RU2388694C2 - Calcium fluoride synthesis method and device for realising said method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in metallurgy and in making protective coatings of welding electrodes. The calcium fluoride synthesis method involves reaction of a solution of hydrofluosilicic acid with a calcium carbonate suspension, holding the reaction mixture, separation of calcium fluoride suspension and drying the product. Calcium carbonate is first mixed with water. Hydrofluosilicic acid is added and a calcium fluoride suspension is obtained. Part of the obtained suspension is separated and added to calcium carbonate suspension as a nucleating agent, and the remaining part of the suspension is filtered and calcium fluoride residue is separated. The calcium carbonate suspension is then mixed with the calcium fluoride nucleating agent and treated with hydrofluosilicic acid. Further, the calcium fluoride nucleating agent and calcium fluoride residue are separated. The nucleating agent is taken in amount of 15-30% of the output of the end product. Final pH of the reaction mixture before separating the calcium fluoride residue must be equal to 5-7. The calcium carbonate suspension is prepared while maintaining the ratio of solid to liquid in the range 1:(2-4.5) based on part of the clear solution obtained during separation of calcium fluoride residue, and the rest of the clear solution is taken for hydrofluosilicic acid synthesis. A calcium fluoride synthesis device is proposed.

EFFECT: invention enables to obtain calcium fluoride with minimal content of impurities, which contains not less than 98 wt % of basic material and increase environmental safety of production.

13 cl, 4 dwg, 2 ex

Description

The invention relates to the chemistry and technology of inorganic products, in particular to the production of synthetic calcium fluoride.

The known method [patent RU No. 2029731, MKI C01F 11/22, priority 06.07.1992, publ. 02.27.1995] obtaining calcium fluoride, based on the interaction of phosphogypsum and fluorosilicate solutions with stirring in an aqueous medium, which are waste products of the extraction of phosphoric acid, a mixture of which is treated with a solution of sodium hydroxide.

The disadvantages of the method are the formation of hard-to-filter fine powder, the need to dispose of aqueous solutions containing sodium silicate and sodium sulfate, a large volume of recycled water, the high cost of the process due to the use of expensive sodium hydroxide in amounts comparable to the mass of phosphogypsum used, high phosphorus content, which in most cases is a harmful impurity.

It was possible to exclude the use of expensive sodium hydroxide and get rid of fluorine impurities in the method for producing calcium fluoride [patent SU No. 1472445, MKI C01B 33/18, priority 04.10.1986, publ. 04/15/1989] treatment with hydrofluoric acid suspension of calcium carbonate with stirring, with the separation of the resulting calcium fluoride from silicon dioxide by filtration. Moreover, to increase the yield of silicon dioxide, the suspension is stirred at a Reynolds criterion of 2000-8000, and the filtrate containing silicon dioxide is spray dried for 1-30 s.

The disadvantage of this method is the high consumption of circulating water. Carrying out the process at low pH values (4.2) causes the use of special equipment materials when spraying acid filtrate and utilizing off-gas acid gases. Spraying the filtrate at temperatures from 150 to 700 ° C and the need to evaporate a large amount of water leads to high energy costs and higher cost of the product. The fineness of the resulting calcium fluoride leads to poor filtration.

It was possible to reduce the volume of circulating water in the method of producing calcium fluoride [patent RU No. 2069179, MKI C01F 011/22, priority 12.04.1994, publ. 11/20/1996], based on the interaction of a solution of hydrofluoric acid with a suspension of calcium carbonate, aging the reaction mixture, introducing an acrylamide copolymer containing 5-20 mol% sodium acrylate units into the resulting suspension of calcium fluoride, separating the suspension of calcium fluoride by known methods and drying the product.

The disadvantages of the method are the presence of an acrylamide impurity in calcium fluoride, the cost of the product due to the use of copolymer additives, the presence of an impurity of unreacted calcium carbonate residues in the final product, the low rate of formation and growth of calcium fluoride crystals, the fineness of the resulting calcium fluoride, which leads to poor filtration.

To reduce the content of impurities in the resulting calcium fluoride was possible in the method [patent RU No.2010003, MKI C01F 011/22, priority 03.06.1991, publ. 03/30/1994] of two stages, namely, that first the calcium carbonate suspension is treated with hydrofluoric acid, taken in a mixture with the clarified solution from the second stage, and then the suspension is treated with hydrofluoric acid, taken in an amount of 20-50% of stoichiometrically necessary, when 40-80 ° C, after which the precipitate of calcium fluoride is separated, and the clarified solution is sent to the first stage of processing.

