JPH0413408B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dust processing method. More specifically, the present invention relates to a dust processing method for separating and recovering alkali metal salts from dust generated from a waste incinerator, such as a municipal garbage incinerator. Various wastes such as municipal garbage, sewage sludge, and treated wastewater discharged from mines and factories are incinerated in incinerators, and the resulting incinerated ash has conventionally been disposed of in landfills. However, due to problems such as the difficulty in securing land for landfills and the fear that the harmful heavy metals contained in them may leach into the ground and contaminate the area around the landfill site, causing secondary pollution, for example, base metals have been A method of melting and solidifying using an electric arc furnace or a direct current melting furnace has been proposed. When waste is incinerated in the above-mentioned incinerator, the generated dust pollutes the atmosphere, so it is captured by various types of dust collectors such as wet dust collectors, electric dust collectors, bag filters, etc. The dust captured by the electrostatic precipitator installed in the incinerator contains water-soluble salts such as NaCl, KCl, and water-insoluble oxides such as CaO, SiO ₂ , Al ₂ O ₃ , and Fe ₂ O ₃ , and As, Cr, Zn, Cd,
It contains heavy metals such as Pb and Hg, which are generally in water-soluble forms such as halides or sulfates. Therefore, if this dust is buried in a landfill as it is, there is a risk that heavy metals will be leached into the ground, so the method of melting and solidifying it, similar to incineration ash, is taken.
The present inventors conducted various studies on the melting process of dust generated during the incineration of waste in an incinerator, and found that when dust is melted in a direct current melting furnace, the slag generated has an upper layer and a lower layer. They discovered that they had different compositions, and that by extracting them separately, they could be used effectively according to their characteristics, and that heavy metals could be rendered harmless. 128637). In such sorted waste, the composition of the upper layer is
The main component is alkali metal salts such as NaCl and KCl, and the composition of the lower layer is CaO, SiO ₂ ,
The slag is mainly composed of oxides such as Al ₂ O ₃ and Fe ₂ O ₃ , but it is inevitable that a small amount of detoxified heavy metals will be present in each slag. However, since the slag in the lower layer is solidified and recycled into fine aggregate such as sand, the presence of detoxified heavy metals is not a problem, but the slag in the upper layer is mixed with the NaCl and KCl contained in it. The ingredients are used as raw materials for NaOH production,
This poses an obstacle to recycling as a raw material for potash fertilizer, a freezing agent, an antifreeze agent, etc. The present inventors have investigated a dust processing method for separating and recovering alkali metal salts useful for manufacturing secondary products, such as NaCl and KCl from which heavy metals have been removed, from the dust generated from waste incinerators. As a result, of the slag separated into the two layers above, the pH of the slag aqueous solution in the upper layer is adjusted, chelation treatment is performed to sediment or adsorb and remove heavy metals, and the solubility difference is utilized to separate and recover alkali metal salts at high concentrations. I learned that it is possible. That is, the present invention processes dust generated from a waste incinerator in a direct current melting furnace equipped with upper and lower slag discharge ports, and processes the generated slag mainly consisting of water-soluble alkali metal salts. The slag is separated into the upper layer slag and the lower layer slag mainly composed of oxides that are poorly soluble in water, and the aqueous solution of the upper layer slag is adjusted to pH 9 to 12 and chelated to be contained. The gist of the present invention is a method for treating dust, which is characterized in that after heavy metals are removed, the alkali metal salts precipitated by cooling are separated and recovered. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on drawings showing an example of an apparatus to which the present invention is applied. Figure 1 is a schematic cross-sectional view of a direct current melting furnace.
The furnace body is made of, for example, SiO2− with a high content of _ZrO2 .
It is hermetically constructed with Al ₂ O ₃ -ZrO ₂ based refractory material 1, and includes an inlet 2 for dust generated during waste incineration, an exhaust pipe 3, and a heating device for initial melting of the input dust. For example, a fuel gas injection nozzle 4, horizontally retractable electrodes 5, 5, an upper slag discharge port 6, a lower slag discharge port 7, etc. are provided. Note that these two discharge ports 6 and 7 are provided with a head difference as much as possible within the allowable range of the furnace structure.
An alternating current is passed through the voltage regulating power transformer 8 to the electrodes 5, 5, and the dust injected from the dust inlet 2 is melted by gas heating from the fuel gas injection nozzle 4, resulting in molten slag 9. The material itself becomes a conductor, generates Joule heat, and maintains a molten state through internal heating. Typical examples of such materials are molybdenum electrodes, while other examples include graphite, iron, tin oxide,
