JP2000024658A - Dephosphorizing agent for water and method for removing phosphorus and regeneration thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain about >90% dephosphorizing rate even for raw water having such a low concn. of phosphorus dissolved as about 1 ppm phosphorus concn., and to provide an nontoxic dephosphorizing agent and dephosphorizing method by which the dephosphorizing agent is easily regenerated and phosphorus is easily recovered. SOLUTION: This dephosphorizing agent of phosphorus dissolved in water contains hydrotalcite expressed by the formula of M2+1-xM3+x(OH)2An-x/nmH2O as an effective component. Also the regenerating method of the dephosphorizing agent and the recovering method of phosphorus are provided. In the formula, M2+ is at least one kind of bivalent metal, M3+ is at least one kind of tervalent metal, An- is SO42- or Cl-, and (x) and (m) satisfy 0<x<0.5 and 0<=m<2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an agent for removing phosphate ions dissolved in water which causes eutrophication, to recover the removed phosphate ions, and to a method for regenerating the phosphorus remover.

[0002]

BACKGROUND OF THE INVENTION Increasing concentrations of phosphorus and nitrogen in water result in reduced eutrophication. In other words, algae proliferate and emit toxins, clog waterways, spoil landscapes, reduce species, and dehydrate water. Since the nitrogen content of rivers is replenished by special nitrogen-fixing bacteria and lightning, even if nitrogen is artificially removed, it is only temporary and it is difficult to remove nitrogen substantially. Therefore, it is phosphorus dissolved in water that controls eutrophication, and the phosphorus concentration affects the eutrophication. Most of this phosphorus exists in the ionized form of phosphoric acid (H ₃ PO ₄ ). In order to remove phosphorus dissolved in water, various phosphorus removing agents as described below have been proposed.
Such dephosphorizing agents are metallic iron fibers, metallic aluminum, activated carbon, aluminum hydroxide, iron hydroxide, activated sludge, mussels, clay and the like. However, the conventional phosphorus removing agent has a phosphorus removal rate of about 50% or less, which is insufficient to prevent eutrophication. Further, in the conventional dephosphorizing agent, slime is generated from about 2 days after the passage of raw water, and the dephosphorizing activity is reduced.

[0003]

The dephosphorization rate, which is a drawback of the conventional dephosphorizing agent, is as low as about 50%.
% Dephosphorization rate is about 1 ppm in terms of phosphorus (PO ₄ -P)
To achieve even low concentrations of phosphorus-dissolved raw water,
Furthermore, it is easy to regenerate the phosphorus-removing agent and can recover phosphorus. Therefore, there is no need to dispose of the phosphorus-removing agent, and even if it is disposed, it is safe, non-toxic and does not cause environmental destruction. There is a strong desire to provide a phosphorus agent and a method for dephosphorization. Further, a dephosphorizing agent which does not affect slime is desired. An object of the present invention is to provide a novel dephosphorizing agent which satisfies the above-mentioned various requirements and a method for removing phosphorus including recovery of phosphorus and regeneration of the dephosphorizing agent.

[0004]

