JPH0975897A - Method for solidifying metal in waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal solidifying method in which a small amount of chemical is used and the elution of harmful metal is scarcely generated for a long period of time. SOLUTION: This method consists of a process 1 for crushing fly ash and the like into a small diameter, a process 2 for adding an oxidizer such as hydrogen peroxide, a process 3 for mixing sufficiently by a mixer or the like, a process 4 for adding a heavy metal treating agent, a process 5 for kneading, a process 6 for adding a solidifying agent, a process 7 for kneading and a process 8 for leaving a metal to be disposed for approximately 24 hours and curing the same. Reducing atmosphere contained in fly ash and the like is converted into oxidizing atmosphere by the above processes, and as hydrogen sulfide generated by the heavy metal treating chemical of a sulfur compound family is not formed, and the heavy metal turns into the passive state or into a corrosive metal, the chemical acts extremely effectively and the reaction is performed smoothly, and a reacted material is provided with the stabilized properties for a long period of time. Also the consumption is reduced as the chemical acts effectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for immobilizing metal in waste, which has a step of preventing metal from being eluted from the waste, and is used in the fields of pollution prevention and resource reuse.

[0002]

2. Description of the Related Art Conventionally, harmful wastes containing a certain amount or more of heavy metals, such as fly ash of general waste incineration plants and waste plastic incinerators, and sludge, are treated by chemical treatment or concrete solidification treatment. The heavy metals are fixed and rendered harmless before being discarded. Some of such hazardous wastes have an inherently reducing atmosphere like fly ash and generate a large amount of hydrogen by adding water.

In the chemical treatment method, as chemicals, sulfides of alkali metals and earth metals and those composed of sulfur compounds such as thiol type and dithiocarbamic acid type have been generally used conventionally. However, in the conventional treatment method using such an agent, due to its reducing atmosphere, sulfur is reduced or reacted to generate hydrogen sulfide, which inhibits the reaction of forming a sparingly soluble metal sulfide, There is a problem in that the amount of added drug increases. Further, heavy metals may be eluted rather by the addition of chemicals. Further, the elution of the heavy metal may occur with the lapse of time after the treatment with the chemical.

In the case of concrete hardening treatment,
Due to the effect of the generated hydrogen gas, there is a problem that concrete is cracked or broken to prevent sufficient solidification, and under high alkaline conditions, trivalent chromium is air-oxidized to produce hexavalent chromium.

On the other hand, a method of adding a metal scavenger and a water-soluble polymer as a waste treatment method or a chemical agent for preventing elution of metals when exposed to rainwater, particularly acid rain (Japanese Patent Laid-Open No. 2-267982). (See Japanese Patent Laid-Open No. 6-166862), a method of adding a certain metal scavenger and chemicals (see Japanese Patent Laid-Open No. 500555), and a heavy metal fixing agent containing a chelating agent and an inorganic sulfide (Japanese Laid-Open Patent Publication No. 6-166862). Etc.) are proposed. However, even with such a treatment method using a chemical, there is a problem that the amount of the chemical is large and the chemical cost is high, and the treatment cost is high.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in the prior art, and enables stable treatment with a small amount of chemicals for a long period of time in which toxic metal elution hardly occurs and in waste products. It is an object to provide a metal fixing method.

[0007]

In order to solve the above-mentioned problems, the present invention provides a method for immobilizing a metal in a waste, comprising the step of preventing the elution of metal from the waste. In the above, the method according to claim 2 further comprises an oxidizing agent adding step of adding an oxidizing agent at an initial stage of the step, and in addition to the above, the step includes a heavy metal treating agent adding step. To do. According to a third aspect of the present invention, in a method for immobilizing a metal in a waste, which includes a step for preventing metal elution from the waste, an oxidizing agent and a heavy metal treating agent are mixed in advance in the initial stage of the step. It is characterized by having a mixed drug addition step of adding a drug. Claim 4
In addition to the features of the invention of claim 1 or 3, the invention of 1 is characterized in that the step includes a cement adding step of adding cement.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an embodiment of a method for immobilizing metal in waste which suppresses the elution of metal from the waste, and FIG. 2 is a partial modification of the method of FIG. Another example is shown. The method of FIG. 1 includes an oxidizing agent addition step of adding an oxidizing agent in the initial stage of the step, and includes a crushing step 1, an oxidizing agent addition step 2, a kneading step 3, a heavy metal treatment chemical addition step 4, a kneading step 5, It is composed of a fixed chemical addition step 6, a kneading step 7, and a curing step 8. In the method of FIG. 2, a mixed chemical, which is a chemical in which an oxidizing agent and a heavy metal treating agent are premixed, is used, and the three steps 2, 3 and 4 of FIG. 1 are made one step of the mixed chemical addition step 2 ′. ing.

