JP4523936B2 - Synthetic fluorite manufacturing method and synthetic fluorite manufacturing apparatus - Google Patents

Description

  The present invention relates to a method for producing synthetic fluorite using fluorine in a gas containing fluorine such as exhaust gas generated in a process of producing tricalcium phosphate by thermal decomposition of phosphate ore.

  Examples of the method for producing tricalcium phosphate include a method of reacting calcium chloride and sodium phosphate with excess ammonia, a method of synthesizing from slaked lime and a phosphoric acid solution, and the like. Particularly, tricalcium phosphate for fertilizer and livestock feed. A thermal decomposition method is used which is produced by thermal decomposition of phosphorus ore.

  In such a process for producing tricalcium phosphate by the pyrolysis method, since phosphorous ore contains several percent (about 3 to 4%) of fluorine, the exhaust gas generated in the process contains fluorine. Will be included. If no treatment is performed on this exhaust gas, exhaust gas containing fluorine will be released into the atmosphere. However, fluorine is harmful to the human body and causes great environmental damage, so it should be removed from the exhaust gas. The emission concentration is also regulated by the Prevention Law.

For this reason, conventionally, fluorine is removed from exhaust gas by reacting fluorine and calcium hydroxide by contacting exhaust gas generated by pyrolysis with a slurry containing calcium hydroxide to produce calcium fluoride. Has been done. Further, NaOH, Na ₂ SO _{4 and the} like are also used in the absorbing solution and are recovered as sodium salts such as acidic sodium fluoride and sodium fluoride. Such fluorine removal methods include a dry treatment method and a wet treatment method, but a wet treatment method superior in performance is mainly used. Examples of the wet processing method include an absorption tower method using a spray tower, a scrubber, a packed tower, and the like.

In such a wet processing method, water is used as an absorbing solution to recover as hydrogen fluoride (HF), and sodium fluoride (NaF) or sodium hydrogen fluoride (NaHF ₂ ) is used using a sodium hydroxide solution. However, when water is used as an absorbing solution, there is a problem that the equipment requires high corrosion resistance. When sodium hydroxide solution is used as an absorbing solution, in addition to the problem of equipment corrosion resistance, Wastewater treatment problems will also arise. Therefore, the method of recovering calcium fluoride (CaF ₂ ) using calcium hydroxide (Ca (OH) ₂ ) slurry is the simplest and less expensive, and at the same time, the waste water treatment and the problem are solved. The calcium fluoride recovered at this time is treated as industrial waste.

  By the way, fluorite, a mineral mainly composed of calcium fluoride, is in demand for chemical raw materials (fluorine raw materials), pottery raw materials, steel applications, etc., but in recent years resource depletion and accompanying exports from producing countries Due to regulations, stable supply cannot be expected. Therefore, if calcium fluoride produced in the process of producing tricalcium phosphate by the above pyrolysis method can be used, it can replace natural fluorite and contribute to the stable supply of calcium fluoride, and industrial waste Can also be reduced.

  However, in the reaction between the exhaust gas containing fluorine and the slurry containing calcium hydroxide by the wet processing method as described above, the pH of the reaction system is set to the alkali side (pH 7.5 or more) in order to efficiently recover fluorine. Therefore, the amount of calcium hydroxide used relative to the amount of fluorine recovered will exceed the stoichiometric amount. As a result, the calcium fluoride content in the resulting product remains at about 65 to 70% by weight, and the market value is low. Here, the purity required for fluorite used for chemical raw materials (acid grade) is 98% by weight or more, and the purity required for ceramic raw materials (ceramic grade) (containing calcium fluoride) Rate) is 85% by weight or more, and the purity required for those used in steel applications (metaradical grade) is 75% by weight or more, so the calcium fluoride content of the product recovered by exhaust gas treatment is the metaradical It will not reach the grade.

Conventionally, a method for obtaining high-purity fluorite by a flotation method has been proposed for natural fluorite (see Patent Documents 1 and 2), but this method is applied to the recovered product. However, it is difficult to sufficiently improve the purity, and there also arises a problem of wastewater treatment that occurs with the implementation of the method.
JP 47-112824 Japanese Patent Publication No.49-10882

  The present invention has been made in view of the above points, and removes fluorine from a fluorine-containing gas such as an exhaust gas containing fluorine generated in a process of producing tricalcium phosphate by thermal decomposition of phosphate ore. An object of the present invention is to provide a method for producing a synthetic fluorite capable of producing a product (synthetic fluorite) having a high calcium fluoride content from fluorine.

  The method for producing a synthetic fluorite according to claim 1 includes calcium fluoride and calcium hydroxide by reacting fluorine in a gas containing fluorine with calcium hydroxide in an amount exceeding the stoichiometric amount with respect to the fluorine. A calcium fluoride recovery step for producing a mixture, a hydrogen fluoride recovery step for producing a hydrogen fluoride aqueous solution by bringing a gas containing fluorine into contact with water, and the mixture obtained in the calcium fluoride recovery step and the fluoride And a re-reaction step of producing a synthetic fluorite by reacting with the hydrogen fluoride aqueous solution obtained in the hydrogen recovery step.

