JPH101667A - Semihydrated gypsum agent for improving water-containing soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject improving agent comprising semihydrated gyp sum as a main component and incinerated sludge ash as a subsidiary component, capable of shortening a time for preparing improved soil, also contributing to the recycling of sludges, excellent in safety, gas permeability, water permeabil ity and plant growability, and useful for solidifying water-containing soil to improve the soil. SOLUTION: This semihydrated gypsum agent used for improving water- containing containing soil and useful for solidifying the water-containing soil such as construction sludge to improve the soil comprises (A) semihydrated gypsum (CaSO4 .1/2H2 O)[e.g. the semihydrated gypsum obtained by thermally treating crystalline gypsum (CaSO4 .2H2 O) at a temperature of 100-160 deg.C] as a main component and (B) incinerated sludge ash (e.g. the ash obtained by incinerating sewage sludges) as a subsidiary component preferably in amounts of 60-80wt.% and 20-40wt.%, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel soil conditioner for hydrous soil. More specifically, the present invention provides:
The hydrous soil solidified as a main component hemihydrate gypsum _{(CaSO 4 · 1/2 H 2 O} ) to be used in order to achieve soil improvement, and the ash obtained by incineration of sludge such as sewage sludge by- The present invention relates to a semi-hydrated gypsum-based hydrous soil conditioner produced.

[0002]

2. Description of the Related Art A new sludge treatment technology has been established in light of recent severe pollution regulations. In the case of construction sludge, one example is the ban on marine dumping (illegal dumping), as well as the complete disposal of construction workers. The construction sludge mentioned above is a cone index confirmation test (JS
In F T 716), it is a sludge having a cone index of less than 2.0, which is slightly inaccurate but too soft to allow humans to walk with boots. On the other hand, the soil having a cone index of 2.0 or more is a soil having a hardness that can be walked by a human.

[0003] Construction sludge is generated in large quantities at construction sites in various places, and due to its properties, it is difficult to reuse it as it is. For this reason, construction sludge has been dewatered (dried) in its own storage yard, or landfilled in its own landfill, or transported to another landfill. And landfilled. In the process of transportation to another disposal site,
The current situation is that construction sludge spills and causes secondary pollution. However, under the recent severe pollution regulations, construction sludge cannot be disposed by the above-mentioned approach, that is, landfill disposal, and urgent measures are taken. In particular, construction sludge employs a shield method and a bentonite method as a method of constructing underground structures, and measures are urgently required in view of the large amount of sludge having a high PH value.

In the industry, the construction sludge is solidified,
A solidification technique of construction sludge has been proposed in which an improved soil having a cone index of 2.0 or more is used for landfilling (for backfilling) and the like in the same manner as the third or fourth kind of construction-generated soil. In the conventional solidification technology for construction sludge described above, the solidification agents, which are the cores of the technologies, are (1) cement-based solidification agents, (2) quicklime (CaO) -based solidification agents, and (3) synthetic polymer-based solidification agents. Agents (for example, Japanese Patent Application Laid-Open No. 4-345885, a water-soluble organic polymer having a carboxyl group and lime (Ca
O, CaCO ₃ ) has been proposed).

[0005]

The above-mentioned conventional soil conditioners (solidifying agents) have various disadvantages. For example, in the cement-based solidifying agent and the quick-lime-based solidifying agent of the above (1) and (2), although the construction sludge can be solidified, the solidification rate is slow or the PH of the solidified soil is low.
The value becomes a problem. That is, the solidifying agents (1) and (2) are strongly alkaline, and when the solidified soil is reused for landfill, highly alkaline leachate such as groundwater or rainwater after landfill is used in biological systems. Has a great adverse effect on

Further, the synthetic polymer-based solidifying agent of the above (3) is expensive, so that there is a problem in economical efficiency when solidifying a large amount of construction sludge. Further, the above
Since the synthetic polymer-based solidifying agent of (3) contains lime (CaO.CaCO ₃ ) as an essential component, it inherently contains the problem of alkalinity of solidified soil as described above.

