KR20140063449A - 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

FIELD OF THE INVENTION The present invention relates to a method for removing Si from a Si-containing fluoric acid-based waste liquid and a method for recovering hydrofluoric acid from a Si-containing hydrofluoric acid mixed waste liquid and a recovering apparatus for recovering H 2 SO 4 WASTE LIQUID OF Si-CONTAINING HYDROFLUORIC ACID, AND RECOVERY DEVICE}

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

At present, hydrofluoric acid-based solutions such as hydrofluoric acid aqueous solution, hydrofluoric acid-hydrochloric acid aqueous solution and hydrofluoric acid-nitric acid aqueous solution are used as etchants in semiconductor factories and the like. Since the etching function is deteriorated by repeating etching, a large amount of fluoric acid-based waste liquid is discharged from such a semiconductor factory. The fluoric acid-based waste solution after etching contains metal such as Si and can not be reused. This fluoric acid-based waste solution is neutralized and drained (see Patent Document 1).

Japanese Patent Application Laid-Open No. 2002-1267222 (paragraph 0002)

However, since the neutralization treatment contains a trace amount of fluorine in the wastewater, it is inevitable that environmental pollution is caused to a small extent. From the viewpoint of environmental preservation, the method of discharging the wastewater by neutralization is a preferable means I can not say.

In recent years, the cost of raw materials for hydrofluoric acid has been rising, and it is strongly desired to reuse such fluorine resources.

However, when the hydrofluoric acid mixed waste liquid is distilled to remove the mixed metal such as Si, SiF ₄ (silicon tetrafluoride) or the like is produced. Since this SiF ₄ is highly volatile, it is mixed into the effluent As a result, it was impossible to obtain a hydrofluoric acid mixed solution in which Si was reduced or removed.

SUMMARY OF THE INVENTION The present invention has been made in view of such a technical background, and it is an object of the present invention to provide a method for removing Si from a Si-containing fluoric acid-based waste liquid that can efficiently reduce or remove Si contained in a fluoric acid- It is an object of the present invention to provide a method for recovering hydrofluoric acid from a Si-containing hydrofluoric acid mixed waste liquid which can recover hydrofluoric acid in which Si is reduced or removed from a mixed acid waste liquid.

In order to achieve the above object, the present invention provides the following means.

[1] A method for removing Si from a Si-containing fluoric acid-containing waste solution, which comprises a step of adding a salt to a waste liquid containing hydrofluoric acid and Si, and then removing a precipitate produced by the addition of the salt to obtain a Si- / RTI >

[2] A method for removing Si, comprising: a Si removing step of adding a salt to a waste liquid containing hydrofluoric acid and Si, removing a precipitate formed by the addition of the salt,

And a distillation step of distilling the Si-removing waste liquid to distill out the hydrofluoric acid-containing liquid to obtain an effluent.

[3] The method for removing Si from a Si-containing fluoric acid-based waste liquid, characterized in that, in the method [1] or [2], at least one salt selected from the group consisting of a metal fluoride salt and a metal chloride salt is used as the salt How to.

[4] The method according to [1] or [2], wherein the salt is at least one selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride and lithium fluoride Wherein the Si is removed from the Si-containing hydrofluoric acid-based waste solution.

[5] The method according to any one of [1] to [4], wherein the adding step of adding a salt to the waste liquid is performed by supplying the waste liquid to a mixing tank through a supply pipe, Before this addition step,

A measuring step of measuring a flow rate and a density of a waste liquid passing through the supply pipe by a mass flow meter installed in the supply pipe;

Calculating the mass of Si in the waste liquid that has passed through the supply pipe based on the flow rate and density data measured by the mass flowmeter in the calculator and calculating the mass of the salt necessary for the sedimentation of Si based on the calculated value The process,

And a metering step of measuring the salt of the mass calculated in the calculator by a meter and transferring the salt to the mixing tank.

[6] A method for removing Si from a mixed waste liquid containing hydrofluoric acid, hydrochloric acid, and Si, comprising the steps of: adding a salt to a mixed waste liquid;

A first distillation step of distilling the Si-removed mixed waste liquid to flow out the mixed liquid to obtain a first effluent,

And a second distillation step of distilling the first effluent obtained in the first distillation step to distill out the mixed liquid to obtain a second effluent and recovering the hydrofluoric acid-concentrated mixture liquid as a distillation residue. A method for recovering hydrofluoric acid from a mixed acid waste liquid.

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

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

[9] A method for producing a silicon-containing hydrofluoric acid mixed wastewater treatment liquid according to any one of [6] to [8], wherein at least one salt selected from the group consisting of a metal fluoride salt and a metal chloride salt is used as the salt A method of recovering hydrofluoric acid.

[10] The positive resist composition according to any one of [6] to [8], wherein 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 Wherein the hydrofluoric acid is recovered from the Si-containing hydrofluoric acid mixed waste liquid.

[11] The method according to any one of [6] to [10], wherein the adding step of adding a salt to the waste liquid is performed by supplying the waste liquid to a mixing tank through a supply pipe, Before this addition step,

A measuring step of measuring a flow rate and a density of a waste liquid passing through the supply pipe by a mass flow meter installed in the supply pipe;

Calculating the mass of Si in the waste liquid that has passed through the supply pipe based on the flow rate and density data measured by the mass flowmeter in the calculator and calculating the mass of the salt necessary for the sedimentation of Si based on the calculated value The process,

And a metering step of measuring the salt of the mass calculated by the calculator by a meter and transferring the salt to the mixing tank.

[12] A mixing tank for mixing a waste liquid containing hydrofluoric acid and Si with a salt by stirring to obtain a mixed liquid,

A solid-liquid separator used for solid-liquid separation of the precipitate present in the mixed solution,

And a distillation column used for distilling the filtrate separated and separated by the solid-liquid separator. The recovering apparatus for recovering hydrofluoric acid from a Si-containing hydrofluoric acid waste liquid.

[13] A mixing tank for mixing a mixed waste liquid containing hydrofluoric acid and Si and a salt by stirring to obtain a mixed liquid,

A solid-liquid separator used for solid-liquid separation of the precipitate present in the mixed solution,

A first distillation column used for distilling the filtrate separated and separated by the solid-liquid separator,

And a second distillation column used for distilling the effluent flowing out from the first distillation column. The recovering apparatus for recovering hydrofluoric acid from a Si-containing hydrofluoric acid mixed waste liquid.

[14] A mass flow meter according to [12] or [13], further comprising: a mass flow meter installed in a supply pipe for supplying the waste liquid to the mixing tank and measuring a flow rate and density of the waste liquid passing through the supply pipe;

A calculator for calculating the mass of Si in the waste liquid passing through the supply pipe based on the flow rate and density data measured by the mass flowmeter and calculating the mass of salt required for the sedimentation of Si based on the calculated value,

And a meter for measuring the salt of the mass calculated by the calculator and transferring the measured salt to the mixing tank.

[15] A solid-liquid separator comprising: a solid-liquid separator capable of separating a solid component from a liquid and discharging the separated solid component from the bottom;

A sludge pot that receives the solid content discharged from the bottom of the solid-liquid separator,

A discharge pipe communicated with an outlet formed at the bottom of the sludge pot,

A discharge valve provided in the discharge pipe,

And an interfacial position detector for detecting a position of an upper surface of a solid portion contained in the sludge pod.

[16] The solid-liquid separator according to [15], wherein an ultrasonic interface detection system is used as the interface position detector.

[17] The solid-liquid separation device according to [15] or [16], wherein a liquid cyclone is used as the solid-liquid separator.

[18] The solid-liquid separation device according to any one of [15] to [17], further comprising a circulation pipe for re-supplying the liquid separated by the solid-liquid separator into the solid-liquid separator.

[19] The image forming apparatus according to any one of [15] to [18], further comprising a control section for performing opening / closing operation or opening degree adjustment of the discharge valve on the basis of data of the top surface position of the solid component detected by the interface position detector Liquid separator.

[20] In any one of [15] to [18], when the top surface position of the solid component detected by the interface position detector has risen to the first predetermined height in the sludge pod, And a control unit for controlling the discharge valve to close when the top surface position of the solid component detected by the interface position detector is lowered to the second predetermined height in the sludge pod by discharging the solid content Liquid separator.