The objects to be processed by these methods are:
It is mainly soot and dust (fly ash) from garbage incinerators and industrial waste incinerators, but it also contains hazardous waste such as sludge, cinders, and slag that elute heavy metals. When the object to be treated is a hard material or a cake-like material such as fly ash, the crushing step 1 is provided as a pretreatment as described above.
In this step, using a crusher, for example, the particle size is 5 mm
The object to be processed is crushed until the amount becomes less than the above. According to this treatment, the surface area of the object to be treated is increased as a whole, so that the reaction between the object to be treated and the chemical is made uniform and the kneading time is shortened. The crushed material to be treated is put into an appropriate kneading device such as a batch mixer.

In the oxidizing agent adding step 2 of FIG. 1, for example, 30% hydrogen peroxide is used as an oxidizing agent, and this is diluted with about 20 times the amount of water.
About 70% by weight of an aqueous solution of hydrogen peroxide is added to 0. Examples of the oxidizing agent include ozone, chlorine dioxide, a persulfate compound, a permanganate compound, and a chloric acid compound in addition to hydrogen peroxide, and any of these may be used.

In the kneading step 3 of FIG. 1, the material to be treated to which the aqueous hydrogen peroxide solution has been added is thoroughly mixed in a mixer or the like until it becomes a paste.

Heavy metal treating agents added in step 4 of FIG. 1 include sodium sulfide, potassium sulfide, calcium sulfide, sodium hydrosulfide, potassium hydrosulfide, sodium polysulfide, potassium polysulfide, dithiocarbamic acid type / carboxylic acid type Various kinds of chelating agents such as dithio acid-type, phosphoric acid-type, thiourea-type, thiol-type and amino-type chelating agents have been generally used conventionally and proposed as effective agents. Any of these agents may be used in the method of the present invention.

In the mixed chemical addition step 2'of FIG. 2, a mixed chemical in which, for example, 30% hydrogen peroxide as an oxidizing agent and a phosphoric acid type chelating agent as a heavy metal treating agent are mixed in advance is added. Also in this example, the oxidizing agent used in the method of FIG. 1 can be used as the oxidizing agent used in the mixed drug.
As a heavy metal treatment agent that can be mixed with an oxidizing agent, a phosphoric acid type agent,
There are carboxylic acid type and the like.

The amount of the heavy metal treating agent added in the method of FIG. 1 differs depending on the properties of the object to be treated and the amount of heavy metal contained, but in the present invention, the oxidizing agent adding step 2 is performed in the initial stage before the step 4. Since it is provided, for example, with respect to fly ash, half or less than usual is sufficient. Also in the method of FIG. 2, since the heavy metal treating agent is used together with the oxidizing agent, the addition amount can be halved as in the case of FIG.

In the state up to the step 5 in which the heavy metal treating agent in FIG. 1 is added and kneaded or the step 5 in which the mixed chemicals in FIG. 2 is added and kneaded, the object to be treated is in a slurry state. Disposal requires long-term curing, and
Difficulties are involved in transportation and disposal. For this reason, it is desirable to add a solidifying agent and then provide kneading steps 7 and 8. As the solidifying agent, any of Portland cement, alumina cement, hemihydrate gypsum, blast furnace cement, dolomite cement, silica cement, water glass, fly ash cement, high sulfate cement and the like can be used.

In the curing step 8, the material to be treated is aged for about 24 hours, for example, until it is fixed by the solidifying agent and its properties are stabilized. If a solidifying agent of about 5% is added, it will start to set after a few hours and will solidify after 24 hours. The solidified material has low water permeability and its value is about the same as the viscosity. Therefore, when it is used for landfill, penetration of rainwater into the interior is prevented. Further, since this solidified material has a certain degree of compressive strength and a small amount of compressive deformation, it does not cause ground subsidence.

FIG. 3 shows a concrete solidifying method as another example of the embodiment. This method includes a crushing step 11,
It comprises an oxidizing agent adding step 12, a kneading step 13, a step 14 of adding cement or cement and aggregate as required, a kneading step 15 of adding water to these and kneading, and a curing step 16. In this method, due to the oxidizing agent adding step, the originally reducing atmosphere of fly ash is changed to an oxidizing atmosphere, and hydrogen gas is not generated, so that a strong solidified product is formed.

In the above, examples of the heavy metal addition treatment and the concrete solidification treatment method have been shown as the treatment method including the oxidizing agent addition step. The hydroxide method of addition, the sulfide method of forming a metal sulfide that is hardly soluble in water, the chelate compound method of selectively forming a complex insoluble with metal ions, etc. The way you are
Various known steps such as a method using a recently proposed drug can be used. Then, in each of the methods, it is possible to make the waste into an oxidizing atmosphere by adding an oxidizing agent, to reliably fix the heavy metal, and to reduce the amount of treatment chemicals.

