TW201439010A - Method for removing si from waste liquid of si-containing hydrofluoric acid, method for recovering hydrofluoric acid from mixed acid waste liquid of si-containing hydrofluoric acid, and recovery device - Google Patents

Abstract

A removing method according to the present invention comprises a Si removing process which adds salts to a waste fluid containing hydrofluoric acid and Si and removes precipitates produced by the addition of the salts thereby obtaining Si-removed waste fluid. It is desirable to use one or more kinds of salts selected from the group consisting of metal fluoride salts and chloride metal salts for salts. According to the removing method, it is possible to effectively reduce or remove Si contained in Si-containing hydrofluoric acid waste fluid.

Description

Method for removing Si from a hydrofluoric acid-based waste liquid containing Si, and method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si, and a recovery device

The present invention relates to a method for removing Si from a hydrofluoric acid-based waste liquid such as an etchant used as a semiconductor, and a method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid, and a recovery apparatus.

At present, a hydrofluoric acid (hydrofluoric acid) solution such as a hydrofluoric acid aqueous solution, a hydrofluoric acid-hydrochloric acid aqueous solution, or a hydrofluoric acid-nitric acid aqueous solution is used as an etchant in a semiconductor factory or the like. Since the etching function is reduced by repeated etching, a large amount of hydrofluoric acid-based waste liquid is discharged from the semiconductor factory. In the hydrofluoric acid-based waste liquid after the etching, a metal such as Si is mixed, so that it cannot be reused. In the present case, the hydrofluoric acid-based waste liquid is subjected to a neutralization treatment and then discharged (for example, refer to Patent Document 1).

Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-126722 (paragraph 0002)

However, due to the aforementioned neutralization treatment, a trace amount of fluorine is contained in the drainage water, and even a small amount is inevitably caused by environmental pollution. From the viewpoint of environmental preservation, the method of applying the neutralization treatment is not a comparison. Good means.

In addition, in recent years, the price of raw materials for hydrofluoric acid has risen, so it is strongly demanded that such fluorine resources can be reused.

However, when the hydrofluoric acid-based mixed acid waste liquid is distilled by removing the mixed metal such as Si, SiF ₄ (antimony tetrafluoride) or the like is formed, and since the volatility of the SiF ₄ is high, it is mixed in the distillate. As a result, it was not possible to obtain a hydrofluoric acid-based mixed acid waste liquid in which Si was reduced or removed.

The present invention has been made in view of the above technical background, and an object thereof is to provide a method for efficiently removing or removing Si contained in a hydrofluoric acid-based waste liquid and removing Si from a hydrofluoric acid-based waste liquid containing Si. And a method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si by recovering hydrofluoric acid in which Si is reduced or removed from a hydrofluoric acid-based mixed acid waste liquid containing Si.

In order to achieve the foregoing objects, the present invention provides the following means.

[1] A method for removing Si from a hydrofluoric acid-based waste liquid containing Si, comprising: adding a salt to a waste liquid containing hydrofluoric acid and Si, and removing a precipitate generated by the addition of the salt The Si removal step of removing the waste liquid of Si is obtained.

[2] A method for removing Si from a hydrofluoric acid-based waste liquid containing Si, which comprises: adding a salt to a waste liquid containing hydrofluoric acid and Si, and then removing a Si removing step of removing a waste liquid for removing Si by a precipitate generated by the addition of the salt; and distilling the liquid containing hydrofluoric acid by distilling the waste liquid containing Si by distillation to obtain a distillate step.

[3] The method for removing Si from a hydrofluoric acid-based waste liquid containing Si according to the above item 1 or 2, wherein the salt is one or two selected from the group consisting of a metal fluoride salt and a metal chloride salt. More than one kind of salt.

[4] The method for removing Si from a hydrofluoric acid-based waste liquid containing Si according to the above item 1 or 2, wherein the salt is selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride. And one or more salts of the group consisting of lithium fluoride.

[5] The method for removing Si from a hydrofluoric acid-based waste liquid containing Si according to any one of the items 1 to 4, wherein the step of adding the salt to the waste liquid is to supply the waste liquid through a supply pipe. The mixing tank is supplied to the mixing tank at the same time, and before the adding step, the flow rate and the density of the waste liquid passing through the supply pipe are measured by a mass flow meter provided in the supply pipe. a measuring step; calculating, in the computer, the mass of Si in the waste liquid passing through the supply pipe according to the aforementioned flow rate and density measured by the mass flow meter, and calculating a salt required for precipitation of Si according to the calculated value a calculation step of the mass; and a metering step of measuring the mass of the mass calculated by the computer and feeding the salt into the mixing tank.

[6] A method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si, comprising: adding a salt to a mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si, and removing the salt Adding the generated precipitate to obtain a Si removal step of removing the mixed acid waste liquid of Si; and distilling the mixed acid waste liquid of Si to distill off the mixed acid solution to obtain a first distillation step of the first distillate; The second distillate obtained by distilling the first distillate obtained in the first distillation step, distilling the mixed acid solution to obtain a second distillate, and simultaneously recovering the hydrofluoric acid concentrated mixed acid solution as a distillation residue.

[7] The method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si according to the above item 6, wherein the distillation temperature in the first distillation step is set in a range of from 80 °C to 130 °C.

[8] The method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si according to the above item 6 or 7, wherein the distillation temperature in the second distillation step is set in a range of from 80 °C to 130 °C.

[9] The method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si according to any one of items 6 to 8, wherein the salt is selected from the group consisting of a metal fluoride salt and a metal chloride salt. One or two or more salts of the group.

[10] The method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si according to any one of items 6 to 8, wherein the salt is selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, One or two or more salts of the group consisting of sodium chloride, magnesium fluoride, and lithium fluoride.

[11] The hydrofluoric acid system containing Si according to any one of items 6 to 10 above A method for recovering hydrofluoric acid from a mixed acid waste liquid, wherein the step of adding a salt to the waste liquid is performed by supplying the waste liquid to a mixing tank via a supply pipe, and supplying the salt to the mixing tank, and adding Before the step, there is: a measuring step of measuring a flow rate and a density of the waste liquid passing through the supply pipe by a mass flow meter disposed in the supply pipe; and the flow rate and the density measured by the mass flow meter in the computer Data, calculating a mass of Si in the waste liquid passing through the supply tube, and calculating a mass of the salt required for precipitation of Si based on the calculated value; and measuring the mass calculated by the computer by a meter The salt is fed to the metering step of the aforementioned mixing tank.

[12] A recovery apparatus for recovering hydrofluoric acid from a hydrofluoric acid-based waste liquid containing Si, comprising: mixing a waste liquid containing hydrofluoric acid and Si and a salt by stirring to obtain a mixed liquid; a mixing tank for a solid-liquid separator for solid-liquid separation of a precipitate present in the mixed liquid, and a distillation column for distilling the filtrate separated by the solid-liquid separator.

[13] A recovery apparatus for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si, comprising: mixing a mixed acid waste liquid containing hydrofluoric acid and Si and a salt by stirring to obtain a mixture a liquid mixing tank for solid-liquid separator for solid-liquid separation of a precipitate present in the above-mentioned mixed liquid, a first distillation column for distilling the filtrate separated by the solid-liquid separator, and a second distillation column for distilling the distillate distilled from the first distillation column.

[14] The recovery device according to the above item 12 or 13, further comprising: a mass flow meter provided in the supply pipe for supplying the waste liquid to the mixing tank, and measuring the flow rate and density of the waste liquid passing through the supply pipe, according to a data of the aforementioned flow rate and density measured by the mass flow meter, a calculation of the mass of Si in the waste liquid of the supply pipe, and a calculation of the mass of the salt required for the precipitation of Si based on the calculated value, and the measurement of the foregoing The mass of the salt calculated by the computer is fed to the meter of the aforementioned mixing tank.

[15] A solid-liquid separation device comprising: a solid-liquid separator capable of separating a solid component and a liquid, and discharging the separated solid component from a bottom portion, and accommodating a solid component discharged from a bottom portion of the solid-liquid separator a sludge tank connected to a discharge port provided at a bottom of the sludge tank, a discharge valve provided in the discharge pipe, and an interface for detecting an upper position of a solid component contained in the sludge tank Position detector.

[16] The solid-liquid separation device according to Item 15, wherein an ultrasonic interface detector is used as the aforementioned interface position detector.

[17] The solid-liquid separation device according to the above item 15 or 16, wherein a liquid scroll machine is used as the aforementioned solid-liquid separator.

