RU2543172C2 - Method of producing sodium silicofluoride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes reacting hydrofluorosilicic acid and a mixture of sodium-containing compounds, separating the product, washing and drying, wherein the mixture of sodium-containing compounds used is an aqueous solution with density of 1.1-1.13 g/cm³ of a mixture of sodium chloride, sulphate and hydroxide, taken in weight ratio of (6-12):(0.5-2):1; the mixture of sodium-containing compounds is taken in amount of 110-120% of the stoichiometrically required amount for reaction with hydrofluorosilicic acid, and the reactants react via a continuous method at 0-50°C for 15-30 minutes to obtain a suspension; the suspension is then settled; the mother solution is separated by decantation to obtain pulp; the pulp is diluted with water in volume ratio of 1:1 and filtered; the product precipitate is washed with water and dried. The mixture of sodium-containing compounds used can be caustic soda production wastes which are pre-diluted with water in volume ratio of 1:1.

EFFECT: obtaining an easy to filter precipitate and low corrosive activity of the mother solution.

2 cl, 1 dwg, 1 tbl

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 [A.S. No. 859293, cl. СВВ 33/10, В01Д 53/14, publ. 07/18/79] from fluorine-containing gases in the production of extraction phosphoric acid and fertilizers by their aqueous absorption, neutralization of the obtained CPVA soda or caustic soda at pH 0.2-3 for 0.25-1 h, sedimentation of the obtained crystals, their separation and drying. Get the bulk of the crystals of Na ₂ SiF ₆ with a size of 40-60 microns. The method allows to increase the rate of sedimentation up to 5-7 m / h and use KFVK contaminated with silicon dioxide. However, the known method is characterized by an insufficiently high yield of sodium silicofluoride.

A known method of producing sodium silicofluoride by reacting hydrofluoric acid with sodium hydroxide [RF patent No. 2226502, class. СВВ 33/10, publ. 04/10/2004], separation from the mother liquor of the precipitate and its drying; the interaction is carried out at a molar ratio of fluorine and silicon of 6: 1 and a change in pH in the range of 5.0-6.5. The known method allows to obtain high-quality easily-filtered sodium silicofluoride. However, the known method is characterized by an insufficiently high yield of sodium silicofluoride.

A known method of producing sodium silicofluoride [A.S. No. 1030311, cl. СВВ 33/10, publ. 07/23/1983], including the interaction of CPVC with sodium salt, separation of the product from the mother liquor, neutralization of the mother liquor with soda followed by evaporation and return to the stage of interaction, moreover, neutralization of the mother liquor with soda is carried out before its separation from the product, soda is introduced in an amount of 85- 95% of stoichiometrically necessary. Sodium sulfate or chloride is used as the sodium salt. The method allows to increase the yield of the product. The disadvantage of this method is the complexity of the process associated with the need for evaporation of the mother liquor, an additional stage of neutralization with soda ash.

A known method of producing sodium silicofluoride [A.S. No. 1028597, class СВВ 33/10, publ. 07/15/1983], including the interaction of KFVK with a sodium-containing reagent, preliminary separation of acid from silica gel, treatment of silica gel with sodium salt and separation of the precipitate from the solution, where sulfate or chloride is taken as the sodium salt in the processing of silica gel, and the solution after separation is used as the sodium-containing reagent draft. Sulfate or sodium chloride is taken in an amount of 100-125% of the stoichiometrically necessary for interaction with CPVK. The known method allows to increase the degree of use of fluorine. The disadvantage of this method is the complexity of the process and the high corrosivity of the mother liquor, insufficient sedimentation rate of sodium cremofluoride.

The closest to the proposed technical essence and the achieved result is a method of producing sodium cremofluoride [A.S. No. 1000396, class СВВ 33/10, publ. 02/28/1983], including the interaction of hydrofluoric acid and a mixture of sodium-containing compounds, separation of the product, washing and drying thereof, and a mixture of sodium-containing compounds using a mixture of sodium sulfate and sodium chloride, which are taken in a mass ratio of 20-50: 1. As a mixture of sulfate and sodium chloride, waste from the production of chlorosulfonic acid is used. The known method allows to increase the content of the main substance in the target product.

