JPS5916590A - Treatment of waste water containing heavy metal - Google Patents

Abstract

PURPOSE:To remove efficiently harmful metallic ions, by adding ferrous ions and an alkali to the waste water, which is brought into contact with the magnetite particles formed with an iron oxyhydroxide layer on the surface, to control the pH thereof to neutral or above then stirring the water. CONSTITUTION:The magnetite or ferrite particles having an iron oxyhydroxide layer on the surface are charged into waste water contg. heavy metals, and the pH of the liquid is controlled to adsorb heavy metals ions on said particles, whereby the liquid is separated to precipitate and supernatant liquid. Ferrous ions and an alkali are added to the liquid contg. precipitate to control the pH thereof to >=8, and an oxidizing gas is blown to oxidize the ferrous salt compd. The blowing of the oxidizing gas is then stopped and ferrous ions are added to the liquid; further, the pH of the liquid is controlled to neutral or above, whereafter the liquid is stirred to form the crystal particles precipitated with magnetite or ferrite so that the heavy metallic ions are incorporated into the crystal lattice of the above-described precipitated crystal particles.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment method for removing harmful metals contained in waste water such as factory waste liquid.

The so-called "ferrite method" has been developed as a method for removing harmful metals from wastewater, and is already in practical use as an effective method for wastewater treatment.This method consists of the following steps: The amount of ferrous salt (mainly ferrous sulfate, FeSO4, 7
H20) Pour into waste water and stir.

■ p l-1 adjustment step Next, add q of alkali (e.g. caustic soda Na0H),
Adjust the pH of the mixed wastewater and generate mixed hydroxide in the wastewater.

(2) Oxidation process pH After adjusting the pH, heat to 60-70°C using steam or a heater, then introduce air into the waste water to proceed with the ferrite reaction. As the ferrite reaction progresses, heavy metals are incorporated into the ferrite crystal lattice and precipitate as ferrite sludge.

By carrying out the above treatment steps, the ferrite precipitate is finally separated from the demolding metal water and the heavy metals are removed from the waste water.

This method utilizes the reaction of , but since the type of compound ultimately produced by the oxidation of ferrous ions is determined by the reaction conditions, specific conditions are required to produce ferrite. Processing must be carried out under certain conditions. Figure 1 shows how the crystal structure of the iron compound produced changes depending on the alkali addition ratio and reaction temperature when an alkali is added to a ferrous salt solution and an oxidation reaction is actively carried out. It is. As is clear from the figure, Fe3O4 is produced at high reaction temperatures, and Fe00H is produced at low temperatures. Therefore, in order to generate ferrite, it is necessary to process at a high temperature of at least 60°C, and ferrite generation also depends on the amount of alkali added, oxidation time, etc., so setting the processing conditions is difficult. It had been.

Separately, there have been attempts to carry out the oxidation reaction quietly at room temperature, but these had drawbacks such as requiring special equipment for the oxidation reaction and requiring a long time for the oxidation reaction.

In addition, when using the above method, the conditions for magnetite production and the optimal conditions for completely incorporating the metal ions (such as Cd2+) into the crystal lattice of magnetite do not necessarily match, so heavy metal ions that can be processed It was considered unavoidable that there were limits to the types and concentrations of carbon dioxide.

Although the above method is effective when applied to the treatment of wastewater containing relatively large amounts of harmful metal ions, there is no conventional method that is effective for the treatment of large quantities of dilute liquids containing small amounts of harmful metal ions (
In many cases, the liquid should be discharged as is, so in order to achieve the so-called total volume control, it is necessary to develop an effective treatment for diluted liquid (
It was wanted.