  The invention according to claim 2 is characterized in that, in claim 1, the gas containing fluorine is exhaust gas generated in a process of producing tricalcium phosphate by thermal decomposition of phosphate ore.

  The synthetic fluorite manufacturing apparatus according to claim 3 includes calcium fluoride and calcium hydroxide by reacting fluorine in a gas containing fluorine with calcium hydroxide in an amount exceeding the stoichiometric amount with respect to the fluorine. A calcium fluoride recovery unit 1 that generates a mixture, a hydrogen fluoride recovery unit 2 that generates a hydrogen fluoride aqueous solution by bringing a gas containing fluorine into contact with water, and a mixture obtained by the calcium fluoride recovery unit 1 And a re-reaction unit 3 for generating a synthetic fluorite by reacting with the hydrogen fluoride aqueous solution obtained in the hydrogen fluoride recovery unit 2.

  According to a fourth aspect of the present invention, in the third aspect, the gas supply path 4 for supplying a gas containing fluorine to the calcium fluoride recovery unit 1 and the fluorine branched to the hydrogen fluoride recovery unit 2 from the gas supply path 4 are provided. And a branch path 5 for supplying a gas containing the gas.

  The invention according to claim 5 comprises the gas supply path 4 for supplying a gas containing fluorine to the calcium fluoride recovery section 1 according to claim 3, and the hydrogen fluoride recovery section 2 flows through the gas supply path 4 It is characterized in that an aqueous hydrogen fluoride solution is generated from a part of fluorine in the gas to be produced.

According to a sixth aspect of the present invention, in the fourth or fifth aspect , the starting end of the gas supply passage 4 is connected to a tertiary calcium phosphate production section 6 that produces tertiary calcium phosphate by thermal decomposition of phosphate ore, and as a gas containing fluorine The exhaust gas generated in the process of producing the tertiary calcium phosphate by the thermal decomposition of the phosphate ore in the tertiary calcium phosphate production unit 6 is supplied.

  According to the first aspect of the present invention, fluorine in a gas containing fluorine can be recovered and used for the synthesis of synthetic fluorite. At this time, in the calcium fluoride recovery step, the fluorine is removed with high efficiency and the mixture And the calcium hydroxide remaining in the mixture and the hydrogen fluoride obtained in the hydrogen fluoride recovery step are reacted in the re-reaction step, thereby containing calcium hydroxide in the mixture. It is possible to reduce the amount and improve the calcium fluoride content, and to produce highly pure synthetic fluorite with high efficiency. Further, even in the case of using a low concentration hydrogen fluoride aqueous solution of about 5 to 10% by weight in the re-reaction step, it is possible to obtain synthetic fluorite with high efficiency and high purity. Therefore, the equipment provided for this purpose does not need to be subjected to a high degree of anticorrosion treatment, and the equipment cost for producing synthetic fluorite can be reduced. Furthermore, by removing fluorine from the gas containing fluorine, the fluorine content of this gas can be reduced, so that even if this gas is released into the atmosphere, the emission standards will not be satisfied and the environment will not be deteriorated. Is something that can be done.

  Further, according to the invention of claim 2, by removing fluorine from the exhaust gas generated in the process of producing tricalcium phosphate, the environment can be prevented from deteriorating even if this gas is released into the atmosphere. In addition, industrially useful synthetic fluorite can be obtained as this product without making the product generated when removing fluorine from the exhaust gas into a waste product. It can contribute.

  According to the invention which concerns on Claim 3, it is highly pure by making the mixture obtained by the calcium fluoride collection | recovery part 1 and the hydrogen fluoride obtained by the hydrogen fluoride collection | recovery part 2 react in the re-reaction part 3. Synthetic fluorite can be obtained with high efficiency. Further, the re-reaction unit 3 can obtain a highly efficient and high-purity synthetic fluorite even when a low concentration hydrogen fluoride aqueous solution of about 5 to 10% by weight is used. For this reason, the hydrogen fluoride recovery unit No. 2 need not be subjected to a high degree of anticorrosion treatment, and the equipment cost for producing synthetic fluorite can be reduced. Furthermore, by removing fluorine from the gas containing fluorine, the fluorine content of this gas can be reduced, and even if this gas is released into the atmosphere, the environment can be prevented from deteriorating. .

  According to the fourth aspect of the invention, the gas containing fluorine is supplied to the calcium fluoride recovery unit 1 through the gas supply path 4, and the fluorine is supplied to the hydrogen fluoride recovery unit 2 through the branch path 5. Thus, the gas required for the calcium fluoride recovery unit 1 and the hydrogen fluoride recovery unit 2 can be separately supplied.

  According to the invention which concerns on Claim 5, with respect to the gas containing the fluorine which distribute | circulates the gas supply path 4, the process by the hydrogen fluoride recovery part 2 and the process by the calcium fluoride recovery part 1 can be performed sequentially. is there.

  According to the invention according to claim 6, by removing fluorine from the exhaust gas generated in the tertiary calcium phosphate production section 6, it is possible to prevent the environment from being deteriorated even if this gas is released into the atmosphere. In addition, industrially useful synthetic fluorite can be obtained as this product without making the product generated when removing fluorine from exhaust gas into waste, and this contributes to the reduction of waste. It is something that can be done.