According to the present invention, there is provided a compound represented by the following formula (1): M 2 ⁺ _{1 -x} M ³⁺ _x (OH) _{2 An} ^- _{x / n} · mH ₂ O (1) ²⁺ is at least one of divalent metals such as Mg ²⁺ , Zn ²⁺ , Cu ²⁺ , preferably Mg ²⁺ , and M ³⁺ is Al
^3+, at least one trivalent metal Fe ^3+, etc., preferably Al ^3+, A ^n-is SO ₄ ^2-or Cl ^-, preferably SO
₄ represents ^2- , wherein x and m each represent a number satisfying the following range: 0 <x <0.5, preferably 0.2 ≦ x ≦
0.4, 0 ≦ m <2, x / n is about 20 to 30
% Of which may be increased to about 0.1%) as an active ingredient. In the present invention, the compound of the above formula (1) is represented by the following formula (2): Mg _1-x Al _x (OH) ₂ (SO ₄ ) _{x / 2} · mH ₂ O (2) 0.1 <x <0.5, preferably 0.2 <x <, representing a number satisfying the following range:
0.4, 0 ≦ m <2, preferably 0 <m <2) Provided is a phosphorus-removing agent represented by hydrotalcites. The present invention further provides a dephosphorizing agent wherein the hydrotalcites are granulated in a spherical or columnar shape having a minor axis of at least 1 mm or more. The present invention further provides (A)
Raw water is passed through the packed bed of the hydrotalcites,
A dephosphorization step of ion-exchanging ^An- with phosphate ions,
(B) An aqueous solution of an alkali metal carbonate or ammonium carbonate is passed through a packed bed of the hydrotalcites whose dephosphorization capacity has reached saturation, and the captured phosphate ions are CO ₃
Step of recovering by ion exchange in ^2- , (C) at least p
H1 contacting the above aqueous solution of sulfuric acid or hydrochloric acid, A ^n-is a hydrotalcite became carbonate ion exchanged ions and sulfate ions or hydrochloric ion, step of regenerating the hydrotalcite of formula (1) And a method for regenerating a phosphorus removing agent.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Among the hydrotalcites of the formula (1), the following formula (2) or (3): Mg _1-x Al _x (OH) ₂ (SO ₄ ) _{x / 2} · mH ₂ O (2) Mg _1-x Al _x (OH) ₂ (Cl) _x · mH ₂ O (3) (where x and m each represent a number satisfying the following range, 0.1 <x <0 .5, preferably 0.2 ≦ x ≦
0.4, particularly preferably 0.25 ≦ x ≦ 0.35, 0 ≦
It is preferable to use hydrotalcites having a composition represented by m <2, preferably 0 <m <2), and most preferably to use a compound of the formula (2). The hydrotalcites of the formula (1) including the formulas (2) and (3) are non-toxic, inexpensive, and have high dephosphorization capacity (although Mg and Al are light elements). Having. M
As a raw material for g, inexpensive seawater or the like can be used.
Both g and Al are safe and non-toxic. Even if SO ₄ ^2- and Cl ⁻ are ion-exchanged into phosphate ions and eluted in water, they do not contaminate the water. NO ₃ ^- and organic acid ions cause new water pollution. In addition, SO ₄ ^2- is more advantageous than Cl ⁻ when considering the ease of regeneration, the regeneration rate, and the cost during regeneration.

A ^n- is ion-exchangeable and its amount is M
^Since it depends on the amount of ³⁺ ions, the larger x is, the higher the ion exchange capacity is, which is preferable. The greatest feature of the present invention is that the conventional dephosphorizing agent is a reaction between phosphoric acid and a metal,
In ion exchange, addition A ^n- is SO ₄ ^2- or Cl ^-, and particularly preferably it SO ₄ ^2-. The second feature is
Washing (ion exchange) with Na ₂ CO ₃ etc. followed by H
_The regeneration method comprises washing (ion exchange) with ₂ SO ₄ or HCl. CO such as Na ₂ CO ₃ and K ₂ CO ₃ which has higher selectivity than phosphate ion and enables the next regeneration
By washing with ₃ ^2- ions efficiently phosphate ions can be recovered in a very reused easily form. Furthermore, the pH of H ₂ SO ₄ or HCl is 1 or more, preferably pH
1-4, more preferably by contacting with an aqueous solution of pH 2-3, A ^n-is SO ₄ ^2-or Cl ^- can be easily and economically to play the compound of formula (1).
In particular, regeneration with an aqueous solution of H ₂ SO ₄ is economical because it has a higher regeneration rate than HCl and requires only half the number of moles of HCl because of the required number of equivalents. Moreover, the present inventor has found that A ^n-
SO ₄ ^2-is, 2 Ataikage no less only 1 dianion in ion was first discovered easily be ion-exchanged with phosphate ions. By reaction with H ₂ SO ₄ or HCl, CO ₃ ^2- is H ₂ CO ₃ becomes a A ^n-, A ^n- is S
It is ion-exchanged to O ₄ ^2- or Cl ⁻ . The discovery of this reaction is also one of the features of the present invention. H ₂ CO ₃ continues to be CO
₂ and H ₂ O. Furthermore, it has been found that the dephosphorizing agent of the present invention does not affect the dephosphorizing activity of slime. Although the reason is not necessarily clear, the dephosphorization reaction of the dephosphorizing agent of the present invention is ion exchange, and the conventional dephosphorizing agent is
This is probably because the reaction mechanism is different.

