JP2020062614A - Method for producing anion sorbent - Google Patents

Abstract

To provide a method for producing an anion sorbent, which can be used as a filler of a water conduction column or can be used in soil pollution countermeasure construction where water permeability is required, by making a porous body carry shwertmannite to provide shape and strength, the shwertmannite being known to sorb hazardous anions such as arsenic ions, arsenous ions, fluoride ions, and the like.SOLUTION: The sorbent for hazardous ions such as arsenic and the like, which has high strength, can be obtained by a simple process by synthesizing and precipitating shwertmannite inside fine pores and on a surface of a porous body where a substance constituting the porous body and pores are each continuously connected. The process comprises: a first step of impregnating the porous body with an iron salt solution; and a second step of synthesizing shwertmannite inside the pores or on the surface of the porous body with an impregnated iron salt used as a raw material.SELECTED DRAWING: None

Description

  The present invention imparts shape and strength by supporting Schwertmannite, which is known to sorb harmful anions such as arsenate ions, arsenite ions, and fluoride ions, on a porous body. , A method for producing an anion sorbent that can be used as a packing material for a water column that was difficult with Schwertmannite alone, or for soil pollution control work that requires water permeability. is there.

Adsorption as a scientific term refers to a phenomenon in which a specific component is concentrated at a two-phase interface such as a solid-liquid interface.
On the other hand, in the schwertmannite, which is an iron compound having anion sorption in the present invention, a specific substance such as a harmful ion is taken in not only at the interface but also inside the solid. Including such phenomena, it is called "sorption" in the sense that it becomes difficult to capture and release harmful ions.

Further, regarding the silicic acid introduced to improve the stability of the schwertmannite in the present invention, the case where the silicic acid is introduced by ion exchange with the sulfate ion in the structure of the schwertmannite and the case where it is attached or condensed to the surface However, in the present specification, these are collectively referred to as “sorption”, unless otherwise specified. However, "adsorption" is used when it is widely used as a technical term such as the adsorption layer method in civil engineering work and the adsorption layer used for it.
Since the silicate ion may be condensed and sorbed in the schwertmannite, or may be condensed after the sorption, hereinafter, in the present specification, whether or not the silicic acid is in the ionic state is used. In any case, the description may be made by omitting the “ion” like the sorption of silicic acid.

  Elements such as arsenic, selenium, fluorine, and chromium are harmful to humans and animals and plants if they are ingested in excess, so their emissions from factories are strictly limited. These elements are widely distributed in nature and are contained in soil, rocks, groundwater, hot spring water, and the like. In addition, it may be included in excavation debris such as rocks and soil generated in mines and tunnel construction, etc.If rainwater etc. comes into contact with such excavation debris, it may dissolve into rivers and groundwater, resulting in health hazards. There is concern. Since the sources are diverse and widely distributed, countermeasures against them are an issue. Further, since the harmful elements form anions, they cannot be insolubilized by forming a sparingly water-soluble hydroxide by raising the pH as is the case with many heavy metals, and it is difficult to remove or insolubilize them. .

  On the other hand, when contaminated water flows out due to an accident at a nuclear power plant, etc., it is said that iodate ion, which is an anion containing radioactive iodine, exists in the contaminated water and is difficult to remove.

Schwertmannite is a low crystalline compound containing iron and sulfate ions, and is known to have high sorption performance for anions such as arsenate ions. Schwertmannite is represented by the following chemical formula 1. Its main structure is composed of a stack of units in which one iron ion is surrounded by eight irons in a ring shape, and as a result, iron has a tubular structure, and sulfate ions are present inside the tube. It is said that.
Fe ₈ O ₈ (OH) _8-2x (SO ₄ ) _x (1)
However, in the formula (1), x is 1 to 1.75.
Fukushi et al. Reported in Non-Patent Document 1 that this compound also exists in nature, and takes in water-soluble arsenic existing in nature to insolubilize it, and is attracting attention as a sorbent and an insolubilizer for arsenic and the like. It is also known that its sorption performance is higher than that of other sorbent materials.

It is said that the structure of schwertmannite is more stable because the sulfate ion contained in the structure is replaced with an anion containing arsenic and the like, so that the effect thereof sorbs an arsenic compound.
However, it is known that the schwertmannite before incorporating the arsenic compound is low in stability, and when left to stand, it is transformed into goethite having higher crystallinity and the ability to sorb arsenic and the like is significantly reduced. Therefore, when the arsenic concentration around the sorbent is low, it is feared that the arsenic compound sorption will be reduced by conversion to goethite before sorption of sufficient arsenic to stabilize the structure. It Such a problem is that the original ability of Schwertmannite cannot be exhibited in applications such as the adsorption layer method used in civil engineering that requires sorption of exuding arsenic for a long period of time. , Get serious. As a method for improving this, in Patent Document 1, it is proposed to replace a part of the sulfate ion in the structure of the schwertmannite with a silicate ion. Further, Patent Document 2 proposes an improved method for greatly improving the stability.

  As schwertmannite, bulky powder or slurry is used for soil pollution countermeasures, and when mixed with contaminated soil, harmful ions such as arsenate ions are prevented from eluting into groundwater. To do.

  In addition, an adsorbent layer method has been proposed as a countermeasure for contaminated soil generated in civil engineering works such as tunnels, and measures using schwertmannite for the adsorbent layer have also been implemented. As one of the civil engineering construction methods, excavated soil is recycled as embankment material for roads, but if the excavated soil is contaminated, a harmful substance adsorption layer can be provided below it. The adsorption layer method is a method of preventing contaminants from dissolving in the infiltrated water and flowing out from the embankment. This adsorbent layer is required to have water permeability for the purpose of preventing the strength of the embankment from decreasing. Since schwertmannite has fine particles and becomes clay-like when it contains water, its water permeability tends to decrease when it is used in the adsorption layer. In order to prevent this, measures such as mixing with crushed stone and paving it have been taken, but this is not sufficient.

