JP2012183457A - Separation method and separation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separation method and device, capable of simply separating a hydrofluoric acid of high purity from a mixed acid containing at least the hydrofluoric acid, ammonium hydrogen fluoride, silicon and water.SOLUTION: The separation method includes separating the hydrofluoric acid from the mixed acid 100 containing at least the hydrofluoric acid, ammonium hydrogen fluoride, silicon and water. The method has a first distillation step of recovering a distillate 200 containing the hydrofluoric acid and water by distilling the mixed acid 100, and also of recovering a bottom product 500 containing the ammonium hydrogen fluoride and silicon; and a second distillation step of separating mainly water from the distillate 200 by distilling the distillate 200 and of recovering a bottom product 600 in which the concentration of the hydrofluoric acid is higher than that of the distillate 200.

Description

  The present invention relates to a separation method and a separation apparatus.

Conventionally, an etchant containing hydrofluoric acid and ammonium fluoride is known. Further, a technique for recovering hydrofluoric acid (fluorine) from an etching waste liquid that has been used for etching with such an etching liquid is also widely known (see, for example, Patent Document 1).
In Patent Document 1, fluorine is recovered as high-purity calcium fluoride having a low silica content by reacting calcium carbonate with an etching solution containing hydrofluoric acid and ammonium fluoride, and again from the recovered calcium fluoride. A method for producing hydrofluoric acid for an etchant is described.

  However, such a method cannot directly separate and recover hydrofluoric acid from the etching solution. That is, after recovery as calcium fluoride, a process of using this calcium fluoride as hydrofluoric acid is required, and efficient recovery cannot be performed. Further, there are many processes from the etching waste liquid to the production of a new etching liquid (hydrofluoric acid), and a large amount of secondary waste liquid is generated during the process. Therefore, there is also a problem that the environmental performance is bad. In addition, since there are many processes, there is a problem that the apparatus configuration becomes large and complicated.

JP-A-5-170435

  An object of the present invention is to provide a separation method and a separation apparatus that can easily separate high-purity hydrofluoric acid from a mixed acid containing at least hydrofluoric acid, ammonium hydrogen fluoride, silicon and water.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
[Application Example 1]
The separation method of the present invention is a separation method for separating the hydrofluoric acid from a mixed acid containing at least hydrofluoric acid, ammonium hydrogen fluoride, silicon and water,
A first liquid containing the hydrofluoric acid and water is recovered as a distillate by distilling the mixed acid, and a second liquid containing the ammonium hydrogen fluoride and the silicon is recovered as a bottom liquid. 1 distillation step;
By distilling the first liquid, the water is mainly separated from the first liquid, and the third liquid having a higher concentration of hydrofluoric acid than the first liquid is recovered as a bottom liquid. And a second distillation step.
Thereby, it is possible to easily separate and recover high purity hydrofluoric acid from the mixed acid at a relatively high concentration.

[Application Example 2]
In the separation method of the present invention, it is preferable that the heating temperature of the first liquid in the second distillation step is a set temperature lower than the heating temperature of the mixed acid in the first distillation step.
Thereby, when removing moisture from the first liquid, the amount of hydrofluoric acid mixed into the removed distillate and removed together with moisture can be reduced. Therefore, the yield of hydrofluoric acid can be increased.

[Application Example 3]
In the separation method of the present invention, the solid containing the ammonium hydrogen fluoride and the silicon is crystallized from the second liquid,
The fourth liquid obtained by separating the solid from the second liquid is preferably treated together with the mixed acid in the first step.
Thereby, more hydrofluoric acid can be separated and recovered from the mixed acid.

[Application Example 4]
In the separation method of the present invention, the first distillation step is preferably performed while stirring the mixed acid.
Thereby, the crystallization in the distillation can is suppressed.
[Application Example 5]
The separation method of the present invention preferably has a separation step of separating the ammonium hydrogen fluoride from the solid.
Thereby, it is possible to further separate and recover ammonium hydrogen fluoride from the mixed acid.

