JP2022108470A - Reduction material, production method thereof, cement composition, and soil improver - Google Patents

Abstract

To provide a reduction material capable of reducing occurrence of granular floating matters on a surface of slurry when being formed into the slurry.SOLUTION: There is provided a reduction material including sulfur particles, a Ca-containing object, and a reaction product of them. In the reduction material, with a total amount of the sulfur particles, a Ca-containing object, and reaction product of them as a reference, a dissolution ratio of the sulfur particles, a Ca-containing object, and reaction product to water in a prescribed condition is 3 mass% or greater. The reduction material may satisfy the following formula (1). The formula (1) is WLRa≥(WLS×RS+WLCa×RCa)/(RS+RCa)+0.5. In formula (1), WLRa, WLS, and WLCa indicate, respectively, the dissolution ratio of the reduction material, the sulfur particles before reaction, and the Ca-containing object before reaction to water under the prescribed condition, and RS and RCa respectively indicate a molar ratio of the sulfur particles before reaction and the Ca-containing object before reaction.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a reducing material, a method for producing the same, a cement composition, and a ground improvement material.

Cement clinker is produced using limestone, clay, silica stone, iron oxide and the like as main raw materials. In the production of cement clinker, in addition to these main raw materials, various industrial by-products and industrial wastes are effectively used as raw materials and fuels. Therefore, a small amount of heavy metals such as cadmium, chromium, lead and molybdenum derived from various raw materials and fuels may be mixed in cement clinker depending on the selection of raw materials. Therefore, a technique is known in which a sulfur-containing reducing agent is used to reduce the heavy metal ions derived from cement clinker, thereby reducing the amount of eluted heavy metal ions. (See Patent Document 1, for example). On the other hand, as a method for ground improvement, there is known a method of excavating while feeding a solidified slurry for ground improvement into the ground, stirring and mixing the excavated soil and the solidified slurry, and solidifying the mixture (see, for example, Patent Document 2). ).

JP 2018-145077 A Japanese Patent Application Laid-Open No. 2004-346108

When the cement composition containing cement clinker and the soil to be ground improvement (soil to be ground improvement) contain heavy metal components such as hexavalent chromium, by using a reducing agent containing sulfur, hexavalent chromium etc. Elution of heavy metals can be suppressed. However, for example, when a slurry construction method such as Patent Document 2 is applied to ground improvement, the sulfur contained in the reducing material floats on the slurry surface, sulfur is not uniformly dispersed in the slurry, and is reduced in the ground improvement soil. There is concern that the distribution of the material will be uneven. Soil improvement and construction of cement compositions are often carried out on a large scale, and there is concern that uneven distribution of the reducing agent may result in variations in the effect of suppressing the elution of heavy metal components.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a reducing material capable of reducing particulate floating matter generated on the surface of a slurry when it is made into a slurry, and a method for producing the reducing material. Further, the present invention provides a cement composition and a soil improvement material capable of improving the uniformity of distribution of the reducing agent by using such a reducing agent.

As a result of intensive studies aimed at achieving the above object, the present inventors have found that the dispersibility of the reducing material in water is improved by reacting sulfur particles with a Ca-containing material, and have completed the present invention. came to.

In one aspect, the present invention includes sulfur particles, Ca-containing materials and reaction products thereof, and sulfur particles under predetermined conditions based on the total amount of sulfur particles, Ca-containing materials and reaction products, Provided is a reducing material in which a Ca-containing material and a reaction product have a solubility in water (WL _Ra ) of 3% by mass or more.

Sulfur particles are poorly dispersible in water, and when slurried, the sulfur particles float on the surface of the slurry. However, the reducing agent containing the reaction product of the sulfur particles and the Ca-containing material has excellent dispersibility in water. The reason is presumed as follows. Since sulfur particles are originally hydrophobic, they tend to float on the surface of water. However, by reacting the sulfur particles with the Ca-containing material, the surface of the sulfur particles is modified to become hydrophilic and easily dispersed in water. Here, in the reducing material, the dissolution ratio (WL _Ra ) of the reducing material containing the reaction product of sulfur and the Ca-containing material in water is 3% by mass or more. In such a reducing agent, the surface of the sulfur particles is sufficiently modified, and the dispersibility in water is sufficiently good. For this reason, it is considered possible to reduce particulate floating matter generated on the surface of the slurry when it is made into a slurry.

