JP2013060330A - Method of producing calcium fluoride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing calcium fluoride suitable for a raw material for producing hydrofluoric acid, the method eliminating the concern about interfusion of a hydrochloric acid component when the hydrofluoric acid is produced.SOLUTION: The method of producing the calcium fluoride by the reaction of hydrofluoric acid-containing water and calcium carbonate includes a synthesis reaction step [1] that has a ripening time during which the reaction of the calcium carbonate is promoted in the hydrofluoric acid-containing water having a fluorine concentration of 50,000 mg/L or larger.

Description

  The present invention relates to a method for producing calcium fluoride suitable as a raw material for producing hydrofluoric acid by reacting raw water containing hydrofluoric acid with calcium carbonate.

  Conventionally, calcium compounds such as calcium hydroxide, calcium oxide, calcium carbonate, and calcium chloride are added to raw water containing fluorine and phosphoric acid discharged in the semiconductor industry, chemical industry, etc., and difficulties such as calcium fluoride and calcium phosphate occur. A technique for crystallizing, recovering, and reusing a soluble salt 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。

上記の反応式（２）および反応式（３）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、通常キルン装置に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、フッ化水素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。 Using this type of crystallization technique, 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. Has been done.

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. .

When water is by-produced as shown in the above reaction formula (2) and reaction formula (3), the kiln is in a hydrofluoric acid environment, so the iron-based metal material usually used in the kiln apparatus is corroded. End up. This shortens the device life of the hydrofluoric acid production apparatus, so that 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, naturally occurring acid grade fluorite is used, so that the natural fluorite can flow in the kiln, for example, to a particle size of about 15 to 300 μm. Crushed and used.

  Against this background, calcium fluoride is recovered using crystallization technology, and hydrofluoric acid is produced using the recovered calcium fluoride. It is an important factor to arrange them appropriately and to use calcium fluoride having a high purity not containing impurities.

また、フッ素含有廃液等において、フッ化カルシウムの結晶を成長させる技術も知られているが、一般に合成したフッ化カルシウムは粒径が１０μｍ以下の微粒子になってしまうことが多い。この問題点を改善する技術として、例えば、特許文献２には、晶析技術を駆使して結晶を成長させる方法として、下記の反応式５のように、フッ化カルシウムの溶解度が比較的大きな塩酸酸性条件下で、フッ酸を含有する原水と塩化カルシウム水溶液を反応させることによって、純度が高く、粒径が大きなフッ化カルシウムを析出させる技術が開示されている。

As a technique for recovering and reusing calcium fluoride, for example, in Patent Document 1, as shown in the following reaction formula 4, calcium carbonate and hydrogen fluoride having an appropriate particle size are reacted to form calcium carbonate. A technique for producing calcium fluoride while maintaining the skeleton is disclosed.

In addition, a technique for growing calcium fluoride crystals in a fluorine-containing waste liquid or the like is also known, but generally synthesized calcium fluoride often becomes fine particles having a particle size of 10 μm or less. As a technique for improving this problem, for example, in Patent Document 2, as a method of growing a crystal by making full use of a crystallization technique, hydrochloric acid having a relatively high solubility of calcium fluoride as shown in the following reaction formula 5 A technique for precipitating calcium fluoride having high purity and a large particle size by reacting raw water containing hydrofluoric acid with an aqueous calcium chloride solution under acidic conditions is disclosed.

Japanese Patent Application Laid-Open No. 06-063561 JP 2005-206405 A

  The technique described in Patent Document 1 can be recovered as calcium fluoride while keeping the particle size of most calcium carbonates moderately, and for example, a rotary kiln used for hydrofluoric acid production. In the case of a particle size (about 15 to 300 μm) that can be charged into the material, there is a problem that the central portion of calcium carbonate remains unreacted and the purity becomes insufficient at about 70%.

  Moreover, when using the crystallization technique as described in Patent Document 2, it is necessary to dissolve the reaction raw material, and therefore calcium chloride is used as the raw material for calcium fluoride. When calcium chloride is used as a synthetic raw material for calcium fluoride, it is difficult to avoid a trace amount of chlorine components from being mixed into the recovered calcium fluoride.

  Therefore, when calcium fluoride is obtained by the crystallization technique of Patent Document 2 and hydrofluoric acid is produced using calcium fluoride mixed with a small amount of chlorine component, It is desirable to avoid the use of a calcium compound containing a chlorine component as much as possible since the hydrochloric acid component is mixed in and there is a concern about deterioration of quality.