[0019]

EXAMPLE The method of the present invention was carried out using fly ash as a hazardous waste, and the results of comparison with the conventional method are shown in Table 1 and described below.

[0020]

[Table 1]

Exhaust gas from the incinerator contains acid gases such as hydrogen chloride gas and sulfurous acid gas. Since the discharge of these gases is regulated by law, recent incinerators are equipped with an exhaust gas cleaning device. , These gases are neutralized and absorbed with alkali such as caustic soda to eliminate them. However, in order to clarify the action and effect of the present invention, various tests in Examples and Comparative Examples were carried out by collecting fly ash of an old type incinerator in which measures for acid gas as described above are not taken. This fly ash contains 14000 and 540 mg / kg, respectively, as a large amount of lead and cadmium.
In the same table, since the elution of hexavalent chromium and other heavy metals was at the lower limit of quantification in any of the following Examples and Comparative Examples, those values are not described.

Example 1 3 ml of 30% hydrogen peroxide was used as an oxidizing agent. This was mixed with 67 ml of water to form a diluted hydrogen peroxide solution, which was added to 100 g of fly ash and kneaded for 10 minutes. As a heavy metal treating agent, a dithiocarbamic acid type chelating agent polyethyleneimine sodium dithiocarbamate was added. 3 ml of a mixture of 15% liquid 2 and 30% sodium hydrosulfide 8 was added, and the mixture was kneaded for 10 minutes, allowed to stand for a day and night, and then subjected to an elution test. According to the results, the amounts of lead and cadmium eluted were 0.05 and 0.005 mg / l or less, respectively. That is, although the fly ash containing a large amount of lead and cadmium was used as the object to be treated, these heavy metals could be suppressed to a very small elution amount. Currently, the standard value set by law for landfill is 0.3 mg / l.
As will be described below, the results of this embodiment sufficiently clear this. The heavy metal treating agent contained a large amount of sulfur, but the generation of hydrogen sulfide odor was slight. Also, similar results were obtained in the results obtained by using sodium polyacrylate, sodium polyphosphate, etc. as the heavy metal treating agent.

Example 2 3 ml of a mixed drug prepared by mixing 30% hydrogen peroxide 1 as an oxidizing agent and 30% sodium polyphosphate solution 9 as a heavy metal treating agent was mixed with 70 ml of water to prepare a diluted mixed drug solution. Was added to 100 g of fly ash, kneaded for 10 minutes, allowed to stand for a day and night, and then subjected to an elution test.
According to the results, the amounts of lead and cadmium eluted were 0.05 and 0.005 mg / l or less, respectively. That is,
It was demonstrated that the same effect as in Example 1 can be obtained by using a chemical in which an oxidizing agent and a heavy metal treating agent are mixed in advance. According to this method, the processing steps in fly ash processing and the like can be further simplified.

Example 3: Instead of adding the heavy metal treating agent in Example 1, 1 ml of 48% caustic soda was added as an alkali treatment. In this example, the lead and cadmium elution amounts were 0.02 and 0.012 mg, respectively.
/ L was obtained, and similarly, the result was obtained that the landfill standard value could be sufficiently cleared. Next, a comparative example performed to clarify the effect of adding hydrogen peroxide, which is a feature of the present invention, will be shown.

Comparative Example 1: The same treatment as in Example 1 was carried out by adding 70 ml of water without adding hydrogen peroxide and caustic soda. That is, 70 ml of water was added to 100 g of fly ash, the mixture was kneaded for 10 minutes, and allowed to stand overnight for an elution test. In this example, the lead and cadmium elution rates were 2.1 and 21.2 mg / l, respectively.

Comparative Example 2: 70 ml of water in Comparative Example 1
Instead of adding the above, hydrogen peroxide solution obtained by mixing 3 ml of 30% hydrogen peroxide with 67 ml of water was added in the same manner as in Example 1. In this case, the pH is also increased, and the lead and cadmium elution amounts are 0.30 and 0.95 mg / l, respectively,
It was significantly reduced as compared with Comparative Example 1. Therefore, the effect of adding hydrogen peroxide as an oxidizing agent was clearly shown.

Comparative Example 3: In Comparative Example 1, since the fluidity is improved when the temperature is high, 70 ml of water is replaced with 35 ml of water.
The kneading temperature was set to 60 ° C. and kneading was performed for 20 minutes. In this case, the elution amount of lead and cadmium are each 0.2
It was 1 and 2.00 mg / l, which was much lower than in Example 1. This revealed the effect of heating, ie air oxidation. However, it has not reached the level that can satisfy the landfill landfill standard value.

