JP5506076B2 - Soil improving material and method for producing the same - Google Patents

Description

  The present invention relates to a soil improvement material and a method for producing the same. More specifically, the present invention relates to a soil improvement material that can be particularly suitably used when regenerating mud with high water content generated in civil engineering work as soil, and a method for producing the same.

  In order to move mud with high water content generated in civil engineering work quickly and easily from the site, it is necessary to absorb the mud's moisture and regenerate it as soil. As means for absorbing the mud water, a method of adding and mixing (1) incinerated ash, (2) cement, (3) polymer absorbent, etc. at the construction site has been known.

  However, in the method of adding and mixing (1) incineration ash, although incineration ash is excellent in water absorption, since it is in the form of fine particles, there is a problem that handling is not easy and dust is generated. (2) In the method of adding and mixing cement, the cement is excellent in solidification strength, but not only takes time for solidification but also requires crushing when the mud after treatment is reused. Moreover, since elution pH is high, there exists a bad influence on a vegetation, and there exists a problem that it is not suitable for reuse. (3) In the method of adding and mixing the polymer absorbent, although the polymer absorbent is excellent in water absorption, the treated soil obtained contains gel-like polymer absorbent. When used, there is a problem that the earth resistance is small.

  In addition, (1) Incinerated ash contains hazardous substances such as hexavalent chromium, boron, and fluorine regulated by the Ministry of the Environment Notification No. 18 “Matters for Measuring Soil Elution Survey” Therefore, if incinerated ash is used, it must be treated to satisfy the soil environmental standards.

  Therefore, as a method for insolubilizing and / or making the harmful substances contained in the incinerated ash insoluble, for example, a method of adding limestone or the like to the combustion furnace (Patent Document 1), or a calcium compound, cement, or aluminum sulfate in the incinerated ash Has been proposed (Patent Document 2) in which the amount of fluorine and boron eluted is adjusted to a soil environment standard value or less.

  However, in the method described in Patent Document 1, due to the solidification and aggregation of limestone, sufficient water absorption cannot be ensured, and the particle diameter of limestone is fine. Similarly, there is a problem of dust generation during handling and use. On the other hand, Patent Document 1 does not mention the possibility that hexavalent chromium is eluted from soil using a soil improver. In addition, it does not pay attention to the removal of harmful substances derived from soil and the elution of harmful substances caused by soil when mixed with soil, and when it is mixed with soil, a sufficient harmful substance removal effect is exhibited. I can't expect that.

  According to the method described in Patent Document 2, although the amount of fluorine and boron eluted from the treated incineration ash itself satisfies the soil environmental standard, it is mixed with mud soil whose own fluorine elution is less than the soil environmental standard value. When the treated product is used as a soil improvement material, there is a problem that the amount of fluorine elution from the mixed mud is greatly increased in some cases. The reason why the amount of fluorine elution from the mixed mud is greatly increased is not certain, but the following reason can be given, for example. That is, at least cement can be mixed with incinerated ash in the presence of water to suppress the elution amount of fluorine, which is generally due to the incorporation of fluorine into the ettringite crystal structure, This is probably because the crystal structure is relatively easily broken by carbon dioxide or the like and liberates fluorine.

  Further, among the incineration ash, the incineration ash of paper sludge has a risk of elution of hexavalent chromium and lead from pigments contained in the printed matter and the like, and there is a limit to the use without treatment.

  On the other hand, the soil of general environment contains trivalent chromium and fluorine at a concentration of 90 to 600 ppm, but the elution amount is less than about 0.8 ppm relative to the content of trivalent chromium and fluorine. Exists in the form of stabilized trivalent chromium, and it is presumed that fluorine is ionically coordinated with aluminum in the soil.

  However, when incinerated ash treated with alkaline treating agents such as cement, calcium, magnesium, etc., or soil improvement material made from incinerated ash of papermaking sludge containing a large amount of calcium, was mixed with mud, it was oxidized by incineration. Hexavalent chromium and hydroxide ions derived from alkaline substances coordinate with aluminum and liberate fluorine.

  Therefore, for example, in addition to pulp sludge ash and cement, a composite contaminated soil stability purification agent (patent document 3) obtained by mixing and stirring artificial zeolite, activated carbon, silica and the like, and a raw material containing incinerated ash in the presence of water, Method of manufacturing construction and civil engineering materials by performing treatment including drying treatment (Patent Document 4), and mixing treatment by adding a specific proportion of aluminum sulfates and sulfur compounds to fluorine-containing combustion ash, and the amount of fluorine elution from combustion ash Although the method (patent document 5) which suppresses is proposed, the elution amount of hexavalent chromium and fluorine is not fully suppressed by mixing with mud.

