JP3105347B2 - How to treat phosphate sludge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of treating phosphate sludge generated when a metal material is treated with phosphate, as a technique for effectively utilizing industrial waste.

[0002]

2. Description of the Related Art Phosphate treatment, which is widely used industrially for coating undercoating of metal materials, rust prevention and lubrication, generates phosphate sludge during the treatment. Currently, this phosphate sludge is almost an industrial waste, and its amount in the country alone reaches 5,000 t / year or more as dry sludge. In recent years, a technique for reusing industrial waste, that is, a recycling technique, has been studied and studied.

[0003] There have been some methods in the past for extracting and reusing the effective components of phosphating sludge, but they have not been put into practical use due to the large amount of impurities and economical efficiency. A method for producing an alkali phosphate or phosphate chemical conversion chemical from sludge generated at the time of phosphating described in JP-B-55-19316 and JP-B-54-18866 is a method of treating a sludge containing zinc, Specificity is lacking because zinc ions in sludge have been reduced in recent years due to improvements in processing technology. The method of Japanese Patent Application Laid-Open No. 1-100008 is improved, and the method for producing an alkali phosphate with a reduced number of steps has a drawback that the purpose of use is limited due to the large amount of impurities. The method for producing an alkali phosphate or a phosphate coating chemical disclosed in JP-A-3-134181 requires a large number or quantity of chemicals for effective use of sludge and removal of impurities. There is a disadvantage that the process is complicated, and practical application is severe, including economical efficiency.

In the prior art, (1) economy (2)
(3) Step is complicated (4) There is a concentration crystallization step (5) There is a problem that the use is limited because the final treatment product contains impurities. JP-A-3-131
48 solves (5) among these problems,
Japanese Patent Laid-Open No. 1-100008 has solved (1), (2) and (3). However, none of them solves all the problems of the items (1) to (5).

As an advanced method for removing residual fluorine ions as a wastewater treatment method, a chelate resin (JP-A-56-11) is used.
3391) and activated alumina (Yoshihiro Endo, Tadashi Takadoi; water and wastewater, Vol. 20, No. 6, p. 31 (197)
8)) or a method in which phosphate ions are added in the presence of calcium ions (slaked lime) to neutralize, coagulate and precipitate as fluorapatite. However, fluorine adsorbents and chemicals have the disadvantage that they are expensive as wastewater treatment chemicals.

[0006] Therefore, hydroxyapatite is useful as a fluoride ion remover in wastewater and is one of the objects for recycling phosphate sludge.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems (1) to (5), and is economical, requires a low cost of chemicals, and has a simple process. It is another object of the present invention to provide a method for treating phosphate sludge which does not require a concentration crystallization step and enables effective utilization of a final treatment product. It is a further object of the present invention to provide a method for removing phosphate from fluorine-containing wastewater in the treatment of phosphate sludge.

[0008]

SUMMARY OF THE INVENTION According to a first aspect of the present invention, sodium hydroxide is added to a phosphate sludge generated when a metal material is subjected to a phosphating treatment, and a reaction product is filtered. The product obtained by adding and reacting slaked lime, quick lime or a mixture of slaked lime and quick lime to the filtrate containing sodium acid is filtered, the filtrate containing sodium hydroxide is recirculated to the above step, and the filtration residue is filtered. Provided is a method for treating phosphate sludge, which comprises washing with water, drying, and collecting a treatment product containing hydroxyapatite as a main component.

[0009] In the second aspect of the present invention, sodium hydroxide is added to phosphate sludge generated when a metal material is subjected to phosphating, and a reaction product obtained by the reaction is filtered. The product obtained by adding and reacting slaked lime, quick lime or a mixture of slaked lime and quick lime to the liquid is filtered, the filtrate containing sodium hydroxide is recirculated to the above step, the filtration residue is washed with water, dried, The treated product containing hydroxyapatite as a main component is recovered, and the product obtained by adding sulfuric acid to the treated product containing hydroxyapatite as a main component and then reacting is filtered to remove orthophosphoric acid as a filtrate. A method for treating phosphate sludge, which is characterized by being recovered.

