JP4905397B2 - Method and apparatus for treating fluorine-containing water - Google Patents

Description

The present invention obtains treated water with reduced fluorine concentration by adding a calcium (Ca) compound to fluorine-containing wastewater such as semiconductor factory wastewater and solid-liquid separation of fluorine as calcium fluoride (CaF ₂ ). In wastewater treatment, the concentration of reaction inhibitor in raw water is measured, and the amount of calcium compound added is controlled based on the measured value. The present invention relates to a method and apparatus for treating fluorine-containing water.

  Fluorine-containing water, such as fluorine-containing wastewater discharged from silicon wafer manufacturing processes in semiconductor parts manufacturing, pickling wastewater discharged from stainless steel sheet manufacturing processes, hydrofluoric acid manufacturing wastewater, waste incineration wastewater, etc. The method of adding calcium compounds to the reaction, reacting fluorine and calcium compounds in the vicinity of neutrality to form calcium fluoride insoluble salts, and separating them into solid and liquid is widely used due to low drug costs is doing.

  In this method, since fluorine in fluorine-containing water reacts with calcium ions according to the following reaction formula, to obtain a treated water with a low fluorine concentration by sufficiently reacting fluorine in fluorine-containing water, the following formula is used. The most common method is to allow the reaction to proceed by adding more calcium compound than the amount of calcium compound added in a reaction equivalent to the fluorine in the fluorine-containing water. In general, slaked lime is used as the calcium compound.

Ca ²⁺ + 2F ⁻ → CaF ₂ (precipitation)
Calcium compound addition amount (mg-Ca / L)
= Raw water fluorine concentration (mg / L) x 40/38

By the way, although the solubility product of calcium fluoride is generally represented by the following formula, the reaction does not reach the equilibrium represented by the solubility product in the reaction time performed in actual waste water treatment.
[F ⁻ ] ² [Ca ²⁺ ] = 4.9 × 10 ⁻¹¹ mol ³ / L ³

  Therefore, in order to make the fluorine concentration of treated water 8 mg / L or less of the wastewater standard value, it is necessary to make the residual calcium ion concentration excessive. Conventionally, the residual calcium ion concentration of treated water is 200 to 300 mg / L. Thus, the addition amount of calcium compounds such as slaked lime is controlled.

  However, in this way, in the method of controlling the amount of calcium compound added so that the residual calcium ion concentration in the treated water is 200 to 300 mg / L regardless of the raw aqueous state other than the fluorine concentration, the amount of the raw aqueous solution is changed. The fluorine concentration of the treated water fluctuated, and it was not possible to stably treat the fluorine to the emission standard value of 8 mg / L or less.

  For this reason, a method of treating the treated water fluorine concentration to 8 mg / L or less by setting the calcium compound addition amount high in advance and making the residual calcium ion concentration higher than 200 to 300 mg / L is adopted. In some cases, however, the excessive addition of the calcium compound has a problem in that the processing cost increases.

  Patent Document 1 discloses a substance that reacts with calcium ions contained in fluorine-containing water to form a sparingly soluble salt (for example, sulfate ion or phosphate ion) in a method of adding calcium salt to fluorine-containing water for treatment. A method of controlling the amount of calcium salt added based on the concentration of is described.

In addition, in Patent Document 2, in addition to fluorine ions, calcium ions are added to wastewater containing magnesium ions and sulfate ions to remove fluorine ions as precipitates. A method for controlling the amount of calcium salt added as an agent is described.
JP 2001-212574 A JP 2000-301165 A

  The method of Patent Document 1 is based on the knowledge that when a polyvalent anion such as sulfate ion coexists in the waste water, these form a poorly soluble calcium salt, and thus adversely affect fluorine removal. The concentration of the polyvalent anion that forms the water is detected, and the amount of calcium salt added is controlled based on this result. However, even with this method, fluorine may not be sufficiently removed.