  Further, in Patent Document 3, when schwertmannite is used for the treatment of iodate ion in contaminated water generated in connection with a nuclear power plant, the sorption capacity is large as compared with other anion supplement materials, and It has been shown to have excellent selective sorption even in an environment with many interfering ions such as seawater.

  On the other hand, when it is necessary to remove harmful anions contained in water, a powdered sorbent may be mixed and then filtered, or a flocculating agent may be added to perform solid-liquid separation, and powder may be used. Although it can be applied, there is a problem that the use is limited because the process is complicated and the apparatus tends to be large such as a settling tank. As a method of easily removing impurities contained in water, a method of continuously removing impurities by passing contaminated water through a packed column (column) packed with a sorbent for impurities is widely used. In this case, if the sorbent for filling is in powder form, the liquid passing rate is low, and even if a filter is provided on the outlet side of the packing tower, it easily clogs or if the filter is coarse, it will pass through the filtration tower. There is a problem that it will end up, and it cannot be practically used. For this reason, a granular sorbent material that allows easy passage of liquid is used. As an example of using a granular sorbent in a column, a method of using an ion exchange resin obtained by molding a resin having an ion exchange group into a bead shape for water treatment is well known. However, since the ion exchange resin is expensive, it is almost always used for treating contaminated water generated in factories, and it is economically difficult to use it for treating contaminated water such as groundwater. Further, since the resin is an organic substance, there is a risk of deterioration in strength due to deterioration, and it is difficult to apply it to the adsorption layer construction method and the like.

  In order to meet such demand, Patent Document 4 proposes that a fibrous substance such as rock wool is loaded with an iron compound such as schwertmannite and used for treating acidic mining wastewater. In addition, a granular sorbent is obtained by processing the inorganic fiber into a granular shape. However, although water permeability is easily obtained with a fibrous substance, there is a problem that when it is used for an adsorption layer, the particles are easily crushed by rolling.

  Further, in Patent Document 5, Schwertmannite powder is fixed to the outside of the zeolite particles through an organic binder with the particles of zeolite or the like, which is an inorganic porous material, as the nucleus to obtain a granular sorbent. In this method, since the schwertmannite powder particles are larger than the pore size of the molecular size of zeolite, it is difficult to let the schwertmannite penetrate into the inside of the porous body, and rather the pores of the zeolite have cation exchange. It is not necessary for Schwertmannite to enter inside the hole in order to take advantage of its ability. Moreover, there was concern about long-term stability by using an organic binder.

  Patent Document 6 proposes a method of granulating a porous body such as schwertmannite and activated carbon using a water-soluble inorganic salt as a binder. Although this method can form a granular sorbent with only inorganic substances, a sufficient binding effect cannot be obtained with only a small amount of a salt that generates hydraulic properties, and when used in an adsorption layer, it collapses due to rolling pressure or the like. There is a risk that the particles may rub against each other and become powdered. Even when used in a packed tower packed with a sorbent, pulverization may cause problems such as clogging and outflow to the outside of the packed tower.

JP-A-2005-871 JP, 2016-216299, A Japanese Patent Laid-Open No. 2016-123902 Japanese Patent Laid-Open No. 2005-58955 Patent No. 5037950 WO2014 / 003120

K Fukushi, M Sasaki, T Sato, N Yanase, H Amano and H Ikeda, Applied Geochemistry, 18 (8), 1267-1278, 2003.

  When granulating using a binder, there is a problem that not only the manufacturing process is complicated, but also the portion covered with the binder is formed and the sorption capacity is impaired. In addition, if the amount of binder is reduced to improve the performance, the binding force will decrease and the sorbent material will easily fall off or the particles will collapse, which may cause clogging in the filtration tower used for water treatment. . In addition, there is a possibility that problems such as a decrease in water permeability and deformation of the land surface after construction may occur with the adsorption layer method in civil engineering work. Further, when a sorbent is attached to a porous body in which fibers are entangled with each other, there are problems that the porous body made of fibers is deformed by its own weight and the adsorbent is easily desorbed when the column is packed. Further, also when used in the adsorption layer method, when a fibrous porous body is used as a carrier, there is a problem that it is deformed by rolling and the water permeability is impaired.

  The present invention, in view of the above situation, by synthesizing and depositing schwertmannite in the pores inside and on the surface of the porous body in which the constituent material and the pores are continuously connected, respectively, to obtain high strength in a simple process. An object of the present invention is to provide a sorbent or an insolubilizer for harmful anions such as arsenic.

  The present inventor, as a result of extensive studies in order to solve the above-mentioned problems, impregnated with a ferrous salt solution a porous material in which hard substances made of minerals such as rock and ceramics and pores are continuously connected, respectively. Then, by depositing Schwertmannite, which is an iron compound having anion sorption, inside and on the pores of the porous body, it is possible to support Schwertmannite also in the pores present in the porous body, It was found that the utilization rate of Schwertmannite is high because a binder is not used, and a granular sorbent having high strength can be obtained.

That is, the present invention is a method for producing an anion sorbent in which a Schwertmannite is supported on a porous body, which comprises at least the following two steps.
First step: a step of impregnating a porous body with a solution of an iron salt Second step: a step of synthesizing schwertmannite from the impregnated iron salt as a raw material inside and on the pores of the porous body.

  In the second step, the iron salt-impregnated porous body obtained in the first step was added to a solution containing sulfate ions and having a pH of 2.5 to 4.5, and then the pH was adjusted to 2 It is preferable to appropriately adjust the pH so as to maintain between 0.5 and 4.5.

  After impregnating the porous body with the iron salt in the first step, it is preferable to perform the second step after drying to make the iron salt a solid or increase the concentration to suppress the fluidity.

  The substance constituting the porous body is an inorganic substance such as rock, ceramic, or glass, which is not due to the entanglement of the inorganic fibers, and the substance constituting the porous body and internal pores are continuously connected to each other. Is preferred.

  It is preferable that the diameter of the continuously connected pores inside the porous body is 0.1 to 10 μm.

