JP3265528B2 - Treatment of soil contaminated by heavy metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for repairing soil contaminated with heavy metals, and more particularly to a method for chemically reacting heavy metal in soil with ferrous iron under specific conditions to obtain a chemically stable double oxide. The purpose is to prevent heavy metals from being eluted by generating substances.

[0002]

2. Description of the Related Art In recent years, due to active industrial development, concerns about environmental pollution due to new chemical substances, and the presence of soil pollution containing harmful substances accumulated in the past in connection with the rapidly increasing problem of waste disposal have been increasing. It has been.

[0003] Of these, the factory sites where the factories located in urban areas have shrunk and relocated are now being used for large-scale development such as construction of condominiums and waterfronts. Therefore, it is necessary to take measures to remove and detoxify polluted soil in accordance with the "Land Environment Standards".

As a means for restoring the soil environment contaminated by these heavy metals, a method of confining after performing a chemical treatment, a method of solidifying with concrete, for example,
A method of reducing soil contaminated with valent chromium (Japanese Patent Publication No. 53-15990) is disclosed.

However, in the case of the above-mentioned processing method for carrying out the containment, a containment treatment such as a water-blocking work or a cut-off work is required in accordance with the degree of elution after the insolubilization treatment, so that the cost is expensive.

[0006] In the case of the cement solidification method, when the treated soil is left untreated, carbon dioxide gas in the air lowers the pH, and there is a concern that harmful metals may be re-eluted.

On the other hand, the hexavalent chromium reduction treatment method is intended for the contamination of hexavalent chromium alone and detoxifies heavy metals other than chromium or soil contaminated with chromium and a plurality of other heavy metals. Had the disadvantage of not being able to do so.

[0008]

As described above, in the conventional treatment method, it has not been determined that the soil contaminated with heavy metals is completely rendered harmless. There is a demand for the development of a treatment method.

[0009]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and as a result, have developed a chemically stable chemical treatment method as a method for detoxifying soil contaminated with heavy metals. I was able to.

That is, in the present invention, the particle size is preferably 8 mm or less, more preferably 5 mm or less.
mm and add heavy water and ferrous salt to the soil contaminated with heavy metals to insolubilize heavy metals in the soil by stirring ,
The above stirring was carried out at a pH of 7 to 12, preferably 7.5.
It is characterized in that it is carried out while keeping it at ~ 11.5 .

[0011]

The heavy metal contaminated soil to be treated in the present invention has a particle size of 8 mm or less, preferably 5 mm or less. The larger the particle size, the more the heavy metal in the soil will be treated in the next stirring process. And reaction with ferrous iron does not occur more than enough.

Then, water for kneading is added to the contaminated soil having the above-mentioned particle diameter, and a ferrous salt and, if necessary, an acid or alkali are added to the wet mixture, and the mixture is uniformly dispersed and stirred.

In this case, stirring is maintained while adjusting the pH of the mixture to 7 to 12, preferably 7.5 to 11.5, but the added ferrous iron reacts with the heavy metal in the mixture, and during the kneading, In the process of gradually forming a crystal lattice of iron oxide while being subjected to air oxidation, it changes into an iron-based double oxide having a spinel-type crystal structure.

The reaction of the spinel-type iron-based double oxide is as follows:
Divalent metal oxide (XO) and trivalent metal oxide (Y ₂ O)
₃ ) is equimolarly bonded to form a spinel compound represented by the general formula of normal spinel type XY ₂ O ₄ and reverse spinel type Y (XY) O ₄ , wherein X is Fe,
It is a heavy metal such as Zn or Pb, and it is considered that these heavy metals are taken in place of iron at the position to be occupied by iron atoms and fixed.

In the embodiment, ferrous sulfate is used as the above-mentioned ferrous salt. In addition, iron salts obtained by dissolving iron scrap in sulfuric acid and other iron salts can be used.

Further, in the present invention, an insolubilization test was carried out under the temperature conditions during the stirring, and when the amount of ferric iron added and the soil particle size were the same, the treatment was carried out at a constant temperature of 70 ° C. as an example. Cd in soil
It was confirmed that it had an effect on the insolubilization of.

Therefore, in the case of Cd-containing soil, the reaction can be promoted by setting the stirring temperature below the boiling point of the solution, if necessary. However, it is preferable to adjust the temperature to 80 ° C. or less from the viewpoint of cost.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to examples, but the scope of the present invention is not limited to these examples.

(Embodiment 1)

The contaminated soil containing heavy metals adjusted to the particle size shown in Table 1 was put into a screw-type kneader, and then ferrous sulfate as a ferrous salt and water were added, and both were uniformly mixed and dispersed. In this case, the proportion of ferrous iron added to Cu ²⁺ , Pb ²⁺ , and Zn ²⁺ in the contaminated soil A was one equivalent of the chemical equivalent required for the reaction. Appropriate amounts were added as determined in advance.

[0022]

[Table 1]

Since the wet mixture thus obtained is acidic, the mixture obtained is divided into two types of 500 g each while adding nitrite lime to keep the pH at 8.0, one at room temperature and the other at room temperature. The kneading reaction was carried out for 60 minutes while heating to 70 ° C. to obtain the desired spinel-type double oxide.

Table 2 shows the results obtained by performing a dissolution test on the spinelized soil obtained by the above-mentioned reaction in accordance with the Environment Agency Notification No. 13 method.

[0025]

[Table 2]

For comparison, two kinds of dissolution tests were carried out using the above-mentioned contaminated soil A in the conventional method: (1) use as is, (2) concrete hardening method, and the results are shown in Table 2. Was.

As a result, as shown in Table 2, the heavy metals of any of the samples treated by the method of the present invention were used in accordance with the "Guidelines for Survey and Countermeasures for Soil Pollution Related to Heavy Metals" disclosed in the Water Quality Conservation Bureau, Environment Agency shown in Table 3. It is below the range setting standard, and it has been found that it has a remarkable effect particularly on the insolubilization of Pb even when compared with the concrete solidification method which has been frequently used in the past.

[0028]

[Table 3]

(Example 2)

Except that the contaminated soil B shown in Table 4 was used as the test soil, stirring was performed in the same manner as in Example 1 to obtain the results shown in Table 5.

[0031]

[Table 4]

[0032]

[Table 5]

For comparison, the results of two types of dissolution tests (1) used as is and (2) concrete solidification method as in Example 1 are shown in Table 5, and the results are shown in Table 5. It was confirmed that the soil of the example completely satisfies the measure range setting criteria shown in Table 3 as in Example 1 by the spinelization reaction.

[0034]

As described above, the method of the present invention can completely prevent the elution of heavy metals, as is apparent from comparison with the conventional concrete solidification method.

According to the method of the present invention, various kinds of heavy metals can be treated simultaneously regardless of the content of heavy metals.
Furthermore, since the heavy metal can be completely fixed in a short time, the processing time can be significantly reduced and the processing equipment can be significantly reduced in size.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B09B 3/00-5/00 A62D 1/00-9/00

Claims (1)

(57) [Claims] 1. A heavy metal-contaminated soil having a particle size of 8 mm or less, preferably 5 mm or less, is added with water and a ferrous iron salt and stirred to insolubilize heavy metals in the soil .
PH in the solution is 7 to 12, preferably 7.5 to 11.5
A method for treating soil contaminated with heavy metals, which is carried out while maintaining the soil.