  As described above, various techniques for recovering and reusing calcium fluoride by a conventional crystallization technique have been disclosed, but there are problems such as the particle size and purity of the recovered calcium fluoride, so The present situation is that the utilization technology has not been established yet.

  The present invention has been made in view of the above-described problems, and there is no concern of mixing hydrochloric acid components during the production of hydrofluoric acid, and a method for producing calcium fluoride suitable as a raw material for hydrofluoric acid production is provided. The purpose is to provide.

  As a result of intensive studies to solve the above problems, the present inventors have focused on calcium carbonate that does not substantially contain a chlorine component, and when reacting hydrofluoric acid-containing water and calcium carbonate, hydrofluoric acid and carbonic acid are reacted. Hydrofluoric acid is obtained by reacting in an excess amount of hydrofluoric acid at a molar ratio of calcium (reaction equivalent), and ensuring sufficient aging time so that the reaction proceeds completely to the center of calcium carbonate. The inventors have found that calcium fluoride suitable as a raw material for production can be obtained, and have reached the present invention.

  That is, the present invention relates to a method for producing calcium fluoride by a reaction between hydrofluoric acid-containing water and calcium carbonate, and the aging time for allowing the calcium carbonate reaction to proceed in hydrofluoric acid-containing water having a fluorine concentration of 50000 mg / L or more. A method for producing calcium fluoride, comprising a synthesis reaction step [1] having

  Further, in the present invention, the neutralization step [2] for adjusting the pH of the slurry liquid containing calcium fluoride obtained in the step [1] and the neutralization step [2] are further obtained. Further, a dehydration step [3] for dehydrating the neutralized slurry liquid and a washing step [4] for washing the calcium fluoride dehydrated in the dehydration step [3] may be included.

  According to this configuration, the calcium fluoride synthesized in step [1] can be efficiently neutralized and washed, and impurities can be further reduced.

  In the present invention, in the step [1], it is preferable to directly add granular calcium carbonate to the hydrofluoric acid-containing water.

  According to this configuration, since the hydrofluoric acid concentration of the slurry liquid in the synthesis reaction step [1] can be kept high, conversion from calcium carbonate to calcium fluoride can be performed efficiently. Furthermore, since it is only necessary to directly add granular calcium carbonate to hydrofluoric acid-containing water, there is no need to prepare a slurry adjusting tank for adjusting the calcium carbonate slurry liquid and introducing the slurry liquid into the hydrofluoric acid-containing water. The process and the manufacturing apparatus can be simplified.

  Moreover, in this invention, it is preferable that the quantity of the calcium carbonate used at the said process [1] shall be 0.7 equivalent or more and 0.98 equivalent or less of the fluorine concentration of the said hydrofluoric acid containing water.

  According to this configuration, the hydrofluoric acid-containing water can be aged in a state where hydrofluoric acid remains sufficiently excessive with respect to the concentration of calcium carbonate, and the reaction can be efficiently performed to the center of calcium carbonate. It is possible to proceed.

  Moreover, in this invention, it is preferable that the average particle diameter of the calcium carbonate used at the said process [1] shall be 15 micrometers or more and 300 micrometers or less. Furthermore, it is particularly preferably 30 μm or more and 150 μm or less. 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.

  According to this configuration, it is possible to obtain calcium fluoride having a suitable particle diameter that can be charged into a rotary kiln that is generally used for hydrogen fluoride production, and the calcium fluoride is pulverized in the previous step of charging into the rotary kiln. It is not necessary to provide a separate process such as, and the process and the manufacturing apparatus can be simplified.

  According to the present invention, when reacting hydrofluoric acid-containing water and calcium carbonate containing substantially no chlorine component, a sufficient aging time is ensured in a state where the hydrofluoric acid in the reaction field is excessive, and the central portion of the calcium carbonate. Until the reaction can proceed completely. Therefore, there is no concern of mixing hydrochloric acid components during the production of hydrofluoric acid, and calcium fluoride suitable as a raw material for producing hydrofluoric acid can be provided.

It is the schematic which shows an example of the manufacture recovery apparatus of calcium fluoride which concerns on embodiment of this invention. It is the schematic which shows the modification of the manufacture collection | recovery apparatus of the calcium fluoride which concerns on embodiment of this invention. 1 is a schematic view of a small experimental apparatus according to an embodiment of the present invention.

