JP2010029833A - Method for removing and recovering halogen ion using adsorbent - Google Patents

Abstract

The present invention provides a novel method capable of effectively removing halogen ions from an aqueous phase when halogen ions are present in the aqueous phase.
An acidic aqueous phase obtained by adding an acid to water to be treated containing halogen ions (for example, iodine ions) is brought into contact with an adsorbent (preferably activated carbon) so that the content of the halogen ions is reduced. A treated water lower than the treated water is obtained.
[Selection] Figure 1

Description

  The present invention relates to a method for removing halogen ions, and more particularly to a method for removing and collecting halogen ions using an adsorbent.

Wastewater from factories and the like may contain halogen ions, especially iodine ions. There is currently no wastewater regulation on iodine ions per se. However, since iodine ion (I ⁻ ) is oxidized by, for example, air or light to produce iodine (I ₂ ), the iodine ion concentration in the wastewater is sufficiently satisfied so as to sufficiently satisfy the wastewater regulations regarding the coloring level. Is preferably as small as possible.

  Conventionally, when there is a concern about the presence of iodine ions in wastewater, the iodine ion concentration is measured and managed, and when the iodine ion concentration exceeds a predetermined value, the wastewater is typically discharged by dilution.

Japanese Industrial Standard (JIS Standard) K1474 Activated Carbon Test Method

By the way, it is well known that iodine (I ₂ ) can be adsorbed by activated carbon, as it is used in the Japanese Industrial Standard (JIS standard) to evaluate the adsorption ability of activated carbon in the liquid phase (for example, non-patent). (Ref. 1).

Therefore, when there is a concern about the presence of iodine ions in the wastewater, it is considered that iodine ions are actively oxidized with an oxidizing agent to form iodine (I ₂ ), and the generated iodine is adsorbed on activated carbon and removed.

However, oxidants that can be used to oxidize iodine ions (eg, chlorine (Cl ₂ ), hypochlorous acid (HClO), hydrogen peroxide (H ₂ O ₂ ), etc.) require careful handling and are therefore routine. It is better to avoid using it. In addition, there are drawbacks such as that it takes time and effort to cause an oxidation reaction and that the reaction proceeds excessively and may be oxidized to iodic acid.

  An object of the present invention is to provide a novel method capable of effectively removing a halogen ion such as iodine ion from the aqueous phase when a halogen ion such as iodine ion is present in the aqueous phase.

  According to the first aspect of the present invention, an acidic aqueous phase obtained by adding an acid to water to be treated containing halogen ions is brought into contact with an adsorbent, and the halogen ions are compared with the aqueous phase before contact. A method for obtaining treated water having a reduced content of is provided.

  Conventionally, the use of an adsorbent for removing halogen ions has not been studied.

  However, in the present invention, an acid is added to the water to be treated containing halogen ions, and the obtained acidic aqueous phase is brought into contact with the adsorbent, whereby the halogen ions in the treated water after the contact are brought into contact. The content is lower than the content of halogen ions in the aqueous phase before contact. The present invention is not bound by any theory, but the reason is considered as follows. Halogen ions, together with hydrogen ions in the water to be treated, are in equilibrium with the hydrogen halide corresponding to the halogen ions:

（式中、Ｘ⁻はハロゲンイオン、Ｈ^＋は水素イオン、ＨＸはハロゲン化水素である。）
にあると考えられる。これに酸を添加すると、上記平衡がハロゲン化水素生成方向（上記式（Ｉ）の右方向）にシフトして、ハロゲンイオン（Ｘ⁻）はハロゲン化水素（ＨＸ）として存在し易くなる。生じたハロゲン化水素（ＨＸ）は分子状態であるので、ハロゲンイオン（Ｘ⁻）に比べて吸着材に物理吸着され易く、この結果、水相中のハロゲンイオンが減少するものと考えられる。

(In the formula, X ⁻ is a halogen ion, H ⁺ is a hydrogen ion, and HX is a hydrogen halide.)
It is thought that there is. When an acid is added thereto, the equilibrium is shifted in the hydrogen halide production direction (the right direction of the formula (I)), and the halogen ion (X ⁻ ) is likely to exist as hydrogen halide (HX). Since the generated hydrogen halide (HX) is in a molecular state, it is more likely to be physically adsorbed by the adsorbent than the halogen ions (X ⁻ ), and as a result, the halogen ions in the aqueous phase are considered to decrease.

