JP2003088880A - Method for removing water-soluble phosphorus by using calcium sulfate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treating agent for phosphorus-containing water. SOLUTION: The treating agent contains calcium sulfate or contains calcium sulfate and an iron compound. The method for treating water containing phosphorus is carried out by using the above agent. By the above method and by the treating agent, phosphorus can be efficiently removed and wastes can be effectively used.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a treatment agent for phosphorus-containing water and a treatment method using the same.

[0002]

2. Description of the Related Art Inorganic phosphates contained in fertilizers, synthetic detergents, etc. discharged into lakes, rivers, and oceans, and water-soluble phosphorus such as organic phosphates contained in human waste, etc. cause eutrophication. Therefore, a method for efficiently and economically removing water-soluble phosphorus is demanded. Until now, calcium hydroxide has been widely used as a method for removing phosphorus in water using a calcium-based treating agent. However, since calcium hydroxide has a low phosphorus removing ability and is in the form of fine powder, there is a problem that it is difficult to handle, for example, unreacted ones are difficult to filter and separate.
On the other hand, in recent years, a treating agent containing calcium sulfate such as gypsum has been produced in large quantities as a by-product in the desulfurization process of exhaust gas or the neutralization process of various waste acids. In addition, a large amount of construction materials such as gypsum board are discharged as waste, and the development of an effective use method as a calcium source is an urgent issue.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a treatment agent for phosphorus-containing water which is excellent in the ability to remove phosphorus from phosphorus-containing water and which is economically advantageous, and a method for treating phosphorus-containing water using the same. This is an issue.

[0004]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors, the treating agent containing calcium sulfate has an excellent phosphorus-removing ability under an alkaline condition of at least pH 8. The present invention has been completed by finding that a treating agent containing an iron compound in addition to this has a further excellent phosphorus removing ability.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a phosphorus-containing water treatment agent for use at a pH of at least 8, characterized by containing calcium sulfate. The phosphorus-containing water to be treated is water in which phosphorus is dissolved, and examples thereof include domestic wastewater, agricultural wastewater, and water in natural environments such as lakes, rivers, and oceans into which the wastewater flows. The calcium sulfate used in the present invention includes calcium sulfate dihydrate (dihydrate gypsum),
Calcium sulfate hemihydrate (hemihydrate gypsum), anhydrous calcium sulfate (anhydrite) and mixtures thereof are included, and any of these may be used. Calcium sulfate has a large particle size and is easy to handle. However, the form of the treatment agent can be various forms such as powder, granules, and molded bodies, and can be appropriately selected according to the treatment method. Industrially, natural gypsum may be used as gypsum, but various types such as recovered gypsum produced as a by-product in the desulfurization treatment of exhaust gas and waste of gypsum-based construction materials such as gypsum board can be widely used. Therefore, the present invention also contributes to the reuse of waste. These wastes, for example, the recovered gypsum has a large particle size and is easy to handle, and may be used as it is, or may be in various forms such as powder, granules, and molded bodies. It may be crushed before use.

Next, the present invention relates to a method for treating phosphorus-containing water, which comprises contacting phosphorus-containing water with the above treating agent while maintaining the pH at at least 8 to produce a calcium phosphate precipitate, and then treating the precipitate. It is characterized by being separated from water. In order to form a precipitate of calcium phosphate by contacting the phosphorus-containing water with the treatment agent while maintaining the pH at least 8, (1) adding an amount of an alkali having a pH of at least 8 after treatment to the phosphorus-containing water After that, a powdery or granular treatment agent is added to produce calcium phosphate precipitates, or (2) a powdery or granular treatment agent is added to phosphorus-containing water, and then alkali is added to adjust the pH. While maintaining at least 8, precipitate of calcium phosphate is generated, or (3) after adding an amount of alkali having a pH of at least 8 after treatment to water containing phosphorus, for example, using a molded treating agent as a fixed layer, It is possible to use a method in which a substance is brought into contact with phosphorus-containing water to form a precipitate of calcium phosphate. When the pH becomes lower than 8 during the treatment, an alkali may be appropriately added during the reaction so as to maintain the pH at at least 8. As the alkali used for pH adjustment, various alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide, ammonium compounds and alkali metal carbonates can be used. ,
It is preferable to use various alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Further, since calcium hydroxide has a phosphorus removing ability as described above, calcium hydroxide may be used for pH adjustment to obtain the effect of pH adjustment and the effect of phosphorus removal at the same time. The amount of the treating agent used is not particularly limited and is appropriately set according to the phosphorus content.

