JP4880574B2 - Method for treating water containing organic arsenic compounds - Google Patents

Description

  The present invention relates to a method for treating water containing an organic arsenic compound. That is, the present invention relates to a treatment method for oxidizing and decomposing an organic arsenic compound contained in water to be treated based on the Fenton method.

《Technical background》
Industrial wastewater and groundwater often contain organic arsenic compounds that do not normally exist in nature. Organic arsenic compounds are known to be persistent and highly toxic.
Typical examples of this type of organic arsenic compound include diphenylarsinic acid (DPAA), monophenylarsonic acid (MPAA), phenylarsonic acid (PAA), and the like.
Recently, gallium arsenide and indium arsenide are being used frequently as compound semiconductors, surpassing conventional single semiconductors such as silicon and germanium.
Industrial wastewater containing monomethyl arsenic or dimethyl arsenic, which are organic arsenic compounds, is discharged from the production reaction process and the wafer manufacturing process. In other words, waste water from the compound semiconductor factory is discharged with the organic arsenic compound as a component.

<Conventional technology>
Conventionally, for example, the following treatment techniques for purifying industrial wastewater and groundwater containing this hardly decomposable and toxic organic arsenic compound have been used.
a. Activated carbon adsorption + coagulation sedimentation treatment method: After adsorbing an organic arsenic compound to powdered activated carbon, it is degraded with sulfuric acid to be in an inorganic state and coagulated, precipitated and separated as an iron salt and a compound.
b. UV / ozone treatment method: An organic arsenic compound is oxidized, decomposed, aggregated, precipitated, and separated by OH radicals generated by irradiating ultraviolet rays onto a photocatalyst or ozone.
c. RO membrane treatment method: Organic arsenic compounds are aggregated and precipitated with iron chloride, and then separated by RO membrane treatment.
d. Fenton treatment method (conventional method): Organic arsenic compounds are oxidized, decomposed, aggregated, precipitated, and separated by OH radicals generated with hydrogen peroxide and iron salt, that is, divalent iron ions.

《Information on prior art documents》
As this type of Fenton treatment method, for example, the one shown in the following Patent Document 1 can be mentioned.
JP 2006-239507 A

By the way, the following problems have been pointed out with respect to such conventional technology for treating water containing an organic arsenic compound.
<First problem>
First, the conventional Fenton treatment method has been pointed out that the treatment performance is poor and the running cost (chemical use cost) is increased.
For example, hydrogen peroxide, which is a source of OH radicals that oxidize and decompose organic arsenic compounds, is easily wasted during processing, and a large amount of hydrogen peroxide has been added in advance. That is, hydrogen peroxide has a high ratio of being decomposed into water and oxygen without generating OH radicals. Therefore, in order to cover this, a large amount of oxygen peroxide is added to the excess, and the efficiency is improved. It was bad.
Such a problem has become a major bottleneck when the Fenton treatment method is scaled up and applied to large-scale treatment and large-capacity treatment of industrial wastewater and groundwater.

<< Second problem >>
Secondly, the conventional Fenton treatment method has been pointed out that the post-treatment is also costly.
That is, as described above, since hydrogen peroxide was excessively added, the residual content of hydrogen peroxide in the industrial wastewater and groundwater after the organic arsenic compound was oxidized, decomposed and separated increased, and the ion concentration increased. It was very expensive.
Therefore, in order to avoid water pollution and discharge as purified water, neutralization treatment by adding a large amount of a neutralizing agent such as catalase is indispensable as post-treatment, which further increases the cost of chemical use. The difficulty of increasing was pointed out. This is also a major bottleneck when applying the Fenton treatment method to scale-up and large-capacity treatment.

《Third problem》
Thirdly, in addition to these, the conventional Fenton treatment method has also been pointed out that it is not easy to control the amount of chemical added.
That is, it was not easy to respond to fluctuations in the quality of supplied industrial wastewater and groundwater and to respond to changes in the content of organic arsenic compounds, that is, to control the amount of hydrogen peroxide and iron salt added. Hydrogen peroxide and iron salt should be added in appropriate amounts, but the appropriate amount addition rate has not been established and tends to be too little or too much. In many cases, it has been added excessively.
In the above-mentioned Patent Document 1, iron powder is also used for post-treatment and adsorption treatment of Fenton treatment, and it becomes more difficult to ensure the quantitativeness of iron powder, and iron powder remains or is insufficient. And the processing performance has become unstable. These points are also the bottleneck in applying scale-up to large-scale processing and large-capacity processing.

《Fourth problem》
Fourthly, on the other hand, the following problems have been pointed out with respect to the aforementioned activated carbon adsorption + coagulation precipitation treatment method, UV / ozone treatment method, RO membrane treatment method, etc., and scale-up to large-scale treatment and large-capacity treatment. It became a bottleneck for application.
a. With regard to the activated carbon adsorption + coagulation sedimentation treatment method, it has been difficult to reduce the treatment capacity due to activated carbon breakthrough, and problems have been pointed out in terms of treatment stability, activated carbon replacement cost, equipment installation space, and the like.
b. Regarding the UV / ozone treatment method, problems have been pointed out due to poor OH radical production efficiency, excessive equipment, initial cost, power waste cost, UV lamp degradation, and the like.
c. Regarding the RO membrane treatment method, the membrane treatment does not change the components of the organic arsenic compound itself, and the processing capacity reduction due to clogging has also become a problem.

<< About the present invention >>
In view of such a situation, the method for treating organic arsenic compound-containing water of the present invention has been made to solve the above-described problems of the conventional examples.
In the present invention, first, OH radicals are efficiently generated, and the running cost is excellent. Second, the post-processing cost is excellent. Third, the chemical addition amount is easily controlled. Another object of the present invention is to propose a method for treating water containing an organic arsenic compound that is excellent in treatment stability, initial cost, space, and the like.

<About Claim>
The technical means of the present invention for solving such a problem is as follows.
The method for treating water containing an organic arsenic compound according to claim 1 oxidizes and decomposes the organic arsenic compound contained in the water to be treated based on the treatment process of the Fenton method. Then, hydrogen peroxide, a divalent iron ion solution, and a pH adjuster are added to the water to be treated containing the organic arsenic compound.

Then, the entire amount of hydrogen peroxide is added to the treatment tank at the beginning of the reaction.
In the treatment tank, the divalent iron ion solution is intermittently added repeatedly by repeating a plurality of cycles after the addition of hydrogen peroxide, so that the OH radicals generated below return to water and are wasted. It works to avoid.
As for the pH adjuster, an acid pH adjuster is first added to the water to be treated supplied to the treatment tank in the pH adjustment tank, and divalent iron is added in the treatment tank after the addition of hydrogen peroxide. An alkaline pH adjuster is added each time the ionic solution is added in a divided manner, so that the water to be treated is maintained at a weak acidity of pH 3 to pH 5, and the reaction in which hydrogen peroxide is decomposed and wasted into water and oxygen is suppressed. It works as much as possible.