  According to the above method of the present invention, when halogen ions are present in the aqueous phase, the halogen ions can be effectively removed from the aqueous phase.

“Treatment” refers to treatment for the purpose of removing halogen ions, and in the present invention means contact with an adsorbent. Further, “treated water” means a water phase to be treated (liquid phase based on water), and the treated water phase (after contact with the adsorbent in the present invention) is called “treated water”. To tell. The “acid” means Arrhenius acid, that is, a substance that generates protons (H ⁺ ) in an aqueous solution.

  The adsorbent is preferably a porous adsorbent, especially activated carbon. However, the present invention is not limited to this, and an adsorbent that can be used in an acidic aqueous phase, such as activated clay, kaolin, talc, or zeolite, may be used.

As the adsorbent, a material to which counter ions are attached in advance may be used. In the present invention, the “counter ion” means an ion having a polarity opposite to that of the halogen ion to be removed, that is, a positive polarity. If an adsorbent to which counter ions are previously added is used, it is considered that halogen ions themselves can be chemically adsorbed in addition to the above-described physical adsorption, and a synergistic effect between physical adsorption and chemical adsorption can be expected. Examples of counter ions that are attached in the present invention include ions of Group 2 metals (for example, alkaline earth metals) such as magnesium ions (Mg ²⁺ ) and calcium ions (Ca ²⁺ ), sodium ions (Na ⁺ ), and Examples thereof include alkali metal ions such as K (K ⁺ ).

  The halogen is preferably of a somewhat large mass for physisorption (primarily due to van der Waals forces) and is well matched to the size of the pores that may be present in the adsorbent. In addition, the acid strength of hydrogen halide is too strong to be able to shift the equilibrium in the direction of hydrogen halide production (right direction of the above formula (I)) using an easily available acid. It is better not to. From this point of view, the halogen can preferably be selected from the group consisting of iodine, bromine and chlorine, more preferably iodine. However, the present invention is not limited to this, and the halogen may be fluorine.

  By adding an acid to the water to be treated, the pH of the aqueous phase can be 5 or less (but before contact with the adsorbent). According to such a pH range, the equilibrium state can be effectively shifted in the direction of hydrogen halide (HX) generation, and thus treated water from which halogen ions have been effectively removed can be obtained. When such an aqueous phase is brought into contact with the adsorbent, the pH of the aqueous phase may change depending on the adsorbent used. For example, when activated carbon is used as the adsorbent, the pH of the aqueous phase after contact with the adsorbent can be 0-7.

  According to the second aspect of the present invention, the adsorbent used in the method of the first aspect is brought into contact with another neutral or alkaline aqueous phase from the adsorbent into the other aqueous phase. A method for recovering halogen ions is also provided.

In the present invention, the used adsorbent is brought into contact with another neutral or alkaline (pH 7 or higher) aqueous phase, whereby halogen ions are recovered in this aqueous phase. The present invention is not bound by any theory, but the reason is considered as follows. When the used adsorbent is brought into contact with a neutral or alkaline aqueous phase, the above-mentioned equilibrium is under the influence of acid (at the time of adsorption of halogen ions). (Left direction of (I)), the hydrogen halide (HX) adsorbed in the molecular state on the adsorbent tends to be a halogen ion (X ⁻ ), and the physical adsorption force is weakened. It is considered that ions are desorbed (or desorbed) into the aqueous phase.

  According to the above method of the present invention, halogen ions contained in the water to be treated can be recovered from the adsorbent into another water phase.

  Such a method according to the second aspect of the present invention can desorb halogen ions from the adsorbent, and at least partially recover the apparent adsorption capacity of the adsorbent for halogen ions. Therefore, the method according to the second aspect of the present invention can be understood as a method for regenerating the adsorbent.

  In addition, the “apparent adsorption capacity for halogen ions” of the adsorbent indicates how the halogen is adsorbed to the adsorbent in any form (which is considered to be a form of molecular hydrogen halide, but is not limited thereto). Regardless, it means the ability to adsorb halogen ions in the water phase apparently.

