JPS6124074B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a crystallized product using waste incineration ash such as sewage sludge incineration ash and municipal waste incineration ash as a raw material. Traditionally, most of the sewage sludge and garbage generated from sewage treatment plants and garbage treatment plants in various places have been incinerated and disposed of as incinerated ash in landfills, as dumping them in landfills poses hygiene and odor pollution problems. , it is becoming difficult to secure land for landfills, and the secondary pollution associated with landfill disposal, such as the elution of heavy metals from incinerated ash, has become a major social problem.In addition, waste incineration is becoming more and more important from the viewpoint of resource and energy conservation. Consideration is being given to melting the ash and making effective use of it. An attempt was made to melt and mold waste incineration ash to effectively use it as aggregate, etc.
As shown in Publication No. 24010, there is a method of dropping a molten material into a water-sealed box and solidifying it in water to obtain a solidified material in the form of small lumps, but the molded product obtained by this method is weak in strength and It has the problem that its shape varies, and it also has the problem that the
As shown in Publication No. 11877, the method of obtaining a large lump of solidified material by pouring the molten material into a water-cooled mold and solidifying it requires a crushing device to make aggregate, and also removes heavy metals from the crushed surface. This method had problems such as the elution of certain substances. The present invention solves the above-mentioned problems by creating a waste material that has excellent mechanical strength and chemical stability, and which can be easily mass-produced into high-strength crystallized products that are formed from the beginning into a product shape that matches the intended use. It was completed for the purpose of producing a crystallized product using incineration ash as a raw material, and contains 25 to 45% SiO ₂ (weight%, same hereinafter),
_{Al2O3 5-15} %, _{Fe2O3 5-25} %, CaO20-40%,
The surface temperature of the molten material obtained by melting waste incineration ash at 1350 to 1500°C with a main composition of 1 to 5% MgO and 1 to 10% P ₂ O ₅ and a (CaO + MgO) / SiO ₂ ratio of 0.8 to 1.2 It is characterized in that it is poured into a mold held at 300 to 600°C and molded, and then the molded product is held at a temperature of 1020 to 1180°C for 30 minutes or more to crystallize. The waste incineration ash used as a raw material in the present invention is sewage sludge incineration ash or municipal waste incineration ash, etc., and these waste incineration ash contain:
In addition to mainly containing SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , CaO, MgO, and P ₂ O ₅ , it also contains K ₂ O, Na ₂ O, etc., and their content varies depending on the type of incineration ash. It varies slightly depending on the situation. Looking at the melting characteristics of waste incineration ash, that is, the relationship between viscosity and melting temperature, the forming temperature range corresponding to the viscosity range suitable for forming ordinary glass is extremely narrow compared to ordinary glass.
It has the properties of so-called "short-legged glass," and its viscosity in the melting temperature range of 1,350°C or higher is considerably lower than that of ordinary glass, making it suitable for pouring after melting. However, in order to further crystallize waste incineration ash having such a composition after melting and forming, SiO ₂ 25 to 45% (weight %, the same hereinafter) is preferably 30 to 40%, Al ₂ O ₃ 5 to 5%.
15% preferably 5-10%, _{Fe2O3 5-25} % preferably 5-15%, CaO20-40% preferably 30-35
%, MgO 1-5% preferably 2-5%, P ₂ O ₅ 1-5%
It is important that the (CaO+MgO)/ _SiO2 ratio is in the range of 0.8 to 1.2, preferably 0.9 to 1.1, and for this reason, the The waste incineration ash is analyzed, and if the composition range is not within the specific composition range, it is adjusted to fall within the composition range. In addition, when adjusting the composition, it is preferable to use inexpensive clay, whitebait, red iron, coal, dolomite, bone ash, etc. In this way, the composition-adjusted waste incineration ash is heated to 1350~
After melting at about 1500℃, the molten material is poured into a mold whose cavity part surface temperature, that is, the surface temperature of the mold, is maintained at 300 to 600℃, preferably 400 to 500℃, depending on the application, and then molded. The molded product is heated to 1020-1180℃ preferably by melting furnace exhaust gas etc.