  In addition, in order to prevent elution of hexavalent chromium, a method of maintaining trivalent chromium that is stable in nature without being oxidized to hexavalent chromium at the time of commercialization, and even if it is oxidized to hexavalent chromium In addition, as a method of reducing and stabilizing to trivalent chromium, a method of adding sodium bisulfite to a soil improvement material has been conventionally studied. For example, in a burned material such as paper sludge ash, Portland cement, calcium sulfate A treatment agent for hexavalent chromium soil containing sulfuric acid band, sodium bisulfite and the like has been proposed (Patent Document 6).

  However, like the treatment agent disclosed in Patent Document 6, especially a treatment agent mainly made of paper sludge incineration ash contains a large amount of ink-derived chromium discharged from the deinking process, and it is heavy on the incineration ash. By simply mixing sodium sulfite or adding a conventional solidifying agent, the elution of hexavalent chromium oxidized by incineration may be sufficiently suppressed depending on the moisture content and pH of the target soil. Can not.

JP 2005-134098 A JP 2006-181535 A JP 2005-048147 A JP 2007-225166 A JP 2009-034611 A JP-A-2005-232341

  The present invention has been made in view of the background art described above, and sufficiently suppresses elution of hexavalent chromium even when mixed with general soil, regardless of the water content, pH, and other qualities of the target soil. The purpose of the present invention is to provide a soil improvement material and a method for producing the same, in which the soil to be treated is not limited, and furthermore, elution of fluorine can be sufficiently suppressed and the ground strength is excellent.

That is, the present invention
A method for producing a soil improvement material comprising incinerated ash as a main component,
At least a blending step of blending cement and water with the incinerated ash, a granulation step performed after the blending step, and a drying step;
In the steps from the blending step to the drying step, granulate after adding a powdery sulfur compound to a mixture consisting of at least incineration ash, cement and water and adjusting the water content to 50% by mass or less. It is related with the manufacturing method of the soil improvement material characterized by this, and the soil improvement material obtained by the said manufacturing method.

  The soil improvement material produced by the production method of the present invention sufficiently suppresses elution of hexavalent chromium even when mixed with general soil, regardless of the water content, pH, and other qualities of the target soil. The soil to be treated is not limited, and further, elution of fluorine can be sufficiently suppressed, and the ground strength is excellent.

Schematic flowchart showing the steps of the method for producing a soil improvement material according to Embodiment 1 Schematic configuration diagram of horizontal fluidized bed dryer

  Chromium usually exists in nature as trivalent and hexavalent ions as described above, and is necessary for living organisms, but hexavalent chromium is known to be a carcinogenic substance having strong toxicity. ing. Industrially, it is widely used for plating, paints, printing inks, plastics, paints, crayons, magnetic tapes, and the like, and the waste liquid of its production plant contains a large amount of hexavalent chromium. Because untreated hexavalent chromium can cause soil contamination, national and local governments have established emission standards and regulated them, but technical and chemical definitive solutions have been found. Not.

Hexavalent chromium compounds are chromate and dichromate, making use of the water-soluble nature of hexavalent chromium, and in the water from which hexavalent chromium is eluted, for example, ferrous chloride, ferrous sulfate, sodium sulfite, A reducing agent such as sodium bisulfite or a sulfur-containing compound such as thiol or thioether is added and stirred. As a result, a reduction reaction occurs in the system, and the hexavalent chromium compound forms a stable hexacoordinate complex to become a trivalent chromium compound. The trivalent chromium compound is a complex salt, in which water molecules are coordinated to Cr ³⁺ and are often stabilized by forming complex ions such as hexaaquachromium ion [Cr (H ₂ O) ₆ ] ^3+. .

However, even this stabilized trivalent chromium compound is relatively easily oxidized in the presence of a strong alkaline solution, dissolves as a chromite such as Na ₂ Cr ₂ O ₄ , and is toxic. Becomes valent chromium. Even trivalent chromium that has been completely reduced may be oxidized by contact with air to return to hexavalent chromium.

