JPH10192812A - Treatment of heavy metal and dioxin in incineration ash by catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce such safe cement-based material of general incineration ashes of municipal refuse that the environment is not contaminated by heavy metals and dioxin in the future. SOLUTION: In pretreatment for making incineration ashes harmless, discharged incineration ashes are held at constant temperature at constant time in the oxygen-reducing atmosphere and incineration ashes are efficiently dissociated mutually. Heavy metallic compounds contained therein are acted as a catalyst and thereby incineration ashes and various compounds of different kinds of metals containing heavy metals contained therein are changed into stable compounds by chemical reaction. Before treatment, incineration ashes are previously crushed and treated to enlarge surface area and previously regulated to about 50 mesh and maintained at 400-600 deg.C at 30-50 minutes. In treatment, a second kiln is used in combination with a first kiln. After prescribed time elapses, temperature is lowered to 180 deg.C (±10 deg.C) in the oxygen-reducing atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment method using a catalytic reaction at a low temperature for detoxifying incinerated ash. TECHNICAL FIELD The present invention relates to a method for treating heavy metals and dioxins in incinerated ash by a catalytic reaction at a low temperature of the incinerated ash. The present invention relates to a method for treating incinerated ash that is harmless even if municipal garbage general incinerated ash that is finally landfilled is eroded by rainwater or seawater and heavy metals and dioxins are discharged along with leaching water.

[0002]

2. Description of the Related Art Up to now, most of general incinerated ash (fly ash and main ash) of municipal waste has been finally disposed of in landfills. These incinerated ash that has been landfilled is eroded by rainwater and seawater over a long period of time, but the dioxin contained in heavy metals and fly ash undergoes various changes due to the waste that coexists in the erosion process. It is expected that species will flow out with the leaching water. Heavy metals are oxides or chlorides,
Since it is a metal compound that is relatively soluble in water, dioxin is not a water-soluble substance, but the development and establishment of a treatment method is required from the viewpoint of environmental pollution when it is gradually dissolved in water.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pretreatment method for detoxifying municipal incineration ash. It is an object of the present invention to provide a method for producing safe cement-based materials from general incinerated ash from municipal waste without polluting the environment with heavy metals and dioxins in the future.

[0004]

SUMMARY OF THE INVENTION The present invention is a pretreatment for detoxifying incineration ash. The incineration ash discharged is kept in a reduced oxygen atmosphere, at a constant temperature for a certain time, and the incineration ash is removed. By efficiently dissociating each other and using the heavy metal compound therein as a catalyst, various compounds of different metals including the incinerated ash and heavy metals therein are changed into stable compounds by a chemical reaction. The method of treating incinerated ash is summarized. In order to efficiently dissociate the discharged incinerated ash, one effective means is to pulverize the incinerated ash before processing to increase the surface area. Specifically, the incineration ash is reduced to about 50 mesh before the treatment. The above temperature is 400 ° -6
Maintain at 00 °. The above time is maintained for 30 to 50 minutes. The method for treating incinerated ash of the present invention comprises the first kiln and the second kiln.
This is a processing method that uses a temperature difference by combining kilns. That is, after a lapse of a predetermined time, the temperature is set to 180 in a reduced oxygen atmosphere.
In a preferred embodiment, the temperature is lowered to 10 ° C (± 10 ° C).

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Incinerated ash is generally most difficult to solidify with hydraulic cement since it has a high water content and contains a lot of heavy metals and the like. In order to detoxify the metal having this solidification inhibition factor and to promote the curing of organic compounds,
Eliminate the inhibiting factors by carbonization and combustion in a reduced oxygen atmosphere.