Either by keeping it in a crystallization furnace maintained at a predetermined temperature within the temperature range of 1050 to 1150°C for 30 minutes or more, preferably 40 to 90 minutes, or by raising and lowering the temperature within the temperature range at a slow rate. The entire molded product may be crystallized by maintaining the molded product within the temperature range for 30 minutes or more, preferably 40 to 90 minutes, to cause formation of crystal nuclei in the molded product and crystal growth centered on the crystal nuclei. In the present invention, SiO ₂ is set to 25 to 45% because if SiO ₂ is less than 25%, SiO ₂ as a glass-forming skeleton is insufficient and a high-strength crystallized product cannot be obtained. If the Al ₂ O ₃ content is 5 to 15%, the melting temperature will rise and the viscosity will become high at the above melting temperature, making it unsuitable for casting and having a negative effect on crystallization. ,
If Al ₂ O ₃ is less than 5%, a high-strength crystallized product cannot be obtained, and if it exceeds 15%, the melting temperature becomes too high. Furthermore, setting Fe ₂ O ₃ to 5 to 25% is
Fe ₂ O ₃ is an important component not only as a fluxing agent but also as a nucleating agent; if its amount is less than 5%, its effect as a fluxing agent is weak, the melting temperature does not decrease, and crystal nuclei are not formed. This is because if it exceeds 25%, the strength will be significantly reduced. Also,
The reason why CaO is set at 20 to 40% is because if CaO is less than 20%, the viscosity of the melt will increase, it will have a negative effect on crystallization, and the strength will decrease, and if it exceeds 40%, it will significantly reduce the chemical stability. And furthermore,
The reason why MgO is set at 1 to 5% is that although MgO is used as a composition adjusting agent in place of CaO and has the effect of increasing chemical stability, it has no effect if the content is less than 1%. This is because the effect does not change even if the amount exceeds ₁ % to 10 _% .
% is because P ₂ O ₅ is the most important component as a nucleating agent, and if its amount is less than 1%, it will be 1020 to 1180.
This is because crystal nuclei are not formed in the temperature range of 0.degree. C., and if the temperature exceeds 10%, devitrification occurs during the molding stage. Furthermore, the (CaO + MgO)/SiO ₂ ratio is 0.8
~1.2 is important not only for lowering the melting temperature but also for crystallizing the melt; if this mixing ratio is less than 0.8 or exceeds 1.2, the melting temperature will increase. This is undesirable because it corrodes the furnace material of the melting furnace and increases melting costs. next,
The reason why we limited the melting temperature of waste incineration ash to 1,350 to 1,500℃ is because the molten waste incineration ash adjusted to the above composition range has a so-called "short-legged structure" in which the viscosity decreases rapidly as the melting temperature increases. Because it has the properties of "glass", the viscosity required to continuously introduce the melt into a continuously moving mold at temperatures below 1350℃
Since it is not possible to obtain a viscosity of 10 ¹ poise or less, preferably 10 ^1/2 poise or less, the molded products are connected to each other and are difficult to form into individual, independent molded products, and the molding becomes difficult to release from the mold. Maintaining a melting temperature over 1500°C involves a large loss in terms of both equipment and energy costs, so the upper limit is set at 1500°C, and furthermore, when crystallizing is performed subsequently after molding, a temperature of 1020 to 1180°C is required. For heat treatment, it is best to maintain the melting temperature within the range of 1350 to 1500°C in terms of effective use of thermal energy. Next, the surface temperature of the mold into which the molten material is poured must be maintained at 300 to 600°C, depending on the material and shape of the mold, such as cast iron or graphite, but if it is below 300°C, the molded product will cool rapidly and crack This is because if the temperature exceeds 600°C, the molded product may seize to the mold and become difficult to mold.
In addition, the crystallization temperature was limited to 1020 to 1180°C because the waste incineration ash adjusted to the above composition was heated to 1020°C.