  Hereinafter, the best mode for carrying out the present invention will be described.

  The synthetic fluorite production apparatus shown in FIG. 1 includes a tertiary calcium phosphate production unit 6, a calcium fluoride collection unit 1, a hydrogen fluoride collection unit 2, and a re-reaction unit 3.

  The tertiary calcium phosphate production section 6 produces tertiary calcium phosphate by thermal decomposition of phosphate ore. As this tertiary calcium phosphate production section 6, an appropriate reactor such as a known rotary kiln that employs combustion of an appropriate fuel such as heavy oil or natural gas and heats the phosphate ore with the heat of combustion can be employed.

  The tertiary calcium phosphate production unit 6 and the calcium fluoride recovery unit 1 are connected by a gas supply path 4. The gas supply path 4 is a flow path for supplying a gas containing fluorine to the calcium fluoride recovery unit 1, and in this embodiment, is generated in a process for producing tertiary calcium phosphate by thermal decomposition of phosphate ore in the tertiary calcium phosphate production unit 6. The exhaust gas to be circulated is supplied to the calcium fluoride recovery unit 1.

  The calcium fluoride recovery unit 1 reacts the fluorine in the exhaust gas supplied from the gas supply path 4 with calcium hydroxide in an amount exceeding the stoichiometric amount with respect to the fluorine to thereby generate calcium fluoride and calcium hydroxide. To produce a mixture containing. As the calcium fluoride recovery unit 1, for example, a calcium hydroxide slurry in which calcium hydroxide is dispersed in water is brought into contact with the exhaust gas so that a slurry containing calcium fluoride and calcium hydroxide is obtained by a gas adsorption process. What comprises a spray tower, a scrubber, etc. which produce | generate a mixture can be provided. The exhaust gas after the fluorine is removed is discharged to the outside from the discharge path 12 connected to the calcium fluoride recovery unit 1.

  Further, the gas supply path 4 is provided with a branch path 5 that branches between the tertiary calcium phosphate production section 6 and the calcium fluoride recovery section 1, and this branch path 5 is connected to the hydrogen fluoride recovery section 2. It is connected.

  The hydrogen fluoride recovery unit 2 is for generating an aqueous hydrogen fluoride solution by dissolving fluorine in the exhaust gas supplied from the branch path 5 in water. As this hydrogen fluoride recovery part 2, what comprises a packed tower which produces hydrogen fluoride aqueous solution by a gas adsorption process, for example by making water contact with the exhaust gas can be provided. In the hydrogen fluoride recovery unit 2 shown in FIG. 3, a packed tower 8 filled with a packing and a circulation tank 9 for storing water are connected by a circulation path 10, and a pump 11 provided in the circulation path 10 is used. Water is circulated between the packed tower 8 and the circulation tank 9 by a driving force. A branch path 5 is connected to the packed tower 8, and exhaust gas supplied from the branch path 5 comes into contact with water in the packed tower 8. The packed tower 8 is connected to a discharge pipe 7 from which the exhaust gas from which fluorine has been removed is discharged. The exhaust pipe 7 may be opened to the outside so that the exhaust gas from which fluorine has been removed may be discharged to the outside. Further, as shown in FIG. 1, the exhaust pipe 7 is connected to the gas supply path 4 to remove fluorine. The discharged exhaust gas may be returned to the gas supply path 4 and supplied to the calcium fluoride recovery unit 1.

  The re-reaction unit 3 reacts the mixture obtained in the calcium fluoride recovery step with the hydrogen fluoride aqueous solution obtained in the hydrogen fluoride recovery step to generate synthetic fluorite. The re-reacting unit 3 can be constituted by an appropriate reaction vessel, and both can be reacted by supplying and mixing the mixture and the aqueous hydrogen fluoride solution in the reaction vessel.

  A synthetic fluorite production method using such a synthetic fluorite production apparatus will be described below.

  First, in the tertiary calcium phosphate production section 6, as described above, the tertiary calcium phosphate is produced by thermal decomposition of the phosphate ore. At this time, for example, tricalcium phosphate can be obtained by thermally decomposing phosphor ore by heating to 1300 to 1500 ° C. together with the reaction promoting third component. Here, since about 3 to 4% of fluorine is contained in the phosphate ore, the exhaust gas generated in the production process of tricalcium phosphate by the thermal decomposition contains fluorine contained in the phosphate ore. Will be contained.

  The exhaust gas is sent to the gas supply path 4 and supplied to the calcium fluoride recovery unit 1 through the gas supply path 4. A part of the exhaust gas is supplied to the hydrogen fluoride recovery unit 2 through a branch path 5 branched from the gas supply path 4.

