JP2008188483A - Fluorine removing agent and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluorine removing agent more markedly excellent in its fluorine removing capacity as compared with a conventional fluorine removing agent. <P>SOLUTION: The fluorine removing agent comprises a composite porous body of amorphous hydroxyapatite and porous silica and preferably has an ion exchange capacity of which the F-concentration in an equilibrium state with a fluorine containing liquid with an F-concentration of 10 mg/l is 1% or above and is characterized in that its solubility of phosphorus to water is 3.5 mg/l or below. This fluorine removing agent is manufactured by adding phosphoric acid to a slurry or aqueous solution of calcium silicate compound at a temperature of below 70° to react it with the calcium silicate compound not only to make silica porous but also to produce amorphous hydroxyapatite. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fluorine removing agent having an excellent fluorine removing effect and a method for producing the same.

  Fluorine is the wastewater discharged from the electrolytic refining process of aluminum, the manufacturing process of phosphate fertilizer, the pickling process of stainless steel, etc., the cleaning process of electrical parts such as silicon, the waste incineration smoke cleaning wastewater, the coal fired smoke Although it is contained in desulfurization wastewater, etc., the wastewater standard is prescribed for the fluorine concentration in the wastewater, and wastewater treatment is carried out so as to be below the standard value.

Fluorine treatment methods that are currently in practical use include (I) a method of adding calcium salt to form poorly soluble calcium fluoride (CaF ₂ ) and precipitating it, and (II) adding an aluminum salt. A method of co-precipitation with aluminum hydroxide (Al (OH) ₃ ) and separation, and a method (III) of combining the coagulation precipitation method using the calcium salt and the coagulation precipitation method using the aluminum salt are common.

  On the other hand, there has recently been a trend toward stricter effluent standards for fluorine due to a review of living environment items, and it has become necessary to further remove fluorine. Specifically, in April 1999, the environmental standard value for fluorine was set at 0.8 mg / L (1999 Environmental Agency Notification No. 14). On the other hand, in the Water Pollution Control Law, the fluorine emission standard was strengthened from 15 mg / L to 8 mg / L in 2001 and has been in effect since July of the same year. Therefore, a technology for reducing the fluorine concentration in the wastewater to the above environmental standards is desired.

Therefore, as a fluorine removing agent that replaces the conventional method using calcium salt or aluminum salt, for example, one made of calcium hydroxide having a specific surface area of 20 m ² / g or more (Patent Document 1), phosphoric acid or phosphoric acid compound is used. Using a slurry of basic salt [3Ca ₃ (PO ₄ ) ₂ · Ca (OH) ₂ ] composed of calcium hydroxide and calcium phosphate (Patent Document 3), calcium oxide and calcium carbonate Has been proposed (Patent Document 4), in which calcium phosphate and zirconium are coordinated on the surface after treatment with a saturated potassium hydrogen phosphate solution and a zirconium solution.

On the other hand, hydroxyapatite [Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ] adsorbs fluorine in water by an ion exchange reaction between its hydroxide ion and fluorine ion, but it has low reactivity to fluorine, so that it is practical as it is. Cannot be used as a new fluorine adsorbent.
JP 2002-254086 A JP 2002-370093 A JP 2003-24953 A Japanese Patent Laid-Open No. 2003-62457

  The present invention solves the above-mentioned problems of conventionally known fluorine removing agents, and provides a fluorine removing agent that has a remarkably superior removing ability with respect to fluorine than conventional removing agents.

