Method for improving the recovery rate of evaporation crystallization and freezing salt separation process by adopting nanofiltration film separation

Abstract

The invention relates to a method for improving the recovery rate of an evaporation crystallization and freezing salt separation process by adopting nanofiltration film separation, and the specific implementation method comprises the following steps: (1) exchanging heat on frozen mother liquor after freezing crystallization of high-salt waste water, and heating the frozen mother liquor to 15-25 DEG C; (2) allowing the frozen mother liquor after heat exchange to enter a nanofiltration film device for concentration and separation; and (3) allowing treated nanofiltration concentrated water to return to the front end of freezing crystallization and enter a freezing crystallization section together with the high-salt waste water, and allowing nanofiltration produced water to enter a sodium chloride treatment section for treatment to finally obtain high-purity sodium chloride crystallized salt. The method effectively solves the problems of low recovery rate of sodium sulfate crystal salt inthe system, low purity of the subsequent sodium chloride crystal salt, high impurity salt content and the like caused by poor freezing effect of a freezing crystallizer and high sulfate content of thefreezing mother liquor, and fully ensures the purity and the recovery rate of the product salt in the system. The ''zero emission'' and ''recycling'' of the waste water are realized. The method has great significance for the popularization of ''evaporation crystallization and freezing'' salt separation process in the field of zero waste water discharge.

Description

technical field [0001] The invention relates to a zero-discharge method for wastewater treatment, in particular to a method for improving the recovery rate of the "evaporation crystallization + freezing" salt separation process by adopting nanofiltration membrane separation. Background technique [0002] As the requirements for zero discharge of wastewater are getting higher and higher, the zero discharge technology of high-salt wastewater "evaporation + freezing" salt separation as the end point of treatment has been more and more recognized by the industry, but as more and more in recent years Many "evaporative crystallization + freezing" are used as a salt and nitrate separation process in various types of wastewater treatment. In the salt separation process, the purity of sodium chloride crystal salt is not up to standard, the recovery rate of finished salt is low, and the proportion of miscellaneous salts has become a constraint. A major problem in development. Conten...

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Problems solved by technology

[0003] In view of the above deficiencies in the prior art, the researchers of the present invention have worked out a method of using nanofiltration membrane separation to improve the recovery rate of the "evaporative crystallization + freezing" salt separation process through a large number of in-depth research work, which solves the current problem. There are problems such as the purity of crystallized salt is not up to standard, the recovery rate of finished salt is low, and the proportion of miscellaneous salt is large in the "evaporation + freezing" salt separation process