[Application Example 6]
In the separation method of the present invention, in the separation step, the ammonium hydrogen fluoride is preferably separated from the solid by a crystallization method.
Thereby, separation of ammonium hydrogen fluoride can be easily performed.
[Application Example 7]
In the separation method of the present invention, in the separation step, a solution in which the solid is dissolved is prepared, the first crystallization step is performed by cooling the solution to a predetermined temperature, and the temperature of the first crystallization. And a second crystallization step performed at a low temperature.
Thereby, higher purity ammonium fluoride can be separated and recovered.

[Application Example 8]
In the separation method of the present invention, the mixed acid is preferably an etching waste solution generated by etching a material containing silicon.
Thereby, the etching waste liquid can be reused, and the cost of the etching process can be reduced. Moreover, since the amount of waste liquid to be discarded can be reduced, it is excellent in terms of environment.
[Application Example 9]
The separation apparatus of the present invention has the separation method of the present invention.
Thereby, the apparatus which isolate | separates and collect | recovers high purity hydrofluoric acid or ammonium hydrogen fluoride from mixed acid can be provided.

It is the schematic of the separation apparatus which concerns on suitable embodiment of this invention. It is the schematic for demonstrating the separation method which concerns on suitable embodiment of this invention. It is a table | surface for demonstrating an Example. It is a table | surface for demonstrating an Example. It is a table | surface for demonstrating an Example.

Hereinafter, a separation method and a separation apparatus of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
FIG. 1 is a schematic diagram of a separation apparatus according to a preferred embodiment of the present invention, FIG. 2 is a schematic diagram for explaining a separation method according to a preferred embodiment of the present invention, and FIGS. It is a table | surface for demonstrating an example.

1. Separation device First, the configuration of the separation device 1 will be described.
The separation apparatus 1 shown in FIG. 1 illustrates a distillation apparatus. The distillate obtained from the distillation apparatus in each step is taken out into a collection container 300, or the distillate is taken out from a distillation can. A batch type separation method in which the discharged liquid and the bottom liquid are transferred to the supply unit of the distillation apparatus in the next step will be described below as an example. However, a separation method may be configured in which a plurality of these distillation apparatuses are arranged, the apparatuses are connected by an infusion pipe, and are separated in an inline manner by valve operation.

Such a separation apparatus 1 includes hydrofluoric acid and hydrogen fluoride from a mixed acid 100 containing hydrofluoric acid [HF], ammonium hydrogen fluoride [(NH ₄ ) HF ₂ ], silicon [Si] and water [H ₂ O]. It is an apparatus (distillation apparatus) for separating and recovering ammonium with high purity and relatively high concentration. The silicon is present in the mixed acid 100 as a silicon compound, specifically, ammonium silicofluoride [(NH ₄ ) ₂ SiF ₆ )].

The mixed acid 100 is, for example, an etching waste liquid. Specifically, for example, the waste liquid is obtained by etching a member containing silicon with an etching liquid containing hydrofluoric acid and ammonium hydrogen fluoride. Examples of the member containing silicon include various types of glass and crystal.
In such a mixed acid 100, a considerable amount of unreacted hydrofluoric acid and ammonium hydrogen fluoride remain as components in the etching process. Therefore, these can be used again as a component of the etching solution by separately collecting them.

Thus, by separating unreacted etching components from the etching waste liquid, the etching waste liquid can be reused, and the cost of the etching process can be reduced. Moreover, since the amount of the etching waste liquid to be disposed of is reduced, excellent environmental properties can be exhibited.
Although the density | concentration of the hydrofluoric acid before isolation | separation in the mixed acid 100 is not specifically limited, For example, it is about 10-20 wt%. Further, the concentration of ammonium hydrogen fluoride before separation in the mixed acid 100 is not particularly limited, but is, for example, about 25 to 35 wt%. Further, the concentration of silicon before separation in the mixed acid 100 is not particularly limited, but is, for example, about 0.1 to 1.0 wt%.

Here, the concentrations of hydrofluoric acid, ammonium hydrogen fluoride, and silicon in the mixed acid 100 can be obtained as follows.
(Silicon concentration measurement)
Qualitative and quantitative analysis of metal elements contained in the mixed acid 100 is performed using an IPC emission spectrometer (for example, product name “ICPS-7510” manufactured by Shimadzu Corporation). Thereby, since the metal atom in the mixed acid 100 is only silicon, the concentration A (mol / l) of silicon in the mixed acid 100 can be obtained thereby.