The present invention relates to a fluorine-removing adsorbent that has solved the above-described problems with the following configuration.
(1) A fluorine removing agent comprising a composite porous body of amorphous hydroxyapatite and porous silica.
(2) The fluorine removing agent according to the above (1) having an ion exchange capacity in which the F concentration in an equilibrium state with a fluorine-containing liquid having an F concentration of 10 mg / l is 1% or more.
(3) The fluorine removing agent as described in (1) or (2) above, wherein the total pore volume of the composite porous material is 0.5 ml / g or more.
(4) A peak separated at a relative intensity of 100 cps or more in a range of 2θ = 35.0 ° after the strongest peak in a relative intensity of 2θ = 31.8 ° in a Cu-α X-ray diffraction image is 1000 cps or less. The fluorine removing agent according to any one of (1) to (3) above, which is a composite porous body of amorphous hydroxyapatite and porous silica having a diffraction image not shown.
(5) The fluorine removing agent according to any one of (1) to (4) above, wherein the molar ratio of calcium to phosphorus (Ca / P) is 1.5 to 2.0.
(6) The fluorine removing agent as described in any one of (1) to (5) above, wherein the molar ratio of calcium to silicon (Ca / Si) is 0.1 to 2.0.
(7) The fluorine removing agent according to any one of (1) to (6) above, wherein the solubility of phosphorus in water is 3.5 mg / l or less.
(8) The fluorine removing agent as described in any one of (1) to (7) above, having an average particle size of 10 to 60 μm and a BET specific surface area of 100 m ² / g or more.
(9) Adding phosphoric acid to a calcium silicate compound slurry or aqueous solution at a temperature of less than 70 ° C. to react to make the silica porous and produce amorphous hydroxyapatite to form a composite with porous silica A method for producing a fluorine removing agent comprising a porous material.

  The fluorine removing agent of the present invention comprises a composite porous body of amorphous hydroxyapatite and porous silica, and has a large pore volume, preferably a composite pore having a total pore volume of 0.5 ml / g or more. Since it is a material, it has excellent properties such as a large ion exchange capacity with respect to fluorine and a high exchange rate.

  Specifically, when the fluorine removing agent of the present invention is added to a fluorine-containing aqueous solution, the F concentration of the composite porous body is 1% or more when in equilibrium with the fluorine-containing aqueous solution having an F concentration of 10 mg / l. Ion exchange capacity.

  The hydroxyapatite forming the fluorine removing agent of the present invention is amorphous. Specifically, for example, the relative intensity of the peak at 2θ = 31.8 ° in the Cu-α X-ray diffraction image is 1000 cps or less, and the relative intensity is 100 cps or more in the range of 2θ = 35.0 ° after the strongest peak. Since it is an amorphous hydroxyapatite having a diffraction image that does not show a separated peak, the effect of removing fluorine is larger than that of crystalline hydroxyapatite.

  In the fluorine removing agent of the present invention, preferably, the molar ratio of calcium to phosphorus (Ca / P) of hydroxyapatite is 1.5 to 2.0, and the phosphorus content is controlled within a certain range. Therefore, phosphorus does not easily elute. For example, the solubility of phosphorus is 3.5 mg / l or less, so that it has excellent water resistance and does not contaminate the water quality after fluorine removal.

  Furthermore, the fluorine removing agent of the present invention preferably has a molar ratio of calcium to silicon (Ca / Si) of 0.1 to 2.0 and contains amorphous hydroxyapatite and porous silica in an appropriate ratio. Therefore, the fluorine removal effect is high.

The fluorine removing agent of the present invention preferably has an average particle size of 10 to 60 μm and a BET specific surface area of 100 m ² / g or more. Since this particle size has a sufficiently large contact area with the fluorine-containing liquid, it has excellent ion exchange properties, excellent fluorine removal effect, and good filterability and sedimentation. The solid-liquid separation treatment of the removing agent after removing the fluorine is extremely easy.

  The fluorine-removing agent of the present invention is a composite of porous silica with silica made porous by reacting calcium silicate compound with phosphoric acid at a temperature of less than 70 ° C. to produce amorphous hydroxyapatite. A fluorine removing agent comprising a porous body can be produced.

Hereinafter, the present invention will be specifically described based on embodiments. In addition,% is mass% except the case intrinsic | native to a unit.
[Fluorine remover]
The fluorine removing agent of the present invention is a composite porous body of amorphous hydroxyapatite and porous silica. Hydroxyapatite is a calcium phosphate compound represented by the general formula [Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ]. It has ion exchange capacity by substitution of hydroxyl groups, etc., but hydroxyapatite alone has low reactivity and is practical. Since the property is poor, the fluorine removing agent of the present invention has a high fluorine removing performance by forming a composite of amorphous hydroxyapatite and porous silica. Silica that does not contain hydroxyapatite does not cause an ion exchange reaction with fluorine even if it is porous, and therefore has no effect of removing fluorine.