  By contacting the anion sorbent produced in the present invention with a liquid or solid containing an anionic harmful substance, the anionic harmful substance can be adsorbed and removed or insolubilized.

  The sorbent material of the present invention can be preferably applied to an anionic harmful substance in which the anionic harmful substance contains any element of arsenic, selenium, fluorine, chromium and iodine.

  Granular sorbent obtained by the method of the present invention, compared with the conventionally known production method, it is possible to easily obtain a particulate sorbent, without using a binder, to a porous body having sufficient strength Since it carries Schwertmannite having anion sorption, it has high strength and is not easily deformed by external force. Further, if a porous rock such as lava or a porous ceramic waste material such as a unglazed product is used as the porous body, the granular sorbent can be manufactured at an extremely low cost. Therefore, it is suitable for use where water permeability is required as a sorbent removal material for toxic substances contained in contaminated water, contaminated soil, scraps and excavated earth and sand generated in civil engineering works, incinerated ash landfilled at disposal sites, industrial waste, etc. A sorbent can be provided and is extremely useful as a material for treating harmful substances.

1 shows a powder X-ray diffraction pattern measured by grinding the sorbent material obtained in Example 1 and carrying schwertmannite on pearlite. The powder X-ray-diffraction pattern measured by grinding the pearlite used in Example 1 is shown. The electron micrograph which observed the pumice stone from Gunma prefecture Akagi mountain used in the comparative example 2 at 100 times the magnification is shown. The electron micrograph which observed the pumice stone from Gunma Prefecture Akagiyama used in the comparative example 2 at 1000 times is shown. The electron micrograph which observed the pumice stone from Akagiyama, Gunma which carried the schwertmannite produced in Comparative Example 2 at 100 times the magnification is shown. The electron micrograph which observed the pumice stone from Akagiyama, Gunma which carried the schwertmannite produced in Comparative Example 2 by 1000 times is shown. The powder X-ray-diffraction pattern which measured the Schwertmannite synthesize | combined in Comparative Example 1 is shown.

A method for producing an anion sorbent in which a Schwertmannite is supported on a porous body, comprising at least the following two steps.
First step: Step of impregnating a solution of iron salt into a porous body Second step: Step of synthesizing schwertmannite using the impregnated iron salt as a raw material inside and on the pores of the porous body.

The method for producing an anion sorbent supporting Schwertmannite in the pores and the outer surface of the porous body in the present invention comprises a first step of impregnating a solution of an iron salt into the porous body,
A second step of synthesizing schwertmannite, which is a compound insoluble in water, having anion sorption and using an impregnated iron salt as a raw material, inside and inside the pores of the porous body is included.
Hereinafter, the first step, the second step, the raw materials to be used, and the usage method and application will be described.

1. Description of process
1-1. First Step The first step of the manufacturing method in the present invention is a step of impregnating a porous body with an iron salt. In this step, the iron salt solution penetrates into the pores of the porous body by bringing the porous body and the iron salt solution into contact with each other.

  The method of contacting the porous body with the iron salt solution is not particularly limited as long as they can contact each other, such as a method of immersing the porous body in the iron salt solution and a method of spraying the iron salt solution on the porous body.

  Although the immersion time depends on the type of the porous body and the viscosity of the iron salt solution, the impregnation amount will be saturated if both are contacted for several tens of minutes to 1 day. As a method of impregnation faster or a method of more impregnation, use of a surfactant, method of giving vibration such as ultrasonic wave during impregnation, method of pouring iron salt solution into porous body placed under reduced pressure, impregnation A method of repeating depressurization and pressurization (or returning to normal pressure) of the whole can be used. As an example of the step in the case of using a surfactant, a method of immersing the porous body in an aqueous solution of a surfactant in advance and then removing water to carry out a surfactant treatment, or a method of adding a surfactant to an iron salt solution A method of adding it can be used.

  When a surfactant is used, its type is not particularly limited, but it is preferable to use a surfactant having an antifoaming effect because fine bubbles are easily generated when the porous body is impregnated with the liquid. Such surfactants are known as defoaming agents and wetting agents, and include, for example, acetylene glycol-based Surfynol (trade name, manufactured by Nissin Chemical Industry Co., Ltd.), Dynol (trade name, Nisshin Chemical Industry Co., Ltd.). Manufactured by Nisshin Chemical Industry Co., Ltd., etc. These surfactants are used by diluting them with water or by directly adding and mixing necessary amounts to the iron salt solution.

  After impregnation with the iron salt solution, the excess liquid can be removed by filtration and the like, and the solution can be used as it is in the second step, but the solvent component such as water is volatilized to precipitate or concentrate the iron salt, and then the second step. Is preferably performed. The reason for doing this is that after impregnation, while the iron salt is highly fluid as a solution inside the porous body, if the following step is performed, the iron salt will elute outside the porous body before the schwertmannite precipitates. Then, the amount of schwertmannite carried may decrease, and this is to prevent this.

1-2. Second step The second step is a step of synthesizing schwertmannite from the impregnated iron salt as a raw material inside and on the surface of the pores of the porous body.
Although several methods are known for synthesizing schwertmannite, a solution containing iron ions and sulfate ions is stirred at a temperature of about room temperature to about 90 ° C. and stirred, and a base is added to adjust the pH to 2.5. When it is adjusted to about 4.5, crystals of schwertmannite precipitate to form a yellowish brown precipitate. The schwertmannite can be obtained by filtering this and washing with water to remove unnecessary salts and the like.

  In the method of the present invention, since it is necessary to cause the above reaction to occur in the pores of the porous body, if necessary, the pH and temperature of the aqueous solution containing sulfate ions are adjusted to an appropriate range, and the iron salt is added thereto. Add the impregnated porous body. Regarding the meaning of containing sulfate ions as needed, when iron sulfate is used as an iron salt, it is not necessary to add sulfate ions to the pH-adjusted aqueous solution, and if necessary, This is the case where iron chloride does not contain sulfate ions such as iron chloride and iron nitrate.

