JP3489650B2 - Treatment method of boron-containing wastewater - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating boron-containing wastewater produced during treatment of exhaust gas during coal combustion.

[0002]

2. Description of the Related Art In many cases, a coal-fired power plant has reached an agreement with local residents to meet high environmental standards as a condition for its installation. Therefore, although there is no national regulation on boron at present, it may be subject to regulation because boron is known to cause plant growth disorders. BACKGROUND ART Conventionally, as a method for treating boron-containing wastewater that is discharged during exhaust gas treatment during coal combustion, a method is known in which boron is removed through the entire amount of boron-containing wastewater through a boron-selective ion exchange resin. Then, in this case, the regeneration operation is performed due to the deterioration of the capacity of the boron-selective ion exchange resin, but since the regeneration waste liquid contains concentrated boron,
Naturally, the recycled waste liquid cannot be discharged, and it is temporarily stored in a tank and subjected to heat treatment such as concentration.

Further, boron is extracted from a boron-containing wastewater by using a mixture of diols such as 2-butyl-2-ethyl-1,3-propanediol as an extractant and 2-ethylhexanol as an organic solvent, and the normal extraction is performed. It has already been announced that the extracted oil phase is back-extracted with sodium hydroxide and recovered as sodium borate.

[0004]

However, in the above-mentioned conventional method, the entire amount of the boron-containing wastewater is passed through the boron-selective ion exchange resin to remove boron, so that the equipment becomes huge and the boron-selective ion exchange is often performed. It is necessary to regenerate the resin. Further, heat treatment of the recycled waste liquid of the boron-selective ion-exchange resin is not sufficient even at a power plant at the present time when the heat utilization efficiency is advanced. Further, for example, even if boron is extracted from the recycled waste liquid with the above-mentioned extractant and organic solvent, the extraction rate is 90% at the maximum, so if the boron concentration of the recycled waste liquid is 200 mg / l, after the treatment, Concentration of Boron in Recycled Wastewater of 20mg
It becomes / l, and it is not possible to clear the ultimate standard value (for example, 2 mg / l of boron), and it cannot be discharged.
If you try to clear the standard value by calculating backward from the extraction rate,
The boron concentration in the recycled waste liquid is up to 10 mg / l, which is far from the actual boron concentration in the recycled waste liquid.

In the method disclosed above, the boron-containing wastewater is directly forward-extracted with a mixture of the above-mentioned extractant and an organic solvent, and the oil phase component thus forward-extracted is back-extracted with sodium hydroxide. Although it is excellent that boron can be recovered, the treatment liquid obtained by the forward extraction cannot be discharged for the same reason as above, and with sodium hydroxide, it is difficult to maintain the concentration because the optimum concentration range at the time of the back extraction is narrow. There is a problem.

Therefore, the problem to be solved by the present invention is to make it possible to discharge the treatment liquid after the forward extraction, to facilitate the back extraction of the boron recovery, and also to simplify the boron selective ion exchange resin equipment. It is an object of the present invention to provide a method for treating boron-containing wastewater, which reduces the number of regeneration treatments and facilitates the treatment of regeneration wastewater.

[0007]

Under such circumstances, the present inventor has conducted diligent studies, and as a result, not only regeneration waste liquid of boron-selective ion-exchange resin but also boron-containing waste water was treated with diols as an extractant, and 2- It can be directly extracted with a mixture of ethylhexanol as an organic solvent, and its oil phase can be back-extracted and recovered as potassium borate by alkali, especially potassium hydroxide that can maintain a high back-extraction rate in a wide concentration range. Then, they have found that the mixture of the above-mentioned extractant and organic solvent after recovery can be reused, and completed the present invention.

That is, according to the first aspect of the invention, the step of positively extracting boron contained in the wastewater with a mixture of diols and an organic solvent, and then the treatment liquid obtained by the forward extraction is subjected to boron-selective ion exchange. It is a method for treating boron-containing wastewater, which comprises the step of treating with a resin.
As a result, the oil phase containing boron transferred to the mixture in the forward extraction step is separated into the treatment liquid from which most of the boron contained in the wastewater is removed, reducing the load in the next step and containing the remaining boron. The treatment liquid can be finished by a boron-selective ion-exchange resin treatment step to remove boron up to the discharge standard.

