JP2002346574A - Boron-containing water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boron-containing water treatment method capable of efficiently removing boron in a high removal ratio by using a reduced amount of a chemical agent and reducing the generation amount of sludge. SOLUTION: Raw water 11 is introduced into an aluminum adding tank 1, and an aluminum compound 12, a pH control agent 13, or the like, are added to the raw water 11 to adjust the pH thereof to 8 or more and this raw water is held for 2 min or more while stirred by a stirrer 14. This aluminum compound 2-added water 15 is introduced into a reaction tank 2, and a calcium compound 16, a pH control agent 17, or the like, are injected in the aluminum compound-added water 15 to adjust the pH thereof to 9 or more and reacted with the aluminum compound-added water 15 while stirred and mixed by a stirrer 18 to form an insoluble precipitate. The reaction liquid 21 is sent to a solid-liquid separation tank 3 and, if necessary, a flocculant 22 such as a polymeric flocculant is added to the reaction liquid to form flocs at this time and the reaction liquid is allowed to stand in the slid-liquid separation tank 3 to be subjected to solid-liquid separation. The separated liquid separated in the solid-liquid separation tank 3 is discharged as treated water 23. The separated sludge 24 is introduced into a neutralization tank 4 in a neutralization process and neutralized with an acid 26 to be discharged as waste sludge 27.

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 water with 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 a method of treating boron-containing water, there is a method of precipitating as an insolubilized substance at a pH of 9 or more with an aluminum compound and a calcium compound, followed by solid-liquid separation (JP-A-57-81881). However, this method uses a large amount of chemicals to generate a large amount of sludge, and the boron removal rate is not always satisfactory.

[0004]

An object of the present invention is to propose a method for treating boron-containing water which can efficiently remove boron at a high removal rate with a small amount of chemicals and generate a small amount of sludge. is there.

[0005]

The present invention relates to the following method for treating boron-containing water. (1) An aluminum addition step of adding an aluminum compound to boron-containing water, and the aluminum addition water in the aluminum addition step is subjected to pH 9 in the presence of a calcium compound.
A reaction step of producing an insoluble precipitate by adjusting the above,
A solid-liquid separation step of solid-liquid separation of the reaction liquid in the reaction step into a separated liquid and a separated sludge; (2) When the boron-containing water contains a calcium compound,
The method according to the above (1), wherein the aluminum compound is added so that the pH of the aluminum-added water is 8 or less.

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 pharmaceuticals, cosmetics, soaps, metals, semiconductors, manufacturing process wastewater using other boron compounds, plating wastewater, radioactive wastewater generated from nuclear power plants, geothermal wastewater, waste incineration plants, etc. Smoke-wash drainage.

[0007] The boron-containing water may have a different boron content depending on the generation source, generation time, and the like. 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. When the boron-containing water contains a solid content, the solid content and the like can be removed by performing pretreatment such as sedimentation and filtration in advance.

[0008] In the present invention, the above boron-containing water (water to be treated)
, An aluminum compound is added in an aluminum addition step. The addition amount of the aluminum compound varies depending on the boron concentration of the water to be treated and other conditions.
It is desirably 6 times, preferably 2 to 4 times. For example, when the concentration of boron in the water to be treated is 1,000 mg / L,
2,000 to 6,000 mg / L as aluminum,
Preferably, it is 2,000 to 4,000 mg / L. If the water to be treated contains aluminum, the shortage is 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. In the aluminum added water, is the aluminum compound dissolved?
Alternatively, it must be present as aluminum hydroxide in a neutral pH range.

When the boron-containing water contains a calcium compound, for example, when containing calcium at a concentration of 10,000 mg / L or more, an insoluble precipitate may be formed by the addition of the aluminum compound. In such a case, the generation of insoluble precipitates can be prevented by adding the aluminum compound so that the pH of the aluminum-added water after the addition of the aluminum compound is 8 or less, preferably 7 or less. When no insoluble precipitate is formed, the pH of the aluminum-added water is not limited, and may be higher than 8.

