JP2013220955A - Method and apparatus for producing calcium fluoride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provided a method for producing, from drain water containing hydrosilicofluoric acid, calcium fluoride having a particle size and high purity suitable as a material for producing hydrofluoric acid.SOLUTION: A method for producing calcium fluoride comprises: a step [1] of reacting hydrosilicofluoric acid-containing water with a potassium compound and producing a first reaction product that includes insoluble silica and a potassium fluoride aqueous solution; a step [2] of separating the insoluble silica from the first reaction product; a step [3] of reacting the first reaction product, from which the insoluble silica has been separated, with calcium carbonate and producing a second reaction product that includes calcium fluoride and a potassium carbonate aqueous solution; and a step [4] of separating the potassium carbonate aqueous solution from the second reaction product.

Description

The present invention relates to a method and an apparatus for producing calcium fluoride suitable as a raw material for producing hydrofluoric acid by decomposing wastewater containing silicohydrofluoric acid (H ₂ SiF ₆ ).

  Conventionally, calcium fluoride is synthesized and recovered from wastewater containing hydrofluoric acid discharged in the semiconductor industry, chemical industry, etc., and recycled using the obtained calcium fluoride as a raw material for the production of hydrofluoric acid Technology is known.

上記の反応式（１）のような反応を用いてフッ化水素酸を製造する場合、例えば、２００℃以上の反応温度で、ローターリーキルン内にて行われる。この時、原料となるフッ化カルシウム中に水酸化カルシウムや炭酸カルシウムが存在した場合、下記の反応式（２）および反応式（３）に示すように、水を副生する反応が生じてしまう。

また、ＳｉＯ_２を含むフッ化カルシウムを使用した場合、下記の反応式（４）に示すように、キルン内で生成したフッ化水素酸との反応により、Ｈ_２ＳｉＦ_６を形成し、合成するフッ化水素酸をロスするばかりか、副生するＨ_２Ｏにより、やはり、ロータリーキルンの腐食の原因となってしまう。

上記の反応式（２）〜（４）のように水が副生した場合、キルン内はフッ酸環境下であるため、キルン装置に通常用いられている鉄系金属材料を腐食させてしまう。このことにより、フッ酸製造装置の装置寿命が短くなってしまうため、できるだけフッ化カルシウムは純度の高いものが好ましい。 By utilizing this kind of recycling technology, calcium fluoride is recovered and, as shown in the following reaction formula (1), calcium fluoride and sulfuric acid are reacted to generally produce hydrofluoric acid. It has been broken.

When manufacturing hydrofluoric acid using reaction like said Reaction formula (1), it is performed in a rotary kiln with the reaction temperature of 200 degreeC or more, for example. At this time, when calcium hydroxide or calcium carbonate is present in the calcium fluoride used as a raw material, as shown in the following reaction formula (2) and reaction formula (3), a reaction that produces water as a by-product occurs. .

Further, when calcium fluoride containing SiO ₂ is used, H ₂ SiF ₆ is formed and synthesized by reaction with hydrofluoric acid generated in the kiln as shown in the following reaction formula (4). Not only does hydrofluoric acid be lost, but also by-product H ₂ O still causes corrosion of the rotary kiln.

When water is by-produced as in the above reaction formulas (2) to (4), since the inside of the kiln is in a hydrofluoric acid environment, the iron-based metal material usually used in the kiln apparatus is corroded. As a result, the life of the hydrofluoric acid production apparatus is shortened, so that the calcium fluoride is preferably as pure as possible.

  Moreover, when manufacturing hydrofluoric acid with a rotary kiln, it is necessary to make the calcium fluoride used as a raw material into the magnitude | size which can flow in a kiln. As the raw material calcium fluoride, acid grade fluorite (mainly calcium fluoride) that is naturally present is generally used, and the natural fluorite can be flowed in a kiln, for example, 15 It is used after being pulverized to an average particle size of about ˜300 μm. Therefore, when recovering calcium fluoride by a recycling technique, it is preferable to obtain an average particle size of about 15 to 300 μm.

  Against this backdrop, calcium fluoride is recovered using fluorine-containing wastewater recycling technology such as silicofluoric acid, and hydrofluoric acid is produced using the recovered calcium fluoride. For this, it is important to make the particle size of calcium fluoride moderately and to use calcium fluoride having high purity not containing impurities.

  As a technique for recovering calcium fluoride from wastewater containing silicofluoric acid, mainly, 1) a method of directly synthesizing hydrofluoric acid-containing water and calcium carbonate to synthesize calcium fluoride, and 2) hydrogen silicofluoride A method of synthesizing calcium fluoride by passing fluorine contained in acid-containing water through a fluoride salt is known.

