JPH05170435A - Method for recovering calcium fluoride from fluorine-containing etchant - Google Patents

Abstract

PURPOSE:To purify and recover fluorine from an etchant as calcium fluoride by making the etchant having a specific molar composition range of ammonium fluoride and hydrogen fluoride to react with calcium carbonate at a specific temperature. CONSTITUTION:In a method to recover fluorine as calcium fluoride from the etchant containing mainly hydrogen fluoride or hydrogen fluoride and ammonium fluoride, calcium carbonate is allowed to react with ammonium fluoride/ hydrogen fluoride of <=1.0 molar equivalent ratio at >=50 deg.C to recover high purity calcium fluoride having about <=3% unreacted calcium carbonate content and little silica content.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Hydrogen fluoride, or an etching agent containing hydrogen fluoride and ammonium fluoride as main components and various chemical-function-promoting additives, is used in the etching process in the semiconductor manufacturing field and related fields. In addition to being widely used in the field of surface treatment of various metal materials, single crystal materials, optical materials, etc., the demand for recovery technology is increasing from the viewpoint of environmental purification, especially resource recovery as the demand increases. It was

Therefore, an object of the present invention is to establish a technique for purifying and recovering fluorine as calcium fluoride from the above-mentioned etching agent, and it can be effectively used again as an industrial resource for hydrogen fluoride production, metal refining, ceramics, etc. It is something that you try to do.

[0003]

2. Description of the Related Art Many techniques have been developed for treating fluorine-containing wastewater with calcium salts.

However, the reaction mechanism in treating an ammonium fluoride-containing solution with a calcium salt has not been studied in detail, and thus remains a difficult problem to be solved.

First, the fluorine waste water treatment technology is as follows. JP-A-51-19364 is used as a wastewater treatment for cleaning stainless steel surface hydrofluoric acid, and JP-B-56-1012 is a treatment for removing fluorine and phosphorus from wastewater of phosphoric acid process.
No. 0, JP-B-57-39985, JP-B-59-843
No. 8, as a semiconductor process wastewater treatment Japanese Patent Publication Sho 56-1447
No. 92, Japanese Patent Publication No. 60-48191, Japanese Patent Publication No. 61-25
No. 690 and Japanese Examined Patent Publication No. 63-270595 are presented. All of these use excess calcium salt,
Since the purpose is to purify the wastewater by the secondary treatment or the separation of the coexisting components or the combination of the separation treatments, the purification of the generated calcium fluoride cannot be achieved.

US Pat. Nos. 2,780,521 and US Pat. No. 2,780,521 are used as a technique for producing calcium fluoride by using calcium carbonate for the purpose of recovering colloidal silica from a hydrosilicofluoric acid solution and separating silica in the filtrate. Although No. P.2,780,523 is presented, the recovered calcium fluoride purity is CaF ₂ 92% per dry substance, has stopped on the SiO ₂ 0.52%.

Japanese Patent Application Laid-Open No. 50142496 has proposed a method of adding calcium carbonate in two stages as a wet phosphoric acid process waste water purification technique. Excess calcium carbonate is removed from the recovered solid by washing with mineral acid. ..

As a technique for treating exhaust gas containing fluorine, the exhaust gas is absorbed by caustic potash, and 1.0 ± 0.2 equivalents of potassium hydroxide is added to the potassium fluoride to be reacted to react with calcium fluoride as the main component. After separating the precipitate and the solution layer mainly containing potassium hydroxide, an acid is added to the precipitate layer,
Japanese Patent Publication No. 57-47132 is disclosed as a technique for neutralizing unreacted alkali Ca (OH) ₂ , KOH. With this technology, the KF reaction rate when adding 1.0 equivalent is 90%.
Since it contains a large amount of unreacted material, it is necessary to neutralize hydrochloric acid, and the residual fluoride ion concentration is as high as about 900 ppm, which is 200 p by adding 1.2 equivalents of excess equivalents.
It has been reduced to pm.

Further, as a treatment technique for the fluorine-containing ammonium waste liquid, a method of adding slaked lime in two stages is disclosed in Japanese Patent Laid-Open No. 58-4.
No. 6355. That is, in the first stage, a small amount of slaked lime is added to the fluorine to precipitate and separate high-grade calcium fluoride, and in the second stage, 2 equivalents of slaked lime is further added to the low-grade fluorinated calcium. In this method, calcium is separated by precipitation, returned to the first step, and the residual liquid is distilled to recover ammonia.

