Reducing agent and method for producing the same, cement composition, ground improvement material, and method for suppressing generation of hydrogen sulfide gas

Abstract

To provide a reduction material that can inhibit the generation of hydrogen sulfide gas while containing calcium sulfide.SOLUTION: A reduction material contains calcium sulfide, and one or both of calcium sulfite and calcium carbonate. The content of the calcium sulfide is 20 mass% or more. The total content of the calcium sulfite and the calcium carbonate is 0.1-49 mass%.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a reducing material and a method for producing the same, a cement composition, a ground improvement material, and a method for suppressing the generation of hydrogen sulfide gas. [Background technology]

[0002] Cement clinker is produced using limestone, clay, silica, iron oxide, etc. as main raw materials. In addition to these main raw materials, various industrial by-products and industrial waste are effectively used as raw fuels in the production of cement clinker. For this reason, depending on the selection of raw materials, small amounts of heavy metals such as cadmium, chromium, lead, and molybdenum derived from various raw fuels may be mixed into the cement clinker. Therefore, techniques are known that use various reducing agents to reduce heavy metal ions derived from cement clinker and reduce the amount of elution (Patent Documents 1 to 4).

[0003] For example, Patent Document 1 proposes a technique for reducing hexavalent chromium to trivalent chromium and suppressing the elution of hexavalent chromium by using a mixture of ferrous sulfate and sulfite as a solidification material when solidifying soft ground. Patent Document 2 proposes a technique for suppressing the elution of hexavalent chromium by using a ground improvement material having a specific pH and redox potential and containing a specified amount of MgO. Patent Documents 3 and 4 propose techniques for suppressing the elution of heavy metals by using a heavy metal immobilization agent containing calcium sulfide.

[0004] The surface of calcium sulfide may decompose due to moisture in the air, carbon dioxide, etc., and generate a small amount of hydrogen sulfide. In response to this, Patent Document 4 proposes a technology for reducing the generation of hydrogen sulfide by adding a specific ratio of calcium sulfate to calcium sulfide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-201406 A [Patent Document 2] JP 2017-155141 A [Patent Document 3] JP 2006-102643 A [Patent Document 4] JP 2005-306911 A Summary of the Invention [Problem to be solved by the invention]

[0006] If the generation of hydrogen sulfide gas caused by calcium sulfide could be further reduced, the working environment could be further improved. Therefore, the present disclosure provides a reducing agent that contains calcium sulfide but is capable of sufficiently suppressing the generation of hydrogen sulfide gas, a manufacturing method thereof, a cement composition, and a ground improvement material. Also provided is a method for suppressing the generation of hydrogen sulfide gas by using such a reducing agent. [Means for solving the problem]

[0007] In one aspect, the present disclosure provides a reducing material containing calcium sulfide and one or both of calcium sulfite and calcium carbonate, the calcium sulfide content being 20 mass% or more and the total content of calcium sulfite and calcium carbonate being 0.1 to 49 mass%.

[0008] The reducing agent contains a predetermined amount of calcium sulfide and a predetermined amount of either or both of calcium sulfite and calcium carbonate, thereby making it possible to sufficiently suppress the generation of hydrogen sulfide gas while containing calcium sulfide.

[0009] The reducing agent preferably contains calcium sulfite and calcium carbonate in a total amount of 0.1 to 100 parts by mass per 100 parts by mass of calcium sulfide, thereby making it possible to suppress the generation of hydrogen sulfide gas and achieve a high level of reduction activity at the same time.

[0010] The reducing agent preferably contains 2.8 parts by mass or more of free lime per 100 parts by mass of calcium sulfide, which can further suppress the generation of hydrogen sulfide gas.

[0011] The reducing agent preferably contains a calcium sulfide-containing material containing a carbon-reduced product of gypsum and an additive. More preferably, the calcium sulfide-containing material contains 50 mass % or more of calcium sulfide, and at least a part of free lime is contained in the additive. Such a reducing agent is easy to manufacture, can be manufactured at low manufacturing cost, and has a high reducing effect.

[0012] In the reducing agent, it is preferable that the additive contains 20 mass % or more of free lime, which makes it possible to more effectively suppress the generation of hydrogen sulfide gas.

[0013] The additive preferably includes one or both of clinker dust and dehydrated cake of Ca-containing slurry, which can sufficiently reduce the production cost of the reducing material.

[0014] In one aspect, the present disclosure provides a cement composition including any one of the reducing agents described above. Since such a cement composition includes the reducing agent, it is possible to sufficiently suppress the generation of hydrogen sulfide gas while including calcium sulfide.