また、特許文献２には、下記の反応式（６）のように、ケイフッ化水素酸を含むフッ素含有排水と炭酸ナトリウムなどのナトリウム化合物を混合して、ケイフッ化水素酸を分解し、不溶性のシリカとフッ化ナトリウムの水溶液との混合物を生じさせ、次いで、得られたフッ化ナトリウムの水溶液から、晶析技術などによって、フッ化カルシウムを回収する技術が開示されている。

For example, in Patent Document 1, when the silicohydrofluoric acid water and calcium carbonate are directly reacted, the concentration of silicohydrofluoric acid water and the pH during the reaction are controlled as shown in the following reaction formula (5). Discloses a technique for directly synthesizing calcium fluoride.

Further, in Patent Document 2, as shown in the following reaction formula (6), a fluorine-containing wastewater containing hydrofluoric acid and a sodium compound such as sodium carbonate are mixed to decompose hydrofluoric acid, thereby insoluble. A technique is disclosed in which a mixture of silica and an aqueous solution of sodium fluoride is formed, and then calcium fluoride is recovered from the obtained aqueous solution of sodium fluoride by a crystallization technique or the like.

U.S. Pat. No. 2,780,523 JP 2009-196858 A

  In the method of directly synthesizing calcium fluoride by directly reacting silicohydrofluoric acid water and calcium carbonate as in Patent Document 1, as shown in the reaction formula (5), calcium fluoride and silica are simultaneously precipitated and mixed. In reality, it is difficult to recover high-purity calcium fluoride.

  The method via a fluoride salt such as sodium fluoride as described in Patent Document 2 does not cause calcium fluoride and silica to precipitate simultaneously as in the above reaction formula (5). It is an excellent method for synthesizing and recovering calcium fluoride.

  However, in the method described in Patent Document 2, since sodium fluoride has low solubility in water, it is necessary to enlarge the reaction system in order to form a sufficient amount of aqueous sodium fluoride solution. As a result, there has been a problem that the recovery device and the like are likely to be large and complicated, and the running cost for manufacturing and maintaining the device becomes high.

  As described above, various techniques for recovering and reusing calcium fluoride from fluorine-containing wastewater such as silicohydrofluoric acid have been disclosed. However, the recovered particle size, purity, cost of the recovery device, etc. There is a problem, and the recycling technology of the collected material has not been established yet.

  The present invention has been made in view of the above problems, and provides a simple method for producing calcium fluoride suitable as a raw material for producing hydrofluoric acid from wastewater containing hydrofluoric acid. With the goal.

  As a result of intensive studies to solve the above problems, the present inventors have paid attention to the solubility in water of a fluoride salt that is passed through when the fluorine of silicofluoric acid water is converted to calcium fluoride. It has been found that high purity and particle size calcium fluoride suitable as a raw material for the production of hydrofluoric acid can be produced by reacting a potassium compound having a high solubility with respect to silicic hydrofluoric acid water.

  That is, the present invention is a method for producing calcium fluoride using silicohydrofluoric acid-containing water, wherein the first reaction includes insoluble silica and an aqueous potassium fluoride solution by reacting silicohydrofluoric acid-containing water with a potassium compound. A step [1] of generating a product, a step [2] of separating insoluble silica from the first reaction product, a reaction of the first reaction product from which the insoluble silica has been separated with calcium carbonate, and calcium fluoride, A method for producing calcium fluoride comprising a step [3] of generating a second reaction product containing an aqueous potassium carbonate solution and a step [4] of separating the aqueous potassium carbonate solution from the second reaction product.

  Moreover, in this invention, you may make it also include the process [5] which reuses the potassium carbonate aqueous solution isolate | separated at the said process [4] as a potassium compound raw material of the said process [1].

  According to this configuration, since the separated potassium carbonate aqueous solution can be reused as a potassium compound raw material, the amount of potassium compound used in this step can be reduced, and the merit of manufacturing cost reduction can be obtained. It is done.

  According to the present invention, the fluoride salt that is passed through when the fluorine of silicohydrofluoric acid water is converted to calcium fluoride has sufficient solubility in water. Therefore, to provide calcium fluoride having a high purity and particle size suitable as a raw material for producing hydrofluoric acid with a simpler apparatus configuration without increasing the size of the apparatus in the calcium fluoride production process. Is possible.

It is process schematic of the manufacturing method of the calcium fluoride which concerns on this invention. It is the schematic which shows an example of the manufacturing apparatus of the calcium fluoride which concerns on this invention. It is detail drawing of the calcium fluoride synthesis tank vicinity which concerns on this invention. 2 is an X-ray diffraction pattern of calcium fluoride obtained in Example 1. FIG. 2 is an X-ray diffraction pattern of a sedimentation component obtained in Example 1. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. First, with reference to FIGS. 2 and 3, an example of a calcium fluoride production apparatus 100 applicable to the embodiment of the present invention will be described.