  When the porous material impregnated with iron salt is adjusted to the pH necessary for the production of schwertmannite and added to an aqueous solution containing sulfate ions as necessary, schwertmannite is produced in the pores and on the surface of the porous body. However, since the pH gradually decreases, it is necessary to keep the pH within the range necessary for the production of schwertmannite while adding a basic component such as sodium carbonate.

2. Materials used
2-1. Iron Source Examples of iron salts that can be used in the present invention include ferrous chloride, ferric chloride, iron nitrate, and iron sulfate. Of these, ferric chloride is most preferable because it does not generate a wastewater-regulating substance other than iron such as nitrate in the waste liquid after synthesis, is cheaper than other salts, and has a high solubility in water. Since it contains chlorine, by-products such as Akaganeite (β-FeOOH) tend to form when synthesized at high temperature, but by synthesizing at 75 ° C or less, even if a small amount of Akaganeite etc. is generated, sorption performance is improved. Has little effect.

2-2. Carrier In the present invention, the carrier for supporting the schwertmannite is a porous material, but it is not due to the entanglement of fibers, but a hard material in which the substance forming the porous body and the internal pores are continuously connected. Since the larger the specific surface area is, the more sorption components can be supported, it is preferable to use a porous body having communication holes extending from the surface to the inside. Such a porous body may be produced naturally, such as minerals, or artificially produced, such as ceramics and plastics. Produced in nature, typical examples of porous bodies that can be used as carriers in the present invention include lava such as pumice, sedimentary rock such as sandstone, mudstone, and tuff, and skeleton of ancient organisms such as diatomaceous earth. And the like having fine pores. Examples of artificially made porous materials include ceramics, porous glass, silica gel, and porous materials intentionally produced as porous such as used in tiles, bricks, pottery such as flower pots, exhaust gas filters for automobiles, etc. Alumina, a porous resin, etc. are mentioned. Also, a semi-artificial porous body such as perlite obtained by expanding natural glassy minerals such as obsidian and pearlite at high temperature can be used.

  The substance forming the porous body and the internal pores are continuously connected to each other, for example, as in the case of sponge, the constituent material is not due to contact, but the material itself is continuous, and the adjacent bubbles are formed. Are connected to each other or to cracks or the like. This structure allows liquids or expectations to permeate and penetrate. An interface such as a crystal grain boundary of ceramics or the like cannot be permeated with a liquid or a gas, and is therefore regarded as a continuous connection. Even when sand grains are mixed inside the unglazed pottery or porous rock, there is a case where it is firmly in contact with the material that makes up the rock or pottery and there is no risk of displacement due to external forces, such as when fibers are in contact with each other. Considered as a continuous connection. In this case, the sponge has been taken as an example for explaining the structure, but the sponge itself is not suitable for the carrier of the present invention because the constituent material is flexible.

  Among these, products such as roof tiles and unglazed flowerpots are preferable because they generate a large amount of nonstandard products and used products and are required to be recycled, and are inexpensive and available in large quantities. Lava ejecta such as pumice stone is also preferable because it can be obtained inexpensively and in large quantities.

  On the other hand, rocks such as limestone and dolomite and concretes whose main component is an alkaline substance which dissolves in acid are not preferable because iron chloride as a raw material is acidic.

  The sorbent body obtained in the present invention has a feature that the smaller the pore size of the porous body, the more the stability in a wet heat environment is improved as compared with the case of Schwertmannite alone, but the stability improving effect is When the carrier is insufficient or a carrier containing no silicic acid component is used, silicic acid can be inserted using a silicate such as sodium silicate after carrying the schwertmannite. Specifically, silicic acid can be easily inserted by adding a sodium silicate to the water in a state where the granular sorbent supporting the schwertmannite is put in water, stirring and filtering and drying. At that time, if the pH of the aqueous solution is adjusted to 5 to 8 by adding a base component, the higher the pH, the easier the anion exchange proceeds, and the silicic acid insertion amount can be adjusted. If the pH at this time is 9 or more, the crystal structure of schwertmannite is easily broken, which is not preferable.

  An organic material such as plastic may be used as the porous body. Examples of usable plastics include porous polystyrene manufactured for applications such as ion exchange resins. However, for the purpose of sorbing arsenic contained in water contaminated with arsenic or the like, or water eluted from soil, extremely inexpensive materials are required, and plastics are less likely to deteriorate in the environment than inorganic substances. The inorganic materials described above are preferred because they are faster.

  Porosity, pore diameter, specific surface area and the like are used as an index showing the properties of the porous body. These are not particularly limited, but a preferable range can be selected according to the application.

  With respect to the porosity, the higher the amount of schwertmannite supported, the more preferable, and some porous materials such as pearlite have a porosity of 80 to 90%.

  On the other hand, those with a very high porosity often have large pore diameters, and in the case of the above-mentioned pearlite, the pore diameters exceed several tens of μm, so Schwertmannite deposited inside easily falls off. Therefore, it may not be suitable as a packing material for water treatment columns. On the other hand, when the pore diameter is 10 μm or less, it is preferable that the Schwertmannite deposited in the pores does not easily fall off. Although there are various natural products and unglazed products depending on the place of origin, manufacturing method, etc., the pumice used in the examples of the present specification has a large number of pores of several μm, and the unglazed flowerpot has pores of 1 μm or less. It was recognized that there were many. In all of these cases, the loss of Schwertmannite when soaked in water and shaken was extremely small. Therefore, when used for water treatment, the pore diameter of the porous body is preferably 10 μm or less. There may be some large pores, but most of them may be 10 μm or less.