In one aspect, the present invention provides a reducing material containing sulfur particles, a Ca-containing material and a reaction product thereof, and satisfying the following formula (1).
WL _Ra ≧(WL _S ×R _S +WL _Ca ×R _Ca )/(R _S +R _Ca )+0.5 (1)
In the above formula (1), WL _Ra , WL _S and WL _Ca respectively represent the dissolution ratios of the reducing agent, the sulfur particles before the reaction, and the Ca-containing material before the reaction in water under predetermined conditions, and R _S and R _Ca respectively indicate the molar ratio of the sulfur particles before the reaction and the Ca-containing material before the reaction.

In the reducing material, the dissolution ratio in water of the reducing material containing the reaction product of sulfur and the Ca-containing material is higher than the dissolution ratio of each of the sulfur and the Ca-containing material, as represented by the above formula (1). is also large enough. Those that satisfy the formula (1) have sufficiently modified sulfur particle surfaces and have sufficiently good dispersibility in water. For this reason, it is considered possible to reduce particulate floating matter generated on the surface of the slurry when it is made into a slurry.

In one aspect, the present invention provides a reducing material obtained by reacting sulfur particles and a Ca-containing material in the presence of water for 1 minute or more. In such a reducing material, it is considered that the surface of the sulfur particles is sufficiently modified by the reaction of the Ca-containing material. Therefore, the dispersibility in water becomes sufficiently good. It is considered that this can reduce particulate floating matter generated on the surface of the slurry when it is made into a slurry.

The Ca-containing material preferably contains one or more selected from the group consisting of calcium oxide, calcium carbonate, calcium chloride, calcium hydroxide, calcium sulfide, calcium sulfate, and calcium sulfite. This can further improve the dispersibility of the reducing agent in water.

The Ca-containing material preferably contains calcium sulfite and/or calcium hydroxide. This can further improve the dispersibility of the reducing agent in water.

The Ca-containing material preferably contains calcium sulfite and/or calcium sulfide. Calcium sulfite and calcium sulfide have an effect of inhibiting elution of hexavalent chromium. Therefore, by including calcium sulfite and/or calcium sulfide, it is possible to further reduce the elution of hexavalent chromium while suppressing the generation of particulate suspended matter on the surface of the slurry.

The Ca-containing material is preferably contained in raw concrete sludge and/or clinker dust. As a result, the manufacturing cost of the reducing material can be sufficiently reduced.

In one aspect, the present invention provides a cement composition containing any of the reducing materials described above. The reducing material contained in this cement composition has excellent dispersibility in water as described above. Therefore, this cement composition can improve the uniformity of the distribution of the reducing agent.

In one aspect, the present invention provides a soil improvement material containing any of the reducing materials described above. The reducing agent contained in this soil improvement material has excellent dispersibility in water as described above. Therefore, such a soil improvement material can improve the uniformity of the distribution of the reducing material even when used as a slurry. Therefore, even if it is used in a ground improvement method using slurry, the variation in the properties of the ground improvement soil can be sufficiently reduced.

In one aspect, the present invention provides a method for producing a reducing material, which comprises mixing sulfur particles and a Ca-containing material and reacting them in the presence of water for 1 minute or more. In the above step, it is considered that the surface modification of the sulfur particles proceeds sufficiently due to the reaction with the Ca-containing material. Therefore, the reducing material obtained through such steps has sufficiently good dispersibility in water. It is considered that this can reduce particulate floating matter generated on the surface of the slurry when it is made into a slurry.

It is possible to provide a reducing material that can reduce particulate floating matter that occurs on the surface of a slurry when it is made into a slurry, and a method for producing the reducing material. Moreover, by using such a reducing agent, it is possible to provide a cement composition and a soil improvement material capable of improving the uniformity of distribution of the reducing agent.

4 is a photograph showing the dispersibility in water of the reducing material of Example 2. FIG. 4 is a photograph showing the dispersibility in water of the reducing material of Comparative Example 1. FIG.

Embodiments of the invention are described below. However, the following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents.

The reducing material according to one embodiment includes sulfur particles, Ca-containing substances and reaction products thereof, and is based on the total amount of sulfur particles, Ca-containing substances and reaction products, under predetermined conditions (A) The dissolution ratio (WL _Ra ) of the sulfur particles, the Ca-containing material and the reaction product in water is 3% by mass or more.

In this specification, the dissolution ratio in water (WL _Ra ) under the predetermined condition (A) is derived by the following procedure. First, 4 g of a reducing agent and 100 mL of distilled water (20° C.) are introduced into a 200 ml beaker and stirred at 20° C. for 30 minutes using a magnetic stirrer with a length of 30 mm (240 rpm). Thereafter, the resulting dispersion is filtered through a filter paper (membrane filter, manufactured by ADVANTEC, cellulose acetate type, pore size: 0.45 μm, diameter: 47 mm), and the collected solid content is dried in a dryer set at 40 ° C. dry for 15 hours. When the mass of the dried product (moisture content: 4% by mass or less) obtained in this way is D _Ra [g], WL _Ra is calculated by {(4-D _Ra )/4}×100. Desired.

