JP2000344556A - Manufacture of soil based inorganic material and method for using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide methods for manufacturing and using a soil based inorganic material utilizable for civil building materials, vegetation greening materials and the like which has high strength and low level of alkali elution by treating mud such as construction sludge, dredge mud or the like. SOLUTION: Inorganic powder which forms a hydrate is mixed with mud beforehand dried into a dispersed state and mechanical energy (e.g. impact or frictional force) is given to the resultant mixture. The mud may consists essentially of silty or clayey powder. As the inorganic powder which forms the hydrate, cement (e.g. Portland cement), cement mixed with at least one kind of powder selected from the group consisting of limestone powder and gypsum powder and inorganic powder consisting essentially of blast furnace slag fine powder and the like can be used. The soil based inorganic material can be used only by adding water to be solidified at the time of using the material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to mud such as construction sludge and dredged mud (including muddy and muddy mud depending on the water content). ) To produce a soil-based inorganic material that can be used for civil engineering construction materials, vegetation revegetation, and the like, and a method of using the soil-based inorganic material.

[0002]

2. Description of the Related Art A large amount of construction sludge containing water is generated during tunnel excavation work, building work, and the like, and a large amount of dredging sludge containing water is also discharged during harbor construction and dredging of bottom soil of lakes and marshes. Is done. Its emissions amount to over a thousand million tons per year.

Most of these mud are fine particles containing a large amount of water having a particle size of several tens of μm, so that they cannot be piled up on a dump truck, and difficult-to-treat materials that cannot be walked on by humans. It has become. Therefore, it cannot be reused as it is, and most of it has conventionally been landfilled as sludge of industrial waste. However, recycling is being performed, albeit slightly, and in particular, in recent years, development of technologies for recycling such mud has been actively pursued in various fields.

For example, regarding construction sludge, technical guidelines for recycling are compiled by the Ministry of Construction, and technical standards for sediment separation, dehydration treatment, stabilization treatment, and the like are set forth. A method of applying a dewatered cake obtained by dewatering to a certain extent to a backfill material or stabilizing it with an improved material and applying it to an embankment has been studied. As the dewatering method, various techniques such as centrifugal filtration (screw decanter), pressure filtration (filter press), pressure squeezing filtration (roll press), and high-pressure thin layer dehydration can be applied. I have.

[0005] The above-mentioned stabilization treatment is a treatment for chemically improving the properties of construction sludge by mixing an improving material. The improving materials include cement and cement-based improving materials, lime (quick lime, slaked lime).
And lime-based improving materials are applied.

[0006] Regarding the dredged soil as well, solids are settled and separated in a raw mud tank, and the settled mud is extracted by a pump and added with a dehydration aid, then concentrated and dewatered, and used or used as residual soil. It has been landfilled. In some cases, a solidifying agent is added to the dewatered cake and used as cover soil. In addition,
The treated water discharged in the above-mentioned steps of concentration and dehydration is discharged after being subjected to treatments such as coagulation sedimentation and neutralization.

[0007] In addition, in the dredging performed due to the necessity of environmental purification of lakes and marshes, a method of discharging the dredged mud to a vast agricultural land borrowed for a long period of time and drying it naturally for several years has been adopted.

[0008]

In the prior art described above, dewatering by a screw decanter or filter press used in dewatering mud, roll dewatering,
In high-pressure thin-layer dehydration or the like, mud solidifies during dehydration and does not turn into a powdery state, so that it is difficult to uniformly mix with an improving material when performing a stabilization treatment. Therefore, the performance (strength) of the recycled material obtained by the treatment for improving the properties of the sludge by mixing the above-mentioned improving material is low, and in order to enhance the performance, a large amount of the improving agent must be added, which increases the cost. become. Also,
The strength of the obtained reclaimed soil itself is limited, and it can be used only for backfilling and embankment, and it has not been possible to provide a material with higher added value.

Further, in the material solidified by the conventional method,
The permeation of water during use causes alkaline components such as calcium contained in cement and cement-based modifiers, lime (quick lime, slaked lime), and lime-based modifiers to elute into the water, so that the surroundings become alkaline. For example, when the pH rises to about 12, and the pH is 10 or less,
There is a problem that the condition of 6.5 to 8.5 adversely affects the growth of crops, forests, flowers, and the like, which are required, and often causes death.

