JPS6254560B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating bottom sludge, which is characterized by drying, granulating, and firing bottom sludge deposited on the bottom of water such as rivers, lakes, and sea areas to obtain a strong granular solidified product that is rendered harmless. It is. Bottom sludge, commonly referred to as sludge, that accumulates on the bottom of rivers, lakes, oceans, etc. (hereinafter simply referred to as bottom sludge) causes environmental damage such as polluted water quality and the death of aquatic plants. If it contains harmful substances, it may develop into a pollution problem that harms the health of local residents. Therefore, there is a strong need to remove the bottom mud. The conventional method for removing and disposing of bottom sludge is to dredge the bottom sludge and dispose of it by dumping it into the ocean, reclamation on the sea surface or on land, or the like. However, ocean dumping also poses the risk of water pollution, and recently landfills have become the main method of disposal. When disposing of bottom sludge in a landfill, since the bottom sludge is a soft mud material with a high water content (in liquid form), if the bottom sludge is disposed of in a landfill as it is, there is a problem that the landfill will remain soft and the ground will be difficult to solidify. There is a problem with land use. Therefore, in order to use the land, we drain the reclaimed land using the sand drain method and consolidate it to harden the ground, and then mix cement, lime, and other solidifying agents into the surface layer to an appropriate depth to increase the strength of the soil. Furthermore, methods such as covering it with a thick layer of gravel or mountain soil have been used. However, this method also requires a long period of time for it to solidify on the ground at the reclaimed site, so in recent years, methods have been adopted such as mixing cement, lime, etc. with the dredged bottom mud to improve the strength of the soil before reclamation, or mechanically dewatering. Methods of processing and disposing of it in a landfill are also being considered. Mixing solidification agents such as cement and lime with the bottom mud to stabilize the soil before disposing of it in a landfill is also effective in preventing the elution of heavy metals and other harmful substances when the bottom mud contains them. In this way, conventional methods for treating bottom mud include simply discarding the bottom mud, using a solidifying agent to stabilize the soil quality, or at the same time removing harmful substances from the bottom mud in a stable form that is insoluble in water. It concerned disposal methods for landfilling, such as methods for converting the materials into solid waste. In any case, in order to remove and dispose of a large amount of bottom sludge, a disposal site is required to receive it. Even if bottom sludge is to be disposed of in a landfill, it is necessary to secure a larger area of landfill space than can accommodate the bottom sludge, as solidification materials and new mountain soil are added to the bottom sludge. In other words, even if the removal of bottom sludge is desperately desired, the current situation is that unless a disposal site can be secured, the bottom sludge cannot be removed, and therefore environmental purification is slow to progress. In view of the above-mentioned conventional bottom mud treatment, the present invention provides an effective solidification treatment of bottom mud, in particular, enables solidification by the components contained in the bottom mud itself without requiring solidification of cement, etc. The purpose is to provide a processing method that drastically reduces the Another object of the present invention is to recycle and recycle solidified materials. The present invention involves drying the bottom mud deposited on the bottom of rivers, lakes, marshes, sea areas, etc., granulating it into a spherical shape, etc., and firing the granulated product at a temperature of 950°C to 1250°C to form a granular solidified product. The gist of this paper is a method for treating bottom sludge, which is characterized by obtaining sludge. The bottom sludge treatment method of the present invention consists of the steps of drying, granulation, and firing, which will be explained below. (1) Drying process During dredging, the dredged bottom mud is dried until it can be turned into a fine powder after removal of bulky debris and other contaminants. This drying may be done by either solar (natural) drying or forced mechanical drying such as an electric drying oven or a fluidized fluid dryer (utilizing kiln waste).
Furthermore, in order to make the drying process more efficient, the dredged bottom mud can be dehydrated using a mechanical dehydrator or the like to lower the water content before drying. (2) Granulation process The powdered bottom mud material is then molded into spheres, charcoal, rods, and other granules. As the granulation method, various methods such as dish granulation, extrusion granulation, briquette granulation and others can be used.
To give an example of 2 and 3, for example, in the case of dish-type granulation, water is sprayed onto the powder raw material using a dish-type granulator, and in the case of extrusion granulation, water is removed by a press molding machine. Extrude and granulate the raw material moistened to about 30%. When making a rod-shaped product into a spherical shape, it is further shaped using a dish-type granulator. Dry and powdered bottom mud is mostly fine particles such as clay and silt, and since it also contains organic matter, it can be easily granulated simply by adjusting the moisture content without using a binder. The thus formed granules are dried naturally or in a dryer to adjust the moisture content to such an extent that the granules do not fuse together or collapse during the firing process. It is usually dried to a moisture content of 15% or less. (3) Firing process Next, the granules are fired in a firing furnace such as a rotary kiln at a maximum temperature of 950°C to 1250°C. By this firing, the granules are fused (sintered) and a granular solidified product can be obtained. Since the bottom mud contains organic matter, the surface of the sintered granular solidified material tends to become porous due to foaming. However, sintering is good. Maximum firing temperature is 950℃
When it descends, the granular solidified material obtained is sintered, but the organic matter in the bottom mud is carbonized and remains inside for a while. Also, it is insufficient in strength to be used as aggregate. When the maximum temperature exceeds 1250°C, sintering of the resulting solidified particles progresses, causing the solidified particles to fuse together or partially collapse. The firing process can be performed in multiple stages to prevent excessive foaming during sintering. for example,
The first stage of firing is performed at a maximum temperature of about 950°C and by blowing air to promote the firing and gasification of organic matter in the granules and prevent rapid foaming. Baking at 1100℃~1250
Bake at ℃. This method can reduce voids in the granular solidified product after sintering and produce a product with high specific gravity and strength. Thus, the granular solidified material obtained by the method of the present invention is sufficiently sintered, insoluble in water, and does not elute harmful substances at all, and has a strength superior to that of natural aggregates such as gravel and slag. Although it is not as strong as these aggregates, it has a stable strength that can be used as a substitute for those aggregates. In the method of the present invention, the ability to produce such artificial aggregate using only bottom mud as a raw material is due to the soil fine particles of bottom mud and its mineral and chemical composition. Next, in order to understand the present invention, the results of experiments on bottom sludge treatment of Lake Kasumigaura and the results of aggregate application tests using the method of the present invention will be explained. The Kasumigaura mud used in the treatment experiment was dredged and then drained, with a water content of 150 to 300% and a plasticity content of 150 to 300%.
It has a content of 41 to 63%, and its chemical and mineral compositions are shown in Table 1.

