JP2001335778A - Soil improver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a soil improver giving a high rate of an exothermic reaction accompanying solidification by water absorption when it is brought into contact with water. SOLUTION: This soil improver contains a calcined gypsum whose flake crystals are laminated in layers to form a needle-like particle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soil conditioner capable of adding sludge containing a large amount of water and solidifying the sludge so that the sludge can be reused.

[0002]

2. Description of the Related Art Conventionally, as an effective use of sludge such as mud and mud discharged in construction work and dredging work, it has been proposed to solidify the sludge and use it for landfill. As a solidifying agent for solidifying sludge, cement and a cement-based solidifying agent are widely used. Also,
Some also use lime-based solidifying agents. Cement and cement-based solidifying agents are inexpensive, but when mixed with mud, it takes about three days to solidify, and it is necessary to secure a wide area for solidification. Furthermore, the solidified product obtained using cement or a cement-based solidifying agent exhibits an alkaline pH of 9.0 or more, and the landfill site is limited. On the other hand, although the lime-based solidifying agent can shorten the solidification time compared to the cement-based solidifying agent, it generates a large amount of heat during solidification,
The environment around the workplace deteriorates due to odor. Furthermore, as in the case of the cement-based solidifying agent, it exhibits alkalinity with a pH of 9.0 or more, and the landfill site is limited. In recent years, a solidified material using gypsum as a main raw material has been announced, but it is not suitable for treating soil where harmful hydrogen sulfide is generated, and it may become a source of hydrogen sulfide depending on the situation when reclaimed. There is.

[0003]

SUMMARY OF THE INVENTION The present invention overcomes the problems of the prior art and provides a soil conditioner having a high rate of an exothermic reaction accompanying solidification of water upon contact with water.

[0004]

Means for Solving the Problems The present inventors have found that flaky gypsum crystals are stacked in layers to form a single particle, and the flaky laminated gypsum having a needle-like particle shape is in contact with water. The rate of the exothermic reaction accompanying the solidification of water absorption when it is made is high, and the soil conditioner characterized by containing it is quickly solidified when added to sludge containing a large amount of water, and reclaims and refills the sludge. And so on. Furthermore, they found that when this calcined gypsum contained an iron compound, it was possible to treat hydrogen sulfide, and completed the present invention.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a soil conditioner characterized by containing flaky gypsum in which flaky crystals are stacked in layers to form one particle and the shape of which is acicular. is there. In the present invention, calcined gypsum is a compound whose main component is represented by hemihydrate gypsum (chemical formula CaSO ₄ .0.5H ₂ O) and / or type III anhydrous gypsum (CaSO ₄ ), and a part of dihydrate gypsum ( CaSO ₄ .2H ₂ O) and / or type II anhydrous gypsum (CaSO ₄ ) may be included.

[0006] The flaky laminated gypsum contained in the soil conditioner of the present invention is formed by stacking flaky crystals in a layer to form one particle, and has a needle-like shape. It is considered that as a result, the rate of the exothermic reaction accompanying the solidification of water absorption upon contact with water increases. The flaky laminated gypsum particles have a specific surface area of 2 m ² / g to 70 m
² / g, and it is preferable to suppress suspended particles.
In terms of working environment, more preferably 6m ² / g~30m ² /
g. Commonly used calcined gypsum is natural gypsum or excreted gypsum, but these have a slower heat generation rate due to water absorption and solidification even when the hydration start time is equal to that of lamellar laminated gypsum. The hydration start time was slow and the solidification time was long. Therefore, in order to give the soil improvement treatment ability equivalent to that of the soil improvement agent of the present invention, it is necessary to add a heat generating substance to promote solidification or to increase the size of the treatment equipment, both of which are factors that increase costs. .

