JPH11207291A - Solidifying agent for incineration residue and residue solidifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solidified body high in strength while holding the sufficient elution preventing properties of heavy metals by mixing incineration residue with a solidifying agent. SOLUTION: A solidifying agent mixed with incineration ash to solidify the ash consists of 1-30 wt.% gypsum, 4-99 wt.% admixture showing latent hydraulic properties such as blast furnace slag and 0-29 wt.% cement. This solidifying agent 10-70 wt.% and incineration ash 30-90 wt.% are mixed and subsequently kneaded with a necessary amt. of water to obtain a solidified body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solidifying agent for solidifying incineration residues such as incineration ash and dust generated in an incinerator of a waste incineration plant and the like, and thereby to use as a civil engineering material such as a roadbed material. The present invention relates to a method for solidifying a solidified body for recycling incineration residues that can be produced.

[0002]

2. Description of the Related Art Cadmium (bottom ash) generated when incinerating industrial waste and municipal waste and dust (fly ash and fly ash) collected by an electric dust collector and the like are incinerated. Harmful heavy metals such as Cd) and lead (Pb) are often contained, and when these are disposed of as landfills by recycling, they must be treated to prevent the contained heavy metals from being eluted, such as by solidifying with cement. It is stipulated by law that it must be disposed of.

As means for solidifying the incineration residue, means such as addition of chemicals such as chelate, various cement-based solidifying agents and gypsum have been proposed, and a method of solidifying the incineration residue using this solidifying agent has been proposed. Have been proposed.

[0004] These prior arts are disclosed in
Japanese Patent Application Laid-Open No. 10399 and No. 60-41589 are known. In the former of this prior art, the height of the calcium silicate is less than 40%.
It is 0 to 25%, free lime less than 5%, and gypsum 40% or less, where awine and calcium silicate are the main components of Portland cement. This means that the solidifying agent contains at least 55% of Portland cement.

[0005] In the latter case of the prior art, cement, gypsum or slaked lime, gypsum or cement alone are mixed with coal ash, and water is added to the mixed material to knead it.

[0006]

Among the above prior arts, the former is a solidifying agent mainly composed of an expanding material for expansion and cement, and the Portland cement content is at least 55% as described above. Despite the high content, when this was mixed with the incineration residue and solidified, the solidified product could not obtain a predetermined hardness.

[0007] This is because some of the incineration residues contain organic impurities such as tannic acid and humic acid. When the incineration residues containing these organic impurities are solidified with Portland cement, they are not hydrated. Amorphous substances are formed around the particles, and these substances are adsorbed on the surface of the cement particles depending on the polarity, or combine with Ca ⁺⁺ to form a film, which inhibits the hydration reaction of cement and hardens. Is obstructed. This becomes more pronounced as the amount of cement increases.

[0008] Further, in the former, it is described in the specification that Pb and Cd are not eluted from the solidified product, but the method for testing the elution of heavy metals is not disclosed. It was not clear in what state the substance was not eluted.

Regarding the leaching of heavy metals, numerical values reported by the Environment Agency in 1994 are used as soil environmental standards which are currently used as criteria for leaching of waste. In the case of the above, it is considered that the judgment is made based on a more stringent standard than before the enforcement of the above standard. In the former case, it is considered that the present soil environmental standard cannot be satisfied because the cement component is too large and the alkalinity is too high.

On the other hand, in the latter case of the above-mentioned prior art,
The hardness of the solidified product is also up to 15 with a uniaxial compressive strength of 28 days curing.
It was not as high as 3.3 kg / cm ^2, and the elution amount of heavy metals such as Pb was as high as 0.04 or less.

As described above, the conventional method for solidifying incineration residues using a solidifying agent has a strength required for landfill disposal at a final disposal site (uniaxial compressive strength of 10 kg / cm ² or more);
In most cases, the purpose is to prevent elution (3 mg / L in the case of Pb), and even if the material is recycled for civil engineering materials, the uniaxial compressive strength of 50 to 50% equivalent to fine aggregate used for roadbed materials 100 kg / cm ² or more, or uniaxial compressive strength of 400 kg / c equivalent to coarse aggregate used for roadbed material
A solidifying agent capable of obtaining a solidified material that satisfies both high strength of at least m ² and a soil environmental standard of 0.01 mg / L or less for Pb in the dissolution test of the Environment Agency Notification No. 46. And there was no solidification method.

The inventors of the present invention have conducted various experiments, and have found in Japanese Patent Application No. 7-252611 (Japanese Patent Application Laid-Open No. 9-9454).
No. 8), the incineration residues such as incineration ash and dust were converted to mechanical strength (uniaxial compression strength 50 equivalent to fine aggregate used for roadbed material).
１００100 kg / cm ² or more) and heavy metal elution prevention properties (soil environmental standards clear, Pb: 0.01 mg / L or less), and a solidifying agent for incinerated ash, which can be solidified using this solidifying agent A method for solidifying incineration residues is proposed and proposed.

