JPH105716A - Treatment of heavy metal-containing ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and efficiently treat heavy metal-contg. ash in a safe manner and to surely prevent the leaching of heavy metals from the treated ash. SOLUTION: Clay, water and a liq. phosphoric acid-base heavy metal fixing agent or an aq. soln. of a phosphoric acid-base heavy metal fixing agent are added to heavy metal-contg. ash and they are kneaded. The heavy metals such as lead and cadmium in the ash are fixed as slightly soluble salts such as lead phosphate and cadmium phosphate by reaction with the heavy metal fixing agent and these slightly soluble salts and the remaining heavy metals can stably be fixed by adsorption on the surface of the clay. Since the heavy metal fixing agent is liq., it has high reactivity with heavy metal-contg. ash and constant rate feed of the heavy metal. fixing agent is easily carried out with a simple apparatus for injecting chemicals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating heavy metal-containing ash, and more particularly, to a method for easily and efficiently converting heavy metal-containing ash.
In addition, the present invention relates to a method for safely treating and reliably preventing heavy metals from being eluted from a treated product.

[0002]

2. Description of the Related Art When municipal garbage and industrial waste are incinerated in an incineration plant, fly ash (hereinafter, incinerated ash and fly ash are referred to as heavy metal-containing ash) is generated along with incinerated ash and combustion exhaust gas. Conventionally, a bag filter or an electric dust collector has been installed to capture the fly ash, and the collected fly ash and incinerated ash have been effectively used for landfill and ground construction.

By the way, since the heavy metal-containing ash thus obtained contains heavy metals, when the heavy metal-containing ash is used for landfilling, etc., a treatment for preventing elution of the heavy metal in the heavy metal-containing ash is performed. Need to be applied. In particular, fly ash containing a large amount of unreacted slaked lime generated when removing HCl and SO _X in slaked lime with slaked lime has a high pH when contacted with water and lead may be eluted in large amounts. It is necessary to prevent this.

[0004] Conventionally, as a method for preventing heavy metal-containing ash from eluting heavy metals, a melting method, a cement solidification method, an extraction method using an acid or other solvent, a chemical treatment method, and the like have been proposed. For this reason, the chemical treatment method is emphasized.

As a chemical treatment method, a specific amount of water-soluble phosphoric acid or a salt thereof is added to fly ash or a mixture of fly ash and incinerated ash in the presence of calcium hydroxide to prevent elution of cadmium and lead. A method (Japanese Patent Publication No. 4-61710) has been proposed.

Japanese Unexamined Patent Publication (Kokai) No. 7-204605 proposes a waste treatment material containing a solid acid and an anti-caking agent as main components. In Japanese Patent Application Laid-Open No. 7-204605, solid acids include (1) acid clay, bentonite, kaolin and other natural clay minerals, (2) silica gel and alumina to which sulfuric acid, phosphoric acid, etc. are attached, and (3) ) Cation exchange resins and the like are exemplified. Examples of the anti-caking agent include silica gel, diatomaceous earth, bentonite, and activated clay.

[0007]

[Problems to be Solved by the Invention]
In the method of adding a water-soluble phosphoric acid or a salt thereof described in JP-A No. 5-2, for fly ash containing a large amount of unreacted slaked lime, the water-soluble phosphoric acid or a salt thereof added to the reaction with unreacted slaked lime is used. Because the salt is consumed, the pH of the eluate does not decrease,
There is a problem that lead elution cannot be prevented.

Further, the waste treatment material described in Japanese Patent Application Laid-Open No. 7-204605 is a powdery material comprising a solid acid and a solid anti-solidification agent, and therefore has a sufficient reactivity with heavy metal-containing ash. However, there is a drawback in that it is difficult to handle and that quantitative supply is not easy.

The present invention solves the above-mentioned conventional problems, and uses a treating agent having high reactivity with heavy metal-containing ash and excellent handling properties to easily remove heavy metal-containing ash without requiring pH adjustment. It is an object of the present invention to provide a method for efficiently and safely treating and reliably preventing elution of heavy metals from a treated product.

[0010]

According to the present invention, there is provided a method for treating heavy metal-containing ash, comprising adding a heavy metal-containing ash to clay, water and a liquid phosphate-based heavy metal-fixing agent or an aqueous solution of clay and a phosphate-based heavy metal-fixing agent. And kneading the mixture to fix the heavy metals in the heavy metal-containing ash.

According to the present invention, heavy metals such as lead and cadmium in the heavy metal-containing ash are fixed by adding the clay and the liquid phosphoric acid-based heavy metal fixing agent to the heavy metal-containing ash. By reacting with a reagent and immobilizing as a hardly soluble salt such as lead phosphate and cadmium phosphate, by immobilizing these hardly soluble salt and heavy metal on the surface of clay, it is possible to stably immobilize.

In such an immobilization reaction mechanism, in the present invention, since a phosphoric acid-based heavy metal immobilizing agent is used in a liquid state, the reactivity between the phosphoric acid-based heavy metal immobilizing agent and the heavy metal-containing ash is high, and It is possible to easily supply a fixed amount of the phosphate-based heavy metal fixing agent with a simple chemical injection equipment.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

In the present invention, the heavy metal-containing ash is mixed with clay and water and a liquid phosphoric acid-based heavy metal fixing agent or an aqueous solution of a phosphoric acid-based heavy metal fixing agent and kneaded. Immobilize heavy metals.