Next, the precipitate of calcium phosphate is separated by a filtration operation or the like to remove phosphorus from the phosphorus-containing water. When the unreacted treating agent remains, it can be separated at the same time when the precipitate is separated. If the pH of the treated water after phosphorus removal exceeds the drainage standard, neutralize with acid and then discharge into the environment such as lakes, rivers and oceans.

According to the findings of the present inventors, calcium sulfate itself does not have the ability to remove phosphorus in the region of pH less than 8. However, under alkaline conditions where the pH is at least 8,
Calcium sulfate has an excellent phosphorus removing ability. The present invention is not bound by any theory, but the reason is considered as follows. Calcium sulfate is poorly soluble in water, but is soluble at about 0.3%. on the other hand,
Phosphorus is solubilized as a phosphate and exists in the form of a dibasic phosphate below pH 8, but is considered to exist in the form of a tertiary phosphate above pH 8. (Refer to the following reaction formula (1)) This tertiary phosphate and the dissolved calcium sulfate react as shown in the following reaction formula (2) to form a precipitate of tricalcium phosphate, which results in the formation of excellent phosphorus. It is considered that the removal ability is shown. The following reaction formula shows the case where NaOH is used for pH adjustment. The above reaction is a neutralization reaction, and the alkali such as sodium hydroxide added for pH adjustment is consumed for the production of calcium phosphate. Therefore, when an acid is required to neutralize the wastewater after phosphorus removal as described below, the amount of acid can be saved. Further, since calcium sulfate has a high ability to remove phosphorus even under weak alkali, it is preferable to set the pH of the reaction to 12 or less because the amount of acid used for neutralization can be further saved. on the other hand,
Not only does calcium hydroxide, which has been used conventionally, have a lower phosphorus-removing ability than calcium sulfate, but when it is reacted with a phosphate in water as described below, calcium phosphate is produced and alkali remains, which is a large amount for neutralization. Is the one that needs the acid. 3Ca (OH) ₂ + 2M ₂ HPO ₄ = Ca ₃ (PO ₄ ) ₂ +4
MOH + 2H ₂ O (where M represents an alkali metal element such as Na or K)

