JPH0818026B2 - Ion removing material and method for removing ions in water using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is effective for trace amounts of phosphate ions (also referred to as PO ₄ ^3- ions) contained in sewage, various wastewater, biologically treated water of sewage, water such as dams, lakes and rivers. The present invention provides a new crystallization dephosphorization material that can be adsorbed and removed selectively, and also provides a new substance that removes ions such as fluorine and heavy metals in water.

[0002]

2. Description of the Related Art Phosphate ions (PO ₄ ^3- ions) are described below.
Will be described as an example. A crystallization dephosphorization method for removing phosphate ions in water has been conventionally known. In the crystallization dephosphorization method, Ca ²⁺ ions and OH ⁻ ions are added to water containing PO ₄ ³⁻ ions as needed, and this water is used as a seed crystal (phosphorus ore, bone charcoal, etc.) that serves as a nucleus for hydroxyapatite crystal purification. consisting essentially) and the contacting crystallization reaction of hydroxyapatite proceeds at the surface of the seed crystal, a dephosphorylation method utilizing a phenomenon that PO ₄ ^3- ions in the water are removed. (Ions such as fluorine and heavy metals are also removed.)

This crystallization dephosphorization method has a great feature that sludge is hardly generated, but since the following drawbacks cannot be overcome, it has not been put into practical use. Since phosphorus ore is used as seed crystals, complicated accompanying work such as importing, sieving, and filling of the ore into the equipment is required. Therefore, the labor cost is inevitably increased. For raw water with high alkalinity (sewage is an example), acid is added in advance and the pH is adjusted to 4.5, air stripping is performed, and the alkalinity component is discharged as carbon dioxide (CO ₂ ) to the outside of the system. I have to let you. As a result, the cost of acid and aeration power for air strips increase, further increasing the cost of dephosphorization.

When the raw water contains a large amount of SS, the SS must be filtered by previously providing a filtration device before the crystallization dephosphorization step. Otherwise, SS will adhere to the surface of the dephosphorization material (phosphorus ore) and hinder the crystallization reaction.
If crystallization dephosphorization is operated in a fluidized bed instead of a fixed bed, SS
Since it does not adhere to the surface of the dephosphorization material, the previous filtration step is unnecessary, but since the specific gravity is large, it is necessary to increase the rising water flow in order to operate the phosphate rock as a fluidized bed.
Therefore, the power cost will increase.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems (1) to (3). Specifically, 1. Eliminates the need to import, screen, and transport ion removal materials such as dephosphorization materials to the site. 2. It significantly facilitates the filling of the ion removing device with the ion removing material. 3. Eliminates the decarbonation step. 4. The power to maintain the fluidized bed is significantly reduced. The purpose is to achieve the task.

[0006]

The above object can be achieved by a method for removing ions in water using the ion removing material of the present invention. That is, (1) an ion removing material comprising a superabsorbent polymer, wherein hydrogel particles that swell in water and exhibit elasticity retain a calcium phosphate compound solid phase. (2) A method for removing ions in water, which comprises contacting the ion removing material according to (1) with water to remove the ions in the water. Is.

That is, according to the present invention, the conventional crystallization dephosphorization material (phosphorus ore, bone charcoal, etc.) is used in place of the above, instead of the hydrogel particles of the superabsorbent polymer, a calcium phosphate compound solid phase such as hydroxyapatite is solid phased. This is a technique in which a material holding the above is used as a seed crystal of the crystallization dephosphorization method.

Also in the case of removing the fluorine ion, if the water containing the fluorine ion and the fluorine removing material in which the solid phase of the calcium phosphate compound such as hydroxyapatite is held inside the hydrogel particles of the present invention are brought into contact with each other, the phosphate ion can be removed. Fluorine ions are removed by the same mechanism as the removal of (PO ₄ ^3- ions). That is, the fluorine ion is removed as a result of exchanging the fluorine ion with the phosphate group (PO ₄ ^3- group) of the hydroxyapatite in the hydrogel.
Further, the heavy metal ions are also removed by replacing the Ca ²⁺ ions with the heavy metal ions in the water. That is, heavy metals (Hg, Ag, Cr, Cu, Ni, Co, Fe, Mn,
Ions (Zn, Pb, Cd, etc.) are also removed by contact with the hydrogel composite type ion removing material of the present invention.

(Function) A superabsorbent polymer means that when it is put into water, it absorbs an extremely large amount of water (100 to 400 of its own weight).
A polymer that absorbs twice as much water) and swells remarkably to form a hydrogel, which is a substance that has been widely used in the field of conventional diapers. Super absorbent polymers are hydrophilic macromolecules, but there are two types: one that absorbs water to form a paste-like hydrogel, and one that forms an elastic hydrogel (shaped hydrogel particles). Water that cannot be separated by filtration cannot be separated into water, but a hydrogel with high strength that maintains its unique shape and exhibits elasticity (that is, that that exhibits finite swelling) is water that is not absorbed by the gel when made into particles. Can be easily separated by filtration. The superabsorbent polymer used in the dephosphorizing material or the fluorine removing material of the present invention is of a kind that becomes a hydrogel having elasticity and high elasticity.

