JPS5853594B2 - Method for detoxifying incineration ash containing heavy metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detoxifying incineration ash such as municipal garbage, municipal sewage sludge, and paint sludge containing heavy metals.

A cyclone removes dust generated in incinerators such as city garbage.
Incineration ash collected by an electrostatic precipitator or the like often contains harmful heavy metals such as lead, cadmium, and zinc, although the types and concentration ratios of metals included vary depending on the type of incinerated material.

As one of the treatment methods, a method has been considered in which an aqueous solution and incinerated ash are mixed and the soluble metals are eluted into the water system and then separated. (dehydrated cake) often contains harmful ionic heavy metals in the water, and if one of them is dumped, it may cause secondary pollution.

It is also possible to add an insolubilizer for harmful heavy metals, etc. before flowing into a dehydrator, etc., and separate the solution after insolubilization.In this case, the separated material is rendered harmless, but the harmful heavy metals that remain in the separated material The absolute amount of metals does not decrease, and valuable metals often cannot be recovered due to the high content of contaminants, so this method could not be considered an appropriate method.

This invention was made to eliminate the above-mentioned drawbacks.
After incineration ash containing heavy metals is mixed with water or an acidic solution to dissolve the soluble heavy metals in the incineration ash, when the slurry containing a large amount of undissolved residual ash is subjected to solid-liquid separation, 1 is contained in the separated product and the filtrate is removed. The heavy metal ions adsorbed on the surface of the solid material are first washed with water to separate the soluble heavy metals, and then washed with a cleaning solution containing an insolubilizing agent such as an organic insolubilizing agent, sodium sulfide, or sodium phosphate. It is characterized by this.

In addition, this invention mixes incinerated ash containing heavy metals with water or an acidic solution, dissolves the soluble heavy metals in the incinerated ash, and then dehydrates the slurry containing a large amount of undissolved residual ash to form a solid-liquid solution in the first stage. Separation is performed, and the separated product is repulped with a solution containing an insolubilizer for harmful heavy metals to obtain a slurry in which the heavy metal ions contained in the separated product are insolubilized, and this is subjected to a second stage of solid-liquid separation. This is a characteristic feature.

Next, an embodiment in which the present invention is applied to municipal waste incineration ash will be described with reference to the drawings.

Municipal garbage collected in the garbage storage tank is incinerated in an incinerator, but at this time, incinerated ash is collected from the bottom of the incinerator, and incinerated ash is collected by a dust collector connected to the gas discharge part of the incinerator. are mixed in a mixing tank (charcoal mixing ratio 5-25).

Add water or acidic solution before mixing.

When mixed in a mixing tank, soluble heavy metals are dissolved.

Let me now mention the dissolution characteristics of incineration ash.

In many cases, metals account for 30-40% of the incineration ash composition,
These include Pb, Cd, Cr+', T-Cr, and Zn.

Mn, Cu, AI, Na, Fe, Mg, Ca, Si
, Sn.

Contains Hg, As, etc.

Most of these are Na and K. Mainly occupied by Zn, Ca, AI, and Si.

Most of these metals are in the form of oxides, with some chlorides and sulfides also present.

Here, some of the chlorides and sulfates and oxides are soluble in water, and Pbs"d2'Cr +6s Hg *
Mn m N etc. consist almost entirely of water-soluble components.

$i, o, I NHCl or 0, 1 NH2B
When dissolved with O4, the elution ratios of Zn, Ni, Cu, and Fe increase, but Pb, Cd, Cr+'Hg, etc. do not change.

As an example, Table 1 shows the concentrations of metals eluted into the water system in the incinerated ash 15 mixed slurry solution.

The slurry containing heavy metals is passed through a solid-liquid separator and separated into a filter cake and liquid F.

Water is injected into the solid-liquid separator, and the slurry is dehydrated and washed with water. After that, the slurry is washed again with an insolubilizer, and then turned into a cake and discharged outside the solid-liquid separator.

An example of the treatment of incineration ash of municipal waste using this method is described below.

The mixing ratio of incinerated ash is 15 parts, and the solvent is water or 0. IN sulfuric acid,
The dissolution time was 15 to 30 minutes using a precoat vacuum dehydrator C (filtration area: 0.9 m2).

The ionic heavy metal concentrations in the cakes without washing and after washing are shown in Tables 2 and 3, respectively.

Conditions: Washing water amount Water: Wash with an insolubilizing agent using at least 2 to 3 times the weight of the solids, and then rewashing with 1 to 3 times the amount of water as the solids.Insolubilizing agent: Organic insolubilizing agent or phosphoric acid and sulfur. A mixed solution of ions whose pH was adjusted to pH 6 to 11 with acid or alkali was used.

In addition, in this experimental example, where the washing pH was 1 to 3 times the amount of solid matter, the dissolution of the detoxified cake was below the standard value of the dissolution test notified by the Environmental Agency.

+6,,.

In other words, Hg... is not detected, and Cr.
...Not detected, Cd<0.05, Pb<0.3
, Mn<0.3.

Zn<0.1, Cu<0.1, As<0.05
, CN==not detected.

Next, an embodiment related to another invention is shown in FIG.

Here, a dehydration device different from the above invention is divided into two stages, and in the first stage dehydration device, after washing with water, the dehydrated cake is repulped with a liquid containing an insolubilizer, and the pH is adjusted as necessary.
After the mixture is adjusted to almost neutrality, a detoxified separated cake with a moisture content of about 50 to 70 is obtained using the dehydrator again, and is discharged outside the machine.

In this method, the pH of the separated cake is adjusted by repulping and washing with water in the second stage dehydration equipment as needed.
It is also possible to adjust the amount and discharge it outside the machine.

According to this invention, the absolute amount of harmful heavy metals contained in the separated product is reduced, and even the slightest remaining amount is converted into a stable form by the insolubilizing agent, resulting in a thermal treatment method that is one step ahead of conventional methods.

In addition, the cost of chemicals for detoxification is significantly reduced compared to conventional methods, and valuable metals are separated in ionized form in the P solution, making it possible to use them effectively.

Incidentally, in the above example, an example of municipal waste incineration ash is given, but incineration ash containing one heavy metal may be used, for example, municipal sewage sludge,
Can be used for paint sludge, etc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing one embodiment of the present invention, and FIG. 2 is a schematic diagram showing another embodiment of the invention.

Claims (1)

[Claims] 1. Mixing incineration ash containing heavy metals with a water container or an acidic solution,
After dissolving the soluble heavy metals in the incineration ash, when solid-liquid separation is performed on the slurry containing a large amount of undissolved residual ash, it is possible to remove the adsorbed heavy metal ions from the water contained in the separated product and the adsorbed heavy metal ions on the surface of the solid matter. A method for detoxifying incinerated ash containing heavy metals, which is characterized by washing as much as possible by washing with water, separating soluble heavy metals, and then washing with a cleaning solution containing an insolubilizing agent. 2. Converting incinerated ash containing heavy metals into water. or mixed with acidic solution,
After dissolving the soluble heavy metals in the incineration ash, the slurry containing a large amount of undissolved residue is subjected to the first solid-liquid separation using a dehydrator, etc., and the separated product is repulped with a solution containing an insolubilizer for harmful heavy metals. 1-5 A slurry containing heavy metals is obtained by insolubilizing the heavy metal ions contained in the separated product and the heavy metal ions adsorbed on the surface of the solid material, and the slurry is subjected to a second stage of solid-liquid separation. How to make incineration ash harmless.