This technical solution is the closest in technical essence and therefore adopted as a prototype.

The disadvantage of this method is the use of solutions of hydrofluoric acid in two concentrations of 0.4 and 20%, which necessitates the dilution of part of the acid and concentration (evaporation) of the other part. In practice, the production of phosphate fertilizers produces hydrofluoric acid with a concentration of 12-15%. During evaporation, the acid solution is saturated with finely divided silica, the purification of which is time-consuming and requires the introduction of additional operations and special equipment. The evaporation process itself is energy-consuming, environmentally unsafe and requires special corrosion-resistant equipment. Calcium fluoride is formed as a hard-to-filter fine precipitate. The implementation of the process at low pH values (2-3) necessitates the neutralization of acidic clarified solution and disposal of the resulting sludge. A large consumption of circulating water and the second stage of the process at a temperature of 40-80 ° C is energy-intensive and leads to a rise in price of the product.

An object of the invention is the waste-free, environmentally friendly production of cheap calcium fluoride for metallurgy and the production of cheap calcium fluoride with a minimum content of impurities for the production of welding electrodes.

There are various devices for producing calcium fluoride, for example a device [patent RU No. 2069179, MKI C01F 011/22, priority 04/12/1994, publ. November 20, 1996], consisting of a reaction vessel equipped with a stirrer, a Buchner funnel for filtering the resulting suspension, a vacuum pump, and a dryer.

The disadvantages of the device are the impossibility of obtaining large batches of products, the presence of impurities, including calcium carbonate in the final product, the low rate of formation and growth of calcium fluoride crystals, the fineness of the resulting calcium fluoride.

Closest to the claimed device is [patent SU No. 1472445, MKI C01B 33/18, priority 04.10.1986, publ. 04/15/1989], which is accepted by us as a prototype. The device includes a reactor with an anchor stirrer, a belt vacuum filter, a device for spraying the filtrate in a coolant stream.

The disadvantage adopted for the prototype of the device is the high consumption of circulating water, high energy consumption.

An object of the invention is a waste-free, environmentally friendly production of cheap calcium fluoride with an acceptable content of silicon dioxide.

The stated technical problem is achieved by using a known method of producing calcium fluoride, including the interaction of a solution of hydrofluoric acid with a suspension of calcium carbonate, exposure of the reaction mixture, separation of the suspension of calcium fluoride and drying of the product. New in the method is that first calcium carbonate is mixed with water, hydrofluoric acid is added, a suspension of calcium fluoride is obtained, part of the resulting suspension is separated and sent to a suspension of calcium carbonate as a seed, and the rest of the suspension is filtered and the calcium fluoride precipitate is separated, then the suspension calcium carbonate is mixed with a seed of calcium fluoride and treated with hydrofluoric acid, then the seed of calcium fluoride and the precipitate of calcium fluoride are separated, and the seed is taken ut at the rate of 15-30% of the yield of the final product, the final pH of the reaction mixture before separation of the calcium fluoride precipitate should be in the range of 5-7, a suspension of calcium carbonate is prepared in compliance with the ratio of solid to liquid in the range of 1: (2-4.5 ) based on part of the clarified solution, and the rest of the clarified solution is directed to obtain hydrofluoric acid.

This eliminates the formation of finely divided calcium fluoride. The rate of formation and growth of calcium fluoride crystals increases. A single use of hydrofluoric acid makes the process more technologically advanced and reduces the cost of the final product.

With a decrease in the amount of seed less than 15% of the product yield, the rate of formation and size of crystals of calcium fluoride decreases, the degree of crystallinity of the product decreases, which leads to an increase in the duration of the process (and hence to an increase in the energy consumption of the method), and a decrease in the filtration performance. An increase in the amount of seed (more than 30% of the final product being produced) is inefficient, and relative productivity decreases. This amount of added seed allows to achieve the greatest productivity of the process.

It was experimentally established that a suspension of calcium carbonate must be prepared in compliance with the ratio of solid to liquid in the range of 1: (2-4.5), a decrease in the amount of liquid in the suspension will not provide the necessary intensity of mixing the reaction mass, and an increase in the amount of liquid in the suspension is inefficient, i.e. to. will lead to unreasonable increase in the volume of circulating water.