[18] The solid-liquid separation device according to any one of the items 15 to 17, further comprising: a circulation pipe that supplies the liquid separated by the solid-liquid separator to the solid-liquid separator.

[19] The solid-liquid separation device according to any one of the items 15 to 18, wherein the opening/closing operation or the opening degree adjustment of the discharge valve is performed based on information on an upper position of a solid component detected by the interface position detector. The control department.

[20] The solid-liquid separation device according to any one of the items 15 to 18, wherein when the upper position of the solid component detected by the interface position detector rises to a first predetermined height in the sludge tank Opening the discharge valve to discharge the solid content in the sludge tank, and lowering the upper position of the solid component detected by the interface position detector to the second predetermined height in the sludge tank due to the discharge of the solid component At the time, the control unit that controls the discharge valve is closed.

[21] The solid-liquid separation device according to any one of the items 15 to 18, wherein, when the upper position of the solid component detected by the interface position detector is lowered, the opening degree of the discharge valve is reduced. When the upper position of the solid component detected by the interface position detector rises, the opening degree of the discharge valve is increased to control the upper position of the solid component in the sludge tank to be controlled at a substantially constant position. unit.

In the invention of [1], by adding a salt to a waste liquid containing hydrofluoric acid and Si, a precipitate containing Si can be formed. Therefore, the waste liquid from which Si is removed can be obtained by removing the precipitate. Since Si can be precipitated and removed, for example, when the waste liquid is subjected to a distillation operation, SiF ₄ (highly volatile substance) is not mixed into the distillate. Therefore, it is possible to recover a distillate (hydrofluoric acid or mixed acid, etc.) having less impurities such as Si.

In the invention of [2], by adding a salt to a waste liquid containing hydrofluoric acid and Si, a precipitate containing Si can be formed. Therefore, the waste liquid from which Si is removed can be obtained by removing the precipitate. Then, by removing the waste liquid of Si by distillation, the metal component other than Si existing in the waste liquid can be distilled off and left in the distillation column or the like, so that it is possible to recover a small amount of impurities (metal components other than Si or Si). Liquid (liquid containing hydrofluoric acid or liquid containing mixed acid, etc.). In this way, since the distillate has less impurities, it can be reused. In addition, it is not necessary to neutralize the waste liquid, so the waste liquid treatment cost can be reduced.

In the invention of the above [3], since the salt is one or two or more salts selected from the group consisting of a metal fluoride salt and a metal chloride salt, a waste liquid in which Si is sufficiently removed can be obtained.

In the invention of [4], the salt is one or more salts selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride, and lithium fluoride. Therefore, the waste liquid after removing Si more fully can be obtained.

In the invention of [5], since the salt required for the precipitation of Si can be supplied to the mixing tank with high precision and automatically, the waste liquid can be efficiently and accurately processed.

In the invention of [6], by adding a salt to hydrofluoric acid, hydrochloric acid, and The mixed acid waste liquid of Si can form a precipitate containing Si, so that the mixed acid waste liquid from which Si is removed can be obtained by removing the precipitate. Then, by removing the mixed acid waste liquid of Si by distillation, the metal component other than Si existing in the mixed acid waste liquid can be distilled off and left in the distillation column or the like, so that impurities (metal components other than Si or Si) can be recovered. The first distillate (liquid containing a mixed acid). Then, by distilling the first distillate, a hydrofluoric acid concentrated mixed acid solution having a small amount of impurities can be recovered as a distillation residue, and a mixed acid solution having a small amount of impurities can be recovered as a distillate (second distillate). In this way, since the distillation residue and the distillate have few impurities, they can be reused. In addition, it is not necessary to neutralize the mixed acid waste liquid, so the waste liquid treatment cost can be reduced.

In the invention of the above [7], since the distillation temperature in the first distillation step is set in the range of 80 ° C to 130 ° C, the liquid containing the mixed acid can be sufficiently distilled as the first distillate.

In the invention of [8], since the distillation temperature in the second distillation step is set in the range of 80 ° C to 130 ° C, the hydrofluoric acid concentrated mixed acid solution can be sufficiently left in the distillation residual liquid, and the mixed acid can be sufficiently distilled off. The liquid was used as a distillate (second distillate). Further, the concentration ratio of hydrofluoric acid as a distillation residue can be increased.

In the invention of the above [9], since the salt is one or more salts selected from the group consisting of a metal fluoride salt and a metal chloride salt, a mixed acid waste liquid in which Si is sufficiently removed can be obtained, and The hydrofluoric acid concentrated mixed acid solution with less impurities and the mixed acid solution with less impurities are separately recovered.

In the invention of [10], the salt is selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride, and lithium fluoride or Since two or more kinds of salts are used, it is possible to obtain a mixed acid waste liquid after sufficiently removing Si, and to separately collect a hydrofluoric acid concentrated mixed acid solution having less impurities and a mixed acid solution having less impurities.

In the invention of [11], since the salt required for the precipitation of Si can be supplied to the mixing tank with high precision and automatically, it is possible to recover the hydrofluoric acid concentrated mixed acid having less impurities at a sufficient processing speed. And mixed acid with less impurities.

In the invention of [12], since the mixing tank, the solid-liquid separator, and the distillation column are provided, a precipitate containing Si can be formed in the mixing tank, and the precipitate can be separated from the waste liquid by a solid-liquid separator. Then, by the distillation operation in the distillation column, it is possible to remain in the distillation column without distilling off the metal component other than Si, and by this operation, it is possible to recover a small amount of impurities (metal components other than Si or Si). Effluent (hydrofluoric acid concentrated mixed acid or liquid containing mixed acid, etc.).

In the invention of [13], since the mixing tank, the solid-liquid separator, the first distillation column, and the second distillation column are provided, a precipitate containing Si can be formed in the mixing tank, and the solid-liquid separator can be used. The precipitate is separated from the waste liquid, and then, by the distillation operation in the first distillation column, the metal component other than Si can be distilled out in the first distillation column, whereby impurities can be recovered (other than Si or Si). The metal component is a first distillate (containing a mixed acid or the like). Then, the first distillate is subjected to a distillation operation by the second distillation column, whereby a hydrofluoric acid concentrated mixed acid solution having a small amount of impurities can be recovered as a distillation residue, and a mixed acid solution having a small amount of impurities is recovered as a distillate (second distillation) Liquid).

In the invention of [14], it is possible to accurately and automatically precipitate Si The amount of salt is supplied to the mixing tank. The recycling device of the invention of [12] to [14] can be used regardless of whether the liquid feeding is in a batch mode or a continuous mode.

The apparatus of the invention of [15] is applicable to a device in which a solid component is mixed and stored in a waste liquid, and according to the device, since the sludge tank containing the solid component discharged from the bottom of the solid-liquid separator is provided, solids can be prevented The component is filled in the solid-liquid separator and blocked. In addition, since the interface position detector for detecting the upper position of the solid component contained in the interior of the sludge tank is provided, the opening and closing or opening degree of the discharge valve can be controlled based on the information of the upper position of the solid component, and the like. Under the discharge of liquid (mixed acid, etc.), only the solid components are discharged as much as possible. It is also possible to increase the recovery rate of the recovered liquid (recovery of mixed acid, etc.). The solid-liquid separation device of the present invention is particularly effective (the increase in recovery rate is effective) when the concentration of the solid component (precipitate) in the supply liquid fluctuates (generally, this case is more in the waste liquid). The solid-liquid separation device of the present invention can be used regardless of whether the liquid supply is in a batch mode or a continuous mode.

In the invention of [16], since the ultrasonic interface detector is used as the interface position detector, the upper position of the solid content inside the sludge tank can be detected with high precision.

In the invention of [17], since the liquid scroll is used as the solid-liquid separator, it is possible to achieve miniaturization and to improve the processing ability (processing speed) of the solid-liquid separation.

In the invention of [18], since the circulation pipe for supplying the liquid separated by the solid-liquid separator to the solid-liquid separator is further provided, it can be supplied to the solid-liquid separator through the circulation pipe, thereby having Can fully reduce the recovery liquid The advantage of the content of solid impurities in (recovering mixed acid, etc.).

In the invention of the invention, the control unit for opening and closing the opening and closing the opening of the discharge valve is provided based on the information on the position of the upper surface of the solid component detected by the interface position detector, so that liquid (mixed acid, etc.) can be avoided as much as possible. Discharge from the sludge tank.

