JP2017064569A - Method and apparatus for treating fluorine-containing wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluorine-containing industrial wastewater treatment method for more reliably removing fluoride ions from fluorine-containing industrial wastewater containing coexisting ions, and a fluorine-containing wastewater treatment apparatus.SOLUTION: In a treatment method and apparatus 10 for treating fluorine-containing wastewater 1 where a calcium salt is added to the fluorine-containing wastewater 1 to perform coagulation-sedimentation treatment, the treatment method for treating the fluorine-containing wastewater 1 measures the fluoride ion concentration of the fluorine-containing wastewater 1 by a fluoride ion electrode method 21, and applies the measured fluoride ion concentration to the expression (I) to calculate the calcium concentration of the calcium salt to be added. Expression (I): 200≤C1-C2×Aw (Ca)/2Aw (F)≤1500 [C1 is the calcium ion concentration of the calcium salt [mg/L]; C2 is the measured fluoride ion concentration [mg/L]; Aw (Ca) is the atomic weight of calcium; and Aw (F) is the atomic weight of fluorine]SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a method for treating fluorine-containing wastewater and a treatment apparatus therefor, and more particularly, to a method for treating fluorine-containing wastewater and a treatment apparatus for the same, in which a calcium salt is added to fluorine-containing wastewater to perform coagulation precipitation treatment.

In factories that manufacture semiconductors and facilities that perform metal surface treatment, chemicals mainly composed of hydrogen fluoride (HF) or ammonium fluoride (NH ₄ F) are used, and wastewater containing fluorine (hereinafter referred to as fluorine-containing wastewater). Is discharged. Further, in an industrial waste incineration facility, if fluorine is included in the composition of the incineration object, hydrogen fluoride is included in the exhaust gas from the facility. Although the hydrogen fluoride in the exhaust gas is absorbed by the cleaning liquid in the exhaust gas purification apparatus and becomes fluoride ions and removed from the exhaust gas, the cleaning liquid needs to be treated as fluorine-containing waste water.

When such fluorine-containing wastewater has a high concentration, it is subjected to an individual treatment for removing fluorine from the wastewater, and then mixed with other wastewater to be treated as a general wastewater for a business establishment. As a method of individual treatment for removing fluorine from wastewater, generally, calcium salt such as calcium hydroxide (Ca (OH) ₂ ) is added to produce insoluble matter of calcium fluoride (CaF ₂ ), and coagulation precipitation treatment And solid-liquid separation.

  The amount of calcium salt added is the amount of calcium ion required to measure the concentration of fluoride ions present in the wastewater and react with the fluoride ions at that concentration to produce calcium fluoride insolubles. This is the amount.

  However, when measuring fluoride ions, the fluoride ion concentration in the fluorine-containing wastewater is measured with an ion electrode type measuring instrument due to the influence of coexisting components such as anions and metal ions present in the wastewater. In the case of measurement, there is a possibility that a difference occurs between the actual fluoride ion concentration and the measured concentration. If there is a difference between the actual fluoride ion concentration and the measured concentration, an appropriate amount of calcium salt cannot be added.

  Patent Document 1 discloses a method for treating fluorine-containing wastewater that takes this difference into account. Specifically, in Patent Document 1, the measurement concentration of fluoride ions, which are components to be treated in industrial wastewater, is corrected based on the concentration of coexisting ions (calcium ions, magnesium ions, etc.) that affect the measurement results. To determine the true fluoride ion concentration, calculate the amount of calcium salt that is a necessary treatment agent based on the fluoride ion concentration in the true industrial wastewater, and add it to the industrial wastewater. Is disclosed.

  According to this treatment method, fluoride ions can be removed from industrial wastewater while minimizing the amount of treatment chemical used.

  According to Patent Document 1, the concentration of coexisting components may be obtained by measuring industrial wastewater, or may be obtained from a blending database.

Japanese Patent No. 5532017

  However, according to the treatment method of fluorine-containing wastewater disclosed in Patent Document 1, the true fluoride ion concentration in industrial wastewater is obtained, and the treatment chemical is added in the minimum amount required. There is a risk that proper removal of ions may not be performed. For example, the calcium salt (treatment agent) may form an insoluble salt with coexisting ions other than fluoride ions, and in this case, the amount of calcium salt to be reacted with the fluoride ion concentration is insufficient. In addition, since the equilibrium between the reaction in which calcium ions form an insoluble salt with fluoride ions and the reverse reaction are generally greatly inclined to the reverse reaction side, the calcium ions simply have a concentration corresponding to the fluoride ions. If calcium salt is added to the solution, fluoride ions in industrial wastewater cannot be removed sufficiently.

  The present invention has been made in view of the above problems, and the object thereof is a treatment method of fluorine-containing industrial wastewater and fluorine-containing wastewater that more reliably remove fluoride ions from fluorine-containing industrial wastewater in which coexisting ions exist. It is in providing a processing apparatus.

In order to achieve the above object, the invention described in claim 1 is directed to a fluorine-containing wastewater treatment method in which a calcium salt is added to fluorine-containing wastewater to perform a coagulation sedimentation treatment. The fluoride ion concentration measurement step measured by the fluoride ion electrode method and the fluoride ion concentration measured by the fluoride ion concentration measurement step are represented by the following formula (I):
200 ≦ C1-C2 × Aw (Ca) / 2Aw (F) ≦ 1500
[However, C1 represents the calcium concentration [mg / L] of the calcium salt, C2 represents the fluoride ion concentration [mg / L] measured in the fluoride ion concentration measurement step, and Aw (Ca) is calcium. And Aw (F) represents the atomic weight of fluorine.]
And a calcium concentration calculating step for calculating the calcium concentration of the calcium salt to be added.

  According to this configuration, based on the formula (I), an excess of 200 mg / L or more and 1500 mg / L or less than the calcium concentration corresponding to the fluoride ion concentration in the fluorine-containing wastewater measured in the fluoride ion concentration measurement step. Thus, since the calcium salt is added to the fluorine-containing wastewater, a sufficient amount of calcium can remain in the fluorine-containing wastewater.

  In addition, by allowing calcium to be present in the fluorine-containing waste water in an excess amount of 200 mg / L or more and 1500 mg / L or less, the equilibrium between the reaction in which calcium ions form an insoluble salt with fluoride ions and the reverse reaction is reduced. It becomes possible to incline in the direction of formation, and it is possible to more reliably precipitate and remove fluoride ions in the fluorine-containing wastewater.

  The invention according to claim 2 is the treatment method of fluorine-containing wastewater according to claim 1, wherein in the fluoride ion concentration measurement step, the fluoride ion concentration of the fluorine-containing wastewater is directly based on the standard addition method. It is measured.

  According to this configuration, even if coexistence ON other than fluoride ions exists in the fluorine-containing wastewater to be measured, the influence of the coexisting ions is eliminated, and the true fluoride in the fluorine-containing wastewater is removed. It is possible to determine the ion concentration. Therefore, fluoride ions can be more reliably removed from fluorine-containing industrial wastewater in which coexisting ions are present.

  The fluoride ion standard solution used in the standard addition method may be a commercially available standard solution or a solution prepared by dissolving sodium fluoride or acidic ammonium fluoride in pure water to a predetermined concentration.

