Method for producing sulfur-containing composition, cement composition, and ground improvement material

Abstract

To provide a method of producing a sulfur-containing composition, capable of producing a sulfur-containing composition at a low cost with high production efficiency.SOLUTION: A method of producing a sulfur-containing composition for obtaining a sulfur-containing composition including calcium sulfide, from a carbon source and gypsum-containing waste, with the carbon source containing an inorganic component including Si and Al, comprises a heating step of heating the carbon source and the gypsum-containing waste at a temperature in a range of 600 to 1400°C to allow them to react with each other to obtain a heat-treated material, and a modification step of modifying the heat-treated material to obtain the sulfur-containing composition.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a sulfur-containing composition, a cement composition, and a ground improvement material. [Background technology]

[0002] Cement clinker is produced from 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. However, depending on the selection of raw materials, cement clinker may be contaminated with extremely small amounts of heavy metals such as cadmium, chromium, and lead derived from the various raw fuels.

[0003] Among heavy metals, hexavalent chromium differs from other heavy metals in that it is converted into chromate ions (CrO4 2- ) and does not form poorly soluble hydroxides even under high pH conditions. Therefore, when a cement-based ground improvement material is used to perform a ground solidification treatment, there is a concern that hexavalent chromium may be eluted depending on the conditions of use, such as soil quality, amount added, and strength expression. Many studies have been conducted on methods for suppressing the elution of hexavalent chromium from solidified soil using a cement-based solidification material. For example, Patent Document 1 proposes a method for reducing the elution of hexavalent chromium from solidified soil by adding a reducing agent to cement (see Patent Document 1). Patent Document 2 also proposes a technology for producing a calcium sulfide-based heavy metal immobilizing agent by mixing gypsum waste and waste wood and firing the mixture under a reducing atmosphere. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-222795 A [Patent Document 2] JP 2004-269822 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, as described in Patent Document 2, a relatively long period of calcination is required to obtain a calcium sulfide-based heavy metal immobilizing agent from waste gypsum and waste wood. This manufacturing method results in inefficient production. On the other hand, if high-purity raw materials with stable quality are used instead of waste gypsum and waste wood to increase production efficiency, the raw material costs will increase, and the manufacturing costs of calcium sulfide will also increase.

[0006] Therefore, the present disclosure provides a method for producing a sulfur-containing composition, which can produce a sulfur-containing composition at low production cost and high production efficiency. In addition, by using such a sulfur-containing composition, a cement composition can be produced at low production cost. of The present invention provides a method for producing a cement composition which is capable of producing a ground improvement material at low production costs. [Means for solving the problem]

[0007] A method for producing a sulfur-containing composition according to one aspect of the present disclosure is a method for producing a sulfur-containing composition comprising obtaining a sulfur-containing composition containing calcium sulfide from a carbon source and a gypsum-containing waste, the carbon source containing an inorganic component including Si and Al, and the method includes a heating step of heating the carbon source and the gypsum-containing waste in a temperature range of 600 to 1400° C. to react with each other to obtain a heat-treated product, and a modification step of modifying the heat-treated product to obtain a sulfur-containing composition.

[0008] In the above-mentioned method for producing a sulfur-containing composition, since waste containing gypsum is used, the raw material cost can be reduced. In addition, since the carbon source containing inorganic components including Si and Al can promote the reduction reaction of gypsum, the sulfur-containing composition can be produced with high production efficiency. In addition, the fuel consumption required for production can also be reduced. Therefore, according to the above-mentioned production method, the sulfur-containing composition can be produced with low production cost and high production efficiency. The sulfur-containing composition obtained in this manner is also effective in suppressing the elution of hexavalent chromium.

[0009] It is preferable that the molar ratio of gypsum to carbon contained in the gypsum-containing waste and the carbon source used in the above-mentioned heating step satisfies the following formula (1). In formula (1), C represents the number of moles of carbon, and CaSO4 represents the number of moles of gypsum. By setting such a molar ratio, sufficient carbon is supplied for the reduction of gypsum, and the unreacted portion remaining in the heat-treated product can be sufficiently reduced. C / CaSO4≧3 (1)

[0010] It is preferable to have a granulation step in which the carbon source and the gypsum-containing waste are mixed and granulated before the above-mentioned heating step. This improves the uniformity of the mixed state of the sulfur-containing waste and the carbon source, and the granulation also improves the handling properties. By providing such a granulation step, the reactivity variation in the heating step is reduced, and the reaction proceeds more quickly. This also reduces impurities remaining in the heat-treated product.

[0011] In the above-mentioned modification step, it is preferable to remove coarse powder from the heat-treated product to obtain a sulfur-containing composition. Si and Al remaining in the heat-treated product tend to form foamed coarse powder. Therefore, by removing the coarse powder, it is possible to reduce the impurities Si and Al and produce a sulfur-containing composition with high purity.

[0012] In the above-mentioned modification step, it is preferable to remove coarse powder from the mixture obtained by mixing the inorganic powder containing CaO with the heat-treated product to obtain a sulfur-containing composition. When the heat-treated product contains calcium sulfide or the like, it may react with moisture in the air to generate a small amount of hydrogen sulfide or the like. Therefore, by adding an inorganic powder containing CaO to maintain an alkaline environment, the generation of hydrogen sulfide or the like can be sufficiently suppressed.

