RU2492142C1 - Method of producing sodium silicofluoride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of fluorine compounds and can be used in production of sodium silicofluoride. Sodium silicofluoride is obtained by neutralising hydrofluorosilicic acid with soda in the presence of a sodium salt at pH 0.2-3 for 0.25-1 h, settling the obtained crystals, separation thereof and drying, wherein the sodium salt used is a sodium fluoride precipitate separated from the reaction mixture, which is obtained by decomposing a calculated amount of hydrofluorosilicic acid with sodium hydroxide solution at pH 11.5-12.5 and temperature 85-95°C, and a calculated amount of hydrofluorosilicic acid fed for decomposition to obtain a sodium fluoride precipitate is determined based on concentration of acid C_H2SiF6 and content of silicon dioxide C_siO2 in the initial hydrofluorosilicic acid using the formula: N=C_siO2×M_H2SiF6/C_H2SiF6×M_siO2=2.4×C_SiO2/C_H2SiF6, where M_M2SiF6 is the molecular weight of hydrofluorosilicic acid, which is equal to 144.09 g/mol, M_SiO2 is the molecular weight of silicon dioxide, which is equal to 60.085 g/mol.

EFFECT: invention enables to obtain an easily filtered end product - sodium silicofluoride with high content of the basic substance.

1 ex

Description

The invention relates to the production of fluorine compounds and can be used in the production of sodium silicofluoride (KFN) from hydrofluoric acid (KFVK).

A known method of producing sodium silicofluoride from hydrofluoric acid containing an excess of silicon tetrafluoride SiF ₄ or colloidal dissolved silicic acid by neutralizing sodium carbonate with the introduction of a slight excess of hydrofluoric acid [I.G. Ryss. Chemistry of fluorine and its inorganic compounds. State scientific and technical publishing house of chemical literature. Moscow. 1956, p.401]. The method allows to obtain easily filtered crystals of silicofluoride, the target product with a low content of impurities of silicon dioxide.

The disadvantage of this method is the use of hydrofluoric acid - a scarce and relatively expensive reagent.

A known method of producing sodium silicofluoride [USSR Author's Certificate No. 859293, class. СВВ 33/10, B01D 53/14, publ. 08/30/1981] by neutralizing CPVC with soda or sodium hydroxide, settling the obtained crystals, separating and drying them, and neutralization is carried out at a pH of 0.2-3 for 0.25-1 hours. The method allows to increase the rate of settling of CFN crystals from 3 to 5-7 m / h. In addition, the method allows the use of the original hydrofluoric acid contaminated with silicon dioxide.

The disadvantage of this method is the need for preliminary filtration KFVK, as well as low filterability of the target product due to the significant content of silicon dioxide.

A known method of producing silicofluoride salts [RF Patent No. 2024429, class. СВВ 33/10, publ. 12/15/1994], including mixing hydrofluoric acid with alkaline compounds of ammonium, or sodium, or potassium to a predetermined pH of the solution, and mixing the reagents is carried out to a pH of 1.5-3.0 in no more than 3 seconds. The method allows to reduce the content of silicon dioxide in salts.

The disadvantage of this method is the use of high-speed stirrer propeller type, significant energy consumption. The target product is characterized by low filterability.

A known method of sodium silicofluoride [RF Patent No. 2226502, class. СВВ 33/10, publ. 04/10/2004] by the interaction of hydrofluoric acid with sodium hydroxide, the precipitate is separated from the mother liquor and dried, the interaction being carried out at a molar ratio of fluorine and silicon of 6: 1 and changing the pH to one of the values in the range of 5.0-6.5. With an excess of fluoride ion, sodium metasilicate or amorphous silicon dioxide is preliminarily introduced into the solution, and with its lack, hydrogen fluoride or sodium fluoride. The method provides high-quality easily-filtered sodium silicofluoride.

The disadvantages of this method are the need for preliminary adjustment of the composition of hydrofluoric acid, the use of relatively expensive reagents such as hydrogen fluoride and sodium fluoride.

