JP7256493B2 - Method for producing adsorbent containing fine hydrotalcite - Google Patents

Description

The present invention is an adsorbent containing fine hydrotalcite for adsorbing and removing anionic harmful substances such as arsenic, selenium, fluorine, boron, hexavalent chromium, cyanide and phosphoric acid, and halogen substances such as chlorine and bromine. related to the manufacturing method of

In Japan, the Soil Contamination Countermeasures Law was enacted in 2003, and since then, more than 10,000 soil contamination surveys have been carried out annually. In most cases, soil contamination discovered by surveys has been removed by excavation in order to remove the contamination in a short period of time. According to statistics, more than 90% of the contaminated soil is removed from the site by excavation and removal, and about half of it is processed at cement plants. In 2010, the Soil Contamination Countermeasures Law was amended to include a policy of restraint on excavation and removal measures from the viewpoint of environmental risk reduction and economic rationality.

Along with this revision of the law, the need for in-situ treatment of contaminated soil is increasing. Recently, large-scale soil excavation work has been carried out due to large-scale railway construction and highway network development in the Tokyo metropolitan area for the Olympic Games. . Among the harmful substances contained in contaminated soil and groundwater, it is difficult to efficiently treat fluorine, boron, selenium, etc., which exist as anions in the environment. There is a demand for the development of highly economical adsorbent products that have high adsorption performance for these harmful substances.

Since the 1980s, the Asian region has experienced economic expansion due to an increase in industrial production. Until now, sufficient measures have not been taken to control the emission of hazardous substances, and as a result, soil and groundwater pollution has become a serious problem. . For example, in countries such as China, there are many cases in which the content of harmful substances is high in concentrations of several grams per kilogram of soil, causing soil pollution. Under these circumstances, there is a need in the Asian region for adsorbents that can efficiently treat high-concentration hazardous substances.

Next, in Japan's Water Pollution Control Law, in 2001, uniform effluent standards for boron and its compounds of 10 mg/L or less and fluorine and its compounds of 8 mg/L or less were set as effluent standards for boron and fluorine. However, since an economical water treatment method for boron and fluorine has not yet been established, in actual operation, provisional wastewater standards will be set for industries with technical problems, and regulations will be relaxed. was Partial revisions have been made since then, but some industries still operate according to the provisional wastewater standards.

As described above, establishing a technique for efficiently treating harmful anionic elements such as boron and fluorine is of great social significance. In addition, in Asian regions such as China and Thailand, wastewater regulations are gradually being strengthened, and the demand for water treatment technology for harmful anionic elements such as boron and fluorine is increasing, as is the case in Japan. is.

Hydrotalcite is known to be a layered anion exchanger represented by the structural formula Mg ²⁺ _1-x Al ³⁺ _X (OH) ₂ (A ⁿ⁻ ) _X/n ·zH ₂ O. Since then, research into its use as an adsorbent has been carried out. However, hydrotalcite is not generally used as a soil treatment agent or water treatment agent because of its high production cost and poor treatment performance.

Under such circumstances, in recent years, various research and development efforts have been made to improve the adsorption performance of hydrotalcite. Patent Documents 1 to 3 are cited as prior arts relating to nano-sized hydrotalcite adsorbents with high adsorption performance and production methods thereof. In Patent Document 1, it is synthesized by mixing an acidic solution and an alkaline solution containing aluminum ions and magnesium ions, removing or neutralizing water without aging, and characterized by a crystallite size of 20 nm or less. A hydrotalcite-like substance is shown. Patent Document 2 describes a crystalline layered double hydroxide powder containing no carbonic acid and having a crystallite size of 20 nm or less. It is shown to be produced by a process of mixing an acidic solution containing metal cations and an alkaline solution containing alkali at once to generate a precipitate, followed by drying and pulverizing immediately. In addition, Patent Document 3 discloses a layered double hydroxide characterized by having high ion exchange capacity, hardly causing carbonic acid contamination, capable of maintaining anion adsorption capacity for a long period of time, and having excellent stability. is shown, which is an acidic solution in which divalent metal cations (M ²⁺ ) and trivalent metal cations (M ³⁺ ) as well as n-valent anions are present and alkali metal elements (A ⁺ ) are present and an alkaline aqueous solution, adjusted to a molar ratio of A ⁺ /M ²⁺ in the range of 2.5 to 3.0 so that the reaction system always has a pH of 8 or less, and mixed at once. ing.

These prior art hydrotalcites are characterized by having excellent adsorption performance because they are composed of nano-sized crystallites and have a large surface area. However, in these production methods, in order to obtain nano-sized crystallites, facilities such as freeze-drying, freeze-vacuum drying, etc. are required to immediately mix the acid solution and the alkali solution and immediately dry the precipitate of hydrotalcite. As a result, manufacturing costs are high. In addition, in these production methods, a sodium salt corresponding to several times the mass of hydrotalcite is produced at the same time during hydrotalcite synthesis, and the production cost is high due to the separation/removal, drying, and waste liquid treatment. Furthermore, there is a problem that the residual sodium salt lowers the adsorption performance of the synthesized hydrotalcite.

