JPH11216443A - Method of removing lead compound from incineration ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of removing efficiently a Pb compound in incineration ash at a low cost. SOLUTION: In a method of removing a Pb compound contained in incineration ash from it, the incineration ash is kept under an alkali hydrothermal condition, the Pb compound in the incineration ash is subjected to the alkali hydrothermal reaction, and the resultant is dissolved in an alkali aqueous solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently removing lead compounds contained in incinerated ash discharged from an incineration plant.

[0002]

2. Description of the Related Art Incinerated ash containing heavy metals is increasing year by year, and its disposal and disposal is mainly landfilled. Is required. Other methods of treatment and disposal include concrete solidification, oxidative combustion, high-temperature plasma, and melt solidification, but there are many issues to be studied in terms of secondary pollution and cost. In particular, it is difficult to remove a lead compound contained in incineration ash, and it is desired to develop a method for efficiently removing the lead compound at low cost.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for efficiently and efficiently removing a lead compound from incinerated ash at low cost.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, in the method for removing lead compounds contained in incinerated ash, the incinerated ash is maintained under alkaline hydrothermal conditions, and the lead compound in the incinerated ash is subjected to alkaline hydrothermal reaction. And dissolving it in an aqueous alkaline solution.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The incinerated ash used as a raw material to be treated in the present invention contains a lead compound. Such incinerated ash includes incinerated ash discharged from a municipal waste incineration plant. The lead compound in the incinerated ash is lead oxide P
It is present as bO _{2 and the} like, and its content is usually about 600 to 4950 mg / kg as Pb metal. The incineration ash includes incineration fly ash in addition to ordinary furnace bottom incineration ash.

In the present invention, in order to remove the lead compounds contained in the incinerated ash, the incinerated ash is maintained under alkaline hydrothermal conditions, and the lead compound in the incinerated ash is subjected to an alkaline hydrothermal reaction. As a result, the lead compound in the incineration ash becomes water-soluble lead hydroxide, dissolves in the alkaline aqueous solution, and is removed from the incineration ash. The alkaline hydrothermal condition can be formed by adding water and an alkali hydroxide to a pressure-resistant container, and maintaining the temperature at a high temperature and a high pressure. In this case, the temperature under hydrothermal conditions is 473K or more, preferably 50K or more.
0 to 550K, and the pressure is at least the saturated steam pressure at that temperature, usually at least 20 Mpa. The inside of the pressure-resistant container can be pressurized with air or an inert gas, if necessary, so that the pressure in the container can be adjusted. As the alkali hydroxide, sodium hydroxide or potassium hydroxide is used, but sodium hydroxide is preferably used. The amount of alkali hydroxide added to water is
0.25 to 2.0 mol per liter, preferably 1.
The ratio is 0 to 1.5 mol. The amount of incinerated ash used is 0.5 to 3 kg, preferably 1.0 to 1.5 kg, per liter of water.

The energy required for carrying out the present invention can effectively utilize thermal energy generated in an incineration plant that discharges the incinerated ash, for example, a municipal waste incineration plant. This makes it possible to remove the lead compound from the incinerated ash at low cost.

In the present invention, the lead compound in the incinerated ash is dissolved in water as water-soluble lead hydroxide and removed from the incinerated ash. In this case, other heavy metals, for example, Zn
When Ni, Al, Cd, etc. are present, their heavy metals are also dissolved and removed in water. Lead and other heavy metals dissolved in water can be recovered from water by a conventionally known method and reused as resources.

[0009]

Next, the present invention will be described in more detail with reference to examples.

Example 1 As incineration ash, ZnO: 2508, PbO ₂ : 689.
1, NiO ₂ : 13.01, CdO: 324.3, Mn
O ₂ : 247.2, Fe ₂ O ₃ : 2150, CuO: 15
_{2.2, MgO: 235.3, Na 2} O: 2547, C
aO: 3040 (mg / kg) containing
10 g thereof, 245 cc of distilled water, and 1.
5 mol was put into an autoclave (withstand pressure 50 MPa, heat-resistant temperature 750 k, internal volume 300 cc) and 523 k
And the pressure was increased to 1 under alkaline water heat conditions of 20 MPa.
Time processed. The Pb compound contained in the incineration ash was hardly removed by the one-hour treatment under hydrothermal conditions (temperature: 523 k, pressure: 20 MPa) in the absence of alkali hydroxide. In contrast, 0.25 sodium hydroxide,
In 1 hour treatment under alkaline hydrothermal conditions added in the range of 0.5, 0.75, 1.0 and 1.5 mol, the Pb removal rates were 37%, 55%, 64% and 78%, respectively. %,
87%, and it was confirmed that the Pb compound was removed. Other heavy metal removal rates are shown as sodium hydroxide 1.
In 1 hour treatment under alkaline hydrothermal conditions to which 5 mol was added, ZnO removal rate: 50%, NiO ₂ removal rate: 84%,
CdO removal rate: 31%, MnO ₂ removal rate: 32%, Fe ₂
O ₃ removal rate: 29%, CuO removal rate: 62%.

[0011]

The present invention utilizes the waste heat of the incineration plant to create an alkaline hydrothermal state, thereby reducing the P contained in the incineration ash.
Heavy metals including the b compound can be removed. In addition, a large amount of energy and large-scale equipment and devices are not required unlike the oxidizing combustion method and the high-temperature plasma, so that the method can be performed simply and at low cost.

Claims (1)

[Claims] 1. A method for removing lead compounds contained in incinerated ash, wherein the incinerated ash is maintained under alkaline hydrothermal conditions, and the lead compound in the incinerated ash is subjected to alkaline hydrothermal reaction to form an alkaline aqueous solution. A method characterized by dissolving.