JPS6219919B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention applies to so-called sludge, such as sludge deposited on the bottom of rivers and sea areas, sedimentation tank sludge drained from water and sewage water purification facilities, and waste sludge generated during construction work. Landfill materials, embankment materials, and roadbeds that are easy to handle, have good workability, have excellent filling properties, and have solidifying properties after filling, by adding and mixing cement-based solidifying agents and quicklime that has an extremely slow digestion rate. The present invention relates to a method for producing granular soil from sludge for the purpose of obtaining civil engineering materials such as raw materials.

In conventional technology, when granulating sludge by mixing cement and quicklime, a curing period is required for the sludge to gain a certain degree of strength due to the caking effect of the solidifying agent such as cement, and the sludge is hard to digest. If the reaction proceeds rapidly, the solidified sludge cannot be granulated because the quicklime will self-destruct due to expansion due to the digestive reaction. Therefore, it is necessary to suppress the start of the digestive reaction of quicklime, so methods are used to increase the particle size and relatively reduce the specific surface area, thereby reducing the contact area with water. However, in this case, if the mixing ratio (weight ratio) of quicklime is the same, the distribution of quicklime particles in the compacted soil will be coarser as the particle size increases, and granular soil will also be caused by self-collapse due to the digestion reaction. It also forms large clumps.

On the other hand, in order to make the particle size of granular soil similar to that of sand, it is necessary to reduce the particle size of quicklime so that it is densely distributed in the compacted soil. Reducing the particle size of quicklime inevitably increases the rate of digestion, and also requires stirring using a mixer to even out the distribution of quicklime particles, so conventional methods using cement and quicklime Therefore, it is almost impossible to obtain shaped soil from sludge. Therefore, the method currently used to obtain granular soil is to mechanically crush sludge sufficiently solidified with a solidifying agent using a crusher or the like.

Furthermore, most of the sludge granular soil produced by conventional methods has already been consolidated, and even if it is backfilled or compacted, there is almost no consolidation effect afterward, so it cannot be considered an effective civil engineering material. .

This invention was made to eliminate the drawbacks of the conventional method, and will be explained in detail as follows.

First, a simplified example of an apparatus for mixing cement solidifying agent and quicklime with sludge is shown in FIG. 1. Slurry pumps P ₁ and P ₂ pump the sludge in container 1 and the solidifying agent in container 2, respectively.
Accordingly, the mixture is mixed by a mixer M through the respective flowmeters F ₁ and F ₂ , and granular quicklime is dropped and scattered onto the sludge layer from a hopper 3 opened near the outlet of the mixer M, and processed by a belt conveyor 4. Transfer to soil curing box 5.

Here, it is desirable that the solidifying agent has a rapid solidifying rate, while the quicklime has a slow digesting rate. Therefore, use early-strengthening cement as the hardening agent, or
Alternatively, ordinary cement to which cement setting accelerators such as sodium sulfate, sodium carbonate, and calcium chloride are added is often used. In addition, quicklime is generally made by firing at 900 to 1200℃, but in order to reduce the digestion rate, the particle size is large (preferably 5 to 10 mm diameter) and it is produced at a particularly high temperature in a vertical kiln using co-fired coke. for a long time (for example
1200-1500℃, 24hr) Calcined carbide quicklime is preferable. The surface of this kind of carbide baked quicklime is in a molten state and the specific surface area is significantly reduced, so it has excellent digestion retardation properties.However, in order to further increase the delay effect, it is necessary to use carbide baked quicklime grains. Coat the surface with light oil, kerosene, heavy oil, polyvinyl alcohol, etc. by dipping or spraying, or spray acid gas such as carbon dioxide, sulfur dioxide, or hydrochloric acid gas to coat the surface with calcium carbonate, calcium sulfate, A layer of calcium chloride, etc. is formed.
In addition, treating curing granular soil with acid gas has the effect of preventing calcium oxide or calcium hydroxide from leaching out by rainwater, etc., resulting in highly alkaline wastewater when used as a civil engineering material. It also has

If sludge is mixed in advance with a solidifying agent that has a high solidifying rate as described above and has a certain degree of strength, then if quicklime grains that have a slow digesting rate are mixed in without forced mixing, the solidifying agent and sludge can be mixed. As the solidification progresses, the digestive reaction of the quicklime grains, which have kept their original shape, gradually progresses, causing the quicklime grains to gradually expand and eventually self-disintegrate.As a result, the solid matter itself becomes moderately large. It can be crushed into civil engineering materials that are easy to handle, have good workability, and have excellent filling properties. In addition, since self-disintegrating quicklime is contained as slaked lime after the digestion reaction, it causes a pozzolanic reaction with the clay components contained in the sludge and reconsolidates, so the strength after compaction continues to increase. , exhibits extremely effective properties as a civil engineering material.

As described above, in the conventional solidification treatment method, dredged sludge remains highly fluid, has extremely poor workability, and has various problems when dumping.
The main focus is on solving this problem, and even if it is reused as a civil engineering material, it is only a passive material such as a filling material, but this invention It is characterized by its emphasis on increasing bond strength and its active use as an effective civil engineering material.