  The invention according to claim 3 is the method for treating fluorine-containing wastewater according to claim 1, wherein the fluorine-containing wastewater is wastewater in which the concentration of fluoride ions in the wastewater varies with time, and the fluoride ions Prior to the concentration measurement step, the fluoride ion concentration of the fluorine-containing wastewater in which the fluoride ion concentration fluctuated with time is determined using a fluoride ion electrode meter based on the standard addition method, and the determined fluorine-containing concentration is determined. A calibration curve creating step for creating a calibration curve passing through the origin from the relationship between the fluoride ion concentration of the waste water and the indicated value of the fluoride ion electrode meter when the standard substance in the standard addition method is not added, and the fluoride After the ion concentration measurement step and before the calcium concentration calculation step, the fluoride ion concentration of the fluorine-containing wastewater at any point measured in the fluoride ion concentration measurement step A fluoride ion concentration calculating step of calculating a fluoride ion concentration in the fluorine-containing wastewater at an arbitrary time point by applying the measured value to the calibration curve, and calculating the fluoride ion concentration calculated in the fluoride ion concentration calculating step. The value of the fluoride ion concentration is used as the value of C2 (fluoride ion concentration [mg / L] measured by the fluoride ion concentration measurement step) of the formula (I) in the calcium concentration calculation step.

  According to this configuration, even for fluorine-containing wastewater whose fluoride ion concentration varies with time, the fluoride ion concentration of fluorine-containing wastewater whose fluoride ion concentration varies with time is determined in advance by the standard addition method. Create a calibration curve that passes through the origin from the relationship between the determined fluoride ion concentration and the indicated value of the fluoride ion electrode meter. Fluorine-containing wastewater at any point measured in the fluoride ion concentration measurement process is created on this calibration curve. The fluoride ion concentration can be calculated by applying the measured value of the fluoride ion concentration, and the concentration of the calcium salt to be added can be calculated by applying the fluoride ion concentration to the formula (I).

  Therefore, by creating a calibration curve using the above-mentioned characteristic method and measuring the fluorine ion concentration in the fluorine-containing wastewater at any point in time using a commercially available ion electrode meter, it is accurate even if coexisting ions exist. It is possible to calculate a proper fluorine ion concentration.

  Moreover, since it is not necessary to measure the coexisting ions not only in the fluoride ion concentration measurement step but also in creating a calibration curve, there is no need to use a device for measuring the coexisting ions when processing the fluorine-containing waste water, In addition, fluoride ions can be removed from the fluorine-containing waste water more simply and reliably.

  In addition, the fluoride ion concentration determined by the standard addition method and the indicated value data of the fluoride ion electrode meter are written in a sequential scatter diagram, a reliable calibration curve is created, and this calibration curve is used to calculate the fluoride ion concentration. By using this, it is possible to calculate a more reliable fluoride ion concentration.

Invention of Claim 4 is the processing method of the fluorine-containing waste water of any one of Claims 1-3, When a sulfate ion exists in the said fluorine-containing waste water in the density | concentration of 1000 mg / L or more,
In order to compensate for calcium lost by agglomeration and precipitation by reacting with the sulfate ions in the calcium of the added calcium salt, the following formula (II):
C3 = (C4-1000) × Aw (Ca) / Fw (SO ₄ ²⁻ )
[However, C3 represents the calcium concentration of the calcium salt to be supplemented, C4 represents the concentration of sulfate ion in the fluorine-containing wastewater, Aw (Ca) represents the atomic weight of calcium, and Fw (SO ₄ ²⁻ ) represents sulfuric acid. Represents the formula weight of ions]
A calcium salt having a calcium concentration calculated by applying to the above is further supplemented in the fluorine-containing waste water.

  According to this configuration, when the sulfate ion is present in the fluorine-containing wastewater in an amount of 1000 mg / L or more, the sulfate ion competes with the fluoride ion to form calcium ion derived from the calcium salt added and insoluble salt. In such a case, the fluoride ion removal rate is lowered. In such a case, an amount of calcium salt that is calculated based on the formula (II) in consideration of the sulfate ion concentration in the fluorine-containing wastewater is further added. By supplementing, it becomes possible to more reliably remove fluoride ions in the fluorine-containing waste water.

The fluorine-containing wastewater treatment apparatus according to claim 5 includes a mixing means for mixing fluorine-containing wastewater and calcium salt, and a fluoride capable of measuring a fluoride concentration in the fluorine-containing wastewater by a fluoride ion electrode method. The ion concentration measuring means and the fluoride ion concentration measured by the fluoride ion concentration measuring means are represented by the following formula (III):
200 ≦ C1-C2 × Aw (Ca) / 2Aw (F) ≦ 1500
[However, C1 represents the calcium concentration [mg / L] of the calcium salt, C2 represents the fluoride ion concentration [mg / L] measured in the fluoride ion concentration measurement step, and Aw (Ca) is calcium. And Aw (F) represents the atomic weight of fluorine.]
Calculating means capable of calculating the amount of the calcium salt to be mixed by applying to
Injection means for injecting the amount of calcium salt calculated by the calculation means into the mixing means.

  According to this configuration, based on the formula (III), an excess of 200 mg / L or more and 1500 mg / L or less than the calcium concentration corresponding to the fluoride ion concentration in the fluorine-containing wastewater measured in the fluoride ion concentration measurement step. Thus, the calcium salt can be injected into the fluorine-containing wastewater in the mixing tank by the injection means, so that a sufficient amount of calcium ions can remain in the fluorine-containing wastewater.

  In addition, by allowing calcium ions to be present in the fluorine-containing waste water in an excess amount of 200 mg / L or more and 1500 mg / L or less, the equilibrium between the reaction of calcium ions forming an insoluble salt with fluoride ions and the reverse reaction thereof is obtained. It becomes possible to incline in the direction in which the water is formed, and it is possible to more reliably precipitate and remove the fluoride ions in the fluorine-containing wastewater.

  According to the present invention, the calcium salt is added so as to be an excess amount of 200 mg / L or more and 1500 mg / L or less than the calcium concentration corresponding to the measured fluoride ion concentration in the fluorine-containing wastewater. Of calcium can be left in the fluorine-containing waste water.

  In addition, it is possible to tilt the equilibrium between the reaction of calcium ions forming insoluble salts with fluoride ions and the reverse reaction in the direction of forming insoluble salts, and more reliably aggregate and precipitate fluoride ions in fluorine-containing wastewater. Can be removed.

  Furthermore, by measuring or calculating the true fluoride ion concentration in fluorine-containing wastewater based on the standard addition method, fluoride ions can be more reliably removed from fluorine-containing wastewater in which coexisting ions exist. Become.

It is a block diagram which shows the processing apparatus of the fluorine-containing waste_water | drain concerning embodiment of this invention. 5 is a flowchart for explaining calcium salt injection control by a control unit 45; It is a block diagram which shows the modification of the control part of this Embodiment. It is a figure which shows the regression line by the standard addition method for determining the fluoride ion density | concentration of the fluorine-containing waste water from which the fluoride ion density | concentration fluctuated in three steps with time. 4 shows a calibration curve (regression line) created from the relationship between the fluoride ion concentration of each fluorine-containing wastewater determined in FIG. 4 and the indicated value of the fluoride ion electrode meter when the standard substance in FIG. 4 is not added. FIG. 5 is a flowchart for explaining calcium salt injection control by a control unit 50; Fluoride ion concentration meter indication values (Y axis, unit: mg / L) of each raw water A to D and the respective fluoride ion standard substance additive and addition concentration of fluoride ion standard substance (X axis, unit: mg) / L). The fluoride ion concentration of each raw water A to D determined in FIG. 7 is taken as the value of the X axis, and the indicated value of the fluoride ion electrode meter at the point where the regression line of each raw water A to D intersects with the Y axis It is a figure which shows the regression line (calibration curve) created by the least square method as a value. Fluoride ion concentration meter instruction value (Y axis, unit mg / L) and fluoride ion standard substance addition concentration (X axis, unit mg / L) of fluorine-containing wastewater 1 to which fluoride ion standard stock solution is added FIG.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. A method for treating fluorine-containing wastewater and a treatment apparatus therefor will be described with reference to FIGS. FIG. 1 is a block diagram showing a fluorine-containing wastewater treatment apparatus 10 according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining calcium salt injection control by a control unit 45.

