JP7542235B2 - Anion adsorbents, adsorbent bags, methods for using anion adsorbents, and methods for purifying well water. - Google Patents

Description

The present invention relates to an anion adsorbent, an adsorbent bag, a method for using an anion adsorbent, and a method for purifying well water.

In recent years, water pollution by harmful inorganic anions has become a global problem. Serious cases include fluoride contamination of groundwater in Lemna upazila, Balasore district, Odisha state, located in eastern India, arsenic contamination of wells in Southeast Asia, and selenium contamination of water and soil near coal mines in the western United States and China.

Water pollution by inorganic ions is closely related to the mobility of elements. Many heavy metal species dissolved as cations have low mobility except under strongly acidic conditions. In contrast, iodine, fluorine, and other elements dissolved as anions are highly mobile in any environment, regardless of the liquid pH. Arsenic and selenium are also highly mobile unless the environment is reducing. These properties lead to the progression of groundwater pollution, regardless of whether they are of natural or man-made origin.

The most widely used methods for treating these anionic species are coagulation sedimentation, membrane treatment, and adsorption.

The coagulation sedimentation method is a method in which an aqueous solution is mixed with an inorganic coagulant and/or a polymer coagulant in a reaction tank, and the mixture is separated into a settled sludge and supernatant water in a settling tank. In Japanese water purification plants, the coagulation sedimentation method is widely used as a treatment to remove harmful inorganic anions. However, for arsenic, for example, the coagulation sedimentation method, which is currently the main method of treatment, has issues with the constant discharge of arsenic-containing sludge and the large space required for equipment installation. It is often difficult to establish a new coagulation sedimentation treatment plant for small-scale water supply systems in groundwater systems or geothermal or hot spring wastewater. In addition, the coagulation sedimentation method is large-scale and requires high equipment costs, making it difficult to adopt it as a water treatment method in developing countries.

The membrane treatment method is a technique in which a water treatment membrane with pores on the order of μm to nm (10 ^-6 m to 10 ^-9 m) is attached to a device (unit) called a module, and impurities that cannot pass through the pores are removed from the water. However, the membrane is expensive, and the electricity costs to operate the plant are also high, making it difficult to adopt as a water treatment method in developing countries.

The adsorption method is similar to the ion exchange method, and is a technique for removing harmful substances by adsorbing inorganic ions to an adsorbent. The adsorption method has excellent performance in removing harmful inorganic anions, and is less expensive than the coagulation-sedimentation method and membrane treatment method. Therefore, it is expected to be useful in places where groundwater is used as drinking water, where it is difficult to adopt coagulation-sedimentation methods that require a large investment, and in geothermal and hot spring wastewater with high arsenic concentrations. It is also expected to be useful in developing countries that lack financial resources and find it difficult to introduce large investment facilities.

As an adsorbent, for example, an arsenic adsorbent consisting of a rare earth element hydroxide and a polymer resin that coats its surface has been proposed (see Patent Document 1). In this adsorbent, the rare earth element hydroxide has a central cavity and a microporous portion surrounding it, and the polymer resin that coats the surface of the rare earth element hydroxide is a porous skin layer that is water-resistant. The adsorbent described in Patent Document 1 can purify large amounts of water contaminated with arsenic at high speed, and can also efficiently purify water to be treated that contains low concentrations of arsenic. In addition, since the adsorption activity can be maintained for a long period of time, maintenance is easy. Furthermore, there is no elution of the adsorbent or resin components.

Also, an arsenite ion adsorbent using at least one compound selected from orthotitanic acid, metatitanic acid, and titanium oxide has been proposed (see Patent Document 2). And an adsorbent composition has been proposed that contains a bismuth material and an arsenic material on a carrier containing at least one of a metal oxide, a semi-metal oxide, and activated carbon, and the metal oxide is selected from the group consisting of titanium oxide, cerium oxide, aluminum oxide, silicon oxide, zirconium oxide, magnesium oxide, zeolite, activated carbon, and mixtures thereof (see Patent Document 3). The adsorbents described in Patent Documents 2 and 3 have good removal performance for arsenic materials.