Patent Document 4 describes a method for producing an adsorbent using magnesium oxide and a soluble aluminum salt as raw materials. Also, an adsorbent obtained by repeatedly reacting magnesium oxide and an aluminum salt in an aqueous solution over a long period of time is disclosed, in which magnesium oxide particles are coated with hydrocite. In the production method of Patent Document 4, since the adsorbent is produced by stirring the aqueous solution for a long time for the purpose of improving the yield of the adsorbent, the synthesized hydrotalcite crystallites are large and fine. It is not possible to obtain an adsorbent containing such hydrotalcite. Furthermore, in this production method, there is a problem that a large amount of energy is required for solid-liquid separation, drying, water treatment, etc. in the process of synthesizing the adsorbent.

Patent Document 5 describes a method for producing fine hydrotalcite particles, in which a mixed aqueous solution of magnesium salt and aluminum salt, an alkaline substance and an interlayer anion are reacted in a thin-film microreactor having a reaction field clearance of 1 to 30 μm. It is shown.

Thus, until now, various technical improvements have been made and research has been conducted on methods for producing hydrotalcite having fine crystallites. However, in these techniques, since raw materials containing a large amount of chloride and nitric acid are dissolved in an aqueous solution for synthesis, a sodium salt several times the mass of hydrotalcite is produced at the same time, and this by-product is washed and separated. There is a problem that a large amount of energy is required for waste liquid treatment, drying, etc., and production becomes extremely difficult.

As a method for separating and removing the sodium salt, which is a by-product generated during the synthesis of hydrotalcite, dehydration by a filter press is first considered. However, filter press dehydration usually leaves about 40-50% of the sodium salt, which is difficult to remove sufficiently.

As a method for reliably removing sodium salts, there is a method of repeating washing several times with water of 3 to 5 times the mass of hydrotalcite. Although this method enables reliable removal of sodium salts, it takes several days to one week to produce several tons of dry hydrotalcite, for example.

As described above, in the prior art, it is difficult to efficiently produce hydrotalcite due to processes such as solid-liquid separation, drying, removal of by-products, and waste liquid treatment, resulting in high production costs and high product quality. It takes a long time to manufacture. In addition, there is a problem that residual sodium salt generated during production clogs the pores of hydrotalcite, and competition between residual chloride ions and nitrate ions lowers the adsorption performance. Performance degradation due to residual ions has a particularly large effect on the treatment of harmful substances such as selenium and boron, which have low adsorption selectivity.

International publication WO2005/087664 pamphlet JP 2005-306667 A JP 2006-334456 A JP 2012-106227 A International publication WO2013/147285 pamphlet

The problem to be solved by the present invention is to provide a method for producing an adsorbent containing hydrotalcite having excellent adsorption performance for anionic harmful elements. Another object of the present invention is to provide an economical and high-performance adsorbent that can be suitably used for environmental purification of harmful elements such as fluorine, boron, and selenium, which are difficult to treat by conventional techniques.

The inventor of the present invention uses magnesium oxide and aluminum chloride as raw materials, and when the sum of the masses of the solid content excluding the water of crystallization in the raw materials is 1, the sum of the masses of the water and the water of crystallization in the raw materials is 1. The present inventors found that an adsorbent containing fine hydrotalcite and having excellent adsorption performance can be obtained by curing after adding and mixing water adjusted as follows.

In the method for producing an adsorbent containing fine hydrotalcite according to the present invention, magnesium oxide and aluminum chloride are used as raw materials. and water adjusted so that the sum of the mass of water of crystallization in the raw material is 1 or less, and mixing to obtain a mixture; and curing the mixture obtained in this mixing step to obtain an adsorbent. It is characterized by comprising steps.

Also, in the mixing step, the molar ratio of magnesium and aluminum in the raw materials is in the range of 3:1 to 13:1.

In the mixing step, at least one of slaked lime, clinoptilolite, mordenite, A-type zeolite, X-type zeolite, iron powder, and magnetite powder is further mixed.

The adsorbent obtained after the curing step is washed with water, dried and pulverized.

The adsorbent containing fine hydrotalcite and magnesium oxide of the present invention is characterized by being produced by the method for producing an adsorbent containing fine hydrotalcite according to the present invention.

INDUSTRIAL APPLICABILITY According to the present invention, an adsorbent containing fine hydrotalcite and having excellent adsorption performance can be efficiently produced. The adsorbent of the present invention is suitably used as a waste liquid, wastewater, groundwater, water treatment for water purification, contaminated soil, incineration ash, an adsorbent for treating waste, etc., and an additive for plastics for removing halogen substances. can be used.