However, the method using slaked lime is unsuitable for the treatment solution containing hydrogen fluoride, or hydrogen fluoride and ammonium fluoride, which is the object of the present invention. That is, hydrogen silicofluoride ions present in the etching solution react with slaked lime, and almost all of the silica content is contained in calcium fluoride, which impedes its purification.

As described above, none of the prior arts satisfies the areas to be solved by the present invention and the objects to be achieved, which will be described later.

[0012]

DISCLOSURE OF THE INVENTION The object of the present invention is to recover pure calcium fluoride by using calcium carbonate from hydrogen fluoride or an etching agent containing hydrogen fluoride and ammonium fluoride as main components. However, one of the issues that must be solved is to minimize the content of unreacted calcium carbonate, and the other one is the hydrosilicofluoric acid and calcium carbonate that are usually introduced from the etching process. This is to minimize the content of silica produced by the reaction of. The problems of each issue are further described.

Composition region of the etching agent of interest:

For example, in a semiconductor manufacturing process, which is a main application field of hydrogen fluoride / ammonium fluoride based etching agents, extremely various etching compositions are used with 50% HF and 40% NH ₄ F as stock solutions. FIG. 1 shows a typical example with a ● mark composition. Hydrogen fluoride concentration 0.5
% To 40% ammonium fluoride concentration, the ammonium fluoride / hydrogen fluoride molar equivalent ratios of various etching agents range from 0 to infinity, and therefore the fluorine species in the solution are also undissociated HF, F ⁻ ions, There are various kinds of HF ₂ ⁻ ions, and the reaction mechanism with calcium carbonate is not unique. Regarding the presence or absence of a composition region capable of optimizing the reaction rate of calcium carbonate, there have been no studies so far, so this must first be clarified in the present invention.

The resource value when the unreacted calcium carbonate is contained in the recovered calcium fluoride is shown below for the hydrogen fluoride producing raw material which is the most typical use. In parallel with Reaction 1 [Chemical Formula 1] that heats calcium fluoride and sulfuric acid to generate hydrofluoric acid,
The coexisting calcium carbonate proceeds reaction 2 [Chemical Formula 2]. However, () in these equations shows the physical quantity ratio.

[0016]

[Chemical 1]

[0017]

[Chemical 2]

That is, calcium carbonate consumes sulfuric acid, causes moisture and carbon dioxide to be contained in hydrogen fluoride gas, and at the same time, consumes various substances and heat for its treatment. Therefore, if 1.0% of calcium carbonate is contained in calcium fluoride, a cost loss equivalent to about 3% in pure calcium fluoride will be caused. Therefore, optimization of the reaction rate of calcium carbonate is an important economic problem not only in the recovery process but also in the reuse process.

Hydrogen fluoride in the etchant:

Since the fluorine-based etching agent is particularly excellent in reactivity with silicon compounds, it is used for etching and cleaning single crystal silicon, silicon semiconductor devices, quartz, glass and other silicon-containing substances, and is used in an etching solution. Hydrofluoric acid is often present. It is known that in parallel with the reaction between the fluorine ion and the calcium salt in the etching agent, the precipitation of silica from the hydrogen fluorosilicate ion by reaction 3 [Chemical Formula 3].

[0021]

[Chemical 3]

The resource value when the recovered calcium fluoride containing the silica component is used as a raw material for producing hydrogen fluoride is as follows. Silica and calcium fluoride endothermically react with sulfuric acid to generate hydrosilicofluoric acid according to the following formula 4 [Formula 4]. Figures in parentheses indicate physical quantity ratios.

[0023]

[Chemical 4]

That is, for example, in calcium fluoride,
3.9% Ca when 1.0% silica is included
F _2, 4.9% of the H ₂ consumes SO ₄ and heat still requires consumption of a process and raw material to exclude processing 2.4% H ₂ SiF ₆ by-produced, overall calcium fluoride A net loss of about 10-15% is incurred. Therefore, minimizing the silica content in the recovered calcium fluoride contributes significantly to the reuse value.

[0025]

The relationship between the composition of an etching agent containing hydrogen fluoride and ammonium fluoride as a main component and the reactivity of calcium carbonate has not been clarified. In FIG. 1, the entire composition range is arranged by ammonium fluoride molar concentration / hydrogen fluoride molar concentration (represented by [NH ₄ F] / [HF]). The chemical reaction formulas 5 to 9 [Chemical formula 5] to [Chemical formula 9] are shown below.

