JPS633674B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for solidifying incinerated ash discharged from the incineration process of municipal garbage, sludge, sludge, etc., and fine powder waste such as dust generated from various gas processing processes. Traditionally, the mainstream methods for treating or disposing of these fine powder wastes have been direct landfilling and ocean dumping, but since they are fine powders, they are difficult to handle, and they are prone to scattering and spilling during transportation and at landfill sites. There were many issues that needed to be improved, such as the elution of heavy metals contained in the residue. In addition, various solidification techniques have been proposed to facilitate the handling of these residues and prevent the elution of heavy metals, etc., but these conventional solidification techniques include methods of adding solidifying agents such as cement and asphalt, There was a method of heating, melting, and then cooling and solidifying (melting method). Among these methods, the method of adding a solidifying agent is effective in containing harmful substances and improving the soil quality of a landfill, but the cost of the solidifying agent is high and
It is difficult to solidify the entire amount of the fine powder waste that is discharged every day. On the other hand, the melting method is an excellent method because the volume of the waste is significantly reduced and the waste becomes granular or lumpy, making it easy to handle and containing harmful substances such as heavy metals.
The problem is that the waste must be heated and maintained at a high temperature, which consumes a large amount of energy. In recent years, a method using a steam autoclave has been developed as a solidification method that can solve these problems and also save resources and energy, and has been attracting attention. This method is an excellent method for solidifying fine powder waste at low cost and making it possible to use it as roadbed material, sand, etc. However, if a large amount of sulfate radicals are contained in the fine powder waste, there is a concern that a small amount of sulfate radicals will leach out from the solidified material and have an adverse effect on surrounding concrete products. This has become an obstacle when used as a The purpose of the present invention is to provide a method for solidifying fine powder waste that completely prevents the outflow of sulfate radicals from the solidified material and allows the solidified material to be fully used as artificial aggregate for concrete. That is. The present invention involves adding a sulfuric acid radical fixing agent to fine powder waste in the presence of a calcium component, mixing with at least one of a solidification accelerator or a reducing agent as needed, molding the waste, and solidifying it by steam autoclaving. It is characterized by: The present invention was completed by revealing that the method using this sulfuric acid root fixative is very effective. That is, as a result of numerous experimental studies, the present inventors have found that water-soluble strontium salts, water-soluble barium salts, water-soluble radium salts, water-soluble lead salts, and wastes containing these substances are used alone as sulfate root fixing agents. It was also confirmed that it is effective when used in combination. The optimum amount of these sulfate fixatives to be added varies significantly depending on the type of fine powder waste, and also depends on the type of sulfate fixative, the method of addition, etc., and cannot be unconditionally defined.
It is effective to increase the amount above the theoretical amount required to fix the total amount of sulfate radicals contained in the fine powder waste.
As for the method of adding the sulfuric acid root fixing agent, mixing it as an aqueous solution has the advantage of reducing the amount added, rather than adding and mixing it as a powder. In the present invention, the presence of calcium component is an essential condition, and if the fine powder waste contains sufficient calcium component, it is not necessary to add calcium component, but if it is insufficient, Add calcium component in advance to reduce the calcium content in the mixture to 10% by weight (calcium equivalent, hereinafter referred to as "%")
(all are expressed on a weight basis) or higher. In addition, the forms of calcium components to be added include calcium carbonate, quicklime, calcium sulfate, calcium chloride, slaked lime, etc. These can be added singly or in combination, but slaked lime is the most suitable, and in some cases Depending on the situation, a residue obtained by incinerating various types of sludge dehydrated using calcium components may also be used. In addition, if the calcium content is sufficient but hard to solidify, silicic acid materials such as diatomaceous earth, silica, silicate clay, silica stone, quartz, silicate glass, water glass, and sand can be used as a solidification accelerator as necessary. substances, clays such as kaolinite, bentonite, pernite, zeonite, hallosite, aluminum compounds such as aluminum hydroxide, aluminum oxide,
Or waste such as fly ash, red mud incineration ash, etc. containing the above substances alone or in combination to an appropriate value (e.g. 1 to 30%, preferably 10 to 30%)
It is effective to add and process. Furthermore, when treating fine powder waste containing a large amount of hexavalent chromium as a heavy metal, it is also effective to add a reducing agent in advance. In this case, reducing agents include salts of divalent iron ions, sulfites or sulfites, coal carbon black, coke husks, organic carbons such as lignin, metals such as magnesium, calcium, zinc, etc., or wastes containing these. A solid substance can be used in the form of a fine powder, and a water-soluble salt or an aqueous solution can be used in the form of a spray. The fine powder waste whose chemical composition has been adjusted in this way is molded to increase the number of points of contact between the fine powders, and this molding method can use conventional techniques such as pressurization, rolling, extrusion, etc. . The thus shaped waste is placed in an autoclave using steam as a medium and solidified by being left in the presence of pressurized steam. The mechanism of the reaction that occurs in the steam autoclave process is not necessarily clear due to the difficulty in identifying and quantifying the reaction products, but it is possible that calcium silicate hydrate or calcium aluminate hydrate is produced, resulting in solidification due to the mutual bonding of fine powders. It is thought that the development of strength, the formation reaction of poorly soluble salts between the sulfate radicals in the waste and the added fixative, and the oxidation-reduction reaction between hexavalent chromium and the reducing agent are proceeding simultaneously. As described above, according to the present invention, fine powder waste is molded in the presence of a calcium component, with the addition of a sulfuric acid root fixing agent and, if necessary, at least one of a solidification accelerator or a reducing agent. Afterwards, by steam autoclave treatment, a solid solidified product that is strong and has a significantly small amount of sulfate radicals eluted can be easily obtained. That is, the present invention not only improves the handling of fine powder waste and prevents the elution of heavy metals, but also makes it possible to reuse it as roadbed material, sand, and even as artificial aggregate for concrete. Furthermore, since the heat and steam generated from the waste incineration process can be used directly or indirectly through a steam boiler, the present invention can be satisfied as an energy-saving and resource-saving process. It not only has an extremely useful effect on pollution prevention, but also accurately eliminates various conventional problems.
Moreover, the processing cost is low, and the waste can be disposed of economically. Next, examples of the present invention will be shown. Example 1 Sludge generated at a certain sewage treatment plant was dehydrated by adding slaked lime and ferric chloride, dried, and then incinerated. The composition of incinerated ash was as follows.

