JP5553160B2 - Method for treating boron-containing water - Google Patents

Description

  The present invention relates to a method for treating boron-containing water in which treated water containing dissolved boron is energized and aggregates are separated from the treated water.

Ingestion of large amounts of boron may cause health problems such as loss of appetite and vomiting. Therefore, in February 1999, “boron 1 mg / L or less” was added to the environmental standard for water (environmental standard related to water pollution), and then “boron” became the environmental standard for soil (environmental standard related to soil contamination). Added to item. Furthermore, since July 2004, drainage standards for boron and its compounds have been set to 230 mg / L or less for sea areas and 10 mg / L or less for areas other than sea areas.
The main method for removing boron from the water to be treated containing dissolved boron is as follows.
(1) A chemical | medical agent is added to the to-be-processed water containing a dissolved boron, and a dissolved boron is precipitated and separated as a hardly soluble substance. For example, a method for treating boron-containing wastewater in which a polyvalent anionic substance and rare earth element ions are present in water to be treated containing dissolved boron, and the pH is 9 to 13 to precipitate and separate dissolved boron as a hardly soluble substance. However, it was examined as one of the said methods (for example, refer patent document 1).
(2) Using a reverse osmosis membrane, the dissolved boron is membrane-separated from the water to be treated containing dissolved boron (see, for example, Patent Document 2).
(3) The water to be treated containing dissolved boron is brought into contact with the wood powder, and the dissolved boron is adsorbed onto the wood powder (for example, see Non-Patent Document 1).
(4) The water to be treated containing dissolved boron is electrolyzed using an aluminum electrode, and the dissolved boron is separated as an aggregate (see, for example, Non-Patent Document 2).
(5) The water to be treated containing dissolved boron is brought into contact with the resin to remove the dissolved boron. One of the methods is a method in which water to be treated containing dissolved boron is adjusted to a boron concentration of 30 mg / L or less, pH 7.0 to 9.5, and passed through a boron selective adsorption resin tower to remove boron. (For example, refer patent document 3).

JP 2004-963 A JP 2006-102624 A JP 2001-340851 A

Chemical Engineering, Vol. 35, No. 1, 2009, pp. 55-59 J.-Q.Jiang et al., Environ. Chem. 3, 2006, pp. 350-354

Even when groundwater containing various ions was treated by the methods (3) to (4) above, dissolved boron could not be effectively removed from the groundwater, and a considerable amount of boron remained in the groundwater. The method (1) is not practical because a large amount of chemicals is required and a large amount of residue is generated. The above method (2) is a method that has been developed for drinking water and requires various pretreatments to increase the efficiency of membrane separation, as well as treatment of high-concentration boron wastewater. There are challenges. Furthermore, in the method (4), the concentration of aluminum ions in the water to be treated eluted from the aluminum electrode is 700 mg / L or more (current consumption is 1000 A · hr / m ^3).
In this case, the viscosity of the water to be treated becomes large and filtration of the aggregate becomes difficult, and according to the results of the experimental study by the present inventor, the removal effect is significantly lost due to the coexisting components. Although the method (5) was able to remove dissolved boron from groundwater containing various ions relatively effectively, the resin from which the dissolved boron is removed is quite expensive, and the residue generated by resin regeneration is treated separately. Must. Therefore, the running cost of removing dissolved boron from groundwater containing various ions by the method (5) is expensive.
In recent years, there has been a demand for an inexpensive method capable of effectively removing dissolved boron from groundwater containing various ions, but no effective method has been found. Therefore, the inventors of the present invention provide an inexpensive method capable of effectively removing dissolved boron from groundwater containing various ions, and therefore, an electrode containing iron as a component of water to be treated containing dissolved boron. A treatment method for boron-containing water was examined in which the current was treated as an anode and the aggregate was separated from the water to be treated (Japanese Patent Application No. 2010-148460).

The preferable pH of the water to be treated after the energization treatment in the above treatment method (hereinafter referred to as “the treatment method of the prior application”) is 7.5 to 10.5. The mechanism by which dissolved boron is removed from the water to be treated treated by the treatment method of the prior application is not yet elucidated, but the interaction between boron and aggregates mainly composed of Fe ²⁺ and Fe (OH) ₂ It is assumed that boron is adsorbed on the aggregate. However, in the treatment method of the prior application, since there are substances generated by changing the components in the drainage, hydroxide ions generated during energization, and other components during energization, the pH change of the water to be treated is It was complicated. Furthermore, considering that the components in the wastewater change, such as wastewater from the construction site, the pH of the treated water after the energization treatment in the treatment method of the prior application is controlled to 7.5 to 10.5. That was not easy. The problem to be solved by the present invention is to treat the water to be treated containing dissolved boron by using an electrode containing iron as a component as an anode and reducing the pH change of the water to be treated for energization. Provided is a method for treating boron-containing water separated from treated water.