HF-H ₂ O 2 component system: [NH ₄ F] / [HF] = 0

[0027]

[Chemical 5]

HF-NH ₄ F-H ₂ O 3 component system: [NH ₄ F] / [H
F] = 1

[0029]

[Chemical 6]

[0030]

[Chemical 7]

NH ₄ F—H ₂ O 2 component system: [NH ₄ F] / [HF] = ∞

[0032]

[Chemical 8]

[0033]

[Chemical 9]

At each composition, the prototype of the reaction and the ionic species of the product system are different, and it is expected that the reaction will proceed at each reaction rate and reaction equilibrium constant. The inventor has found that the whole composition range, that is, each [NH ₄ F] / [H
F] ratio and the reaction at each concentration were investigated, and the obtained findings are shown in FIG. However, FIG. 2 was measured under the following conditions.

[0035]

[Fig. 2]

Calcium carbonate is added in a chemical equivalent amount to fluorine in the treatment liquid, and the reaction temperature is 70 ° C. or higher. From this result, the composition range of [NH ₄ F] / [HF] ratio is 1.0 or less (where [NH ₄ F] / [HF] ratio is 0, that is, HF
(In the case of a single solution, it is different)
It was revealed that a reaction rate of 97% or more was achieved over the concentration range of 1.0 to 10.0%. In the case of the HF alone solution, the fluorine recovery rate is 94% after 9 hours when treated with granular calcium carbonate at room temperature. However, in the case of powdered calcium carbonate, a recovery rate of 99% or more could already be achieved after 3 hours. The results are shown in Fig. 3. When an ammonium salt is contained, the effect of heating and calcium carbonate reduces the effect of defluorination unless deammonia is used. FIG. 4 shows the effect of temperature on the reaction rate. From this result, it is clear that treatment at a liquid temperature of 50 ° C. or higher, preferably 70 ° C. or higher is effective. However, the symbols in FIG. 4 indicate the following, respectively. Also, Ca
As CO ₃ pure content, 1.0 equivalent was added to all HF in the liquid, and the mixture was kept at each temperature for 1 hour.

[0037]

FIG. 5 shows the results of an examination of the binary system of hydrogen fluoride / hydrosilicofluoric acid. HF and H ₂
Even if SiF ₆ is present at an equal concentration in F concentration, when treated with calcium carbonate at room temperature, all fluorine is converted to C
It was confirmed that SiO ₂ remained at the initial concentration in the liquid separated as aF ₂ . The purification effect by using calcium carbonate was clearly recognized.

FIG. 6 shows the results of investigating changes in the SiO ₂ concentration over the entire HF-NH ₄ F-H ₂ O 3 component system. The total HF concentration in the treatment liquid is 1.0% to 2.0, the SiO ₂ concentration is 200 ppm to 400 ppm, and at the liquid temperature of 70 ° C., a chemical equivalent of calcium carbonate to the F concentration is added to generate fluorination. shows the SiO ₂ removal rate from the liquid separation of the calcium. It was revealed that the production effect of calcium carbonate does not depend on the change of the [NH ₄ F] / [HF] ratio at all. Under the same conditions,
By using calcium hydroxide, most of SiO ₂ is contained in calcium fluoride, and the SiO ₂ removal rate becomes extremely large, which is shown in contrast to the figure.

[0040]

Composition and Action of the Invention Composition of the step of using hydrogen fluoride or / and ammonium fluoride based etching agent,
The concentration conditions are different in each industry and are considered to change as necessary, but they do not leave the composition range shown in FIG. In this composition range, it is possible to recover high-purity calcium fluoride using calcium carbonate.

Generally, the semiconductor manufacturing process uses HF-H ₂
O 2 component etching process and HF-NH ₄ F-H ₂ O 3
Since the component-based etching step is coexistent, the [NH ₄ F] / [HF] ratio is usually 1.0 or less as a whole, and the present invention can be applied by integrating the recovery series.
In other industries, [NH ₄ F] / [HF] is 1.0
Even in the above cases, 1.0 or less or HF-H ₂ O
The present invention can be applied to a two-component processing industry.

