JPH0975892A - Process of solidifying heavy metal in fly ash by low-molecular polyamine derivative - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process of solidifying a heavy metal in fly ash generated by an incinerator for municipal waste, industrial waste and the like by using a heavy metal catching agent of high chelating capability so that the heavy metal is not eluted by rainwater or seawater. SOLUTION: Dithiocarbamic acid derived from a polyethylenepolyamine of 4-8 nitrogen atoms or at least one kind of its dithiocarbamate is mixed into fly ash together with water and kneaded.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the treatment of fly ash from an incinerator plant such as municipal waste and industrial waste, which is harmful to lead, mercury, chromium, cadmium, zinc and copper contained in the fly ash. The present invention relates to a method for more efficiently immobilizing and immobilizing heavy metals.

[0002]

2. Description of the Related Art Fly ash discharged from an incineration plant such as municipal waste or industrial waste is collected by an electric dust collector (EP) or a bag filter (BF) and then landfilled or dumped in the ocean. However, these fly ash contains a lot of harmful heavy metals, and elution of lead, mercury, etc. from landfill by rainwater etc. may cause environmental pollution. For this reason, fly ash is designated as a specially controlled waste, and after undergoing any of the "cement solidification method", "acid or other solvent extraction method", "melt fixation method" or "chemical addition method" , Must be discarded. Among them, the drug addition method is generally studied in various ways because it is simpler in equipment and handling than other methods. For example, a method of using an inorganic sulfide in combination with a dithiocarbamate salt made from a polyamine such as polyethyleneimine is disclosed in JP-A-5-50055, and a method using a dithiocarbamate salt made from diethylenetriamine as a raw material is disclosed in JP-A-6-55005. It is disclosed in Japanese Patent Publication No. 79254.

[0003]

[Problems to be Solved by the Invention] Regarding fly ash treatment,
In addition to measures against soot and dust by collecting EP or BF, measures against exhaust gas and dioxins are necessary. The properties of fly ash obtained by these measures are very different, especially in highly alkaline fly ash treated with slaked lime spray. It is known that the heavy metal elution amount increases. In order to fix such heavy metals in fly ash, the amount of conventional chemicals used should be greatly increased, or a combination method with a pH regulator such as ferric chloride or other chemicals such as cement. However, there has been a problem that the cost of the processing chemicals increases or the processing method becomes complicated.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for easily immobilizing heavy metals contained in fly ash by using a highly stable chelating agent. Is.

[0005]

The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, have 4 to 8 nitrogen atoms.
It was found that dithiocarbamic acid or a salt thereof derived from individual polyethylene polyamines has a high chelating ability for heavy metals, and that even in alkaline fly ash, heavy metals can be immobilized with a small addition amount, and the present invention has been completed.

That is, the present invention is characterized in that at least one kind of dithiocarbamic acid or a salt thereof derived from polyethylene polyamine having 4 to 8 nitrogen atoms is added to fly ash together with water and kneaded. The present invention relates to a method for immobilizing heavy metals in ash.

The fly ash used in the method of the present invention is
Although not particularly limited, it is usually discharged from an incineration plant such as municipal waste and industrial waste.

The polyethylene polyamine having 4 or more carbon atoms, which is a raw material of dithiocarbamic acid used in the method of the present invention, is a polyethylene polyamine having 4 to 8 primary or secondary amino groups capable of introducing carbodithioic acid groups. There is no particular limitation so long as it can be used even if it contains, for example, a tertiary amine having a cyclic or branched structure in the molecule. When polyethylene polyamine with 3 or less nitrogen atoms is used as a raw material, the ability to immobilize heavy metals is low, and the crystallization point is low, so the concentration of dithiocarbamate in the product cannot be increased. It is not preferable because a large amount is required for the treatment of. Further, in the case of polyethylene polyamine having 9 or more nitrogen atoms, the dispersibility is poor during the treatment due to its high molecular weight, and as a result, a large amount is required, which is also not preferable. Examples of suitable polyethylene polyamines having 4 to 8 nitrogen atoms include triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, heptaethyleneoctamine, and mixtures thereof.

The dithiocarbamic acid used in the method of the present invention is usually easily synthesized from the above-mentioned polyethylene polyamine and carbon disulfide. At this time, a corresponding dithiocarbamate can be obtained by coexisting a base such as caustic soda.