In the invention of [20], since the control unit that performs the specific control is provided, it is possible to prevent the liquid (mixed acid or the like) from being discharged together with the solid component as much as possible, and further improve the recovery liquid (mixed acid recovery liquid, hydrofluoric acid concentrated mixed acid) Recovery rate of recycled liquid, etc.). Further, when the waste liquid treatment is carried out in a batch operation, the recovery rate of the recovered liquid can be further improved by performing the batch operation.

In the invention of [21], since the control unit that performs the specific control is provided, it is possible to prevent the liquid (mixed acid or the like) from being discharged together with the solid component as much as possible, and further improve the recovery liquid (mixed acid recovery liquid, hydrofluoric acid concentrated mixed acid) Recovery rate of recycled liquid, etc.).

1‧‧‧Recycling device

9‧‧‧ mixing tank

10‧‧‧ solid liquid separator

11‧‧‧1st distillation tower

12‧‧‧2nd distillation tower

23‧‧‧ Solid component removal device (solid-liquid separator)

25‧‧‧Mass flow meter

26‧‧‧ computer

27‧‧‧meter

31‧‧‧Supply tube

43, 63‧‧‧ solid liquid separator

44, 64‧‧‧Sludge tank

45, 65‧‧‧ discharge tube

46, 66‧‧‧ discharge valve

47, 67‧‧‧ interface position detector

48, 68‧‧‧Control Department

50‧‧‧Circulation tube

52, 72‧‧‧Export

81‧‧‧1st established height

82‧‧‧2nd established height

83‧‧‧About a certain height position

100A, 100B‧‧‧ solid-liquid separation device (solid-liquid separation system)

Fig. 1 is a schematic explanatory view showing an example of a removal method and a recovery method of the present invention.

Fig. 2 is a schematic explanatory view showing an example of an automatic salt adding system in the apparatus used in the removal method and the recovery method of the present invention (a detailed configuration diagram of Fig. 1 is shown in detail).

Fig. 3 is a schematic block diagram showing the entire collection device using the solid-liquid separation device according to the embodiment of the present invention.

Fig. 4 is a view showing a detailed configuration of a part of a recovery apparatus using a solid-liquid separation device according to an embodiment of the present invention (a detailed configuration diagram of a part of the apparatus shown in Fig. 3).

Figure 5 is a longitudinal cross-sectional view showing a sludge tank equipped with an interface position detector.

A method for removing Si ⁴⁺ from a hydrofluoric acid-based waste liquid containing Si ⁴⁺ according to the present invention, comprising: adding a salt to a waste liquid containing hydrofluoric acid and Si ⁴⁺ , and removing the addition of the salt The resulting precipitate is ^{subjected to a} Si ⁴⁺ removal step of removing the Si ⁴⁺ waste liquid.

The above-described removal method, by adding a salt containing waste liquid of hydrofluoric acid and Si ⁴⁺ to produce a precipitate containing the Si ^4+, it can be removed by the precipitate obtained by removing the waste Si ⁴⁺ . Since Si ⁴⁺ can be precipitated and removed by the addition of a salt, for example, when the waste liquid from which Si ⁴⁺ is removed is subjected to a distillation operation after the above removal step, SiF ₄ (highly volatile substance) is not mixed into the distillate. in.

After the step of removing the Si ^4+, preferred system settings: the removal by distillation of Si ⁴⁺ waste liquid containing hydrofluoric acid and distilled off to obtain a first distillate of the distillation step. At this time, by the distillation operation of removing the waste liquid of Si ⁴⁺ , it is possible to remove the metal component other than Si and leave it in the distillation column or the like, thereby recovering impurities (metal components other than Si or Si) and containing hydrogen. A liquid of fluoric acid (a liquid containing hydrofluoric acid or a mixed acid liquid containing hydrofluoric acid) is used as a distillate.

The waste liquid to which the object of the above removal method is applied may, for example, be:

‧ Waste liquid containing Si ⁴⁺ and hydrofluoric acid (hydrogen fluoride)

‧ Mixed acid waste liquid containing Si ⁴⁺ , hydrochloric acid and hydrofluoric acid (hydrogen fluoride)

‧ Mixed acid waste liquid containing Si ⁴⁺ , nitric acid and hydrofluoric acid (hydrogen fluoride).

The aforementioned waste liquid may contain other acids in addition to hydrofluoric acid. Further, the aforementioned mixed acid waste liquid may contain other acids in addition to hydrochloric acid and hydrofluoric acid. In the hydrofluoric acid-based mixed acid waste liquid discharged from the semiconductor manufacturing plant, in addition to the Si ⁴⁺ which is H ₂ SiF ₆ , most of the metal ions other than Si are contained.

Further, in the method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si ⁴⁺ according to the present invention, the method comprises the steps of: adding a salt to a mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid and Si ⁴⁺ ; removed by the addition of the salt of the resulting precipitate was obtained by removing Si ⁴⁺ mixed acid waste liquid of the step of removing the Si ^4+; Si ⁴⁺ removed by distillation of the waste mixed acid, mixed acid so obtained first distillate a first distillation step of distillate; and distilling the first distillate obtained in the first distillation step to distill off the mixed acid solution to obtain a second distillate, and recovering the hydrofluoric acid concentrated mixed acid solution as a distillation The second distillation step of the raffinate.

The recovery methods described above, can be by adding a salt containing hydrofluoric acid, hydrochloric acid and the mixture of Si ⁴⁺ waste generated precipitates containing Si ⁴⁺ of, it can be removed by the precipitate obtained by removing Si ⁴⁺ Mixed acid waste liquid. Then, by removing the Si ⁴⁺ mixed acid waste liquid by distillation, it is possible to obtain a first distillate having few impurities (such as a metal component other than Si or Si) without remaining a metal component other than Si in the distillation column. (Liquid containing mixed acid). Then, by distilling the first distillate, a hydrofluoric acid concentrated mixed acid solution having a small amount of impurities can be recovered as a distillation residue, and a mixed acid solution having a small amount of impurities can be recovered as a distillate (second distillate).

The waste liquid to which the above-mentioned recovery method is applied may, for example, be as follows:

‧ Mixed acid waste liquid containing Si ⁴⁺ , hydrochloric acid and hydrofluoric acid (hydrogen fluoride)

‧ Mixed acid waste liquid containing Si ⁴⁺ , nitric acid and hydrofluoric acid (hydrogen fluoride).

The mixed acid waste liquid may contain other acids in addition to hydrochloric acid and hydrofluoric acid. In the hydrofluoric acid-based mixed acid waste liquid discharged from the semiconductor manufacturing plant, in addition to the Si ⁴⁺ which is H ₂ SiF ₆ , most of the metal ions other than Si are contained.

The distillation temperature in the first distillation step (the temperature of the mixed acid waste liquid at the time of distillation) is preferably set in the range of 80 ° C to 130 ° C. When it is 80 ° C or more, the distillation efficiency can be improved, and when it is 130 ° C or less, the heat energy cost required for distillation can be suppressed. In the above, the distillation temperature in the first distillation step is preferably set in the range of 110 ° C to 130 ° C, more preferably in the range of 115 ° C to 125 ° C.

The distillation temperature in the second distillation step (the temperature of the first distillate at the time of distillation) is preferably set in the range of 80 ° C to 130 ° C. By setting the temperature to 80 ° C to 130 ° C, the hydrofluoric acid concentrated mixed acid solution can be sufficiently left in the distillation residue, and the mixed acid solution can be sufficiently distilled off as a distillate (second distillate). Further, the concentration ratio of hydrofluoric acid as a distillation residue can be further increased. In the above, the distillation temperature in the second distillation step is preferably set in the range of 110 ° C to 130 ° C, more preferably in the range of 115 ° C to 125 ° C.

In the above-mentioned removal method and the above-mentioned recovery method, the salt is not particularly limited, and one or two or more salts selected from the group consisting of a metal fluoride salt and a metal chloride salt are preferably used.

The metal fluoride salt is not particularly limited, and examples thereof include potassium fluoride, sodium fluoride, magnesium fluoride, and lithium fluoride.

The metal chloride salt is not particularly limited, and examples thereof include potassium chloride and sodium chloride.

In particular, the salt is preferably one or more salts selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride, and lithium fluoride.

In addition, the amount of the salt to be added to the waste liquid is preferably 5% by mass to 10% by mass based on the content of the salt added to the "added salt waste liquid" formed by the waste liquid. The scope. In particular, the content ratio of the salt in the waste liquid to which the salt is added is preferably in the range of 5 mass% to 7 mass%.