[0015] In one aspect, the present disclosure provides a soil improvement material containing any one of the reducing agents described above. Since such a soil improvement material contains the reducing agent, it is possible to sufficiently suppress the generation of hydrogen sulfide gas while containing calcium sulfide.

[0016] In one aspect, the present disclosure provides a method for producing a reducing material, the method comprising: an evaluation step of evaluating components contained in a calcium sulfide-containing material and an additive containing one or both of calcium sulfite and calcium carbonate; and a blending step of blending the calcium sulfide-containing material and the additive, wherein the blending step obtains a reducing material having a calcium sulfide content of 20 mass % or more and a total content of calcium sulfite and the calcium carbonate of 0.1 to 49 mass % based on the evaluation result in the evaluation step.

[0017] According to the above-mentioned manufacturing method, a reducing material having a high reducing effect can be stably manufactured. The reducing material obtained by this manufacturing method contains calcium sulfide and a predetermined amount of either or both of calcium sulfite and calcium carbonate. As a result, while containing calcium sulfide, the generation of hydrogen sulfide gas can be sufficiently suppressed.

[0018] The production method preferably includes a step of heating a raw material containing a gypsum source and a carbon source to reduce at least a part of the gypsum to obtain the calcium sulfide-containing material, thereby making it possible to produce the reducing material at a sufficiently low production cost.

[0019] In one aspect, the present disclosure provides a method for suppressing generation of hydrogen sulfide gas, comprising a step of blending a calcium sulfide-containing material with an additive containing one or both of calcium sulfite and calcium carbonate, and blending the calcium sulfide-containing material with the additive so that the total content of calcium sulfite and calcium carbonate is 0.1 to 100 parts by mass per 100 parts by mass of calcium sulfide. According to this method, when it is necessary to suppress the elution of heavy metal ions such as hexavalent chromium from soil, cement, etc., the generation of hydrogen sulfide gas can be sufficiently suppressed. Effect of the Invention

[0020] According to the present disclosure, it is possible to provide a reducing agent that contains calcium sulfide but is capable of sufficiently suppressing the generation of hydrogen sulfide gas, a method for producing the reducing agent, a cement composition, and a ground improvement material. It is also possible to provide a method for suppressing the generation of hydrogen sulfide gas by using such a reducing agent. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram for explaining a method for evaluating the amount of hydrogen sulfide generated. [Diagram 2] FIG. 1 is a diagram showing a procedure for measuring the amount of generated hydrogen sulfide. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The following describes embodiments of the present disclosure. However, the following embodiments are merely examples for describing the present disclosure, and are not intended to limit the present disclosure to the following contents.

[0023] The reducing material according to one embodiment contains calcium sulfide and either or both of calcium sulfite and calcium carbonate. The calcium sulfide content is 20% by mass or more, and the total content of calcium sulfite and calcium carbonate is 0.1 to 49% by mass.

[0024] The content of calcium sulfide in the reducing agent is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and particularly preferably more than 50% by mass, from the viewpoint of sufficiently increasing the reducing action and sufficiently suppressing the elution of hexavalent chromium and the like. The content of calcium sulfide can be determined, for example, by the XRD-Rietveld method. From the viewpoint of ensuring the content of at least one of calcium sulfite and calcium carbonate, the content of calcium sulfide may be, for example, 95% by mass or less, or 90% by mass or less.

[0025] The total content of calcium sulfite and calcium carbonate in the reducing agent is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 3% by mass or more, and particularly preferably 5% by mass or more, from the viewpoint of sufficiently reducing the amount of hydrogen sulfide gas generated. The total content of calcium sulfite and calcium carbonate in the reducing agent is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and particularly preferably 12% by mass or less, from the viewpoint of maintaining a high reducing action.

[0026] The total content of calcium sulfite and calcium carbonate relative to 100 parts by mass of calcium sulfide is preferably 0.1 to 100 parts by mass from the viewpoint of suppressing the generation of hydrogen sulfide gas and achieving a high level of high reducing action. From the viewpoint of further reducing the amount of hydrogen sulfide gas generated, the content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more. From the viewpoint of ensuring the content of calcium sulfide, the content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 25 parts by mass or less.

[0027] The reducing agent may contain both calcium sulfite and calcium carbonate, or may contain only one of them. From the viewpoint of suppressing the generation of hydrogen sulfide gas, it is preferable that the reducing agent contains calcium carbonate, and it is more preferable that the content of calcium carbonate is greater than that of calcium sulfite. From the viewpoint of increasing the reducing action and suppressing the elution of heavy metals, it is preferable that the reducing agent contains calcium sulfite, and it is more preferable that the content of calcium sulfite is greater than that of calcium carbonate.