(Measurement of ammonium hydrogen fluoride concentration)
An indophenol blue absorptiometry was carried out using an ultraviolet / visible spectrophotometer (for example, product name “IUV-1240” manufactured by Shimadzu Corporation). The total concentration B (mol / l) of (NH 4 ⁺ ) possessed by ammonium fluoride can be determined. As described above, since silicon in the mixed acid 100 exists as ammonium silicofluoride, by subtracting the (NH 4 ⁺ ) concentration 2A of ammonium silicofluoride from the total concentration B, the fluorination in the mixed acid 100 is performed. The concentration C (mol / l) of ammonium hydrogen can be determined. That is, C = B-2A.

(Measurement of hydrofluoric acid concentration)
The acid concentration of the mixed acid 100 is measured using an automatic potentiometric titrator (for example, product name “AT-510” manufactured by Kyoto Electronics Industry Co., Ltd.). Specifically, the acid concentration of the mixed acid 100 is measured by neutralization with a 0.1 mol / dm 3 sodium hydroxide aqueous solution. Thereby, the total acid concentration D which hydrofluoric acid in the mixed acid 100, ammonium hydrogen fluoride, and ammonium silicofluoride has can be calculated | required. As described above, since the ammonium silicofluoride concentration A and the ammonium hydrogen fluoride concentration B in the mixed acid 100 are known, the acid concentration 4A possessed by ammonium silicofluoride and the acid concentration B possessed by ammonium hydrogen fluoride are subtracted from the total acid concentration D. Thus, the hydrofluoric acid concentration E (mol / l) in the mixed acid 100 can be obtained. That is, E = D-4A-B.
The example of the method for measuring the concentration of hydrofluoric acid, ammonium hydrogen fluoride, and silicon in the mixed acid 100 has been described above.

  As shown in FIG. 1, the separation device 1 of the present embodiment includes a distillation can (distillation vessel) 11, a supply unit 12 that supplies the mixed acid 100 to the distillation can 11, a heating unit 13 that heats the distillation can 11, Stirring means 14 for stirring the mixed acid 100 in the distillation can 11, a cooling unit 15 for cooling the vapor generated from the distillation can 11 to obtain a distillate 200, a recovery unit 16 for recovering the distillate 200, and an exhaust gas treatment And means 17.

Among each part which comprises the separation apparatus 1, what can contact the mixed acid 100 has acid resistance, respectively. In this embodiment, acid resistance is imparted by forming a portion that can come into contact with the mixed acid 100 with polytetrafluoroethylene (PTFE).
The method for imparting acid resistance is not limited to this. For example, the site that can come into contact with the mixed acid 100 is composed of an acid-resistant plastic such as vinyl chloride resin or acrylic resin, or a metal material. Alternatively, the main body surface may be constituted by coating a fluororesin. Since the mixed material of these metals and acid-resistant resin has good thermal conductivity, it is convenient because liquid temperature adjustment by external heating and cooling can be performed in a short time.

(Supply unit 12)
A mixed acid 100 is stored in the supply unit 12. Such a supply unit 12 is provided above the distillation can 11. A cock 181 is provided in the middle of the flow path connecting the supply unit 12 and the distillation can 11, and the mixed acid 100 stored in the supply unit 12 is supplied to the distillation can 11 by operating the cock 181. Or, conversely, the supply can be stopped.

(Distillation can 11)
The distillation can 11 is a tank for distilling the mixed acid 100. In such a distillation can 11, a guide path 111 for guiding the generated steam to the cooling unit 15 is formed. In the distillation can 11, a thermometer 191 that measures the temperature of the mixed acid 100 and a thermometer 192 that measures the temperature of the steam flowing in the induction path 111 are installed.