The second distillate (mixed acid recovery liquid) obtained above can be used as it is, or the concentration of the acid can be adjusted depending on various uses. Further, the distillation residue (hydrofluoric acid concentrated mixed acid recovery liquid) obtained above can be used as it is, or the concentration of the acid can be adjusted depending on various uses.

Fig. 1 is a view showing an example of a recovery device 1 used in the recovery method of the present invention. 9 is a mixing tank, 10 is a solid-liquid separator, 11 is a first distillation column, and 12 is a second distillation column. Here, the description will be made by taking an example of a mixed acid waste liquid containing hydrochloric acid and hydrofluoric acid (the impurity contains at least Si ⁴⁺ ).

The mixing tank 9 is provided with a stirring blade. When the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) and the salt are placed in the mixing tank 9, the mixture is stirred and mixed by the stirring blade to obtain a mixed liquid. In the mixed solution, a precipitate (containing a precipitate of Si ⁴⁺ ) is generated due to the presence of a salt.

Next, the mixed liquid is introduced into the solid-liquid separator 10, and the solid-liquid separator 10 is separated into a precipitate and a liquid (mixed acid waste liquid; no precipitate). In the present embodiment, a centrifugal separator is used as the solid-liquid separator 10, and the precipitate is sedimented downward by centrifugal separation to carry out solid-liquid separation. The filtrate (supernatant) in the solid-liquid separator 10 can reduce or remove Si ⁴⁺ by removing precipitates.

Then, the filtrate (the mixed acid waste liquid from which Si ⁴⁺ is removed) in the solid-liquid separator 10 is introduced into the first distillation column 11 and distilled in the first distillation column 11 . By the first distillation operation, the first distillate (mixed acid solution containing hydrofluoric acid and hydrochloric acid) is distilled off from the top of the first distillation column 11, and the metal component other than Si remains in the first distillation column 11. Thus, the first distillate having few impurities (such as a metal component other than Si or Si) can be obtained.

Then, the first distillate distilled from the first distillation column 11 is introduced into the second distillation column 12, and is distilled in the second distillation column 12. The second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12 by the second distillation operation. The acid mixture can be recovered in this way.

After the second distillation operation, a hydrofluoric acid concentrated mixed acid solution as a distillation residue is obtained inside the second distillation column 12. Thus, the liquid containing concentrated hydrofluoric acid (hydrofluoric acid concentrated recovery liquid) can be recovered.

The input of the salt to the mixing tank 9 is preferably provided in the apparatus 1 as The salt is automatically added to the system as shown in Fig. 2. In Fig. 2, 21 is the waste liquid tank, 22 is the pump, 23 is the solid component removal device, 24 is the sludge tank, 25 is the mass flow meter, 26 is the computer, 27 is the meter, 28 is the salt tank, 29 is Pump.

The pump 22, the solid component removing device 23, the mass flow meter 25, the switching valve 51, and the mixing tank 9 are sequentially connected to the downstream side of the transport liquid from the waste liquid tank 21 via the supply pipe 31 (refer to Fig. 2). Further, the mixing tank 9 is connected to the solid-liquid separator 10 via a pump 29 (refer to Fig. 2). The mass flow meter 25 is provided in a supply pipe 31 that supplies the waste liquid to the mixing tank 9.

The mass flow meter 25 measures the flow rate and density of the waste liquid passing through the supply pipe 31, and the data (flow rate and density) is transmitted to the computer 26. In the computer 26, the mass of Si in the used waste liquid is calculated from the above data (flow rate and density). Here, an example of the calculation method is shown in which the density of the "liquid from which Si is deducted" in the waste liquid is 1.0 g/cm ³ and the density of Si is 2.33 g/cm ³ , and the density of the waste liquid is measured from these values. The Si content in the waste liquid is obtained, and the Si mass (that is, the mass of Si applied to the mixing tank 9) can be calculated from the Si content and the measured value of the flow rate. In the hydrofluoric acid-based mixed acid waste liquid and the hydrofluoric acid-based waste liquid discharged from a semiconductor manufacturing plant, many metal components other than Si are contained, but the content is extremely small, and can be ignored in the evaluation of the density. These "metal components other than Si" are calculated (even if they are ignored, the accuracy of the salt automatic addition system will not be affected).

Further, in the computer 26, "the mass of the salt required for the precipitation of Si" is calculated based on the "passing quality of Si" calculated above, and the calculated value is transmitted to the meter 27. For example, when KF (potassium fluoride) is used as the salt, the precipitation reaction formula is: 2KF+H ₂ SiF ₆ →K ₂ SiF ₆ +2HF

Therefore, the mass of the salt required for the precipitation of Si (the formation of K ₂ SiF _{6 which} is insoluble in water) can be calculated from this (2 equivalents of KF is required with respect to 1 equivalent of Si).

When NaCl (sodium chloride) is used as the salt, the precipitation reaction formula is: 2NaCl+H ₂ SiF ₆ →Na ₂ SiF ₆ +2HCl

Na ₂ SiF ₆ which does not dissolve in water is formed.

In addition, when KCl (potassium chloride) is used as the salt, the precipitation reaction formula is: 2KCl + H ₂ SiF ₆ → K ₂ SiF ₆ + 2HCl

It produces K ₂ SiF ₆ which is insoluble in water.

When NaF (sodium fluoride) is used as the salt, the precipitation reaction formula is: 2NaF+H ₂ SiF ₆ →Na ₂ SiF ₆ +2HF

Na ₂ SiF ₆ which does not dissolve in water is formed.

The meter 27 measures a salt having a predetermined amount (mass of the above calculated value) from the salt tank 28, and feeds it to the mixing tank 9.

In the present embodiment, a Coriolis type is used as the mass flow meter 25, and a weight reduction method is used as the gauge 27, but it is not particularly limited. The mass flow meter 25 is preferably a Coriolis type which is made of an acid resistant material.

The mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) is stored in the waste liquid tank 21 described above. The mixed acid waste liquid in the waste liquid tank 21 is passed through the solid component removing device 23 by the pump 22, and then introduced into the mixing tank 9 through the mass flow meter 25. In the present embodiment, the solid component removing device 23 uses a liquid scroll machine, and when passing through the liquid scroll machine, solid components (impurities, sludge, and the like) in the waste liquid are sedimented and removed. The solid component after the sedimentation removal is appropriately transported to the sludge tank 24 by opening and closing of the valve 30.

In the mass flow meter 25 described above, the flow rate and density of the waste liquid passing through the supply pipe 31 are measured, and the data (flow rate and density) are transmitted to the aforementioned computer 26 (measurement step).

In the computer 26, the data (flow rate and density) transmitted from the mass flow meter 25 is used to calculate the "mass of Si in the waste liquid passed through", and the "precipitation of Si" is calculated based on the calculated value. The mass of the salt, the calculated value (the mass of the salt required for the precipitation of Si) is sent to the aforementioned meter 27 (calculation step).

Then, by the above-described meter 27, the predetermined amount (mass of the calculated value) is measured from the salt tank 28, and is sent to the mixing tank 9 (measurement step).

By providing the salt automatic addition system having the configuration shown in FIG. 2 in the apparatus 1, it is possible to add the salt required for the precipitation of Si to the mixing tank 9 with high precision and automatically. The salt automatic addition system described above can be used in either a batch mode or a continuous mode.

In the above embodiment, the foregoing in the supply pipe 31 is employed. The switching valve 51 is disposed between the mixing tank 9 and the mass flow meter 25, and one end of the circulation pipe 50 is connected to the switching valve 51, and the other end of the circulation pipe 50 is connected to the waste liquid tank 21, so that it can be When the switching valve 51 is switched, the liquid separated by the solid component removing device 23 is supplied to the solid component removing device 23 through the waste liquid tank 21 and the pump 22 1 to a plurality of times, and the solid component removing process is performed a plurality of times. The solid content is reduced as much as possible (the solid content is reduced to a desired density), and then introduced into the mixing tank 9 (refer to Fig. 2).

The removal method and the recovery method of the present invention can also be carried out using a recovery apparatus having the configuration shown in Figs. 3 to 5 . The recovery device 1 shown in Fig. 3 differs from the recovery device 1 shown in Fig. 1 in the following configuration.

1) The above-mentioned mixed acid waste liquid is not directly introduced into the mixing tank 9, but the solid acid liquid waste liquid (the solid-liquid separation system) 100A described later is subjected to pretreatment of the mixed acid waste liquid to remove solid components (impurities, etc.). The mixed acid waste liquid is supplied to the mixing tank 9.