The present invention has been made in view of the above-mentioned drawbacks and limitations of the conventional soil conditioner (soil hardener). Means for Solving the Problems The present inventors have intensively studied the improvement of conventionally proposed soil conditioners for construction sludge. In the examination process, the present inventors have determined that (i) gypsum (CaSO ₄ .2H ₂ O), or more correctly, gypsum dihydrate (crystal gypsum) is present in a natural soil system and is a non-polluting substance. , (ii) the gypsum _{(CaSO 4 · 2 H 2 O} ), more correctly, gypsum hemihydrate gypsum prepared by calcining (crystalline _{gypsum) (CaSO 4 · 1/2 H 2} O) rapidly The idea was to make use of the chemical knowledge that it changes into gypsum by absorbing water in the soil conditioner.

[0008] Then, the present inventors have proposed that hemihydrate gypsum (Ca
When SO ₄ 1/2 H ₂ O) is used as a solidifying agent for construction sludge with a high water content, it is possible to obtain an improved soil with a high solidification rate and sufficient solidification strength (sufficient cone index). I got Further, it has been found that the improved soil described above does not have a high alkaline PH value as in the prior art, and furthermore has excellent air permeability and water permeability, so that it can be used as backfill soil. .

The present inventors have previously proposed a hydrous soil conditioner mainly composed of hemihydrate gypsum (CaSO ₄ .1 / 2H ₂ O) based on the above findings (Japanese Patent Application No. Hei 7-308495).
issue). The present inventors have found that the hemihydrate gypsum (CaSO ₄ 1/2 H
After proposal ₂ O) based solidifying agent are also evolving research. As an improvement study of a gypsum-based solidifying agent, see JP-A-7-17.
No. 9854 is known. JP-A-7-1798
The solidifying agent disclosed in Japanese Patent No. 54 comprises the following components. (i) Anhydrite (CaSO ₄ ) and / or hemihydrate gypsum (CaSO ₄ • 1 /
2H ₂ O): 80% by weight or more; (ii). Inorganic salts having a sulfate group and potassium dihydrogen phosphate: 15% by weight or less. The component (ii) is used as a gypsum reaction accelerator (hydration reaction accelerator) which is a main component of the solidifying agent. The solidifying agent disclosed in JP-A-7-179854 also includes an embodiment in which slaked lime or cement is added in addition to gypsum and / or hemihydrate gypsum as described above.

After the previous proposal by the present inventors (Japanese Patent Application No. 7-308495), the present inventors narrowed down the main development task to the improvement of the strength of the improved soil with a hemihydrate gypsum-based solidifying agent. This point is, of course, extremely important for reforming soft sludge such as construction sludge. The above-mentioned development goal is the same as that described in
This is not seen in 79854.

The present inventors have made intensive studies on the improvement of the hemihydrate gypsum-based solidifying agent based on the above-mentioned development problems and on the condition that no alkaline leachate is produced from the improved soil. . In order to improve the strength of the improved soil, the present inventors use other components that are solidified by hemihydrate gypsum (CaSO ₄ .1 / 2H ₂ O) and hydraulic reaction (hydration reaction, pozzolan reaction). It is important to find out other components that can be hydrated in the neutral region in view of the requirement that the alkaline leachate should not flow out of the improved soil. We considered it based on the idea.

In the course of such studies, the present inventors have paid attention to calcined ash obtained by calcining sludge by-produced by sewage treatment, as another component to be combined with the hemihydrate gypsum-based solidifying agent. . This is because, in view of the fact that the calcined ash of the sewage sludge is applied as a building material such as lightweight fine-grained materials from the viewpoint of resource reuse, and that the calcined ash is a by-product in a substantially neutral region, It is based on the idea that a hydraulic reaction is expected in a water gypsum-based solidifying agent system.