(Heating unit 13)
The heating unit 13 has a function of heating the mixed acid 100 through the distillation can 11. As the heating part 13, it can be comprised with the mantle heater provided so that the lower part of the distillation can 11 might be covered like this embodiment, for example. Such a heating part 13 can control the drive so that the temperature of the mixed acid 100 and the steam becomes a predetermined temperature based on the detection results of the thermometers 191 and 192.
In addition, as the heating part 13, if the mixed acid 100 can be heated, it will not be limited to said structure.

(Stirring means 14)
The separation device 1 preferably has a stirring means 14.
The stirring means 14 has a function of stirring the mixed acid 100 in the distillation can 11. By performing distillation while stirring the mixed acid 100 by the stirring means 14, mass transfer is promoted in the mixed acid 100, and crystallization of a solid (solid) can be suppressed. In particular, it is possible to suppress crystallization and the like due to concentration localization near the liquid surface or the inner wall of the container.

Such a stirring means 14 has a stirrer bar (stirring bar) 141 disposed in the distillation can 11 and a hot stirrer (stirring device) 142 on which the distillation can 11 and the heating unit 13 are placed. The mixed acid 100 is stirred by rotating the stirrer bar 141 by the stirrer 142.
Instead of the hot stirrer 142 provided with heating means, a stirrer that does not have heating means may be used. Further, even if the stirrer is not provided, the liquid in the distillation can 11 may be stirred by physical means such as applying vibration to the wall surface of the container.

(Cooling unit 15)
The cooling unit 15 has a function of cooling the vapor generated by heating the mixed acid 100 and obtaining the distillate 200. As such a cooling unit 15, a generally known cooling pipe can be used. That is, the cooling unit 15 includes an inner tube 151 and an outer tube 152, and is configured such that steam flows through the inner tube 151 and cooling water flows between the inner tube 151 and the outer tube 152. . Thereby, the steam flowing through the inner pipe 151 is cooled by the cooling water and liquefied, and the distillate 200 is obtained.
The length of the inner pipe 151, the temperature of the cooling water, and the like are not particularly limited as long as the distillate 200 can be obtained.

(Recovery unit 16)
The recovery unit 16 is connected to the cooling unit 15 and has a function of recovering the distillate 200. A cock 182 is provided at the bottom of the recovery unit 16, and by operating the cock 182, the distillate 200 collected in the recovery unit 16 is removed from the separation device 1 (for example, as shown in FIG. 1). Such a recovery container 300) can be discharged.

(Exhaust gas treatment means 17)
The exhaust gas treatment means (gas cleaning unit) 17 has a function of neutralizing exhaust gas that has not been liquefied by the cooling unit 15. Such an exhaust gas treatment means 17 has a container in which water or an alkaline cleaning liquid 400 is stored, and performs exhaust gas neutralization by inducing the exhaust gas into the cleaning liquid 400.
The configuration of the separation device 1 has been described above.

2. Next, a method for separating and recovering hydrofluoric acid from the mixed acid 100 (the separation method of the present invention) will be described.
The separation method of the present invention shown schematically in FIG. 2 has a first distillation step and a second distillation step. The separation method described below is a separation method in which the distillate 200 is taken out from the mixed acid 100 in the first distillation step and then the bottoms 600 are taken out from the distillate 200 in the second distillation step. After the completion of the first distillation step, the batch processing method for carrying out the second distillation step and the distillation apparatus used for each of the first distillation step and the second distillation step are installed side by side. The system may be either an in-line system in which a space is connected by an infusion pipe and processing is performed by a valve operation or a pump operation.

(First distillation step)
For example, the mixed acid 100 is supplied from the supply unit 12 to the distillation can 11, and the mixed acid 100 is heated to a predetermined temperature by the heating unit 13, thereby distilling the mixed acid 100 under atmospheric pressure. At this time, the mixed acid 100 in the distillation can 11 may be stirred by the stirring means 14. Although it does not specifically limit as heating temperature (the said predetermined temperature) of the mixed acid 100, For example, it is about 120-140 degreeC.

  As a result, water and hydrofluoric acid mainly evaporate from the mixed acid 100, and these vapors reach the cooling unit 15 via the induction path 111. The vapor that reaches the cooling unit 15 is cooled by the cooling unit 15, becomes a distillate (first liquid) 200, and is collected by the collection unit 16. The distillate 200 collected in the collection unit 16 is a relatively low concentration hydrofluoric acid (hydrofluoric acid aqueous solution) mainly composed of water and hydrofluoric acid.

