JP7304029B2 - Method for preventing elution of heavy metals from incinerated ash - Google Patents

Description

TECHNICAL FIELD The present invention relates to an elution prevention method capable of effectively preventing elution of heavy metals from incineration ash generated from various industries.

Municipal waste and industrial waste are burned in various incinerators and reduced in volume as incineration ash such as soot and fly ash, most of which is landfilled at controlled final disposal sites. In recent years, from the perspective of environmental conservation, the prevention of the diffusion of environmental pollutants into the atmosphere, soil, and water is of utmost importance. tend to When the incinerated ash and residue are to be landfilled as industrial waste, an elution test shall be performed in accordance with the method for examining metals, etc. contained in industrial waste (Environment Agency Notification No. 13), and heavy metals, etc. The amount of elution must satisfy the landfill disposal criteria.
Heavy metals such as lead and cadmium may be eluted from the incineration ash of municipal waste and industrial waste. /L. Chemical treatment using cement or a chelating agent is generally used to prevent the elution of heavy metals from incinerated ash. However, there are cases where the incineration ash becomes highly alkaline and the amount of lead elution increases due to the solidification treatment with cement. Dithiocarbamic acid-based or piperazine-based chelating agents are mainly used as chelating agents, but since they are organic, there is a problem in stability after landfill disposal if they are treated alone. For this reason, it is desired that heavy metals are not re-eluted even after landfilling, and that the landfill is stably treated. Specifically, as shown in Table 1, the amount of heavy metals (lead, cadmium, arsenic, selenium, hexavalent chromium, total mercury) eluted from incinerated ash must be kept below the landfill disposal criteria.

Among the six types of heavy metals, lead is said to be an amphoteric element, and the amount of lead tends to increase in the acidic or alkaline pH range. It has been known. Generally, in incineration plants such as waste incineration plants, chemicals such as slaked lime are sprayed into dust collectors to reduce the emission of acid gases (hydrogen chloride and sulfur oxides) generated by the incineration of municipal waste. . Therefore, the pH of the incineration ash becomes highly alkaline, and lead is easily eluted. On the other hand, depending on the type of industrial waste and the incinerator, the amount of sprayed chemicals such as slaked lime for exhaust gas countermeasures may be small or may not be sprayed, and the pH of the incinerated ash is in the acidic to neutral range (pH 3- 8) may be indicated.
In this way, the pH of the incineration ash is not constant and may be in a wide range (pH 3 to 13).In particular, the incineration ash that exhibits a low pH (pH 5 or less) or a high pH (pH 12 or more) has a large amount of heavy metals eluted. Since it becomes high, it becomes difficult to suppress elution. Furthermore, when incineration ash contains heavy metals with different elution behaviors such as cadmium, arsenic, selenium, hexavalent chromium, and mercury together with lead, it is extremely difficult to simultaneously suppress the elution of these heavy metals. .

Under such circumstances, various methods for suppressing elution of heavy metals in various incinerated ash and hazardous wastes have been proposed. That is, piperazine carbodithioic acid or a salt thereof, which is a chelating agent for heavy metals such as lead, mercury, chromium, cadmium, zinc, and copper contained in incineration ash discharged from incineration plants for municipal waste and industrial waste. (Patent Document 1), heavy metals such as mercury, lead, cadmium, copper, arsenic, nickel, and chromium contained in municipal waste incineration ash are fixed by mixing with polysaccharides, chelating agents, and sulfides. A heavy metal scavenger (Patent Document 2), a treatment method for preventing elution by mixing dioxins and heavy metals such as cadmium and lead contained in incinerated ash with a chelating agent (Patent Document 3), allophane-containing volcanic ash is used as a raw material, and by conducting drying, particle size adjustment, and lead adsorption property confirmation tests, a technology to make lead in ash insoluble (Patent Document 4), a thiosulfate compound is added to contaminated soil and ash, and ash (Patent Document 5), technology related to equipment that insolubilizes heavy metals such as arsenic and selenium contained in incineration ash by heating, cement for incineration ash, sludge, soil, etc. containing harmful substances such as heavy metals is added, a granule precursor is produced by a stirring granulator, and a harmful substance insolubilization method (Patent Document 6), sewage sludge After adding and mixing a solidifying material such as Portland cement and water to the incinerated ash and granulating it by a rolling granulation method or a compression granulation method, an asphalt film is applied to the surface of the granules using an asphalt/water emulsion. By using a technology to physically suppress the elution of heavy metals such as arsenic (Patent Document 7), and an elution inhibitor of harmful elements containing iron powder, calcium oxide, and aluminum oxide as essential ingredients, fly A technique for suppressing the elution of fluorine, boron, arsenic, selenium, and other heavy metals from ash has been reported (Patent Document 8).

