JP4439067B2 - Method for producing iron-based double hydroxide and water treatment material using the double hydroxide - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an iron-based double hydroxide having a pyroolite type structure. Furthermore, using this double hydroxide, such as alkali metals, alkaline earth metals, metals such as lead, zinc, aluminum, manganese and phosphorus contained in water during water treatment, or organic anions such as humic substances, etc. The present invention relates to a water treatment material that adsorbs substances harmful to human health and a method for producing the same.
[0002]
[Prior art]
Conventionally, solid adsorbents such as activated carbon, iron hydroxide, and ion exchange resins are known as this type of water treatment material. However, these adsorbents have low performance in removing metal dissolved in water in terms of capacity or speed, and are not suitable for removing metal at high speed with a high adsorption rate. In order to solve this problem, Al-based double hydroxide (eg, Mg ₆ Al ₂ (OH) ₁₆ (CO ₃ ) · 4H ₂ O) having a hydrotalcite structure is used as a water treatment material. Yes. This Al-based double hydroxide is made by a hydrothermal synthesis method. Specifically, carbonate such as sodium carbonate is added as a layer cross-linking anion to a mixed solution of magnesium salt aqueous solution and aluminum salt aqueous solution, and the pH is 9 to 12 at a high temperature of 60 to 150 ° C. for several hours. It is made by aging for tens of hours.
[0003]
[Problems to be solved by the invention]
However, this method for producing an Al-based double hydroxide has the inconvenience of adding a carbonate and aging for a long time for crystallization. Also, if this water treatment material is used for the treatment of human drinking water such as the treatment of tap water, this water treatment material contains Al, which is concerned about the causal relationship with Alzheimer's disease. There is a concern about using it.
[0004]
An object of the present invention is to provide a method for easily producing an iron-based double hydroxide without adding a carbonate.
Another object of the present invention is to provide a water treatment material using the above double hydroxide and a method for producing the same, which removes harmful substances contained in water, particularly harmful metals in extremely low concentration, at a high rate at a high rate. It is in.
Still another object of the present invention is to provide a water treatment material using the above-mentioned double hydroxide and a method for producing the same, which is free from concern for human health in drinking water treatment.
[0005]
[Means for Solving the Problems]
The invention according to claim 1 is an alkaline earth metal salt aqueous solution so that the molar ratio of Fe to M (M / Fe) is between 1 and 4, where M is an alkaline earth metal that is magnesium or calcium. The aqueous raw material solution obtained by mixing the aqueous raw material solution and the trivalent iron salt aqueous solution with vigorous stirring in the air or by adding ultrasonic waves to the aqueous raw material solution in the air until the pH is 13 or higher. Is crystallized through a gel state to produce a layered iron-based double hydroxide represented by the following formula (1) having a pyroaulite type structure.
[0006]
M ²⁺ _(8-x) Fe ³⁺ _x (OH) ₁₆ (CO ₃ ^2- ) _{x / 2} · mH ₂ O (1)
However, 0 <x ≦ 6 and 0 <m ≦ 5.
[0007]
In the invention according to claim 1, the raw material aqueous solution is vigorously stirred in the air, or the pH is set to 13 or more while applying ultrasonic waves in the air, so that the air is added without adding carbonate as in the prior art. Carbon dioxide is dissolved from the inside, and carbonate ions are taken in as layer cross-linking anions, and Mg ions and Fe ions are uniformly dispersed. This makes it possible to synthesize iron-based double hydroxides that are easily crystallized in a relatively short period of time without using the conventional hydrothermal synthesis method.
[0008]
The invention according to claim 2 is a layered composite having an average particle size of 1 to 250 μm obtained by pulverizing the layered double hydroxide according to claim 1 in a solution obtained by dissolving a hydrophobic polymer powder in a good solvent. After the hydroxide particles are dispersed, the solution in which the layered double hydroxide particles are dispersed is dried under atmospheric pressure while stirring, or the solution in which the layered double hydroxide particles are dispersed is stirred or not stirred. The method for producing a water treatment material in which a porous body composed of a hydrophobic polymer is produced by dropping it into a poor solvent for the hydrophobic polymer and lamellar double hydroxide particles are supported inside the porous body. .