The present invention is a method of recovering fluorine as calcium fluoride from an etching agent containing hydrogen fluoride or hydrogen fluoride and ammonium fluoride as main components. The addition reaction is performed to recover 99% or more of fluorine in the waste water, and also to recover high-purity calcium fluoride having a low unreacted calcium carbonate content of 1% or less and a low silica content.

In order to achieve "recovery of 99% or more of fluorine and at the same time 1% or less of unreacted calcium carbonate in recovered calcium fluoride", "a reaction rate is obtained by adding a chemical equivalent amount of calcium carbonate to fluorine. First, it is clarified that there is no means other than "to make it almost 100%".

Even if the reaction rate is not approximately 100%, the objective of fluorine recovery can be achieved by adding an excess of calcium carbonate. This was the means of conventional wastewater treatment technology. However, the recovered calcium fluoride contains excess calcium carbonate, and the purpose of high purity recovery is not achieved. Further, addition of a chemical equivalent in which the reaction rate is not approximately 100% results in a decrease in both the recovery rate and the recovery purity. Therefore, there is no means for increasing the recovery rate of high-purity calcium fluoride to 99% or more without developing a new technique that makes the reaction rate approximately 100% by adding a chemical equivalent.

The present inventors have found that the reaction rate is approximately 10 in chemical equivalent.
As a means for reducing the amount to 0%, a technique is proposed in which the transport direction of the etching agent and calcium carbonate is countercurrent. As a result, both high purification of the recovered calcium fluoride and reduction of the fluorine content in the wastewater have been achieved. In this system, it goes without saying that an increase in the amount of processing liquid leads to an increase in the scale of equipment. The present inventors have proposed a means for suppressing the expansion of the equipment scale and further improving the effect of the countercurrent method.
As a result of repeated various studies, a combination method of cocurrent flow and countercurrent flow, and from the results of Fig. 3, a two-stage addition method of granular calcium carbonate and powdered calcium carbonate, hydrogen fluoride system and hydrogen fluoride system,
We came up with the idea of a two-series combination method of ammonium fluoride. The principle and characteristics of each method will be described below.

The first point to note is the solid / liquid phase ratio in the processing system. Hydrogen fluoride type etching agent is usually H
Since F is used at a concentration of 0.5% and is diluted about 10 times in the washing step, the ratio of recovered calcium fluoride / treatment liquid amount is about 1/1000. Hydrogen fluoride / ammonium fluoride etchant system is 2-5% HF concentration after cleaning process.
And the ratio of recovered calcium fluoride / treatment liquid is about 4 ~
It is 10/100. If a large amount of liquid phase treatment, that is, recovery of fluorine in the liquid is carried out in a parallel flow system, and a small amount of solid phase treatment, that is, purification of the recovered calcium fluoride is carried out in a counter flow system, the counter flow system equipment scale becomes parallel. It is possible to reduce in proportion to the solid phase / liquid phase ratio as compared with the case of the flow system.

Further, the particle size of the recovered calcium fluoride is an important characteristic that affects the reuse value. Regarding the reaction between the fluorine-based etching agent and the granular calcium carbonate, it has been clarified that the reaction is a solid-phase formation reaction in the solid phase, that is, calcium carbonate is converted into calcium fluoride without changing the particle shape. Even if the recovered calcium fluoride is pure, if it is in the form of powder, the use value may be significantly reduced not only in the separation, washing, drying and transportation steps but also in the reuse step. For example, it cannot replace natural fluorite currently used as a hydrogen fluoride generating raw material.

In the co-current treatment of the liquid phase, when the particle size of calcium carbonate is increased, it takes a sufficient time to reduce the concentration of fluorine in the liquid, so that it is necessary to expand the scale of treatment equipment. .. The present inventors added most of the calcium carbonate in the form of particles to the first-stage reaction tank, and added the rest in the form of powder to the second-stage reactor to react, thereby increasing the overall particle size and reacting. We devised a method that can shorten the time and reduce the equipment scale.

The particle size of the granular calcium carbonate for coarsening the recovered calcium fluoride is preferably 0.05 to 0.15 mm, but is not particularly limited. The powdery calcium carbonate preferably has a specific surface area of 1000 to 6000 cm ² / g (particle size 30 to 3 μm).