[0007] The laminated flaky gypsum contained in the soil conditioner of the present invention preferably contains an iron compound. Although the solidification rate is slightly delayed due to the inclusion of iron compounds, when mixed with soil where harmful hydrogen sulfide is generated, the iron compounds contained detoxify by absorbing and fixing hydrogen sulfide be able to. Examples of the iron compound contained include various compounds such as iron oxide hydroxide, iron oxide, and iron hydroxide. Further, the preferable content of the iron compound is 0.2 to 0.2 as Fe ₂ O _{3 based on} the weight of calcined gypsum.
It is 50% by weight, preferably 0.6 to 30% by weight, more preferably 0.6 to 10% by weight in terms of solidification rate, and more preferably 10 to 10% by weight in terms of treating hydrogen sulfide.
To 50% by weight, more preferably 30 to 50% by weight. Further, as a secondary effect, by using the solidified material obtained by the solidification treatment for landfill, a favorable result can be obtained for the growth of organisms in the soil.

The laminated flaky gypsum contained in the soil conditioner of the present invention is obtained by adding neutralized lime to sulfuric acid containing iron, for example, used sulfuric acid generated from a process of producing titanium oxide by a sulfuric acid method to neutralize it. The gypsum can be produced by a method including a first step of obtaining gypsum, and a second step of obtaining dehydrated gypsum by heating and dehydrating the obtained dihydrate gypsum using, for example, a rotary kiln, a flat-bed furnace, and a fluidized-bed furnace.

[0009] The heat dehydration temperature is preferably 97 ° C to 25 ° C.
It is 0 degreeC, More preferably, it is 110 to 190 degreeC. The heating and dehydrating time is desirably set so that the water adhering to the gypsum is completely dehydrated and the crystallization water is dehydrated in a required amount.

[0010] The soil conditioner of the present invention contains a large amount of moisture because flake crystals are stacked in layers to form one particle, and contains flaky gypsum in the form of needles. When added to sludge to be produced, for example, construction sludge, dredging sludge, etc., it can be quickly solidified and the soil can be reused.

The content of the lamellar gypsum in the soil conditioner of the present invention can be appropriately set depending on the type of sludge to be treated, but is usually 20 to 100% by weight based on the weight of the soil conditioner. , Preferably 30 to 99% by weight, more preferably 50 to 90% by weight.

Further, the soil conditioner of the present invention includes fly ash, bentonite,
It is preferable to appropriately contain an aluminum compound and silicon dioxide.

[0013] By incorporating fly ash and / or bentonite into the soil conditioner of the present invention, a large amount of water is absorbed at the beginning of mixing, which has the effect of facilitating the handling of sludge. Further, fly ash and / or bentonite have an effect of increasing hydrated crystals such as ettringite by reacting with flaky gypsum to increase solidification strength by increasing water absorption. Fly ash is also called coal ash and is generated by burning coal in a boiler of a thermal power plant. Bentonite is an ultra-fine clay made by decomposing the glassy part of volcanic ash. The chemical composition is not constant and contaminates lime, feldspar, mica, sulfur ore and the like. The content of fly ash and / or bentonite is 5 to 50% by weight based on the weight of the soil conditioner.
Is more preferable, and 10 to 30% by weight is a more preferable range.

By including an aluminum compound in the soil conditioner of the present invention, the solidification reaction can be further promoted because the aluminum compound reacts with water and generates heat. When the soil improver of the present invention contains an aluminum compound and an alkali component such as fly ash, the neutralization can be maintained because the aluminum compound serves as a neutralizing agent. As the aluminum compound, a heat-generating compound such as aluminum alum or aluminum sulfate is used. In addition, from the viewpoint of reducing the production cost, an inexpensive industrial by-product containing reactive aluminum can be used. The content of the aluminum compound is preferably in the range of 1 to 40% by weight, more preferably 1 to 10% by weight, based on the weight of the soil conditioner.