1 is an X-ray diffraction pattern of an adsorbent containing fine hydrotalcite according to one embodiment of the present invention; FIG.

The general formula of hydrotalcite is Mg ²⁺ _1−x Al ³⁺ _x (OH) ₂ (A ⁿ⁻ ) _X/n ·zH ₂ O. Here, A ⁿ⁻ _X/n represents an interlayer anion. Under the synthesis conditions of hydrotalcite, the molar ratio of magnesium to aluminum is generally in the range of 2:1 to 5:1, and by adopting these composition conditions, a high yield can be obtained. . Hydrotalcite is a hydroxide, and when a mixed salt solution of magnesium ions and aluminum ions is mixed with an alkaline solution, it immediately forms as a precipitate. As a method for producing hydrotalcite, a method of neutralizing an aqueous solution in which magnesium ions and aluminum ions are dissolved to synthesize hydrotalcite is usually employed, taking advantage of this property.

The adsorption containing fine hydrotalcite of the present invention and the method for producing the same will be described in detail below.

In the method for producing an adsorbent containing fine hydrotalcite according to the present invention, magnesium oxide and aluminum chloride are used as raw materials. and water adjusted so that the sum of the mass of water of crystallization in the raw material is 1 or less, and mixing to obtain a mixture; and curing the mixture obtained in this mixing step to obtain an adsorbent. It is characterized by comprising steps. Hereinafter, in this specification, the ratio of the sum of the mass of the solid content excluding the water of crystallization in the raw material and the sum of the mass of water and the sum of the mass of the water of crystallization in the raw material is referred to as the solid-liquid ratio (mass ratio ). Therefore, when aluminum chloride hexahydrate containing water of crystallization is used as aluminum chloride, the amount of water to be added is adjusted in consideration of the mass of water of crystallization contained in aluminum chloride hexahydrate. .

Further, in the present invention, preferably, in the mixing step, the molar ratio of magnesium and aluminum in the raw materials is adjusted to be in the range of 3:1 to 13:1. The obtained adsorbent has a composite composition containing fine hydrotalcite, magnesium oxide, etc., but since it contains fine hydrotalcite with an average crystallite size of 10 nm or less and has a large surface area, it is harmful to anions. It has excellent adsorption performance of substances.

In the method for producing an adsorbent containing fine hydrotalcite according to the present invention, the amount of water to be mixed is set at a solid-liquid ratio (mass ratio) of 1:1 or less. These conditions are characterized by ten to several dozen times higher solid content than the general hydrotalcite synthesis method in which magnesium and aluminum are dissolved in an aqueous solution. Due to such characteristics, in the production of the adsorbent of the present invention, the mixture after curing becomes powdery, which is greatly different from the conventional method of synthesizing hydrocite in a liquid phase. By adopting this new production method, in the present invention, an adsorbent with excellent performance can be produced economically by a simple method using a known mixing device such as a mixer for powders, a mixing granulation device, or the like. be able to.

In the production of the adsorbent containing fine hydrotalcite of the present invention, magnesium oxide and aluminum chloride are used as raw materials, and the molar ratio of magnesium and aluminum is adjusted to be in the range of 3:1 to 13:1. preferably. More preferably, the molar ratio of magnesium to aluminum is 3:1 to 9:1. This composition condition is a composition with a larger amount of magnesium component than general hydrotalcite synthesis conditions. This is because caustic soda, which requires careful handling, is not used, the pH is adjusted to a neutral to weakly alkaline range, and the amount of chloride ions remaining in the adsorbent is suppressed.

Magnesium oxide is used in the method for producing the adsorbent of the present invention. The magnesium oxide used here is preferably light burned magnesia obtained by burning magnesium carbonate at 700 to 900°C. In addition, it is preferable to use magnesium oxide having a particle size of 200 to 325 mesh or a finer particle size product.

Aluminum chloride hexahydrate is preferably used as the aluminum chloride used in the method for producing the adsorbent of the present invention. Powdered polyaluminum chloride can also be used as a raw material for the adsorbent of the present invention. Since polyaluminum chloride is inexpensive, the adsorbent of the present invention can be produced more economically by using it as a raw material. However, since polyaluminum chloride contains sulfate radicals to stabilize its basicity, its use tends to reduce the performance of the adsorbent.

It is also possible to replace a portion of the magnesium oxide with magnesium chloride hexahydrate or the like, but if this is used as a raw material, the amount of residual chloride increases and the performance of the adsorbent deteriorates, which is not preferable. It is also possible to add sodium hydroxide and slaked lime as raw materials to the production method of the present invention. need to be adjusted to some extent.