Examples include tungsten electrodes. Therefore, in the present invention, when incinerating waste such as municipal garbage, sewage sludge, mine and industrial wastewater, etc., the dust generated from the waste incinerator, especially the dust generated from the salt-rich waste incinerator, is directly energized as described above. When melting is performed using a processing furnace capable of non-oxidizing melting such as a type melting processing furnace, the composition of the upper layer of the generated slag is that water-soluble alkali metal salts such as NaCl and KCl in the dust are used. Based on the knowledge that the main layer has a specific gravity of 1.9 to 2.1, and the lower layer mainly contains poorly water-soluble components such as CaO, SiO ₂ , Al ₂ O ₃ , and Fe ₂ O ₃ and has a specific gravity of 2.5 to 2.7. The slag is discharged separately from the discharge ports of the furnace main body, which is provided in upper and lower stages, thereby facilitating the processing for effective utilization of the slag after it is discharged, which will be described later. To treat dust generated in a waste incinerator using the direct current melting furnace shown in Fig. 1, the dust is introduced into the furnace body through the dust inlet 2, and then through the fuel gas injection nozzle 4 for initial melting. Gas is heated to bring it into a molten state and form slag 9. The temperature of the slag 9 in this case depends on the type of dust introduced, but
The temperature ranges from approximately 1200 to 1350°C. At this time, the electrodes 5, 5 attached to the furnace body are immersed in the slag in advance and an alternating current is passed through it, and the slag is maintained in a molten state by the generated Joule heat using this as a conductor. The current at this time is in the range of approximately 700 to 1200 KW/t (material to be treated), although it depends on the nature of the applied dust. Note that 10 is a covering layer of unmelted dust which is successively introduced. Next, the upper layer of the generated slag 9 is discharged from the discharge port 6, which is located at a higher position of the two discharge ports provided in the furnace body, and is discharged into a pit filled with water. As a result, the main components, alkali metal salts such as NaCl and KCl, are eluted into the water. Also, slag 9
The slag discharge port is located at the lower position of the two discharge ports provided in the furnace main body, and the lower layer mainly contains components that are poorly soluble in water such as CaO, Al ₂ O ₃ , SiO _{2 ,} and Fe ₂ O 3 . The slag is extracted from 7 and transported and solidified together with detoxified heavy metals. Next, Figure 2 is a diagram showing the flow of separating and recovering alkali metal salts such as NaCl and KCl, which are the main components, from the upper layer of slag separated and extracted by the direct current melting furnace shown in Figure 1. It is. The slag discharged from the upper discharge port 6 of the direct current melting furnace shown in Fig. 1 passes through the line 11 and reaches a temperature of 80 to 90°C due to waste heat generated from a waste incinerator, for example.
The mixture is poured into a pit 13 filled with hot water 12 heated to 200 mL and dissolved. And to this, from line 14
Add an alkali such as NaOH to adjust the pH to 9 to 12, and add a chelating agent from line 15 to remove traces of heavy metals contained in the slag solution in the form of hydroxides and chelate bonds. Precipitate in shape. The slag solution containing heavy metal precipitates is transferred by a pump 16 via a line 17 to a filter 18 for filtration to remove heavy metals, and the filtration mother liquor is sent to a cooling tank 19 equipped with, for example, cold water or brine cooling piping, where approximately Cooled to below 20℃. Of NaCl and KCl contained in the filtration mother liquor, KCl has a lower solubility than NaCl at this temperature and precipitates, so the separator 20, for example, a centrifuge,
KCl is separated from the saturated filtration mother liquor to recover KCl crystals 21 having a purity of about 90% and containing no heavy metals. Further, the saturated filtered mother liquor of NaCl and KCl, which does not contain heavy metals, is transferred through a line 22 by a pump 23, heated by a heater 24, and recycled to the pit 13. It is also extracted from the branch pipe 22a and evaporated using waste heat generated from a waste treatment furnace, for example, to recover NaCl-rich crystals containing KCl.
As the chelating agent used in the above separation operation, for example, Miyoshi Yushi Co., Ltd., product name "Epofrock L-
1" is mentioned. Incidentally, instead of adding the chelating agent through the line 15, a chelate ion resin filtration layer may be provided in the filter 18 to adsorb and filter heavy metals in the molten slag. For example, the chelate resin layer may be manufactured by Sumitomo Chemical under the trade name "Sumikylate".
MC-30''. As described above, the present invention processes dust generated from a waste incinerator in a directly energized melting furnace equipped with upper and lower slag discharge ports, and converts the generated sludge into water-soluble alkali metals. The slag is separated into an upper slag consisting of salt and a lower slag consisting of hardly soluble oxides, and the aqueous solution of the upper slag is chelated to remove heavy metals and used for fertilizer production, electrolysis, etc. NaCl, which is useful as a raw material for cryogens used in the production of caustic soda, etc.
This is a dust processing method that separates and recovers alkali metal salts such as KCl with high purity, and has a great potential to contribute to waste treatment and recycling projects. Example 1 Dust generated from a municipal waste incinerator was captured with an electric dust collector to obtain dust having the composition shown in Table 1.