By incorporating silicon dioxide into the soil conditioner of the present invention, it is possible to prevent the solidification of the sludge and the solidifying agent partially, and to solidify the whole uniformly. Silicon dioxide is also called silicic anhydride or silica.
As the material containing silicon dioxide, for example, silica balloon, colloidal silica, shirasu, shirasu balloon and the like are used. In addition, from the viewpoint of reduction in production cost, inexpensive industrial by-products such as foundry sand containing a large amount of silica and incinerated ash from papermaking sludge can be used. The content of silicon dioxide is preferably in the range of 1 to 10% by weight, more preferably 1 to 5% by weight, based on the weight of the soil conditioner.

As the soil conditioner of the present invention, known gypsum, lime, cement, organic absorbent and the like can be used in combination within a range not to impair the object of the present invention. When each of lime and cement is used alone, the soil after use exhibits alkalinity.
However, by using in combination with the soil conditioner of the present invention, the soil after use becomes neutral over time,
It will be recyclable. When the organic absorbent is used alone, the soil strength after use is insufficient. However, when used in combination with the soil conditioner of the present invention, the soil after use has increased strength and can be recycled.

[0017]

The present invention will be further described with reference to the following examples, which do not limit the present invention.

EXAMPLES 1-3 Sulfuric acid method Spent sulfuric acid generated from the process of producing titanium oxide was neutralized by adding lime milk to obtain gypsum and calcined at 120 ° C. for 1 hour in a fluidized-bed furnace. A flaky laminated gypsum (sample a) was obtained. The BET specific surface area value of sample a is 10 m ² / g
The components are 61% by weight of type III anhydrous gypsum, gypsum hemihydrate 3
It was 6% by weight and 2% by weight gypsum. Further, the content of the iron compound was 1% by weight as Fe ₂ O ₃ . In addition, FIG. 1 shows an electron micrograph showing the particle shape of the lamellar calcined gypsum (sample a). Flake laminated gypsum (sample a),
Table 1 shows incinerated ash containing a large amount of calcined alum as an aluminum compound and silica as silicon dioxide.
The soil improving agent of the present invention (Sample A,
B and C) were obtained.

[0019]

[Table 1]

Comparative Examples 1 to 3 Each of natural gypsum, waste gypsum and phosphate gypsum was mixed in a fluidized furnace for 1 hour.
The calcined gypsum of the comparative sample was obtained by baking at a temperature of 20 ° C. for 1 hour (samples D, E and F). Table 2 shows the composition of Samples D, E and F.
Shown in FIG. 2 shows an electron micrograph showing the particle shape of Sample D.

[0021]

[Table 2]

Comparative Examples 4 and 5 Slaked lime and cement were used as comparative samples (samples G and H).

Evaluation 1 Sludge generated at a quarry factory (dry basis water content 30%, pH
About 7.5), the water content was adjusted as shown in Table 3, and the soil conditioner of the present invention (sample A) was added. Immediately after the addition, mixing was carried out. It was left for one day, and the obtained solid was tamped. Table 3 shows the cone index of the obtained solidified product after one hour. P of the solid
When H was measured, all were in the neutral range of pH 7.3 to 7.7. As the pH test method, a soil pH test method (JSF T 211-1990) based on the Japan Society of Geotechnical Engineers was used. The addition, mixing, standing, and measurement were all performed in a constant temperature room. Mixing was performed using a soil mixer for 5 minutes. Indoor conditions of constant temperature room are temperature 20 ℃, humidity 60% R
H.

[0024]

[Table 3]

The sludge usually generated at a quarry has a moisture content of 30% on a dry basis. In order to satisfy the corn index of 200 kN / m ² or more, which is the industrial waste regulation value, only 2% by weight of the soil conditioner of the present invention (sample A) is sufficient. Add water to reduce sludge moisture content to 60
%, The addition amount of 5% by weight is sufficient to satisfy the above-mentioned industrial waste regulation value. This addition amount is equivalent to the addition amount of the cement or the lime-based solidifying agent.
Furthermore, the soil conditioner of the present invention has the advantage of maintaining the pH at a neutral level, and is considered to be advantageous because the use of recycled sludge after solidification is widened.