2) The solid-liquid separator disposed between the mixing tank 9 and the first distillation column 11 is replaced by the solid-liquid separator (solid-liquid separation system) 100B described later.

Fig. 4 is a view showing the detailed configuration of the first half of the constituent components of the above-described two solid-liquid separation devices (solid-liquid separation systems) 100A and 100B in the recovery device 1 shown in Fig. 3.

In Fig. 4, 41 is a waste liquid tank, 42 is a pump, 43 is a solid-liquid separator, 44 is a sludge tank, 45 is a discharge pipe, 46 is a discharge valve, and 47 is an interface. The position detector 48 is a control unit and 49 is a sludge tank. The solid-liquid separation device (solid-liquid separation system) 100A includes a solid-liquid separator 43, a sludge tank 44, a discharge pipe 45, a discharge valve 46, an interface position detector 47, and a control unit 48.

In addition, in Fig. 4, 62 is a pump, 63 is a solid-liquid separator, 64 is a sludge tank, 65 is a discharge pipe, 66 is a discharge valve, 67 is an interface position detector, 68 is a control part, and 69 is a sludge. groove. The solid-liquid separation device (solid-liquid separation system) 100B includes a solid-liquid separator 63, a sludge tank 64, a discharge pipe 65, a discharge valve 66, an interface position detector 67, and a control unit 68.

In Fig. 4, the respective configurations, functions, connection types, and the like of the mass flow meter 25, the computer 26, the gauge 27, the salt tank 28, and the supply tube 31 are the same as those in Fig. 2, and the repeated description thereof will be omitted here. . In addition, the respective configurations, functions, connection types, and the like of the components on the downstream side after the first mixing column 11 and the first distillation column 11 in the third embodiment are the same as those in the first embodiment, and the repeated description thereof will be omitted.

Hereinafter, the above-described solid-liquid separation device (solid-liquid separation system) 100A, the above-described solid-liquid separation device (solid-liquid separation system) 100B, and the like will be described.

A pump 42 and a solid separation device (solid-liquid separation system) 100A are connected to the downstream side of the transfer liquid from the waste liquid tank 41 via the supply pipe 40 (refer to FIG. 4). The liquid (the mixed acid waste liquid from which solid components such as impurities are removed) after being subjected to the solid-liquid separation treatment in the solid-liquid separation device 100A is transported to the supply pipe 31 provided with the mass flow meter 25 at a midway position. Mixing tank 9.

In the present embodiment, the solid-liquid separator 43 is a liquid scroll. Further, the other end of the supply pipe 40, which is connected to the bottom of the waste liquid tank 41 at one end, is horizontally connected to the upper position of the liquid scroll 43. The liquid scroll machine 43 can separate a solid component (solid) suspended in a liquid from a liquid by centrifugal force. When the mixed acid waste liquid is supplied to the liquid scroll machine 43 in the horizontal direction, a spiral downward flow is generated along the inclined surface of the peripheral wall portion of the liquid scroll 43, and solids (impurities, etc.) are driven by the spiral downward flow. It is discharged to the bottom of the liquid scroll and discharged to the sludge tank 44. On the other hand, in the center portion of the liquid scroll 43, an upward flow is generated in reverse, and the liquid (mixed acid waste liquid) is driven by the upward flow, and is discharged from the upper portion of the liquid scroll 43 and passed through the supply pipe 31. It is sent to the aforementioned mixing tank 9. The liquid scroll 43 can be made of an acid-resistant material (for example, polyvinyl chloride or the like) to form an acid-resistant device, and can be easily produced.

A sludge tank 44 is disposed at the bottom of the liquid scroll 43. The discharge port at the bottom of the liquid scroll unit 43 is connected to and connected to the introduction port 53 at the upper portion of the sludge tank 44. One end of the discharge pipe 45 is connected to the discharge port 52 at the bottom of the sludge tank 44, and the other end of the discharge pipe 45 is connected to the upper opening of the sludge tank 49, and a discharge valve 46 is attached to the middle of the discharge pipe 45.

Further, an interface position detector 47 is attached to the upper portion of the sludge tank 44 (refer to Fig. 5). In the present embodiment, the interface position detector 47 uses an ultrasonic interface detector. Further, in the upper wall of the sludge tank 44 (in the present embodiment, a part of the outer peripheral portion of the upper wall), The ultrasonic wave passage 54 that penetrates the vertical direction is formed, and the ultrasonic interface detector 47 is attached to the sludge so that ultrasonic waves can be transmitted to the internal space of the sludge tank 44 via the ultrasonic passage path 54. The upper portion of the tank 44. The ultrasonic interface detector 47 can detect the upper position of the solid content contained in the inside of the sludge tank 44. The ultrasonic interface detector 47 is not particularly limited, and for example, an "ultrasonic type interface meter SL-200A" manufactured by Horiba, Ltd., and an ultrasonic type liquid level gauge YU-L20 manufactured by Yamamoto Electric Co., Ltd. "Wait. The aforementioned ultrasonic interface detector 47 is preferably formed of a material having corrosion resistance.

The control unit 48 performs an opening/closing operation or an opening degree adjustment of the discharge valve 46 based on the information on the upper position of the solid component detected by the interface position detector 47.

In the present embodiment, when the upper position of the solid component detected by the interface position detector 47 rises to the first predetermined height 81 in the sludge tank 44, the control unit 48 opens the discharge valve 46 to discharge the dirt. The solid component in the clay tank 44, and when the upper position of the solid component detected by the interface position detector 47 is lowered to the second predetermined height 82 in the sludge tank 44 due to the discharge of the solid component, the discharge valve 46 is closed. The way to control (refer to Figure 5). The first predetermined height 81 is located higher than the second predetermined height 82 (refer to FIG. 5).

The sludge tank 44 is for temporarily accommodating solid components (impurities, etc.) discharged from the discharge port at the bottom of the liquid scroll 43; In a part of the liquid), by providing the sludge tank 44, the liquid mixing rate discharged into the solid content of the sludge tank 49 can be reduced. Therefore, the recovery rate of the recovered liquid (mixed acid recovery liquid, hydrofluoric acid concentrated mixed acid recovery liquid, etc.) finally recovered by the distillation operation can be improved.

Then, the mixed acid waste liquid (the impurities or the like which are removed) is discharged from the liquid scroll unit 43 and sent to the mixing tank 9 via the supply pipe 31, and the mixed tank 9 is stirred and mixed with the salt to form a mixed liquid. In the mixed solution, a precipitate (solid content; precipitate containing Si ⁴⁺ ) was generated due to the addition of salt.

From the mixing tank 9 to the downstream side of the transport liquid, a pump 62 and a solid separation device (solid-liquid separation system) 100B are sequentially connected via a supply pipe 60 (refer to Fig. 4). The liquid (the mixed acid waste liquid from which Si ⁴⁺ is removed) which is sent out after the solid-liquid separation treatment in the solid-liquid separation device 100B is sent to the first distillation column 11 via the supply pipe 61. The content of the treatment from the first distillation column 11 and the like are the same as those of the above-described embodiment (the recovery apparatus of Fig. 1).

In the present embodiment, the solid-liquid separator 63 is a liquid scroll machine. Further, the other end of the supply pipe 60, which is connected at one end to the bottom of the mixing tank 9, is horizontally connected to the upper position of the liquid scroll 63. The liquid scroll 63 can separate solid components (solids) and liquid suspended in the liquid by centrifugal force. When the mixed acid waste liquid (mixed acid waste liquid from which impurities or the like are removed) is horizontally introduced into the liquid scroll 63, a spiral downward flow is generated along the inclined surface of the peripheral wall portion of the liquid scroll 63, and the solid ( The Si ⁴⁺ precipitate is driven by the spiral downward flow, is discharged to the bottom of the liquid scroll, and is discharged to the sludge tank 64. On the other hand, in the center portion of the liquid scroll 63, an upward flow is generated in the opposite direction, and the liquid (the mixed acid waste liquid after the Si ⁴⁺ is removed) is driven by the upward flow, and is discharged from the upper portion of the liquid scroll 63. And it is sent to the 1st distillation tower 11 via the said supply pipe 61.

A mass flow meter 70 is provided in the middle of the supply pipe 61 (refer to Fig. 4). In order to reduce the amount of the precipitate (solid content) transported to the first distillation column 11, it is also possible to provide a path (not shown) for recycling the supply pipe 61 to the mixing tank 9, and by the foregoing The monitoring of the mass flow meter 70 is carried out until the desired density (solid content) is transferred to the first distillation column 11.