  The inventors of the present invention have made extensive studies in order to solve the above-mentioned problems. As a result, when conducting an energization process using an electrode containing iron as a component, water to be treated containing dissolved boron, the dissolved magnesium is energized. It has been found that the concentration of dissolved boron can be made lower than the treatment method of the prior application by conducting the current treatment in the presence of dissolved magnesium so that it remains in the water to be treated after the treatment, and the present invention has been completed.

  In the method for treating boron-containing water of the present invention, the treated water containing dissolved boron is used so that the electrode containing iron as a component is used as an anode and dissolved magnesium remains in the treated water after the energization treatment. In the presence of magnesium, current treatment is performed to separate the agglomerates from the water to be treated.

  The energization process is performed so that the magnesium concentration in the water to be treated after the energization process is 20 mg / L or more.

  The pH of the water to be treated after the energization treatment is 7.5 to 10.5. The water-soluble magnesium salt must be added to the water to be treated containing dissolved boron before the energization treatment.

  The method for treating boron-containing water of the present invention can effectively remove dissolved boron from groundwater containing various ions at a low current, and the amount of residue is small, so its running cost is low.

Diagram showing energization processing tank Figure showing the relationship between initial magnesium concentration, pH after energization treatment, and boron concentration after energization treatment Figure showing the relationship between the initial magnesium concentration, residual magnesium concentration after energization treatment, and boron concentration after energization treatment The figure which shows the relationship between the initial pH, the pH after the current treatment, and the boron concentration after the current treatment Diagram showing the relationship between current consumption and boron concentration after energization treatment Diagram showing the relationship between current consumption and magnesium consumption

  The treated water containing dissolved boron treated by the method for treating boron-containing water of the present invention can contain ions other than boron ions. Specific examples of the ions other than boron ions are sodium ion, potassium ion, magnesium ion, calcium ion, ammonium ion, fluorine ion, chlorine ion, and sulfate ion. These ions are contained in groundwater.

At least one of the anodes of the apparatus used in the method for treating boron-containing water of the present invention is an electrode containing iron as a component. Fe ²⁺ is eluted from the electrode containing iron as a component, and Fe ²⁺ reacts with OH ⁻ to produce Fe (OH) ₂ . Although the mechanism by which dissolved boron is removed from the water to be treated that is treated by the method for treating boron-containing water of the present invention is not yet elucidated, an aggregate composed mainly of Fe ²⁺ and Fe (OH) ₂ and boron It is presumed that boron is adsorbed on the aggregates by the interaction. An electrode made of a metal other than iron may be used together as a part of the anode, but the main body is made of iron. Specific examples of metals other than iron are aluminum and aluminum / magnesium alloys (duralumin).

  The cathode of the apparatus used in the method for treating boron-containing water according to the present invention is formed using a material such as iron, aluminum, or carbon.

  The water to be treated containing dissolved boron is energized in the presence of dissolved magnesium so that the dissolved magnesium remains in the water to be treated after the energization treatment. If dissolved magnesium disappears from the water to be treated during the energization treatment, the pH of the water to be treated becomes too high, and boron may be re-eluted from the aggregate.

The magnesium concentration in the water to be treated after the energization treatment is 20 mg / L or more, preferably 50 mg / L or more. When the water to be treated before the energization treatment contains a sufficient amount of magnesium, the water to be treated may be directly subjected to the energization treatment. When the water to be treated before energization treatment does not contain a sufficient amount of magnesium, a water-soluble magnesium salt such as magnesium chloride or magnesium sulfate is dissolved in the water to be treated before energization treatment. The amount of the water-soluble magnesium salt dissolved in the water to be treated is determined by the method described later.
Although the upper limit of the magnesium concentration in the water to be treated after the energization treatment is not specified, the magnesium concentration higher than 1000 mg / L is not preferable from the viewpoint of cost.

  The energization process in the present invention can be performed in multiple stages. The addition of the water-soluble magnesium salt in the multi-stage energization process can be performed either before the first-stage energization process or before each energization process after the second stage.

The dissolved boron concentration in the for-treatment water is affected by the pH of the for-treatment water after the energization treatment. Although affected by the components of groundwater, the pH is 7.5 to 10.5, and the preferred pH is 7.7 to 9.0. The pH of the water to be treated after the energization treatment is adjusted by the initial pH of the water to be treated, the current, the energization time, and the like. The initial pH of the water to be treated is adjusted before or after the addition of the water-soluble magnesium salt.

A polymer flocculant may be added before the energization treatment to facilitate separation of the aggregates after the energization treatment.
After the energization treatment, the aggregate is separated from the water to be treated by a separation means such as filtration and centrifugation.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.
Qualitative analysis and quantitative analysis of various ions in water were performed by a high frequency inductively coupled plasma (ICP) method.
FIG. 1 is a diagram illustrating an energization processing tank. The water 2 to be treated is stored in the energization treatment tank 1, and the two carbon electrodes 3 are used as cathodes and the two metal electrodes are used as anodes. One metal electrode 4 a faces one carbon electrode 3. The other metal electrode has two metal electrodes 4 b and 4 c welded to face the two carbon electrodes 3.