A known method of producing sodium cremofluoride [RF Patent No. 2356933, class. СВВ 33/10, publ. May 27, 2009], including the neutralization of hydrofluoric acid with soda in the presence of sodium bicarbonate at a pH of 0.2-3 for 0.25-1 h at a mass ratio of soda: sodium bicarbonate equal to 1: 1-4, sedimentation of the obtained crystals, their separation and drying. The method allows to increase the rate of sedimentation of crystals by increasing the proportion of crystals with a particle size of 60-70 microns.

The disadvantage of this method is the relatively low filterability of the target product, as well as the relatively low content of the main substance in the product (98.5-99.2% Na ₂ SiF ₆ ).

Closest to the proposed technical essence and the achieved result is a method of producing sodium cremofluoride [RF Patent No. 2411183, cl. СВВ 33/10, publ. 02/10/2011] by neutralizing hydrofluoric acid with soda in the presence of a sodium salt at a pH of 0.2-3 for 0.25-1 h, sedimenting the obtained crystals, separating and drying them, using sodium sulfate taken as the mass ratio of soda: sodium sulfate, equal to 1: 0.1-0.4. This method allows to increase the yield of the finished product, to reduce the residual fluorine content in wastewater.

The disadvantage of this method is the low filterability of the product.

The purpose of the invention is the preparation of a easily-filtrated target product - sodium silicofluoride.

и содержания диоксида кремния $$C_{Si{O}_2}$$

C в исходной КФВК по формуле:This goal is achieved by the fact that in the method of producing sodium silicofluoride by neutralizing hydrofluoric acid with soda in the presence of a sodium salt at a pH of 0.2-3 for 0.25-1 h, sedimenting the obtained crystals, separating and drying, while as salts sodium precipitate use sodium fluoride isolated from the reaction mixture obtained by decomposing the calculated amount of hydrofluoric acid with sodium hydroxide solution at a pH of 11.5-12.5 at a temperature of 85-95 ° C. The estimated amount of hydrofluoric acid (N) sent to obtain a precipitate of sodium fluoride is determined based on the concentration of acid $$C_{H_{2}Si{F}_6}$$

and silica content $$C_{Si{O}_2}$$

C in the original KFVK according to the formula:

$$N=C_{Si{O}_2}\times M_{H_{2}Si{F}_6}/C_{H_{2}Si{F}_6}\times M_{Si{O}_2}=2,\mathrm{four}\times C_{Si{O}_2}/C_{H_{2}Si{F}_6},$$

- молекулярная масса КФВК, равная 144,09 г/моль; $$M_{Si{O}_2}$$

- молекулярная масса диоксида кремния, равная 60,085 г/моль.Where $$M_{H_{2}Si{F}_6}$$

- molecular weight KFVK equal to 144.09 g / mol; $$M_{Si{O}_2}$$

- molecular weight of silicon dioxide equal to 60.085 g / mol.

The invention consists in the following.

Fluorosilicic acid obtained from fluorine-containing gases produced by extraction phosphoric acid, as a rule, contains a certain amount of soluble silicon dioxide. This CPVC concentration of 16-20% H ₂ SiF ₆ contains up to 1.8% SiO ₂ . The resulting sodium silicofluoride based on this acid by the soda method, followed by sedimentation of the resulting suspension, separation of CFN crystals in the form of pulp and drying, contains silicon dioxide and is characterized by low filterability. The presence of even an insignificant amount of silicon dioxide sharply reduces the filterability of the target product - sodium silicofluoride.

The exclusion of the content of silicon dioxide in the target product and the improvement of its filtering properties is achieved in the proposed method for producing sodium silicofluoride by neutralizing CPVA soda in the presence of sodium fluoride, while sodium fluoride is obtained by decomposing the acid with sodium hydroxide. In the proposed method, the starting acid containing silicon dioxide is divided into two streams. One, calculated part of the acid, is sent for decomposition with a sodium hydroxide solution to produce sodium fluoride, which is precipitated. The liquid phase is a sodium silicate solution. The precipitate of sodium fluoride is separated from the solution of sodium silicate and mixed with the main part of KFVK. In this case, sodium fluoride reacts with CPVC to form sodium silicofluoride and hydrofluoric acid. In turn, hydrofluoric acid reacts with the silica contained in the initial CPVC to form hydrofluoric acid. The amount of sodium fluoride precipitate is sufficient to completely transfer the impurity of silicon dioxide into hydrofluoric acid. Further, the conversion of CPVC to sodium silicofluoride is ensured by the reaction of acid neutralization with soda.