  Therefore, in the production method of the present invention, the granulation step and the drying step are performed after the blending step of blending cement and water with the incinerated ash, and at least in the steps from the blending step through the granulation step to the drying step, A soil improvement material is prepared by adding a powdered sulfur compound to a mixture consisting of incinerated ash, cement and water, and having a predetermined water content, and after the obtained soil improvement material and mud are mixed In addition to the effect of significantly reducing the elution amount of hexavalent chromium and fluorine, the soil improvement material itself can be prevented from generating dust and can be easily handled. Hereinafter, preferred embodiments of the production method of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic flowchart showing an example of steps of the manufacturing method according to Embodiment 1 of the present invention. In the first embodiment, first, cement and preferably a polyvalent metal salt compound are blended and mixed while blending water with incineration ash to prepare a mixture.

  Incineration ash used as raw material is incineration ash generated when burning coal, RPF (fuel consisting of paper, waste materials, waste plastics, etc.), waste tires, wood chips, building waste materials, papermaking sludge, etc. However, in order to obtain a stable soil improvement material, incineration ash (paper sludge incineration ash) generated when papermaking sludge is burned is preferably used.

  The paper sludge incineration ash is an ash that is captured by a dust collector when incinerating sludge produced by waste water treatment from a paper mill, and an ash that is discharged from the lower part of the incinerator without being scattered from the incinerator. , Which includes incinerated ash that has been discharged from paper mills and was generally forced to be landfilled after incineration, and is usually a trace amount of hexavalent chromium, fluorine, boron, etc. Contains hazardous substances controlled by No. 18.

  For example, in order to insolubilize the harmful substances, cheap and environmentally friendly cement and water are blended together with the incineration ash.

  The cement not only has an effect of insolubilizing harmful substances, but also has a suitable granulating property and further has an action of adjusting the strength of the obtained soil improvement material. As the cement, for example, blast furnace cement obtained by uniformly mixing blast furnace slag with Portland cement can be preferably used. The blast furnace cement has a small amount of hexavalent chromium, fluorine and boron contained in its components, and can suppress generation of harmful substances derived from raw materials.

  In the blending step, a polyvalent metal salt compound is preferably further blended with the incineration ash.

  Examples of the polyvalent metal salt compound suitably used in the present invention include aluminum sulfates. Examples of the aluminum sulfate include anhydrous aluminum sulfate, aluminum sulfate 14-18 hydrate, aluminum sulfate 12 hydrate, aluminum potassium sulfate 12 hydrate, aluminum sodium sulfate 12 hydrate, and ammonium aluminum sulfate 12 hydrate. These may be used alone or in combination of two or more. Among these, aluminum sulfate 14-18 hydrate is particularly preferable in terms of improving the fluorine elution prevention effect.

  In order to immobilize fluorine, it is preferable to use sulfate radicals for the production of ettringite that incorporates fluorine in addition to solidification with cement, and the effect is also manifested in sulfuric acid, calcium sulfate, magnesium sulfate, iron sulfate, etc. However, by using aluminum sulfates among the sulfate group-containing compounds, a larger and more stable fluorine elution inhibitory effect can be expressed more rapidly.

  Furthermore, in the blending step, in addition to the cement and the suitably used polyvalent metal salt compound, a material having a harmful substance aggregating ability and a harmful substance adsorbing ability, such as sulfates and phosphates other than aluminum sulfates, Depending on the type and content of the toxic substance, they can be used alone or in combination of two or more, and the amount added can be adjusted appropriately.

  In the blending step, it is preferable to blend a solidifying agent for adjusting the strength of the resulting soil improvement material when mixing incinerated ash, cement, a polyvalent metal salt compound that can be suitably used, and the like. As the solidifying agent, in addition to the cement, for example, a calcium compound such as gypsum and lime, a material that exhibits a solidifying ability and aggregating ability by a hydration reaction or the like, alone or in combination of two or more kinds, the amount of addition is appropriately determined. Can be used with adjustment.

  In the blending process, by mixing raw materials such as incinerated ash and cement in the presence of water, the raw materials can easily form a lump, and the water content of the lump can be made uniform to obtain a uniform strength. The earth bearing capacity is improved. In addition to the insolubilization reaction of hexavalent chromium and fluorine and the appropriate solidification reaction of the soil amendment material, the mixing amount of water, the granulation property described later and the porosity of the granulated material, the drying time can be shortened. From the viewpoint of drying, such as energy suppression, it is possible to adjust the moisture content of the entire mixture of at least incinerated ash, cement and water to 50% by mass or less, further 45% by mass or less, and particularly 35% by mass or less. It is preferable to adjust so that it may become 5 mass% or more, Furthermore, 10 mass% or more.