A method of efficiently decomposing incinerated ash, which is a mixture of dissimilar metals containing heavy metals, elute metal salts by using heavy metal salts as a catalyst, and then stabilize them by crystallization (hereinafter, referred to as " Incineration ash recycling method ”)
(Japanese Patent Application Laid-Open Nos. 6-15248 and 8-
66494, Japanese Patent Application No. 8-151594, Japanese Patent Application No. 8-15
1595). In Japanese Patent Application Laid-Open No. 6-15248, not only solidification by the action of ettringite with incinerated ash together with cement, but also sodium,
This is a method for stably solidifying incinerated ash, which comprises adding a harmful substance stabilizing agent containing potassium, nitrogen, boron, calcium and the like in an ionic state. Stabilized by metals such as oxides, hydroxides, sulfates, sulfides and phosphides. As, P, etc. react with CaO to become stable compounds. Hydroxides of metals other than alkali metals and alkaline earth metals [Cu (OH) ₂ , Al (OH) ₂ , Zn (O
H) ₂ , Pb (OH) ₂ , Fe (OH) _{2 and the} like. ] Is a compound that is hardly soluble in water.

Further, incinerated ash has a high basicity CaO / SiO ₂ , has a property of being crystallized by slow cooling and water cooling, and becomes vitreous when rapidly cooled. That is, it is to produce a stable and safe substance as a substance that is hardly soluble in water. As a reaction, some elements tend to be electrically positive and others tend to be negative, and a stable compound is produced by a combination of yin and yang. Many metal elements are positive elements, and non-metal elements are negative elements. Compounds (salts) produced by the combination are composed of a positive component and a negative component, and are single salts, double salts and / or complex salts.

[0008] Metals other than metals called noble metals are not produced as a simple substance. Alkali metals exist as ions in water. Many metals have a tendency to ionize and tend to dissolve in acid solutions. Elements are circulated through rocks, the atmosphere, seawater and metamorphism by solar energy and crustal energy inside the earth, and O, Si, Al,
Mostly made of silicate with Fe, Ca, Na, K, Mg. Other types of compounds include halides, carbonates, sulfides, oxides, hydroxides, sulfates, nitrates, phosphates, arsenates, and borates, all of which are ionic compounds. Have. Halides and sulfides,
Oxides are formed by the negative element alone becoming an anion and binding to the cation.In all other compounds, the negative element is combined with oxygen to form an oxoacid ion, which binds to the cation. It was made. Cations are chloride ions (Cl ⁻ ), sulfide ions (S ²⁻ ), oxide ions (O ²⁻ ), etc., and oxo acid ions are carbonate ions (CO ₃ ²⁻ ) and phosphate ions (PO ₄ ^{3). -),} hydroxide ions (OH ^-), arsenate ion (AsO ₄ ^3-), sulfate ion (S
O ₄ ^2- ), borate ion (BO ₃ ^3- ), nitrate ion (NO
₃ ^-), silicate ions (SiO ₄ ^4-) are exemplified.

[0009] A than these ions constitute the compound, the cation of the ionic compound is defined as the amount the solubility that can dissolve the respective anion, S ^2-
And SO ₄ ^2- and CO ₃ ^3- react with metal ions to form poorly soluble compounds. However, since water is a strong ligand, it is easy to coordinate with metal element ions, and many metal complexes immediately turn into aqua complexes when dissolved in water.

It is necessary to convert a water-soluble substance into a hardly soluble substance, but using high temperature and high pressure is not economical. In order to promote the metal reaction by the catalytic action and to facilitate the formation of the substance by the ionic reaction, the reaction surface area is increased by powdering, and the temperature is constant in the deoxygenated space insulated from the outside air such as the reaction atmosphere. And maintain for a certain time. There are a wide variety of substances that can be catalysts, whether gas, liquid, or solid. Since the metal catalyst has a small metal surface area and is inefficient as a catalyst, the metal is used as a fine powder with the surface area being as large as possible. That is, when the incinerated ash containing these catalyst components is pulverized to reduce the particle size and then treated, as a result, the catalyst components also have an increased surface area and a higher catalytic activity.

The catalyst contains iron oxide (Fe) as a main component.
₃ O ₄ ), potassium oxide (K ₂ O) (0.5
1.5%), alumina _{(Al 2 O 3) (2~4} %), calcium oxide (CaO) (1 to 3%), silica (SiO
₂ ) (0.2-1%), magnesium oxide (MgO)
(0.2 to 4%). A sparingly soluble compound is formed by the action of a catalyst. The main reaction is a sulfidation reaction.