Evaluation 2 Mud generated at the dredging site of the pond (dry basis water content 100
%, PH 7.5), as shown in Table 4, 1 m of sludge
³ was added each predetermined amount soil improvement agent (Sample A) and hydrated lime (Comparative Sample G) per the present invention, and mixed and immediately after the addition, then after removal from the mixer, allowed to stand for one day in a thermostatic chamber to obtain The solidified product was tamped and cured for 7 days, and the uniaxial compressive strength and pH were measured. Table 4 shows the results. The addition, mixing, standing, and measurement were all performed in a constant temperature room. Mixing was performed using a soil mixer for 5 minutes. Indoor conditions of constant temperature room are temperature 20 ℃, humidity 60% RH
Met.

[0027]

[Table 4]

The soil conditioner of the present invention (sample A) was added in an amount of 1
200 kg in the case of slaked lime (comparative sample G) at 00 kg / m ³
It was found that a uniaxial compressive strength almost equivalent to the amount of kg / m ³ was exhibited. Further, although the strength does not change even when the added amount of slaked lime is increased, the unconfined compressive strength of the soil conditioner of the present invention dramatically increases with the added amount, and the added amount is 20%.
At 0 kg / m ³ , it was found to exhibit a uniaxial compressive strength of 75 kN / m ² . This is because the soil conditioner of the present invention takes up the surrounding soil while reacting with the water in the sludge and solidifies, so that the strength increases as the added amount increases, but in the case of slaked lime, it reacts with the water in a short time It is considered that the strength does not increase unless a long period of one month or more is required. As for the pH, it was found that slaked lime exhibited high alkali, whereas the soil conditioner remained neutral.

Evaluation 3 Mud generated at the construction site (dry basis water content 60%, pH
8.0), as shown in Table 5, 20% by weight of the soil conditioner of the present invention (Sample C) and 7% by weight of cement (Comparative Sample H) were added to the sludge, and mixing was performed immediately after the addition. Then, after taking out from the kneading machine, in order to prevent evaporation of water, it is sealed in a plastic bag and left in a constant temperature room, and the obtained solidified product has a cone index of 1 hour, 3 days and 1 week later,
The pH was measured after 1 hour, 3 days and 1 week. Table 5 shows the results. The addition, mixing, standing, and measurement were all performed in a constant temperature room. Mixing was carried out using a soil mixer until solidification was visually confirmed. The room conditions of the constant temperature room were a temperature of 20 ° C. and a humidity of 60% RH.

[0030]

[Table 5]

[0031] The second, widely used range specified by the Ordinance of the Ministry of Construction
When the cone index of the seed-improved soil is 800 kN / m ² as a standard after 3 days of solidification, the soil conditioner of the present invention (sample C) approaches the target value from 1 hour after solidification and does not change much after 1 week. For cement, the target value will be close to the target in three days, but it will rise too much in one week. This implies that re-excavation is often used to use the improved land, but in that case, re-excavation becomes difficult on land using cement, and the problem of high cost of re-use occurs. Suggests. On the other hand, since the land using the soil conditioner of the present invention can be easily excavated, it is considered to be advantageous for the construction of land reuse.

Evaluation 4 Mud generated at the construction site (dry basis water content 30%, pH
Regarding 7.5), the soil conditioner of the present invention (Sample B), natural gypsum (Comparative Sample D), waste gypsum (Comparative Sample E) and phosphate gypsum (Comparative Sample F) were each added to sludge by 20% by weight. The mixture was mixed immediately after the addition, and then taken out of the kneader, and then left in a constant temperature chamber. The corn index of the obtained solidified product after 30 minutes and 1 day, and the pH after 30 minutes and 1 week were measured. did. Table 6 shows the results. The addition, mixing, standing, and measurement were all performed in a constant temperature room. Mixing was carried out using a soil mixer until solidification was visually confirmed. The room conditions of the constant temperature room were a temperature of 20 ° C. and a humidity of 60% RH.

