JP3511612B2 - Treatment method for acidic molten fly ash - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating molten fly ash generated when melting waste or incineration residues. Melting treatment is performed on incineration residues such as municipal solid waste, industrial waste, and sludge in order to reduce the volume and render it harmless. When these are melted, molten fly ash is generated in addition to the molten slag.Generally, the molten slag is granulated and solidified, and the molten fly ash is stabilized with a chemical so that the heavy metals contained therein will not elute. You. The present invention relates to a method for treating acidic molten fly ash among the molten fly ash as described above. Heretofore, as a method of treating molten fly ash, there has been proposed a method in which water and a chelating agent are added to a molten fly ash at predetermined ratios and kneaded (Japanese Patent Laid-Open No. Hei 5-8732).
4). However, this conventional method is uneconomical because the chelating agent used is expensive. On the other hand, as a method for treating incineration residues, a method has been proposed in which divalent iron is added to the incineration residues, followed by stirring and heating (JP-A-6-134436). Therefore, it is conceivable that the molten fly ash is kneaded by adding divalent iron, for example, ferrous chloride. In fact, the method of adding and kneading ferrous chloride is, for example, when melting incineration ash remaining in the incinerator among the incineration residue of municipal waste, the generated molten fly ash shows an alkaline pH of about 11 to 12, Such alkaline molten fly ash has a corresponding effect. However, the method of simply adding and kneading ferrous chloride is a method of melting and burning incinerated fly ash that is scattered together with exhaust gas and usually collected by a dust collector on the downstream side when incinerating municipal waste.
When plastic and rubber wastes are melt-processed, and furthermore, when they are melt-processed together with incineration ash, the generated molten fly ash shows an acidity of about pH 3 to 6, which is effective against such acidic molten fly ash. And elution of heavy metals contained therein cannot be sufficiently prevented. [0004] The problem to be solved by the present invention is that the conventional method is uneconomical or prevents elution of heavy metals contained in acidic molten fly ash sufficiently. It is impossible. SUMMARY OF THE INVENTION The present invention relates to a method for treating acidic molten fly ash generated when a waste or incineration residue is subjected to a melting treatment, wherein slaked lime is added to the acidic molten fly ash. In addition, the pH is adjusted to 8.5 or more, and then ferrous chloride is added in an amount of 2 to 5 parts by weight per 100 parts by weight of the acidic molten fly ash, and when the pH is out of the range of 8.5 to 10.0, further addition is performed. After adding slaked lime or ferrous chloride to adjust the pH to 8.5 to 10.0, it was used as water to solidify molten slag generated during melting treatment of waste and its incineration residue. The present invention relates to a method for treating acidic molten fly ash, comprising adding 10 to 30 parts by weight of circulating water per 100 parts by weight of acidic molten fly ash and kneading. The acidic molten fly ash to be treated in the present invention is scattered together with the exhaust gas when the waste or the incineration residue is melted, and is usually one of the molten fly ash collected by a dust collector on the downstream side. Melt fly ash showing acidity. The acidic molten fly ash is generated when the incinerated fly ash is melt-processed, when plastics and rubbers are melt-processed, and when these are melt-processed together with the incinerated ash, and has a pH of about 3 to 6. In the present invention, first, slaked lime (calcium hydroxide) is added to the acidic molten fly ash and mixed, and the pH is adjusted to 8.
5 or more. Slaked lime is in powder form, is inexpensive and easily available, and does not extremely increase pH even when added in excess.
Since there is no generation of gas, it is advantageous for use. On the other hand, sodium hydroxide is too alkaline and it is difficult to obtain a powdery product industrially. Calcium carbonate generates gas in the acidic region. Furthermore, quicklime (calcium oxide) has poor stability and is easily changed to calcium carbonate or slaked lime. Next, in the present invention, ferrous chloride is added in an amount of 2 to 5 parts by weight per 100 parts by weight of the acidic molten fly ash. Usually, a high-concentration aqueous solution of ferrous chloride, for example, an aqueous solution of about 30% by weight is added and kneaded by adding 2 to 5 parts by weight in terms of ferrous chloride per 100 parts by weight of the original acidic molten fly ash. Ferrous chloride has a reducing action and a chloride-producing action, reducing harmful hexavalent chromium contained in acidic molten fly ash to trivalent chromium and converting heavy metals into chloride form. It is advantageous. The heavy metals in the form of chlorides become hardly soluble hydroxides at least when kneaded with circulating water used later as water. In contrast, ferric chloride has no reducing action. When the amount of ferrous chloride to be added is less than 2 parts by weight per 100 parts by weight of the acidic molten fly ash, the elution thereof can be sufficiently prevented in relation to the concentration of heavy metals normally contained in the acidic molten fly ash. On the contrary, if the amount exceeds 5 parts by weight, the effect of preventing the elution of heavy metals is not improved, and in any case, it is inconvenient. When ferrous chloride is added and kneaded, if the pH of the kneaded product is in the range of 8.5 to 10.0, p
There is no need to adjust H. However, the pH of the kneaded material is 8.