[21] The method as described in any one of [15] to [18], further comprising: reducing the opening degree of the discharge valve when the top surface position of the solid component detected by the interface position detector falls, And a control unit for controlling the position of the top surface of the solid in the sludge pod to be substantially constant by performing control to increase the opening degree of the discharge valve when the top surface position of the sludge pod rises.

(Effects of the Invention)

In the invention of [1], a Si-containing precipitate can be produced by adding a salt to a waste liquid containing hydrofluoric acid and Si, and thus the precipitate can be removed to obtain a Si-removing waste liquid. Si can be precipitated and removed, so that SiF ₄ (which is a highly volatile material) is not mixed into the effluent when the distillation operation is performed on the waste liquid, for example. Therefore, it is possible to recover the effluent (such as hydrofluoric acid or mixed acid) having little impurities such as Si.

The description of [2] can generate a Si-containing precipitate by adding a salt to a waste liquid containing hydrofluoric acid and Si, and thus the Si-removing waste liquid can be obtained by removing this precipitate. Subsequently, the Si-removing waste liquid is distilled, so that the metal components other than Si present in the waste solution do not flow out but are left in the distillation column and the like, so that the effluent (hydrofluoric acid-containing liquid, mixed acid- ) Can be recovered. Thus, the effluent can be reused because the amount of impurities is small. In addition, since it is not necessary to neutralize and treat the waste liquid, the waste liquid treatment cost can be reduced.

In the invention of [3], one or more salts selected from the group consisting of a metal fluoride salt and a metal chloride salt are used as a salt, so that a waste liquid from which Si is sufficiently removed can be obtained.

In the invention of [4], one or more salts selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride and lithium fluoride are used as the salt, .

According to the invention of [5], since the amount of salt necessary for the salting of Si can be supplied to the mixing tank with high precision and automatically, the waste liquid can be efficiently treated with high accuracy.

In the invention of [6], a Si-containing precipitate can be produced by adding a salt to a mixed waste liquid containing hydrofluoric acid, hydrochloric acid and Si, and thus the precipitate can be removed to obtain a Si-removed mixed waste liquid. Subsequently, the Si-removed mixed wastewater is distilled, so that the metal components other than Si present in the mixed acid waste solution do not flow out but remain in the distillation column and the like, so that a first effluent (mixed acid containing Solution) can be obtained. Subsequently, the first effluent is distilled to recover the hydrofluoric acid-enriched mixed liquor having a small amount of impurities, as a distillation residue, and the mixed liquid having a small amount of impurities can be recovered as a distillate (second effluent). Thus, the distillation residue and the effluent can be reused because the impurities are small. In addition, since it is not necessary to neutralize the mixed acid waste liquid, it is possible to reduce the waste liquid treatment cost.

According to the invention of [7], since the distillation temperature in the first distillation step is set in the range of 80 ° C to 130 ° C, the mixed acid-containing liquid can sufficiently flow out as the first effluent.

According to the invention of [8], since the distillation temperature in the second distillation step is set in the range of 80 ° C to 130 ° C, it is possible to sufficiently leave the hydrofluoric acid-enriched mixed liquid in the distillation residue and to separate the mixed liquid into the effluent (second effluent) As shown in Fig. Further, the concentration ratio of hydrofluoric acid as the distillation residue can be improved.

In the invention of [9], one or more salts selected from the group consisting of a metal fluoride salt and a metal chloride salt are used as a salt. Therefore, a mixed acid waste liquid from which Si is sufficiently removed can be obtained. Furthermore, It is possible to collect each of the acid liquid and the mixed liquid having a small amount of impurities.

In the invention of [10], one or more salts selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride and lithium fluoride are used as the salt, And further, it is possible to recover the hydrofluoric acid-concentrated mixed solution having less impurities and the mixed solution having less impurities.

According to the invention of [11], since the amount of salt necessary for the salting of Si can be supplied precisely and automatically to the mixing tank, it is possible to recover a fluoric acid-enriched mixed solution having less impurities and a mixed solution having less impurities at a sufficient treating rate .

Since the invention of [12] includes the mixing tank, the solid-liquid separator and the distillation tower, it is possible to generate the Si-containing precipitate in the mixing tank and to separate the precipitate from the waste liquid by the solid-liquid separator, The metal components other than Si can be left in the distillation column without disturbing the operation, whereby the effluent (such as a hydrofluoric acid-enriched mixed-acid solution or mixed acid-containing solution) having little impurities (Si, can do.

Since the invention of [13] includes the mixing tank, the solid-liquid separator, the first distillation column, and the second distillation column, the Si-containing precipitate can be produced in the mixing tank and the precipitate can be separated from the waste liquid by the solid- , And then the metal components other than Si can be left in the first distillation column without distilling out by the distillation operation in the first distillation column, whereby the first effluent (the second distillation column) containing a small amount of impurities (Si, Mixed acid containing solution, etc.) can be obtained. Subsequently, the first effluent is subjected to a distillation operation by the second distillation column, whereby the hydrofluoric acid-concentrated mixed-organic solution having a small amount of impurities can be recovered as a distillation residue, and the mixed liquid having a small amount of impurities can be recovered as an effluent (second effluent) .

According to the invention of [14], the amount of salt necessary for the salting of Si can be supplied to the mixing tank with high accuracy and automatically. The recovering apparatus according to the invention of [12] to [14] can cope with the delivery system of the delivery system, and can cope with the continuous system.

The apparatus according to the invention of [15] is a device applied when solid matters are mixed in a waste liquid. According to this apparatus, since the sludge pod accommodating the solid component discharged from the bottom of the solid-liquid separator is provided, It can be prevented from being closed and closed. Further, since the interface position detector for detecting the position of the top surface of the solid portion contained in the sludge pod is provided, liquid (mixed acid or the like) can be obtained by controlling the opening / closing of the discharge valve or the opening degree based on the data of the solid surface position, It is possible to discharge only the solid matter as much as possible without discharging it as much as possible. That is, it is possible to improve the recovery rate of the recovered liquid (such as recovered mixed liquid). The solid-liquid separating apparatus of the present invention is particularly effective in improving the recovery rate in the case where the concentration of the solid content (precipitate) in the feed liquid fluctuates (in many cases, this is often the case in the waste liquid). The solid-liquid separator according to the present invention can cope with a pumping system in a batch mode and can cope with a continuous system.

In the invention of [16], since the ultrasonic interface detection system is used as the interface position detector, it is possible to detect the position of the top surface of the solid content in the sludge pod with higher precision.

Since the liquid cyclone is used as the solid-liquid separator in the invention of [17], it can be downsized and the processing ability (processing speed) of solid-liquid separation can be improved.

According to the invention of [18], since the circulation pipe for re-feeding the liquid separated in the solid-liquid separator into the solid-liquid separator is provided, the solid-liquid separator is supplied again through the circulation pipe to recover solid impurities There is an advantage that the content ratio can be sufficiently reduced.

According to the invention of [19], there is provided a control unit for performing opening / closing operation or opening degree adjustment of the discharge valve on the basis of the data of the top surface position of the solid component detected by the interface position detector. It is possible to avoid the discharge as much as possible.

In the invention of [20], since the control unit for performing the specific control is provided, it is possible to avoid the discharge of the liquid (mixed acid or the like) together with the solid content to the utmost, and the recovery of the recovered liquid (mixed recovery liquid, The recovery rate can be further improved. Further, when the waste liquid treatment is carried out by batch operation, the recovery rate of the recovery liquid can be further improved by performing the batch operation.

In the invention of [21], since it is provided with the control unit for performing the specific control, it is possible to avoid the discharge of liquid (mixed acid or the like) together with the solid fraction to the utmost, and the recovery rate Can be further improved.

1 is a schematic explanatory view showing an example of a removing method and a recovering method according to the present invention.
FIG. 2 is a schematic explanatory diagram (a part of FIG. 1 showing a detailed structure) showing an example of an automatic salt addition system in an apparatus used in a removing method and a recovery method according to the present invention.
3 is a schematic configuration diagram showing the entire recovery apparatus constructed using a solid-liquid separator according to an embodiment of the present invention.
4 is a detailed configuration diagram (a configuration diagram partially showing a part of the apparatus of FIG. 3) showing a part of the recovery apparatus constructed using the solid-liquid separation apparatus according to the embodiment of the present invention.
5 is a vertical sectional view showing a sludge pot with an interface position detector.