[0028] The hydration number of calcium sulfite contained in the reducing agent is not particularly limited, and may be, for example, hemihydrate or anhydrous. The content of calcium sulfite in the present disclosure is the content as hemihydrate, and is obtained by converting all calcium sulfite into hemihydrate. Calcium sulfite may be a commercially available product (reagent), may be chemically synthesized, or may be naturally occurring. 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.

[0029] The calcium carbonate contained in the reducing agent may be a commercially available product (reagent), may be chemically synthesized, or may be naturally occurring, for example, limestone or may be contained in clinker dust.

[0030] The reducing agent may contain components other than calcium sulfide, calcium sulfite, and calcium carbonate. However, the content of gypsum (CaSO4) in the reducing agent is preferably less than 57 mass%, more preferably less than 40 mass%, even more preferably less than 35 mass%, and particularly preferably less than 30 mass%, calculated on an anhydrous basis. This makes it possible to provide a reducing agent that can achieve both a high level of reduction action and a high level of a hydrogen sulfide gas suppression action.

[0031] The reducing agent preferably contains free lime. The content of free lime relative to 100 parts by mass of calcium sulfide is preferably 2.8 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 12 parts by mass or more, from the viewpoint of sufficiently and stably suppressing the generation of hydrogen sulfide gas. The content of free lime may be, for example, less than 40 parts by mass or less than 30 parts by mass, from the viewpoint of ensuring a high reducing action.

[0032] The content of free lime in the reducing agent may be, for example, 0.5% by mass or more, 2% by mass or more, or 3% by mass or more, from the viewpoint of sufficiently suppressing the generation of hydrogen sulfide gas. The content of free lime in the reducing agent may be, for example, less than 30% by mass, less than 20% by mass, or less than 15% by mass, from the viewpoint of sufficiently exerting a high reducing action.

[0033] The free lime (f.CaO) content may be a value (measured value) measured by the Cement Association standard test method (JCAS I-01-1997 "Method for quantification of free calcium oxide"). It may also be the total value (α+β) of the CaO content (α) determined by the XRD-Rietveld method and the value (β) obtained by converting the Ca(OH)2 content determined by the XRD-Rietveld method into the CaO content. The measured value, total value, and calculated value calculated based on these values ​​determined by the above methods may be within the above-mentioned numerical range.

[0034] The reducing agent may include a calcium sulfide-containing material containing a carbon-reduced product of gypsum. The carbon-reduced product of gypsum includes calcium sulfide. The calcium sulfide-containing material containing a carbon-reduced product of gypsum may be a heat-treated product obtained by heating a composition containing a gypsum source containing gypsum and a carbon source. The gypsum source is not particularly limited, and examples thereof include waste gypsum dihydrate by-produced from a thermal power plant, natural dihydrate gypsum, natural anhydrous gypsum, and waste gypsum board. Of these, waste gypsum board is preferably used from the viewpoint of waste utilization. Examples of the carbon source include carbon-containing materials such as paper, waste plastic, carbon fiber, biomass, charcoal, coal, coal gasification slag, and petroleum. The above composition may be heated in the air or in a reducing atmosphere with a lower oxygen concentration than the air at a temperature range of 500 to 1500°C to obtain a calcium sulfide-containing material containing a carbon-reduced product of gypsum.

[0035] The content of calcium sulfide in the calcium sulfide-containing material may be, for example, 40% by mass or more, 50% by mass or more, or 60% by mass or more from the viewpoint of obtaining a reducing agent with a high reducing effect. From the viewpoint of ease of production, the content of calcium sulfide in the calcium sulfide-containing material may be less than 90% by mass.

[0036] The ratio of calcium sulfide contained in the calcium sulfide-containing material to the total calcium sulfide contained in the reducing agent (the ratio of calcium sulfide derived from the calcium sulfide-containing material) is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. This can enhance the effect of the reducing agent.

[0037] The reducing material may contain an additive containing one or both of calcium sulfite and calcium carbonate together with the calcium sulfide-containing material. As the additive, clinker dust and dehydrated cake of Ca-containing slurry are preferably used from the viewpoint of reducing the manufacturing cost of the reducing material. The additive may contain at least one of clinker dust and dehydrated cake of Ca-containing slurry and calcium sulfite. Clinker dust is, for example, recovered from a chlorine bypass facility of a cement plant. On the other hand, the dehydrated cake of Ca-containing slurry (hereinafter, sometimes referred to as "dehydrated cake") is not particularly limited, and examples thereof include hydrocake, which is a residue generated when producing magnesium hydroxide from seawater, and dehydrated cake by-produced in the desulfurization process. The dehydrated cake may be dried as necessary.

