JP4678229B2 - Heavy metal insolubilizer, method for insolubilizing heavy metals in fly ash - Google Patents

Description

The present invention provides an inorganic compound insolubilizer capable of easily insolubilizing heavy metals, particularly Pb, Cd, As and the like.
Further, the present invention provides a method for insolubilizing a pollutant containing heavy metals such as fly ash by using an insolubilizing agent so that the heavy metals are not eluted.

  The fly ash discharged from the incinerator contains harmful components such as heavy metals (especially lead) and dioxins. Among these, for heavy metals such as lead, addition of liquid polymer chelating agents and cement solidification methods, etc. Insolubilization by is generally performed.

However, in the case of the polymer chelating agent, generation of harmful gas may be confirmed, and there is a concern about adverse effects on the ecosystem.
In addition, the cement solidification method does not have a sufficient effect of insolubilizing heavy metals unless a large amount of cement solidifying agent is added. There is.

Until now, a substance obtained by heat treatment of calcium aluminate hydrate, a substance mainly composed of CaO and Al ₂ O ₃ , or a substance composed of lime and calcium aluminate has been used as a heavy metal insolubilizer. It is known (patent documents 1 to 3).

JP 2000-93927 A JP 2002-1553836 A Japanese Patent Laid-Open No. 2004-136160

  In the techniques described in Patent Documents 1 to 3, it is difficult for the insolubilizing agent to be mixed and contacted with the contamination target sufficiently uniformly, and the mixing method is also limited.

  Therefore, it is difficult to say that the solubilizers / adsorbents of toxic heavy metals known so far sufficiently satisfy the currently required level.

  Therefore, as a heavy metal insolubilizer, there is no risk of the generation of harmful gases such as macromolecules, the impact on the ecosystem is small, and it can be easily mixed uniformly with contaminated objects (calcium aluminate is the main component). Provide the agent.

  The technical problem can be achieved by the present invention as follows.

  That is, the present invention is an insolubilizing agent comprising calcium oxide and calcium aluminate, wherein the insolubilizing agent has a bulk density of 0.2 to 0.7 g / ml. (Invention 1).

The present invention also relates to an insolubilizing agent comprising calcium oxide and calcium aluminate, wherein the insolubilizing agent has a bulk density of 0.2 to 0.7 g / ml and is measured by a dry particle size distribution meter. diameter _{(D 50)} is the insolubilizing agent of heavy metals according to claim 1, characterized in that the 1.0 to 5.0 m (invention 2).

In addition, the present invention is the heavy metal insolubilizer according to the first or second aspect of the present invention, wherein the calcium aluminate is Ca ₁₂ Al ₁₄ O ₃₃ and / or Ca ₃ Al ₂ O ₆ (invention 3).

  In addition, the present invention is the heavy metal insolubilizer according to any one of the present inventions 1 to 3, wherein the insolubilized object is a heavy metal in fly ash (Invention 4).

  Further, the present invention is a method for insolubilizing heavy metals in fly ash, characterized in that fly ash and the insolubilizing agent according to any one of the present inventions 1 to 4 are mixed and cured in the presence of moisture (Invention 5). ).

  In addition, the present invention blows the insolubilizer according to any one of the present inventions 1 to 4 together with a carrier gas into the interior from the combustion chamber of the incinerator to the dust collector, and the fly ash discharged from the dust collector is present in the presence of moisture. This is a method for insolubilizing heavy metals in fly ash characterized by curing with (Invention 6).

  Since the insolubilizing agent according to the present invention behaves as fine particles and has a low bulk density, it can be easily mixed with the substance to be insolubilized even in a solid content such as in airflow or powder, and the function of the insolubilizing agent is It can be sufficiently exerted, and the heavy metal in the material to be insolubilized can be strongly insolubilized.

  Furthermore, since the insolubilizing agent according to the present invention is composed of harmless elements or compounds, even when the insolubilizing agent is disposed of in landfill, the burden on the environment is small.