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

  The calcium fluoride production and recovery apparatus 100 of the present invention includes a calcium fluoride synthesis tank 10 that synthesizes calcium fluoride by reacting hydrofluoric acid-containing water and calcium carbonate, and calcium fluoride synthesized in the calcium fluoride synthesis tank 10. The aging tank 20 for sufficiently advancing the reaction to the central part of the water and the dehydrating device 30 for dehydrating the slurry liquid containing the synthesized calcium fluoride by solid-liquid separation operation are provided.

  The hydrofluoric acid-containing water supply pipe 11 that introduces hydrofluoric acid-containing water into the calcium fluoride synthesizing tank 10 and the calcium carbonate into the calcium fluoride synthesizing tank 10 are introduced into the calcium fluoride synthesizing tank 10 through the supply pump 10a. The calcium carbonate introducing means 40 for performing the operation and the first slurry liquid discharge pipe 14 for discharging the slurry liquid containing the synthetic calcium fluoride are connected via the discharge pump 10b. In the calcium fluoride synthesis tank 10, a stirrer 13 is installed via a motor 15.

  An aging tank 20 is connected to the downstream of the first slurry liquid discharge pipe 14 via a discharge pump 10b, and the aging tank 20 is supplied with a neutralizing liquid for neutralizing the stored slurry liquid. The neutralization liquid supply pipe 21 is connected via a supply pump 20a. Further, the aging tank 20 is provided with a second slurry liquid discharge pipe 22 for discharging the slurry liquid and sending it to the dehydrator 30. In the aging tank 20, a stirrer 23 is installed via a motor 24.

  A dehydrator 30 is connected to the downstream of the second slurry liquid discharge pipe 22 via a discharge pump 20b, and the slurry liquid sent via the second slurry liquid discharge pipe 22 is supplied to the dehydrator 30. A cleaning liquid supply pipe 31 for supplying a cleaning liquid for cleaning is connected via a supply pump 30a. 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 5 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.

  A cooling jacket 12 is provided around the outer periphery of the calcium fluoride synthesis tank 10, and the temperature of the slurry liquid (a mixture of hydrofluoric acid-containing water and calcium carbonate) in the synthesis tank 10 is adjusted. The method of the cooling jacket 12 is not particularly limited. For example, in the reaction between hydrofluoric acid and calcium carbonate, the temperature may be adjusted using a simple cold water circulation method as a suitable method for suppressing heat generation.

  In the calcium fluoride synthesis tank 10 and the aging tank 20, the material of the tank is not particularly limited. For example, a fluororesin such as PFA or PTFE or a rubber lining tank can be used.

  The calcium carbonate introducing means 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 calcium carbonate is adjusted by the screw feeder 42. The The supply rate of calcium carbonate is appropriately adjusted so that rapid heat generation due to the reaction does not occur.

  Next, a process for producing and recovering calcium fluoride according to the embodiment of the present invention will be described.

  The present invention relates to a method for producing calcium fluoride by the reaction of hydrofluoric acid-containing water and calcium carbonate, in a high concentration hydrofluoric acid-containing water, that is, in a hydrofluoric acid-containing water having a fluorine concentration of 50000 mg / L or more. It includes a synthetic reaction step [1] having a ripening time for allowing the calcium reaction to proceed.

  Furthermore, in this invention, in addition to said process [1], neutralization process [2] which adjusts the pH of the slurry liquid containing the synthetic calcium fluoride obtained by process [1], and process [2] It is preferable to include the dehydration step [3] for dehydrating the slurry liquid after neutralization obtained in step 1 and the washing step [4] for washing the synthetic calcium fluoride dehydrated in step [3].

  Hereinafter, each step will be described in detail with reference to FIG.

  First, the synthesis reaction step [1] of the present invention will be described. Step [1] is a step of reacting calcium carbonate with hydrofluoric acid (HF) containing hydrofluoric acid to synthesize calcium fluoride. First, hydrofluoric acid-containing water is supplied to a calcium fluoride synthesis tank 10 through a hydrofluoric acid-containing water supply pipe 11 from a tank that stores hydrofluoric acid-containing water such as a hydrofluoric acid waste liquid. Next, the granular calcium carbonate accommodated in the receiving hopper 41 is introduced into the calcium fluoride synthesis tank 10 while adjusting the supply amount via the screw feeder 42. In addition, in the step [1], a batch process that can easily secure a sufficient aging time is preferably used in order to completely advance the conversion reaction of calcium fluoride from calcium carbonate.