In a third aspect of the present invention, sodium hydroxide is added to phosphate sludge generated when a metal material is subjected to phosphating, and a reaction product obtained by the reaction is filtered. The product obtained by adding and reacting slaked lime, quick lime or a mixture of slaked lime and quick lime to the liquid is filtered, the filtrate containing sodium hydroxide is recirculated to the above step, the filtration residue is washed with water, dried, Recovering a treated product containing hydroxyapatite as a main component, mixing and stirring the treated product containing hydroxyapatite as a main component, and fluorine-containing wastewater to obtain a treated wastewater from which fluorine has been removed. A method for treating salt sludge is provided.

Hereinafter, the configuration of the present invention will be described in detail. First, the first invention will be described. In the present invention, iron, zinc, aluminum, alloys thereof, and the like are typical examples of metal materials to be subjected to the phosphate treatment.

There are various types of phosphating solutions depending on the type and purpose (corrosion resistance, coating adhesion, lubrication treatment for plastic working, etc.) of the metal to be treated. Typical examples thereof include a phosphorous zinc-based coating, an iron phosphate-based coating, a calcium phosphate-based coating, and a manganese phosphate-based coating depending on the type of the formed film.

Table 1 shows a typical composition (dry state) of sludge generated when a metal material such as iron, zinc, and aluminum is subjected to a phosphate treatment.

[0014]

[Table 1]

The sludge generated during the phosphate treatment of the metal material is added to a 5 to 30% by weight sodium hydroxide solution and mixed to adjust the pH to 11 to 13. This is filtered. The filtrate is a solution containing sodium phosphate as a main component. The filtration residue is mainly composed of ferric hydroxide.

The filter residue is washed with a NaOH solution to dissolve unreacted PO ₄ ^3- ions. The undissolved material is ferric hydroxide containing some zinc ions. This is currently discarded, but it can be used for ferrite and other applications as iron ion purification technology advances. The washing liquid is mixed with the filtrate containing the sodium phosphate.

Slaked lime, quick lime or a mixture of slaked lime and quick lime are added to the filtrate containing sodium phosphate,
Upon stirring and mixing, a white precipitate forms. This is filtered. Since the filtrate is mainly composed of NaOH, it is recycled and used for dissolving sludge. The filtration residue is washed with water and dried to remove unreacted lime and sodium phosphate. As a result of analysis of this, hydroxyapatite Ca ₅ (PO ₄ ) ₃ (OH) was the main component. FIG. 1 shows a process flow sheet of the first invention.

The second invention will be described. A treatment product containing hydroxyapatite is obtained by exactly the same treatment as in the first invention. To this is added sulfuric acid. Although the concentration of sulfuric acid is not particularly limited, for example, sulfuric acid of about 70% by weight is used. The addition amount is preferably equal to or more than an equivalent that decomposes hydroxyapatite. Sulfuric acid is gradually added while heating and stirring. After holding for a certain time, a white precipitate is obtained. The product is filtered after cooling. As a result of the analysis, the filtration residue was gypsum dihydrate, and the filtrate was an aqueous solution containing orthophosphoric acid.

The third invention will be described. According to the first invention, a treated product containing hydroxyapatite is obtained.
This is mixed with the wastewater containing fluorine ions. Fluorine ion-containing wastewater is wastewater generated by a surface treatment agent used for metal surface treatment, and has a high concentration of fluorine ions (for example, 15%).
ppm or more). To this, ferric chloride or the like is added as a coagulant, and the pH is adjusted to 8 to 8.5 with sodium hydroxide. A treatment product containing hydroxyapatite is added to the supernatant, the pH is adjusted to about 6.0 with dilute sulfuric acid, and the mixture is stirred and mixed. The amount of the treatment product containing hydroxyapatite is about 1 kg per 1 m ³ of waste water. Fluorine is adsorbed on hydroxyapatite, and wastewater from which fluorine has been removed to 2 ppm or less can be obtained.

It is also possible to wash the hydroxyapatite having adsorbed fluorine with sodium hydroxide to desorb fluorine, and to recycle the desorbed hydroxyapatite to reuse it as a fluorine adsorbent.