  Here, the ratio of the supply amount of the exhaust gas to the calcium fluoride recovery unit 1 and the supply amount of the exhaust gas to the hydrogen fluoride recovery unit 2 is appropriately set. For example, the calcium fluoride recovery unit 1 and the hydrogen fluoride The supply amount of exhaust gas to the hydrogen fluoride recovery unit 2 with respect to the total supply amount of exhaust gas to the recovery unit 2 can be in the range of 30 to 70%. The adjustment of the ratio of the supply amount is, for example, an adjustment valve that adjusts the ratio of the inner diameters of the gas supply passage 4 and the branch passage 5 or adjusts the gas supply amount in one or both of the gas supply passage 4 and the branch passage 5. This can be done by adjusting the adjusting valve.

  In the calcium fluoride recovery unit 1, fluorine in the gas containing fluorine reacts with calcium hydroxide in an amount exceeding the stoichiometric amount with respect to the fluorine to generate a mixture containing calcium fluoride and calcium hydroxide. (Calcium fluoride recovery process). At this time, as described above, the calcium hydroxide slurry in which calcium hydroxide is dispersed in water is brought into contact with the exhaust gas to react fluorine in the exhaust gas with calcium hydroxide. As this calcium hydroxide slurry, one having a calcium hydroxide content of 20% by weight or less can be used. When the calcium hydroxide slurry comes into contact with the exhaust gas in this way, fluorine is absorbed into the calcium hydroxide slurry and reacts with calcium hydroxide to produce calcium fluoride. This reaction proceeds at a sufficient reaction rate if the pH of the reaction system is 7.5 or higher, but when this pH reaches about 7.5, the reaction rate is not sufficient, and fluorine is sufficiently recovered from the exhaust gas. I can't do that. For this reason, it is preferable that the mixture obtained by the reaction is removed from the calcium fluoride recovery unit 1 when the pH reaches about 7.5. Thereby, an amount of calcium hydroxide exceeding the stoichiometric amount is provided for the reaction with fluorine, and an excessive amount of calcium hydroxide remains in the mixture.

  This mixture contains calcium fluoride produced by the reaction as described above and an excess amount of calcium hydroxide. The content of calcium fluoride in the solid content of this mixture varies depending on the type and content of components other than fluorine in the exhaust gas, but is about 65 to 70% by weight.

  The exhaust gas from which fluorine has been removed by this calcium fluoride recovery step is released from the calcium fluoride recovery unit 1 to the outside. At this time, the fluorine content in the exhaust gas is greatly reduced by removing the fluorine in the calcium fluoride recovery step, and thus the exhaust gas with the reduced fluorine content can be released to the outside.

  On the other hand, in the hydrogen fluoride recovery unit 2, as described above, the exhaust gas and water come into contact with each other to generate a hydrogen fluoride aqueous solution (hydrogen fluoride recovery step). At this time, an aqueous hydrogen fluoride solution is generated by contact between the water circulating between the packed tower 8 and the circulation tank 9 and the exhaust gas, and the concentration of hydrogen fluoride in the aqueous hydrogen fluoride solution reaches a predetermined value. Then, this hydrogen fluoride aqueous solution can be taken out from the hydrogen fluoride recovery unit 2. The concentration of the aqueous hydrogen fluoride solution generated at this time is preferably in the range of 5 to 10% by weight. Even within this range, high-purity synthetic fluorite can be obtained by reaction with the mixture obtained in the calcium fluoride recovery step in the re-reaction step described later. In addition, by reducing the concentration of the aqueous hydrogen fluoride solution in this way, the equipment such as the packed tower 8 of the hydrogen fluoride recovery unit 2 in the hydrogen fluoride recovery step has a high temperature and high concentration aqueous hydrogen fluoride solution. No need for corrosive treatment with hastelloy, noble metals (silver, etc.), copper alloys, monel, molybdenum, etc., which is required when handling the steel. For this reason, for example, the packed tower 8 and the circulation tank 9 of the hydrogen fluoride recovery unit 2 can be formed of vinyl chloride or the like, the packing can be formed of polyethylene or the like, and the piping can be formed of vinyl chloride or polyethylene or the like. .

  The exhaust gas from which fluorine has been removed by the hydrogen fluoride recovery step is discharged to the outside from the hydrogen fluoride recovery unit 2 when the discharge pipe 7 is open to the outside. At this time, the fluorine content in the exhaust gas is greatly reduced by removing the fluorine in the calcium fluoride recovery step, and thus the exhaust gas with the reduced fluorine content can be released to the outside.

  When the exhaust pipe 7 is connected to the gas supply path 4, the exhaust gas from which fluorine has been removed is returned to the gas supply path 4 and supplied to the calcium fluoride recovery unit 1. In this way, when fluorine remains in the exhaust gas after the treatment in the hydrogen fluoride recovery step, the remaining fluorine can be used for generation of calcium fluoride in the calcium fluoride recovery unit 1.

  Next, the mixture obtained in the calcium fluoride recovery step and the hydrogen fluoride aqueous solution obtained in the hydrogen fluoride recovery step are reacted in the re-reaction unit 3 (re-reaction step). At this time, calcium fluoride present in the mixture reacts with hydrogen fluoride in the hydrogen fluoride aqueous solution to produce calcium fluoride. Thereby, a slurry of synthetic fluorite having a calcium fluoride purity higher than that of the mixture is obtained.