An anion adsorbent containing ferric hydroxide produced under conditions in which ferrous species are present has also been proposed (see Patent Document 4). The adsorbent described in Patent Document 4 has the ability to adsorb multiple types of harmful anions, namely phosphate ions, arsenate ions, and arsenite ions. In order to prevent the hydroxyl groups from being dehydrated from the ferric hydroxide, which would reduce the adsorption performance, the anion adsorbent preferably contains glycerin, an organic binder, and is in a dried state by freeze drying, spray drying, or the like.

JP 2005-288363 A JP 2018-027517 A Special table 2018-525218 publication International Publication No. 2008/001442

However, the adsorbent described in Patent Document 1 requires high raw material costs, and the product price of the arsenic adsorbent is also high. To make it available in developing countries, it is preferable to keep the product price lower.

Even with the adsorbents described in Patent Documents 2 and 3, the raw material costs are high, and the product price of the adsorbent is also high. Therefore, it is preferable to keep the product price as low as possible.

The adsorbent described in Patent Document 4 is an iron-based adsorbent, and is less expensive than the adsorbents described in Patent Documents 1 to 3. However, in order to prevent a decrease in adsorption performance, it is necessary to apply an organic binder to the ferric hydroxide and then subject it to freeze drying, spray drying, or the like. Therefore, even if the material itself is low cost, the processing costs for making it into an adsorbent are high, and it may not be suitable for mass production. In that respect, there is still room for further improvement in terms of reducing costs.

Incidentally, when trying to eliminate water pollution in a well, if an adsorbent is sprayed directly into the well, the contaminated soil with adsorbed harmful anions will appear on the surface if the soil in the well is dredged. In addition, there is a possibility that the adsorbent with adsorbed harmful anions may be pumped up along with the well water.

In that case, it is preferable to place a container containing the adsorbent in the well and pass the well water through the container. In this case, the adsorbent is required to have high filtering properties in order to (1) provide safety so that the well water meets the legal standards simply by passing it through the container, and (2) enable a large amount of processing capacity to be achieved per unit time.

The present invention was made in consideration of these circumstances, and its purpose is to provide an anion adsorbent at a lower cost that has high filtering performance in terms of both the adsorption performance of harmful inorganic anions and the amount of processing per unit time, and is capable of dealing with fluoride contamination, arsenic contamination, and selenium contamination.

As a result of intensive research into solving the above problems, the inventors discovered that the above object can be achieved by using particles containing an iron oxyhydroxide component, a sulfur component, and a silica component and having a diameter within a specified range as an anion adsorbent, and thus completed the present invention. Specifically, the present invention provides the following:

The first aspect of the invention provides an anion adsorbent that contains an iron oxyhydroxide component, a sulfur component, and a silica component, and has a particle diameter D10 of 1 μm or more at which the cumulative value becomes 10% in a volume frequency particle size distribution measurement by a laser diffraction scattering method.

According to the first aspect of the invention, the anion adsorbent contains an iron oxyhydroxide component. The iron oxyhydroxide component has sufficient adsorption performance for harmful anions such as fluoride ions, arsenate ions, arsenite ions, selenate ions, and selenite ions. Therefore, one type of adsorbent according to the first aspect of the invention can be used to deal with arsenic contamination, fluoride contamination, and selenium contamination, without the need to use multiple types of adsorbents.

In addition, according to the first aspect of the invention, the anion adsorbent contains a sulfur component and a silica component in addition to the iron oxyhydroxide component. This increases the shape stability of the particles, making it possible to make the particle diameter D10 1 μm or more, and increasing the processing volume per unit time.

Therefore, according to the first aspect of the invention, the filtering ability of particles can be greatly improved in terms of both the adsorption performance of harmful inorganic anions and the processing amount per unit time.

The components that make up the anion adsorbent are iron oxyhydroxide, sulfur, and silica, all of which are inexpensive. And because the iron component is iron oxyhydroxide, not ferric hydroxide, the degradation of adsorption performance due to repeated use is suppressed without the need for organic binder development, freeze drying, spray drying, etc. Therefore, not only the cost of raw materials but also the processing cost is suppressed, making it more cost-effective than conventional adsorbents.