As for the addition amount of hydrogen peroxide and divalent iron ions, the required number of moles actually prepared is more calculated based on the theoretical reaction value based on the reaction formula.
First, from the specific content of the organic arsenic compound contained in the water to be treated, the number of moles of the theoretical reaction value of the OH radical is obtained as a standard, and then the actual required number of moles of the OH radical is obtained based on this standard. From the required number of moles of OH radicals, the theoretical number of moles of reaction of hydrogen peroxide and divalent iron ions, which are OH radical products, is obtained as a reference, and The required number of moles of hydrogen peroxide and divalent iron ions that are actually prepared is calculated from this criterion.
The addition timing of hydrogen peroxide and divalent iron ions is when hydrogen peroxide is used up and hydrogen peroxide is exhausted from the water to be treated in the treatment tank. This is a time when divalent iron ions disappear from the water to be treated in the treatment tank after the previously added portion is used up.

As for the OH radical production reaction, hydrogen peroxide is reduced with divalent iron ions each time it is added in a divided manner, and in addition to the Fenton main reaction, in which OH radicals are produced, the hydrogen peroxide is further reduced. The generated hydroxide ions are oxidized by trivalent iron ions generated by the oxidation reaction of divalent iron ions to generate OH radicals, and the generated OH radicals are further covered. The reaction of reacting with the water of the treated water to generate new OH radicals and water is repeated in a chain, and the trivalent iron ions generated by the oxidation reaction of the divalent iron ions The reaction of reacting with hydrogen oxide to generate at least new OH radicals is repeated in a chain, and the generation of OH radicals ends when hydrogen peroxide is exhausted in the treatment tank.
Therefore, the organic arsenic compound contained in the water to be treated is oxidized and decomposed by the OH radicals thus generated, and is mineralized into water, carbon dioxide, and inorganic arsenic compound.

<About the action>
Since the present invention comprises such means, the following is achieved.
(1) Water to be treated containing an organic arsenic compound such as diphenylarsinic acid, monomethylarsenic, or dimethylarsenic is supplied to a treatment apparatus. The organic arsenic compound is oxidized and decomposed by a treatment method based on the treatment process of the Fenton method.
(2) The treatment apparatus is provided with treated water supply means, treatment tank, post-treatment tank, etc., and the treatment tank is provided with hydrogen peroxide addition means, iron ion addition means, pH adjustment means, etc. Yes.
(3) The water to be treated is supplied to the treatment tank, but before that, sulfuric acid or the like is added from the pH adjusting means to make it weakly acidic at about pH 4.
(4) In the treatment tank, all the hydrogen peroxide is first added to the water to be treated from the hydrogen peroxide addition means.
(5) Then, a divalent iron ion solution is dividedly added from the iron ion adding means, and caustic soda or the like is added from the pH adjusting means for each divided addition, so that the weak acidity of the water to be treated is maintained.

(6) Now, hydrogen peroxide generates OH radicals using divalent iron ions as a catalyst. In this OH radical production reaction, first, iron ions are added in portions, so there is no risk of waste of OH radicals and iron ions, and the catalytic function of iron ions is promoted because of a weakly acidic atmosphere. At the same time, hydrogen peroxide is prevented from being decomposed and wasted into water and oxygen.
(7) Moreover, OH radical is produced | generated also by reaction of the trivalent iron ion produced | generated by the said reaction, and a hydroxide ion.
(8) Further, OH radicals react with hydrogen peroxide by trivalent iron ions produced by the above reaction by reacting the OH radicals produced by the above reaction with water to be treated. Also, each is newly generated repeatedly in a chain.

(9) In the treatment tank, the organic arsenic compound in the water to be treated is oxidized and decomposed by the strong oxidizing power of the OH radicals generated in this way, and is mineralized into inorganic arsenic compound, water, carbon dioxide, etc. .
(10) Then, the water to be treated is drained externally after the complex of inorganic arsenic compound is floculated, aggregated, precipitated and removed in the post-treatment tank.
(11) In this processing method, the amount of chemical addition such as Fenton reagent is easily calculated from the theoretical reaction value, and the configuration of the apparatus and method is relatively simple, and stable processing is possible.
(12) Therefore, the method for treating water containing an organic arsenic compound of the present invention exhibits the following effects.

<< First effect >>
First, OH radicals are efficiently generated without waste, and the running cost is excellent.
That is, in the processing method of the present invention, first, a. OH radicals are efficiently generated by maintaining the water to be treated in a weak acidity, adding all of the hydrogen peroxide, split addition of divalent iron ions, or the like.
b. OH radicals are also generated by the reaction of trivalent iron ions and hydroxide ions. Further, the generated OH radical reacts with the water to be treated, or the trivalent iron ion and hydrogen peroxide react to generate repeatedly in a chain manner. Thus, OH radicals are generated with high efficiency.
c. Like the above-mentioned conventional treatment technology, hydrogen peroxide is not decomposed and wasted into water and oxygen, and it is not necessary to add an excessive amount of hydrogen peroxide, and chemicals such as Fenton reagent are used. Cost is reduced.
With these a, b, and c, in the processing technique of the present invention, the organic arsenic compound is easily and reliably oxidized, decomposed, and removed, and the scale-up application to full-scale processing, large-scale processing, large-capacity processing, etc. Practical application is easy.

<< Second effect >>
Secondly, the residual content of hydrogen peroxide is very low, reducing the post-treatment costs.
That is, in the treatment method of the present invention, OH radicals are efficiently generated as described above, and the organic arsenic compound is oxidized, decomposed, and removed. Like the above-mentioned conventional treatment technology of this kind, hydrogen peroxide is not excessively added, and the water to be treated has a small residual content of hydrogen peroxide after the treatment, and the post-treatment cost by the neutralizing agent Is also reduced.
Therefore, the treatment technique of the present invention also reduces the cost of using chemicals from this aspect, and opens the way to scale-up application to full-scale processing, large-scale processing, large-capacity processing, etc., that is, practical application.

《Third effect》
Thirdly, the chemical addition amount can be easily controlled. That is, the amount of hydrogen peroxide added corresponding to the content of the organic arsenic compound in the water to be treated, the amount of divalent iron ions added corresponding to the amount of hydrogen peroxide added, and the amount of pH adjuster added accordingly Etc. are easily calculated from theoretical reaction values, and the required number of moles is obtained.
Therefore, it is possible to add an appropriate amount of chemicals without excess or deficiency, and these automatic controls are easy. For example, as in the above-described conventional processing technique of this type, there is no situation in which quantitative properties cannot be ensured for the divalent iron ions, and there is no surplus or shortage, and the processing performance is stabilized.
In view of this, the processing technique of the present invention can be easily applied to scale-up, ie, practical use, for full-scale processing, large-scale processing, large-capacity processing, and the like.

<< 4th effect >>
Fourth, it is excellent in processing stability, initial cost, running cost, space, and the like.
That is, in the processing method of the present invention, the processing capacity is reduced due to use over time, the replacement cost of activated carbon, the installation space for the activated carbon, the OH radical generation efficiency, the equipment overload, Problems such as power wasting costs, UV lamp degradation, etc. are eliminated.
Therefore, the processing technique of the present invention also supports the scale-up application to full-scale processing, large-scale processing, large-capacity processing, etc., that is, practical use from these aspects.
As described above, the effects exerted by the present invention are remarkably large, such as all the problems existing in this type of conventional example are solved.

《About drawing》
Hereinafter, the method for treating water containing an organic arsenic compound of the present invention will be described in detail based on the best mode for carrying out the invention shown in the drawings.
FIG. 1 is a configuration flow diagram of an example of the best mode for carrying out the present invention.