[0013] The inorganic powder preferably contains at least one selected from the group consisting of free lime, gypsum, calcium sulfite, cement clinker, calcium hydroxide, and calcium carbonate. This makes it easier to maintain the heat-treated product and the sulfur-containing composition alkaline. In addition, the inorganic powder adheres to the surface of calcium sulfide particles, reducing the chance of direct contact with moisture in the air.

[0014] The inorganic powder preferably includes a by-product generated during the cement manufacturing process. In this manner, the sulfur-containing composition can be produced at a sufficiently low production cost while reducing the environmental load by using the by-product.

[0015] When Si and Al contained in the inorganic components of the carbon source are converted to SiO2 and Al2O3, respectively, the total ratio of SiO2 and Al2O3 to the entire inorganic components is preferably 10 mass% or more. By containing Si and Al, which promote the reduction of gypsum, in the inorganic components of the coal source at a concentration of a predetermined value or more, the reaction efficiency in the heating step can be improved.

[0016] The carbon source preferably includes coal gasification slag. Coal gasification slag is available as a by-product or waste material and tends to have a high carbon, Al and Si content. Therefore, the sulfur-containing composition can be produced at a lower production cost and with a higher production efficiency while promoting the effective use of resources.

[0017] The gypsum-containing waste preferably contains at least one selected from the group consisting of waste gypsum board, flue gas desulfurization gypsum, and sulfur-containing sludge. These can be obtained as by-products or waste, so that the sulfur-containing composition can be produced at a lower production cost.

[0018] The content of calcium sulfide in the sulfur-containing composition is preferably 5% by mass or more based on the total amount of the sulfur-containing composition. Such a sulfur-containing composition has a sufficiently high heavy metal suppression effect, and can be suitably used as a reducing material.

[0019] In the above-mentioned modification step, it is preferable to set a classification point within the range of 20 to 200 μm, classify the heat-treated product into coarse powder and fine powder at the classification point, and obtain the sulfur-containing composition as fine powder. Since Si and Al remaining in the heat-treated product tend to form coarse powder in a foamed state, by classifying at a classification point within the above-mentioned range, Si and Al can be effectively removed from the heat-treated product.

[0020] It is preferable to have a gas treatment step in which the reaction exhaust gas generated in the above-mentioned heating step is brought into contact with an alkali-containing slurry containing an alkali source to obtain a gas treatment product slurry, and a recovery step in which a desulfurization composition generated by a reaction between an acid gas contained in the reaction exhaust gas and an alkali source is recovered from the gas treatment product slurry. In the heating step, an acid gas containing sulfur may be generated by reduction of the gypsum-containing waste. When the reaction exhaust gas contains such an acid gas, the acid gas can be effectively recovered by contacting the reaction exhaust gas with an alkali-containing slurry containing an alkali source, and the environmental load caused by the exhaust gas can be reduced. In addition, by recovering the desulfurization composition from the gas treatment product slurry obtained in the gas treatment step, a by-product useful for various applications can be obtained.

[0021] It is preferable that the reaction exhaust gas contains sulfur dioxide gas, the alkali source contains a calcium salt, and the desulfurization composition contains at least one of calcium sulfite and gypsum. When the alkali source contains a calcium salt, the absorption efficiency of sulfur dioxide gas can be increased. In addition, by contacting the reaction exhaust gas containing sulfur dioxide gas with an alkali-containing slurry, a desulfurization composition containing calcium sulfite and gypsum can be obtained as a solid content. These are highly useful by-products. For example, calcium sulfite can be used as a reducing agent, and gypsum can be used as a cement raw material, etc.

[0022] A method for producing a cement composition according to one aspect of the present disclosure includes a mixing step of obtaining a cement composition using a sulfur-containing composition obtained by any one of the above-mentioned production methods, cement clinker, and gypsum. Since this production method uses a sulfur-containing composition produced at low production cost, it is possible to produce a cement composition capable of suppressing elution of heavy metals at low production cost.

[0023] The ground improvement material according to one aspect of the present disclosure uses a sulfur-containing composition obtained by any one of the above-mentioned methods for producing a sulfur-containing composition and / or a cement composition obtained by the above-mentioned method for producing a cement composition. Therefore, the ground improvement material capable of suppressing the elution of heavy metals can be produced at low production cost. Effect of the Invention

[0024] According to the present disclosure, it is possible to provide a method for producing a sulfur-containing composition capable of producing a sulfur-containing composition at low production cost and high production efficiency. In addition, it is possible to provide a method for producing a cement composition capable of producing a cement composition at low production cost by using such a sulfur-containing composition. In addition, it is possible to provide a method for producing a ground improvement material capable of producing a ground improvement material at low production cost. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 illustrates an example of a method for producing a sulfur-containing composition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings as needed. However, the following embodiment is an example for explaining the present disclosure, and is not intended to limit the present disclosure to the following content.

