Method For Recovering Alkali Metal Salt And Apparatus For Recovering Alkali Metal Salt

Abstract: The present invention relates to a method for recovering an alkali metal salt, said method comprising steps 1 and 2 below. Step 1 is a first nanofiltration step in which a solution X containing alkali metal ions is fed, as a to-be-treated liquid A, to a nanofiltration membrane unit A and is thereby separated into a liquid permeate A and a concentrated liquid B, then the concentrated liquid B is mixed with the residue of the to-be-treated liquid A and the result thereof is fed to the nanofiltration membrane unit A again, and more of the liquid permeate A is obtained. Step 2 is a second nanofiltration step in which: the liquid permeate A obtained in step 1 or a concentrated liquid of the liquid permeate A is fed, as a to-be-treated liquid B, to the nanofiltration membrane unit A and is thereby separated into a liquid permeate C and a concentrated liquid D, then the concentrated liquid D is mixed with the residue of the to-be-treated liquid B and the result thereof is fed to the nanofiltration membrane unit A again, and more of the liquid permeate C is obtained; or alternatively, the liquid permeate A obtained in step 1 or a concentrated liquid of the liquid permeate A is fed, as a to-be-treated liquid B, to a nanofiltration membrane unit B and is thereby separated into a liquid permeate C and a concentrated liquid D, then the concentrated liquid D is mixed with the residue of the to-be-treated liquid B and the result thereof is fed to the nanofiltration membrane unit B, and more of the liquid permeate C is obtained.

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