JP2014200743A - Method of treating waste liquid containing boron fluoride ion and apparatus of treating waste liquid containing boron fluoride ion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of treating a waste liquid containing boron fluoride ions capable of effectively treating a waste liquid containing boron fluoride ions.SOLUTION: There is provided a method of treating a waste liquid containing boron fluoride ions, the method comprising: a decomposition step of decomposing boron fluoride ions by adding an aluminum compound to the waste liquid containing boron fluoride ions; a solidification step of solidifying the boron fluoride ions by adding a calcium compound to decomposition treatment water containing boron fluoride ions generated in the decomposition step; and a solid-liquid separation step of solid-liquid separating a sludge generated in the solidification step. The decomposition step comprises: a first decomposition step of performing reaction at a pH of 2 or more; and a second decomposition step of reacting the first decomposition treatment water obtained in the first decomposition step at a pH of 2 to 4.

Description

  The present invention relates to a method for treating borofluoride ion-containing wastewater and a treatment apparatus for borofluoride ion-containing wastewater.

  As a method for treating wastewater containing borofluoride ions, a method has been proposed in which an aluminum compound is added and heated to decompose borofluoride ions at pH 5 or lower.

  For example, in Patent Document 1, aluminum hydroxide is added to a waste liquid containing borofluoride adjusted to pH 5 or lower, and reacted in a temperature range of 20 to 100 ° C. to decompose the borofluoride into boric acid and aluminum fluoride. Then, a method is described in which a calcium compound is added to the treatment liquid to fix aluminum fluoride as calcium fluoride.

In Patent Document 2, raw water is heated to 60 ° C. or higher, and Al ₂ (SO ₄ ) ₃ is added to thermally decompose borofluoride in an acidic region of pH ₂ to 4, and the pH is increased to the alkali side with Ca (OH) _2. Adjust to decompose fluoride, cool to 40 ° C. or lower, add a flocculant to cause the first stage of precipitation, separate the supernatant, and then add Al ₂ (SO _{2) to the} supernatant at room temperature. ₄ ) A method is described in which ₃ and Ca (OH) ₂ are added, a flocculant is further added to cause the second stage of precipitation, and this operation is repeated a plurality of times.

  In Patent Document 3, polyvalent metal ions are added to a waste liquid containing borofluoride ions at a pH of 3 or less, heated to 35 ° C. or more to decompose the borofluoride ions into boron ions and fluorine ions, and then added with slaked lime to a pH of 10 A method is described in which fluorine ions are insolubilized with calcium fluoride, cooled to 35 ° C. or lower, aluminum sulfate is added as a flocculant, and the resulting aggregate is filtered off.

  In Patent Document 4, an aluminum compound is added to borofluoride-containing water, a first step of decomposing borofluoride at pH 2 to 4, a calcium compound is added to treat fluorine generated by decomposition, and pH 9 to 10 And a third step of adding an aluminum salt to the liquid obtained by solid-liquid separation to obtain a porcelain containing aluminum by solid-liquid separation at pH 6-7, and a third step The method of using the residue containing aluminum obtained in step 1 as an aluminum compound for the decomposition of borofluoride-containing water in the first step is described.

  The reaction rate of breaking borofluoride ions into fluorine and boron is very slow, so in order to obtain treated water that can meet the discharge standard, a large amount of aluminum compound is added, or excessive energy is used for heating. Therefore, it was necessary to adopt a method for increasing the reaction rate.

Japanese Patent Publication No.54-005628 Japanese Patent Publication No. 5-051359 Japanese Patent No. 4338705 Japanese Patent No. 4954131

  The objective of this invention is providing the processing method and processing apparatus of the wastewater containing a borofluoride ion which can process the wastewater containing a borofluoride ion efficiently.

  The present invention adds an aluminum compound to waste water containing borofluoride ions, decomposes the borofluoride ions, adds a calcium compound to the decomposition treated water containing fluoride ions generated in the decomposition step, A solidification step for solidifying fluoride ions, and a solid-liquid separation step for solid-liquid separation of the sludge generated in the solidification step, wherein the decomposition step is a first decomposition step for reacting at pH 2 or lower, And a second decomposition step in which the first decomposition treatment water obtained in the first decomposition step is further reacted at a pH of 2 to 4.