  In addition, the method of Patent Document 2 solves the problem that the amount of alkali agent used and the amount of generated sludge increase due to the reaction of magnesium ions and / or sulfate ions in waste water with an alkali agent for removing fluorine. In addition, the electrical conductivity of water after addition of the alkali agent (that is, treated water) is obtained by utilizing the fact that the electric conductivity decreases when magnesium ions or sulfate ions react with the alkali agent and precipitate as an insoluble salt. The addition amount of the alkaline agent is controlled so that it does not become less than a predetermined specified electrical conductivity. Specifically, this method measures the electrical conductivity of both the raw water and the water after the addition of the alkali agent. However, the control of the addition amount of the alkali agent itself is based on the electric conductivity of the water after the addition of the alkali agent. It is performed so that it does not become a predetermined value or less, and based on the measured value of the electrical conductivity of the raw water, the addition amount control of the alkaline agent is not performed in conjunction with the increase / decrease. In addition, the fluorine-containing water to be treated in Patent Document 2 is a wastewater containing magnesium ions at a high concentration, such as containing magnesium ions of 2000 mg / L or more and further sulfate ions of 5000 mg / L or more. Document 1 makes no mention of monovalent anions such as nitrate ions which are problematic as fluorine treatment inhibitors in the present invention.

  The present invention solves the above-mentioned conventional problems, and when adding a calcium compound to fluorine-containing wastewater to separate solid and liquid as fluorine as calcium fluoride, it is possible to obtain an accurate calcium compound for fluorine-containing water whose water quality varies. It is an object of the present invention to provide a method and apparatus for performing stable and efficient fluorine reduction treatment by controlling the amount of addition.

  As a result of intensive studies on the treatment of fluorine-containing water using a calcium compound, the present inventor has obtained the following knowledge.

In the treatment of fluorine-containing water using a calcium compound, fluorine in the water is precipitated as calcium fluoride, and this is solid-liquid separated to obtain treated water with reduced fluorine. As described above, the solubility product of calcium fluoride is represented by the following formula.
[F ⁻ ] ² [Ca ²⁺ ] = 4.9 × 10 ⁻¹¹ mol ³ / L ³

  However, in the reaction time performed in actual wastewater treatment, the reaction does not reach the equilibrium represented by the solubility product. Therefore, in order to make the treated water fluorine concentration 8 mg / L or less of the wastewater standard value, it is necessary to make the residual calcium ion concentration excessive. Conventionally, the residual calcium ion concentration is 200 to 300 mg / L. Thus, the addition of a calcium compound has been performed.

  However, as a result of the inventor's investigation, if the wastewater contains coexisting ions other than fluorine, such as sulfate ions, chloride ions, nitrate ions, etc., the amount of calcium compound added based on the residual calcium ion concentration as before In the control, it was found that the concentration of fluorine in the treated water was high. Further examination of this phenomenon revealed that as the ionic strength derived from coexisting ions in the wastewater increases, the solubility of calcium fluoride increases and the concentration of treated water fluorine increases. Moreover, it became clear that when the ionic strength of waste water became high, the reaction rate of a fluorine and calcium ion also became slow, and this also became a cause of the treated water fluorine concentration becoming high.

  From the above, in order to obtain the target treated water fluorine concentration, based on the ionic strength of fluorine-containing water, when the ionic strength is high, to compensate for the increased solubility of calcium fluoride, It has been detected that the amount of calcium compound added needs to be increased so that the residual calcium ion concentration is increased to compensate for the slower reaction rate.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

The method for treating fluorine-containing water of the present invention (Claim 1) is a method for solid-liquid separation of fluorine as calcium fluoride by adding a calcium compound to the fluorine-containing water, and measuring the ionic strength of the fluorine-containing water. Based on the measured value, the amount of calcium compound added to the fluorine-containing water is controlled such that the residual calcium ion concentration in the treated water increases as the measured value of the ionic strength of the fluorine-containing water increases. It is characterized by that .

Processing method of the fluorine-containing water 請 Motomeko 2, and measuring Oite to claim 1, by the fluorine containing water conductivity meter ionic strength.

The method for treating fluorine-containing water according to claim 3 is the method according to claim 1 or 2 , wherein the fluorine-containing water contains nitrate ions, sulfate ions, and chloride ions, and the magnesium ion content is less than 2000 mg / L. Features.

The apparatus for treating fluorine-containing water according to the present invention (Claim 4 ) includes a calcium compound addition means for adding a calcium compound to fluorine-containing water, and calcium fluoride precipitated by the reaction between fluorine and calcium compound in the fluorine-containing water. In a treatment apparatus for fluorine-containing water having a means for liquid separation, the ion intensity measuring means for measuring the ion intensity of the fluorine-containing water, and the measurement of the ion intensity measuring means based on the measured value of the ion intensity measuring means Control means for controlling the calcium compound addition amount of the calcium compound addition means is provided so that the higher the value is, the higher the residual calcium ion concentration of the treated water is .