As a result, the present inventors have found that a solidifying agent mainly composed of calcined ash obtained from hemihydrate gypsum (CaSO ₄ .1 / 2 H ₂ O) and sewage sludge can be used for improving soil containing water such as construction sludge. It has been found to be extremely useful as an agent.

Furthermore, hemihydrate gypsum (CaSO ₄ 1/2 H)
Second naturally occurring a starting material ₂ O) gypsum (CaSO ₄ · 2
H ₂ O) depends on the ore composition of the place of origin, but generally N (nitrogen), P (phosphorus), K (potassium) important for plant cultivation
(Ca), M
g (magnesium), S (sulfur), and the like, so that the improved soil obtained by solidifying the construction sludge with the semi-hydrated gypsum is optimal as planting soil.
The knowledge that was obtained.

The present invention has been completed on the basis of the above findings. According to the present invention, not only construction sludge having a high water content but also various sludges (sludge from rivers and lakes, marine sludge,
Human waste sludge) can be rapidly solidified, and an economical semi-hydrated gypsum-based hydrous soil conditioner (solidifying agent) is provided.

[0016]

In summary, the present invention relates to a hydrous soil conditioner for solidifying hydrous soil to improve the soil, wherein the hydrous soil conditioner comprises (i): Hemihydrate gypsum (CaSO ₄ 1/2 H ₂ O) as the main component and (i
i). A semi-hydrated gypsum-based hydrous soil conditioner comprising sludge incineration ash as a secondary component.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The technical constitution of the present invention will be described below in detail. The semi-hydrated gypsum-based hydrous soil conditioner for solidifying hydrous soil, such as construction sludge, for soil improvement according to the present invention comprises, as described above, hemihydrate gypsum (CaSO ₄ 1/2 H ₂ O) and sewage treatment. The main component is sludge incineration ash obtained by firing sewage sludge and the like produced as a by-product. Hereinafter, the main components of the semi-hydrated gypsum-based hydrous soil conditioner of the present invention will be described.

In the present invention, the hemihydrate gypsum (CaSO
₄ · 1/2 H ₂ O) is dihydrate gypsum (crystalline _{gypsum) (CaSO 4 · 2 H 2} O) to 60 ° C. to 160 ° C., it preferably is heated to 100 ° C. to 150 DEG ° C. The starting material It is prepared by In the present invention, the hemihydrate gypsum (Ca
SO ₄ · 1/2 H ₂ O) which is the starting material for preparing the dihydrate gypsum (crystalline gypsum) may be one naturally occurring,
Alternatively, it may be a synthetic product. Furthermore, it may be a mixture of natural products and synthetic products.

[0019] In general, naturally occurring gypsum (CaSO ₄ · 2
H ₂ O) contains N (nitrogen), P (phosphorus), and K (potassium) compound components important for plant cultivation, depending on the place of origin, and also contains Ca (calcium), Mg (magnesium), and S It contains a compound component such as (sulfur). Therefore, the hemihydrate gypsum-based soil conditioner prepared from naturally produced dihydrate gypsum contains the main component for planting. For this reason, the solidified soil (improved soil) after solidifying high moisture content soil such as construction sludge using a semi-hydrated gypsum-based soil conditioner prepared from naturally produced dihydrate gypsum is converted into planting soil. Will be useful.

For example, a hemihydrate gypsum-based soil conditioner prepared from natural dihydrate gypsum from Australia has the following elemental composition (units are expressed in%). N ... 0.040 (%) S ... 16.500 P ... 0.011 Mg ... 0.055 Ca ... 22.500 K ... 0.066 Al ... 0.079 Fe ... 0.140

Further, the above-mentioned hemihydrate gypsum soil improver has the following elemental composition as another trace component (expressed in unit mg / 1000 g). Se ... <4 (mg / 1000g) Mo ... <2 Ni ... <2 Cu ... 1.8 Mn ... 6.0 B ... 5.0 As described above, the book The semi-hydrated gypsum-based soil improver prepared from the naturally produced dihydrate gypsum of the present invention contains an important component for planting, and from the viewpoint of effective use as soil for planting on improvement, It can be called a high value-added solidifying agent.

