JP2741998B2 - Inorganic flocculant produced from phosphoric acid waste liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inorganic coagulant for coagulating and sedimenting components in various waste liquids discharged from paper mills, human waste treatment plants, sewage treatment plants, etc. to produce harmless waste liquids. is there. In particular, the present invention relates to an inorganic coagulant produced by treating a waste liquid generated from a production process of an aluminum electrolytic capacitor, for example.

[0002]

2. Description of the Related Art Conventionally, the above-mentioned wastewater treatment involves the use of
Iron-based flocculants such as iron, ferrous sulfate, and ferric sulfate or aluminum-based flocculants such as polyaluminum chloride, sulfate bands, and waste aluminum chloride have been used. However, these flocculants did not have a sufficient effect of removing the COD component in the waste liquid. Therefore, the present inventors first set CO2
We have proposed ferric polysulfate as an inorganic coagulant excellent in the ability to remove the D component and the BOD component, and further proposed and put into practical use an inorganic coagulant containing iron and aluminum. These coagulants often have a chance to be manufactured using factory waste liquid consisting of a single acid containing iron or aluminum, and have greatly contributed to effective use of the waste liquid.

However, in recent years, for wastewater discharged from, for example, the production process of aluminum electrolytic capacitors, processing techniques such as etching and chemical formation have been advanced, and the acids used are monobasic acids such as hydrochloric acid and nitric acid, and phosphoric acid and phosphoric acid. A mixed acid to which sulfuric acid is added has been used, and the composition of the discharged waste liquid has been complicated. Examples of the flocculant produced by concentrating or crystallizing this kind of aluminum-containing waste liquid containing a phosphoric acid component include aluminum-based flocculants, such as waste aluminum chloride and sulfate bands.
It is difficult to remove phosphoric acid during production, and they contain phosphate ions. When these are used as a flocculant, the phosphorus component contained in the flocculant as an impurity remains in the wastewater, causing a eutrophic value, and the formed floc formed has poor consolidation properties, poor dehydration properties, etc. Also, it was difficult to reuse the sludge after treatment as fertilizer.

In order to improve the above-mentioned drawbacks of the conventional phosphoric acid-containing flocculant, development of a novel flocculant has been desired.

[0005]

Accordingly, an object of the present invention is to provide a novel inorganic coagulant containing phosphoric acid in order to solve the above-mentioned problems. It is another object of the present invention to provide an inorganic flocculant that can be produced by treating, for example, an aluminum-containing waste liquid generated from a production process of an aluminum electrolytic capacitor.

For example, a flocculant produced by concentrating or crystallizing a waste liquid containing phosphoric acid generated from a production process of an aluminum electrolytic capacitor,
Poor removal of phosphorus in wastewater. However, as a result of various studies conducted by the present inventor to eliminate this disadvantage, the following has been found. That iron ions are more effective than aluminum ions in removing COD components, phosphorus, and BOD components;
The COD component, phosphorus and B are better when using a mixed composition of both than the iron-based coagulant and the aluminum-based coagulant are added separately.
Excellent removal effect of OD components, phosphoric acid content in flocculant is effective in preventing corrosion of equipment, sludge generated after use of flocculant has high nutritional value and can be effectively used as fertilizer, etc. It is. Therefore, a basic inorganic coagulant was produced by adding iron to aluminum-containing waste liquid containing phosphoric acid. Phosphorus in the wastewater at the time of use was equivalent to a coagulant such as a sulfate band and ferric polysulfate. It has been found that it exhibits a removing effect. The present invention is based on such findings.

[0007]

According to the present invention, the molar ratio of trivalent iron to aluminum is 5> aluminum ion / 3
When the valence iron ion> 0.1, the molar ratio of phosphate ion and trivalent iron is 1> phosphate ion / trivalent iron ion> 0.05, and the molar ratio of phosphate ion to sulfate ion is 0.4> phosphate ion / Sulfuric acid ion> 0.02 is an inorganic coagulant containing phosphoric acid, which is essential.

[0008] The coagulant of the present invention must first have a molar ratio of trivalent iron and aluminum of 5> aluminum ion / trivalent iron ion> 0.1. When the molar ratio of aluminum ion / ferric iron ion is 0.1 or less, C
Although the removal rate of OD components, phosphorus, suspended substances and the like is good, there is a problem that the treated wastewater is colored. On the other hand, when the molar ratio is 5
In the above case, the removal rate of phosphorus in the waste liquid is significantly reduced.