  The other aqueous phase may be neutral, but is preferably alkaline having a pH of 10 or more. Thereby, it is considered that the above-described equilibrium can be greatly shifted in the halogen ion generation direction (the left direction of the above formula (I)), and the recovery of the halogen ions and the regeneration of the adsorbent can be performed more effectively. .

  The other aqueous phase may contain a reducing agent. Thereby, it can be considered that hydrogen halide can be reduced to a halogen ion by a reducing agent, and the recovery of the halogen ion can be more effectively performed. This other aqueous phase may be alkaline and contain a reducing agent.

  According to the present invention, when a halogen ion (particularly iodine ion) is present in the aqueous phase, a novel method capable of effectively removing the halogen ion from the aqueous phase is provided. The present invention also provides a method for recovering halogen ions from a used adsorbent and / or a method for regenerating a used adsorbent.

  Embodiments of the present invention are described in detail below.

First, an acid is added to the water to be treated containing halogen ions (X ⁻ ).

The halogen ion (X ⁻ ) may be an ion such as iodine, bromine or chlorine, and is preferably an iodine ion.

The acid may be any acid as long as it can shift the equilibrium in the direction of hydrogen halide (HX) production, depending on the amount to be added. Examples of such an acid include inorganic acids such as sulfuric acid (H ₂ SO ₄ ), hydrochloric acid (HCl), nitric acid (HNO ₃ ), and particularly strong acids.

The pH of the water to be treated depends on the amount of HX, but is generally 8 or less, such as 5 or less, particularly 3 or less. The pH of the water to be treated may be 1 or less when it contains a large amount of HX. The treated water may be almost neutral, for example, pH 6-8.
By adding an acid to the water to be treated, the pH of the resulting aqueous phase can be 5 or less, preferably 1 or less (but before contact with the adsorbent). Specifically, the pH of the aqueous phase can be adjusted by appropriately selecting the type, concentration and amount of the acid to be added.

  The halogen ion content in the aqueous phase obtained by adding an acid to the water to be treated is, for example, about 500 to 100,000 ppm (by weight), although it depends on the amount of acid to be added.

  Then, the aqueous phase thus obtained is brought into contact with the adsorbent.

The adsorbent may be any adsorbent that can adsorb apparently halogen ions in the aqueous phase under acidic conditions (strictly speaking, the substance is not limited to an ionic form as long as it is a substance derived therefrom). Such an adsorbent may be a porous adsorbent and may have, for example, a specific surface area (N ₂ , BET method) of 800-2500 m ² / g.

  The adsorbent is preferably activated carbon. The activated carbon may have any shape (pellet shape, powder shape, granular shape, fiber shape, etc.), and any raw material (coal, coconut shell, charcoal, etc.) and activation method may be used.

In addition to activated carbon, activated clay, kaolin, talc, zeolite or the like may be used as the adsorbent. These can also have any shape (such as pellets, powders, or granules).
The adsorbent may be particles having an average particle diameter of 0.01 μm to 30 mm. The activated carbon may have an average particle diameter of 0.05 mm to 5 mm, for example 0.07 mm to 2 mm. Kaolin and talc may have an average particle size of 0.1 μm to 100 μm. The zeolite may have an average particle size of 0.01 μm to 30 mm.

Although the temperature and pressure at the time of contact may be set as appropriate, it can be conveniently at ordinary temperature (for example, 10 to 30 ° C.) and normal pressure (for example, about 0.1 MPa).
The contact time may preferably be 5 minutes to 20 hours, for example 15 minutes to 5 hours. The supply method of the water to be treated may be either a batch type or a continuous type.

  The treated water obtained after contact has a halogen ion content smaller than the content of halogen ions in the aqueous phase before contact, and is, for example, about 0 to 20 ppm (weight basis). The pH of the treated water obtained after contact may differ from the pH of the aqueous phase before contact depending on the adsorbent used. For example, when activated carbon is used as the adsorbent, the pH of the aqueous phase after the contact can be 7 or more compared to the pH 0-5 of the aqueous phase before the contact with the adsorbent.

  From the above, it is possible to obtain treated water in which halogen ions are apparently adsorbed by the adsorbent and are effectively removed.