  Three types of groundwater were prepared. Table 1 shows the types and concentrations of ions contained in the groundwater.

Reference example 1
The three metal electrodes 4a, 4b, and 4c of the energization treatment tank shown in FIG. 1 are used as iron electrodes, and magnesium chloride is dissolved in groundwater A to C to conduct energization. The dissolved boron in the groundwater A to C is 10 mg / L. The amount of current consumed and the amount of iron electrode consumed until reaching 1 mg / L were measured. The results are shown in Table 2.

  As the amount of magnesium chloride dissolved increased, the amount of current consumed and the amount of iron electrode consumed until the treated water from which boron was removed to the target dissolved boron concentration were reduced.

Reference example 2
The three metal electrodes 4a, 4b and 4c of the energization treatment tank shown in FIG. 1 are used as iron electrodes, magnesium chloride is dissolved in ground water A to C, and energization treatment is performed. The relationship between the residual magnesium concentration after the energization treatment and the boron concentration after the energization treatment was examined. The results are shown in FIGS. As the initial magnesium concentration increased to a certain initial magnesium concentration, the pH after the energization treatment and the boron concentration after the energization treatment decreased (FIG. 2). Furthermore, when the residual magnesium concentration in groundwater A is 30 mg / L or more, the residual magnesium concentration in groundwater B is 20 mg / L or more, and the residual magnesium concentration in groundwater C is 80 mg / L or more, the boron concentration after the current treatment is It has not changed much (Fig. 3).

Reference example 3
The three metal electrodes 4a, 4b and 4c of the energization treatment tank shown in FIG. 1 are adjusted together with iron electrodes, the initial pH (pHini) of the groundwater A to C is adjusted with 1M HCl or 1M NaOH, and magnesium chloride is added to the groundwater A. It melt | dissolved in -C, it energized, and investigated the relationship between initial pH, pH after an energization process, and the boron concentration after an energization process. The results are shown in FIG. As the initial magnesium concentration (Mg) increased, the pH change decreased and the boron concentration after the energization treatment decreased.

Example and Comparative Example Three metal electrodes 4a, 4b, and 4c of the energization treatment tank shown in FIG. 1 are changed together with iron electrodes, and the amount of magnesium chloride dissolved in groundwater A to C is changed. The relationship between the magnesium concentration (Mg-r) and the boron concentration after the energization treatment was examined. The results are shown in FIG. When the magnesium concentration after the energization treatment of the groundwater A to C was less than 50 mg / L, the residual boron concentration did not decrease much even when the power consumption increased. On the other hand, when the magnesium concentration after the energization treatment of the groundwater A to C was 50 mg / L or more, the maximum boron removal efficiency could be maintained.

Reference example 4
The three metal electrodes 4a, 4b, and 4c of the energizing treatment tank shown in FIG. 1 were used as iron electrodes, and magnesium chloride was dissolved in groundwater A to C to conduct energization, and the relationship between the consumption current and the magnesium consumption was examined. The results are shown in FIG. The consumption current corresponding to the target boron concentration is obtained from FIG. 5, and then the magnesium consumption corresponding to the consumption current is obtained from FIG. And the quantity of the magnesium salt melt | dissolved in groundwater AC can be calculated from the said magnesium concentration.
In addition, the figure which shows the relationship between the current consumption as shown in FIG. 5 and the boron concentration after the energization treatment, and the figure showing the relationship between the current consumption and the magnesium consumption as shown in FIG. Calculate the minimum amount of magnesium salt dissolved in groundwater required to remove boron to the boron concentration.

  The method for treating boron-containing water of the present invention is suitable for effective and inexpensive removal of dissolved boron from groundwater containing various ions. The voltage required for removing boron from groundwater containing various ions including boron by the method for treating boron-containing water of the present invention is 12 V or less, usually about 5 V, and can be obtained with a solar cell. The method for treating boron-containing water of the present invention can be performed with electric power. Furthermore, the method for treating boron-containing water of the present invention does not require a large amount of chemicals and large-scale equipment. Therefore, the method for treating boron-containing water of the present invention can be implemented in remote areas.

DESCRIPTION OF SYMBOLS 1 ... Energization processing tank, 2 ... Water to be treated, 3 ... Carbon electrode, 4 ... Metal electrode

Claims (2)

Using the treated water containing dissolved boron as an anode with an electrode containing iron as a component,
The magnesium concentration in the treated water after the energization treatment is 20 mg / L or more, the energization treatment is performed so that the pH of the treated water after the energization treatment is 7.5 to 10.5, and the aggregates are separated from the treated water. A method for treating boron-containing water. The method for treating boron-containing water according to claim 1 , wherein the water-soluble magnesium salt is added to the water to be treated containing dissolved boron before the energization treatment.

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