  The apparatus 100 for producing calcium fluoride according to the present invention reacts hydrofluoric acid-containing water with a potassium compound to produce a first reaction product containing insoluble silica and an aqueous potassium fluoride solution by neutralization and decomposition. 60, a calcium fluoride synthesis tank 10 for reacting calcium carbonate with a first reaction product from which insoluble silica has been separated to produce a second reaction product containing calcium fluoride and an aqueous potassium carbonate solution, and synthesized calcium fluoride And a dehydrating device 30 for dehydrating the slurry liquid containing the solid liquid separation operation.

  The neutralization / decomposition tank 60 includes a raw water supply pipe 61 for introducing wastewater containing hydrofluoric acid-containing water into the neutralization / decomposition tank 60 via a supply pump 60a, and a potassium compound that promotes the neutralization / decomposition reaction. An alkali agent supply unit 62 for supplying an alkali agent and a silica separation water discharge pipe 63 for discharging silica separation water (first reaction product from which insoluble silica has been separated) as a supernatant of the reaction solution are provided via a discharge pump 60b. It is connected. Further, a first slurry discharge pipe 64 for discharging the precipitated insoluble silica slurry is connected to the bottom of the neutralization decomposition tank 60 via a discharge pump 67a. In addition, in the neutralization decomposition tank 60, you may make it install the stirrer 66 and the pH measuring device (not shown) which measures the pH of the reaction solution in the neutralization decomposition tank 60 via the motor 65. . Moreover, you may provide the dilution water supply part (not shown) which supplies dilution water in the neutralization decomposition tank 60 as needed. As a preferred example of the dilution water supply unit, a heat source may be secured by using steam instead of dilution water in order to dissolve the alkali agent and promote the neutralization reaction.

  A dehydrator 67 for dehydrating the discharged insoluble silica slurry is connected to the downstream of the first slurry discharge pipe 64 via a discharge pump 67a. Furthermore, a circulation pipe 68 for returning the desorbed water separated by the dehydration to the neutralization decomposition tank 60 may be connected to the dehydrator 67. Since the desorbed water recovered via the circulation pipe 68 contains an alkali component derived from a potassium compound, it can be reused as a raw material liquid for the neutralization decomposition reaction. The separated silica cake (silica slurry having a low water content) is separately collected. Similarly, the desorbed water recovered via the circulation pipe 69 may be connected to the waste liquid storage tank 70 so that the desorbed water is reused as a raw material liquid.

  A storage tank (not shown) for adding a flocculant for precipitating insoluble silica components that could not be separated may be provided in the path of the silica separation water discharge pipe 63 as necessary. As the aggregating agent to be used, generally known ones such as an inorganic type and a polymer type can be used. For example, aluminum sulfate, polyaluminum chloride, sodium aluminate, iron (II) sulfate, chlorinated green vane, sodium caseinate, gelatin, gum arabic, dextrin, starch and the like can be mentioned.

  Further, a calcium fluoride synthesis tank 10 is connected downstream of the silica separation water discharge pipe 63 via a discharge pump 60b, and calcium carbonate is added to the calcium fluoride synthesis tank 10 in the calcium fluoride synthesis tank 10. A calcium carbonate introduction device 40 to be introduced into the second slurry discharge pipe 14 is connected to a second slurry discharge pipe 14 for discharging a slurry liquid (second reaction product) containing synthetic calcium fluoride and a potassium carbonate component via a discharge pump 20b.

  As shown in FIG. 3, a dehydrator 30 is connected downstream of the second slurry liquid discharge pipe 22 via a discharge pump 20b. A cleaning liquid supply pipe 31 for supplying a cleaning liquid for cleaning the slurry liquid sent via the second slurry liquid discharge pipe 22 is connected to the dehydrator 30 via a supply pump 30a as necessary. . As the cleaning liquid, an organic solvent such as water or ethanol can be used. For example, pure water having a chlorine component of 10 mg / L or less may be used from the viewpoint of the residual chlorine component.

  Further, the dehydrating device 30 is provided with a calcium fluoride recovery pipe 32, and the synthetic calcium fluoride 50 after dehydration and washing is recovered by the pipe 32. As the dehydrator 30, a centrifugal separator is usually used, but as other methods, for example, a filter press dehydrator or a filtration dehydrator (nonwoven fabric filter type) may be used.

  An outer jacket 12 through which a heat medium or the like can be circulated is provided around the outer periphery of the calcium fluoride synthesis tank 10, and the internal temperature is adjusted in order to promote the reaction between the aqueous potassium fluoride solution and calcium carbonate. The method of the outer jacket 12 is not particularly limited, but for example, an electric heater using a Peltier element or the like may be used. In addition, a stirrer 13 may be installed in the calcium fluoride synthesis tank 10 via a motor 15 to stir the inside. When an external jacket is not used, heated steam as a heat source may be directly fed into the calcium fluoride synthesis tank 10.

