Abstract:

With huge reserves of underground potassium-rich brine,the Heibei concave is located in the piedmont of the Altun Mountains.The ion species in the brine are few except for Na or Cl whose content accounts for absolute advantage.Be-cause of its simple chemical composition and easy extraction,the brine has a great value in industrial development and utiliza-tion.Taking the potassium-rich brine as the research object,the natural evaporation experiment was carried out on site.It was found through experiments that the brine reached the precipitation stage of carnallite（KCl·MgCl₂·6H₂O） and bischofite （MgCl₂·6H₂O） after a long period of halite precipitation of（NaCl）,and finally dried out at the antarctic stage,and the sequ-ence of the mineral crystallization during evaporation was halite,carnallite,bischofite and antarcticite.And potassium was only precipitated from carnallite minerals,and the precipitation stage was relatively concentrated.During the whole evaporation process,boron oxide（B₂O₃） and lithium were concentrated and enriched in the brine without precipitation.According to the crystallization law of brine during the evaporation process,it was consistent with the metastable phase diagram of K ⁺,Na ⁺,Mg ²⁺//Cl ^--H₂O（25 ℃）.The evolution trend of the brine during the evaporation process was that it moved from the NaCl point in the halite phase area to the sylvite and carnallite phase area and when reaching the univariant curve of halite and sylvite,it moved along the curve and arrives at the invariant point of halite,sylvite and carnallite.Then it moved along the univariant curve of halite and carnallite,and finally arrived at the invariant point of halite,carnallite and bischofite.After analyzing the variation of brine pH and density during the whole evaporation process,it was pointed out that the halogen production process of brine could be controlled by changes in pH and density.Through the evaporation experiment,it would provide a scientific basis for the potassium extraction process experiment and post-development of the underground brine in the Heibei concave.

Key words: Heibei concave, underground brine, natural evaporation, potassium, phase diagram, crystallization regularity