  As the calcium carbonate introduction means 40, in addition to the method of directly charging granular calcium carbonate, a separate adjustment tank is provided to adjust the calcium carbonate slurry solution, and the calcium carbonate slurry solution is charged to 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%. In addition, when a thin slurry solution having a concentration of about 10 wt% is used, the fluorine concentration of the hydrofluoric acid-containing water in the calcium fluoride synthesis tank 10 is lowered, and as a result, the fluorine concentration of the reaction solution is sufficiently increased. In the present invention, it is difficult to obtain the effect of sufficient calcium fluoride to the center of calcium carbonate due to the high concentration of fluorine in the reaction field, which is a feature of the present invention. Direct injection is particularly preferred.

The slurry liquid, which is a mixture of hydrofluoric acid-containing water and calcium carbonate introduced into the calcium fluoride synthesis tank 10, is an exothermic reaction with foaming of carbon dioxide (CO ₂ ) gas, as shown in the above reaction formula (4). Therefore, the temperature of the slurry liquid is kept constant by the cooling jacket 12 provided around the outer periphery of the calcium fluoride synthesis tank 10. The temperature setting conditions should be set as appropriate depending on the amount of calcium carbonate used, the particle diameter, the volume of the reaction vessel of the calcium fluoride synthesis tank 1, and the like. For example, when using calcium carbonate having a particle size of 15 μm or more and 300 μm or less, the set temperature may be adjusted in the range of 5 ° C. to 95 ° C., particularly 20 to 50 ° C.

  The particle size 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 is that if it exceeds 300 μm, the conversion rate from calcium carbonate to calcium fluoride decreases, and the aging time in the present invention becomes longer, 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.

  In the calcium fluoride synthesis tank 10, as shown in the above reaction formula (4), hydrofluoric acid contained in the hydrofluoric acid-containing water reacts with granular calcium carbonate to synthesize calcium fluoride crystals. In order to complete the reaction up to the center of the granular calcium carbonate, it is preferable to carry out the reaction in a state where the acid is excessive in the reaction field. Specifically, the fluorine concentration in the hydrofluoric acid-containing water is preferably 50000 mg / L or more and 530000 mg / L or less, and more preferably 100000 mg / L or more and 530000 mg / L or less.

When the fluorine concentration is greater than 530000 mg / L, the hydrofluoric acid vapor pressure in the hydrofluoric acid-containing water increases, so that the hydrogen fluoride is accompanied by the generation of carbon dioxide (CO ₂ ) gas generated when reacting with calcium carbonate. Since steam is generated, it leads to corrosion of devices such as a stirrer and a calcium carbonate powder charging machine, which is not preferable. Moreover, when the fluorine concentration is smaller than 50000 mg / L, the concentration of the acid in the reaction field is not sufficient, and the reaction of calcium carbonate to calcium fluoride cannot be efficiently performed, which is not preferable.

  Based on the above reaction formula (4), in order to completely react to the center of the granular calcium carbonate, the reaction field is reacted in an excess of acid. In order to make the acid concentration excessive, the reaction solution is adjusted so that the hydrofluoric acid is larger than the chemical equivalent in the reaction formula (4). Specifically, it is preferable to adjust the amount of calcium carbonate added to 0.7 equivalents or more and 0.98 equivalents or less of the amount necessary for the reaction with hydrofluoric acid. If it is less than 0.7 equivalent, a large amount of pH adjuster is required in the pH adjustment in the neutralization step [2], leading to high costs and a decrease in the yield of calcium fluoride. Therefore, it is not preferable.

After the introduction of calcium carbonate and the bubbling of carbon dioxide (CO ₂ ) gas from the slurry liquid is stopped, this slurry liquid is discharged from the first slurry liquid connected to the calcium fluoride synthesis tank 10 by the discharge pump 10b. It is pulled out through the pipe 14 and fed to the aging tank 20.

  The slurry liquid sent to the aging tank 2 is a mixture of hydrofluoric acid-containing water and calcium carbonate in the calcium fluoride synthesis tank 10 so that the amount of hydrofluoric acid is equivalent to that required for the reaction with calcium carbonate. It is adjusted with an excessive amount. That is, the hydrofluoric acid concentration is in an excessive state. In this state, the slurry liquid is left to be aged, whereby the reaction is completely advanced to the central part of calcium carbonate which is a raw material for the synthetic calcium fluoride, and calcium fluoride with high purity is synthesized.