The required amount of CPVC to obtain a sodium fluoride precipitate sufficient to completely transfer the silica impurity present in the starting acid is determined by calculation, taking into account the concentration of hydrofluoric acid and the content of silica impurity.

The ongoing processes are described by the following chemical equations:

H ₂ SiF ₆ + 8NaOH = 6NaF ↓ + Na ₂ SiO ₃ + 5H ₂ O

6NaF + 3H ₂ SiF ₆ = 6HF + 3Na ₂ SiF ₆

SiO ₂ + 6HF = H ₂ SiF ₆ + 2H ₂ O

H ₂ SiF ₆ + Na ₂ CO ₃ = Na ₂ SiF ₆ ↓ + 2H ₂ O + CO ₂ ↑

The process of obtaining sodium silicofluoride in the specified range of technological parameters ensures the release of easily filtering target product with a high content of the main substance.

, обеспечивает получение требуемого количества фторида натрия для связывания и перевода диоксида кремния в H₂SiF₆ и тем самым исключает присутствие данной примеси в целевом продукте. Проведение процесса разложения КФВК раствором гидроксида натрия при рН 11,5-12,5 и температуре 85-95°C обеспечивает полноту протекания процесса разложения кислоты с образованием фторида натрия. Снижение рН реакционной смеси менее 11,5 и температуры 85°C приводит к неполному разложению КФВК, уменьшению выхода фторида натрия и ухудшению фильтрующих свойств целевого продукта. Повышение показателя рН более 12,5 приводит к перерасходу гидроксида натрия. Повышение температуры процесса более 95°C приводит к перерасходу энергоресурсов на нагрев реакционной смеси.Consumption of the estimated amount of KFVK, equal according to the ratio $$2,\mathrm{four}\times C_{Si{O}_2}/C_{H_{2}Si{F}_6}$$

, provides the required amount of sodium fluoride for binding and conversion of silicon dioxide in H ₂ SiF ₆ and thereby eliminates the presence of this impurity in the target product. The process of decomposition of CPVC with a solution of sodium hydroxide at a pH of 11.5-12.5 and a temperature of 85-95 ° C ensures the completeness of the process of decomposition of acid with the formation of sodium fluoride. Lowering the pH of the reaction mixture to less than 11.5 and a temperature of 85 ° C leads to incomplete decomposition of CPVC, a decrease in the yield of sodium fluoride and a deterioration in the filtering properties of the target product. Raising the pH to more than 12.5 leads to an overspending of sodium hydroxide. An increase in the process temperature of more than 95 ° C leads to an excess of energy for heating the reaction mixture.

The method is illustrated by the following example.

. На разложение направляется 0,20×1000=200 кг кремнефтористоводородной кислоты. Для разложения КФВК в реактор подается 186,54 кг 45%-ного раствора гидроксида натрия. Процесс разложения кислоты проводят при температуре 90°C и показателе рН реакционной смеси 11,8 в течение 1 часа. При этом необходимая температура обеспечивается за счет теплоты реакции разложения и дополнительного нагрева реакционной смеси. Реакционная смесь представляет суспензию, далее из которой фильтрацией выделяют осадок фторида натрия в количестве 62,9 кг. Фильтрат (323,6 кг) представляет собой раствор силиката натрия и содержит 36,6 кг Na₂SiO₃. В реактор нейтрализации подают основную часть КФВК (1000 кг) и полученный осадок фторида натрия в количестве 62,9 кг. При этом протекает обменная реакция с образованием 140,9 кг кремнефторида натрия и 30,0 кг плавиковой кислоты. Плавиковая кислота реагирует с 15 кг диоксида кремния, содержащимся в КФВК, с образованием 36,0 кг H₂SiF₆. В реактор нейтрализации подают 397 кг 20%-ного раствора Na₂CO₃. Процесс нейтрализации кремнефтористоводородной кислоты содой проводят в течение 1 часа при показателе рН среды 2,5. Полученную суспензию кремнефторида натрия отстаивают, сгущенную пульпу с отношением Т:Ж=1:3 направляют на сушку. После сушки кристаллов в аппарате кипящего слоя получают 282 кг целевого продукта с содержанием 99,5% Na₂SiF₆.Example 1. Hydrofluoric acid with a concentration of 18% H ₂ SiF ₆ and containing 1.5% SiO ₂ in an amount of 1000 kg is fed to neutralize soda. CPVC contains 180 kg of H ₂ SiF ₆ and 15 kg of SiO ₂ . The calculated amount of acid to be decomposed to obtain a sodium fluoride precipitate is determined by the formula $$C_{Si{O}_2}\times M_{H_{2}Si{F}_6}/C_{H_{2}Si{F}_6}\times M_{Si{O}_2}=\mathrm{1,5}\times 144.09/\mathrm{eighteen}\times \mathrm{60,085}=\mathrm{2,4}\times \mathrm{1,5}/\mathrm{eighteen}=0.20$$