In the invention according to claim 2, the double hydroxide particles according to claim 1 are dispersed in a solution of the hydrophobic polymer powder, and the solution is phase-converted to form a porous body made of the hydrophobic polymer. The layered double hydroxide particles can be supported inside the porous body.
[0009]
The invention according to claim 3 is a water treatment in which a layered double hydroxide particle represented by the formula (1) having a pyroaulite structure is supported in a porous body made of a hydrophobic polymer. It is a material.
In the invention according to claim 3, the layered double hydroxide having a pyroaulite type structure is a kind of clay mineral and has water swellability, and when particles are formed, there is cohesion between particles. . By supporting this double hydroxide in a porous body made of a hydrophobic polymer, the double hydroxide is filled in the column and treated with water, and the harmful substances are not increased without increasing the water resistance of the column. Can be adsorbed at high speed with a high adsorption rate.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described.
[a] Method for producing iron-based double hydroxide The iron-based double hydroxide of the present invention is a crystallized layered double hydroxide having a pyroaulite structure represented by the following formula (1). is there.
M ²⁺ _(8-x) Fe ³⁺ _x (OH) ₁₆ (CO ₃ ^2- ) _{x / 2} · mH ₂ O (1)
Here, M is magnesium or calcium among alkaline earth metals. Further, 0 <x ≦ 6 and 0 <m ≦ 5. When x is set to 0, the harmful substance removal performance decreases, and when x exceeds 6, the layered double hydroxide is not formed. Moreover, it is very difficult to prepare a layered double hydroxide in which m is 0, and if it exceeds 5, the water treatment material itself becomes wet and becomes difficult to handle when used as a water treatment material. Preferably, 1.6 ≦ x ≦ 4 and 0 <m ≦ 3. As an example of this layered double hydroxide, Mg ²⁺ ₄ Fe ³⁺ ₄ (OH) ₁₆ (CO ₃ ^2- ) ₂ .3H ₂ O, Ca ²⁺ ₄ Fe ³⁺ ₄ (OH) ₁₆ (CO ₃ ^{2-) ₂} · 3H ₂ O, and the like.
[0011]
This iron-based double hydroxide is synthesized by the following method.
As shown in FIG. 1A, first, an aqueous solution of an alkaline earth metal salt of Mg or Ca, such as MgCl ₂ , Mg (NO ₃ ) ₂ , CaCl ₂ , Ca (NO ₃ ) ₂ , FeCl ₃ , Fe A raw material aqueous solution is prepared by mixing with an aqueous solution of a trivalent iron salt such as (NO ₃ ) ₃ and put into the container 10. At this time, when magnesium or calcium is represented by M, both aqueous solutions are vigorously stirred and mixed with the stirrer 11 in the air so that the molar ratio of Fe to M (M / Fe) is between 1 and 4. The concentration range of each aqueous solution is set to 0.01 to 0.5 mol / l. If M / Fe is less than 1, it is difficult to synthesize a crystallized double hydroxide. If M / Fe exceeds 4, the metal adsorption performance decreases. Preferably it is between 1 and 3. Next, as shown in FIG. 1 (b) or (c), the raw material aqueous solution is vigorously stirred with a stirrer 11 in air at room temperature, or the raw material aqueous solution is mixed with the ultrasonic generator 12 in air at room temperature. While adding ultrasonic waves, the alkaline aqueous solution is gradually added until the pH is 13 or more. The addition amount is about 2 to 10 ml / min, and it is preferable to add in a dropwise state. Here, “strongly stirring” means strong stirring that stirs at a rotational speed of 500 to 1000 rpm, for example. By adding the alkaline aqueous solution, the raw material aqueous solution is gelled. By vigorously stirring or applying ultrasonic waves, carbon dioxide in the air dissolves in the liquid, and this carbonate ion is taken in as a layer cross-linking anion, and Mg ions and Fe ions are uniformly dispersed. It crystallizes through a gel state. By setting the pH to 13 or more, polymerization, that is, crystallization is further promoted at room temperature. The alkaline aqueous solution to be added is an aqueous solution of an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide or lithium hydroxide having a concentration of 1 to 10% by weight.
[0012]
In the case of crystallization only by stirring, the stirring time is preferably 1 hour or longer, and more preferably 6 hours or longer. The longer the stirring time, the more crystallization is promoted. When applying ultrasonic waves, the applied output is preferably 50 to 300 W, and the applied time is preferably about 10 to 60 minutes. When the applied output is increased, crystallization is promoted in a shorter time. Crystallization is promoted by applying ultrasonic waves rather than by vigorous stirring.