  As shown in the figure, the fluorine-containing wastewater treatment apparatus 10 includes a raw water tank 15, a metering tank 20, a mixing / reaction tank 25, a coagulation tank 30, a precipitation tank 35, and a control unit 45 including a calculation means 47. The calcium salt storage tank 55 is mainly composed of.

  The fluorine-containing waste water 1 is waste water containing fluoride ions, and the concentration thereof is not limited.

  The raw water tank 15 is a large tank having a function of adjusting the flow rate of the fluorine-containing waste water 1 to be treated. Further, the fluorine-containing waste water 1 in the raw water tank 15 is sent to the measuring tank 20 by the raw water pump 16. The raw water tank 15 may be provided with an adjustment tank (not shown) to receive the fluorine-containing waste water 1.

  The measuring tank 20 includes a fluoride ion concentration measuring unit 21 and a sulfate ion concentration measuring unit 22, and can measure the fluoride ion concentration and the sulfate ion concentration of the liquid in the measuring tank 20. The measured values of the measured fluoride ion concentration and sulfate ion concentration are transmitted to the control unit 45. The measuring tank 20 has a function of setting the amount of treated water of the fluorine-containing waste water 1 to a predetermined flow rate.

  The measurement location of the fluoride ion concentration and the sulfate ion concentration is not limited to the measuring tank 20, and may be upstream of the mixing / reaction tank 25 where the fluorine-containing waste water 1 and the calcium salt are mixed. That's fine. For example, the measurement may be performed in a measuring tank or a raw water tank 15 that is pumped from the raw water tank 15. The fluorine-containing waste water 1 is sampled upstream of the mixing / reaction tank 25, and the fluoride ion concentration and sulfuric acid are sampled. The ion concentration may be measured.

  As the fluoride ion concentration measuring means 21, a commercially available fluoride ion concentration meter adopting the fluoride ion electrode method can be used. Similarly, the sulfate ion concentration measuring means 22 is also commercially available sulfate ion by the sulfate ion electrode method. A densitometer can be used. The sulfate ion concentration measuring means 22 is not limited to the sulfate ion electrode method, and any of the official analysis methods may be used. Furthermore, a means for estimating the sulfate ion concentration from the amount of chemical used or the SOx concentration of the exhaust gas may be used.

  The frequency of calibration of the fluoride ion concentration meter of the present invention may be from once a week to about once a month, but changes in the properties of coexisting substances in the inflowing fluorine-containing wastewater and changes in the manufacturing production process If there is any, perform it.

Measurement of fluoride ion concentration and sulfate ion concentration can be performed continuously or at short intervals.
The mixing / reaction tank 25 (mixing means) includes a stirrer that stirs and mixes the liquid in the tank and a calcium salt injection unit. The calcium salt is stored in the calcium salt storage tank 55 in a liquid state. The calcium salt is injected into the mixing / reaction vessel 25 via the path 57. A pump 59 is provided in the path 57, and the amount of calcium salt injected from the calcium salt storage tank 55 into the mixing / reaction tank 25 is controlled by the control unit 45 described later.

  The calcium salt only needs to be a water-soluble calcium compound, and in this embodiment, a liquid one is used, but a powder product may also be used. When the calcium salt is a powder product, a hopper or the like provided with an open / close valve at the bottom can be adopted as the calcium salt storage tank. In such a case, the amount of calcium salt injected into the mixing / reaction tank 25 is controlled by controlling the opening / closing valve of the control unit 45.

Examples of the calcium salt include lime milk, calcium hydroxide (Ca (OH) ₂ ), calcium chloride (CaCl), powdered calcium carbonate (CaCO ₃ ), and powder dolomite (Ca · Mg (CO ₃ ) ₂ ).

  In addition, in the mixing / reaction tank 25, a pH meter (not shown) is interlocked so that an insoluble salt of calcium fluoride generated by the reaction of fluoride ions and calcium ions is generated. Alkali or mineral acid is added.

  The pH suitable for producing the insoluble salt of calcium fluoride is in the range of 6 to 10, more preferably in the range of pH 6 to 8. Since calcium is consumed under the influence of bicarbonate ions at pH 8 or higher, the pH is preferably 8 or lower, and since generation of calcium fluoride starts at pH 5 or higher, the reaction pH should be pH 6 or higher. Is preferred.

  The agglomeration tank 30 includes a stirrer for agitating the liquid in the tank and an injection part into which the polymer flocculant is injected. In the aggregating tank 30, insoluble matters such as calcium fluoride formed in the mixing / reacting tank 25, suspended substances in the fluorine-containing waste water 1 (hereinafter referred to as SS), and the like are aggregated by the polymer flocculant. Suspended matter (SS) is one of the indicators of turbidity of water. Particles contained in water are filtered through glass fiber filter paper or MF membrane filter paper having a pore diameter of 1 μm, and the dry matter weight (mg) of the particles. / L).

  As the polymer flocculant added to the aggregating tank 30, those commonly used for aggregating SS in the waste water can be used. For example, any of cationic polymer flocculants, anionic polymer flocculants and amphoteric polymer flocculants may be used, and powder products are mainly used.

  In the sedimentation tank 35, the aggregates aggregated in the aggregation tank 30 settle to the lower part and are separated from the liquid. The liquid that flows downstream from the upper part of the settling tank 35 is discharged as treated water 37, and the aggregate that has settled in the lower part of the settling tank 35 is removed from the settling tank 35 as a precipitate 38.

  The fluoride ion concentration measurement means 21 and the sulfate ion concentration measurement means 22 measure the fluoride ion concentration and the sulfate ion concentration in the waste water 1 in the measuring tank 20, and the control unit 45 injects based on the measurement result. The amount of calcium salt to be calculated is calculated by the calculation means 47, and the pump 59 is operated for a time during which the calculated amount of calcium salt can be injected from the calcium salt storage tank 55 to supply it to the mixing / reaction tank 25.

  The controller 45 may perform processing by controlling the flow rate of the pump.

  Here, the amount of the calcium salt to be added calculated by the calculation means 47 is described as follows.

のとおりである。しかし、式（ＩＶ）の平衡は両者がイオンの状態で存在する側（すなわち、左側）に傾いているため、フッ素含有排水１中にはカルシウムを過剰量に添加し、式（ＩＶ）の平衡をＣａＦ_２（不溶性塩）が生成される側（すなわち、右側）にシフトさせることが重要となる。 The reaction between fluoride ions and calcium ions in the fluorine-containing wastewater 1 is represented by the formula (IV):

It is as follows. However, since the equilibrium of the formula (IV) is inclined to the side where both of them exist in an ionic state (that is, the left side), an excessive amount of calcium is added to the fluorine-containing waste water 1, and the equilibrium of the formula (IV) Is shifted to the side where CaF ₂ (insoluble salt) is produced (ie, the right side).