In the method for producing an adsorbent containing fine hydrotalcite of the present invention, as described above, by mixing magnesium oxide, aluminum chloride hexahydrate, and water with adjusted composition, heat generation accompanying hydrotalcite generation occurs, The mixed composition is heated to approximately 90° C. and fine hydrotalcite is synthesized. This production method is characterized in that the hydrotalcite is aggregated and heated to solidify the adsorbent. In the production of the adsorbent of the present invention, known mixing equipment such as mixers for powder processing, mixing granulation equipment, etc. can be used. Advantages such as being able to continuously manufacture by controlling the temperature of

The curing in the method for producing the adsorbent of the present invention does not require heating of the mixture because heat is generated during production. Since the heat generated by the synthesis reaction usually continues for about 20 to 30 hours, the mixture is taken out from the mixing apparatus, sealed and cured while keeping the mixture moist. Here, the curing time is suitable from several hours to 72 hours, and a short curing time is not preferable because a sufficient amount of hydrotalcite cannot be synthesized. Alternatively, after removing the mixture from the mixing apparatus, steam may be discharged for one to several hours, and then the mixture may be sealed and cured for several to 72 hours. Furthermore, in the production of the adsorbent of the present invention, the mixture can be hermetically sealed and heated and cured at a temperature of 200° C. or less for several hours to 72 hours.

As described later, the adsorbent produced by the production method of the present invention contains hydrotalcite and unreacted magnesium oxide as main components, and in addition, has a complex composition consisting of aluminum hydroxide and magnesium chloride. However, since it contains fine hydrotalcite with an average crystallite size of 10 nm or less, it has excellent adsorption performance for anionic harmful substances.

In the production of the adsorbent of the present invention, water is added to the above raw materials in an amount with a solid-liquid ratio (mass ratio) of 1:1 or less, and mixed under conditions where the solid content is higher than that in the conventional production method, to obtain hydrotalcite. Synthesize an adsorbent containing The amount of water used is preferably such that the solid-liquid ratio (mass ratio) is in the range of 1:0.2 to 1:0.8. More preferably, it ranges from 1:0.4 to 1:0.7. Even more preferably, it is in the range of 1:0.5 to 1:0.6. If the water content is too low, it will be difficult to evenly disperse the water in the mixture, and if the water content is too high, the mixture will become slurry, and after curing, the mixture will solidify as a whole, making handling difficult. Here, the solid-liquid ratio (mass ratio) is obtained by dividing the total mass of magnesium oxide and aluminum chloride excluding the water of crystallization by the total mass of the water of crystallization and water to be added. The added water is consumed in the synthesis of hydrotalcite, and part of it is vaporized as steam due to the heat generated by the chemical reaction. By adding an appropriate amount of water according to the raw material composition, powder with a dry surface can be obtained after curing, and it is possible to use it as an adsorbent without drying. The adsorbent of the present invention has the property of being solidified by aggregation of hydrotalcite and heat generation during synthesis. The solidified composition can be pulverized using a known pulverizer or pulverizer before use. If a large amount of water is added during production, the mixture may solidify to a large extent and water may remain on the surface. Even in such a case, it can be used as an adsorbent after being dried and pulverized. In the method for producing an adsorbent of the present invention, it is possible to suitably produce a granular adsorbent by using a granulator such as a mixing granulator.

Next, in the method for producing an adsorbent of the present invention, various additives can be homogeneously mixed inside the adsorbent in the mixing step. By mixing a porous material such as perlite, zeolite, pumice stone, pulverized foam glass, etc. as an additive, it is possible to improve the porosity of the produced adsorbent. Moreover, by adding natural zeolites such as clinoptilolite and mordenite, and synthetic zeolites such as A-type zeolite and X-type zeolite, the ability to adsorb cations can be added. By adding slaked lime, the pH of the adsorbent can be adjusted to the alkaline side.

Furthermore, if magnetic powder such as iron powder or magnetite is mixed, magnetism is imparted to the adsorbent, and magnetic separation can be performed. As a result, it becomes possible to adsorb, concentrate, and separate and remove harmful substances from contaminated soil, wastewater, and the like. The mixing ratio of the iron powder and the magnetite powder is preferably 10 to 80% by mass, more preferably 20 to 60% by mass, of the total mass of the powder raw materials including water of crystallization. If the mixed amount of the iron powder or magnetite powder is too small, the magnetic separation becomes difficult, and if the mixed amount of the iron powder or magnetite powder is too large, the ability to adsorb anion-type harmful substances decreases.

Fine iron powder is difficult to handle because it reacts exothermically with oxygen in the air. By using it mixed with magnetite, it is possible to improve safety during production.

When additives such as slaked lime, clinoptilolite, mordenite, A-type zeolite, X-type zeolite, iron powder, and magnetite powder are further mixed, the amount of water added in the mixing process is adjusted according to the amount of these additives. do not have to. That is, in the mixing step, according to the definition of the solid-liquid ratio described above, the amount of water calculated by focusing only on the masses of magnesium oxide and aluminum chloride may be added.