  In addition, various known mixers can be used for mixing incineration ash, cement, a polyvalent metal salt compound that can be suitably used, water, and the like.

  Here, in particular, in order to suppress elution of hexavalent chromium, in the process up to the drying process, for example, in a granulation process in which a mixture of at least incinerated ash, cement and water forms a lump, Add powdered sulfur compound.

  Among sulfur compounds, liquid sulfur compounds are easily oxidized to inhibit the reduction reaction effect of hexavalent chromium and generate sulfurous acid gas, so that a sulfurous acid gas treatment facility is required. Therefore, a powdery sulfur compound is used in the present invention.

  Furthermore, the sulfur compound is unevenly distributed on the surface of the granulated product by taking a means of adding a powdery sulfur compound to a mixture of incinerated ash, cement, a polyvalent metal salt compound that can be suitably used, water, and the like. And insolubilization of hexavalent chromium and fluorine can be further promoted.

Examples of the powdery sulfur compound include powdery, for example, bisulfite (HSO ₃ ⁻ ), thiosulfate (S ₂ O ₃ ²⁻ ), sulfide (S ₂ ⁻ ), and hydrosulfide (SH _2). ^- ), Hyposulfite (S ₂ O ₄ ²⁻ ), pyrosulfite (S ₂ O ₄ ⁵⁻ ), and the like. These may be used alone or in combination of two or more. Among them, powder bisulfite is preferable from the viewpoints of cost-effectiveness and good workability with powder, miscibility between incinerated ash and polyvalent metal salt compound, and subsequent granulation. Powdered sodium bisulfite is particularly preferred.

  The mixing ratio of incineration ash, cement, water, and powdered sulfur compounds is based on the prevention of elution of fluorine and hexavalent chromium, miscibility at the time of mixing, ease of subsequent granulation, and shape of the resulting granulated product From the viewpoint of stability, 5 to 15 parts by mass of cement, further 8 to 13 parts by mass, 20 to 50 parts by mass of water, and further 25 to 45 parts by mass of powder with respect to 100 parts by mass of incinerated ash in solid content The sulfur-like sulfur compound is preferably 0.5 to 2.5 parts by mass, more preferably 0.7 to 2.0 parts by mass. Moreover, when using a polyvalent metal salt compound, the compounding quantity is 20-40 mass parts with respect to 100 mass parts of incineration ash with solid content from the point of expression of the stable fluorine elution inhibitory effect, Furthermore, 25-25. It is preferably 35 parts by mass.

  As mentioned above, after adding a powdery sulfur compound to the lump which consists of a mixture thru | or a mixture which consists of at least incineration ash, cement, and water, a granulated material is further prepared in a granulation process.

  When granulating the mixture to which the powdery sulfur compound is added, for example, a known type of granulator such as a reverse flow method, a rolling method, a stirring method, an extrusion method, or a crushing method can be appropriately used. Among them, it has both functions of mixing and granulation, and can efficiently mix and granulate, and can easily adjust the porosity and lump flexibility of the intended granulated product. Therefore, a reverse flow mixer is preferable.

  When granulating with the said backflow mixer, the particle diameter of a granulated material can be adjusted with granulation time. When the granulation time is short, granulation does not proceed and the particle size is reduced. Conversely, when the granulation time is long, granulation proceeds and the particle size is increased. However, the particle diameter does not exceed a certain size. This is considered to be because as the particle diameter increases, the force applied to the particles during granulation concentrates on a part of the entire particles, and the particles are more easily broken. For these reasons, the granulation time is preferably 1 to 30 minutes, more preferably 3 to 20 minutes, and particularly preferably 5 to 15 minutes.

  In addition, although granulation can also be performed after the drying process mentioned later, it is preferable to perform before using for a drying process. After granulation and drying, for example, when an alkaline earth metal compound is added to the obtained dried granulated product, it conforms to JIS A 1102 “Aggregate Screening Test Method” and conforms to JIS Z 8801-1 “Sieving Screen for Testing”. -Part 1: The ratio of particles that pass through a sieve having a nominal mesh size of 8 mm and that does not pass through a sieve having a nominal mesh size of 106 μm is 60% by mass or more of the whole. It is preferable to appropriately adjust the granulation time so that the proportion of particles having a particle size of 106 μm or more and 8 mm or less is 80% by mass or more of the whole granulated product. This is because, in the drying step after the granulation step, the particles are destroyed and the particle size is reduced, and since the alkaline earth metal compound described later usually has a particle size of about 0.1 mm, the drying step This is because the soil improvement material obtained by adding an alkaline earth metal compound has a particle size that is smaller than that of the granulated product.