  The hydroxyapatite forming the fluorine removing agent of the present invention is amorphous. Specifically, for example, in a Cu-α X-ray diffraction image, it has the strongest peak around 2θ = 31.8 °, the relative intensity of this peak is 1000 cps or less, and 2θ = 35 after the strongest peak. In the range of 0.0 °, no separated peak having a relative intensity of 100 cps or more is shown, and a gentle diffraction image is obtained.

  Since the hydroxyapatite forming the fluorine removing agent of the present invention is an amorphous material having such low crystallinity, the effect of removing fluorine is great. In addition, the hydroxyapatite having high crystallinity in which the relative intensity of the strongest peak in the vicinity of 2θ = 31.8 ° in the X-ray diffraction image is higher than 1000 cps has lower fluorine removal performance than that of amorphous. Incidentally, as shown in FIGS. 10 to 12 (Comparative Examples 1 to 3), hydroxyapatite with high crystallinity is 2θ = (31.8 °), (32.2 °) in a Cu-α X-ray diffraction image. , (32.9 °), and (34.0 °), four clearly separated peaks having a relative intensity of 100 cps or more are observed, but the hydroxyapatite of the present invention does not show these clearly separated peaks, It is low in nature.

  The fluorine removing agent of the present invention preferably has a hydroxyapatite calcium to phosphorus molar ratio (Ca / P) of 1.5 to 2.0. If the Ca / P molar ratio is less than 1.5, and therefore the phosphorus content is more than the above range, phosphorus is likely to elute. On the other hand, those having a molar ratio exceeding 2.0 are not preferable because unreacted calcium silicate compounds remain, the amount of apatite produced is insufficient, and the fluorine adsorption capacity decreases.

  When the Ca / P molar ratio is within the above range, phosphorus does not easily elute. For example, the solubility of phosphorus is not more than 3.5 mg / L, preferably not more than 10 mg / L. Excellent water resistance. Moreover, since the solubility of phosphorus is low, the water quality after fluorine removal is not contaminated. In order to adjust the Ca / P molar ratio, the mixture amount of the calcium silicate compound and phosphoric acid may be adjusted when the calcium silicate compound is reacted with phosphoric acid to produce the fluorine removing agent of the present invention.

  Furthermore, the fluorine removing agent of the present invention preferably has a calcium to silicon molar ratio (Ca / Si) of 0.1 to 2.0, more preferably 0.8 to 1.2. When the Ca / Si molar ratio is out of this range, the content of either hydroxyapatite or silica becomes too small, so that the fluorine removal performance deteriorates. In order to adjust the Ca / Si molar ratio, the calcium silicate compound used as a raw material may have a Ca / Si molar ratio in the above range.

  The fluorine removing agent of the present invention contains porous silica and has a form in which a large number of fine amorphous hydroxyapatite is precipitated, so there are many gaps, preferably a total pore volume of 0.5 ml / g or more, more preferably Is 0.75 ml / g or more. Therefore, the ion exchange capacity is larger than that of fluorine, and the exchange rate is fast. Specifically, when added to a fluorine-containing aqueous solution, the composite porous body has an ion exchange capacity in which the F concentration is 1% or more when in equilibrium with a fluorine-containing aqueous solution having an F concentration of 10 mg / L.

The fluorine removing agent of the present invention preferably has an average particle size of 10 to 60 μm and a BET specific surface area of 100 m ² / g or more. This particle size has a sufficiently large contact area with the fluorine-containing liquid, so that it has excellent ion exchange performance, excellent fluorine removal effect, and good filterability and sedimentation. The solid-liquid separation treatment of the removing agent after removing the fluorine is extremely easy.