A sludge tank 64 is disposed at the bottom of the liquid scroll 63. The discharge port at the bottom of the liquid scroll 63 is connected to and connected to the inlet 73 of the upper portion of the sludge tank 64. One end of the discharge pipe 65 is connected to the discharge port 72 at the bottom of the sludge tank 64, and the other end of the discharge pipe 65 is connected to the upper opening of the sludge tank 69, and a discharge valve 66 is attached to the middle of the discharge pipe 65.

Further, an interface position detector 67 is attached to the upper portion of the sludge tank 64 (refer to Fig. 5). In the present embodiment, the interface position detector 67 uses an ultrasonic interface detector. Further, in the upper wall of the sludge tank 64 (in the present embodiment, a part of the outer peripheral portion of the upper wall), an ultrasonic passage path 74 that penetrates the vertical direction is formed, and the ultrasonic passage path 74 is provided through the ultrasonic wave. The ultrasonic interface detector 67 is attached to the upper portion of the sludge tank 64 so that the ultrasonic wave is transmitted to the internal space of the sludge tank 64. The ultrasonic interface detector 67 can detect the upper position of the solid component (Si ⁴⁺ -based precipitated solid component) contained in the sludge tank 64. The ultrasonic interface detector 67 is not particularly limited, and for example, "Ultra-wave type interface meter SL-200A" manufactured by Horiba, Ltd., and "Ultra-wave type liquid level gauge YU-L20" manufactured by Yamamoto Denki Kogyo Co., Ltd. "Wait. The aforementioned ultrasonic interface detector 67 is preferably formed of a material having corrosion resistance.

In the present embodiment, the interface position detectors 47 and 67 are of an ultrasonic type, but an optical type may be used, for example. However, for optical types, the detection of slower solid components is slower. The optical position interface position detector described above is preferably also formed of a material having acid resistance. The interface position detector of the optical type is not particularly limited, and for example, an "optical type interface meter OX100 type" manufactured by Nohken Co., Ltd. or the like can be used.

The control unit 68 performs an opening/closing operation or an opening degree adjustment of the discharge valve 66 based on the information on the upper position of the solid component (Si ⁴⁺ -based solid content) detected by the interface position detector 67.

In the present embodiment, the control unit 68 reduces the degree of opening of the discharge valve 66 when the upper position of the sediment detected by the interface position detector 67 is lowered from the specific position 83, and the interface position detector 67 is used. When the upper position of the detected precipitate rises from the specific position 83, the opening degree of the discharge valve 66 is increased to control the upper position of the sediment in the sludge tank 64 to a substantially constant position. 83 (refer to Figure 5).

The sludge tank 64 is configured to temporarily accommodate a solid component (Si ⁴⁺ precipitated solid component; also including a part of liquid) discharged from a discharge port at the bottom of the liquid scroll 63, by providing the sludge tank 64. The liquid mixing ratio of the precipitated solid components discharged to the sludge tank 69 can be reduced. Therefore, the recovery rate of the recovered liquid (mixed acid recovery liquid, hydrofluoric acid concentrated mixed acid recovery liquid, etc.) finally recovered by the distillation operation can be improved.

The removal method and the recovery method of the present invention are not particularly limited to those carried out by the recovery apparatus having the configuration shown in Figs. 1 to 5 .

Example

Next, specific embodiments of the present invention will be described, but the present invention is not particularly limited to the embodiments.

<Example 1>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing the components and the content of each component as shown in Table 1) and 25 g of sodium chloride were placed in the mixing tank 9, and the mixture was stirred and mixed for 24 hours by a stirring blade to obtain a mixed liquid.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to carry out centrifugation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant liquid (the mixed acid waste liquid from which Si ⁴⁺ is removed; Containing sediment). The obtained precipitate was 66 g, and the obtained supernatant was 258 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main component of the precipitate was sodium bismuth fluoride (Na ₂ SiF ₆ ).

(first distillation step)

255 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 120 °C. By the first distillation operation, 220 g of the first distillate (containing a mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Then, a part of 209 g of the first distillate distilled from the first distillation column 11 was placed in the second distillation column 12, and distillation was carried out at a distillation temperature of 120 °C. By the second distillation operation, the second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12, whereby 116 g of the liquid containing the mixed acid is recovered. After the second distillation operation, 92 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue can be recovered in the second distillation column 12.

<Example 2>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing the components and the content of each component as shown in Table 2) and 25 g of potassium fluoride were placed in the mixing tank 9, and the mixture was stirred and mixed for 24 hours by a stirring blade to obtain a mixed liquid.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to perform centrifugal separation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (the mixed acid waste liquid from which Si ^{4 +} is removed; Containing sediment). The obtained precipitate was 103 g, and the obtained supernatant was 222 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main component of the precipitate was potassium cesium fluoride (K ₂ SiF ₆ ).

(first distillation step)

222 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 120 °C. By the first distillation operation, 184 g of the first distillate (containing a mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Then, 184 g of the first distillate distilled from the first distillation column 11 is placed in the second distillation column 12, and steamed at a distillation temperature of 120 °C. Distillation. By the second distillation operation, the second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12, whereby 61 g of the liquid containing the mixed acid is recovered. After the second distillation operation, 113 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue can be recovered in the second distillation column 12.

<Example 3>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing the components and the content of each component as shown in Table 3) and 18 g of sodium fluoride were placed in the mixing tank 9, and the mixture was stirred and mixed for 24 hours by a stirring blade to obtain a mixed liquid.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to perform centrifugal separation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (the mixed acid waste liquid from which Si ^{4 +} is removed; Containing sediment). The obtained precipitate was 69 g, and the obtained supernatant was 248 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main component of the precipitate was sodium bismuth fluoride (Na ₂ SiF ₆ ).

(first distillation step)

248 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 120 °C. By the first distillation operation, 212 g of the first distillate (containing the mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Then, 212 g of the first distillate distilled from the first distillation column 11 was placed in the second distillation column 12, and distillation was carried out at a distillation temperature of 120 °C. By the second distillation operation, the second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12, whereby 76 g of the liquid containing the mixed acid is recovered. After the second distillation operation, 125 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue can be recovered in the second distillation column 12.

<Example 4>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing the components and the content of each component as shown in Table 4) and 32 g of potassium chloride were placed in the mixing tank 9, and then stirred. The mixture was stirred and mixed for 24 hours to obtain a mixed solution.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to perform centrifugal separation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (the mixed acid waste liquid from which Si ^{4 +} is removed; Containing sediment). The obtained precipitate was 112 g, and the obtained supernatant was 220 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main component of the precipitate was potassium cesium fluoride (K ₂ SiF ₆ ).

(first distillation step)

220 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 110 °C. By the first distillation operation, 176 g of the first distillate (containing the mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Next, 176 g of the first distillate distilled from the first distillation column 11 was placed in the second distillation column 12, and distillation was carried out at a distillation temperature of 110 °C. By the second distillation operation, the second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12, whereby 67 g of the liquid containing the mixed acid is recovered. After the second distillation operation, 101 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue was collected in the second distillation column 12.

<Example 5>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing the components and the content of each component as shown in Table 5) and 13 g of magnesium fluoride were placed in the mixing tank 9, and the mixture was stirred and mixed for 24 hours by a stirring blade to obtain a mixed liquid.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to perform centrifugal separation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (the mixed acid waste liquid from which Si ^{4 +} is removed; Containing sediment). The obtained precipitate was 58 g, and the obtained supernatant was 255 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main component of the precipitate was magnesium fluorinated magnesium fluoride (MgSiF ₆ ).

(first distillation step)

255 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 120 °C. By the first distillation operation, 214 g of the first distillate (containing a mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Then, 214 g of the first distillate distilled from the first distillation column 11 was placed in the second distillation column 12, and distillation was carried out at a distillation temperature of 120 °C. By the second distillation operation, the second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12, whereby 61 g of the liquid containing the mixed acid is recovered. After the second distillation operation, 142 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue was collected in the second distillation column 12.

<Example 6>

For discharged from a semiconductor manufacturing plant of the mixed acid waste liquid (containing hydrofluoric acid, hydrochloric acid, and mixed waste of Si ^4+), recovery of the configuration shown in FIG 1 of 1, as described below to remove embodiment Si ⁴⁺ Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing the components and the content of each component as shown in Table 6) and 11 g of lithium fluoride were placed in the mixing tank 9, and the mixture was stirred and mixed for 24 hours by a stirring blade to obtain a mixed liquid.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to perform centrifugal separation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (the mixed acid waste liquid from which Si ^{4 +} is removed; Containing sediment). The obtained precipitate was 56 g, and the obtained supernatant was 255 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main component of the precipitate was lithium lanthanum fluoride (Li ₂ SiF ₆ ).