The reaction of the hydrogen fluoride / ammonium fluoride system does not proceed unless the temperature is high. That is, it takes time to complete the reaction of the central portion of calcium carbonate converted to calcium fluoride, which is also related to the scale of equipment. Without waiting for the completion, by combining the reaction of the central part with the processing system of the hydrogen fluoride-based etching agent,
I learned that it can be effectively resolved. That is, the hydrogen fluoride / ammonium fluoride-based etching agent and calcium carbonate are treated in a parallel flow method in an equivalent amount with respect to the reaction calcium carbonate to complete the liquid phase reaction, and the treatment of the solid phase containing the unreacted calcium carbonate is performed by fluorination. Treat with a hydrogen-based etchant in a countercurrent method. In this countercurrent treatment, the solid phase to be treated, that is, calcium fluoride containing unreacted calcium carbonate may be supplied to a stirring tank or may be packed in a fixed bed. In either case, the hydrogen fluoride-based etchant is of a countercurrent system in which unreacted calcium carbonate is completely converted to calcium fluoride and then merged into the co-current treatment in the preceding stage.

FIG. 7 and FIG. 8 show a method for treating an HF-H ₂ O 2 component type etching agent. In FIG. 7, the hydrofluoric acid discharged from the semiconductor process is once put into a storage tank, and is allowed to react with granular calcium carbonate in the reaction tank R1 in a parallel flow system, and then powdery calcium carbonate is added in the reaction tank R2. Is treated to recover 99% or more of fluorine. The wastewater is discharged from the thickener, and the calcium fluoride containing unreacted calcium carbonate is treated in a reaction tank R3 with a hydrogen fluoride-based etching agent in a countercurrent method to obtain high-purity calcium fluoride having a low silica content. To generate. FIG. 8 shows an example in which the hydrofluoric acid storage tank in FIG. 7 is used as a reaction tank.

9 and 10 show HF-NH ₄ F-H ₂ O.
The method for treating a three-component etching agent (buffered hydrofluoric acid) is shown.

FIG. 9 shows that the buffered hydrofluoric acid is reacted in parallel with the equivalent amount of calcium carbonate in the reaction tank R1 at 70 ° C. or higher to recover 99% or more of the fluorine in the waste water and to remove unreacted calcium carbonate. Calcium fluoride contained in the reaction tank R
Then, the treatment is carried out in a countercurrent manner with a hydrogen fluoride-based etching agent to produce high-purity calcium fluoride having a low silica content. The effluent of R2 is supplied to R1 and integrated with buffered hydrofluoric acid for processing.

FIG. 10 shows a hydrogen fluoride system using a fixed bed filled with a fixed amount of calcium fluoride containing unreacted calcium carbonate discharged from the reaction tank R1 instead of the reaction tank R2 of FIG. The etching agent is passed countercurrently to convert into high-purity calcium fluoride. Hydrogen fluoride, or hydrogen fluoride and ammonium fluoride as a main component, and an etching aid that does not form an insoluble calcium salt, such as nitric acid, hydrochloric acid, acetic acid, hydrogen peroxide, or a surfactant, is mixed with each other. High-purity calcium fluoride can be recovered by the same treatment for the blended etching agent.

[0055]

EXAMPLES The constitution and effects of the present invention will be specifically described below by way of examples.

[0056]

Example 1 Using the system shown in FIG. 7, the hydrofluoric acid etching agent was treated at room temperature. It was put into a reaction tank R1 (volume 20M ² ) at a flow rate of 0.5% hydrofluoric acid 2t / h, and granular calcium carbonate (particle size 0.05 to 0.15 m
m) added at a rate of 25 kg / h, and allowed to react for 10 hours by residence, and then powdered calcium carbonate (specific surface area 2
(000-6000 cm ² / g) was added at a rate of 4 kg / h and the reaction was carried out for a residence time of 10 hours. The solution was introduced into a thickener, solid-liquid separation was carried out, the solid part was put into a reaction tank R3, and this was treated by a countercurrent system. That is, 0.5% hydrofluoric acid 4
After passing through R3 at a flow rate of 00 kg / h to convert unreacted calcium carbonate into calcium fluoride, the reaction tank R1
Integrated into. The fluorine concentration in the wastewater discharged from the thickener was 15 ppm or less. The results are shown in Table 1. For the reaction tanks R1 and R2 with a capacity of 20 M ³ , the reaction tank R3
Is reduced to 2M ³ and about 1/10, and it is 99 by countercurrent treatment.
% Or more of calcium fluoride was recovered.