  Further, the insolubilizing agent according to the present invention has excellent heat resistance and can be added by any method such as direct addition from the combustion chamber of the incinerator to the air preheater, before the dust collector, or directly after the dust collection. Can be expressed.

  The configuration of the present invention will be described in more detail as follows.

  First, the insolubilizing agent according to the present invention will be described.

  The bulk density of the insolubilizing agent according to the present invention is 0.2 to 0.7 g / ml. Particles of 0.2 g / ml or less become difficult to handle due to severe scattering and the like, and the bulk density is smaller than that of fly ash, making it difficult to mix uniformly in exhaust gas or after being discharged from a dust collector. Become. Moreover, when it exceeds 0.7 g / ml, bulk density becomes larger than fly ash, and uniform mixing after discharging from exhaust gas or from a dust collector becomes difficult. Preferably it is 0.2-0.5 g / ml.

The average particle diameter (D ₅₀ ) measured by a dry particle size distribution meter of the insolubilizing agent according to the present invention is preferably 1.0 to 5.0 μm. Since the insolubilizing agent according to the present invention is prepared by firing at a high temperature of 850 to 1200 ° C., particles of 1.0 μm or less are difficult to produce industrially. Moreover, although there is no functional problem even if it is less than 1.0 micrometer, handling of powder is difficult. When it exceeds 5.0 μm, the contact area between the harmful heavy metal ions and the insolubilizing agent becomes small, which is not preferable. Preferably it is 1.0-4.0 micrometers. These particles pass through a 500 μm sieve.

The BET specific surface area value of the insolubilizing agent according to the present invention is preferably 1.5 to 10.0 m ² / g. When the BET specific surface area value is less than 1.5 m ² / g, the contact area between harmful heavy metal ions and the insolubilizing agent becomes small, such being undesirable. Insolubilizers exceeding 10.0 m ² / g are difficult to industrially produce because they are prepared by firing at a high temperature of 850 to 1200 ° C. Insolubilizers having a BET specific surface area value exceeding 10.0 m ² / g have no functional problem, but are difficult to handle as a powder. More preferably, it is 1.5-5.0 m < ² > / g.

The Sm value measured by the dry particle size distribution meter of the insolubilizing agent according to the present invention is preferably 0.7 to 5.0 m ² / g. When the Sm value is less than 0.7 m ² / g, the contact area between harmful heavy metal ions and the insolubilizing agent becomes small, which is not preferable. Insolubilizers exceeding 5.0 m ² / g are difficult to industrially produce because they are prepared by firing at a high temperature of 850 to 1200 ° C. Insolubilizers having an Sm value exceeding 5.0 m ² / g have no functional problem, but are difficult to handle as a powder. More preferably, it is 0.7-2.5 m < ² > / g.

  The particle shape of the insolubilizing agent according to the present invention is not particularly limited, but is preferably granular.

The insolubilizing agent according to the present invention comprises calcium oxide and calcium aluminate. Calcium aluminate _{is Ca 12 Al 14 O 33, Ca} 3 Al 2 O 6 and CaAl ₂ O ₄ or the like, preferably a _{Ca 12 Al 14 O 33, Ca} 3 Al 2 O 6. It is difficult to say that calcium aluminate alone and calcium oxide alone have a sufficient function of insolubilizing heavy metals.
In addition, since the insolubilizing agent according to the present invention is a fine particle, calcium oxide may react with moisture in the air to become slaked lime or carbon dioxide to react with calcium carbonate, but the insolubilizing effect of heavy metals is It is maintained.

  The molar ratio (Ca / Al) between calcium and aluminum of the insolubilizing agent comprising calcium oxide and calcium aluminate according to the present invention is preferably 50/50 to 80/20. When the molar ratio of calcium to aluminum is outside the above range, it is difficult to sufficiently insolubilize the heavy metal.

  Next, a method for producing the insolubilizer according to the present invention will be described.

