JPH07284748A - Method for immobilizing heavy metal in alkaline substance containing heavy metal - Google Patents

Abstract

PURPOSE:To fix a heavy metal even when special pretreatment is not performed and an auxiliary agent is not used especially and to prevent the elution thereof by mixing a heavy metal-containing alkaline substance with dimethyldithiocarbamic acid or a salt thereof in the presence of moisture. CONSTITUTION:A heavy metal is fixed by mixing a heavy metal-containing alkaline substance with dimethyldithiocarbamic acid or a salt thereof in the presence of moisture. As the heavy metal-containing alkaline substance, fly ash, slag or contaminated soil showing alkalinity is meant. As a heavy metal, lead, chromium, cadmium, mercury, copper, zinc and the like are designated. As a salt of dimethyldithiocarbamic acid, an alkali metal salt, an alkaline earth metal salt or an ammonium salt is designated and, especially, an alkali metal salt is pref. The heavy metal-containing alkaline substnace, dimethyldithiocarbamic acid or a salt thereof and water may be sufficiently mixed and a heavy metal can be fixed immediately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal immobilization method for immobilizing harmful heavy metals present in an alkaline solid substance and preventing elution of the metal from the solid substance.

[0002]

2. Description of the Related Art Heavy metal-containing solid waste has a problem that harmful heavy metals eluted therefrom cause environmental pollution, and various techniques for preventing the harmful heavy metals from eluting have been proposed. Especially as a technique for insolubilizing heavy metals eluted from solid waste, hydroxide, sulfide,
A method of contacting with a chelating agent has been proposed, and further, a combination thereof and addition of a polymer compound can be mentioned.

For example, Japanese Patent Application Laid-Open No. 1-218672 discloses a treatment method in which alkali-containing fly ash is insolubilized with a chelate compound in the presence of water when the pH of its aqueous phase is 12 or less. Further, Japanese Patent Application Laid-Open No. 4-267982 discloses a method of immobilizing various waste heavy metals with a metal scavenger and a water-soluble polymer in order to prevent the heavy metals from being eluted.

[0004]

Fly ash generated during refuse incineration contains a large amount of heavy metals, and in addition to slaked lime added to trap acidic gases such as hydrochloric acid and sulfurous acid gas in exhaust gas of incineration. Alkaline agent is mixed and it has strong alkalinity. In the method described in JP-A-1-218672, various adjustments are required in advance so that the performance of the chelating agent is not sufficiently exhibited in high alkalinity and the pH becomes 12 or less there.

Therefore, in the present invention, a substance containing a heavy metal is left in a high alkali region without special pretreatment.
Furthermore, a treatment method for immobilizing the heavy metal without using an auxiliary agent and preventing elution is provided.

[0006]

The present invention is a heavy metal immobilization method in which a heavy metal-containing alkaline substance is mixed with dimethyldithiocarbamic acid or a salt thereof in the presence of water.

The heavy metal-containing alkaline substance of the present invention is
Alkali fly ash, slag, pollution, soil, etc.
Heavy metals are not special ones, but lead, chromium, cadmium, mercury, copper, zinc, etc.

The salt of dimethyldithiocarbamic acid is an alkali metal or alkaline earth metal ammonium group, of which the alkali metal is preferred.

The amount of the dithiocarbamic acid or its salt is
0.01 to 100 parts by weight of heavy metal-containing alkaline substance
It is 100 parts by weight, and this amount may be appropriately changed depending on the content of the heavy metal.

The amount of water is 1
It is about 0.1 to 50 parts by weight per 00 parts by weight. It is preferable to supply the water by using the dithiocarbamic acid or its salt in the form of an aqueous solution.

The heavy metal-containing alkaline substance, the dithiocarbamic acid or its salt and water may be mixed by any method, and known solid-liquid mixing and kneading methods can be applied. Heavy metals can be immobilized immediately if mixed well.

[0012]

According to the present invention, a heavy metal can be easily immobilized without further pretreatment with an alkaline substance containing a heavy metal, or even without using an auxiliary agent. The immobilization can be stable for a long period of time, that is, the amount of heavy metals eluted can be set to be equal to or less than the elution standard value of industrial waste, so that there is no problem in dumping.