  Then, the synthetic fluorite can be obtained by removing the moisture by filtering and drying the synthetic fluorite slurry.

  When synthetic fluorite is produced in this way, calcium hydroxide remaining in the mixture obtained in the calcium fluoride recovery step is further reacted with the hydrogen fluoride aqueous solution obtained in the hydrogen fluoride recovery step, A calcium fluoride content can be improved and a synthetic fluorite with high purity can be obtained.

  That is, in the calcium fluoride recovery step, as described above, in order to recover fluorine efficiently, the pH of the reaction system needs to be in an alkaline region of 7.5 or more. Calcium hydroxide remains in the resulting mixture, and there is a limit in improving the content of calcium fluoride only by the calcium fluoride recovery process, but this remaining calcium hydroxide is converted into hydrogen fluoride. By reacting with hydrogen fluoride in the aqueous hydrogen fluoride solution obtained in the recovery step, calcium fluoride can be generated, the calcium fluoride content can be improved, and high purity synthetic fluorite can be obtained. It is.

  Here, when recovering fluorine from exhaust gas, all the fluorine is recovered as a hydrogen fluoride aqueous solution only by the hydrogen fluoride recovery step, and this aqueous hydrogen fluoride and calcium hydroxide are reacted to generate calcium fluoride. However, in this case, it is necessary to produce a large amount of high-concentration hydrogen fluoride aqueous solution, and the equipment of the hydrogen fluoride recovery unit 2 required for the hydrogen fluoride recovery process is increased in size and The hydrogen fluoride recovery unit 2 needs to be subjected to a corrosion treatment with hastelloy, noble metal (silver, etc.), copper alloy, monel, molybdenum, and the like, resulting in an increase in equipment cost. On the other hand, in the present invention, the equipment of the hydrogen fluoride recovery unit 2 can be downsized, and it is not necessary to perform a corrosive treatment with hastelloy, noble metal (silver, etc.), copper alloy, monel, molybdenum, etc. If there is an existing facility that recovers fluorine in the exhaust gas only by the calcium fluoride recovery process, the hydrogen fluoride recovery unit 2 can be added to the existing facility. The invention can be carried out.

  The other example of the synthetic fluorite manufacturing apparatus shown in FIG. 2 is shown. This synthetic fluorite production apparatus also includes a tertiary calcium phosphate production unit 6, a calcium fluoride collection unit 1, a hydrogen fluoride collection unit 2, and a re-reaction unit 3.

  In the present embodiment, the branch path 5 is not provided, and the hydrogen fluoride recovery unit 2 is provided in the path of the gas supply path 4. As in the example shown in FIG. 1, the hydrogen fluoride recovery unit 2 is configured to generate a hydrogen fluoride aqueous solution by bringing a gas containing fluorine into contact with water. At this time, in the gas flowing through the gas supply path 4 A hydrogen fluoride aqueous solution is generated from a part of the fluorine.

  As such a hydrogen fluoride recovery part 2, the thing provided with the packed tower 8 and the circulation tank 9 similarly to what is shown in FIG. 3 can be used. At this time, a portion of the gas supply path 4 that connects the third calcium phosphate production section 6 and the hydrogen fluoride recovery section 2 is connected to the upstream path 4a, and the hydrogen fluoride recovery section 2 and the calcium fluoride recovery section 1 are connected. The portion is defined as a downstream path 4b. The upstream path 4 a is connected to the packed tower 8, whereby exhaust gas can be supplied to the packed tower 8. Further, the downstream path 4b is led out from the packed tower 8 so that the exhaust gas after being treated in the packed tower 8 can be supplied to the calcium fluoride recovery unit 1 through the downstream path 4b. It has become.

  Other configurations are the same as those shown in FIG.

  Even with such a synthetic fluorite production apparatus, high-purity synthetic fluorite can be obtained in the same manner as shown in FIG. Hereinafter, a method for producing synthetic fluorite will be described.

  First, in the third calcium phosphate production section 6, the third calcium phosphate is produced by thermal decomposition of phosphate ore in the same manner as shown in FIG. 1, and the exhaust gas generated thereby is sent to the gas supply path 4.

  The exhaust gas flowing through the gas supply path 4 is first supplied to the hydrogen fluoride recovery unit 2 from the upstream path 4a. In the hydrogen fluoride recovery unit 2, as in the case shown in FIG. 1, the exhaust gas and water come into contact with each other to generate a hydrogen fluoride aqueous solution (hydrogen fluoride recovery step). At this time, only a part of the fluorine contained in the exhaust gas is used for the generation of the hydrogen fluoride aqueous solution. For this purpose, it is necessary to adjust the fluorine removal performance in the hydrogen fluoride recovery unit 2. For example, this adjustment can be performed by adjusting the superficial velocity, the height of the packed column, the liquid gas ratio, hydrogen fluoride during recovery of the hydrogen fluoride aqueous solution. This can be done by adjusting the density or the like. At this time, it is preferable to adjust so that 30 to 70% of the fluorine initially contained in the exhaust gas is used for the production of hydrogen fluoride in the hydrogen fluoride recovery unit 2.