  The insolubilizer according to the present invention can be obtained by mixing a calcium compound and an aluminum compound and then heat-treating at a temperature of 850 to 1200 ° C. in an oxidizing or atmospheric atmosphere. Further, if necessary, pulverization / dry surface treatment can be performed.

  As the calcium compound, calcium hydroxide (slaked lime), calcium carbonate, calcium oxide, calcium nitrate and the like can be used, and calcium hydroxide and calcium carbonate are preferred. The average particle size of the calcium compound is preferably 0.2 to 20 μm.

  As the aluminum compound, aluminum hydroxide, aluminum oxide, aluminum nitrate or the like can be used, and aluminum hydroxide is preferable. The average particle size of the aluminum compound is preferably 0.1 to 20 μm.

  What is necessary is just to mix the mixing ratio of a calcium compound and an aluminum compound so that it may become 50/50-80/20 by the molar ratio of Ca / Al.

  As a mixer in the manufacturing method, a raking machine, a roller type mixer, a vibration mill, a bead mill, a disk type wet stirring and mixing tank, or the like can be used.

  In the mixing state of the mixture which is a precursor of the insolubilizing agent according to the present invention, the subsequent solid phase reaction is caused uniformly and promptly, so selection of a mixer and mixing conditions is important. However, it is sufficient if uniform mixing is possible.

  When the heating temperature is less than 850 ° C., the dehydration reaction, decarboxylation reaction and solid phase reaction of the mixed powder do not proceed, or the proceeding speed is extremely slow, which is not preferable. On the other hand, when the heating temperature exceeds 1200 ° C., the particle size of the generated composite oxide particles increases, and the reactivity with harmful heavy metals in the aqueous system decreases, which is not preferable. The heat treatment temperature is more preferably 900 to 1150 ° C. In consideration of industrial productivity, the heating time is preferably 30 minutes to 180 minutes. The heating atmosphere may be an oxidizing or atmospheric atmosphere.

  In the present invention, it is important to dry pulverize the powder after the heat treatment, and then a dry surface treatment may be performed.

In order to make the bulk density of the insolubilizing agent 0.2 to 0.7 g / ml and to make the powder fine and less agglomerated, it is preferable to control the BET specific surface area to 1.5 to 10 m ² / g. It is necessary to perform a dry grinding process.

Since the dry pulverization treatment can reduce the average particle size (D ₅₀ ) of the powder after the heat treatment, the reactivity of the powder of the present invention with harmful heavy metals in the presence of water can be improved. As an apparatus that can be used for the dry pulverization treatment, a free pulverizer, a hammer mill, a vibration mill, or the like can be used.

  In addition, by subjecting the powder after the heat treatment to a dry surface treatment with an organic substance or the like, the reactivity with harmful heavy metals in the presence of water can be controlled. Examples of the surface treatment agent include rosin compounds, silane coupling agents, higher fatty acids and the like. The coating amount of the surface treatment agent on the insolubilizer powder is preferably 0.1 to 5% by weight in terms of C with respect to the composite oxide particle powder. As a dry surface treatment machine, a rough machine, a vibration mill, a roller type mixer, or the like can be used.

  Next, a treatment method using the insolubilizer according to the present invention will be described.

  In the insolubilization method according to the present invention, an insolubilizing agent is allowed to coexist in a solid substance (such as fly ash) that may release harmful heavy metals, and moisture is present to suppress elution of the harmful heavy metals into the water system. Hereinafter, the method for insolubilizing heavy metals in the present invention will be described.

  In the present invention, the amount of the insolubilizing agent added to the solid content may be an appropriate amount depending on the heavy metal content or the elution amount in the solid content, but is preferably about 1 to 15% by weight. When the amount is less than 1% by weight, the contact between the insolubilizing agent and the solid content is insufficient, and the insolubilization reaction does not proceed sufficiently, which is not preferable. If it exceeds 15% by weight, the effect is saturated, so there is no point in adding more than necessary. More preferably, it is 1 to 10% by weight.