  Further, in the treatment method of the borofluoride ion-containing wastewater, the wastewater further contains fluoride ions, a calcium compound is added to the wastewater containing the borofluoride ions and fluoride ions, and the fluoride ions are solidified. It is preferable to carry out treatment with borofluoride ions after conversion.

  The borofluoride ion-containing wastewater treatment method preferably further includes a return step of returning at least part of the sludge solid-liquid separated in the solid-liquid separation step to the second decomposition step.

  In the present invention, an aluminum compound is added to waste water containing borofluoride ions, a decomposition means for decomposing the borofluoride ions, and a calcium compound is added to decomposition water containing fluoride ions generated by the decomposition means. And a solidification means for solidifying the fluoride ions, and a solid-liquid separation means for solid-liquid separation of the sludge generated by the solidification means, wherein the decomposition means is a first decomposition means for reacting at a pH of 2 or less. And a second decomposition means for further reacting the first decomposition treated water obtained in the first decomposition step at a pH of 2 to 4, and a borofluoride ion-containing wastewater treatment apparatus.

  Further, in the borofluoride ion-containing wastewater treatment apparatus, the wastewater further contains fluoride ions, a calcium compound is added to the wastewater containing the borofluoride ions and fluoride ions, and the fluoride ions are solidified. It is preferable to carry out treatment with borofluoride ions after conversion.

  The borofluoride ion-containing wastewater treatment apparatus preferably further comprises a return means for returning at least a part of the sludge separated by solid-liquid separation in the solid-liquid separation means to the second decomposition means.

  In the present invention, the borofluoride is efficiently produced by making the decomposition step of decomposing borofluoride ions into a two-step reaction of a first decomposition step of reacting at pH 2 or lower and a second decomposition step of further reacting at pH 2-4. A borofluoride ion-containing wastewater treatment method and treatment apparatus capable of treating wastewater containing ions can be provided.

It is a schematic block diagram which shows an example of the processing apparatus of the borofluoride ion containing waste_water | drain which concerns on embodiment of this invention. It is a schematic block diagram which shows the other example of the processing apparatus of the borofluoride ion containing waste_water | drain which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  The outline of an example of the borofluoride ion containing waste water treatment equipment concerning the embodiment of the present invention is shown in Drawing 1, and the composition is explained. The waste water treatment apparatus 1 includes a first decomposition tank 10 and a second decomposition tank 12 as decomposition means, a solidification tank 14 as solidification means, and a precipitation tank 16 as solid-liquid separation means.

  1, the raw water pipe 18 is connected to the inlet of the first decomposition tank 10, and the outlet of the first decomposition tank 10 and the inlet of the second decomposition tank 12 are connected by the first decomposition water pipe 20. The outlet of the second decomposition tank 12 and the inlet of the solidification tank 14 are connected by a second decomposition water pipe 22, and the outlet of the solidification tank 14 and the inlet of the precipitation tank 16 are connected by a solidification water pipe 24. A treated water pipe 26 is connected to the upper outlet of the sedimentation tank 16. The first decomposition tank 10, the second decomposition tank 12, and the solidification tank 14 may be provided with stirring devices 28, 30, and 32 having stirring blades as stirring means.

  An operation of the borofluoride ion-containing wastewater treatment method and wastewater treatment apparatus 1 according to this embodiment will be described.

Borofluoride ion-containing wastewater containing borofluoride ions (BF ⁴⁻ ), which is raw water, is sent to the first decomposition tank 10 through the raw water pipe 18, and an aluminum compound is added in the first decomposition tank 10 to contain borofluoride ions. A decomposition reaction in which borofluoride ions contained in the waste water are decomposed into boron ions and fluoride ions is performed at a pH of 2 or less (first decomposition step). In the first decomposition tank 10, the contents may be stirred by the stirring device 28.

  The first decomposition treated water decomposed in the first decomposition step is sent to the second decomposition tank 12 through the first decomposition treated water pipe 20, and further decomposed at pH 2 to 4 in the second decomposition tank 12. (Second decomposition step). In the second decomposition tank 12, the contents may be stirred by the stirring device 30.