The present invention uses a relatively small amount of harmful metal ions (heavy metal ions).
It provides an effective method for treating dilute wastewater containing iron oxyhydroxide in the form of iron oxyhydroxide on the surface. The resulting magnetite or ferrite particles are put into heavy metal-containing wastewater, the pH of the liquid is adjusted to allow each particle to adsorb heavy metal ions, and the precipitate that has settled in the liquid is separated from the clear liquid. By adding ferrous ions and alkali to a solution containing a precipitate, p in the solution can be reduced.
After adjusting the temperature to I-128 or higher and oxidizing the ferrous salt compound by blowing in air or other oxidizing gas, stop blowing in the oxidizing gas, add ferrous ions, and then add alkali. Adjust the pH of the liquid to around neutrality or higher, and then do not blow in oxidizing gas (stir the liquid) to finally form magnetite or ferrite precipitate in the liquid, and turn it into iron oxyhydroxide. This method is characterized by incorporating the adsorbed heavy metal ions into the crystal lattice of precipitated crystal particles.

In the present invention, the magnetite or ferrite particles formed on the surface of the iron oxyhydroxide 2 can be obtained by the following treatment. That is, add an alkali to the liquid containing ferrous ions, set its p f ('118 to 11), blow air or other oxidizing gas at room temperature,
The oxidation of the ferrous salt compound is progressed while stirring with air bubbles generated in the liquid. As is clear from Figure 1, when the liquid is warm and at room temperature, most of the precipitate is yellowish brown iron oxyhydroxide, with a small amount of black magnetite mixed in, resulting in a brownish brown precipitate as a whole. . After this precipitation occurs, stop blowing in the oxidizing gas and add ferrous ions to the liquid. Since the pI-1 of the liquid decreases due to the addition of the ion, add an alkali to return the pH to around neutrality or higher, and then add an oxidizing gas (mechanical or inert gas such as A gas is blown into the liquid and the liquid is stirred.As a result of this stirring, all the iron oxyhydroxide produced in the liquid changes to magnetite, which becomes a precipitate with excess ferrous ions adsorbed on its surface. By further blowing an oxidizing gas such as air into this precipitate-depleting liquid at room temperature, the precipitate F
When Fe2+ ions adsorbed on the surface of e3O4 are oxidized, at room temperature, iron oxyhydroxide Fe0
011, and as shown in FIG. 2, magnetite (or ferrite) whose surface is covered with a layer of iron oxyhydroxide is generated in the liquid.

In the present invention, the Fe001-1 particles are adsorbed (and the filtration state is also referred to as the Fe001-1 oxide layer).

The present invention utilizes the precipitate obtained in step 1 above and uses the precipitate as a treatment agent to treat heavy metal-containing wastewater.

As is well known, iron oxyhydroxide has excellent adsorption properties for heavy metal ions, and it forms a precipitate in liquids containing heavy metal ions. By introducing heavy metal ions, such as Cd,
Mn, Co, Ni, Pl), Zn, Cu,
Which ion M2+ (or M”) &
Well, as shown in Figure 6, it is adsorbed on the surface of the precipitate.

In addition, since the above precipitate is mainly composed of magnetite (or ferrite) with a high specific gravity, it settles in a short time.
Concentrated solution of heavy metal ions including the precipitate except for the supernatant iY 2
Transfer to a small container. This /1: Add ferrous ions to the concentrated liquid in the container, and then add an alkali to increase the pI of the liquid.
After adjusting −1 to 8 to 11, air or other oxidizing gas is fed into the liquid to oxidize the Fe” ions. After the oxidation reaction is complete, the blowing of the oxidizing gas is stopped, and then ferrous ions are added. was added, and further alkali was added to increase the pI-1 of the solution.
i Return the temperature to near neutrality and then stir it mechanically or by blowing in a gas such as nitrogen without supplying an oxidizing gas.

Through the above treatment, the heavy metal ions adsorbed on the iron oxyhydroxide layer on the magnetite surface are incorporated into the crystal lattice of magnetite to form ferrite, which precipitates in the liquid, and the surface of the precipitate contains excess Fe2+ ions. is absorbed. If this precipitate is washed and separated from the liquid, Fe2+ ions remain in the liquid.

This liquid containing Fe2+ ions becomes the stock solution of the filtration treatment agent used in the method of the present invention, and if an oxidizing gas is injected at room temperature into the liquid containing magnetite and ferrite 7 which have adsorbed Fe2+ ions, the Fe2+ ions can be oxidized. The iron oxyhydroxide Fe0O1-I Ffi 'Y forms a precipitate of magnetite and ferrite particles, and this precipitate serves as the treatment agent of the present invention as it is.