Processor of fluorine containing water 請 Motomeko 5, in claim 4, wherein the ionic strength measuring means is a conductivity meter.

The treatment apparatus for fluorine-containing water according to claim 6 is the treatment apparatus according to claim 4 or 5 , wherein the fluorine-containing water contains nitrate ions, sulfate ions, and chloride ions, and the magnesium ion content is less than 2000 mg / L. Features.

  According to the present invention, the degree of reaction inhibition by reaction inhibitors such as nitrate ion, sulfate ion and chloride ion contained in fluorine-containing water is measured by ionic strength, and the amount of calcium added is controlled based on the result. Therefore, it is possible to prevent the calcium compound from being excessive or deficient and perform a stable and efficient treatment.

  Hereinafter, embodiments of the method and apparatus for treating fluorine-containing water of the present invention will be described in detail.

The present invention measures the ionic strength of the fluorine-containing water when adding a calcium compound to the fluorine-containing water and solid-liquid separates the fluorine as calcium fluoride, and based on the measured value, Controlling the amount of calcium compound added, specifically, controlling the amount of calcium compound added so that the residual calcium ion concentration of treated water increases as the measured value of the ionic strength of fluorine-containing water increases. It is what.
Here, the residual calcium ion concentration refers to the calcium ion concentration remaining in the treated water obtained by adding a calcium compound to fluorine-containing water, and the reaction of Ca ²⁺ + 2F ⁻ → CaF ₂ (precipitation) described above. It corresponds to the value obtained by dividing the theoretical amount of the calcium compound required for the reaction with fluorine in the fluorine-containing water calculated by the following formula from the added amount of the calcium compound actually added. In addition, the measured value obtained by measuring the calcium ion concentration of the actually obtained treated water may be used.
Calcium compound addition amount (mg-Ca / L)
= Raw water fluorine concentration (mg / L) x 40/38

  In the present invention, the ionic strength of fluorine-containing water is preferably measured by a conductivity meter, and the fluorine-containing water to be treated in the present invention includes nitrate ions, sulfate ions, and chloride ions, and magnesium. The ion content is less than 2000 mg / L, and the effect of the present invention is particularly effectively exerted on fluorine-containing water containing a monovalent anion in addition to the polyvalent anion. .

<Advantage over Patent Document 1>
In Patent Document 1, the amount of calcium compound added is calculated in consideration of reaction inhibition by a polyvalent anion that forms a sparingly soluble salt with calcium, such as phosphate ions and sulfate ions, as in the following equation.
Ca (mg / L) = (F ⁻ concentration × Ca / 2F) + (PO ₄ ³⁻ concentration × 3Ca / 2PO ₄ )
+ (SO ₄ ²⁻ concentration × Ca / SO ₄ ) + (CO ₃ ²⁻ concentration × Ca / CO ₃ )

  In this method, nitrate ions and chloride ions in the wastewater that do not produce calcium and sparingly soluble salts are not involved in controlling the amount of Ca salt added. However, the present inventors have found through various studies that monovalent anions such as nitrate ions and chloride ions that do not form a sparingly soluble salt with calcium are also factors that increase the concentration of treated water fluorine.

  In the present invention, not only the polyvalent anion in the fluorine-containing water but also the content of the monovalent anion is controlled based on the ionic strength so as to be involved in the control of the addition amount of the calcium compound.

<Fluorine-containing wastewater>
The fluorine-containing wastewater treated in the present invention includes a monovalent anion such as nitrate ion in particular, so that the method of Patent Document 1 in which only the polyvalent anion is considered as a coexisting ion performs a stable and reliable treatment. Examples of the water quality include the following.

