JPS60166087A - Treatment of waste water containing high-concentration salts, copper and zinc - Google Patents

Abstract

PURPOSE:To enhance the flocculating property, and to treat the waste water without contaiminating the membrane by adding zinc and then an alkaline agent to the waste water to regulate the pH of the waste water to 9-11, separating liquid from solid, and desalting the formed treated water with the reverse osmosis method. CONSTITUTION:A zinc salt is added to the waste water contg. high-concn. salts, copper, and zinc, and agitated. An alkaline agent is added to the waste water to regulate the pH to 9-11. Subsequently, solid is separated from liquid, and the treated water is desalted by the reverse osmosis method. The formed sludge contg. zinc is recovered, and reutilized for the treatment of the original waste water. Zinc sulfate, zinc chloride, zinc nitrate, etc., for example, can be used as the zinc salt. The zinc salt, 0.25 times the zinc concn. in the original water, is usually added. By said method, the dissolved metals can be satisfactorily flocculated without using any high molecular flocculants.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying strongly acidic wastewater containing high concentrations of salts, copper, and zinc, such as pickling wastewater discharged from copper rolling mills and the like.

Strongly acidic wastewater containing highly concentrated salts, copper, and zinc is discharged from copper rolling mills. In recent years, discharge regulations have become stricter, and salts must also be removed, especially when the wastewater is used for agricultural purposes, so closed systems are increasingly being adopted in which the wastewater is reused without being discharged outside the system. . Conventionally, the method used to treat this type of wastewater was to neutralize the wastewater with caustic soda, coagulate and precipitate metals as hydroxides, separate them, and then desalinate them using a reverse osmosis device. There is. However, when metal-containing wastewater is subjected to neutralization treatment, the sedimentation properties of flocs deteriorate, resulting in deterioration of treated water quality and membrane contamination. In this case, there is a method to improve sedimentation by adding a polymer flocculant, but when desalting with a reverse osmosis device, the polymer flocculant remaining in the treated water causes membrane contamination. The polymer flocculant must be removed using activated carbon treatment, ozone oxidation, etc., which has the disadvantage of complicating the operation.

The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art, to improve the flocculating property with a simple operation without using a polymer flocculant, and to produce wastewater containing high concentration salts, copper, and zinc that does not cause membrane contamination. The purpose is to provide a processing method. This objective is achieved according to the invention by adding zinc salts.

That is, the method for treating wastewater according to the present invention can treat highly concentrated salts,
Zinc salts are added to strongly acidic wastewater containing copper and zinc, and after stirring, an alkali agent is added to adjust the wastewater to a PTT of 9 to 11, followed by solid-liquid separation, and the treated water is desalted by reverse osmosis. The feature is that the resulting zinc-containing sludge is recovered and reused for the treatment of raw wastewater.

When treating strongly acidic wastewater containing high concentrations of salts, copper, and zinc, it is difficult to form flocs even if aluminum-based flocculants or iron-based flocculants are added. However, it was found that when zinc salt was added, flocs were formed well and flocculation and sedimentation properties were significantly improved.

This improvement in sedimentation is probably due to the fact that the flocs produced by the addition of the zinc salt act as a mother floc and coprecipitate the metal hydroxide flocs produced after the pit adjustment.

In the method of the present invention, as the zinc salt, for example, zinc sulfate, zinc chloride, zinc nitrate, etc. can be used. The amount added is usually 0.25 times or more the zinc concentration in the raw water.

When zinc salt is added to wastewater and stirred, the pI (pI) is adjusted to 9 to 11 with a commonly used alkaline agent such as sodium hydroxide, and the metals dissolved in the wastewater form flocs, and the above-mentioned mother floc Therefore, the flocs have good flocculation and sedimentation properties, and the flocs are easily separated into solid and liquid.

The treatment liquid thus obtained is desalted by reverse osmosis.

According to the method of the present invention, it is possible to successfully achieve flocculation and precipitation of dissolved metals without using a polymer flocculant, so that membrane contamination in a reverse osmosis device can be significantly reduced. In addition, by reusing the collected sludge that has been separated into solid and liquid for the treatment of raw wastewater, it is possible to similarly improve the flocculation and sedimentation of dissolved metals, thereby reducing the amount of zinc salt added and purifying wastewater. Processing can be performed effectively.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto.

Example The samples were wastewater with the following water quality.

pH1,94 SO41830■/P = NO3866mg/β Cu 163IT1g//! Zn 578 mg/β Electrical conductivity 7740 μS/cm 0.3 g of zinc sulfate as Zn was added to the sample 1j2 and stirred for 5 minutes at 1100 rpm using a stirring device. Next, after adjusting to pIIIO by adding sodium hydroxide, the mixture was stirred for 5 minutes, stirred at 40 rpm for 10 minutes, and left to stand.

The SV and Fl values were measured while varying the standing time. Fl
The value is an index of colloid concentration in water, and for hollow fiber spiral RO, in the case of Fl<3,
If there is no trouble, if 3<l"l<6, then trouble will gradually occur, and if F I > 6, it is said to be impossible to operate.

For comparison, the same operation as the conventional method was performed except that zinc sulfate was not added, and the SV and Fl values of the treated water were measured.

The results are shown in the table below.

As is clear from this table, according to the method of the present invention, sedimentation separation can be performed in a much shorter time than the conventional method.

The treated water after sedimentation separation could be efficiently desalinated using a reverse osmosis device, and membrane contamination did not occur over a long period of time.

Similar good results were also obtained when the separated sludge was reused to treat raw wastewater.

patent applicant Hitachi Plant Construction Co., Ltd.

Claims (1)

[Claims] In order to purify strongly acidic wastewater containing high concentrations of salts, copper, and zinc, zinc salts are added to the wastewater, and after stirring, an alkali agent is added to adjust the wastewater to pH 9 to 11, followed by solid-liquid separation.
A method for treating wastewater containing highly concentrated salts, copper, and zinc, characterized in that treated water is desalinated by reverse osmosis, and the resulting zinc-containing sludge is recovered and reused for the treatment of raw wastewater.