The compound of the formula (1) can be synthesized by a conventionally known method. For example, reacting a mixed aqueous solution of magnesium hydroxide and aluminum sulfate or a mixed aqueous solution of magnesium chloride and aluminum chloride with an alkali such as sodium hydroxide at a pH of about 8 or more, preferably at a pH of 9 or more under stirring. Can be obtained by

[0008] The dephosphorizing agent of the present invention can also be used in powder form. However, in consideration of advantages such as elimination of the solid-liquid separation step and labor saving, it is preferable to use granules having a short diameter of 1 mm or more, preferably 3 to 7 mm, in a spherical or cylindrical shape. Granulation can be performed by a known granulation method. For example, known binders (clay, CM
C, diatomaceous earth, boehmite, activated alumina, etc.) with or without the addition of a hydrotalcite powder of the formula (1) using a kneader or the like, while gradually adding an appropriate amount of water under kneading and kneading sufficiently. The mixture can be extruded into a strand having a desired diameter by using an extruder, and then granulated by a method of sizing with a marmellaizer and drying. Preferably, no binder is added. When added, the binder is used in an amount of about 5 to 100 parts by weight of the hydrotalcite sieve of the formula (1).
30 parts by weight.

The method of contacting the dephosphorizing agent with raw water is represented by the following formula (1)
Is packed in a column or a nonwoven fabric, and water is passed through the column in an upward flow, downward flow or horizontal flow. The contact time with water is from about 1 minute to about several tens of hours. Preferably, it is about 5 to 60 minutes.

After the dephosphorizing ability of the hydrotalcites reaches saturation, phosphorus is desorbed and recovered. This is Na
An aqueous solution of ₂ CO ₃ , K ₂ CO ₃ or (NH ₄ ) ₂ CO ₃ , preferably an aqueous solution of Na ₂ CO _{3 is} passed through at least the equivalent of phosphate ions, preferably 1.5 to 2 equivalents. Do it. Phosphorus is recovered as Na, K or NH ₄ salts of phosphoric acid. The recovered phosphorus can be reused. Then, about 0.5 mol / H ₂ SO ₄ or HCl
An aqueous solution of up to about 1 mol, preferably up to about 0.2 mol / l, is brought to a pH of about 1 or more, preferably about 2 mol / l.
, More preferably about 1 to 2 equivalents, preferably about 1.5 to 2.5 equivalents to CO ₃ ^{2- in} hydrotalcite, while maintaining the pH at about 2 to 4. To the hydrotalcite. At this time, H ₂ SO ₄ or H ₂ SO ₄
Cl or the like is carried out by a method in which the dephosphorizing agent is suspended or soaked in water, and preferably added with stirring, in addition to the method in which the dephosphorizing agent is passed through the lower or upper part of the column filled with the dephosphorizing agent of the present invention. You can also.

The dephosphorizing agent of the present invention produces a large difference in performance as compared with the conventional dephosphorizing agent as the phosphorus concentration in raw water is as low as about 1 to 60 ppm (PO ₄ -P). That is, the dephosphorizing agent of the present invention is superior. For example, a phosphorus concentration of 1 ppm (P
When the raw water of O ₄ -P) is treated with the dephosphorizing agent of the present invention,
It can be reduced to 0.1 ppm or less. This 0.1
When phosphorus is removed to the ppm level, eutrophication is substantially prevented. The realization of such a low concentration, that is to say almost complete inhibition of eutrophication, has been realized for the first time by the dephosphorizing agent of the present invention. The dephosphorizing agent of the present invention is represented by Formula 1.
It can also be used as a 00 mm molded body by standing on a river or pond.

