JP2003200044A - Heavy metal adsorbent and cartridge for water purifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adsorbent which has an excellent adsorption performance for heavy metals in water, has a high strength, enables the resistance of water passing to decrease to the utmost and exhibits a stable adsorption performance for a long period, and to provide a cartridge for a water purifier packed with such an adsorbent. <P>SOLUTION: The adsorbent is an adsorbent for adsorbing and removing heavy metals in water, comprises low-crystalline hydroxyapatite containing an alkaline earth metal salt and is granularly formed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent capable of stably exhibiting excellent adsorption performance for heavy metals over a long period of time, and a water purifier cartridge using such adsorbent.

[0002]

2. Description of the Related Art Various heavy metals are contained in drainage water and drinking water, and these heavy metals have an adverse effect on the human body and therefore must be effectively removed. Especially lead (Pb)
Regarding, regarding lead pipes used as old water pipes, lead ions are often dissolved in tap water, and the Pb concentration in drinking water is 10 ppb or less in consideration of its adverse effect on the human body. It is recommended that [World Health Organization guidelines (199
3)].

Various adsorbents have been used so far as means for removing harmful heavy metals contained in water including Pb, and zeolite has been generally known as a typical one. . However, since zeolite mainly adsorbs heavy metals by a physical adsorption action, when attempting to adsorb a plurality of heavy metal ions, it is necessary to select one having pores matching the individual ion diameters. , Its use is not versatile. Therefore, various adsorbents have been proposed so far.

As such a technique, it has been proposed to use a bead-shaped chelating resin as an adsorbent. However, the chelate resin has a problem that it is difficult to efficiently adsorb and separate low-concentration dissolved metal ions, and a large amount of resin is required. In addition, the washing water for industrial waste and the like is alkaline, so that not only the adsorption performance of the chelate resin decreases in an alkaline environment, but also the resin itself deteriorates. Further, since the chelate resin is generally expensive, there is a drawback that it is uneconomical.

It has also been proposed to use an aluminosilicate type inorganic ion exchanger as a material for the adsorbent (for example, JP-A-8-132026). However, such an ion exchanger may contain side reaction products and impurities in the manufacturing process thereof, and there is a problem that these are eluted during use.

On the other hand, hydroxyapatite [Ca ₁₀ (P
O _{4) 6} (OH) ₂ or _{Ca 10-z (HPO 4)} z (PO 4)
_6-z (OH) ₂ · nH ₂ O, which may be abbreviated as “HAP” below, is originally a major constituent of living hard tissues and has a good affinity with living bodies. It is widely used as a material for artificial teeth. And this HAP is
It is also known that by substitution with calcium ions, it has an excellent adsorptivity for polluting heavy metals such as lead (Pb), cadmium (Cd), and mercury (Hg). HAPs are being used as adsorbents.

By the way, when the above HAP is used as an adsorbent for a water purifier, it is usually used in a state of being filled in a cartridge of the water purifier. However,
The HAPs that have been used as adsorbents so far are fine crystal particles that have needle-like or columnar crystals as primary particles, so even if these HAP particles are filled in a water purifier cartridge, the HAP particles will flow out and disappear. Will you do HA
There is a drawback that P particles aggregate to block the water channel and increase the liquid passage resistance. For this reason, when HAP is used as an adsorbent, it is generally used in a state in which HAP is carried on the surface of the base material (carrier) by some method.

As such a technique, for example, Japanese Patent No. 311
No. 6507 proposes a method in which an inorganic porous hard body containing calcium is immersed in a phosphoric acid aqueous solution and then cured to precipitate hydroxyapatite on the surface of the hard body and to use it as an adsorbent. In addition, JP 2001
No. 47038 discloses that a molded product obtained by combining fibrous activated carbon, HAP, and a binder is used as a purifier cartridge. Further, Japanese Patent No. 3091
In No. 1226, HAP that has been highly crystallized by firing has an inefficient calcium elution and an insufficient adsorption performance for heavy metals. An adsorbent for heavy metals containing a high quality HAP is disclosed. Further, Japanese Patent Laid-Open No. 7-27580 discloses that
A technique has also been proposed in which HAP is generated in the pores of activated carbon and used as an adsorbent.