Next, sludge incineration ash which is another component of the semi-hydrated gypsum-based hydrous soil conditioner of the present invention will be described. A typical starting material of sludge incineration ash is sewage sludge by-produced by sewage treatment. Hereinafter, the situation of sewage treatment will be described based on “Recycled Readers” edited by the Tokyo Metropolitan Sewerage Bureau.

According to the above-mentioned "recycled reader", about 4.6 million m ³ of sewage is treated every day in the ward of Tokyo, and the sludge to be treated is about 126,0 m.
00 m ³ / day (FY 1994). The sludge is dewatered and about 82% is treated by incineration or the like, and the generated incineration ash and the remaining dewatered sludge are used for landfill at a waste disposal plant. However, recently, as a method of disposing of sludge generated in large quantities, a method of reusing it as a resource has been developed. ), Used for sludge fuel.

The contents of the above-mentioned sludge treatment are as follows. (i) Treat sludge (raw sludge) close to sewage in a concentration tank.
(→ The volume of the concentrated sludge is 1/2 to 1/4 of the sludge.) (Ii) The concentrated sludge is treated in a digestion tank (40 ° C, 20 days), and methane gas, desorbed liquid, and digested sludge are treated. Is separated. (iii) Dewater the digested sludge with a dehydrator. (→ The volume of dewatered sludge is 1/20 of raw sludge.) (Iv) Dehydrated sludge is incinerated in an incinerator to produce incinerated ash. (→
The volume of the incinerated ash becomes 1/100 of the raw sludge. )

Next, the chemical components of incineration ash produced as a by-product from sewage sludge are shown in the following [Table 1]. The notes in [Table 1] below are as follows. (1). Inorganic incineration ash: An inorganic solidifying agent (cement, lime, etc.) added to accelerate the aggregation of sewage sludge. (2). Incineration ash without inorganic additives: A polymer-based coagulant (such as polyacrylamide) is added to accelerate the coagulation of sewage sludge. (3) For reference, chemical composition values of expansive shale and bentonite are also shown.

[0026]

[Table 1]

As shown in Table 1 above, the incinerated ash of sewage sludge has a high content of (SiO ₂ ) component, and in this respect, it has the same tendency as shale and bentonite. In addition, domestic wastewater such as detergents is also subject to sewage treatment,
The content of the (P ₂ O ₅ ) component is higher than that of shale or bentonite. The sludge incineration ash of the present invention is typically incineration ash obtained from sewage sludge, but is not limited thereto. For example, the sludge incineration ash of the present invention includes the above [Table 1].
Incinerated ash prepared from various sludges having the chemical component values shown in the above or similar component values are included.

The mixing ratio of the hemihydrate gypsum and the sludge incineration ash of the hemihydrate gypsum-based hydrous soil conditioner (solidifying agent) of the present invention should generally be based on the hemihydrate gypsum component. In addition, from the viewpoint of improving the strength of the improved soil (improving the cone index), the sludge incineration ash is generally 20% by weight to 40% by weight.
Should be used less. As a result of many experiments, when the incineration ash content of sludge is about 30% by weight, the cone index is improved by about 50%. The improvement of the strength (corn index) is extremely remarkable as compared with the case of using the hemihydrate gypsum component alone.

In the present invention, as the amount of the sludge incineration ash increases, for example, in a region exceeding 30% by weight, the solidification time tends to increase, and the improved soil tends to change color. There is. Therefore, the mixing amounts of the semi-hydrated gypsum component and the sludge incineration ash may be appropriately set with these factors in mind.