  The material of the calcium fluoride synthesis tank 10 is not particularly limited, but for long-term durability, for example, a fluororesin such as PFA or PTFE, a resin such as FRP, or a rubber lining tank may be used.

  The calcium carbonate introduction device 40 includes a granular calcium carbonate receiving popper 41 and a screw feeder 42 for supplying calcium carbonate, and the supply amount (supply speed) of the calcium carbonate is adjusted by the screw feeder 42. The The supply rate of calcium carbonate is appropriately adjusted depending on the reaction situation.

  A desorption water discharge pipe 71 for discharging desorption water (potassium carbonate aqueous solution) obtained by solid-liquid separation operation of the dehydration apparatus 30 is connected to the dehydration apparatus 30 via a discharge pump 70a. A waste liquid storage tank 70 for storing desorbed water is provided downstream of the discharge pipe 71. Further, the waste liquid storage tank 70 is connected to a circulation pipe 72 for returning the stored desorbed water to the neutralization decomposition tank 60, and the desorbed water whose potassium carbonate concentration is adjusted is used as a raw material for the alkaline component. It can be reused in the sum decomposition tank 60. In order to adjust (for example, concentrate) the potassium carbonate concentration of the stored desorbed water in the waste liquid storage tank 70, a method using sun drying and membrane separation can be used.

  Next, a method for producing calcium fluoride (steps [1] to [5]) will be described. FIG. 1 is a process schematic diagram of a method for producing calcium fluoride according to the present invention.

  First, step [1] of the present invention will be described. Step [1] is a step [1] in which silicohydrofluoric acid-containing water and a potassium compound are reacted to generate a first reaction product containing insoluble silica and an aqueous potassium fluoride solution.

  Specifically, as shown in FIG. 2, the hydrofluoric acid-containing water is supplied to the neutralization / decomposition tank 60 through the raw water supply pipe 61 from a tank in which wastewater containing hydrofluoric acid is stored. The Next, a potassium compound such as potassium carbonate is added from the alkali agent supply unit 62, and as shown in the following reaction formula (7), hydrofluoric acid is neutralized and decomposed to contain insoluble silica and an aqueous potassium fluoride solution. A first reaction product is produced.

  The reaction conditions of the reaction formula (7) are preferably such that the pH is 7 to 14, the reaction temperature is 40 to 100 ° C., more preferably 50 to 80 ° C., and the reaction time is at least 1 hour or more. . Moreover, it is preferable to adjust the quantity of the potassium compound thrown in to 1.1-10 equivalent of the quantity required for reaction with silicohydrofluoric acid. In addition, the pressure at the time of performing reaction does not have a restriction | limiting in particular, It is good to carry out at a normal pressure.

カリウム化合物は、カリウムイオンの水和エネルギーが高いため水に対する溶解性が非常に高く、例えば、フッ化カリウム（ＫＦ）の溶解度は、常温で約９２０ｇ／１０００ｇ−Ｈ_２Ｏである。本発明の工程にて経由するフッ化物塩（フッ化カリウム）は、特開２００９−１９６８５８（特許文献２）にて開示されるフッ化物塩である、フッ化ナトリウム（溶解度：４０ｇ／１０００ｇ−Ｈ_２Ｏ）に比べて溶解度が極めて大きい。そのため、フッ化カリウムの場合、溶解度の低さに起因するフッ化ナトリウムのような結晶析出（沈降）が起こりにくく、より少量の水で、より多くのフッ素源を水溶液中に存在させることができ、反応系を大型化する必要がない。また、特許文献２のような析出したフッ化ナトリウム結晶を溶解するための希釈水配管などを別途設置する必要がなく、製造設備を簡便化することができる。さらに、本発明によれば、フッ化物塩の濃度を高くできるため、より純度の高いフッ化カルシウムを合成することが可能となる。 When the pH is less than 7, reaction formula (7) is difficult to proceed, and the reaction for producing potassium salt (K ₂ SiF ₆ ) as shown in reaction formula (8) proceeds, which is not preferable. When the reaction temperature is lower than 40 ° C., a sufficient reaction of the following reaction formula (7) does not proceed and the reaction formula (8) proceeds, which is not preferable. As the volatilization amount of the liquid increases or it may cause boiling, it is not suitable as the reaction temperature. If the reaction time is less than 1 hour, the reaction may not be completed.