<< Organic Arsenic Compound 1 >>
First, the organic arsenic compound 1 that is a treatment target of the treatment method of the present invention will be described.
Industrial wastewater such as mines, refining, chemicals, pesticides, insecticides, pigments, glass, petroleum, etc., and contaminated groundwater with residual toxic gas permeating into the soil, contains organic arsenic compounds 1 that do not normally exist in nature. There are many things that have been done. It is known that the organic arsenic compound 1 is hardly decomposable and has strong toxicity as an arsenic (As) compound.
The organic arsenic compound 1 is typically diphenylarsinic acid (DPAA), but its related substances such as monophenylarsonic acid (MPAA), phenylarsonic acid (PAA), and the like are also conceivable. In addition, phenylmethylarsinic acid (PMAA), arsenobetaine (AsB), methylarsonic acid (MAA), dimethylarsinic acid (DMAA), tolphenylarsine (TPA), phenylmethylarsinic acid (PMAA), etc. are also considered. It is done.

Recently, gallium arsenide (GaAs) and indium arsenide (InAs) have been widely used as compound semiconductors along with single semiconductors such as silicon (Si) and germanium (Ge). In other words, the semiconductor characteristics depend on the outer electronic structure of the electronic structure, but gallium arsenide and indium arsenic have the same structural characteristics as the outer electronic structure under crystal growth of silicon, germanium, etc. during the crystal growth process. A semiconductor electronic structure is realized.
For crystal growth of gallium arsenide or indium arsenide, vapor phase epitaxy is relatively easy, and a metal organic chemical vapor deposition method is used. In this metal organic vapor phase epitaxy, gallium (Ga) and indium (In) are used as raw materials for trimethylgallium [(CH ₃ ) ₃ -Ga] and trimethylindium [(CH ₃ ) ₃ -In, which are organic metals. Arsine (AsH ₃ ) is used as a raw material for the arsenic formation.
Then, from the process of generating gallium arsenide and indium arsenic by reacting both, and the wafer manufacturing process (processing process, cleaning process), trivalent or pentavalent methylated arsenic, which is the organic arsenic compound 1, that is, Monomethyl arsenic [CH ₃ —As (OH) ₂ , CH ₃ —As (═O) (OH) ₂ ] and dimethyl arsenic [(CH ₃ ) ₂ —As (═O) (OH)] Will be discharged in large quantities.
There may be cases where such organic arsenic compound 1 is contained in industrial wastewater or groundwater. In the present invention, the organic solvent arsenic compound 1 contained in the water to be treated 3 is treated.

<Outline of processing method>
In the treatment method of the present invention, the organic arsenic compound 1 contained in the water to be treated 3 is oxidized and decomposed based on the treatment process of the improved Fenton method.
That is, in the treatment method of the present invention, the water containing the organic arsenic compound 1 is treated water 3. The organic arsenic compound 1 contained in the fenton reagent hydrogen peroxide (H ₂ O ₂ ) and divalent iron ions (Fe ²⁺ ) are used to generate OH radicals (.OH) generated by the Fenton main reaction. , Oxidation and decomposition by OH radicals generated by incidental, secondary, and chain reactions of Fenton's main reaction, and mineralization into low molecular weight compounds such as inorganic arsenic compounds, water, and carbon dioxide To do.
And the processing method of this invention is equipped with the processing tank 4, the to-be-processed water supply means 5, the hydrogen peroxide addition means 6, the iron ion addition means 7, and the pH adjustment means 8 which were attached to the processing tank 4. Yes.
Hereinafter, these will be described in detail.

<< About treated water supply means 5 etc. >>
First, the treated water supply means 5 and the like will be described. The treated water supply means 5 supplies the treated water 3 containing the organic arsenic compound 1 to the treatment tank 4 as a treatment target.
That is, in the illustrated example, the treated water 3 is introduced into the raw water tank 9 of the treated water supply means 5, and the treated water 3 is supplied to the treated tank 4 via the raw water tank 9 and the pH adjustment tank 10. Is supplied. The treated water 3 introduced into the raw water tank 9 is subjected to pretreatment such as dust sludge removal and biological treatment in advance as necessary. In the pH adjusting tank 10, a pH adjusting agent is added from the attached pH adjusting means 8.
In this way, the pH adjusting means 8 adds the pH adjusting agent to the treated water 3 being supplied from the raw water tank 9 of the treated water supply means 5 to the treated tank 4 so that the treated water 3 is predetermined. After being adjusted to weak acidity, it is supplied to the treatment tank 4. That is, the water 3 to be treated from the raw water tank 9 is often at a pH of 6 or more, for example, so that the pH is adjusted to about pH 5 to about 3, typically about pH 4. A modifier is used.
The reason for adjusting the pH in advance in this way is that, as will be described later, in order to ensure that the OH radical production reaction with hydrogen peroxide and divalent iron ions is performed efficiently as expected. is there. The pH adjusting tank 10 is used for large-volume treatment, continuous treatment of the water to be treated 3, treatment of a high concentration organic arsenic compound 1, and the like.
The treated water supply means 5 and the like are as described above.

<About hydrogen peroxide addition means 6>
Next, the hydrogen peroxide addition means 6 attached to the processing tank 4 will be described. The hydrogen peroxide addition means 6 adds a total amount of an aqueous solution of hydrogen peroxide (H ₂ O ₂ ) to the treated water 3 in the treatment tank 4 as a Fenton reagent at the beginning of the reaction. Hydrogen peroxide is a source of OH radicals.
The amount of hydrogen peroxide added per reaction depends on the specific content and specific concentration of the organic arsenic compound 1 contained in the water 3 to be treated. The actual amount calculated (number of moles required) calculated for the eyes is added all at once at the beginning of the reaction. The next addition is when hydrogen peroxide is exhausted from the water 3 to be treated in the treatment tank 4, that is, at the next reaction, and the same amount is added in the same manner.
Thus, in this specification, the addition of the total amount means that 100% of the total amount of the drug necessary for the reaction is added all at once.
In this way, the entire amount of hydrogen peroxide is added from the hydrogen peroxide addition means 6.

<< About iron ion addition means 7 >>
Next, the iron ion addition means 7 attached to the processing tank 4 will be described. The iron ion adding means 7 intermittently repeats a plurality of cycles with respect to the water to be treated 3 of the treatment tank 4 after the addition of hydrogen peroxide as described above, thereby supplying a divalent iron ion (Fe ²⁺ ) solution to Fenton. Add in portions as reagents.
That is, substances that generate divalent iron ions in the liquid, such as ferrous sulfate heptahydrate (FeSO ₄ · 7H ₂ O), are typically used as such iron salts, but other anhydrous Salts and hydrated salts such as iron chloride (FeCl ₂ ) and hydrates thereof can also be used. The divalent iron ion functions as a catalyst for the OH radical generation reaction of hydrogen peroxide.
The amount of iron ion added per reaction is calculated based on the theoretical reaction value, but a larger actual required amount is, for example, about 0.5 mol per 1 mol of hydrogen peroxide.
Moreover, this iron ion is divided and added in multiple times. That is, the necessary amount for one reaction is not added in the whole amount, but is divided into about 3 to 7 times, for example, 5 times, and is added sequentially. As for the addition timing for each time, the next time is added at the stage where the previous addition is gone. Thus, in this specification, divided addition means that the amount of drug necessary for the reaction is added in multiple portions.