From the above, according to the invention relating to the first feature, it is possible to provide an anion adsorbent at a lower cost that has high filtering performance in terms of both the adsorption performance of harmful inorganic anions and the processing amount per unit time, and is capable of dealing with fluoride contamination, arsenic contamination, and selenium contamination.

The second aspect of the invention is the first aspect of the invention, which provides an anion adsorbent in which the content of the sulfur component is 1 part by mass or less per 100 parts by mass of the anion adsorbent, and the content of the silica component is 0.1 parts by mass or less per 100 parts by mass of the anion adsorbent.

According to the second feature of the invention, the inclusion of sulfur and silica components provides high filtering properties for the particles, while the content of sulfur and silica components is kept within a predetermined range, so that the adsorption performance of fluoride ions, arsenate ions, arsenite ions, selenate ions, and selenite ions, which is the function of the iron oxyhydroxide component, can be maintained.

The third aspect of the invention is an adsorbent bag in which the anion adsorbent of the first or second aspect of the invention is contained in a water-permeable bag-shaped body.

According to the invention relating to the third feature, since the adsorbent has high filtering properties, the water quality of a well can be improved simply by placing a container containing the adsorbent in the well. Furthermore, unlike directly spraying the adsorbent into the well, even if the soil in the well is dredged, contaminated soil with adsorbed harmful anions will not appear on the surface, and the adsorbent with adsorbed harmful anions will not be pumped up along with the well water. If the adsorbent with adsorbed harmful anions is pumped up, there is a risk that it will lead to oral ingestion of substances containing harmful anions. If the substance is ingested through the mouth, stomach acid will increase the elution of the harmful anions, and the problem of harmful anions may become apparent.

Therefore, according to the third aspect of the invention, the anion adsorbent can be supplied with even higher safety.

The fourth aspect of the invention is a method for using an anion adsorbent, which includes contacting an aqueous material having a pH of less than 10 with a water-permeable bag-shaped body containing the anion adsorbent of the first or second aspect of the invention. The fifth aspect of the invention is the fourth aspect of the invention, which is a method for using an anion adsorbent, which includes filling the bag-shaped body in a column and passing the aqueous material through the column.

In the anion adsorbent according to the first or second aspect of the invention, the iron oxyhydroxide component is capable of adsorbing anions in the neutral to acidic range, and has the property of desorbing anions in the alkaline range of pH 10 or higher. Therefore, when an aqueous material with a pH of less than 10 is brought into contact with the anion adsorbent, the particles can function as an adsorbent.

The bag is then removed and brought into contact with an aqueous material with a pH of 10 or higher, causing the anions adsorbed to the adsorbent to be released, making it possible to reuse the particles as an adsorbent.

The invention according to the fourth and fifth features makes it possible to provide an anion adsorbent that has high filtering properties and can deal with fluoride contamination, arsenic contamination, and selenium contamination at a more reasonable cost, not only in terms of raw material costs but also in terms of reusability.

The sixth aspect of the invention is a method for purifying well water, which includes placing a water-permeable bag containing the anion adsorbent of the first or second aspect of the invention on the bottom of a well.

As explained in the third aspect of the invention, the sixth aspect of the invention makes it possible to purify well water while ensuring an even higher level of safety.

The present invention makes it possible to provide an anion adsorbent that has high filtering properties and can deal with fluoride contamination, arsenic contamination, and selenium contamination at a lower cost.

FIG. 1 shows an example in which the anion adsorbent of this embodiment is used for purifying well water in the form of an adsorbent bag in which the anion adsorbent is housed in a water-permeable bag-shaped body. FIG. 2 shows an example in which the anion adsorbent of this embodiment is used as a packing material to be packed in a column.

The present invention will be described in detail below. However, the present invention is not limited to the following description, and can be modified as appropriate within the scope of the object of the present invention.

<Anion adsorbent>
In this embodiment, the anion adsorbent contains an iron oxyhydroxide component, a sulfur component, and a silica component, and has a 10% particle size D10 of 1 μm or more.

[Iron oxyhydroxide component]
The anion adsorbent contains an iron oxyhydroxide component.