The remainder of the clarified solution obtained by separating the precipitate of calcium fluoride is sent to obtain hydrofluoric acid by any known method (for example, by absorption of fluorine-containing gases).

These distinctive features of the method make it possible to fully use the clarified solution in the technological cycle, minimizing water consumption in the cycle.

It was experimentally established that the final pH of the reaction mixture before separation of the precipitate should be in the range of 5-7, under these conditions, the reagents interact almost without residue with the formation of calcium fluoride and silicon dioxide.

Monitoring the pH of the medium allows you to completely neutralize hydrofluoric acid, while reducing the content of calcium carbonate impurities in the final product.

A method is possible in which the supply of hydrofluoric acid is regulated at the rate of 0.05-0.2 kg of 100% acid per hour in 1 kg of a suspension of calcium carbonate. It was experimentally established that the supply of hydrofluoric acid is less than 0.05 kg of 100% acid per hour in 1 kg of a suspension of calcium carbonate sharply reduces the rate of formation of calcium fluoride. And an increase in supply over 0.2 kg leads to strong gas formation, which leads to a decrease in production safety and an increase in the loss of the final product (as a result of entrainment).

A variant of the method is the treatment of a suspension of calcium carbonate with hydrofluoric acid at a temperature of 40-65 ° C. At temperatures below 40 ° C, there is a sharp decrease in the rate of formation of calcium fluoride. At temperatures above 65 ° C, hydrofluoric acid begins to boil and evaporate intensively. Moreover, an increase in temperature does not give a noticeable increase in the rate of formation of calcium fluoride.

This temperature regime allows to reduce energy consumption while maintaining a high rate of formation of calcium fluoride.

A variant of the invention is possible in which a solution of ammonium hydroxide is preliminarily fed into a solution of hydrofluoric acid, a precipitate of silicon oxide is filtered off and removed.

This allows you to get calcium fluoride containing at least 98 wt.% The main substance.

A variant of the method is possible in which the mixing of a suspension of calcium carbonate with the seed of calcium fluoride and its processing is carried out at a temperature of 70-95 ° C.

At temperatures below 70 ° C, there is a sharp decrease in the rate of formation of calcium fluoride. At temperatures above 95 ° C, production safety decreases, suspension losses as a result of entrainment increase. Moreover, an increase in temperature does not give a noticeable increase in the rate of formation of calcium fluoride.

A method is possible in which the consumption of ammonium hydroxide is regulated at the rate of 0.05-0.15 kg of 100% ammonium hydroxide per hour per 1 kg of hydrofluoric acid. It was experimentally established that the supply of ammonium hydroxide less than 0.05 kg per hour (in terms of 100% NH ₄ OH) sharply reduces the intensity of its interaction with acid. And an increase in feed over 0.15 kg leads to strong gas formation, which leads to a decrease in production safety and an increase in the loss of reagents as a result of entrainment.

A variant of the invention is possible in which the ammonia formed during the exposure of the reaction mixture is used to produce ammonium hydroxide, which is sent for the treatment of hydrofluoric acid.

This reduces the amount of recycled water, increases manufacturability and environmental safety of production, and also reduces the cost of the final product.

The stated technical problem is solved by means of a device containing a reactor with a stirrer, connected by a pipeline to a filter and then to a dryer. New in the device is that on the pipeline between the reactor with a stirrer and a filter there is a unit for separating seeds, additionally connected to the inlet to the reactor for feeding the seed of calcium fluoride into the reactor.

This eliminates the formation of finely divided calcium fluoride.

A variant of the device is possible, in which a granulator is additionally installed on the pipeline between the filter and the dryer, the granulator inlet connected to the filter outlet and the granulator outlet connected to the dryer inlet.

This allows the production of calcium fluoride in granules, which meets the requirements of metallurgical production.

A variant of the device is possible in which the filter outlet is additionally connected to the reactor inlet for supplying a clarified solution.

This reduces the amount of recycled water.

A variant of the device, in which there is an absorber, for the production of hydrofluoric acid, connected inlet to a source of fluorine-containing gases, connected to the inlet of the reactor with an output, and an additional filter at the outlet connected to the absorber to supply a clarified solution to it.

This reduces the amount of recycled water, increases manufacturability and environmental safety of production.

