JP2001187386A - Treating method of boron-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treating method of boron-containing water by which boron can be efficiently removed with a small chemical amount by repeating the same processes. SOLUTION: The boron-containing water 6 is introduced into a first reaction tank 1 to adjust pH to >=9 under presence of an aluminum compound and a calcium compound, and a precipitated deposition is separated from the solution at a first solid-liquid separation tank 2, and the separated liquid is introduced into a second reaction tank 3 to adjust pH to >=9 under presence of the aluminum compound and the calcium compound, and the deposition is separated at a second solid liquid separation tank 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating boron-containing water in the presence of an aluminum compound and a calcium compound.

[0002]

2. Description of the Related Art Boron compounds are used in various fields, and some wastewaters generated from these fields and those discharged from other fields contain those containing boron compounds.
Since such compounds are considered harmful, treatments have been performed to remove boron from boron-containing water.

As methods for treating boron-containing water, methods such as coagulation, ion exchange, evaporation and concentration, and reverse osmosis (RO) treatment are known, but each has its advantages and disadvantages. Of these, the coagulation treatment requires the use of a large amount of chemicals for the treatment of high-concentration boron-containing water. Also, in the case of high-concentration boron-containing water in the ion exchange treatment, the amount of chemicals used and the amount of regenerated waste liquid generated increase. Evaporative concentration is suitable for the treatment of high-concentration boron-containing water, but requires heat for evaporation and easily transfers boron into condensed water. In the RO treatment, the boron removal rate is low.

[0004] Therefore, in order to make up for the respective disadvantages, a method of combining them has been performed. For example, a method is known in which boron-containing water is separated and removed by coagulation precipitation using aluminum ions and calcium ions, and the separated water is subjected to an ion exchange treatment (Japanese Patent Publication No. 59-2).
No. 4876). However, in this method, it is necessary to treat boron to a low concentration by the first flocculation treatment, so that it is necessary to use a large amount of chemicals, the amount of generated sludge is large, and the treatment is difficult.

Further, the boron-containing water is subjected to a coagulation treatment in the presence of aluminum ions and calcium ions, the separated liquid from which the precipitate is separated is concentrated by evaporation, and the condensed liquid is again coagulated in the presence of aluminum ions and calcium ions. Has been proposed to separate precipitates (Japanese Patent Laid-Open No. 7-323292). However, although this method is effective in reducing the amount of drug, it has a problem that the device is complicated and large-scale, and the amount of heat required for evaporation is also required.

[0006] The process of combining the coagulation and other methods is performed as described above. The coagulation is suitable for roughly processing a high-concentration boron-containing water into a low-concentration boron-containing water. This is because the contained water was considered to be suitable for another treatment method. In general, various processing methods each have a density region suitable for processing. Therefore, in order to perform processing efficiently, a combination of processing methods suitable for each density is performed. However, there is a problem that combining such different kinds of processing complicates the processing steps and increases the cost.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to propose a method for treating boron-containing water that can remove boron with a small amount of chemicals and a high removal rate by repeating the same operation. is there.

[0008]

The present invention relates to the following method for treating boron-containing water. (1) A first step of adjusting the pH of the boron-containing water to pH 9 or higher in the presence of an aluminum compound and a calcium compound to separate a precipitate, and an aluminum compound and a calcium compound without concentrating the separated liquid in the first step. A method for treating boron-containing water, comprising a second step of separating the precipitate by adjusting the pH to 9 or more in the presence of water. (2) The method according to the above (1), wherein the precipitate in the second step or a step subsequent thereto is returned to the first step.

The boron-containing water to be treated in the present invention is usually water containing boron in the form of orthoboric acid (H ₃ BO ₃ ), but it may be borate or other forms containing boron. Such boron-containing water includes medicine, cosmetics, soap, metals, semiconductors, manufacturing process wastewater using boron compounds, plating wastewater, radioactive wastewater generated from nuclear power plants, geothermal wastewater, waste incineration plants, etc. Smoke-wash drainage.

[0010] These boron-containing waters may have different boron contents depending on the generation source or generation timing. For example, in a surface treatment step of a metal or semiconductor using boric acid, high-concentration boron-containing water is generated during the surface treatment, and low-concentration boron-containing water is generated in a subsequent washing step. In addition, different sources produce different concentrations of boron-containing water. These boron-containing water can also be treated by mixing different kinds of water,
It can also be processed separately.

In the present invention, such a boron-containing water is subjected to pH adjustment in the presence of an aluminum compound and a calcium compound.
The step of separating the precipitate by adjusting it to 9 or more, preferably 11 or more is performed a plurality of times without concentrating the separated liquid. The boron concentration and the boron removal rate of the water to be treated in each process can be arbitrarily determined according to the quality of the water to be treated and the target quality of the treated water. What is necessary is just to select the conditions in each process so that the total may be minimized. The boron removal rate in the first step is 50 to 9
Preferably, it is 0%. The above steps can be performed three or more times.