Next, the present invention is a phosphorus-containing water treating agent, wherein the treating agent containing calcium sulfate further contains an iron compound. When the treating agent further contains an iron compound, the phosphorus compound removal ability by the iron compound is added to the phosphorus removal ability by the calcium sulfate, so that the phosphorus removal ability is further improved. There are various iron compounds to be used, but iron oxides, hydroxides, and hydrous oxides are preferable because they have excellent phosphorus adsorption ability. As the treating agent containing calcium sulfate and an iron compound, (1) a mixture of each component, (2) gypsum containing an iron compound by-produced in the step of neutralizing various waste acids containing an iron component is used. For example, waste sulfuric acid containing an iron component generated in the production process of titanium oxide by the sulfuric acid method, sludge (residue) obtained by neutralizing an iron acid cleaning waste liquid with an alkali containing a calcium component such as lime, and the like can be given. . The treatment agent of the present invention is prepared from these wastes, for example, as follows. The first method is to add sulfuric acid containing an iron component, for example, waste sulfuric acid generated in the production process of a titanium oxide by a sulfuric acid method, to an alkali containing a calcium component to neutralize it in a pH range of 7.0 to 9.0. Meanwhile, air is blown into the liquid or an oxidizing agent is added to oxidize. The sulfate in the waste sulfuric acid reacts with the calcium component and precipitates as gypsum, and at the same time, the iron component also precipitates as iron oxide.
The treating agent of the present invention is obtained. In the second method, first, as the first step, sulfuric acid containing an iron component, for example, waste sulfuric acid generated in the manufacturing process of a titanium oxide by a sulfuric acid method is added with an alkali containing a calcium component to obtain a pH of 4.0 to 6. Neutralize in the range of 0. A part of the sulfate in the waste sulfuric acid preferentially reacts with the calcium component and precipitates as gypsum containing almost no iron component, which is removed by solid-liquid separation such as concentration or filtration. Subsequently, in the second step, an alkali containing a calcium component is further added to the supernatant liquid or the filtrate after solid-liquid separation, and the pH is neutralized in the range of 7.0 to 9.0 in the same manner as in the first method. Blow air into the liquid or add an oxidizer to oxidize it. The unreacted sulfate and iron component in the supernatant or filtrate react with the alkaline component and precipitate as gypsum and iron oxide, respectively, so they are solid-liquid separated. In the second method, a treatment agent having a high concentration of iron oxide is obtained,
Gypsum containing no iron component produced as a by-product can be used as a gypsum resource such as gypsum board. As the alkali containing a calcium component to be used, for example, the first method or the first method of the second method is used.
It is preferable to use a strong alkali such as calcium hydroxide in the step of (2) and a weak alkali such as calcium carbonate in the second step of the second method because it is not necessary to adjust the pH. Processing agent obtained by the second method, for example, 20 to 50% by weight of gypsum as CaSO ₄ · 2H ₂ O, containing 20 to 60 wt% of iron oxide as Fe ₂ O _3. It may contain a small amount of other components, and when waste sulfuric acid of the sulfuric acid method titanium oxide is used, the titanium oxide becomes 1% as TiO _2.
About 15% by weight is contained. These mixtures can be dried, if necessary, and can be used after being appropriately molded according to the treatment method such as powder, granules, and molded products.

Furthermore, the present invention is a method for treating phosphorus-containing water using the above-mentioned treating agent containing calcium sulfate and an iron compound, wherein the pH of the phosphorus-containing water and the treating agent is at least 8.
While maintaining the contact with each other to generate a precipitate of calcium phosphate, the dissolved phosphorus is adsorbed to the iron compound,
Then, the precipitation and the treating agent are separated from the treated water. In order to cause calcium phosphate to precipitate by contacting the phosphorus-containing water with the treatment agent while maintaining the pH at at least 8 and to adsorb the dissolved phosphorus to the iron compound, (1) after the treatment with the phosphorus-containing water After adding an amount of alkali that makes the pH of at least 8 to add powdery or granular treatment agent to generate calcium phosphate precipitate, and to allow the dissolved phosphorus to be adsorbed on the iron compound, (2) Powder or granular treatment agent is added to phosphorus-containing water, and then alkali is added to adjust the pH to at least 8
While precipitating calcium phosphate while maintaining the above, the dissolved phosphorus is adsorbed to the iron compound, and (3) after adding an amount of alkali having a pH after treatment of at least 8 to the phosphorus-containing water, for example, molding It is possible to use a method in which the treated agent is used as a fixed layer, and this is brought into contact with phosphorus-containing water to generate a calcium phosphate precipitate, and dissolved phosphorus is adsorbed to an iron compound. If the pH drops below 8 during processing,
Optionally an alkali may be added during the reaction to maintain the pH at least 8.

As the alkali used for pH adjustment, various alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide, ammonium compounds and alkali metal carbonates are used as described above. Etc. can be used, but it is preferable to use various alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Further, since calcium hydroxide has a phosphorus removing ability as described above, calcium hydroxide may be used for pH adjustment to obtain the effect of pH adjustment and the effect of phosphorus removal at the same time. pH of at least 8
There is no particular limitation as long as it is alkaline, but if it is 12 or less, not only the amount of acid used for neutralization after the treatment can be further saved, but also the adsorption ability of phosphorus by the iron compound is easily exhibited, which is preferable. From the viewpoint of the phosphorus adsorption capacity of the iron compound, it is more preferable to adjust the pH by adding an amount of alkali such that the pH after treatment is 10 or less. The amount of the treating agent used is not particularly limited and is appropriately set according to the phosphorus content.