Fluorine concentration: 15 to 3000 mg / L, preferably 50 to 500 mg / L
Nitrate ion concentration: 5-2000 mg / L, preferably 10-1000 mg / L
Sulfate ion concentration: 5-2000 mg / L, preferably 10-1000 mg / L
Chloride ion concentration: 1 to 500 mg / L, preferably 1 to 100 mg / L

  The fluorine-containing wastewater to be treated in the present invention includes, for example, electronic industrial wastewater, fluorine-containing wastewater discharged from a silicon wafer manufacturing process in semiconductor component manufacturing, pickling wastewater discharged from a stainless steel plate manufacturing process, and hydrofluoric acid manufacturing wastewater. These waste waters are generally waste water that does not contain magnesium ions and that is substantially free of magnesium ions with a magnesium ion concentration of less than 2000 mg / L and even 200 mg / L or less. .

<Calcium compound / pH adjuster>
In the present invention, the calcium compound added to the fluorine-containing wastewater may be any calcium compound that releases calcium ions, and examples thereof include calcium chloride, calcium hydroxide (slaked lime), and calcium carbonate.
Moreover, as a pH adjuster, acids, such as alkalis, such as sodium hydroxide, potassium hydroxide, and calcium hydroxide, hydrochloric acid, nitric acid, a sulfuric acid, can be used.
However, as described later, from the viewpoint of not increasing the ionic strength, it is preferable to use slaked lime as the calcium compound, and it is preferable to use a monovalent acid such as hydrochloric acid as the acid.

<Correlation between ionic strength and electrical conductivity>
The ionic strength is the sum of the product of the molar concentration of ions and the square of the valence of various ions in the liquid, and the value is further divided by 2. Therefore, the measurement of ionic strength can be calculated by measuring the molar concentration of various coexisting ions in the raw water and using the measured value according to the following equation (I). Further, since there is a correlation between the coexisting ion concentration ionic strength and the electrical conductivity, the ionic strength can be substituted by measuring the electrical conductivity from the measured value.

  It is a well-known matter that there is a correlation between ionic strength and electrical conductivity, but fluorine in wastewater does not affect ionic strength and electrical conductivity, and only coexisting ions other than fluorine are related to ionic strength and electrical conductivity. Was verified by the following experiment.

  The ionic strength was calculated and the electrical conductivity was measured for various water effluents A to F shown in Table 1, and the results are shown in Table 1. The relationship between ionic strength and electrical conductivity is shown in FIG. 2 (a), and the relationship between fluorine concentration and electrical conductivity is shown in FIG. 2 (b).

  The ionic strength was calculated from the concentration of coexisting ions (sulfate ion, nitrate ion, chloride ion) in the waste water by the above formula (I).

  From Table 1 and FIGS. 2 (a) and 2 (b), it can be seen that there is a correlation between the concentration of coexisting ions other than fluorine and conductivity, and fluorine has little effect on ionic strength and conductivity.

  This is probably because hydrofluoric acid is a weak acid, so that only part of it dissociates in the state of acidic fluorine-containing water, and the contribution to conductivity is low. It is thought that the ionic strength derived from the origin has a correlation with the conductivity.

<Relationship between ionic strength and reaction rate of fluorine and calcium ions>
As described above, the present invention has been achieved on the basis of the knowledge that the reaction between fluorine and calcium ions is slower in wastewater with high ionic strength than in wastewater with low ionic strength. FIG. 3 shows the relationship between the reaction rate of fluorine and fluorine.

  FIG. 3 shows that the fluorine concentration is equal to 100 mg / L, but slaked lime is added so that the calcium ions to be added are 305 mg / L for various fluorine-containing waters having different coexisting ion concentrations and different ionic strengths. It is a figure which shows the reaction time (Time required for a fluorine to react with a calcium ion and a density | concentration reduction) when it is made to react by pH 7.0, This ionic strength is higher than this FIG. It can be seen that the wastewater requires more time for the reaction between fluorine and calcium ions and the reaction rate is slower.

  As a result, for example, in a wastewater having a sulfate ion concentration of 500 mg / L and a wastewater having a sulfate ion concentration of 200 mg / L and a nitrate ion concentration of 1000 mg / L, a conventional method in which only the coexisting concentration of polyvalent anions is considered The drainage with an ion concentration of 500 mg / L results in less reaction, whereas the control based on the ionic strength of the present invention allows the nitrate ion concentration even when the sulfate ion concentration is 200 mg / L. It is confirmed that the reaction can be enhanced by detecting that the reaction of the wastewater having a higher overall ionic strength at 1000 mg / L is less likely to proceed and increasing the amount of calcium compound added accordingly. .