The amount of the aluminum compound and the calcium compound to be present depends on the boron concentration of the water to be treated and other conditions.
In the case of 2,000 to 3,000 mg / l, in the first step, 200 to 5,000 mg / l, preferably 400 to 3,000 mg / l as aluminum and 2,000 to 50,000 mg / l, preferably 4.0, as calcium.
It can be from 00 to 30,000 mg / l. Second
In the following steps, the amount can be reduced, but it is preferable that the amount is substantially the same. In order to obtain such aluminum and calcium concentrations, when these are insufficient in the water to be treated, an aluminum compound and / or a calcium compound can be added.

As the aluminum compound to be added, aluminum salts such as aluminum sulfate, aluminum chloride and polyaluminum chloride are preferable, but aluminum hydroxide and other aluminum compounds may be used. As the calcium compound, calcium hydroxide is preferable because it can also serve as a pH adjuster, but calcium oxide, calcium chloride,
Calcium sulfate or other calcium compounds may be used. In addition, when a pH adjuster is required, an alkali such as sodium hydroxide or potassium hydroxide can be generally added. In some cases, an acid such as hydrochloric acid or sulfuric acid can be added.

The order of adding these agents is not particularly limited, but it is preferable to add the pH adjusting agent containing calcium hydroxide last. Therefore, when the aluminum compound and the calcium compound are salts, either of them may be added first, but when the compound is also used as a pH adjuster like calcium hydroxide, calcium hydroxide is added last.
When an insoluble or poorly soluble compound such as aluminum hydroxide or calcium carbonate is added, the compound can be dissolved and ionized by adding it under acidic conditions.

In the first step, if necessary, an aluminum compound and a calcium compound are added to the water to be treated to adjust the pH.
By adjusting to 9 or more, a composite precipitate of an insoluble aluminum compound and a calcium compound including calcium aluminate and the like is precipitated. During this time, stirring can be performed in order to advance the reaction. It is presumed that boron (boric acid) is adsorbed by the precipitate and removed. The reaction time is 10 to 120 minutes, preferably 30 to 6 minutes.
It can be 0 minutes.

The precipitate produced by the agglutination reaction in the first step is separated by solid-liquid separation. As the solid-liquid separation means, sedimentation separation is generally used, but filtration, centrifugation, membrane separation, or other separation methods may be used. The separated precipitate is discharged as sludge, and the separated liquid is sent to the second step to perform the coagulation treatment again.

In the second step, an aluminum compound and a calcium compound having almost the same level as in the first step are present, and the pH is adjusted to 9 or more, preferably 11 or more, so that the aluminum compound and the calcium compound are precipitated as precipitates. Boron is adsorbed on the precipitate.
In the second step, boron can be removed by allowing an aluminum compound and a calcium compound to be substantially the same as those in the first step in the separation liquid in the first step in which the concentration of boron is low. The third and subsequent steps are performed in substantially the same manner.

In general, when an aluminum compound and a calcium compound are present in a high-concentration boron-containing water to remove boron at a high removal rate, a large amount of the aluminum compound and the calcium compound are required. When the treatment is performed in the step (1), the amount of the chemical used can be reduced or the chemical can be removed at a high removal rate.

That is, in the first step, since the treatment is performed roughly using a relatively small amount of chemicals, the boron concentration in the reaction system is high, so that the amount of boron removed per aluminum amount is large. When the same concentration of a chemical is further added to the separated liquid in the second step to perform coagulation in the second step, a relatively large amount of aluminum compound and calcium compound are used with respect to a small amount of boron. Therefore, boron can be removed at a high removal rate. In addition, since coexisting substances such as sulfate ions that adversely affect boron removal are also removed in the first step, it is considered that the removal performance in the second and subsequent steps is improved.

After the coagulation in the second step as described above, solid-liquid separation is performed, and the separated liquid can be taken out as treated water, or the treatment after the third step can be performed. The separated sludge can be discharged as it is, but since the amount of adsorbed boron is small, if it is returned to the first step to adsorb boron, the boron can be efficiently treated.

When the sludge after the second step is returned to the first step, the sludge is simply returned to the first step, and is discharged together with the precipitate deposited in the first step to the outside of the system. Boron is adsorbed and removed by the deposited precipitate. When the sludge after the second step is mixed with the liquid to be treated or before mixing, the sludge may be dissolved under acidic conditions, and then adjusted to pH 9 or more to precipitate aluminum ions and calcium ions as insoluble compounds. .

If the sludge after the second step is returned without being dissolved, the amount of the pH adjuster can be reduced. Since the returned aluminum and calcium again participate in aggregation, the amount of aluminum and calcium added in the first step can be reduced. And in some cases, even if it is not newly added in the first step,
In some cases, the boron removal rate in the first step can be obtained by the aluminum compound and the calcium compound contained in the returned precipitate.