Here, the normal extraction means that boron is transferred from the boron-containing wastewater and the regeneration waste liquid of the boron-selective ion exchange resin to a mixture of diols and an organic solvent. Back extraction refers to transferring boron extracted in a mixture of diols and an organic solvent to an alkaline agent. The oil phase component means a mixture of diols containing boron and an organic solvent.

The origin and concentration of the boron contained in the wastewater are not particularly limited, but in the case of the boron-containing wastewater discharged during the treatment of exhaust gas during coal combustion, the boron content varies depending on the quality of the coal, and the boron content is usually Several mg / l to several hundred mg
In the case of the recycling waste liquid of the boron-selective ion exchange resin, the content of boron is several thousand mg / l.

The diols used in the present invention include 2-butyl-2-ethyl-1,3-propanediol (hereinafter referred to as BEPD).
Or 2-ethyl-1,3-hexanediol (hereinafter E
(Referred to as HD) is preferably used, and of these, BEPD is preferable because of its high extraction rate. The concentration of the extractant with respect to the organic solvent is not particularly limited, but an emulsification phenomenon occurs at a high concentration close to the saturation solubility, and therefore it is preferable to use at a concentration lower than this. Specifically, for example, when the boric acid concentration is 0.03 kmol / m ³ , 2
The range of ˜3 kmol / is preferable because an extraction rate of about 90% can be obtained. Further, the water temperature at the time of normal extraction is in the range of 10 to 50 ° C, but when the water temperature is high, the separation of the oil phase component and the treatment liquid is poor, and the oil phase component is dissolved in the treatment liquid to cause COD. From this, preferably 10 to 30
It is in the range of ° C.

The organic solvent dissolves BEPD and EHD which are extractants, and is not particularly limited, but 2-ethylhexanol (hereinafter referred to as EHA), octanol (hereinafter referred to as OCA), and kerosene can be used. The relationship between the extraction rate and the number of extractions in these various organic solvents is shown in FIG. 1, which shows that EHA is good. The mixing ratio of the extractant and the organic solvent is not particularly limited, but it can be used in a wide range of 10:90 to 90:10,
It is particularly preferably 50:50.

Further, the boron-selective ion exchange resin used in the present invention is, for example, n-type after chloromethylating a matrix or the like obtained by copolymerizing styrene-divinylbenzene.
It is a compound bound to a polyhydric alcohol compound such as methyl-glucamine and has the basic structure shown below.

[0014]

[Chemical 1]

Boron in water usually exists as borate ion, but borate ion utilizes the above-mentioned reaction of polyhydric alcohol compound such as mannite, and n-methyl-glucamine constituting an exchange group. By reacting with borate ion, boron is adsorbed. Moreover, since this reaction selectively proceeds, a small amount of boron can be selectively removed from water having a very high concentration of coexisting salts such as seawater. The method of using this boron-selective ion-exchange resin is to fill the column in the same way as a normal ion-exchange resin, and pass the boron-containing wastewater through it, or add this resin to the boron-containing wastewater to carry out a batch reaction. By adsorbing, boron is adsorbed. As the boron-selective ion exchange resin, Amberlite (registered trademark) IRA-74 is used.
There is 3T.

A second aspect of the present invention is a method for treating boron-containing wastewater, characterized in that the recycled waste liquid of the boron-selective ion exchange resin is returned to the normal extraction step. The boron-selective ion-exchange resin, after reaching the adsorption limit of boron, is contacted with a mineral acid such as sulfuric acid or hydrochloric acid or an alkali as a regenerant, so that the boron is desorbed and the boron in the wastewater is selectively removed again. You will be able to remove it. From the viewpoint of desorption effect of boron, it is preferable to use sulfuric acid because mineral acid is superior to alkali, does not generate corrosive gas, and is inexpensive. This recycled waste liquid is concentrated boron (several thousand mg /
Since it contains l), it is returned to the forward extraction step to remove most of the concentrated boron.

According to a third aspect of the present invention, the step of positively extracting boron contained in the wastewater with a mixture of diols and an organic solvent soluble in them, and then the positively extracted oil phase component is dissolved in a potassium hydroxide solution. The method for treating boron-containing wastewater is characterized by comprising the step of back-extracting with. When the solution of the alkaline agent as the back extractor is added to the oil phase component from which the boron has been positively extracted, the boron shifts to the solution of the alkaline agent.
Examples of the alkaline agent include sodium hydroxide and ammonia in addition to potassium hydroxide. Fig. 2 shows the relationship between the concentration of the alkaline agent and the back extraction rate of boron in these oil phase components.
Shown in. According to FIG. 2, it is preferable to use potassium hydroxide as the back-extracting agent, because the optimal back-extraction rate does not change with changes in concentration in the order of potassium hydroxide>ammonia> sodium hydroxide.

