According to the data in Table 1 to Table 3 draw the hydrofluoric acid and nitric acid recovery and the relationship between the concentration of KOH, the change in Figure.

As can be seen from the figure, only KOH concentration of more than 1.0eq /L, the recovery of hydrofluoric acid can be significantly improved.

Therefore, in the conventional metal pickling process, the concentration of the hydrofluoric acid and the nitric acid in the spent acid liquid containing hydrofluoric acid and nitric acid is not less than 4.0 eq /L, and the concentration ratio of HF to HNO3 is in the range of 1:1 ~ 1:3 is better than 1:1, when the concentration of HF: HNO3 than 1:1, the recovery of hydrofluoric acid KOH minimum concentration of 1.14eq /L.

According to Table 1 to 3 data to draw the new hydrofluoric acid, nitric acid supplementation and the relationship between the concentration of KOH, the change in the law. As can be seen from the figure, the higher the concentration of recovered acid, the less the amount of drug to be replenished.