<Relationship between additive and ionic strength>
As described above, when the ionic strength is high, the reaction rate between fluorine and calcium ions becomes slow. Therefore, in the present invention, it is more preferable that the chemical added to the waste water can suppress the increase in ionic strength.

For example, when the wastewater is acidic wastewater containing HF, H ₂ SO ₄ , or HNO ₃ , as shown in the following formulas (i) and (ii), as the calcium compound, neutral calcium chloride is used to adjust the pH. Therefore, it is more preferable to use alkaline slaked lime than to add alkali, because an increase in ionic strength can be suppressed.
2HF + CaCl ₂ + 2NaOH → CaF ₂ + NaCl + 2H ₂ O (i)
2HF + Ca (OH) ₂ → CaF ₂ + 2H ₂ O (ii)

  Similarly, as shown in the following formula (iii), when neutralizing slaked lime added as surplus calcium, neutralization of 1 mol of slaked lime increases 1 mol of sulfate ions, that is, an ionic strength of 4 mol. On the other hand, as shown in the following formula (iv), neutralization of 1 mol of slaked lime increases 2 mol of chloride ions, that is, an ionic strength of 2 mol. Therefore, as the acid for neutralizing slaked lime, it is more preferable to use a monovalent acid such as hydrochloric acid or nitric acid because an increase in ionic strength can be suppressed. Further, calcium chloride may be used as the excess calcium.

Ca (OH) ₂ + H ₂ SO ₄ → CaSO ₄ + 2H ₂ O (iii)
Ca (OH) ₂ + 2HCl → CaCl ₂ + 2H ₂ O (iv)

<Control of addition amount of calcium compound based on ionic strength>
In the present invention,
(1) Fluorine-containing water with high ionic strength has a slower reaction rate between fluorine and calcium ions than fluorine-containing water with low ionic strength. (2) When the ionic strength is high, the solubility of calcium fluoride increases. If the ionic strength of the fluorine-containing water is high based on the above findings, the ionic strength is low to compensate for the increased solubility of calcium fluoride and to compensate for the slow reaction rate. The amount of calcium compound added is increased so that the residual calcium ion concentration is higher than when treating the fluorine-containing water.

  The method for controlling the addition amount of the calcium compound based on the ionic strength of the fluorine-containing water is not particularly limited, and examples thereof include the following methods I, II, and III. These methods can be combined appropriately.

  Method I: For simulated wastewater adjusted to various ionic strengths, the ionic strength and fluorine concentration of the wastewater, and the wastewater ionic strength and fluorine concentration and the concentration of calcium compound added and the fluorine concentration of the treated water are treated. Investigate the relationship with the amount of calcium compound addition necessary to obtain treated water with the desired fluorine concentration, determine the set value of the calcium compound addition amount with respect to the ionic strength and fluorine concentration of the wastewater in advance, and the actual fluorine-containing water In the treatment, the ionic strength and fluorine concentration of the fluorine-containing water are measured, and the amount of calcium compound added is adjusted so that it becomes a preset value or a value obtained by adding a predetermined constant to this preset value. Control.

  Method II: For simulated wastewater adjusted to various ionic strengths, the ionic strength and fluorine concentration of the wastewater and the wastewater ionic strength and fluorine concentration, and the residual calcium ion concentration are treated from the ionic strength and fluorine concentration of the wastewater. Investigate the relationship with the residual calcium ion concentration of treated water necessary to obtain treated water with the desired fluorine concentration, and determine the set value of the treated water residual calcium ion concentration with respect to the ionic strength and fluorine concentration of the wastewater in advance. In the treatment of fluorine-containing water, the ionic strength and fluorine concentration of fluorine-containing water and the residual calcium ion concentration of the treated water are measured and set to a predetermined set value, or a predetermined constant is set to this set value. The amount of calcium compound added is controlled so that the integrated value is obtained.

  Method III: Measure the ionic strength and fluorine concentration of fluorine-containing water and the residual calcium ion concentration of the treated water in the actual treatment system of fluorine-containing water, and the amount of calcium compound addition required for the treatment of wastewater with a certain fluorine concentration Set the residual calcium ion concentration of the treated water determined in advance in the jar test, so that if an increase in the ionic strength of the wastewater is detected, the residual calcium ion concentration of the treated water will increase, and the ionic strength of the wastewater When a decrease is detected, the amount of calcium compound added is feedback controlled from the residual calcium ion concentration of the treated water so that the residual calcium ion concentration of the treated water becomes low.