Here, the hydrofluoric acid concentration of the distillate 200 is not particularly limited, but is about 0.75 A to 1.1 A (wt%) when the hydrofluoric acid concentration of the mixed acid 100 is A (wt%). Is preferred.
Further, the yield (%) of hydrofluoric acid recovered as the distillate 200, that is, {(amount of hydrofluoric acid contained in the distillate 200 / amount of hydrofluoric acid contained in the mixed acid 100) × 100} It is preferably about 55% or more. Thereby, the quantity of the hydrofluoric acid collect | recovered as the distillate 200 can be made sufficient.

The distillate amount (%) of the distillate 200, ie, {(weight of distillate 200 / weight of mixed acid 100) × 100} is not particularly limited, but is preferably about 55 to 70%. . Thereby, a sufficient amount of the distillate 200 can be obtained while ensuring the safety of the apparatus.
By sufficiently performing such a first distillation step, water and hydrofluoric acid can be separated from the mixed acid 100.

(Second distillation step)
After finishing the first distillation step described above, the bottoms (second liquid) 500 present in the distillation can 11 is discharged from the distillation can 11 and transferred to a collection container (not shown). The bottoms 500 is subjected to another process as will be described later.
Next, in the empty distillation apparatus 1, the distillate 200 is supplied from the supply unit 12 to the distillation can 11, and the distillate 200 is heated to a predetermined temperature by the heating unit 13. Distill under atmospheric pressure. At this time, the distillate 200 in the distillation can 11 may be stirred by the stirring means 14. Although it does not specifically limit as heating temperature (the said predetermined temperature) of the distillate 200, For example, it is about 100-120 degreeC.

As a result, water and a small amount of hydrofluoric acid are evaporated from the distillate 200, and the vapor reaches the cooling unit 15 via the guide path 111. The steam that has reached the cooling unit 15 is cooled by the cooling unit 15, and hydrofluoric acid having a relatively low concentration is recovered by the recovery unit 16.
By sufficiently performing such a second distillation step, more water than hydrofluoric acid can be separated from the distillate 200. That is, the distillate 200 can be concentrated, and the distillate (third liquid) 600 remaining in the distillation can 11 after the second distillation step has a hydrofluoric acid concentration higher than that of the distillate 200. It becomes high hydrofluoric acid (hydrofluoric acid aqueous solution).

In particular, it is removed when water is removed from the distillate 200 by setting the heating temperature of the distillate 200 in the second distillation step lower than the heating temperature of the mixed acid 100 in the first distillation step. The amount of hydrofluoric acid mixed into the distillate and removed together with moisture can be reduced. Therefore, the yield of hydrofluoric acid can be increased.
Here, the hydrofluoric acid concentration of the bottoms 600 is not particularly limited, but when the hydrofluoric acid concentration of the mixed acid 100 is A (wt%), it is about 2.0 A to 3.0 A (wt%). Is preferred.

Further, the yield (%) of hydrofluoric acid recovered as the bottoms 600, that is, {(amount of hydrofluoric acid contained in bottoms 600 / amount of hydrofluoric acid contained in the mixed acid 100) × 100} It is preferably about 30% or more. Thereby, the quantity of the hydrofluoric acid collect | recovered as the bottoms 600 can be made sufficient.
The bottoms 600 (hydrofluoric acid) thus obtained can be used again as an etching solution. When used as an etching solution, for example, it may be mixed with a new etching solution. Moreover, the bottoms 600 can be used for the purpose of adjusting the hydrofluoric acid concentration of a new etching solution.

The method for separating hydrofluoric acid from the mixed acid 100 has been described above.
According to such a method, it is possible to easily and efficiently separate and recover high-purity hydrofluoric acid having a relatively high concentration from the mixed acid. In addition, a new etching solution can be generated by mixing chemicals separated and recovered from the etching waste solution, so that the etching waste solution can be reused and the cost of the etching process can be reduced. . In addition, since the amount of etching waste liquid that is discarded without being reused is reduced, excellent environmental performance can be exhibited.