Based on this concept, the calcium concentration of the amount of calcium salt to be added from the measured fluoride ion concentration of the fluorine-containing waste water 1 of the present invention is expressed by the following formula (V):
200 ≦ C1-C2 × Aw (Ca) / 2Aw (F) ≦ 1500
[However, C1 represents the calcium concentration [mg / L] of the calcium salt to be added to the fluorine-containing wastewater, and C2 represents the fluoride ion concentration [mg / L] measured in the fluoride ion concentration measurement step described later. , Aw (Ca) represents the atomic weight of calcium, and Aw (F) represents the atomic weight of fluorine.]
It is calculated by applying to

The part of “C2 × Aw (Ca) / 2Aw (F)” in the formula (V) has a theoretical amount of fluoride ions and calcium ions on the left side of the formula (IV) (that is, both are 2: 1 by mass ratio). Represents the calcium concentration (hereinafter also referred to as a theoretical value) of the calcium salt when present in the mixing / reaction tank 25, and when this calcium concentration is A, the formula (V) is It can be divided into two expressions, “A + 200 ≦ C (Ca ²⁺ )” and “C (Ca ²⁺ ) ≦ A + 1500”.

  That is, the calcium concentration [mg / L] of the calcium salt to be added to the fluorine-containing wastewater 1 is a concentration (theoretical value) at which calcium is present in a theoretical amount with respect to fluoride ions, 200 mg / L to 1500 mg. The concentration becomes excessive in the range of / L.

  When the concentration of excess calcium falls below 200 mg / L, the addition of calcium salt becomes insufficient, and the reaction shown by formula (IV) is inclined to the left side, so that the fluoride ions in the fluorine-containing waste water 1 can be reliably removed. It becomes difficult. In addition, if the concentration of excess calcium exceeds 1500 mg / L, the concentration of calcium in the fluorine-containing waste water 1 becomes excessively large, which increases the cost of the calcium salt, and further, downstream piping, agglomeration tank 30, precipitation This is not preferable because it causes a scale failure due to residual calcium salt in the tank 35.

  The excess calcium concentration is preferably in the range of 300 mg / L to 1000 mg / L, more preferably in the range of 400 mg / L to 800 mg / L, and particularly preferably 500 mg / L.

  Further, in consideration of the properties and empirical rules of the fluorine-containing waste water 1, it is possible to set and correct the coefficient in the formula (V) to determine the optimum amount of calcium salt added.

  When the calcium concentration of the calcium salt to be added is determined, the addition concentration (mg / L) of the calcium salt is also determined. The added concentration of calcium salt (mg / L) refers to the concentration of calcium salt in the fluorine-containing wastewater 1 in the mixing / reaction tank 25 after being added to the mixing / reaction tank 25.

For example, when the calcium salt is calcium hydroxide (Ca (OH) ₂ ), the addition concentration of the calcium salt is represented by the formula (VI):
C5 = C6 × Mw (Ca (OH) ₂ ) / Aw (Ca)
[However, C5 represents the addition concentration of calcium hydroxide, C6 represents the calcium concentration [mg / L] of the calcium salt to be added, Mw (Ca (OH) ₂ ) represents the molecular weight of calcium hydroxide, and Aw (Ca) represents the atomic weight of calcium. ]
Determined by.

  Based on the addition concentration of calcium hydroxide (calcium salt) determined by the formula (VI) and the concentration of calcium salt in the calcium salt storage tank 55, the calcium salt fed from the calcium salt storage tank 55 to the mixing / reaction tank 25 is sent. The liquid speed and the liquid supply amount are determined.

  Furthermore, in addition to the addition amount of the calcium salt determined by the above formulas (V) to (VI), a case where the calcium salt is further supplemented will be described.

  When the sulfate ion concentration in the fluorine-containing waste water 1 at a liquid temperature of 20 ° C. to 25 ° C. exceeds 1000 mg / L, an amount of calcium salt corresponding to the calcium ion concentration determined by the above formula (V) is added. Then, it is empirically known that sulfate ions form insoluble salts with calcium ions derived from calcium salts added in competition with fluoride ions, and the fluoride ion removal rate decreases.

  Therefore, when the sulfate ion concentration in the fluorine-containing wastewater 1 exceeds 1000 mg / L, in addition to the calcium salt addition concentration calculated based on the formula (VI), the calcium calculated based on the following formula (VII) An amount of calcium salt corresponding to the added concentration of salt is supplemented.

Formula (VII):
C3 = (C4-1000) × Aw (Ca) / Fw (SO ₄ ²⁻ )
[However, C3 represents the calcium concentration of the calcium salt to be supplemented, C4 represents the concentration of sulfate ion in the fluorine-containing wastewater, Aw (Ca) represents the atomic weight of calcium, and Fw (SO ₄ ²⁻ ) represents sulfuric acid. Represents the formula weight of ions]

  Next, a fluorine-containing wastewater treatment method using the fluorine-containing wastewater treatment apparatus 10 according to the present embodiment having the above-described configuration will be described using the flowchart of FIG. 2 in comparison with the configuration of FIG.

[Measurement step of fluoride ion concentration or fluoride ion concentration and sulfate ion concentration]
As shown in FIG. 2, in step S101, the fluoride ion concentration in the fluorine-containing waste water 1 or the fluoride ion concentration and the sulfate ion concentration in the measuring tank 20 are the fluoride ion concentration measuring means 21 and the sulfate ion concentration. It is measured by the measuring means 22.

  When only the fluoride ion concentration is measured, the sulfate ion is measured in advance, or the sulfate ion concentration is estimated in advance from the amount of chemical used or the SOx concentration of the exhaust gas.

  Moreover, the case where the sulfate ion concentration is estimated or measured in advance is included.

[Calcium concentration calculation process]
Next, the control unit 45 performs control to calculate the measured values of the fluoride ion concentration and the sulfate ion concentration in the fluorine-containing wastewater 1 by the calculation means 47.

  In step S102, when information on the fluoride ion concentration and the sulfate ion concentration in the fluorine-containing waste water 1 in the measuring tank 20 is transmitted to the control unit 45, the control unit 45 determines whether the sulfate ion concentration is 1000 mg / L or more. Determine whether. When the sulfate ion concentration is 1000 mg / L or more (YES determination), the process proceeds to step S103. When the sulfate ion concentration is less than 1000 mg / L (NO determination), the process proceeds to step S104.

  In step S103, the measured value of sulfate ion measured in S101 is substituted into the above formula (VII) for the calcium concentration calculated by substituting the measured value of fluoride ion measured in S101 into the above formula (V). Then, the calculated calcium concentration is added, and the concentration of the calcium salt to be added (including the concentration of the supplemented calcium salt) corresponding to the calcium concentration after the addition is calculated. Thereafter, the process proceeds to step S105 for calcium salt injection.

  On the other hand, in step S104 of the NO determination of less than 1000 mg / L described above, only the calcium concentration calculated by substituting the measured value of the fluoride ion concentration measured in S101 into the above formula (V) is calculated. Thereafter, the process proceeds to step S105 for calcium salt injection.

[Calcium salt injection process]
In step S105, calcium salt is injected from the calcium salt storage tank 55 into the mixing / reaction tank 25 in the fluorine-containing waste water 1 in the mixing / reaction tank 25 so as to have the concentration calculated in step S103 or step S104. The calcium salt is injected by a pump 59 driven by the control unit 45, and the adjustment of the injection speed and the injection amount is also performed by the control unit 45.