In the present invention, it may be preferable to use the sludge incineration ash after pretreatment, from the viewpoint of not generating alkaline effluent from the improved soil. That is, when the sludge incineration ash is alkaline, particularly strongly alkaline, it is preferable to use the incineration ash after neutralizing it. Generally, sludge incineration ash is in a neutral region, as can be seen from the chemical component values in [Table 1], and thus the neutralization treatment is not necessary.

The semi-hydrated gypsum-based hydrated soil improver of the present invention is 3 to 20% by weight based on the hydrated soil, depending on the moisture content.
, Whereby rapid solidification and high strength after solidification can be realized.

The water-containing soil to which the semi-hydrated gypsum-based soil conditioner of the present invention is applied generally has a water content of 20 to 200%, but is not limited thereto. A typical example of the high water content soil is construction sludge. The solidification target of this type of construction sludge is determined by the cone index confirmation test (JSF T 716) from the viewpoint of pollution control.
Anything above 2.0 is important. Those with a cone index of less than 2.0 are subject to pollution control, and the duty of complete disposal is imposed on the responsibility of the construction work owner. On the other hand, those having a cone index of 2.0 or more can be reused for backfilling at a construction site or for transporting to another place for landfilling.

As described above, the semi-hydrated gypsum-based soil conditioner of the present invention is applied to, but not limited to, the solidification treatment of construction sludge having a high water content (cone index less than 2.0). is there. For example, the semi-hydrated gypsum-based soil conditioner of the present invention can be applied to the treatment of various sludges having a high water content, more specifically, sludge of rivers and lakes, marine sludge, and human waste sludge. is there.

The hemihydrate gypsum-based soil conditioner of the present invention comprises hemihydrate gypsum (CaSO ₄ .1 / 2H ₂ O) as a main component and sludge incineration ash as an auxiliary component. In the semi-hydrated gypsum-based hydrous soil conditioner of the present invention, other components may be used. For example, as another component, when semi-hydrated gypsum as a main component is prepared by heat-treating naturally-produced gypsum (CaSO ₄ .2H ₂ O) as described above, N which is important for planting is prepared. , P, K, etc., but may contain these components. Further, a conventionally known cement-based, lime-based, or synthetic polymer-based solidifying agent can be appropriately compounded within a range in which a high PH value does not adversely affect a biological system. In order to uniformly disperse the semi-hydrated gypsum-based hydrous soil conditioner into various sludges, a surfactant can be appropriately compounded.

[0035]

EXAMPLES dihydrate gypsum _{(CaSO 4 · 2 H 2 O} ) 100~1
Hemihydrate gypsum heat-treated at 60 ° C (CaSO ₄ 1/2 H ₂ O)
, And 30% by weight of sludge incineration ash (inorganic incineration ash of [Table 1]) (prepared with semi-hydrated gypsum-based hydrous soil conditioner (particle size: 10 µm, specific gravity: 2.5)) The solidification ability of construction sludge was tested using a solidifying agent. (i) Properties of construction sludge The properties of construction sludge collected from the construction site are as follows.・ Moisture content (JSF T121): 60% ・ PH value (based on JSF T21) (Note 1): 8.
2-8.6 ・ Cone index confirmation test (JSF T 716) (Note 2): Compaction with a rammer is not possible. (Note 1) Construction sludge has a high PH value because it is collected from construction sites that employ the shield method. (Note 2) Three layers are formed by tamping 10 times per layer with a 10 cm × 12.7 cm mold and a 2.5 kg rammer to measure.

(Ii) Properties of the <improved soil> The construction sludge and the solidifying agent were stirred for 3 minutes, and the properties of the improved soil were examined. In order to uniformly mix the solidifying agent, 100 g of added water was used in the following experiments.