Regarding the specific surface area, those having a large specific surface area are preferably used as the carrier for the catalyst used in the chemical reaction. For example, an alumina porous body has a specific surface area of about 200 m ² / g. It can be said that the larger the specific surface area of the porous body used in the present invention is, the larger the specific surface area of the schwertmannite itself precipitated in the pores is. It is possible to obtain a sorbent having a large value. For example, in an experiment conducted by the present inventors, the temperature at the time of precipitation and the specific surface area of schwertmannite are related, and the specific surface area of schwertmannite precipitated at 25 ° C. is about 1 m ² / g, while The specific surface area of the schwertmannite precipitated at 40 to 90 ° C. was very large, 100 to 150 m ² . Therefore, the sorbent obtained by supporting Schwertmannite in the pores of the porous body having a small specific surface area has a large specific surface area as a whole.

  When the precipitation temperature exceeded 90 ° C, formation of red ganeite and jarosite was observed in addition to schwertmannite, and the arsenic sorption performance tended to peak at around 65 ° C. Therefore, the temperature for depositing schwertmannite is preferably 40 to 90 ° C. If the temperature is lower than 40 ° C, the specific surface area of the schwertmannite is small, and if the temperature is 90 ° C or higher, a large amount of by-products are formed and the sorption performance is deteriorated as compared with the case of precipitation at a preferable temperature.

3. Method of Use The granular sorbent obtained by the method of the present invention can be used as a countermeasure against soil and water pollution by heavy metals forming anions such as arsenic and selenium. In particular, by imparting a shape like particles, the powder is less likely to rise during use, the water permeability is improved, and it is easy to separate from water. It can be preferably used in a place where it was not present. For example, when treating contaminated water, it is possible to easily and continuously remove pollutants by packing the granular sorbent obtained by the present invention in a packed tower and passing the contaminated water. Such usage could not be performed with the powder as it is. Also, in civil engineering work, when laying excavated soil containing arsenic, etc. generated at the site of tunnel excavation under the road, an adsorption layer construction method is known in which an adsorption layer called an adsorption layer is laid under the excavated soil. ing. In such a construction method, it is required to sorb and remove pollutants dissolved in rainwater and the like that have passed through the contaminated soil, and allow the water to quickly pass through the adsorption layer. Conventionally, when a powdery sorbent is used alone, there is a problem that clogging occurs and sufficient water permeability cannot be secured. In addition, it is necessary to mix with rocks etc. because the strength cannot be secured with a layer of only powder, the process is complicated, not only the uniformity of construction is impaired, but also the problem that powder is scattered during construction and the work environment deteriorates there were. In order to cope with such a problem, a method of applying Schwertmannite to a block of inorganic fibers such as rock wool and performing the construction has been developed and used. In this case as well, the schwertmannite does not become clogged, but the lumped fibers themselves have low strength, and because of the strength problem that they are easily deformed by the pressure of the earth and sand, it is necessary to mix rocks and the like. It was Therefore, the sorbent material produced by the present invention, which has Schwertmannite supported on the porous body having high strength, is extremely useful.

Since the produced schwertmannite coexists with ionic impurities derived from the raw materials, it is possible to remove these impurities by washing with water etc. after depositing the schwertmannite in the second step. preferable.
Since the obtained schwertmannite easily changes to goethite in the presence of water, it is preferably dried after separation.

The sorbent material obtained by supporting the Schwertmannite on the porous body obtained by the production method of the present invention can be preferably used as a sorbent material for harmful metals and the like.
Hazardous substances targeted for use are sorbed on Schwertmannite such as fluoride ion, arsenite ion, arsenate ion, selenate ion, selenite ion, chromate ion, and dichromate ion. However, examples thereof include, but are not limited to, iodate ion, chlorate ion, and bromate ion.
Among these, it is suitable for sorption of an anionic harmful substance containing any element of arsenic, selenium, fluorine, chromium and iodine.

As it is widely distributed in nature and has strong toxicity, arsenic has been attracting attention as an element which is a problem in many places. Arsenic can take several valences, but the ones that cause problems with water quality and soil pollution are trivalent arsenic forming arsenite and pentavalent arsenate. There are two types of arsenic. These tend to be arsenite ions under anaerobic conditions and arsenate ions under aerobic conditions. Since the valence is likely to change due to the oxygen concentration and bacteria, trivalent and pentavalent coexist in many cases, and their ratio also changes due to changes in the environment. Therefore, it is necessary for the arsenic sorbent material to support both ions as required. In some cases, the valence of either one of them is almost the same in the oxidizing atmosphere or the reducing atmosphere.
The sorbent material carrying Schwertmannite obtained by the production method of the present invention can be preferably used as a trivalent or pentavalent arsenic sorbent material.

The schwertmannite-supported sorbent material of the present invention is an industrial wastewater, groundwater, sorbent removal material for harmful substances from polluted water containing harmful substances such as hot spring water, polluted soil, excavated soil generated in civil engineering, etc. It can be used as a sorbent material for hazardous substances such as drilling scraps, incineration ash, and industrial waste.
When it is used as a sorbent removal material for harmful substances from contaminated water, known methods can be applied. For example, there is a method in which a sorbent of the present invention is packed in a packed tower or the like, and waste water containing a harmful substance is supplied to the packed tower to sorb the harmful substance.

  Since the sorbent material supporting schwertmannite of the present invention has high strength and hardly deforms even when spread under contaminated soil, it absorbs harmful ions by waiting for harmful ions, such as an adsorption layer method for preventing diffusion of pollutants to the surroundings. It is extremely suitable for use such as insolubilization.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

<Explanation of analysis / evaluation method>
(1) Measurement of Specific Surface Area The specific surface area of the porous body was determined by the BET method using a measuring device Autosorb-1 manufactured by Kantachrome Instruments Japan GK.

(2) Observation by Electron Microscope The platinum-vapor-deposited porous body sample was observed under magnification at an accelerating voltage of 1.0 kV using a Hitachi High-Tech S-4800 type FE-SEM.

(3) Powder X-ray diffraction (XRD)
The powder X-ray diffraction pattern was measured by using an X-ray diffractometer D8 ADVANCE manufactured by Bruker AXS KK and using CuKα ray as an X-ray source in the range of 2θ of 10 to 80 °.

