Acid / alkali recovery methods, boric acid recovery and manufacturing methods, and polarizing plate manufacturing methods.

Abstract

An acid / alkali recovery method comprises the following steps: separating the liquid to be treated into an acidic solution, an alkaline solution, and a boric acid-based liquid by electrodialysis, wherein the liquid to be treated is obtained by adding the acidic and alkaline solutions to waste liquid containing boric acid and potassium iodide generated during the manufacturing process of a polarizing plate. An acid / alkali recovery method further comprises the following steps: an NF membrane separation step, in which the liquid to be treated is passed through an NF membrane to separate a permeate and a concentrate, wherein the permeate contains iodide ions and the concentrate contains iodide ions at a lower concentration than the permeate; and an electrodialysis step, in which the concentrate is passed through an electrodialysis apparatus to separate a boric acid-based liquid, an acidic liquid, and an alkaline liquid.

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