The reason why the divalent iron ions are added separately is as follows: a, b, c. First a. If the total amount is added, in the chemical reaction to be described later, the OH radical is wasted at the same time as the intended positive reaction from the original system using hydrogen peroxide as a reactant to the production system using OH radical as a product. Reaction is likely to occur.
That is, a reaction in which surplus OH radicals return to water easily occurs, loss occurs, and iron ions used for generating OH radicals are wasted. On the other hand, when the addition is divided, such a reaction is suppressed and the waste of iron ions is eliminated.
B. OH radicals have a very short reaction time due to their intense reaction, and have a very short life. When the total amount is added in a divided manner, OH radicals are generated each time, and the corner of the treated water 3 in the treatment tank 4 is generated. I will come across. Accordingly, the oxidation and decomposition of the organic arsenic compound 1 can be ensured, made efficient, and accelerated accordingly.
C. When the addition is divided, the remaining hydrogen peroxide is smaller than the total addition, and accordingly, the post-treatment cost by the neutralizing agent is reduced accordingly.
In this way, divalent iron ions and the like are dividedly added from the iron ion adding means 7.

<About pH adjusting means 8>
Next, the pH adjusting means 8 attached to the processing tank 4 will be described. The pH adjusting means 8 adjusts the pH of the water to be treated 3 before being supplied from the water to be treated supplying means 5 to the treatment tank 4 and the water to be treated 3 after being supplied to the treatment tank 4 as described above. An agent is added to maintain the water to be treated 3 at a weak acidity of about pH 4, for example.
That is, the pH adjusting means 8 adds an acid pH adjuster such as sulfuric acid (H ₂ SO ₄ ) before the addition of hydrogen peroxide, and after the addition of hydrogen peroxide, An alkaline pH adjuster such as caustic soda (NaOH) is added.

The reasons for maintaining the water to be treated 3 at about pH 3 to about pH 5 typically about pH 4 are as follows: a, b, c.
First a. As will be described later, it functions to suppress a wasteful decomposition reaction of hydrogen peroxide into water and oxygen that inhibits the intended reaction. With this, b. It functions to promote electron donation of divalent iron ions to hydrogen peroxide. C. It functions to promote and ensure the incidental, secondary, and chain-repeated OH radical generation reactions described below. With these a, b, and c, generation of OH radicals proceeds efficiently.
On the other hand, first, the treated water 3 from the raw water tank 9 of the treated water supply means 5 is often, for example, pH 6 or higher, and therefore, as described above, in the pH adjusting tank 10, Sulfuric acid is added to adjust the pH to about 4, for example.
Then, after the fact, when divalent iron ions are added in the treatment tank 4, the pH of the water to be treated 3 is lowered to, for example, about 2.8 and the acidity is excessively increased. For each divided addition, for example, caustic soda is added to adjust the pH of the water to be treated 3 to about pH 4, for example.
The pH adjusting means 8 is as described above.

<< Reaction in Treatment Tank 4 (OH Radical Generation: Part 1) >>
Next, the chemical reaction (generation of OH radicals: part 1) in the treatment tank 4 will be described. In the treatment tank 4 of this treatment method, firstly, the water to be treated 3 is stirred and flowed down, and the added hydrogen peroxide is reduced by divalent iron ions added as a catalyst. , Generating OH radicals.
The generation of such OH radicals will be further described in detail. In the treatment tank 4, OH radicals are generated based on the following chemical formulas 1 and 2 (chemical formula 3). This is the Fenton main reaction.

These will be further described in detail. In this Fenton main reaction, in the reaction formula of Chemical Formula 1, divalent iron ions (Fe ²⁺ ) that are sequentially added from the iron ion adding means 7 are maintained in a weakly acidic atmosphere in which the treated water 3 has a pH of about 4, for example. Therefore, as a catalyst, electrons (e ⁻ ) are sequentially supplied to the hydrogen peroxide (H ₂ O ₂ ) of the chemical formula 2 as a catalyst, and self oxidizes to trivalent iron ions (Fe ³⁺ )
Therefore, in the reaction formula of Chemical Formula 2, all of the hydrogen peroxide initially added from the hydrogen peroxide addition means 6 is sequentially supplied with electrons based on the chemical formula of Chemical Formula 1, and in each case, OH radical (.OH) And hydroxide ions (OH ⁻ ) are produced. When the reaction formulas of Chemical Formula 1 and Chemical Formula 2 are synthesized together, the reaction formula of Chemical Formula 3 is obtained.
By the way, in such a reaction, since the to-be-processed water 3 is maintained in the weakly acidic atmosphere as mentioned above, it is suppressed that hydrogen peroxide is decomposed | disassembled into water and oxygen, and wasted. On the other hand, if it is not maintained in a weakly acidic atmosphere, hydrogen peroxide becomes water molecules (H ₂ O) while generating oxygen (O) in the nascent stage according to the following reaction formula 4; The reaction formula of Chemical Formula 2 (Chemical Formula 3) is wasted without generating OH radicals. It should be noted that such nascent oxygen is oxygen molecules (O ₂ ) and leaves the system when there is no oxidation target.
In the treatment tank 4, first, OH radicals are generated by such a Fenton main reaction.

<< Reaction in treatment tank 4 (generation of OH radicals: 2) >>
Next, the chemical reaction (generation of OH radical: part 2) in the treatment tank 4 will be described. Secondly, in the treatment tank 4, OH radicals (.OH) can be generated also by the following reaction formulas 5 and 6.
That is, in the treatment tank 4, firstly, OH radicals are generated by the Fenton main reaction in the reaction formula of the chemical formula 3 (Chemical formula 1 and chemical formula 2) described above. Also according to the formula, OH radicals are generated incidentally, secondaryly and in a chain.

This will be further described in detail. In the treatment tank 4, the hydroxide ions (OH ⁻ ) generated by the reduction reaction of hydrogen peroxide are converted into trivalent iron ions (Fe ³⁺ ) generated by the oxidation reaction of divalent iron ions. Oxidized to generate OH radicals (.OH).
That is, the trivalent iron ion generated by the chemical formula 1 is deprived of the electron (e ⁻ ) by the chemical formula 5 and chemical formula 6 from the hydroxide ion generated by the chemical formula 2 OH radicals are generated, and themselves are reduced to divalent iron ions and returned.
In this way, when not only the reaction formula of Chemical Formula 3 (Chemical Formula 1, Chemical Formula 2) but also the chemical formulas of Chemical Formula 5 and Chemical Formula 6 occur in a chain-balanced manner, OH radicals are generated more efficiently. The
Secondly, in the treatment tank 4, OH radicals can be generated by such a reaction.

<< Reaction in Treatment Tank 4 (Generation of OH radical: Part 3) >>
Next, the chemical reaction (OH radical generation: part 3) in the treatment tank 4 will be described. In the treatment tank 4, in addition to the first and second described above, new OH radicals are generated incidentally, secondary, and chained by the third reaction.
That is, OH radicals generated by the reaction formulas of Chemical Formula 3 (Chemical Formula 1, Chemical Formula 2), Chemical Formula 5, and Chemical Formula 6 react with the water of the water to be treated 3 to generate new OH radicals and water. This reaction is repeated in a chain manner according to the following reaction formulas 7 and 8.