3. Ammonium hydrogen fluoride separation method Ammonium hydrogen fluoride can be separated and recovered from the bottoms 500 obtained during the hydrofluoric acid separation method described above. Hereinafter, this separation method will be described with reference to FIG.
The bottoms 500 obtained in the first distillation step described above is crystallized by cooling or the like to precipitate a solid containing ammonium hydrogen fluoride and ammonium silicofluoride. Depending on the evaporation amount of water from the mixed acid 100, the solid 900 containing ammonium hydrogen fluoride and ammonium silicofluoride may be deposited without performing the cooling.

Therefore, first, the solid 900 is separated from the bottoms 500. The separation method is not particularly limited, and for example, a general precipitation method can be used. That is, the solid 900 can be separated from the bottoms 500 by precipitating the solids 900 in the bottoms 500.
Here, in the liquid (fourth liquid) 700 obtained by separating the solid 900 from the bottoms 500, hydrofluoric acid that cannot be separated in the first distillation step remains. Therefore, such a liquid 700 may be returned to the supply unit 12 and treated together with the mixed acid 100 through the first distillation step. Thereby, more hydrofluoric acid can be separated and recovered from the mixed acid 100. In addition, since this process is suitable and is not essential, the arrow in FIG. 2 is shown with the dashed-dotted line.

Next, after the solid 900 is dried, the solid 900 is completely dissolved in a solvent such as water (about 50 to 70 ° C.) to obtain a solution (fifth liquid) 801. Thereafter, the solution 801 is cooled in two stages, and solids having different weight ratios of ammonium hydrogen fluoride and ammonium silicofluoride are precipitated at each stage using the difference in solubility.
First, the solution 801 is cooled to about 35 to 60 ° C. (first crystallization step). As a result, a solid 810 is deposited in the solution 801. Next, after removing the solid 810 from the solution 801 (a solution obtained by removing the solid 810 from the solution 801 is referred to as “solution 802”), the solution 802 is cooled to about 5 to 20 ° C. (second crystallization step) ). As a result, a solid 820 is precipitated in the solution 802.

The dried solid 810 contains, for example, about 70-80 wt% ammonium hydrogen fluoride and about 20-30 wt% ammonium silicofluoride. The dried solid 820 contains about 95 to 99 wt% ammonium hydrogen fluoride and about 1 to 5 wt% ammonium silicofluoride.
In this way, by depositing the solid 820, ammonium hydrogen fluoride can be separated and recovered from the mixed acid 100 at a high concentration (high purity).

If the first crystallization step is sufficient depending on the concentration of ammonium hydrogen fluoride to be obtained, the obtained solid 810 may be used as a raw material for a new etching solution without performing the second crystallization step.
Here, in the solution 803 obtained by removing the solid 820 from the solution 802, ammonium hydrogen fluoride that could not be separated in this step remains. Therefore, such a solution 803 may be returned to the supply unit 12 and treated together with the mixed acid 100 by the first distillation step. As a result, more ammonium hydrogen fluoride can be separated and recovered.

  As mentioned above, although the separation method and the separation apparatus of the present invention have been described based on the illustrated embodiments, the separation method and the separation apparatus of the present invention are not limited to these, and other arbitrary components and processes. May be added. Moreover, although the combination of the several distillation process and the crystallization process was demonstrated, even if it implements only the separation method which isolate | separates a hydrofluoric acid using a some distillation process, the reproduction | regeneration technique with favorable environmental property can be provided.

Hereinafter, specific examples of the present invention will be described.
Example 1
A mixed acid as an etching waste liquid was prepared. The hydrofluoric acid concentration before separation of the mixed acid is 12.6 wt%, the concentration of ammonium hydrogen fluoride before separation is 27.6 wt%, and the concentration before separation of silicon is 0.4 wt%. The rest was almost water. These concentrations were measured using the apparatus and method described above (the same applies to the concentrations described below).