The disadvantage of this method is the high corrosivity of the mother liquor, the low rate of clarification and filtration of a suspension of sodium silicofluoride.

The aim of the invention is to obtain a readily filtering precipitate of sodium cremofluoride and reduce the corrosive activity of the mother liquor.

This goal is achieved by the fact that in the method of producing sodium silicofluoride, including the interaction of hydrofluoric acid and a mixture of sodium-containing compounds, separation of the product, washing and drying thereof, moreover, an aqueous solution of a mixture of sodium chloride, sulfate and sodium hydroxide taken in a weight ratio is used as a mixture of sodium-containing compounds (6-12) :( 0.5-2): 1 and a solution density in the range of 1.1-1.13 g / cm ³ ; a mixture of sodium-containing compounds is taken in an amount of 110-120% of the stoichiometrically necessary for interaction with CPVK. And the interaction of the reagents is carried out by a continuous method at a temperature of 0-50 ° C for 15-30 minutes to obtain a suspension; then the suspension is defended, the mother liquor is separated by decantation to obtain pulp; the pulp is diluted with water in a volume ratio of 1: 1 and filtered; the product precipitate is washed with water and dried.

The essence of the method is as follows. Obtaining sodium silicofluoride in the interaction of CPVC and sodium compounds is based on the reactions:

2NaCl + H ₂ SiF ₆ = Na ₂ SiF ↓ + 2HCl

Na ₂ SO ₄ + H ₂ SiF ₆ = Na ₂ SiF ₆ ↓ + H ₂ SO ₄

2NaOH + H ₂ SiF ₆ = Na ₂ SiF ₆ ↓ + 2H ₂ O

The interaction of sodium chloride and sulfate with CPVC proceeds with the formation of the target product, hydrochloric and sulfuric acids. And the presence in the mixture of sodium-containing reagent sodium hydroxide provides a decrease in the acidity of the reaction mass - a suspension of sodium silicofluoride due to the reaction of CPVA with alkali with the formation of the target product and water. It is also possible to neutralize hydrochloric and sulfuric acids with sodium hydroxide. Reducing the acidity of the reaction mass provides a decrease in the corrosion activity of the mother liquor, wastewater installation for the production of sodium silicofluoride.

Obtaining a precipitate and suspension of sodium silicofluoride, which have increased deposition and filtration rates, is one of the main indicators of the technological process that determine the productivity of the plant for the production of CFP.

Obtaining easy-to-filter precipitate of sodium cremofluoride is achieved by carrying out the process of interaction KFVK with a mixture of sodium-containing compounds in optimal conditions, namely:

- mass ratio in a mixture of NaCl: Na ₂ SO ₄ : NaOH, equal to (6-12) :( 0.5-2): 1;

- the use of a mixture with a density in the range of 1.1-1.13 g / cm ³ ;

- the implementation of the interaction KFVK and a mixture of sodium salts by a continuous method at a temperature of 0-50 ° C for 15-30 minutes

At the same time, the consumption of the mixture of sodium-containing compounds is 110-120% of the stoichiometrically necessary amount for interaction with CPVC, and the product is separated: by sedimentation of the suspension; decantation of the mother liquor to produce pulp; dilution of the pulp with water in a volume ratio of 1: 1.

The feasibility of the selected limits of the process indicators is given in the examples and in table 1.