[0013]
Next, as shown in FIG. 1D, the crystallized crystallized by strong stirring or ultrasonic waves is separated from the aqueous solution. This solid-liquid separation is performed by a method such as filtration or centrifugation. The crystal separated from the aqueous solution is washed with distilled water and dried at a temperature of room temperature to 120 ° C., preferably about 120 ° C. under atmospheric pressure, to thereby form a layered double hydroxide represented by the above formula (1). Things are obtained.
[0014]
[b] Method for Producing Water Treatment Material Next, a method for producing a water treatment material from the layered double hydroxide will be described. The water treatment material of the present invention is harmful to human health such as alkali metals, alkaline earth metals, metals such as lead, zinc, aluminum, manganese, and phosphorus contained in water, or organic anions such as humic substances. It is an adsorbent that is suitable for mainly removing unnecessary substances. The layered double hydroxide having a pyroolite type structure is a kind of clay mineral and has water swellability. When the synthesized double hydroxide is filled into the adsorption column as it is and water containing harmful substances is passed through, the double hydroxide swells with water to form aggregates, increasing the water flow resistance of the column, and the adsorbent. Not suitable as.
First, particles having an average particle diameter of 1 to 250 μm, preferably several μm to several tens of μm, are prepared for the layered double hydroxide, which is a double hydroxide synthesized by the method [a]. Specifically, since the above-mentioned dried crystals are usually agglomerated, the layered double hydroxide particles within the above average particle diameter range having a uniform particle diameter using a sieve after pulverization with a pulverizer Prepare. When the average particle size exceeds 250 μm, the adsorption performance of harmful substances decreases, and when it is less than 1 μm, the layered double hydroxide particles can be easily formed from the porous material during the water treatment even if supported on the porous material of the hydrophobic polymer. There is a problem that falls off.
[0015]
As shown in FIG. 2 (a), a cellulose derivative such as cellulose acetate, and a hydrophobic polymer powder 13 such as carboxylic acid and chitosan are then added to and stirred in the hydrophobic polymer good solvent 14 such as acetone and acetonitrile. To dissolve and store in the container 15. The addition ratio of the hydrophobic polymer is preferably 5 to 80% by weight of the good solvent. If it is less than 5% by weight, it is difficult to immobilize the carrier, and if it exceeds 80% by weight, the adsorption performance may be lowered. As shown in FIG. 2 (b), the layered double hydroxide particles 17 having the above average particle diameter are added to the solution 16 in which the hydrophobic polymer is dissolved and mixed by stirring to uniformly disperse the double hydroxide particles. Let The addition ratio of the double hydroxide particles is preferably 5 to 30% by weight of the above solution. If it is less than 5% by weight, the adsorbing performance of harmful substances is lowered, and if it exceeds 30% by weight, there is a disadvantage that the water flow resistance increases.
Next, as shown in FIG. 2 (c) or (d), the solution 18 in which the layered double hydroxide particles are dispersed is dried under atmospheric pressure while stirring, or the solution in which the layered double hydroxide particles are dispersed. 18 is added dropwise to the poor solvent 19 of the hydrophobic polymer while stirring. At this time, the porous body 20 made of various hydrophobic polymers can be produced by adjusting the stirring speed and changing the kind of the poor solvent to realize phase change of the solution. Examples of the poor solvent for the hydrophobic polymer include hexane, ethanol, air, and the like. For example, when making a porous body using cellulose acetate, a porous body of spherical particles having an average particle diameter of about 2 mm is formed when dropped into hexane without stirring, and an average when dropping into hexane with stirring. A particulate porous body having a particle size of 500 μm or less is formed. Further, when ethanol is used as the poor solvent, a fibrous (loofer) porous body is formed. Further, when air is used as a poor solvent and is dropped onto a flat plate or the like in the air with stirring, a flat porous body is formed. Simultaneously with the formation of the porous body, the iron-based double hydroxide particles of the present invention are fixed and supported inside the porous body.