The second decomposition treated water containing fluoride ions generated through the first decomposition step and the second decomposition step (sometimes referred to as “decomposition step” together) passes through the second decomposition treatment water pipe 22. The solution is fed to the solidification tank 14, and a calcium compound is added in the solidification tank 14, and fluoride ions are solidified to produce sludge containing calcium fluoride (CaF ₂ ) (solidification step). In the solidification tank 14, the contents may be stirred by the stirring device 32.

  The solidified treated water containing the sludge generated in the solidification step is sent to the precipitation tank 16 through the solidified treatment water pipe 24 and is solid-liquid separated by sedimentation separation or the like in the precipitation tank 16 (solid-liquid separation step). The treated water subjected to the solid-liquid separation is discharged from the upper outlet of the sedimentation tank 16 through the treated water pipe 26. On the other hand, the sludge separated into solid and liquid is discharged from the lower outlet of the settling tank 16.

  In the borofluoride ion-containing wastewater treatment method and treatment apparatus according to the present embodiment, the borofluoride ion decomposition tank is multi-staged, first reacted at pH 2 or lower, and then reacted at pH 2 to 4 for particularly warming. Even if it is not, the quality of the treated water that can satisfy the discharge standard can be obtained in a reaction time of several hours, for example. The concentration of borofluoride ions can be effectively reduced rather than simply reacting under a certain condition of pH 5 or lower.

  The reason for this is not clear, but by first reacting at a low pH of 2 or less, the reaction between the borofluoride ion and the aluminum compound is efficiently carried out under conditions where the influence of the inhibitor is small. As the decomposition reaction proceeds, the fluoride ion concentration increases, and it is considered that the decomposition efficiency of borofluoride ions decreases.

Moreover, the waste water discharged | emitted from the grinding | polishing process etc. of liquid product glass may contain silicofluoride, aluminum, etc. other than a borofluoride ion. In the case of such wastewater, since complex ions such as SiF ₆ ²⁻ , AlF ₆ ^3−, and AlF ₆ ³⁻ progress around pH ²⁻⁴ , borofluoride ions are simply decomposed within this range. Decomposition efficiency may decrease. First, borofluoride ions are decomposed at a pH of 2 or less at which complex ions are difficult to be generated, and the borofluoride ions may be efficiently decomposed by raising the pH after reducing the borofluoride ion concentration to some extent. .

  The pH in the first decomposition step is 2 or less, preferably in the range of 0.5-2. If the pH in the first decomposition step exceeds 2, the decomposition efficiency of borofluoride ions will deteriorate.

  The pH in the second decomposition step is in the range of 2 to 4 and preferably in the range of 2 to 3. When the pH in the second decomposition step is less than 2 or exceeds 4, the decomposition efficiency of borofluoride ions is deteriorated.

  The acid used for pH adjustment is not particularly limited, and examples thereof include hydrochloric acid, sulfuric acid, and nitric acid. The alkali is not particularly limited, and examples thereof include calcium hydroxide and sodium hydroxide.

When the raw water also contains fluoride ions in advance, such as polishing wastewater for liquid glass, the fluoride ions inhibit the decomposition of the borofluoride ions, so the calcium compound is added in the previous stage to produce CaF ₂ and solidify it. Therefore, the borofluoride ion decomposition treatment after the first decomposition step is preferably performed. This CaF ₂ may be separated by solid-liquid separation, or may be allowed to flow into the first decomposition tank 10 as it is.

In this case, first, the reaction is carried out at a low pH of 2 or less, and the wastewater in which some of the borofluoride ions are decomposed is further reacted at pH 2 to 4, whereby F in which the borofluoride ions are decomposed reacts with Ca in the liquid. Then, when an appropriate amount of CaF ₂ is generated, the fluoride ion concentration is decreased, and the fine CaF ₂ particles are used as nuclei to promote the generation of CaF ₂ , thereby increasing the decomposition rate of borofluoride. Conceivable.

When the pH is 2 or less, because the high solubility of CaF _2, CaF ₂ is hardly generated, and because the decomposition efficiency is the fluoroborate hydride ion at pH4 or falls remarkably, it is a range of pH2~4 .