According to the method of producing a hydroxyapatite silica composite porous body by reacting calcium silicate compound with phosphoric acid, the calcium content of the calcium silicate compound is eluted with phosphoric acid, and hydroxyapatite is precipitated on the particle surface. A composite porous body having a particle size almost equal to that of the raw material calcium silicate compound is produced. Therefore, in order to obtain a fluorine removing agent having an average particle size of 10 to 60 μm and a BET specific surface area of 100 m ² / g or more, a calcium silicate compound having a particle size and BET specific surface area comparable to this may be used as a raw material.

〔Production method〕
The hydroxyapatite silica composite porous body used as a fluorine removing agent of the present invention is prepared by reacting phosphoric acid with a calcium silicate compound to elute the calcium component to make the silica component porous and to convert the eluted calcium component to hydroxyapatite. It can be produced by conversion and precipitation.

  As in the conventional manufacturing method, the porous material such as porous silica is impregnated or precipitated with hydroxyapatite. Even if the substrate is porous, the porosity is impaired by the precipitation of hydroxyapatite. Therefore, the porous body as in the present invention cannot be obtained.

  On the other hand, according to the production method in which the calcium silicate compound is reacted with phosphoric acid, the calcium content of the calcium silicate compound reacts with phosphoric acid to produce hydroxyapatite and the silica is made porous. The body is formed. Moreover, since fine hydroxyapatite precipitates on the surface of the porous silica particles, a composite porous body having a large pore volume, good filtration characteristics, sedimentation, and water permeability can be obtained and further generated. Hydroxyapatite has the advantage of low solubility in water.

  In addition, the silica raw material is not added, and the hydroxyapatite simple substance formed by simply reacting the calcareous raw material with phosphoric acid has a low degree of porosity, and therefore does not have sufficient fluorine removal performance, filtration characteristics, sedimentation The nature is also low.

  The calcium silicate compound used as the raw material of the fluorine removing agent of the present invention is a generally well-known compound synthesized by subjecting a silicic acid raw material and a lime raw material to an aqueous slurry, for example, by hydrothermal reaction in an autoclave. Can be suitably used. The type is not particularly limited as long as it is a calcium silicate compound. For example, any calcium silicate compound such as a crystalline calcium silicate compound such as tobermorite, gyrolite, and zonotlite, or an amorphous calcium silicate compound can be used. . These may be used alone or in combination of two or more. In addition, these calcium silicate compounds are not limited to powders, and may be molded bodies or lumps.

  The fluorine removing agent of the present invention preferably has a calcium to silicon molar ratio (Ca / Si) of 0.1 to 2.0, and more preferably 0.8 to 1.2. It is preferable to use a calcium silicate compound having a ratio.

  Porous formation and hydrochiapatite formation of the calcium silicate compound can be performed by adding phosphoric acid to a slurry of the calcium silicate compound or an aqueous solution of the calcium silicate compound.

  For example, a silicic acid raw material such as silica powder and a lime raw material such as slaked lime are mixed, water is added thereto, and hydrothermal reaction is performed to produce a calcium silicate compound slurry, and phosphoric acid is added to the generated slurry, Hydroxiapatite is recommended. By causing phosphoric acid to act on calcium silicate produced by hydrothermal reaction, the calcium component reacts with phosphoric acid to make the silica porous, and hydroxyapatite is produced. Further, amorphous hydroxyapatite is precipitated by controlling the reaction conditions such as the concentration of phosphoric acid, the addition rate, and the liquid temperature.

  The phosphoric acid concentration is 2 to 50%, preferably 5 to 40%. If the phosphoric acid concentration is less than 2%, the amount of the liquid to be treated increases, which is inconvenient. If it is higher than 50%, fine hydroxyapatite and silica particles are likely to be generated due to a local decrease in pH of the liquid. This is not preferable. Instead of phosphoric acid, a water-soluble phosphate such as ammonium phosphate or sodium phosphate can be used.