Next, the precipitation of calcium phosphate and the treating agent are separated from the treated water by a filtering operation or the like to remove phosphorus from the phosphorus-containing water. After the treatment, the pH of the treated water is adjusted by adding an acid as necessary, and the water is discharged into the environment. Apparatuses known to those skilled in the art can be used in the method of the present invention, and are not particularly limited.

[0013]

The present invention will be described in more detail with reference to the following examples, which are not intended to limit the present invention.

Example 1 A sodium phosphate solution was diluted to prepare a test solution containing phosphorus at a concentration of 10 mg / liter. This test solution 30
To 0 ml, 10 g of commercially available calcium sulfate dihydrate
added. Sodium hydroxide (20 mg) was added thereto, and the mixture was stirred for 1 hour, and the formed precipitate was separated, and the phosphoric acid concentration in the filtrate was adjusted to J
It was analyzed by IS-K0102 (drainage test method). Table 1 shows the phosphorus concentration and pH in the liquid before and after the treatment.

Comparative Example 1 The same treatment as in Example 1 was carried out except that sodium hydroxide was not added. The phosphorus concentration and pH in the liquid before and after the treatment are shown in Table 1 together with the results of Example 1.

In the case of Comparative Example 1 in which the water containing phosphorus and the calcium sulfate were brought into contact with each other at a pH of less than 8, the phosphorus concentration did not change before and after the treatment, and the phosphorus removing effect was not recognized. In addition, in the case of Example 1 in which the pH was maintained at at least 8, the phosphorus concentration after the treatment was remarkably reduced, and an excellent phosphorus removing effect was observed.

[0017]

[Table 1]

Example 2 A test solution containing phosphorus at a concentration of 4 mg / liter was prepared in the same manner as in Example 1, and 300 g of this test solution contained 10 g of calcium sulfate dihydrate and 2 parts of sodium hydroxide.
0 mg was added. After stirring for 1 hour, the precipitate generated by filtration was removed.

Example 3 A treatment was carried out in the same manner as in Example 2 except that 2 g of the following treating agent A was added in place of 10 g of calcium sulfate dihydrate. The treating agent A is obtained by neutralizing waste sulfuric acid containing an iron component produced in the production process of the titanium oxide by the sulfuric acid method with an alkali containing calcium, solid-liquid separating the produced residue, and drying the powder. And contains calcium sulfate and an iron compound. The analysis results are shown in Table 5.

Table 2 shows the phosphorus concentration and pH before and after the treatments of Examples 2 and 3. In each case, phosphorus was significantly reduced from 4 mg / liter before the treatment, and an excellent phosphorus removing effect was recognized.

[0021]

[Table 2]

Example 4 Example 3 was added to 300 ml of the test solution used in Example 1.
2 g of the processing agent A powder used in step 2 and 20 m of sodium hydroxide
g was added, the mixture was stirred for 1 hour, and the precipitate formed by filtration was separated.

Comparative Example 2 The same treatment as in Example 4 was carried out except that 20 mg of calcium hydroxide was added in place of 2 g of the treatment agent A powder and 20 mg of sodium hydroxide in Example 4.

Table 3 shows the phosphorus concentration and pH before and after the treatment of Example 4 and Comparative Example 2. The treatment method using the treatment agent of the present invention (Example 4) showed higher phosphorus removal ability than the treatment method using calcium hydroxide of Comparative Example 2.

[0025]

[Table 3]

Example 5 A sodium phosphate solution was diluted to prepare a test solution containing 5 mg / liter of phosphorus, and 20 g of the powder of the treating agent A used in Example 3 and sodium hydroxide were added to 3 liters of this test solution. After adding 60 mg and stirring for 1 hour, the precipitate produced by filtration was separated. The weight of the treating agent A decreased with dissolution of calcium sulfate and the like, and the weight of the precipitate recovered after the treatment was 11.4 g. Table 4 shows the phosphorus concentration and pH in the liquid before and after the treatment. It can be seen that 99% of the phosphorus in the test water was removed. The components of the treatment agent A before and after the treatment were analyzed by a fluorescent X-ray analyzer (manufactured by Rigaku Corporation), and the results are shown in Table 5. The increase in the iron oxide content is due to the fact that most of the calcium sulfate content in Treatment Agent A was dissolved and used for phosphorus removal. Further, the phosphorus concentration in the treating agent A was from 0.048 g / 100 g (dry) before treatment to 0.19 g / 1.
It was increased to 00 g (dry). From the above results, the treatment agent A containing calcium sulfate and an iron compound, when used in the treatment of phosphorus-containing water, has the ability to remove phosphorus by calcium sulfate, as well as the adsorption and removal ability of phosphorus by an iron compound. It was found that the phosphorus removal ability was excellent.