As the salt of dithiocarbamic acid derived from the polyethylene polyamine having 4 to 8 nitrogen atoms in the present invention, an alkali metal salt, an alkaline earth metal salt or an ammonium salt can be used. Of these, salts of lithium, sodium, potassium, magnesium, calcium and ammonium, which have high solubility in water, are preferable. Furthermore, the thermally stable and inexpensive sodium salts and potassium salts are particularly preferable.

The amount of dithiocarbamic acid or its salt derived from the polyethylene polyamine having 4 to 8 nitrogen atoms of the present invention varies depending on the content of heavy metal in the fly ash to be treated and the form of heavy metal. 0.0 for ash
It is used in the range of 1 to 10% by weight.

The amount of water used in the method of the present invention is
It is usually used in the range of 5 to 60% by weight with respect to the fly ash to be treated. If the amount is 5% by weight or less, the kneading state with the chemicals may not be sufficient, and if the amount is 60% by weight or more, the fly ash obtained by the treatment may become liquid and the disposal may be difficult. .

In the method of the present invention, water and the number of nitrogen atoms are 4
There is no particular limitation on the method of adding dithiocarbamic acid or a salt thereof derived from ~ 8 polyethylene polyamines. For example, a method in which fly ash is kneaded within the range of the amount of water used and then treated with an aqueous solution in which the carbodithioic acid or a salt thereof is dissolved in advance, or a predetermined amount of the dithiocarbamic acid is added to the total amount of water used. Alternatively, a method of dissolving the salt and treating it can be adopted.

In the method of the present invention, the heavy metal in the fly ash to be immobilized is generally a metal that can be insolubilized from an aqueous solution by chelating a dithiocarbamic acid group,
Lead, mercury, chromium, cadmium, zinc, copper, nickel,
Examples include arsenic and selenium.

According to the method of the present invention, even in the case of highly alkaline fly ash, which has a high ability to fix heavy metals and a large amount of heavy metal is eluted, it is economical with the addition of a small amount thereof.
It can be carried out by a simple processing method.

[0016]

EXAMPLES Next, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the following examples.

Synthesis Example 1 Triethylenetetramine-N
1, N2, N3, N4-Sodium tetracarbodithioate (Compound No. 1) Triethylenetetramine (manufactured by Tosoh Corporation, diethylenetriamine content 0.5%) in a glass container under a nitrogen atmosphere.
Below) 46 parts by weight, 48% NaOH 93 parts by weight, water 80
1 part by weight was added, and 84 parts by weight of carbon disulfide was added dropwise to this mixed solution at 40 ° C. or lower over 4 hours while stirring. After completion of dropping, aging was carried out for 1 hour at the same temperature. Nitrogen was blown into the reaction solution to distill off unreacted carbon disulfide to obtain a yellowish brown transparent liquid. As a result of measurement by iodine titration, the concentration of dithiocarbamate in this aqueous solution was 15 wt%.

Synthesis Example 2 Tetraethylenepentamine-N
1, N2, N3, N4, N5, -Pentacarbodithioate sodium (Compound No. 2) Tetraethylene pentamine (manufactured by Tosoh Corporation, triethylenetetramine content 1% or less, diethylenetriamine) was prepared using the same device as in Synthesis Example 1. 53 parts by weight (content: 0.1% or less), 91 parts by weight of 48% NaOH, 821 parts by weight of water were added, and 82 parts by weight of carbon disulfide was added dropwise to this mixed solution at 40 ° C. or lower with stirring for 4 hours. . After dropping,
Aging was performed at the same temperature for about 1 hour. When nitrogen was blown into the reaction solution to distill off unreacted carbon disulfide, a yellowish brown transparent liquid was obtained. As a result of measurement by iodine titration, the concentration of dithiocarbamate in this aqueous solution was 15 wt%. Synthesis Example 3 Ethylenediamine-N1, N2-sodium biscarbodithioate (Compound No. 3) 39 parts by weight of ethylenediamine (manufactured by Tosoh Corporation, purity 99.9%), 48% NaOH 1 using the same apparatus as in Synthesis Example 1
10 parts by weight and 863 parts by weight of water were added, and 99 parts by weight of carbon disulfide was added dropwise to the mixed solution at 40 ° C. or lower over 4 hours while stirring. After completion of dropping, aging was carried out at the same temperature for about 1 hour. When nitrogen was blown into the reaction solution to distill off unreacted carbon disulfide, a yellowish brown transparent liquid was obtained. As a result of measurement by iodine titration, the concentration of dithiocarbamate in this aqueous solution was 15 wt%.