[0038] The additive may contain free lime (f.CaO). The free lime contained in the reducing agent may be preferably 10 mass% or more, more preferably 20 mass% or more, and even more preferably 25 mass% or more of the free lime contained in the additive. This can further enhance the effect of suppressing the generation of hydrogen sulfide gas.

[0039] The Blaine specific surface area of ​​the additive is preferably 2000 cm 2 / g or more, and more preferably 4000 cm2 / g or more, more preferably 6000 cm 2 / g or more. This makes it possible to more effectively suppress the generation of hydrogen sulfide gas. This Blaine specific surface area can be measured in accordance with JIS R5201:2015 "Physical Testing Methods for Cement."

[0040] The clinker dust contains one or both of calcium carbonate and free lime. From the viewpoint of providing a reducing agent having a high reducing action while sufficiently suppressing the generation of hydrogen sulfide gas, the content of calcium carbonate in the clinker dust is preferably 2% by mass or more, more preferably 3% by mass or more, further preferably 4% by mass or more, and particularly preferably 5% by mass or more. From the viewpoint of ease of production of the clinker dust, the content of calcium carbonate may be, for example, less than 20% by mass or less than 15% by mass. The content of calcium carbonate in the clinker dust can be determined by the XRD-Rietveld method.

[0041] The free lime content in the clinker dust is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and particularly preferably 35% by mass or more, from the viewpoint of providing a reducing agent having a high reducing effect while sufficiently suppressing the generation of hydrogen sulfide gas. From the viewpoint of ease of production of the clinker dust, the free lime content may be, for example, less than 60% by mass or less than 50% by mass.

[0042] The free lime content in the clinker dust is measured by the Cement Association Standard Test Method (JCAS I-01-1997 "Quantitative Method for Free Calcium Oxide"). When the clinker dust contains magnesium oxide, it is preferable that the total content of the free lime and magnesium oxide is within the above-mentioned range. The magnesium oxide content in the clinker dust can be determined by the XRD-Rietveld method.

[0043] The dehydrated cake contains at least one compound selected from the group consisting of calcium sulfite, free lime, and calcium carbonate. The total content of the compounds in the dehydrated cake is preferably 10% by mass or more, more preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, from the viewpoint of obtaining a reducing agent having a high reducing effect while sufficiently suppressing the generation of hydrogen sulfide gas. From the viewpoint of easy availability of the dehydrated cake, the total content of the compounds in the dehydrated cake may be, for example, less than 95% by mass or less than 80% by mass. The content of free lime in the dehydrated cake is measured by the Cement Association Standard Test Method (JCAS I-01-1997 "Method for Quantitative Analysis of Free Calcium Oxide"). When the dehydrated cake contains both free lime and calcium carbonate, it is preferable that the total content of the free lime and calcium carbonate is in the above-mentioned range. The content of calcium carbonate in the dehydrated cake can be determined by the XRD-Rietveld method.

[0044] The sulfate content in the clinker dust and the dehydrated cake is preferably low. For example, the calcium sulfate content in the clinker dust may be less than 20 mass%, less than 15 mass%, or less than 10 mass%. The total content of calcium sulfate and magnesium sulfate in the dehydrated cake may be less than 40 mass%, or less than 20 mass%. The sulfate content can be determined by the XRD-Rietveld method.

[0045] The content of clinker dust in the reducing agent may be 3% by mass or more, 5% by mass or more, or 8% by mass or more, from the viewpoint of sufficiently reducing the manufacturing cost of the reducing agent while further suppressing the generation of hydrogen sulfide gas. The content of clinker dust in the reducing agent may be less than 40% by mass or less than 30% by mass, from the viewpoint of maintaining a sufficiently high reduction action. The numerical range of the content of dehydrated cake in the reducing agent may also be the same as the above numerical range of the content of clinker dust. In addition, the numerical range of the total content in the case where both dehydrated cake and clinker dust are included may also be the same as the above numerical range of the content of clinker dust.

[0046] The additive is not limited to clinker dust and dewatered cake, and may contain various inorganic compounds in combination with one or both of them, or alone. Examples of inorganic compounds include chlorides, oxides, hydroxides, sulfates, sulfites, and carbonates. Specific examples include calcium hydroxide, ferrous chloride, calcium carbonate, magnesium oxide, magnesium hydroxide, ferrous sulfate, and calcium sulfate. Calcium sulfate may include any of dihydrate (gypsum dihydrate), hemihydrate (gypsum hemihydrate), and anhydrite (gypsum anhydride). The reducing material may include at least one of the above-mentioned components.