[0027] The method for producing the sulfur-containing composition according to the present embodiment includes a heating step of heating a carbon source and a gypsum-containing waste in a temperature range of 600 to 1400° C. to react with each other to obtain a heat-treated product, and a modification step of treating the heat-treated product to obtain a sulfur-containing composition.

[0028] Examples of gypsum-containing waste include waste gypsum board, flue gas desulfurization gypsum, sulfur-containing sludge, desulfurization sludge, and desulfurization slag. The gypsum-containing waste preferably includes at least one of these examples. The waste gypsum board may include organic matter such as resin and paper attached to the surface of the gypsum board, and inorganic impurities such as metals. When organic impurities are included, the carbon content of the gypsum-containing waste may also be evaluated, and the carbon source may be taken into consideration when setting the blending ratio. From the viewpoint of more stably producing the sulfur-containing composition, the gypsum-containing waste preferably includes waste gypsum board.

[0029] The gypsum content of the gypsum-containing waste is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, and most preferably 55% by mass or more, calculated as SO3. By adjusting the content to such a level, a sulfur-containing composition having excellent quality can be obtained. The number of moles of gypsum (CaSO4) contained in the gypsum-containing waste can be determined by converting the content based on mass into moles using the molecular weight of CaSO4.

[0030] The gypsum content in the gypsum-containing waste can be, for example, a value obtained by the XRD Rietveld method.

[0031] The gypsum-containing waste is preferably granular. The average particle size of the gypsum-containing waste is preferably 30 mm or less, more preferably 20 mm or less, even more preferably 10 mm or less, particularly preferably 8 mm or less, and most preferably 5 mm or less. The particle size of the gypsum-containing waste in this specification is measured as the diameter of a circumscribed circle circumscribing the outer edge of the particle in a two-dimensional image. The average particle size is determined by measuring the particle sizes of 100 arbitrarily selected particles using the above-mentioned method and calculating the arithmetic average value.

[0032] Of the total number of particles contained in the gypsum-containing waste, it is preferable that 80% or more of the particles pass through a sieve with a mesh size of 30 mm, it is more preferable that 80% or more of the particles pass through a sieve with a mesh size of 20 mm, it is even more preferable that 80% or more of the particles pass through a sieve with a mesh size of 10 mm or less, it is particularly preferable that 80% or more of the particles pass through a sieve with a mesh size of 8 mm, and it is most preferable that 80% or more of the particles pass through a sieve with a mesh size of 5 mm.

[0033] The carbon source contains at least one of inorganic carbon and organic carbon. The content of carbon (C) relative to the total amount of the carbon source is preferably 20% by mass or more, more preferably 40% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

[0034] The carbon source contains inorganic components including Si and Al. The inorganic components may be contained in the carbon source as amorphous or crystalline. The inorganic components may contain components other than Si and Al. The Si and Al contained in the carbon source may be contained as simple substances, or may be contained as alloys or compounds. When multiple types of carbon sources are used, it is sufficient that at least one of them contains Si and Al. When the Si and Al contained in the inorganic components are converted to SiO2 and Al2O3, respectively, the total ratio of SiO2 and Al2O3 to the entire inorganic components is preferably 10 mass% or more, more preferably 20 mass% or more, and even more preferably 50 mass% or more.

[0035] From the viewpoint of sufficiently increasing the production efficiency of the sulfur-containing composition, when Si and Al contained in the carbon source are converted into SiO2 and Al2O3, respectively, the total ratio of SiO2 and Al2O3 to the total amount of the carbon source is preferably 5 to 40 mass%, more preferably 8 to 30 mass%, and further preferably 10 to 20 mass%. By using such a carbon source, the reaction with the gypsum-containing waste can be sufficiently promoted.

[0036] Examples of carbon sources containing inorganic components containing Al and Si include coal gasification slag, coal ash, municipal waste incineration ash, biomass ash, wood chips, and sewage sludge incineration ash. However, the carbon source is not limited to these and may be any carbon source containing Al and Si. In addition to the carbon source containing Al and Si, other carbon sources not containing one or both of Al and Si may be used.

[0037] The carbon source may include resin waste. The resin waste may include not only resins with a relatively high resin content such as RPF and RDF, but also resins containing various impurities such as ASR and CFRP. In this way, by using by-products or waste, it is possible to further reduce the production cost of the sulfur-containing composition while reducing the environmental load. RPF is an abbreviation for Refuse Paper & Plastic Fuel, which is a solid fuel obtained from waste paper and plastics. RDF is an abbreviation for Refuse Derived Fuel, which is a refuse-derived fuel made mainly from general waste such as household waste. ASR is an abbreviation for Automobile Shredder Residue, which is automobile shredder residue. CFRP is an abbreviation for Carbon Fiber Reinforced Plastic, which is a carbon fiber reinforced plastic.

[0038] The carbon (C) content in the carbon source can be measured based on JIS M 8812 "Fixed carbon content and ignition loss as specified in Coals and cokes-Proximate analysis method". From the viewpoint of sufficiently increasing the production efficiency of the sulfur-containing composition, the carbon (C) content in the carbon source is preferably 5 to 90 mass%, more preferably 20 to 90 mass%, and even more preferably 50 to 90 mass%. The number of moles of carbon (C) in the carbon source can be determined by converting the carbon content thus determined into moles.