JP-A-1996-224560 JP-A-1998-113677 Japanese Patent Application Laid-Open No. 2002-052373 JP 2016-077940 A Japanese Patent Application Laid-Open No. 2006-000746 JP 2004-008945 A JP-A-1995-060222 JP-A-2005-279413

However, these conventional heavy metal elution prevention technologies have problems with long-term stability because the chelating agent is an organic substance, and re-elution may occur. is insufficient, the amount of chemicals added is large, expensive ingredients are used, the elution inhibitor manufacturing process and elution prevention treatment process are complicated, and large-scale equipment such as special stirring granulators and heating devices are used. Furthermore, there are problems such as that it is only a means capable of suppressing the elution of only some of the harmful substances, and that the elution of a plurality of heavy metals including lead and other heavy metals cannot be suppressed at the same time.
Therefore, the object of the present invention is to determine landfill disposal by determining the amount of elution of heavy metals including lead contained in incineration ash generated from each industry and one or more selected from cadmium, arsenic, selenium, hexavalent chromium and total mercury. The object is to provide an economical and efficient treatment technology that can reduce emissions below the standard value.

Therefore, as a result of repeated studies, the present inventors have found that when treating incineration ash containing lead as heavy metals and one or more selected from cadmium, arsenic, selenium, hexavalent chromium and total mercury, calcium aluminate , aluminum sulfate, ferrous sulfate and an alkali metal phosphate, and a chelating agent are used in combination, even if the pH of the incinerated ash is in a wide range from acidic to strongly alkaline, the above 2 The present inventors have found that the amount of eluted heavy metals above the species can be simultaneously reduced to less than the landfill disposal criterion value, and have completed the present invention.

That is, the present invention provides the following [1] to [4] .

[1] An elution inhibitor containing 100 parts by mass of calcium aluminate, 5 to 100 parts by mass of aluminum sulfate, 20 to 200 parts by mass of ferrous sulfate, and 0.5 to 10 parts by mass of an alkali metal phosphate, and a chelate characterized by combining agents and adding them to incinerated ash,
The incineration ash is an incineration ash in which the elution amount of heavy metals containing lead and at least one selected from cadmium and total mercury exceeds the landfill disposal criteria,
1 to 10 parts by mass of an elution inhibitor and 0.5 to 3 parts by mass of a chelating agent in terms of solid content are added to 100 parts by mass of the incinerated ash,
A method for preventing elution of heavy metals containing lead and one or more metals selected from cadmium and total mercury from incineration ash.
[2] The elution prevention method according to [1], wherein the elution prevention agent further contains 100 to 1200 parts by mass of slaked lime.
[3] The elution prevention method according to [1] or [2], wherein the chelating agent is a dithiocarbamic acid chelating agent.
[4] The calcium aluminate is a crystalline calcium aluminate having an equimolar ratio of CaO and Al ₂ O ₃ and a molar ratio of CaO to Al ₂ O ₃ is CaO/Al ₂ O ₃ =1.6 to 2. The method for preventing elution according to any one of [1] to [3], which comprises the amorphous calcium aluminate of .6.

According to the present invention, even if the incineration ash exhibits a low pH (pH 5 or less) or a high pH (pH 12 or more), lead, cadmium, arsenic, and selenium are contained in the incineration ash in an economical and efficient formulation. , hexavalent chromium and total mercury elution amount can be reduced below the landfill disposal criteria. INDUSTRIAL APPLICABILITY The present invention is an extremely useful technology for smooth management and operation of final disposal sites.