<Example 1> Example in which perlite is used as a carrier Perlite (manufactured by Akagi Horticultural Co., Ltd.) derived from pearlite and having a particle size adjusted to 1 to 3 mm, which is commercially available, is wrapped with 100 mesh polyethylene mesh and washed in running water. Along with that, fine strips were removed. This was dried under reduced pressure at 70 ° C. and used as a carrier. The bulk specific gravity after drying was 0.084 g / cm ³ , the porosity was 70.2%, and the specific surface area determined by the BET method was 1.1 m ² / g.
Next, 10.0 g of this perlite was weighed in a 200 ml poly cup, and 100 g of an iron (III) chloride aqueous solution (manufactured by Toagosei Co., Ltd., 42 ° Baume Periron) was added to it, and all the perlite became a liquid. Soaked Since perlite floated on the liquid, it was occasionally stirred. The mixture was left as it was for 2 hours, filtered with paper, and dried under reduced pressure at 50 ° C. overnight to give a total weight of 20.6 g. The weight increase was assumed to be iron (III) chloride hexahydrate, and the number of moles was estimated to be 39.2 mmol.
Next, 5.57 g (39.2 mmol) of sodium sulfate was weighed into a 500 ml polybeaker, and 150 g of water was added and dissolved. This poly beaker was placed in hot water and the temperature was adjusted so that the internal temperature became 65 ° C. Sulfuric acid was added little by little, and the pH was once lowered to 2.0. Next, sodium carbonate was added little by little and stirred to adjust the pH to 3.5.
When a small amount of the above-mentioned perlite impregnated with ferric chloride was added while keeping the sodium sulfate aqueous solution adjusted to pH 3.5 at 65 ± 5 ° C., a decrease in pH was observed, so sodium carbonate was added to adjust the pH to 3 I kept it at 4. In this way, while maintaining the pH at 3 to 4, perlite impregnated with ferric chloride and sodium carbonate were added little by little. After the total amount of perlite impregnated with iron chloride was added, the mixture was stirred for 30 minutes while keeping the temperature and pH as it was, and then the stirring was completed and the mixture was taken out from the hot water bath. During this period, the pH was similarly maintained at 3-4.
Next, perlite in the polybeaker was taken out on a 100-mesh polyethylene mesh, filtered, and washed with running water while being kept in the mesh to remove fine products and the like. This was dried under reduced pressure at 50 ° C. overnight to obtain 16.0 g of a sorbent having pearlite carrying schwertmannite. Hereinafter, the sorbent in which the Schwertmannite is supported on the porous body is abbreviated as the supported sorbent.
When this supported sorbent was ground in a mortar and the XRD pattern was measured, the peak of the pattern of Schwertmannite synthesized in Comparative Example 1 (Fig. 7) overlapped with the pattern that seems to be perlite as shown in Fig. 1. The obtained pattern was obtained, and it was found that schwertmannite was formed inside the porous body by this method. The XRD pattern of perlite alone is shown in FIG.
Using this supported adsorbent, an arsenic sorption test from an aqueous arsenic compound solution was carried out, and it was found that it had an arsenic sorption capacity. Further, when comparing the sorption capacities per supported Schwertmannite, the values were comparatively close to those of Comparative Example 1, and the efficiency was not significantly reduced by the supporting. In addition, since it was shaken in an aqueous solution, a supported sorbent which was rubbed into fine particles was generated due to the falling off of the supported Schwertmannite. A filter that removes the generated powder is expected to be used as a filter material for water treatment, but this is not enough to prevent filtration, and it is not possible with powdered Schwertmannite alone. It has been found that it can be applied as a sorbent. Further, the amount of powder generated is not so large as to impair the water permeability, and it can be used without problems in the adsorption layer construction method.

<Example 2> Example of using pumice as a carrier Pumice stone from Akagiyama, Gunma Prefecture (cleaned products are sold by Akagi Horticultural Co., Ltd.) is crushed, and a size of 1 mm to 2 mm is obtained by using a sieve with openings of 1 mm and 2 mm. It was classified and collected. This was wrapped with 100 mesh polyethylene mesh, washed in running water, and fine particles were removed. This was dried under reduced pressure at 70 ° C. overnight as a carrier. The bulk specific gravity after drying was 0.48 g / cm ³ , the porosity was 52.2%, and the specific surface area determined by the BET method was 2.4 m ² / g.
Next, 20.0 g of this pumice stone was weighed in a 200 ml poly cup, and 40 g of an iron (III) chloride aqueous solution (manufactured by Toagosei Co., Ltd., 42 ° Baume Periron) was added thereto, and all the pumice stone was liquified. Soaked in. After leaving it as it was for 2 hours, it was filtered with a filter paper. When this was dried under reduced pressure at 50 ° C. overnight, the total weight became 25.1 g. The weight increase was assumed to be iron (III) chloride hexahydrate, and the number of moles was estimated to be 18.9 mmol.
Next, 2.68 g (18.9 mmol) of sodium sulfate was weighed into a 500 ml polybeaker, and 140 g of water was added and dissolved.
Thereafter, the same operation as in Example 1 was carried out to obtain 22.8 g of a supported sorbent in which crushed pumice was loaded with schwertmannite.
Electron micrographs of pumice used as a carrier are shown in FIGS. 3 and 4. It can be seen that there are innumerable holes with a diameter of several μm. Electron micrographs after loading are shown in FIGS. 5 and 6. It can be seen that the Schwertmannite is deposited so as to fill the pores.