[0039] The particle size of the granular carbon source is 100 mm or less, preferably 30 mm or less, more preferably 10 mm or less, even more preferably 5 mm or less, and particularly preferably 2.5 mm or less, from the viewpoint of sufficiently increasing the frequency of contact with gypsum. On the other hand, from the viewpoint of classification after foaming in the modification step described below, the particle size of the carbon source is preferably 20 μm or more, more preferably 45 μm or more, and even more preferably 90 μm or more. The particle size of the carbon source can be measured, for example, as the diameter of a circumscribing circle circumscribing the outer edge of the particle in a two-dimensional image of the granular carbon source.

[0040] In the heating step, the carbon source and the gypsum-containing waste are heated to react with each other. The heating step may be performed using a normal heating device. The heating device may be a continuous type or a batch type. Either an external heating type or an internal heating type may be used as the heating method. The heat source is not particularly limited, and may be, for example, heavy oil, pulverized coal, or electricity. Specific examples of the heating device include a rotary kiln and a fluidized bed furnace. However, the present invention is not limited to these. It is preferable that each part of the heating device is sealed so that the reaction atmosphere can be easily controlled.

[0041] In the heating step, for example, a reaction represented by the following reaction formula (1) proceeds. At the same time, a reaction represented by the following reaction formula (2) also proceeds, generating SO2. The gypsum-containing waste may also contain carbon. The carbon is contained in at least one material selected from the group consisting of paper, waste plastic, carbon fiber, biomass, coal, and petroleum. CaSO4+2C → CaS+2CO2(1) CaSO4+CaS → 2CaO+2SO2(2)

[0042] In the heating step, the gypsum-containing waste and the carbon source are heated in a temperature range of 600 to 1400° C. The temperature range is preferably 800 to 1300° C., and more preferably 900 to 1250° C. By heating in such a temperature range, the reaction between gypsum and carbon can be sufficiently promoted while suppressing loss due to combustion of the carbon source.

[0043] The heating time in the above temperature range is not particularly limited, and may be, for example, 5 minutes or more, preferably 15 minutes or more, more preferably 30 minutes or more, even more preferably 45 minutes or more, and particularly preferably 60 minutes or more. The heating time in the above temperature range is, for example, less than 4 hours, preferably 3 hours or less, more preferably 2 hours or less, and particularly preferably 90 minutes or less. In such a range, the sulfur-containing composition can be efficiently produced. Note that, under conditions where the heating time is short, the content of calcium sulfide in the sulfur-containing composition tends to be low, but the content of gypsum tends to be high. Gypsum is also useful as a component of cement compositions and ground improvement materials. The heating time may be adjusted according to the target value of the content of calcium sulfide in the sulfur-containing composition.

[0044] The oxygen concentration of the heating atmosphere in the heating step is preferably less than 21% by volume, more preferably less than 10% by volume, and even more preferably less than 5% by volume. By lowering the oxygen concentration, the combustion of carbon contained in the carbon source is suppressed, and the amount of carbon that reacts with the sulfur-containing waste can be increased. The oxygen concentration of the heating atmosphere in the heating step may be 100 ppm by volume or more, or may be 1000 ppm by volume or more. The presence of a certain amount of oxygen allows the sulfur-containing composition to be produced efficiently.

[0045] The molar ratio of gypsum to carbon contained in the gypsum-containing waste and the carbon source used in the heating step preferably satisfies the following formula (3), more preferably the following formula (4), and even more preferably the following formula (5): In the formulas (3), (4), and (5), C represents the number of moles of carbon, and CaSO4 represents the number of moles of gypsum. C / CaSO4≧3 (3) C / CaSO4>4 (4) C / CaSO4>5 (5)

[0046] When both the carbon source and the gypsum-containing waste contain carbon, the carbon (C) in each of the above formulas is the sum of the carbon contained in each. Similarly, when both the carbon source and the gypsum-containing waste contain gypsum (CaSO4), the gypsum (CaSO4) in each of the above formulas is the sum of the gypsum contained in each.

[0047] In the heating step, the carbon source and the gypsum-containing waste are reacted in the above-mentioned molar ratio, so that the unreacted portion is prevented from remaining in the heat-treated product, and the sulfur-containing composition can be produced with sufficiently high production efficiency. Note that, from the viewpoint of preventing the generation of CO2 in the heating step, C / CaSO4 is preferably 20 or less, more preferably 10 or less.

[0048] When a continuous heating device that continuously supplies a carbon source and a gypsum-containing waste is used, the supply rate of the carbon source and the gypsum-containing waste may be adjusted based on the carbon and gypsum contents contained in the carbon source and the gypsum-containing waste so that the molar ratio of gypsum to carbon satisfies any of the above formulas. When the carbon and gypsum contents vary, an adjustment step may be performed to adjust the blending ratio of the carbon source and the gypsum-containing waste based on the carbon and gypsum contents. In the adjustment step, the blending ratio of the gypsum-containing waste and the carbon source is adjusted so as to preferably satisfy the above formula (3), more preferably the above formula (4), and even more preferably the above formula (5).