Calcium aluminate used in the elution inhibitor of the present invention is basically a substance obtained by heat-treating a CaO raw material and an Al ₂ O ₃ raw material. Calcium aluminate may be any hydration-active substance having a crystalline or vitrified structure composed of CaO and Al ₂ O ₃ as chemical components, and other chemical components are added in addition to CaO and Al ₂ O ₃ . It may be a compound, solid solution, vitreous substance, or mixture thereof. Examples of the former (crystalline) include 12CaO.7Al ₂ O ₃ , CaO.Al ₂ O ₃ , 3CaO.Al ₂ O ₃ , CaO.2Al ₂ O ₃ , 11CaO.7Al ₂ O ₃ .CaF ₂ , Na ₂ O. 8CaO.3Al ₂ O ₃ and the like, and examples of the latter (vitreous) include 12CaO.7Al ₂ O ₃ and CaO.Al ₂ O ₃ .

Furthermore, the calcium aluminate used in the present invention includes crystalline calcium aluminate having an equimolar ratio of CaO and Al ₂ O ₃ and CaO/Al ₂ O ₃ having a molar ratio of CaO and Al ₂ O ₃ of 1.5. 7 amorphous calcium aluminates are preferred.

A crystalline calcium aluminate having an equimolar ratio of CaO and Al ₂ O ₃ was obtained by mixing the CaO source and the Al ₂ O ₃ source as described above so as to obtain an equimolar ratio in terms of CaO and Al ₂ O ₃ . It can be obtained by heating the material at, for example, 1600° C. and then slowly cooling it. For slow cooling, natural cooling in the heating device can generally be adopted, but if the temperature drops rapidly due to the structure of the heating device, the heating should be adjusted so that the temperature drop rate is approximately 10°C/min or less. is preferred. The CaO source is not particularly limited, but suitable examples thereof include limestone powder, slaked lime powder and quicklime powder. Preferred Al ₂ O ₃ sources include bauxite powder, aluminum hydroxide, aluminum carbonate, aluminum residual ash, alumina powder and the like. can be mentioned. The Blaine specific surface area of the crystalline calcium aluminate is preferably 3,000 to 10,000 cm ² /g, and is preferably approximately the same as the Blaine specific surface area of the amorphous calcium aluminate used therewith.

Amorphous calcium aluminate having a molar ratio of CaO to Al ₂ O ₃ of CaO/Al ₂ O ₃ =1.7 is obtained by converting the CaO source and the Al ₂ O ₃ source into CaO and Al ₂ O ₃ respectively. It can be obtained by heating and melting, for example, 1400 to 1900° C., and then quenching the mixture in the molar ratio range. The quenching can be performed by a known quenching method such as removing the melt from the heating temperature outside the furnace, quenching in water, or blowing a cooling gas. It is preferable to use the amorphous calcium aluminate having a Blaine specific surface area of 3,000 to 10,000 cm ² /g by appropriately adjusting the particle size by pulverizing, classifying, sieving, and the like. The same CaO source and Al ₂ O ₃ source as those used for the crystalline calcium aluminate can be used.

The calcium aluminate used in the present invention includes crystalline calcium aluminate having an equimolar ratio of CaO and Al ₂ O ₃ and CaO/Al ₂ O ₃ having a molar ratio of CaO/Al ₂ O ₃ =1. Even if the amorphous calcium aluminate of .7 is blended in an arbitrary ratio and used as a mixture, or if each is used alone, the elution prevention effect on the incineration ash containing the above-mentioned plurality of heavy metals can be exhibited satisfactorily. can.

Aluminum sulfate used in the present invention may be either a hydrate represented by Al ₂ (SO ₄ ) _{3.nH 2} O or an anhydrous salt represented by Al ₂ (SO ₄ ) ₃ as a chemical component. Hydrates with n of 14 to 18 are preferred because they are excellent in preventing the elution of the heavy metals.
The content of aluminum sulfate in the elution inhibitor of the present invention is preferably 5 to 100 parts by mass with respect to 100 parts by mass of calcium aluminate, from the viewpoint of the elution preventing effect of the plurality of heavy metals. It is more preferably 80 parts by mass, and even more preferably 5 to 50 parts by mass.