<Example 3> Example using a unglazed pot as a carrier A commercially available unglazed flowerpot (purchased from Kama Home Center) was crushed and classified to a size of 1 mm to 2 mm using sieves with openings of 1 mm and 2 mm. This was wrapped with 100 mesh polyethylene mesh, washed in running water, and fine particles were removed. This was dried under reduced pressure at 70 ° C. overnight as a carrier. The bulk specific gravity after drying was 0.92 g / cm ³ , the porosity was 32.2%, and the specific surface area determined by the BET method was 8.8 m ² / g.
Next, 20.0 g of this ground unglazed pot was weighed in a 200 ml poly cup, and 20 g of an aqueous solution of iron (III) chloride (manufactured by Toagosei Co., Ltd., 42 degrees Baume per iron) was added thereto, and all The crushed unglazed pot was immersed in the liquid. After leaving it as it was for 2 hours, it was filtered with a filter paper. When this was dried under reduced pressure at 50 ° C. overnight, the total weight became 22.2 g. The weight increase was assumed to be iron (III) chloride hexahydrate, and the number of moles was estimated to be 8.12 mmol.
Next, 1.15 g (8.12 mmol) of sodium sulfate was weighed into a 500 ml polybeaker, and 140 g of water was added and dissolved.
Thereafter, the same operation as in Example 1 was carried out to obtain 21.3 g of a supported sorbent in which schwertmannite was supported in a crushed unglazed flowerpot.

<Comparative Example 1> 62.7 g (0.23 mol) of iron (III) chloride hexahydrate and 28.4 g (0.20 mol) of sodium sulfate were weighed into a beaker of 2 L of schwertmannite alone , and the whole amounted to 800 ml. Until water was added. It was set in a warm water bath and equipped with a stirrer, thermometer and pH meter. While heating in a warm water bath, the inside of the beaker was stirred and uniformly dissolved, and this aqueous solution was kept at about 65 ° C. At this time, the pH was 1.3. Sodium carbonate was added little by little while continuing stirring and keeping the temperature, and when the pH of the aqueous solution reached 2.7, the addition of sodium carbonate was stopped. The amount of sodium carbonate added was 30.4 g. At this point, the liquid was a yellowish brown and opaque slurry. After stirring and keeping the temperature for 15 minutes, the heating of the water bath was stopped, the hot water in the water bath was replaced with water, and the mixture was cooled to around room temperature.
Then, the reaction liquid was filtered using the Buchner funnel which set the filter paper. In order to remove extra ions and the like, the obtained solid content was added to 1 L of water, stirred, and filtered again, which was repeated 3 times, taken out in a petri dish, and vacuum dried at 50 ° C. overnight. . The yield of the obtained yellowish brown dry solid was 25.1 g. When powder X-ray diffraction of the powder obtained by grinding this in a mortar was measured, the typical diffraction pattern of schwertmannite shown in FIG. 7 was obtained, and it was confirmed that schwertmannite was obtained. When the specific surface area of this schwertmannite was determined by the BET method, it was 120 m ² / g.
The powder synthesized by this method was used as Comparative Example 1 and used for the sorption test.
The powder was analyzed by fluorescent X-rays, and the mass ratio of iron: silicon: sulfur determined from the X-ray intensity ratio was 46.3: 0.00: 5.33. This numerical value was divided by each atomic weight to obtain the molar ratio of each element, and this numerical value was converted to the molar ratio of each element with iron being 8.00. Iron: silicon: sulfur = 8.0: 0. It was 00: 1.60. Since the schwertmannite contains 8 moles of iron in 1 mole, the schwertmannite obtained by this synthesis has a value of x in the chemical formula (1) of 1.60, which is described in the literature. Consistent with the element ratio of knight.
Fe ₈ O ₈ OH _8-2x (SO ₄ ) _x (1)
However, in the formula (1), x is 1 to 1.75.

<Comparative Examples 2 to 4>
The size of the porous body used in Examples 1 to 3 was adjusted to that of each Example, and the porous body was used as it was in the sorption test without supporting anything. Comparative Example 2 is pearlite, Comparative Example 3 is pumice stone, and Comparative Example 4 is a unglazed flowerpot.

  The porous bodies used as the carrier are summarized in Table 1.

  In each case, a sieve having a mesh size of 2 mm and a sieve having a mesh size of 1 mm was not used. In addition, since the pores of the porous body observed with a microscope have an indeterminate shape, an approximate size was visually estimated.

<Various evaluation results of examples and comparative examples samples>
Arsenic sorption test Table 2 shows the arsenic sorption test results for the examples and comparative examples. It was found that all of Examples 1-3 sorb arsenic. On the other hand, the porous bodies themselves used as these carriers did not have the ability to sorb arsenic as shown in Comparative Examples 2 to 4. From this, it was found that by supporting Schwertmannite, a sorbent in which arsenic sorption performance was imparted to the porous body was formed.

The arsenite ion sorption results are shown in the column of As (III), and the arsenite ion sorption results are shown in the column of As (V).
Regarding Examples 1 to 3, the arsenic sorption amount per 1 g of Schwertmannite was also calculated and posted from the amount of supported Schwertmannite and compared with Comparative Example 1.

  In Table 2, the arsenic sorption test results were compared with the amount of arsenic sorption per weight of the supported schwertmannite. The smaller the pore size of the used porous body and the larger the specific surface area of It can be seen that the amount of arsenic sorbed in the Furthermore, in Examples 2 and 3, the sorption amount was higher than that in the case where the sorption test was performed using the Schwertmannite powder alone in Comparative Example 1. The reason is not clear, but it is presumed that the effective area of the schwertmannite is increased by the loading. The effect appears when the average pore diameter of the pores observed with a microscope is less than about 10 μm, and becomes remarkable when it is less than 1 μm. Therefore, the average pore diameter of the carrier used is more preferably less than 10 μm. It can be said that this effect is obtained by supporting the porous body.

Durability test by wet heat leaving test Examples 1 to 3 and Comparative Example 1 are shown in Table 3 as a result of the arsenic sorption test measured after being left for 2 weeks in an environment of 50 ° C and relative humidity of 98% by the method described below. . The sorption performance retention rate after standing under moist heat was determined by comparison with the results in Table 2. In Comparative Example 1 evaluated by Schwertmannite alone, the arsenic sorption performance was significantly reduced as described in Patent Document 1 and the like described above. On the other hand, in Examples 1 to 3, a high performance retention rate was obtained even though the stabilization treatment as in Patent Documents 1 and 2 was not performed. It can be said that this is also the effect of supporting the porous body.