  The addition amount of phosphoric acid is desirably determined so that the molar ratio (Ca / P) of calcium content and phosphoric acid of the calcium silicate compound is 1.5 to 2.0. When this molar ratio exceeds 2.0, an unreacted calcium silicate compound remains, the amount of hydroxyapatite produced becomes insufficient, and the fluorine removal effect is reduced. On the other hand, when the molar ratio is lower than 1.5, the solubility of phosphorus tends to increase, and the water resistance decreases.

  In order to produce amorphous hydroxyapatite, phosphoric acid is added to convert the calcium silicate compound to hydroxyapatite at a temperature of less than 70 ° C. When the temperature is 70 ° C. or higher, hydroxyapatite crystals develop, and the hydroxyapatite does not become amorphous, so that the fluorine removal performance decreases. The lower the temperature, the lower the crystallinity and improve the fluorine removal ability, but a temperature of room temperature or higher is recommended for the manufacturing process.

Amorphization can also be promoted by controlling the addition rate of phosphoric acid. Specifically, phosphoric acid may be added so as to maintain a pH of less than 7, preferably a pH of less than 3.0 to 7.0.

  In addition, when the addition rate of phosphoric acid is extremely fast, the particle shape of the calcium silicate compound collapses, and fine hydroxyapatite and silica particles are generated, resulting in deterioration of filterability and sedimentation. By adding phosphoric acid so that the pH of the solution during the reaction is in the above range, amorphous hydroxyapatite is precipitated, and a composite porous body excellent in fluorine adsorption ability, filterability and sedimentation is obtained. Obtainable.

  The reaction time of the hydroxyapatite formation varies depending on the type and particle size of the raw material, and the shape of the powder or the molded body, and cannot be determined generally, but usually about 10 to 120 minutes is sufficient.

  A porous composite of amorphous hydroxyapatite and porous silica can be obtained by reacting a calcium silicate compound with phosphoric acid, but if the porosity of this composite is to be further increased, Prior to the addition of phosphoric acid, a complex having a high pore volume can be obtained by previously acting an acid other than phosphoric acid on the calcium silicate compound and removing the calcium component by acid treatment. In place of the acid treatment, carbon dioxide may be blown, or an acidic cation exchange resin may be added to the calcium silicate compound slurry to remove calcium.

  As the acid used for removing the calcium content in advance, inorganic acids such as hydrochloric acid and nitric acid, and organic acids such as acetic acid can be used. As described above, the acid may be added gradually at a rate commensurate with the rate at which calcium is eluted from the calcium silicate compound, specifically, at a rate that maintains a pH of 3.0 or higher. preferable. If the pH is less than 3.0, fine silica particles are generated and the filtration process takes time, which is not preferable.

  The reaction rate can be accelerated by raising the liquid temperature or stirring the liquid. The reaction time for removing calcium varies depending on the type, particle size, shape, etc. of the raw material calcium silicate, but approximately 0.5 to 3 hours is sufficient.

  After reacting with an acid other than phosphoric acid, solid-liquid separation is performed to recover the calcium silicate compound, which is washed with water and then immersed again in an aqueous slurry or water, and phosphoric acid is added to effect hydroxyapatite formation.

  After reacting calcium silicate compound with phosphoric acid to make silica porous and hydroxyapatite, the product is solid-liquid separated by filtration or centrifugation, and the recovered starch is dried, A fluorine removing agent comprising an amorphous hydroxyapatite-silica composite porous body having an average particle size of 10 to 60 μm and a BET specific surface area of 100 m 2 / g or more can be obtained.

  Examples of the present invention are shown below together with comparative examples. In addition, the physical property of the manufactured fluorine adsorbent body was calculated | required with the following measuring method.

[X-ray diffraction image]
Measurement was performed using a mini-flex X-ray diffractometer (manufactured by Rigaku Corporation) under the conditions of Cu tube, tube voltage 30 kV, tube current 15 mA, sampling width 0.02 °, and scan speed 4 ° / min.
[Average particle size]
The measurement was performed using a laser diffraction particle size distribution analyzer (Horiba, Ltd. product: LA-300).