How to remove the Si ⁴⁺ from the hydrofluoric acid-based waste liquid containing Si ⁴⁺ according to the present invention, since after addition of salt to the waste liquid containing hydrofluoric acid and Si ^4+, removing the precipitate produced by the addition of a salt Si ⁴ obtaining a ⁺ removed waste liquid characterized by including the step of removing Si ^4+.

According to the above removal method, a Si ⁴⁺ -containing precipitate can be produced by adding a salt to a waste liquid containing hydrofluoric acid and Si ⁴⁺ , and thus the precipitate can be removed to obtain a Si ^{4+ -soluble} waste liquid. Si ⁴⁺ can be precipitated and removed by the addition of the salt. For example, when the distillation operation is performed on the Si ^{4+ -subsequent} waste liquid after the above-mentioned removal step, SiF ₄ (a substance having high volatility) is mixed into the effluent none.

After the step of removing the Si ⁴⁺ to spill by the hydrofluoric acid-containing solution to install a first distillation step to obtain a distillate by distilling the removed waste liquid Si ⁴⁺ being preferred. In this case, since a metal component other than Si does not flow out in the distillation column by the distillation operation of the Si ⁴⁺ removing waste liquid, a hydrofluoric acid-containing liquid (a hydrofluoric acid-containing liquid containing a small amount of impurities Mixed liquid containing liquid or hydrofluoric acid, etc.) can be recovered as an effluent.

As the waste liquid of the object to which the removal method is applied, for example,

Waste liquids containing Si ⁴⁺ and hydrofluoric acid (hydrofluoric acid)

· Mixture wastewater containing Si ⁴⁺ , hydrochloric acid and hydrofluoric acid (hydrofluoric acid)

· Mixture wastewater containing Si ⁴⁺ , nitric acid and hydrofluoric acid (hydrofluoric acid)

And the like. The waste liquid may contain an acid other than hydrofluoric acid. Further, the mixed waste liquid may further contain other acid than hydrochloric acid and hydrofluoric acid. In addition, the hydrofluoric acid mixture waste discharged from a semiconductor manufacturing factory often contains other metal ions besides Si in addition to dissolved Si ⁴⁺ as H ₂ SiF ₆ .

Further, a method for recovering hydrofluoric acid from a Si ⁴⁺ -containing fluoric acid mixed waste liquid according to the present invention is characterized in that after a salt is added to a mixed waste liquid containing hydrofluoric acid, hydrochloric acid and Si ⁴⁺ , the precipitate produced by the addition of the salt is removed by the obtained in the first distillation step, the first distillation step and the Si ⁴⁺ remove Si ⁴⁺ removed to obtain a mixed acid waste liquid process, by distilling the Si ⁴⁺ removed by mixed acid waste fluid outlet of the horn approximation to obtain a first effluent 1 effluent to distill the mixed liquid to obtain a second effluent, and recovering the hydrofluoric acid-concentrated mixed liquid as a distillation residue.

According to the above recovering method, it is possible to produce a Si ⁴⁺ -containing precipitate by adding a salt to a mixed waste liquid containing hydrofluoric acid, hydrochloric acid and Si ⁴⁺ , and thus the precipitate can be removed to obtain a Si ⁴⁺ -enriched mixed waste liquid. Subsequently, the Si ⁴⁺ -enriched mixed waste liquid is distilled to leave a metal component other than Si out of the distillation column without leaving, so that a first effluent (mixed acid-containing liquid) containing few impurities (Si, metal components other than Si, etc.) can be obtained . Subsequently, the first effluent is distilled to recover the hydrofluoric acid-enriched mixed liquor having a small amount of impurities, as a distillation residue, and the mixed liquid having a small amount of impurities can be recovered as an effluent (first effluent)

As the waste liquid of the object to which the recovery method is applied, for example,

· Mixture wastewater containing Si ⁴⁺ , hydrochloric acid and hydrofluoric acid (hydrofluoric acid)

· Mixture wastewater containing Si ⁴⁺ , nitric acid and hydrofluoric acid (hydrofluoric acid)

And the like. The mixed waste liquid may contain other acids other than hydrochloric acid and hydrofluoric acid. In addition, the hydrofluoric acid mixture waste discharged from a semiconductor manufacturing factory often contains other metal ions besides Si in addition to dissolved Si ⁴⁺ as H ₂ SiF ₆ .

The distillation temperature (the temperature of the mixed acid waste solution at the time of distillation) in the first distillation step is preferably set in the range of 80 ° C to 130 ° C. By setting the temperature to 80 占 폚 or higher, the distillation efficiency can be improved, and at 130 占 폚 or lower, the thermal energy cost required for distillation can be suppressed. Among them, the distillation temperature in the first distillation step is more preferably set in the range of 110 ° C to 130 ° C, and more preferably set in the range of 115 ° C to 125 ° C.

The distillation temperature (the temperature of the first effluent at the time of distillation) in the second distillation step is preferably set in the range of 80 ° C to 130 ° C. By setting the temperature in the range of 80 占 폚 to 130 占 폚, it is possible to sufficiently leave the hydrofluoric acid-enriched mixed liquid in the distillation residue, and at the same time, the mixed liquid can sufficiently flow out as the effluent (second effluent). Further, the concentration ratio of hydrofluoric acid as the distillation residue can be further improved. Among them, the distillation temperature in the second distillation step is more preferably set in the range of 110 ° C to 130 ° C, and more preferably set in the range of 115 ° C to 125 ° C.

In the removing method and the recovering method, the salt is not particularly limited, but it is preferable to use one or more salts selected from the group consisting of a metal fluoride salt and a metal chloride salt.

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

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

Among them, it is particularly preferable to use one or more salts selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride and lithium fluoride.

It is preferable that the addition amount when the salt is added to the waste solution is set so that the salt content in the " salt addition waste solution " obtained by adding the salt to the waste solution is in the range of 5% by mass to 10% by mass . Among them, the content of salt in the salt addition waste solution is more preferably in the range of 5% by mass to 7% by mass.

The second effluent (mixed acid recovered solution) obtained as described above can be used as it is, or it can be used by adjusting the concentration of acid corresponding to various uses. The distillation residue (the hydrofluoric acid-concentrated mixed acid recovery liquid) obtained as described above may be used as it is, or it may be used by adjusting the concentration of acid in accordance with various uses.

Fig. 1 shows an example of the collection device 1 used in the collection method according to 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, a description will be given by taking as an example a case where the present invention is applied to a mixed acid waste solution containing hydrofluoric acid and hydrochloric acid (including at least Si ⁴⁺ as an impurity).

The mixing tank 9 is provided with a stirring blade. The mixed waste solution (mixed acid waste solution containing hydrofluoric acid, hydrochloric acid and Si ⁴⁺ ) and salt are put into the mixing tank 9 and mixed with stirring with the stirring vane to obtain a mixed solution. In this mixed solution, a precipitate (precipitate containing Si ⁴⁺ ) is generated by the presence of a salt.

Then, the mixed solution is introduced into a solid-liquid separator 10, and the solid and liquid separator 10 are separated into a precipitate and a liquid (not including a mixed acid waste solution and a precipitate). In the present embodiment, a centrifugal separator is used as the solid-liquid separator 10, and sediment is lowered by centrifugal separation to perform solid-liquid separation. Since the precipitate is removed from the filtrate (supernatant) in the solid-liquid separator 10, Si ⁴⁺ is reduced or eliminated.

Subsequently, the filtrate (Si ⁴⁺ -removed mixed waste liquid) in the solid-liquid separator 10 is introduced into the first distillation column 11, and distillation is performed in the first distillation column 11. By this first distillation operation, the first effluent (mixed liquid containing hydrofluoric acid and hydrochloric acid) flows out from the top of the first distillation column 11, and metal components other than Si remain in the first distillation column 11. [ Thus, a first effluent having few impurities (Si, metal components other than Si, etc.) is obtained.