[Table] As is clear from Table 1, the loss on ignition was approximately 17%, and it can be concluded that this sample contains a large amount of combustion and decomposition components such as organic substances. In addition, the mineral composition is quartz, feldspar,
It is broadly classified into clays, and it can be assumed that clays contain carrion as a main component and are relatively large in quantity. Experimental Example 1 After drying the bottom mud in the sun, it was pulverized to a powder state, and then granulated using two methods: dish granulation and extrusion granulation. Dish-type granulation was performed by spraying water on the finely powdered raw material using a dish-type granulator to granulate the material to a diameter of about 10 mm.
On the other hand, in extrusion granulation, raw materials with 30% moisture content were granulated using an extruder to a diameter of 5 mm and a length of about 10 mm, and then shaped and granulated using a dish-type granulator. Next, the granules were naturally dried indoors until the moisture content was about 10% or less.
Next, transfer the granules to a rotary kiln (diameter 40cm, length
700cm). As a result of preliminary experiments, it was found that the raw material for firing was extremely foamable, so as a means of suppressing foaming, the rotary kiln was set to a two-stage firing condition, and the maximum temperature inside the furnace was set at 950°C ( 600℃) at the bottom of the furnace, and cooled once after firing while blowing air.
The granules were fired under two conditions with a maximum temperature in the furnace of 1130°C and 1170°C (600°C at the bottom of the furnace) without blowing stage firing air. In the first stage firing, a granular solidified product with considerable strength was obtained. However, when the granular solidified material is broken down, some carbonized portions of organic matter remain, and its strength is much lower than that of aggregates such as stone and gravel. In the second stage firing, it was possible to obtain a granular solidified material that was sufficiently fired without containing carbides and had a strength comparable to that of slagstone or gravel. Tables 2 and 3 show the results of the particle size test and aggregate test of the granular solidified material obtained by firing. For comparison, the results of a similar test on river gravel (from Sagami River) with approximately the same particle size are also shown in Tables 2 and 3.

[Table] * The coarse particle ratio of river gravel is determined by sieving to match the artificial aggregate.

[Table] This shows that even at the same firing temperature, different granulation methods have a significant effect on physical properties such as specific gravity, water absorption, and compression strength. This is because the bottom mud raw material has foaming properties as mentioned above.
It is thought that the differences in internal and external conditions of the raw material during granulation greatly influenced the physical properties of the raw material after firing. In other words, since extrusion granulation is granulated under pressure, the density of the surface of the raw material increases, and even if the firing temperature is increased, the organic matter contained is less likely to dissipate to the outside of the solidified raw material as CO ₂ gas, which reduces the tendency for foaming. This seems to be because it increases. On the other hand, in dish-type granulation, the raw material is grown and granulated while spraying the powder raw material and water onto the fine particles, so many pores are generated on the surface of the granule, and the surface of the granule becomes viscous during firing. It is thought that before reaching the indicated temperature, much of the carbon content dissipated as CO ₂ gas and became a solidified product with high specific gravity, low absorption rate, and high compression strength value. Next, Table 4 shows the results of a toxic metal elution test performed on the granular solidified product obtained by the above firing. As a result, it was confirmed that the granular solidified material becomes harmless after firing.