[0016]
Finally, as shown in FIG. 2 (e), the porous body is washed with distilled water and dried. If necessary, the water treatment material 20 of the present invention can be obtained by pulverizing into a porous body having a desired particle size. FIG. 3A shows an enlarged cross-sectional view of the water treatment material made of this porous body, and FIG. 3B shows a diagram schematically showing the water treatment material. By fixing the iron-based double hydroxide inside the porous body made of a hydrophobic polymer in the form of particles, the iron-based double hydroxide particles can be dispersed in the support of the porous body. This prevents aggregation of the double hydroxide particles due to swelling of the iron-based double hydroxide during water treatment, and the carrier is a hydrophobic porous body. The increase in water pressure can be reduced.
[0017]
[c] Method for Using Water Treatment Material As a method for using the water treatment material of the present invention, there are a batch (batch) method and a liquid flow method using a column as in the case of a conventional adsorbent. The batch method is a method in which water to be treated is stored in a predetermined container or tank, a water treatment material is put therein, and the water treatment material is sufficiently brought into contact with the water to be treated. After the treatment, the water treatment material and the water to be treated are separated into solid and liquid.
In the liquid flow method using a column, as shown in FIG. 4A, a water treatment material 20 made of a porous material is filled in a column 21 so as to have a predetermined height, and the water to be treated 22 is fed. Water is passed through the pump 23. As shown in FIG. 4B, the water treatment material 20 is preferably fixed by sandwiching the upper surface and the lower surface between the filter paper 24 and the mesh 25.
[0018]
[d] Mechanism of Adsorption of Hazardous Substances by Water Treatment Material The mechanism of adsorption of harmful substances by the crystallized layered iron-based double hydroxide having the pyroolite structure of the present invention will be described by taking lead removal as an example.
When the column is packed with the iron-based double hydroxide water treatment material of the present invention and an aqueous solution containing a low concentration of lead of less than 100 ppb, which cannot be removed even by pH adjustment, is passed through the column, High removal performance despite the short contact time between the treatment material and the aqueous lead solution. This is considered that lead (Pb) is removed on the outer surface of the adsorbent 20 as shown in FIG. That is, the pyroolite type compound has a hydroxyl group (OH) on the surface of the layered skeleton structure, and lead is exchanged by proton exchange (H ⁺ ) and lead ion (Pb ²⁺ ) of this hydroxyl group. It is considered to be removed. There are two types of adsorption modes, monodentate (O—Pb ⁺ ) and bidentate (O—Pb—O), as shown in FIG. 5, both of which are iron ions (Fe ³⁺ ). It is thought that it adsorbs in the vicinity of.
[0019]
FIG. 6 shows an example in which a solution in which high concentration lead of 100 ppb or more is dissolved is similarly passed through the column. Pyroaurite type compound has a function to dissolve a part of its skeletal structure (Mg ²⁺ , Fe ³⁺ ) in an aqueous lead solution and buffer the pH on the alkali side near 6-9 (fine dissolution of water treatment material) Function). At this time, hydroxides of iron and magnesium (Fe (OH) ₃ , Mg (OH) ₂ ) are generated in the aqueous solution. As the pH rises, lead forms hydroxide (Pb (OH) ₂ ) and is removed as a precipitate. At the same time, lead is also removed by the aggregating action of Mg (OH) ₂ and Fe (OH) ₃ produced in the aqueous solution. Aggregates are considered to be adsorbed on the surface hydroxyl groups of the pyroolite type compound. Since this aggregating action is slow, its contribution is considered to be small in the case of high-speed removal. For example, the concentration of lead contained in tap water is said to be several tens of ppb due to the use of a lead water pipe, but the present invention is also applicable to a case where lead that has accumulated in a water pipe due to a sudden accident flows out to a high concentration. The water treatment material functions effectively.
As described above, the water treatment material of the present invention is (1) a hardly soluble layered crystallized hydroxide having exchangeable protons (hydroxyl groups) that trap lead on the surface of the water treatment material, and (2) water treatment. An alkaline atmosphere is formed by slightly dissolving the material skeleton, and the effect of precipitation and aggregation of lead is expressed.
[0020]
【Example】
Next, examples of the present invention will be described together with comparative examples.