[0010] The present invention, as a part of the technology for actively promoting the recycling of mud such as construction sludge and dredging mud, treats these mud and has high strength and low alkali elution (low alkali elution). It is an object of the present invention to provide a method for producing a soil-based inorganic material that can be widely used for civil engineering building materials, vegetation revegetation, and the like, and a method for using the same.

[0011]

Means for Solving the Problems In treating mud containing a large amount of water, such as construction sludge and dredging mud, the present inventors have conducted various studies on pretreatment of mud.
As a result, the mud is subjected to a drying treatment so as to be in a state in which the agglomerated particles are small and the particles of the mud are dispersed, and further, a solidified material (including a material referred to as an improving material here) or a water-permeable material. After mixing with additives for imparting functions such as pH adjustment, mechanical energy such as impact force is applied to significantly improve the performance (eg, strength) of the resulting product (soil-based inorganic material). I found something that could be done.

By applying mechanical energy to a substance, it is possible to change the physical and chemical properties of the substance or cause a chemical reaction, which is generally known as a mechanochemical reaction. It is also possible to cause a synthesis reaction or a decomposition reaction by a mechanochemical reaction.For example, a method of mixing multiple metal powders and then adding mechanical energy to synthesize an alloy is called mechanical alloying, and practical use is also possible. Have been. In addition, there is an invention of a method of obtaining a hydraulic substance by mixing an inorganic material containing calcium with a mineral containing alumina (see, for example, JP-A-8-33743 and JP-A-8-91831). .

The present invention is an application of this mechanochemical reaction to mud treatment (reaction of mud with a solidifying material and other additives). The gist of the present invention is to provide a method for producing a soil-based inorganic material as described in (1) below. , And (2) in its use.

(1) A method for producing a soil-based inorganic material in which mud is dried in a dispersed state, mixed with an inorganic powder that forms a hydrate, and mechanical energy is applied to the mixture.

(2) A method of using a soil-based inorganic material which solidifies by adding water to the soil-based inorganic material produced by the method described in the above (1).

The mud may be based on silt or clay powder.

As inorganic powders for producing hydrates, cement (eg, Portland cement), limestone powder, or a mixture of limestone powder and gypsum powder as a main component, and granulated blast furnace slag A powder mainly composed of fine powder or a powder mainly composed of granulated blast furnace slag, gypsum powder and limestone powder can be used.

The mechanical energy may be any one of compression, impact, friction and shear or a combination of two or more of them.

Here, "mud" is, as described above,
This refers to construction sludge with a large amount of moisture generated by construction work (excluding dredging) such as tunnel excavation work and building work, dredged mud generated by harbor work and dredging of the bottom soil of lakes, and other mud-like inorganic powder. Further, soil generated in a specific area (for example, “red soil” in Okinawa Prefecture) is also included in “mud”. This is because when treated, water is added to show properties similar to construction sludge and dredging mud.

The term "silt or clay" refers to mud from which relatively coarse-grained gravels and sand have been removed, and most of which are mud having a particle size of 75 μm or less. In addition, exceeding 5 μm and 75
Silt up to μm is clay and 5 μm or less is clay. Also, 7
Sand exceeding 5 μm and up to 2 mm is called sand, and sand exceeding 2 mm is called gravel.

Further, "drying the mud in a dispersed state" means performing a drying treatment so that the mud particles are not aggregated but in a dispersed state. Specifically, the water content is reduced to 70% by weight (hereinafter, “%” means “% by weight”) by a drying method described below (pulse jet engine, spray dryer or medium fluidized bed type dryer).
It means to dry below. The mud is originally composed of fine particles except for relatively coarse gravels and sand, and can be made into fine-grained mud by drying the mud in a dispersed state.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing a soil-based inorganic material of the present invention (hereinafter, also referred to as “method of the present invention”) and a method of using the material will be described in detail.

First, mud dried in a dispersed state is prepared as a base material.

The method of the drying treatment is not particularly limited. However, as described above, in the dehydration by a screw decanter or a filter press, a roll press dehydration, a high-pressure thin-layer dehydration, and the like, which are conventionally used in the dehydration of the mud, the mud is solidified at the time of dehydration and dried in a dispersed state. No powder mud is obtained.

One of the recommended methods is a method in which hot water accompanied by a shock wave is blown onto a slurry-like mud flow to evaporate water, and can be carried out, for example, by a drying apparatus equipped with a pulse jet engine. According to this method, since the evaporation of water is remarkably promoted, the mud containing a large amount of water is dried in a state in which the particles are dispersed without going through a dehydration step, and directly into fine-grained mud powder. Can be.