[First distillation step]
500 g of mixed acid was put into a distillation can, and distillation was performed by heating the mixed acid to 120 ° C. under atmospheric pressure. Thereby, hydrofluoric acid (hydrofluoric acid aqueous solution) was obtained as a distillate A. This step was performed until the distillate amount reached 60%, and 297 g of distillate A was obtained.
When the concentration of each component in the distillate A was measured, the concentration of hydrofluoric acid was 10.5 wt%, the concentration of ammonium hydrogen fluoride was 0.01 wt%, and the concentration of silicon was 0.02 wt%. The yield of hydrofluoric acid with respect to the mixed acid was 49.6%.

[Second distillation step]
Next, the distillate A obtained in the first distillation step was put into a distillation can, and distillation was performed by heating the distillate A to 120 ° C. under atmospheric pressure. As a result, a relatively low concentration of hydrofluoric acid was obtained as distillate B. This step was performed until the distillate amount reached 80%, and 223 g of distillate B was obtained. When the concentration of each component in the distillate B was measured, the concentration of hydrofluoric acid was 4.8 wt%, the concentration of ammonium hydrogen fluoride was 0 wt%, and the concentration of silicon was 0.008 wt%.

On the other hand, 53 g of bottoms C was obtained from the distillation can. When the concentration of each component in the bottoms C was measured, the concentration of hydrofluoric acid was 32.1 wt%, the concentration of ammonium hydrogen fluoride was 0.08 wt%, and the concentration of silicon was 0.08 wt%. Moreover, the yield of hydrofluoric acid with respect to the mixed acid was 27.0%.
Thus, high concentration and high purity hydrofluoric acid could be recovered as bottoms C.

[Separation process]
In the first distillation step, 193 g of bottoms D was obtained from the distillation can. A solid (solid content) was precipitated in the bottoms D. This solid was separated from the bottoms D by a precipitation method and dried. This gave 97 g of solid E. As a result of measuring the components of the solid E, the solid E contained 85.1 wt% ammonium hydrogen fluoride and 11.0 wt% ammonium silicofluoride.

  Next, 80 g of solid (solid E before drying) precipitated in the bottoms was mixed with 50 g of distilled water, and completely dissolved at 50 ° C. to obtain 130 g of solution F. Next, the solution F was cooled to 35 ° C., and a solid G was precipitated in the solution F. Next, the solid G was separated from the solution F by the precipitation method, and the solid G was dried. As a result, 13 g of solid G was obtained. As a result of measuring the components of the solid G, the solid G contained 77.7 wt% ammonium hydrogen fluoride and 21.3 wt% ammonium silicofluoride.

Next, 108 g of the solution F from which the solid G was separated was cooled to 20 ° C., and the solid H was precipitated in the solution F. Next, the solid H was separated from the solution F by the precipitation method, and the solid H was dried. As a result, 14 g of solid H was obtained. As a result of measuring the components of the solid H, the solid H contained 96.6 wt% ammonium hydrogen fluoride and 3.4 wt% ammonium silicofluoride. The yield of ammonium hydrogen fluoride based on the mixed acid was 29.1%.
Thus, high purity ammonium hydrogen fluoride could be recovered as solid H.
In addition, the above result is shown in FIG. 3 and FIG.

(Example 2)
A mixed acid as an etching waste liquid was prepared. The hydrofluoric acid concentration of this mixed acid is 16.8 wt%, the concentration of ammonium hydrogen fluoride is 31.2 wt%, the concentration of silicon is 0.11 wt%, and the remainder is almost water. It was.
[First distillation step]
Next, 500 g of mixed acid was put into a distillation can, and distillation was performed by heating the mixed acid to 120 ° C. under atmospheric pressure. Thereby, hydrofluoric acid (hydrofluoric acid aqueous solution) was obtained as a distillate A ′. This step was performed until the distillate amount reached 65%, and 322 g of distillate A ′ was obtained.
When the concentration of each component in the distillate A was measured, the concentration of hydrofluoric acid was 18.2 wt%, the concentration of ammonium hydrogen fluoride was 0.01 wt%, and the concentration of silicon was 0.01 wt%. The yield of hydrofluoric acid with respect to the mixed acid was 69.8%.