Then, the first effluent flowing out of the first distillation tower 11 is introduced into the second distillation tower 12, and the distillation is performed in the second distillation tower 12. By this second distillation operation, the second effluent (mixed liquid) flows out from the top of the second distillation tower 12. Thus, the mixed liquid can be recovered.

After the second distillation operation, a hydrofluoric acid-concentrated mixed liquid is obtained as a distillation residue in the second distillation tower (12). Thus, the concentrated hydrofluoric acid-containing liquid (hydrofluoric acid concentration recovery liquid) can be recovered.

It is preferable that the apparatus 1 is provided with a salt automatic addition system as shown in Fig. 2 for the introduction of the salt into the mixing tank 9. In Fig. 2, reference numeral 21 denotes a waste liquid tank, 22 denotes a pump, 23 denotes a solids removal device, 24 denotes a sludge tank, 25 denotes a mass flow meter, 26 denotes a calculator, 27 denotes a meter, 28 denotes a salt tank and 29 denotes a pump.

The pump 22, the solids removal device 23, the mass flow meter 25, the switching valve 51 and the mixing tank 9 are arranged in this order from the waste liquid tank 21 toward the downstream side of the feed liquid, (See FIG. 2). The mixing tank 9 is connected to the solid-liquid separator 10 through a pump 29 (see FIG. 2). The mass flow meter 25 is installed in a supply pipe 31 for supplying 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 calculator 26. The calculator 26 calculates the mass of Si in the waste liquid that has passed from the data (flow rate and density). An example of the calculation method is as follows. Since the density of the "liquid excluding Si" in the waste liquid is 1.0 g / cm 3 and the density of Si is 2.33 g / cm 3, the density of the waste liquid is measured, And the mass of Si (that is, the mass of Si injected into the mixing bath 9) can be calculated from the measured Si content and the measured flow rate. In addition, the hydrofluoric acid waste liquid and the hydrofluoric acid waste liquid discharged from semiconductor manufacturing plants often contain metal components other than Si, but the content thereof is at a very low level. Therefore, in the evaluation of the density, these " (Ignoring and ignoring does not affect the precision of the automatic salt addition system).

Further, the calculator 26 calculates the " mass of salt required for the Si sputtering " based on the calculated " passing mass of Si ", and the calculated value is sent to the meter 27. For example, in the case of using KF (potassium fluoride) as a salt,

2KF + H ₂ SiF ₆ ? K ₂ SiF ₆ + 2HF

, It is possible to calculate the mass of the salt required for the Si precipitate (K ₂ SiF ₆ formation which does not dissolve in water) based on this (two equivalents of KF are required for one equivalent of Si).

The precipitation reaction formula in the case of using NaCl (sodium chloride)

2NaCl + H ₂ SiF _{6 -} > Na ₂ SiF ₆ + 2HCl

, And Na ₂ SiF ₆ which is not dissolved in water is produced.

The precipitation reaction formula in the case of using KCl (potassium chloride)

2KCl + H ₂ SiF ₆ ? K ₂ SiF ₆ + 2HCl

, And K ₂ SiF ₆ which is not dissolved in water is produced.

The precipitation reaction formula in the case of using NaF (sodium fluoride)

2NaF + H ₂ SiF ₆ ? Na ₂ SiF ₆ + 2HF

, And Na ₂ SiF ₆ which is not dissolved in water is produced.

The meter 27 meters a predetermined amount of the salt (the mass based on the calculated value) from the salt tank 28 and transfers it to the mixing tank 9.

In the present embodiment, the mass flow meter 25 is of the collier type and the meter 27 is of the loss in weight type, but the present invention is not limited thereto. As the mass flow meter 25, it is preferable to use a collier type of acid resistant material.

The mixed waste liquid (mixed acid waste liquid containing hydrofluoric acid, hydrochloric acid and Si ⁴⁺ ) is stored in the waste liquid tank 21. The mixed waste liquid in the waste liquid tank 21 is passed through the solid-liquid separator 23 by the pump 22 and then passed through the mass flow meter 25 to be introduced into the mixing tank 9. In the present embodiment, a liquid cyclone is used as the solids removal device 23, and solid components (foreign matter, sludge, etc.) in the waste liquid are precipitated and removed while passing through the liquid cyclone. The sediment-removed solid content is appropriately transported to the sludge tank 24 by opening and closing the valve 30.

The flow rate and density of the waste liquid having passed through the supply pipe 31 are measured in the nitrogen flow meter 25 and the data (flow rate and density) are transmitted to the calculator 26 (measurement step).

Based on the data (flow rate and density) transmitted from the mass flow meter 25 in the calculator 26, the " mass of Si in the passing waste liquid " is calculated, and based on this calculated value, Is calculated, and this calculated value (the mass of the salt necessary for the salting of Si) is transmitted to the calculator 27 (calculation step).

Then, the salt is metered by the meter 27 from the salt tank 28 to a predetermined amount (the mass of the calculated value) and transferred to the mixing tank 9 (metering step).

By providing the automatic salt addition system having the structure shown in Fig. 2 in the apparatus 1, it is possible to add a salt to the mixing tank 9 with a high degree of accuracy and automatically, which is necessary for the salting of Si. In the automatic salt addition system, the waste liquid may be fed in a batch mode or in a continuous mode.

In the above embodiment, the switching valve 51 is disposed between the mixing tank 9 and the mass flow meter 25 in the supply pipe 31, and one end of the circulation pipe 50 is connected to the switching valve And the other end of the circulation pipe 50 is connected to the waste liquid tank 21 so that the waste liquid tank 21 is separated from the waste liquid tank 21 by the switching valve 51, The liquid is supplied from the waste liquid tank 21 and the pump 22 to the solid-content-separating device 23 one or more times to perform the solid-content-removing treatment a plurality of times to reduce the solid content as much as possible The solid content may be lowered), the mixture may be introduced into the mixing tank 9 (see FIG. 2).

The removing method and the recovering method of the present invention may be carried out by using the recovery apparatus having the configuration shown in Figs. 3 to 5. The recovery device 1 shown in FIG. 3 has the following structure in comparison with the recovery device 1 shown in FIG.

1) The mixed waste liquid is not directly introduced into the mixing tank 9, but the mixed waste liquid is pretreated in a solid-liquid separating apparatus (solid-liquid separation system) 100A to be described later to remove the solid matter (foreign matters) Into the tank (9).

2) A solid-liquid separator (solid-liquid separation system) 100B, which will be described later, is used in place of the solid-liquid separator 10 as a solid-liquid separator disposed between the mixing tank 9 and the first distillation tower 11.

Fig. 4 shows the detailed configuration of the front half constituent part including the two solid-liquid separators (solid-liquid separation systems) 100A and 100B in the recovery device 1 shown in Fig.

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

4, reference numeral 62 denotes a pump, 63 denotes a solid-liquid separator, 64 denotes a sludge pot, 65 denotes a discharge pipe, 66 denotes a discharge valve, 67 denotes an interface position detector, 68 denotes a control unit, and 69 denotes a sludge tank. The solid-liquid separator (solid-liquid separation system) 100B includes a solid-liquid separator 63, a sludge pod 64, a discharge pipe 65, a discharge valve 66, an interface position detector 67, 68).

4, each of the mass flow meter 25, the calculator 26, the meter 27, the salt tank 28, and the supply pipe 31, the respective functions, the connection forms, and the like are the same as those in Fig. Will not be described again. The configuration, functions, connection forms, and the like of the mixing vessel 9 and the components downstream of the first distillation tower 11 in FIG. 3 are the same as those in FIG. 1, and therefore their explanation is omitted.

Hereinafter, the solid-liquid separating apparatus (solid-liquid separating system) 100A and the solid-liquid separating apparatus (solid-liquid separating system) 100B will be described.

A pump 42 and the solid-liquid separating apparatus (solid-liquid separating system) 100A are connected in this order from the waste liquid tank 41 to the downstream side of the liquid sending through the supply pipe 40 (see FIG. 4). A liquid (a mixed waste liquid from which solids such as foreign substances are removed) subjected to solid-liquid separation treatment from the solid-liquid separator 100A is sent to the mixing tank 9 through a supply pipe 31 provided with a mass flow meter 25 at an intermediate position .