A fourth aspect of the present invention is the method for treating boron-containing wastewater, wherein the potassium hydroxide solution containing potassium borate obtained by the back extraction is returned to the back extraction step again. That is, since potassium borate obtained by back extraction still contains potassium hydroxide that can be sufficiently back extracted, it is possible to increase the concentration of potassium borate by circulating it back into the back extraction step. ,
It is also possible to take out as crystals.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a method of treating boron-containing wastewater will be described with reference to the flowchart of FIG. Boron-containing wastewater of various origins such as exhaust gas treatment during coal combustion is once received in the wastewater storage tank 2 from the line 1 and the downstream load is adjusted. The boron-containing wastewater is sent from the wastewater storage tank 2 to the normal extraction tank 4 via the line 3, the boron concentration and the flow rate are measured at that time, and sent to the operation management device. At the same time, based on the boron concentration and flow rate measured in line 3, B
The required amount of the mixture is sent from the mixture storage tank 5 of EPD and EHA to the positive extraction tank 4 through the line 6, and the boron-containing wastewater and the mixture are mixed by stirring. By such an operation, boron is positively extracted into the mixture, and when left still, the liquid in the normal extraction tank 4 is separated into two layers. About 90% of boron in the boron-containing wastewater was transferred to the mixture in the upper layer liquid, that is, an oil phase component, and the remaining lower layer liquid was about 1%.
It is a treatment liquid containing 0% of boron.

The treatment liquid of the lower layer is sent to a boron-selective ion-exchange resin packed column 8 using Amberlite IRA-743T in line 7, and the boron concentration is measured at that time.
Sent to the operation management device, until the operation set value of the packed tower 8, for example, boron concentration (mg / l) × processing double amount (liquid passing amount l / boron selective ion exchange resin amount l) = about 1600, The flow rate of the processing liquid is automatically controlled. Since the treatment liquid is treated to have a boron concentration of 1 mg or less while passing through the boron-selective ion-exchange resin packed tower 8, the boron can be discharged as it is to the public water area through the line 9 (see Example 1). Here, since the boron-selective ion exchange resin has a low boron concentration in the treatment liquid, the adsorption limit of boron is reached by continuing to pass the treatment liquid.
When sulfuric acid is sent from the line 19 to the boron-selective ion-exchange resin packed column 8 and brought into contact therewith, most of the boron is desorbed from the boron-selective ion-exchange resin to produce a recycled waste liquid containing concentrated boron. Since the pH of the regenerated waste liquid is low, the regenerated waste liquid is neutralized and returned to the waste water storage tank 2 through the line 20 branched from the line 9.

The oil phase component in the upper layer of the normal extraction tank 4 is sent to the back extraction tank 11 through the line 10, and at the same time, the back extraction tank 11 is fed.
The potassium extract solution, which is a back extractant, is sent through the line 13 from the alkaline storage tank 12 so that the necessary amount of the solution is controlled so that the internal pH is maintained at pH 8 to 13, preferably pH 10 to 11. When the oil phase component and the potassium hydroxide solution are mixed by stirring in the back extraction tank 11 and the boron is back extracted into the potassium hydroxide solution and left to stand, the back extraction tank 11
Is separated into two layers. The upper layer liquid is a back-extracted oil phase component containing almost no boron, that is, a mixture of BEPD and EHA, and the lower layer liquid is a potassium hydroxide solution containing a large amount of potassium borate.

The upper layer mixture of BEPD and EHA is
The potassium hydroxide solution containing a large amount of potassium borate, which is the lower layer liquid, is sent to the mixture storage tank 5 through the line 14 for circulation and is sent to the boron recovery tank 16 through the line 15. When the lower layer solution contains a large amount of potassium borate, but contains potassium hydroxide that can be sufficiently back-extracted, it is returned to the back-extraction tank 11 through the line 17.
That is, by circulating and using the lower layer liquid, the contained potassium borate can be gradually concentrated to a high concentration, and the load in the case of drying treatment can be reduced.