Sorption test for harmful ions other than arsenic For Example 2 and Comparative Example 1, sorption tests for anions containing fluorine, chromium, and selenium were performed by the method described below, and Table 4 shows the sorption per 1 g of schwertmannite. The amounts are listed. It was found to have sorption performance for all the evaluated ions.

  FIG. 1 is a powder X-ray diffraction pattern measured by grinding the sorbent obtained by Example 1 and carrying schwertmannite on pearlite. Comparing the X-ray diffraction pattern of pearlite alone in FIG. 2 and the X-ray diffraction pattern of schwertmannite alone in FIG. 7, it can be seen that these diffraction patterns were observed in duplicate.

  FIG. 2 is a powder X-ray diffraction pattern measured by grinding the pearlite used in Example 1.

  3 and 4 are electron micrographs of pumice stones used in Comparative Example 2 from Akagiyama, Gunma Prefecture, observed at 100 and 1000 times, respectively. Many pores of about 1 to 10 μm can be confirmed.

5 and 6 are electron micrographs of pumice stones produced in Comparative Example 2 and carrying Schwertmannite from Akagiyama, Gunma Prefecture, observed at 100 times and 1000 times magnification, respectively.
It can be seen from comparison with FIGS. 3 and 4 that the schwertmannite is deposited so as to fill the inside of the pores.

  FIG. 7 is a powder X-ray diffraction pattern obtained by measuring the Schwertmannite synthesized in Comparative Example 1. It is a typical Schwertmannite diffraction pattern.

  Table 5 summarizes the test solutions used in the sorption test. A potassium salt was used only in the case of dichromate ion, and a sodium salt was dissolved in pure water to prepare a test solution. Test liquids A and B were used in the sorption tests of all Examples and Comparative Examples. Further, the test liquid A was used to compare the deterioration after being left in a moist heat environment. The test liquids C, D, E, and F were used for the sorption test using Example 2 and Comparative Example 1.

Evaluation method 1 g of each of the sorbents of forced deterioration Examples 1 to 3 and Comparative Example 1 was weighed into a wide-mouthed plastic bottle having a capacity of 50 ml, and a constant temperature and constant humidity set to 50 ° C. and 98% relative humidity without a lid. It was left in the container for 2 weeks. The sample taken out from the thermo-hygrostat was vacuum dried at 50 ° C. overnight, and evaluated by a harmful anion sorption test described later to examine the degree of deterioration.

Sorption Test For the test liquids A and B shown in Table 1, each sorbent material sample was placed in a 100 ml polypropylene bottle and 0.25 g in the case of Example 1 and Comparative Example 2, Examples 2 and 3 and Comparative Example 3 In the case of 4, 0.5 g was weighed, 50 ml of the test solution was added, and the container was tightly stoppered. In the case of Comparative Example 1 which is a powdered schwertmannite, 0.1 g of the test solution A and 0.05 g of the solution B were weighed, and 50 ml of the test solution was put therein and tightly stoppered.
Regarding the test liquids C to F shown in Table 1, 0.25 g of each sorbent sample was weighed in a 100 ml polypropylene bottle in the case of Example 1 and 0.5 g in the case of Examples 2 and 3, and A test solution (50 ml) was put therein and the container was tightly closed. In the case of Comparative Example 1 which is a powdered Schwertmannite, 0.05 g of each was weighed, 50 ml of the test liquid was put therein, and the container was sealed.
In addition, the amount of sorbent added to the test solution is such that the sorption amount of harmful substances is less than 80% of the total amount because the sorption capacity of each sorbent with different loading is measured. Because of this, the amount of sample collected is changed.
These plastic bottles were set on a shaker equipped with a water bath and shaken at 40 ° C. for 24 hours. After the shaking was completed, the sorbent and the test solution were separated by filtration with a hydrophilic membrane filter having a pore size of 0.45 μm, and the concentration of harmful substances in the filtrate was measured by ICP-AES (iCAP7600 manufactured by Thermo Fisher Scientific Co.). . Fluorine was measured by ion chromatography (column; IonPac ™ AS12A (φ4 mm × 200 mm, manufactured by DIONEX). The entire sorbent material including a porous body using the toxic substance sorption amount (mmol / g) of each sample as a carrier. And for supported Schwertmannite were calculated respectively.

Claims (7)

A method for producing an anion sorbent in which schwertmannite is supported on a porous body, comprising at least the following two steps.
First step: a step of impregnating a porous body with a solution of an iron salt.
Second step: a step of synthesizing schwertmannite using the impregnated iron salt as a raw material inside and on the pores of the porous body.   In the second step, the iron salt-impregnated porous body obtained in the first step was added to a solution containing sulfate ions and having a pH of 2.5 to 4.5, and then the pH was adjusted to 2. The method for producing an anion sorbent according to claim 1, wherein the pH is appropriately adjusted so as to maintain a value between 5 and 4.5.   In the first step, after impregnating the porous body with the iron salt, the porous body is dried to solidify the iron salt or increase the concentration to suppress fluidity, and then the second step is performed. The method for producing the anion sorbent material according to claim 1 or 2.   The substance constituting the porous body is an inorganic substance such as rock, ceramic, or glass, and it is not due to the entanglement of inorganic fibers, but the substance forming the porous body and the internal pores are continuously connected. The method for producing an anion sorbent according to any one of claims 1 to 3, which is characterized in that.   The method for producing an anion sorbent according to any one of claims 1 to 4, wherein the pore diameters of the pores that are continuously connected inside the porous body are 0.1 to 10 µm.   An anionic toxic substance, characterized in that the anionic sorbent produced by the production method according to any one of claims 1 to 5 is brought into contact with a liquid or solid containing an anionic toxic substance. Method of adsorption removal or insolubilization.   The method for adsorbing, removing or insolubilizing an anionic harmful substance according to claim 6, wherein the anionic harmful substance is an anionic harmful substance containing any element of arsenic, selenium, fluorine, chromium and iodine.

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