[0047] The sulfite may contain a sulfite other than calcium sulfite. For example, the sulfite may contain calcium sulfite and at least one selected from the group consisting of sodium sulfite, magnesium sulfite, calcium bisulfite (Ca(HSO3)2), sodium bisulfite, and magnesium bisulfite. Each sulfite may be a commercially available chemically synthesized product or a naturally occurring product.

[0048] The additive may contain sulfur. Although the sulfur is not particularly limited, elemental sulfur may be used. Examples of elemental sulfur include sulfur produced from natural sulfur, sulfur obtained from pyrite, and sulfur obtained as a by-product of the desulfurization process during petroleum refining. If elemental sulfur obtained from a by-product among these is contained, the manufacturing cost can be reduced. Sulfur may be contained in a calcium sulfide-containing material.

[0049] The reducing agent described above can sufficiently suppress the generation of hydrogen sulfide gas, and when used in cement compositions and ground improvement materials, can sufficiently suppress the elution of heavy metals such as hexavalent chromium.

[0050] The method for producing the reducing agent includes a reduction step of heating a raw material containing a gypsum source and a carbon source to reduce at least a part of the gypsum contained in the gypsum source to obtain a calcium sulfide-containing material containing calcium sulfide, an evaluation step of evaluating the components contained in the calcium sulfide-containing material and an additive containing one or both of calcium sulfite and calcium carbonate, and a blending step of blending the calcium sulfide-containing material and the additive. In the blending step, a reducing agent having a calcium sulfide content of 20 mass% or more and a total content of calcium sulfite and calcium carbonate of 0.1 to 49 mass% is obtained based on the evaluation results of each component contained in the evaluation step. In the blending step, the calcium sulfide-containing material and the additive may be blended based on the evaluation results so that the total content of calcium sulfite and calcium carbonate is 0.1 to 100 mass parts per 100 parts by mass of calcium sulfide.

[0051] The method of evaluating each component in the evaluation step is not particularly limited. For example, the contents of calcium sulfide, calcium sulfite, and calcium carbonate may be measured using an analyzer, or data correlating with these contents may be derived. The evaluation result may be a specific analytical value or data derived as described above. Any evaluation method may be adopted without particular limitation as long as it can calculate or estimate the contents of calcium sulfide, calcium sulfite, and calcium carbonate in the reducing material.

[0052] By such a production method, the above-mentioned reducing material can be stably produced. The gypsum source and the carbon source are as described above. This production method can be carried out based on the description of the above-mentioned embodiment of the reducing material. The above description of the reducing material is applied to this production method.

[0053] The reducing agent obtained by the above-mentioned production method can sufficiently suppress the generation of hydrogen sulfide gas. Furthermore, when used in cement compositions and ground improvement materials, the reducing agent can sufficiently suppress the elution of heavy metals such as hexavalent chromium.

[0054] The method for suppressing the generation of hydrogen sulfide gas according to one embodiment includes a blending step of a calcium sulfide-containing material and an additive containing one or both of calcium sulfite and calcium carbonate, and suppresses the generation of hydrogen sulfide gas by blending the calcium sulfide-containing material and the additive so that the total content of calcium sulfite and calcium carbonate is 0.1 to 100 parts by mass relative to 100 parts by mass of calcium sulfide. In addition to this blending step, other steps described in the above-mentioned method for producing a reducing agent may be included. This method for suppressing the generation of hydrogen sulfide gas can be performed in the same manner as the above-mentioned embodiment of the reducing agent and the embodiment of the method for producing a reducing agent. The above-mentioned description of the reducing agent and the method for producing the reducing agent is applied to this method for suppressing the generation of hydrogen sulfide gas.

[0055] The cement composition and ground improvement material according to an embodiment may contain the above-mentioned reducing agent, cement, and gypsum. By containing the above-mentioned reducing agent, the cement composition and ground improvement material can maintain the amount of hexavalent chromium elution at a sufficiently low level from short-term to long-term material ages. The content of the reducing agent in the cement composition and ground improvement material is preferably 0.1 to 30 mass%, more preferably 0.5 to 20 mass%, and further preferably 1.0 to 10 mass%. This can sufficiently suppress the elution of hexavalent chromium from the resulting mortar, concrete, and ground improvement soil.

[0056] The content of calcium sulfide in the cement composition and the ground improvement material is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and particularly preferably 4% by mass or more. By including calcium sulfide in such a range, it is possible to sufficiently suppress the elution of hexavalent chromium from the obtained mortar, concrete, and ground improvement soil. The content of calcium sulfide in the cement composition and the ground improvement material may be less than 30% by mass, less than 20% by mass, or less than 10% by mass from the viewpoint of the strength expression of the cement composition and the ground improvement material.