In the present invention, ferrous sulfate can be suitably used as a reducing component because it is easy to handle and relatively inexpensive. Ferrous sulfate includes ferrous sulfate heptahydrate, which has seven waters of crystallization, and ferrous sulfate monohydrate, which has one water of crystallization. More preferably, hydrates are used.
The content of ferrous sulfate in the elution inhibitor of the present invention is preferably 20 to 200 parts by mass with respect to 100 parts by mass of calcium aluminate from the viewpoint of the elution prevention effect of the plurality of heavy metals. It is more preferably 50 to 200 parts by mass, even more preferably 50 to 150 parts by mass.

Alkali metal phosphates used in the present invention include readily soluble salts such as sodium phosphate and potassium phosphate. In the present invention, by blending an alkali metal phosphate, a good elution prevention effect of the plurality of heavy metals can be obtained. As the alkali metal phosphate, potassium phosphate represented by the following formulas (1) to (3) is preferable, and potassium dihydrogen phosphate represented by the following formula (2) is preferable because of its excellent elution suppression effect. more preferred.

_{K2HPO4 (} 1)
_{KH2PO4 (} 2)
_{K3PO4 (} 3)

The content of the alkali metal phosphate in the elution inhibitor of the present invention is 0.5 to 10 parts by mass with respect to 100 parts by mass of calcium aluminate from the viewpoint of the elution-preventing effect of the plurality of heavy metals. is preferable, 0.5 to 8 parts by mass is more preferable, and 0.5 to 5 parts by mass is even more preferable.

In the present invention, when slaked lime is used in combination with the elution inhibitor, the elution amount of heavy metals such as lead and cadmium can be sufficiently reduced even in the case of acidic incineration ash.
The slaked lime used in the present invention can be suitably used as long as it contains calcium hydroxide represented by the chemical formula Ca(OH) ₂ as a main component. Slaked lime that can pass through a sieve with a diameter of 600 μm is particularly preferable in order to exhibit the elution prevention effect well.
The content of slaked lime in the elution inhibitor of the present invention is 100 to 1200 parts by mass with respect to 100 parts by mass of calcium aluminate from the viewpoint of the elution prevention effect of the plurality of heavy metals when targeting acidic incineration ash. parts, more preferably 200 to 1200 parts by mass, even more preferably 200 to 1000 parts by mass.

In addition, the elution inhibitor may be blended with a reducing agent, a solidifying agent such as cement, an extender such as blast furnace slag or tankl powder, etc., as long as the elution prevention effect is not impaired.

In the present invention, a chelating agent is used in combination with the elution inhibitor. By using a chelating agent together, heavy metals can be prevented from eluting even in the case of incineration ash with low pH (pH 5 or less) or high pH (pH 12 or more), where the amount of heavy metals eluted is high and it is difficult to suppress elution. can be ensured.
The chelating agent used in the present invention is not particularly limited, but includes dithiocarbamic acid chelating agents, piperazine chelating agents, and the like. More specific examples include dithiocarbamate, dialkyldithiocarbamate, cycloalkyldithiocarbamate, piperazine dithiocarbamate, tetraethylenepentamine dithiocarbamate, polyamine dithiocarbamate, and the like.
These chelating agents can be used in either liquid or powder form.
In addition, commercially available products of these chelating agents can be used.