[Second distillation step]
Next, the distillate A ′ obtained in the first distillation step was put into a distillation can, and distillation was performed by heating the distillate A ′ to 120 ° C. under atmospheric pressure. As a result, a relatively low concentration of hydrofluoric acid was obtained as distillate B ′. This step was performed until the distillate amount reached 69%, and 222 g of distillate B ′ was obtained. When the concentration of each component in the distillate B ′ was measured, the concentration of hydrofluoric acid was 12.4 wt%, the concentration of ammonium hydrogen fluoride was 0 wt%, and the concentration of silicon was 0.004 wt%.

On the other hand, 80 g of bottoms C ′ was obtained from the distillation can. When the concentration of each component in the bottoms C ′ was measured, the concentration of hydrofluoric acid was 34.5 wt%, the concentration of ammonium hydrogen fluoride was 0.23 wt%, and the concentration of silicon was 0.01 wt%. The yield of hydrofluoric acid with respect to the mixed acid was 32.8%.
Thus, high concentration and high purity hydrofluoric acid could be recovered as the bottoms C ′.

[Separation process]
In the first distillation step, 171 g of bottoms D ′ was obtained from the distillation can. A solid (solid content) was precipitated in the bottoms D ′, and this solid was separated from the bottoms D ′ and dried. This gave 76 g of solid E ′. As a result of measuring the components of the solid E ′, the solid E ′ contained 96.6 wt% ammonium hydrogen fluoride and 3.0 wt% ammonium silicofluoride.
The same operation as in Example 1 was performed to recover high purity ammonium hydrogen fluoride.
The above results are shown in FIG.

  DESCRIPTION OF SYMBOLS 1 ... Separator 11 ... Distillation can 111 ... Guidance path 12 ... Supply part 13 ... Heating part 14 ... Stirring means 141 ... Stirrer bar 142 ... Hot stirrer 15 ... Cooling part 151 ... Inner pipe 152 ... Outer pipe 16 ... Recovery part 17 ... Exhaust gas treatment means 181 ... Cock 182 ... Cook 191 ... Thermometer 192 ... Thermometer 100 ... Mixed acid 200 ... Distillate 300 ... Recovery container 400 ... Cleaning liquid 500 ... Takeout liquid 600 ... Takeout liquid 700 ... Liquid 801 ... Solution 802 ... Solution 803 ... Solution 810 ... Solid 820 ... Solid 900 ... Solid

Claims (9)

A separation method for separating the hydrofluoric acid from a mixed acid containing at least hydrofluoric acid, ammonium hydrogen fluoride, silicon and water,
A first liquid containing the hydrofluoric acid and water is recovered as a distillate by distilling the mixed acid, and a second liquid containing the ammonium hydrogen fluoride and the silicon is recovered as a bottom liquid. 1 distillation step;
By distilling the first liquid, the water is mainly separated from the first liquid, and the third liquid having a higher concentration of hydrofluoric acid than the first liquid is recovered as a bottom liquid. And a second distillation step.   The separation method according to claim 1, wherein the heating temperature of the first liquid in the second distillation step is a set temperature lower than the heating temperature of the mixed acid in the first distillation step. Crystallizing the ammonium hydrogen fluoride and the solid containing silicon from the second liquid,
The separation method according to claim 1 or 2, wherein the fourth liquid obtained by separating the solid from the second liquid is treated again with the mixed acid in the first step.   The separation method according to claim 1, wherein the first distillation step is performed while stirring the mixed acid.   The separation method according to claim 1, further comprising a separation step of separating the ammonium hydrogen fluoride from the solid.   The separation method according to claim 5, wherein in the separation step, the ammonium hydrogen fluoride is separated from the solid by a crystallization method.   In the separation step, a solution in which the solid is dissolved is prepared, a first crystallization step is performed by cooling the solution to a predetermined temperature, and a second crystallization step is performed at a temperature lower than the temperature of the first crystallization. The separation method according to claim 5, further comprising:   The separation method according to claim 1, wherein the mixed acid is an etching waste liquid generated by etching a material containing silicon.   A separation apparatus comprising the separation method according to claim 1.

Images