  The fluorine concentration of fluorine-containing water can be measured by ion electrode method, ion chromatograph method, or lanthanum-alizarin complexone spectrophotometry method. In order to reflect, the ion electrode method is suitable.

  The residual calcium ion concentration of the treated water can be measured by an ion electrode method, chelate titration method, flame atomic absorption method, ion chromatography method or the like. Of these, the ion electrode method is preferable because rapid measurement is possible.

<Treatment of fluorine-containing water>
A specific processing procedure for processing fluorine-containing water according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a system diagram showing an embodiment of the apparatus for treating fluorine-containing water of the present invention. In FIG. 1, 1 is a first reaction tank, 2 is a second reaction tank, 3 is a coagulation tank, and 4 is a precipitation tank. Reference numeral 5 denotes a sludge adjusting tank.

The method of FIG. 1 employs a sludge return method in which a part of sludge separated into solid and liquid in the sedimentation tank 4 is added to raw water as return sludge. In this sludge return, the return sludge is returned to the sludge adjustment tank. 5, it reacts with an alkali (in FIG. 1, slaked lime (Ca (OH) ₂ )) and is added to raw water.
The reason is as follows.

  The raw water or the calcium compound added to the system contains a polyvalent metal such as aluminum as an impurity. This polyvalent metal adheres to the surface of calcium fluoride and causes the growth of calcium fluoride crystals in the first reaction tank 1 and the like. In FIG. 1, the return sludge is mixed with alkali in the sludge adjusting tank 5 to dissolve the aluminum hydroxide on the surface of the calcium fluoride sludge, thereby suppressing the growth inhibition of calcium fluoride crystals in the first reaction tank 1 and the like. To do. For this reason, in the sludge adjusting tank 5, in order to dissolve aluminum hydroxide, alkali is added so that the pH of the treated sludge (alkali sludge) is 7 or more, more preferably 9 or more. The upper limit of the pH of the sludge adjusting tank 5 is not particularly limited, but usually about 13 is sufficient. Since the alkaline agent for pH adjustment can be used together as a calcium compound added to raw water and is economical, it is preferable to use slaked lime.

  Moreover, in FIG. 1, reaction with raw | natural water and a calcium compound is performed with the 1st reaction tank 1 and the 2nd reaction tank 2 which were arrange | positioned in series in two steps, and in the 1st reaction tank 1, the alkali from the sludge adjustment tank 5 is carried out. After adding sludge and a calcium compound and a pH adjuster as necessary to insolubilize most of the fluorine in the raw water, the residual fluorine in the second reaction tank 2 by adding a pH adjuster as necessary Insolubilize.

  It is preferable to adjust the solution pH in the first reaction tank 1 to 3 to 11, particularly 3 to 6. When the pH of the liquid in the first reaction tank 1 is less than 3, the solubility of calcium fluoride is large and the fluoride ion concentration cannot be reduced. When the pH is higher than 11, precipitation of calcium carbonate becomes remarkable, which causes a problem of scale. Arise. In the case of pH 3-6, fluorine ions can be precipitated as calcium fluoride with a small amount of calcium compound added. At that time, the above-mentioned alkaline sludge serves as a nucleus, and calcium fluoride precipitates on the surface. At the same time as the generation of calcium fluoride is suppressed, the calcium fluoride particles grow greatly.

  Moreover, it is preferable to adjust the solution pH in the second reaction tank 2 to 5.8 to 8.6 in consideration of the release of treated water.

  However, the optimum pH of the first reaction tank 1 and the second reaction tank 2 varies depending on the purpose of treatment, and is optimum when the purpose is to prevent the inhibition of aluminum hydroxide and to obtain sludge having a lower water content. The pH is about 7 to 10, and the optimum pH is about 4 to 6.5 for the purpose of enhancing the cohesiveness of sludge and obtaining a higher treated water quality.

  In the present invention, the ionic strength of raw water is measured, and based on this result, the amount of slaked lime added is set, and the amount of slaked lime added to the raw water as alkaline sludge is added to the returned sludge in the sludge adjusting tank 5; The amount of slaked lime added is controlled so that the total amount of slaked lime added in one reaction tank 1 becomes the set amount of slaked lime added.

