Investigation On Factional Crystallization Of High Salinity Wastewater From Coal Industry

The current energy situation in China is"rich in coal,less in oil,and poor in gas."Given the unique energy situation in China,the development of the coal chemical industry is in line with the national situation,but coal chemical enterprises often produce a large amount of coal chemical industry high salt wastewater.The domestic coal chemical industry high salt wastewater treatment methods mainly include evaporation crystallization and evaporation pond drying salt.These two methods are used to treat various salts with high content of heavy metals and organic substances,which have been regarded as hazardous solid waste by the state,endangering the environment and wasting resources.Therefore,it is urgent to develop new high-salt wastewater treatment technology using crystallization technology to achieve the resource nation of trash salt.Based on the above background,a systematic study on the basis of crystallization of high-salt wastewater from the coal chemical industry is carried out in this paper.Firstly,this paper investigates the effect of impurity dimethoxymethane in coal chemical hypersaline wastewater on the thermodynamic properties of sodium sulfate and sodium chloride crystallization.Dimethoxymethane will reduce the solubility of sodium sulfate and sodium chloride in water,and widen the metastable region of sodium sulfate at the same time and the induction period will be longer,making it difficult for sodium sulfate to nucleate in water.Secondly,based on the measured thermodynamic data,the ternary phase diagram,equilibrium liquid phase density,and precipitated crystal morphology of Na Cl+Na₂SO₄+H₂O pseudo-ternary system in the simulated wastewater environment were investigated in the temperature range of 303.15?333.15 K.The crystallization region of Na₂SO₄is more significant than that of Na Cl in the simulated wastewater environment,and the density of the system is positively correlated with the amount of Na₂SO₄,which leads to a nucleation rate of Na₂SO₄ larger than the growth rate due to the presence of salt precipitation.Finally,on the basis of the above theoretical research,the batch dynamic method was used to determine the nucleation rate and growth rate of sodium sulfate crystals under simulated wastewater conditions,and the kinetic equation of sodium sulfate under simulated wastewater conditions was obtained.The nucleation is a secondary nucleation process,and the growth process is controlled by surface reactions.The research results of this thesis reveal the thermodynamic and kinetic laws of crystallization of various salts in binary and ternary systems of high-salt wastewater,and lay a theoretical foundation for the fractional crystallization and salt extraction of high-salt wastewater of coal chemical industry.