[Table] The above granular solidified material is cement concrete,
Mixed with asphalt concrete, etc., road paving,
It can be used as an artificial aggregate for buildings, etc. Next, we will explain the aggregate application test for cement concrete and asphalt concrete. (1) Application test to cement concrete (1) Materials and equipment used (a) Cement: Ordinary Portland cement (b) Fine sand: Made from Sagami River, specific gravity 2.63 FM3.33 (c) River gravel for comparison: Made from Sagami River (d) Mixer: Forced kneading mixer (2) Specimen dimensions (a) Specimen dimensions for strength testing Both compression and tensile strength tests φ10 x 20 cm (b) Dry compression dimensions: 10 x 10 x 50 cm Measurement method: Dial gauge method (3) Curing and test methods (a) Strength test After concrete was placed, it was left at room temperature at 20℃, and after being removed from the mold two days later, it was cured in a water tank at 2±1℃ to the age of each material. (b) Drying shrinkage and weight loss test The next day after concrete was poured, the mold was removed and the first
After measurement was carried out twice, the joint specimen was cured in water at 21 ± 1 °C and the age of the specimen reached 7 days.
The pieces were stored in a room with a temperature of ±3% until each age, and changes in length and weight were measured. (c) Mixing of concrete As shown in Table 5, the mixing of concrete is based on the unit cement amount, unit water amount, and s/ The formulation was such that a was kept constant.

[Table] Table 6 shows the general properties of fresh concrete and hardened concrete.

[Table] According to the results, it can be seen that the dish-shaped granulated aggregate of Test No.-1 had the smallest slump of 8.8 cm, and the extrusion granulation of Test No.-2 had the largest slump. This is thought to be due to the fact that the aggregate had many surface cracks when it was granulated in a dish type at a firing temperature of 1170°C, and the cement paste in the concrete was used to fill in the cracks during mixing, resulting in smaller slump. In addition, in terms of compressive strength, it shows the same strength development rate as river gravel concrete even after a long period of age, but in terms of tensile strength, it shows a lower strength than river gravel concrete, although there are fluctuations between ages. There is. The drying shrinkage and weight loss rate are shown in Table 7. In particular, the drying shrinkage is uniformly smaller than river gravel concrete, but this is because the aggregate absorption rate is higher than river gravel. This is because, in a dry state, water is gradually released, reducing shrinkage.

[Table] (2) Application test to asphalt concrete We report an example of a mixing test for using the granular solidified product obtained by firing as the main aggregate of a heated asphalt mixture. Materials used (a) Powder and sieve fired aggregate 10 to 5
The particles were classified into particle sizes of mm, 5 to 2.5 mm, and 2.5 to 0.074 mm. (b) Coarse sand and fine sand are from Tochigi, Chiba sand, and
The stone powder used was from Chichibu. (c) Asphalt used was Mitsubishi Oil Straight Asphalt 60-80. Composition of heated asphalt mixture (a) Type of heated asphalt mixture Particle size of dense asphalt concrete (b) Mixing ratio Burnt aggregate 10-5 mm 35 Weight ratio 〃 5-2.5 mm 22 〃 〃 2.5-0.074 mm 20 〃 Coarse sand 8 〃 Fine sand 9 weight ratio stone powder 6 〃 (c) Amount of asphalt added (relative to aggregate) 5.5, 6.0, 6.5, 7.0, 7.5 and 10.0% by weight Test method Marshall of Asphalt Paving Guidelines (published by Japan Road Association) According to the stability test method. Results (a) Comparison of properties of calcined aggregate with aggregates used in general asphalt mixtures

【table】

[Table] As seen from Table 8, calcined aggregate has a lower specific gravity than general slag. b High water absorption. In particular, the amount of absorption of pulverized calcined aggregate is large. (b) Marshall stability test results Table 9 shows the test results of dense-grained asphalt concrete using aggregate used in general asphalt mixtures and the standards stipulated in the asphalt pavement guidelines for comparison. Values are also listed.

[Table] a Asphalt using calcined aggregate has a lower density and lower stability than asphalt using general aggregate, but the stability exceeds the standard value so there is no problem, but the porosity is large and the asphalt is saturated. The degree is smaller than the standard value. b In the conventional mix design, asphalt was absorbed into the aggregate over time after the mixture was prepared due to the high absorption rate of the fired aggregate, which caused problems in determining the optimum amount of asphalt. This is because the fired aggregate is pulverized into spherical particles, making the surface more porous and absorbing more asphalt, thus requiring an extra amount of asphalt. Therefore, it is necessary to pave the mixture as soon as possible after producing the mixture, for example, within about 2 to 3 hours after mixing. For asphalt concrete, these problems can be solved by creating aggregate with rich ridges during firing. The test results show that it can be fully used for pavements below simple pavements that do not have severe technical requirements. As is clear from the above applied tests, according to the bottom mud treatment method of the present invention, the bottom mud can be effectively treated to render it harmless, and the granular solidified product obtained by granulation and firing can be used as an artificial aggregate. It can be recycled and recycled as well as natural and artificial aggregates.

Claims (1)

[Claims] 1 A process of drying the bottom mud deposited on the bottom of rivers, lakes, and sea areas, and then granulating it into spherical or other shapes, a process of drying this granulated product to a moisture content of 15% or less, and a process of drying this dried granulation. A first firing process in which the product is fired in a firing furnace while blowing air while setting the maximum temperature in the furnace to 950℃, and a granulated product after this first firing process is heated to the maximum temperature in the furnace without blowing air. 1100℃~1250
A method for treating bottom sludge, which comprises obtaining a granular solidified product through a second firing step of firing at a temperature set at ℃.