These will be further described in detail. First, in a neutral to alkaline atmosphere, OH radicals extract hydrogen atoms from water molecules and oxidize them to generate oxygen molecules, and are themselves reduced to water molecules.
On the other hand, in an acidic atmosphere, the OH radical (.OH) draws electrons (e ⁻ ) from water molecules (H ₂ O) according to the reaction formula of Chemical Formula 7, and itself becomes hydroxide ions (OH ⁻ ). However, this abstraction reaction radically splits and activates water molecules to generate new OH radicals (.OH) and protons (H ⁺ ). The generated hydroxide ions and protons disappear by generating new water (H ₂ O) according to the reaction formula (8).
Since the water 3 to be treated in the treatment tank 4 is maintained in a weakly acidic atmosphere, new OH radicals are generated in this way. Further, based on the OH radicals thus generated, A series of reactions like this occur in a chain, and the subsequent process is repeated in a chain.
That is, once OH radicals are generated by the reaction formulas such as Chemical Formula 3, etc., OH radicals are obtained semipermanently by a chain reaction afterwards using this as an initiation reaction and reaction initiator. The OH radicals excluding the amount consumed in the oxidation and decomposition processes of the organic arsenic compound 1 are repeatedly generated and disappeared in a coexistence with proton generation and disappearance. Considering that the OH radical has a very short lifetime, the significance of such repeated generation is great.
Thirdly, in the treatment tank 4, OH radicals are also generated by such a reaction.

<< Reaction in Treatment Tank 4 (OH Radical Generation: Part 4) >>
Next, the chemical reaction (generation of OH radical: part 4) in the treatment tank 4 will be described. In the treatment tank 4, in addition to the first, second, and third described above, OH radicals are newly generated incidentally, subsidiaryly, and continuously by the following reaction.
That is, the reaction in which trivalent iron ions generated by the oxidation reaction of divalent iron ions react with hydrogen peroxide to newly generate OH radicals or the like is represented by the following chemical formulas 9 and 10. The reaction formula (reaction formula of Formula 11) is repeated in a chain.

These will be further described in detail. The trivalent iron ion (Fe ³⁺ ) generated by the reaction formula of the chemical formula 3 (Chemical formula 1) reacts with hydrogen peroxide (H ₂ O ₂ ) by the reaction formula of the chemical formula 9 to obtain trivalent iron. The ions are reduced to divalent iron ions (Fe ²⁺ ), and superoxide anions (.O ₂ ⁻ ), which are ions generated by combining oxygen molecules with electrons, are generated.
The radical superoxide anion can react with hydrogen peroxide by the reaction formula of Chemical Formula 10 to generate OH radicals (.OH). When the reaction formulas of the chemical formulas 9 and 10 are synthesized together, the chemical formula of the chemical formula 11 is obtained.
In this way, as long as hydrogen peroxide that was the source of OH radical generation in the reaction formula of Chemical Formula 3 (Chemical Formula 2) remains, OH radicals are converted during the oxidation and decomposition processes of the organic arsenic compound 1, for example. Even if it is consumed up, as long as surplus hydrogen peroxide remains, new OH radicals will continue to be generated semipermanently in a chain based on the hydrogen peroxide. become. Considering that the OH radical has an extremely short lifetime, the significance of such generation continuation is great.
However, in order to ensure that the reaction formula of Chemical Formula 11 (Chemical Formula 9, Chemical Formula 10) occurs, even a weakly acidic atmosphere that does not decompose hydrogen peroxide into water and dissolved oxygen (see the chemical formula of Chemical Formula 4), A pH operation is required, such as adding caustic soda or the like to the water 3 to be treated in the treatment tank 4 by the pH adjusting means 8, and it is necessary to move the pH value to the alkali side.
Furthermore, although the divalent iron ion generated by the reaction formula of Chemical Formula 11 (Chemical Formula 9) lowers the pH, the necessary pH operation is performed in order to coexist with hydrogen peroxide that is stably present in the weakly acidic atmosphere as described above. If carried out, the generation of OH radicals can be expected by the Fenton main reaction of the reaction formula such as Chemical Formula 3 above.
In the treatment tank 3, fourthly, OH radicals are also generated by such a reaction.

<< Reaction in Treatment Tank 4 (Oxidation and Decomposition of Organic Arsenic Compound 1) >>
Next, oxidation, decomposition, and mineralization of the organic arsenic compound 1 by OH radicals will be described. In the treatment tank 4, the organic arsenic compound 1 contained in the water to be treated 3 is oxidized and decomposed by the OH radicals generated by the Fenton main reaction and others to be mineralized.
These will be described in more detail. The OH radical, that is, the hydroxy radical (.OH) has a strong oxidizing power as is well known. In other words, it has an extremely powerful electron (e ⁻ ) deprivation power, oxidation power, that is, active power and decomposition power that are unparalleled as an active oxygen species. Because of its intense nature, its existence time is a very short-lived chemical species.
Now, the OH radicals dispersed in the water phase oxidize the organic arsenic compound 1 contained in the water 3 to be treated and eventually decompose. In other words, the OH radical targets, for example, a π-electron bond of a double bond of the aromatic ring, a hydrogen atom H, a carbon atom C, etc. in the organic structure of the organic arsenic compound 1, and adds or substitutes this with an OH group. Following the chain process, the carbon chain, organic bond, and molecular bond of the organic arsenic compound 1 are sequentially cut, decomposed, and divided, so that the organic arsenic compound 1 is finally oxidized, decomposed, and mineralized into an inorganic arsenic compound. To do.
As described in detail later, diphenylarsinic acid (DPAA), dimethylarsenic, monomethylarsenic, and the like, which are representative examples of the organic arsenic compound 1, are oxidized and decomposed by OH radicals to become inorganic, and arsenous acid (H ₃ AsO ₃ ) Or arsenic acid (H ₃ AsO ₄ ). In other words, arsenic (As) is mineralized from pentavalent tetracoordinate diphenylarsinic acid or pentavalent tetracoordinate dimethylarsenic to trivalent tricoordinate arsenous acid or pentavalent tetracoordinate arsenic acid. In particular, low molecular compounds such as water (H ₂ O) and carbon dioxide (CO ₂ ) are also decomposed and produced.
In the treatment tank 4, the organic arsenic compound 1 is thus oxidized, decomposed and mineralized.

<< About the post-treatment tank 11 >>
Next, the post-treatment tank 11 will be described. A post-treatment tank 11 is attached to the treatment tank 4, and in the post-treatment tank 11, the complex in which the organic arsenic compound 1 is mineralized as described above is floculated to be aggregated, precipitated, removed, and thus treated water. 3 is purified and drained externally.
Such a post-treatment tank 11 will be further described in detail. The illustrated post-treatment tank 11 includes a neutralization tank 12, a coagulation tank 13, a storage tank 14, a dehydration tank 15, a treated water tank 16, and the like in order toward the downstream.