  The concentration of borofluoride ions in the borofluoride ion-containing wastewater to be treated is not particularly limited, but is, for example, in the range of 10 mg / L to 10000 mg / L.

  Examples of the aluminum compound used in the decomposition step include aluminum salts such as polyaluminum chloride (PAC), aluminum chloride, and aluminum sulfate.

  The amount of aluminum compound added in the decomposition step is, for example, in the range of 3 mol to 10 mol as aluminum with respect to 1 mol of borofluoride ions in the borofluoride ion-containing wastewater to be treated. When the addition amount of the aluminum compound is less than 3 mol per mol of the borofluoride ion, the decomposition rate may be remarkably reduced, and when it exceeds 10 mol, the cost may be disadvantageous.

  Although the reaction temperature in a decomposition process does not have a restriction | limiting in particular, For example, it is the range of 10 to 30 degreeC. If the reaction temperature is less than 10 ° C, the decomposition rate may be remarkably reduced, and if it exceeds 30 ° C, heating is required, which may be disadvantageous in terms of cost.

  Examples of the calcium compound used in the solidification step include calcium salts such as calcium hydroxide, calcium carbonate, and calcium chloride, and calcium hydroxide is preferable from the viewpoint of cost.

  The addition amount of the calcium compound in the solidifying step is, for example, in the range of 2 mol to 2.5 mol with respect to 1 mol of borofluoride ions in the borofluoride ion-containing wastewater to be treated. When the amount of calcium compound added is less than 2 moles per mole of borofluoride ions, fluorine may not be solidified sufficiently, and when it exceeds 2.5 moles, the cost may be disadvantageous. There is.

  Although the reaction temperature in a solidification process does not have a restriction | limiting in particular, For example, it is the range of 10 to 30 degreeC.

  The reaction pH in the solidification step is preferably in the range of 7-9. If the reaction pH in the solidification step is less than 7, the solidification reaction may be inhibited. If it exceeds 9, the cost may be disadvantageous.

  The separation method in the solid-liquid separation step is not particularly limited, and examples thereof include sedimentation separation by natural sedimentation, pressurized flotation, membrane separation and the like, and sedimentation separation is preferable from the viewpoint of cost.

  The schematic structure of the other example of the borofluoride ion containing waste water treatment equipment which concerns on embodiment of this invention is shown in FIG. In the waste water treatment apparatus 3, in addition to the configuration of FIG. 1, the lower outlet of the sedimentation tank 16 and the second decomposition tank 12 are connected by a return pipe 34 as return means.

At least a part of the solid-liquid separated sludge is returned to the second decomposition tank 12 through the return pipe 34 (return process). By returning sludge produced in the solid-liquid separation step and containing CaF ₂ to the second decomposition step, it is considered that an appropriate amount of CaF ₂ can be present in the system and the effect of promoting the decomposition of borofluoride ions can be obtained. It is done.

  The return amount in the return step is, for example, in the range of 5 to 30% by mass in the sludge that has settled and separated. If the return amount is less than 5% by mass, the return amount may be insufficient and the decomposition efficiency may be reduced. If it exceeds 30% by mass, mechanical problems such as blockage of piping may occur.

  The treatment method and treatment device for borofluoride ion-containing wastewater according to the present embodiment are, for example, treatment of borofluoride ion-containing wastewater discharged from flue gas desulfurization equipment, borofluoride ion-containing wastewater discharged from a glass etching step, and the like. It can be suitably applied to.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

<Examples 1-8, Comparative Examples 1-6>
Using the processing apparatus shown in FIG. 2, borofluoride ions: 200 mg / L, fluoride ions: 2000 mg / L, and pH 2 glass etching wastewater, calcium hydroxide (Ca (OH) ₂ ) as a calcium compound in advance to 5000 mg / L was added, reacted at pH 9 for 10 minutes to solidify fluoride ions, and the supernatant liquid after stationary precipitation was used as raw water for the experiment under the following conditions.