If it is less than 5, slaked lime is added to adjust its pH to 8.
Adjusted to the range of 5 to 10.0, and the pH of the kneaded material was adjusted to 1
If it exceeds 0.0, ferrous chloride is added and its pH
Is prepared in the range of 8.5 to 10.0. When the pH of the kneaded material is out of the range of 8.5 to 10.0, the elution of amphoteric metals such as lead and zinc contained in the acidic molten fly ash increases in both the acidic range and the alkaline range, and cadmium increases in the acidic range. As for arsenic, its elution increases in the alkaline region. In the present invention, finally, if necessary, slaked lime or ferrous chloride is added as described above to adjust the pH of the kneaded product to a range of 8.5 to 10.0, and then the mixture is used as water. 10 to 3 parts per 100 parts by weight of the original acidic molten fly ash
Add 0 parts by weight and knead. If the amount of the circulating water is less than 10 parts by weight per 100 parts by weight of the acidic molten fly ash, the acidic molten fly ash cannot be sufficiently muddy. Is in a slurry state, and in any case, the handling property is poor, which is inconvenient. As the water to be kneaded with the acidic molten fly ash, use is made of circulating water used for granulating and solidifying molten slag generated when melting wastes and incineration residues. When waste and its incineration residue are melted, molten slag is generated. Generally, molten slag is granulated and solidified. In the granulation and solidification, usually, once used cooling water is reused as circulating water while replenishing cooling water, while a part of the circulating water contaminated by repeated reuse is extracted.
Heavy metals are concentrated in the extracted circulating water, which cannot be discharged as it is. Therefore, when such circulating water is used as water for kneading with the above-mentioned acidic molten fly ash, heavy metals contained in the circulating water can be stabilized as a result. Example 1 An acidic molten fly ash (pH 6.0) collected by a bag filter was treated from an exhaust gas when a mixture of incinerated ash and incinerated fly ash of municipal waste was subjected to a melting treatment. Slaked lime (commercially available slaked lime special name, JIS-R9001) was added and mixed at 6 parts by weight per 100 parts by weight of acidic molten fly ash, and the pH was adjusted to 8.5 or more. Next, ferrous chloride (32% by weight aqueous ferrous chloride solution) was added and kneaded at 3 parts by weight (equivalent to ferrous chloride) per 100 parts by weight of the original acidic molten fly ash. Since the pH of the kneaded material was 9.7, the circulating water used to granulate and solidify the molten slag obtained by melting the mixture as water was added to the kneaded material without adjusting the pH. 20 parts by weight per 100 parts by weight of the original acidic molten fly ash were added and kneaded. The obtained kneaded product was subjected to a dissolution test (Notification No. 13 of the Environment Agency in 1973). The treatment conditions are shown in Table 1, and the dissolution test results are shown in Table 2. Comparative Examples 1 and 2 The same procedure as in Example 1 was carried out except that the amount of ferrous chloride was changed and that industrial water was used as the water. The treatment conditions are shown in Table 1, and the dissolution test results are shown in Table 2. Comparative Example 3 The same operation as in Example 1 was carried out except that 3 parts by weight of ferrous chloride alone was added without adding slaked lime, and industrial water was used as the water. The treatment conditions are shown in Table 1, and the dissolution test results are shown in Table 2. Comparative Examples 4 and 5 Slaked lime and ferrous chloride were not added, and a commercially available inorganic stabilizer (GEOSTA-F manufactured by Kaneka Chemical Industry Co., Ltd.) was used as a stabilizer.
13) or a polymeric stabilizer (NEW manufactured by Miyoshi Yuka Co., Ltd.)
-Epolva 500) and industrial water was used as the water in the same manner as in Example 1. The treatment conditions are shown in Table 1, and the dissolution test results are shown in Table 2. [Table 1] In Table 1, the addition amount: the addition amount per 100 parts by weight of the original acidic molten fly ash * 1: GEOSTA-F13 * 2: NEW-Epolva 500 pH: pH of the finally obtained kneaded material [Table 2] In Table 2, Judgment: は indicates that heavy metals are sufficiently insoluble (stabilized), and △ indicates industrial waste landfill standards (Primary Office Ordinance No. 61 dated November 7, 1994). ), But it cannot be said that heavy metals are not sufficiently eluted.
Means that the above-mentioned industrial waste landfill standard has not been achieved. As is apparent from the above description, the present invention described above does not dissolve heavy metals contained in acidic molten fly ash. It can be economically and sufficiently prevented, and consequently has the effect of stabilizing heavy metals contained in the circulating water used to granulate and solidify the molten slag.

Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B09B 3/00 F23J 1/00

Claims (1)

(57) [Claims 1] A method for treating acidic molten fly ash generated when a waste or incineration residue is melted, wherein slaked lime is added to the acidic molten fly ash to adjust the pH. 8.5 or more, and then ferrous chloride is added in an amount of 2 to 5 parts by weight per 100 parts by weight of the acidic molten fly ash. If the pH is out of the range of 8.5 to 10.0, slaked lime or chloride is added. PH is adjusted to 8.5 by adding 1 iron
After adjusting to 10.0, waste or incineration residue as water
Granulate and solidify molten slag generated during melting
The circulating water used for the smelting was 1 per 100 parts by weight of
A method for treating acidic molten fly ash, comprising adding 0 to 30 parts by weight and kneading.