[0057] The gypsum may be any of gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum. From the viewpoint of strength development of the ground improvement material, it is preferable to contain gypsum dihydrate or anhydrous gypsum. For example, when obtaining a ground improvement material, gypsum mixed with gypsum dihydrate and anhydrous gypsum may be used. From the viewpoint of strength development of the ground improvement soil, the content of gypsum in the ground improvement material in terms of anhydride is, for example, 1 to 25 mass%, preferably 3 to 20 mass%, more preferably 4 to 15 mass%, and further preferably 5 to 12 mass%. The range of the gypsum content in the cement composition may be the same.

[0058] The cement may be any of the various Portland cements specified in JIS R5210:2003 "Portland cement". Among these, from the viewpoint of availability and increasing the compressive strength at a short age, normal Portland cement or high-early-strength Portland cement is preferred. From the viewpoint of availability, the total chromium content in the cement may be, for example, 30 to 250 mg / kg or 50 to 200 mg / kg. From the same viewpoint, the water-soluble hexavalent chromium content of the cement may be, for example, 3 to 40 mg / kg or 4 to 30 mg / kg. The total chromium content of the cement is measured in accordance with the method described in JIS R5202:2010, and the water-soluble hexavalent chromium content is measured in accordance with the method described in the Cement Association Standard Test Method I-51-1981.

[0059] The content of cement in the cement composition and the ground improvement material is, for example, 50 to 98 mass%, preferably 70 to 95 mass%, more preferably 75 to 90 mass%. If the content of cement is less than 50 mass%, the strength of the cement composition and the ground improvement soil tends to be difficult to exhibit. On the other hand, if the content of cement is more than 98 mass%, the amount of hexavalent chromium eluted from the obtained mortar, concrete, and ground improvement soil may increase depending on the content of hexavalent chromium in the cement.

[0060] Cement clinker can be used as a substitute for cement. When using cement clinker, it is preferable to adjust it to an appropriate fineness before use.

[0061] The cement composition and the ground improvement material may further contain blast furnace slag powder. The content of the blast furnace slag powder may be, for example, 1 to 50 mass%, 5 to 30 mass%, or 10 to 20 mass%. When the blast furnace slag is contained in such a range, the amount of hexavalent chromium eluted from the obtained mortar, concrete, and ground improvement soil can be further suppressed, and the amount of reducing agent used can be reduced.

[0062] The fineness of the cement composition and the ground improvement material is not particularly limited, and the Blaine specific surface area is, for example, 1000 to 6000 cm 2 / g, and 2000 to 5500 cm 2 / g, and 3000 to 5000 cm 2 / g, and 4000 to 4500 cm 2 / g. If the range is within this range, the amount of hexavalent chromium elution can be suppressed while maintaining the strength of the resulting mortar, concrete, and ground improvement soil. This Blaine specific surface area can be measured in accordance with JIS R5201:2015 "Physical test methods for cement."

[0063] There are no particular limitations on the method for producing the cement composition and the ground improvement material. They may be produced by mixing raw materials adjusted to a predetermined fineness, or by mixing and grinding the raw materials.

[0064] The improved soil contains the above-mentioned soil improvement material and the soil to be improved. Such improved soil is obtained by mixing the above-mentioned soil improvement material and the soil to be improved. 3 The content of the soil improvement material relative to the above may be, for example, 20 to 500 kg, 50 to 450 kg, 50 to 400 kg, or 100 to 350 kg.

[0065] The soil to be improved is not particularly limited, and may be volcanic ash clayey soil (e.g., Kanto loam) in which it is relatively difficult to suppress the elution of hexavalent chromium. By using the ground improvement material according to the present embodiment, it is possible to sufficiently suppress the elution of hexavalent chromium from the improved soil while maintaining the compressive strength of the improved soil at a high level.

[0066] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-mentioned embodiments. For example, the application of the reducing material is not limited to a ground improvement material or a cement composition, and the reducing material may be mixed with incineration ash or construction generated soil, etc. EXAMPLES

[0067] The contents of the present disclosure will be described in detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0068] [Production of reducing materials] The following raw materials were prepared: ·Waste gypsum board ·charcoal ·Anhydrite Coal gasification slag Calcium sulfite hemihydrate: Wako Pure Chemical Industries, Ltd., chemical grade (pH of the supernatant when 10 g of this product is dispersed in 100 g of distilled water: 8.40, oxidation-reduction potential (ORP) of the supernatant: 260 mV) Calcium hydroxide: Wako Pure Chemical Industries, Ltd., chemical grade Calcium carbonate: Wako Pure Chemical Industries, Ltd., chemical grade Clinker dust (1) and (2): Recovered from the chlorine bypass facility of a cement plant.