[0033]

[Table 6]

Sample B is the soil conditioner of the present invention containing only lamellar gypsum, but it was found that the solidification time was shortened by half to one third as compared with the calcined gypsum of the comparative sample. When sludge is treated using a mixing device, work such as backfilling can be performed immediately without having to take a long residence time and being cured at the outlet of the device without curing. Therefore, an excellent effect can be exhibited in that the on-site work can be performed more efficiently and economically. The soil conditioner containing only the lamellar calcined gypsum of the present invention (sample B)
The corn index after 30 minutes is higher than that of the calcined gypsum of the comparative sample.
After a day, the difference was found to widen further.
This is because the lamellar laminated gypsum constituting the soil conditioner of the present invention forms one particle in a laminar state of flaky crystals, so that the effective area for reacting with moisture increases, so that the solidification reaction Is faster and the strength is considered to have increased.

Evaluation 5 Onions were ground and mixed with mud generated at the port dredging site,
The created hydrogen sulfide generating mud (dry basis moisture content 110%,
pH 8.3), the soil conditioner of the present invention (Sample B) and phosphogypsum (Comparative Sample F) were each added to the sludge in an amount of 20% by weight, mixed immediately after the addition, and then taken out of the kneading machine. And sealed in a glass container, left in a thermostat, and measured the hydrogen sulfide concentration after 3 days and 1 week in the glass container. Mixing was performed using a soil mixer for 5 minutes. The room temperature of the constant temperature room is 35 ° C.
Humidity was 60% RH. The concentration of hydrogen sulfide was measured by using a detector tube having a scale range of 2 to 20 ppm and aspirating 100 cc for 1 minute.

[0036]

[Table 7]

In the case where no soil conditioner was added and the case where Comparative Sample F was added, the concentration of hydrogen sulfide increased with the passage of time, whereas the soil conditioner of the present invention (sample B) was added. It was found that those did not generate hydrogen sulfide. This is considered to be because the iron compound contained in the laminated flaky gypsum constituting the soil conditioner of the present invention reacts with hydrogen sulfide to be stabilized as iron sulfide. This can suppress the generation of hydrogen sulfide in mud generated on site, which is advantageous for work environment conservation.

[0038]

As described above, the soil conditioner of the present invention contains flaky gypsum, which has a high rate of exothermic reaction due to water absorption and solidification upon contact with water, and thus was added to soil containing a large amount of water. In this case, since the solidification proceeds quickly, a large place for solidification is not required, and the workplace can be used effectively. In addition, for all kinds of sludge, the soil after soil improvement using the soil improvement agent of the present invention is neutral and has soil strength that can be recycled immediately. Available. Further, when the soil conditioner of the present invention containing the flaky laminated gypsum containing an iron compound is used in soil that generates hydrogen sulfide, its generation can be suppressed, which is advantageous for work environment conservation.
Furthermore, it is suitable for growing organisms in soil after soil improvement.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (1,000-fold magnification) showing the particle shape of sample a.

FIG. 2 is an electron micrograph (magnification: 500 times) showing the particle shape of Comparative Sample D.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // C09K 103: 00 C09K 103: 00

Claims (7)

[Claims] 1. A soil conditioner comprising flaky gypsum in which flaky crystals are stacked in layers to form one particle, and the particle shape is acicular. 2. The soil conditioner according to claim 1, wherein the laminated flaky gypsum contains an iron compound. 3. The total amount of the laminated flaky gypsum in which the content of the iron compound is reduced.
Fe to quantity₂O ₃0.2 to 50% by weight as
The soil conditioner according to claim 2, wherein: 4. A thin laminated calcined gypsum 2m ² / g~70m ² /
The soil conditioner according to claim 1, having a specific surface area of g. 5. The soil conditioner according to claim 1, further comprising fly ash and / or bentonite. 6. The soil conditioner according to claim 1, further comprising an aluminum compound. 7. The soil conditioner according to claim 1, further comprising silicon dioxide.