Example 1. Pre-prepare a mixture of sodium-containing compounds by dissolving in water the calculated amounts of chloride, sulfate and sodium hydroxide to obtain a solution containing 120 g / l NaCl, 18 g / l Na ₂ SO ₄ and 12 g / l NaOH. The density of the aqueous solution of a mixture of sodium salts of 1.11 g / cm ^{3 the} mass ratio of the components of NaCl: Na ₂ SO ₄ : NaOH is 10: 1.5: 1. In a three-necked flask equipped with a mechanical stirrer, 100 g of an 18% solution of KFVK and 117 g of an aqueous solution (105.4 ml) of a mixture of sodium-containing compounds are simultaneously fed. A mixture of sodium-containing compounds was taken in an amount of 110% of the stoichiometrically necessary for interaction with CPVC. The reaction mixture was stirred at 25 ° C for 20 min to obtain a suspension of sodium cremofluoride. The resulting suspension is defended. The deposition rate of the crystals of CFN is 3.2 m / h After settling, decantation is carried out, while the liquid phase representing the mother liquor is separated from the precipitate. The fluorine content in the mother liquor is 0.35%. The resulting slurry pulp (30 ml) was diluted with water in a volume ratio of 1: 1 and filtered. Filtering duration 8 sec. The filtration rate of the diluted pulp is 9.5 m ³ / m ² * h in suspension or 3.5 t / m ² * h in dry product. Next, the product precipitate is washed with water and the washed precipitate is dried. Obtain 22.3 g of the target product, the content of the main substance is 99% Na ₂ SiF ₆ . The yield of product is 94%.

Example 2. As a mixture of sodium-containing compounds take sulfate brine - waste production of caustic soda, containing 257.4 g / l NaCl, 21.8 g / l Na ₂ SO ₄ and 32.2 g / l NaOH. The density of sulfate brine 1.21 g / cm ³ . The sulfate brine is diluted with water in a volume ratio of 1: 1 to obtain a solution with a density of 1.11 g / cm ³ and containing 128.7 g / l NaCl, 10.8 g / l Na ₂ SO ₄ and 16.1 g / l NaOH. The mass ratio of the components of the diluted sulfate brine NaCl: NaiSO ₄ : NaOH is 8: 0.7: 1. In a three-necked flask equipped with a mechanical stirrer, 100 g of an 18% solution of KFVK and 113 g of an aqueous solution (101.8 ml) of a mixture of sodium compounds are simultaneously fed. A mixture of sodium-containing compounds was taken in an amount of 110% of the stoichiometrically necessary for interaction with CPVC. The reaction mixture was stirred at 25 ° C for 20 min to obtain a suspension of sodium cremofluoride. The resulting suspension is defended. The deposition rate of the crystals of CFN is 3.1 m / h After settling, decantation is carried out, while the liquid phase representing the mother liquor is separated from the precipitate. The fluorine content in the mother liquor is 0.33%. The resulting slurry pulp (30 ml) was diluted with water in a volume ratio of 1: 1 and filtered. Filtration Duration 9 sec. The filtration rate of the diluted pulp is 8.8 m ³ / m ² * h in suspension or 3.25 t / m ² * h in dry product. Next, the product precipitate is washed with water and dried. Obtain 22.3 g of the target product, the content of the main substance is 99% Na ₂ SiF ₆ . The yield of product is 94%.

The density of an aqueous solution of a mixture of chloride, sulfate and sodium hydroxide determines the concentration of a mixture of sodium compounds. The use of a mixture solution with a density of less than 1.1 g / cm ³ leads to an increase in the volume of the mother liquor and to a decrease in the yield of the target product due to an increase in fluorine losses with the mother liquor (experiment 2, Table 1). An increase in the density of the mixture solution above 1.13 g / cm ³ leads to a significant decrease in the filtration rate of the pulp of CFN crystals (experiment 4, Table 1) due to the increase in the viscosity of the reaction mixture and the high dispersion of crystals of sodium silicofluoride.

Maintaining the flow rate of the mixture of sodium-containing compounds at the level of 110-120% of the stoichiometrically necessary amount for interaction with CPVC provides a high yield of the target product (at the level of 94%) and minimal loss of fluorine with the mother liquor. Reducing the consumption of a mixture of sodium-containing compounds of less than 110% of the stoichiometrically required amount (experiment 5) leads to a decrease in the yield of the product to 88%. With an increase in the flow rate of the mixture solution above 120% of the stoichiometrically necessary amount (experiment 7), the product yield does not change; there is an increased unproductive consumption of the reagent.