. 0.20 × 1000 = 200 kg of hydrofluoric acid is sent for decomposition. To decompose CPVC, 186.54 kg of a 45% sodium hydroxide solution is fed into the reactor. The acid decomposition process is carried out at a temperature of 90 ° C and a pH of 11.8 for 1 hour. In this case, the required temperature is provided due to the heat of the decomposition reaction and additional heating of the reaction mixture. The reaction mixture is a suspension, from which 62.9 kg of sodium fluoride precipitate is isolated by filtration. The filtrate (323.6 kg) is a sodium silicate solution and contains 36.6 kg of Na ₂ SiO ₃ . The main part of KFVK (1000 kg) and the resulting precipitate of sodium fluoride in the amount of 62.9 kg are fed into the neutralization reactor. In this case, an exchange reaction proceeds with the formation of 140.9 kg of sodium silicofluoride and 30.0 kg of hydrofluoric acid. Hydrofluoric acid reacts with 15 kg of silicon dioxide contained in KFVK, with the formation of 36.0 kg of H ₂ SiF ₆ . In the neutralization reactor serves 397 kg of a 20% solution of Na ₂ CO ₃ . The process of neutralization of hydrofluoric acid with soda is carried out for 1 hour at a pH of 2.5. The resulting suspension of sodium cremofluoride is defended, the thickened pulp with a ratio of T: W = 1: 3 is sent for drying. After drying the crystals in a fluidized bed apparatus, 282 kg of the expected product with a content of 99.5% Na ₂ SiF ₆ are obtained.

Determination of the filterability of the target product was carried out on a bench at a vacuum of 0.4 atm. and on a Buchner funnel with a diameter of 14.8 cm. A suspension was prepared by adding 100 g of product to 100 ml of distilled water. For the duration of the filtration of the product suspension, the time was taken from the start of filtration until the appearance of a "mirror surface" of the precipitate in the Buchner funnel. The duration of the filtration of the suspension of the product was 20 seconds.

The method allows to obtain easily filtering the target product is sodium silicofluoride with a high content of the main substance.

Claims (1)

A method of producing sodium silicofluoride by neutralizing hydrofluoric acid (CPVC) with soda in the presence of a sodium salt at pH 0.2-3 for 0.25-1 h, sedimenting the obtained crystals, separating and drying them, characterized in that they use sodium salts a precipitate of sodium fluoride isolated from the reaction mixture obtained by decomposing the estimated amount of hydrofluoric acid with a solution of sodium hydroxide at pH 11.5-12.5 and a temperature of 85-95 ° C, and the estimated amount of hydrofluoric acid, directed my decomposition to obtain a precipitate of sodium fluoride, is determined based on the concentration of acid $$C_{H_{2}Si{F}_6}$$

and silica content $$C_{Si{O}_2}$$

in the original KFVK according to the formula
$$N=C_{Si{O}_2}\cdot M_{H_{2}Si{F}_6}/C_{H_{2}Si{F}_6}\cdot M_{Si{O}_2}=2,\mathrm{four}\cdot C_{Si{O}_2}/C_{H_{2}Si{F}_6},$$

Where $$M_{H_{2}Si{F}_6}$$

- molecular weight KFVK equal to 144.09 g / mol, $$M_{Si{O}_2}$$

- molecular weight of silicon dioxide equal to 60.085 g / mol.