The present invention was made during the improvement and development of the invention filed in Japanese Patent Application No. Hei 7-252611, and has a heavy metal elution prevention property (soil environmental standard clear, Pb: 0.01 mg / L). The solidification agent of the incineration residue capable of obtaining further high strength (uniaxial compressive strength of 400 kg / cm ² or more equivalent to coarse aggregate used for roadbed material) while sufficiently maintaining It is an object of the present invention to provide a method for solidifying incineration residues.

[0014]

It is known that the elution amount of heavy metals such as Cd and Pb contained in incineration residues such as incineration ash and dust greatly depends on the pH of the solidified product. ing. The solubility of Pb is small in the pH range of 9.5 to 11.5, but large before and after this,
The solubility on the alkali side where H exceeds about 12 is significantly increased.

When the cement is kneaded with the addition of water, it undergoes a chemical change, for example, as shown in the following formula, and Ca ⁺⁺ is released from the surface of C ₃ S by hydrolysis of C ₃ S and the like, and the liquid layer is rapidly formed. Change to alkaline. 2 (3CaO.SiO ₂ ) + 6H ₂ O → 3CaO.2S
iO ₂ .3H ₂ O + 3Ca (OH) _{2 where} 3CaO.SiO ₂ is C ₃ S and alite.

For this reason, for example, when incineration residues and the like are solidified with a cement-based solidifying agent, the solidified solution generally shows strong alkalinity, so that elution of amphoteric heavy metals such as Pb becomes a major problem. If there is a solidifying agent that exhibits mechanical strength while keeping the pH low, both the above-mentioned mechanical strength and anti-elution properties can be achieved.

The present inventors have disclosed in Japanese Patent Application No. 7-252611 (Japanese Unexamined Patent Application Publication No. 9-94548) that an admixture exhibiting latent hydraulic properties such as blast furnace slag exhibits alkalinity when cured by addition of water. Paying attention to the action of reducing oxide ions (OH), it has been found that a hydraulic cement and a latent hydraulic admixture are blended in a certain ratio to form a solidifying agent.

[0018] An admixture exhibiting latent hydraulic properties, such as blast furnace slag, forms an impermeable hydration product (protective film) when it comes into contact with water, and the particle surface is covered with the product to prevent water contact. Therefore, the hydration reaction cannot proceed.

However, when an alkaline stimulant such as Ca (OH) ₂ is added, the protective film, which is the hydration product, reacts with the stimulant and is removed from the particle surface to remove water. The reaction proceeds continuously, and a cured body mainly composed of C—S—H is obtained by the solidifying agent. This process is represented by the following equation, which is called latent hydraulicity. xSiO ₂ + yCa (OH) ₂ + zH ₂ O → aCaO.
bSiO ₂ · cH ₂ O In the formula, xSiO ₂ is a soluble silica and a blast furnace slag main component, and aCaO · bSiO ₂ · cH ₂ O is CS-
H-gel, calcium silicate hydrate.

In this solidifying agent, if the amount of cement (Portland cements) that causes strong alkalinity is small, the pH value also drops to 11 or less, and the amphoteric properties of Pb and the like contained in incinerated ash and the like solidified using the cement are reduced. Although the prevention of metal elution is expected, this cement is an alkali stimulant for admixtures that exhibit latent hydraulic properties, such as blast furnace slag. Can not be obtained.

That is, in the case of a solidifying agent that solidifies an incineration residue containing no organic impurities, generally, when the cement mixing ratio is large, the strength of the solidified material becomes large, the pH becomes large (heavy metal elution is large), and the cement mixing ratio becomes large. If it is small, the strength of the solidified product will be low and the pH will be low (heavy metal elution is small).

Here, the present inventors have noticed that gypsum also has an effect of accelerating the hydration reaction of an admixture exhibiting latent hydraulicity such as blast furnace slag, and has considered that hydraulic cement and latent hydraulic A solidifying agent and a solidifying method for obtaining a high-strength solidified body by mixing an admixture and gypsum (CaSO ₄ ) at a certain ratio have been found.

The gypsum in the solidifying agent, when kneaded with water, produces an ettrine guide, which is a needle-like crystal combined with a large amount of water, as shown in the following formula. At this time, initially, et Trinh guide _{(CaA · 3CaSO 4 · 32H 2} O) to produce large amounts to form a skeleton, dense structure by filling the periphery of calcium silicate hydrate C-S-H Therefore, a solid body having high hardness can be obtained. 3CaO.Al ₂ O ₃ + 3CaSO ₄ + 32H ₂ O → 3
CaO.Al ₂ O ₃ .3CaSO ₄ .32H ₂ O In the formula, 3CaO.Al ₂ O ₃ .3CaS ₄ .32H ₂
O is an ettrine guide.

That is, the solidifying agent for producing the solidified body for recycling incineration residues according to the present invention is gypsum:
30 wt%, admixture showing potential hydraulic properties such as blast furnace slag:
41 to 99 wt%, cement: 0 to 29 wt%,
The solidifying agent and the incineration residue are mixed at a predetermined mixing ratio, and a necessary amount of water is added and kneaded to form a solidified body and a roadbed material.