[0013]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples. The evaluation and measurement methods are as follows.
The heavy metal content in the fly ash was measured by first mixing the fly ash with aqua regia and measuring the solution by flame atomic absorption spectrometry-Hitachi model Z-8200.・ Cd concentration: JISK0102-55.2 ・ Pb concentration: JISK
0102-54.2 ・ Zn concentration: JISK0102-53.2 ・ Cu concentration: JISK
0102-52.2 ・ Cr concentration: JISK0102-65.1.2 ・ Ca amount: JISK
0102-50.2 ・ Amount of Mg: JISK0102-51.2 ・ Amount of Na: JISK
0102-48.2 ・ K amount: JISK0102-49.2 ・ Al amount: JISK
0102-58.2 ・ Hg concentration: Fly ash is mixed with sulfuric acid / nitric acid and the solution is subjected to reduction vaporization atomic absorption spectrometry JIS K0102-66.1.1 The dilute heavy metal concentration in the eluate is ICP emission spectrometry
It was measured by ICPS-1000 manufactured by Shimadzu Corporation.・ Cd concentration: JISK0102-55.4 ・ Pb concentration: JI
SK0102-54.4 ・ Zn concentration: JISK0102-53.3 ・ Cu concentration: JI
SK0102-52.4 ・ Cr concentration: JISK0102-65.1.4 ・ pH: In accordance with JISK0102-12, measured with a glass electrode PH meter-Toa Denpa Kogyo HM-40S.

The composition of various fly ash as the heavy metal-containing alkaline substance used is shown in Table 1.

[0015]

[Table 1]

Examples 1 to 3 100 g of each of the three types of fly ash shown in Table 1 was added with ion-exchanged water 20.
A solution in which 1.5 g of sodium dimethyldithiocarbamate was dissolved was added to g, and the mixture was lightly kneaded in a mortar for treatment. Immediately after treating the treated fly ash, one year later treated ash 10
90 g of ion-exchanged water and hydrochloric acid were added to ion-exchanged water, and the mixture was shaken in 90 g of water having a pH of 1 at room temperature for 6 hours to elute heavy metals and filtered using a 5C filter paper. The heavy metal concentration and pH in the filtrate were measured. The results are shown in Tables 2 and 3.

Comparative Examples 1 to 3 The same treatments were carried out as in Examples 1 to 3 except that sodium dimethyldithiocarbamate was not used. Heavy metal was eluted from the fly ash immediately after the treatment in the same manner as in Examples 1 to 3, and the heavy metal concentration and pH were measured. The results are shown in Tables 2 and 3.
Shown in.

Comparative Examples 4 to 6 The same measurement was performed except that the same amount of sodium dibutyldithiocarbamate was used instead of sodium dimethyldithiocarbamate in Examples 1 to 3. The results are shown in Table 4.

Examples 4 to 6 The same procedure as in Examples 1 to 3 was carried out except that the amount of sodium dimethyldithiocarbamate was 3 g and the amount of water was 10 g. The results are shown in Table 4.

Examples 7 to 9 The same procedure as in Examples 1 to 3 was carried out except that the amount of sodium dimethyldithiocarbamate was 10 g and the amount of water was 20 g. The results are shown in Table 4.

Comparative Examples 7-9 The same amount of commercially available chelating agent Unipolva 50 was used in place of sodium dimethyldithiocarbamate in Examples 1-3.
0 (manufactured by Miyoshi Yushi Co., Ltd.) was used, and the same measurement was performed. The results are shown in Table 4.

Comparative Examples 10 to 12 The same measurement was carried out in the same manner as in Examples 1 to 3 except that the same amount of the commercially available chelating agent UML-8100 (manufactured by Unitika Ltd.) was used instead of sodium dimethyldithiocarbamate. went. The results are shown in Table 4.

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

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Claims (1)

[Claims] 1. A method for immobilizing a heavy metal, which comprises mixing a heavy metal-containing alkaline substance with dimethyldithiocarbamic acid or a salt thereof in the presence of water.