  The exhaust gas from which part of the fluorine has been removed in the hydrogen fluoride recovery step is supplied to the calcium fluoride recovery unit 1 through the downstream path 4 b of the gas supply path 4. In the calcium fluoride recovery unit 1, as in the case shown in FIG. 2, fluorine in the gas containing fluorine reacts with an amount of calcium hydroxide exceeding the stoichiometric amount with respect to the fluorine, and calcium fluoride and water A mixture containing calcium oxide is generated (calcium fluoride recovery step), and the exhaust gas from which fluorine has been removed by this calcium fluoride recovery step is released from the calcium fluoride recovery unit 1 to the outside.

  Next, the mixture obtained in the calcium fluoride recovery step and the hydrogen fluoride aqueous solution obtained in the hydrogen fluoride recovery step are reacted in the re-reaction unit 3 in the same manner as shown in FIG. 1 (re-reaction step). . Thus, a synthetic fluorite slurry can be obtained, and the synthetic fluorite slurry can be filtered and dried to remove moisture to obtain a synthetic fluorite.

  In each of the above embodiments, the tricalcium phosphate production unit 6 is used as a supply source of fluorine-containing gas, and exhaust gas generated in the process of producing tricalcium phosphate by pyrolysis of phosphate rock is used as the fluorine-containing gas. However, the gas containing fluorine is not limited to this, and an appropriate gas can be used.

  Hereinafter, the present invention will be described in more detail with reference to examples.

  As a synthetic fluorite production apparatus, the one shown in FIG. 1 was used.

  At this time, what was comprised with the rotary kiln was used as the tertiary calcium-phosphate manufacturing part 6. FIG. This tertiary calcium phosphate production section 6 uses C heavy oil as combustion fuel, and heats the pulverized phosphate ore together with the reaction promoting third component in the range of 1300 to 1500 ° C. to produce tertiary calcium phosphate. Equipment.

  Further, as the calcium fluoride recovery unit 1, a unit having the same apparatus configuration as that shown in FIG. 3 was used. However, in this calcium fluoride collection | recovery part 1, it replaces with the packed tower 8 in FIG. 3, and the spray tower is provided. In this calcium fluoride recovery unit 1, a calcium hydroxide slurry having a concentration of 6% by weight is used as an absorbing solution, and when the pH of the absorbing solution is gradually lowered to a value close to 7.5, A part was extracted and 10% by weight of lime milk was supplemented to the reduced absorption liquid. By repeating this operation, the pH of the absorbing solution was maintained in an alkaline state in the range of 9 to 7.5. And the extracted absorption liquid was collect | recovered as a slurry-like mixture of pH 7.5 containing calcium fluoride and calcium hydroxide.

The hydrogen fluoride recovery unit 2 includes a packed tower 8 made of vinyl chloride having a height of 4000 mm and a diameter of 200 mm and filled with a polyethylene filler (“HIREX II 125” made by Toyo Rubber), and an absorbing solution. A vinyl chloride circulation tank 9 for storing industrial water is connected by a circulation path 10 made of vinyl chloride and polyethylene. Then, the exhaust gas is circulated in the packed tower 8 and the industrial water is circulated between the circulation tank 9 and the packed tower 8 by the pump 11 so that the liquid gas ratio L / G = 1 L / 1 m ³ and the superficial velocity 1 m. It was operated under the conditions of / sec to obtain an aqueous hydrogen fluoride solution.

Example 1
In the container, the aqueous solution of hydrogen fluoride having a temperature of 60 ° C. obtained in the hydrogen fluoride recovery step was added to the slurry mixture having a temperature of 45 ° C. obtained in the calcium fluoride recovery step over 10 minutes. At this time, the same operation was performed for each of the 5% by weight and 10% by weight hydrogen fluoride aqueous solutions, and the amount of hydrogen fluoride aqueous solution added was the same as that of hydrogen fluoride relative to the amount of calcium hydroxide remaining in the mixture. The amount of hydrogen fluoride was 1.2 times (120%) the stoichiometric amount.

  After the addition of hydrogen fluoride was completed, the mixture was allowed to react for 4 hours in a container. After filtering under reduced pressure using 5C filter paper, it was dried by heating at 105 ° C. for 6 hours to obtain synthetic fluorite. The result of measuring the calcium fluoride content of this synthetic fluorite by the ion electrode method defined in JIS K0105 is shown in FIG.

  As shown in the figure, the measurement result of the purity of the synthetic fluorite when using an aqueous solution of hydrogen fluoride having a concentration of 5% by weight is 90.5% by weight, and when the aqueous solution of hydrogen fluoride having a concentration of 10% by weight is used. The purity measurement result is 89% by weight, and almost the same high-purity synthetic fluorite can be obtained, and high-purity synthetic fluorite is obtained when the concentration of the aqueous hydrogen fluoride is in the range of 5 to 10% by weight It was confirmed that it was possible.

(Example 2)
In a container, the aqueous hydrogen fluoride solution at a temperature of 60 ° C. obtained at the hydrogen fluoride recovery step was added to the slurry mixture at a temperature of 45 ° C. obtained at the calcium fluoride recovery step over 10 minutes. At this time, an aqueous hydrogen fluoride solution having a concentration of 5% by weight is used, and the addition amount of the aqueous hydrogen fluoride solution is 1. the stoichiometric amount of hydrogen fluoride with respect to the amount of calcium hydroxide remaining in the product. The amount of hydrogen fluoride contained twice (120%).