<Example 1>
0.0375 mol of MgCl ₂ and 0.0125 mol of FeCl ₃ were added and mixed in 100 ml of distilled water to prepare a raw material aqueous solution having a Mg / Fe molar ratio of 3. While this raw material aqueous solution was vigorously stirred at a rotational speed of 1000 rpm, a 10 wt% aqueous NaOH solution was added dropwise at a rate of 2 ml / min until the pH of the raw aqueous solution reached 13. The raw material aqueous solution was gelled by dropwise addition of NaOH aqueous solution. This gelled room temperature liquid was further stirred in air at the same rotational speed for 10 hours. After filtering this liquid with No. 1 filter paper, the solid content separated by filtration was washed with a large amount of distilled water and dried at 120 ° C. for 24 hours to obtain an iron-based double hydroxide.
[0021]
<Example 2>
A starting aqueous solution having a Mg / Fe molar ratio of 1 was prepared by adding and mixing 0.0125 mol of MgCl ₂ and 0.0125 mol of FeCl ₃ in 100 ml of distilled water. While this raw material aqueous solution was vigorously stirred at the same rotational speed as in Example 1, a 10 wt% NaOH aqueous solution was added dropwise at a rate of 2 ml / min until the pH of the raw aqueous solution reached 13. The raw material aqueous solution was gelled by dropwise addition of NaOH aqueous solution. Ultrasonic waves were applied to the gelled room temperature liquid in air at an output of 200 W for 30 minutes. The liquid to which the ultrasonic wave was applied was filtered with the same filter paper as in Example 1, and the solid content after filtration was washed and dried in the same manner as in Example 1 to obtain an iron-based double hydroxide.
[0022]
<Comparative Example 1>
While stirring the raw material aqueous solution having the same Mg / Fe molar ratio of 1 as in Example 2 at the same rotational speed as in Example 1, 10% by weight NaOH aqueous solution was adjusted to 2 ml / min until the pH of the aqueous raw material solution reached 10. It was dripped at a rate. In the same manner as in Example 2, ultrasonic waves were applied to the raw material aqueous solution gelled by this dropping for 30 minutes. The liquid to which the ultrasonic wave was applied was filtered with the same filter paper as in Example 1, and the solid content after filtration was washed and dried in the same manner as in Example 1 to obtain an iron-based double hydroxide.
<Comparative example 2>
An iron-based double hydroxide was obtained in the same manner as in Comparative Example 1 except that the molar ratio of Mg / Fe in the raw material aqueous solution was 3.
[0023]
<Example 3>
While stirring the raw material aqueous solution having the same Mg / Fe molar ratio of 3 as in Example 1 at the same rotational speed as in Example 1, 10% by weight NaOH aqueous solution was adjusted to 2 ml / min until the pH of the raw material aqueous solution reached 13. It was dripped at a rate. In the same manner as in Example 2, ultrasonic waves were applied to the raw material aqueous solution gelled by this dropping. The liquid to which the ultrasonic wave was applied was filtered with the same filter paper as in Example 1, and the solid content after filtration was washed and dried in the same manner as in Example 1 to obtain an iron-based double hydroxide.
<Example 4>
An iron-based double hydroxide was obtained in the same manner as in Example 3 except that the ultrasonic wave was applied for 60 minutes.
[0024]
<Comparison evaluation>
The production phases of the iron-based double hydroxides of Examples 1 to 4 and Comparative Examples 1 and 2 were examined by an X-ray diffraction method using copper Kα rays as a light source. The result is shown in FIG. The higher the peak value of the curve in FIG. 7, the higher the crystallinity. From the results of X-ray diffraction and elemental analysis, the formation phase of each iron-based double hydroxide is Mg ²⁺ ₆ Fe ³⁺ ₂ (OH) ₁₆ (CO ₃ ^2- ) · 3H ₂ O or Mg ²⁺ ₄ Fe ³⁺ _{It was 4} (OH) ₁₆ (CO ₃ ²⁻ ) ₂ · 3H ₂ O. Further, as apparent from FIG. 7, the crystallinity of Example 1 which was vigorously stirred for 10 hours was almost the same as that of Example 3 in which ultrasonic waves were applied for 5 minutes. The crystallinity of Example 4 where ultrasonic waves were applied for 60 minutes was the highest. On the other hand, the crystallinity of Comparative Examples 1 and 2 where the pH was 10 and ultrasonic waves were applied was low.