As described above, the adsorbent containing fine hydrotalcite of the present invention can be synthesized by a simple process of adding a small amount of water to raw material powder, mixing, and curing. , it can be produced with extremely low energy compared to the production method of hydrotalcite in which aluminum is dissolved in an aqueous solution. In addition, according to the production method of the present invention, basically, it is possible to produce an adsorbent efficiently because it is not necessary to perform separation/removal treatment of sodium salts generated during synthesis and waste liquid treatment.

Furthermore, in order to improve the adsorption performance of the adsorbent containing fine hydrotalcite of the present invention, the adsorbent obtained by the above production method is washed with water to remove residual chloride ions, dried, and dried. Grinding may be performed. For example, in the treatment of selenic acid and boron, which have low adsorption selectivity, such a method of removing chloride ions, which are inhibitors, and modifying them is effective. The adsorbent produced according to the present invention has the advantage that solid-liquid separation and dehydration after washing are facilitated, because hydrotalcite aggregates and solidifies through a chemical reaction accompanied by heat generation. In addition, the adsorbent containing fine hydrotalcite of the present invention has the characteristic that it can be mixed with iron powder, zeolite, etc. to produce a granular composite adsorbent by utilizing the property of being solidified during production.

The adsorbent containing fine hydrotalcite of the present invention contains hydrotalcite with an average crystallite size of 10 nm or less and has excellent adsorption performance, so it is suitable for arsenic, selenium, fluorine, boron, hexavalent chromium, It can be used to remove various harmful substances in anionic form, such as cyanide, phosphoric acid, and silicic acid. Fields of application include water treatment of waste liquids, wastewater, groundwater, purified water, elution prevention treatment of polluted soil, incineration ash, wastes, and the like. In addition, the adsorbent of the present invention processed into granules can be suitably used as a water treatment agent for use in column treatment.

The particle size of the adsorbent of the present invention can be adjusted to a size of 0.1 to several mm and used by filling it in a cloth mat, bag, or the like. In this way, by processing the product in combination with the cloth, it is possible to control the flow rate of the water flow passing through the adsorbent, and to prevent the adsorbent from being washed away by the running water. Such products can be used as adsorbents for treating contaminated soil and as adsorbents for purifying ground water.

Furthermore, the adsorbent containing fine hydrotalcite of the present invention has excellent adsorption performance and is used as an additive for plastics for removing halogen substances such as chlorine and bromine generated from resins due to heating and deterioration. is also possible.

An adsorbent containing fine hydrotalcite of the present invention was experimentally produced by the following method.

(1) A total of 700 g of powdery raw materials of magnesium oxide and aluminum chloride hexahydrate were placed in a desktop Hobart type mixer and mixed for 3 minutes, after which a predetermined amount of deionized water was added and mixed for 4 minutes. Here, raw materials were blended and adjusted so that the molar ratio of magnesium and aluminum was Mg/Al=8.6, and ion-exchanged water was added under the conditions of a solid-liquid ratio of 1.0:0.64.

(2) When the temperature after mixing was measured, it was 68°C. After left for 1 hour, the mixture in the mixer was transferred to a resin container, and the top was covered with a lid to seal the container.

(3) The mixture was allowed to stand as described above for 24 hours for curing. The temperature of the mixture after curing was room temperature of 20°C.

(4) 100 g of the mixture was weighed and pulverized in a mortar so that the particle size was 1 mm or less.

Here, in the above trial, magnesium oxide (produced in China, purity 90%, particle size -325 mesh) and aluminum chloride hexahydrate (manufactured by Nippon Light Metal Co., Ltd., purity 97% or higher) were used as raw materials for magnesium and aluminum. bottom.

Using RINT ULTIMA3 manufactured by Rigaku Corporation, the trial adsorbent was analyzed by X-ray diffraction. This X-ray diffraction diagram is shown in FIG.

From FIG. 1, it can be seen that the adsorbent of the present invention is composed mainly of hydrotalcite and magnesium oxide and also contains a small amount of aluminum hydroxide and magnesium chloride. As shown in FIG. 1, the synthesized hydrotalcite exhibits a broad peak shape. When the crystallite size was determined by Scherrer's method, the crystallite size was 20 nm or less, and the average crystallite size was 8 nm. 0.6 nm. As described above, it was confirmed that an adsorbent composition containing fine hydrotalcite was synthesized by the production method of the present invention.

In the same procedure as in Example 1, the adsorbent containing the fine hydrotalcite of the present invention was prepared under the conditions of a molar ratio of magnesium and aluminum of Mg/Al=5.7 and a solid-liquid ratio of 1.0:0.55. I made a prototype. Formation of hydrotalcite with a crystallite size similar to that of Example 1 was confirmed by X-ray diffraction of the trial adsorbent.

100 g of the adsorbent prepared as a trial in Example 2 was put into a beaker, 300 g of purified water was added, and after stirring with a jar tester for 10 minutes, filtration and dehydration were performed with an aspirator, and dehydration was good. The adsorbent after dehydration was dried at 120° C. in an electric furnace and lightly pulverized in a mortar to a particle size of 1 mm or less.