〔Specific surface area〕
Using a Shimadzu apparatus (Flow Sob II), the BET one-point method was used for measurement.
(Pore volume)
About the sample which vacuum deaerated at 150 degreeC for 1 hour, it measured by the nitrogen adsorption method (BJH method) using the Japan BEL apparatus (BELSORP-mini).

[Fluorine concentration and adsorption isotherm]
To 100 ml of an aqueous solution adjusted to 5 to 200 mg / L by dissolving sodium fluoride in water, 0.20 g of the sample was added and shaken in a 60 ° C. constant temperature bath for 24 hours to achieve an equilibrium state. This sample solution was filtered, and the fluorine concentration in the solution was determined by an ion meter. The amount of fluorine adsorbed by the sample was calculated from the amount of decrease in fluorine in the liquid. The relationship between the fluorine concentration of the solution and the amount of fluorine adsorbed by the sample was plotted on a log-log graph to create an adsorption isotherm. From this adsorption isotherm graph, the F concentration of the liquid equilibrated to 1% fluorine concentration in the solid phase was read and shown in Table 1. This adsorption isotherm is shown in FIG. 1 and FIG. 2 for each example and each comparative example.

[Phosphorus concentration]
0.20 g of a sample was added to 100 ml of pure water, shaken in a constant temperature bath at 60 ° C. for 24 hours, and after filtering this sample solution, the phosphorus concentration was determined by the molybdenum blue method.

[Example 1]
To 100 g of silicic acid raw material (amorphous silica powder having an average particle size of 20 μm) and 100 g of slaked lime (Ca / Si molar ratio of 0.8), water corresponding to a water-solid content ratio of 15 is added and stirred while stirring in an autoclave. A hydrothermal reaction was carried out at 4 ° C. for 4 hours to form a calcium silicate compound slurry. The slurry was heated to 60 ° C., and phosphoric acid in an amount such that the Ca / P molar ratio was 1.67 was added while stirring the slurry at a rate that maintained the pH below 7. After the addition, the mixture was stirred for 1 hour, the slurry was filtered to separate the starch, and dried to obtain a composite porous body composed of amorphous hydroxyapatite and porous silica. The physical property values are shown in Table 1 and FIG. 1, and the SEM photograph is shown in FIG. An X-ray diffraction graph is shown in FIG.

[Example 2]
A composite porous body composed of amorphous hydroxyapatite and porous silica was obtained in the same manner as in Example 1 except that 100 g of silica powder having an average particle size of 10 μm was used as the silicic acid raw material. The physical property values are shown in Table 1 and FIG. 1, and the SEM photograph is shown in FIG. An X-ray diffraction graph is shown in FIG.

Example 3
To 100 g of silicic acid raw material (amorphous silica powder having an average particle diameter of 20 μm) and 127 g of slaked lime (Ca / Si molar ratio of 1.0), water corresponding to a water-solid content ratio of 10 is added and stirred while stirring in a warm bath. A hydrothermal reaction was carried out at 15 ° C. for 15 hours to form a calcium silicate compound slurry. The slurry was heated to 60 ° C., and phosphoric acid in an amount such that the Ca / P molar ratio was 1.67 was added while stirring the slurry at a rate that maintained the pH below 7. After the addition, the mixture was stirred for 1 hour, the slurry was filtered to separate the starch, and dried to obtain a composite porous body composed of amorphous hydroxyapatite and porous silica. The physical property values are shown in Table 1, FIG. 1 and FIG. 2, and the SEM photograph is shown in FIG. An X-ray diffraction graph is shown in FIG.

Example 4
The same calcium silicate compound slurry as in Example 3 was heated to 30 ° C., and phosphoric acid was added in such an amount that the Ca / P molar ratio was 1.67 while stirring the slurry at a rate that maintained the pH of 7 or higher. . After the addition, the mixture was stirred for 1 hour, the slurry was filtered to separate the starch, and dried to obtain a composite porous body composed of amorphous hydroxyapatite and porous silica. The physical property values are shown in Table 1 and FIG. An X-ray diffraction graph is shown in FIG.

