JP3378892B2 - Method for recovering calcium fluoride from fluorine-based etchant - Google Patents

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 functional additive components, is used in the semiconductor manufacturing field and its related fields. In addition to being widely used in the surface treatment field of various metal materials, single crystal materials, optical materials, etc., with the increasing demand for them, the need for recovery technology is increasing from the viewpoint of environmental purification, especially resource recovery. It was

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

[0003]

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

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

First, the fluorine-based wastewater treatment technology is as follows. Japanese Patent Application Laid-Open No. 51-19364 as a wastewater treatment for cleaning the surface of hydrofluoric acid on stainless steel, and Japanese Patent Publication No. 56-1012 as a treatment for removing fluorine and phosphorus from wastewater of phosphoric acid process
No. 0, Japanese Patent Publication No. 57-39985, Japanese Patent Publication No. 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. Each of these uses excess calcium salt,
Since the purpose is to purify wastewater by secondary treatment or separation of coexisting components or a combination of separation treatments, purification of calcium fluoride produced cannot be achieved.

US Pat. Nos. 2,780,521 and US Pat. No. 2,780,521 are used as a technique for separating calcium in a filtrate by producing calcium fluoride using calcium carbonate for the purpose of recovering colloidal silica from a hydrosilicofluoric acid solution. 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 Laid-Open Patent Publication No. 50142496 proposes a method of adding calcium carbonate in two stages as a waste phosphoric acid process wastewater purification technique. The recovered solid is washed with mineral acid to remove excess calcium carbonate. .

As a technique for treating exhaust gas containing fluorine, the exhaust gas is absorbed in caustic potash, and 1.0 ± 0.2 equivalents of potassium hydroxide is added to the produced potassium fluoride to react them, and calcium fluoride is mainly used. 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 matter, 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.

A method of adding slaked lime in two stages is a technique for treating the fluorine-containing ammonium waste liquid.
No. 6355. That is, in the first stage, a small amount of slaked lime was added to the fluorine to precipitate and separate high-grade calcium fluoride, and in the second stage, 2 equivalents of slaked lime was further added to obtain low-grade fluorinated calcium. In this method, calcium is precipitated and separated, 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, which is the object of the present invention, or ammonium fluoride. 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 is to use 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 subject 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 an ammonium fluoride concentration of 40%, the ammonium fluoride / hydrogen fluoride molar equivalent ratios of various etching agents range from 0 to infinity, so that the chemical species of fluorine 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. In the present invention, this has to be clarified first, since there has been no study on the existence of a composition region capable of optimizing the reaction rate of calcium carbonate.

The resource value when the unreacted calcium carbonate is contained in the recovered calcium fluoride is shown below for the hydrogen fluoride production 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,
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 and causes hydrogen fluoride gas to contain water and carbon dioxide gas, and at the same time consumes various substances and heat for its treatment. For this reason, if calcium fluoride contains 1.0% of calcium carbonate, 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 a silicon compound, 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. Often, hydrosilicofluoric acid is 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 fluoride ion by the 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 to 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]

In 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 where the [NH ₄ F] / [HF] ratio is 1.0 or less (where the [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, when treated with granular calcium carbonate at room temperature, the recovery rate of fluorine is 94% after 9 hours. 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 defluorination is diminished by the action of heating and calcium carbonate 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 investigation conducted on a binary system of hydrogen fluoride / hydrosilicofluoric acid. HF and H ₂
Even if SiF ₆ is present at an equal F concentration, when it is 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 a 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 is extremely large.

[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 type of industry and are considered to change as needed, but they do not leave the composition range shown in FIG. In this composition range, high-purity calcium fluoride can be recovered 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 process is coexisting, 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 hydrogen fluoride, or an etching agent containing hydrogen fluoride and ammonium fluoride as main components, in which an equivalent amount of calcium carbonate is added to the etching agent. In this way, 99% or more of the fluorine in the waste water is recovered, and the unreacted calcium carbonate content is 1% or less,
It is characterized in that high-purity calcium fluoride having a silica content of 0.08% or less is recovered.

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. Granular calcium carbonate has a particle size of 3
0 to 3 μm, and its specific surface area is 1000 to 6
It is preferably 000 cm ² / g.