  In the present specification, when the particle diameter varies depending on the measurement position, the “particle diameter” means “particle long diameter”.

  There are two reasons why it is preferable to adjust the particle size of the granulated product.

  First, by adjusting the specific surface area of the granulated product within a predetermined range by granulation, the fluorine incorporated into the ettringite crystal structure can be prevented from being destroyed by carbon dioxide. This is because the ratio of contact with carbon can be adjusted.

  Secondly, for example, when an alkaline earth metal compound is added in the drying step to obtain a soil improving material, the alkaline earth metal compound can be appropriately attached to the surface of the dried granulated product. That is, when the granulated product having a particle diameter of less than 106 μm increases, the surface area per unit mass increases, and the alkaline earth metal compound can be attached only to a part of the dry granulated product surface. On the contrary, when the granulated product having a particle diameter exceeding 8 mm increases, the alkaline earth metal compound may be excessive with respect to the surface area of the granulated product in the large granulated product, and elution of hexavalent chromium and fluorine. It is difficult for the alkaline earth metal compound in such an amount that the effect of suppressing the above is sufficiently expressed to adhere uniformly to the surface of each dried granulated product. In either case, it is difficult to improve the effect of suppressing the elution of fluorine from the treated soil obtained by mixing the obtained soil improving material and mud.

  In addition, in this Embodiment 1, in order to further improve the effect of suppressing elution of hexavalent chromium and fluorine, and to suppress the generation of dust and improve handling, sieving of the granulated material is performed before drying. May be. For sieving, a known system such as a vibration type or a rotary type can be used.

  The average particle diameter of the granulated product obtained in the granulation step is preferably 0.1 to 8 mm, more preferably 0.2 to 2 mm. If the average particle size of the granulated product before drying is less than 0.1 mm, the drying property is good, but it becomes fine particles and fluorine is likely to elute, and on the other hand, dust may be generated during use. Conversely, if the average particle diameter of the granulated product before drying exceeds 8 mm, it may be difficult to perform a uniform drying treatment.

  The granulated product having a particle diameter of less than 0.1 mm obtained when sieving can be added to the raw material before granulation and reused. Such a granulated product having a small particle diameter has an effect of promoting the production of the granulated product as a seed lump in granulation, and can improve the production efficiency. Moreover, the granulated product with a particle diameter exceeding 8 mm obtained when sieving can be made into a granulated product with a desired particle diameter by crushing with a crusher. As the crusher, those of various known methods can be used. However, as in the first embodiment, the moisture content of the entire granulated product is, for example, a soft material of about 20 to 40% by mass. It is preferable to use a vertical crusher from the viewpoint of improving the production efficiency and hardly generating unnecessary fine granules.

  In addition, although the process of sieving and crushing may be performed after curing, which will be described later, it is preferably performed after granulation and before curing in order to efficiently obtain a granulated product having stable quality.

  In order to promote the reaction between the sulfur compound and raw materials such as incinerated ash, cement, and polyvalent metal salt compound, and water, curing is preferably performed after granulation. The curing period is preferably 4 hours to 7 days, more preferably 12 hours to 2 days, and particularly preferably 18 to 36 hours. If it is cured for 7 days or more, the granulated product may solidify. On the other hand, if it is less than 4 hours, harmful substances may not be sufficiently fixed and may be eluted, and the moisture distribution of the granulated product is not stable. In many cases, the lump of the granulated product may be broken in the next drying step.

  The granulated product obtained in the granulation step is preferably subjected to a drying treatment after sieving and curing. For drying, for example, a known system such as a kiln type, a conveyor belt conveyance type, or a fluidized bed type can be adopted. Among these, a method in which the granulated product is not miniaturized by a mechanical external force during drying and the thermal efficiency is favorable is preferable.

  The kiln type refers to a system in which a granulated material is continuously charged from one end of a rotating drum, and the granulated material which is dried by heating directly inside the drum is continuously taken out from the other end of the drum. .