If the reaction between the sulfur particles and the Ca-containing material does not proceed sufficiently (=the amount of reaction products is small) and the surface of the sulfur particles is not sufficiently modified, the dissolution ratio (WL _Ra ) becomes small. There is a tendency. On the other hand, when a sufficient amount of reaction product is generated between the sulfur particles and the Ca-containing material (=the amount of the reaction product is large), the dissolution ratio (WL _Ra ) tends to increase. The dissolution ratio (WL _Ra ) is preferably 3.5 mass or more, from the viewpoint of further improving the dispersibility in water and further reducing particulate suspended matter generated on the surface of the slurry when it is made into a slurry. , more preferably 5% by mass or more, more preferably 7% by mass or more.

On the other hand, from the viewpoint of smooth production of the reducing agent, the dissolution ratio (WL _Ra ) is, for example, 90% by mass or less, preferably 70% by mass or less, more preferably 50% by mass or less, and even more preferably It is 30% by mass or less, and particularly preferably 10% by mass or less. The reducing material according to this embodiment may satisfy the following formula (1). This makes it possible to further reduce particulate floating matter generated on the surface of the slurry. The meaning, preferred form, and numerical range of each symbol in formula (1) are as described in the following embodiments.

A reducing material according to another embodiment contains sulfur particles, a Ca-containing material, and a reaction product thereof, and satisfies the following formula (1).
WL _Ra ≧(WL _S ×R _S +WL _Ca ×R _Ca )/(R _S +R _Ca )+0.5 (1)
Here, in the above formula (1), WL _Ra , WL _S and WL _Ca are respectively the reducing agent, the pre-reaction sulfur particles, and the pre-reaction Ca-containing substance into water under the predetermined condition (A). The dissolution ratio (mass basis) is indicated, and R _S and R _Ca indicate the molar ratio of sulfur particles before reaction and Ca-containing substance before reaction, respectively.

WL _Ra in the above formula (1) is the dissolution ratio (WL _Ra ) described in the above embodiment, and is derived by the above procedure. WL _S and WL _Ca in the above formula (1) are the dissolution ratios of the sulfur particles before the reaction and the Ca-containing substance before the reaction in water under the predetermined condition (A), and are derived in the same manner as WL _Ra . be done. That is, when 4 g of sulfur particles before the reaction are used instead of 4 g of the reducing agent and the mass of the dried product (water content: 4% by mass or less) obtained by the same procedure as described above is D _S [g], WL _S is obtained by the formula {(4−D _S )/4}×100. In addition, when 4 g of the Ca-containing material before the reaction is used instead of 4 g of the reducing agent, and the mass of the dried product (water content: 4% by mass or less) obtained by the same procedure as described above is D _Ca [g] , WL _Ca are obtained by the formula {(4−D _Ca )/4}×100.

If the reaction between the sulfur particles and the Ca-containing material does not proceed sufficiently (=the amount of reaction products is small) and the surface of the sulfur particles is not sufficiently modified, the value of WL _Ra and the above formula ( The difference from the value of "(WL _S ×R _S +WL _Ca ×R _Ca )/(R _S +R _Ca )" on the right side of 1) becomes smaller. On the other hand, when the reaction product of the sulfur particles and the Ca-containing material is sufficiently generated (=the amount of the reaction product is large), the value of WL _Ra is "(WL _S ×R _S +WL _Ca ×R _Ca ) /(R _S +R _Ca )”. In the above formula (1), the value of WL _Ra is higher than the value obtained by adding "0.5" to the value of "(WL _S ×R _S +WL _Ca ×R _Ca )/(R _S +R _Ca )". is large, the reaction product between the sulfur particles and the Ca-containing material is sufficiently generated, and the surface of the sulfur particles is sufficiently modified. For this reason, it is considered that the dispersibility in water is sufficiently good, and when the slurry is made into a slurry, particulate floating matter generated on the surface of the slurry can be reduced.

From the viewpoint of further reducing particulate suspended matter generated on the surface of the slurry, the reducing agent preferably satisfies the formula (2), and more preferably satisfies the formula (3).
WL _Ra ≧(WL _S ×R _S +WL _Ca ×R _Ca )/(R _S +R _Ca )+1.2 (2)
WL _Ra ≧(WL _S ×R _S +WL _Ca ×R _Ca )/(R _S +R _Ca )+1.5 (3)

From the viewpoint of smooth production of the reducing material, the upper limit of WL _Ra in the above formula (1), (2) or (3) is "(WL _S ×R _S +WL _Ca ×R _Ca )/(R _S +R _Ca ) +10” or “(WL _S ×R _S +WL _Ca ×R _Ca )/(R _S +R _Ca )+8”.