[0057]

Example 2 Using the system shown in FIG. 8, the hydrofluoric acid etching agent was treated at room temperature. Granular calcium carbonate was added to a 50 M ³ stock solution tank R1 into which 0.5% hydrofluoric acid was introduced at 2 t / h at an addition rate of 25 kg / h. The stock solution tank has a stirring mechanism, stays in a solid-liquid mixed state for about 24 hours, and is continuously introduced into the reaction tank R2 in a slurry state. An example of the stirring mechanism in this stock solution tank is shown in FIG. Powdered calcium carbonate was reacted in the reaction vessel R2 at an addition rate of 4 kg / h. Solid-liquid separation was performed with a thickener, and the solid portion was placed in the reaction tank R3 and subjected to countercurrent treatment in the same manner as in Example 1. That is, 0.5% hydrofluoric acid is supplied at a rate of 400 kg / h in a countercurrent manner to convert unreacted calcium carbonate into calcium fluoride, and then the solution exiting R3 is integrated into R1. The results are shown in Table 1.

[0058]

[Table 1]

[0059]

[Embodiment 3] A hydrogen fluoride / ammonium fluoride-based etchant (fluorine content 100
(00 ppm) in a reaction tank R1, first, approximately equivalent amount of granular calcium carbonate was added and reacted at 70 ° C. for 10 hours, and then powdered calcium carbonate was added in approximately equivalent amount to residual fluorine to obtain 10
By reacting for a time, 99% or more of fluorine in the etching agent was removed. The solid-liquid was separated, the solid-phase part was transferred to the reaction vessel R2, and the unreacted calcium carbonate was converted to calcium fluoride by reacting it with a 0.5% HF hydrogen fluoride-based etching agent in a countercurrent manner. By countercurrent treatment, 99% or more of calcium fluoride was recovered. The results are shown in Table 2.

[0060]

[Embodiment 4] Hydrogen fluoride / ammonium fluoride based etching agent (fluorine content 100
00 Ppm) in a reaction vessel R1 and first, approximately equivalent amount of granular calcium carbonate is added and reacted at 70 ° C. for 10 hours, and then approximately equal amount of powdered calcium carbonate is added to the residual fluorine content to obtain 10
By reacting for a time, 99% or more of fluorine in the etching agent was removed. The solid-liquid is separated and the solid-phase part is filled in the fixed bed R2,
Countercurrent treatment was carried out with 0.5% hydrofluoric acid. That is, HF0.
After reacting 5% hydrogen fluoride-based etching agent with liquid to convert unreacted calcium carbonate into calcium fluoride, R
Integrate into 1. The results are shown in Table 2.

[0061]

[Table 2]

[0062]

[Embodiment 5] Wastewater of a system in which various etching aids are mixed with hydrogen fluoride or hydrogen fluoride / ammonium fluoride based etching agents can be treated in the same manner as in the above-mentioned embodiments. That is, the hydrogen fluoride system is at room temperature as shown in FIG.
The hydrogen fluoride / ammonium fluoride system was treated by reacting calcium carbonate in two steps at 70 ° C. using the system of FIG. 9 or FIG. Solid-liquid separation was performed, the liquid phase was discharged as waste water, and the solid phase was reacted with a 0.5% HF hydrogen fluoride etching agent in a countercurrent method to obtain 99% or more of recovered calcium fluoride. The results are shown in Tables 3 and 4.

[0063]

[Table 3]

[0064]

[Table 4]

In any of the examples, almost no silica was recovered in calcium fluoride.

[0066]

[Brief description of drawings]

[0067]

[Figure 1]

FIG. 1 shows hydrogen fluoride-ammonium fluoride-
It is a composition diagram of water 3 element composition.

[0069]

[Fig. 2]

FIG. 2 is an explanatory diagram showing the reactivity of calcium carbonate in the hydrogen fluoride / ammonium fluoride composition region.

[0071]

[Figure 3]

FIG. 3 is a graph showing the relationship between the type of calcium carbonate and its fluorine content.

[0073]

[Figure 4]

FIG. 4 is a graph showing the relationship between reaction rate and temperature.

[0075]

[Figure 5]

FIG. 5 is a composition diagram of a molar composition region such as hydrofluoric acid / hydrosilicofluoric acid.

[0077]

[Figure 6]

FIG. 6 is a graph showing the deposition rate of silica in the calcium fluoride produced by the reaction of the hydrogen fluoride / ammonium fluoride based etching agent with calcium carbonate or calcium hydroxide.