[Comparative Example 1]
Calcium silicate compound (zonotlite) slurry for fireproof coating building material is preheated to 60 ° C., and the slurry is stirred at such a rate that the pH of the Ca / P molar ratio is 1.67 and maintained at a pH of 7 or higher. While adding. After the addition, the mixture was stirred for 1 hour, and the slurry was filtered and dried to obtain a composite porous body composed of crystalline hydroxyapatite and porous silica. The physical property values are shown in Table 1 and FIG. An X-ray diffraction graph is shown in FIG.

[Comparative Example 2]
The same calcium silicate compound slurry as in Example 3 was heated to 70 ° C., and phosphoric acid in an amount such that the Ca / P molar ratio was 1.67 was added while stirring the slurry at a rate that maintained the pH below 7. . After the addition, the mixture was stirred for 1 hour, the slurry was filtered to separate the starch, and dried to obtain a composite porous body composed of crystalline hydroxyapatite and porous silica. The physical property values are shown in Table 1 and FIG. The X-ray diffraction graph is shown in FIG.

[Comparative Example 3]
The slaked lime slurry was previously heated to 60 ° C., and phosphoric acid in an amount such that the Ca / P molar ratio was 1.67 was added while stirring the slurry at a rate that maintained the pH below 7. After the addition, the mixture was stirred for 1 hour, and the slurry was filtered and dried to obtain crystalline hydroxyapatite. The physical property values are shown in Table 1 and FIG. An X-ray diffraction graph is shown in FIG.

[Reference Example 1]
The calcium silicate compound slurry of Example 3 above was heated to 60 ° C. in advance and phosphoric acid in an amount such that the Ca / P molar ratio was 1.45 was added while stirring the slurry at a rate that maintained the pH below 7. did. After the addition, the mixture was stirred for 1 hour, and the slurry was filtered and dried to obtain a hydroxyapatite silica composite porous body. The physical property values are shown in Table 1 and FIG.

[Reference Example 2]
The calcium silicate compound slurry of Example 3 above was heated to 60 ° C. in advance, and phosphoric acid in an amount such that the Ca / P molar ratio was 2.5 was added while stirring the slurry at a rate that maintained the pH below 7. did. After the addition, the mixture was stirred for 1 hour, and the slurry was filtered and dried to obtain a hydroxyapatite silica composite porous body. The physical property values are shown in Table 1 and FIG.

  As shown in FIG. 1, in each of Examples 1 to 4 of the present invention, the amount of adsorption of fluorine is far superior to the comparative example. For example, when the F concentration in the liquid is 10 mg / l, The F concentration in the solid phase in an equilibrium state is 1.0% or more. Moreover, as shown in Table 1, the fluorine concentration in the liquid equilibrated to 1% fluorine concentration in the solid phase is 1.9 to 3.2 mg / l in Examples 1 to 4 of the present invention. Comparative Example 1 is 291 mg / l, Comparative Example 2 is 70 mg, and Comparative Example 3 is 74 mg / l, indicating that the concentration of fluorine in the examples of the present invention is remarkably low and has a high fluorine adsorption capacity. ing.

  Comparative Example 1 and Comparative Example 2 are a composite of hydroxyapatite and porous silica. As shown in FIGS. 10 to 11, four clear peaks are observed at the diffraction angle of hydroxyapatite, and the peak intensity is large. The crystallinity of hydroxyapatite is high. For this reason, as shown in Table 1, the fluorine concentration in the liquid is significantly high, indicating that the fluorine adsorption capacity is low. Moreover, since the comparative example 3 is a hydroxyapatite simple substance which does not contain porous silica, its fluorine adsorption capacity is low.

  On the other hand, the hydroxyapatite of Examples 1 to 4, as shown in FIGS. 6 to 9, shows the strongest peak in the vicinity of the diffraction angle 2θ = 31.8 °, but this peak relative intensity is 1000 cps or less, In addition, the peak separated in the range of 2θ = 35.0 ° after the strongest peak is not shown, and it has a gentle diffraction image, indicating that it is amorphous. Therefore, as shown in Table 1, the concentration of fluorine in the liquid is low and the fluorine adsorption capacity is high.

