JP4624583B2 - Heavy metal solidifying agent and waste treatment method - Google Patents

Description

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[0001]
[Industrial application fields]
The present invention includes a heavy metal solidifying agent for immobilizing so as not to elute harmful heavy metals from wastes such as fly ash, incineration ash, or molten fly ash generated at a waste disposal facility, and a toxic carbon disulfide gas during treatment. The present invention relates to a heavy metal solidifying agent capable of simplifying equipment because it does not occur and can be used in one liquid, and a waste treatment method using the solidifying agent.
[0002]
[Prior art]
Incineration ash and fly ash, such as municipal waste and industrial waste, contain a large amount of heavy metals that are harmful to the human body. In particular, fly ash that has been treated with alkali to suppress hydrochloric acid gas generated during incineration. Pb and Cd are eluted in large quantities. In order to detoxify these heavy metals, a solidification method using cement, a chemical treatment using a chelating agent, and an acid extraction treatment for extracting the metal using mineral acid or the like are performed. In recent years, in order to prevent dioxins and to reduce the volume of waste, a melting and solidifying process for melting a mixture of fly ash and incinerated ash or the waste itself at a high temperature of 1500 ° C. or higher is performed.
[0003]
However, in the case of simply treating cement, neutralization of the cement proceeds with acid rain or carbon dioxide in the air after the treatment, and lead re-elutes due to the decay of the cement. Also, fly ash with a large amount of lead elution increases the amount of cement added, leading to a shorter life of the final disposal site.
In many cases, the chelating agent treatment uses a dithiocarbamic acid-based heavy metal fixing agent, so that a large amount of carbon disulfide is generated, which is problematic in terms of the working environment. In addition, it has been pointed out that decomposition of the chelating agent occurs at the final disposal site (especially unstable under acidic conditions) and lead is eluted again.
[0004]
In the acid extraction method, the extraction work is complicated, and a large amount of drainage is generated together with the dehydrated cake, so that a separate treatment is required.
Incineration ash is not generated in the melting and solidification treatment, so that waste can be reduced. However, fly ash is generated, and heavy metals are concentrated and collected in the fly ash. Therefore, it is necessary to treat fly ash separately.
In addition, a waste treatment method using water glass is disclosed in JP-A-9-308771.
As is apparent from the examples of the present invention, sufficient heavy metal solidifying action cannot be exhibited with water glass alone against fly ash having a lead elution amount exceeding 30 mg / L.
[0005]
Separately, a method of curing by adding a gelling agent such as calcium chloride, barium chloride, or aluminum sulfate to water glass and combined use with powdered aluminum silicate are disclosed in JP-A-8-155416 and JP-A-9-155317, respectively. Although it is open to the public, there are problems in terms of work and equipment, such as the fact that one tank is powder and two tanks are required, and heat is applied at 40 to 80 ° C.
[0006]
[Problems to be solved by the present invention]
The present invention provides a heavy metal solidifying agent and a simple treatment method using the same, which solve the above-mentioned problems and fix heavy metals without adjusting complex liquids.
[0007]
[Means for Solving the Problems]
The heavy metal solidifying agent according to the present invention is characterized by comprising a mixed liquid of water glass and a carbonyl group-containing chain hydrocarbon compound.
Here, the water glass is represented by A ₂ O.nSiO ₂ (A: alkali metal, n: number of moles), and the molar ratio (SiO ₂ / A ₂ O) is 0.5 to 4.2, alkali. Preferably, the content in terms of oxide is 6.00 to 21.50% by weight and SiO ₂ is 9.50 to 38.00% by weight.
[0008]
The carbonyl group-containing chain hydrocarbon compounds include R ₁ -CHO, R ₁ -CO-R ₂ , CHO (R ₃ ) _m CHO (R ₁ and R ₂ are each independently a hydrogen atom, an alkyl group or A water-soluble compound represented by the following is preferably used: a carboxyl group, R ₃ is an alkyl group, and m is an integer of 0 to 3.
In the heavy metal solidifying agent of the present invention, the mixing ratio of water glass and carbonyl group-containing chain hydrocarbon compound is such that the carbonyl group-containing chain is 100 parts by weight of water glass having a SiO ₂ concentration of 9.50 to 38.00% by weight. The formula hydrocarbon compound is preferably 0.5 to 40.0 parts by weight.
[0009]
The waste treatment method according to the present invention is characterized in that the heavy metal solidifying agent, water and waste are mixed and kneaded.