A possible embodiment of the invention is that between the absorber and the reactor there is an additional reactor for the interaction of an aqueous solution of ammonium hydroxide with hydrofluoric acid, the input of which is ammonium hydroxide, and an additional filter is installed at the outlet for separating silicon oxide.

These distinctive features make it possible to obtain calcium fluoride containing not less than 98 wt.% Of the basic substance.

A variant of the device is possible, in which there is an additional absorber for capturing ammonia, to the input of which ammonia is fed from the outlet of the reactor and water, and the outlet is connected to the inlet of the additional reactor through a container for the accumulation of ammonium hydroxide.

This allows you to increase manufacturability, environmental safety of production and reduce the consumption of ammonium hydroxide.

The invention is illustrated by drawings.

Figure 1 presents the technological block diagram of a method for producing calcium fluoride for the needs of metallurgy.

Figure 2 presents a block diagram of a device for producing calcium fluoride for the needs of metallurgy.

In figure 3. The technological block diagram of a method for producing calcium fluoride with additional treatment of hydrofluoric acid with a solution of ammonium hydroxide is presented.

Figure 4 presents a block diagram of a device for producing calcium fluoride with an additional treatment of hydrofluoric acid with a solution of ammonium hydroxide.

Example 1

A method of producing calcium fluoride from a suspension of calcium carbonate and a solution of hydrofluoric acid for the needs of metallurgy (figure 1).

The following raw materials are used: an aqueous solution of hydrofluoric acid 1 (H ₂ SiF ₆ ), which is a by-product of the production of phosphate fertilizers and contains 12-15 wt.% Acid H ₂ SiF ₆ ; natural chalk 2 with a content of calcium carbonate CaCO _{3 of} at least 98 wt.%.

To prepare a suspension of calcium carbonate 3 take calcium carbonate 2 and clarified solution 4, released during the filtration of a suspension of calcium fluoride 5 (water is used at startup). Seed 6 is added in the form of a suspension of calcium fluoride (ready-made calcium fluoride is used at startup). Hydrofluoric acid H ₂ SiF ₆ 7 is fed.

Part of the suspension of calcium fluoride is separated 8 and sent to the prepared suspension of calcium carbonate as a seed 6. The remaining suspension is filtered 5. The resulting filtered precipitate of calcium fluoride is granulated 9 and dried 10. Part of the clarified solution 4 is used to prepare an aqueous suspension of calcium carbonate 3, and the rest the clarified solution 11 is directed to obtain hydrofluoric acid by absorption of gases (HF, SiF ₄ ) 12 formed during the production of phosphate fertilizers.

The method of producing calcium fluoride is implemented on the line (figure 2), including a reactor 1, designed to produce calcium fluoride, connected by a conveyor 2 to the calcium carbonate supply line, pipe 3 with a standard absorber 4, designed to produce hydrofluoric acid. The output of the reactor 1 is connected by a pipe 5 to the input of the unit 6, designed to separate the seed in the form of a suspension of calcium fluoride. The output of the unit 6 is connected by a pipe 7 to the inlet of the reactor 1. In addition, the output of the unit 6 is connected by a pipe 8 to the input of the filter 9, which serves to filter the suspension of calcium fluoride. The output of the filter 9 is connected by a pipe 10 to the inlet of the reactor 1 for supplying a clarified solution to prepare a suspension of calcium carbonate. The output of the filter 9 is connected by a line 11 to a granulator 12, the output of which is connected by a line 13 to a furnace 14, intended for drying calcium fluoride. The output of the filter 9 is also connected by a pipe 15 to the input of a standard absorber 4, intended for the production of hydrofluoric acid by absorbing production fluorine-containing gases 16.

A device for producing calcium fluoride from a suspension of calcium carbonate and a solution of hydrofluoric acid (figure 2) works as follows. To obtain 100 kg of calcium fluoride by reaction:

H ₂ SiF ₆ + 3СаСО ₃ = 3СаF ₂ ↓ + SiO ₂ ↓ + Н ₂ О + 3СО ₂ ↑

a suspension of calcium carbonate is prepared in compliance with a solid to liquid ratio of 1: 2.5, for which 260 kg of clarified solution obtained after filtering a suspension of calcium fluoride is sent via line 10 to reactor 1, where it is heated to a temperature of 50 ° C and mixed with 104 kg of carbonate calcium. Calcium carbonate in the reactor 1 is loaded through the conveyor 2 with constant stirring. Then, as a seed, add a suspension of calcium fluoride, which enters through a pipe 7 from the unit 6, designed to separate part of the suspension - 20-25%.

