes.

Key words: phase diagram, non-equilibrium state, evaporation, salt-forming, bittern