Known iron oxyhydroxides include α-FeOOH (α-iron oxyhydroxide: also called goethite, goethite), β-FeOOH (β-iron oxyhydroxide: also called akaganeite, akaganite), γ-FeOOH (γ-iron oxyhydroxide: also called lepidocrocite), δ-FeOOH (δ-iron oxyhydroxide: also called ferrooxyhite), Fe ₅ HO ₈ .4H ₂ O (ferrihydrite), high pressure FeOOH (schwertmannite), and Fe ^(III) _x Fe ^(II) _y (OH) _3x+2y-z (A ⁻ ) _z (green rust). In the present embodiment, the type of iron oxyhydroxide is not particularly limited.

The anion adsorbent described in this embodiment is capable of adsorbing harmful anions such as fluoride ions, arsenate ions, arsenite ions, selenate ions, and selenite ions. According to this embodiment, one type of adsorbent described in this embodiment can be used to deal with arsenic contamination, fluoride contamination, and selenium contamination without using multiple types of adsorbents.

[Standards for arsenic]

Table 1 shows the environmental abundance of arsenic. The abundance of arsenic in the earth's crust is said to be 1.8 mg/kg, but it is not uniformly distributed throughout the earth's crust, and it is known that the abundance is greater in volcanic regions than in other regions. It is said that water containing 0.2 mg or more of arsenic per liter can cause chronic arsenic poisoning. The ministerial ordinance that determines wastewater standards stipulates that the arsenic emission standard (permissible limit) is 0.1 mg/L or less per liter of water.

Table 2 shows the environmental standards for water pollution set out in the Water Pollution Control Act. Table 3 shows the water quality standards based on the Water Supply Act. These standards are stricter than the arsenic discharge standards shown in Table 1, stipulating that the arsenic content be 0.01 mg or less per liter of water. WHO guidelines also recommend that the arsenic content be 0.01 mg or less per liter of water.

Local governments and other operators are required to keep the arsenic content below 0.005 mg/L per liter of water, which is stricter than the standards set by law and WHO guidelines.

[Standards for fluorine and selenium]

Table 4 shows an excerpt of water quality standard items and standard values (51 items) for tap water quality standards. Fluorine and selenium are also set to be below 0.01 mg/L per liter of water.

According to this embodiment, it is possible to adsorb all of arsenic, fluorine, and selenium with one type of adsorbent described in this embodiment, without using multiple types of adsorbents, and the content of arsenic, fluorine, and selenium in the water after adsorption can be reduced to or below the standards set by law and WHO guidelines. In this embodiment, selenium includes both selenite and selenate, unless otherwise specified.

[Sulfur components]
The sulfur component contributes to the shape of the iron oxyhydroxide component constituting the anion adsorbent during production, and has a catalytic ability to increase the particulate nature of the crystals. According to this embodiment, the anion adsorbent contains a sulfur component, so that the 10% particle diameter D10 of the anion adsorbent can be made 1 μm or more. And, according to this embodiment, since the 10% particle diameter D10 of the anion adsorbent is 1 μm or more, the amount of water treated per unit time can be increased.

The lower limit of the amount of sulfur component is not particularly limited, so long as the presence of sulfur can be detected by inductively coupled plasma (ICP) atomic emission spectrometry (ICP-AES). More preferably, the lower limit of the amount of sulfur component is 0.001 parts by mass or more per 100 parts by mass of the anion adsorbent.

The upper limit of the amount of sulfur component is 1 part by mass or less per 100 parts by mass of anion adsorbent. If the amount of sulfur component is too high, the crystal structure of iron may change, which may affect the adsorption performance of harmful anions. The upper limit of the amount of sulfur component is preferably 0.1 part by mass or less per 100 parts by mass of anion adsorbent.

In the present invention, whether or not the anion adsorbent contains sulfur components is confirmed by completely dissolving the sample in a high-temperature acid or alkali, and then measuring the emission intensity of the sample solution at a wavelength of 182.625 nm using an ICP optical emission spectrometer based on inductively coupled plasma atomic emission spectrometry (ICP-AES).

[Silica component]
The silica component increases the granulation and binding properties of the iron oxyhydroxide particles that constitute the anion adsorbent, and contributes to shape stability. According to this embodiment, the anion adsorbent contains a silica component, which increases the shape stability of the particles and stabilizes the water permeability and filterability. Furthermore, according to this embodiment, the amount of water treated per unit time can be increased.