As wastes to be treated in the present invention, stoker type, fluidized bed type, incinerated ash discharged from the bottom of a rotary incinerator or ash discharged together with exhaust gas, such as a bag filter, an electric dust collector, Fly ash collected by a multi-cyclone, etc., or a mixture of incineration ash and fly ash, which has been implemented as a measure against dioxins in recent years, or molten fly ash discharged when molten slag is made at a high temperature of 1500 ° C or higher. Although it is mentioned, it is not limited to these.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
As described above, the heavy metal solidifying agent according to the present invention contains water glass and a carbonyl group-containing chain hydrocarbon compound as main components.
The water glass used in the present invention is not particularly limited, such as sodium metasilicate, sodium orthosilicate, and solution type water glass.
[0011]
Among these water glasses, a water glass represented by A ₂ O · nSiO ₂ (A: alkali metal, n: number of moles) is particularly preferable. Here, lithium, sodium, and potassium can be illustrated as an alkali metal. Sodium silicate is preferred from the viewpoint of industrial availability and price.
The molar ratio (SiO ₂ / A ₂ O) is defined as the ratio between the oxide equivalent of silicon (SiO ₂ ) and the oxide equivalent of alkali (A ₂ O), and its value is in the range of 0.5 to 4.2 It is desirable to be.
[0012]
The content of alkali in terms of oxide (A ₂ O) is 6.00 to 21.50% by weight, and the content of silicon in terms of oxide (SiO ₂ ) is arbitrarily in the range of 9.50 to 38.0% by weight. You can choose.
In general, silicates such as water glass have a higher alkali component and a lower molar ratio, the better the reactivity with the metal salt, but if it is too high, the viscosity becomes high and it becomes difficult to knead with the treated product. Become. When the molar ratio is 1.5 or less, crystals may precipitate. Therefore, the molar ratio is 2.10 to 3.20, and the alkali (A ₂ O) content in terms of oxide is 9.00 to 15. Water glass with 30% by weight and SiO ₂ and silicon content in the range of 28.00 to 34.00% by weight is preferred. Moreover, these water glasses can also be diluted and used as needed.
[0013]
Carbon-containing chain hydrocarbon compounds mixed with water glass are R ₁ -CHO, R ₁ -CO-R ₂ , CHO (R ₃ ) _m CHO (R ₁ and R ₂ are independent hydrogen atoms and alkyl groups, respectively. Or a carboxyl group, R ₃ is a methylene group, and m is an integer of 0 to 3). Particularly preferred is a compound having high water solubility, that is, a low molecular weight compound having a small number of carbon atoms.
Examples of such carbonyl group-containing chain hydrocarbon compounds include formaldehyde, acetaldehyde, acetone, propionaldehyde, n-butyraldehyde, methyl ethyl ketone, methyl glyoxal, methyl isobutyl ketone, glyoxal, glyoxylic acid, and n-hexaldehyde. , Paraformaldehyde, glyceraldehyde, diethyl ketone, pyruvic acid, acetoacetic acid, ethyl acetoacetate, acetylacetone, valeraldehyde, glycolaldehyde, glutaraldehyde, 1,3-propadial, 1,4-hexadial, 1,5-pentadial, etc. Is shown. In particular, the dialdehyde compound glyoxal (1,2-ethadial), 1,3-propadial, 1,4-hexadial, and 1,5-pentadial are preferred, and are the simplest in terms of industrial availability and price. Glyoxal is preferred.
[0014]
Taking the case of using a water glass having a SiO ₂ concentration of 9.50 to 38.00% by weight as an example, the mixing ratio (C / W (C)) of the water glass (W) and the carbonyl group-containing chain hydrocarbon compound (C) The weight ratio)) is preferably from 0.5 / 100 to 40/100, particularly preferably from 1/100 to 20/100, more preferably from 3/100 to 10/100. When the mixing ratio is below this range, the effect of organic substances is not sufficiently exhibited. When the mixing ratio is above this range, the amount of elution increases compared to the case of using water glass alone, and it may solidify during storage. When mixing the water glass and the carbonyl group-containing chain hydrocarbon compound, they may be mixed immediately before use or may be mixed in advance. When considering the simplification of equipment, it is preferable to mix them in advance.
[0015]
The amount of the heavy metal solidifying agent of the present invention added to the waste is about 5 to 20 parts by weight in general fly ash such as a fluidized bed furnace or sootka furnace. If it is 0.3 to 1.0 parts by weight with respect to 100 parts by weight of ash, the elution amount of heavy metals can be reduced to a landfill environmental standard value or less, for example, 0.3 mg / L or less for lead. In molten fly ash with a very large amount of lead leaching, the amount of heavy metal leaching can be reduced to the landfill environmental standard or less by adding about 50 to 80% by weight.
[0016]
When processing the above waste, the heavy metal solidifying agent, water, and waste are mixed and kneaded.