Further, it is necessary that the molar ratio of the phosphate ion to the trivalent iron is 1> phosphate ion / trivalent iron ion> 0.05. When the molar ratio of phosphate ion / ferric iron ion is 0.05 or less, precipitation of iron sulfate (III) hydrate or iron hydroxide is likely to occur during long-term storage, and the corrosion prevention effect of the device is reduced. On the other hand, when the molar ratio is 1 or more, the removal rate of phosphorus in the waste liquid deteriorates.

Further, the molar ratio of phosphate ions to sulfate ions must be 0.3> phosphate / sulfate ions> 0.02. In this composition range, the stability of the flocculant is good, but if the molar ratio of phosphate ion / sulfate ion is 0.02 or less, iron (III) sulfate hydrate and the like will precipitate during long-term storage. When the molar ratio is 0.3 or more, precipitation of fine iron phosphate particles easily occurs, and the removal rate of phosphorus in the waste liquid after the treatment is deteriorated.

The coagulant of the present invention can be prepared by dissolving aluminum sulfate, iron sulfate, and phosphoric acid in water at the above molar ratio. The preparation method is described below.

Sulfuric acid is prepared so that the molar ratio of sulfate ion / aluminum ion becomes 3 or more with respect to waste nitric acid containing phosphoric acid and aluminum, and nitrate in the waste liquid is reacted with sulfuric acid to convert nitrate into nitric acid. The thus produced free nitric acid is concentrated by distillation and distilled together with water to recover the nitric acid. Next, after distilling and recovering the nitric acid, iron is added to the remaining liquid with hydrated iron oxide or the like to convert the free acid in the remaining liquid to an iron salt. Here, the amount of iron added is such that the molar ratio of free sulfuric acid to the ferrous compound in the residual liquid (free sulfuric acid / ferrous compound) is less than 0.5 (preferably 0.1%).
35 to 0.45). Next, ferrous iron in the residual liquid is oxidized to remove insolubles, thereby obtaining a solution containing aluminum sulfate, ferric sulfate and phosphoric acid as main components. This solution can be used as a liquid coagulant which forms a harmless waste liquid by subjecting components in various waste liquids discharged from a paper mill or the like to coagulation and sedimentation.

As described above, according to the flocculant of the present invention, the effect of removing COD components, phosphorus, BOD components and the like in wastewater is large, there is no coloring of wastewater after treatment, and the generated sludge is It is nutritious and can be reused for fertilizer.

[0014]

EXAMPLES The present invention will be described below in more detail with reference to examples, but these examples do not limit the scope of the present invention.

[0015] Example 1 Ferrous sulfate _{(FeSO 4 · 7H 2 O)} 37.2g, aluminum sulfate _{(Al 2 (SO 4) 3} · 18H 2 O) 89.5
g, phosphoric acid (H ₃ PO ₄ , 85% by weight), 7.68 g, and sulfuric acid (98% by weight), 4.67 g, were dissolved in water, stirred for 30 minutes and mixed. 2.37 g of sodium acid salt (NaClO ₃ ) was added to oxidize divalent iron ions in the solution to trivalent iron ions to obtain a flocculant.

Example 2 Ferrous sulfate 27.9 g, aluminum sulfate 100.6
g, 4.61 g of phosphoric acid (85% by weight), and 3.00 g of sulfuric acid (98% by weight) were dissolved in water, stirred for 30 minutes and mixed, and then diluted to 200 ml, and 1.77 g of sodium chlorate was added. Was added to oxidize divalent iron ions in the solution to trivalent iron ions to obtain a flocculant.

Example 3 Aluminum (Al) generated in the manufacturing process of an aluminum electrolytic capacitor, 18.0 g / liter, phosphate ion (PO ₄ )
1.2 kg of sulfuric acid (98% by weight) was added to 5 liters of aluminum-containing waste liquid having a composition of 13.5 g / liter and 144 g / liter of nitrate ion (NO ₃ ), and concentrated by distillation to distill and remove nitric acid. Add 2.1 liters of water,
28.0 g / l of aluminum, phosphate ions
About 1.5 L of a solution having a composition of 5 g / L, nitrate ion 30.9 g / L, and sulfate ion (SO ₄ ) 265 g / L was obtained. Next, a part of the free sulfuric acid of the solution was recovered in a diffusion dialysis tank equipped with an anion exchange membrane, and the obtained permeate was concentrated to obtain 40.2 g / l of aluminum, 26.0 g / l of phosphate ions, Nitrate ion
About 1.5 liter of a solution having a composition of 9 g / liter and 265 g / liter of sulfuric acid was obtained. About 68 g of hydrated iron oxide (43.4% by weight of trivalent iron ions and 11.4 g / liter of divalent iron ions) were dissolved in the solution at a liquid temperature of 80 ° C.
Oxidized and filtered to remove insolubles, 25.0 g of trivalent iron ions
Per liter, 40.2 g / l of aluminum, 26.0 g / l of phosphate ions, 0.1 g / l of nitrate ions, and 265 g / l of sulfate ions.