The lower limit of the amount of silica component is not particularly limited, so long as the presence of silica can be detected by inductively coupled plasma atomic emission spectrometry (ICP-AES). More preferably, the lower limit of the amount of silica component is 0.0001 parts by mass or more, and even more preferably 0.001 parts by mass or more, per 100 parts by mass of the anion adsorbent.

The upper limit of the amount of silica component is 0.1 parts by mass or less per 100 parts by mass of anion adsorbent. If the amount of silica component is too large, it may have a negative effect on crystal growth during the reaction and affect the adsorption capacity. It is more preferable that the upper limit of the amount of silica component is 0.01 parts by mass or less per 100 parts by mass of anion adsorbent.

In the present invention, whether or not the anion adsorbent contains silica components is confirmed by completely dissolving the sample with a high-temperature acid or alkali, and then measuring the emission intensity of the sample solution at a wavelength of 251.612 nm using an ICP optical emission spectrometer based on inductively coupled plasma atomic emission spectrometry (ICP-AES).

[Particle size]
In this embodiment, X% particle diameter DX refers to a particle diameter whose cumulative value is X% when a volume frequency particle size distribution is measured using a particle size distribution measuring device based on a laser diffraction scattering method. For example, 10% particle diameter D10 is a particle diameter whose cumulative value is 10% when a volume frequency particle size distribution is measured using a particle size distribution measuring device based on a laser diffraction scattering method, and 5% particle diameter D5 is a particle diameter whose cumulative value is 5% when a volume frequency particle size distribution is measured using a particle size distribution measuring device based on a laser diffraction scattering method.

The 10% particle diameter D10 of the anion adsorbent is 1 μm or more. It is more preferable if the 5% particle diameter D10 is 1 μm or more, and it is even more preferable if the 1% particle diameter D10 is 1 μm or more. Since the size of the iron oxyhydroxide particles contained in the anion adsorbent is a predetermined size or more, the amount of water treated per unit time can be increased.

<Method of manufacturing anion adsorbent>
Next, a method for producing the anion adsorbent will be described. The anion adsorbent is obtained by mixing a solution containing a trivalent iron component and a sulfur component with an aqueous solvent at a predetermined temperature while maintaining the temperature at the predetermined temperature, and adding an alkaline solution containing a silica component as a neutralizing agent as necessary to maintain the pH at 2 to 3, and then subjecting the resulting solid-liquid mixture to solid-liquid separation to extract the solid.

[Addition step]
[Aqueous Solvent]
The aqueous solvent refers to water, a polar organic solvent, or a mixed solvent of water and a polar organic solvent. Examples of the aqueous material include water, alcohols, carboxylic acids, ketones, ethers, esters, amides, amines, sulfur compounds, and mixtures thereof.

Examples of alcohols include methanol, ethanol, isopropyl alcohol, t-butyl alcohol, propylene glycol, and phenol.

Carboxylic acids include lower carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and caproic acid.

Ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

Examples of ethers include ethylene glycol monobutyl ether, ethylene glycol monoethyl ether, tetrahydrofuran, dioxane, and methyl cellosolve.

Examples of esters include ethyl acetate and butyl acetate.

Examples of amides include formamide, dimethylformamide, acetamide, dimethylacetamide, nitromethane, and acetonitrile.

Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine.

Examples of sulfur compounds include dimethyl sulfoxide.

Among them, because of ease of handling, the water-based material preferably contains one or more selected from water, alcohols, and carboxylic acids, and more preferably is water.

In addition, in order to increase the efficiency of the reaction from ferric iron to iron oxyhydroxide, it is preferable that the aqueous solvent is heated to a predetermined temperature. There are no particular limitations on the lower limit of the temperature of the aqueous solvent, so long as the oxidation of the iron oxide component added to the aqueous solvent to the iron oxyhydroxide component proceeds and a precipitate can be formed in the liquid after oxidation. The lower limit of the temperature of the aqueous solvent is preferably 60°C or higher, and more preferably 70°C or higher.

The upper limit of the temperature of the aqueous solvent is not particularly limited as long as the aqueous solvent does not boil. The upper limit of the temperature of the aqueous solvent is preferably 90°C or less, and more preferably 80°C or less.