In general, when chemical treatment of fly ash (including molten fly ash) is performed, water is added to prevent scattering during carry-out and ease of handling during kneading. Also in the heavy metal solidifying agent of the present invention, it is preferable to use water together. The amount of water added varies depending on the properties of fly ash (such as good water absorption), but is added in an amount of 10 to 30 parts by weight. Even if more water is added, the effect of significantly reducing the amount of elution of heavy metals does not appear, so the total weight of waste increases and the processing cost only increases. This kneaded water can be used by previously mixing with water glass.
[0017]
As a method for treating fly ash (including molten fly ash) related to the heavy metal solidifying agent of the present invention, water and a heavy metal solidifying agent are mixed in advance and added to the fly ash. Alternatively, after adding water to the fly ash, the heavy metal solidifying agent is added again. Alternatively, after adding the heavy metal solidifying agent to the fly ash, water is added again. After adding by any of these methods, mixing, kneading and discharging are performed. Also, a method of adding fly ash to water and heavy metal solidifying agent, mixing and kneading can be used.
[0018]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.
[0019]
[Comparative Example 1]
50 g of fly ash A generated at a municipal waste incineration facility was put in a 1000 ml plastic container, 500 g of pure water was placed therein, and the elution test (hereinafter simply referred to as the elution test) was conducted for 6 hours and shaken for 6 hours.
[0020]
[Comparative Example 2]
50 g of fly ash A was mixed with a mixture of 10 g of water (20 parts with respect to 100 parts by weight of fly ash (hereinafter simply referred to as “parts”)) and 2.5 g of additive (5 parts with respect to 100 parts of fly ash). The material was cured for 24 hours. After solidification, the mixture was pulverized, classified with a sieve having an opening of 5 mm, and 50 g of the sample that passed through the sieve was collected and subjected to the same elution test as in Comparative Example 1.
[0021]
There are seven types of additives: sodium carbonate, potassium carbonate, sodium sulfate, aluminum hydroxide, phosphoric acid, PAC, and aluminum sulfate as inorganic chemicals. Diethylene glycol, triethylamine, polyethylene glycol, glyoxal 40% solution, and citric acid as organic chemicals. Sodium acid, CMC (carboxymethylcellulose), EDTA · 2Na, methanol, and 9 types of dextrin were used.
[0022]
Of these, sodium carbonate, potassium carbonate, sodium sulfate, aluminum hydroxide, aluminum sulfate, sodium citrate, CMC, EDTA · 2Na, and dextrin were mixed with water as a powder.
[0023]
[Comparative Example 3]
A mixture obtained by adding 10 g of water to 50 g of fly ash A and mixing and kneading was cured for 24 hours. The solidified product was pulverized and subjected to the same dissolution test as in Comparative Example 2.
[0024]
[Comparative Example 4]
A dissolution test similar to Comparative Example 2 was performed, except that 50 g of fly ash A was mixed with kneaded water and 2.5 g of water glass and mixed and kneaded.
As the water glass, No. 1 sodium silicate C ₂ , No. ₂ sodium silicate H ₃ , No. ₃ sodium silicate T ₂ , No. 4 sodium silicate manufactured by Toso Sangyo Co., Ltd. were used.
[0025]
The component table of each water glass is shown in Table 1.
The results of Comparative Examples 1 to 4 are shown in Table 2.
From Table 2, it was confirmed that water glass has an excellent heavy metal solidifying action. In particular, it was confirmed that the effect of No. 1 water glass or No. 2 water glass having high alkali was high. At the same time, however, it was also confirmed that lead-free landfill environmental standard values of 0.3 mg / L or less cannot be achieved with water glass alone.
[0026]
[Comparative Example 5]
The same elution test as in Comparative Example 2 was conducted except that 50 g of fly ash A was added with a mixture of 10 g of water, 2.5 g of No. 2 sodium silicate H ₃ and 0.25 g of additive and mixed and kneaded. It was. Sodium carbonate, sodium sulfate, aluminum hydroxide, PAC, diethylene glycol, CMC, EDTA · 2Na, methanol, and dextrin were used as additives.
[0027]
The reason why No. 1 sodium silicate H ₃ was used instead of No. 1 sodium silicate C ₂ is that the No. 1 product has extremely high viscosity and poor handling.
[0028]
[Example 1]
50 g of fly ash A, 10 g of water, 2.5 g of sodium silicate H ₃ 2.5 g (5 parts of fly ash) and 0.25 g of glyoxal 40% solution (0.5 part of fly ash) were mixed in advance. Was added and mixed and kneaded, and the same dissolution test as in Comparative Example 2 was performed.
The results of Comparative Example 5 and Example 1 are shown in Table 3.
[0029]
From Table 3, it was confirmed that the mixed solution of glyoxal and water glass had a clear solid metal action, and the lead landfill environmental standard value was 0.3 mg / L or less.
[0030]
[Comparative Example 6]
The dissolution test similar to the comparative example 1 was done about the fly ash B which generate | occur | produced in the municipal waste disposal facility.
[0031]
[Comparative Example 7]
The same dissolution test as in Comparative Example 2 was conducted except that a solution prepared by previously kneading 2.5 g or 5.0 g of sodium silicate H ₃ and 10 g of water was added to 50 g of fly ash B, and mixing and kneading were performed. It was.