  After the end of step S105, the flow of FIG. 2 returns to the start, and the control from step S101 is repeated continuously or at short intervals.

  Thereafter, the liquid in the mixing / reaction tank 25 is subjected to a coagulation process in the coagulation tank 30 at a constant flow rate, flow rate and amount of water, subjected to a precipitation process in the precipitation tank 35, and treated water 37 from which fluorine has been removed is set in the precipitation tank. Out of 35.

  Therefore, based on the formula (V), the calcium concentration corresponding to the fluoride ion concentration in the fluorine-containing wastewater 1 measured in the fluoride ion concentration and sulfate ion concentration measurement step (S101), that is, calcium is converted into fluoride ions. On the other hand, the calcium salt is added to the fluorine-containing wastewater 1 in the mixing / reaction tank 25 so as to be excessive at a concentration 200 mg / L or more and 1500 mg / L or less than the calcium concentration that exists in a theoretical amount.

  Even when the added calcium salt reacts somewhat with coexisting ions other than fluoride ions, a sufficient amount of calcium ions can remain in the fluorine-containing waste water 1.

  In addition, when calcium is present in the fluorine-containing wastewater 1 in an excess amount of 200 mg / L or more and 1500 mg / L or less, the reaction between the calcium ion forming an insoluble salt with fluoride ion and the reverse reaction (formula (See (IV)) can be inclined in the direction of forming an insoluble salt, and the fluoride ions in the fluorine-containing waste water 1 can be more reliably coagulated and removed.

  Further, when sulfate ions are present in the fluorine-containing waste water 1 in an amount of 1000 mg / L or more, the sulfate ions compete with fluoride ions to form calcium ions derived from the added calcium salt and form insoluble salts. In such a case, the calcium ion removal rate is reduced. In such a case, based on the formula (VII), the calcium ion is further supplemented in the mixing / reaction tank 25 in consideration of the sulfate ion concentration in the fluorine-containing waste water 1. Thus, it is possible to reliably remove fluoride ions in the fluorine-containing wastewater 1.

  In addition, in the fluoride ion concentration measuring means 21 in the present embodiment, the fluorine-containing waste water 1 is obtained as a measured value of the fluoride ion concentration in the fluorine-containing waste water 1 by using commercially available fluoride ions adopting the fluoride ion electrode method. Although the value measured with the densitometer is used as it is, it is not limited to this. For example, true fluoride of fluorine-containing wastewater 1 containing coexisting ions is obtained by a standard addition method in which a fluoride ion standard substance having a known fluoride ion concentration is added to fluorine-containing wastewater 1 whose fluoride ion concentration is to be measured. The ion concentration may be measured.

  According to this, even if coexistence ON other than fluoride ions exists in the fluorine-containing wastewater 1 to be measured, the influence of the coexisting ions is eliminated and the true fluoride in the fluorine-containing wastewater 1 is removed. It is possible to determine the ion concentration. Therefore, fluoride ions can be more reliably removed from fluorine-containing industrial wastewater in which coexisting ions are present.

  Next, modified examples of the control unit 45 will be described below with reference to FIGS.

  FIG. 3 is a block diagram showing a control unit 50 according to a modified example, and FIG. 4 is a standard addition for determining the fluoride ion concentration of fluorine-containing wastewater in which the fluoride ion concentration fluctuates in three stages over time. FIG. 5 is a graph showing a regression line obtained by the method, and FIG. 5 shows the fluoride ion concentration of each fluorine-containing waste water determined in FIG. 4 and the indication value of the fluoride ion electrode meter when the standard substance of FIG. 4 is not added. FIG. 6 is a diagram showing a calibration curve (regression line) created from the relationship, and FIG. 6 is a flowchart for explaining calcium salt injection control by the control unit 50.

  As shown in FIG. 3, the control unit 50 includes a calibration curve creation unit 52, a fluoride ion concentration calculation unit 54, and a calculation unit 56.

  What is characteristic in this modification is that the calibration curve creating means 52 is a fluorine-containing material in which the fluoride ion concentration is determined by using a fluoride ion electrode meter based on the standard addition method and the fluoride ion concentration fluctuates in at least three stages over time. From the relationship between the respective fluoride ion concentrations of the wastewater 1 and the indicated value of the fluoride ion electrode meter when the standard substance in the above-described standard addition method of the fluorine-containing wastewater 1 in which the fluoride ion concentration is determined is not added The point is to create a calibration curve that passes through the origin.

  The standard addition method is a system that is affected by coexisting substances.For example, a standard curve of a known concentration is added to an unknown sample to create a calibration curve series, and the concentration of the unknown sample is determined from this relationship line. It is to be quantified.

  In this modification, the fluoride ion standard stock solution is added to the fluorine-containing wastewater 1 in which the concentration of fluoride ions is unknown and other ions coexist, and the concentration of fluoride ions added is, for example, 100 mg / The solutions added so as to be L, 200 mg / L, and 300 mg / L are prepared. FIG. 9 shows the fluoride ion concentration meter instruction value (Y axis, unit mg / L) and the addition concentration of fluoride ion standard substance (X axis, unit mg / L) of the fluorine-containing wastewater 1 to which the fluoride ion standard stock solution was added. FIG.

  In this modification, the fluoride ion concentration (mg / L) is applied. However, the present invention is not limited to this, and the indicated value may be a potential (mV).

  As shown in FIG. 9, it is possible to draw one straight line connecting three plots for the solutions to which each fluoride ion standard stock solution is added, and the fluorine containing waste water 1 is obtained by a point z where this straight line intersects the X axis. The fluoride ion concentration in it will be shown.

  Next, how to obtain a regression line by the standard addition method will be described with reference to FIGS.

  Specifically, as shown in FIG. 4, the fluorine-containing wastewater 1 in which the fluoride ion concentration fluctuated in three stages with time is indicated by 1A, 1B, and 1C, respectively, and the fluoride ion concentration a, b and c are determined respectively.

  Fluoride ion concentrations a to c in the determined fluorine-containing wastewater 1A to 1C are X-axis values, and the fluoride ion electrode meter indication values at points a to c where the fluorine-containing wastewaters 1A to 1C intersect with the Y-axis, That is, three points are plotted with the indicated value of the fluoride ion electrode meter when the standard substance is not added as the value of the Y-axis, and as shown in FIG. When a straight line is drawn, this straight line becomes the above-mentioned calibration curve.

  For example, this straight line can be obtained as a regression line created using the least square method while passing through the origin. The values a to c in FIG. 5 are absolute values of the values a to c in FIG.

  The fluoride ion concentration calculating means 54 is an arbitrary value obtained by applying the fluoride ion concentration (measured value) measured by the fluoride ion concentration measuring means 21 and transmitted to the control unit 50 to the calibration curve (regression equation of the regression line). This is a program for calculating the fluoride ion concentration in the fluorine-containing wastewater 1 at the point of time.

  The calculation means 56 applies the concentration of fluoride ions in the fluorine-containing wastewater 1 at any time calculated by the fluoride ion concentration calculation means 54 as the value of C2 in the above formula (V), and the calcium salt to be added. Calculate the calcium concentration.

  Next, the fluorine-containing wastewater treatment method using the fluorine-containing wastewater treatment apparatus 10 to which the standard addition method and the calibration curve described above are applied will be described with reference to the flowchart of FIG.