These will be further described in detail. First, the organic arsenic compound 1 contained is oxidized, decomposed, and mineralized as described above, and the treated water 3 that has become an inorganic arsenic compound 17 such as arsenic acid (H ₃ AsO ₄ ) is then discharged from the treatment tank 4. It is discharged to the neutralization tank 12 of the treatment tank 11.
In the neutralization tank 12, a pH adjuster such as caustic soda is added to the water 3 to be treated, and the pH is adjusted to the optimum value for the inorganic flocculant. When hydrogen peroxide remains even in the treated water 3, a neutralizing agent such as catalase is added in order to avoid water pollution.
Next, in the coagulation tank 13, for example, polyaluminum chloride (PAC, Al ₂ (OH) _n Cl _6-n ) or ferric chloride ( FeCl ₃ ) is added and stirred, and the colloidal complexed inorganic arsenic compound 17 is agglomerated and can be removed by precipitation.
In addition, when the residual amount of trivalent iron ions (Fe ³⁺ ) generated by the Fenton method in the water to be treated 3 is large, the iron ions (Fe ³⁺ ) function as an inorganic flocculant. The addition of is unnecessary.
Next, the to-be-processed water 3 is supplied to the dehydration tank 15 from such a storage tank 14 in the example of illustration. In the dehydration tank 15, the water to be treated 3 that has been precipitated and sludged is solid-liquid separated by, for example, an F / P type dehydrator, and the inorganic arsenic compound 17 that has been flocked and dehydrated is separated and stored in a container 18. After that, it is heat treated as a contaminant.
And the to-be-processed water 3 purified in this way passes through the treated water tank 16, is further purified, adjusted to a pH value suitable for external discharge, and then discharged externally.
The post-treatment tank 11 is as described above.

《Action etc.》
The method for treating water containing organic arsenic compound 1 according to the present invention is configured as described above. Therefore, it becomes as follows.
(1) The treated water 3 containing diphenylarsinic acid (DPAA), monomethyl arsenic, dimethyl arsenic, and other organic arsenic compounds 1 is supplied to the treatment device 2.
Then, the treatment apparatus 2 is used to purify the treated water 3 by oxidizing and decomposing the organic arsenic compound 1 by a treatment method based on the treatment process of the Fenton method.

(2) And this processing apparatus 2 is equipped with the raw | natural water tank 9, the pH adjustment tank 10, the processing tank 4, the post-processing tank 11, etc. of the to-be-processed water supply means 5 in order.
A pH adjusting means 8 is attached to the pH adjusting tank 10. The treatment tank 4 is provided with hydrogen peroxide adding means 6, iron ion adding means 7, pH adjusting means 8 and the like, and hydrogen peroxide, divalent iron ions, pH adjusting agents and the like can be added. It has become.

(3) Now, the treated water 3 is supplied from the raw water tank 9 of the treated water supply means 5 to the treated tank 4.
In addition, before the to-be-processed water 3 is supplied to the processing tank 4, in the pH adjustment tank 10, acid pH adjusters, such as a sulfuric acid, are added from the pH adjustment means 8, for example, pH 3-pH 5, for example about pH4 weakness. It is considered acidic.

  (4) To the treated water 3 supplied to the treatment tank 4, first, an aqueous solution of hydrogen peroxide is added from the hydrogen peroxide addition means 6. The total amount of hydrogen peroxide is added at the beginning of the reaction.

(5) In the treatment tank 4, after the hydrogen peroxide is added in this way, a divalent iron ion solution is added from the iron ion addition means 7 to the water to be treated 3. The divalent iron ions are added repeatedly in a plurality of cycles intermittently in a plurality of times by divided addition during the reaction after the addition of hydrogen peroxide.
For each divided addition of iron ions, an alkaline pH adjuster such as caustic soda is added from the pH adjusting means 8 so that the water to be treated 3 always maintains a weak acidity of about pH 4, for example. That is, the pH is adjusted to an optimum pH for OH radical generation.

(6) Now, in the treatment tank 4, OH radicals are generated based on the following first, second, third and fourth reactions.
First, the total amount of hydrogen peroxide added as described above is reduced by divalent iron ions added in portions as a catalyst, and OH radicals are generated each time the addition is performed.
That is, by the Fenton main reaction in the reaction formula of Chemical Formula 3 (Chemical Formula 1, Chemical Formula 2), the divalent iron ion donated an electron to hydrogen peroxide to become a trivalent iron ion, and the electron was donated. Hydrogen peroxide generates OH radicals. Since the OH radical is divided and added with divalent iron ions, there is no risk of wasteful reaction of the OH radical and divalent iron ions. .
In addition to this, the generation of OH radicals by this Fenton main reaction is more efficiently and reliably performed by being maintained in a weakly acidic atmosphere having a pH of about 4. That is, under such a weak acid atmosphere, first, electron donation of divalent iron ions is promoted, and hydrogen peroxide is further decomposed and wasted into water and oxygen according to the reaction formula (4). Reaction is suppressed and avoided, and OH radicals with full capacity are efficiently generated.

(7) Second, OH radicals are hydroxylated by a reduction reaction of hydrogen peroxide with trivalent iron ions generated by an oxidation reaction of divalent iron ions in the treatment tank 4. Ions can also be generated by oxidation.
That is, OH radicals are also generated by the reaction formulas of Chemical Formula 5 and Chemical Formula 6 based on the trivalent iron ions and hydroxide ions generated by the reaction formula of Chemical Formula 3 (Chemical Formula 1, Chemical Formula 2). . Also from this aspect, OH radicals are efficiently generated. The generation of OH radicals is also generated in a chain each time iron ions are dividedly added.

(8) Furthermore, OH radicals are generated more efficiently by the following third and fourth in addition to the first and second described above. That is, OH radicals continue to be efficiently generated by the incidental, secondary, and chain reactions other than the Fenton main reaction of (6).
Third, OH radicals generated by the chemical formula 3 and the like react with water of the water to be treated 3 according to the chemical formulas of the chemical formulas 7 and 8, and thus new OH radicals are repeatedly generated in a chain. Is done. Such a series of OH radical generation reactions are repeated.
Fourthly, the trivalent iron ion generated by the reaction formula of Chemical Formula 3 (Chemical Formula 1) and hydrogen peroxide react by the reaction formula of Chemical Formula 11 (Chemical Formula 9 and Chemical Formula 10). New OH radicals are repeatedly generated in a chain. Such a series of OH radical generation reactions are repeated.
The generation of the first, second, third, and fourth OH radicals ends when the hydrogen peroxide of the Fenton reagent is not used up in the treatment tank 4.

(9) Now, the OH radical is generated efficiently as described above and has an extremely strong oxidizing power.
Therefore, in the treatment tank 4, the organic arsenic compound 1 contained in the water to be treated 3 is oxidized and decomposed by this OH radical, so that the inorganic arsenic compound 17 such as arsenous acid and arsenic acid, water, carbon dioxide, etc. It becomes mineralized into molecular compounds.

(10) In the water 3 to be treated, the organic arsenic compound 1 contained therein is mineralized into the inorganic arsenic compound 17 and the like, and is discharged from the treatment tank 4 to the post-treatment tank 11. The illustrated post-treatment tank 11 includes a neutralization tank 12, a coagulation tank 13, a storage tank 14, a dehydration tank 15, a treated water tank 16, and the like.
Since hydrogen peroxide is effectively used for generating OH radicals as described above, the residual amount after the treatment is very small, and the use of the neutralizing agent in the neutralization tank 12 is negligible or absent ( For example, the residual peroxide ion concentration is about 0 to 3% or less of the hydrogen peroxide used).
And the to-be-processed water 3 passes through the post-treatment tank 11, and the complex of the inorganic arsenic compound 17 is flocked and aggregated, precipitated, and removed. Therefore, it is adjusted to a state where it can be drained, purified and drained to the outside.

