SU919984A1 - Method of purifying hydrofluoric acid - Google Patents

Description

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This invention relates to the chemical industry, in particular to the purification of hydrofluoric acid from silicon compounds.

The known method of purification of hydrofluoric acid from silicon compounds by treating it with sodium compounds with subsequent sedimentation and: filtration of the precipitate 1.

The disadvantage of this method is the low rate of settling and filtration during the purification of an acid with a fluorosilicic acid content of 10-25%.

The closest in technical essence and the achieved result to the proposed is a method of hydrofluoric acid containing 2-TO hydrofluoric acid, by treating it with soda, followed by settling the precipitate and separating it from the solution by filtration.

The reactor receives crude hydrofluoric acid and the required

For its purification, the amount of a solution of calcined SODA with a concentration of g / l of Na (iCp3. Between cream; hydrofluoric acid NLZ i 1 and soda is reacted with sodium silicofluoride chloride (the least soluble of the sodium salts of this acid);

NaoCO

"+ H, 0

ten

Cleaning lead so as to precipitate most fully hydrofluoric acid and neutralize hydrofluoric acid. Content

15, in the purified acid should be no higher than 1. Pulp consisting of purified hydrofluoric acid and sodium silicofluoride, with a ratio of 20: 1 from the reactor enters the thickener, where it settles and thickens. The sodium silicofluoride precipitate in the form of a thickened pulp with a certain amount of hydrofluoric acid (with a solid-to-liquid weight ratio of 0.6-0.8: 1) is sent for filtration to more completely remove hydrofluoric acid. When cleaning an acid with a low content of hydrofluoric acid (up to 10%), relatively large crystals of silicon-fluorine sodium are formed, which, along with a low solids content in the pulp (g: m 2: i 20: 1, contributes to the rather rapid oTctaMBBHMro pulp and sediment filtration. at the same time, the purified hydrofluoric acid contains a small amount of solid suspension (0.5 l), and the sodium fluoride fluoride paste has a low content of purified acid. At the same time, the loss of fluorine is minimal, and the quality of fluoride salts obtained from this acid OTA, high G2. The disadvantage of this method is the low rates of settling and filtration during the purification of hydrofluoric acid containing 10-25 hydrofluoric acid, associated with the formation of more than 13 fine fraction in the sediment (0.5-3 µm) °. This is an increase in the rate of settling and filtration during the purification of hydrofluoric acid containing 10–25% of hydrofluoric acid by reducing the fines in the sediment (0.5–3 µm) to 4–5%. This goal is achieved according to the described method of purification of molten acid, which consists in treating it with soda, followed by sedimentation of the precipitate and separating it from the solution by filtration. Before treatment with soda, sodium silicate is introduced into the acid first to saturation and then in quantity from the pulp weight. First, crushed sodium fluoride cream is injected to saturate the solution. The saturation process depends on the initial acid concentration and process temperature. In the temperature range of 40–65 and the concentration of hydrofluoric acid, 20–30%, the solubility of sodium fluoride is 1.0–1.5%. The introduction of sodium silicofluoride in the first stage prior to solubility prevents the formation of a large number of crystallization centers and the grinding of the precipitate. The addition of sodium silicofluoride in the first stage, less than 1.0%, does not allow complete saturation of pactaopa and this causes additional dissolution of (sodium efluoride, introduced in the second stage, and leads to the formation of a fine precipitate. The addition of sodium silicofluoride in the first stage is more than 1 , 5% supersaturated solution, which leads to the formation of fine-crystalline deposition centers, which ultimately causes the formation of a fine-crystalline structure of sodium silicofluoride sludge from the acid. The total amount of solid sodium silicofluoride is from the weight of the pulp, i.e., in such a quantity as to provide the necessary surface for precipitating the precipitate formed during the further purification of the acid and for shortening the duration of crystalline l and the precipitate formed. Sodium is not subjected to a dissolution process, the size of its crystals is preserved, and sodium fluorosilicate fluoride is precipitated on their surface on their surface. The addition of sodium silicofluoride in the second stage to less than 15% does not provide the necessary surface for the precipitation of sodium silicofluoride from acid. With the addition of more than 20%, a fine crystallization of the precipitate occurs, which leads to a deterioration of further settling. When cleaning the acid with soda, the resulting sodium fluoride is precipitated on the surface of the crystals introduced in the second stage, creating large crystals. The resulting crystalline precipitate is quickly settled and easily filtered. Solid content in the discharge after condensation, i.e. in purified hydrofluoric acid, it is at the level of the existing standards established for acids used for cooking fluorine salts (0.5 g / l). Example. When cleaning the hydrofluoric acid composition,%: HF 25; 25, it is subjected to pretreatment with sodium fluoride. Before serving in the specified acid cleansing agent (soda)

Claims (1)

Claim The method of purification of hydrofluoric acid by treating it with soda followed by sedimentation of the precipitate and separating it from the solution by filtration, characterized in that, in order to increase the rates of sedimentation and filtration during purification of hydrofluoric acid containing 10-25% hydrofluoric acid, before treatment with soda sodium silicofluoride is introduced into the acid first to saturation, and then in an amount of 15 ~ 20% of the weight of the pulp.