Distillation of Hydrofluoric Acid from Acid Fluoride-Sulphate Solutions

The paper describes distillation of hydrofluoric acid from model and process acid fluoride-sulphate solutions. Conditions for the most complete distillation of hydrofluoric acid from fluoride-sulphate solutions were determined and proposed. Fluorosulphonic acid is formed in large amounts, as shown for model solutions containing hydrofluoric and sulphuric acids. Herewith, with increasing the concentration of acids, their interaction degree rises and fluorosulphonic acid is formed, as demonstrated. An increase in the heating temperature of the mixture leads to a substantial increase in acidity due to HSO3F content decrease. The larger the concentration of acids (especially, sulphuric) is, the higher heating temperatures are required to decompose HSO3F, as established. The formation of fluorosulphonic acid may have a significant effect on HF distillation degree, as shown. The energetic and economic cost in the processing of 1 m(3) of process acid fluoride-sulphate solution is calculated with an account of the initial concentration of HF of 78 g/L. Considering sulphuric acid regeneration and having excluded lime content for its neutralization, energy costs for processing of this solution do not exceed 4500 RUB. The findings explain high solubility of lanthanide fluorides compared to their dissolution in monobasic acids, as noted in a series of papers. Our earlier observations of decreasing the concentration of fluorine determinable by potentiometric titration relatively to initially introduced one at pH correction by using sulphuric acid, unlike that with nitric or hydrochloric ones were also explained.