  Reference Example 1 is a composite of amorphous hydroxyapatite and porous silica, and the fluorine concentration in the liquid is low, but the Ca / P molar ratio is lower than the preferred range, so that phosphorus easily elutes, High phosphorus concentration. Reference Example 2 is a composite of amorphous hydroxyapatite and porous silica, but the Ca / P molar ratio is higher than the preferred range, so the hydroxyapatite content is low and the fluorine adsorption capacity is somewhat low. The fluorine density | concentration in a liquid is higher than Examples 1-4.

  As shown in FIG. 2, the lower the Ca / P molar ratio of the composite porous body of the present invention, the better the fluorine adsorption capacity. In particular, when the Ca / P molar ratio is higher than 2.0 (Reference Example 2), since the slope of the adsorption isotherm becomes steep, the decrease in the fluorine adsorption ability at a low concentration becomes remarkable. A lower Ca / P molar ratio is better to have sufficient fluorine removal capability. On the other hand, as shown in Table 1, when the Ca / P molar ratio is less than 1.5, the solubility of phosphorus rises rapidly (Reference Example 1), phosphorus is eluted and the concentration of phosphorus in the liquid increases, and the treated water becomes Since there is a concern that causes eutrophication, the Ca / P molar ratio is preferably 1.5 or more in practical use.

  As shown in FIGS. 3 to 5, the powders of Examples 1 to 3 of the present invention have fine acicular particles growing on the surface and inside, and there are many voids.

Graph showing adsorption isotherm for fluorine Graph showing adsorption isotherm for fluorine Electron microscope (SEM) photograph showing the structural state of the composite porous body of Example 1 Electron microscope (SEM) photograph showing the structural state of the composite porous body of Example 2 Electron microscope (SEM) photograph showing the structural state of the composite porous body of Example 3 X-ray diffraction pattern of hydroxyapatite of Example 1 X-ray diffraction pattern of hydroxyapatite of Example 2 X-ray diffraction pattern of hydroxyapatite of Example 3 X-ray diffraction pattern of hydroxyapatite of Example 4 X-ray diffraction pattern of hydroxyapatite of Comparative Example 1 X-ray diffraction pattern of hydroxyapatite of Comparative Example 2 X-ray diffraction pattern of hydroxyapatite of Comparative Example 3

Claims (9)

A fluorine removing agent comprising a composite porous body of amorphous hydroxyapatite and porous silica.
The fluorine removing agent according to claim 1, which has an ion exchange capacity in which an F concentration in an equilibrium state with a fluorine-containing liquid having an F concentration of 10 mg / l is 1% or more.
The fluorine removing agent according to claim 1 or 2, wherein the total pore volume of the composite porous body is 0.5 ml / g or more.
Diffraction in which the relative intensity of the peak at 2θ = 31.8 ° in the Cu-α X-ray diffraction image is 1000 cps or less and does not show a separated peak with a relative intensity of 100 cps or more in the range of 2θ = 35.0 ° after the strongest peak. The fluorine removing agent according to any one of claims 1 to 3, which is a composite porous body of amorphous hydroxyapatite having an image and porous silica.
The fluorine removing agent according to any one of claims 1 to 4, wherein a molar ratio of calcium to phosphorus (Ca / P) is 1.5 to 2.0.
The fluorine removing agent according to any one of claims 1 to 5, wherein a molar ratio of calcium to silicon (Ca / Si) is 0.1 to 2.0.
The fluorine removing agent according to any one of claims 1 to 6, wherein the solubility of phosphorus in water is 3.5 mg / l or less.
The fluorine removing agent according to any one of claims 1 to 7, which has an average particle size of 10 to 60 µm and a BET specific surface area of 100 m ² / g or more.
A composite porous body with porous silica by adding phosphoric acid to a slurry or aqueous solution of a calcium silicate compound at a temperature of less than 70 ° C. to react to make the silica porous and to produce amorphous hydroxyapatite. A method for producing a fluorine removing agent comprising: