Potassium fluoride,anhydrous
           Potassium fluoride,extra pure
           Potassium fluoride,Granular
           Silicon Dioxide
           Hydrofluoric acid
           Synthetic Cryolite
           Potassium Fluoaluminate
           Ammonium bifluoride
           Potassium Bifluoride
           Aluminium fluoride
           Sodium fluoride
           Potassium Fluorosilicate
           Fluorosilicic Acid
           Sodium silicofluoride
           Potassium Hydroxide Flakes
           Magnesium Fluoride
           Magnesium fluorosilicate
           Barium Fluoride
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In the experiment, a different concentration of KOH was used to observe the recovery of hydrofluoric acid. For example, 10 liters of a 4.0 g /L KOH solution was added to a 10 L metal waste washing solution containing 2.0 eq /L of hydrofluoric acid and 2.0 eq /L of nitric acid to carry out a neutralization reaction to precipitate a metal acid sludge. (Eq /L is the amount of sol equivalent in 1 L of solution). After filtration, the filtrate thus obtained had a KF of 1.0 eq /L and a KNO3 of 1.0 eq /L. Subsequently, the filtrate was transferred to a bipolar membrane electrodialysis cell, and 8.31 L of the mixed acid was recovered. Among them, hydrofluoric acid concentration reached 1.59eq /L, nitric acid concentration reached 2.41eq /L, hydrofluoric acid recovery rate reached 66.2%. The concentration of KF in the recovered 13.53 L desalting solution was 0.5 eq /L.

In the same waste acid solution of 10 L, 35 L of 1.14 eq /L KOH solution was added to carry out neutralization reaction to precipitate the metal acid sludge and filtrate. The obtained 45 L filtrate contained 0.44 eq /L of KF and 0.44 eq of KNO3 /L. Then, the filtrate was transferred to a bipolar membrane electrodialysis cell, and 5 L of a mixed acid was recovered in which the concentration of nitric acid reached 4.0 eq /L and the hydrofluoric acid was not recovered, resulting in a concentration of KF of 35 L in the desalting solution 0.57 eq /L.

From the data analysis of the above examples and comparative examples, it was found that the potassium hydroxide solution used must be at least a certain concentration in order to increase the hydrofluoric acid recovery concentration. In addition, it can be seen from the experiments that the KOH solution used in Experiment 5 was only 10 L when the KOH concentration was increased and the volume of the solution at neutralization was reduced, whereas the amount of the base used in Comparative Example 3 was 35 L, reduced by more than 2/3.