That is, the "hydrogel particles" referred to in the present invention which are swollen in water and exhibit elasticity are the following:
It means a hydrogel particle that reversibly returns to its original shape when the external force disappears again after being deformed by an external force or when it is deformed, or when it swells due to water absorption, and the shape of each particle is not necessarily the same. The size of the hydrogel particles, that is, the ultimate swelling degree, depends on the degree of cross-linking of the superabsorbent polymer constituting the hydrogel particles and the properties of the aqueous solution into which it is charged.
Also, the elastic strength of the hydrogel particles can be adjusted by the type of constituent polymer and the degree of swelling. Further, the hydrogels of the present invention have a property that they do not fuse or adhere to each other.

Various polymers can be used as the superabsorbent polymer used in the present invention. Particularly preferred are isobutylene and maleic anhydride copolymers, vinyl alcohol and maleic anhydride copolymers, and polyacrylic acid copolymers. A good example is coalescing. Hydrogel particles, which consist of these super absorbent polymers and become swellable elastic particles of fixed size, when the dried particles are put into an aqueous solution, the individual particles absorb a large amount of the aqueous solution and swell. It is then restored to hydrogel particles. When these hydrogel particles absorb water and swell, each particle has a fixed shape such as a spherical shape or a square shape and has high strength (particle size is on the order of several mm).
It has the property of changing to
When bringing the dephosphorizing material into contact with water containing phosphate ions,
There is an advantage that the dephosphorization material particles do not break.

The present invention consists of this superabsorbent polymer, which forms swellable elastic particles in water to form a fixed particle, and hydrophobite particles having a solid phase of calcium phosphate compound such as hydroxyapatite are used. Is a technology for removing. In order to remove phosphate ions (PO ₄ ^3- ions) in water with the dephosphorizing material of the present invention,
Basically, the same operation as in the conventional crystallization dephosphorization method may be performed, but the decarboxylation step is unnecessary.

An example of the method for producing the dephosphorizing material and the fluorine removing material of the present invention will be described in detail below. (Manufacturing method of dephosphorization material or fluorine removal material) The super absorbent polymer powder (or granules) in a dry state is
Add and disperse in an aqueous solution of calcium chloride (CaCl ₂ ). A few minutes later, hydrogel particles (particle diameter of about 2 to 4 mm) of a superabsorbent polymer that has absorbed the calcium chloride aqueous solution are generated. Next, the hydrogel particles incorporating the calcium chloride aqueous solution are immersed in an alkaline aqueous solution of Na ₃ PO ₄ (pH 9 to 10) for several hours to 24 hours. As a result, 10Ca ²⁺ + 6PO ₄ ³ + 2OH ⁻ − → Ca ₁₀ (OH) ₂ (PO ₄ ) ₆ ↓ {Ca ₁₀ (OH) ₂ (PO ₄ ) ₆ is hydroxy in the hydrogel particles of the superabsorbent polymer. The solid phase formation reaction of apatite} proceeds, and the hydroxyapatite is retained in the hydrogel particles made of the superabsorbent polymer.

The above is one example of the method for producing the dephosphorization material or the fluorine removal material of the present invention. In the present invention, as shown in FIG. 1, superabsorbent polymer hydrogel particles 1 in which hydroxyapatite 2 is deposited and retained therein. Is a seed crystal of the crystallization dephosphorization method or the defluorination method. However, in the present invention, the dephosphorization material or the fluorine removal material may be produced not only by the method of precipitating hydroxyapatite as described above but also by the method of immobilizing hydroxyapatite in the hydrogel particles.

A typical embodiment of water treatment according to the present invention will be described below with reference to FIG. If necessary, Ca ²⁺ ions and OH ⁻ ions are added to raw water containing phosphate ions to adjust the pH to 8.5 to 9.0, and the hydrogel dephosphorization material of the present invention is brought into contact with the inside of the hydrogel particles. The crystallization reaction of apatite proceeds on the
Remove O ₄ ³⁻ ions. The method of contacting the hydrogel dephosphorization material of the present invention with the raw water is most preferably such that the raw water is caused to flow in an upward flow and brought into contact with the hydrogel dephosphorization material as an expanded bed (Expanded Bed). The expanded bed refers to an intermediate state between the fixed bed and the fluidized bed. The hydrogel dephosphorization material of the present invention has a specific gravity almost equal to that of water, and a specific gravity of 1.01 to 1.01.
It is on the order of 1.09, and the expansion layer can be formed very easily even at a low rising flow rate. Therefore, it is not necessary to provide the SS filtration device in the previous stage.