The sulfur particles in each of the above-described embodiments are not particularly limited, and may be composed of elemental sulfur or may contain impurities other than sulfur. Sulfur particles may be obtained, for example, from natural sulfur, from pyrite, or as a by-product of the desulfurization process during petroleum refining. Sulfur particles may be one of these alone or in combination of two or more. From a cost standpoint, the sulfur particles preferably include those obtained from by-products. The size of sulfur particles is not particularly limited.

The Ca-containing material in each of the above-described embodiments may be granular (Ca-containing particles) like sulfur. The Ca-containing material is preferably sparingly soluble in water having a pH of 7 or higher. This can sufficiently modify the surface of the sulfur particles. The Ca-containing material is not particularly limited, and examples thereof include various Ca salts such as calcium oxide, calcium carbonate, calcium chloride, calcium hydroxide, calcium sulfide, calcium sulfate, calcium sulfite, calcium nitrate, and calcium nitrite. Calcium sulfate may include any of a dihydrate (gypsum dihydrate), a hemihydrate (gypsum hemihydrate), and an anhydrate (gypsum anhydrite).

From the viewpoint of sufficiently suppressing the elution of Cr (VI) from the ground improvement soil, the Ca-containing material preferably contains at least one selected from the group consisting of calcium hydroxide, calcium sulfide and calcium sulfite, calcium sulfide and / Or it is more preferable to contain calcium sulfite.

The Ca-containing material may be contained in the raw concrete sludge and/or clinker dust. As a result, the procurement cost of the Ca-containing material can be lowered, and the production cost of the reducing material can be lowered.

From the viewpoint of sufficiently suppressing the elution of hexavalent chromium from the soil improvement soil when the reducing agent is used in the soil improvement material, the Ca-containing material may contain a sulfite. Sulfites include calcium bisulfite (Ca(HSO ₂ ) ₂ ) in addition to the calcium sulfite described above. As each sulfite, chemically synthesized commercial products or naturally occurring ones can be used. Calcium sulfite may be, for example, calcium sulfite anhydride and/or calcium sulfite hemihydrate contained in gypsum generated in a flue gas desulfurization process or the like.

The reaction product contained in the reducing material in each of the embodiments described above may contain, for example, a composite oxide having S (sulfur), Ca (calcium) and O (oxygen) as constituent elements. Such reaction products may, for example, adhere to the surface of the sulfur particles. It is believed that this modifies the surface of the sulfur particles to make them hydrophilic. However, such a complex oxide may be present in such a trace amount that it cannot be detected by analysis such as XRD, or it may be in a crystalline form (amorphous) that is difficult to detect by such analysis.

There are no particular restrictions on the mixing ratio of the sulfur particles and the Ca-containing substance when preparing the reducing material, and the content ratio of the sulfur particles, the Ca-containing substance and the reaction product in the reducing material. From the viewpoint of achieving both the dispersibility of the reducing agent in water and the reduction of the elution of hexavalent chromium at a sufficiently high level, the molar ratio of the Ca-containing material based on the sulfur particles contained in the reducing agent is 0.2 to 0.2. It may be 5, it may be 0.5-3, it may be 1.5-2. In addition, the molar ratio of the Ca-containing material based on the sulfur particles when preparing the reducing material may be 0.2 to 5, may be 0.5 to 3, and may be 1.5 to 2. There may be.

When the reducing material contains calcium sulfite as a Ca-containing material, the content of sulfur particles with respect to a total of 100 parts by mass of sulfur particles and calcium sulfite is the elution of hexavalent chromium from the soil improvement soil at the material age of 7 to 28 days. From the viewpoint of further reducing the amount, it is preferably 1 to 85 parts by mass, more preferably 5 to 70 parts by mass, more preferably 10 to 60 parts by mass, and still more preferably 15 to 45 parts by mass. .

The reducing material may consist of sulfur particles, Ca-containing substances and reaction products thereof, or may contain components other than sulfur particles, Ca-containing substances and these reaction products. Such components include hydroxides, chlorides, carbonates, sulfates, and the like (excluding those containing Ca). Specific examples include ferrous chloride, magnesium hydroxide and ferrous sulfate. The reducing material may contain at least one of the components described above.