If the temperature is less than 1180°C, crystal growth is difficult to occur, and if it exceeds 1180°C, stable crystal growth will be hindered due to remelting of crystallized substances. In addition, during crystallization, it is more preferable to maintain a constant temperature within each specific temperature range for a predetermined period of time in order to form uniform crystal nuclei and crystal growth. Almost the same results can be obtained even if the temperature is gradually lowered or increased over time. Further, the reason why the crystallization time is set to 30 minutes or more is because crystallization cannot be completed completely with a holding time of less than 30 minutes, and a high-strength crystallized product cannot be obtained. The mold into which the molten material is introduced should be made of a material with good leakage and good slipperiness, such as graphite or boron nitride, or the surface of the mold should be made of cast iron, etc., with a release material such as graphite or boron nitride. In addition, the shape of the cavity of the mold may be compatible with the shape of the product so that it can be used as it is depending on the purpose of the crystallized product being manufactured. When used as an aggregate for manufacturing products, it is preferable to form irregularities or irregularities on the surface, so it is preferable to form irregularities on the mold surface of the cavity part. The crystallized product obtained in this way not only has high strength but also has a smooth and glossy surface, making it easy to handle. Since it is formed from the beginning, there is no need for post-processing such as crushing, cutting, and processing, and there is no risk of heavy metals leaching from the processed surface. As is clear from the above description, the present invention is achieved by melting waste incineration ash having a specific composition range under specific melting conditions, putting it into a mold and shaping it, and further treating it under specific crystallization conditions. Crystallized products with excellent mechanical strength and chemical stability can be easily obtained by using these materials. Crushed stone used for backfilling and paving, tiles laid on sidewalks and floors, building materials such as exterior wall materials used for building walls and columns, and other uses are extremely wide. Furnace exhaust gas can be used effectively, so it can be obtained at low cost and has excellent energy savings.Furthermore, it eliminates the need for landfills and secondary pollution of waste incineration ash, which has traditionally been disposed of in landfills. There are various advantages such as: Example Waste incineration ash from sewage treatment plants in various places was adjusted to the chemical composition and composition ratio listed in the table below, and melted in a melting furnace maintained at a temperature of 1380 to 1480°C according to the respective melting characteristics. The molten material is poured into graphite molds continuously installed on an endless conveyor kept at 400°C and molded, and then heated to a temperature of 1050 to 1150°C using melting furnace exhaust gas.
Crystallized products No. 1 to No. 12, which were crystallized by being held for 40 minutes in a crystallization furnace maintained at a temperature of , are listed as examples of the present invention in the table. Next, crystallized products obtained with compositions and heat treatment conditions outside the numerically limited range of the present invention
No.13 to No.20 are listed as reference examples in the table,
In addition, in order to compare the strength, chemical stability, etc. of crystallized products made from waste incineration ash with those of slag and glass, these are used as reference examples in the table: slag is No. 21, glass is No. 22, It was listed as No.23. The average values of 10 samples comparatively measured for compressive strength, bending strength, hardness, and sodium sulfate stability test for these various crystallized products were as shown in the table. As is clear from this result,
It was confirmed that the crystallized product obtained by the present invention has superior mechanical strength and chemical stability compared to the crystallized product obtained by the reference example.

[Table] In the table, the microhardness indicates the Bitkers hardness (load 1 kg), and the sodium sulfate stability test indicates the weight loss rate (%) of 5 repetitions according to the JIS A-1122 aggregate stability test method.

Claims (1)

[Claims] 1 SiO ₂ 25-45% (weight%, same below), Al ₂ O ₃ 5
~15%, _Fe2O3 5~25%, CaO20~ ₄₀ %, MgO1~
5%, P ₂ O ₅ 1-10% as the main composition, and
(CaO + MgO) / SiO ₂ ratio is 0.8 to 1.2 waste incineration ash is melted at 1350 to 1500℃.
It is poured into a mold kept at 300-600℃ and molded.
1. A method for producing a crystallized product using waste incineration ash as a raw material, characterized in that the molded product is then held at a temperature of 1020 to 1180° C. for 30 minutes or more to crystallize it.