According to the data in Table 1 to Table 3, the relationship between the desalting solution discharge and the KOH concentration is shown in Fig. It can be seen from Fig. 5 that when the concentration of recovered hydrofluoric acid is highest when solid KOH is added, the resulting desalting solution discharge is also lowest.

From the above results, it can be seen that in the process of recovering waste acid from the bipolar membrane electrodialysis cell, the concentration of the alkali used in the neutralization process exceeds 1 N, the concentration of the generated salt is increased, and the acid concentration is recovered, When the acid is hydrofluoric acid or nitric acid waste acid, the desired hydrofluoric acid recovery concentration can be achieved, and the recovered hydrofluoric acid concentration is increased, and the amount of the supplemented product (HF replenishment amount). At the same time, due to increased alkali concentration, the corresponding reduction in the volume of alkaline solution, then through the bipolar membrane electrodialysis cell after the desalination solution discharge is also reduced, reducing the amount of desalting fluid discharged outside the system. At the same time, when the newly added alkali as a solid, the recovery of hydrofluoric acid concentration is higher, to achieve the purpose of recovery of hydrofluoric acid.