[0049] The carbon source and the gypsum-containing waste may be introduced into the heating device separately, or may be mixed or granulated in advance and then the mixture or granulated product may be introduced into the heating device. In addition to the carbon source and the gypsum-containing waste, one of sulfur, clay-based material, silica sand, and pulverized coal may be introduced into the heating device alone or in combination of two or more of them.

[0050] FIG. 1 is a diagram showing an example of the manufacturing method of this embodiment. In the example of FIG. 1, the method includes, in this order, a blending step of mixing a carbon source and a gypsum-containing waste to obtain a blended raw material, and a granulation step of granulating the blended raw material, prior to the heating step. In the blending step, it is preferable to determine the blending ratio of the gypsum-containing waste and the carbon source based on the gypsum content in the gypsum-containing waste and the carbon content in the carbon source, and blend the gypsum-containing waste and the carbon source based on the blending ratio. During blending, water, a clay-based substance, an inorganic substance such as water glass, or a polymer compound may be added as a binder. When a binder is added, the binder may contain carbon or gypsum, so it is preferable that the carbon and gypsum contained in the blended raw material satisfy the above formula (3), (4), or (5). It should be noted that even if a binder is not added, a granulated product can be obtained in the granulation step by the adhesive force of the carbon source.

[0051] In the granulation step, in order to obtain a more stable granulated product, for example, a pan-type granulator, a briquette machine which is a pressure molding machine, or a granulation machine may be used. In addition, in order to maintain the strength of the granulated product, the moisture content may be adjusted. The granulated product thus obtained may be introduced into a heating device and subjected to a heating step. By including the granulation step, it is possible to suppress the dispersion of the mixed raw materials in the facility. In addition, it is possible to ensure the breathability of the granulated product, and the reactivity between the carbon source and gypsum can be improved.

[0052] In a modified example, a raw material grinding step of grinding the gypsum-containing waste and / or the carbon source may be included. In this way, a raw material grinding step of grinding the gypsum-containing waste and the carbon source separately may be included, or a blended raw material may be prepared by grinding the gypsum-containing waste and the carbon source while mixing them in the blending step. A granulation step may be performed using this blended raw material, or the blended raw material may be introduced into a heating device and a heating step may be performed without performing a granulation step. The raw material grinding step may be performed using a normal grinder. Note that it is not essential to perform the raw material grinding step.

[0053] The heat-treated product obtained in the heating step contains calcium sulfide, unreacted gypsum, impurities derived from the raw materials, and coarse powder generated by foaming of inorganic components including Si and Al contained in the carbon source. Although the detailed mechanism by which the inorganic components foam to generate the coarse powder is unknown, it is presumed that the inorganic components melt in the heating step, are then further heated, and the encapsulated carbon is gasified, causing foaming and generating the coarse powder. The heat-treated product may contain by-products such as calcium oxide and calcium polysulfide.

[0054] The content of the modification process can be selected according to the properties required for the sulfur-containing composition. For example, examples of the modification process include sieving (screening), removal of coarse powder or foreign matter by wind sorting, magnetic sorting, eddy current sorting, etc., particle size adjustment such as crushing and classification, washing and drying, slurrying, and blending of additives. The modification process may be performed by one of these alone or in combination of two or more. Thus, in the modification process, a process is performed to change the physical or chemical properties of the heat-treated product. For example, since the heat-treated product contains coarse powder due to foaming caused by Si and Al, the modification process can easily improve the quality of the sulfur-containing composition by including a coarse powder separation process for removing the coarse powder from the heat-treated product.

[0055] The method of removing the coarse powder from the heat-treated product is not particularly limited, and a classifier may be used, or a simple method such as sieving may be used. The fine powder (under the sieve in the case of sieving) obtained by removing the coarse powder is collected as a sulfur-containing composition. By removing the coarse powder, inorganic components such as Si and Al are removed, and the purity of the target component of the sulfur-containing composition can be increased.

[0056] When classification is performed in the modification step, a classification point is set within the range of 20 to 200 μm, and the heat-treated product is classified into coarse powder and fine powder at the classification point, so that the sulfur-containing composition can be obtained as fine powder. The classification point is preferably set within the range of 20 to 150 μm, more preferably within the range of 20 to 110 μm, even more preferably within the range of 20 to 90 μm, and particularly preferably within the range of 20 to 50 μm. The smaller the classification point, the higher the purity of the sulfur-containing composition that is recovered tends to be. On the other hand, the larger the classification point, the higher the yield of the sulfur-containing composition tends to be.

[0057] When the heat-treated product contains calcium sulfide, etc., it may react with moisture in the air to generate a small amount of hydrogen sulfide, etc. Therefore, by adding an inorganic powder to maintain an alkaline environment, the generation of hydrogen sulfide, etc. can be sufficiently suppressed. In this case, after mixing the inorganic powder containing CaO with the heat-treated product, coarse powder may be removed from the mixture. The inorganic powder containing CaO may contain at least one selected from the group consisting of free lime, gypsum, calcium sulfite, cement clinker, calcium hydroxide, and calcium carbonate. This makes it easier to maintain the heat-treated product and the sulfur-containing composition alkaline. And, by adhering the inorganic powder to the particle surface of calcium sulfide, it is possible to reduce the opportunity for direct contact with moisture in the air. The inorganic powder containing CaO may contain a by-product generated in the cement manufacturing process. This allows the manufacturing cost of the sulfur-containing composition to be kept sufficiently low.