A potassium compound has a very high solubility in water since the hydration energy of potassium ions is high. For example, the solubility of potassium fluoride (KF) is about 920 g / 1000 g-H ₂ O at room temperature. The fluoride salt (potassium fluoride) passed through the process of the present invention is a sodium fluoride (solubility: 40 g / 1000 g-H) which is a fluoride salt disclosed in JP2009-196858 (Patent Document 2). _The solubility is much higher than that of ₂ O). Therefore, in the case of potassium fluoride, crystal precipitation (precipitation) unlike sodium fluoride due to low solubility is unlikely to occur, and more fluorine source can be present in the aqueous solution with a smaller amount of water. It is not necessary to enlarge the reaction system. Further, it is not necessary to separately install a dilution water pipe for dissolving the precipitated sodium fluoride crystal as in Patent Document 2, and the manufacturing equipment can be simplified. Furthermore, according to the present invention, since the concentration of the fluoride salt can be increased, calcium fluoride with higher purity can be synthesized.

  The potassium compound is not particularly limited as long as it has sufficient solubility in water. For example, common compounds such as potassium carbonate, potassium hydrogen carbonate, potassium oxide, and potassium hydroxide can be used. These compounds can be used as at least one kind or a mixture of two or more kinds thereof. Among these, potassium carbonate is particularly suitable from the viewpoints of chemical stability and availability.

  Next, process [2] in this invention is demonstrated. Step [2] is a step of separating insoluble silica from the first reaction product obtained in step [1]. A potassium fluoride-containing liquid is separated from the first reaction product by a sedimentation operation. As separate. The separated supernatant liquid is discharged from the silica separated water discharge pipe 63 and is sent to the calcium fluoride synthesis tank 10 via the discharge pump 60b. The method for the sedimentation operation is not particularly limited, and can be performed, for example, by an operation (such as decantation) of allowing the first reaction product to stand still for a predetermined time.

反応式（９）の反応条件は、反応温度は、４０〜８０℃、より好ましくは５０〜７０℃、反応時間は、少なくとも３時間以上、の範囲で行うことが好ましい。また、フッ化カリウムは、投入する炭酸カルシウムとの反応に必要な量の１．１〜１０当量になるように調整することが好ましい。なお、反応を行う際の圧力は特に制限はなく、常圧にて行うとよい。また、反応条件におけるｐＨは、特に制限はないが、中和処理剤などの処理上の負担が掛からない範囲（例えば、ｐＨが７〜１０程度）で適宜設定するとよい。 Next, process [3] in this invention is demonstrated. In the step [3], the first reaction product (potassium fluoride-containing liquid) obtained by separating the insoluble silica obtained in the step [2] is reacted with calcium carbonate, so that the second containing the calcium fluoride and the potassium carbonate aqueous solution. This is a step of generating a reaction product. In the synthesis of calcium fluoride, the reaction proceeds as shown in the following reaction formula (9).

Regarding the reaction conditions of the reaction formula (9), the reaction temperature is preferably 40 to 80 ° C., more preferably 50 to 70 ° C., and the reaction time is preferably at least 3 hours. Moreover, it is preferable to adjust potassium fluoride so that it may become 1.1-10 equivalent of the quantity required for reaction with the calcium carbonate to introduce | transduce. In addition, the pressure at the time of performing reaction does not have a restriction | limiting in particular, It is good to carry out at a normal pressure. The pH under the reaction conditions is not particularly limited, but may be appropriately set within a range where the processing burden such as the neutralizing agent is not applied (for example, the pH is about 7 to 10).

  When the reaction temperature is lower than 40 ° C., the reaction of the above reaction formula (9) does not proceed sufficiently, which is not preferable. On the other hand, when the reaction temperature is higher than 80 ° C., calcium fluoride collapses during synthesis. Is not preferable because calcium fluoride having an average particle diameter (15 to 300 μm) suitable as a raw material for hydrofluoric acid production cannot be obtained. If the reaction time is less than 3 hours, the reaction may not be completed.

  In the present specification, the “average particle diameter” means a particle diameter at an integrated value of 50% (median diameter) in a particle size distribution obtained by a laser diffraction / scattering method. A detailed method for measuring the average particle diameter will be described in Example 1 described later.

  Specifically, as shown in FIG. 3, the granular carbonic acid contained in the receiving hopper 41 in the first reaction product (potassium fluoride aqueous solution) obtained by separating the insoluble silica sent to the calcium fluoride synthesis tank 10. Calcium is introduced into the calcium fluoride synthesis tank 10 through the screw feeder 42 while adjusting the supply amount.

  In addition, in this invention, the introduction method of calcium carbonate is not limited to said method, It sets suitably. In addition, for the step [3], it is preferable to use a batch process that easily secures a sufficient reaction time in order to cause the conversion reaction of calcium fluoride from calcium carbonate to proceed completely.