[Table] According to issue.
Next, Sample 1 in Table 1 was melted in the direct current melting furnace shown in Figure 1, and the upper layer slag A discharged from the upper slag discharge port 6 and the lower layer slag discharged. Table 2 shows the results of investigating the composition of the lower layer slag B discharged from outlet 7.

[Table] From the above results, the slag in the upper layer is mainly composed of components that are soluble in water (NaCl, KCl), whereas the slag in the lower layer is mainly composed of components that are resistant to water (CaO, Al ₂ O ₃ , SiO ₂ ,
It is clear that the main component is Fe ₂ O ₃ etc.).
It is also seen that the heavy metals in the sample dust were significantly reduced in the slag. Next, 120 kg of slag A in the upper layer in Table 2 was heated to 90℃ as shown in the flow diagram in Figure 2.
The solution was discharged and dissolved into a pit 13 filled with 200 ml of water, NaOH was added through line 14 to adjust the pH of the liquid to 9 to 12, and chelating agent Epofloc L-1 was added through line 15. The treatment solution containing the generated heavy metal precipitate is transferred to the filter 18 via the line 17 by the pump 16 and filtered, and the filtration mother liquor is transferred to the cooling layer 19 and cooled to about 25° C. to precipitate KCl crystals. Ta. The precipitated KCl 21 is separated by a separator 20, and the filtered mother liquor saturated with NaCl and KCl is transferred through a line 22 by a pump 23, heated by a heater 24, and circulated to the pit 13. In addition, some water is evaporated in an evaporator (not shown) through the branch pipe 22a.
Crystals consisting mainly of NaCl were obtained. Table 3 shows the results of investigating the obtained KCl and NaCl. For comparison, in the flow diagram shown in Figure 2,
KCl crystals precipitated by directly transferring the slag solution in the pit 13 without addition of NaOH and chelating agent to the cooler 19 (indicated by the dotted line), and recovery
The results of the investigation on NaCl crystals are also listed.

【table】

[Table] As is clear from the results in Table 3, the alkali metal salts such as KCl and NaCl recovered from the chelate-treated slag solution have almost no heavy metal content, and are used for KCl fertilizer and electrolytic NaOH production. It was fully usable for various purposes.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a direct current melting furnace to which the method of the present invention is applied, and FIG. 2 is a flow diagram for recovering and separating alkali metal salts from the upper layer of slag in the method of the present invention. 1... Fireproof material, 2... Dust inlet, 3...
... Ventilation pipe, 4... Fuel gas injection nozzle, 5... Electrode, 6, 7... Slag discharge port, 8... Power supply transformer for voltage adjustment, 9... Slag, 10... Covering layer, 11... ... line, 12 ... hot water, 13 ... pit, 14, 15 ... line, 16 ... pump,
17...Line, 18...Filter, 19...Cooling tank, 20...Separator, 21...KCl crystal, 22...
...Line, 23...Pump, 24...Heater.

Claims (1)

[Claims] 1. Dust generated from a waste incinerator is treated in a direct current melting furnace equipped with upper and lower slag discharge ports, and the generated slag is treated with a water-soluble alkali metal salt. The slag is separated into the upper layer containing slag and the lower layer containing oxides that are poorly soluble in water, and the aqueous solution of the upper layer slag is adjusted to pH 9 to 12 and chelated to contain the slag. A method for treating dust, which comprises removing heavy metals, followed by cooling and separating and recovering precipitated alkali metal salts. 2 The upper layer slag is made of water-soluble alkali metal salts mainly composed of NaCl or KCl, and the lower layer slag is poorly soluble in water mainly composed of CaO, Al ₂ O ₃ , Fe ₂ O ₃ , and SiO ₂ The method for treating dust according to claim 1, which comprises an oxide of. 3. Claim 1 or 2, wherein the chelation treatment is either sedimentation separation by adding a chelating agent or adsorption separation on a chelate ion resin layer.
How to dispose of dust as described in section.