[Calibration curve creation process]
In this modification, prior to the treatment of fluorine-containing wastewater using the fluorine-containing wastewater treatment apparatus 10, the fluoride ion concentration measurement and the calibration curve are prepared by the standard addition method.

<Measurement of fluoride ion concentration by standard addition method>
As shown in FIG. 1, the fluoride ion concentration of the fluorine-containing waste water 1 is measured by the fluoride ion concentration measuring means 21, and then the fluorine-containing waste water 1 in the measuring tank 20 in which the fluoride ion concentration is measured. Thus, the fluoride ion standard substance is added stepwise such that the addition concentration of the fluoride ion standard substance is 100 mg / L, 200 mg / L, 300 mg / L, and so on. The concentration is measured. That is, for fluorine-containing wastewater 1, measurement data for determining the fluoride ion concentration is collected by the standard addition method.

  As shown in FIG. 6, in the measurement of the fluoride ion concentration by the standard addition method (S301), the measurement of the fluoride ion concentration by the standard addition method of the fluorine-containing waste water 1 varies with time in at least three stages. For the fluoride ion concentration.

<Calibration curve creation>
In the calibration curve creation step (S302), the control unit 50 determines the fluoride ion concentration that has fluctuated in at least three stages over time for the fluorine-containing wastewater 1 based on the measurement value, and determines the determined fluoride ion concentration. As shown in FIG. 4, the indicated value of the fluoride ion electrode meter at the point where each straight line intersects the Y axis, that is, the indicated value of the fluoride ion electrode meter when the standard substance is not added, as shown in FIG. As a value of the Y axis, as shown in FIG. 5, a regression line by the least square method, that is, a calibration curve passing through the origin is created.

[Fluoride ion concentration measurement process]
In step S <b> 201, the fluoride ion concentration in the fluorine-containing waste water 1 is measured by the fluoride ion concentration measuring means 21 in the measuring tank 20.

[Fluoride ion concentration calculation process]
In step S202, the calculation means 47 of the control unit 50 calculates the fluoride ion concentration in the fluorine-containing waste water 1 by applying the measured value of the fluoride ion concentration to the calibration curve created in the calibration curve creation process.

[Calcium concentration calculation process]
In step S203, the calculation means 47 of the control unit 50 substitutes the fluoride ion concentration value calculated in step S202 for the above formula (V), and the addition concentration of the calcium salt to be added to the mixing / reaction vessel 25 The calcium ion concentration corresponding to is calculated.

[Calcium salt injection process]
In step S204, calcium salt is injected from the calcium salt storage tank 55 into the mixing / reaction tank 25 in the fluorine-containing waste water 1 of the mixing / reaction tank 25 so as to have the concentration calculated in step S203. The calcium salt is injected by the control unit 50 in the same manner as in the above-described embodiment.

  After the end of step S204, the flow of FIG. 6 returns to the start, and the control from step S201 to S204 is repeated continuously or at short intervals.

  Thereafter, the liquid in the mixing / reaction tank 25 is subjected to the aggregation treatment in the aggregation tank 30 and the precipitation treatment in the precipitation tank 35, and the treated water 37 from which fluorine has been removed flows out of the precipitation tank 35.

  From the above, according to the fluorine-containing wastewater treatment apparatus 10 and the fluorine-containing wastewater treatment method according to this modification, even in the fluorine-containing wastewater 1 in which the fluoride ion concentration fluctuates over time, Each fluoride ion concentration of the fluorine-containing waste water 1 whose ion concentration has fluctuated over time in at least three stages is determined by the standard addition method, and from the relationship between the determined fluoride ion concentration and the indicated value of the fluoride ion electrode meter A calibration curve is created, and the fluoride ion concentration calculation step (S202) is performed by applying the measurement value of the fluoride ion concentration of the fluorine-containing wastewater measured at the fluoride ion concentration measurement step (S201) to the calibration curve. Calculating the fluoride ion concentration with the formula, and applying this fluoride ion concentration to the formula (I), calculate the calcium salt concentration to be added. It can be calculated in step (S203).

  Therefore, by creating a calibration curve with the above characteristic method and measuring the fluorine ion concentration in the fluorine-containing wastewater 1 at an arbitrary time point using a conventional ion electrode meter, the coexisting ions existed However, it becomes possible to measure a substantially accurate fluorine ion concentration.

Further, since it is not necessary to measure the coexisting ions not only in the fluoride ion concentration measuring step (S202) but also in creating a calibration curve, an apparatus for measuring the coexisting ions is completely used for treating the fluorine-containing waste water 1. In addition, fluoride ions can be removed from the fluorine-containing waste water more simply and reliably.

  In the above-described embodiment, the calcium salt is set to a concentration that is a predetermined amount, for example, 200 mg / L to 1500 mg / L in excess of the concentration at which calcium is present in a theoretical amount with respect to fluoride ions. By adding to the mixing tank, the influence of coexisting ions (anions such as chloride ions, sulfate ions and nitrate ions, and cations such as iron ions and aluminum ions) in the fluorine-containing wastewater 1 was suppressed. Due to the measurement of fluoride ions by the electrode method, it is due to the presence of coexisting ions between the measured value of fluoride ions in the fluoride-containing wastewater 1 and the actual concentration of fluoride ions in the fluoride-containing wastewater 1. There was still concern that errors would occur.

  In addition, if a separate measuring device is provided for the fluorine-containing wastewater treatment apparatus 10 to measure the concentration of other coexisting ions, the apparatus configuration becomes complicated, and the fluoride ion concentration in the fluorine-containing wastewater 1 increases with time. Therefore, if the fluoride ion concentration and the concentration of other coexisting ions are all measured each time, the labor of measurement increases.

  Therefore, in the fluorine-containing wastewater treatment apparatus 10 and its treatment method according to the above-described modification of this embodiment, fluoride ions can be more easily and more reliably removed from fluorine-containing industrial wastewater in which coexisting ions are present. Is possible.

  The present invention is not limited to the above-described embodiment. For example, in the modification of the above-described embodiment, fluorine-containing waste water whose concentration fluctuated in three stages over time was used in preparing a calibration curve. However, it is not limited to this. Simulated fluorine-containing wastewater can be used as fluorine-containing wastewater instead of actual fluorine-containing wastewater. Specifically, the concentration of anions and cations contained in the fluorine-containing wastewater to be treated is comparable. As described above, simulated fluorine-containing wastewater that does not contain fluoride ions can be used to create a calibration curve instead of actual fluorine-containing wastewater by dissolving reagents and chemicals in tap water and demineralized water. Good.

  Measure the concentration of cations such as chloride ion, sulfate ion, nitrate ion and cation such as iron ion, aluminum ion, sodium ion, potassium ion, etc. in the fluorine-containing wastewater beforehand. Dissolve reagents such as sodium, potassium sulfate, sodium nitrate, potassium nitrate, iron chloride, iron sulfate, aluminum chloride, and aluminum sulfate in tap water and demineralized water to prepare simulated fluorine-containing wastewater that does not contain fluoride ions. .

  A fluoride ion standard stock solution is added to the simulated fluorine-containing wastewater to produce fluorine-containing wastewater having at least three or more stages of fluoride ion concentration, and calibration is performed in the manner shown in FIGS. 4 and 5 using the standard addition method. Lines can also be made.

  Further, in the above modification, in the modification of the above embodiment, the fluorine-containing waste water whose concentration fluctuated in three stages over time was used in preparing the calibration curve. However, the present invention is not limited to this. Among the fluorine-containing wastewater whose fluoride ion concentration fluctuates with time, the fluoride ion concentration of one stage of fluorine-containing wastewater is determined as shown in FIG. 4 based on the standard addition method, and then in the manner of FIG. It is also possible to create a calibration curve that passes through the origin.