(first distillation step)

255 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 130 °C. By the first distillation operation, 205 g of the first distillate (containing the mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Then, 205 g of the first distillate distilled from the first distillation column 11 was placed in the second distillation column 12, and distillation was carried out at a distillation temperature of 130 °C. By the second distillation operation, the second distillate (mixed acid solution) was distilled off from the top of the second distillation column 12, whereby 69 g of a liquid containing a mixed acid was recovered. After the second distillation operation, 124 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue can be recovered in the second distillation column 12.

<Example 7>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing components and the content of each component as shown in Table 7), 26 g of sodium chloride, and 33 g of potassium chloride were placed in the mixing tank 9, and then stirred and mixed for 24 hours by a stirring blade to obtain a mixture. liquid.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to perform centrifugal separation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (the mixed acid waste liquid from which Si ^{4 +} is removed; Containing sediment). The obtained precipitate was 156 g, and the obtained supernatant was 203 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main components of the precipitate were sodium bismuth fluoride (Na ₂ SiF ₆ ) and potassium cesium fluoride (K ₂ SiF ₆ ).

(first distillation step)

203 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 120 °C. By the first distillation operation, 172 g of the first distillate (containing the mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Then, 172 g of the first distillate distilled from the first distillation column 11 was placed in the second distillation column 12, and distillation was carried out at a distillation temperature of 120 °C. By the second distillation operation, the second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12, whereby 95 g of the liquid containing the mixed acid is recovered. After the second distillation operation, 64 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue can be recovered in the second distillation column 12.

<Example 8>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing the components and the content of each component as shown in Table 8), 33 g of potassium chloride, and 19 g of sodium fluoride were placed in the mixing tank 9, and then stirred and mixed for 24 hours by a stirring blade to obtain a mixture. liquid.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to perform centrifugal separation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (the mixed acid waste liquid from which Si ^{4 +} is removed; Containing sediment). The obtained precipitate was 162 g, and the obtained supernatant was 190 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main components of the precipitate were sodium bismuth fluoride (Na ₂ SiF ₆ ) and potassium cesium fluoride (K ₂ SiF ₆ ).

(first distillation step)

190 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 120 °C. By the first distillation operation, 166 g of the first distillate (containing the mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Then, 166 g of the first distillate distilled from the first distillation column 11 was placed in the second distillation column 12, and distillation was carried out at a distillation temperature of 120 °C. By the second distillation operation, the second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12, whereby 76 g of the liquid containing the mixed acid is recovered. After the second distillation operation, 83 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue was collected in the second distillation column 12.

<Example 9>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing components and the content of each component as shown in Table 9), 26 g of sodium chloride, and 26 g of potassium fluoride were placed in the mixing tank 9, and then stirred and stirred for 24 hours by a stirring blade to obtain a mixture. liquid.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to carry out centrifugation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant liquid (the mixed acid waste liquid from which Si ⁴⁺ is removed; Containing sediment). The obtained precipitate was 160 g, and the obtained supernatant was 192 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main components of the precipitate were sodium bismuth fluoride (Na ₂ SiF ₆ ) and potassium cesium fluoride (K ₂ SiF ₆ ).

(first distillation step)

192 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 120 °C. By the first distillation operation, 169 g of the first distillate (containing the mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Then, 169 g of the first distillate distilled from the first distillation column 11 was placed in the second distillation column 12, and distillation was carried out at a distillation temperature of 120 °C. By the second distillation operation, the second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12, thereby recovering 78 g of the liquid containing the mixed acid. After the second distillation operation, 81 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue was collected in the second distillation column 12.

<Example 10>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing the components and the content of each component as shown in Table 10), 19 g of sodium fluoride, and 26 g of potassium fluoride were placed in the mixing tank 9, and then stirred and mixed for 24 hours by a stirring blade to obtain a mixture. liquid.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to perform centrifugal separation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (the mixed acid waste liquid from which Si ^{4 +} is removed; Containing sediment). The obtained precipitate was 158 g, and the obtained supernatant was 187 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main components of the precipitate were sodium bismuth fluoride (Na ₂ SiF ₆ ) and potassium cesium fluoride (K ₂ SiF ₆ ).

(first distillation step)

187 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 120 °C. By the first distillation operation, 162 g of the first distillate (containing the mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Next, the first distillate discharged from the first distillation column 11 is 162 g. It was placed in the second distillation column 12 and distilled at a distillation temperature of 120 °C. By the second distillation operation, the second distillate (mixed acid solution) was distilled off from the top of the second distillation column 12, whereby 59 g of a liquid containing a mixed acid was recovered. After the second distillation operation, 95 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue can be recovered in the second distillation column 12.

<Example 11>

For the mixed acid waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ ) discharged from a semiconductor manufacturing plant, the recovery apparatus 1 having the configuration shown in Fig. 1 is used, and Si ⁴⁺ removal is performed as described below. Step, first distillation step, and second distillation step.

(Si ⁴⁺ removal step)

300 g of the mixed acid waste liquid (containing components and the content of each component as shown in Table 11), 18 g of sodium chloride, 13 g of sodium fluoride, and 18 g of potassium fluoride were placed in the mixing tank 9, and then stirred and mixed by a stirring blade. A mixture was obtained for 24 hours.

Next, the mixed liquid is placed in a centrifugal separator (solid-liquid separator) 10 to perform centrifugal separation, and the mixed liquid is separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (the mixed acid waste liquid from which Si ^{4 +} is removed; Containing sediment). The obtained precipitate was 154 g, and the obtained supernatant was 195 g.

From the analysis results of XRD (X-ray spectroscopic analysis), it was confirmed that the main components of the precipitate were sodium argon fluoride (Na ₂ SiF ₆ ) and potassium cesium fluoride (K ₂ SiF ₆ ).

(first distillation step)

195 g of the supernatant (the mixed acid waste liquid from which Si ^{4+ was} removed) in the solid-liquid separator 10 was placed in the first distillation column 11 and distilled at a distillation temperature of 120 °C. By the first distillation operation, 171 g of the first distillate (containing the mixed acid solution of hydrofluoric acid and hydrochloric acid) was distilled off from the top of the first distillation column 11.

(Second distillation step)

Then, 171 g of the first distillate distilled from the first distillation column 11 was placed in the second distillation column 12, and distillation was carried out at a distillation temperature of 120 °C. By the second distillation operation, the second distillate (mixed acid solution) is distilled off from the top of the second distillation column 12, thereby recovering 66 g of the liquid containing the mixed acid. After the second distillation operation, 99 g of a hydrofluoric acid concentrated mixed acid solution (recovered liquid containing concentrated hydrofluoric acid) as a distillation residue can be recovered in the second distillation column 12.

<Comparative Example 1>

The first distillation step was carried out in the same manner as in Example 1 except that sodium chloride was not introduced into the mixing tank (the Si ⁴⁺ removal step was not carried out), that is, the mixed acid waste liquid (containing the components and discharged from the semiconductor manufacturing plant) The content of each component is directly introduced into the first distillation column 11 and is distilled at a distillation temperature of 120 ° C. The first distillate obtained from the top of the first distillation column 11 is subjected to distillation. Si remaining in the content ratio (2.23 mass%) equivalent to the Si content (2.02 mass%) of the mixed acid waste liquid to be treated was not completely removed, and Si ⁴⁺ could not be completely removed.

In the above examples and comparative examples, the concentration (% by mass) of each component of HF, HCl, and H ₂ SO ₄ in each liquid was measured using an ion mass spectrometer ("ICS-1000" manufactured by Dionex Japan Co., Ltd.).

In addition, the qualitative and quantitative analysis of Si was carried out using an ICP emission spectrometer ("ICPS-7510" manufactured by Shimadzu Corporation).

From this table and the like, may be explicitly known recovery method in the embodiment of the present invention is applied 1 to 11, containing from hydrofluoric acid, hydrochloric acid, and mixed waste of Si ^4+, impurities were recovered (containing the Si ⁴⁺ A mixed acid solution containing a small amount of metal ions and a small amount of hydrofluoric acid concentrated mixed acid having a small amount of impurities (metal ions containing Si ⁴⁺ ).