[0021]

(First invention) A typical example of the composition of phosphate sludge is a hydrate of FePO ₄ and Zn ₃ (PO ₄ ) ₂ . When sodium hydroxide is allowed to act on this, trisodium phosphate is produced by the reaction formula of FePO ₄ + 3NaOH → Na ₃ PO ₄ + Fe (OH) ₃ Zn ₃ (PO ₄ ) ₂ + 6NaOH → 2Na ₃ PO ₄ + 3Zn (OH) ₂ I do. Zn ions are amphoteric ions, so if too much NaOH is added, Zn ions
Ions are contained as impurities. For this reason, pH adjustment at the time of adding NaOH is important, and the pH is adjusted to 11 to 13.
When lime is allowed to act on the obtained sodium phosphate solution, hydroxyapatite can be obtained by a reaction formula of 3Na ₃ PO ₄ + 5Ca (OH) ₂ → Ca ₅ (PO ₄ ) ₃ (OH) + 9NaOH.

(Second Invention) Orthophosphoric acid can be obtained by adding sulfuric acid to the obtained hydroxyapatite by a conventional method. Ca ₅ (PO ₄ ) ₃ (OH) + 5H ₂ SO ₄ → 3H ₃ PO ₄ + 5CaSO ₄ + H ₂ O

(Third invention) Hydroxyapatite acts as a fluoride ion adsorbent. Ca ₅ (PO ₄ ) ₃ (OH) + NaF → Ca ₅ (PO ₄ ) ₃ F + NaOH It also contains Ca (OH) ₂ when producing hydroxyapatite. It is considered that this increases the fluorine ion adsorption effect. Ca (OH) ₂ + 2NaF → CaF ₂ + 2NaOH

Theoretically, 38 mg of fluorine can be adsorbed per 1 g of hydroxyapatite. The adsorption power of the hydroxyapatite obtained in the present invention was tested. 8
50 as ^- 6.5% hydroxyapatite 10 g F
Add to 1L of NaF solution containing 0ppm, pH with sulfuric acid
Was adjusted to 6.0, followed by stirring for 30 minutes at room temperature, filtered, F in the filtrate ^- Analysis of the was 215Ppm. From this result, the F ^- adsorption rate of the present apatite is 87.
It was 0%. The residue, that is, F ^- was adsorbed and fluorapatite was added to 1 L of a 0.1 N sodium hydroxide solution and stirred for 30 minutes. F in the supernatants ^- the analyzing the 1
It was 95 ppm. This indicates that the fluoroapatite has been converted into hydroxyapatite again by sodium hydroxide (alkaline).

[0025]

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. (Example 1) PO ₄ 52.1 wt%, Fe11.4 wt%, Zn1.6 wt%, Mn0.14 wt%, Ni0.
1% by weight, 0.95% by weight of Na, 0.5% by weight of NO ₃ ,
Sludge generated during general phosphating with a composition having a water content of 52.1% by weight was used as raw material sludge. Approximately 270 L of a 10 W / V% NaOH solution was added to 100 kg of this sludge, and dissolved by heating at 50 to 60 ° C. for 1 hour.
The pH was adjusted to 12.0 with a NaOH solution. This was filtered. The residue was washed with 20 L of a 20 W / V% NaOH solution, and the washing was mixed with the filtrate. The filtrate or solution is a concentrated solution mainly composed of trisodium phosphate, and the residue is mainly composed of ferric hydroxide and discarded. As a result of analysis, the yield of the obtained sodium phosphate solution was 85% by weight. To the sodium phosphate solution, 29 kg of slaked lime (industrial special name) was added in a slurry form, and the mixture was heated and stirred at 60 ° C. for 1 hour. The resulting pure white crystals were filtered. The residue was washed with water and dried to remove unreacted slaked lime and sodium phosphate. As a result of analysis, 30 kg of hydroxyapatite was the main component. The yield was 80% by weight. Thus, hydroxyapatite was synthesized. 250 L of filtrate is NaO
Since H is the main component, it was recycled and used for dissolving the phosphating sludge.

