JP2000246262A - Method of reducing sludge generated when removing heavy metals from waste liquid - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To chemically remove heavy metals from waste liquid,
The generated sludge is greatly reduced, the burden on processing operations such as filtration and drying of the sludge is reduced, the volume reduction effect in the case of radioactive sludge is increased, and storage costs and storage area are made more efficient. The waste liquid containing heavy metal is iron chloride (FeCl ₃ ).
And neutralized to generate iron hydroxide (Fe (OH) ₃ ). The iron hydroxide is brought into a floc state to adsorb and precipitate the various heavy metals contained therein, and the precipitated iron hydroxide floc is filtered. In the method of removing heavy metals from the waste liquid, the filtered iron hydroxide sludge is further dissolved in an HCl solution, the pH is adjusted, and added to the waste liquid of the next lot for reuse. This operation is repeated a required number of times to reduce the amount of generated sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing sludge generated when a heavy metal is chemically removed from a waste liquid as much as possible, particularly when the generated sludge is radioactive waste. It is concerned with the above method which is effective.

[0002]

2. Description of the Related Art There are various methods for chemically removing heavy metals from waste liquors, and a typical one is neutralization. However, since it is difficult to remove a trace amount of impurities by this method, generally, FeCl ₃ is added to the waste liquid and neutralized to generate iron hydroxide Fe (OH) ₃ . ) Is a method of adsorbing and precipitating various metals. This method has a wider range of application than other methods and is an effective means that has been practiced for a long time.

[0003]

However, this method involves the generation of a large amount of precipitates, that is, sludge, as compared with the heavy metals to be removed, and there is one aspect in which this disposal is problematic.
This is not a problem even if the waste liquid is a general waste liquid, even if a little sludge is generated. However, especially when the object to be removed is radioactive sludge such as uranium (U). In this case, the generated sludge cannot be carried out of the controlled area and will be stored permanently.

Therefore, at present, fresh FeCl ₃ is added to each lot of wastewater, and the generated sludge is filtered, dried and stored as it is. Therefore, in such a radioactive sludge, it is an important subject to suppress the generation before the generation.

The present invention addresses the above-mentioned situation, and in particular, attempts to reuse sludge that has been subjected to precipitation treatment by the above-mentioned chemical method, thereby significantly reducing the amount of generated sludge as compared with the prior art, and for filtering and drying sludge. Reduces the burden on processing work and enhances the effect of reducing the volume of radioactive sludge.
The purpose is to increase the efficiency of the storage area.

[0006]

That is, a feature of the present invention to achieve the above object is that iron chloride (FeCl ₃ ) is added to a waste liquid containing heavy metals and neutralized by adding iron chloride (FeCl ₃ ).
(OH) ₃ ), and the iron hydroxide is brought into a floc state to adsorb and precipitate the various heavy metals contained therein. In addition, the precipitated iron hydroxide floc is filtered to remove heavy metals from the waste liquid, and the filtered water is used to remove heavy metals. H to iron oxide sludge
It is to dissolve in a Cl solution, adjust the pH, add to the waste liquid of the next lot and reuse it, and thereafter repeat the addition to the next lot a required number of times to reduce the amount of generated sludge. In particular, the invention according to claim 2 is the most effective one for implementing the present invention when the heavy metal contained in the waste liquid is a radioactive substance.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the method of the present invention will be described in detail.

First, according to the method of the present invention, FeCl ₃ is added to a conventional waste liquid, and then neutralized to generate iron hydroxide. Various heavy metals are added to a floc of the iron hydroxide (a flocculent floating substance). Is adsorbed and precipitated, followed by filtration.

In this method, as shown in FIG.
FeCl containing HCl ₃And then
Neutralized with NaOH in neutralization tank 2
(OH)₃Generate. And this iron hydroxide
It is sent to a settling tank 3 called a thickener to adsorb heavy metals
The floc of iron hydroxide precipitated at the bottom and
Separate the treated water and confirm the control value of the separated supernatant
And drain below that.

On the other hand, the precipitated iron hydroxide flocs adsorbed on heavy metals are subsequently filtered by a filter 4 such as a filter press, and the iron hydroxide sludge is stored as it is, and the squeeze liquid is returned to the waste liquid tank 1.

As described above, this method has a problem in storage of sludge. Therefore, the method of the present invention further includes a step after filtration in the above method. That is, as shown by the following chemical reaction formula, once the generated iron hydroxide sludge is
Is used again, and this is used repeatedly.