Hereinafter, the present invention will be described in detail with reference to examples. Example 1 2 kg of commercially available hydrotalcites (Mg _0.67 Al _{0.33
(OH) 2 (CO 3)} 0.165 · 0.5H 2 O, a BET specific surface area of 89m ² / g) powder, 0.05 mol / l H ₂
The solution was added to 80 liters of an aqueous SO ₄ solution with stirring, and stirring was continued for 1 hour. Then, filtration, washing with water, and drying (about 120 ° C,
150 hours). As a result of chemical analysis of the dried product, the chemical composition was as follows. Mg _0.67 Al _0.33 (OH) ₂ (SO ₄ ) _0.148 (CO ₃ )
_0.018・ 0.36H ₂ O After 2 kg of the dried product was pulverized by an atomizer, the mixture was put into a kneader and kneaded for about 20 minutes while gradually adding 1.95 kg of water. The kneaded material was taken out, and a strand having a diameter of 3 mm was formed using a pre-press type extruder. This strand is put into a marmellaizer, and it is about 30 seconds, about 50 g of SO.
Type ₄ non-granulated dry powder of the present invention was sprinkled and dried. As a result, a cylindrical granule having a minor axis of about 3 mm and a major axis of about 5 mm was obtained. About 500 cc of this granulated product is
The column was packed into a column having a length of 7 mm and a length of 120 cm. Raw water in which 0.6-1 ppm of phosphorus is dissolved in terms of PO ₄ is dissolved in this column by using a metering pump,
Water was passed from the bottom of the column continuously for 20 days at a flow rate of 42 ml / min (SV = 5, contact time 12 minutes). The phosphorus concentration of the treated water coming out of the upper part of the column was measured with an absorptiometer. The phosphorus concentration in the treated water is measured once a day,
In PO ₄ conversion, was 0.05~0.1ppm. Therefore, the removal rate of phosphorus reached 90 to 95%. From the second day, slime was formed on the surface of the granules, but did not affect the dephosphorization rate.

Example 2 A mixed aqueous solution of magnesium sulfate and aluminum sulfate (M
g ²⁺ = 1.5 mol / l, Al ³⁺ = 0.5 mol / l) and 4 mol / l of sodium hydroxide were placed in a reaction vessel having a capacity of 2 liters for about 100 The reaction was carried out at a temperature of about 40 ° C. while maintaining the pH at about 9.5 with stirring and feeding at a rate of milliliter / min. The reaction product was filtered, washed with water and dried. The chemical composition of this product was as follows. Mg _0.75 Al _0.25 (OH) ₂ (SO ₄ ) _0.13・ 0.46H
₂ O 2 kg of this powder was operated in the same manner as in Example 1, and after kneading,
A strand having a diameter of 5 mm was prepared by a pre-pressing extruder. This strand is not dried with a marmellaizer,
Treated for about 20 seconds and dried. As a result, a columnar granule having a minor axis of 5 mm and a major axis of 7 mm was obtained. 100g of this granulated material
Was packed in a column having an inner diameter of 20 cm and a total length of 40 cm, and tap water in which phosphorus was dissolved at 10 ppm in terms of PO ₄ was supplied at a flow rate of 20 ml / min (SV = 2.4, contact time 25
Min), water was passed from the lower part of the column with a metering pump. As a result of passing water continuously for 30 days, the phosphorus concentration of the treated water was 0.1 to 0.2 ppm as a result of concentration measurement once a day, and the removal rate exceeded 90%.

Comparative Example 1 500 cc of stainless steel fiber having a diameter of 0.1 mm was packed in the same column as in Example 1, and water was passed in the same manner as in Example 2. As a result, the phosphorus concentration of the treated water was PO _{4 for} 6 days.
It was 4 to 6 ppm in terms of ^2- , but on the seventh day, the phosphorus concentration was almost the same as that of the raw water.