The decrease in the content of sodium hydroxide in the mixture of sodium-containing compounds is less than the mass ratio of NaCl: Na ₂ SO ₄ : NaOH equal to (6-12) :( 0.5-2): 1, leads to increased corrosion activity of the mother liquor (experiment 8) . The increase in the content of sodium chloride in the mixture is higher than the mass ratio of NaCl: Na ₂ SO ₄ : NaOH equal to 12: (0.5-2): 1, also leads to an increase in the corrosive activity of the mother liquor and a decrease in the filtration rate of CFN pulp (experiment 9 ) The decrease in the content of sodium chloride in the mixture is less than the mass ratio of 6: (0.5-2): 1, leads to a decrease in the yield of the target product and an increase in the volume of the mother liquor (experiment 10). The decrease in the sodium sulfate content in the mixture is less than the mass ratio (6-12): 0.5: 1, which leads to a decrease in the yield of the product (experiment 11). An increase in the sodium sulfate content in the mixture of sodium-containing compounds by more than (6-12): 2: 1 leads to a decrease in the rate of filtration of sodium cremofluoride pulp (experiment 12).

The interaction of CPVC and an aqueous solution of sodium-containing compounds by the continuous method provides high productivity, ease of implementation of the process with obtaining easily filtered precipitate of sodium silicofluoride. When carrying out the interaction process by a periodic method by adding a solution of a mixture of chloride, sulfate and sodium hydroxide to CPVC, the obtained CFN suspension is characterized by relatively low filterability, the filtration rate is 1.8-3.0 m ³ / m ² * h in suspension.

For complete passage of the process of interaction of CPVC and an aqueous solution of sodium-containing compounds with the formation of sodium silicofluoride, it is sufficient to mix the reaction mass for 15-30 minutes. A process duration of less than 15 min is insufficient to complete the formation of FSC, and an increase of more than 30 min is impractical due to a decrease in the process productivity.

The possibility of interaction between CVF and a mixture of sodium-containing compounds at a temperature of 0 ° C ensures the implementation of the process in the winter season without the cost of heat for heating the starting reagents. The process below 0 ° C is difficult due to the crystallization of the reaction mass. The process of interaction above 50 ° C is impractical due to the increase in the cost of maintaining the temperature of the reaction mass.

The separation of the product from a suspension of sodium silicofluoride obtained by the interaction of CPVC and a solution of a mixture of chloride, sulfate and sodium hydroxide without decanting the mother liquor is difficult due to the low filtration rate (at a level of not more than 0.5 m ³ / m ² * h in suspension). The formation of sodium silicofluoride is accompanied by the release of silica gel in colloidal form. The presence of colloidal silica gel dramatically reduces the filterability of a suspension of sodium silicofluoride. Removal of silica gel is achieved by sedimentation and subsequent decantation of the mother liquor. The separation of the product by sedimentation of the suspension, decantation of the mother liquor to obtain pulp, dilution of the pulp with water in a volume ratio of 1: 1 provide a high rate of filtration and washing of the precipitate of sodium cremofluoride. Dilution of pulp of CFN sediment with water in a volume ratio of 1: 1 also makes it possible to pump diluted pulp with pumps. The volumetric ratio of sediment: water, equal to 1: 1, is optimal. With a decrease in water consumption, transportation of pulp is difficult, and an increase in water consumption leads to an increase in the volume of wash water, which must be disposed of.

Claims (2)

1. The method of producing sodium silicofluoride, including the interaction of hydrofluoric acid and a mixture of sodium-containing compounds, separation of the product, washing and drying thereof, characterized in that an aqueous solution of a density of 1.1-1.13 g / cm ^{3 of a} mixture of chloride is used as a mixture of sodium-containing compounds sulfate and sodium hydroxide taken in a mass ratio (6-12) :( 0.5-2): 1; the mixture of sodium-containing compounds is taken in an amount of 110-120% of the stoichiometrically necessary for interaction with hydrofluoric acid, and the interaction of the reagents is carried out by a continuous method at a temperature of 0-50 ° C for 15-30 minutes to obtain a suspension, then the suspension is settled, the mother liquor is separated by decantation to obtain pulp, the pulp is diluted with water in a volume ratio of 1: 1 and filtered, the product precipitate is washed with water and dried. 2. The method of producing sodium silicofluoride according to claim 1, characterized in that as a mixture of sodium-containing compounds take the waste of production of caustic soda, pre-diluted with water in a volume ratio of 1: 1.