The pH can be adjusted by adding a pH adjuster. As the pH adjuster, a mineral acid such as hydrochloric acid or sulfuric acid can be used, and in some cases, an alkali such as sodium hydroxide or potassium hydroxide can be used.

After the addition of the aluminum compound, 2 minutes or more, preferably 2 to 10 minutes, more preferably 5 minutes
It is desirable to hold for 10 minutes. By shifting to the next reaction step after holding for 2 minutes or more, the removal rate of boron can be increased. The aluminum addition step is performed by adding an aluminum compound, a pH adjuster, and the like to the water to be treated and stirring. The aluminum addition step can be performed at normal temperature and normal pressure, but may be performed under heat and pressure.

In the reaction step, the aluminum-added water in the aluminum addition step is subjected to pH adjustment in the presence of a calcium compound.
The reaction is adjusted to 9 or more, preferably 11 or more, to precipitate an insoluble precipitate. The amount of the calcium compound varies depending on the boron concentration of the water to be treated and other conditions, but is preferably 20 to 50 times, preferably 20 to 30 times the weight ratio of calcium to the amount of boron in the water to be treated. For example, when the boron concentration in the water to be treated is 1,0
In the case of 00 mg / L, 20,000 to calcium
50,000 mg / L, preferably 20,000 to 3
Desirably, the concentration is 0000 mg / L. If the water to be treated contains calcium, add the insufficient amount.

As the calcium compound to be added, calcium hydroxide is preferable because it can also serve as a pH adjuster.
Calcium oxide, calcium chloride, calcium sulfate and other calcium compounds may be used. When calcium hydroxide is used as the calcium compound, the amount of the calcium compound existing is sufficient if the pH is about 10 or more. 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 reaction in the reaction step is carried out by adding a calcium compound, a pH adjuster and the like to the water containing aluminum and stirring the mixture. In this case, when the aluminum compound and the calcium compound are precipitated as hydroxide (calcium aluminate), boron is taken into the insoluble precipitate to be precipitated. The reaction time is 10 to 60 minutes, preferably 10 to 3 minutes.
Desirably, it is 0 minutes. The reaction can be carried out at normal temperature and pressure, but may be carried out under heat and pressure.

After the reaction, the reaction liquid is separated into a separated liquid and a separated sludge in a solid-liquid separation step. Thereby, boron is separated in a state where it is captured in the separated sludge, and is removed from the water to be treated. As the solid-liquid separation means, sedimentation separation is generally used, but filtration, centrifugation, membrane separation or other separation means may be used. When the boron concentration is within the allowable limit, the separated liquid may be discharged as it is or may be reused, but when the boron concentration exceeds the allowable limit, it can be separately treated. Separated sludge is acid pH5
After neutralized to 8, it can be discharged. In this case, as the acid to be neutralized, a mineral acid such as sulfuric acid or hydrochloric acid can be used.

In the method of the present invention, the insoluble precipitate is formed in the presence of the calcium compound after the addition of the aluminum compound, so that the boron removal rate can be increased. In addition, the addition amount of the aluminum compound and the calcium compound can be reduced, and the sludge generation amount is reduced accordingly. In this case, when the amount of the chemical added is equal to that of the conventional method in which the aluminum compound and the calcium compound are simultaneously added, the boron concentration in the treated water becomes low.

Although it is not clear why the method of the present invention in which an aluminum compound and a calcium compound are sequentially used has a higher boron removal rate than the conventional method of simultaneously adding a drug, it is difficult to dissolve boron and aluminum in the aluminum addition step. It is presumed that some reaction occurs with aluminum or aluminum hydroxide, and this reactant is efficiently adsorbed on insoluble precipitates generated in the reaction step and removed in the solid-liquid separation step.