If you mix a solidifying agent with the sludge and add quicklime granules to it and leave it for 2 to 24 hours, the quicklime will self-disintegrate during this time, and if you leave the curing period for another week, the strength of the granular soil will increase to 2. The strength increases to ~3Kg/ ^cm2 . However, if it is desired to shorten such a time lapse, a heating device may be appropriately installed in the process as illustrated in FIG. The heating device may be a commonly used dryer such as a ventilated band dryer, ventilated rotary dryer, fluidized bed dryer, ventilated shelf dryer, etc. that uses heavy oil, gas, other combustion gas, or steam as the heat source. It goes without saying that the use of solar drying is also extremely economical.

Next, examples will be given.

Example 1 Target sludge: Water treatment plant precipitated sludge Initial moisture content 750% Solidifying agent: Cement-based solidifying agent (mixture of cement and dihydrate gypsum) Quicklime: Hard burnt lime Solidified by weight ratio to target sludge Additive milk (solidifying agent: water = 2:1) to (1) 22.5% or (2) 26.0%
% added and mixed, and then 5% quicklime was added and air curing was performed for one week. During this time, the quicklime underwent a digestive reaction, and the expansion pressure at that time crushed the treated soil into granular soil. In order to know the applicability of this granular soil as a civil engineering material, a soil test was conducted according to the conventional method. The particle size distribution curve of the obtained granular soil is shown in Figure 2, and the γd-N curve is shown in Figure 3. In the figure,
The CBR-N curve is shown in Figure 4, the change in penetration resistance over time is shown in Figure 5, and the change in CBR value over time is shown in Figure 6. I found out that it works.

Note that the cumulative passage rate % shown on the vertical axis in Figure 2 is the weight percentage (%) of soil particles smaller than the soil particle when the particle size distribution of soil is displayed, and γd (dry Density) is the unit volume weight when considering only the weight of soil particles relative to the total volume of soil, and if the wet density of soil is γt and the water content ratio is W, then γd=100/W+100×γt The relationship holds true. In addition, the CBR value in Figure 4 refers to a piston with a diameter determined based on the California Beaving Ratio test (a type of penetration test called subgrade soil bearing capacity ratio test) (defined as 5 cm in JIS) on the surface of the specimen. When penetrated, it is the ratio of the pressure for a constant penetration amount and the pressure for standard material,
This is a numerical value that is widely used mainly in the design of flexible pavement such as subgrade soil and roadbed. Furthermore, the cone bearing capacity in FIG. 5 is the ground penetration resistance value when a rod with a cone at the tip is penetrated into the soil, and is a numerical value indicating the properties of the soil layer.

Example 2 Target sludge: Marine clay Initial water content 100% Solidifying agent: Cement solidifying agent Quicklime: Kerosene coating quicklime Add and mix 5% solidifying agent (cement: water = 2:1) by weight to the target sludge. Then, 5% quicklime was added and the mixture was cured in air or in a sealed container for one week, and the soil test was conducted in the same manner as in Example 1. The particle size distribution curve of the resulting granular soil is shown in Figure 7.
The γd-N curve is shown in Figure 8, and the CBR-N curve is shown in Figure 9.
As shown in the figure, just by looking at the results alone, it can be seen that this is an extremely excellent civil engineering material.

Example 3 Granular soil mixed and treated in the same manner as in Example 1 was mixed with exhaust gas from a gas furnace at around 100°C (combustion gas of commercially available propane gas in a cylinder) using an aerated rotary dryer to reduce carbon dioxide to about 15%. %, containing about 75% nitrogen gas and about 10% moisture and other substances) for about 10 minutes. After one day, a strength of 2 to 3 kg/cm ² was already obtained, and the soil test results were almost the same as in Example 1.

[Brief explanation of the drawing]

Figure 1 is a simplified diagram showing an example of an apparatus for producing granular soil from sludge, Figure 2 is the particle size distribution curve of Example 1, Figure 3 is the same γd-N curve, and Figure 4 is the same.
CBR-N curve, Figure 5 shows the change in penetration resistance value over time, Figure 6 shows the change in CBR value over time, and Figure 7 shows the change in CBR value over time.
The figure shows the particle size distribution curve of Example 2, and FIG. 8 shows the same γd-
The N curve and FIG. 9 are the same CBR-N curves. 1... Sludge container, 2... Solidifying agent container, 3...
Hopper, 4...belt conveyor, 5...curing box, _P1 , _P2 ...slurry pump, _F1 , _F2 ...flow meter, M...mixer.

Claims (1)

[Claims] 1. A mixture of sludge and cement or an early-strengthening cement-based solidifying agent added with a caking accelerator, which is then treated with cemented carbide or coated with an inorganic or organic material on the surface to improve the digestion rate. A method for producing granular soil from sludge, which is characterized by evenly dispersing and blending quicklime with extremely low carbon content. 2. The method for producing granular soil from sludge according to claim 1, characterized in that when the target sludge is sedimentation tank sludge, a mixture of cement and gypsum is used as a solidifying agent. 3. A method for producing granular soil from sludge according to claim 1, characterized in that consolidation is promoted by drying or heating and curing the granular soil. 4. The method for producing granular soil from sludge according to claim 1, which comprises blowing an acidic gas such as carbon dioxide gas or sulfur dioxide gas onto the surface of the granular soil.