Freezing-Antisolvent Crystallization For Treatment And Resource Of The High Sodium Chloride Wastewater From Coal Chemical Industry

The coal chemical industry is widely known as a high-energy,high-water-consumption,and high-pollution industry.Due to the environmental concerns,researchers are exploring ways to achieve "zero discharge" and resource utilization of high-salinity wastewater produced during the production process.Freeze concentration and antisolvent crystallization are two effective desalination methods with great potential in treating high-salinity wastewater and recovering inorganic salts in coal chemical industry.This study proposes the development of a freezingantisolvent crystallization technology that combines two methods:suspension freeze concentration and low-temperature antisolvent crystallization.This technology can effectively treat high-salinity wastewater of coal chemical industry with low energy consumption while achieving high-quality recovery of inorganic salts.By providing a new approach for "zero discharge" and resource utilization,this technology contributes to the sustainable use of resources in the industry.Firstly,cooling curve method,static method and turbidity method were used to investigate the thermodynamic processes of freezing and low-temperature antisolvent crystallization.The phase change point and subcooling degree of aqueous sodium chloride solution are affected by the concentration,where the eutectic point is-19.7℃ and the eutectic subcooling degree is the largest,while the single crystal subcooling degree decreases with increasing concentration.The solubility model consisting of Apelblat equation,Van’t hoff equation and Jouyban-Acree equation was established,and it was found that the metastable zone of the system was related to temperature and solvent ratio,and an increase in the proportion of methanol or a decrease in the temperature of the system would lead to a decrease in the width of the metastable zone and a decrease in the formation barrier of sodium chloride.Secondly,the coupled freezing-antisolvent crystallization process was optimized by the single factor method and theoretical energy consumption calculation.The effects of ice formation rate and freezing temperature on the concentration effect of freeze concentration suspension crystallization,and the effects of stirring,concentration,alcohol to water ratio and temperature on the treatment effect of low temperature antisolvent crystallization were investigated.The energy consumption is only 375.06 kJ/kg,which is 32.10%of the theoretical energy consumption of the triple effect evaporation process for the same volume of wastewater.Finally,the mechanism of sodium chloride crystal shape regulation by low temperature antisolvent crystallization was analyzed with the help of molecular dynamics simulation results.The AE model was used to calculate and simulate the interaction energy,adhesion energy and modified adhesion energy for different temperature and solvent ratio conditions.The results of the molecular dynamics simulations show that the percentage of(0 1 1),(0-1-1),(1 0 1)and(-1 01)crystalline planes of sodium chloride crystals decreases with decreasing temperature or increasing solvent ratio due to the different molecular arrangements of the exposed planes,and the(110)and(-1-10)crystalline planes increase gradually,and the shape of the precipitated sodium chloride crystals changes from rectangular to square,which is consistent with the experimental results.