Phosphated sludge of the same composition 100 k
The filtrate was added to g, and the mixture was heated and dissolved in the same manner as described above. The same operation was carried out as follows, slaked lime was added to the sodium phosphate solution, and the mixture was heated and stirred to obtain hydroxyapatite. 80% recovery of hydroxyapatite from first sludge
However, it was 84% at the second time and 87% at the third time. The recovery rate is unlimited by repeating the process.
It approaches 0%. Table 2 shows the analysis results of the obtained hydroxyapatite.

[0027]

[Table 2]

Example 2 30 kg of hydroxyapatite (49.1% PO ₄ ) obtained in Example 1 was added to 500 kg of water.
L was added to form a slurry.
kg, slowly add and mix, heat at about 70 ° C for 1 hour,
After stirring and cooling, a white precipitate deposited was filtered. As a result of analysis, the residue was dihydrate gypsum, and the filtrate was a phosphoric acid aqueous solution. The results of the analysis are shown in Table 3. The yield from hydroxyapatite was 89% by weight. 46 kg of the obtained phosphoric acid was obtained at a concentration of about 30% by weight. It contains small amounts of sulfuric acid and gypsum. This phosphoric acid aqueous solution can be further concentrated and purified by a method such as solvent extraction, and can be sufficiently used as a raw material for a metal surface treating agent.

[0029]

[Table 3]

Example 3 Table 2 shows the quality of the constantly drained water used in the high-concentration fluorine-containing chemical conversion treatment line.
0.3 kg of ferric chloride as a coagulant was added to 3 m ³ of the waste water, and the pH was adjusted to 8 to 8.5 with sodium hydroxide. Its quality of treated liquid, as shown in Table 4 F ^- is still 1
8 ppm remains. 3 kg of the hydroxyapatite obtained in Example 1 was added to the supernatant, the pH was adjusted to about 6.0 with dilute sulfuric acid, and the mixture was stirred for 30 minutes. F ^- is adsorbed to hydroxyapatite, it was reduced to 1.4 ppm.

Example 4 The apatite adsorbent used in Example 2 was backwashed with 0.1N sodium hydroxide solution by filtration or the like, and stirred for 30 minutes. F in sodium hydroxide solution
Since dissociates, this F until concentrated ^{- -} was used again as the desorption solution. F ^- desorbs apatite is filtered,
Washed with water and used again as F ^- adsorbent. Results of testing wastewater treatability for regenerated adsorbent in the same manner as in Example 3, F as shown in Table 5 ^- shows the adsorption capacity for.

[0032]

[Table 4]

[0033]

[Table 5]

[0034]

The sludge generated during the phosphate film conversion treatment has been discarded until now, but the present invention allows its effective use. That is, the treatment product containing hydroxyapatite obtained by the treatment method of the present invention can be used for orthophosphoric acid synthesis, that is, as a raw material that replaces phosphate rock. Gypsum, a by-product, is also available.
Further, by mixing the treatment product containing hydroxyapatite and the wastewater containing fluorine, wastewater from which fluorine has been removed can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a process flow of the first present invention.

Claims (2)

(57) [Claims] 1. A product obtained by adding and reacting sodium hydroxide to a phosphate sludge generated when a metal material is subjected to a phosphating treatment, filtering a product obtained, and adding slaked lime and quick lime to a filtrate containing sodium phosphate. Alternatively, a product obtained by adding and reacting a mixture of slaked lime and quick lime is filtered, the filtrate containing sodium hydroxide is recirculated to the above step, the filtration residue is washed with water, dried, and mainly composed of hydroxyapatite. A method for treating phosphate sludge, comprising adding sulfuric acid to a treated product to be reacted and filtering the product, and recovering orthophosphoric acid as a filtrate. 2. A product obtained by adding and reacting sodium hydroxide to a phosphate sludge generated when a metal material is subjected to a phosphate treatment, and filtering a product obtained therefrom, and adding slaked lime and quick lime to a filtrate containing sodium phosphate. Alternatively, a product obtained by adding and reacting a mixture of slaked lime and quick lime is filtered, the filtrate containing sodium hydroxide is recirculated to the above step, the filtration residue is washed with water, dried, and mainly composed of hydroxyapatite. A method for treating phosphate sludge, comprising mixing and stirring a treated product to be treated and fluorine-containing wastewater to obtain treated wastewater from which fluorine has been removed.