  As the calcium carbonate introduction device 40, in addition to the method of directly adding granular calcium carbonate, a separate adjustment tank is provided, the calcium carbonate slurry solution is adjusted, and the calcium carbonate slurry solution is charged into the calcium fluoride synthesis tank 10. However, in the present invention, the direct injection method of granular calcium carbonate is more preferable.

  The reason for this is that when a slurry solution of calcium carbonate is added, an adjustment tank for adjusting the slurry solution needs to be provided separately, or the volume of the calcium fluoride synthesis tank 10 needs to be increased, which complicates the apparatus. In addition, since there is a concern about clogging of piping for supplying the slurry liquid, it is necessary to make the slurry liquid about 10 wt%. Further, when a thin slurry liquid having a concentration of about 10 wt% is used, it is difficult to adjust the concentration of the reaction solution in the calcium fluoride synthesis tank 10.

  The average particle diameter of calcium carbonate is preferably 15 μm or more and 300 μm or less. Furthermore, it is particularly preferably 30 μm or more and 150 μm or less. The reason for this is that if it is larger than 300 μm, the conversion rate from calcium carbonate to calcium fluoride decreases, which is not efficient. Further, if the particle size of the synthesized calcium fluoride is smaller than 15 μm, it is not preferable because a problem is caused in the fluidity when a rotary kiln is used as a raw material for producing hydrogen fluoride. For use as a raw material for producing hydrogen fluoride by a rotary kiln, a particle size of calcium carbonate of 30 μm or more and 150 μm or less is particularly suitable. By setting this range, it is possible to synthesize calcium fluoride having a suitable size.

  Step [3] is different from the conventional step of growing calcium fluoride crystals by using a known crystallization technique from a hydrofluoric acid-containing solution and a calcium chloride aqueous solution (for example, Patent Document 2). It is not necessary to make the acidity of hydrochloric acid as large as possible, and the burden of processing and equipment such as mass use of chemicals such as hydrogen peroxide for neutralization and corrosion of equipment are small.

  Further, since the step [3] does not use a chlorine-containing compound such as calcium chloride, there is no fear that a trace amount of chlorine component derived from calcium chloride is mixed into calcium fluoride. In particular, when hydrofluoric acid is produced using calcium fluoride in which a small amount of chlorine component is mixed, the hydrochloric acid component is mixed into the produced hydrofluoric acid, and there is a concern that quality may deteriorate. Therefore, according to the step [3], it is possible to synthesize higher-purity calcium fluoride with less concern about impurities.

  Next, process [4] of this invention is demonstrated. Step [4] is a step of separating the potassium carbonate solution from the second reaction product that has undergone step [3] and recovering the synthetic calcium fluoride obtained by the reaction of the above reaction formula (9).

  Specifically, the slurry liquid containing the synthetic calcium fluoride and the potassium carbonate component obtained in the step [3] is sent to the dehydrator 30 via the second slurry liquid discharge pipe 22 by the discharge pump 20b. And dehydrated by a solid-liquid separation operation such as a centrifuge. Further, the dehydrated synthetic calcium fluoride 50 is washed with a washing liquid such as water or ethanol, and the synthetic calcium fluoride is recovered. Note that dehydration and washing may be repeated as necessary. For example, the slurry liquid may be dehydrated to perform most of the dehydration, and then washed with a cleaning liquid such as water or ethanol, and then a dehydration operation may be performed to completely perform the dehydration process.

  When calcium fluoride is produced and recovered in the above steps [1] to [4], the average particle size suitable as a raw material for producing hydrofluoric acid is 15 μm or more and 300 μm or less, High quality calcium fluoride having a purity of 95% wt or more can be obtained.

  Further, step [5] of the present invention will be described. Step [5] is a step of reusing the potassium carbonate aqueous solution separated in step [4] as the potassium compound raw material in step [1].

  Specifically, the desorbed water (potassium carbonate aqueous solution) is sent and stored in the waste liquid storage tank 70 via the desorbed water discharge pipe 71 by the discharge pump 70a. Next, the potassium carbonate concentration of the desorbed water (potassium carbonate aqueous solution) is adjusted in the waste liquid storage tank 70 as necessary. Further, the liquid is sent by the discharge pump 70b through the circulation pipe 72 and reused as a calcium compound raw material. The method for adjusting the concentration (concentration method) is not particularly limited, but moisture can be removed using sun drying, membrane separation, or the like.

  Further, in addition to the above steps [1] to [4], the insoluble silica separated in step [2] is washed, and the washing liquid obtained by the washing is added to step [1] and / or step [3]. You may make it introduce. Similarly, the calcium fluoride separated in step [3] may be washed, and the cleaning liquid obtained by the washing may be introduced into step [1] and / or step [3].

