JP2000254638A - Treatment of metal-containing waste water and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment method of metal-containing waste water and a device, which is capable of efficiently removing heavy metallic ions in the waste water, and an installation space of the treating device is small. SOLUTION: Heavy metal-containing waste water is added with NaOH and H2O2 in branched pipes 12, then is caused to flow in a floating separation tank 20. The heavy metallic ions become hydroxide flocks by an addition of the NaOH, and also the H2O2 is decomposed to generate gaseous O2 and the gaseous O2 is stuck to the hydroxide flocks and the flocks are floated. The flocks are taken out from a tank 20 via a takeout part 30. The liquid from which the flock is separated is taken out from a treated water takeout pipe 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating metal-containing wastewater, and more particularly to a method and an apparatus for aggregating metal ions in the wastewater as hydroxide to separate them by flotation.

[0002]

2. Description of the Related Art As a method for treating metal-containing wastewater, especially heavy metal-containing wastewater, a method of adding an alkali to form a metal hydroxide floc and sedimenting and separating the floc has been widely adopted. A method of coagulating and filtering this metal hydroxide floc is also employed. Further, a method of removing a metal by an ion exchange method is also performed.

[0003]

The method of coagulating sedimentation of metal hydroxide flocs by adding alkali to metal-containing wastewater requires a coagulation tank and a sedimentation tank, and requires a large installation space for the apparatus.

[0004] In the coagulation filtration method, when the metal concentration in the wastewater is high, the operation efficiency decreases, such as the frequency of backwashing increases. The ion exchange method is suitable for treating low-concentration metal-containing wastewater, but is not suitable for treating high-concentration metal-containing wastewater.

An object of the present invention is to provide a method and an apparatus for treating metal-containing wastewater which can efficiently treat even high-concentration metal-containing wastewater.

[0006]

According to the present invention, there is provided a method for treating a metal-containing wastewater, comprising adding an alkali and hydrogen peroxide to the metal-containing wastewater and separating the metal-containing wastewater by air bubbles which generate metal hydroxide flocs. It is characterized by the following.

Further, the apparatus for treating metal-containing waste water of the present invention has means for adding alkali and hydrogen peroxide to metal-containing waste water, and separation means for floating and separating metal hydroxide flocs.

In the method and apparatus according to the present invention,
The metal ions in the wastewater become metal hydroxide flocs due to the added alkali. Also, the added hydrogen peroxide decomposes in an alkaline liquid to generate oxygen,
The oxygen bubbles adhere to the metal hydroxide flocs and cause the flocs to float. Thus, according to the present invention,
Metal ions in wastewater can be rapidly floated and separated as metal hydroxide flocs.

In the present invention, the floating separation means includes a plurality of compartments divided by an inclined plate, a means for introducing a liquid to be treated into the upper part of each compartment, and a process water flowing out from the lower part of each compartment. What has a means is preferable.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, metal-containing wastewater to be treated is wastewater containing metal ions, particularly heavy metal ions. Examples of heavy metal ions include Fe, Cu,
Alkaline pH such as Mn, Cr, Co, Ni, Zn, Cd
One that produces a water-insoluble hydroxide in the region. The concentration of this heavy metal ion is 50-5000 mg / L
If so, it is suitable for processing by the method and apparatus of the present invention, and if necessary, it is concentrated or conversely diluted to this concentration range.

Specific examples of the metal-containing wastewater include plating wastewater, flue gas desulfurization wastewater, and photographic developer wastewater.

The alkali added to the heavy metal-containing waste water is preferably added as an aqueous solution. As the alkali,
NaOH, KOH, Ca (OH) 2, CaO, Na 2 CO
_{Although 3 and the} like can be used, NaOH is preferred from the viewpoint of cost and solubility. In the case of NaOH, 10 to 60
It is preferable to add to the metal-containing wastewater as an aqueous solution having a concentration of about wt%.

The alkali is the pH of the metal-containing waste water after the addition.
Is preferably added so as to be about 6 to 12, particularly about 9 to 11.

The hydrogen peroxide is preferably added as an aqueous solution of about 10 to 50% by weight. Hydrogen peroxide was added to the wastewater at a concentration of 0.01% in the wastewater after the addition.
It is preferably added to be about 10 to 10 mg / L, particularly about 0.05 to 3 mg / L.

Any of the alkali and the hydrogen peroxide may be added to the metal-containing wastewater first, or may be added simultaneously.
After adding the alkali and / or hydrogen peroxide to the metal-containing wastewater, the wastewater may be stirred with an appropriate stirring strength. The alkali and / or hydrogen peroxide may be added to the wastewater before entering the flotation tank, or may be added to the wastewater in the flotation tank.