The catalyst must dissociate the strongly covalent compound from the atom. For that purpose, it is necessary to dissociate and adsorb the molecules. For example, in the case of ammonia synthesis, N ₂ →
In order to make N + N, K + 1 / 2N ₂ → KN. The K atom plays this role, and one N of N≡N precedes the chemisorption of KN and at the same time, one of the dissociated N becomes F
It is attracted to the e atom to form FeN, and the H atom dissociated on the acid point of one alumina and N of FeN are bonded.

[0013] Another important role of potassium is in its basicity. Neutralizing and weakening the acid strength at the acid sites facilitates the elimination of the product and improves the flow of the synthesis. These acid sites are in an atom-deficient state at the active site of the catalyst and have an electron accepting ability. This means that if the reactive position of the reaction molecule is a donor electron, the reaction substrate is easily adsorbed to the acid site.When the reaction substrate is adsorbed and dissociated on the catalyst surface, the atoms or The group is exchanged. In the electron deficient state, the bond is easily added, but the reaction is liable to occur because of the unstable state. In other words, when an electron accepting substrate is added to the electron donating group, the excess or deficiency of electrons is naturally complemented, and a chemical covalent bond is established and the reaction is repeated.

Cement reacts with water to precipitate hydrate crystals, which are interconnected and solidified, and the hydrate crystals are stable at room temperature. The main component is coal (C
aO), followed by silicic acid (SiO ₂ ), whose content is 88% of the total. Next are alumina (Al ₂ O ₃ ), iron (Fe ₂ O ₃ ), sulfate (SO ₃ ) and the like. These chemical components do not simply exist as oxides, but as compounds and react with water to form hydrates. It exists as a so-called hydraulic hard material.

[0015] For ordinary Portland cement, the minerals that govern its hydration strength are 3CaO, SiO ₂ , which is commonly called Alite, and 2Ca, which is called Belite.
CaO, in SiO _2, accounts for 76% of the total Alite and Belite. Each of these compounds is a compound of lime (CaO) and silicic acid (SiO ₂ ), and forms hydrate crystals by the following reaction upon contact with water. _{2Ca 3 SiO 5 + 6H 2 O} = Ca 3 Si 2 O 7 · 3H 2 O + 3Ca (OH) 2 2Ca 2 Si 4 + 4H 2 O = Ca 3 Si 2 O 7 · 3H 2 O + Ca (OH) 2

Although these hydraulic silicate lime salts differ in the hydration reaction speed and the mechanism of crystallization, all of them result in the hydration of silicate lime salt in the form of 3CaO.2SiO ₃ .3H ₂ O. They agree in forming things. On the other hand, as the other major compounds, alumina content _{(Al 2 O 3) 3CaO ·} Al 2 O 3 to a phase containing (aluminate tricalcium) _{and, 4CaO · Al 2 O 3 ·} Fe 2 O 3 ( aluminate iron Acid lime), which react with water to produce 3CaO
Crystals of the form Al ₂ O ₃ .6H ₂ O precipitate. In addition,
Here, when sulfate groups (SO ₃ ) are present, lime aluminate hydrate combines with SO ₃ to form an inorganic double salt. This is ettringite (3CaO.Al ₂ O ₃ .3CaSO ₄ .3H ₂ O) generally called cement paillus. This ettringite is a crystal that encapsulates heavy metals in cement. As many as 32 molecules of water are contained in one molecule as a unit of the crystal structure, but when the supply of SO ₃ is stopped, it changes to 3CaO.Al ₂ O ₃ .CaSO ₄ .12H ₂ O and the structure is changed by such conversion. Changes in body density and generation of free water weakens the binding force.

The product of the present invention (hereinafter sometimes referred to as “incinerated ash cement”) has latent hydraulic properties, and exhibits hydraulic properties by stimulating action of alkali or sulfate. The basicity value (CaO + Al
_{2 O 3 + MgO)% /} SiO 2% is about 1.35 to 1.45. Compared with Portland cement, its basicity is about 1% lower and its hydration power is lower. For this reason, Portland cement and incineration ash are mixed and pulverized to enhance hydration and hardening properties. Portland cement is 10% to 30% cement
%, The properties of the incinerated ash cementitious materials differ depending on the composition ratio and fineness of the compounds contained in the incinerated ash.