  According to said structure, since the desorption water obtained in the process which concerns on this invention can be used efficiently, the usage-amount of the potassium compound used at this process can be reduced further, and manufacturing cost can be reduced. Reduction can be expected.

  The calcium fluoride obtained in the present invention can be suitably used as a raw material for producing hydrofluoric acid. The hydrofluoric acid or anhydrous hydrofluoric acid produced is used as a starting material for various fluorine compounds.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the Example which concerns.

  Calcium fluoride was manufactured using the calcium fluoride manufacturing apparatus 100 according to the present invention shown in FIG. As an evaluation of the calcium fluoride produced and recovered, the purity of calcium fluoride and the concentration of impurities contained in calcium fluoride were measured.

[Example 1]
As a calcium fluoride production apparatus 100 shown in FIG. 2, first, using a diaphragm type supply pump in a 2 liter PTFE reaction vessel (neutralization cracking tank 60) having a PTFE stirrer installed therein, first, the concentration of hydrofluoric acid 0.72 kg of raw water adjusted to 10 wt% was supplied. Furthermore, 0.4 kg of potassium carbonate was added as a potassium compound, and as shown in the reaction formula (7), hydrofluoric acid was neutralized and decomposed with potassium carbonate to produce an aqueous potassium fluoride solution and insoluble silica. The reaction conditions are shown below. In addition, pH of reaction conditions shows the value at the time of completion | finish of reaction. The amount of potassium carbonate to be added was adjusted to be 2 equivalents of the amount required for the reaction with silicohydrofluoric acid.

<Reaction conditions>-Reaction formula (7)
Reaction temperature: 70 ° C
Reaction time: 3 hours pH: 10
Potassium carbonate addition amount: 2 equivalents

Next, the supernatant liquid (potassium fluoride aqueous solution) that had been subjected to sedimentation separation was collected to synthesize calcium fluoride. As a reaction tank, a 2 L PFA-lined synthesis reaction vessel (calcium fluoride synthesis tank 10) around which an external jacket (silicon oil was used as a heat medium) capable of adjusting the temperature inside the reactor was used.

  As a means for introducing calcium carbonate (calcium carbonate introducing device), calcium carbonate having an average particle diameter of 60 μm was introduced into a receiving hopper, and a total of 0.1 kg was introduced while adjusting the supply amount with a screw feeder. Further, a PTFE stirrer was installed inside the reaction vessel to carry out the reaction while stirring. The reaction conditions are shown below. In addition, pH of reaction conditions shows the value at the time of completion | finish of reaction. The amount of calcium carbonate added was adjusted to be 0.6 equivalent of the amount required for the reaction with potassium fluoride.

<Reaction conditions>-Reaction formula (9)
Reaction temperature: 50 ° C
Reaction time: 7 hours pH: 7
Calcium carbonate addition amount: 0.6 equivalent

After 7 hours of reaction time after the granular calcium carbonate was added, the stirring was stopped, the slurry liquid after the reaction was withdrawn from the discharge pipe (second slurry pipe 14) connected to the synthesis reaction vessel, and the centrifugal separator (dehydration) The solution was sent to the apparatus 30) for dehydration, and the pure and synthetic calcium fluoride was washed to remove impurities. The obtained sample was dried at 100 ° C. and subjected to X-ray diffraction measurement and particle size distribution measurement.

  The average particle diameter of the powder was measured using a laser diffraction particle size distribution analyzer SALD2200 manufactured by Shimadzu Corporation. In the laser diffraction type particle size distribution measuring device, the particle size distribution is calculated from the data of the light intensity distribution of the diffracted / scattered light by the particles detected by the sensor. The average particle size is obtained by multiplying the value of the measured particle size by the relative particle amount (difference%) and dividing by the total relative particle amount (100%). The average particle diameter is the average diameter of the particles. In this example and specification, the “average particle diameter” means a particle diameter at an integrated value of 50% (median diameter) in a particle size distribution obtained by a laser diffraction / scattering method.

  In the X-ray diffraction measurement, the powder sample was sufficiently ground in a mortar so that calcium carbonate inside the crystal could be detected. For the analysis of the purity of the synthesized calcium fluoride and the concentration of calcium carbonate contained as impurities, the standard reagents of calcium fluoride and calcium carbonate are mixed in advance at a predetermined concentration, thoroughly mixed on a mortar, and X-ray A calibration curve was prepared by performing diffraction measurement. Using the prepared calibration curve, the purity of the synthesized calcium fluoride and the concentration of calcium carbonate contained as impurities were calculated.

  When the purity and average particle diameter of the synthesized calcium fluoride were measured by the above method, the purity of calcium fluoride was 98 wt% or more, and the average particle diameter was 55 μm. Moreover, when the chlorine content in calcium fluoride was analyzed using a fluorescent X-ray analyzer (model number: SYSTEM 3270, manufactured by Rigaku Corporation), it was a sufficiently low value of less than 100 ppm.