  As aging conditions, it is preferable to hold for at least 30 minutes, and it is particularly preferable to provide an aging time of 1 hour or more. Further, the aging can be performed at normal temperature, but the temperature may be adjusted by providing a temperature adjusting means such as a jacket in the aging tank 2 as necessary as in the calcium fluoride synthesis tank 10 as necessary. The term “ripening time” as used herein refers to the start of supplying a neutralizing solution to hydrofluoric acid-containing water mixed with calcium carbonate, starting from the point where the required amount of calcium carbonate has been added to hydrofluoric acid-containing water ( It means the time until the end of ripening when the neutralized solution is added to hydrofluoric acid-containing water.

  Next, the neutralization step [2] in the present invention will be described. Step [2] is a step of adjusting the pH of the slurry liquid containing synthetic calcium fluoride. Since the slurry liquid obtained in Step [1] has a high fluorine concentration, a pH adjusting agent such as alkali is used. Add to neutralize (pH about 6-7). In addition, the pH adjuster can reduce the influence on the purity of the synthetic calcium fluoride 5 to be recovered. In particular, from the viewpoint of the adjuster containing no chlorine component, calcium hydroxide, sodium hydroxide, potassium hydroxide, An aqueous ammonia solution or the like may be used. A method for monitoring the pH of the slurry is not particularly limited. For example, monitoring may be performed by a method using a commercially available pH test paper or a measuring means such as a pH meter.

  Furthermore, the dehydration step [3] and the washing step [4] in the present invention will be described. In Step [3] and Step [4], the slurry liquid containing the neutralized synthetic calcium fluoride obtained in Step [2] is dehydrated (Step [3]), and the separated synthetic calcium fluoride is further separated. This is a step (step [4]) for removing impurities (Na ions and the like) contained therein.

  Specifically, the slurry liquid containing the neutralized synthetic calcium fluoride obtained in the step [2] is sent to the dehydrator 30 by the discharge pump 20b via the second slurry liquid discharge pipe 22. It is 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. The dehydration step [3] and the washing step [4] 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% or more can be obtained. Furthermore, since the obtained calcium fluoride is less concerned about impurities of the chlorine component in particular, the calcium fluoride according to the present invention is a high quality product that does not contain a hydrochloric acid component when used as a raw material for hydrofluoric acid production. Hydrogen fluoride can be produced.

  In the above description, as shown in FIG. 1, the calcium fluoride synthesis tank 10 and the aging tank 20 suitable for improving the production efficiency of calcium fluoride production are described as separate tanks. As a modification of the calcium fluoride production / recovery apparatus 100 of the present invention, as shown in the calcium fluoride production / recovery apparatus 200 shown in FIG. The tank 20 may be a single reaction tank. That is, the calcium fluoride synthesis tank 10 may perform calcium fluoride synthesis, aging reaction, and neutralization reaction. 2, parts having the same configuration and function as those of the calcium fluoride production and recovery apparatus 100 of FIG.

  According to the present invention, it can be applied to a method for producing and recovering calcium fluoride, and the obtained calcium fluoride 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.

  Production and recovery of calcium fluoride was performed using a calcium fluoride production and recovery apparatus 100 applicable to the embodiment of the present invention as shown in FIG. As an evaluation of the manufactured calcium fluoride, the purity of calcium fluoride and the concentration of impurities contained in calcium fluoride were measured.

[Example 1]
As a small experimental apparatus 300 as shown in FIG. 3, a powder feeder (screw feeder 42) capable of supplying a constant amount per unit time from above using a 1-liter PFA beaker 60 with a PTFE stirrer (stirrer 13) installed therein. ) To allow for the introduction of calcium carbonate. The PFA beaker 60 was charged with 500 g of hydrofluoric acid-containing water having a hydrofluoric acid concentration of 151000 mg / L, and the PTFE stirrer was rotated at a rotation speed of 150 rpm.

  Next, 186 g of calcium carbonate manufactured by Bihoku Flour Industry Co., Ltd. having an average particle size of 60 μm was charged into a powder feeder and charged into a PFA beaker at a rate of 8 g / min. The equivalent of calcium carbonate to hydrofluoric acid is 0.94 equivalent. After all the amount of 186 g has been charged with the powder feeder, the inside of the PFA beaker is 5 minutes, 15 minutes, 30 minutes, 60 minutes and 120 minutes later (see Examples 1-1 to 1-5). A sample (synthetic calcium fluoride) was taken from. The collected sample was subjected to suction filtration and pure water washing using a Kiriyama funnel, then 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, “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.