[0032]
[Example 2]
The same elution test as Comparative Example 2 was conducted except that 2.5 g of No. 2 sodium silicate H ₃ , 10 g of water and 40% glyoxal liquid were added to 50 g of fly ash B and mixed and kneaded. .
The amount of Glyoxal 40% solution was 0.01, 0.03, 0.05, 0.1, 0.2 g.
[0033]
[Example 3]
The same operation was performed except that the amount of No. 2 sodium silicate H ₃ added in Example 2 was changed to 3 g.
The results of Comparative Examples 6 and 7 and Examples 2 and 3 are shown in Table 4.
From Table 4, the addition amount of glyoxal is preferably 0.3 to 1 part by weight with respect to 100 parts by weight of fly ash, and the mixing ratio of glyoxal to water glass is 1 to 20 parts by weight with respect to 100 parts by weight of water glass. Parts, preferably 3 to 10 parts by weight.
[0034]
[Comparative Example 8]
The same elution test as Comparative Example 1 was performed on fly ash C generated in a municipal waste treatment facility.
[0035]
[Comparative Example 9]
A dissolution test was performed in the same manner as in Comparative Example 2 except that 1.5 g or 2.5 g of a dithiocarbamic acid-based organic chelating agent and 10 g of water were added to 50 g of fly ash C and mixed and kneaded.
[0036]
[Comparative Example 10]
A test similar to Comparative Example 2 was conducted except that 50 g of fly ash C was added with a solution prepared by mixing 10 g of water glass and 10 g of water in advance and mixed and cured.
The same three types of water glass as in Comparative Example 4 were used.
[0037]
[Example 4]
A dissolution test was performed in the same manner as in Comparative Example 2 except that 10 g of water glass, 10 g of water and 0.25 g or 0.5 g of glyoxal 40% liquid were mixed in advance and mixed and kneaded. .
The same three kinds of water glass as in Comparative Example 4 were used.
[0038]
The results of Comparative Examples 8 to 10 and Example 4 are shown in Table 5.
From Table 5, it was confirmed that even water glass other than No. 2 was effective in fixing lead by mixing with glyoxal. In view of immediate effect, it is confirmed that the No. 2 product is preferable. Moreover, from the comparison with the chelating agent of Comparative Example 9, it is confirmed that the heavy metal solidifying agent of the present invention is very effective from the viewpoint of cost although it is necessary to add 4 times as much as the addition amount. In addition, as a result of the dissolution test of the treated ash performed in the treatments of Example 7-1 and Example 2-2 again after one month, lead was not detected.
From this, it was confirmed that it is a long-term stable heavy metal solidifying agent.
[0039]
[ Reference Example 5]
Comparative Example 2 except that 50 g of fly ash C was added with a mixture of 10 g of sodium silicate H ₃ No. 2 and 0.5 g of a chain hydrocarbon carbonyl compound other than glyoxal and 10 g of water, mixed and kneaded. The dissolution test was conducted. As the chain hydrocarbon carbonyl compound used, acetone, methyl ethyl ketone, acetylacetone, and methylglyoxal were used.
[0040]
The results of Reference Example 5 are shown in Table 6. Table 6 shows that there is an effect on fixation of lead other than glyoxal, but there seems to be a problem in the working environment because of its unique irritating odor including methylglyoxal.
[0041]
[Comparative Example 11]
The dissolution test similar to the comparative example 2 was done with respect to the molten fly ash A discharged | emitted from the melting furnace which incinerates industrial waste.
[0042]
[Comparative Example 12]
Elution similar to Comparative Example 2 except that 50 g of molten fly ash A was mixed with a solution prepared by mixing 15 g of water (30 parts by weight with respect to molten fly ash) and 15 g of a dithiocarbamic acid-based organic chelating agent in advance. A test was conducted.
[0043]
[Example 6]
A dissolution test similar to Comparative Example 2 was conducted except that 50 g of molten fly ash A was mixed with 15 g of sodium silicate 2 and 15 g of water and 0.75 g of glyoxal 40% solution in advance and mixed and cured.
[0044]
[Example 7]
A dissolution test similar to Comparative Example 2 was performed, except that 50 g of molten fly ash A was mixed with 25 g of sodium silicate No. 2, 15 g of water and 1.25 g of glyoxal 40% in advance and mixed and cured.
[0045]
[Example 8]
A dissolution test similar to Comparative Example 2 was conducted except that 50 g of molten fly ash A was mixed with 40 g of No. 2 sodium silicate, 15 g of water and 2.00 g of glyoxal 40% in advance and mixed and cured.
Table 7 shows the results of Comparative Example 11, Comparative Example 12, and Examples 6 to 8.
[0046]
From Table 7, it was confirmed that the heavy metal solidifying agent of the present invention can reduce the lead elution amount to a landfill environmental standard value or less by adding twice the amount of the chelating agent.
From the above results, it was shown that the waste treatment method of the present invention is effective.
[0047]
[Table 1]