[Table] Also, the concentration of hexavalent chromium eluted from this incineration ash is
It was 1.5ppm. After adding various sulfuric acid root fixing agents to this incineration ash, it is compression molded at a pressure of 1 ton/cm ² to a length of 20 mm in diameter.
A 20 mm green pellet was prepared and subjected to steam autoclave treatment at 20 atm for 1 hour to obtain a solidified product. Table 1 shows the strength of this solidified product and the results of the elution test according to the method specified in Environment Agency Notification No. 13 (1972).

【table】

[Table] From the results in Table 1, the addition of the sulfate radical fixative significantly reduces the amount of sulfate radicals eluted without reducing the strength of the solidified product or increasing the amount of hexavalent chromium eluted. I understand that. Example 2 The composition of EP dust discharged from a certain municipal garbage incinerator was as follows.

[Table] A predetermined amount of barium chloride was added in the form of an aqueous solution to this EP dust, and granulated to a diameter of 8 to 10 mm using a rolling granulator. This green pellet was treated in a steam autoclave at 20 atmospheres for 1 hour to obtain a solidified product.
The solidified product strength and sulfate radical elution concentration (tested using the same method as in Example 1) were measured. The results are shown in Table 2.

[Table] The theoretical amount of barium chloride required to fix the total amount of sulfate radicals contained in this EP dust as barium sulfate was calculated to be approximately 5%. The results in Table 2 show that the amount of leached sulfate radicals is significantly reduced by adding 5% or more of barium chloride. From the above, the amount of sulfate root fixative added is:
It can be seen that it is better to keep the total amount of sulfate radicals contained in the waste at least the theoretical amount required to fix them as sparingly soluble salts.

Claims (1)

[Scope of Claims] 1 Fine powder waste is molded by adding a sulfuric acid radical fixing agent in the presence of a calcium component, and optionally mixing at least one of a solidification accelerator or a reducing agent, and then heated in a steam autoclave. A method for solidifying fine powder waste, characterized by processing and solidifying it. 2 As the sulfate root fixing agent, a water-soluble strontium salt, a water-soluble barium salt, a water-soluble radium salt,
The solidification treatment method according to claim 1, wherein a water-soluble lead salt and waste containing these substances are used alone or in combination. 3. Solidification according to claim 1 or 2, wherein the amount of the sulfate radical fixing agent added is greater than or equal to the theoretical amount necessary to fix the entire amount of sulfate radicals contained in the fine powder waste. Processing method.