If the flocs cannot be sufficiently floated by oxygen bubbles generated from hydrogen peroxide alone, water-soluble salts such as copper, iron, manganese, and chromium (eg, chlorides, sulfates, nitrates) ) May be added to the wastewater in small amounts.

The flotation tank preferably has an interior partitioned into a plurality of compartments by an inclined plate to enhance the separation efficiency. The inclination angle of the inclined plate is preferably about 10 to 60 °. The interval between the inclined plates is preferably about 10 to 500 mm.

FIG. 1 is a schematic vertical sectional view of an apparatus for separating and floating a metal-containing wastewater according to an embodiment of the present invention.

This treatment apparatus is provided with a pipe 10 for introducing metal-containing wastewater, a flotation tank 20, a take-out section 30 for taking up sludge (flock), and a pipe 40 for taking out treated water. .

The flotation tank 20 is divided into a plurality of compartments 26 by a plurality of inclined plates 24. Each inclined plate 2
4 has an upper end separated from one tank wall 21 and a lower end connected to the other tank wall 22. The metal-containing drainage introduction pipe 10 branches into the same number of branch pipes 12 as the compartment 26,
It is inserted into each compartment 26. This branch pipe 12
Is connected to a pipe 14 for adding an aqueous solution of hydrogen peroxide and a pipe 16 for adding an aqueous solution of alkali (sodium hydroxide in this embodiment).

The sludge take-out section 30 is provided so as to surround at least a part of the outer periphery of the upper end portion of the flotation tank 20.
The sludge that overflows the upper end of the tank 20 is discharged from the discharge unit 30.
And is taken out from the sludge discharge pipe 32. Note that a sludge scraping device may be provided above the tank 20.

The heavy metal-containing wastewater flows into the flotation tank 20 after NaOH and H ₂ O ₂ are added in the branch pipe 12. The addition of this NaOH causes heavy metal ions to become hydroxide flocs and decomposes H ₂ O ₂ to O ₂
A gas is generated, and this O ₂ gas adheres to the hydroxide flocs to lift the flocs. This floc is taken out of the tank 20 through the take-out part 30. The liquid from which the flocs have been separated is taken out from the treated water take-out pipe 40.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, 50 cupric chloride was prepared using the apparatus shown in FIG.
An experimental example in which a 0 ppm aqueous solution is treated will be described.

To this aqueous solution, a 10N aqueous solution of NaOH was added so that the pH after the addition became 11, and H
Concentration of H ₂ O ₂ in water after addition of 35 wt% aqueous solution of ₂ O ₂ was added so that the respective concentrations shown in Table 1.

This liquid is supplied to the flotation tank 20 at 1 m ³ / Hr
At an inflow speed of. The inclination angle of the inclined plate 24 is 30
°, the vertical interval of the inclined plate 24 is 200 mm, the length of the inclined plate 24 in the inclined direction is 500 mm, and the number of the compartments 26 is three.

Table 1 also shows the measurement results of the amount of sludge flowing out of the treated water discharge pipe 40 per unit time.

[0027]

[Table 1]

As shown in Table 1, in this experimental example, it is found that the outflow of heavy metal sludge (flock) is completely prevented by adding hydrogen peroxide at 13 mg / L or more.

The concentration of the cupric chloride aqueous solution is set to 1000
The same experiment was carried out except that the concentration was changed to 25 mg / L or 1500 mg / L. Floc efflux was caused by adding a 35% aqueous solution of hydrogen peroxide to the former by 26 mg / L or more, and the latter to 39 mg / L or more. Was completely prevented.

When ferric chloride, manganese chloride and chromium chloride are used in place of cupric chloride, the floc outflow is completely prevented by adding sodium hydroxide and hydrogen peroxide at substantially the same level. Was recognized.

[0031]

As described above, according to the present invention, heavy metal ions in wastewater can be efficiently removed. Further, according to the present invention, there is provided a metal-containing wastewater treatment apparatus having a small installation space.

[Brief description of the drawings]

FIG. 1 is a schematic vertical cross-sectional view of a floating separation treatment apparatus for metal-containing wastewater according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 20 flotation separation tank 21, 22 tank wall 24 inclined plate 26 compartment 30 sludge discharge section

Claims (3)

[Claims] 1. A method for treating metal-containing wastewater, comprising adding an alkali and hydrogen peroxide to the metal-containing wastewater, and separating the metal-containing wastewater by air bubbles that generate metal hydroxide flocs. 2. An apparatus for treating metal-containing wastewater, comprising: means for adding alkali and hydrogen peroxide to metal-containing wastewater; and separation means for floating and separating metal hydroxide flocs. 3. The method according to claim 2, wherein the separation unit includes a plurality of compartments partitioned by an inclined plate, a unit for introducing a liquid to be separated into the upper portion of each compartment, and a process water from a lower portion of each compartment. Means for draining metal-containing wastewater.