However, in these techniques, since HAP is basically carried on the surface of the base material, there is a problem that complicated processing steps are required. Further, in the HAP so far, highly crystalline or non-crystalline ones have been used, but these HAPs cannot be said to have sufficient adsorption performance, and further improvement in adsorption performance is desired. There is. Furthermore, there is a drawback in that the adsorbing performance is deteriorated in the case of a fired product or a product with a binder added.

Further, in order to exhibit excellent adsorption performance over a long period of time, the adsorbent needs to have a strength that can maintain a predetermined shape without causing elution or pulverization by a liquid. However, the actual situation is that an adsorbent having such strength and the above-mentioned adsorption performance has not been realized.

[0011]

SUMMARY OF THE INVENTION The present invention has been made under these circumstances, and its purpose is to have excellent adsorption performance for heavy metals in water and high strength, and to reduce water flow resistance as much as possible. An object of the present invention is to provide an adsorbent capable of exhibiting stable adsorption performance over a long period of time, and a water purifier cartridge filled with such an adsorbent.

[0012]

The adsorbent of the present invention, which has achieved the above object, is an adsorbent for adsorbing and removing heavy metals in water, which contains an alkaline earth metal salt. The gist is that it is made of crystalline hydroxyapatite and is formed into a granular shape.

As the alkaline earth metal salt contained in the adsorbent of the present invention, various ones may be mentioned, but one or more kinds selected from the group consisting of magnesium chloride, calcium chloride and calcium lactate are particularly preferable. preferable.
The content of the alkaline earth metal salt is preferably 0.05 to 10% by mass.

On the other hand, the heavy metals to be used in the present invention include at least one selected from the group consisting of Pb, Cd and Hg, and the adsorbent of the present invention has excellent adsorption performance for these heavy metals. Will be shown. The adsorbent of the present invention is in the form of granules, and the average particle size of the granules is preferably 50 μm or more and 30 mm or less.

By filling the adsorbent as described above, a useful water purifier cartridge can be realized.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have examined various aspects of the optimum form and composition of an adsorbent, assuming that HAP is used as a basic material in the adsorbent. As a result, they have found that the above-mentioned objects can be achieved satisfactorily in the form of granules of low crystalline HAP containing an alkaline earth metal salt, and completed the present invention.
The HAP used as the material for the adsorbent in the present invention is tricalcium phosphate [3 which has been conventionally used as a food additive.
Ca ₃ (PO ₄ ) ₂ · Ca (OH) ₂ ] is also included.

HA used as an adsorbent so far
As the P, one having a crystallinity as high as possible or an amorphous one has been used. However, according to a study by the present inventors, HAP having a relatively low crystallinity is superior to various substances. It was found that it exhibited excellent adsorption performance. In addition, such a low crystalline HAP containing an alkaline earth metal salt and formed into a granule has high strength and can maintain its shape for a long period of time. The water flow resistance can be reduced as much as possible, and stable adsorption performance can be exhibited over a long period of time.

The adsorbent of the present invention is made of HAP having a low crystallinity as described above. The "low crystallinity" means a state in which the degree of crystal development of apatite is low, for example, powder X-ray diffraction. In 2θ = 25.878 ° and a surface spacing (d) = 3.44Å (hkl = 002), the full width at half maximum (FWHM) is 0.2 ° or more. That is, the FWHM is 0.
When the angle is 2 ° or more, the crystallites are small and the arrangement is nonuniform, and such a state is called “low crystallinity” in the present invention.

With such a low crystalline HAP, it is possible to effectively adsorb an extremely low concentration of heavy metals in a solution,
The adsorption saturation is higher than that of conventional adsorbents. It is not possible to elucidate all of the reasons why the adsorption performance is further improved by using this low crystallinity HAP, but it is probably because the bonding force between the ions constituting the crystal is weak. It can be considered that the ion exchange reaction is likely to occur with respect to heavy metals and the surface adsorption capacity is enhanced. Further, the heavy metal targeted by the present invention includes at least one selected from the group consisting of Pb, Cd and Hg, and the adsorbent of the present invention exhibits excellent adsorption performance for these heavy metals. Become.