Further, since the incinerated ash cementitious product does not react with water and carbon dioxide, it does not weather and solidify like cement. The incinerated ash cementitious material reacts violently depending on the component ratio of the components. Since alumina and magnesia are much higher than calcium, the reaction speed is high and the expansion coefficient is high. Depending on the purpose of use, if the expansion coefficient is not required and solidification is considered as a satisfactory point, the expansion is stopped by adjusting gypsum and ammonium chloride. The rock formation property and the long-term strength are greater than that of cement because the compound of calcium hydroxide and incineration ash formed by hydration with cement reacts 28 days before the material age, and the latent hydraulic property of incineration ash is exhibited. As the hydration proceeds, the hydration of the cement is promoted, and the strength is increased over a long period of time. Therefore, the initial strength (age 3 to 7 days) shows a value slightly lower than that of cement.

The incinerated ash cementitious material is resistant to structures of seawater, sewage, and groundwater. The reason why the concrete structure is easily broken is that sulfate combines with Ca (OH) ₂ in the concrete to form calcium sulfate (CaSO ₄ ), and further, tricalcium aluminate hydrate (3CaO · Al ₂ O ₃₎・ NH ₂
This is because they combine with O) to become cement patilus.
The incinerated ash cementitious material has a large expansion coefficient and the reaction starts at an early stage, so that Ca (OH) ₂ in the hardened material is reduced and C ₃ A is also reduced, and conversely, the resistance is increased. Cemented incineration ash has a large surface activity,
It has excellent foaming and dispersing ability necessary for solidification, has fluidity, has these aspects, and promotes the hydration reaction of cement.

Thermal decomposition of dioxin The idea of heat treating fly ash in a low oxygen atmosphere is as follows.
Heating fly ash in an oxidizing atmosphere (250 ° -40
0 ° C.), and dioxin is formed by the catalytic action of various metal compounds. That is, by performing fly ash heating in a low oxygen atmosphere under oxygen deficiency, dechlorination / hydrogenation of dioxins can be achieved. The following are conceivable as absolute conditions based on these assumptions. A. Maintaining an oxygen-deficient state: heating in a deoxygenated space insulated from the outside air B. Maintaining a constant temperature: Maintain the heating temperature between 400 ° and 600 °. D. Retention time: Maintain a dry distillation time of 40 minutes to 60 minutes. Discharge after cooling: After a predetermined time has elapsed, the temperature is lowered to 180 ° C or less in a deoxidized state

Dioxin generation and decomposition Dioxin generation mechanism is generated from the reaction mechanism and the processing mechanism due to thermodynamics, reaction rate, and electronic state of molecules in the combustion process of burning municipal garbage, and the unburned matter remains. It consists of the formation of organic chlorine compounds by the reaction of carbon, oxygen and chlorides (such as metal chlorides).

In the incinerator, incineration of vinyl chloride plastic and generation of hydrogen chloride due to the reaction of water-soluble chlorine with CO ₂ and SO _{2 in} the exhaust gas are observed, but a large amount of hydrocarbon (C _n H _m ) is generated. Are generated and are decomposed into carbon dioxide (CO ₂ ) and water (H ₂ O) by contact with O ₂ . However, incomplete combustion may produce dioxins and precursors.

The C ₂ and C ₄ compounds generated during the combustion are chlorinated in a catalytic reaction by chlorine gas or metal chloride generated at a high temperature from hydrochloric acid and oxygen, and pass through chloroethylene and chloroacetylene compounds. Chlorobenzene is formed. Chlorobenzene is a hydroxyl radical (OH
·) And oxygen, become other flue gas reacts with chlorophenol and chloro phenoxyl radicals, C ₂ and compound binds to polychlorotrifluoroethylene mono Ben Uz dioxin and polychlorotrifluoroethylene mono benzofuran of C _4, further generates dioxin .