In carrying out this method,
According to the average particle size and shape of the soil particles contained in the mud, the water content of the mud is adjusted to an appropriate water content (that is, the dispersion state of the soil particles in the mud is good, and the mud is subjected to smooth and smooth drying treatment. (Predetermined in advance with a water content ratio that can be obtained).

Next, hot air accompanied by a shock wave is blown onto the flow of the mud whose water content has been adjusted. In order to create a flow of mud, for example, slurry mud may be continuously flowed from a nozzle having a circular or elliptical cross section. A plurality of nozzles may be used, or a thin strip-shaped flow may be formed using a slit-shaped nozzle.

The slurry-like mud is blown off by blowing hot air accompanied by a shock wave on the flow of the mud, and at the same time, water and soil particles in the slurry are finely dispersed by the action of the shock wave, and the water (liquid) inside the soil particles is dispersed. Oozes out on the surface of the particles and is blown off by the shock wave, and evaporates quickly because it is in a high temperature air stream. A pulse jet engine may be used as a device for generating hot air accompanied by shock waves, and slurry containing mud may be supplied into the exhaust of the pulse jet engine.

Further, a method of evaporating water by a drying device equipped with a spray drier or a drier of a medium fluidized bed system may be used.

In the spray drier, slurry-like mud is jetted in a mist state, and hot air is blown there, and the mud is dried by the heat. In a medium fluidized bed dryer, a medium (ball) is present in the fluidized bed.
The supplied slurry-like mud is dried by the heat of the hot air while being crushed by the balls. In any case, the slurry-like mud can be directly converted into mud powder in a state where particles are dispersed.

The water content of the mud powder is 70% or less. When the water content exceeds 70%, the mud becomes sticky and does not become a dispersed state, and it is difficult to adjust the water content to an optimum water content for a hydration reaction described later. It is preferably at most 50%, more preferably at most 40%.

The mud may be based on silt or clay. Sand and gravels separated from mud are
It is easy to use effectively as a construction material and is still used relatively frequently after being classified by a sieve or the like, but the silt and clay remaining after separation are difficult to reuse and are discarded, so the mud is silt or If it is mainly made of clay, it is particularly important in promoting the recycling of mud. The term “mainly composed of silt or clay” refers to mud containing 50% or more silt or clay.

An inorganic powder that forms a hydrate is mixed with the thus obtained mud as a base material that has been dried in a dispersed state.

The inorganic powder that forms a hydrate has the function of reacting with water to form a hydrate by solidifying the mud by adding it to fine-grained mud, adding water and mixing. As described above, cement or limestone powder, or a mixture of limestone powder and gypsum powder as a main component can be used. These inorganic powders have been conventionally used for solidification of mud, but when used in the method of the present invention, a remarkable effect is recognized as compared with the case of using the conventional solidification method.

Further, as an inorganic powder for producing a hydrate,
It is desirable to use a blast furnace granulated slag fine powder as a main component, or a blast furnace granulated slag fine powder, a gypsum powder and a limestone powder as main components.

The granulated blast furnace slag powder has excellent hydraulic properties and high long-term strength. Portland cement is obtained by finely pulverizing raw materials such as limestone, clay and silica stone, calcining them to form a hydraulic mineral phase (calcium silicate, etc.), and then finely pulverizing again. This is because the crushed slag fine powder is obtained by subjecting a molten blast furnace slag, which is a by-product generated during the production of pig iron, to water granulation and finely pulverizing the obtained granulated slag, and is extremely inexpensive as compared with Portland cement or the like.

The granulated blast furnace slag powder may be used alone as a solidifying material, or the granulated blast furnace slag powder may be used as a main component, that is, at least 50% is granulated blast furnace slag powder, and gypsum (dihydrate gypsum) or lime. A mixture of (quick lime) powder may be used. Since dihydrate gypsum discharged from flue gas desulfurization equipment and lime powder discharged as dust from a lime burning kiln can be used, it is an inexpensive, high-strength, and desirable solidifying material.

The amount of the solidifying material to be used and the amount to be mixed with the soil-based inorganic material may be appropriately determined according to the use of the obtained soil-based inorganic material.