[0058] The sulfur-containing composition obtained in the modification step preferably contains calcium sulfide. It may also contain other components contained in the heat-treated product and additives such as CaO added in the modification step. The content of calcium sulfide in the entire sulfur-containing composition is preferably 5 mass% or more, more preferably 30 mass% or more, even more preferably 50 mass% or more, and particularly preferably 70 mass% or more. The content of calcium sulfide in the sulfur-containing composition can be determined, for example, by the XRD-Rietveld method. By containing a high content of calcium sulfide in the sulfur-containing composition, the action as a reducing agent can be further strengthened.

[0059] The reaction exhaust gas generated in the heating step contains an acidic gas. The acidic gas includes, for example, sulfurous acid gas generated by the reaction of the above formula (2). The reaction exhaust gas may also contain SO3, Cl2, CO2, CO, and the like depending on the components contained in the carbon source and the gypsum-containing waste, as well as the reaction conditions in the heating step. A gas treatment step for treating the reaction exhaust gas containing such components may be performed. The gas treatment step may include contacting the reaction exhaust gas with an alkali-containing slurry containing an alkali source and water, performing secondary combustion, and collecting dust with a wet EP.

[0060] In the example of Fig. 1, the reaction exhaust gas is contacted with an alkali-containing slurry in the gas treatment step. Examples of the alkali source include hydroxides and carbonates of alkali metals, and hydroxides and carbonates of alkaline earth metals. The alkali source may contain at least one of these, and preferably contains a calcium salt.

[0061] The alkali source may include by-products in the cement manufacturing process, such as fine powder mainly composed of calcium carbonate generated during grinding of raw materials for cement clinker, dust particles of calcium compounds extracted from the chlorine bypass, washed dust particles obtained by washing the dust particles with water, sludge containing at least one of cement and cement hydrate, etc. This can reduce the cost of treating exhaust gas from the reaction with the alkali-containing slurry.

[0062] A slurry preparation step of preparing an alkali-containing slurry containing an alkali source and water may be carried out prior to the gas treatment step. The solid content of the alkali-containing slurry is preferably 0.1 to 50 mass%, more preferably 1 to 30 mass%, further preferably 3 to 28 mass%, and particularly preferably 10 to 25 mass%, from the viewpoints of improving handleability and facilitating dehydration and drying.

[0063] In the gas treatment step, the alkali source contained in the alkali-containing slurry is brought into contact with the reaction exhaust gas generated in the reaction step to obtain a gas treatment product slurry. The gas treatment unit performing the gas treatment step may be a bubbling tank. The gas treatment product slurry may contain a desulfurization product. The desulfurization product preferably contains at least one of a sulfite such as calcium sulfite and gypsum. As shown in FIG. 1, a recovery step may be performed in which the desulfurization product is recovered as a solid desulfurization composition from such a gas treatment product slurry in a recovery unit. The desulfurization composition recovered in the recovery step can be suitably used, together with the sulfur-containing composition, as a reducing agent or cement raw material in cement production, for example.

[0064] The gas treatment product slurry may contain components other than sulfite. For example, when the reaction exhaust gas generated in the reaction step contains hydrogen sulfide, salts such as calcium sulfide, sodium sulfide, and magnesium sulfide may be generated in the gas treatment step in addition to sulfite. In this case, the gas treatment product slurry may contain salts such as calcium sulfide, sodium sulfide, and magnesium sulfide as desulfurization products in addition to sulfite.

[0065] Other components of the gas treatment product slurry include calcium hydroxide, calcium carbonate, magnesium hydroxide, and calcium sulfate. The gas treatment product slurry may contain at least one of these components. Calcium sulfate may include any of dihydrate (gypsum dihydrate), hemihydrate (gypsum hemihydrate), and anhydrite (anhydrous gypsum).

[0066] The product obtained in the gas treatment step does not have to be in the form of a slurry. In a modified example, in the gas treatment step, a powdery desulfurization product may be obtained by spray drying in which an alkali-containing slurry is sprayed into a reaction exhaust gas containing sulfur dioxide gas and the like and dried. In another modified example, instead of an alkali-containing slurry, a component (alkali source) contained in the alkali-containing slurry may be brought into contact with a reaction exhaust gas containing sulfur dioxide gas and the like in a solid (powder) state in the gas treatment step. In this case, the gas treatment step may be performed using, for example, a fluidized bed in which the alkali source, calcium compound, ash, and the like are made into solid particles. In this case, a powdery desulfurization product can also be obtained.

[0067] In the method for producing a sulfur-containing composition of the present embodiment, since waste containing gypsum is used, the raw material cost can be reduced. In addition, since the carbon source containing inorganic components including Si and Al can promote the reduction reaction of gypsum, the sulfur-containing composition can be produced with high production efficiency. In addition, the fuel consumption required for production can also be reduced. Therefore, according to the above-mentioned production method, the sulfur-containing composition can be produced at low production cost and high production efficiency.

