| Frozen water treatment technology realizes the separation of water and pollutants,the core of which is the preparation of high-purity ice crystals.However,in the process of low temperature freezing,relationship between process conditions and ice crystal purity has not been studied in depth.Based on low-temperature freezing crystallization technology for wastewater treatment,this paper studies the influence of factors such as medium temperature,cooling rate,salt concentration,organic matter concentration and other factors on the degree of supercooling,Effect of supercooling and stirring methods on the purity of the formed ice crystals was further explored;low-temperature freezing crystallization technology was applied in the production of the azo dye carmine,it achieved wastewater purification and economic benefits,while recycling the carmine products in the solution.Taking simulated seawater as the research object,relationship between supercooling control method,supercooling degree and ice crystal purity is studied.Results show that when the cooling rate of simulated seawater solution increases from 0.5?/min to 2?/min,solution supercooling increases from 0.6? to 3.7?,and COD,electrical conductivity of ice crystals increase from 165mg/L,12.7ms/cm to 502mg/L,40.5ms/cm;as the temperature of cooling medium decreases from-12 ?to-20 ?,supercooling degree of the solution increases from 0.5? to 3.9?,and COD,electrical conductivity of ice crystals increase from 183mg/L,15.6 ms/cm increased to 537mg/L,45.2ms/cm;when the salt concentration increased from 2.5%to 20%,solution supercooling decreased from 4.3? to 0.7?,and the ice crystal COD reduction rate and conductivity reduction rate decreased from 64.20%,50.30%rose to 91.20%,84,20%;when concentration of organic matter increased from 1%to 8%,degree of supercooling decreased by 2.8?,the reduction was 82.3%,ice crystal COD reduction rate,conductivity reduction rate from 65.20%,55.40%rose to 84.60%,82.30%;with the acceleration of the stirring speed,purity of ice crystals will gradually decrease,and axial-flow stirring paddle is more conducive to the formation of high-purity ice crystals.In the process of wastewater treatment by the freezing crystallization process,the greater the degree of supercooling,the smaller the ice crystal grains formed,and content of pollutants entrained will increase,thereby reducing the purity of the ice crystals.Traditional salting-out method requires high salting-out agent and generate a large amount of high-salinity wastewater.A novel technology named the freeze salting-out technology was developed.By the freeze salting-out technology,the cooling rate of the solution was controlled to 0.5?/min,the medium temperature was set to-8?,and the supercooling degree of the solution was measured as low as 0.5?.the dosage of salting-out agent dropped to 1.25 wt%from 20 wt%of the traditional technology.91 g carmine with the high purity of 92.8%was produced from one liter crude carmine solution.Electrical conductivity of the freeze salting-out effluent was 35.7 ms/cm,which was lower than effluent with high electrical conductivity of 330 ms/cm generated by traditional technology.The salting-out action inspired by freeze concentration played the crucial role in freeze salting-out processes.Cost for carmine production using freeze salting-out technology was lower than conventional salting-out method.Freeze salting-out technology provided a new idea for extracting carmine and other salting-out process. |
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