[0024] In controlling the generation and emission reduction of these dioxins, the combustion process in the incinerator, heat recovery from the discharge port to the exhaust gas treatment device, the gas cooling process, and the air pollutants such as dust in the exhaust gas treatment device. Is suppressed by the removal or the like. The generation of dioxins can be suppressed by complete combustion, and there is no danger of generating dioxins unless incomplete combustion products are generated during the combustion and exhaust gas treatment processes.

Therefore, in order to perform complete combustion, the discharged incinerated ash is further burned to remove incombustible substances, the temperature of the combustion gas is kept constant by the combustion kiln, and sufficient gas agitation in the kiln is performed with a sufficient gas residence time. And mixing with secondary air to reduce substances such as unburned carbon and hydrocarbons in the combustion gas.

Next, the particles are made into a 100 mesh to increase the surface area, and then charged into a combustion kiln in a reduced oxygen atmosphere. The chemical reaction in the kiln is a catalytic reaction, in which the free energy is reduced, the reaction rate is increased, radicals are generated, and the radicals are diffused into the gas phase by a chain mechanism to accelerate the reaction. CaO, K
_A catalyst having a high active point is obtained by synthesizing a substance having a catalytic function on the surface by contacting a reactive gas by adsorption of a solid surface or a temperature change by the reaction of radicals such as ₂ O, Al ₂ O ₃ , and SiO ₂ . In an oxidizing atmosphere, a large amount of dioxins are generated from precursor materials at around 300 ° C. using chlorides and carbon in fly ash as catalysts, but can be decomposed by a catalytic action when heated to 200 ° C. or less in a reducing atmosphere. First, a dehydrochlorination reaction occurs, followed by reduction, resulting in a dechlorination / hydrogenation process. Ammonia (NH ₃ ) from this dry distillation state
Is discharged, and NOx can be suppressed by its reducing power. At the same time, a stabilization treatment for heavy metals is performed.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to embodiments. The present invention is not limited by these examples.

Example 1 In accordance with the flow sheet of an incinerated ash recycling plant for performing a method of treating heavy metals and dioxins in incinerated ash at a low temperature shown in FIG. 1, general municipal incinerated ash (fly ash, main ash) To A. B. Maintaining an oxygen-deficient state (heating in a deoxygenated space insulated from the outside air); C. maintaining a constant temperature (heating temperature is maintained at 400 ° to 600 °); D. retention time (maintain 40-60 minutes dry distillation time);
Emission after cooling (after a predetermined time, the temperature is 18
(Lower than 0 ° C.). Tables 1 to 3 show the component analysis of the manufactured products.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

According to the present invention, it is possible to produce a safe cement-based material which does not pollute the environment with heavy metals and dioxins from general incinerated ash from municipal waste.

[Brief description of the drawings]

FIG. 1 is a drawing showing a main part of an incineration ash recycling plant flow sheet for carrying out the treatment method of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B09B 5/00 N

Claims (7)

[Claims] Claims: 1. A pretreatment for detoxifying incinerated ash, wherein the discharged incinerated ash is held in a reduced oxygen atmosphere, at a constant temperature for a fixed time, and the incinerated ash is efficiently dissociated from each other; A method for treating incinerated ash, characterized in that a heavy metal compound therein acts as a catalyst to thereby convert the incinerated ash and various compounds of different metals including heavy metals therein into stable compounds by a chemical reaction. 2. The method for treating incinerated ash according to claim 1, wherein the incinerated ash is pulverized in advance before the treatment to increase the surface area. 3. The method for treating incinerated ash according to claim 2, wherein the incinerated ash is reduced to about 50 mesh before the treatment. 4. The method for treating incinerated ash according to claim 1, wherein the temperature is maintained at 400 ° to 600 °. 5. The time is maintained for 30 to 50 minutes.
5. The method for treating incinerated ash according to any one of claims 4 to 4. 6. The method for treating incinerated ash according to claim 1, wherein the treatment is performed by combining a first kiln and a second kiln and utilizing a temperature difference. 7. The method for treating incinerated ash according to claim 1, wherein the temperature is lowered to 180 ° C. (± 10 ° C.) in a reduced oxygen atmosphere after a predetermined time has elapsed.