(11) In this treatment method, as described above, based on the treatment process of the Fenton method, etc., the organic arsenic compound 1 that is a harmful organic compound contained in the water to be treated 3 is mineralized. Easy to realize.
That is, the required amount of chemicals such as hydrogen peroxide, divalent iron ions, and Fenton's reagent such as a pH adjuster can be easily calculated from the theoretical reaction values. For example, about several times larger than the theoretical reaction value is added as an actual required amount, so that the addition amount is optimized.
The treatment apparatus 2 is provided with a raw water tank 9 and a post-treatment tank 11 with a treatment tank 4 as the center, and a hydrogen peroxide addition means 6, an iron ion addition means 7, a pH adjustment means 8 and the like. It consists of the structure which was made. That is, in this processing method, the processing device 2 having a relatively simple configuration is used, and stable processing is possible.
The operation of the present invention is as described above.

<< Oxidation and decomposition process of diphenylarsinic acid (DPAA) >>
Here, regarding the treatment method of the present invention, details of the oxidation and decomposition processes of diphenylarsinic acid (DPAA), which is one example thereof, will be described. That is, one example of the above-mentioned place entitled “Reaction in the treatment tank 4 (oxidation and decomposition of the organic arsenic compound 1)” is theoretically verified.
Diphenylarsinic acid is an organic arsenic compound 1 which is contained in the treatment water _{3 [DPAA, C 6 H 5} -As (OH) O-C 6 H 5] , the organic structure of unstable intermediates in the degradation process Are followed by the chain process of Chemical Formula 12 to Chemical Formula 23 described below, and are sequentially oxidized with OH radicals (.OH). Then, it is decomposed and mineralized into arsenic acid (H ₃ AsO ₄ ), water (H ₂ O), carbon dioxide (CO ₂ ) and the like.
These will be further described in detail. First, oxidation and decomposition reactions by OH radicals proceed sequentially following the chain processes of the following reaction formulas 12 to 15.

The reaction formulas of Chemical Formulas 12 to 15 are as follows. First, diphenylarsinic acid as a starting material is oxidized by an OH radical in the aromatic group (—C ₆ H ₅ ) in the reaction formula of Chemical Formula 12. Then, in the reaction formula of Chemical Formula 13, the OH group is oxidized by OH radicals and water is generated respectively.
Then, the reaction formula proceeds to Chemical Formula 14, and the benzene ring is opened by the OH radical. And the produced | generated carboxylic acid will be oxidized and decomposed | disassembled into water and a carbon dioxide by OH radical in Reaction formula of Chemical formula 15.
Now, after the chain process of the reaction formulas of Chemical Formulas 12 to 15, the chain process of the chemical formulas of Chemical Formulas 16 to 19 is followed.

The reaction formulas of Chemical Formula 16 to Chemical Formula 19 are as follows. The residue containing arsenic remaining in the reaction formula of Chemical formula 14 generates water by depriving the OH radical of the hydrogen atom of the OH group in the chemical formula of Formula 16. Then, the reaction formula proceeds to Chemical Formula 17 and the C—C bond is cleaved by the OH radical.
And the residue part containing arsenic produced | generated by the reaction formula of Chemical formula 17 is deprived of the hydrogen atom of OH group by the OH radical by the chemical formula of Chemical formula 18, and C and O become a double bond, and C Since the bonded electrons move, C is liberated from -As (OH) O-, thereby generating carbon dioxide and water. Note that unpaired electrons remain in [-As (= O) (OH)].
Thereafter, 2 mol of OH is added to [-As (= O) (OH)] in the inorganic part in the reaction formula of Chemical Formula 19, and arsenic acid [chemical formula H ₃ AsO ₄ , structural formula As (OH) ₃ O ] Is generated.
By following the chain process of the reaction formulas of Chemical Formula 12 to Chemical Formula 18, the aromatic rings at both ends of diphenylarsinic acid are oxidized and decomposed, and inorganic arsenic acid is generated by the chemical formula of Chemical Formula 19.
In the reaction formula of Chemical formula 17, the 2OH-CH = CH-OH moiety follows the chemical formula of the following chemical formulas 20 to 22, and the 2OH-CHO moiety is represented by the chemical formula of Chemical formula 23, respectively. OH radicals oxidize and decompose into water and carbon dioxide.

In conclusion, diphenylarsinic acid which is the organic arsenic compound 1 is theoretically oxidized, decomposed and mineralized by following the chain process of the reaction formulas of Chemical Formula 12 to Chemical Formula 23.
By the way, when the place explained above is summarized (that is, when the respective reaction formulas are added up), the following general reaction formula of the following chemical formula 24 is obtained.

That is, in the general reaction formula of Chemical Formula 24, 1 mole of diphenylarsinic acid is theoretically mineralized to 34 moles of water, 12 moles of carbon dioxide and 1 mole of arsenic acid by 60 moles of OH radicals. .
In this example, 60 mol of OH radicals may be prepared in advance as a theoretical reaction value, but the actual required amount is prepared, for example, several times as many. Of course, the same applies to hydrogen peroxide, divalent iron ions, and the like, which are OH radical products.
The details of the oxidation and decomposition processes of diphenylarsinic acid are as described above.

<Oxidative decomposition process of dimethyl arsenic>
Next, the details of the oxidation and decomposition process of dimethyl arsenic, which is an example of the processing method of the present invention, will be described.
That is, one example of the above-mentioned place entitled “Reaction in the treatment tank 4 (oxidation and decomposition of the organic arsenic compound 1)” is theoretically verified.
Dimethylarsenic [(CH ₃ ) ₂ -As (= 0) (OH)], which is a methylated organic arsenic compound 1 in the water 3 to be treated, includes an organic structure of an unstable intermediate of its decomposition process, Following the chain process of Chemical Formula 25 to Chemical Formula 28 described below, oxidation and decomposition are sequentially performed with OH radicals (.OH). Then, arsenic acid _(H 3 _AsO 4), water _(H 2 O), to carbon dioxide (CO _2), etc., are mineralized.

The reaction formulas of Chemical Formulas 25 to 28 will be described in detail. First, in the reaction formula of Chemical Formula 25, dimethyl arsenic that is a starting material is oxidized with an OH radical, and water is generated as well as its methyl group [(CH ₃ ) ₂ —].
Next, in the reaction formula of Chemical Formula 26, the OH radical oxidizes the hydrogen atom (H) of the alcohol (OH) with respect to the alcoholated methyl group (OH—CH ₂ —), and converts the oxygen atom (O) to carbon. Double bonds with atoms.
And OH radical cuts | bonds with an arsenic atom (As) by the combined electron transfer accompanying this, produces | generates formaldehyde (H-CHO), and turns into water itself. Then, the reaction formula proceeds to Chemical Formula 27, and formaldehyde is returned to carbon dioxide and water via formic acid (H—COOH) by oxidation with OH radicals.
At the same time, the residue containing arsenic in the reaction formula of Chemical Formula 26 proceeds to the chemical formula of Chemical Formula 28, and unpaired electrons remain on the left and right of the pentavalent arsenic atom after the left and right methyl groups are eliminated. Two moles of OH radicals are combined. The bonded OH group is also ionized and oxo-oxidized to generate inorganic arsenic acid [chemical formula H ₃ AsO ₃ , structural formula As (OH) ₃ O].
In conclusion, dimethyl arsenic, which is the organic arsenic compound 1, is theoretically oxidized, decomposed, and mineralized by following the chain process of the reaction formulas of Chemical Formula 25 to Chemical Formula 28.
By the way, when the place explained above is summarized (that is, when the respective reaction formulas are added up), the following general reaction formula of Chemical Formula 29 is obtained.