In the present embodiment, a liquid cyclone is used as the solid-liquid separator 43. The other end of the supply pipe 40, one end of which is connected to the bottom of the waste liquid tank 41, is horizontally connected to the upper position of the liquid cyclone 43. The liquid cyclone 43 can separate the solid (solid) suspended in the liquid and the liquid by centrifugal force. When a mixed acid waste liquid is injected horizontally into the liquid cyclone 43, a spiral downward flow is generated along the inclined surface of the peripheral wall portion of the liquid cyclone 43, and a solid (foreign matter, etc.) And is conveyed to the sludge pod 44. On the other hand, an upward flow is generated at the center of the liquid cyclone 43, and the liquid (mixed acid waste liquid) is discharged from the upper portion of the liquid cyclone 43 in this ascending flow, (9). The liquid cyclone 43 can be made into an acid-resistant device by using an acid-resistant material (for example, polyvinyl chloride or the like) and is easy to produce.

A sludge pod (44) is disposed at the bottom of the liquid cyclone (43). The outlet of the bottom of the liquid cyclone 43 and the inlet 53 of the upper part of the sludge pod 44 are connected to each other. One end of the discharge pipe 45 is connected to the discharge port 52 at the bottom of the sludge pod 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 on the way.

An interface position detector 47 is attached to the upper portion of the sludge pod 44 (see FIG. 5). In the present embodiment, an ultrasonic interface detection system is used as the interface position detector 47. [ An ultrasonic wave passage 54 penetrating in the vertical direction is formed on the upper wall of the sludge pod 44 (part of the outer peripheral edge of the upper wall in this embodiment) of the sludge pod 44. The ultrasonic wave passage 54 penetrates through the ultrasonic wave passage 54, The ultrasonic interface detection system 47 is attached to the upper part of the sludge pod 44 so as to be able to transmit the ultrasonic wave to the inner space of the sludge pod 44. The top surface position of the solid contained in the sludge pod (44) can be detected by the ultrasonic interface detecting system (47). The ultrasound interface detection system 47 is not particularly limited, and for example, an ultrasound interface system SL-200A manufactured by Horiba Seisakusho Co., Ltd. and an ultrasonic level meter YU-L20 system manufactured by Yamamoto Denki Kogyo Co., Ltd. can be used have. The interface position 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 on the basis of the data of the top surface position of the solid component detected by the interface position detector 47.

The control unit 48 opens the discharge valve 46 when the upper surface position of the solid component detected by the interface position detector 47 rises to the first predetermined height 81 in the sludge pod 44 When the upper surface position of the solid portion detected by the interface position detector 47 is lowered to the second predetermined height 82 in the sludge pod 44 by discharging the solid content while discharging the solid content in the sludge pod 44, So as to close the valve 46 (see Fig. 5). In addition, the first predetermined height 81 is located higher than the second predetermined height 82 (see FIG. 5).

The sludge pod 44 is used to temporarily receive a solid matter (including foreign matter and some liquid) discharged from a discharge port at the bottom of the liquid cyclone 43. By providing the sludge pod 44, It is possible to reduce the liquid mixing ratio in the solid content discharged to the liquid crystal shutter 49. Therefore, it is possible to improve the recovery rate of the recovered solution (mixed recovery solution, hydrofluoric acid-condensed mixed recovery solution, etc.) finally recovered through the distillation operation.

Then, the mixed waste liquid discharged from the liquid cyclone 43 and transferred to the mixing tank 9 through the supply pipe 31 (with foreign matters removed) is stirred in the mixing tank 9 with the salt And mixed to form a mixed solution. In this mixed solution, a precipitate (solid content: precipitate containing Si ⁴⁺ ) is formed by the addition of a salt.

A pump 62 and a solid-liquid separator (solid-liquid separation system) 100B are connected in this order from the mixing tank 9 toward the downstream side of the liquid feed through the supply pipe 60 (see FIG. 4). The liquid (the mixed acid waste liquid from which Si ⁴⁺ is removed) subjected to the solid-liquid separation treatment from the solid-liquid separation device 100B is sent to the first distillation tower 11 through the supply pipe 61. The contents of the treatment from the first distillation column 11 are the same as those of the above embodiment (the recovery device in FIG. 1).

In this embodiment, a liquid cyclone is used as the solid-liquid separator 63. The other end of the supply pipe 60, one end of which is connected to the bottom of the mixing tank 9, is horizontally connected to the upper position of the liquid cyclone 63. The liquid cyclone 63 can separate the solid (solid) suspended in the liquid and the liquid by centrifugal force. A spiral descending flow is generated along the inclined surface of the peripheral wall portion of the liquid cyclone 63 when the mixed caustic liquor (mixed waste liquid from which foreign matter has been removed) is injected into the liquid cyclone 63 in the horizontal direction, The solid (Si ⁴⁺ based precipitate) is guided to the bottom of the liquid cyclone and discharged to the sludge pod 64. On the other hand, an upward flow is generated at the center of the liquid cyclone 63, and the liquid (the mixed waste liquid from which Si ⁴⁺ is removed) is discharged from the upper portion of the liquid cyclone 63, To the first distillation column (11).

A mass flow meter 70 is provided on the way of the supply pipe 61 (see FIG. 4). A path (not shown) for recirculating the supply pipe 61 to the mixing tank 9 is also provided in order to reduce the amount of sediment (solid content) going to the first distillation tower 11, and the mass flow meter 70 To the desired distillation column (11) by lowering the concentration to a desired density (solid fraction) by monitoring the distillation column.

A sludge pod (64) is disposed at the bottom of the liquid cyclone (63). The outlet of the bottom of the liquid cyclone 63 and the inlet 73 of the upper portion of the sludge pod 64 are connected to each other. One end of the discharge pipe 65 is connected to the discharge port 72 at the bottom of the sludge pod 64 and the other end of the discharge pipe 65 is connected to the upper opening of the sludge tank 69, A discharge valve 66 is attached in the middle.

An interface position detector 67 is attached to the upper portion of the sludge pod 64 (see FIG. 5). In the present embodiment, an ultrasonic wave interface detection system is used as the interfacial position detector 67. However, an ultrasonic wave passage 74 penetrating in the vertical direction is formed on the upper wall of the sludge pod 64 (part of the outer peripheral edge of the upper wall in this embodiment), and the ultrasonic wave passage 74, The ultrasonic interface detection system 67 is attached to the upper part of the sludge pod 64 so that the sludge pod 64 can be transmitted to the inner space of the sludge pod 64. The position of the top surface of the solid (Si ⁴⁺ system precipitated solid) contained in the sludge pod 64 can be detected by the ultrasonic interface detecting system 67. The ultrasonic interface detection system 67 is not particularly limited. For example, "Ultrasonic interface system SL-200A" manufactured by Horiba Seisakusho Co., Ltd. and "Ultrasonic level meter YU-L20 type" available from Yamamoto Denki Kogyo Co., . The interface position detector 67 is preferably formed of a material having corrosion resistance.

In the present embodiment, the interface position detectors 47 and 67 are of the ultrasonic type, but an optical type, for example, may be used. However, in the case of the optical type, the detection becomes slow at a solid content having a low sedimentation speed. The optical interface position detector is also preferably formed of a material having acid resistance. The optical interface position detector is not particularly limited, and examples thereof include "Optical interface type OX100" manufactured by NONKEN Corporation.

The control unit 68 performs opening / closing operation or opening degree adjustment of the discharge valve 66 on the basis of the top surface position data of the solid component (Si ⁴⁺ system precipitated solid) detected by the interface position detector 67.

The control unit 68 reduces the degree of opening of the discharge valve 66 when the top surface position of the sediment detected by the interface position detector 67 falls from the specific position 83, When the position of the top surface of the sediment detected by the position detector 67 rises from the specific position 83, by controlling the opening degree of the discharge valve 66 to be increased, the top surface position of the sediment in the sludge pod 64 It is controlled to approximately the fixed position 83 (see Fig. 5).