Further, FIG. 4 shows an X-ray diffraction pattern of the synthesized calcium fluoride. From the obtained diffraction pattern, the peak of calcium carbonate (CaCO ₃ ) was not observed, and only the peak of calcium fluoride (CaF) was observed. Therefore, it turns out that the purity of the calcium fluoride manufactured in Example 1 is high. Further, FIG. 5 shows an XRD diffraction pattern of the sediment component when the sedimentation is performed by the reaction formula (7). The peak of K ₂ SiF ₆ is not confirmed and is only a peak that is considered to be amorphous silica. Accordingly, reaction formula (8) does not proceed, and only reaction formula (7) occurs. It could be confirmed.

[Comparative Example 1]
Calcium fluoride was produced using the same calcium fluoride production apparatus and operating conditions as in Example 1 except that no potassium compound (potassium carbonate) was added. As a result, the purity of calcium fluoride was 55 wt% only by directly reacting silicofluoric acid and calcium fluoride, and calcium fluoride with sufficient purity could not be obtained.

[Comparative Example 2]
Using the same apparatus as in Example 1, the reaction was carried out by changing the raw material from potassium carbonate to sodium carbonate. An XRD analysis of the precipitated component after performing the reaction (7) revealed a NaF component in addition to SiO ₂ . Therefore, it was confirmed that NaF was precipitated in the solution without being completely dissolved.

DESCRIPTION OF SYMBOLS 100 Calcium fluoride manufacturing apparatus 10 Calcium fluoride synthesis tank 30 Dehydration apparatus 40 Calcium carbonate introduction apparatus 50 Calcium fluoride 60 Neutralization decomposition tank 70 Waste liquid storage tank

Claims (11)

A method for producing calcium fluoride using siliceous hydrofluoric acid-containing water,
Reacting silicofluoric acid-containing water with a potassium compound to produce a first reaction product containing insoluble silica and an aqueous potassium fluoride solution [1];
Separating the insoluble silica from the first reaction product [2];
Reacting the first reaction product from which insoluble silica has been separated with calcium carbonate to form a second reaction product containing calcium fluoride and an aqueous potassium carbonate solution [3];
Separating the potassium carbonate aqueous solution from the second reaction product [4],
A method for producing calcium fluoride.   Furthermore, the manufacturing method of the calcium fluoride of Claim 1 including the process [5] which reuses the potassium carbonate aqueous solution isolate | separated at the said process [4] as a potassium compound raw material of the said process [1].   The manufacturing method of the calcium fluoride of Claim 2 in which the said process [5] includes the concentration process of potassium carbonate aqueous solution.   Further, the insoluble silica separated in the step [2] is washed, and the cleaning liquid obtained by the washing is introduced into the step [1] and / or the step [3]. The manufacturing method of any one of these.   Furthermore, the calcium fluoride separated in the step [3] is washed, and the liquid obtained by the washing is introduced into the step [1] and / or the step [3]. 4. The method for producing calcium fluoride according to any one of 4 above.   The manufacturing method of the calcium fluoride in any one of Claims 1-5 whose average particle diameter of the calcium carbonate used for the said process [3] is 15-300 micrometers.   The manufacturing method of the calcium fluoride in any one of Claims 1-6 whose reaction temperature of the said process [1] is 40-100 degreeC.   The method for producing calcium fluoride according to any one of claims 1 to 7, wherein a reaction temperature in the step [3] is 40 to 80 ° C.   The method for producing calcium fluoride according to any one of claims 1 to 8, wherein the potassium compound is at least one compound selected from the group consisting of potassium carbonate, potassium hydrogen carbonate, potassium oxide, and potassium hydroxide. An apparatus for producing calcium fluoride using silicohydrofluoric acid-containing water,
A neutralization decomposition tank for reacting hydrofluoric acid-containing water with a potassium compound to produce a first reaction product containing insoluble silica and an aqueous potassium fluoride solution;
A calcium fluoride synthesis tank connected to the neutralization decomposition tank and reacting calcium carbonate with a first reaction product from which insoluble silica has been separated to produce a second reaction product containing calcium fluoride and an aqueous potassium carbonate solution;
A separation device connected to the calcium fluoride synthesis tank and separating an aqueous potassium carbonate solution from the second reaction product,
Calcium fluoride production equipment.   Further, the storage device is connected to the separation device and includes a storage tank for storing the potassium carbonate aqueous solution separated from the second reaction product, the storage tank connecting the neutralization decomposition tank and the storage tank, The manufacturing apparatus of the calcium fluoride of Claim 10 which has a circulation piping for sending potassium carbonate aqueous solution to the said neutralization decomposition tank.

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