An example of the method for producing the reducing material of each of the embodiments described above includes a step of mixing sulfur particles and a Ca-containing material and allowing the sulfur particles and the Ca-containing material to react in the presence of water for 1 minute or longer. In this step, for example, a composite oxide having S (sulfur), Ca (calcium) and O (oxygen) as constituent elements is generated as a reaction product on the surface of the sulfur particles, and the surface is modified. good too. This makes it possible to obtain a reducing material with excellent dispersibility in water. Mixing may be performed by stirring the water containing the sulfur particles and the Ca-containing material using a stirrer, a stirring blade, or the like. For example, sulfur particles and a Ca-containing material may be mixed in advance, and water vapor may be brought into contact therewith. Further, in the above step, after preparing a mixture containing sulfur particles and a Ca-containing material, the mixture may be put into water and mixed, or the sulfur particles and the Ca-containing material may be separately put into water. may be mixed together. The blending molar ratio of the Ca-containing material based on the sulfur particles when mixing the sulfur particles and the Ca-containing material may be 0.2 to 5, 0.5 to 3, 1.5 ~2.

From the viewpoint of further reducing particulate floating matter on the surface of the slurry when the slurry is prepared using the reducing agent, the lower limit of the reaction period of the sulfur particles and the Ca-containing substance is 1 minute, 5 minutes, 10 minutes, and 30 minutes. , 3 hours, 6 hours, 12 hours, 24 hours, 3 days or 7 days. The upper limit of the reaction period of the sulfur particles and the Ca-containing material may be, for example, 30 days, 3 weeks, 2 weeks, or 7 days from the viewpoint of reducing material production efficiency.

The reaction temperature is, for example, 10° C. or higher, preferably 20° C. or higher, more preferably 30° C. or higher, still more preferably 40° C. or higher, and particularly preferably 50° C. or higher. The upper limit of the reaction temperature may be 90°C, 85°C, or 80°C. The pH of the water used in the above step is preferably 7 to 13, more preferably 10 to 13, from the viewpoint of sufficiently advancing the reaction between the sulfur particles and the Ca-containing material.

The ratio of the mass of water to the mass of solids containing sulfur particles and Ca-containing material may be 0.2-2, or 0.4-1. This allows the reaction between sulfur and the Ca-containing substance to proceed smoothly while the solids are sufficiently dispersed in water. The solid matter may contain only sulfur particles and Ca-containing materials, or may contain other components.

A reducing material according to yet another embodiment is obtained by mixing sulfur particles and a Ca-containing material and allowing them to react for 1 minute or longer. The reaction time is calculated from the time when the sulfur particles, Ca-containing material and water coexist. The lower limit of reaction time (period) may be 5 minutes, 10 minutes, 30 minutes, 3 hours, 6 hours, 12 hours, 24 hours, 3 days or 7 days. The upper limit of the reaction time (period) may be, for example, 30 days, 3 weeks, 2 weeks, or 7 days from the viewpoint of reducing material production efficiency. This reducing material may also contain sulfur particles, Ca-containing substances, and reaction products thereof. For example, reaction products may adhere to the surface of the sulfur particles. The types of sulfur particles and Ca-containing material, and the blending molar ratio and content molar ratio thereof are the same as in the above-described embodiment. Also, the reaction conditions may be the same as in the production method described above. That is, the reaction temperature is preferably 10° C. or higher, more preferably 20° C. or higher, and even more preferably 30° C. or higher. The upper limit of the reaction temperature may be 90°C or 80°C. The description of the reducing material and the manufacturing method thereof according to the above-described embodiments is applied to the reducing material of the present embodiment.

In such a reducing material, it is considered that the surface of the sulfur particles is sufficiently modified by the reaction with the Ca-containing material. Therefore, the dispersibility in water becomes sufficiently good. It is considered that such a reducing material can reduce particulate floating matter generated on the surface of the slurry when it is made into a slurry.

The reducing material in each of the above embodiments may be in the form of powder, or may be water and a slurry (reducing material slurry) in which solids are dispersed in the water. The reducing material can be suitably used as a ground improvement material or a cement composition. The reducing material has excellent dispersibility in water. Therefore, uneven distribution of the reducing agent can be suppressed when used for various purposes. Therefore, it is possible to sufficiently suppress the occurrence of property variation and the occurrence of poor appearance due to uneven distribution of the reducing agent. For example, when a soil improvement material containing such a reducing agent is applied to a slurry construction method, particulate floating matter on the surface of the slurry is sufficiently reduced, and the appearance during construction can be improved. In addition, the soil improvement material can stably suppress the elution amount of hexavalent chromium from the solidified soil.

A cement composition according to one embodiment may comprise cement or cement clinker and the reducing agent of any of the embodiments described above. Such a cement composition contains a reducing material that is highly dispersible in water. Therefore, the uniformity of distribution of the reducing agent can be improved. Such a cement composition can be suitably used as a soil improvement material.