In addition, in addition to the above-mentioned solidified material, at least one of a neutralizing material and a ventilation material may be added. As will be described later, the soil-based inorganic material of the present invention has a low alkali elution, but is completely neutralized by adding a neutralizing material (for example, sulfuric acid previously impregnated into acidic soil or dry mud powder). It is possible to do. In addition, the soil-based inorganic material used may have low water permeability and poor drainage, which may hinder plant growth and the like. However, a ventilation material (for example, porous zeolite or the like) may be mixed in advance. These adverse effects can be prevented or mitigated.

The mixing method is not particularly limited. Various general blenders and mixers for powder can be used. Since the mud is mud powder that has been dried in a dispersed state,
Uniform mixing is easily possible, and the apparatus itself used in the subsequent step of applying mechanical energy has a mixing effect. Therefore, in this mixing step, it is only necessary to mix to some extent uniform.

Thereafter, the mixture of the mud and the inorganic powder that forms a hydrate is subjected to a treatment for applying mechanical energy (mechanochemical treatment) to produce a soil inorganic material.

The mechanical energy is usually given by applying a compressive force, an impact force, a frictional force, a shearing force and the like to the above mixture. What is necessary is just to apply the force which combined one or two or more of those forces.

As a method or an apparatus therefor, a ball mill capable of giving relatively strong energy,
Planetary ball mills and attritors are suitable. Many of these are devices in which balls are filled, and the powder is mixed and mechanical energy is applied (transmitted) to the powder by rotating the entire device at high speed.

For example, when a ball mill is used, the mud which is to be treated by the method of the present invention, if the rotation speed is set to several hundred rpm and the treatment is performed for several hours, a mechanochemical reaction occurs.

Here, in producing the soil-based inorganic material by the method of the present invention, it is necessary to dry the mud in a dispersed state, and to prepare an inorganic powder (hydratable inorganic powder) that produces a hydrate with the mud. The reason why mechanical energy is added to the mixture of (1) will be described.

(1) Necessity of drying mud in dispersed state a. Uniform mixing effect When the particles composing the mud become fine, the presence of a certain amount of moisture outside the particles increases the adsorbing force between the particles, making it difficult to disperse even when an external force is applied. This is because if the mud is mainly silt or clay,
Especially remarkable.

When the conventional mud containing a large amount of water is forcibly dewatered by a conventional mechanical dehydrator such as a filter press, the water can be removed to some extent, but the water is limited to about 80%, and the mud particles are aggregated. After the solidification material is added to the dewatered mud, a considerable amount of mechanical energy is required to mix it uniformly. In addition, uniform mixing cannot be guaranteed.

On the other hand, since the mud dried in a dispersed state is a fine-grained mud powder, it can be easily and uniformly mixed. This homogeneity is extremely important and is the dominant factor for strength development when a reaction between each particle is required, such as a hydration reaction.

B. Moisture control effect The purpose of mixing the hydrated inorganic powder with the mud dried in a dispersed state is to use the hydration reaction of this inorganic powder to generate a hydrate, and integrate it with the dried mud Drying the mud makes it possible to adjust the amount of water to be added to the soil-based inorganic material to an optimal amount of water for the hydration reaction, and the performance (strength) of the obtained soil-based inorganic material ) Can be improved.

That is, if the mud is insufficiently dried and contains excess moisture, when water is added and solidified, the portion where the excess moisture is present becomes voids due to natural drying after solidification. However, the strength as a structural body is reduced due to remaining structural defects. However, in the soil-based inorganic material of the present invention, the water content can be adjusted to an optimum water content, and such a strength reduction does not occur.

(2) Reason for Applying Mechanical Energy to the Mixture The particles of the mud and the hydratable inorganic powder are physically torn off by the mechanical energy, and a highly active molecular surface is formed. It becomes an activated state that is likely to occur. Therefore, when water is added to the obtained soil-based inorganic material, the hydration reaction is remarkably promoted as compared with the case where no mechanical energy is applied, and the effect of improving the performance (strength) of the soil-based inorganic material is large. In addition, the hydration reaction is promoted and solidification is firmly performed, so that elution of alkali is suppressed.

When using the soil-based inorganic material obtained by the above-mentioned method of the present invention, the material is transported to the site, then molded by adding necessary moisture, and cured according to an ordinary method. Alternatively, the material may be formed before adding water, and then the necessary water may be added and cured. Thereby, functions such as strength are exhibited.