Comparative Example 4: 70 ml of water in Comparative Example 1
To 20 ml, and the same heavy metal treating agent as in Example 1 was added in the same amount of 3 ml. In this case, the elution amounts of lead and cadmium were 3.4 and 7.9 mg / l, respectively, which were so large that they could not be compared with Example 1.
The result was that the landfill landfill standard value could not be cleared at all. Also from this example, the effect of the addition of the oxidizing agent became very clear. In this example, the smell of hydrogen sulfide was large.

Comparative Example 5: In Comparative Example 4, the amount of the heavy metal treating agent added was increased to 8 ml. In this case, the lead and cadmium elution amounts are 0.05 and 0.005 m, respectively.
The value was less than g / l, the same result as in Example 2 was obtained, and the result was that the landfill standard value was sufficiently satisfied. Therefore, if the amount of the heavy metal treatment agent added is increased, the step of adding the oxidizing agent, which is a feature of the present invention, need not be provided. However, the cost of the heavy metal treating agent is about 5 to 10 times the price of the oxidizing agent, and the method of this comparative example has a problem that the treating cost becomes high. In this example, too, the generation of hydrogen sulfide odor was large, and it was revealed that the heavy metal treating agent did not act effectively.

Comparative Example 6: In Example 2, the step of adding an oxidizing agent was omitted. In this case, the lead and cadmium elution amounts were 0.13 and 0.92 mg / l, respectively, and the landfill standard value could not be cleared at all. As a result, when the alkali treatment method is used, the effect of providing the oxidizing agent addition step, which is a feature of the present invention, has become extremely clear.

[0031]

EFFECTS OF THE INVENTION According to the present invention, by providing a step of actively adding an oxidizing agent which has been conventionally regarded as an inhibitor in the detoxification treatment of hazardous waste, hazardous waste such as fly ash is provided. The reducing atmosphere of is converted into an oxidizing atmosphere.

As a result, in the subsequent step, when the chemical treatment is carried out with the usually used sulfur-based heavy metal elution inhibitor, hydrogen sulfide is not generated even when the waste and the chemical react with each other, and the heavy metal is removed. Since the insensitive metal becomes a passive or corrosive metal, the drug acts extremely effectively, and the reaction with the eluted heavy metal is smoothly performed. As a result, the reaction product of the heavy metal and the drug becomes a strong chelate bond, and the amount of the unreacted product becomes very small, so that the property is stable for a long period of time. Further, since the heavy metal treating agent acts effectively, the consumption amount thereof is significantly reduced, and the cost for the treatment for fixing the metal in the waste is also reduced. If a heavy metal treatment agent is used in addition to the oxidizing agent, these chemicals should be mixed in advance and the mixed chemicals should be added to treat fly ash, etc., in a more simplified process. The same effect as above can be obtained.

On the other hand, even when concrete is solidified as a treatment after the addition of the oxidizing agent, hydrogen gas is not generated and organic substances which inhibit the hydration reaction are decomposed, so that a solid solidified product can be obtained. Since the concrete solidification method itself is an inexpensive construction method, even if a step of adding an oxidizer is added, this method makes it possible to inexpensively and reliably prevent the elution of heavy metals in hazardous waste. it can. The stabilized concrete is convenient for handling during transportation, and has a high packing density, is homogeneous, and has a large bearing capacity and is unlikely to cause ground subsidence when it is used for landfill disposal or as a civil engineering structure. It has good properties.
Therefore, if the waste is solidified with concrete using the method of the present invention, it can contribute to the reuse of resources.

[Brief description of drawings]

FIG. 1 is a process drawing showing an example of a method for immobilizing a metal in waste.

FIG. 2 is a process diagram showing another example of a method for immobilizing a metal in waste.

FIG. 3 is a process drawing showing still another example of the method for immobilizing the metal in the waste.

[Explanation of symbols]

 2 Oxidizing agent adding step 2'Mixed chemical adding step 4 Heavy metal treating agent adding step 12 Oxidizing agent adding step 14 Cement adding step

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location B09B 3/00 301N 304H

Claims (4)

[Claims] 1. A method for immobilizing a metal in a waste, comprising a step for preventing the elution of a metal from the waste, comprising an oxidant addition step of adding an oxidant in an initial stage of the step. Method for immobilizing metals in waste. 2. The method for immobilizing metal in waste according to claim 1, wherein the step includes a step of adding a heavy metal treating agent. 3. A method for immobilizing a metal in waste, comprising a step for preventing the elution of metal from the waste, wherein a chemical prepared by previously mixing an oxidizing agent and a heavy metal treating agent in the initial stage of the step is used. A method for immobilizing a metal in a waste, comprising a step of adding a mixed drug to be added. 4. The method for immobilizing metal in waste according to claim 1, wherein the step includes a cement addition step of adding cement.