The soil improvement material according to one embodiment may be a cement-based soil improvement material containing cement or cement clinker and the reducing agent of any of the embodiments described above. It is thought that the sulfur particles contained in the reducing material gradually dissolve in the moisture in the soil that has been made alkaline by cement, releasing hydrogen sulfide ions. The released hydrogen sulfide ions themselves also reduce hexavalent chromium. When the reducing agent contains sulfite, hydrogen sulfide ions also have the effect of increasing the solubility of sulfite. This can further promote the reduction of hexavalent chromium.

The soil improvement material (cement composition) may include cement or cement clinker, the reducing material of any of the above-described embodiments, and gypsum. The content of the reducing material in the soil improvement material (cement composition) is preferably 0.5 to 30% by mass, more preferably 1 to 20% by mass, still more preferably 2 to 15% by mass, especially It is preferably 3 to 10% by mass. As a result, the elution of hexavalent chromium can be sufficiently suppressed while maintaining the solidification strength of the ground improvement soil.

When the reducing material contains calcium sulfite as a Ca-containing material, the lower limit of the content of calcium sulfite in the soil improvement material (cement composition) may be, for example, 0.1% by mass, even if it is 1% by mass. It may be 2% by mass, 3% by mass, or 4% by mass. The lower limit of the content of sulfur particles in the soil improvement material may be, for example, 0.1% by mass, may be 0.5% by mass, may be 1% by mass, or may be 2% by mass. may be 4% by mass. By containing calcium sulfite and sulfur particles in such a range, elution of hexavalent chromium from the ground improvement soil can be sufficiently suppressed.

The gypsum may be any of gypsum dihydrate, gypsum hemihydrate and gypsum anhydrate. From the viewpoint of strength development of the soil improvement material (cement composition), it is preferable to contain gypsum dihydrate or anhydrous gypsum. For example, when obtaining a soil improvement material (cement composition), a gypsum mixture of gypsum dihydrate and anhydrite may be used. From the viewpoint of strength development of soil improvement soil, the content of gypsum in the soil improvement material (cement composition) is, for example, 1 to 25% by mass, preferably 3 to 20% by mass, more preferably 4 15% by mass, more preferably 5 to 12% by mass.

The cement may be various Portland cements specified in JIS R5210:2003 "Portland cement". Among these, normal Portland cement or high-early-strength Portland cement is preferable from the viewpoint of easy availability and high compressive strength in a short material age. The total amount of chromium in the cement may be, for example, 30-250 mg/kg, or 50-200 mg/kg, from the viewpoint of availability. From the same viewpoint, the water-soluble hexavalent chromium content of cement may also be, for example, 3 to 40 mg/kg, or may be 5 to 30 mg/kg. The total chromium content of cement is measured according to the method described in JIS R5202:2010, and the water-soluble hexavalent chromium content is measured according to the method described in Cement Association Standard Test Method I-51-1981. be.

The content of cement or cement clinker in the soil improvement material (cement composition) is, for example, 50 to 98% by mass, preferably 70 to 95% by mass, more preferably 75 to 90% by mass. When the content of cement or cement clinker is less than 50% by mass, it tends to be difficult to develop the strength of the soil improvement soil. On the other hand, if the cement or cement clinker content exceeds 98% by mass, the amount of hexavalent chromium eluted from the soil improvement soil may increase depending on the hexavalent chromium content of the cement or cement clinker. When cement clinker is used, it is preferable to use it after adjusting it to an appropriate fineness.

The soil improvement material (cement composition) may further contain blast furnace slag powder. The content of blast furnace slag powder is, for example, 1 to 50% by mass, preferably 5 to 30% by mass, more preferably 10 to 20% by mass. When the content of the blast furnace slag is within this range, the amount of hexavalent chromium eluted from the ground improvement soil can be further suppressed, and the amount of reducing agent used can be reduced.

The fineness of the ground improvement material (cement composition) is not particularly limited, but the Blaine specific surface area is 1000 to 6000 cm ² /g, preferably 2000 to 5500 cm ² /g, more preferably 3000 to 5000 cm ² /g. and more preferably 4000 to 4500 cm ² /g. Within such a range, the elution amount of hexavalent chromium can be suppressed while maintaining the strength of the ground improvement soil.

The method for producing a soil improvement material (cement composition) is not particularly limited, and may be produced by mixing raw materials adjusted to a predetermined fineness, or by pulverizing while mixing some or all of the raw materials. may be manufactured.