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 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 method, it goes without saying that an increase in the amount of processing liquid leads to an increase in equipment scale. The present inventors have proposed means for suppressing the expansion of the equipment scale and further enhancing the effect of the countercurrent method.
As a result of various studies, a combined 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 features 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 cleaned with a HF concentration of 2-5%.
And the ratio of recovered calcium fluoride / treatment liquid amount 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 to calcium fluoride without changing the particle shape. Even if the recovered calcium fluoride is pure, if it is in the form of powder, its usefulness may be significantly reduced not only in the separation, washing, drying and transportation steps but also in the recycling step. For example, it cannot replace the 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 of the reaction. We devised a method that can shorten the time and reduce the scale of equipment.

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 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 into 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 unreacted calcium carbonate is performed by fluorination. It is processed in countercurrent with a hydrogen-based etchant. 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 method, and then powdery calcium carbonate is added in the reaction tank R2. And treated to recover 99% or more of fluorine. The wastewater is discharged from the thickener, and 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 with 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.
A 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 fluorine in the wastewater and to remove unreacted calcium carbonate. Calcium fluoride contained in the reaction tank R
Then, it is treated with hydrogen fluoride-based etching agent in a countercurrent method 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 which does not form an insoluble calcium salt, for example, nitric acid, hydrochloric acid, acetic acid, hydrogen peroxide, a surfactant, etc., may be mixed or mixed. 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 with reference to examples.

[0056]

Example 1 Using the system shown in FIG. 7, a hydrofluoric acid etching agent was treated at room temperature. A 0.5% hydrofluoric acid at a flow rate of 2 t / h was put into a reaction tank R1 (capacity 20 M ² ), 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 period of 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] Using the system of FIG. 10, a hydrogen fluoride / ammonium fluoride based etching agent (fluorine content 100
00 Ppm) into the reaction vessel R1 and first add approximately equivalent amount of granular calcium carbonate and react at 70 ° C. for 10 hours, and then add powdery calcium carbonate in approximately equivalent amount to the residual fluorine content to obtain 10
By reacting for a period of 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 a hydrogen fluoride / ammonium fluoride-based etching agent can be treated in the same manner as in the above embodiment. 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 manner 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 / silicofluoric acid.

[0077]

[Figure 6]

FIG. 6 is a graph showing the deposition rate of silica in calcium fluoride produced by the reaction of a 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 of the HF-H ₂ O 2 component type etching agent.

[0083]

[Figure 9]

FIG. 9 is a flow sheet showing an example of the treatment of 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.

Front page continuation (72) Inventor Sorayuki Harada 2-25-43 Nishi-oizumi, Nerima-ku, Tokyo (72) Inventor Masahiro Miki 1-chome, Tezukayama, 1-chome, Tezukayama, Abeno-ku, Osaka, Osaka (72) Inventor, Fukudome Toshiro 68-335 Chibaya Akasakamura, Minamikawachi-gun, Osaka Prefecture Kobuki 68-335 (72) Inventor Matagoro Maeno 2-42-6 Komeidai, Izumi City, Osaka Prefecture (72) Norio Terazawa 1-1-1, Uchikanda, Chiyoda-ku, Tokyo No. 14 Inside Hitachi Plant Construction Co., Ltd. (72) Inventor Yoshihiro Eto 3-4 7 Nishishinjuku, Shinjuku-ku, Tokyo Inside Kurita Kogyo Co., Ltd. (72) Masahiro Sakata 3-4 Nishishinjuku, Shinjuku-ku, Tokyo No. 7 Kurita Industry Co., Ltd. (56) Reference JP-A-5-201726 (JP, A) JP-A-50-10798 (JP, A) US Patent 4120940 (US, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C01F 11/22 C02F 1/58

Claims (3)

(57) [Claims] 1. An 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 to contain unreacted calcium carbonate. In the method for recovering high-purity calcium fluoride having a rate of 1% or less and a silica content of 0.08% or less, the transport direction of the etching agent and calcium carbonate is set to cocurrent to transport the generated calcium fluoride. A method for recovering calcium fluoride, characterized in that the flow direction and the transfer direction of an etching agent containing hydrogen fluoride as a main component are countercurrent. 2. The addition of calcium carbonate to a particle size of 0.05 m
The method for recovering calcium fluoride according to claim 1, wherein 99% or more of fluorine in the discharged liquid is recovered in two stages by adding granular calcium carbonate of m or more and powdered calcium carbonate of 30 μm or less in particle size. . 3. The etching agent and calcium carbonate are co-currently flowed, the generated calcium fluoride is packed in a fixed bed, and the etching agent mainly containing hydrogen fluoride is counter-currently transferred. The method for recovering calcium fluoride according to claim 1, which is characterized in that.