At this time, examples of marginal compounding are (1)
Gypsum: 1 wt%, blast furnace slag 99 wt%, (2) gypsum: 30 wt%, blast furnace slag 70 wt%, (3) cement: 29 wt%, gypsum: 30 wt%, blast furnace slag 49
wt%.

The compounding of the solidifying agent is described below. As a breakdown of the compounding ratio of the solidifying agent for solidifying the incineration residue, as the mixing ratio of cement increases, the mechanical strength of the solidified material hardened using this compound generally decreases (when organic impurities are contained in the incineration residue). ), But at the same time, the pH also increases and the elution amount of heavy metals such as Pb increases, so there is an upper limit to the blending ratio. According to various experiments by the present inventors, it has been found that when the content exceeds 29 wt%, the elution amount of heavy metals such as Pb often increases and exceeds the environmental standard.

Also, the admixture exhibiting latent hydraulic properties such as blast furnace slag does not exhibit curability by itself, but exhibits curability due to the stimulation of gypsum or the like. Therefore, according to various experiments by the present inventors, about 1 wt% was obtained. Gypsum hardening stimulant is required. Further, since excessive addition of gypsum causes expansion and destruction of the solidified body, according to various experiments by the inventors, 7
It turned out that 0 wt% or less, preferably 30 wt% is good.

Further, when the above-mentioned incineration residue and the like are recycled into a civil engineering material or the like having a mechanical strength of about 400 kg / cm ² or more having a uniaxial compressive strength of about 400 kg / cm ² , such as a roadbed material or various blocks, the above-mentioned solidifying agent is used. And incineration residue: 30
９０90 wt%, solidifying agent: 10-70 wt%, experimentally preferably incineration residue: 30-70 wt%, solidifying agent:
The mixture is mixed at a mixing ratio of 30 to 70 wt%, a necessary amount of water is added, and the mixture is kneaded and molded.

The solidified product thus formed had a uniaxial compressive strength of 400 kg / cm ² or more after curing for 28 days, and was subjected to a dissolution test based on the Environment Agency Notification No. 46. 0.01mg / L (Soil environmental standard)
It was below.

The mixing ratio of the incineration residue and the solidifying agent is as follows:
It is generally considered that the upper limit of the solidifying agent is about 70 wt% from the viewpoint of the recycling rate of waste or incineration residue and the processing cost. Also, from the viewpoint of mechanical strength desirable for recycling into civil engineering materials such as roadbed materials, the solidifying agent is 30 wt.
% Is considered to be the lower limit.

As described above, by solidifying the waste or the incineration residue using the solidifying agent, it is possible to obtain an extremely high-strength solidified substance having a heavy metal elution preventing property that meets environmental standards. This can be used as a recycled material such as civil engineering materials. In this case, since the cement content in the solidifying agent is as small as 0 to 29 wt%, even if organic impurities are contained in the incineration residue to be solidified, it does not hinder solidification.

[0032]

Embodiments of the present invention will be described with reference to Table 1. Table 1 shows the composition of the solidifying agent, the composition of the solidified product using the solidifying agent of each composition, and the uniaxial compressive strength and the elution amount of Pb in each solidified product.
5 are shown as experimental examples. The solidified material of each experimental example in Table 1 was obtained by adding an appropriate amount of water to each formulation, kneading the mixture, and press-molding the mixture under a pressure of 100 kg / cm ² . In the case of curing for 28 days under normal pressure, the dissolution amount of Pb is the result of a dissolution test based on the Environment Agency Notification No. 46.

[0033]

[Table 1]

The determination in each of the experimental examples was as follows: in Nos. 1 and 3, the uniaxial compression strength was 450, 430 kg / cm ² and 40.
The soil environmental standard was 0 kg / cm ² or more and the elution amount of Pb was less than 0.01 mg / L in an elution test based on the notification of the Environment Agency No. 46.

On the other hand, No. 2 passed the Pb elution criterion, but lacked strength. No. 4 exhibited high strength, but failed to clear the Pb elution criterion, and could not be judged.

In the above examples, Pb, which is most easily eluted, was shown as a representative for the determination of eluting heavy metals, but other harmful heavy metals such as mercury, cadmium, hexavalent chromium and arsenic were also measured. , Each of which meets the soil environmental standards.

Claims (3)

[Claims] 1. A solidifying agent for solidifying an incineration residue to obtain a recycled material, and gypsum: 1 to 30% by weight;
Admixtures exhibiting potential hydraulic properties such as blast furnace slag: 41-99w
A solidifying agent for incineration residues, characterized in that the solidifying agent comprises 0% to 29% by weight of cement. 2. The solidifying agent for incineration residues according to claim 1, wherein
７０70 wt%, incineration residue: A method for solidifying incineration residue, comprising kneading and shaping 30 to 90 wt% together with a required amount of water. 3. The solidifying agent for incineration residue according to claim 1, wherein the solidifying agent is 10.
A method for solidifying incineration residues, comprising kneading 30 to 90% by weight of incineration residues together with a required amount of water to form a base material for recycling incineration residues.