The hydrofluoric acid H ₂ SiF ₆ obtained in the absorber 4, after determining the concentration and density, is supplied in an amount of 48.3 kg (100% H ₂ SiF ₆ ) per 100 kg of calcium fluoride through line 3 to reactor 1 with a flow rate of about 0, 13 kg / h of acid (100% H ₂ SiF ₆ ) in 1 kg of a suspension of calcium carbonate.

In the process of adding hydrofluoric acid, the pH of the medium is controlled (5.8-6.0). Maintain the reaction mixture with constant vigorous stirring in the reactor 1 for 1 h, while maintaining the temperature of the reaction mixture equal to 50 ° C. During the process, crystals of calcium fluoride and silicon dioxide are formed. Then the suspension from the reactor 1 is sent via line 5 to the unit 6, where about 114 kg is separated (solid to liquid ratio is about 1: 4.7), and through the return line 7 is sent to the reactor 1 as a seed. The remaining suspension is sent via line 8 to filter 9. The wet calcium fluoride precipitate is removed from filter 9 and sent via conveyor 11 to granulator 12, from where forms with wet calcium fluoride granules are transferred via conveyor 13 to dryer 14, where it is heated to a temperature of about 500 ° C. in order to remove moisture and increase the hardness of the granules.

The resulting clarified solution in an amount of 260 kg through a pipe 10 is sent to a reactor 1 to prepare a suspension of calcium carbonate. The rest of the clarified solution through the pipeline 15 enters the standard absorber 4, designed to obtain hydrofluoric acid by absorbing gases 16 generated during the production of phosphate fertilizers.

Example 2

A method of producing calcium fluoride from a suspension of calcium carbonate for the production of protective coatings of welding electrodes (figure 3). Calcium fluoride, containing not less than 98 wt.% Of the basic substance, is obtained by treating calcium carbonate with ammonium fluoride, which is the result of the interaction of 13 hydrofluoric acid 1 with ammonium hydroxide 14.

Ammonium hydroxide solution 13 is supplied to hydrofluoric acid 1. In this case, silicon dioxide and a solution of ammonium fluoride are formed. Then, the resulting suspension 15 is filtered 16, separating the silica precipitate. Ammonium fluoride solution 17 is used to produce calcium fluoride.

To prepare a suspension of calcium carbonate 3, calcium carbonate 2 is added to the clarified solution 4. Then, a suspension of calcium fluoride 6 is added as a seed. Next, a solution of ammonium fluoride 17 is added. In this case, ammonia 20 released during the reaction is captured in water adsorber 18 to obtain hydroxide ammonium 14 used to treat hydrofluoric acid 1.

A portion of the calcium fluoride suspension 8 is then separated off for use as seed 6. The remaining suspension is filtered 5. The resulting filtered calcium fluoride precipitate is granulated 9 and dried 10. The bulk of the clarified solution 4 is used to prepare the calcium carbonate suspension. The remaining clarified solution 11 is used to obtain hydrofluoric acid 1 (by absorbing production gases HF, SiF ₄ ) and / or to absorb ammonia 20. The resulting material contains at least 98% calcium fluoride, depending on the purity of the initial calcium carbonate. The method allows to obtain calcium fluoride of the following grades FF-95 and FF-98.

The line for implementing the proposed variant of the method for producing calcium fluoride includes nodes for separating silicon dioxide and obtaining calcium fluoride (figure 4).

The calcium fluoride precipitation unit includes a reactor 1 for producing calcium fluoride, connected by a conveyor 2 to a calcium carbonate supply line. The output of the reactor 1 by a pipe 5 is connected to the input of the unit 6, designed to separate part of the suspension of calcium fluoride as a seed. The output of the unit 6 is connected by a pipe 7 to the inlet of the reactor 1, and by a pipe 8 - to the input of a filter 9, which serves to filter the suspension of calcium fluoride. The output of the filter 9 is connected by a pipe 10 to the inlet of the reactor 1. In addition, the output of the filter 9 is connected by a line 11 to the granulator 12, the output of which, in turn, is connected by a line 13 to the furnace 14, intended for drying calcium fluoride. In addition, the output of the filter 9 is connected by a pipe 15 to the input of a standard absorber 4, intended for the production of hydrofluoric acid from the production of fluorine-containing gases 16.