Comparative Example 1 93.0 g of ferrous sulfate, 22.4 g of aluminum sulfate,
23.1 g of phosphoric acid (85% by weight), 1 of sulfuric acid (98% by weight)
Dissolve 4.7 g in water, stir and mix for 30 minutes, make up to 200 ml, add 5.91 g of sodium chlorate, and convert divalent iron ions in the solution to trivalent iron. The coagulant was obtained by oxidation to ions.

Comparative Example 2 Ferrous sulfate 27.9 g, aluminum sulfate 100.6
g, 1.15 g of phosphoric acid (85% by weight), and 3.00 g of sulfuric acid (98% by weight) were dissolved in water, stirred for 30 minutes and mixed, then the volume was increased to 200 ml and 1.77 g of sodium chlorate Was added to oxidize divalent iron ions in the solution to trivalent iron ions to obtain a flocculant.

Comparative Example 3 Ferrous sulfate 37.2 g, aluminum sulfate 89.5 g,
0.77 g of phosphoric acid (85% by weight), sulfuric acid (98% by weight)
After dissolving 4.67 g in water and mixing by stirring for 30 minutes, make up to 200 ml, add 2.37 g of sodium chlorate, and convert divalent iron ions in the solution to trivalent iron. The coagulant was obtained by oxidation to ions.

Comparative Example 4 Ferrous sulfate 37.2 g, aluminum sulfate 89.5 g,
15.3 g of phosphoric acid (85% by weight), sulfuric acid (98% by weight)
After dissolving 4.67 g in water and mixing by stirring for 30 minutes, make up to 200 ml, add 2.37 g of sodium chlorate, and convert divalent iron ions in the solution to trivalent iron. The coagulant was obtained by oxidation to ions.

Comparative Example 5 101.5 g of ferrous sulfate and 12.2 of aluminum sulfate
g, 16.7 g of phosphoric acid (85% by weight) and 16.2 g of sulfuric acid (98% by weight) were dissolved in water, stirred for 30 minutes and mixed, and then diluted to 200 ml, and 6.45 g of sodium chlorate was added. Was added to oxidize divalent iron ions in the solution to trivalent iron ions to obtain a flocculant.

Comparative Example 6 Ferrous sulfate 18.6 g, aluminum sulfate 111.8
g, 3.07 g of phosphoric acid (85% by weight), and 1.33 g of sulfuric acid (98% by weight) were dissolved in water, mixed by stirring for 30 minutes, and then diluted to 200 ml to obtain 1.18 g of sodium chlorate. Was added to oxidize divalent iron ions in the solution to trivalent iron ions to obtain a flocculant.

Tables 1 and 2 show the results of treating wastewater from a paper mill using the flocculants obtained in Examples and Comparative Examples. Wastewater undiluted solution has COD = 100ppm, phosphorus = 5ppm
It is. The amount of the coagulant added was constant at 200 ppm relative to the wastewater at each molar ratio. PH after addition of flocculant
Was adjusted to 6.5. As can be seen from the results, the flocculant according to the present invention is a stable flocculant having a high removal rate for COD components and phosphorus.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

As described above, the flocculant according to the present invention has a large effect of removing COD components, phosphorus, BOD components, and the like in wastewater, has a rust-preventive effect, and also has a coloration of wastewater after treatment. The sludge that is not generated is nutritious and can be reused for fertilizer.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hiroya Morita 8-10-16 Shimorenjaku, Mitaka-shi, Tokyo Japan Iron Mining Co., Ltd. (56) References JP-A-48-103475 (JP, A)

Claims (1)

(57) [Claims] 1. The molar ratio of trivalent iron to aluminum is 5> aluminum ion / ferric iron ion> 0.1, and the molar ratio of phosphate ion to trivalent iron is 1> phosphate ion / ferric iron An inorganic coagulant containing phosphoric acid having a composition of ions> 0.05 and a molar ratio of phosphate ions to sulfate ions of 0.3> phosphate ions / sulfate ions> 0.02.