[Raw water concentration]
Boron fluoride ion: 200 mg / L
Fluoride ion: 15mg / L
pH 7

[Experimental conditions]
(1) First decomposition step Aluminum compound to be added: 10% polyaluminum chloride (PAC) aqueous solution Addition amount of aluminum compound: 8000 mg / L
Reaction pH: as shown in Table 1 (adjusted to a predetermined pH with hydrochloric acid)
Flow rate: 1L / h
Reaction temperature: 20 ° C
Residence time: 4 hours (2) Second decomposition step Reaction pH: As shown in Table 1 (adjusted to a predetermined pH with hydrochloric acid)
Flow rate: 1L / h
Reaction temperature: 20 ° C
Residence time: 4 hours (3) Solidification step Calcium compound to be added: Calcium hydroxide (Ca (OH) ₂ )
Reaction pH 9
Reaction temperature: 20 ° C
Residence time: 60 minutes (4) Solid-liquid separation step Solid-liquid separation method: Sedimentation separation pH 7
(5) Return process Presence / absence of return: as shown in Table 1 Return amount: 30% by mass

  About Examples 1-8 and Comparative Examples 1-6, the total fluorine density | concentration (total F) of the obtained treated water was measured using the total-fluorine measuring apparatus (Auto AnalyzerIII, BRAN + LUEBBE product). The results are shown in Table 1. The total fluorine concentration of the treated water is the total value of fluorine of borofluoride ions and fluorine of fluoride ions.

  Thus, the borofluoride ions are efficiently produced by the two-step reaction of the decomposition step for decomposing borofluoride ions at a pH of 2 or less and the second decomposition step for further reaction at pH 2-4. It was possible to treat wastewater containing. Moreover, waste water containing borofluoride ions could be treated more efficiently by returning at least a part of the sludge separated into solid and liquid to the second decomposition step.

  1,3 Wastewater treatment equipment, 10 First decomposition tank, 12 Second decomposition tank, 14 Solidification tank, 16 Precipitation tank, 18 Raw water pipe, 20 First decomposition water pipe, 22 Second decomposition water pipe, 24 Solid Treated water piping, 26 treated water piping, 28, 30, 32 agitator, 34 return piping.

Claims (6)

A decomposition step of adding an aluminum compound to waste water containing borofluoride ions and decomposing the borofluoride ions;
A solidification step of solidifying the fluoride ions by adding a calcium compound to the decomposition-treated water containing fluoride ions generated in the decomposition step;
A solid-liquid separation step for solid-liquid separation of the sludge produced in the solidification step;
Including
The decomposition step includes a first decomposition step for reacting at a pH of 2 or less, and a second decomposition step for further reacting the first decomposition treated water obtained in the first decomposition step at a pH of 2 to 4. To treat wastewater containing borofluoride ions. A method for treating borofluoride ion-containing wastewater according to claim 1,
The waste water further contains fluoride ions;
Treatment of borofluoride ion-containing wastewater characterized by adding a calcium compound to the wastewater containing borofluoride ions and fluoride ions, solidifying the fluoride ions, and then treating the borofluoride ions Method. A method for treating borofluoride ion-containing wastewater according to claim 1 or 2,
A method for treating borofluoride ion-containing wastewater, further comprising a returning step of returning at least a part of the sludge separated in the solid-liquid separation step to the second decomposition step. A decomposition means for adding an aluminum compound to wastewater containing borofluoride ions and decomposing the borofluoride ions;
A solidifying means for solidifying the fluoride ions by adding a calcium compound to the decomposition treated water containing fluoride ions generated by the decomposition means;
Solid-liquid separation means for solid-liquid separation of the sludge produced by the solidification means;
With
The decomposing means comprises first decomposing means for reacting at a pH of 2 or less, and second decomposing means for further reacting the first decomposing water obtained in the first decomposing step at pH 2 to 4. Wastewater treatment equipment containing borofluoride ions. A treatment apparatus for borofluoride ion-containing wastewater according to claim 4,
The waste water further contains fluoride ions;
Treatment of borofluoride ion-containing wastewater characterized by adding a calcium compound to the wastewater containing borofluoride ions and fluoride ions, solidifying the fluoride ions, and then treating the borofluoride ions apparatus. A treatment apparatus for borofluoride ion-containing wastewater according to claim 4 or 5,
An apparatus for treating borofluoride ion-containing wastewater, further comprising a return means for returning at least a part of the sludge solid-liquid separated in the solid-liquid separation means to the second decomposition means.

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