Acta Chimica Sinica ›› 2008, Vol. 66 ›› Issue (12): 1483-1489. Previous Articles     Next Articles

MgSO4-Na2SO4-H2O三元体系100 ℃沸腾蒸发非平衡态成盐特征

周 桓* 崔世广 沙作良 袁建军   

  1. (天津科技大学天津海洋资源与化学重点实验室 天津 300457)
  • 收稿日期:2007-10-24 修回日期:2007-12-07 出版日期:2008-06-28 发布日期:2008-06-28
  • 通讯作者: 周桓

Non-equilibrium Behavior of Salt-forming in Boiling Evaporation Process for the System of MgSO4-Na2SO4-H2O at 100 ℃

ZHOU, Huan* CUI, Shi-Guang SHA, Zuo-Liang YUAN, Jian-Jun   

  1. (Tianjin Key Laboratory of Marine Resources and Chemistry, Tianjin University of Science and Technology, Tianjin 300457)
  • Received:2007-10-24 Revised:2007-12-07 Online:2008-06-28 Published:2008-06-28
  • Contact: ZHOU, Huan

The non-equilibrium behavior of salt forming was experimentally determined for the system of MgSO4-Na2SO4-H2O during evaporation. The experiments of evaporation were carried out at a constant boiling temperature of 100 ℃ by a heating agent of fixed temperature of 140 ℃. The used evaporation intensity was about 140~160 g/(h•L). The compositions of liquid and solid phases were analyzed at the occurring point of the primary nucleation and the following points of further evaporation. Based on the results, the concept of primary and extended salt forming region was given. The experimental results show that: (1) Both 3Na2SO4•MgSO4 and Na2SO4•MgSO4•2.5H2O belong to the same-composition complex-salt in an equilibrium state, but change to different-composition complex-salt in a non-equilibrium state. (2) When evaporating solution which was co-saturated for Na2SO4 and 3Na2SO4•MgSO4 in equilibrium diagram, the Na2SO4 was only crystallized out. The Na2SO4 can be only crystallized up to 60.86% of the total Na2SO4 in the original solution. The same behavior was found for the co-saturated solution of 3Na2SO4•MgSO4 and Na2SO4•MgSO4•2.5H2O. (3) The primary salt-forming region is largely different from the equilibrium region. Based on the Jänecke index, the width of the primary forming region of Na2SO4 was extended from 21.02 to 32.76, the width of the primary forming region of Na2SO4•MgSO4•2.5H2O was reduced from 41.40 to 25.71. (4) Under the condition of having crystal seeds, the width of salt-forming region is larger than that of the primary salt-forming region in different degrees for different salts, for example the region width of Na2SO4 and 3Na2SO4•MgSO4 increased by 7.72 and 8.81 respectively. The overlay region of the primary and extended salt-forming region was found in the non-equilibrium state. The kinds of salt forming depend on those of crystal seeds.

Key words: phase diagram, boiling evaporation, non-equilibrium state, MgSO4-Na2SO4-H2O