In producing the low-crystal HAP as described above, any method can be adopted as long as the HAP can have low crystallinity, for example, the method previously developed by the present inventors. The method disclosed in JP-A-9-40408 and the known Tiselius method can be used.

Among them, according to the method of Japanese Patent Application Laid-Open No. 9-40408, CaHPO ₄ .2 having an average particle size of about 5 to 30 μm.
H ₂ O powder and CaCO ₃ powder having an average particle size of 5 μm or less are used as raw materials, and these are mixed at an appropriate mixing ratio (for example, Ca
Atomic ratio of atoms to phosphorus atoms is in the range of 1.4 to 1.8) to form a water suspension liquid, and the suspension is heated to a temperature of about 40 to 70 ° C. It is to hold and react gently. Meanwhile, Chiselius (Tis
In the method of (elius), an alkaline aqueous solution is added to CaHPO ₄ .2H ₂ O powder to form an aqueous suspension, and this suspension is heated.
It is held, filtered and dried.

In addition to these methods, (a) Ca (OH) ₂
A method in which phosphoric acid is added dropwise to the aqueous solution to generate a precipitate,
(B) Ion exchange reaction between calcium nitrate [Ca (NO ₃ ) ₂ ] and ammonium hydrogen phosphate [(NH ₄ ) ₂ HPO ₄ ], (c) Ca (OH) ₂ with Mg (OH) ₂ Mix and react with phosphoric acid to part of Ca in the crystal
A method of substituting with g (for example, “Chemistry of apatite for making teeth and bones”, Tokai University Press), (d) a method of utilizing a hydration reaction of α-type tricalcium phosphate, and the like can be adopted.

Whichever method is adopted, in order to obtain low crystallinity HAP, the reaction rate may be increased or the reaction conditions may be such that the crystal arrangement becomes nonuniform. Specifically, the reaction rate can be increased by carrying out the reaction at a high temperature or by using a water-soluble and ionizable raw material. In addition, HAP easily produces one having a structure in which a part of constituent ions are replaced with different kinds of ions (for example, PO ₄ ³⁻ ion or OH ⁻ ion is CO ₃
^2- ions, Ca ²⁺ ions are replaced with alkaline earth metal ions such as Mg ²⁺ ) and different ions have different ionic radii, resulting in non-uniform crystal arrangement.

The adsorbent of the present invention contains an alkaline earth metal salt. The alkaline earth metal salt means a salt synthesized from an alkaline earth metal and an organic acid or an inorganic acid. As the alkaline earth metal constituting the salt,
Be, Mg, Ca, Sr, Ba and the like are mentioned, and of these, Mg and Ca are preferably used. Examples of the acid that forms a salt include inorganic acids such as hydrochloric acid, nitric acid and hydrogen bromide; and organic acids such as acetic acid, gluconic acid, benzoic acid and lactic acid.

The salts obtained by appropriately combining these alkaline earth metals and inorganic acids are specifically BeCl ₂ , Be (NO
₃ ), BeBr ₂ , Be (CHCOO) ₂ , Be (C ₆ H _{11
O 7) 2, Be (C} 6 H 5 COO), Be (C 3 H 5 O 3) Be salt ₂ such _{as; CaCl 2, Ca (NO 3} ), CaBr 2, C
a (CH ₃ COO) ₂ , Ca (C ₆ H ₁₁ O ₇ ) ₂ , Ca (C ₆
Ca salts such as H ₅ COO) ₂ and Ca (C ₃ H ₅ O ₃ ) ₂ ; MgC
l ₂ , Mg (NO ₃ ) ₂ , MgBr ₂ , Mg (CH ₃ CO
O) ₂ , Mg (C ₆ H ₁₁ O ₇ ) ₂ , Mg (C ₆ H ₅ CO
O) ₂ , Mg (C ₃ H ₅ O ₃ ) _{2 and} other Mg salts; SrCl ₂ , S
r (NO ₃ ), SrBr ₂ , Sr (CH ₃ COO) ₂ , Sr
(C ₆ H ₁₁ O ₇ ) ₂ , Sr (C ₆ H ₅ COO) ₂ , Sr (C ₃
Examples thereof include Sr salts such as H ₅ O ₃ ) ₂ . In particular, when the adsorbent of the present invention is used for a water purifier, magnesium chloride (MgCl ₂ ), calcium chloride (CaCl ₂ ), and calcium lactate [C] which are recognized as food additives.
It is preferable to use at least one selected from the group consisting of a (C ₃ H ₅ O ₃ ) ₂ ]. Further, if HAP used in this case is also tricalcium phosphate that has been conventionally used as the above-mentioned food additive, an adsorbent for a water purifier with further improved safety can be realized.

