SU819061A1 - Method of producing cryolite - Google Patents

Description

one

The invention relates to a process for the preparation of fluoride compounds and can be used in the manufacture of cryolite from a mixture of hydrofluoric acid and hydrofluoric acid.

A known method for producing cryolite is by introducing a solution of aluminum fluoride into acidified sodium fluoride solution (1. Both solutions are preheated to 80-95 ° C. The NaF solution is acidified with hydrochloric or nitric acid in an amount of 0.2-0.6 mol per 1 mol NaF depending on the amount of silicic acid impurities. After precipitation of NasAlFs, NaCl is introduced into the mixture. The resulting precipitate of cryolite is filtered and dried. The highest yield (91%) is obtained with an AliFa solution concentration of 32.6 g / l and an HC1 amount of 0.23 mol per 1 mole AlFs.

The known method is characterized by an insufficiently high product yield (91%).

The closest in technical dryness and the achieved result to the proposed method is a method of obtaining cryolite, including purification of hydrofluoric acid with soda, taken in stoichiometric amount, separation of sodium fluorosilicate from the acid, interaction of the purified acid with aluminum hydroxide and soda, separation of the precipitate cryolite and its drying 2.

The disadvantages of this method are; low product yield (94-96%) and insufficiently low silica content in the product (0.5-1.5%).

The aim of the invention is to increase the yield of the product to 99.4-99.8% and reduce the content of silica therein.

up to 0.04-0.33%.

The goal is achieved by the fact that according to the proposed method, the purification of hydrofluoric acid is carried out to contain 0.5-2.5% sodium fluoride in it, and before interacting with aluminum hydroxide and soda, the acid is treated with a solution: aluminum fluoride or cryolite.

Distinctive features of the method are to carry out the purification of hydrofluoric

acid to contain sodium fluoride in the range of 0.5-2.5 ° and treatment of the acid before reacting with aluminum hydroxide and soda with a solution of aluminum fluoride or cryolite.

The essence of the method is as follows.

To the mixture of hydrofluoric acid, hydrofluoric acid and sulfuric acid is added a solution of soda in the amount of 160-180% of the stoichiometric required. This amount provides a content in the solution of 0.5-2.5% NaF. The solution is separated from the precipitated sodium fluoride precipitate.

Sodium fluorinated hydrofluoric acid, in which the content of silicon dioxide is 0.15-0.04%, is treated with dissolved aluminum fluoride or cryolite for 5-30 minutes at 80-95 ° C. The resulting cryolitheater: kaitsu 0 hydrofluoric acid is decomposed with aluminum hydroxide. Part of the dissolving aluminum fluoride formed in this way is sent to the treatment of the sodium fluorine containing her nlavic acid. The rest of the neutralized solution of soda. This forms cryolite. Part of the cryolite susneisy can be sent instead of dissolved aluminum fluoride to the treatment of hydrofluoric acid, containing dissolved sodium fluoride. The resulting cryolite suspension is separated to obtain a product that is dried at 100-150 ° C and a mother liquor. The mother liquor, containing 0.1-0.2% F, is directed to the preparation of soda solution used in the purification of the initial mixture of hydrofluoric acid and hydrofluoric acid and the preparation of cryolite.

In the presence of sodium fluoride in ilavic acid, the solubility of sodium fluoride decreases dramatically due to the salting out effect. However, aluminin hydroxide is not soluble in such an acid due to the formation of cryolite solid reactant on the reaction surface. To exclude the passivating effect of sodium fluoride on the dissolution of aluminum hydroxide, the acid is preliminarily purified from sodium fluoride by treating it with dissolved aluminum fluoride or cryolite.

The content of sodium fluoride in the acid less than 0.5% does not have a noticeable effect on the solubility of sodium silicofluoride and therefore does not lead to a decrease in the silica content of the product. An increase in the sodium fluoride content in the acid of more than 2.5% does not lead to a further decrease in the silica content of the product and is therefore impractical.

Example. To 1000 kg of a mixture of hydrofluoric acid, hydrofluorosilicic acid and sulfuric acid containing 26% HF; 4.5% HaSiFe; 0.8% H2SO4; 200 kg of a 20% soda solution are added over a period of 5-10 minutes at 30-60 ° C. The sodium silicofluoride formed is separated from the solution, thereby obtaining 82 kg of precipitate containing 9% HF; 65% NaaSiFe; 0.2% NaF. 1102 kg of acid-free acid composition,%: 23 HF; 0.5 NaF; 0.15 SiOs treated with 52 kg. aluminum fluoride solution. Cryolitic hydrofluoric acid is decomposed by 186 kg of aluminum hydroxide supplied as an aqueous suspension with a weight ratio of T: W 1 1. Part of the resulting fluorine-aluminum fluoride solution is treated with sodium fluoric hydrofluoric acid, the rest is neutralized with 1485 kg of 20% soda solution. The resulting cryolite suspension is separated to obtain 645 kg of wet sediment and 2191 kg of stock solution,%: 0.15 F; 0.02 A1; 0.1 Na; 0.03 SiOa. After drying, the precipitate contains (in%) 53.5 F; 29 Ma: 14.2 A1; 0.33 SiOg.

1348 kg of the mother liquor are directed to the preparation of the soda solution used in the purification of the initial mixture of acids and the preparation of cryolite. Excessive mother liquor is removed from the process. The technological yield of fluorine in the product is 99.8%.

Example 2. To 1000 kg of a mixture of hydrofluoric acid, hydrofluoric acid and sulfuric acid containing 26% FIF; 4.5% H2SiF6; 0.8% H2SO4; 296 kg of a 20% soda solution are added over a period of 5-10 minutes at 30-60 ° C. The sodium silicofluoride formed is separated from the solution to obtain 87 kg of precipitate containing 9% nF; 65% N2SiF6; 0.5% NF. 1184.5 kg of scaly acid composition,%: 20.5 HF; 1.7 NaF; 0.06 SiOa treated with 203 kg of a solution of aluminum fluoride. Cryolitic hydrofluoric acid is decomposed into 184 kg of aluminum hydroxide supplied as an aqueous suspension with a T: Ж ratio of 1: 1. A part of the formed aluminum fluoride solution is sent to the treatment of sodium fluoric hydrofluoric acid, the rest is neutralized with 1375 kg of 20% soda solution. The resulting suspension of cryolite is separated to obtain 639 kg of wet sediment and 2171 kg of stock solution of the composition,%; 0.12 F; 0.02 A1; 0.08 Na; 0.03 SiOg. After the precipitate, the precipitate contains 53.5% F; 29% Na; 14.2% A1; 0.1% SiOz1337 kg stock solution is prepared to prepare soda solution used to clean the initial mixture of acids and to obtain cryolite. Excess mother liquor is removed from the process. The technological yield of fluorine in the product is 99.40%.

Claims (2)

PRI me R 3. To 1000 kg of a mixture of hydrofluoric acid, hydrofluoric acid and sulfuric acid containing 26% PR; 4.5% HsSiFe; 0.8% P2504; 367.5 kg of a 20% soda solution are added over 5-10 minutes at 30-60 ° C. The sodium silicofluoride formed is separated from the solution to obtain 88 kg of sediment composition,%: 9 HF; 65 NajSiFe; 1 NaF. 1249 kg of frittered acid composition,%: 19 HF; 2.5 NaF; 0.04 SiO2 is treated with 327 kg of aluminum fluoride solution. Cryolitic hydrofluoric acid is decomposed into 184 kg of aluminum hydroxide supplied as an aqueous suspension with a T: Ж ratio of 1: 1. A part of the formed aluminum fluoride solution is directed to the treatment of sodium fluoric hydrofluoric acid, and the rest is neutralized with 1300 kg of 20% soda solution. The resulting suspension of cryolite is separated to obtain 638 kg of wet sediment and 2171 kg of stock solution of the composition,%: 0.1 F; 0.02 A1; 0.08 Na; 0.03 SiO2. After drying, the precipitate contains 53.5% F; 29% Na; 14.2% 0.04% SiOa1334 kg of mother liquor is directed to the preparation of soda solution used in the purification of the initial mixture of acids and the preparation of cryolite. Excess mother liquor is removed from the process. The technological yield of fluorine in the product is 99.5%. The proposed method allows to increase the yield of the product to 99.4-99.8%, reduce the content of silicon dioxide in the product to 0.04-0.33% n and increase the cryolite modulus from 1.8 to 2.0. Claim Method A method for producing cryolite, which includes purification of hydrofluoric acid with soda, separation of impurities from the acid, interaction of the acid with aluminum hydroxide and soda, separation and drying of the product, characterized in that, in order to increase the yield of the product and its content of silica, cleaning hydrofluoric acid is made to contain 0.5-2.5% sodium fluoride, and the acid is treated with a solution of aluminum fluoride or cryolite before reacting with aluminum hydroxide and soda. Sources of information taken into account in the examination 1. Austria's patent number 303684, cl. 12 V 15/05, published 12.12.72. 2.Guz S. Yu. And Baranovska RG. Production of cryolite, aluminum fluoride and sodium fluoride. M., “Metallurgists, 1964, p. 100-119.