JPS6052876B2 - How to dispose of electrostatically collected ash - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating electrostatically collected ash discharged from a garbage incinerator or the like.

Electrostatic precipitated ash discharged from a garbage incinerator differs slightly depending on the type of garbage, but generally, as shown in Table 1, the slag component is 50-70%, and the chloride and sulfate content is 25-25%.
Mainly contains 45% and 3% other harmful heavy metals and general heavy metals.
Contains ~5%.

Some of these toxic heavy metals exist in the form of chlorides that are soluble in water, and if they are dumped as is, there is a risk that the toxic heavy metals will elute beyond the emission regulation value, as shown in the elution test results in Table 2.

For this reason, a treatment method using ferrite formation, for example, has been proposed as a method for preventing the elution of heavy metals.

In this method, as shown in Fig. 1, electrostatically precipitated ash 2 containing heavy metals, dissolved water 3, and sulfuric acid 4 are put into an extraction tank 1, and then passed through a filter 4 into a residue 4 and a solution 5 containing heavy metal ions. Separate into This residue 4 can be discarded because the amount of leachable heavy metal salts has been reduced. On the other hand, solution 6 is processed by the so-called ferrite method. In this method, a solution 6 is put into a dissolution tank 8 together with ferrous sulfate 7, and then put into a reactor 9, and the solution is brought to a predetermined PHL temperature by alkali 10, steam heating 12, etc., and air oxidized by aeration 11. In this process, Fe(0
H) 2 converts into ferrite while incorporating heavy metals. The generated ferrite is separated by magnetism or sedimentation, dehydrated by a filter 14, and becomes ferrite sludge 15. Further, the solution 16 is neutralized in a pH adjustment tank 17 before entering the next step. However, this method requires a large amount of ferrous sulfate to be added, which is expensive to run, and requires a complete sewage system because a large amount of solution is produced.

Furthermore, since ferritic sludge consists of an important iron resource, it must be used effectively. Another method is to treat electrostatic precipitated ash with alkali to convert heavy metals into hydroxides, then add an auxiliary agent to make pellets, and then sinter and solidify using a rotary kiln, etc. There are disadvantages such as operational complexity.

The present invention has been made in view of the above circumstances, and its purpose is to provide electrostatic precipitated ash that can reliably prevent the elution of harmful heavy metals, reduce the amount of wastewater, and reduce running costs. The purpose of this study is to find a method for processing this.

That is, in the present invention, electrostatically precipitated ash is pickled to separate it into a residue and a solution containing heavy metal ions, and then the solution is treated with an alkali to precipitate and separate heavy metal hydroxides. Add a part of the above residue and a flux to 90%
This is a method for treating electrostatically precipitated ash, which is characterized by heating and melting and solidifying at 0 to 1100°C.

Further, in the present invention, electrostatically precipitated ash is pickled to separate it into a residue and a solution containing heavy metal ions, and then the solution is treated with alkali and sulfurized to precipitate and separate heavy metal hydroxides and heavy metal sulfides. The method is characterized in that a part of the above residue and a flux are added to the heavy metal hydroxide and heavy metal sulfide and then melted and solidified.

In addition, in the present invention, the pickling treatment removes dissolved water from the electrostatically precipitated ash by 0.00%. Add more than the heel amount and adjust the solution to pH 4. O~6.5
It is characterized by the fact that it is carried out as follows.

Further, the present invention is characterized in that the alkali treatment is carried out at a pH of 9.5 to 11.5.

In addition, the present invention melts and solidifies the heavy metal hydroxide with a residue of 0.5 to 5.0 parts by weight and 0 fluxing agent per 1 part by weight of the heavy metal hydroxide.
．． It is characterized by adding 1 to 1.0 parts by weight and heating at 900 to 1100°C.

In addition, the present invention provides melting and solidification of heavy metal hydroxides and heavy metal sulfides to 1 part by weight of heavy metal hydroxides and heavy metal sulfides.
Residue 0.5-5. Heel weight part, flux 0.1-1. It is characterized by adding a filtration part and heating at 900 to 1100°C.

The method of the present invention will be explained in detail below with reference to FIG.

The electrostatic precipitated ash 21 is pickled and separated into a residue 22 and a solution 23 containing heavy metal ions.