The principle chemical reaction formula in the method of the present invention is as follows: FeCl ₃ + NaOH → Fe (OH) ₃ (adsorption removal of heavy metal) Fe (OH) ₃ + HCl → FeCl ₃ FeCl ₃ + NaOH → Fe (OH) ₃ (Heavy metal adsorption removal) This is a repetition of Fe (OH) ₃ + HCl → FeCl ₃ .

Therefore, in the method of the present invention, a pH adjusting tank 5 is provided following the filter 4 such as a filter press in FIG. 1, and the heavy metal-containing iron hydroxide sludge filtered by the filter 4 is supplied to the pH adjusting tank 5. And adding HCl to reflux the FeCl ₃ to the initial waste liquid tank 1 containing the waste liquid of the next lot while keeping the heavy metal adsorbed.

[0014] Then, the method of the present invention is essentially required several times a FeCl ₃ was used such as described above, it is repeatedly used that for example up to about 10 times, when Thereby repeated about 10 times, introduction of FeCl ₃ is Only the first one can process 10 lots of wastewater,
The generated sludge is 1/10 of the conventional method. Reducing the amount of sludge generation to, for example, 1/10 in this manner not only reduces sludge, but also reduces the burden on processing operations such as filtration and drying of sludge.

[0015]

EXAMPLES Examples of the method of the present invention for uranium waste liquid will be described below. First, uranium waste liquid (uranium radioactivity measurement 6
In order to maintain the state of FeCl ₃ at 6.8 mBq / cc), an FeCl ₃ solution containing HCl is added to pH 2.2. Thereafter, the mixture was neutralized with NaOH to pH 8 to cause coagulation and precipitation, followed by filtration.
It was completely dissolved with Cl, added to the waste liquid of the next lot, neutralized and filtered, and the filtrate was measured for radioactivity. Then, the above operation was repeated six times. FIG. 2 shows the results of the implementation.

As shown in FIG. 2, the operation was performed six times, but the uranium removal rate hardly changed. Also, naturally, heavy metals such as uranium adsorbed during sludge adsorption also dissolve in HCl,
It is expected that the initial uranium concentration will increase twice after the second time, but it can be seen that the increase in the initial uranium concentration does not significantly affect the uranium removal rate.

From the above results, it can be seen that even when the sludge is repeatedly reused by dissolving in HCl a plurality of times, the results are almost the same as those of the first lot. The above example is repeated up to six times, but this is because the same effect is obtained by repeating up to six times, and thereafter, the operation is stopped. Thus, ten or more repetitions are possible. It appears to be.

Further, although the above-described embodiment is a case where uranium is used, it is easy to guess that the present invention is not limited to uranium and can be applied to other radioactive wastewater and general heavy metal removal.

[0019]

According to the present invention, as described above, iron hydroxide sludge generated during the chemical removal of heavy metals from wastewater is filtered, dissolved in HCl, and used again for treatment. Is a method of reducing FeC
l ₃ is turned relative to sludge formation amount conventionally by treating multiple batches wastewater reused only once at the beginning, significantly with it out to reduce, as a result of the sludge load suppression, sludge treatment The operation also has a noticeable effect that is greatly reduced.

Furthermore, when the sludge produced by the method of the present invention is radioactive waste, there is a remarkable advantage that the storage cost and storage area are greatly reduced as compared with the prior art.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing the steps of carrying out the method of the present invention.

FIG. 2 is a chart showing the relationship between the number of repetitions and the radioactivity concentration of a filtrate after treatment.

[Explanation of symbols]

 Reference Signs List 1 waste liquid tank 3 sedimentation tank 4 filter 5 pH adjustment tank

Claims (2)

[Claims] 1. A waste liquid containing a heavy metal contains iron chloride (FeC).
l ₃ ) and neutralized with iron hydroxide (Fe (O
H) ₃ ), the iron hydroxide is brought into a floc state to adsorb and precipitate the various heavy metals contained therein, and the precipitated iron hydroxide floc is filtered to remove heavy metals from the waste liquid. H to iron oxide sludge
A waste liquid characterized by reducing the amount of generated sludge by dissolving in a Cl solution, adjusting the pH, adding to the waste liquid of the next lot and reusing it, and thereafter repeating addition to the waste liquid of the next lot a required number of times. Of sludge generated when removing heavy metals from wastewater. 2. The method according to claim 1, wherein the heavy metals contained in the waste liquid are radioactive substances.