Experimental Example 1 A solidifying agent was added to 1927.6 g of construction sludge.
202.9 g and 100 g of added water were added, and the mixture was stirred and mixed (for 3 minutes), and properties for improvement were examined. The use ratio of the solidifying agent to the total amount of the construction sludge and the added water is 10%.
The improved soil showed a cone index of 3.0 and a PH value of 7.6.
When water and the improved soil were put in a beaker and re-mudification was visually evaluated, no re-mudification phenomenon was observed.
In the case of hemihydrate gypsum _{(CaSO 4 · 1/2 H 2 O} ) alone, the cone index of the modified soil was 2.0. This means that the solidifying agent of the present invention has a 50% strength improving effect.

Experimental Example 2 A solidifying agent was added to 2009.1 g of construction sludge.
304.1 g and 100 g of added water were added, mixed with stirring (for 3 minutes), and examined for improvement. The use ratio of the solidifying agent to the total amount of the construction sludge and the added water is 15%.
The improved soil showed a cone index of 5.1 and a PH value of 7.6.
No re-mudification phenomenon was observed in both mud evaluations. In the case of using hemihydrate gypsum (CaSO ₄ 1/2 H ₂ O) alone, the cone index of the improved soil was 3.7.

[0039]

EFFECT OF THE INVENTION The semi-hydrated gypsum-based hydrous soil conditioner (solidifying agent) of the present invention is an improved soil in comparison with the conventional cement type, lime type and synthetic polymer type soil improving agents (solidifying agent). Is very short and economical due to low cost. Since the semi-hydrated gypsum-based hydrated soil conditioner (solidifying agent) of the present invention is composed of sludge incineration ash conventionally prepared for landfilling and the like prepared from sludge such as sewage sludge, the sludge is recycled. It contributes to the development. Further, since sludge incineration ash is used, the above-described economic efficiency is doubled. Furthermore, since sludge incineration ash is used, the disposal of incineration ash and the securing of land for landfill are eased.

The improved soil improved by the semi-hydrated gypsum-based hydrous soil conditioner of the present invention has high safety without any adverse effects on biological systems derived from a high PH value as in the prior art. Furthermore, the improved soil improved by the semi-hydrated gypsum-based hydrous soil improver of the present invention is excellent in air permeability and water permeability, and contains an important element in plant growth. It will be a valuable planting soil.

As described above, the semi-hydrated gypsum-based hydrous soil conditioner of the present invention can meet the strict pollution regulations for various types of sludge having a high water content such as construction sludge in recent years, and has a high safety. High and economical.

Claims (7)

[Claims] 1. A hydrated soil conditioner for solidifying hydrated soil to improve the soil, wherein the hydrated soil conditioner comprises: (i) hemihydrate gypsum (CaSO ₄ .1 / 2 H ₂ O) (Ii) sludge incineration ash as a secondary component;
A semi-hydrated gypsum-based hydrous soil conditioner characterized by the following. 2. The hydrous soil conditioner comprises: (i) hemihydrate gypsum (CaSO ₄ .1 / 2 H ₂ O)... 60% or more to less than 80% by weight; (ii) sludge incineration Ash ... 20% by weight or more to 4
The hemihydrate gypsum-based hydrous soil conditioner according to claim 1, which is constituted by less than 0% by weight. 3. Hemihydrate gypsum (CaSO ₄ .1 / 2H ₂ O), which is a main component of the hemihydrate gypsum-based hydrous soil conditioner, is used to convert crystalline gypsum (CaSO ₄ .2H ₂ O) to 100 ° C. to 160 ° C. The amniotic fluid gypsum-based hydrous soil conditioner according to claim 1, which is prepared by heat treatment at a temperature of ℃. 4. The hemihydrate gypsum-based hydrous soil conditioner according to claim 1, wherein the sludge incineration ash is prepared by incineration of sewage sludge. 5. The hemihydrate gypsum-based hydrous soil conditioner according to claim 1, wherein the hydrous soil has a water content of 20 to 200%. 6. The hemihydrate gypsum-based hydrous soil conditioner according to claim 1, wherein the hydrous soil is construction sludge. 7. The hemihydrate gypsum-based hydrous soil conditioner according to claim 6, wherein the cone index of the construction sludge is less than 2.