The electrostatic precipitated ash 21 is discharged from an electrostatic precipitator such as a garbage incinerator, and its chemical composition includes many heavy metals as shown in Table 1 above. The pickling process is carried out in an extraction tank 26 equipped with a residue scraper 24 such as a belt conveyor and a stirrer 25 and filled with a solution prepared in advance to have a predetermined composition.
The electrostatic precipitated ash 21 and dissolved water 27 such as a hydrochloric acid solution are put therein, and the mixture is stirred with a stirrer 25. Here, the composition of the solution hardly changes. By adding dissolved water 27, electrostatically collected ash 2
A small amount of heavy metal chloride and a large amount of alkali chloride in 1 are dissolved. In this case, the amount of dissolved water 27 to be added is such that when the chloride contained in the electrostatically precipitated ash 21 is dissolved, the chloride concentration in the solution is close to saturation (approximately 30% by weight). is desirable. The reason for this is that it is preferable to minimize the input amount in order to minimize the subsequent amount of waste liquid. For example, 0.00% for 211 parts by weight of electrostatically collected ash. Add at least a seed amount and adjust the solution to PH4.
．． O to 6.5. The residue 22 after the pickling treatment is carried by a belt conveyor 24 and washed with washing water 28, and then transferred to a storage tank 29.
will be put into the

On the other hand, the solution 23 containing heavy metal ions is sent to a precipitation tank 31 by a pump 30 and subjected to alkali treatment.

The alkali treatment is performed by charging sodium hydroxide 32 into a precipitation tank 31 and stirring it with a stirrer 33, and by this treatment, heavy metal ions become heavy metal hydroxides and precipitate. The pH at which precipitation is most likely to occur is 10.5,
Therefore, it is preferable to add sodium hydroxide 32 so that the pH inside the tank is in the range of 9.5 to 11.5. Further, in the present invention, when heavy metal ions cannot be sufficiently precipitated in the alkali treatment step described above, it is desirable to further perform a sulfurization treatment on the furnace liquid.

In the sulfurization treatment, the solution and precipitate after the alkali treatment are flowed into the sulfurization tank 34, and sodium sulfide (Na2S) is added thereto.
35 and stirring with a stirrer 36, and this treatment causes a small amount of remaining heavy metal ions to precipitate as heavy metal sulfides. The solution containing the precipitate after this treatment is separated by a filter 37 into a solution 38 and heavy metal hydroxide or a mixture of this and heavy metal sulfide (hereinafter referred to as heavy metal hydroxide etc. 39).

The solution 38 enters a neutralization tank 40 and is neutralized with hydrochloric acid 41. On the other hand, the heavy metal hydroxide etc. 39 is washed with water to remove adhesion of NaCL and KCL, and after drying, it is kneaded in a kneader 43 with a portion 22'' of the residue 22 obtained by the pickling treatment and a flux 42.

The residue 22 is for fixing the heavy metal hydroxide etc. 39 here, and the mixing ratio thereof is 0.5 to 5.0 parts by weight per 1 part by weight of the heavy metal hydroxide etc., considering the cost of the flux. The traffic volume part is appropriate. Further, when melting this mixture, the fluxing agent 42
This is to lower the temperature to prevent heavy metals from evaporating, and the appropriate mixing ratio is 0.1 to 1.0 parts by weight per 1 part by weight of heavy metal hydroxide, etc. Suitable examples of the flux 42 include boric anhydride and phosphoric anhydride. A mixture of heavy metal hydroxide etc. 39, residue 22'' and flux 42 is melted in a melting furnace 44, and the heavy metal hydroxide etc. is in the form of oxides and sulfides in glassy or crystalline slag. Fixed.

The melting furnace 44 is for melting the kneaded material, and since heavy metals evaporate at high temperatures, the kneaded material is heated and melted at 900 to 1100 C. As the melting furnace 44, a general furnace such as a high frequency electric furnace or a gas-fired heating furnace can be used. According to this treatment method, harmful heavy metals are fixed in a glassy or crystalline residue, so the elution of heavy metals can be reliably prevented, and since the heavy metals are in a form that is difficult to elute, such as oxides, it can be used for a long period of time. Overall, it's stable.

Further, the remaining residue that is not used for immobilizing heavy metals can be discarded because the eluted concentration of heavy metals is low. Examples of the present invention will now be described.

Example Electrostatic precipitated ash 4.0k9 dissolved in water 2.4e and 10N CL
Acid treatment with 6 ml of alcohol was carried out, and alcoholic acid separation was carried out.