[0019]

According to the present invention, boric acid is removed by adding an aluminum compound to boron-containing water and then adjusting the pH to 9 or more in the presence of a calcium compound to precipitate insoluble precipitates and remove boric acid. Boron can be efficiently removed at a high removal rate by the chemical, and the amount of generated sludge is small.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing a method for treating boron-containing water according to an embodiment, where 1 is an aluminum addition tank,
Reference numeral 2 denotes a reaction tank, 3 denotes a solid-liquid separation tank, and 4 denotes a neutralization tank.

In the treatment method shown in FIG. 1, raw water 11 is introduced into an aluminum addition tank 1 in an aluminum addition step, and an aluminum compound 12, a pH adjuster 13 and the like are added, and p
It is adjusted to H8 or less and kept for 2 minutes or more while stirring with the stirrer 14. This aluminum added water 15 is introduced into the reaction tank 2 in the reaction step, and the calcium compound 16, pH
Adjusting the pH to 9 or more by injecting a regulator 17 or the like, the stirrer 1
The mixture is stirred and mixed in step 8 to form an insoluble precipitate.

The reaction liquid 21 in the reaction tank 2 is used as a solid-liquid separation step.
Is fed to the solid-liquid separation tank 3, where a flocculant 22 such as a polymer coagulant is added as needed to generate flocs, and the solid-liquid separation is performed by allowing the floc to stand still in the solid-liquid separation tank 3. As a result, boron in the raw water 11 is separated while being trapped by the insoluble precipitate. The separated liquid separated in the solid-liquid separation tank 3 is discharged as treated water 23. Separated sludge 24 is introduced into neutralization tank 4 as a neutralization step, and acid 26
And neutralized, and discharged as waste sludge 27.

[0023]

EXAMPLES Examples of the present invention and comparative examples will be described below. In each case,% is% by weight unless otherwise specified.

Example 1 Coal-fired flue gas desulfurization wastewater having a pH of 6.5 and containing 267 mg / L of boron was passed according to the flow shown in FIG. First, 5,000 mg / sulfuric acid band was added to the above wastewater
L (solid) was added and reacted for 3 minutes. The pH of this aluminum-added water was 3.7. Next, 8 g of a calcium compound and slaked lime as a pH adjuster were added, and p
H was adjusted to 12.4 and reacted for 27 minutes to form an insoluble precipitate. Thereafter, the reaction solution was filtered to separate insoluble precipitates, and the boron concentration in the filtrate was measured.
mg / L.

Comparative Example 1 5,000 mg / L (solid) of a sulfate band was added to the same waste water as in Example 1 while adjusting the pH to 12.4 with slaked lime and reacted for 30 minutes. Thereafter, the concentration of boron in the filtrate was measured in the same manner as in Example 1;
L. To remove boron to the same level as in Example 1, it was necessary to add 7,600 mg / L (solid) of a sulfuric acid band.

[Brief description of the drawings]

FIG. 1 is a flowchart of a method for treating boron-containing water according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Aluminum addition tank 2 Reaction tank 3 Solid-liquid separation tank 4 Neutralization tank 11 Raw water 12 Aluminum compound 13, 17 pH adjuster 14, 18, 25 Stirrer 15 Aluminum addition water 16 Calcium compound 21 Reaction liquid 22 Coagulant 23 Treated water 24 Separated sludge 26 Acid 27 Waste sludge

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Asada 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo F-term in Kurita Kogyo Co., Ltd. 4D038 AA08 AB25 BB13

Claims (2)

[Claims] 1. An aluminum addition step of adding an aluminum compound to boron-containing water; and a reaction step of adjusting the pH of the aluminum-added water in the aluminum addition step to 9 or more in the presence of a calcium compound to form an insoluble precipitate. A solid-liquid separation step of solid-liquid separation of the reaction liquid in the reaction step into a separated liquid and a separated sludge; 2. The method according to claim 1, wherein when the boron-containing water contains a calcium compound, the aluminum compound is added so that the pH of the aluminum-added water is 8 or less.