In the method of the present invention, the clay may be any of general soil constituent salts such as activated clay, acid clay, bentonite, kaolin, and clay. These clays are 1
The seeds may be used alone or in combination of two or more.

In the present invention, the amount of clay added is preferably 1 to 50% by weight based on the heavy metal-containing ash.

As the liquid phosphoric acid-based heavy metal fixing agent, phosphoric acid or a salt thereof, which itself is a liquid phosphoric acid or an aqueous solution of a water-soluble phosphoric acid or a salt thereof is used. Acid (H ₃ PO ₄ ), sodium phosphate (Na
H ₂ PO ₄ , Na ₂ HPO ₄ , Na ₃ PO ₄ ) aqueous solution,
Potassium phosphate (KH ₂ PO ₄ , K ₂ HPO ₄ , K ₃ P
O ₄ ) aqueous solution and the like. One of these phosphate-based heavy metal fixing agents may be used alone, or two or more thereof may be used in combination. In the case of a phosphate aqueous solution, the concentration is 20 to
Preferably it is 90% by weight.

In the present invention, the amount of the phosphoric acid-based heavy metal fixing agent to be added is preferably 1 to 20% by weight based on the heavy metal-containing ash.

In the present invention, the amount of water added to the heavy metal-containing ash is preferably 10 to 60% by weight. Therefore, when adding the aqueous solution of the phosphoric acid-based heavy metal fixing agent, the concentration of the aqueous solution is adjusted so that the amount of water is added, or water is separately added as necessary. However, there is no significant difference in the effect of the water content after the treatment, and the amount of water can be arbitrarily set from the viewpoint of workability and the like. In the method of the present invention, water, clay and a liquid phosphate-based heavy metal fixing agent, or an aqueous solution of a clay and a phosphate-based heavy metal fixing agent are added to the heavy metal-containing ash. They may be added in any order and may be added simultaneously. Alternatively, these may be mixed in advance and added in the form of slurry.

According to the present invention, a heavy metal-containing ash is mixed with water, clay and a liquid phosphate-based heavy metal fixing agent or an aqueous solution of a clay and a phosphate-based heavy metal fixing agent and kneaded, whereby the heavy metal is removed. A kneaded product with little elution is obtained.

The kneading method may be any method as long as the heavy metal-containing ash and the additive are uniformly mixed. This mixture is usually landfilled.

[0022]

The present invention will be described more specifically below with reference to examples and comparative examples.

In the examples and comparative examples, the composition of the treated fly ash (raw ash) is as shown in Table 1.

[0024]

[Table 1]

Examples 1 to 4 and Comparative Examples 1 to 11 50 g of raw ash was placed in a 500 ml polybeaker, water was added to the raw ash at 40% by weight, and activated clay and / or orthophosphoric acid was added thereto. 2 (however, no additive was used in Comparative Example 1) and kneaded sufficiently with a spatula. This treated product was subjected to a dissolution test according to the Environment Agency Notification No. 13 test, and the results are shown in Table 2.

[0026]

[Table 2]

The following is clear from Table 2.

That is, Pb elutes without treatment (Comparative Example 1). In addition, in the case of activated clay only (Comparative Examples 2 to 6), the elution of Pb cannot be prevented even when added in a large amount, and in the case of phosphoric acid alone (Comparative Examples 7 to 11), in order to prevent the elution of Pb, It is necessary to add as much as 20% by weight to the raw ash.

On the other hand, when activated clay and orthophosphoric acid are added, elution of Pb can be prevented with a small amount.

Comparative Example 12 Water and activated clay were added to raw ash, and 4 g of orthophosphoric acid was added.
Was treated in the same manner as in Example 4 except that 6 g of the ash was adhered to 10 g of silica gel in terms of orthophosphoric acid with respect to the raw ash. As a result of performing .4), the Pb concentration was 1.1 mg / l, and the elution of Pb could not be prevented.

From these results, it can be seen that the reactivity is not sufficient when solid phosphoric acid is used.

[0032]

As described in detail above, according to the method for treating heavy metal-containing ash of the present invention, any fly ash such as fly ash containing unreacted slaked lime and fly ash not containing unreacted slaked lime can be used. In addition, harmful heavy metals such as lead and cadmium can be reliably fixed without adjusting the pH.

Since clay, which is a general soil component, is used, it is stable and safe even after detoxification or landfill disposal.

Since the liquid phosphoric acid-based heavy metal fixing agent is used, the reactivity with heavy metal-containing ash is high, and the quantitative supply of the phosphoric acid-based heavy metal fixing agent is easy with a simple chemical injection equipment. Can supply.

Under such effects, the heavy metal-containing ash can be easily and efficiently and safely treated, so that the elution of heavy metals from the processed product can be surely prevented.

Claims (2)

[Claims] 1. A process for treating heavy metal-containing ash, wherein the heavy metal in the heavy metal-containing ash is fixed by adding water, clay and a liquid phosphoric acid-based heavy metal fixing agent to the heavy metal-containing ash and kneading the mixture. Method. 2. A method for treating heavy metal-containing ash, comprising adding a clay and an aqueous solution of a phosphoric acid-based heavy metal fixing agent to the heavy metal-containing ash and kneading the mixture to fix the heavy metal in the heavy metal-containing ash. .