[0069] Charcoal and waste gypsum board were mixed and heated to 950°C in a small test kiln to obtain calcium sulfide-containing material A (Ca sulfide-containing material A) containing gypsum reduced by carbon. In addition, coal gasification slag was mixed with anhydrous gypsum and heated to 950°C in an electric furnace to obtain a heated product containing gypsum reduced by carbon. The heated product was sieved using a sieve with 90 μm openings, and the fine particles that passed through the sieve were designated calcium sulfide-containing material B (Ca sulfide-containing material B). The obtained calcium sulfide-containing materials A and B were each pulverized using a planetary mill.

[0070] Table 1 shows the results of quantitative analysis of calcium sulfide-containing materials A and B and the above raw materials by XRD-Rietveld method, as well as the amount of free lime (f.CaO). For composition analysis by XRD-Rietveld method, an X-ray diffractometer (manufactured by Bruker AXS, accelerating voltage: 30 kV, current: 10 mA, tube: Cu) was used. Rietveld analysis was performed on the obtained powder X-ray diffraction pattern, and each component was quantified. For Rietveld analysis, analysis software (manufactured by Bruker AXS, Topas) was used.

[0071] Regarding the amount of free lime (f.CaO), in Table 1, the value measured by the Cement Association standard test method (JCAS I-01-1997 "Quantitative method for free calcium oxide") is shown as "measured value". In addition, the total value (α + β) of the CaO content (α) obtained by XRD Rietveld analysis and the value (β) obtained by converting the Ca(OH)2 content obtained by XRD Rietveld analysis into the CaO content is shown as "calculated value". The conversion from the Ca(OH)2 content to the CaO content was performed using the following formula. In the following formula, the Ca molecular weight is 56 and the Ca(OH)2 molecular weight is 74. CaO content = Ca(OH)2 content x CaO molecular weight / Ca(OH)2 molecular weight

[0072] [Table 1]

[0073] The raw materials shown in Table 1 were added as additives to the crushed Ca sulfide-containing material A or Ca sulfide-containing material B in the proportions shown in Table 2 to prepare reducing materials. The mass-based content of each component was as shown in Table 3. The content of each component based on CaS (100 parts by mass) was as shown in Table 4. The content of each component in Tables 3 and 4 is a calculated value based on the composition shown in Table 1 and the blending amount in Table 2. Tables 3 and 4 also show the content of f.CaO by origin (the content of f.CaO derived from calcium sulfide-containing materials A and B, and the content of f.CaO derived from additives (1) and (2)), calculated based on the value of f.CaO shown in Table 1 and the blending amount in Table 2.

[0074] [Table 2]

[0075] [Table 3]

[0076] [Table 4]

[0077] [Evaluation of hydrogen sulfide gas generation rate] The amount of hydrogen sulfide gas generated was evaluated using the apparatus shown in FIG. 1 and the procedure shown in FIG. 2. A sample 30 (30 g of reducing material (approximately 30 cm3)) was placed in a 250 ml polyethylene container 10. 3)) was placed in the container 10, and the opening of the container 10 was covered with cloth 20, and the container 10 was left to stand for a predetermined period (1 day, 3 days, 7 days, 14 days) in a thermo-hygrostat set at a temperature of 60°C / humidity of 60%RH. After the predetermined period, the container 10 was taken out of the thermo-hygrostat and cooled at room temperature for 10 minutes, after which the cloth 20 was removed and a detector tube was inserted into the container 10 from the opening. As the detector tube, GV-110,4LT (detection range: 0.1 to 4 ppm, suction volume: 100 mL) manufactured by Gastec Corporation was used. After 1 minute had passed since the detector tube was inserted, the gas in the container was sucked in with the detector tube at a position about 10 mm high from the top surface of the sample 30 in the container 10 for 90 seconds. After 1.5 minutes of suction, the value of the detector tube was read to determine the H2S concentration. The H2S concentration determined for each reducing agent is shown in Table 5.

[0078] [Table 5]

[0079] Table 5 also shows the percentage of f.CaO by origin based on the total amount (the percentage of f.CaO derived from calcium sulfide-containing materials A and B, and the percentage of f.CaO derived from additives (1) and (2)).

[0080] It was confirmed that, compared with the reducing materials of Comparative Examples 1 to 3 which contained only a calcium sulfide-containing substance, the reducing materials of Examples 1 to 10, which contained various additives and thus a predetermined amount of either or both of calcium sulfite and calcium carbonate, were able to sufficiently suppress the amount of hydrogen sulfide gas generated.