[Ferrous iron content]
The trivalent iron component is not particularly limited, and examples thereof include ferric chloride.

[Sulfur components]
The sulfur component is not particularly limited, and examples thereof include sodium sulfate and potassium sulfate.

The lower limit of the sulfur content is preferably 0.001% or more, more preferably 0.02% or more, in molar ratio relative to the content of the trivalent iron component. The inclusion of the sulfur component provides a catalytic ability that increases the particulate nature of the iron oxyhydroxide component that constitutes the anion adsorbent as crystals.

The upper limit of the sulfur content is preferably 0.1% or less, more preferably 0.05% or less, in molar ratio relative to the content of the trivalent iron component. By keeping the amount of sulfur components below a predetermined threshold, the function of the iron oxyhydroxide component, that is, the ability to adsorb harmful anions, can be fully exhibited.

[Heating temperature]
The lower limit of the heating temperature of the post-addition liquid obtained by adding the trivalent iron component and the sulfur component to the aqueous solvent is not particularly limited as long as the oxidation of the components contained in the post-addition liquid proceeds and a precipitate can be formed in the post-oxidation liquid. The lower limit of the heating temperature of the post-addition liquid is preferably 60° C. or higher, and more preferably 70° C. or higher.

The upper limit of the heating temperature of the added liquid is not particularly limited as long as the added liquid does not boil. The upper limit of the heating temperature of the added liquid is preferably 90°C or less, and more preferably 80°C or less.

[Neutralizing agent]
The neutralizing agent is not particularly limited as long as it is an alkaline component, and examples thereof include sodium hydroxide (caustic soda) and sodium carbonate (sodium bicarbonate).

(Silica component)
The neutralizing agent contains a silica component. The silica component increases the granulation and binding properties of the iron oxyhydroxide particles constituting the anion adsorbent, and contributes to shape stability. According to this embodiment, the anion adsorbent contains a silica component, which increases the shape stability of the particles and stabilizes the water permeability and filterability.

The type of silica component is not particularly limited, but examples include sodium metasilicate.

The lower limit of the content of the silica component is preferably 0.01% or more, more preferably 0.02% or more, in molar ratio relative to the content of the trivalent iron component. The inclusion of the silica component increases the granulation and binding properties of the iron oxyhydroxide particles that make up the anion adsorbent, contributing to shape stability.

The upper limit of the silica content is preferably 1% or less in molar ratio relative to the trivalent iron content, and more preferably 0.2% or less. By keeping the amount of silica content below a predetermined threshold, the crystal growth of the trivalent iron component during the reaction can be favorably promoted, and the anion adsorbent as a product can fully exhibit its ability to adsorb harmful anions.

[Neutralization time]
In order to adequately promote the neutralization reaction and crystal growth of the components contained in the post-addition liquid, the time required for neutralization, together with heating of the post-addition liquid, is preferably 2 hours or more, and more preferably 4 hours or more.

The upper limit of the time required for neutralization is not particularly limited, but from the viewpoint of the production efficiency of the anion adsorbent, it is preferable that it be 12 hours or less, and more preferably 24 hours or less.

The neutralized solution contains iron oxyhydroxide, which contributes to the adsorption of harmful anions.

[Solid-liquid separation process]
In order to remove the precipitate contained in the neutralized liquid, the neutralized liquid is subjected to solid-liquid separation.

The method of solid-liquid separation is not particularly limited, and examples include filtration. By setting the mesh size of the filter used for filtration to 1 μm or more, it is possible to make the 10% particle diameter D10 of the extracted particles 1 μm or more.

The solid extracted by solid-liquid separation is dried (105°C, approximately 5 hours) to obtain the anion adsorbent described in this embodiment.

<Applications of anion adsorbents>
[Use as a water purification agent]
The anion adsorbent of the present embodiment can be used as a water purification agent.

The object to be purified is not particularly limited as long as it is an aqueous material with a pH of less than 10. The type of aqueous material is the same as the "aqueous solvent" described above.

In the anion adsorbent described in this embodiment, the iron oxyhydroxide component is capable of adsorbing anions in the neutral to acidic range, and has the property of desorbing anions in the alkaline range of pH 10 or higher. Therefore, when an aqueous material with a pH of less than 10 is brought into contact with the anion adsorbent, the particles can function as an adsorbent.