  A conveyor belt conveyance type means the system which conveys a granulated material with a conveyor belt toward the other end from the heated dome, and dries.

  The fluidized bed type is a method in which a granulated material is continuously charged into a fluidized bed having a large number of hot air blowing holes on the bottom, and the granulated material is moved upward or laterally as the drying progresses by the hot air blown from the bottom of the fluidized bed. And finally the dried granulated product is continuously taken out from the take-out port. The fluidized bed type includes a vertical type and a horizontal type, both of which can be used, but a horizontal type with less destruction of the granulated material due to dropping is preferable, and a stirring and feeding mechanism that applies external force to the material to be dried inside the drying apparatus A method that does not have the above is more preferable. In addition, weirs are provided inside to divide the fluidized bed into a plurality of sections, and the granulated material thrown into the upstream section moves upward as the drying proceeds with hot air blown from the bottom, and further downstream Those designed to move to the compartment are more preferable in terms of drying efficiency.

  In FIG. 2, the schematic block diagram of the horizontal type fluidized bed type drying apparatus which provided the weir in the inside and divided the fluidized bed into plurality is shown. In FIG. 2, the horizontal fluidized bed dryer 12 includes a vent plate 1 and a plurality of weirs 2 that partition the vent plate 1 into a plurality of compartments. 10 is supplied. Below the ventilation plate 1, a fan 3 for taking in outside air and a heater 4 for heating the air from the fan 3 with steam are provided. The hot air supplied from the heater 4 passes through the ventilation plate 1 and comes into contact with the granulated product 10, whereby the granulated product 10 is dried. The air after coming into contact with the granulated material 10 is discharged to the outside through the fan 5 and the silencer 6. The granulated product 10 heated on the ventilation plate 1 loses moisture and becomes gradually lighter, and moves over the weir 2 to the next section. The granulated product 10 moved to the next section is further heated and finally discharged onto the conveyor 8 on the downstream side.

  In order to prevent the solidification reaction of the cement from proceeding excessively and to effectively attach, for example, an alkaline earth metal compound added in a post-process to the dried granulated product, the moisture content of the dried granulated product is 3.0 mass. % Or less, more preferably 0.5 to 3.0% by mass, and particularly preferably 1.0 to 2.5% by mass. When the moisture content of the dried granulated product is adjusted to such a range, the alkaline earth metal compound effectively adheres to the surface of the dried granulated product, and the effect of suppressing elution of free fluorine is high. That is, when the soil conditioner obtained is mixed with mud, even if hydroxide ions are generated from the alkaline substance derived from the soil conditioner and coordinate to aluminum and fluorine in the mud is liberated, When an alkaline earth metal compound is present on the surface of the soil improvement material where oxide ions are generated, the liberated fluorine reacts immediately with the alkaline earth metal compound, so that the elution of fluorine is effectively suppressed.

  When the moisture content of the dried granulated product is less than 0.5% by mass, the moisture content is too low, and the alkaline earth metal compound does not sufficiently adhere to the surface of the dried granulated product. Conversely, the moisture content is 3.0% by mass. If it exceeds 50%, the water content is too high, and the alkaline earth metal compound is difficult to uniformly adhere to the surface of the dried granulated product. In either case, the effect of suppressing elution of hexavalent chromium and fluorine is likely to be uneven, and in particular, the effect of suppressing elution of fluorine from the treated soil is difficult to improve.

  In addition, although it can obtain as a soil improvement material aiming at the dried granulated material which passed through the drying process as mentioned above, then, for example, an alkaline earth metal compound is added to the dried granulated material to obtain a soil improving material. You can also. Examples of the method for adding the alkaline earth metal compound include a method in which a predetermined amount of the alkaline earth metal compound stored in the silo is added to the dried granulated product with a quantitative feeder.

  The alkaline earth metal compound is preferably a calcium compound and / or a magnesium compound, and is preferably at least one selected from calcium oxide, calcium hydroxide, magnesium oxide and magnesium hydroxide, for example. Among these, at least one of magnesium oxide and magnesium hydroxide is more preferable, since magnesium has a high effect of suppressing elution when a compound is formed with fluorine and the risk of an exothermic reaction in storage and handling is low. Magnesium oxide is particularly preferable. preferable.