In the present invention, the incineration ash to be prevented from elution is incineration ash containing lead and one or more metals selected from cadmium, arsenic, hexavalent chromium, selenium and total mercury, and a plurality of these heavy metals. It is more preferable that the incineration ash has an elution amount exceeding the landfill disposal criteria. Incineration ash containing multiple heavy metals includes incineration ash such as municipal waste incineration ash, industrial waste incineration ash, sewage sludge incineration ash, biomass boiler incineration ash, and disaster waste incineration ash. Municipal waste incineration ash is incinerated to reduce and stabilize municipal waste discharged from general households. Industrial waste incineration ash is incineration ash generated when automobile shredder dust (ASR), construction waste, or the like is incinerated or melted. Sewage sludge incineration ash is incinerated to dehydrate sewage sludge and further reduce and stabilize it. Biomass boiler incineration ash is incineration ash generated when wood chips such as thinned wood and pruned branches, pellets, rice husks, coffee grounds pellets, etc. are burned as fuel. Incinerated disaster waste ash is incinerated ash generated when combustible disaster waste generated by large-scale natural disasters such as the Great East Japan Earthquake and the Kumamoto Earthquake is incinerated and reduced in volume.

In the present invention, an elution inhibitor and a chelating agent may be added to the incinerated ash containing the plurality of heavy metals, particularly the incinerated ash in which the plurality of heavy metals exceeds the landfill disposal criteria, and water is added and mixed at the same time. preferably.
The amount of the elution inhibitor added to the incinerated ash depends on the content of heavy metals, but is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the incinerated ash, in terms of economy, uniform mixing and elution prevention performance. Therefore, it is more preferably 2 to 8 parts by mass, more preferably 3 to 5 parts by mass.
In addition, the amount of the chelating agent added to the incinerated ash is preferably 0.5 to 3 parts by mass in terms of solid content per 100 parts by mass of the incinerated ash. Parts by mass are more preferable.
Furthermore, the amount of water to be added is not particularly limited as long as the incinerated ash to which the elution inhibitor and chelating agent are added is uniformly mixed with water and granulated or aggregated.

The method of mixing the incinerated ash, which is the target of elution suppression, with the elution inhibitor, chelating agent, and water is not particularly limited. An inhibitor, a chelating agent, and water can be mixed to prevent elution of heavy metals.
The incineration ash thus treated to prevent elution can be directly landfilled because the elution of the plurality of heavy metals is prevented below the landfill disposal criteria.

The present invention will now be described in more detail with reference to examples.

(elution inhibitor)
Limestone (CaO content: 56 _% by mass) is used as _the CaO source, and coarsely crushed granules (particle size of about 1 mm or less) are used as the Al ₂ O ₃ source. Calcium aluminate powders represented by A1 and A2 were prepared. The manufacturing method is to mix a CaO source and an Al ₂ O ₃ source at a predetermined molar ratio, heat it to 1800 ° C. (± 50 ° C.) in an electric furnace, hold it for 60 minutes, then stop heating and turn it into a furnace. (A1). Similarly, after heating to 1800 ° C. (± 50 ° C.) and holding for 60 minutes, the heated object is taken out from the electric furnace at a temperature of 1800 ° C. to room temperature, and immediately after taking out, nitrogen gas is applied to the heated object surface at a flow rate of about 100 cc / sec. (A2) was obtained by spraying and quenching. The obtained cooled product was pulverized by a ball mill, and the fineness was adjusted by changing the pulverization time so that the Blaine specific surface area was 5000±500 cm ² /g.
A1; CaO/ _Al2O3 = _crystalline calcium aluminate with a molar ratio of 1.0 A2; _CaO / _Al2O3 = amorphous calcium aluminate with a molar ratio of 1.7

Calcium aluminates A1 to A2 and materials selected from B to E shown below were dry-mixed for 3 minutes using a Henschel mixer at the blending ratios shown in Table 2 to prepare dissolution inhibitors.
B; aluminum sulfate 14-18 hydrate: manufactured by Kanto Chemical Co., Ltd. powder reagent C; ferrous sulfate monohydrate: manufactured by Fuji Titanium Industry D; potassium dihydrogen phosphate: manufactured by Kanto Chemical Co., Ltd. powder reagent E; slaked lime : Powder reagent F manufactured by Kanto Kagaku Co., Ltd.; Chelating agent: diethyldithiocarbamic acid-based chelating agent (commercially available)

(Incineration ash)
As incineration ash containing heavy metals, three types of incineration ash 1 (incineration plant A), incineration ash 2 (incineration plant B), and incineration ash 3 (industrial waste incineration plant) were used. For these incinerated ash, the eluted amounts of lead, cadmium, arsenic, selenium, hexavalent chromium and total mercury, and the pH of the test solution in the elution test by the same method were measured. Table 3 shows the measurement results.