  This is because the calibration curve shown in FIG. 5 always passes through the origin, so the fluoride ion concentration value of the fluorine-containing wastewater determined using the standard addition method of the one stage that is the origin and the fluoride ion electrode meter If the indicated value is known, a calibration curve can be theoretically created.

  Further, not only fluoride ions but also coexisting ions and the concentration of the anion or cation whose concentration varies with time is one as in the above modification, the calibration curve and A method for preparing a calibration curve is applicable.

  Anions or cations whose concentrations change over time include divalent cations such as sodium ion, potassium ion, chlorine ion, bromine ion, iodine ion, cyanide ion, lead ion, cadmium ion, copper ion and mercury ion. , Nitrate ion, chlorate ion, calcium ion, and ammonium ion.

  In addition to the fluorine treatment, the concentration of the substance to be treated can be easily monitored by the ion electrode method of the present invention, and the treatment performance is improved by adding an appropriate chemical according to the result. Cyanide ions are used to determine the amount of chlorine injected during chlorination treatment, and divalent cations such as lead ions, cadmium ions, copper ions, and mercury ions are used in heavy metal treatment with agents having coordination bonds (hereinafter, liquid chelates). In determining the injection rate of liquid chelates, nitrate ions are used to determine the injection rate of alcohols that are hydrogen donors in biological denitrification, and the injection rate of reducing agents such as hydrazine during catalytic reduction. In addition, chlorate ions can be applied to the determination of the injection rate of a reducing agent such as sulfite in the reduction treatment, and ammonium ions can be applied to the determination of the chlorine injection rate in the chlorine oxidation.

  According to such a calibration curve and a method for producing the calibration curve, in a liquid system in which coexisting ions exist and the concentration of the anion or cation whose concentration varies with time is one as in the above modification, In addition, the concentration of the anion or cation that varies with time can be determined more reliably.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[1. Preparation of calibration curve]
The standard addition method was performed on semiconductor component factory wastewater (corresponding to fluorine-containing wastewater 1, hereinafter referred to as raw water) in which the fluoride ion concentration fluctuated in multiple stages.

  Table 1 shows the properties of raw water (raw water A, raw water B, raw water C, and raw water D) used in the standard addition method and having varying fluoride ion concentrations in four stages.

  Fluoride ion standard substance, sodium fluoride (Wako Pure Chemical Industries, Ltd.) so that the addition concentrations of fluoride ion standard substance are 0 mg / L, 300 mg / L, 600 mg / L, and 1000 mg / L for raw water A to D, respectively. Reagent grade 1 manufactured by Kogyo Co., Ltd. was added, and each raw water and each fluoride ion standard substance additive was measured using a fluoride ion electrode meter (electrode type: HW-30R, manufactured by Toa DKK Corporation). The fluoride ion concentration was measured.

  FIG. 7 shows fluoride ion concentration meter indication values (Y-axis, unit mg / L) and addition concentrations of fluoride ion standard substance (X-axis, unit mg / L) for each raw water and each fluoride ion standard substance additive. FIG.

  Note that the straight line in FIG. 7 is a regression line created by the least square method from the measurement data of the fluoride ion concentration.

  As shown in the figure, the regression line of each raw water A to D is the value of the X axis of about −60 mg / L, about −200 mg / L, about −400 mg / L and about −600 mg / L at the intersection with the X axis. The absolute value of this value almost corresponded to the fluoride ion concentration value of each raw water measured in advance.

  Therefore, it was shown that the value of the fluoride ion concentration in the raw water determined by the standard addition method is highly reliable.

  Next, the fluoride ion concentration of each raw water A to D determined in FIG. 7 is taken as the value of the X axis, and the indicated value of the fluoride ion electrode meter at the point where the regression line of each raw water A to D intersects the Y axis ( That is, a regression line was prepared by the method of least squares with the indicated value of the fluoride ion electrode meter when the standard substance was not added as the value of the Y axis. This regression line, that is, a calibration curve, is shown in FIG.

[2. Check accuracy of calibration curve]
Table 2 is a table | surface which shows the property of the raw | natural water E used for confirmation of the precision of a calibration curve.

  For raw water E, measure the fluoride ion concentration using a fluoride ion electrode meter (electrode type: HW-30R, manufactured by Toa DKK Corporation) and measure the measured value (indicated value of the fluoride ion electrode meter) To determine the fluoride ion concentration. The results are shown in FIG.

  As shown in the figure, the fluoride ion concentration of raw water E was determined to be 140 mg / L. This value is close to 130 mg / L measured by JIS K0102 (2013) 34.1 lanthanum-alizarin complexone spectrophotometric method in Table 2, and the prepared calibration curve is a simple method for determining the fluoride ion concentration. It was shown that it can be utilized.

[3. Treatment of raw water E]
The raw water E was treated using a fluorine-containing wastewater treatment apparatus corresponding to the modification of the above embodiment, and treated water 37 was obtained.

  As described above, the determined value of the fluoride ion concentration of the raw water E is 140 mg / L, 10 wt / wt% slaked lime liquid (specific gravity 1.06) is used as the calcium salt, and the theoretical value of calcium is +100 mg / wt with respect to fluoride ions. L (Test Example 1), theoretical value +200 mg / L (Test Example 2), theoretical value +300 mg / L (Test Example 3), theoretical value +500 mg / L (Test Example 4), theoretical value +700 mg / L (Test Example 5) The theoretical value +1000 mg / L (Test Example 6) and the theoretical value +1500 mg / L (Test Example 7) were added to the mixing / reaction vessel 25.

  That is, with respect to the fluoride ion concentration of raw water E of 140 mg / L, the calculated excessive calcium ion concentration was set to 100 to 1500 mg / L.

  Table 3 shows the treatment conditions of the fluorine-containing wastewater treatment equipment.

  In Test Examples 1 to 7, the measurement of sulfate ion concentration was not performed, and the fluoride ion concentration in the raw water was not changed, so the slaked lime addition rate did not change over time.

  Table 4 shows the test results.

  In Table 4, the fluoride ion concentration of treated water was measured by the method based on JIS K0102 (2013) 34.1 for the filtered water filtered with MF having a pore diameter of 1 μm, as in Table 2.

  As shown in Table 4, when the calcium salt is added so that the calcium concentration in the mixing / reaction vessel 25 is the theoretical value +200 mg / L with respect to fluoride ions, the fluoride ion concentration of the treated water is 16 mg or less. It was possible to reduce until. Moreover, when calcium salt was added so that it might become theoretical value +300 mg / L, the fluoride ion density | concentration of the treated water was able to be reduced further.

[4. Comparison of fluoride ion concentration determination method based on calibration curve and conventional method]
About the raw water E (Test Example 11) and the raw water diluted solution (Test Examples 8 to 10) obtained by arbitrarily diluting the raw water E with tap water, a fluoride ion electrode meter (electrode type: HW-30R, manufactured by Toa DKK Corporation) And [1. Comparison of the fluoride ion concentration calculated using the calibration curve prepared in [Preparation of Calibration Curve] and the determination result of the fluoride ion concentration by the conventional method were compared.

