As the KF, KNO3 continue to be separated, concentration decreased, while constantly adding new filtrate added, then KF and KNO3 contrast, KNO3 will be the first ionization, continue to be separated out. In this way, most of the residue in the desalting solution is KF, that is, HNO3 is easier to recover than hydrofluoric acid during separation, and NO-3 is more likely to pass through the anion exchange membrane than F-. Indicating that the dissociation degree of KF is lower than that of KNO3, and it is difficult for KF to permeate through the ion exchange membrane.

As a result, a part of the KF remains. Therefore, the recovered mixed acid, F- content will be lower than the filtrate F- content, so the recovery of hydrofluoric acid concentration is low. Therefore, during the neutralization reaction, it is necessary to use a certain concentration or more of KOH to increase the concentration of KF and KNO3 produced after neutralization, thereby reducing the amount of desalted solution discharged. Since the amount of the desalination solution is reduced when the concentration of the neutral salt contained in the desalting solution is constant, the salt contained in the desalting solution is also reduced. In order to increase the recovery of the acid and prevent the recovery of the hydrofluoric acid concentration from decreasing, the newly added base is preferably selected from solid bases such as powder and granules so that the amount of the liquid and the concentration of hydrofluoric acid recovered can be increased.

This separation of acid recovery method is also applicable to any waste acid recovery, other metal pickling waste liquid is also applicable.