The sludge pod 64 is used to temporarily receive a solid component (including Si ⁴⁺ -type precipitated solid, including some liquid) discharged from a discharge port at the bottom of the liquid cyclone 63, and the sludge pod 64 is installed It is possible to reduce the liquid mixing ratio in the sedimented solid discharged into the sludge tank 69. [ Therefore, it is possible to improve the recovery rate of the recovered solution (mixed recovery solution, hydrofluoric acid-condensed mixed recovery solution, etc.) finally recovered through the distillation operation.

Further, the removing method and the recovering method of the present invention are not particularly limited to those shown in the collecting apparatus of the constitution shown in Figs. 1 to 5.

[Example]

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

≪ Example 1 >

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed wastewater (content and content of each component are shown in Table 1) and 25 g of sodium chloride were put into a mixing tank 9, and stirred and mixed for 24 hours to obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 66 g, and the obtained supernatant was 258 g.

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

(First distillation step)

255 g of the supernatant liquid (Si ⁴⁺ -enriched mixed waste liquid) in the solid-liquid separator 10 was charged into the first distillation tower 11, and distillation was carried out at a distillation temperature of 120 ° C. By this first distillation operation, 220 g of the first effluent (mixed liquid containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Subsequently, 209 g of a portion of the first effluent flowed out from the first distillation tower (11) was charged into the second distillation tower (12), and the distillation was carried out at a distillation temperature of 120 ° C. By this second distillation operation, the second effluent (mixed liquid) was flowed out from the top of the second distillation tower 12, whereby 116 g of the mixed acid containing liquid was recovered. After the second distillation operation, 92 g of a hydrofluoric acid-concentrated mixture liquid (recovered liquid containing concentrated hydrofluoric acid) could be recovered as a distillation residue inside the second distillation tower 12.

≪ Example 2 >

The mixed recovery wastewater (hydrofluoric acid, hydrochloric acid, and mixed wastewater containing Si ⁴⁺ ) discharged from a semiconductor manufacturing plant is subjected to the Si ⁴⁺ removal process, the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed waste liquid (content and content of each component are shown in Table 2) and 25 g of potassium fluoride were charged into a mixing tank 9, followed by stirring and mixing with a stirring blade for 24 hours to obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 103 g, and the obtained supernatant was 222 g.

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

(First distillation step)

222 g of the supernatant (Si ⁴⁺ -removed mixed waste liquid) in the solid-liquid separator 10 was introduced into the first distillation column 11 and distilled at a distillation temperature of 120 ° C. By this first distillation operation, 184 g of the first effluent (a mixed acid solution containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Then, 184 g of the first effluent discharged from the first distillation tower 11 was charged into the second distillation tower 12, and the distillation was carried out at a distillation temperature of 120 ° C. By this second distillation operation, the second effluent (mixed liquid) was flowed out from the top of the second distillation tower 12, whereby 61 g of the mixed acid containing liquid was recovered. After the second distillation operation, 113 g of a hydrofluoric acid-concentrated mixed liquid (a recovered solution containing concentrated hydrofluoric acid) could be recovered as a distillation residue inside the second distillation tower 12.

≪ Example 3 >

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed waste liquid (content and content of each component are shown in Table 3) and 18 g of sodium fluoride were put into a mixing tank 9, and stirred and mixed for 24 hours to obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 69 g, and the obtained supernatant was 248 g.

From the analysis by XRD (X-ray spectroscopy), it was confirmed that the main component of the precipitate was sodium silicate (Na ₂ SiF ₆ ).

(First distillation step)

248 g of a supernatant (Si ⁴⁺ -removed mixed waste liquid) in the solid-liquid separator 10 was introduced into the first distillation column 11, and the distillation was carried out at a distillation temperature of 120 ° C. By this first distillation operation, 212 g of the first effluent (mixed liquid containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Then, 212 g of the first effluent flowed out from the first distillation tower 11 was introduced into the second distillation tower 12, and the distillation was carried out at a distillation temperature of 120 ° C. By this second distillation operation, the second effluent (mixed liquid) flows out from the top of the second distillation tower 12, whereby 76 g of the mixed acid containing liquid is recovered. After the second distillation operation, 125 g of a hydrofluoric acid-enriched mixed solution (a recovered solution containing concentrated hydrofluoric acid) could be recovered as a distillation residue in the second distillation tower 12.

<Example 4>

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed wastewater (content and content of each component are shown in Table 4) and 32 g of potassium chloride were put into a mixing tank 9, and stirred and mixed for 24 hours to obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 112 g, and the obtained supernatant was 220 g.

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

(First distillation step)

220 g of the supernatant (Si ⁴⁺ -removed mixed waste) in the solid-liquid separator 10 was introduced into the first distillation column 11, and the distillation was carried out at a distillation temperature of 110 ° C. By this first distillation operation, 176 g of the first effluent (the mixed liquid containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Then, 176 g of the first effluent flowed out from the first distillation column 11 was charged into the second distillation column 12, and the distillation was carried out at a distillation temperature of 110 ° C. By this second distillation operation, the second effluent (mixed liquid) flows out from the top of the second distillation tower 12, whereby 67 g of the mixed acid containing liquid is recovered. After the second distillation operation, 101 g of a hydrofluoric acid-enriched mixed-acid solution (concentrated hydrofluoric acid-containing recovered liquid) could be recovered as a distillation residue inside the second distillation tower 12.

&Lt; Example 5 >

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed waste liquid (content and content of each component are shown in Table 5) and 13 g of magnesium fluoride were charged into a mixing tank 9, followed by stirring and mixing for 24 hours with a stirring blade to obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 58 g, and the obtained supernatant was 255 g.

From the analysis results by XRD (X-ray spectroscopy), it was confirmed that the main component of the precipitate was magnesium disilicide (MgSiF ₆ ).

(First distillation step)

255 g of the supernatant liquid (Si ⁴⁺ -enriched mixed waste liquid) in the solid-liquid separator 10 was charged into the first distillation tower 11, and distillation was carried out at a distillation temperature of 120 ° C. By this first distillation operation, 214 g of the first effluent (mixed liquid containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Then, 214 g of the first effluent discharged from the first distillation column 11 was introduced into the second distillation column 12, and the distillation was carried out at a distillation temperature of 120 ° C. By this second distillation operation, the second effluent (mixed liquid) was flowed out from the top of the second distillation tower 12, whereby 61 g of the mixed acid containing liquid was recovered. After the second distillation operation, 142 g of the hydrofluoric acid-concentrated mixed liquid (recovered liquid containing concentrated hydrofluoric acid) could be recovered as the distillation residue in the second distillation tower 12.

&Lt; Example 6 >

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed waste liquid (content and content of each component are shown in Table 6) and 11 g of lithium fluoride were charged into a mixing tank 9, and mixed and stirred for 24 hours with a stirring blade to obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 56 g, and the supernatant obtained was 255 g.

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

(First distillation step)

255 g of the supernatant liquid (Si ⁴⁺ -removed mixed waste liquid) in the solid-liquid separator 10 was charged into the first distillation column 11, and distillation was carried out at a distillation temperature of 130 ° C. By this first distillation operation, 205 g of the first effluent (the mixed liquid including hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Subsequently, 205 g of the first effluent flowed out from the first distillation tower 11 was introduced into the second distillation tower 12, and the distillation was carried out at a distillation temperature of 130 ° C. By this second distillation operation, the second effluent (mixed liquid) flows out from the top of the second distillation tower 12, whereby 69 g of the mixed acid containing liquid was recovered. After the second distillation operation, 124 g of the hydrofluoric acid-concentrated mixture liquid (the recovered liquid containing concentrated hydrofluoric acid) could be recovered as the distillation residue in the second distillation tower 12.

&Lt; Example 7 >

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed wastewater (content and content of each component are shown in Table 7), 26 g of sodium chloride and 33 g of potassium chloride were put into a mixing tank 9 and stirred for 24 hours to obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 156 g, and the obtained supernatant was 203 g.

From the analysis by XRD (X-ray spectroscopy), it was confirmed that the main components of the precipitate were sodium silicate (Na ₂ SiF ₆ ) and potassium silicate (K ₂ SiF ₆ ).

