JP3176162B2 - Treatment method for heavy metal-containing materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to incinerated ash discharged from incineration of solid waste such as municipal waste and industrial waste, heavy metal-containing ash such as exhaust gas dust ash, and heavy metal-containing ash generated in other industries. The present invention relates to a method for treating waste.

[0002]

2. Description of the Related Art With an increase in the amount of municipal solid waste and industrial waste and an increase in the incineration rate, the amount of incinerated ash and ash gas dust ashes, which are incinerated waste, has increased, and heavy metals contained therein have become new. It is attracting attention as a source of environmental pollution. Among these ash wastes, exhaust gas dust ash, in particular, contains a large amount of low-boiling heavy metals such as mercury, zinc, and lead, and when these are released to the environment,
In order to dissolve and elute in rainwater and the like, prevention techniques have been developed.

[0003] For example, Japanese Patent Publication No. 61-47154 discloses a waste ash containing a heavy metal to which an alkali component is added in the presence of an iron salt and mixed, and the mixture is granulated or allowed to stand for 300 minutes. It is disclosed that the heavy metal is fixed as a mixed hydroxide with an iron salt by keeping the temperature at not more than ° C.

[0004] It is said that this has the advantage that the heavy metals in the ash are fixed to a considerable extent, enabling safe dumping.

However, this method of fixing heavy metals involves directly adding an alkali to the ash and mixing the ash. Therefore, an expensive alkali is required for the treatment, and if the mixing is not sufficient, some alkalis are required. PH rises to pH 1
If it exceeds 1.5, heavy metals cannot be fixed, the efficiency of fixing decreases, and a processing time of about two days is required at around normal temperature, resulting in a drawback that the processing time is lengthened or the processing equipment becomes enormous. .

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a means for efficiently fixing heavy metal-containing waste using carbon dioxide in the presence of an iron salt.

[0007]

In order to solve the above problems SUMMARY OF THE INVENTION The present invention is, water containing heavy metals was divalent iron was added, followed the addition while heating and stirring the flue gases in the mixture
The pH of the mixture is 7.0 to 11.5 and the temperature is 30.
~ 99 ° C to produce ferrite, containing heavy metal
The method is characterized in that heavy metals in a product are fixed in ferrite .

[0008] Ferrite is a compound represented by the chemical formula MFe ₂ O ₄ when M is represented as a heavy metal, and the ash ferrite-forming treatment in the present invention means that ferrous iron in a mixture is a ferrous oxide called ferrite. In the process of forming the crystal lattice of an object, it means a process in which heavy metal is taken in place of iron at the position where iron atoms should occupy and is fixed.

The reaction formula is represented as follows.

[0010] Neutralization reaction: M ²⁺ + 2Fe ²⁺ + 6OH ⁻ → MFe ₂ (OH) ₆ (1) Oxidation reaction: MFe ₂ (OH) ₆ + ／ O ₂ → MFe ₂ O ₄ + 3H ₂ O (2) In the reaction formula, if the pH is less than 7.0,
(1) OH in the reaction of the formula ^- ferrite reaction does not proceed in short supply. When the mixture is not stirred, the reaction does not proceed because O _{2 in the} formula (2) is insufficient.

In the ferrite-forming reaction, p
If H is not less than 11.5, the heavy metals will take the form of soluble ions and will not be incorporated into the ferrite. Therefore, when the pH of the mixture exceeds 11.5, it is necessary to adjust the pH by adding an acid. The temperature is 30 ~
A range of 99 ° C. is preferred. The upper limit of the heating temperature is almost zero when the solubility of oxygen in water in the above-mentioned oxidation reaction (2) is 100 ° C. or more.
It must be below 0 ° C.

In the present invention, carbon dioxide in exhaust gas is used as the acid for pH adjustment.

[0013]

[Function] By stirring and heating while adding carbon dioxide to a mixture of a heavy metal-containing substance, ferrous iron and water, the heavy metal elutes to the water side, and the pH is dissolved by dissolving the carbon dioxide in water. During the process in which ferrous iron forms a crystal lattice of iron oxide called ferrite at a pH of 7.0 or more and 11.5 or less, heavy metals are incorporated into the crystal lattice and fixed. .

[0014]

EXAMPLE 1 This example shows an example in which treated ash, ferrous iron and carbon dioxide are mixed in a reactor.

FIG. 1 shows an outline of the processing equipment used.

In FIG. 1, reference numeral 1 denotes a reactor for treating waste ash, 2 denotes a tank containing divalent iron sulfate in an aqueous solution state, and 3 denotes an exhaust gas containing carbon dioxide gas introduced into the reactor 1. And an inlet 4 for the exhaust fan. 5 is a heating device for heating the reactor 1, 6
Is a stirrer in the reactor 1 and is rotated by an external motor 7. Reference numeral 8 denotes a discharge port of the treated ash. 9 denotes a dust collector for collecting fly ash, 10 denotes a fly ash hopper, 11 denotes a flue after dust removal, and 12 denotes a chimney.

In the figure, 1 ton of ash from a dust collecting facility containing heavy metals shown in Table 2 was introduced into the reactor 1 from a fly ash hopper. Tank 2 for this heavy metal-containing ash
From the flue duct at a rate of 10 liters / min per 1 kg of dry matter of the mixture with respect to this stirred mixture. An exhaust gas containing 10% was introduced, the temperature of the mixture was maintained at 70 ° C., and a stirrer 6 was used.
Stirring was continued. Table 1 shows the results of the dissolution test based on the Law No. 13 of the Notification of the Environment Agency after the treatment was continued for one hour. All heavy metals were below the marine dumping standard and showed excellent results.

FIG. 2 shows the relationship between the pH of the mixture after the treatment for a predetermined time and the amount of lead eluted while maintaining the temperature at 70 ° C. When the pH is in the range of 7 and 11.5, lead is substantially eliminated. You can see that it is completely fixed. In addition, the pH is less than 7, and 11.5
It can be seen that the elution amount is extremely increased when the value exceeds.

[0019]

[Table 1]

[Table 2]

[0020]

According to the present invention, the following effects can be obtained.

(1) In the ferrite-forming reaction, the use of carbon dioxide gas in the exhaust gas as the acid for adjusting the pH can greatly reduce the processing cost.

(2) Since the neutralization reaction at the time of pH adjustment proceeds slowly, the heat of reaction also becomes moderate, and no toxic gas is generated when a mineral acid such as hydrogen chloride or hydrogen is used.

(3) Since the temperature of the exhaust gas is 150 to 200 ° C. and can be used as a heat source required for ferrite formation, energy is saved.

(4) Since carbon dioxide is used and fixed, carbon dioxide generated from the chimney can be reduced.

[Brief description of the drawings]

FIG. 1 shows an outline of a processing facility applicable to the present invention.

FIG. 2 shows the elution amount of lead in ash when the pH in the treated material is changed.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 reactor 2 iron sulfate tank 3 exhaust gas inlet 4 exhaust fan 5 heating device 6 stirrer 7 motor 8 ash outlet 9 dust collector 10 fly ash hopper 11 stack 12 chimney

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B09B 3/00 A62D 3/00 C02F 1/62

Claims (1)

(57) [Claims] 1. A water heavy metal inclusions, the divalent iron is added, followed by heating and stirring while adding the combustion exhaust gas in the mixture,
The pH of the mixture is 7.0-11.5 and the temperature is 30-9.
9 ° C. to produce ferrite,
A method for treating a heavy metal-containing material, wherein the heavy metal is fixed in ferrite .