The residue is washed with 2.8' water. The liquid obtained at this time is mixed with the dissolving water in the next similar operation and used for circulation. This operation was repeated 4 times, resulting in a total amount of 17 mL of liquid with pH=6.0.
．． A 50e plastic container is filled with 49e as a dissolving liquid to form an extraction tank. Another new electrostatic precipitated ash 4.0k9 in this again
was added together with 6ml of dissolved water 2.4e110N-HCL, mixed and stirred for 30 minutes, and then separated into a residue and a liquid containing heavy metal ions using a suction filter, and the residue was 2.81? of water to obtain a water-containing residue 3.21k9. Table 3 shows the chemical composition of the electrostatically precipitated ash used in this experiment and the residue obtained in the fifth experiment. Next, solution 19 containing heavy metal ions
．． 331 with 10N-NaOH4Oml pH=10.5
was treated with alkali to obtain 559 g of hydrated heavy metal hydroxide.
Further, sulfurization treatment was carried out using a trace amount of Na2s, and the hydroxide and sulfide thus obtained were washed with 2.11 parts of washing water having a pH of 10.5.

Next, the above residue was dried against 82.8f of dried hydroxide, etc., and 165.6f of a part thereof and 41.4f of a flux (anhydrous boric acid) were added (per 1 part by weight of hydroxide, etc.). (2 parts by weight of residue, 0.5 parts by weight of flux) in a V-type blender. A mixing operation was performed for m. This was transferred to an aluminum crucible and melted in an electric Matsufuru furnace at 1000° C. for 1.0 hour to obtain a cooled solidified product 231f of molten slag.
The chemical composition of precipitates such as hydroxides, the cooled solidification of molten slag, and the presence of harmful heavy metals (Cd, Pb, T-
Table 3 shows the fixed ratio of Cr). In the above table, the fixation rate is defined as the total amount of harmful heavy metals contained in the heavy metal hydroxide, residue, and anhydrous boric acid blended before melting as 100, and the content of harmful heavy metals in the solidified slag obtained after melting as a percentage. This is what is shown.

Next, an elution test was conducted on the residue after the pickling treatment and the cooled solidified product of the molten slag obtained by the above-mentioned method, and the results are shown in Table 4.

From the table above, it was confirmed that both the residue and the solidified material could sufficiently satisfy the landfill disposal regulation values if treated by the method of the present invention.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a conventional method for processing electrostatically collected ash;
FIG. 2 is an explanatory diagram showing a method for treating electrostatically collected ash according to an embodiment of the present invention. 21... Electrostatic precipitated ash, 22... Residue, 23... Solution, 26... Extraction tank, 31... Sedimentation tank, 32...
Sodium hydroxide, 43...kneader, 44...melting furnace.

Claims (1)

[Scope of Claims] 1 Electrostatically precipitated ash is treated with acid to separate it into a residue and a solution containing heavy metal ions, and then the solution is treated with alkali to precipitate and separate the hydroxides of heavy metals, and then the water of the heavy metals is separated. A part of the above residue and a flux are added to the oxide to give a powder of 900 to 1100.
A method for treating electrostatically precipitated ash, which is characterized by heating, melting, and solidifying at ℃. 2. The acidic treatment is performed by adding 0.7 parts by weight or more of a dissolving solution to electrostatically precipitated ash to adjust the pH of the solution to 4.0 to 6.5. Method of processing electrostatically collected ash. 3. The method for treating electrostatically precipitated ash according to claim 1, wherein the alkali treatment is carried out at a pH of 9.5 to 11.5. 4. In melting and solidifying the heavy metal hydroxide, 0.5 to 5.0 parts by weight of the residue and 0.1 to 0.1 parts by weight of the flux are used for 1 part by weight of the heavy metal hydroxide.
2. The method for treating electrostatically precipitated ash according to claim 1, wherein 1.0 part by weight is added and heated at 900 to 1100°C. 5 After the electrostatically precipitated ash is pickled and separated into a residue and a solution containing heavy metal ions, the solution is treated with alkali and sulfurized to precipitate and separate heavy metal hydroxides and heavy metal sulfides, and then the heavy metal water is separated. A method for treating electrostatically precipitated ash, which comprises adding a part of the above residue and a flux to oxides and heavy metal sulfides, and heating and melting and solidifying the mixture at 90 to 1100°C. 6. According to claim 5, the pickling treatment is performed by adding 0.7 parts by weight or more of a dissolving solution to the electrostatically collected ash to adjust the pH of the solution to 4.0 to 6.5. How to dispose of electrostatically collected ash. 7. The method for treating electrostatically precipitated ash according to claim 5, wherein the alkali treatment is carried out at a pH of 9.5 to 11.5. 8 The melting and solidification of heavy metal hydroxides and heavy metal sulfides produces 0 residue per 1 part by weight of heavy metal hydroxides and heavy metal sulfides.
．． 5 to 5.0 parts by weight and 0.1 to 1.0 parts by weight of a flux are added, and the electrostatically collected ash is heated at 900 to 1100°C. Method.