Methods for treating waste liquid, methods for recovering and manufacturing boric acid, and methods for manufacturing polarizing plates.

Abstract

The waste liquid treatment method of this case selectively recovers boric acid from the waste liquid generated during the manufacturing process of polarizing plates. The aforementioned waste liquid treatment method includes the following steps: a first membrane separation step, in which the aforementioned waste liquid with a pH below 8.5 or the aforementioned waste liquid with a pH adjusted to below 8.5 is passed through a first separation membrane module equipped with a reverse osmosis membrane to separate it into a first permeate and a first concentrate. The aforementioned first permeate contains the aforementioned boric acid (B1) and substances other than boric acid in the aforementioned waste liquid (R1), and the aforementioned first concentrate contains the aforementioned boric acid (B2) and substances other than boric acid in the aforementioned waste liquid (R2); and a boric acid concentration and crystallization step, in which boric acid is recovered from the aforementioned first permeate obtained in the aforementioned first membrane separation step by concentration and crystallization.

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