[0068] A method for producing a cement composition according to one embodiment includes a mixing step of obtaining a cement composition using the above-mentioned sulfur-containing composition, cement clinker, and gypsum.

[0069] In the mixing step, the cement clinker, the sulfur-containing composition, and the gypsum are blended and pulverized to obtain a cement composition. The order of pulverization and blending is not particularly limited, and for example, the three types may be blended sequentially or simultaneously, and then, as necessary, pulverized again to obtain a cement composition. Alternatively, before blending the above three types, at least one of the three types may be pulverized alone, or two of the three types may be blended and pulverized, or pulverized while blending. The order of blending and pulverization is not particularly limited, and pulverization and blending can be performed simultaneously. Thus, the blending pattern and the number of times of pulverization are not particularly limited. The mixing step can be performed, for example, using equipment such as a ball mill and / or a vertical mill.

[0070] There is no limitation on the type of cement composition thus produced, and it can be Portland cement as specified in JIS R 5210:2003 "Portland cement". Examples of Portland cement include ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, etc. At least one selected from blast furnace slag, fly ash, and siliceous admixtures may be added to these Portland cements to produce a mixed cement.

[0071] The cement composition preferably contains a sulfide and / or a sulfite. The total content of the sulfide and sulfite in the cement composition is, for example, preferably 0.1 to 15 mass%, more preferably 0.5 to 10 mass%, and further preferably 1 to 5 mass%.

[0072] The cement composition preferably contains calcium sulfide. The calcium sulfide content of the cement composition is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, particularly preferably 4% by mass or more, and most preferably 8% by mass or more. By setting the content in such a range, it is possible to obtain a cement composition that can sufficiently suppress heavy metal elution while maintaining strength development. The calcium sulfide content of the cement composition may be 50% by mass or less from the viewpoint of strength development.

[0073] The Blaine specific surface area of ​​the cement composition is preferably 2500 to 6000 cm 2 / g, and more preferably 3000 to 5000 cm 2 / g. If the Blaine specific surface area is equal to or greater than the lower limit, excellent strength development is easily achieved. On the other hand, if the Blaine specific surface area is equal to or less than the upper limit, the viscosity when used as concrete or solidification material slurry is easily controlled within a suitable range.

[0074] In the method for producing a cement composition, a sulfur-containing composition that can be produced at low production costs is used. Therefore, the cement composition can be produced at low production costs. Since such a cement composition contains the sulfur-containing composition, it is possible to suppress the elution of heavy metals such as hexavalent chromium.

[0075] The method for producing a ground improvement material according to one embodiment includes a step of obtaining a ground improvement material using one or both of the sulfur-containing composition obtained by any of the above-mentioned production methods and the cement composition obtained by the above-mentioned production method. In this step, the sulfur-containing composition may be used as a ground improvement material as it is, or the sulfur-containing composition may be mixed with other raw materials to obtain a ground improvement material. In addition, the cement composition obtained by the above-mentioned method for producing a cement composition may be used as a ground improvement material as it is, or the cement composition may be mixed with other raw materials to obtain a ground improvement material.

[0076] In this production method, since a sulfur-containing composition or a cement composition containing the same that can be produced at low production costs is used, the ground improvement material can be produced at low production costs.

[0077] The sulfur-containing composition contained in the ground improvement material preferably contains calcium sulfide. The calcium sulfide content of the ground improvement material is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and particularly preferably 4% by mass or more. By setting it in such a range, it is possible to sufficiently suppress the elution of heavy metals from the soil. The upper limit of the calcium sulfide content of the ground improvement material is not particularly limited, and may be, for example, 20% by mass or less, or 10% by mass or less.

[0078] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. EXAMPLES

[0079] The present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[0080] (Examples 1 to 5, Comparative Example 1) The following raw materials were prepared: ·Anhydrite Carbon source: Coal gasification slag (C content: 50% by mass, Si content: 30% by mass, Al content: 15% by mass)

[0081] Anhydrous gypsum and coal gasification slag were mixed so that the molar ratio of gypsum (CaSO4) to carbon (C) contained in the coal gasification slag was C / CaSO4=4 to obtain a mixture. The obtained mixture was placed in a magnetic crucible and fired in an electric furnace in air at 950°C (heating step). The firing time at 950°C was as shown in Table 1. The heat-treated product obtained by firing was collected and separated into fine powder (under the sieve) and coarse powder (over the sieve) using a sieve with a mesh size of 90 μm (modification step). The fine powder thus obtained was collected as a sulfur-containing composition. The content of calcium sulfide (CaS) in the collected sulfur-containing composition was quantified by the XRD Rietveld method. The results were as shown in Table 1. In Comparative Example 1, firing in an electric furnace was not performed, the mixture was sieved using a sieve with a mesh size of 90 μm, and the obtained fine powder (under the sieve) was analyzed.

[0082] [Table 1]

[0083] As shown in Table 1, in Example 1, a sulfur-containing composition containing 2.2 mass% of CaS was obtained by firing for only 15 minutes. Moreover, from the results of other Examples, it was confirmed that the CaS content can be increased to 70 mass% or more by firing for 60 to 90 minutes.