  As the adsorbent is used, the apparent adsorption capacity for halogen ions can be reduced. The spent adsorbent with reduced adsorption capacity is brought into contact with another neutral or alkaline aqueous phase to recover halogen ions from the adsorbent into another aqueous phase, and at least the adsorption capacity of the adsorbent is reduced. It can be partially recovered and played back.

Another aqueous phase used for halogen ion recovery and adsorbent regeneration can be neutral or alkaline (e.g., pH 7-14), but is preferably alkaline with a pH of 10 or higher. In the case of alkalinity, another aqueous phase includes, for example, the general formula M (OH) _n (wherein M is an alkali metal such as Na and K, a second group element such as Ca and Mg, or an alkaline earth metal, Al An element selected from the group consisting of other metals such as n, where n is an integer of 1 or more according to M) can be used.

  The other aqueous phase may contain a reducing agent. As the reducing agent, for example, sulfite, sodium thiosulfate, hydrogen sulfite and the like can be used.

  Thus, the regenerated adsorbent can be used again for removing halogen ions, and the recovered halogen ions may be used for other purposes.

Hereinafter, the present invention will be further described through experiments. In the following experiments, “%” means “% by weight” unless otherwise specified.
In Experiments 1 to 3 and Experiments 5 to 7, whether activated carbon is used as an adsorbent and an aqueous phase is prepared by adding an acid to water to be treated containing iodine ions, and whether or not adsorption of iodine ions occurs I investigated. In Experiment 4, it was examined whether iodine ions desorbed from the adsorbent used in Experiment 1.
In any experiment, the iodine ion content (concentration) in the aqueous phase was analyzed and measured using an ion chromatograph (manufactured by Shimadzu Corporation, model AT20).

(Experiment 1: Continuous (distribution) iodine ion removal)
A resin column having a length of 400 mm and an inner diameter of 20 mm was packed with activated carbon (manufactured by Mitsubishi Calgon, highly activated activated carbon, specific surface area 2017 m ² / g (N ₂ , BET method)).

  An aqueous solution of 20% by weight sulfuric acid and 3.2% by weight hydrogen iodide was prepared as an aqueous phase formed by adding acid to water to be treated containing iodine ions. The iodine ion content of this aqueous solution was 32268 ppm (weight basis).

  Referring to FIG. 1, this aqueous phase was circulated from tank 1 by pump 2 from above lower inlet 4 to column 3 at a flow rate of 1.05 cc / min so as to have a linear velocity of 0.20 m / hr. . Treated water was obtained from the upper outlet 5 of the column 3.

  The iodine ion content in the obtained treated water was measured, an adsorption breakthrough curve was drawn based on the iodine ion content in the aqueous phase before contact, and the apparent adsorption ability of activated carbon for halogen ions was confirmed. As a result, until the activated carbon is completely broken through (in other words, the iodine ion content in the treated water becomes substantially equal to the iodine ion content in the aqueous phase before contact, and the activated carbon substantially eliminates the iodine ions. It was found that 0.12 g of iodine ions per 1 g of activated carbon was adsorbed until the time when it was no longer adsorbed.

(Experiment 2: Continuous (distribution) type iodine ion removal)
A resin column having a length of 60 mm and an inner diameter of 20 mm was packed with activated carbon as in Experiment 1.

  As an aqueous phase formed by adding acid to water to be treated containing iodine ions, an aqueous solution of 10% by weight sulfuric acid and 4.5% by weight hydrogen iodide was prepared. The iodine ion content of this aqueous solution was 44648 ppm (weight basis).

  This aqueous phase was circulated from the lower inlet to the column at a flow rate of 0.52 cc / min so that the linear velocity was 0.1 m / hr. Treated water was obtained from the upper outlet of the column.

  As a result of confirming the adsorption ability in the same manner as in Experiment 1, it was found that 0.20 g of iodine ions was adsorbed per 1 g of activated carbon until the activated carbon was completely broken through.

(Experiment 3: Continuous (distribution) iodine ion removal)
An aqueous solution containing 35% by weight sulfuric acid and 4.5% by weight hydrogen iodide was prepared as an aqueous phase formed by adding acid to water to be treated containing iodine ions (the iodine ion content of this aqueous solution was 44648 ppm (weight basis)). This was the same as Experiment 2.