According to the present invention, not only can the by-products produced during heavy metal wastewater treatment be used as wastewater treatment agents, but also the wastewater from which the byproducts have been removed can be used as is as a stock solution for producing treatment agents. In the present invention, when the treatment agent is put into the waste liquid containing heavy metals, all of the heavy metal ions contained in the liquid can be adsorbed and precipitated by the treatment agent, so by removing the supernatant liquid, A major feature is that the wastewater treatment is substantially completed, and the precipitate that has adsorbed heavy metal ions and the liquid containing this precipitate can be regenerated into a wastewater treatment agent through post-treatment. According to the present invention, a large amount of dilute heavy metal ion-containing waste liquid can be treated in large quantities without being affected by temperature conditions or reaction conditions, and without the need for special equipment, and is fully compliant with regulations on the total amount of heavy metal waste liquid. It is something that can be done and has an effect.

The present invention will be explained in detail below.

(Example) Cd, Mn, Co, Ni, Fe, Zn,
90 containing 10 ppm f each of Cu and Cr ions
Magnetite sludge with iron oxyhydroxide layer formed on the surface as a treatment agent in 0me wastewater 0.7y'i water 1o
ome, and further added an appropriate amount of Alka IJY to adjust the p I-1'fg of the liquid to 10.5. This waste water was appropriately stirred to cause heavy metal ions to be adsorbed on iron oxyhydroxide, and after 2 hours, the treatment agent was allowed to settle. The time required for sedimentation was approximately 10 minutes. Confirm that the supernatant liquid does not contain heavy metal ions, and add SO corresponding to 415.
Approximately 100 me including sediment accumulated at the bottom after discharging omg
Transfer the concentrated liquid to a 200 W Le beer force, and add t to the liquid.
' e SO4.7H20w 4 y was added, and an appropriate amount of alkali was added to maintain the p + -1'i of the liquid at 9.5, and air oxidation was performed for about 1 hour by feeding air at 20 m//min. After one hour, the air blowing was stopped, and l'esO4.7H,, Oy 2 y was added again, and an appropriate amount of alkali IJ Y was added to adjust p I-1 to 9. When nitrogen gas was blown into the liquid for about 2 hours and the liquid was stirred, a black precipitate was formed in the liquid. These precipitates were all magnetite and ferrite particles. Surplus Fe2+ added later to these precipitate particles
In order to oxidize the Fe ions, air was blown into the solution for about an hour to convert the Fe 2+ ions into iron oxyhydroxide, which was regenerated as a treatment agent used in the method of the present invention. Of course, heavy metal ions were not eluted from the produced ferrite particles.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the difference in products depending on the addition ratio of alkali and reaction temperature in the oxidation reaction of ferrous ions.
3 are explanatory diagrams showing changes in by-products according to the method of the present invention. Patent Applicant: NEC Environmental Engineering Co., Ltd. Attorney: Naka Kanno Figure 1 not-1/2Fe Figure 2

Claims (1)

[Claims] (1) Magnetite or ferrite particles with an iron oxyhydroxide layer formed on the surface are poured into heavy metal-containing wastewater, the pH of the liquid is adjusted to -1, and heavy metal ions are adsorbed to the iron oxyhydroxide on the surface of each particle. The precipitate that has settled in the liquid is separated from the clear liquid, and ferrous ions and alkali are added to the liquid containing the precipitate to adjust the p l-I Y of the liquid to 8 or more, and then air or After blowing in another oxidizing gas for a certain period of time to oxidize the ferrous salt compound, the blowing of the oxidizing gas is stopped, ferrous ions are added to the liquid, and alkali IJ 'aj is added to the liquid. By adjusting the p + -47 to around neutrality or higher, and then stirring the liquid, magnetite or ferrite precipitated crystal particles are finally generated in the liquid, and the heavy metal ion precipitates that were initially adsorbed on the iron oxyhydroxide layer are A heavy metal wastewater treatment method characterized by working in the crystal lattice of crystal particles.