  The soil improvement material thus obtained is based on JIS A 1102, and passes through a sieve having a nominal aperture of 8 mm as defined in JIS Z 8801-1, and the proportion of particles not passing through a sieve having a nominal aperture of 106 μm It is preferably 60% by mass or more, more preferably 70% by mass or more.

  When the proportion of particles that pass through a sieve having a nominal aperture of 8 mm and that does not pass through a sieve having a nominal aperture of 106 μm is less than 60% by mass, the fluorine incorporated in the ettringite crystal structure is destroyed by carbon dioxide. Since the specific surface area of the granulated material in contact with carbon dioxide is not adjusted to the extent that it can be prevented, hexavalent chromium and fluorine are effectively eluted from the treated soil obtained by mixing the obtained soil conditioner with mud. It becomes difficult to suppress it.

The amount of elution of hexavalent chromium and fluorine eluted from the treated soil prepared by mixing the soil improvement material and mud obtained and adjusting the corn index to 500 kN / m ² or more is based on Notification No. 18 of the Ministry of the Environment in 2003. When measured by the dissolution test method, the dissolution amount of hexavalent chromium is 0.05 ppm or less, more preferably 0.03 ppm or less, and the dissolution amount of fluorine is preferably 0.8 ppm or less, more preferably 0.7 ppm or less. .

In addition, when the obtained soil conditioner and mud are mixed and the pH of the treated soil adjusted to a corn index of 500 kN / m ² or more is measured by a test method based on Environment Agency Notification No. 46 in 1991, It is preferably 7.0 to 10.0, more preferably 8.0 to 9.8.

  Next, although the soil improvement material of this invention and its manufacturing method are demonstrated still in detail based on an Example, this invention is not limited only to these Examples.

Examples 1-12 and Comparative Examples 1-7 (Preparation of soil amendment)
Cement (blast furnace cement), polyvalent metal salt compound and water are blended in proportions shown in Table 1 to 100 parts by mass of incinerated ash (paper sludge incinerated ash) in solid content, and a reverse flow mixer (Nippon Eirich Co., Ltd.) )), And when a lump is formed from these mixtures, the amount of sodium bisulfite added in the amount shown in Table 1 (the amount with respect to 100 parts by mass of incinerated ash as solid content) is added, and finally Mixing and granulation were performed for 10 minutes to obtain a granulated product.

  In addition, the moisture content of the whole mixture at the time of adding sodium bisulfite is as showing in Table 1. In Comparative Examples 1 to 4, no sodium bisulfite was added. In Comparative Examples 5 to 6, liquid sodium bisulfite was used. In Comparative Example 7, no polyvalent metal salt compound was added, and liquid sodium bisulfite was used. Was used.

  Next, the obtained granulated material was sieved using a rotary sieve device (sieve diameter: 3 mmφ). The granulated product having a large particle size separated by this sieving was crushed with a crusher (vertical axis method) and sieved again.

  Next, the granulated product after sieving was cured for 24 hours under conditions of a temperature of 23 ° C. and a relative humidity of 50%.

  Further, the granulated product after curing is subjected to an average residence time inside the drying apparatus with hot air at 150 ° C. using a horizontal fluidized bed drying apparatus in which weirs are provided in the interior shown in FIG. It dried as 1 hour and obtained the soil improvement material.

  About the obtained soil improvement material, based on JISA1102, the ratio of the particle | grains which pass the sieve of nominal aperture 8mm prescribed | regulated to JISZ8801-1 and which do not pass the sieve of nominal aperture 106micrometer was measured. The results are shown in Table 2.

Furthermore, about the obtained soil improvement material, each characteristic was investigated in accordance with the method shown below. The results are shown in Table 2. In addition, each soil improvement material was contained in the pure sand soil of water content 30 mass% so that a corn index might be set to 500 kN / m < ² >, and the treated soil was prepared.

(A) Hexavalent chromium elution amount and fluorine elution amount The elution amount of hexavalent chromium and fluorine eluted from the treated soil was measured by an elution test method based on Notification No. 18 of the Ministry of the Environment in 2003.

(B) pH
The pH of the treated soil was measured by a test method based on the Environment Agency Notification No. 46 in 1991.

  In addition, from the results of (a) and (b), in the case of treated soil, ○ is shown in Table 2 when the soil satisfies the soil environmental standards regulated by the Ministry of the Environment Notification No. 18 in 2003, and x is not satisfied. Show.