(Measurement of elution amount)
To the incinerated ash shown in Table 3, the elution inhibitor, chelating agent, and water shown in Table 2 were added at the mixing ratio shown in Table 5 (the chelating agent is the solid content equivalent), and mixed with a mortar mixer for 3 minutes to form sand granules. The mixture was adjusted so that After the mixture was sealed and cured at a temperature of 20° C. for 7 days, the eluted amounts of lead, cadmium, arsenic, selenium, hexavalent chromium, and total mercury were measured by a method according to Notification No. 13 of the Environment Agency. Table 5 shows the measurement results of the elution amount.

(Method for measuring the amount of elution according to Notification No. 13 of the Environment Agency)
(1) After sealed curing for 7 days, the sample was pulverized, and the portion that passed through a sieve of 0.5 to 5 mm was collected and mixed.
(2) 50 g of a sample was weighed into a plastic container having a capacity of 1000 mL, 500 g of a solvent (pure water) was added, and the mixture was shaken for 6 hours with a shaker (200 shakes/minute).
(3) After shaking, centrifugation was performed, and the supernatant of the sample solution was filtered through a membrane filter with a pore size of 1.0 µm to obtain a test solution.
(4) The components and pH of the sampled test solution were measured by the methods shown in Table 4.

From the results in Table 5, the incineration ash mixed with the elution inhibitor and chelating agent of the present invention (Examples 1 to 22) all had lead, cadmium, arsenic, selenium, hexavalent chromium, and total mercury elution. It can be seen that the elution prevention effect of lead is well exhibited even in the high alkaline region (pH 12 or higher), as it is suppressed to the prescribed value or less of the landfill disposal criteria (Environment Agency Notification No. 13). As calcium aluminate, crystalline calcium aluminate having an equimolar ratio of CaO and Al ₂ O ₃ and amorphous calcium having a molar ratio of CaO and Al ₂ O ₃ of CaO/Al ₂ O ₃ =1.7 Elution inhibitors (Nos. 2 to 4, No. 14) containing aluminate alone or arbitrarily mixed together suppress the elution of the six heavy metals by using them together with a chelating agent. It turned out to be highly effective. On the other hand, when an elution inhibitor other than the present invention and a chelating agent were used together (Comparative Examples 1 to 7), or when a chelating agent was used alone (Comparative Examples 8 to 9), the six heavy metals The elution amount of either exceeded the landfill disposal judgment standard value, and the elution prevention effect was insufficient.

Claims (4)

A combination of an elution inhibitor containing 100 parts by mass of calcium aluminate, 5 to 100 parts by mass of aluminum sulfate, 20 to 200 parts by mass of ferrous sulfate, and 0.5 to 10 parts by mass of an alkali metal phosphate, and a chelating agent and is added to the incinerated ash,
The incineration ash is an incineration ash in which the elution amount of heavy metals containing lead and one or more metals selected from cadmium and total mercury exceeds the landfill disposal criteria,
1 to 10 parts by mass of an elution inhibitor and 0.5 to 3 parts by mass of a chelating agent in terms of solid content are added to 100 parts by mass of the incinerated ash,
A method for preventing elution of heavy metals containing lead and one or more metals selected from cadmium and total mercury from incineration ash. The elution prevention method according to claim 1, wherein the elution prevention agent further contains 100 to 1200 parts by mass of slaked lime. The method for preventing elution according to claim 1 or 2, wherein the chelating agent is a dithiocarbamic acid chelating agent. The calcium aluminate is a crystalline calcium aluminate having an equimolar ratio of CaO and Al ₂ O ₃ and a molar ratio of CaO to Al ₂ O ₃ is CaO/Al ₂ O ₃ =1.6 to 2.6. The method for preventing elution according to any one of claims 1 to 3, which further comprises amorphous calcium aluminate.