The amount of water to be added depends on the content (mixing ratio) of the solidified material in the soil-based inorganic material, the particle size of the solidified material and the inorganic material,
Although it differs depending on the kind and the like, the strength is not exhibited when the amount is too small, and the strength decreases when the amount is too large. If the amount is too small, the hydration reaction does not proceed sufficiently.If the amount is too large, excess water eventually evaporates and dehydrates, but the portion where the excess water was present becomes voids. This is because the strength as a structure is reduced.

According to the method of the present invention described above, construction sludge,
Soil-type inorganic materials with high strength and low alkali elution, such as dredging mud, dam sediment (inflow sediment, sedimentation mud), and other mud-like inorganic powder generated during harbor construction and dredging of lake bottom soil It can be. This soil-based inorganic material has higher strength, such as base materials for river embankments, riverbed improvement materials, subgrade materials, subbase materials, etc., as well as building construction basic materials, bridge basic materials, and subsidence prevention materials for underground buried objects. It is suitable for use in civil engineering and construction materials that require, or for vegetation greening.
In addition, since a large amount of water contained in the mud is removed, there is an advantage that the transportation cost can be significantly reduced.

The soil-based inorganic material obtained by the method of the present invention may be simply added with water when used.

[0056]

[Example] Drying equipment equipped with a pulse jet engine (drying capacity: 20 kg /
h), the obtained mud powder is mixed with blast furnace granulated slag fine powder (approximately 4000 branes), dihydrate gypsum discharged from a flue gas desulfurization facility, and lime powder which is dust of a lime burning kiln. The inorganic powder (solidifying material) which produces a sum was mixed. The mixing ratio of mud powder, granulated blast furnace slag powder, gypsum and lime powder was 50%, 35%, 7.5% and 7.5%, respectively, in terms of solids weight excluding water.

A ball mill (processing capacity: 1) was added to this mixture.
0 kg / charge) at 500 rpm for 2 hours to give mechanical energy,
Soil-based inorganic materials were manufactured.

For comparison, only the drying treatment was performed.
A material not subjected to the mechanochemical treatment (a material subjected to only the drying treatment) was obtained.

Table 1 shows the characteristics of the mud (raw mud) used.
Table 2 shows the characteristics of the raw slurry obtained by adjusting the water content of the raw slurry in the drying treatment, and Table 3 shows the drying conditions of the raw slurry. In addition, the adjustment of the water content of the raw mud was performed so that the range of the appropriate water content was obtained for the mud generated at the time of dredging of the lakes and marshes so as to fall within the range.

The properties (moisture content) of the obtained mud after the drying treatment were as shown in Table 4. In Table 4, the water content of the dried powder recovered in the recovery tank attached immediately below the powder drying chamber of the used drying equipment is shown in the column of “Powder drying chamber” and adjacent to the powder drying chamber. The moisture content of the dry powder recovered by the attached cyclone is shown in the column "Cyclone".

[0061]

[Table 1]

[0062]

[Table 2]

[0063]

[Table 3]

[0064]

[Table 4]

Water is added to the soil-based inorganic material obtained by the above method of the present invention and the material subjected to only the drying treatment so that the water content becomes 55%, and JIS
The uniaxial compressive strength was measured according to the method specified in A1216. Further, the amount of alkali eluted (pH) is determined by a method used in analysis of soil contamination and the like, that is, a method in which a solidified sample is crushed to a particle size of 1 mm or less, and then immersed in water to measure a change in pH. I asked.

Table 5 shows the measurement results. As is clear from these results, the soil-based inorganic material obtained by the method of the present invention had significantly higher strength and a significantly reduced amount of alkali eluted as compared with the material subjected to only the drying treatment.

[0067]

[Table 5]

[0068]

According to the method of the present invention, mud such as construction sludge, dredging mud, etc., has high strength and little alkali elution,
It can be a soil inorganic material suitable for applications such as civil engineering building materials and vegetation greening. In addition, since a large amount of water contained in the mud is removed, there is an advantage that transportation costs can be significantly reduced. When using this soil-based inorganic material, it is only necessary to add water.

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Claims (2)

[Claims] 1. A method for producing a soil-based inorganic material, comprising drying mud in a dispersed state, mixing the powder with an inorganic powder that forms a hydrate, and applying mechanical energy to the mixture. 2. A method for using a soil-based inorganic material, wherein the soil-based inorganic material produced by the method according to claim 1 is solidified by adding water.