[0048]
[Table 2]

[0049]
[Table 3]

[0050]
[Table 4]

[0051]
[Table 5]

[0052]
[Table 6]

[0053]
[Table 7]

Claims (5)

Do from a mixture of water glass and a carbonyl group-containing chain hydrocarbon based compound Ri,
The carbonyl group-containing chain hydrocarbon compound is glyoxal,
The water glass has a SiO ₂ concentration of 9.50 to 38.00% by weight,
The mixing ratio of the water glass and (W) and glyoxal (C) (C / W (weight ratio)) is a heavy metal solidifying agent characterized 0.4 / 100-10 / 100 der Rukoto. The heavy metal solidifying agent according to claim 1, wherein a mixing ratio (C / W (weight ratio)) between the water glass (W) and glyoxal (C) is 3/100 to 10/100. The water glass is represented by A ₂ O · nSiO ₂ (A: alkali metal, n: number of moles), and its molar ratio (SiO ₂ / A ₂ O) is 0.5 to 4.2, converted to an alkali oxide. The heavy metal solidifying agent according to claim 1 or 2 , wherein the content of is 6.00 to 21.50 % by weight.   A waste treatment method comprising mixing and kneading the heavy metal solidifying agent according to claim 1, water and waste. The described waste stoker, fluidized bed, waste treatment method according to claim 4, characterized in that the ash content is discharged together with the ash or flue gas is discharged from the furnace bottom of the rotary incinerator .