  In FIG. 1, the conductivity and fluorine ion concentration of raw water introduced into the first reaction tank 1 are measured by a conductivity meter 10 and a fluorine meter 11. This raw water is introduced into the first reaction tank 1, and the alkaline sludge from the sludge adjusting tank 5, and the pH adjusting agent and slaked lime are added as necessary so that the above-mentioned preferable pH and preferable calcium concentration are obtained, and fluorine is fluorinated. Insolubilized as calcium fluoride.

  A pH adjuster is added as necessary so that the effluent of the first reaction tank 1 is then introduced into the second reaction tank 2 and has the above-mentioned preferred pH.

  The effluent from the second reaction tank 2 is introduced into the agglomeration tank 3 and a polymer flocculant is added for agglomeration.

  The polymer flocculant is not particularly limited as long as it is used for the flocculation treatment of suspended wastewater, but a polyacrylic acid-based anionic polymer flocculant can be suitably used. The addition amount is usually about 0.1 to 10 mg / L.

  The agglomerated water in the agglomeration tank 3 is then introduced into the sedimentation tank 4 for solid-liquid separation, and the separated water is discharged out of the system as treated water. A part of the separated sludge is returned to the sludge adjustment tank 5 as return sludge. The remainder is drained out of the system as excess sludge.

  When the amount of sludge returned is excessively large, the processing efficiency is lowered. When the amount is too small, the above-mentioned effect due to returning the sludge cannot be obtained sufficiently. When the fluorine concentration of the raw water is 0.05 to 0.5 times, it is preferably 0.1 to 10 times for dilution.

  In addition, FIG. 1 shows an example of an embodiment of the present invention, and the present invention is not limited to the method of returning sludge, and slaked lime may be added to the second reaction tank. The reaction tank may be one stage. Moreover, what abbreviate | omitted the coagulation tank may be used. Further, as a solid-liquid separation means, a membrane separation apparatus, a membrane immersion tank, or the like may be used in addition to a precipitation tank. Moreover, you may use calcium compounds other than slaked lime as a calcium compound.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

  In all of the following examples and comparative examples, the fluorine concentration is 100 mg / L and the conductivity varies in the range of 20 to 1500 mS / m due to the concentration fluctuation of the coexisting ions by the apparatus shown in FIG. The following water quality electronic industrial wastewater was used as raw water.

<Raw water quality>
Fluorine ion concentration: 100mg / L
Nitrate ion concentration: 10 to 1000 mg / L
Sulfate ion concentration: 30-1500 mg / L
Chloride ion concentration: 1-100 mg / L
Magnesium ion concentration: 100 mg / L or less Conductivity: 20-1500 mS / m

  The capacity of each tank was as follows, the flow rate of raw water was 60 L / hr, and the amount of returned sludge was 12 L / hr.

First reaction tank 1: 20L
Second reaction layer 2: 20 L
Coagulation tank 3: 5L
Sedimentation tank 4: 40L
Sludge adjustment tank 5: 5L

  As a calcium compound, using slaked lime, it added so that the fluorine ion concentration of the 1st reaction tank 1 might be set to 30-50 mg / L so that pH of the sludge adjustment tank 5 might be set to 11.5-12.5. . Moreover, the total amount of the slaked lime addition amount to the sludge adjustment tank 5, the slaked lime addition amount to the 1st reaction tank 1, and the slaked lime addition amount to the 2nd reaction tank 2 set to the 2nd reaction tank 2 is set. The remainder was added to make up the volume. As the pH adjuster, 20 wt% hydrochloric acid or 5 wt% sodium hydroxide aqueous solution was used, the pH of the first reaction tank 1 was 5 ± 0.5, and the pH of the second reaction tank 2 was 7 ± 0.5. The required amount was added so that

  To the aggregating tank 3, 3 mg / L of an anionic polymer aggregating agent (partial hydrolyzate of “Cliff Rock PA331” polyacrylamide manufactured by Kurita Kogyo Co., Ltd.) was added.