  After completing the addition of hydrogen fluoride, the reaction is carried out in three conditions: 0 hour (immediately after addition), 2 hours, 4 hours, and the slurry-like synthetic fluorite obtained for each reaction time. No. After filtering under reduced pressure using 5C filter paper, it was dried by heating at 105 ° C. for 6 hours to obtain synthetic fluorite. FIG. 5 shows the result of measuring the calcium fluoride content of this synthetic fluorite by the ion electrode method defined in JIS K0105.

  As shown in the figure, the measurement result of the purity of the synthetic fluorite is slightly lower when the reaction time is 0 hour, but the fluctuation of the purity with respect to the reaction time is small, and the synthetic fluorite with high purity due to high reaction efficiency in a short reaction time. I was able to confirm that

(Example 3)
In a container, the aqueous hydrogen fluoride solution at a temperature of 60 ° C. obtained at the hydrogen fluoride recovery step was added to the slurry mixture at a temperature of 45 ° C. obtained at the calcium fluoride recovery step over 10 minutes. At this time, an aqueous hydrogen fluoride solution having a concentration of 5% by weight was used, and the addition amount of the aqueous hydrogen fluoride solution was 90% of the stoichiometric amount of hydrogen fluoride with respect to the amount of calcium hydroxide remaining in the product. , 100%, 110%, or 120% hydrogen fluoride.

  After the addition of hydrogen fluoride was completed, the reaction was allowed to stand for 4 hours. After filtering under reduced pressure using 5C filter paper, it was dried by heating at 105 ° C. for 6 hours to obtain synthetic fluorite. FIG. 6 shows the result of measuring the calcium fluoride content of this synthetic fluorite by the ion electrode method defined in JIS K0105.

  As shown in the figure, the measurement result of the purity of the synthetic fluorite is slightly lower when the addition amount of hydrogen fluoride is 90% of the stoichiometric amount, but the addition amount is 100% or more of the stoichiometric amount. If so, it was confirmed that a synthetic fluorite having a sufficiently high purity could be obtained although the purity gradually increased as the amount added increased.

Example 4
In a container, the hydrogen fluoride aqueous solution having a concentration of 5% by weight obtained in the hydrogen fluoride recovery step was added over 10 minutes to the slurry mixture having a temperature of 45 ° C. obtained in the calcium fluoride recovery step. At this time, as the hydrogen fluoride aqueous solution, one having a temperature of 60 ° C. immediately after obtained in the hydrogen fluoride recovery step and one having been cooled to 25 ° C. were used. The amount of hydrogen fluoride aqueous solution added was an amount containing 120% hydrogen fluoride of the stoichiometric amount of hydrogen fluoride with respect to the amount of calcium hydroxide remaining in the product.

  After the addition of hydrogen fluoride was completed, the reaction was allowed to stand in a container for 4 hours. After filtering under reduced pressure using 5C filter paper, it was dried by heating at 105 ° C. for 6 hours to obtain synthetic fluorite. FIG. 7 shows the result of measuring the calcium fluoride content of this synthetic fluorite by the ion electrode method defined in JIS K0105.

  As shown in the figure, the measurement result of the purity of the synthetic fluorite shows that a synthetic fluorite having a purity of 87% is obtained even when the temperature of the hydrogen fluoride to be added is 25 ° C., but this temperature is higher at 60 ° C. It was confirmed that it is preferable to use an aqueous hydrogen fluoride solution having a temperature of about 60 ° C. immediately after being obtained in the hydrogen fluoride recovery step.

(Example 5)
The slurry-like mixture obtained by the calcium fluoride recovery process was No. After filtration under reduced pressure using 5C filter paper, it was dried by heating at 105 ° C. for 6 hours. As a result of measuring the calcium fluoride content in the obtained solid mixture by the ion electrode method specified in JIS K0105, it was 69% by weight.

  In addition, using the slurry-like mixture obtained at the temperature of 45 ° C. obtained in the same calcium fluoride recovery step as described above, synthetic fluorite was produced seven times under the same conditions as in Example 3, and the resulting synthetic fluorite was obtained. The calcium fluoride content of the stone was measured by the ion electrode method specified in JIS K0105.

  These results are shown in Table 1.

  As shown in Table 1, even when the same method is repeated to produce synthetic fluorite, the purity of the resulting synthetic fluorite is small, so that the method is highly reproducible and practical. It could be confirmed.

(Example 6)
In a container, the aqueous solution of hydrogen fluoride at a temperature of 60 ° C. obtained at the hydrogen fluoride recovery step was added to the mixture at a temperature of 45 ° C. obtained at the calcium fluoride recovery step over 10 minutes. At this time, a hydrogen fluoride aqueous solution having a concentration of 5% by weight was used, and the addition amount of the hydrogen fluoride aqueous solution was 120% of the stoichiometric amount of hydrogen fluoride with respect to the amount of calcium hydroxide remaining in the product. Of hydrogen fluoride.

