Studies On Cooling Crystallization Process Of Mirabilite From The Sodium Sulfate-containing Brine

It is very important for salt industry to vigorously develop the liquid salt especially well and rock salt.Because of different functional departments' attention, mature production technology of the liquid salt and salt making enterprises' effort as to reduce production cost and increase proportion of the liquid salt,the production level and consumption of the liquid salt will be a great enhancement.In order to reduce the well rock salt's energy consumption,state development and reform commission encourages to expand the liquid salt's production and the use.Because the cost of removal SO₄^2- from the liquid salt is very high,which makes it very difficult to use the liquid salt in soda industry.So the removal method of SO₄^2- in production of the liquid salt is a very important question.This article tries to discuss the production method of the liquid salt which is used to soda industry in sodium sulfate-containing brine.The concentration of sodium sulfate is 15～30g/L.But the production of chlor-alkali industry requests the brine whose purity is very high.The brine whose sulfate is removed can save greatly energy consumption and equipment investment in salt industry and production cost in chlor-alkali industry.Based on the above questions,we systematic studied about the thermodynamics and dynamics of mirabilite crystallization process.The raw brine is NaCl-Na₂SO₄-H₂O system in the experiment(material composition,wt,%:Na₂SO₄ 1.75;NaCl 24.17;H₂O 74.08).As for the absent solubility data below 0℃,we determined the solubility of mirabilite between -19℃and 0℃.We get the change law of SO₄^2- in that conditions and put forward empirical formula of SO₄^2- solubility,which provided the basis for the preparation of top quality liquid salt.In view of the existing problems in the desulfurization process(the crystallization process of mirabilite) in brine of salt mine,we determined cooling crystallization dynamics parameter of mirabilite below 0℃by continual stationary method,and systematic studied the operating conditions such as supersaturation,suspention density and stirring rate,which effect on the nucleation rate and the growth rate.we used the size-independent growth model and regressive analysis crystallization kinetics'data and get nucleation rate equation and growth rate equation of mirabilite,which provided the basis for the crystallizer design and the manufacture.These parameters have provided the help for the process optimization and the control.