On the other hand, in Comparative Example 1 in which the salt was not added to the mixed acid waste liquid and the distillation operation was performed, the mixed acid solution distilled by distillation contained a large amount of Si ⁴⁺ , and the mixed Si ⁴⁺ could not be removed.

Industrial applicability:

In the method for removing Si from a hydrofluoric acid-based waste liquid containing Si, for example, a hydrofluoric acid-based waste liquid (for example, a waste liquid containing hydrofluoric acid or a hydrofluoric acid) which is used as an etchant can be used. The method of treating the hydrofluoric acid in the case of recovering hydrofluoric acid, and the like, and the hydrochloric acid waste liquid, etc., is not particularly limited to those suitable for the use.

In the method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si, for example, a hydrofluoric acid-based mixed acid waste liquid (using a mixed acid solution containing hydrofluoric acid and hydrochloric acid) which is used as an etchant or the like can be used. Etc.) separately recovering mixed acid Liquid, hydrofluoric acid concentrated mixed acid solution.

This application is a priority claim of Japanese Patent Application No. 2012-251319, which is filed on November 15, 2012, and Japanese Patent Application No. 2013-193960, filed on September 19, 2013. The disclosure thereof forms a part of this application.

The terms and descriptions used herein are for describing embodiments of the invention, but the invention is not limited thereto. The present invention allows any design change as long as it does not deviate from the spirit within the scope of the patent application.

1‧‧‧Recycling device

9‧‧‧ mixing tank

10‧‧‧ solid liquid separator

11‧‧‧1st distillation tower

12‧‧‧2nd distillation tower

Claims (21)

A method for removing Si from a hydrofluoric acid-based waste liquid containing Si, comprising: removing a precipitate containing the hydrofluoric acid and Si, removing the precipitate generated by the addition of the salt, and removing the salt Si removal step of the waste liquid of Si. A method for removing Si from a hydrofluoric acid-based waste liquid containing Si, comprising: removing a precipitate containing the hydrofluoric acid and Si, removing the precipitate generated by the addition of the salt, and removing the salt a Si removing step of the waste liquid of Si; and a distillation step of distilling the liquid containing hydrofluoric acid to obtain a distillate by distilling the waste liquid from which Si is removed. A method for removing Si from a hydrofluoric acid-based waste liquid containing Si according to claim 1 or 2, wherein the salt is one selected from the group consisting of a metal fluoride salt and a metal chloride salt or Two or more kinds of salts. A method for removing Si from a hydrofluoric acid-containing waste liquid containing Si according to claim 1 or 2, wherein the salt is selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, and fluorination. One or two or more salts of the group consisting of magnesium and lithium fluoride. The method for removing Si from a hydrofluoric acid-based waste liquid containing Si according to any one of claims 1 to 4, wherein the step of adding the salt to the waste liquid is to supply the waste liquid through a supply pipe. To the mixing tank, and simultaneously feeding the salt to the mixing tank, in the adding step Previously, there is provided a measuring step of measuring the flow rate and density of the waste liquid passing through the supply pipe by a mass flow meter disposed in the supply pipe; and the data of the flow rate and density measured by the mass flow meter in the computer Calculating a mass of Si in the waste liquid passing through the supply pipe, and calculating a mass of the salt required for precipitation of Si based on the calculated value; and measuring a salt of the mass calculated by the computer by a meter And feeding the metering step of the aforementioned mixing tank. A method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si, which comprises: adding a salt to a mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid and Si, and removing the addition of the salt a sediment removal step to obtain a Si removal step for removing the mixed acid waste liquid of Si; a first distillation step of obtaining the first distillate by distilling the above-mentioned mixed acid waste liquid of Si to distill off the mixed acid solution; and by distillation In the first distillate obtained in the first distillation step, the second distillate is distilled off to obtain a second distillate, and the second distillation step of the hydrofluoric acid concentrated mixed acid solution as the distillation residue is simultaneously recovered. A method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si according to the sixth aspect of the patent application, wherein the distillation temperature in the first distillation step is set in the range of 80 ° C to 130 ° C. A method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si according to the sixth or seventh aspect of the patent application, wherein the second distillation step is The distillation temperature in the range is set in the range of 80 ° C to 130 ° C. The method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si according to any one of claims 6 to 8, wherein the salt is selected from the group consisting of a metal fluoride salt and a metal chloride salt. One or two or more salts of the group. A method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si according to any one of claims 6 to 8, wherein the salt is selected from the group consisting of potassium fluoride, sodium fluoride, and potassium chloride. One or two or more salts of the group consisting of sodium chloride, magnesium fluoride, and lithium fluoride. The method for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si according to any one of claims 6 to 10, wherein the step of adding the salt to the waste liquid is carried out via a supply pipe The waste liquid is supplied to the mixing tank, and the salt is supplied to the mixing tank. Before the adding step, the flow rate of the waste liquid passing through the supply pipe is measured by a mass flow meter provided in the supply pipe. a measuring step of density; calculating, in the computer, the mass of Si in the waste liquid passing through the supply pipe according to the aforementioned flow rate and density measured by the mass flow meter, and calculating the precipitation of Si according to the calculated value a step of calculating the mass of the salt; and a metering step of measuring the mass of the mass calculated by the computer by the meter and feeding it to the mixing tank. A recovery device for recovering hydrofluoric acid from a hydrofluoric acid-containing waste liquid containing Si, characterized in that A mixing tank for mixing a waste liquid containing hydrofluoric acid and Si and a salt to obtain a mixed liquid, and a solid-liquid separator for solid-liquid separation of the precipitate present in the mixed liquid, And a distillation column for distilling the filtrate separated by the aforementioned solid-liquid separator. A recovery device for recovering hydrofluoric acid from a hydrofluoric acid-based mixed acid waste liquid containing Si, comprising: mixing a mixed acid waste liquid containing hydrofluoric acid and Si and a salt by stirring to obtain a mixed liquid mixture; a solid-liquid separator for solid-liquid separation of a precipitate present in the mixed liquid, a first distillation column for distilling the filtrate separated by the solid-liquid separator, and a pair The second distillation column in which the distillate distilled from the first distillation column is subjected to distillation. The recovery device of claim 12 or 13, further comprising: a mass flow meter disposed on the supply pipe for supplying the waste liquid to the mixing tank, and measuring a flow rate and a density of the waste liquid passing through the supply pipe, Calculating the mass of the Si in the waste liquid passing through the supply pipe according to the aforementioned flow rate and density measured by the mass flow meter, and calculating the mass of the salt required for the precipitation of Si based on the calculated value, and The salt of the mass calculated by the aforementioned computer is metered and sent to the meter of the aforementioned mixing tank. A solid-liquid separation device characterized by comprising: a solid-liquid separator capable of separating a solid component and a liquid, and discharging the separated solid component from the bottom, and accommodating the solid component sludge discharged from the bottom of the solid-liquid separator a tank, a discharge pipe connected to a discharge port provided at a bottom of the sludge tank, a discharge valve provided in the discharge pipe, and an interface position detector for detecting an upper position of a solid component accommodated inside the sludge tank . A solid-liquid separation device according to claim 15 wherein an ultrasonic interface detector is used as the aforementioned interface position detector. A solid-liquid separation device according to claim 15 or 16, wherein a liquid scroll is used as the aforementioned solid-liquid separator. The solid-liquid separation device according to any one of claims 15 to 17, further comprising: a circulation pipe for supplying the liquid separated by the solid-liquid separator to the solid-liquid separator. The solid-liquid separation device according to any one of claims 15 to 18, wherein the opening/closing operation or opening of the discharge valve is performed based on information on an upper position of a solid component detected by the interface position detector Adjust the control department. The solid-liquid separation device according to any one of claims 15 to 18, wherein the solid-liquid separation device has a solidity detected by the interface position detector When the upper position of the body component rises to the first predetermined height in the sludge tank, the discharge valve is opened to discharge the solid content in the sludge tank, and is detected by the interface position detector due to the discharge of the solid component. When the upper position of the solid component falls to the second predetermined height in the sludge tank, the control unit that controls the discharge valve is closed. The solid-liquid separation device according to any one of claims 15 to 18, wherein when the upper position of the solid component detected by the interface position detector is lowered, the opening degree of the discharge valve is reduced. When the position of the upper surface of the solid component detected by the interface position detector increases, the opening degree of the discharge valve is increased to control the upper position of the solid component in the sludge tank to a substantially constant position. Control department.