  After the addition of hydrogen fluoride was completed, the reaction was allowed to stand for 4 hours. After filtering under reduced pressure using 5C filter paper, it was dried by heating at 105 ° C. for 6 hours to obtain synthetic fluorite.

  Moreover, the slurry-like mixture obtained by the calcium fluoride recovery step was filtered and dried under the same conditions as above to obtain a solid mixture.

  Table 2 below shows the results of component analysis of the above solid mixture, synthetic fluorite, and acid grade natural fluorite. Calcium fluoride was analyzed by lanthanum / alizarin complexone spectrophotometry specified in JIS K0105, and other components were analyzed by atomic absorption spectrophotometry specified in JIS K0102.

As shown in Table 2, when the measurement results of the solid mixture and the synthetic fluorite are compared, the content of CaO, which seems to be caused by calcium hydroxide, is greatly reduced in the synthetic fluorite, and the content of CaF ₂ is reduced. In the present invention, it was confirmed that synthetic fluorite with high purity can be obtained by converting calcium hydroxide remaining in the mixture into calcium fluoride.

In addition, comparing the measurement results of synthetic fluorite and acid grade natural fluorite, the content of CaF _{2 in} synthetic fluorite does not reach that of acid grade natural fluorite, and other components other than CaF ₂ are contained. The amount was generally high, and it was confirmed that the sulfur content was particularly high. Impurities in these synthetic fluorites are thought to be mainly due to dusting (scattering) of raw materials used in the production process of tricalcium phosphate in exhaust gas and mixing of components in fuel for heating. For this reason, if these impurities are removed by subjecting the exhaust gas to dust collection before being subjected to the calcium fluoride recovery step and the hydrogen fluoride recovery step, the purity of the synthetic fluorite can be further improved. I can expect. Moreover, since it is thought that the high sulfur content is caused by the use of C heavy oil with a high sulfur content for combustion, a B heavy oil or A heavy oil with a low sulfur content is used as fuel, or If natural gas containing no sulfur is used, further improvement in the purity of the synthetic fluorite can be expected.

It is the schematic which shows an example of embodiment of this invention. It is the schematic which shows the other example of embodiment of this invention. It is the schematic which shows an example of a structure of the hydrogen fluoride collection | recovery part in embodiment same as the above. 4 is a graph showing measurement results in Example 1. 6 is a graph showing measurement results in Example 2. 10 is a graph showing measurement results in Example 3. It is a graph which shows the measurement result in Example 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Calcium fluoride recovery part 2 Hydrogen fluoride recovery part 3 Re-reaction part 4 Gas supply path 5 Branch path 6 Tricalcium phosphate production part

Claims (6)

  A calcium fluoride recovery step of reacting fluorine in the gas containing fluorine with calcium hydroxide in an amount exceeding the stoichiometric amount with respect to the fluorine to produce a mixture containing calcium fluoride and calcium hydroxide; A hydrogen fluoride recovery step of bringing a gas containing the solution into contact with water to generate a hydrogen fluoride aqueous solution; a mixture obtained in the calcium fluoride recovery step; and a hydrogen fluoride aqueous solution obtained in the hydrogen fluoride recovery step. A method for producing synthetic fluorite, comprising a re-reaction step of reacting to produce synthetic fluorite.   The method for producing synthetic fluorite according to claim 1, wherein the gas containing fluorine is exhaust gas generated in a process of producing tricalcium phosphate by thermal decomposition of phosphate ore.   A calcium fluoride recovery unit that reacts fluorine in a gas containing fluorine with calcium hydroxide in an amount exceeding the stoichiometric amount with respect to the fluorine to form a mixture containing calcium fluoride and calcium hydroxide; A hydrogen fluoride recovery unit that generates a hydrogen fluoride aqueous solution by bringing a gas containing the water into contact therewith, a mixture obtained by the calcium fluoride recovery unit, and a hydrogen fluoride aqueous solution obtained by the hydrogen fluoride recovery unit. An apparatus for producing synthetic fluorite, comprising: a re-reaction unit that reacts to produce synthetic fluorite.   A gas supply path for supplying a gas containing fluorine to the calcium fluoride recovery section, and a branch path for branching from the gas supply path to supply a gas containing fluorine to the hydrogen fluoride recovery section, The synthetic fluorite manufacturing apparatus according to claim 3.   A gas supply path for supplying a gas containing fluorine to the calcium fluoride recovery section, and the hydrogen fluoride recovery section generates a hydrogen fluoride aqueous solution from a part of the fluorine in the gas flowing through the gas supply path The apparatus for producing synthetic fluorite according to claim 3, wherein The starting end of the gas supply path is connected to a tertiary calcium phosphate production unit that produces tricalcium phosphate by thermal decomposition of phosphate ore, and as a gas containing fluorine, the tertiary calcium phosphate by pyrolysis of the phosphate ore in the tertiary calcium phosphate production unit The apparatus for producing synthetic fluorite according to claim 4 or 5 , characterized in that exhaust gas generated in a process for producing the fluorite is supplied.

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