[0025]
<Example 5>
An iron-based double hydroxide was obtained in the same manner as in Example 2 except that the raw material aqueous solution was prepared with a Mg / Fe molar ratio of 2. The iron- based double hydroxide particles obtained by pulverizing the iron-based double hydroxide were added to a solution of 0.5 g of cellulose acetate in 10 ml of acetone and stirred for about 1 hour. Hydroxide particles were uniformly dispersed. This dispersion resulted in a highly viscous liquid. This solution was dropped into hexane with stirring. Cellulose acetate was phase-separated by dropping to form a particulate porous carrier having an average particle diameter of about 2 mm, and iron-based double hydroxide particles were fixed in a dispersed state therein. The porous body was washed with distilled water and then dried at 120 ° C. for 24 hours. The dried porous body was pulverized with a pulverizer so that the average particle size was 250 μm or less to obtain a water treatment material.
<Comparative Example 3>
A solution obtained by adding and mixing an aqueous NaOH solution to distilled water to adjust the pH to 10 was used as the water treatment material of Comparative Example 3.
[0026]
<Comparative example 4>
The activated carbon for water treatment made of irregular pulverized coal having an average particle size of 250 μm or less was used as the water treatment material of Comparative Example 4.
<Comparative Example 5>
The goethite (FeO (OH)), which is known as a high concentration lead adsorbent and made of an irregular reagent having an average particle size of 250 μm or less, was used as the water treatment material of Comparative Example 5.
<Comparative Example 6>
A spherical acrylic weak acid type cation exchange resin (IRA-76) having an average particle size of 0.3 to 0.6 mm was used as the water treatment material of Comparative Example 6.
[0027]
<Lead adsorption comparison test 1>
A lead adsorption test was conducted by a batch method. That is, lead nitrate was dissolved in distilled water to prepare a test solution having a lead concentration of 1 ppm. This test solution was put into five test tubes, and each water treatment material of Example 5 and Comparative Examples 3 to 6 was added to the test solution of each test tube at a ratio of 0.5% by weight. Was shaken for 24 hours. A test solution was sampled from each test tube every 30 minutes, 3 hours, and 24 hours with shaking, the dissolved concentration of lead was determined by flameless atomic absorption spectrometry, and the lead removal rate was calculated from the value. The result is shown in FIG.
As is apparent from FIG. 8, in the water treatment material of Comparative Example 3 (water adjusted to pH 10), the dissolved lead becomes lead hydroxide, which removes about 70% after 30 minutes, and about 80% after 3 hours and 24 hours. Although about 20% of lead remains. Further, the water treatment material of Comparative Example 4 (activated carbon for water treatment) can remove about 95% lead after 24 hours, but several percent of lead remains. The water treatment materials of Comparative Examples 5 and 6 had only a removal rate of 40% and 80%, respectively, even after 24 hours. In contrast, the water treatment material of Example 5 was able to remove about 70% after 30 minutes, about 95% lead after 3 hours, and 100% lead after 24 hours.
[0028]
<Example 6>
A water treatment material having an average particle size of 250 μm or less was obtained in the same manner as in Example 5 except that the molar ratio of Mg / Fe in the raw material aqueous solution was set to 1.
<Lead adsorption comparison test 2>
A lead adsorption test was conducted by a liquid flow method using a column. That is, 1.5 g of each water treatment material of Examples 5 and 6 and Comparative Example 4 was packed in three columns each having an inner diameter of 36 mm. The height of the packed bed at this time was about 2 mm, which is the same for all columns. A test solution in which 55 ppb of lead, which corresponds to the upper limit of the allowable lead concentration of tap water at present, was dissolved was prepared by dissolving lead nitrate in distilled water. This test solution was continuously passed through each column at a Sv (space velocity) of 150 / min using a liquid feed pump. Sv is a flow rate / column capacity, and when 150 / min, it means that a test solution having a volume 150 times that of the adsorbent flows in one minute.
The test solution flowing through the column was collected every predetermined time, and the dissolved concentration of lead was determined by flameless atomic absorption spectrometry. The result is shown in FIG. As is clear from FIG. 9, in the water treatment material of Comparative Example 4 (activated carbon for water treatment), the lead concentration at the outlet of the column was about 50 ppb, which was almost the same as the initial concentration of 55 ppb. In the water treatment material No. 6, the lead concentration at the outlet of the column was 5 ppb or less, and the lead concentration at the outlet was almost the same even through the 50 liter test solution.