[0016]

[Example] (Example 1) 1. Manufacture of dephosphorization material or defluorination material 5g of granular superabsorbent polymer particles, which is a copolymer of isobutylene and maleic anhydride, and 5% of calcium chloride (C
aCl ₂ ) aqueous solution and dispersed for 10 minutes, the superabsorbent polymer particles absorb the CaCl ₂ aqueous solution and swell remarkably, resulting in spherical hydrogel particles (particle size 2 to 2).
About 3 mm) was obtained. The total volume of the gel was 1.1 liter. Since the volume of the superabsorbent polymer particles in the dry state was 5 g and 6 ml, it means that the particles were swollen 180 times. The hydrogel particles were separated by sieving to give 1% Na ₃
Immerse in an alkaline aqueous solution of PO ₄ (pH 9.5),
As a result of being left for 24 hours, PO was formed inside the hydrogel particles.
₄ ³⁻ ions and OH ⁻ ions were diffused, the hydroxyapatite formation reaction proceeded inside the hydrogel particles, and hydrogel particles having hydroxyapatite held inside were obtained. The following treatment was performed using this as a dephosphorization material or a fluorine removal material.

2. Removal of Phosphate Ion The hydrogel dephosphorization material was packed in an acrylic column with a diameter of 2.5 cm to a height of 30 cm, and converted into phosphorus atom of 1.3 mg.
Sewage activated sludge treated water containing 1 / liter of PO ₄ ³⁻ ions was fed from below the column in an upward flow. CaCl ₂ aqueous solution in activated sludge treated water of sewage 40 to 50 m in terms of Ca atom
g / l concentration and pH adjusted to 8.8 with NaOH.
And was supplied to a hydrogel dephosphorization material column. The hydrogel dephosphorization material became the expansion layer. The M-alkalinity of the raw water was 98 mg / liter, and in the conventional crystallization dephosphorization method using phosphorus ore as the dephosphorization material, decarboxylation was an essential water quality, but the present invention does not perform decarboxylation. The raw water was directly supplied to the hydrogel dephosphorization column.

As a result of continuous treatment for 8 months under the above conditions, the content of PO ₄ ³⁻ ions in the hydrogel dephosphorization layer effluent was always 0.2 mg / liter or less, and good results were obtained. It was Since the hydrogel dephosphorized material layer outflow water contained SS calcium phosphate, it was removed by filtration.

(Example 2) 1. Removal of Fluoride Ion Apatite-immobilized hydrogel produced by the above-mentioned production method was packed in an acrylic column having a diameter of 2.5 cm to a height of 30 cm, and tap water containing 2 mg / liter of fluoride ion was added from the bottom of the column to SV5 (1 / As a result, the fluorine ion concentration in the column effluent water was 0.
It was 08 mg / liter.

(Example 3) 1. Removal of heavy metal ions 5 g of the same apatite-immobilized hydrogel as used in the phosphate ion removal test was added to 6 mg / liter of Cr.
As a result of adding to 200 ml of water containing ⁶⁺ ions and stirring for 30 minutes, Cr ⁶⁺ ions in the treated water were not detected, and Cr ⁶⁺
It was found that the ions were effectively adsorbed.

[0021]

The present invention has the following great industrial effects. It eliminates the need for importing phosphorus ore, various transportation operations, and sieving of phosphorus ore, which greatly facilitates the production of dephosphorized materials. Crane work was required to fill the dephosphorizing material, but the dephosphorizing material of the present invention, unlike the conventional dephosphorizing material, has a specific gravity which is almost equal to that of water when used, so that it has good fluidity and can be easily pumped. It can be filled in the dephosphorization device.

Since the decarboxylation step can be omitted, the process can be significantly simplified. The reason for this is that in the conventional crystallization dephosphorization method, the apatite formation reaction proceeds only on the surface of phosphate rock or bone charcoal, whereas in the present invention, PO ₄ ³⁻ ions diffuse inside the hydrogel particles and the reaction proceeds there. It is thought that this is related to the difference. Since the dephosphorizing material of the present invention has a specific gravity which is only slightly higher than that of water during use, it can easily form an expansion layer with a slight rising flow rate of raw water, and therefore does not suffer from the disturbance of raw water SS.
Therefore, the process becomes simpler. When replacing the hydrogel dephosphorization material, apatite, which is a useful fertilizer, is incorporated inside the hydrogel particles, and when the hydrogel particles are spread on the forest or soil, it acts as a water retention forest, so the effect of two birds with one stone as a fertilizer and water retention material Therefore, the hydrogel dephosphorization material can be effectively used.

[Brief description of drawings]

FIG. 1 is a schematic diagram of superabsorbent polymer hydrogel particles containing hydroxyapatite inside.

FIG. 2 is a flow chart of a step of performing a dephosphorization treatment using the dephosphorization material of the present invention.

[Explanation of symbols]

 1 Super absorbent polymer hydrogel particles 2 Hydroxyapatite particles

Claims (2)

[Claims] 1. An ion-removing material comprising a hydrogel particle, which is made of a superabsorbent polymer and swells in water and exhibits elasticity, to hold a solid phase of a calcium phosphate compound. 2. A method for removing ions in water, which comprises contacting the ion removing material according to claim 1 with water to remove ions in the water.