The silicon dioxide separation unit includes an additional reactor 17 connected by a conduit 3 to a standard absorber 4 designed to produce hydrofluoric acid, and a conduit 18 with a capacity for the accumulation of ammonium hydroxide 19. The outlet of the reactor 17 by a conduit 20 is connected to the input of the filter 21, the outlet of which is connected by a conduit 22 with the input of the filter 23, designed for control filtering a solution of ammonium fluoride. In addition, the outlet of the filter 21 is connected by a conveyor 24 to a dryer 25 for drying silicon dioxide. The output of the filter 23 by the conveyor 26 is connected to the inlet of the dryer 25, and the pipe 27 is connected to the inlet of the reactor 1. The output of the reactor 1 is connected by a line 28 to an absorber 29 designed to capture ammonia by water supplied through the pipeline 30 and / or clarified solution 15 obtained after filtering a suspension of calcium fluoride. The output of the absorber 29 is connected by a pipe 31 to the input of the tank 19, intended for the accumulation of ammonium hydroxide. If necessary, ready-made ammonium hydroxide 32 may be supplied to the container 19.

A device for producing calcium fluoride from a suspension of calcium carbonate and a solution of ammonium fluoride (figure 4) works as follows.

To obtain 100 kg of calcium fluoride by reaction:

H ₂ SiF ₆ + 6NH ₄ OH = 6NH ₄ F + SiO ₂ ↓ + 4H ₂ O.

61.6 kg of hydrofluoric acid (100% H ₂ SiF ₆ ) are sent through a pipe 3 to the reactor 17. Then, via a pipe 18, 94 kg of ammonium hydroxide (100% NH ₄ OH) are slowly fed with constant stirring to the reactor 17. Ammonium hydroxide consumption should not exceed 0.12 kg of 100% NH ₄ OH per hour per 1 kg of hydrofluoric acid, which avoids the inclusion of ammonium fluoride in the composition of silicon dioxide. Stir the reaction mixture thoroughly for one hour. In the reactor 17, the formation of silicon dioxide and a solution of ammonium fluoride. Then, through the pipeline 20, the suspension from the reactor 17 is sent for filtering to the filter 21. The filtered and thoroughly washed from ammonium fluoride precipitate of silicon dioxide is sent through line 24 to dryer 25, where it is dried at a temperature of about 150 ° C until moisture is removed. The collected solution of ammonium fluoride through a pipe 22 is sent to a filter 23 for control filtering. The precipitate of silicon dioxide through a pipe 26 is fed to the dryer 25. A solution of ammonium fluoride is sent through a pipe 27 to the reactor 1 for interaction with a previously prepared suspension of calcium carbonate by the reaction:

2NH ₄ F + CaCO ₃ = CaF ₂ ↓ + 2NH ₃ ↑ + H ₂ O + CO ₂ ↑.

To prepare a suspension, 128 kg of calcium carbonate are taken along line 2 and sent to reactor 1 with a clarified solution preheated to a temperature of 85 ° C, which in an amount of 256 kg is sent to reactor 1 via pipeline 10. Then, seed in the form of a suspension of calcium fluoride is added to reactor 1 in an amount of not less than 110 kg, which is sent along line 7 from the aggregate 6, designed to separate part of the calcium fluoride suspension. Next, an ammonium fluoride solution is added to reactor 1 via line 27. A temperature of 85 ° C is maintained in reactor 1 with constant thorough mixing, with the formation and growth of calcium fluoride crystals. The reaction time is limited to the maximum by stopping the gas formation of NH ₃ , CO ₂ and H ₂ O, but not less than 1.5 hours. At the same time, ammonia is captured via line 28 to the absorber 29. The obtained ammonium hydroxide from the absorber 29 is sent to the tank through a pipe 31 19. Control the density, determine the concentration and in the required quantity (94 kg of ammonium hydroxide in terms of 100% NH ₄ OH), is fed through a pipe 18 to the reactor 17 for the treatment of hydrofluoric acid. When starting, ready-made ammonium hydroxide is used. Subsequently, the amount of finished ammonium hydroxide added is reduced with the receipt of ammonium hydroxide obtained by capturing ammonia.