  In this experiment, it was found that 0.22 g of iodine ions were adsorbed per 1 g of activated carbon until the activated carbon completely broke through.

(Experiment 4: Continuous (distribution) activated carbon regeneration and iodine ion recovery)
The activated carbon packed in the resin column after being used in Experiment 1 was used as it was.

  As another aqueous phase, a 1% by weight aqueous solution of sodium hydroxide was prepared. This aqueous solution did not contain iodine ions.

  This other aqueous phase was circulated through the column from the lower inlet at a flow rate of 0.26 cc / min so that the linear velocity was 0.05 m / hr. From the upper outlet of the column, recovered water was obtained as an aqueous phase after contact.

  The iodine ion content in the obtained recovered water was measured to confirm the apparent desorption ability of activated carbon to halogen ions. As a result of circulating 748 g of the other aqueous phase (alkaline aqueous solution), it was found that 0.0015 g of iodine ions was desorbed per 1 g of activated carbon. This indicates that 98.8 wt% of the iodine ions adsorbed in Experiment 1 could be recovered.

  From the above experiments 1 to 4, it was confirmed that iodine ions can be adsorbed on activated carbon and iodine ions adsorbed on activated carbon can be desorbed therefrom.

  In Experiments 5 to 7, 30 cc of an aqueous solution containing 0.3 g of activated carbon and 4.5% iodine ion in a 50 cc glass bottle was shaken until the activated carbon broke through a shaker, and the amount of breakthrough adsorption was calculated. . Equilibrium adsorption amount compared iodine ion concentration in raw water and treated water to confirm iodine ion adsorption amount on activated carbon.

(Experiment 5: Batch-type iodine ion removal (10% by weight sulfuric acid))
The iodine ion concentration of the raw water was from 44842 ppm to 42201 ppm after the activated carbon treatment, and the iodine adsorption amount per gram of activated carbon was 264 mg / g. In terms of adsorption rate to activated carbon, it is 26.4%.

(Experiment 6: Batch-type iodine ion removal (pH = 1))
The iodine ion concentration in the raw water was 44842 ppm, and after the activated carbon treatment was 44661 ppm, and the iodine adsorption per gram of activated carbon was 18 mg / g. When converted to the adsorption rate to activated carbon, it becomes 1.8%.

(Experiment 7: Batch-type iodine ion removal (pH = 7))
The iodine ion concentration in the raw water was 44842 ppm, and after the activated carbon treatment was 44842 ppm, and there was no adsorption to the activated carbon.

The present invention can be used for, for example, wastewater treatment in factories and the like to remove halogen ions, particularly iodine ions, before discharging the wastewater to the outside. Therefore, wastewater discharged through this wastewater treatment is colored. The wastewater regulations regarding the level will be fully satisfied.
Moreover, the adsorbent used in the present invention is recyclable and can be used repeatedly for the above wastewater treatment.
Furthermore, the halogen ions can be recovered at the time of regeneration, and the recovered halogen ions can be reused for other purposes.

It is the schematic of the apparatus used in the experiment which confirms the effect of this invention.

Explanation of symbols

1 Tank 2 Pump 3 Column (packed with adsorbent)
4 entrance 5 exit

Claims (9)

  A method for obtaining treated water having a reduced content of halogen ions compared to an aqueous phase before contact, by contacting an acidic aqueous phase obtained by adding an acid to water to be treated containing halogen ions with an adsorbent .   The method according to claim 1, wherein the adsorbent is activated carbon.   The method according to claim 1 or 2, wherein an adsorbent to which counter ions are preliminarily attached is used.   4. The method according to any one of claims 1 to 3, wherein the halogen is selected from the group consisting of iodine, bromine and chlorine.   The method of claim 4, wherein the halogen is iodine.   The method according to claim 1, wherein the acidic aqueous phase has a pH of 5 or less before contact with the adsorbent.   A method for recovering halogen ions from an adsorbent into another aqueous phase by bringing the adsorbent used in the method according to any one of claims 1 to 6 into contact with another neutral or alkaline aqueous phase. .   8. A process according to claim 7, wherein the further aqueous phase is pH 7 or higher.   9. A process according to claim 7 or 8, wherein the further aqueous phase comprises a reducing agent.

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