[0081] [Preparation of ground improvement material] The following raw materials were prepared: Cement: Ordinary Portland cement (total chromium content: 63.5 mg / kg, water-soluble hexavalent chromium content: 4.5 mg / kg) ·Anhydrite: Natural anhydrite - Soil to be improved: Kanto loam

[0082] The above-mentioned raw materials and the reducing materials of Example 5 and Comparative Example 2 after evaluating the amount of hydrogen sulfide gas generated (the number of days in parentheses is the period of storage in a thermostatic and hygroscopic chamber) were mixed in the proportions shown in Table 6 to prepare ground improvement materials (1) and (2).

[0083] [Preparation and evaluation of ground improvement soil] The amount of soil improvement material mixed for the target soil (Kanto loam) is 3 300kg / m 3 The soil improvement materials (1) and (2) were mixed so that the above values ​​were obtained, and mixed in a Hobart mixer. Mixing was carried out for a total of 3 minutes, with the soil adhering to the paddle and ball being scraped off at 1 minute and 30 seconds intervals. After mixing was completed, the mixture was packed into a cylindrical formwork 50 mm in diameter and 100 mm in height using a rammer in three layers, and then sealed and cured at 20°C for material ages of 7 days and 28 days.

[0084] For each of the improved soils of the above ages, a leaching test was conducted in accordance with Environment Agency Notification No. 46 (August 23, 1991) to measure the amount of hexavalent chromium leached out. The improved soil samples used for the measurement were dried overnight by vacuum deaeration using an aspirator. The amount of hexavalent chromium leached out was determined by quantifying the hexavalent chromium concentration in the filtrate after immersion using the diphenylcarbazide spectrophotometric method in 65.2.1 of JIS K0102:2016. During the quantitative measurement procedure, the interval between adding 3 mL of sulfuric acid (1+9) and adding 1 mL of diphenylcarbazide solution (10 g / L) was set to within 20 seconds.

[0085] [Table 6]

[0086] Table 6 also shows the CaS content in the reducing material shown in Table 3 and the CaS content in the ground improvement material calculated based on the mix ratio of the ground improvement material in Table 6. As shown in Table 6, the amount of Cr(VI) eluted from the ground improvement soil at each material age was below the detection limit. From this result, it was confirmed that the reducing material of the embodiment not only suppresses the amount of hydrogen sulfide gas generated during storage, but also sufficiently reduces the amount of Cr(VI) eluted from the ground improvement soil even when added to the ground improvement material after reducing the amount of hydrogen sulfide gas generated. [Explanation of symbols]

[0087] 10...container, 20...cloth, 30...sample.

Claims

1. Contains calcium sulfide and one or both of calcium sulfite and calcium carbonate, The content of the calcium sulfide is 20% by mass or more, A reducing material, wherein the total content of the calcium sulfite and the calcium carbonate is 0.1 to 49 mass%.

2. 2. The reducing material according to claim 1, wherein a total content of the calcium sulfite and the calcium carbonate is 0.1 to 100 parts by mass relative to 100 parts by mass of the calcium sulfide.

3. 3. The reducing material according to claim 1, wherein the content of free lime is 2.8 parts by mass or more relative to 100 parts by mass of the calcium sulfide.

4. The calcium sulfide-containing material contains a carbon-reduced product of gypsum, and an additive, The calcium sulfide is contained in the calcium sulfide-containing material in an amount of 50 mass% or more, The reducing material according to claim 3 , wherein at least a portion of the free lime is contained in the additive material.

5. The reducing material according to claim 4, wherein the additive contains 20 mass % or more of the free lime.

6. The reducing material according to claim 4 or 5, wherein the additive comprises one or both of clinker dust and a dehydrated cake of a Ca-containing slurry.

7. A cement composition comprising the reducing material according to any one of claims 1 to 6.

8. A ground improvement material comprising the reducing material according to any one of claims 1 to 6.

9. an evaluation step of evaluating components contained in a calcium sulfide-containing material and an additive containing one or both of calcium sulfite and calcium carbonate; A blending step of blending the calcium sulfide-containing material and the additive, In the blending step, a reducing material having a calcium sulfide content of 20 mass% or more and a total content of the calcium sulfite and the calcium carbonate of 0.1 to 49 mass% is obtained based on the evaluation results in the evaluation step.

10. The method for producing a reducing material according to claim 9, comprising a step of heating a raw material containing a gypsum source and a carbon source to reduce at least a portion of the gypsum and obtain the calcium sulfide-containing material.

11. The method includes a step of blending a calcium sulfide-containing material with an additive containing one or both of calcium sulfite and calcium carbonate, The method for suppressing generation of hydrogen sulfide gas comprises blending the calcium sulfide-containing material and the additive so that the total content of the calcium sulfite and calcium carbonate is 0.1 to 100 parts by mass per 100 parts by mass of calcium sulfide.

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