[0023]

According to the present invention, the coagulation is performed in the first and second steps, so that boron can be removed with a small amount of chemicals and at a high removal rate.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are flowcharts showing a method for treating boron-containing water according to another embodiment. Figures 1 and 2
, 1 is a first reaction tank, 2 is a first solid-liquid separation tank, 3 is a second reaction tank, 4 is a second solid-liquid separation tank, and 5 is a dissolution tank.

In the treatment method shown in FIG. 1, raw water 6 is supplied to the first reaction tank 1, an aluminum salt 7 such as aluminum sulfate and calcium hydroxide 8 are added, and the mixture is stirred with a stirrer 9 to have a pH of 9 or more, preferably 11 or more. With the above adjustment, the first aggregation is performed to precipitate the precipitate. The reaction liquid 11 is introduced into the first solid-liquid separation tank 2 to perform solid-liquid separation, whereby the precipitate is separated and discharged as sludge 12, and the separation liquid 13 is introduced into the second reaction tank 3.

In the second reaction tank 3, an aluminum salt 14 and calcium hydroxide 15 are added, and the mixture is stirred with a stirrer 16 to adjust the pH to 9 or more, preferably 11 or more, and to cause a second aggregation to precipitate a precipitate. . The reaction liquid 17 is introduced into the second solid-liquid separation tank 4 and subjected to solid-liquid separation, whereby the precipitate is separated and discharged as sludge 18, and the separated liquid is taken out as treated water 19. By the above treatment, boron can be removed at a high removal rate with a small amount of drug.

The basic operation of the treatment method of FIG. 2 is the same as that of FIG. 1, but the sludge 18 discharged from the second solid-liquid separation tank 4 is returned to the first reaction tank 1. . As a result, the precipitate adsorbs boron in the raw water, and the aluminum salt 7 and the calcium hydroxide 8 in the first reactor 1
The amount of addition can be reduced. In this case, the sludge 18 is introduced into the dissolution tank 5, and the acid 21 is added to dissolve the precipitate,
The solution 22 may be returned to the first reaction tank 1 to perform aggregation. By dissolving in the dissolving tank 5, the insoluble compounds of aluminum and calcium dissociate as aluminum ions and calcium ions, which are again used for aggregation and the amount of the aluminum compound added can be further reduced. In this case, boron is also dissolved, but by increasing the removal rate in the first step, the treatment can be performed without increasing the load extremely.

In the above description, the first reaction tank 1 and the second reaction tank 3 may be replaced with a mixing and stirring device such as a line mixer or other types of reaction devices. The solid-liquid separation tank 4 may be replaced with another separation means such as a filtration or centrifugal separator. Further, the above-mentioned reaction and solid-liquid separation may be performed in three or more stages. The larger the number of stages, the smaller the amount of drug and the lower the concentration.

[0030]

Embodiments of the present invention will be described below. Example 1 Aluminum sulfate was added to a solution of boric acid (3020 mg / l as B) and sulfuric acid (50 g / l) dissolved in distilled water.
0 g / l and 69 g / l of calcium hydroxide were added to adjust the pH.
12.1 and stirred for 30 minutes. Filtered with 5A filter paper. 20 g / l of aluminum sulfate was added to the filtered water,
The pH was adjusted to 12.4 by adding 18 g / l of calcium hydroxide, and the mixture was stirred for 30 minutes. Filtration through 5A filter paper revealed that the concentration of boron in the filtered water was 86 mg / l.

Comparative Example 1 The same sample solution as in Example 1 was mixed with 40 g of aluminum sulfate.
1 and calcium hydroxide 78 g / l and pH12.
No. 1 after stirring for 30 minutes. After filtration through 5A filter paper, the boron concentration in the filtered water was 898 mg / l.

From the above results, by performing aggregation and solid-liquid separation by adding aluminum salt and calcium hydroxide in multiple stages, boron can be removed at a higher removal rate than in the case of one stage, and the same removal rate can be obtained. It can be seen that a small amount of drug is sufficient for this purpose.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a boron removing method according to an embodiment.

FIG. 2 is a flowchart showing a boron removing method according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st reaction tank 2 1st solid-liquid separation tank 3 2nd reaction tank 4 2nd solid-liquid separation tank 5 dissolution tank

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshihiro Endo 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo F-term in Kurita Industries Co., Ltd. 4D038 AA08 AB25 BB13 BB17 BB18

Claims (2)

[Claims] A first step of adjusting the pH of the boron-containing water to pH 9 or higher in the presence of an aluminum compound and a calcium compound to separate a precipitate; and removing the aluminum compound without concentrating the separated liquid in the first step. A method for treating boron-containing water, comprising a second step of separating a precipitate by adjusting the pH to 9 or more in the presence of a calcium compound. 2. The method according to claim 1, wherein the precipitate in the second step or subsequent steps is returned to the first step.