An adsorbent containing fine hydrotalcite of the present invention was experimentally produced in the same manner as in Example 1 using magnesium oxide and powdered polyaluminum chloride as raw materials.

(1) A total of 500 g of powdered raw materials of magnesium oxide and powdered polyaluminum chloride was put into a desktop Hobart type mixer and mixed for 3 minutes, then a predetermined amount of deionized water was added and mixed for 4 minutes. Here, raw materials were blended and adjusted so that the molar ratio of magnesium and aluminum was Mg/Al=3.8, and ion-exchanged water was added under the conditions of a solid-liquid ratio of 1.0:0.40.

(2) The mixture was allowed to stand as described above for 24 hours for curing.

(3) 10 g of the mixture was weighed and pulverized in a mortar so as to have a particle size of 1 mm or less.

Here, in the above trial, magnesium oxide (made in China, purity 90%, particle size -325 mesh) and powdered polyaluminum chloride (manufactured by Taimei Chemical Industry Co., Ltd., Al ₂ O ₃ 30%) were used as raw materials for magnesium and aluminum. It was used.

Comparative example 1

In Comparative Example 1, a trial production was performed with a composition that yields hydrotalcite with high purity by a conventional synthesis method. Hydrotalcite was synthesized in an aqueous solution having a solid-liquid ratio of 1:5 and a molar ratio of magnesium to aluminum of Mg/Al=2.0 by the following procedure. After drying the hydrotalcite, it was washed repeatedly with purified water to remove the sodium salt.

(1) Magnesium chloride hexahydrate and aluminum chloride hexahydrate were added to purified water to prepare 120 g of an acidic aqueous solution containing magnesium concentration of 0.88 mol/L and aluminum concentration of 0.43 mol/L.

(2) While vigorously stirring the acid solution with a jar tester, 20.5 g of a 48% sodium hydroxide solution was added by titration to adjust the pH to 8.1, followed by stirring for 1 hour.

(3) All the mixed slurries were placed in an electric furnace and boiled and dried at 130°C.

(4) Purified water was added in an amount four times the weight of the dry powder, stirred for 1 hour, and then allowed to stand for 1 hour.

(5) The supernatant liquid after flocculation and separation was removed using a tube pump.

(6) The above operations (4) to (5) were repeated two more times.

(7) The slurry from which the supernatant was removed was dried by boiling at 120°C in an electric furnace.

(8) The dry powder was pulverized in a mortar to a particle size of 1 mm or less.

Magnesium chloride hexahydrate (reagent manufactured by Nacalai Tesque Co., Ltd., purity 97%) and aluminum chloride hexahydrate (manufactured by Nippon Light Metal Co., Ltd., purity 97% or more) were used. A 48% sodium hydroxide solution was prepared by diluting a sodium hydroxide reagent (manufactured by Nacalai Tesque, Inc., purity 97%).

Comparative example 2

In Comparative Example 2, hydrotalcite was synthesized in an aluminum-dissolved aqueous solution using magnesium oxide and aluminum chloride hexahydrate according to a conventional synthesis method. In this comparative example, the molar ratio of magnesium and aluminum was set to Mg/Al=8.6, which is the same as in Example 1, and the solid-liquid ratio was set to 1:10.

(1) Aluminum chloride hexahydrate was added to 241 g of purified water to adjust the aluminum concentration to 0.23 mol/L, and was completely dissolved by stirring using a jar tester.

(2) Magnesium oxide was added to the above aqueous solution under the condition of the molar ratio Mg/Al=8.6, and the mixture was stirred for 4 hours with a jar tester to synthesize hydrotalcite.

(3) All mixed liquids were dehydrated with an aspirator. The dehydration property of the mixture containing the synthesized hydrotalcite was poor, and it took 1 hour.

(4) Dried at 120° C. in an electric furnace and pulverized in a mortar to a particle size of 1 mm or less.

Here, magnesium oxide and aluminum chloride hexahydrate are magnesium oxide (made in China, purity 90%, particle size -325 mesh) and aluminum chloride hexahydrate (manufactured by Nippon Light Metal Co., Ltd., purity 97% or higher). bottom.

When the synthesized hydrotalcite was analyzed by X-ray diffraction, formation of hydrotalcite, magnesium oxide, etc. was confirmed. From the peak shape of hydrotalcite, the average crystallite size was larger than 20 nm.

Adsorption tests for arsenic acid and selenic acid were carried out using the adsorbents prepared as prototypes in Example 1 and Comparative Example 1 according to the following procedure.

(1) Using an arsenic acid solution reagent, a test solution was prepared with a target As(V) concentration of 1 mg/L.

(2) Using a sodium selenate reagent, a test solution was prepared with a target Se(VI) concentration of 1 mg/L.