The ground improvement soil improved by the soil improvement material includes the above-mentioned soil improvement material and the soil to be improved. Soil improvement soil may be obtained by a method of injecting and mixing a slurry soil improvement material into the ground (slurry method). Since the soil improvement material contains a reducing material that is highly dispersible in water, even if it is made into a slurry, it is possible to suppress the generation of particulate suspended matter on the surface of the slurry. Therefore, it is possible to suppress the segregation of the reducing agent in the ground improvement soil to be improved and the variation in appearance and quality of the soil improvement soil. For example, it is possible to sufficiently suppress an increase in the elution amount of hexavalent chromium due to a local decrease in the content of the reducing agent.

The solid content of the soil improvement material is ^, for example, 20 to 500 kg, preferably 50 to 450 kg, more preferably 50 to 400 kg, and more preferably 100 to 400 kg. 350 kg.

The soil to be improved is not particularly limited, and may be volcanic cohesive soil (for example, Kanto loam) in which it is relatively difficult to suppress the elution of hexavalent chromium. By using the soil improvement material according to the present embodiment, it is possible to sufficiently suppress the elution of hexavalent chromium from the soil improvement soil while maintaining high compressive strength of the soil improvement soil.

Although several embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. For example, the application of the reducing agent is not limited to soil improvement agents or cement compositions, but may be mixed with incineration ash, construction soil, or the like.

EXAMPLES The content of the present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Reducing agent adjustment]
The following raw materials were prepared.
・ Calcium sulfite hemihydrate: manufactured by Wako Pure Chemical Industries, Ltd., for chemical use (when 10 g of this product is dispersed in 100 g of distilled water, the pH of the supernatant is 8.40, the oxidation-reduction potential of the supernatant ( ORP) was 260 mV.)
・Sulfur: Wako Pure Chemical Industries, Ltd., powder, chemical use ・Calcium hydroxide: Wako Pure Chemical Industries, Ltd., chemical use

In each example, the above raw materials (50 g in total) were blended at the blending ratios (R _S , R _Ca ) shown in Table 1, and the water/powder ratio (W/P) was 0.6 (mass ratio). Water was added so as to fill the solution, sealed in a 250 ml plastic container, and reacted under the treatment conditions shown in Table 1. During the period (number of days) shown in Table 1, the plastic container was allowed to stand without stirring. After the reaction, the solid content obtained by filtration was dried in a dryer set at 40° C. for 15 hours and recovered. The dried product (moisture content: 4% by mass or less) thus obtained was used as the reducing agent in each example.

On the other hand, in each comparative example, the above raw materials were blended at the blending ratio (molar ratio) shown in Table 1 to obtain the reducing material of each comparative example.

[Derivation of WL _Ra , WL _S and WL _Ca ]
The dissolution ratios (WL _Ra , WL _S and WL _Ca ) of the reducing agent and the raw material of each example and each comparative example were derived. WL _Ra and WL _S are the dissolution ratios of sulfur particles used as the reducing agent and raw material in water under the predetermined condition (A), and WL _Ca is the sulfurous acid used as the raw material under the predetermined condition (A). It is the dissolution ratio of calcium hemihydrate, calcium hydroxide or a blend thereof in water. The method of deriving each dissolution ratio (WL _Ra , WL _S and WL _Ca ) is as described in the "Mode for Carrying out the Invention". Each derivation result was as shown in Table 1.

Sulfur particles and Ca-containing material (one or both of calcium sulfite hemihydrate and calcium hydroxide) were mixed, and the reducing materials of Examples 1 to 8 obtained by reacting under the treatment conditions shown in Table 1 were: The dissolution ratio (WL _Ra ) was 3% by mass or more, and the relationship of the above formula (1) was satisfied. The reducing materials obtained in Examples 1 and 4 were subjected to qualitative analysis by XRD. As a result, no substances other than sulfur, calcium sulfite, and calcium hydroxide, which are the raw materials used, were detected in either case.

[Evaluation of dispersibility]
Anhydrous gypsum (natural anhydrite) is 10% by mass, the amount of reducing agent added is shown in Table 2, and ordinary Portland cement (total chromium content: 65.5 mg/kg, water-soluble hexavalent chromium content: 5.8 mg/kg) A soil improvement material was prepared by blending so that the balance would be. 100 g of this soil improvement material and 80 g of tap water were placed in a plastic container and mixed with a chemistirrer at a rotation speed of 250 rpm for 1 minute and 30 seconds. After that, the slurry was allowed to stand still, and the surface condition of the slurry was visually evaluated. In addition, the index of evaluation was as follows. The results were as shown in Table 2.

A: There is no floating of solid content.
B: Virtually no floating of solid content.
C: Slight floating of solid content.
D: A large amount of floating solid matter is observed.