Example 3 The flow of water was further continued in Example 1, and since saturation reached on the 125th day, the flow of raw water was stopped, and a 0.2 mol / L aqueous solution of Na ₂ CO ₃ was pumped with a metering pump. A total of 2 liters were passed from the bottom of the column at a flow rate of 2 ml / min. The total phosphorus amount of the water discharged from the upper part of the column was measured.
As a result, it was 0.39 mol in terms of PO ₄ . Then 0.0
10 liters of a 4 mol / l H ₂ SO ₄ aqueous solution was supplied from the lower part of the column by a metering pump at a flow rate of 20 ml / min. Thereafter, about 10 g of the dephosphorizing agent of the present invention was taken out of the column, washed with water, dried, and then subjected to chemical analysis. As a result, the chemical composition was as follows. Mg _0.67 Al _0.33 (OH) ₂ (SO ₄ ) _0.16 (CO ₃ )
To _0.05 · 0.32H ₂ O reproduced invention dephosphorization agent, in the same manner as in Example 1 again PO
Raw water in which 1 ppm of phosphorus in ₄ conversion was dissolved was passed continuously for 20 days. As a result, the treated water was 0.01% in terms of PO _4.
It was removed in the range of ｐｐｍ0.1 ppm.

Example 4 2 kg of the same commercially available hydrotalcite powder as used in Example 1 was stirred and dispersed in 10 liters of water.
To this system was added, with stirring, 4 liters of an aqueous 0.5 mol / l HCl solution while maintaining the pH of the system at about 3 or higher.
Then, it was filtered, washed with water, dried and pulverized. As a result of chemical analysis of the dried powder, the chemical composition was as follows. Mg _0.67 Al _0.33 (OH) ₂ Cl _0.30 (CO ₃ ) _0.02
0.43H ₂ O This dry powder was treated in the same manner as in Example 1 to obtain a short diameter of 3 m.
m, and granulated into a column having a major axis of 5 mm. This granulated material 100
The cc was subjected to a phosphorus removal test under the same conditions as in Example 2. As a result, phosphorus was dephosphorized to a concentration of 0.01 to 0.1 ppm on the 15th day, and the concentration gradually increased from the 16th day to 1.0 ppm on the 20th day.

[0016]

According to the present invention, a dephosphorization rate of about 90% or more can be achieved even with a low concentration of about 1 ppm of phosphorus-dissolved raw water, and the dephosphorizing agent can be easily recycled and used. Provided are a dephosphorizing agent which is nontoxic itself and can recover phosphorus, and a method for regenerating the dephosphorizing agent.

Claims (4)

[Claims] 1. The following formula (1): M ²⁺ _1−x M ³⁺ _x (OH) _{2 An} ⁻ _{x / n} · mH ₂ O (1) (where M ²⁺ is Mg ²⁺ , Zn ^2+, at least one divalent metal Cu ^2+, etc., M ³⁺ is, Al ^3+, at least one trivalent metal Fe ^3+, etc., a ^n-is SO ₄ ^2-or It represents Cl ⁻ , and x and m each represent a number that satisfies the following range, and is characterized by using hydrotalcites represented by 0 <x <0.5, 0 ≦ m <2) as an active ingredient. Remover of phosphorus dissolved in water. 2. The compound of the formula (1) is represented by the following formula (2): Mg _1-x Al _x (OH) ₂ (SO ₄ ) _{x / 2} · mH ₂ O (2) (where x and m are The hydrotalcites represented by 0.1 <x <0.5, 0 ≦ m <2) each representing a number satisfying the following ranges, and are dissolved in water according to claim 1. A phosphorus remover. 3. The agent for removing phosphorus dissolved in water according to claim 1, wherein the hydrotalcites are granulated into a sphere or a column having a minor axis of at least 1 mm or more. . 4. A (A) dephosphorization step in which raw water is passed through the packed bed of hydrotalcites according to claim 1 to ion-exchange ^An- with phosphate ions, and (B) a dephosphorization ability is saturated. Passing an aqueous solution of an alkali metal carbonate or ammonium carbonate through the packed bed of the hydrotalcites that has reached the above, and recovering the trapped phosphate ions by ion exchange with CO ₃ ^2- , (C) at least contacting an aqueous solution of sulfuric acid or hydrochloric acid having a pH of 1 or more, and ion-exchanging carbonate ions with sulfate ions or hydrochloric acid ions to regenerate hydrotalcites of the formula (1). Removal and regeneration of dephosphorizer.