(3) 250 ml of the two types of test solutions are dispensed into resin bottles, and the adsorbent of Example 1 is added thereto at a solid-liquid ratio (mass ratio) of 1:1000, and shaken for 24 hours ( horizontal shaking) adsorption test was performed.

(4) From each resin bottle, the supernatant liquid was filtered with a 0.45 μm syringe filter, and the concentration was measured using ICP-MS.

(5) Using the hydrotalcite of Comparative Example 1, a similar adsorption test was conducted.

Here, arsenic acid solution reagent (manufactured by Kanto Kagaku Co., Ltd., purity 60%) and sodium selenate reagent (manufactured by Nacalai Tesque Co., Ltd., purity 98%) were used.

Table 1 shows the adsorption test results using the two adsorbents. The adsorbent containing the fine hydrotalcite of the present invention was found to have excellent adsorption performance for arsenic and selenium, as well as the high-purity hydrotalcite synthesized by the prior art. In the adsorption test of Se(VI), which has low adsorption selectivity and is difficult to treat, the adsorbent of the present invention outperformed.

Fluorine water treatment tests were carried out using the adsorbents produced experimentally in Example 1 and Comparative Example 1 according to the following procedure.

(1) A sodium fluoride reagent was used to prepare a test solution having a fluorine concentration of 20 mg/L.

(2) 200 g of the test solution was placed in a beaker, 0.5% by mass of two kinds of adsorbents were added, and the mixture was stirred for 1 hour using a jar tester.

(3) After allowing to stand for 15 minutes, the supernatant was filtered through a 0.45 μm syringe filter to collect a test solution.

(4) Fluorine concentration was measured using a spectrophotometer.

Here, in this example, a sodium fluoride reagent (manufactured by Nacalai Tesque Co., Ltd., purity 98%) was used.

Table 2 shows the results of the water treatment test. For both adsorbents, the fluorine concentration after treatment was below the wastewater standard value. In addition, the water treatment effect was slightly better with the adsorbent of the present invention.

Adsorption tests of hexavalent chromium were carried out using the adsorbents produced experimentally in Examples 2 to 4 and Comparative Example 2 according to the following procedure.

(1) Using a sodium dichromate reagent, a test solution with a chromium concentration of 100 mg/L was prepared.

(2) 200 g of the test solution was placed in a resin bottle, 1 mass % of various adsorbents were added, and a shaking adsorption test was performed for 24 hours.

(3) After allowing to stand for 20 minutes, the supernatant was filtered through a 0.45 μm syringe filter to collect a test solution.

(4) Chromium concentration was measured using ICP-AES.

Here, in this example, sodium dichromate reagent (manufactured by Nacalai Tesque Co., Ltd., purity 97%) was used.

Table 3 shows the adsorption test results. In Example 3, the result was below the waste water standard value. The adsorbents of Examples 2 and 3, which were experimentally manufactured by the production method of the present invention, had higher adsorption performance for hexavalent chromium than the adsorbent containing hydrotalcite of Comparative Example 2, which was synthesized in an aqueous solution using the same raw materials as these. was an excellent result. In Example 3, the adsorbent prepared as a trial in Example 2 was washed with water and dried. This treatment removed the chloride ions contained in the adsorbent, improving the adsorption performance. I understand. Moreover, Example 4 using powdered polyaluminum chloride as a raw material also has adsorption performance exceeding that of Comparative Example 2.

Using the adsorbents prepared as prototypes in Example 2, Example 3, and Comparative Example 2, a boron adsorption treatment test was performed according to the following procedure.

(1) A test solution with a boron concentration of 50 mg/L was prepared using a boric acid reagent. Sodium hydroxide was added thereto to adjust the pH to 11.5.

(2) 200 g of the test solution was placed in a resin bottle, 1 mass % of various adsorbents were added, and a shaking adsorption test was performed for 24 hours.

(3) After standing for 20 minutes, the supernatant was filtered through a 0.45 μm syringe filter, and the boron concentration was measured using ICP-AES.

Here, in this example, a boric acid reagent (manufactured by Nacalai Tesque Co., Ltd., purity 99.5%) was used.

Table 4 shows the adsorption test results. The adsorbents of Examples 2 and 3, which were experimentally produced according to the present invention, have better boron adsorption performance than the hydrotalcite of Comparative Example 2 synthesized in an aqueous solution using the same raw materials. The processing result was below the standard value. In Example 3, the adsorbent prepared as a trial in Example 2 was washed with water and dried. It was confirmed that chloride ions were removed by this treatment, thereby improving adsorption performance.

An adsorbent containing the fine hydrotalcite of the present invention mixed with iron powder was prepared by the following method.

(1) A total of 630 g of powder raw materials of magnesium oxide and aluminum chloride hexahydrate and 70 g of iron powder were put into a tabletop Hobart type mixer and mixed for 3 minutes, then a predetermined amount of deionized water was added and mixed for 4 minutes. Here, raw materials were blended and adjusted so that the molar ratio of magnesium and aluminum was Mg/Al=8.6, and ion-exchanged water was added under the conditions of a solid-liquid ratio of 1.0:0.46.