(First distillation step)

203 g of the supernatant (Si ⁴⁺ -removed mixed waste liquid) in the solid-liquid separator 10 was charged into the first distillation column 11 and distilled at a distillation temperature of 120 ° C. By this first distillation operation, 172 g of the first effluent (mixed liquid containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Subsequently, 172 g of the first effluent discharged from the first distillation column 11 was charged into the second distillation column 12, and the distillation was carried out at a distillation temperature of 120 ° C. By this second distillation operation, the second effluent (mixed liquid) flows out from the top of the second distillation tower 12, whereby 95 g of the mixed acid containing liquid is recovered. After the second distillation operation, 64 g of the hydrofluoric acid-concentrated mixture liquid (recovered liquid containing concentrated hydrofluoric acid) was recovered as the distillation residue in the second distillation column 12.

&Lt; Example 8 >

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed waste solution (content and content of each component are shown in Table 8), 33 g of potassium chloride and 19 g of sodium fluoride were charged into a mixing tank 9, followed by stirring and mixing for 24 hours to obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 162 g, and the obtained supernatant was 190 g.

From the analysis by XRD (X-ray spectroscopy), it was confirmed that the main components of the precipitate were sodium silicate (Na ₂ SiF ₆ ) and potassium silicate (K ₂ SiF ₆ ).

(First distillation step)

190 g of the supernatant liquid (Si ⁴⁺ -removed mixed waste liquid) in the solid-liquid separator 10 was charged into the first distillation column 11, and the distillation was carried out at a distillation temperature of 120 ° C. By this first distillation operation, 166 g of the first effluent (mixed liquid containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Subsequently, 166 g of the first effluent discharged from the first distillation column 11 was introduced into the second distillation column 12, and the distillation was carried out at a distillation temperature of 120 ° C. By this second distillation operation, the second effluent (mixed liquid) flows out from the top of the second distillation tower 12, whereby 76 g of the mixed acid containing liquid is recovered. After the second distillation operation, 83 g of the hydrofluoric acid-concentrated mixture liquid (recovery liquid containing concentrated hydrofluoric acid) could be recovered as the distillation residue in the second distillation tower 12.

&Lt; Example 9 >

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed waste liquid (content and content of each component are shown in Table 9), 26 g of sodium chloride and 26 g of potassium fluoride were charged into a mixing tank 9, followed by stirring and mixing for 24 hours to obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 160 g, and the obtained supernatant was 192 g.

From the analysis by XRD (X-ray spectroscopy), it was confirmed that the main components of the precipitate were sodium silicate (Na ₂ SiF ₆ ) and potassium silicate (K ₂ SiF ₆ ).

(First distillation step)

192 g of a supernatant (Si ⁴⁺ -removed mixed waste liquid) in the solid-liquid separator 10 was charged into the first distillation column 11, and the distillation was carried out at a distillation temperature of 120 ° C. By this first distillation operation, 169 g of the first effluent (mixed liquid containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Subsequently, 169 g of the first effluent flowed out from the first distillation column 11 was charged into the second distillation column 12, and the distillation was carried out at a distillation temperature of 120 ° C. By this second distillation operation, the second effluent (mixed liquid) flows out from the top of the second distillation tower 12, whereby 78 g of the mixed acid containing liquid is recovered. After the second distillation operation, 81 g of the hydrofluoric acid-concentrated mixture liquid (the recovered liquid containing concentrated hydrofluoric acid) could be recovered as the distillation residue inside the second distillation tower 12.

&Lt; Example 10 >

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed waste solution (content and content of each component are shown in Table 10), 19 g of sodium fluoride and 26 g of potassium fluoride were charged into a mixing tank 9, and stirred and mixed for 24 hours to obtain a mixed solution .

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 158 g, and the obtained supernatant was 187 g.

From the analysis by XRD (X-ray spectroscopy), it was confirmed that the main components of the precipitate were sodium silicate (Na ₂ SiF ₆ ) and potassium silicate (K ₂ SiF ₆ ).

(First distillation step)

187 g of a supernatant (Si ⁴⁺ -removed mixed waste liquid) in the solid-liquid separator 10 was charged into the first distillation column 11, and the distillation was carried out at a distillation temperature of 120 ° C. By this first distillation operation, 162 g of the first effluent (mixed liquid containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Subsequently, 162 g of the first effluent flowed out from the first distillation tower 11 was introduced into the second distillation tower 12, and the distillation was conducted at a distillation temperature of 120 ° C. By this second distillation operation, the second effluent (mixed liquid) flows out from the top of the second distillation tower 12, whereby 59 g of the mixed acid containing liquid is recovered. After the second distillation operation, 95 g of the hydrofluoric acid-concentrated mixed liquid (the recovered solution containing concentrated hydrofluoric acid) could be recovered as the distillation residue in the second distillation tower 12.

&Lt; Example 11 >

The mixed solution (hydrofluoric acid, hydrochloric acid, and Si ⁴⁺ mixed wastewater) discharged from the semiconductor manufacturing plant was subjected to the Si ⁴⁺ removal process and the first A distillation step and a second distillation step were carried out.

(Si ⁴⁺ removal process)

300 g of the mixed waste solution (content and content of each component are shown in Table 11), 18 g of sodium chloride, 13 g of sodium fluoride and 18 g of potassium fluoride were charged into a mixing tank 9 and stirred and mixed for 24 hours with a stirring blade To obtain a mixed solution.

Subsequently, the mixed solution was put into a centrifuge (solid-liquid separator) 10 to perform centrifugal separation, and the mixed solution was separated into a precipitate (containing Si ⁴⁺ ) and a supernatant (Si ⁴⁺ removed mixed waste solution; . The obtained precipitate was 154 g, and the obtained supernatant was 195 g.

From the analysis by XRD (X-ray spectroscopy), it was confirmed that the main components of the precipitate were sodium silicate (Na ₂ SiF ₆ ) and potassium silicate (K ₂ SiF ₆ ).

(First distillation step)

195 g of a supernatant (Si ⁴⁺ -removed mixed waste liquid) in the solid-liquid separator 10 was introduced into the first distillation column 11, and distillation was carried out at a distillation temperature of 120 ° C. By this first distillation operation, 171 g of the first effluent (mixed liquid containing hydrofluoric acid and hydrochloric acid) was flowed out from the top of the first distillation column 11.

(Second distillation step)

Then, 171 g of the first effluent discharged from the first distillation tower 11 was charged into the second distillation tower 12, and the distillation was conducted at a distillation temperature of 120 ° C. By this second distillation operation, the second effluent (mixed liquid) flows out from the top of the second distillation tower 12, whereby 66 g of the mixed acid containing liquid was recovered. After the second distillation operation, 99 g of the hydrofluoric acid-enriched mixed-acid solution (concentrated hydrofluoric acid-containing recovered liquid) was recovered as the distillation residue in the second distillation tower 12.

&Lt; Comparative Example 1 &

The results of the first distillation step were the same as those of Example 1 except that sodium chloride was not added to the mixing tank (the Si ⁴⁺ removal step was not performed) And the content of each component are shown in Table 12) were directly introduced into the first distillation column and the distillation was carried out at a distillation temperature of 120 ° C. As a result, the first effluent obtained from the top of the first distillation column contained the Si content 2.02% by mass) (2.23% by mass), and Si ⁴⁺ was not removed at all.

In the above Examples and Comparative Examples, the concentration (content by mass) of each component of HF, HCl, and H ₂ SO ₄ in each liquid was measured with an ion chromatograph (ICS-1000 manufactured by Nippon Dio Nex Co., .

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

As apparent from the table, in Examples 1 to 11 in which the recovering method of the present invention was applied, a mixed solution containing impurities (metal ions including Si ⁴⁺ ) and impurities (metal ions containing Si ⁴⁺ ) from the mixed acid waste solution containing hydrofluoric acid, hydrochloric acid and Si ⁴⁺ Si ⁴⁺ -containing metal ions) contained in the hydrofluoric acid-rich mixed acid solution.

On the other hand, in Comparative Example 1 in which the distillation operation was performed without adding salt to the mixed acid waste liquid, the outflow mixed liquid by distillation contained a large amount of Si ⁴⁺ , and it was impossible to remove the mixed Si ⁴⁺ .