The content of the alkaline earth metal salt in the HAP of the present invention is preferably about 0.05 to 10% by mass. That is, when the content thereof is less than 0.05% by mass, the strength of the granules decreases (20% or more based on the granule strength evaluation criteria described later), and when used as an adsorbent,
There is a tendency for the water resistance to increase due to pulverization early with time. On the other hand, if the content exceeds 10% by mass, not only the effect is saturated, but also the strength of the granules is rather lowered due to elution.

The means for incorporating the alkaline earth metal salt into HAP is not particularly limited, and a step of incorporating the alkaline earth metal salt is added at an arbitrary stage of producing the above-mentioned low crystalline HAP. You can do it.
For example, (1) synthesis of HAP from phosphoric acid and calcium hydroxide by a direct precipitation method under reaction conditions of low crystallinity, then adding an alkaline earth metal salt to form a slurry, and (2) ammonium hydrogenphosphate and chloride When synthesizing by an exchange reaction precipitation method using calcium or the like, the adsorbent composition of the present invention is adjusted to be a slurry without adding an alkaline earth metal salt separately, or (3) HAP The powder and the alkaline earth metal salt powder may be suspended in water to form a slurry and then dehydrated and dried.

The alkaline earth metal salt-containing HAP obtained as described above is granulated by an industrially employed method, for example, (a) a pulverizer or the like is combined with a sieve. The method, (b) a method of using a pan-type granulator or an extrusion granulator, and the like can be adopted, and a granular HAP having an appropriately adjusted particle size can be produced by these methods.

Whichever method is used, the state of inclusion of the alkaline earth metal salt in the adsorbent of the present invention is HA.
The particles adhere to the surface of the P particles, and the form of the adhesion may be that the alkaline earth metal salt is simply adhered to a part of the surface of the HAP particles, or the alkaline earth metal salt is coated. The entire surface of the HAP particles may be coated as a layer, or an HAP layer containing an alkaline earth metal salt on the surface of the HAP particles (alkaline earth metal salt rich HA
P layer) may be formed, and various forms of granular HAP can be produced depending on the production method.

The reason why the strength of the HAP adsorbent is improved by incorporating the above alkaline earth metal salt into HAP can be considered as follows. Possibly, the surface-potential of HAP is changed, and the water-reducing effect of decreasing the hydrophilicity occurs without changing the adsorption property.
It is considered that the strength is improved by the closer proximity of the AP particles themselves.

The average particle size of the granules can be adjusted arbitrarily by the above method, but the average particle size of the adsorbent used in the water purifier is preferably 50 μm or more and 30 mm or less. That is, when the granules are less than 50 μm, the water resistance becomes large, which makes them unsuitable as an adsorbent used in a water purifier, and when the average particle size exceeds 30 mm, the packing rate per volume is small and the adsorption efficiency is poor. Therefore, the performance itself as a water purifier will decrease. Further, in general, when used in a water purifier, it is often used in combination with powdered or granular activated carbon or fibrous activated carbon, and in such a case, when the difference in particle size distribution becomes large, the dispersion state deteriorates,
It is suitable that it is 100 μm or more and 1 mm or less.