  In the present invention, it is preferable that 5 to 250% by weight of water is present with respect to the total amount of the solid content and the insolubilizing agent. If the amount of water present is less than 5% by weight, the progress of the insolubilization reaction is slow, which is not preferable. When the amount exceeds 250% by weight, the effect is saturated, and the mixture of the treatment object and the insolubilizing agent is not preferable because it becomes a paste or slurry due to excessive moisture, and the weight increases even in landfill disposal. . More preferably, it is 10 to 70% by weight.

  In the present invention, the temperature at which the insolubilizing agent is brought into contact (the temperature at the time of curing) is not particularly limited, but in the present invention, heavy metals can be easily insolubilized at room temperature. When the temperature is extremely low, for example, when the temperature is 5 ° C. or less, the reaction rate of the insolubilizing agent becomes small, and the trapping rate of harmful heavy metals becomes small. The normally used temperature range is preferably 5 to 90 ° C, more preferably 10 to 50 ° C.

  In the present invention, it is not necessary to control the pressure during curing, and the insolubilization process may be performed under normal pressure (atmospheric pressure).

  The time for curing may be changed according to the heavy metal content or elution amount in the solid content, but is usually several hours to 10 days.

In the present invention, heavy metal insolubilizers can be transported and sprayed and added together with the carrier gas into the exhaust gas from the combustion chamber of the incinerator to the dust collector. When the insolubilizing agent according to the present invention is sprayed and added to the exhaust gas, the bulk density is about the same as that of fly ash and the average particle diameter (D ₅₀ ) is 1.0 to 5.0 μm, which is fine. It is effective in terms of uniform mixing of the insolubilizer and the insolubilizer.

  As the air flow conveying method, pneumatic transportation, nitrogen transportation, or the like can be performed.

  After adding the insolubilizing agent to the exhaust gas by the air current conveying method, the fly ash collected by the dust collector is preferably cured in the same manner as above.

<Action>
The important point in the present invention is that the insolubilizing agent according to the present invention has the ability to efficiently take in harmful heavy metal ions in the process of hydration reaction in the presence of water, and removes harmful heavy metals from low to high concentrations. It can be captured.

  Since the bulk density of the insolubilizing agent according to the present invention is about the same as that of the solid content, particularly fly ash, the solid content and the insolubilizing agent can be sufficiently mixed. Can react tightly, so that heavy metals can be strongly adsorbed and bonded in the insolubilizing agent, and an excellent insolubilizing effect is exhibited.

  A typical embodiment of the present invention is as follows.

The bulk density of the insolubilizing agent was obtained by weighing 10.0 g of the sample with a pan balance, pouring it gently into a 50 ml graduated cylinder, shaking the graduated cylinder lightly to flatten the top of the sample, and reading the scale. It was calculated by the following formula.
Apparent density ρb (g / ml) = 10.0 ÷ Measurement cylinder scale reading (ml)

The average particle size (D ₅₀ ) of the insolubilizer is the 50% particle size of the volume-based particle size distribution measured by a dry method using a HELOS SYSTEM PARTICLE SIZE ANALYZER at a dispersion pressure of 1.00 bar. It is.

  The Sm value of the insolubilizer indicates the surface area per unit weight obtained from the particle size when measured at a dispersion pressure of 1.00 bar by a dry method using HELOS SYSTEM PARTICLE SIZE ANALYZER of Sympatec as well as the average particle size. It is.

  The BET specific surface area value was shown as a value measured by the BET method.

<Evaluation method of elution amount of heavy metals in fly ash using an insolubilizing agent>
Measurements were performed in accordance with Environmental Agency Notification No.13.
That is, the object after curing was air-dried for 1 day, 100 g was measured, 10 times the amount of ion-exchanged water was added, and the mixture was shaken (shaking frequency 200 times / minute, shaking width 4.5 cm). After shaking for a while, the solid content was filtered off from the aqueous solution, and the heavy metal concentration in the filtrate was evaluated using “Plasma Optical Emission Spectrometer SPS4000 (Seiko Electronics Co., Ltd.)”.