[0027]

[Table 4]

[0028]

[Table 5]

[0029]

The treatment agent containing calcium sulfate of the present invention is capable of efficiently removing phosphorus in phosphorus-containing water,
Since it is possible to use gypsum produced as a by-product with exhaust gas and waste acid treatment, waste gypsum in construction waste, etc., it is a low-cost treatment agent and is an advantageous treatment agent for effective utilization of waste. Further, the method of treating phosphorus-containing water using the above-mentioned treating agent is economical because the reaction proceeds even in a weak alkali, so that the amount of alkali used for pH adjustment is small. Further, the removal rate of phosphorus is also extremely high, and it is an extremely effective treatment method in the present day when advanced treatment of sewage's primary treated water is a problem.
Furthermore, the treating agent containing calcium sulfate and an iron compound of the present invention and the method for treating phosphorus-containing water using the same add phosphorus adsorption ability by the iron compound, and can remove phosphorus in phosphorus-containing water more efficiently. Since it is possible to use a mixture of iron oxide and gypsum such as a neutralization residue of waste sulfuric acid of sulfuric acid method titanium oxide, it is industrially advantageous.

Continued front page    (72) Inventor Susumu Kato             3690-1, Sakuramachi, Yokkaichi-shi, Mie Mie Science             Technology Promotion Center, Health and Environmental Research Department (72) Inventor Seiji Iwasaki             3690-1, Sakuramachi, Yokkaichi-shi, Mie Mie Science             Technology Promotion Center, Health and Environmental Research Department (72) Inventor Hideki Kokubun             3690-1, Sakuramachi, Yokkaichi-shi, Mie Mie Science             Technology Promotion Center, Health and Environmental Research Department (72) Inventor Hideo Enjoji             3690-1, Sakuramachi, Yokkaichi-shi, Mie Mie Science             Technology Promotion Center, Health and Environmental Research Department (72) Inventor Kenichi Sasaki             1 Ishihara-cho, Yokkaichi-shi, Mie Ishihara industry stock             Ceremony company Yokkaichi factory (72) Inventor Shunsuke Asano             1 Ishihara-cho, Yokkaichi-shi, Mie Ishihara industry stock             Ceremony company Yokkaichi factory F term (reference) 4D024 AA04 AB12 BA14 BB01 BC04                       CA06 DB12 DB30                 4D038 AA08 AB45 BB06 BB18                 4G066 AA27B CA41 DA08 EA13                       FA21

Claims (7)

[Claims] 1. A phosphorus-containing water treatment agent for use at a pH of at least 8 comprising calcium sulfate. 2. The treating agent according to claim 1, further comprising an iron compound. 3. The treating agent according to claim 2, wherein the iron compound is at least one selected from the group consisting of iron oxide, iron hydroxide and hydrous iron oxide. 4. A method comprising contacting phosphorus-containing water with the treatment agent according to claim 1 while maintaining the pH at at least 8 to generate a calcium phosphate precipitate, and then separating the precipitate from the treatment water. A method for treating phosphorus-containing water. 5. The treatment method according to claim 4, wherein the pH is maintained at 8 to 12. 6. The phosphorus-containing water and the treatment agent according to claim 2 are brought into contact with each other while maintaining a pH of at least 8 to form a precipitate of calcium phosphate, and dissolved phosphorus is adsorbed on an iron compound, A method for treating phosphorus-containing water, comprising separating the precipitate and the treating agent from treated water. 7. The treatment method according to claim 6, wherein the pH is maintained at 8 to 12.