That is, in the general reaction formula of Chemical Formula 29, 1 mol of dimethyl arsenide is theoretically mineralized to 12 mol of water, 2 mol of carbon dioxide, and 1 mol of arsenic acid by 18 mol of OH radical. .
In this example, 18 mol of OH radicals may be prepared in advance as a theoretical reaction value, but the actual required amount is prepared, for example, several times as many as that. Of course, the same applies to hydrogen peroxide, divalent iron ions, and the like, which are OH radical products.
The details of the oxidation and decomposition process of dimethyl arsenic are as described above.

Here, an embodiment of the processing method of the present invention will be described.
First, in Example 1, after supplying the to-be-processed water 3 as sample raw water to the processing tank 4 at normal temperature, each chemical | medical agent was added in predetermined order, and the Fenton process was carried out. The test conditions are as follows.
・ Amount of treated water 3 (L): 5
・ Sulfuric acid (H ₂ SO ₄ ) (mL / L): 0.13
Hydrogen peroxide (H ₂ O ₂ ) (mL / L): 0.09
Ferrous sulfate (FeSO ₄ · 7H ₂ O) (g / L): 0.29
・ Caustic soda (NaOH) (mL / L): 0.50
-Polyaluminum chloride (PAC) (g / L): 0.6
In addition, 1 microgram was used as the lower limit of quantification. Moreover, sulfuric acid and caustic soda were added for pH adjustment, and polyaluminum chloride was added as a flocculant. Hydrogen peroxide and ferrous sulfate were added at the addition amounts according to the theoretical values (for example, see the reaction formula of Chemical Formula 3).

Under such test conditions, the arsenic content of the arsenic compound contained in the water to be treated 3 was measured before and after the Fenton treatment. Obtained.
As a result, arsenic is oxidized and decomposed from organic pentavalent diphenylarsinic acid (DPAA), which is the organic arsenic compound 1, to inorganic trivalent arsenous acid (H ₃ AsO ₃ ) and inorganic pentavalent arsenic acid (H ₃ AsO ₄ ). After mineralization, it was confirmed by data that most of the material was precipitated and removed by a flocculant (PAC) and almost no longer existed in the water 3 to be treated. The remaining target value of the organic arsenic compound 1 is 10 μg / L or less, which was sufficiently cleared.

In Example 2, after supplying the to-be-processed water 3 as sample raw water to the processing tank 4 at normal temperature, each chemical | medical agent was added in predetermined order, and the Fenton process was carried out. The test conditions are as follows.
・ Amount of treated water 3 (L): 1
・ Sulfuric acid (H ₂ SO ₄ ) (mL / L): 0.135
Hydrogen peroxide (H ₂ O ₂ ) (mL / L): 0.90
Ferrous sulfate (FeSO ₄ · 7H ₂ O) (g / L): 1.92
Caustic soda (NaOH) (mL / L): appropriate amount 1 μg was defined as the lower limit of quantification. In addition, sulfuric acid and caustic soda were added for pH adjustment, but unlike Example 1 described above, no flocculant was added. Hydrogen peroxide and ferrous sulfate were added at the addition amounts according to the theoretical values (for example, see the reaction formula of Chemical Formula 3).

Under such test conditions, the arsenic content of the arsenic compound contained in the water to be treated 3 was measured before and after the Fenton treatment. Obtained.
As a result, arsenic is changed from organic pentavalent diphenylarsinic acid (DPAA), which is the organic arsenic compound 1, to inorganic trivalent arsenic (H ₃ AsO ₃ ) and inorganic pentavalent arsenic acid (H ₃ AsO ₄ ). The data confirmed that it was oxidized, decomposed and mineralized. The remaining target value of the organic arsenic compound 1 is 10 μg / L, which was sufficiently cleared.

1 is a configuration flow diagram of one example of the method for treating water containing an organic arsenic compound according to the present invention for explaining the best mode for carrying out the invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic arsenic compound 2 Processing apparatus 3 To-be-processed water 4 Processing tank 5 To-be-processed water supply means 6 Hydrogen peroxide addition means 7 Iron ion addition means 8 pH adjustment means 9 Raw water tank 10 pH adjustment tank 11 Post-treatment tank 12 Neutralization tank 13 Coagulation tank 14 Storage tank 15 Dehydration tank 16 Treated water tank 17 Inorganic arsenic compound 18 Container

Claims (1)

A treatment method for oxidizing and decomposing an organic arsenic compound contained in water to be treated based on a Fenton method treatment process, wherein hydrogen peroxide and divalent iron ions are compared with water to be treated containing the organic arsenic compound. A solution and a pH adjuster are added,
Hydrogen peroxide is added in the treatment tank at the beginning of the reaction,
In the treatment tank, the divalent iron ion solution is intermittently added repeatedly by repeating a plurality of cycles after the addition of hydrogen peroxide, so that the OH radicals generated below return to water and are wasted. Function to avoid
As for the pH adjuster, an acid pH adjuster is first added to the water to be treated supplied to the treatment tank in the pH adjustment tank, and divalent iron is added in the treatment tank after the addition of hydrogen peroxide. An alkaline pH adjuster is added each time the ionic solution is added in a divided manner, so that the water to be treated is maintained at a weak acidity of pH 3 to pH 5, and the reaction in which hydrogen peroxide is decomposed and wasted into water and oxygen is suppressed. Function as
The amount of hydrogen peroxide and divalent iron ions added is calculated based on the theoretical reaction value based on the reaction formula.
First, from the specific content of the organic arsenic compound contained in the water to be treated, the number of moles of the theoretical reaction value of the OH radical is obtained as a standard, and then the actual required number of moles of the OH radical is obtained based on this standard. From the required number of moles of OH radicals, the theoretical number of moles of reaction of hydrogen peroxide and divalent iron ions, which are OH radical products, is obtained as a reference, and The actual required number of moles of hydrogen peroxide and divalent iron ions to be prepared is calculated more than this standard,
The addition timing of hydrogen peroxide and divalent iron ions is when hydrogen peroxide is used up and hydrogen peroxide is exhausted from the water to be treated in the treatment tank. When the previously added portion is used up, the divalent iron ions disappear from the water to be treated in the treatment tank.
As for the OH radical production reaction, hydrogen peroxide is reduced with divalent iron ions each time it is added in a divided manner, and in addition to the Fenton main reaction, in which OH radicals are produced, the hydrogen peroxide is further reduced. The generated hydroxide ions are oxidized by trivalent iron ions generated by the oxidation reaction of divalent iron ions to generate OH radicals, and the generated OH radicals are further covered. The reaction of reacting with the water of the treated water to generate new OH radicals and water is repeated in a chain, and the trivalent iron ions generated by the oxidation reaction of the divalent iron ions The reaction of reacting with hydrogen oxide to at least generate new OH radicals is repeated in a chain, and generation of OH radicals is terminated when hydrogen peroxide is exhausted in the treatment tank,
Thus, the organic arsenic compound contained in the water to be treated is oxidized and decomposed by the OH radicals thus generated, and is mineralized into water, carbon dioxide, and an inorganic arsenic compound. A method for treating water containing arsenic compounds.

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