  The conventional method is a method of measuring the fluoride ion concentration by applying a calibration curve based on a general method without using the standard addition method. That is, a buffer solution and desalted water of JIS K0102 (2013) 34.2 so that a commercially available fluoride ion standard stock solution has a concentration of at least 3 or more (for example, 10 mg / L, 50 mg / L, 100 mg / L...). Each solution was diluted while adding a dilute solution having a plurality of fluoride ion concentrations.

  The diluted solution was measured using a fluoride ion electrode meter (electrode type: HW-30R, manufactured by Toa DKK Co., Ltd.), and the indicated value obtained by measuring the fluoride ion concentration was taken as the Y-axis value. A calibration curve was prepared using the concentration of the fluoride ions in the liquid (10 mg / L, 50 mg / L, 100 mg / L,...) As the value of the X axis.

  Next, using a fluoride ion electrode meter (electrode type: HW-30R, manufactured by Toa DKK Co., Ltd.), raw water E (Test Example 4) and raw water diluted solution obtained by arbitrarily diluting the raw water E with tap water (Test Example) 1 to 3), and the indicated value is measured as described in [1. The calibration curve prepared in [Preparation of calibration curve] and the calibration curve prepared by the conventional method were applied to calculate the fluoride ion concentration.

  The results are shown in Table 5.

  As shown in Table 5, [1. The fluoride ion concentration calculated by applying to the calibration curve prepared in [Preparation of Calibration Curve] is the fluoride ion concentration measured by the official method (that is, the method according to JIS K0102 (2013) 34.1). The value was very close. On the other hand, the measurement value obtained with the calibration curve prepared by the conventional method has a low measurement accuracy at a portion where the fluoride ion concentration is 100 mg / L or less (according to the official method).

  As a cause of the low measurement accuracy in the conventional method, the influence of coexisting substances in the raw water E can be considered.

[5. Calculation of fluoride ion concentration based on known standard addition method for simulated raw water]
Simulated raw water in which fluoride ion standard stock solution, sodium chloride, sodium nitrate, sodium sulfate, iron sulfate and aluminum chloride were added to the desalted water so that the anion concentration and cation concentration (see Table 2) of raw water E were reached (test example) 12) was produced. Accordingly, the fluoride ion concentration in the simulated raw water is 130 mg / L according to the official method (according to JIS K0102 (2013) 34.1).

  Fluoride ion standard stock solution was further added to the simulated raw water to prepare standard added simulated raw water (10 mg / L, 50 mg / L, 100 mg / L,...) Having different fluoride ion concentrations.

  The fluoride ion concentration of these standard addition simulated raw waters was measured using a fluoride ion electrode meter (electrode type: HW-30R, manufactured by Toa DKK Corporation), and a known standard addition method as shown in FIG. A calibration curve was prepared, and the fluoride ion concentration in the simulated raw water was calculated from the intersection of this calibration curve and the X axis.

  The results are shown in Table 6.

  As shown in Table 6, although the known standard addition method is used, the calculated value of fluoride ion concentration is the value of fluoride ion concentration according to the official method (method according to JIS K0102 (2013) 34.1). A value close to the measured value was shown.

  This indicates that the calibration curve shown in FIG. 5 of the modified example can be prepared by using simulated raw water instead of raw water (fluorine-containing wastewater to be treated).

1 Fluorine-containing wastewater 10 Fluorine-containing wastewater treatment equipment 21 Fluoride concentration measuring means (fluoride ion electrode meter)
25 Mixing / reaction tank (mixing means)
47, 56 Calculation means 59 Pump (injection means)

Claims (5)

In the treatment method of fluorine-containing wastewater that adds calcium salt to fluorine-containing wastewater and performs coagulation sedimentation treatment,
A fluoride ion concentration measurement step of measuring the fluoride ion concentration of the fluorine-containing wastewater by a fluoride ion electrode method;
The fluoride ion concentration measured by the fluoride ion concentration measurement step is expressed by the following formula (I):
200 ≦ C1-C2 × Aw (Ca) / 2Aw (F) ≦ 1500
[However, C1 represents the calcium concentration [mg / L] of the calcium salt, C2 represents the fluoride ion concentration [mg / L] measured in the fluoride ion concentration measurement step, and Aw (Ca) is calcium. And Aw (F) represents the atomic weight of fluorine.]
A calcium concentration calculating step for calculating the calcium concentration of the calcium salt to be applied by applying to
A method for treating fluorine-containing wastewater, comprising:   The method for treating fluorine-containing wastewater according to claim 1, wherein in the fluoride ion concentration measuring step, the fluoride ion concentration of the fluorine-containing wastewater is directly measured based on a standard addition method. The fluorine-containing wastewater is wastewater in which the fluoride ion concentration in the wastewater varies with time,
Prior to the fluoride ion concentration measurement step, the fluoride ion concentration of the fluorine-containing waste water whose fluoride ion concentration has changed over time is determined using a fluoride ion electrode meter based on a standard addition method, A calibration curve creation step for creating a calibration curve passing through the origin from the relationship between the determined fluoride ion concentration of the fluorine-containing wastewater and the indicated value of the fluoride ion electrode meter when the standard substance in the standard addition method is not added; ,
After the fluoride ion concentration measurement step and before the calcium concentration calculation step, the measurement value of the fluoride ion concentration of the fluorine-containing wastewater measured at the arbitrary time point measured in the fluoride ion concentration measurement step is used as the calibration curve. And a fluoride ion concentration calculating step for calculating a fluoride ion concentration in the fluorine-containing wastewater at the arbitrary point of time,
The value of the fluoride ion concentration calculated in the fluoride ion concentration calculating step is the C2 of the formula (I) in the calcium concentration calculating step (fluoride ion concentration [mg / L] measured in the fluoride ion concentration measuring step). The method for treating fluorine-containing wastewater according to claim 1, wherein the fluorine-containing wastewater is treated as a value. When sulfate ions are present in the fluorine-containing wastewater at a concentration of 1000 mg / L or more,
In order to compensate for calcium lost by agglomeration and precipitation by reacting with the sulfate ions in the calcium of the added calcium salt, the following formula (II):
C3 = (C4-1000) × Aw (Ca) / Fw (SO ₄ ²⁻ )
[However, C3 represents the calcium concentration of the calcium salt to be supplemented, C4 represents the concentration of sulfate ion in the fluorine-containing wastewater, Aw (Ca) represents the atomic weight of calcium, and Fw (SO ₄ ²⁻ ) represents sulfuric acid. Represents the formula weight of ions]
The method for treating fluorine-containing wastewater according to any one of claims 1 to 3, wherein a calcium salt having a calcium concentration calculated by applying to the above is further supplemented in the fluorine-containing wastewater. Mixing means for mixing fluorine-containing wastewater and calcium salt;
Fluoride ion concentration measuring means capable of measuring fluoride concentration in fluorine-containing wastewater by a fluoride ion electrode method;
The fluoride ion concentration measured by the fluoride ion concentration measuring means is expressed by the following formula (III):
200 ≦ C1-C2 × Aw (Ca) / 2Aw (F) ≦ 1500
[However, C1 represents the calcium concentration [mg / L] of the calcium salt, C2 represents the fluoride ion concentration [mg / L] measured in the fluoride ion concentration measurement step, and Aw (Ca) is calcium. And Aw (F) represents the atomic weight of fluorine.]
Calculating means capable of calculating the amount of the calcium salt to be mixed by applying to
Injection means for injecting the amount of calcium salt calculated by the calculation means into the mixing means;
An apparatus for treating fluorine-containing wastewater, comprising:

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