The granular HAP of the present invention has a specific surface area of about 30 to 70 m ² / g and is porous,
By having such a large specific surface area, excellent adsorption performance is exhibited. On the other hand, the specific surface area is relatively small in the case of firing at a high temperature or in the case of using a granulating agent, but this is also considered to be related to the deterioration of the adsorption performance.

By filling the adsorbent as described above, a useful water purifier cartridge can be realized. When the adsorbent is used in a water purifier, it is possible to use only the HAP containing an alkaline earth metal salt as described above, but if necessary, a carrier such as activated carbon or ion exchange resin for removing malodorous substances and softening water. You may use it by mixing with. When such a carrier is used, the mixing ratio of HAP may be appropriately set according to the type of the carrier. For example, when activated carbon is used as the carrier, the mixing ratio of HAP is about 0.5 to 50% by mass. Is preferred. That is, when the mixing ratio of HAP is less than 0.5% by mass, the function as an adsorbent is lowered, and when it exceeds 50% by mass, the amount of the carrier is relatively small and the function as the carrier cannot be exhibited.

Hereinafter, the adsorbent of the present invention will be described in more detail with reference to Examples. However, the following Examples are not of a nature limiting the present invention, and the design may be changed in view of the above-mentioned and the following points. Any of these are included in the technical scope of the present invention.

[0035]

Example 1 Production Example 1 To 700 g of ion-exchanged water, 300 g of tricalcium phosphate for food additives (manufactured by Taihei Chemical Industry) and 3 g of calcium lactate (manufactured by Taihei Chemical Industry) were added and stirred, and then filtered with a nutsche. 517 g of the dehydrated cake (solid content 58
%) And dried in a dryer at 150 ° C. for 5 hours to obtain 297 g.
A dried product of The obtained dried product was crushed using a mortar and then, using a standard mesh of 42 mesh and 100 mesh, granules of 350 to 150 μm were obtained.

Production Example 2 In 750 g of ion-exchanged water, 250 g of hydroxyapatite (manufactured by Taihei Kagaku Sangyo) and 0.5 of calcium chloride (reagent)
4 g obtained by adding g and stirring, and then filtering through Nutsche
61 g of dehydrated cake (54% solids) was dried in a dryer.
After drying at 50 ° C. for 5 hours, 246 g of a dried product was obtained. The obtained dried product is crushed in a mortar and then 350-150 μm using a standard mesh of 42 mesh and 100 mesh.
Granules of m were obtained.

Production Example 3 To 750 g of ion-exchanged water, 250 g of tricalcium phosphate for food additives (manufactured by Taihei Kagaku Sangyo Co., Ltd.) was added and stirred, and then 621 g of dehydrated cake (solid content was obtained by filtering through a Nutsche. 40%) was dried at 150 ° C. for 5 hours in a dryer to obtain 249 g of a dried product. The obtained dried product was crushed using a mortar and then, using a standard mesh of 42 mesh and 100 mesh, granules of 350 to 150 μm were obtained.

Production Example 4 A dehydrated cake produced in the same manner as in Production Example 3 was heated to 1200 using a baking furnace (“Superburn” manufactured by Motoyama).
The product was baked at 1 ° C for 1 hour to obtain a baked product. The fired product obtained is
After crushing using a mortar, standard granules of 42 mesh and 100 mesh were used to obtain granules of 350 to 150 μm.

Production Example 5 Using a pan-type granulator, while spraying 1 kg of a liquid prepared by adding 1% of an acrylic emulsion as a granulating agent to ion-exchanged water, a food additive tricalcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.) After adding 2 kg and rotating and granulating, it was dried at 150 ° C. for 5 hours in a dryer. The obtained granules were heated to 350-15 using standard meshes of 42 mesh and 100 mesh.
Granules of 0 μm were obtained.

Example 1 Using the HAP granules obtained in each of the above production examples and granular activated carbon (manufactured by Taihei Chemical Industry Co., Ltd., particle size: 250 to 500 μm), these were treated with HAP: activated carbon = 20: 80 (mass ratio). Using the samples mixed in (No. 1 to 5 in Table 1 below), a water flow test and an adsorption test were performed under the following conditions. At this time, the specific surface area of each HAP granule was measured by the nitrogen adsorption BET method, and the low crystallinity and strength of the granule were also evaluated by the following methods.