Example 1 1 l of boron-containing wastewater having a boron concentration of 77.8 mg / l was added to B
A mixture of EPD and EHA in a weight ratio of 18.5: 81.5 was added to a mixture having a volume of 3 l, 2 l, 1 l, 0.5 l,
Positive extraction was performed while changing the amount to 0.33 l, and the boron concentration of the treatment liquid was measured. The results are shown in Table 1. From Table 1, the larger the amount of the mixture with respect to the amount of the waste water containing boron, the lower the boron concentration of the treatment liquid, that is, the higher the extraction rate tends to be.

[0024]

[Table 1]

Next, using a treatment liquid (boron concentration: 13.3 mg / l) when the mixture was 2 liters, the mixture was treated with a boron-selective ion exchange resin at SV = 10 and the boron concentration after the treatment was measured. As a result, it became 1 mg / l or less. The processing magnification at this time is 108 to 122 l / l −R, and the operation set value is 13.3 × (108 to 122) = 14.
It became 40-1620.

Although the embodiment of the present invention has been described above, the specific configuration is not limited to this, and modifications and additions within the scope of the present invention are within the scope of the present invention.

[0027]

As described in detail above, according to the invention of claim 1, an oil phase component containing boron transferred to the mixture in the forward extraction step, and a treatment liquid from which most of the boron contained in the wastewater has been removed. The treatment liquid containing the remaining boron is finished in a boron-selective ion-exchange resin treatment process to remove boron up to the discharge standard. Therefore, the facility for boron-selective ion exchange resin can be simplified, the number of times of the regeneration treatment can be reduced, and the treatment of the waste liquid for regeneration can be facilitated.

According to the second aspect of the present invention, after the boron-selective ion exchange resin reaches the adsorption limit of boron, when a mineral acid or an alkali is brought into contact as a regenerant, the boron is desorbed and the boron is selectively reselective. Since this recycled waste liquid contains concentrated boron, most of the concentrated boron is removed by returning to the normal extraction step, and then the treatment liquid is passed through the boron-selective ion exchange resin again. Therefore, it is easier to process the recycled waste liquid as compared with the conventional dry disposal.

According to the third aspect of the present invention, with respect to the oil phase component which is normally extracted and incorporates boron, the optimum back extraction rate can cope with a wide concentration change by adding potassium hydroxide as a back extraction agent. Therefore, the back extraction operation can be stably performed, and the operation management is easy.

According to the invention of claim 4, by returning the potassium hydroxide solution containing potassium borate to the back extraction step,
The concentration of potassium borate in the back extractant can be raised to the limit, which facilitates dry disposal when recovering boric acid.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between an extraction rate in an organic solvent and the number of extractions.

FIG. 2 is a characteristic diagram showing the relationship between the concentration of an alkaline agent in an oil phase component and the back extraction rate of boron.

FIG. 3 is a flow chart showing a method for treating boron-containing wastewater according to an embodiment of the present invention.

[Explanation of symbols]

1,3,6,7,9,10,13,14,15,17,19,20 Line 2 Waste water storage tank 4 Positive extraction tank 5 Mixture storage tank 8 Boron selective ion exchange resin packed tower 11 Back extraction tank 12 Alkali storage tank 16 Boron recovery tank 18 Reclaimed liquid storage tank

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) C02F 1/26 B01D 11/00-12/00 B01J 49/00

Claims (5)

(57) [Claims] 1. A step of forward-extracting boron contained in wastewater with a mixture of diols and an organic solvent, and then a step of treating a treatment liquid obtained by the forward-extraction with a boron-selective ion exchange resin. A method for treating a boron-containing wastewater, comprising: 2. The recycling waste liquid of the boron-selective ion exchange resin is returned to the normal extraction step.
A method for treating the boron-containing wastewater described. 3. A step of forward-extracting boron contained in wastewater with a mixture of a diol and an organic solvent, and then a step of back-extracting the forward-extracted oil phase with a potassium hydroxide solution. A method for treating boron-containing wastewater. 4. The method for treating boron-containing wastewater according to claim 3, wherein the potassium hydroxide solution containing potassium borate obtained by the back extraction is returned to the back extraction step again. 5. The boron according to claim 1 or 3, wherein the diol is 2-butyl-2-ethyl-1,3-propanediol or 2-ethyl-1,3-hexanediol. Treatment method of wastewater containing.