(C) Ground strength The treated soil after a man (weight: about 80 kg) was stepped 20 times with his / her foot was visually observed and evaluated based on the following evaluation criteria.
(Evaluation criteria)
A: Same as before trampling, no deformation at all.
○: A part is slightly deformed.
Δ: Slightly deformed as a whole.
X: The shape has completely changed.

  In each of the soil improvement materials of Examples 1 to 12, incinerated ash, cement and powdered sulfur compound are used, and at least a powdered sulfur compound is added to a mixture composed of incinerated ash, cement and water, and granulated. The ratio of particles that pass through a sieve with a nominal aperture of 8 mm and do not pass through a sieve with a nominal aperture of 106 μm is 60% by mass or more of the total. Therefore, when the soil improvement material of Examples 1-12 is mixed with mud, not only the elution of hexavalent chromium from the treated soil, but also the elution of fluorine regardless of the water content and pH of the mud. Sufficiently controlled, and the treated soil satisfies the soil environment standards regulated by the Ministry of the Environment Notification No. 18 in 2003. Moreover, excellent ground strength is expressed in the treated soil.

  On the other hand, none of the soil improvement materials of Comparative Examples 1 to 4 contains a sulfur compound, passes through a sieve having a nominal aperture of 8 mm, and does not pass through a sieve having a nominal aperture of 106 μm. Is less than 60% by mass of the total. Therefore, when the soil improvement materials of Comparative Examples 1, 3, and 4 are mixed with mud, the elution of hexavalent chromium and / or fluorine is not sufficiently suppressed, and the treated soil is 2003 Ministry of the Environment Notification No. 18 Does not meet the regulated soil environmental standards. Moreover, when the soil improvement material and mud soil of the comparative example 2 are mixed, although the treated soil satisfies the soil environment standard regulated by the Ministry of the Environment Notification No. 18 in 2003, the soil resistance is inferior.

  On the other hand, since the soil improvement materials of Comparative Examples 5 to 6 are obtained by blending a liquid sulfur compound as a sulfur compound, elution of hexavalent chromium and fluorine is sufficiently suppressed when mixed with mud. In particular, the amount of hexavalent chromium elution is large, and the treated soil does not satisfy the soil environment standards regulated by the Ministry of the Environment Notification No. 18 of 2003.

  Moreover, the soil improvement material of Comparative Example 7 was obtained by blending a liquid sulfur compound as a sulfur compound without blending a polyvalent metal salt compound, and passed through a sieve having a nominal opening of 8 mm. In addition, the proportion of particles that do not pass through a sieve having a nominal aperture of 106 μm is less than 60% by mass. Therefore, when the soil conditioner of Comparative Example 5 is mixed with mud, the elution of hexavalent chromium and fluorine is not sufficiently suppressed, and the treated soil is regulated by the Ministry of the Environment Notification No. 18 of 2003. Not satisfied. Moreover, the ground strength of the treated soil is insufficient.

  By the production method of the present invention, regardless of the soil to be treated, elution of hexavalent chromium and fluorine from the treated soil can be sufficiently suppressed, and a soil improving material excellent in ground strength can be easily produced. it can. The soil improvement material of the present invention can also be used in the field of building materials, for example, as a snow melting material, grassland improvement material, backfilling material, embankment and the like.

DESCRIPTION OF SYMBOLS 1 Ventilation plate 2 Weir 3, 5 Fan 4 Heater 6 Silencer 7, 8 Conveyor 10 Granulated material 12 Horizontal fluid bed type drying apparatus

Claims (3)

A method for producing a soil improvement material comprising incinerated ash as a main component,
At least a blending step of blending cement and water with the incinerated ash, a granulation step performed after the blending step, and a drying step;
In the steps from the blending step to the drying step, granulate after adding a powdery sulfur compound to a mixture consisting of at least incineration ash, cement and water and adjusting the water content to 50% by mass or less. A method for producing a soil amendment, characterized in that For 100 parts by mass of incinerated ash with a solid content, 5-15 parts by mass of cement, 20-50 parts by mass of water and 0.5-2.5 parts by mass of powdered sulfur compound are blended,
In accordance with JIS A 1102, the ratio of particles that pass through a sieve with a nominal aperture of 8 mm specified in JIS Z 8801-1 and that does not pass through a sieve with a nominal aperture of 106 μm is 60% by mass or more. The manufacturing method according to claim 1, which is granulated.   The soil improvement material obtained by the manufacturing method of Claim 1 or 2.

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