[0079]

[Figure 7]

FIG. 7 is a flow sheet showing an example of the treatment of the HF-H ₂ O 2 component type etching agent.

[0081]

[Figure 8]

FIG. 8 is a flow sheet showing an example of the treatment with an HF-H ₂ O 2 component type etching agent.

[0083]

[Figure 9]

FIG. 9 is a flow sheet showing an example of the treatment with the HF-NH ₄ F-H ₂ O 3 component type etching agent.

[0085]

[Figure 10]

FIG. 10 is a flow sheet showing an example of the treatment with the HF-NH ₄ F-H ₂ O 3 component type etching agent.

[0087]

FIG. 11

FIG. 11 is an explanatory view showing an example of the agitator tank in the stock solution tank.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadahiro Omi 2-17-301 Yonegabukuro, Aoba-ku, Sendai-shi, Miyagi (72) Inventor Hiroyuki Harada 2-25-43 Nishioizumi, Nerima-ku, Tokyo (72) Inventor Masahiro Miki 1-23-14, Tezukayama, Abeno-ku, Osaka-shi, Osaka (72) Inventor Toshiro Fukudome 68-335 Kobuki, Chihaya-akasakamura, Minamikawachi-gun, Osaka Prefecture (72) Inventor Maeno Goro Osaka 2-42-6 Koumeidai, Izumi City, Furukawa Prefecture (72) Norio Terasawa Inventor, Norio Terazawa 1-1-14, Kanda, Chiyoda-ku, Tokyo Inside Hirit Plant Construction Co., Ltd. (72) Yoshihiro Eto Nishishinjuku, Shinjuku-ku, Tokyo 3-4-7 Kurita Industry Co., Ltd. (72) Inventor Masahiro Sakata 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Kurita Industry Co., Ltd.

Claims (7)

[Claims] 1. A method of recovering fluorine as calcium fluoride from hydrogen fluoride or an etching agent containing hydrogen fluoride and ammonium fluoride as main components, wherein the molar equivalent ratio of ammonium fluoride / hydrogen fluoride is 1. In the composition range of 0.0 or less, by reacting calcium carbonate at a temperature of 50 ° C. or more, the unreacted calcium carbonate content is about 3%.
A method for recovering calcium fluoride, which is characterized in that high-purity calcium fluoride having a low silica content is recovered. 2. A method for recovering fluorine as calcium fluoride from hydrogen fluoride or an etching agent containing hydrogen fluoride and ammonium fluoride as main components, wherein the etching agent and calcium carbonate are transferred in the same direction. A method for recovering high-purity calcium fluoride having an unreacted calcium carbonate content of about 1% or less and a low silica content by reacting while flowing. 3. Approximately equivalent amount of calcium carbonate is added to and reacted with hydrogen fluoride or an etching agent containing hydrogen fluoride and ammonium fluoride as main components to recover 99% or more of fluorine, and unreacted carbon dioxide. Calcium content is 1%
The following is a method for recovering high-purity calcium fluoride having a low silica content, wherein the transport direction of the etching agent and the transport direction of calcium carbonate are a combination of cocurrent and countercurrent. How to recover calcium. 4. The method according to any one of claims 1 to 3, wherein the addition of calcium carbonate is carried out in two steps, that is, addition of granular calcium carbonate and addition of powdered calcium carbonate to recover 99% or more of fluorine in the discharged liquid. How to recover calcium fluoride. 5. The transfer directions of the etching agent and calcium carbonate are cocurrent, and the transfer directions of the generated calcium fluoride and the etching agent containing hydrogen fluoride as a main component are countercurrent. The method for recovering calcium fluoride according to claim 3. 6. A method in which the transport directions of the etching agent and calcium carbonate are made parallel, the generated calcium fluoride is packed in a fixed bed, and the transport direction of the etching agent containing hydrogen fluoride as a main component is made countercurrent. The method for recovering calcium fluoride according to claim 3, which is characterized in that. 7. An etching aid containing hydrogen fluoride, or hydrogen fluoride and ammonium fluoride as a main component, which does not form an insoluble calcium salt, such as nitric acid, hydrochloric acid, acetic acid, hydrogen peroxide, or a surfactant. A method for recovering high-purity calcium fluoride by the treatment according to any one of claims 1 to 6 from the etching agents mixed individually or mixed.