[0029]
【The invention's effect】
As described above, according to the method for producing an iron-based double hydroxide of the present invention, the pH of the aqueous raw material solution is adjusted to 13 or more while stirring the raw material aqueous solution in the air or applying ultrasonic waves in the air. Without adding a carbonate as in the prior art, carbon dioxide is dissolved from the air, and carbonate ions are taken in as layer cross-linking anions, and Mg ions and Fe ions are uniformly dispersed. This makes it possible to synthesize iron-based double hydroxides that are easily crystallized in a relatively short period of time without using the conventional hydrothermal synthesis method.
In addition, according to the method for producing a water treatment material of the present invention, layered double hydroxide particles can be supported inside a porous body made of a hydrophobic polymer, whereby the double hydroxide is packed in a column. Thus, when water treatment is performed, harmful substances contained in water can be adsorbed at a high speed at a high rate without increasing the water flow resistance of the column.
[Brief description of the drawings]
FIG. 1 is a diagram showing a production process of an iron-based double hydroxide according to the present invention.
FIG. 2 is a view showing a manufacturing process of the water treatment material of the present invention.
FIG. 3 is a view showing a situation where iron-based double hydroxide particles of the present invention are supported in a porous body of a hydrophobic polymer.
FIG. 4 is a view showing a state in which harmful substances are adsorbed by a water treatment material by a liquid passing method using a column.
FIG. 5 is a diagram showing a situation where the water treatment material of the present invention captures lead in a low concentration aqueous lead solution.
FIG. 6 is a diagram showing a situation in which the water treatment material of the present invention captures lead in a high concentration aqueous lead solution.
7 is an X-ray diffraction diagram showing the crystallinity of iron-based double hydroxides of Examples 1 to 4 and Comparative Examples 1 and 2. FIG.
FIG. 8 is a graph showing the lead removal rate of the water treatment material of Example 5 and Comparative Examples 3 to 6 by a batch method.
9 is a graph showing the lead removal rate of the water treatment materials of Examples 5 and 6 and Comparative Example 4 by a liquid passing method. FIG.
[Explanation of symbols]
11 Stirrer 12 Ultrasonic generator 13 Hydrophobic polymer powder (cellulose acetate)
14 Good solvent for hydrophobic polymers (acetone)
16 Solution 17 in which hydrophobic polymer is dissolved 17 Layered double hydroxide particle 19 Poor solvent for hydrophobic polymer (hexane)
20 Water treatment material 21 column made of porous material

Claims (3)

When the alkaline earth metal that is magnesium or calcium is M, the alkaline earth metal salt aqueous solution and the trivalent iron salt aqueous solution are adjusted so that the molar ratio of Fe to M (M / Fe) is between 1 and 4. While mixing the raw material aqueous solution strongly in the air, or applying ultrasonic waves to the raw material aqueous solution in the air, gradually adding the alkaline aqueous solution until the pH becomes 13 or more, and crystallizing the raw material aqueous solution through a gel state. Thus, a layered double hydroxide represented by the following formula (1) having a pyroolite type structure is obtained.
M ²⁺ _(8-x) Fe ³⁺ _x (OH) ₁₆ (CO ₃ ^2- ) _{x / 2} · mH ₂ O (1)
However, 0 <x ≦ 6 and 0 <m ≦ 5. After dispersing the layered double hydroxide particles having an average particle size of 1 to 250 μm obtained by pulverizing the layered double hydroxide according to claim 1 in a solution of hydrophobic polymer powder in a good solvent ,
The solution in which the layered double hydroxide particles are dispersed is dried under atmospheric pressure while stirring, or the solution in which the layered double hydroxide particles are dispersed is poor in the hydrophobic polymer while stirring or without stirring. A method for producing a water treatment material, characterized in that a porous body composed of the hydrophobic polymer is produced by dropping into a solvent, and the layered double hydroxide particles are supported inside the porous body. A water treatment material in which layered double hydroxide particles represented by the following formula (1) having a pyroaulite structure are supported inside a porous body made of a hydrophobic polymer.
M ²⁺ _(8-x) Fe ³⁺ _x (OH) ₁₆ (CO ₃ ^2- ) _{x / 2} · mH ₂ O (1)
However, M is Mg or Ca, and 0 <x ≦ 6 and 0 <m ≦ 5.

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