  The measurement result of the particle size distribution and the analysis result of the calcium fluoride purity are as shown in Table 1. After completion of charging the powder with a powder feeder, 30 minutes passed (ripening time 30 minutes). % Calcium fluoride was confirmed to be obtained. Furthermore, it was confirmed that calcium fluoride having a purity of 99% or more was obtained after 60 minutes. Moreover, it was found that the average particle size is 50 to 60 μm, which is suitable for use as a raw material for producing hydrogen fluoride.

[Example 2]
The same conditions as in Example 1 were followed except that the calcium carbonate used was changed to Yakusen lime having an average particle size of 19 μm. The particle size distribution measurement results and the analysis results of calcium carbonate in calcium fluoride are as shown in Table 1, and after 30 minutes have elapsed after the powder has been charged in the powder feeder, the fluoride having a purity of 99% or more It was confirmed that calcium was obtained (see Example 2-1 to Example 2-4).

[Example 3]
The same experimental apparatus as used in Example 1 was used, 500 g of hydrofluoric acid-containing water having a hydrofluoric acid concentration of 51000 mg / L was charged in the PFA beaker, and the average particle size was 60 μm in the powder feeder. The reaction was carried out by adding 64 g of calcium carbonate. Sampling was performed after 60 minutes of aging, and analysis revealed that the average particle size was 52 μm and the purity of calcium fluoride was 99% or more.

  In addition, the chlorine content of the calcium fluoride samples synthesized in Examples 1-1 to 1-5, Examples 2-1 to 2-5, and Example 3 was measured using a fluorescent X-ray analyzer (model number: SYSTEM3270, stocks). As a result, it was confirmed that any sample contained less than 100 ppm and contained only a trace amount.

[Comparative Example 1]
The test was carried out under the same conditions as in Example 1 except that the filling amount of calcium carbonate in the conditions carried out in Example 1 was changed from 186 g to 200 g. The equivalent of calcium carbonate to hydrofluoric acid is 1.00 equivalent. As a result, even when the aging time was 120 minutes, the purity of calcium fluoride was 88%, and 12% of calcium carbonate was mixed as an impurity.

[Comparative Example 2]
The same experimental apparatus as used in Example 1 was used. A PFA beaker was charged with 500 g of hydrofluoric acid-containing water having a hydrofluoric acid concentration of 4000 mg / L, and the powder feeder had a mean particle size of 60 μm. The reaction was carried out by charging 5 g of calcium carbonate. When the aging time was 60 minutes and sampling was performed, the analysis revealed that the average particle size was 52 μm and the purity of calcium fluoride was 70%.

[Example 4]
Next, the effectiveness of the present invention was examined using a large experimental apparatus. As a production recovery apparatus 100 as shown in FIG. 1, a PFA-lined synthesis reaction vessel (calcium fluoride synthesis tank 10) in which a stirrer with PFA lining is installed inside and a water-cooled cooling jacket is provided around the outer periphery. Then, 484 kg of hydrofluoric acid-containing water adjusted to a hydrofluoric acid concentration of 147000 mg / L was supplied using a diaphragm type supply pump. The synthesis reaction vessel having a volume of 1 m ³ was used. Next, using a calcium carbonate introduction device, granular calcium carbonate having an average particle diameter of 60 μm was introduced into a receiving hopper, and a total of 180 kg was added over 4 hours while adjusting the supply amount with a screw feeder. At this time, in order to suppress heat generation due to the reaction between hydrofluoric acid and calcium carbonate, granular calcium carbonate was added while adjusting the slurry solution in the reaction vessel to 40 ° C. or less using a cooling jacket. The mixing amount of the slurry solution was adjusted so that the amount of calcium carbonate was 0.96 equivalent of the amount necessary for the reaction with hydrofluoric acid.