  The raw water is first introduced into the first reaction tank 1 and the alkaline sludge from the sludge adjustment tank 5 is added, and slaked lime and a pH adjuster are added and mixed as necessary (residence time 15 minutes), and the first reaction is performed. To the effluent of tank 1, a pH adjuster and, if necessary, slaked lime are added and mixed in the second reaction tank 2 (retention time 15 minutes), and the flocculating agent is added to the effluent of the second reaction tank 2 in the flocculation tank 3. Addition and flocculation treatment, the flocculation treatment liquid in the flocculation tank 3 is solid-liquid separated in the precipitation tank 4 to obtain treated water, and the fluorine concentration of this treated water is measured by ion chromatography. Indicated.

[Example 1]
Measure the conductivity of raw water, and based on the measured value, calculate the amount of slaked lime added by the arithmetic formula obtained from the result of jar test using simulated water prepared in advance with hydrofluoric acid, sulfuric acid, nitric acid, etc. And based on this result, the amount of slaked lime added was controlled.

[Comparative Example 1]
Slaked lime was used as a quantitative addition of 305 mg-Ca / L to the raw water so that the residual calcium ion concentration of the treated water was constant at about 200 mg / L.

[Comparative Example 2]
Slaked lime was added in a fixed amount of 1105 mg-Ca / L to the raw water so that the residual calcium ion concentration of the treated water was constant at about 1000 mg / L.

From Table 2, the following is clear.
In Comparative Example 1 in which the amount of slaked lime added is constant at 305 mg-Ca / L so that the residual calcium ion concentration of the treated water is constant at about 200 mg / L, the fluorine concentration of the treated water during the period when the ionic strength of the raw water is high The wastewater standard fluorine concentration does not satisfy 8 mg / L or less.
In Comparative Example 2 in which the amount of slaked lime added was constant at 1105 mg-Ca / L so that the residual calcium ion concentration was constant at about 1000 mg / L, the effluent reference fluorine concentration was 8 mg / liter even during the period when the ionic strength of the raw water was high. Although L or less is satisfied, the amount of slaked lime added is enormous and the processing cost is high.

  In contrast, in Example 1 in which the amount of slaked lime added was controlled based on the ionic strength of the raw water, it was possible to stably obtain treated water having a drainage standard fluorine concentration of 8 mg / L or less while suppressing an increase in the amount of slaked lime added. Can do.

It is a systematic diagram which shows embodiment of the processing apparatus of the fluorine-containing water of this invention. (A) is a graph showing the relationship between ionic strength and electrical conductivity, and (b) is a graph showing the relationship between fluorine concentration and electrical conductivity. It is a graph which shows the relationship between ionic strength and reaction rate.

DESCRIPTION OF SYMBOLS 1 1st reaction tank 2 2nd reaction tank 3 Coagulation tank 4 Precipitation tank 5 Sludge adjustment tank 10 Conductivity meter 11 Fluorine meter

Claims (6)

A method of solid-liquid separation of fluorine as calcium fluoride by adding a calcium compound to fluorine-containing water, measuring the ionic strength of the fluorine-containing water , and based on the measured value, the ionic strength of the fluorine-containing water The method for treating fluorine-containing water is characterized in that the amount of calcium compound added to the fluorine-containing water is controlled so that the residual calcium ion concentration in the treated water increases as the measured value increases . Oite to claim 1, the processing method of the fluorine-containing water and measuring the conductivity meter ionic strength of the fluorine-containing water. 3. The method for treating fluorine-containing water according to claim 1, wherein the fluorine-containing water contains nitrate ions, sulfate ions, and chloride ions, and the magnesium ion content is less than 2000 mg / L. In a fluorine-containing water treatment apparatus comprising calcium compound addition means for adding a calcium compound to fluorine-containing water, and means for solid-liquid separation of calcium fluoride precipitated by the reaction of fluorine and calcium compound in fluorine-containing water.
Ionic strength measuring means for measuring the ionic strength of the fluorine-containing water;
Based on the measured value of the ionic strength measuring means, the calcium compound addition amount of the calcium compound adding means is controlled so that the larger the measured value of the ionic strength measuring means, the higher the residual calcium ion concentration of the treated water becomes. An apparatus for treating fluorine-containing water, comprising a control means. 5. The apparatus for treating fluorine-containing water according to claim 4 , wherein the ionic strength measuring means is a conductivity meter. 6. The treatment apparatus for fluorine-containing water according to claim 4 , wherein the fluorine-containing water contains nitrate ions, sulfate ions, and chloride ions, and the magnesium ion content is less than 2000 mg / L.

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