The method for removing Si from the Si-containing fluoric acid-containing waste solution according to the present invention is a method for removing Si from a fluoric acid-based waste liquid (for example, a waste liquid containing hydrofluoric acid, a mixed acid waste liquid containing hydrofluoric acid and hydrochloric acid) But it is not particularly limited to those applied to these applications.

A method for recovering hydrofluoric acid from a Si-containing hydrofluoric acid mixed waste liquid according to the present invention is a method for recovering hydrofluoric acid from a hydrofluoric acid mixed waste liquid (a mixed acid waste liquid containing hydrofluoric acid and hydrochloric acid) used as an etchant, .

This application is accompanied by priority claims of Japanese Patent Application No. 2012-251319 filed on November 15, 2012 and Japanese Patent Application No. 2013-193960 filed on September 19, 2013, Is a part of the present invention.

The terms and descriptions used herein are used to explain the embodiments of the present invention, and the present invention is not limited thereto. It is intended that the invention not be limited by any of the details of the description set forth herein.

1: Recovery device 9: Mixing tank
10: Solid-liquid separator 11: First distillation tower
12: second distillation column 23: solid fraction removing device (solid-liquid separator)
25: Mass flow meter 26: Calculator
27: meter 31: supply pipe
43, 63: solid-liquid separator 44, 64: sludge pot
45, 65: discharge pipe 46, 66: discharge valve
47, 67: interface position detector 48, 68:
50: circulation pipe 52, 72: outlet
81: first predetermined height 82: second predetermined height
83: Approximate constant height position
100A, 100B: Solid-liquid separation apparatus (solid-liquid separation system)

Claims (21)

A method for removing Si from a Si-containing fluoric acid-based waste liquid, which comprises a step of adding a salt to a waste liquid containing hydrofluoric acid and Si, and then removing a precipitate produced by the addition of the salt to obtain a Si- Way. A Si removing step of adding a salt to a waste liquid containing hydrofluoric acid and Si and then removing the precipitate produced by the addition of the salt to obtain a Si-
And a distillation step of distilling the Si-removing waste liquid to flow out the hydrofluoric acid-containing liquid to obtain an effluent. 3. The method according to claim 1 or 2,
A method for removing Si from a Si-containing fluoric acid-based waste liquid, which comprises using one or more salts selected from the group consisting of a metal fluoride and a metal chloride salt as the salt. 3. The method according to claim 1 or 2,
A method for removing Si from a Si-containing fluoric acid-based waste liquid, which comprises using at least one salt selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride and lithium fluoride. 5. The method according to any one of claims 1 to 4,
Wherein the adding step of adding a salt to the waste liquid is performed by supplying the waste liquid to a mixing tank through a supply pipe and supplying the salt to the mixing tank,
A measuring step of measuring a flow rate and a density of a waste liquid passing through the supply pipe by a mass flow meter installed in the supply pipe;
Calculating the mass of Si in the waste liquid that has passed through the supply pipe based on the flow rate and density data measured by the mass flowmeter in the calculator and calculating the mass of the salt necessary for the sedimentation of Si based on the calculated value The process,
And a metering step of measuring the salt of the mass calculated in the calculator by a meter and transferring the salt to the mixing tank. A Si removal step of adding a salt to a mixed acid waste solution containing hydrofluoric acid, hydrochloric acid and Si, and then removing the precipitate produced by the addition of the salt to obtain a Si-
A first distillation step of distilling the Si-removed mixed waste liquid to flow out the mixed liquid to obtain a first effluent,
And a second distillation step of distilling the first effluent obtained in the first distillation step to distill out the mixed liquid to obtain a second effluent and recovering the hydrofluoric acid-concentrated mixture liquid as a distillation residue. A method for recovering hydrofluoric acid from a mixed acid waste liquid. The method according to claim 6,
Wherein the distillation temperature in the first distillation step is set in a range of 80 ° C to 130 ° C. 8. The method according to claim 6 or 7,
Wherein the distillation temperature in the second distillation step is set in the range of 80 to 130 占 폚. 9. The method according to any one of claims 6 to 8,
A method for recovering hydrofluoric acid from a Si-containing hydrofluoric acid mixed waste liquid, which comprises using at least one salt selected from the group consisting of a metal fluoride salt and a metal chloride salt as the salt. 9. The method according to any one of claims 6 to 8,
A method for recovering hydrofluoric acid from a Si-containing hydrofluoric acid mixed waste liquid, which comprises using at least one salt selected from the group consisting of potassium fluoride, sodium fluoride, potassium chloride, sodium chloride, magnesium fluoride and lithium fluoride. 11. The method according to any one of claims 6 to 10,
Wherein the adding step of adding a salt to the waste liquid is performed by supplying the waste liquid to a mixing tank through a supply pipe and supplying the salt to the mixing tank,
A measuring step of measuring a flow rate and a density of a waste liquid passing through the supply pipe by a mass flow meter installed in the supply pipe;
Calculating the mass of Si in the waste liquid that has passed through the supply pipe based on the flow rate and density data measured by the mass flowmeter in the calculator and calculating the mass of the salt necessary for the sedimentation of Si based on the calculated value The process,
And a metering step of measuring the salt of the mass calculated in the calculator by a meter and transferring the salt to the mixing tank. A mixing tank for mixing the waste liquid containing hydrofluoric acid and Si and the salt by stirring to obtain a mixed solution,
A solid-liquid separator used for solid-liquid separation of the precipitate present in the mixed solution,
And a distillation column used for distilling the filtrate separated and separated by the solid-liquid separator. The recovering apparatus for recovering hydrofluoric acid from a Si-containing hydrofluoric acid waste liquid. A mixing tank for mixing a mixed waste liquid containing hydrofluoric acid and Si and a salt by stirring to obtain a mixed solution,
A solid-liquid separator used for solid-liquid separation of the precipitate present in the mixed solution,
A first distillation column used for distilling the filtrate separated and separated by the solid-liquid separator,
And a second distillation column used for distilling the effluent flowing out from the first distillation column. The recovering apparatus for recovering hydrofluoric acid from a Si-containing hydrofluoric acid mixed waste liquid. The method according to claim 12 or 13,
A mass flow meter installed in a 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,
A calculator for calculating the mass of Si in the waste liquid passing through the supply pipe based on the flow rate and density data measured by the mass flowmeter and calculating the mass of salt required for the sedimentation of Si based on the calculated value,
And a meter for measuring the salt of the mass calculated by the calculator and transferring the measured salt to the mixing tank. A solid-liquid separator capable of separating a solid component and a liquid and capable of discharging the separated solid component from the bottom part,
A sludge pot that receives the solid content discharged from the bottom of the solid-liquid separator,
A discharge pipe communicated with an outlet formed at the bottom of the sludge pot,
A discharge valve provided in the discharge pipe,
And an interfacial position detector for detecting a position of an upper surface of a solid portion contained in the sludge pod. 16. The method of claim 15,
Wherein an ultrasonic interface detection system is used as the interface position detector. 17. The method according to claim 15 or 16,
Wherein a liquid cyclone is used as said solid-liquid separator. 18. The method according to any one of claims 15 to 17,
And a circulation pipe for re-supplying the liquid separated by the solid-liquid separator into the solid-liquid separator. 19. The method according to any one of claims 15 to 18,
And a control section for performing an opening / closing operation or an opening degree adjustment of the discharge valve based on data of an upper surface position of a solid portion detected by the interface position detector. 19. The method according to any one of claims 15 to 18,
When the top surface position of the solid component detected by the interface position detector rises to the first predetermined height in the sludge pod, the discharge valve is opened to discharge the solid content in the sludge pod, And closing the discharge valve when the top surface position of the solid component detected in the sludge pod descends to the second predetermined height in the sludge pod. 19. The method according to any one of claims 15 to 18,
The degree of opening of the discharge valve is reduced when the top surface position of the solid component detected by the interface position detector is lowered and the opening degree of the discharge valve is increased when the position of the top surface of the solid component detected by the interface position detector is increased To control the position of the upper surface of the solid content in the sludge pod to a substantially constant position.

Images