JP2001017942A - Process for removing lead compound from incineration ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove lead compounds in incineration ash from a municipal waste incineration plant at a low cost by maintaining the incineration ash under alkali hydrothermal conditions to subject lead compounds in the ash to hydrothermal reaction and to dissolve the lead compounds into an alkali aqueous solution, and separating and removing the dissolved lead compounds in the solution. SOLUTION: This process comprises: maintaining, for example, incineration ash discharged from a municipal waste incineration plant under hydrothermal conditions to subject lead compounds in the incineration ash to alkali hydrothermal reaction, to convert the lead compounds in the ash into water-soluble lead hydroxide and to dissolve the lead hydroxide into an alkali aqueous solution, wherein this alkali hydrothermal conditions can be formed by adding water and an alkali hydroxide to a heat- resistant vessel and maintaining the contents of the vessel under high temperature and high pressure conditions; and then separating and removing the lead compounds dissolved in the alkali aqueous solution. Thus, lead compounds in such municipal waste incineration ash can efficiently be removed from the ash, wherein the lead compounds in the incineration ash is converted into water-soluble lead hydroxide and the resulting lead hydroxide is dissolved into water and removed from the incineration ash.

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 treatment 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, firstly, (i) a step of incinerating municipal waste to obtain incinerated ash, and (ii) holding the incinerated ash under alkaline hydrothermal conditions, and converting a lead compound contained therein into alkaline water. A method for removing a lead compound from incinerated ash, comprising: a step of causing a thermal reaction to dissolve the compound in an aqueous alkaline solution; and (iii) a step of separating and removing the lead compound dissolved in the aqueous alkaline solution. You. Secondly, in the first method for removing a lead compound, waste heat from the step of obtaining incinerated ash in step (i) is used as energy to be maintained under alkaline hydrothermal conditions in step (ii). A method for removing lead compounds from incinerated ash is provided.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The incinerated ash used as a raw material to be treated in the present invention contains a lead compound obtained by incinerating municipal solid waste. Examples of such incineration ash include, for example, incineration ash discharged from a municipal waste incineration plant. The lead compound in the incineration ash exists as lead oxide PbO ₂ or the like, and its content is usually 600 ppm as Pb metal.
４９4950 mg / kg. 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 ( ii) is adopted. Thereby, the lead compound in the incinerated ash becomes water-soluble lead hydroxide and is dissolved in the alkaline aqueous solution. 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 the hydrothermal condition is 473 K or more, preferably 5
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, preferably 1.0 to 1.5 mol, per liter of water. The amount of incinerated ash used is 0.5 to 3 kg, preferably 1.0 to 1.5 kg, per liter of water.

Next, the present invention employs a step (iii) of separating and removing the lead compound dissolved in the alkaline aqueous solution and efficiently removing the lead compound from the incinerated ash. In the case of the present invention, the lead compound in the incineration ash is dissolved in water as water-soluble lead hydroxide and is removed from the incineration ash. In this case, other heavy metals such as Zn, Ni, Al,
If Cd or the like is present, those 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.

The energy required for carrying out the present invention can effectively utilize the heat energy generated in the incineration plant in the step (i) of discharging the incineration ash, for example, the municipal garbage incineration plant. . This makes it possible to remove the lead compound from the incinerated ash at low cost.

[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:
_{152.2, MgO: 235.3, Na 2} O: 254
7, a solution containing CaO: 3040 (mg / kg) was used, and 10 g thereof, 245 cc of distilled water, and 1.5 mol of sodium hydroxide were placed in an autoclave (withstand pressure 50MP).
a, heat-resistant temperature: 750 k, internal volume: 300 cc), the temperature was raised to 523 k, and the treatment was performed for 1 hour under alkaline water heat conditions of 20 MPa. 0.2% sodium hydroxide
In the treatment for 1 hour under alkaline hydrothermal conditions added in the range of 5, 0.5, 0.75, 1.0, 1.5 mol, the P
b The removal rates were 37%, 55%, 64%, and 78, respectively.
%, 87%, and it was confirmed that the Pb compound was removed. As for other heavy metal removal rates, the treatment for 1 hour under alkaline hydrothermal conditions to which 1.5 mol of sodium hydroxide was added shows a ZnO removal rate of 50% and a NiO ₂ removal rate of 84%.
%, CdO removal rate: 31%, MnO ₂ removal rate: 32%,
Fe ₂ O ₃ removal rate: 29%, CuO removal rate: 62%.

Comparative Example 1 The removal of the lead compound from the incinerated ash was performed in the same manner as in Example 1 except that the reaction was performed under simple hydrothermal conditions (temperature: 523 k, pressure: 20 MPa) without using sodium hydroxide. An attempt was made, but almost no lead compounds could be removed.

Comparative Example 2 In Example 1, the temperature was changed to 2
The lead compound was removed in the same manner as in Example 1 except that the solution was treated with a 6 mol aqueous solution of sodium hydroxide for 6 hours at 5 ° C. and normal pressure. The Pb removal rate was 20%.

[0013]

The method of claim 1 does not require a large amount of energy or large-scale equipment or equipment as in the conventional oxidizing combustion method or high-temperature plasma, but merely creates alkaline hydrothermal conditions. Since heavy metals including Pb compounds contained in the incineration ash can be removed, there is an advantage that the apparatus can be simplified and can be implemented at low cost. In the method of the second aspect, the energy maintained in the alkaline hydrothermal condition in the step (ii) may be the energy of the step (i).
Since waste heat from the process of obtaining incinerated ash is used, there is an advantage that energy efficiency is further improved and cost reduction can be further promoted.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Iwata 16-3 Onogawa, Tsukuba, Ibaraki Pref. 4K001 AA02 AA06 AA09 AA10 AA16 AA19 AA20 AA30 BA14 CA08 DB07 DB08 GB10

Claims (2)

[Claims] (1) a step of incinerating municipal waste to obtain incinerated ash; and (ii) maintaining the incinerated ash under alkaline hydrothermal conditions and subjecting a lead compound contained in the incinerated ash to alkaline hydrothermal reaction to obtain an alkaline aqueous solution. And (iii) a step of separating and removing a lead compound dissolved in the aqueous alkali solution. 2. The incinerated ash according to claim 1, wherein the waste heat from the step of obtaining the incinerated ash in the step (i) is used as the energy maintained in the alkaline hydrothermal condition in the step (ii). For removing lead compounds.