The anion adsorbent of this embodiment can be used anywhere where water purification is required, such as rivers, oceans, lakes, wells, fish tanks, and fish ponds.

The amount of the anion adsorbent used varies depending on the target of water purification, the anion concentration in the water, etc., but is generally preferably about 100 g to 1000 g per 1 m ³ of water.

There is no particular limitation on the method of using the anion adsorbent. For example, it may be sprayed directly onto the object to be purified.

In Southeast Asia, arsenic contamination of wells has become a problem. When an adsorbent is sprayed directly into a well, if the soil in the well is dredged, contaminated soil with adsorbed harmful anions may appear on the surface, or the adsorbent with adsorbed harmful anions may be pumped up along with the well water. If the adsorbent with adsorbed harmful anions is pumped up, there is a risk that the substance containing the harmful anions may be orally ingested. If the substance enters the mouth, stomach acid increases the elution of the harmful anions, and the problem of harmful anions may become apparent.

In this embodiment, the anion adsorbent may be directly sprayed onto the object to be purified, or may be used in a manner in which a water-permeable bag containing the anion adsorbent is brought into contact with an aqueous material having a pH of less than 10.

Anion adsorbents have the property of releasing anions in the alkaline region where the pH is 10 or higher. Therefore, by using the anion adsorbent in a bag-like form, the bag-like body can be removed from the object to be purified and brought into contact with an aqueous material with a pH of 10 or higher, causing the anions adsorbed to the adsorbent to release, and the used particles stored in the bag-like body can be reused as new adsorbents, which has the secondary effect of allowing the particles to be reused as new adsorbents.

Figure 1 shows an example of the anion adsorbent of this embodiment, in the form of an adsorbent bag housed in a water-permeable bag-shaped body, used to purify well water. The bag-shaped body 1 is placed on the bottom of a well W and is submerged in the well water WW.

There are no particular limitations on the bag-shaped body 1 as long as it has water permeability. If it does not have water permeability, water cannot come into contact with the anion adsorbent contained in the bag-shaped body, which is not preferable.

The material of the bag-shaped body 1 is not particularly limited. Examples include nylon, polyester, polypropylene, etc.

The structure of the bag-shaped body 1 is not particularly limited. For example, it may be mesh-shaped, net-shaped, etc. The size of the openings between the threads, strings, ropes, or strips that form the mesh or net is not particularly limited as long as it is a size that does not cause leakage of the adsorbent, i.e., is smaller than the 10% particle size D10 of the anion adsorbent.

The size of the bag-shaped body 1 is not particularly limited, but from the viewpoint of minimizing the number of times the bag-shaped body 1 is placed on the object to be purified, the lower limit of the size is preferably 50 mm square or more, and more preferably 100 mm square or more. Furthermore, considering manual installation, it is not desirable for the bag-shaped body 1 to be too heavy or large, so the upper limit of the size is preferably 1000 mm square or less, and more preferably 500 mm square or less.

The thickness of the filter cloth constituting the bag-shaped body 1 is not particularly limited, but from the viewpoint of preventing damage to the bag-shaped body 1 during use, the lower limit of the thickness of the filter cloth is preferably 0.1 mm or more, and more preferably 0.5 mm or more. Also, from the viewpoint of ensuring water permeability, the upper limit of the thickness of the filter cloth is preferably 2 mm or less, and more preferably 1 mm or less.

[Use as column packing material]
The anion adsorbent of this embodiment can be used as a packing material to be packed in a column.

Figure 2 shows an example of the anion adsorbent of this embodiment used as a packing material to be packed in a column. The bag-shaped body 1 is housed in a column (container for housing the adsorbent bag) C, and is configured in such a way that an aqueous material can pass through the column C from its inlet to its outlet.

When untreated water PW is passed through the inlet of column C, treated water AW is discharged from the outlet of column C. This allows the fluorine, arsenic, and selenium components contained in the untreated water to be efficiently removed.

When the packing material is placed in column C, it may be placed in the form of a bag-shaped body 1 as shown in FIG. 2, or the anion adsorbent may be placed as is.