FIG. 1 is a photograph of the surface of the slurry of Example 2. FIG. As shown in FIG. 1 and Table 2, the slurries of Examples 1-8 had little or no floating solids on the surface. Moreover, when the treatment conditions were high temperature, the surface condition of the slurry could be improved even if the treatment time was short (Examples 3 and 6). 2 is a photograph of the surface of the slurry of Comparative Example 1. FIG. As shown in FIG. 2 and Table 2, in Comparative Example 1 in which only sulfur was added, and in Comparative Examples 2 to 6 in which sulfur and a Ca-containing material were mixed and the predetermined treatment was not performed, solid content on the surface of the slurry A little or a lot of floating was confirmed. From these results, it is inferred that by performing a predetermined treatment by mixing sulfur particles and Ca-containing material, the very surface of the sulfur particles was modified into a hydrophilic substance, and the dispersibility when made into a slurry was improved. be done.

[Evaluation of elution amount of hexavalent chromium]
For the soil improvement target soil (Kanto loam), each implementation so that the amount of the soil improvement material of each example and each comparative example prepared as described above is 300 kg / m ³ per 1 m ³ of the soil improvement target soil. The soil improvement materials of the example and each comparative example were blended and mixed with a Hobart mixer. Mixing was carried out for a total of 3 minutes, and at the point when 1 minute and 30 seconds had passed, the soil adhering to the paddle and the ball was scraped off. After the completion of mixing, the mixture was packed in three layers using a rammer in a cylindrical mold of 50 mm in diameter and 100 mm in height, and then sealed and cured at 20° C. until 7 days of material age and 28 days of material age.

An elution test was performed on each soil improvement soil of the above material age in accordance with Notification No. 46 of the Environment Agency (August 23, 1991) to measure the elution amount of hexavalent chromium. For the measurement, the modified soil sample was dried after vacuum degassing with an aspirator overnight. The eluted amount of hexavalent chromium was obtained by quantifying the hexavalent chromium concentration in the filtrate after immersion by diphenylcarbazide absorption photometry of JIS K0102:2016, 65.2.1. In the operation of quantitative measurement, the interval between adding 3 mL of sulfuric acid (1+9) and adding 1 mL of diphenylcarbazide solution (10 g/L) was within 20 seconds. The measurement results were as shown in Table 3.

As shown in Table 3, the soil improvement material of each example was able to sufficiently reduce the Cr(VI) elution amount. In addition, the reducing agent of Example 6 reduced the Cr(VI) elution amount to the same level as or more than that of Examples 4 and 5, although the reaction period under the treatment conditions was only one day. From this, it is considered that there is a tendency that the higher the reaction temperature between the sulfur particles and the Ca-containing material, the better the effect of suppressing Cr(VI) elution.

Claims (10)

Sulfur particles, Ca inclusions and reaction products thereof,
The dissolution ratio (WL _Ra ) of the sulfur particles, the Ca-containing material and the reaction product in water under predetermined conditions based on the total amount of the sulfur particles, the Ca-containing material and the reaction product A reducing material that is 3% by mass or more. A reducing material containing sulfur particles, Ca-containing substances and reaction products thereof, and satisfying the following formula (1).
WL _Ra ≧ (WL _S ×R _S +WL _Ca ×R _Ca )/(R _S +R _Ca )+0.5 (1)
[In formula (1), WL _Ra , WL _S and WL _Ca respectively represent the dissolution ratios of the reducing material, the sulfur particles before the reaction, and the Ca-containing material before the reaction in water under predetermined conditions. and R _S and R _Ca respectively indicate the molar ratios of the sulfur particles before the reaction and the Ca-containing material before the reaction. ] A reducing material obtained by reacting sulfur particles and a Ca-containing material in the presence of water for 1 minute or more. Any one of claims 1 to 3, wherein the Ca-containing material contains one or more selected from the group consisting of calcium oxide, calcium carbonate, calcium chloride, calcium hydroxide, calcium sulfide, calcium sulfate, and calcium sulfite. The reducing agent described in . The reducing material according to any one of claims 1 to 4, wherein the Ca-containing material includes calcium sulfite and/or calcium hydroxide. The reducing material according to any one of claims 1 to 5, wherein the Ca-containing material includes calcium sulfite and/or calcium sulfide. The reducing material according to any one of claims 1 to 6, wherein the Ca-containing material is contained in raw concrete sludge and/or clinker dust. A cement composition comprising the reducing material according to any one of claims 1 to 7. A ground improvement material comprising the reducing material according to any one of claims 1 to 7. A method for producing a reducing material, comprising a step of mixing sulfur particles and a Ca-containing material in the presence of water and allowing them to react for 1 minute or more.

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