Example 1 Production of Insolubilizer 148.0 g of slaked lime powder (JIS special name, BET specific surface area value 15 m ^{2 /} g, equivalent to Ca = 2.00 mol) and 104.6 g of aluminum hydroxide (C-301, manufactured by Sumitomo Chemical) BET specific surface area value 2 m ^{2 /} g, equivalent to Al = 1.34 mol) was mixed for 1 hour using a Reika machine. The obtained mixed powder was separately placed in an alumina crucible and heat-treated in air at 1000 ° C. for 4 hours in a muffle furnace. The particle powder after the heat treatment was pulverized using a hammer mill. The obtained particle powder was white.

As a result of X-ray diffraction, the obtained insolubilizer was a mixed phase of calcium aluminate and calcium oxide, and the calcium aluminate was Ca ₁₂ Al ₁₄ O ₃₃ and Ca ₃ Al ₂ O ₆ . The bulk density of the insolubilizer was 0.38 g / ml, the average particle size (D ₅₀ ) was 2.12 μm, the Sm value was 1.21 m ² / g, and the BET specific surface area value was 3.2 m ² / g.

Example 2
An insolubilizing agent was obtained in the same manner as insolubilizing agent 1 except that the kind of raw material, the Ca / Al ratio, and the heating temperature were variously changed.
Comparative Example 1
As the Portland cement of Comparative Example 1, a commercially available JIS standard product was used.

  Various characteristics of the obtained insolubilizer are shown in Tables 1 and 2.

Insolubilization test Example 3
2% by weight of insolubilizing agent 1 was added to the fly ash collected from the BF of the municipal waste incinerator, and then 20% by weight of water was added to the total amount of the fly ash and the insolubilizing agent. Then, it was kept for 1 day and used as a curing.
The amount of heavy metal elution was measured according to the above <Evaluation method of heavy metal elution amount of fly ash to which insolubilizing agent was applied>.

Examples 4-9, Comparative Examples 2-8:
The insolubilization test was performed in the same manner as in Example 3 except that the type of the object, the type and addition amount of the insolubilizing agent, the addition amount of water, and the curing period were variously changed. Table 3 shows the conditions for the insolubilization treatment and the heavy metal elution amount of each object after the insolubilization test.

  The insolubilizing agent according to the present invention is suitable as a harmful heavy metal insolubilizing agent because it can insolubilize a wide range of harmful heavy metals, particularly lead, cadmium or arsenic. In addition, the insolubilizing agent according to the present invention does not require a complicated processing step, and thus is suitable as an insolubilizing agent used in a simple processing method.

Furthermore, since the insolubilizing agent according to the present invention is composed of harmless elements or compounds, even when the insolubilizing agent is disposed of in landfill, the burden on the environment is small.

Claims (5)

Heavy metals Ri Do from calcium oxide and calcium aluminate A insolubilizing agent for insolubilizing the heavy metals in fly ash, the bulk density of the insolubilizing agent is characterized in that it is a 0.2 to 0.7 g / ml Insolubilizer. Ri Do from calcium oxide and calcium aluminate A insolubilizing agent for insolubilizing the heavy metals in fly ash, the bulk density of the insolubilizing agent by dry particle size distribution meter a 0.2 to 0.7 g / ml A heavy metal insolubilizing agent having a measured average particle diameter (D ₅₀ ) of 1.0 to 5.0 μm. Insolubilizing agent of heavy metals according to claim 1 or 2, wherein the calcium aluminate is _Ca 12 _Al 14 _{O 33} and / or _Ca 3 _Al 2 _{O 6.} A method for insolubilizing heavy metals in fly ash, comprising mixing fly ash and the insolubilizing agent according to any one of claims 1 to 3 and curing in the presence of moisture. The insolubilizer according to any one of claims 1 to 3 is blown together with a carrier gas into the interior from the combustion chamber of the incinerator to the dust collector, and the fly ash discharged from the dust collector is cured in the presence of moisture. A method for insolubilizing heavy metals in fly ash.