[Use as a soil purification agent]
The anion adsorbent of the present embodiment can also be used as a soil purification agent.

When used as a soil purification agent, the anion adsorbent of this embodiment can be applied to soil (including sludge and dredged sludge) where soil contamination is a problem. The amount of the anion adsorbent used varies depending on the soil to be purified and the anion concentration in the soil, but for example, when the soil contains about 0.1 mg to 10 mg/L of contaminants, about 100 g to 10,000 g (10 kg) per ¹ m3 of soil is appropriate.

Methods for mixing the anion adsorbent of this embodiment with soil include mixing the soil and soil purification agent in a mixer or the like, pump injection, jet injection, simply spraying on the soil surface, and spraying with a sprinkler.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

<Production of Adsorbent>
350 mL of an aqueous solution containing 0.5 mol/L ferric chloride and 0.05 mol/L sodium sulfate was added to 300 mL of 70° C. warm water at a constant rate of about 1.2 mL/min over about 5 hours while maintaining the temperature at 70° C. as a whole. During the addition, a neutralizing agent (an aqueous solution containing 0.75 mol/L sodium carbonate and 0.01 mol/L metasilicic acid) was added as necessary to maintain the pH at 2. The liquid after the neutralization reaction was filtered using a filter with a mesh size of 1 μm to obtain an adsorbent according to the embodiment.

<Evaluation>
[Evaluation 1] Arsenic removal treatment 500 g of the adsorbent according to the embodiment was placed in a water-permeable bag and packed into column C shown in Figure 2. Then, 5 L of an arsenous acid aqueous solution with a concentration of 1 ppm (1 mg/L) was passed through column C, and the arsenous acid concentration in the post-treatment liquid after passing through was measured. As a result, it was confirmed that the arsenous acid concentration was less than 0.01 ppm (0.01 mg/L), which is the lower limit of measurement, and satisfied the standards set forth in the law and WHO guidelines.

A similar test was also conducted by replacing 5 L of arsenous acid aqueous solution with a concentration of 1 ppm (1 mg/L) with 10 L of arsenic acid aqueous solution with a concentration of 1 ppm (1 mg/L). Even in this case, the arsenic acid concentration was less than the lower measurement limit of 0.01 ppm (0.01 mg/L), and it was confirmed that the standard set out in the law and WHO guidelines was met.

[Evaluation 2] Selenium Removal Treatment The same evaluation as in Evaluation 1 was performed, except that 5 L of arsenic trioxide aqueous solution with a concentration of 1 ppm (1 mg/L) was replaced with 5 L of selenium aqueous solution with a concentration of 1 ppm (1 mg/L). As a result, it was confirmed that the selenium concentration was less than 0.01 ppm (0.01 mg/L), which is the lower limit of measurement, and satisfied the standards set forth in the law and the WHO guidelines.

[Evaluation 3] Fluorine Removal Treatment The same evaluation as in Evaluation 1 was performed, except that 5 L of arsenic trioxide aqueous solution with a concentration of 1 ppm (1 mg/L) was replaced with 5 L of fluorine aqueous solution with a concentration of 10 ppm (10 mg/L). As a result, it was confirmed that the fluorine concentration was less than 0.01 ppm (0.01 mg/L), which is the lower limit of measurement, and satisfied the standards set forth in the law and the WHO guidelines.

1 Bag W Well WW Well water

Claims (1)

The method includes placing a water-permeable bag containing one type of anion adsorbent directly on the bottom of a well;
The anion adsorbent is
Contains an iron oxyhydroxide component, a sulfur component, and a silica component,
The content of the sulfur component is 0.001 parts by mass or more and 1 part by mass or less relative to 100 parts by mass of the anion adsorbent,
The content of the silica component is 0.0001 parts by mass or more and 0.1 parts by mass or less relative to 100 parts by mass of the anion adsorbent,
The particle diameter D10 at which the cumulative value reaches 10% in a volume frequency particle size distribution measurement by a laser diffraction scattering method is 1 μm or more,
The size of the openings between the threads, strings, ropes, or strips forming the mesh or net of the bag is smaller than the 10% particle size D10 of the anion adsorbent;
How to purify well water.

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