[0084] The sulfur-containing composition of Example 3 was added to a cement-based solidification material so that the CaS content was 4 mass%, and the resulting solidification material was mixed with volcanic ash clay to prepare a cylindrical improved soil specimen (solidification material addition amount: 300 kg / m 3 , diameter 5 cm × height 10 cm). The amount of hexavalent chromium eluted from the test specimen after 28 days was measured by the Environment Agency Notification No. 46 method, and the amount of hexavalent chromium eluted was less than the lower limit of quantification. From the above, it was confirmed that the sulfur-containing composition manufactured by the manufacturing method disclosed herein is effective in suppressing the elution of hexavalent chromium. [Industrial Applicability]

[0085] According to the present disclosure, it is possible to provide a method for producing a sulfur-containing composition capable of producing a sulfur-containing composition at low production cost and high production efficiency. In addition, it is possible to provide a method for producing a cement composition capable of producing a cement composition at low production cost by using such a sulfur-containing composition. In addition, it is possible to provide a method for producing a ground improvement material capable of producing a ground improvement material at low production cost.

Claims

1. A method for producing a sulfur-containing composition, comprising the steps of: obtaining a sulfur-containing composition containing calcium sulfide from a carbon source and a gypsum-containing waste material, The carbon source contains an inorganic component including Si and Al, a heating step of heating the carbon source and the gypsum-containing waste in a temperature range of 600 to 1400° C. to react with each other to obtain a heat-treated product; A modification step of modifying the heat-treated product to obtain a sulfur-containing composition, In the modification step, a classifier is used to set a classification point within a range of 20 to 200 μm, and the heat-treated product is classified into coarse powder and fine powder generated by foaming of the inorganic component, and the sulfur-containing composition is obtained as the fine powder.

2. The method for producing a sulfur-containing composition according to claim 1, wherein a molar ratio of gypsum to carbon contained in the gypsum-containing waste and the carbon source used in the heating step satisfies the following formula (1): C / CaSO ４ ≧3 (1) [In formula (1), C represents the number of moles of carbon, and CaSO ４ indicates the number of moles of gypsum.]

3. The method for producing a sulfur-containing composition according to claim 1 or 2, further comprising a granulation step of mixing the carbon source and the gypsum-containing waste and granulating the mixture prior to the heating step.

4. A method for producing a sulfur-containing composition, comprising obtaining a sulfur-containing composition containing calcium sulfide from a carbon source and a gypsum-containing waste material, The carbon source contains an inorganic component including Si and Al, a heating step of heating the carbon source and the gypsum-containing waste in a temperature range of 600 to 1400° C. to react with each other to obtain a heat-treated product; A modification step of modifying the heat-treated product to obtain a sulfur-containing composition, In the modification step, a classifier is used to set a classification point within a range of 20 to 200 μm, and the mixture obtained by mixing the inorganic powder containing CaO with the heat-treated product is classified into coarse powder and fine powder generated by foaming of the inorganic component, thereby obtaining the sulfur-containing composition containing the fine powder and the inorganic powder.

5. The method for producing a sulfur-containing composition according to claim 4, wherein the inorganic powder comprises at least one selected from the group consisting of free lime, gypsum, calcium sulfite, cement clinker, calcium hydroxide, and calcium carbonate.

6. The method for producing a sulfur-containing composition according to claim 4 or 5, wherein the inorganic powder comprises a by-product generated in a cement manufacturing process.

7. The Si and Al contained in the inorganic component are each SiO ２ and Al ２ O ３ When converted into SiO ２ and Al ２ O ３ The method for producing a sulfur-containing composition according to any one of claims 1 to 6, wherein the total ratio of is 10% by mass or more.

8. The method for producing a sulfur-containing composition according to any one of claims 1 to 7, wherein the carbon source comprises coal gasification slag.

9. The method for producing a sulfur-containing composition according to any one of claims 1 to 8, wherein the gypsum-containing waste comprises at least one selected from the group consisting of waste gypsum board, flue gas desulfurization gypsum, and sulfur-containing sludge.

10. The method for producing a sulfur-containing composition according to any one of claims 1 to 9, wherein the content of calcium sulfide in the entire sulfur-containing composition is 5 mass% or more.

11. a gas treatment step of contacting the reaction exhaust gas produced in the heating step with an alkali-containing slurry containing an alkali source to obtain a gas treatment product slurry; and recovering a desulfurized composition produced by a reaction between an acidic gas contained in the reaction exhaust gas and the alkali source from the gas treatment product slurry.

12. the reaction exhaust gas contains sulfur dioxide gas, and the alkali source contains a calcium salt; 12. The method of claim 11, wherein the desulfurizing composition comprises at least one of calcium sulfite and gypsum.

13. A method for producing a cement composition, comprising a mixing step of obtaining a cement composition using a sulfur-containing composition obtained by the production method according to any one of claims 1 to 8, cement clinker, and gypsum.

14. A method for producing a ground improvement material, comprising the step of obtaining a ground improvement material using one or both of the sulfur-containing composition obtained by the production method according to any one of claims 1 to 12 and the cement composition obtained by the production method according to claim 13.

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