(Water flow test) Each sample was packed in a packed column having a diameter of 60 mm and a length of 100 mm, and water was flowed at a primary pressure of 0.1 MPa to 1000 L.
The flow rate (water flow rate) was measured when (liters) was passed.

(Adsorption test) The above packed tower was filled with a sample,
Water containing 50 ppb lead ions was flowed at a water flow rate of 1 L / min, and the residual lead ion concentration in the drained water at the time of 1000 L water flow was quantified by flameless atomic absorption spectrometry, and the adsorption performance of each sample Was evaluated.

(Evaluation of low crystallinity) In powder X-ray diffraction, 2θ = 25.878 °, plane spacing (d) = 3.44Å (h
Full width at half maximum (FWHM; fu in the diffraction line of kl = 002)
ll width at half maximum) was measured, and a case of 0.2 ° or more was evaluated as low crystallinity, and a case of less than 0.2 ° was evaluated as high crystallinity.

(Evaluation of granule strength) 80 ml of methanol
After weighing 0.02 g of HAP granules therein and performing ultrasonic treatment for 30 seconds while stirring with a magnetic stirrer, the proportion (mass%) of particles of 150 μm or less was measured with a laser diffraction particle size distribution analyzer ( Shimadzu Corporation), and the one with the smaller ratio was evaluated as high strength.

The results are shown in Table 1 below, and those satisfying the requirements specified in the present invention (Nos. 1 and 2) are as follows.
It can be seen that, while exhibiting good water permeability, it is also excellent in adsorption performance and has sufficient strength.

On the other hand, it can be seen that in the case of lacking any of the requirements defined in the present invention (Nos. 3 to 5), any of the characteristics is deteriorated. That is, No. No. 3 does not contain an additive and is excellent in adsorption performance due to low crystals, but its strength is insufficient.
In addition, No. In No. 4, the strength is remarkably improved by firing, but the crystallinity is high and the adsorption characteristics are deteriorated, and the residual lead Pb concentration is increased. Furthermore, N
o. No. 5 has a granular shape by using a granulating agent and is good in terms of strength and water permeability, but the specific surface area is extremely small due to the coating of the particle surface, Adsorption characteristics are significantly reduced.

[0047]

[Table 1]

[0048]

INDUSTRIAL APPLICABILITY The present invention is constituted as described above, and is a granular adsorption having an excellent adsorption performance for heavy metals and having sufficient strength to stably exhibit this excellent adsorption performance for a long period of time. By obtaining the material, and filling the adsorbent with a cartridge for a water purifier, it is possible to realize a water purifier capable of exhibiting excellent adsorption performance for heavy metals over a long period of time.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuyuki Matsuda             247-1 Kujo-cho, Yamatokoriyama-shi, Nara Press             TE Ichibankan No.601 F-term (reference) 4D024 AA02 AB17 AB18 BA02 BA11                       BA12 BB01 BB05 BB06 CA04                 4G066 AA05C AA17A AA17B AA18A                       AA18B AA50A AA50B AA51A                       AB23A AE10C BA26 BA31                       BA38 CA46 CA47 DA07 FA05                       FA21 FA22

Claims (6)

[Claims] 1. An adsorbent for adsorbing and removing heavy metals in water, which is made of low crystalline hydroxyapatite containing an alkaline earth metal salt and is formed into a granular shape. Adsorbent for heavy metals. 2. The heavy metal adsorbent according to claim 1, wherein the alkaline earth metal salt is one or more selected from the group consisting of magnesium chloride, calcium chloride and calcium lactate. 3. The content of the alkaline earth metal salt is 0.
The heavy metal adsorbent according to claim 1 or 2, which is from 05 to 10 mass%. 4. The adsorbent according to claim 1, wherein the heavy metal is at least one selected from the group consisting of Pb, Cd and Hg. 5. A granular average particle size of 50 μm or more and 30 m
The adsorbent according to any one of claims 1 to 4, which is m or less. 6. A water purifier cartridge filled with the adsorbent according to claim 1.