  After adding the granular calcium carbonate, stirring is stopped, the slurry solution is drawn from the discharge pipe (first slurry liquid discharge pipe 14) connected to the synthesis reaction vessel, and sent to the aging reactor (aging tank 2). And the slurry solution was aged for 2 hours. After aging for 2 hours, sodium hydroxide was supplied as a pH adjuster from a neutralization liquid supply pipe connected to the aging reactor, and neutralized so that the pH of the slurry liquid was 6-7. The pH was measured using a commercially available pH test paper. Next, the slurry liquid that has been neutralized is extracted from the discharge pipe (second slurry liquid discharge pipe 22) connected to the aging reactor, and sent to the centrifuge (dehydration apparatus 30) for dehydration, Furthermore, the synthetic calcium fluoride was washed with pure water to remove impurities.

  When the purity and average particle diameter of calcium fluoride synthesized by the above method were measured, the purity of calcium fluoride was 99% or more and the average particle diameter was 58 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.

[Comparative Example 3]
The test was conducted under the same conditions as in Example 4 except for the aging time. The test was conducted with an aging time of 0 minutes. As a result, the purity of calcium fluoride was 84%, and calcium carbonate remained. The aging time of 0 minutes here means the case where the neutralization solution is started to be added at the same time as the addition of the necessary amount of calcium carbonate to the hydrofluoric acid-containing water.

  Further, hydrogen fluoride was actually synthesized using the calcium fluoride synthesized in Example 4. For the synthesis of hydrogen fluoride, a kiln-type reactor was used, and the test was conducted in the form of mixing 5% of the synthetic calcium fluoride produced in Example 4 with natural calcium fluoride (fluorite). The purity of the obtained hydrogen fluoride was high, and the concentration of hydrochloric acid was 0.5 ppm or less.

From the results shown in Table 1, it was found that in the examples within the scope of the present invention, the purity of calcium fluoride was high and the concentration of contained impurities was sufficiently low. On the other hand, in the comparative example outside the scope of the present invention, calcium carbonate is not completely converted to calcium fluoride, and the purity of calcium fluoride is low, which is insufficient for use as a raw material for producing hydrogen fluoride. It turns out that.

100, 200 Calcium fluoride production and recovery device 10 Calcium fluoride synthesis tank 10a Supply pump 10b Discharge pump 11 Hydrofluoric acid-containing water supply pipe 12 Cooling jacket 13 Stirrer 14 First slurry liquid discharge pipe 15 Motor 20 Aging tank 20a Supply pump 20b Discharge pump 21 Neutralization liquid supply pipe 22 Second slurry liquid discharge pipe 23 Stirrer 24 Motor 30 Dehydrator 30a Supply pump 31 Cleaning liquid supply pipe 32 Calcium fluoride recovery pipe 40 Calcium carbonate introduction means 50 Synthetic calcium fluoride

Claims (9)

  A method for producing calcium fluoride by a reaction between hydrofluoric acid-containing water and calcium carbonate, wherein the hydrofluoric acid-containing water having a fluorine concentration of 50000 mg / L or more has a aging time for advancing the reaction of calcium carbonate [ 1]., The manufacturing method of the calcium fluoride characterized by the above-mentioned.   The neutralization step [2] for adjusting the pH of the slurry liquid containing calcium fluoride obtained in the step [1], and the neutralized slurry liquid obtained in the neutralization step [2] The calcium fluoride according to claim 1, further comprising a dehydration step [3] for dehydration and a washing step [4] for washing the calcium fluoride dehydrated in the dehydration step [3]. Production method.   The method for producing calcium fluoride according to claim 1 or 2, wherein a concentration of fluorine in the hydrofluoric acid-containing water is 50,000 mg / L or more and 530000 mg / L or less.   The method for producing calcium fluoride according to any one of claims 1 to 3, wherein the aging time is at least 30 minutes or more.   The method for producing calcium fluoride according to any one of claims 1 to 4, wherein in the step [1], granular calcium carbonate is directly added to the hydrofluoric acid-containing water.   The method for producing calcium fluoride according to any one of claims 1 to 5, wherein the step [1] is a batch process.   The amount of calcium carbonate used in the step [1] is 0.7 equivalent or more and 0.98 equivalent or less of an amount necessary for the reaction with the hydrofluoric acid containing hydrofluoric acid. The manufacturing method of the calcium fluoride in any one of Claim 1 thru | or 6.   The method for producing calcium fluoride according to any one of claims 1 to 7, wherein an average particle diameter of calcium carbonate used in the step [1] is 15 µm or more and 300 µm or less.   The method for producing calcium fluoride according to any one of claims 1 to 8, wherein the calcium fluoride is a raw material for producing hydrofluoric acid.

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