(2) When the temperature after mixing was measured, it was 83°C. The mixture in the mixer was transferred to a resin container and sealed.

(3) The resin container was placed in an incubator and heated at a temperature of 80° C. for 24 hours.

(4) 100 g of the mixture was weighed and pulverized in a mortar to a particle size of 0.5 mm or less to obtain a granular adsorbent containing iron powder.

Here, in the trial production, the same raw materials as in Example 1 were used as the raw materials of magnesium oxide and aluminum chloride. As the iron powder, reduced iron powder E200 (average particle size 45 μm) manufactured by DOWA IP Creation Co., Ltd. was used.

An adsorbent containing fine hydrotalcite of the present invention mixed with magnetite powder was prepared by the following method.

(1) A total of 490 g of powder raw materials of magnesium oxide and aluminum chloride hexahydrate and 210 g of magnetite powder were put into a tabletop Hobart type mixer and mixed for 3 minutes, then a predetermined amount of deionized water was added and mixed for 4 minutes. Here, raw materials were blended and adjusted so that the molar ratio of magnesium and aluminum was Mg/Al=8.6, and ion-exchanged water was added under the conditions of a solid-liquid ratio of 1.0:0.46.

(2) When the temperature after mixing was measured, it was 83°C. The mixture in the mixer was transferred to a resin container, sealed, and cured at room temperature.

(3) 100 g of the mixture was weighed and pulverized in a mortar to a particle size of 0.5 mm or less to obtain a granular adsorbent containing magnetite.

Here, in the trial production, the same raw materials as in Example 1 were used as the raw materials of magnesium oxide and aluminum chloride. As the magnetite powder, ferrite powder (average particle size: 12 μm) manufactured by DOWA F-Tech Co., Ltd. was used.

Fluorine water treatment tests were conducted using the adsorbents prepared as samples in Examples 9 and 10 according to the following procedure.

(1) A sodium fluoride reagent was used to prepare a test solution having a fluorine concentration of 5 mg/L.

(2) Take 200 g of the test solution into a 500 mL plastic bottle, add 1.0% by mass of each of the two types of adsorbents, and shake with a shaker at 200 rpm for 1 hour. rice field.

(3) After allowing to stand for 15 minutes, the supernatant was filtered through a 0.45 μm syringe filter to collect a test solution.

(4) Fluorine concentration was measured using a spectrophotometer.

Here, in this example, the same sodium fluoride reagent as in Example 6 was used.

Table 5 shows the adsorption test results. It was confirmed that the adsorbents prepared by mixing the iron powder and the magnetite powder of Examples 9 and 10, which were experimentally produced according to the present invention, had high fluorine adsorption performance.

According to the following procedure, the recovery rate of the adsorbents prepared as samples in Examples 9 and 10 by magnetic separation was evaluated.

(1) Take 200 g of ion-exchanged water into a 500 mL plastic bottle, add 5.0% by mass of two kinds of adsorbents, and shake for 1 hour at 200 rpm with a shaker. rice field.

(2) After shaking, the test solution was transferred to a stainless steel vat, and a bar magnet with a surface magnetic force of 0.4 T was used to scan the upper surface of the test solution three times to collect magnetic substances.

(3) The collected magnetized substances were dried and weighed, and the recovery rate was obtained from the difference in the added mass in (1).

The results are shown in Table 6. It was confirmed that Examples 9 and 10, which were experimentally produced according to the present invention, had high magnetic separation recovery rates, and had both performance as an adsorbent and good characteristics as a magnetic material. Moreover, it was found that these trial adsorbents had sufficient strength characteristics without separating the adsorbent components from the iron powder and the magnetite powder.

Claims (4)

Magnesium oxide and aluminum chloride are used as raw materials, and when the sum of the masses of the solid content excluding the water of crystallization in the raw materials is 1, the sum of the masses of the water and the water of crystallization in the raw materials is 0.4-0. 64 is added and mixed to obtain a mixture; and a curing step for curing the mixture obtained in the mixing step to obtain an adsorbent. A method for producing an adsorbent containing talcite. 2. The method for producing an adsorbent containing fine hydrotalcite according to claim 1, wherein in said mixing step, the molar ratio of magnesium and aluminum in the raw materials is in the range of 3:1 to 13:1. 3. The method according to claim 1, wherein at least one of slaked lime, clinoptilolite, mordenite, A-type zeolite, X-type zeolite, iron powder, and magnetite powder is further mixed in the mixing step. A method for producing an adsorbent containing fine hydrotalcite. The method for producing an adsorbent containing fine hydrotalcite according to any one of claims 1 to 3, wherein the adsorbent obtained after the curing step is washed with water, dried and pulverized.

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