A suspension of calcium fluoride from the reactor 1 is sent through line 5 to the unit 6 to separate part of the suspension, which, as a seed, is sent through line 7 to the reactor 1. The rest of the suspension of calcium fluoride is fed through line 8 for filtering to the filter 9. The wet precipitate of calcium fluoride is removed from the filter and sent through line 11 to the granulator 12 and then to the dryer 14, where it is heated to a temperature of about 200 ° C in order to remove moisture.

256 kg of clarified solution are sent via pipeline 10 to reactor 1 to prepare an aqueous suspension of calcium carbonate, and the remaining clarified solution is sent via pipeline 15 to absorber 4, where fluorine-containing gases 16 are recovered to obtain hydrofluoric acid.

Thus, it is possible waste-free, environmentally friendly production of cheap calcium fluoride containing at least 98 wt.% The main substance.

According to the invention, technical documentation is currently being prepared for the implementation of the invention in an industrial enterprise.

Claims (13)

1. A method of producing calcium fluoride, comprising reacting a solution of hydrofluoric acid with a suspension of calcium carbonate, holding the reaction mixture, separating a suspension of calcium fluoride and drying the product, characterized in that the calcium carbonate is first mixed with water, add hydrofluoric acid, a suspension of calcium fluoride is obtained, part the resulting suspension is separated and sent to the suspension of calcium carbonate as a seed, and the rest of the suspension is filtered and the precipitate of calcium fluoride is separated then the suspension of calcium carbonate is mixed with the seed of calcium fluoride and treated with hydrofluoric acid, then the seed of calcium fluoride and the precipitate of calcium fluoride are separated, and the seed is taken at a rate of 15-30% of the yield of the final product, the final pH of the reaction mixture before separation of the precipitate of calcium fluoride should be in the range of 5-7, a suspension of calcium carbonate is prepared in compliance with the ratio of solid to liquid in the range of 1: (2-4.5) based on part of the clarified solution obtained when separated and calcium fluoride precipitate, and the rest of the clarified solution is routed to fluorosilicic acid. 2. The method according to claim 1, characterized in that the supply of hydrofluoric acid is regulated at the rate of 0.05-0.2 kg of 100% acid per hour per 1 kg of a suspension of calcium carbonate. 3. The method according to claim 1, characterized in that the treatment with hydrofluoric acid is carried out at a temperature of 40-65 ° C. 4. The method according to claim 1, characterized in that the solution of hydrofluoric acid is pre-fed with a solution of ammonium hydroxide and the precipitate of silicon oxide is filtered off. 5. The method according to claim 4, characterized in that the mixing of a suspension of calcium carbonate with the seed of calcium fluoride and its processing is carried out at a temperature of 70-95 ° C. 6. The method according to any one of claims 4 to 5, characterized in that the ammonia formed during the exposure of the reaction mixture is used to form ammonium hydroxide, which is sent for the treatment of hydrofluoric acid. 7. The method according to claim 6, characterized in that the consumption of ammonium hydroxide is regulated at the rate of 0.05-0.15 kg of 100% ammonium hydroxide per hour per 1 kg of hydrofluoric acid. 8. The device for implementing the method of producing calcium fluoride according to claim 1, comprising a reactor with a stirrer connected to the filter and then to a dryer, characterized in that between the reactor and the filter there is an aggregate for separating the seed, additionally connected to the inlet of the reactor for feeding the seed calcium fluoride. 9. The device according to claim 8, characterized in that an additional granulator is installed between the filter and the dryer, the granulator inlet connected to the filter outlet and the granulator output connected to the dryer inlet. 10. The device according to any one of paragraphs.7 and 8, characterized in that the output of the filter is additionally connected to the inlet of the reactor for supplying a clarified solution. 11. The device according to claim 10, characterized in that there is additionally an absorber for the production of hydrofluoric acid, inlet connected to a source of fluorine-containing gases, inlet connected to the inlet of the reactor, and an additional filter at the outlet connected to an absorber for supplying a clarified solution to it. 12. The device according to claim 11, characterized in that between the absorber and the reactor there is an additional reactor for the interaction of an aqueous solution of ammonium hydroxide with hydrofluoric acid, the input of which is ammonium hydroxide, and an additional filter is installed at the output for separating silicon oxide. 13. The device according to p. 12, characterized in that there is an additional absorber for capturing ammonia, the input of which serves ammonia from the outlet of the reactor and water, and the output is connected to the inlet of the additional reactor through a tank for the accumulation of ammonium hydroxide.

Images