JPH09235117A - Production of neutralized material having high bulk density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a neutralized material having a high bulk density from a solution containing zinc by preadding zinc oxide to the solution and then raising the pH to a specific value or above when neutralizing the solution containing the zinc. SOLUTION: Zinc oxide is preadded to a solution containing zinc and the pH thereof is then raised to >=9.5 when neutralizing the solution containing the zinc. The amount of the zinc oxide added at that time is preferably 0.03-1 expressed in terms of zinc oxide/zinc hydroxide (weight ratio) based on the amount of zinc in the solution and the pH thereof is preferably raised to 10.0-12.0. For example, various amounts of the zinc oxide (having 80μm average particle diameter) are added to 1.0L solution containing zinc sulfate in an amount of 1.0g/L expressed in terms of zinc and the pH thereof is then regulated to 10.5 by using Ca(OH)2 to precipitate the zinc. After completing the reaction, pH is reduced to 9.5 by using sulfuric acid and a nonionic flocculant is added in an amount of 0.35g/m<3> thereto. The resultant mixture is allowed to stand for 24hr to determine the volume occupied by the neutralized material in the aqueous solution and the amount of the neutralized material. Thereby, the slurry concentration is calculated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a zinc-containing solution,
The present invention relates to a method for producing a neutralized product having a large bulk density.

[0002]

2. Description of the Related Art Generally, in the wastewater treatment process of a factory,
The wastewater containing metal ions is neutralized and the metal ions contained in the waste liquid are fixed as hydroxides. Then, the obtained neutralized product slurry is sent to, for example, a thickener, and the neutralized product is settled and concentrated under the thickener there. The supernatant liquid of the thickener is drained from the upper portion as an overflow liquid and sent to the next step or discharged as it is. The neutralized product that has settled is extracted as an underflow and filtered.

In order to efficiently separate the neutralized product and the supernatant liquid, the neutralized product has a good settling property, and the precipitated neutralized product is concentrated to reduce the volume occupied in the thickener.
It is necessary to be able to increase the volume occupied by the supernatant. For this purpose, coagulants are generally added to crosslink the neutralized product particles suspended in water to form large flocs. For this reason, various organic and inorganic coagulants have been developed, and coagulants suitable for the type and liquidity of the starch are selected.

However, there is no conventional technique for reducing the volume of the neutralized substance settled in the thickener, and it has been dealt with by extending the residence time of the neutralized substance in the thickener.

Generally, a hydroxide is a neutralized product obtained by neutralizing an aqueous solution containing various metal ions, has a fine bulk density, and it is difficult to prepare a neutralized product having a large bulk density. There is. Among them, zinc hydroxide has a particularly low bulk density, and even if the conditions at the time of neutralization were changed, only those having a low bulk density could be produced. As a result, the neutralized product obtained by the treatment of wastewater containing zinc did not fall below a certain level even when it was allowed to settle in the thickener for a sufficient time.

[0006]

An object of the present invention is to provide a method capable of producing a neutralized product having a large bulk density from a solution containing zinc.

[0007]

As a result of various studies for achieving this object, when neutralizing a solution containing zinc, zinc oxide was previously added to the solution containing zinc, and then the pH was adjusted to 9.5. The amount of zinc oxide added is preferably 0.03 to 1 of zinc oxide / zinc hydroxide ratio (weight ratio) with respect to the amount of zinc in the solution, and pH is 10.0 to 1
It is set to 2.5.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention utilizes the fact that a zinc neutralized product produced at high pH has a dense structure, and that zinc oxide particles added in advance promote its growth.

Although a small amount of zinc oxide to be added is effective, it is necessary to change the zinc oxide to be added in accordance with the amount of zinc hydroxide produced in order to effectively act as seed crystals. That is, it is desirable to add zinc oxide in the range that the zinc oxide / zinc hydroxide ratio (weight ratio) is 0.03 to 1. The shape of zinc oxide to be added is not particularly limited, and a sufficient effect can be expected unless the particle size is extremely large.

Neutralization of an aqueous solution containing zinc is carried out by using Ca (OH)
₂ , a so-called general neutralizing agent such as NaOH can be used and is not particularly limited.

A neutralized product having a high bulk density can be obtained by neutralizing an aqueous solution containing zinc as a main component at a pH of 9.5 or higher. It is not clarified why a dense neutralized product is obtained by neutralizing at pH 9.5 or higher. The present inventors found that the isoelectric point of zinc hydroxide was pH 1 depending on the liquid composition.
It is said to be around 0 to 11, and it is considered that a neutralized product having a high bulk density can be obtained by entering or passing the isoelectric point during neutralization.

According to X-ray diffraction, such a neutralized product having a high bulk density has ZnO as a main component. Therefore, if zinc oxide is added to the solution in advance, zinc oxide will become the nucleus of the neutralized product produced by neutralization and act as a so-called seed crystal,
As a result, a neutralized product having large crystals and a high bulk density can be obtained.

When neutralized at a pH of 9.5 or higher, a neutralized product having a high bulk density can be obtained, but at a pH of 10.5 or higher, zinc is redissolved. Therefore, in the case of wastewater treatment, the pH must be adjusted again to pH 9.0 to 9.5, which has the lowest zinc elution amount. However, the bulk density of the neutralized product obtained by such treatment is high and is not affected. However, considering economic efficiency, the pH is 12.5.
It is preferable to set the following.

The method of the present invention can also be used for producing a zinc compound for electronic materials having a high bulk density, which has recently been required.

[0015]

Next, the present invention will be further described with reference to examples.

Example 1 Various amounts of zinc oxide (average particle size: 80 μm) were added to 1.0 liter of a zinc sulfate solution containing 1.0 g / liter of zinc, and then Ca (O 2
The pH was adjusted to 10.5 with H) ₂ to precipitate zinc. After the completion of the reaction, the pH was lowered to 9.5 with sulfuric acid, and 0.35 g / m ^{3 of} a nonionic flocculant (trade name: Aronfloc N-101 manufactured by Toagosei Co., Ltd.) was used.
At a rate of After that, the mixture was allowed to stand for 24 hours, the volume occupied by the neutralized product in the aqueous solution and the weight of the neutralized product were determined, and the slurry concentration was calculated. Table 1 shows the results.

[0017] (Example 2) Zinc was precipitated in the same manner as in Example 1 except that the average particle diameter of the zinc oxide used was 5 µm, and the slurry concentration of the neutralized product was determined. The results obtained were the same as in Example 1.

Example 3 The amount of zinc oxide added was 0.10.
Zinc was precipitated in the same manner as in Example 1 except that the pH at which zinc was precipitated was set as shown in Table 2 to determine the slurry concentration of the neutralized product. The obtained results are also shown in Table 2.

[0019] It can be seen from Table 2 that a neutralized product having a good bulk density is obtained when the pH is 9.5 or more.

[0020]

As described above, according to the method of the present invention,
When neutralizing an aqueous solution containing zinc as a main component, zinc oxide is added to a zinc-containing solution in advance, the zinc oxide is used as a seed crystal, and the pH is neutralized at 9.5 or more. Therefore, a neutralized product having a high bulk density can be manufactured.

Claims (2)

[Claims] 1. When neutralizing a solution containing zinc, zinc oxide is previously added to the solution containing zinc, and then the pH is adjusted to 9.
A method for producing a neutralized product having a large bulk density, which is characterized by increasing the number to 5 or more. 2. A zinc oxide / zinc hydroxide ratio (weight ratio) of 0.03 to 1 with respect to the amount of zinc in the solution, and a pH of 10.0 to 12.5. The manufacturing method described.