Synthesis Example 4 Diethylenetriamine-N1,
N2, N3-Sodium triscarbodithioate (Compound No. 4) 41 parts by weight of diethylenetriamine (manufactured by Tosoh Corporation, purity 99.9%), 48% NaO, using the same apparatus as in Synthesis Example 1
101 parts by weight of H and 826 parts by weight of water were added, and 91 parts by weight of carbon disulfide was added dropwise to this mixed solution at 40 ° C. or lower over 4 hours while stirring. After completion of dropping, aging was carried out at the same temperature for about 1 hour. When nitrogen was blown into the reaction solution to distill off unreacted carbon disulfide, a yellowish brown transparent liquid was obtained. As a result of measurement by iodine titration, the concentration of dithiocarbamate in this aqueous solution was 15 wt%.

Example 1 Heavy metal immobilization ability test BF ash (Ca = 30.7%, Na = 1.4%, K = 1.
6%, including Pb = 2000 ppm and Cu = 150 ppm) 30 parts by weight of water was added to 100 parts by weight, and further triethylenetetramine-N1, N2, N3, N4-sodium tetracarbodithioate (Compound No. 1). 15
% Aqueous solution to be added to 3 parts, 4.5 parts and 6 parts,
After kneading, a dissolution test was conducted according to the Environmental Agency Notification No. 13 test. Table 1 shows the lead elution results. For heavy metals other than lead, zinc is 4ppm or less and chromium is 0.05pp
m or less, and all of cadmium, mercury, copper, and nickel were 0.01 ppm or less.

[0021]

[Table 1]

Example 2 Tetraethylenepentamine-N1, N2, N3, N4
Sodium N5, -pentacarbodithioate (Compound N
o. 2) A heavy metal immobilizing ability test was conducted in the same manner as in Example 1 except that a 15% aqueous solution was used. The results are also shown in Table 1. For heavy metals other than lead, zinc is 4p
pm or less, chromium is 0.05 ppm or less, cadmium,
0.01 ppm for mercury, copper and nickel
It was below.

Comparative Example 1 A heavy metal immobilizing ability test was conducted in the same manner as in Example 1 except that a 15% aqueous solution of sodium ethylenediamine-N1, N2-biscarbodithioate (Compound No. 3) was used. The results are also shown in Table 1.

Comparative Example 2 A heavy metal immobilizing ability test was conducted in the same manner as in Example 1 except that a 15% aqueous solution of sodium diethylenetriamine-N1, N2, N3-triscarbodithioate (Compound No. 4) was used. . The results are also shown in Table 1.

[0025]

According to the method of the present invention, the number of nitrogen atoms is 4 to 4.
By using at least one of polydithiocarbamic acid or its salt derived from 8 polyethylene polyamines, harmful heavy metals in incinerator fly ash can be reliably fixed, and the amount of heavy metal fixative used is reduced. be able to.

Claims (5)

[Claims] 1. A fly ash characterized in that at least one of polydithiocarbamic acid or a salt thereof derived from a polyethylene polyamine having 4 to 8 nitrogen atoms is added to fly ash together with water and kneaded. Heavy metal immobilization method. 2. The polyethylene polyamine having 4 to 8 nitrogen atoms is one or more selected from the group consisting of triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine, hexaethylene heptamine, and heptaethylene octamine. The method of claim 1, wherein: 3. The dithiocarbamate salt derived from a polyethylene polyamine having 4 to 8 nitrogen atoms is an alkali metal salt, an alkaline earth metal salt or an ammonium salt. The method described. 4. The method according to claim 3, wherein the dithiocarbamate derived from polyethylene polyamine having 4 to 8 nitrogen atoms is dithiocarbamate sodium salt or potassium salt. 5. The method according to claim 1, wherein the heavy metal is lead, mercury, chromium, cadmium, zinc and copper.